U.S. patent application number 15/715553 was filed with the patent office on 2018-04-05 for three-dimensional coordinate measuring device.
The applicant listed for this patent is FARO Technologies, Inc.. Invention is credited to Robert E. Bridges, Michael Ferrara, Jun Li, Jacob J. Mertz.
Application Number | 20180095174 15/715553 |
Document ID | / |
Family ID | 61758019 |
Filed Date | 2018-04-05 |
United States Patent
Application |
20180095174 |
Kind Code |
A1 |
Mertz; Jacob J. ; et
al. |
April 5, 2018 |
THREE-DIMENSIONAL COORDINATE MEASURING DEVICE
Abstract
A coordinate measurement device and method of operating is
provided. The coordinate measurement device launches and collimates
visible light through a launch-collimator assembly that is
exchangeable in the coordinate measuring device without realignment
of any elements within the coordinate measuring device. The
coordinate measurement device includes a Fabry-Perot laser, a
lensing system, a first optical fiber, and a thermoelectric cooler.
A fiber network receives the light from the optical fiber and
passes a first portion of the light to a launch-collimator
assembly. The launch-collimator assembly launches the first portion
of the light into space and collimates the launched light into a
first beam. A distance meter measures a first distance to a target
illuminated by the first beam. A processor determines 3D
coordinates of the target based at least in part on a measured
first angle of rotation, a measured second angle of rotation, and
the measured first distance.
Inventors: |
Mertz; Jacob J.; (Elkridge,
MD) ; Li; Jun; (Downingtown, PA) ; Ferrara;
Michael; (Garnet Valley, PA) ; Bridges; Robert
E.; (Kennett Square, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FARO Technologies, Inc. |
Lake Mary |
FL |
US |
|
|
Family ID: |
61758019 |
Appl. No.: |
15/715553 |
Filed: |
September 26, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62402152 |
Sep 30, 2016 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01S 5/0427 20130101;
G02B 6/32 20130101; H01S 5/062 20130101; G01C 15/002 20130101; H01S
5/02415 20130101; G01S 17/36 20130101; G01S 7/4814 20130101; H01S
5/068 20130101; G02F 2203/21 20130101; G01S 17/66 20130101; G01S
7/4818 20130101; G01S 7/497 20130101; G01B 11/002 20130101; G02F
1/0955 20130101; G01S 17/42 20130101 |
International
Class: |
G01S 17/42 20060101
G01S017/42; G01S 17/66 20060101 G01S017/66; G01B 11/00 20060101
G01B011/00; G01S 7/481 20060101 G01S007/481; G02B 6/32 20060101
G02B006/32 |
Claims
1. A coordinate measuring device comprising: a light source
operable to emit a first light, the light source including a
Fabry-Perot laser, a lensing system, a first optical fiber, and a
thermoelectric cooler, the Fabry-Perot laser operable to produce
visible light at a first wavelength, the lensing system operable to
couple the produced first light into the first optical fiber, the
first optical fiber being a single-mode optical fiber, the
thermoelectric cooler operable to hold the Fabry-Perot laser at a
constant temperature; a fiber network operable to receive the first
light from the output optical fiber and to pass a first portion of
the first light to a launch-collimator assembly, the
launch-collimator assembly operable to launch the first portion of
the first light into free space and to collimate the launched first
light into a first beam of light; a first motor and a second motor
operable to direct the first beam of light to a first direction,
the first direction determined by a first angle of rotation about a
first axis and a second angle of rotation about a second axis, the
first angle of rotation produced by the first motor and the second
angle of rotation produced by the second motor; a first angle
measuring device operable to measure the first angle of rotation
and a second angle measuring device operable to measure the second
angle of rotation; a distance meter operable to measure a first
distance to a target illuminated by the first beam of light; and a
processor operable to determine three-dimensional (3D) coordinates
of the target based at least in part on the measured first angle of
rotation, the measured second angle of rotation, and the measured
first distance.
2. The coordinate measuring device of claim 1, further comprising:
a Faraday isolator operable to pass the first light traveling in a
forward direction away from the light source but to block the first
light traveling in a reverse direction toward the light source, the
Faraday isolator including an input optical fiber coupled to the
first optical fiber, the Faraday isolator further including an
output optical fiber, the output optical fiber being a single-mode
optical fiber.
3. The coordinate measuring device of claim 1, wherein a bias
current sent to the Fabry-Perot laser is adjusted to emit light at
a constant average optical power.
4. The coordinate measuring device of claim 1, wherein optical
power losses from the Fabry-Perot laser to the target and back to
the Fabry-Perot laser are large enough are large enough to prevent
destabilization of the Fabry-Perot laser over a range of rated
operating temperatures of the coordinate measuring device.
5. The coordinate measuring device of claim 2, wherein a
combination of isolation from the Faraday isolator and optical
power losses from the Fabry-Perot laser to the target and back to
the Fabry-Perot laser is large enough to prevent destabilization of
the Fabry-Perot laser over a range of rated operating temperatures
of the coordinate measuring device.
6. The coordinate measuring device of claim 5, wherein a
temperature control device is brought into contact with the Faraday
isolator, the temperature control device operable to control the
temperature of the Faraday isolator, thereby increasing the
isolation of the Faraday isolator over the range of rated operating
temperatures.
7. The coordinate measuring device of claim 2, wherein the Faraday
isolator includes a Faraday rotator having a Faraday-rotator
crystal and a magnet, the magnet positioned to immerse the
Faraday-rotator crystal in a magnetic field.
8. The coordinate measuring device of claim 7, wherein the Faraday
isolator is a polarization-independent Faraday isolator including a
first birefringent beam displacer, the Faraday rotator, a half-wave
plate, and a second birefringent beam displacer.
9. The coordinate measuring device of claim 8, wherein the first
optical fiber is not a polarization-maintaining optical fiber and
the input optical fiber is not a polarization-maintaining optical
fiber.
10. The coordinate measuring device of claim 1, wherein the target
is a retroreflector.
11. The coordinate measuring device of claim 1, wherein the
distance meter is an absolute distance meter (ADM).
12. The coordinate measuring device of claim 11, wherein a first
portion of the first returned light from the target passes through
the launch-collimator assembly to the ADM.
13. The coordinate measuring device of claim 1, further including
an ADM module, the ADM module being an integrated unit that
includes the first light source, the Faraday isolator, the fiber
network, and radio-frequency (RF) electronics, the RF electronics
used to modulate the Fabry-Perot laser and to process
electrically-detected optical signals passing through the fiber
network, the ADM module further including an optical-fiber adapter
for coupling the fiber network to the launch-collimator
assembly.
14. A method of determining three dimensional coordinates of a
target, the method comprising: providing a light source operable to
emit a first light, the light source including a Fabry-Perot laser,
a lensing system, a first optical fiber, and a thermoelectric
cooler; producing a visible light at a first wavelength and
coupling the first light into the first optical fiber; maintaining
the Fabry-perot laser at a constant temperature with the
thermoelectric cooler; receiving the first light with a fiber
network operable from an output optical fiber; transmitting a first
portion of the first light to a launch-collimator assembly;
launching with the launch-collimator assembly the first portion of
the first light into free space and to collimate the launched first
light into a first beam of light; directing the first beam of light
to a first direction with a first motor and a second motor, the
first direction determined by a first angle of rotation about a
first axis and a second angle of rotation about a second axis, the
first angle of rotation produced by the first motor and the second
angle of rotation produced by the second motor; measuring the first
angle of rotation with a first angle measuring device and the
second angle of rotation with a second angle measuring device;
measuring a first distance to a target illuminated by the first
beam of light with a distance meter; and determining
three-dimensional (3D) coordinates of the target based at least in
part on the measured first angle of rotation, the measured second
angle of rotation, and the measured first distance.
15. The method of claim 14, further comprising passing the first
light traveling in a forward direction away from the light source
through a Faraday isolator, and preventing the first light
traveling in a reverse direction through the a Faraday isolator
toward the light source, wherein the Faraday isolator includes an
input optical fiber coupled to the first optical fiber, the Faraday
isolator further including an output optical fiber, the output
optical fiber being a single-mode optical fiber.
16. The method of claim 14, further comprising transmitting a bias
current to the Fabry-Perot laser and adjusting the emitted light to
be at a constant average optical power.
17. The method of claim 14, further comprising providing optical
power losses from the Fabry-Perot laser to the target and back to
the Fabry-Perot laser that are large enough are large enough to
prevent destabilization of the Fabry-Perot laser over a range of
rated operating temperatures of the coordinate measuring
device.
18. The method of claim 17, further comprising: contacting a
temperature control device with the Faraday isolator; and
controlling the temperature of the Faraday isolator with the
temperature control device to increase the isolation of the Faraday
isolator over the range of rated operating temperatures.
19. The method of claim 15, wherein the Faraday isolator includes a
Faraday rotator having a Faraday-rotator crystal and a magnet, the
magnet positioned to immerse the Faraday-rotator crystal in a
magnetic field.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a nonprovisional application of U.S.
Provisional Application Ser. No. 62/402,152 filed on Sep. 30, 2016,
the contents of which are incorporated by reference herein.
BACKGROUND
[0002] The present disclosure relates to a coordinate measuring
device. One set of coordinate measurement devices belongs to a
class of instruments that measure the three-dimensional (3D)
coordinates of a target point by sending a beam of light to the
point. The beam of light may impinge directly on the point or on a
retroreflector target in contact with the point. In either case,
the instrument determines the coordinates of the target point by
measuring a distance and two angles to the target. The distance is
measured with a distance-measuring device such as an absolute
distance meter or an interferometer. The angles are measured with
an angle-measuring device such as an angular encoder. The beam may
be steered with a gimbaled mechanism, a galvanometer mechanism, or
other mechanism.
[0003] A laser tracker is a particular type of coordinate-measuring
device that tracks the retroreflector target with one or more beams
it emits, which may include light from a laser or non-laser light
source. Coordinate-measuring devices closely related to the laser
tracker are the time-of-flight (TOF) scanner and the total station.
The TOF scanner steps one or more beams of light to points on a
surface. It picks up light reflected from the surface and in
response determines a distance and two angles to each surface
point. A total station is a 3D measuring device most often used in
surveying applications. It may be used to measure the coordinates
of a diffusely scattering target or a retroreflective target.
Hereinafter, the term laser tracker is used in a broad sense to
include laser scanners and total stations and to include
dimensional measuring devices that emit laser or non-laser
light.
[0004] In many cases, a laser tracker sends a beam of light to a
retroreflector target. A common type of retroreflector target is
the spherically mounted retroreflector (SMR), which comprises a
cube-corner retroreflector embedded within a metal sphere. The
cube-corner retroreflector comprises three mutually perpendicular
mirrors. The vertex, which is the common point of intersection of
the three mirrors, is located at the center of the sphere. Because
of this placement of the cube corner within the sphere, the
perpendicular distance from the vertex to any surface of the SMR
rests remains constant, even as the SMR is rotated. Consequently,
the laser tracker can measure the 3D coordinates of a surface by
following the position of an SMR as it is moved over the surface.
Stating this another way, the laser tracker needs to measure only
three degrees of freedom (one radial distance and two angles) to
fully characterize the 3D coordinates of a surface.
[0005] One type of laser tracker contains only an interferometer
(IFM) without an absolute distance meter (ADM). If an object blocks
the path of the laser beam from one of these trackers, the IFM
loses its distance reference. The operator must then track the
retroreflector to a known location to reset to a reference distance
before continuing the measurement. A way around this limitation is
to put an ADM in the tracker. The ADM can measure distance in a
point-and-shoot manner, as described in more detail below. Some
laser trackers contain only an ADM without an interferometer.
[0006] A gimbal mechanism within the laser tracker may be used to
direct a laser beam from the tracker to the SMR. Part of the light
retroreflected by the SMR enters the laser tracker and passes onto
a position detector. A control system within the laser tracker uses
position of the light on the position detector to adjust the
rotation angles of the mechanical axes of the laser tracker to keep
the beam of light centered on the SMR. In this way, the tracker is
able to follow (track) a moving SMR.
[0007] Angle measuring devices such as angular encoders are
attached to the mechanical axes of the tracker. The one distance
measurement and two angle measurements of the laser tracker are
sufficient to completely specify a three-dimensional location of
the SMR. In addition, several laser trackers are available or have
been proposed for measuring six degrees-of-freedom (six-DOF),
rather than the ordinary three degrees-of-freedom.
[0008] Although laser trackers are generally suitable for their
intended purpose, some limitations still exist in tracker
complexity, maintenance, resistance to shock, and identification of
target objects. What is needed is a laser tracker having features
to overcome these limitations.
SUMMARY
[0009] According to an embodiment of the present invention, a
coordinate measuring device is provided. The coordinate measurement
device includes a light source operable to emit a first light, the
light source including a Fabry-Perot laser, a lensing system, a
first optical fiber, and a thermoelectric cooler, the Fabry-Perot
laser operable to produce visible light at a first wavelength, the
lensing system operable to couple the produced first light into the
first optical fiber, the first optical fiber being a single-mode
optical fiber, the thermoelectric cooler operable to hold the
Fabry-Perot laser at a constant temperature. A fiber network is
operable to receive the first light from the output optical fiber
and to pass a first portion of the first light to a
launch-collimator assembly, the launch-collimator assembly operable
to launch the first portion of the first light into free space and
to collimate the launched first light into a first beam of light. A
first motor and a second motor are operable to direct the first
beam of light to a first direction, the first direction determined
by a first angle of rotation about a first axis and a second angle
of rotation about a second axis, the first angle of rotation
produced by the first motor and the second angle of rotation
produced by the second motor. A first angle measuring device is
operable to measure the first angle of rotation and a second angle
measuring device operable to measure the second angle of rotation.
A distance meter is operable to measure a first distance to a
target illuminated by the first beam of light. A processor is
operable to determine three-dimensional (3D) coordinates of the
target based at least in part on the measured first angle of
rotation, the measured second angle of rotation, and the measured
first distance.
[0010] According to another embodiment of the present invention, a
method of determining three dimensional coordinates of a target.
The method comprises providing a light source operable to emit a
first light, the light source including a Fabry-Perot laser, a
lensing system, a first optical fiber, and a thermoelectric cooler;
producing a visible light at a first wavelength and coupling the
first light into the first optical fiber; maintaining the
Fabry-perot laser at a constant temperature with the thermoelectric
cooler; receiving the first light with a fiber network operable
from an output optical fiber; transmitting a first portion of the
first light to a launch-collimator assembly; launching with the
launch-collimator assembly the first portion of the first light
into free space and to collimate the launched first light into a
first beam of light; directing the first beam of light to a first
direction with a first motor and a second motor, the first
direction determined by a first angle of rotation about a first
axis and a second angle of rotation about a second axis, the first
angle of rotation produced by the first motor and the second angle
of rotation produced by the second motor; measuring the first angle
of rotation with a first angle measuring device and the second
angle of rotation with a second angle measuring device; measuring a
first distance to a target illuminated by the first beam of light
with a distance meter; and determining three-dimensional (3D)
coordinates of the target based at least in part on the measured
first angle of rotation, the measured second angle of rotation, and
the measured first distance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Referring now to the drawings, exemplary embodiments are
shown which should not be construed to be limiting regarding the
entire scope of the disclosure, and wherein the elements are
numbered alike in several FIGURES:
[0012] FIG. 1A is an isometric view of a laser tracker and a
retroreflector target in accordance with an embodiment of the
present invention;
[0013] FIG. 1B is an isometric view of a laser tracker in
accordance with an embodiment of the present invention;
[0014] FIG. 1C is an isometric view of a laser tracker in
accordance with an embodiment of the present invention;
[0015] FIG. 2A is an isometric view of an external power supply in
accordance with an embodiment of the present invention;
[0016] FIGS. 2B-2D are front, left-side, and right-side views,
respectively, of a cable according to an embodiment of the present
invention;
[0017] FIGS. 2E-2F are front and left-side views, respectively, of
a cable according to an embodiment of the present invention;
[0018] FIGS. 3A-3B are isometric and top views, respectively, of a
battery pack according to an embodiment of the present
invention;
[0019] FIG. 3C is an isometric view of the battery pack attached to
an industrial tripod according to an embodiment of the present
invention;
[0020] FIGS. 4A-4B are front and rear isometric views of an
auxiliary box according to an embodiment of the present
invention;
[0021] FIGS. 5A-5Q are views of six cables used in conjunction with
a laser tracker according to an embodiment of the present
invention;
[0022] FIGS. 6A, 6B, 6C, 6D, 6E are a top view, a front view, a
detail, a first perspective view, and a second perspective view,
respectively, according to an embodiment of the present
invention;
[0023] FIGS. 6F, 6G are a sectional view and a detail,
respectively, according to an embodiment of the present
invention;
[0024] FIG. 7 is a front view of a laser tracker according to an
embodiment of the present invention;
[0025] FIGS. 8A, 8B are isometric views of a base-assembly
structure according to an embodiment;
[0026] FIG. 9A is an isometric view of a plenum assembly according
to an embodiment of the present invention;
[0027] FIG. 9B is an exploded view of the plenum assembly according
to an embodiment of the present invention;
[0028] FIGS. 10A, 10B are top and section views, respectively of
the base-assembly structure according to an embodiment of the
present invention;
[0029] FIG. 10C is an isometric view of a mandrel according to an
embodiment of the present invention;
[0030] FIGS. 11A, 11B, 11C, 11D are isometric, front, section, and
exploded views, respectively, of a shock absorber according to an
embodiment of the present invention;
[0031] FIG. 12 is a isometric view of structural elements of the
laser tracker according to an embodiment of the present
invention;
[0032] FIGS. 13A, 13B are front and sectional views of
laser-tracker structural elements according to an embodiment of the
present invention;
[0033] FIG. 14 is an exploded view of structural elements according
to an embodiment of the present invention;
[0034] FIG. 15 is an exploded view of elements with the yoke
assembly structure according to an embodiment of the present
invention;
[0035] FIGS. 16A, 16B are front and section views, respectively, of
the payload assembly according to an embodiment of the present
invention;
[0036] FIGS. 16C, 16D are front and isometric views of elements
internal to the payload structure according to an embodiment of the
present invention;
[0037] FIGS. 17A, 17B, 17C are isometric, rear, and section views
of a launch/collimator assembly according to an embodiment of the
present invention;
[0038] FIG. 18 is an exploded view of the central optics assembly
400 according to an embodiment of the present invention;
[0039] FIG. 19 is a block diagram of the electrical system of the
laser tracker according to an embodiment of the present
invention;
[0040] FIG. 20A is a perspective view of an ADM module and an ADC
board according to an embodiment of the present invention;
[0041] FIG. 20B is a block diagram of components within the ADM
module and coupled to the ADM module according to an embodiment of
the present invention;
[0042] FIG. 20C is a schematic representation of components
relevant to a packaged laser assembly according to an embodiment of
the present invention;
[0043] FIGS. 21A, 21B are block diagrams of elements within a
polarization-dependent Faraday isolator and a
polarization-independent Faraday isolator, respectively, according
to embodiments of the present invention;
[0044] FIG. 22 is a fiber-optic network according to an embodiment
of the present invention;
[0045] FIG. 23 shows elements of the ADM electrical and
electro-optical system according to an embodiment of the present
invention; and
[0046] FIGS. 24A, 24B are perspective and exploded views of a
six-DOF launch attached to an optics body according to an
embodiment of the present invention.
DETAILED DESCRIPTION
[0047] A laser tracker 10 is shown in FIG. 1. Although element 10
is referred to as a laser tracker, it may be more generally
referred to as a 3D coordinate measuring device. As explained in
the introduction, the term laser tracker is here used to refer to
laser tracker in a general sense and may include a TOF scanner, a
total station or other related device. As further explained herein
above, a laser tracker does not necessarily launch light from a
laser but instead may launch light from a superluminescent diode, a
light emitting diode (LED), or other light source. Likewise if the
element 10 is a TOF scanner that measures distance and two angles
to a point on an arbitrary surface, the TOF scanner may emit a
laser beam, light from a superluminescent diode, an LED, or any
other light source.
[0048] The laser tracker 10 in FIGS. 1A, 1B, 1C sends outgoing
light 90 through an exit aperture 74 to a retroreflector 95, which
returns the light along a parallel path as returning light 92,
which passes a second time through the exit aperture 74. The
tracker includes a base assembly 30, a yoke assembly 60, and a
payload assembly 70. An outer portion of the payload assembly 70
includes payload assembly covers 72, a first locator camera 76, a
second locator camera 78, and payload indicator lights 80. In an
embodiment, the indicator lights may shine green to indicate found
target, red to indicate measuring, and blue or yellow for
user-definable or six-DOF indications. An outer portion of the yoke
assembly 60 includes yoke-assembly covers 62 and yoke indicator
lights 64. Yoke indicator lights may advantageously be seen at
large distances from the tracker. An outer portion of the base
assembly 30 includes base-assembly covers 32 and magnetic
home-position nests 34 operable to hold SMRs of different
diameters. In an embodiment, three magnetic home-position nests 34
accept SMRs having diameters of 1.5 inches, 0.875 inch, and 0.5
inch. A mandrel 20 may optionally be attached to a lower portion of
the laser tracker 10.
[0049] The base assembly 30 includes a base pan 120, which includes
a handle 122, an air intake 140, and a fan 122 that serves as an
air exhaust. In an embodiment, the base assembly 30 further
includes an interface panel 40 having a number of buttons, ports,
and indicator lights. Buttons include an on-off button 42 and a
Wi-Fi (IEEE 802.11) button 44. In an embodiment, indicator lights
56 lights indicate laser power, system health, tracker Ethernet
(IEEE 802.3) activity, or six-DOF Ethernet activity.
[0050] In an embodiment, a temperature-sensor port 54 may accept an
air temperature sensor cable 1200 (FIG. 5A, 5B) or a material
temperature sensor cable 1210 (FIGS. 5D, 5D). The air temperature
sensor cable 1200 attaches to the tracker temperature sensor port
54 with the connector 1202 and senses air temperature with a cabled
air-temperature sensor 1204. The material temperature sensor cable
1210 attaches to the tracker temperature sensor port 54 with the
connector 1212 and senses material temperature with a cabled
material temperature sensor 1214.
[0051] In an embodiment, the interface panel 40 includes a
power-input port 50 that receives power from a cable 1020 (FIGS.
2B, 2C, 2D), which attaches with connector 1024 to the power-input
port 50. The cable 1020 further attaches a connector 1022 to a
second connector 1004 of an external power supply 1000 (FIG. 2A). A
cable 1010 attaches with connector 1012 to a first connector 1002
of the external power supply 1000. The cable 1010 attaches to power
mains with a country-specific power-mains plug 1014.
[0052] In an embodiment, a port 48 provides an Ethernet connection
for bidirectional communication between a computing device and the
laser tracker 10. In an embodiment, a cable 1250 (FIGS. 5P, 5Q)
attaches with a connector 1252 to the Ethernet port 48, and it
attaches with an Ethernet connector 1254 to the computing device.
In an embodiment, the Ethernet port 48 supports Gigabit
Ethernet.
[0053] In an embodiment, a tracker B port 52 provides auxiliary
interface signals to a B port 1156 of an auxiliary box 1150 (FIG.
4B). The auxiliary interface signals, which include power to the B
port 1156, may be delivered by a cable 1230 (FIGS. 5H, 5J, 5K),
which attaches with connector 1232 to the tracker B port 52 and
with connector 1234 to the auxiliary box B port 1156. A user
trigger signal may be delivered by a trigger cable 1240 (FIGS. 5L,
5M), which attaches with connector 1242 to a port 1168 of the
auxiliary box 1150. The trigger cable 1240 attaches at the other
end 1244 to a user trigger device.
[0054] In an embodiment, a tracker A port 46 provides a 24 VDC
power signal, a synchronization (sync) signal, and a time stamp to
a port 928 of a six-DOF probe 900 (FIGS. 6A-6G). The six-DOF probe
900 returns six-DOF signals to the tracker A port 46. In an
embodiment, the laser tracker 10 and the six-DOF probe 900
communicate bidirectionally over 100-Mb Ethernet between the A port
46 and the port 928. In an alternative embodiment, the signals from
the tracker A port 46 are sent first to the A port 1154 of the
auxiliary box 1150 before being sent on to the port 928 of the
six-DOF probe 900.
[0055] In an embodiment, the auxiliary box 1150 includes a front
panel 1161 and a rear panel 1155. The front panel 1161 includes a D
port 1164 and an E port 1166, each supporting industrial Ethernet.
In an embodiment, a cable 1220 attaches to the D port 1164 or the E
port 1166 with the connector 1222 of the cable 1220 and to an
industrial Ethernet component through the connector 1224.
Industrial Ethernet is Ethernet having protocols that provide
determinism and real-time control. Examples of protocols for
industrial Ethernet include EtherCAT, EtherNet/IP, PROFINET,
POWERLINK, SERCOS III, CC-Link IE, and Modbus/TCP.
[0056] In an embodiment illustrated in FIGS. 3A, 3B, a battery pack
1100 is used with the laser tracker 10. In an embodiment, the
battery pack 1100 includes a battery enclosure 1102, a battery
handle 1104, a first battery cover 1106, a second battery cover
1108, battery latches 1110, and input port 1116, and an output port
1112. Also included in the battery pack are a first battery unit
1107 and a second battery unit 1109 held inside the battery
enclosure 1102. A top side of the battery enclosure includes an
on/off button 1120 and battery indicator lights 1122. The battery
indicator lights 1122 show the amount of power left in the
batteries of the battery pack. In an embodiment, the power from the
two batteries is depleted in parallel. In another embodiment, the
power form the two batteries is depleted one at a time. In an
embodiment, the batteries may be hot-swapped without first powering
down the power supply unit. This enables power to be continuously
supplied to the laser tracker 10 even if the batteries have to be
replaced with freshly charged battery units.
[0057] In one mode of operation, the battery pack 1100 is used
stand-alone without being connected to the external power supply
1000. In this mode of operation, the battery pack 1100 provides DC
power through the output port 1112 to the laser tracker 10. In
another mode of operation, the battery pack 1100 receives DC power
from the external power supply 1000. In this case, DC power 1118 is
provided from the external power supply 1000 to the input port 1116
and passes through the output port 1112 to provide the DC out power
1114. In an embodiment shown in FIG. 3C, the battery handle 1104 of
the battery pack 1100 is hung from a tripod hook 1134 of an
industrial tripod 1130. A laser tracker 10 is coupled to the
industrial tripod 1130 through a threaded mount 1132. Hanging the
battery pack 1100 from the industrial tripod 1130 provides an
advantage in reducing the number of components in a limited work
area.
[0058] FIG. 7 shows a front view of the laser tracker 10. The base
assembly 30 is ordinarily stationary with respect to a work area,
for example, being mounted on an instrument stand or an industrial
tripod, possibly with a mandrel 20 placed between the laser tracker
10 and the mount 1132. The yoke assembly 60 rotates about an
azimuth axis 12, sometimes referred to as a standing axis or a
vertical axis, although it should be appreciated that the laser
tracker 10 may, in general, be positioned upside down or be rotated
to an arbitrary angle with respect to a floor. The payload assembly
70 rotates about a zenith axis 14, sometimes referred to as a
transit axis or a horizontal axis.
[0059] FIG. 8A shows elements of a base-assembly structure 110,
which includes a post 150, a plenum 130, a base pan 120, and a fan
122 that sits between the base pan 120 and the plenum assembly 130.
The base pan 120 and its integrated handle 122 is also seen in FIG.
1B. FIG. 8B shows the base-assembly structure 110 with the plenum
assembly 130 removed. With the plenum assembly 130 removed, the air
intake 140 and the fan 122 are more clearly shown. The SMR cutouts
152 accept additional components to become the magnetic
home-position nests 34 of FIG. 1A.
[0060] FIGS. 9A, 9B are isometric and exploded views, respectively,
of the plenum assembly 130. In an embodiment, room-temperature air
is pulled in through the air intake 140 and is expelled through the
air exhaust 142 before reaching the fan 122, which is attached to
the fan flange 144. As room temperature air is pulled into the
tracker, its temperature is measured with an air temperature sensor
placed in the air flow. The air temperature sensor is inserted into
the plenum assembly 130 through the plenum temperature sensor port
146. This air temperature sensor may be used along with a measured
pressure and a measure relative humidity to determine an index of
refraction of the air. Such a calculation may be done using an
Edlin equation or a Ciddor equation, as is known in the art.
Alternatively, the air temperature may be determined using an
external air temperature sensor 1200 as shown in FIGS. 5A, 5B. Such
an external air temperature sensor 1200 may be attached to the
temperature sensor port 54 or to one of the temperature sensor
ports 1160 of the auxiliary box 1150.
[0061] The relatively cool air entering the air intake 140 removes
heat from the electrical components within the tracker base
assembly 30 and expels heated air through the air exhaust 142. By
keeping the air drawn in from the outside enclosed within the
plenum assembly, electrical components may be cooled without the
possibility of contaminating other portions of the laser tracker
with dirt or moisture drawn in from outside the tracker. In an
embodiment, heat sinks 136 are attached on the inside of the
left-half plenum frame 132 and the right-half plenum frame 134 at
locations directly opposite hot electrical circuit components on
the outside of the plenum frame. In an embodiment, electrical
circuit components are attached to the outside of the plenum frame
with thermal adhesive to maximize heat transfer into the
circulating air within the plenum assembly 130. In an embodiment,
plenum gaskets 138 are used to seal the left-half plenum frame 132
to the right-half plenum frame 134.
[0062] FIGS. 10A, 10B show top and cross-sectional views of the
base-assembly structure 110. The post 150, the plenum assembly 130,
the heat sinks 136, and the base pan 120 are shown in the
cross-sectional view. FIG. 10B also shows a shock absorber 200 and
a mandrel receptacle 40. The mandrel receptacle is not a part of
the laser tracker 10 but may be attached to the post 150 by
receptacle threads 42.
[0063] FIGS. 11A, 11B, 11C, 11D are isometric, front, sectional,
and exploded views, respectively, of the shock absorber 200. A cap
202 provides a feature to accept a preload spacer 204 adjacent to a
damper 206 of compressible material. A stationary cover 220 having
an upper lip 222 and a lower lip 224 fits over a bell 210 having a
retractable surface 214 and a bell lip 212. Screws 232 attach a
threaded cover 230 onto the cap 202 to hold the bell 210 and
stationary cover 220 in place over the damper 206. The threaded
cover screws 230 into the post 150 to affix the shock absorber to
the post 150 as shown in FIG. 10B.
[0064] With the mandrel receptacle 40 screwed into the post 150, a
mandrel 20 may be coupled to the laser tracker 10. Many types of
mandrels and receptacles may be designed for us with the laser
tracker 10. A simple way to mount a laser tracker 10 on a stand or
a tripod is to attach the laser tracker 10 directly to a threaded
mount 1132 as shown in FIG. 3C. In this case, to rotate an entire
tracker assembly, including the base assembly 30, about a vertical
axis, the entire stand or tripod must be rotated. A mandrel
provides a way to rotate the entire tracker assembly 10 without
rotating the stand. In the case of the particular mandrel 20 shown
in FIG. 10C, mandrel inner threads shown in FIG. 1B are screwed
onto a threaded mount 1132 (FIG. 3C). A first wing 24 and second
wing 25 may assist in tightening or loosening the mandrel on the
threaded mount 1132. A laser tracker 10 placed on the mandrel with
the latch 28 opened is enabled to seat within the mandrel
receptacle 40 so that the flat mandrel contact surface 26 is
brought into contact with the lower flat contact surface 44 of the
mandrel receptacle 40. When the latch 28 is closed, one or more of
the teeth 30 extends outward to make contact with a tooth contact
surface 46, thereby locking the mandrel 20 to the post 150. There
are many alternative methods of locking a mandrel to a mandrel
receptacle beside the method described here.
[0065] Before the mandrel 20 is locked onto the post 150, while the
mandrel 20 is pushed into the mandrel receptacle 40, the mandrel 20
may suddenly drop a several millimeters onto the mandrel 20,
thereby exposing the laser tracker 10 to a mechanical shock. To
minimize the potential of such a shock to the laser tracker 10, the
shock absorber 200 may be integrated into the post 150. When the
laser tracker 10 begins to drop onto the mandrel 20, the mandrel
pressing surface 32 contacts the retractable surface 214, thereby
causing a compression of the damper 206 in the direction of
compression 240.
[0066] In an embodiment, a coordinate measuring device such as a
laser tracker 10 includes a housing, which is a structural support
of the coordinate measuring device. For example, in the laser
tracker 10, the housing is post 150 or the post 150 when combined
with the mandrel receptacle 40. The shock-absorber assembly 200 is
coupled to a lower portion of the housing 150. The shock-absorber
assembly reduces mechanical shock to the coordinate measuring
device 10 when the coordinate measuring device is brought into
contact with an external element (for example, the industrial
tripod 1130) that supports the housing.
[0067] FIG. 12 is an isometric view of a yoke frame 302 and a
zenith shaft 304 attached to the post 150 and base pan 120. FIG.
13A is a top view of the yoke frame 302, zenith shaft 304, post
150, and base pan 120. FIG. 13B is a cross section view of these
same components, and further includes some components internal to
these structural components. In an embodiment, the yoke frame 302
is a monolithic element of a metal, cast and then machined. FIG. 14
is an exploded view of elements in FIG. 13B. In an embodiment, a
yoke-assembly structure 300 includes the yoke frame 302. The
yoke-assembly structure 300 rotates within the post 150 about a
lower azimuth bearing 176 and an upper azimuth bearing 198, the two
azimuth bearings separated by a bearing spacer 196. The lower
azimuth bearing 176 is held in place with a bearing retaining ring
174 and an azimuth-bearing spindle nut 172. In an embodiment, an
azimuth rotor 194 is affixed to the bearing spacer 196. The azimuth
rotor 194, which in an embodiment includes permanent magnets,
rotates in response to changing electromagnetic fields produced by
an azimuth stator 192. Hence the azimuth rotor 194 and the azimuth
stator 192 are elements of an azimuth motor that rotates the yoke
frame 302 about the azimuth axis 12.
[0068] An azimuth encoder disk 166 is affixed to the yoke frame 302
and rotates with the yoke frame 302. A read-head circuit board 162
attaches to an alignment plate 164 that is affixed to the post 150.
The read-head circuit board 162 includes one or more read-heads
configured to read light reflected off fine markings evenly spaced
around a circumference of the azimuth encoder disk 166. Electronic
processing within the read-head circuit board 162 enables
determination of an azimuth angle of rotation about the azimuth
axis 12. An azimuth-encoder pack 160 includes the read-head circuit
board 162, the alignment plate 164, and the azimuth encoder disk
166.
[0069] An azimuth slip ring 180 is mounted within an interior
portion of the yoke frame 302. The azimuth slip ring 180 includes a
slip-ring housing 182, a slip-ring shaft 184, and a slip-ring
collar 186, which screws onto the yoke frame 302. A lower
collection of electrical wires feeds into the slip-ring shaft 184,
and an upper collection of electrical wires feed out of the
slip-ring housing 182. Electrical contacts internal to the azimuth
slip ring 180 cause electrical continuity to be maintained as the
housing rotates relative to the shaft. Electrical power and
electrical signals passing through the lower collection of
electrical wires passes through to the upper collection of
electrical wires and into electrical windings that create
electromagnetic fields in the azimuth stator 192. Signals from the
read-head circuit board 162 pass directly to circuit boards in the
base assembly 30 for processing to determine the azimuth angle of
rotation about the azimuth axis 12.
[0070] In an embodiment, the post 150 includes cutout regions
providing an on-tracker retroreflector 154 and an on-tracker mirror
156. These are covered by thin glass windows 155, 157,
respectively. In an embodiment, the on-tracker retroreflector 154
and on-tracker mirror 156 are each measured in a front-sight mode
and a back-sight mode, which enables extraction of compensation
parameters. Methods for determining such parameters are described
in U.S. Pat. No. 7,327,446 ('446), the contents of which are
incorporated by reference. A front-sight measurement is a 3D
measurement performed in a front-sight mode, which is a usual mode
of operation of the laser tracker 10. A back-sight measurement is a
3D measurement performed in a back-sight mode, which is a mode
obtained by starting with the tracker in the front-sight mode,
rotating the yoke frame by 180 degrees about the azimuth axis and
then rotating the zenith axis to point back and lock onto the
retroreflector or mirror target. In an ideal tracker, the pointing
direction in azimuth and zenith angles will be the same in the
front-sight and back-sight modes. Any discrepancy in the pointing
direction is indicative of an error, which can be corrected with a
compensation parameter, as described in '446.
[0071] The zenith shaft 304 is affixed to the yoke frame 302 as
shown in the cross-section view of FIG. 13B and the exploded view
of FIG. 15. In an embodiment, the zenith shaft 304 rotates within
the yoke frame 302 about zenith bearings 320, 340. In an
embodiment, the zenith bearings 320, 340 are spaced by zenith
bearing spacers 306, over which are placed spacer gaskets 308.
[0072] On one side of the zenith shaft 304, the zenith bearings
320, 340 are held in place with a bearing retaining ring 342 and a
bearing spindle nut 344. A rotor hub 356 attached to this side of
the zenith shaft 304 provides support for a zenith rotor 358, which
includes permanent magnet elements. A stator mount 352 attached to
the yoke frame 302 provides support for a zenith stator 354, which
includes electrical windings operable to produce electric fields
timed to produce rotation of the zenith rotor 358. The zenith motor
350 includes the rotor hub 356, the zenith rotor 358, the stator
mount 352, and the zenith stator 354.
[0073] In an embodiment, zenith encoder elements are positioned on
a side of the zenith shaft opposite that of the zenith motor 350.
On this side, the zenith bearing 320 is held in place with a
bearing retaining ring 322 and a bearing spindle nut 324. An
encoder disk 334 affixed to an encoder-disk mount 332 rotates with
the zenith shaft 304. An encoder board 338 affixed to an
encoder-board mount 336 is fixed with respect to the yoke frame
302. A zenith-encoder pack 330, which includes the encoder-disk
mount 332, the encoder disk 334, the encoder-board mount 336, and
the encoder board 338, enables determination of the zenith angle of
rotation about the zenith axis 14.
[0074] In an embodiment, a zenith slip ring 310 is positioned
within the zenith shaft 304, with the zenith slip-ring shaft 314
fixed with respect to the yoke frame 302 and the zenith slip-ring
housing 312 fixed with respect to the zenith shaft 304. An incoming
collection of electrical wires feeds into the slip-ring shaft 314,
and an outgoing collection of electrical wires feeds out of the
slip-ring housing 312. Electrical contacts internal to the zenith
slip ring 310 cause electrical continuity to be maintained as the
housing rotates relative to the shaft. Electrical power and
electrical signals pass from the incoming collection of electrical
wires and through to the outgoing collection of electrical wires
and into electrical windings that create electromagnetic fields in
the zenith stator 354.
[0075] FIG. 16A is a front view of the payload assembly 70 and an
upper portion of the yoke assembly 60. FIG. 16B is a
cross-sectional view D-D showing optical elements within the
payload assembly 70. Optical elements placed mainly along a central
portion of the payload assembly 70 are referred to as a
central-optics assembly 400, which includes a launch/collimator
assembly 410 and a position-detector assembly 460. Outside the
central-optics assembly 410 are an ADM module 600 and a six-DOF
launch 800.
[0076] FIGS. 17A, 17B, 17C are an isometric view, a rear view, and
a cross-sectional view, respectively, of the launch/collimator
assembly 410. In an embodiment, an optical fiber 422 attaches to a
flange 424 and a ferrule 426. The ferrule 426 may be polished at a
small angle such as 8 degrees to minimize back reflections. The
ferrule 426 attaches to a ferrule mount 430, which along with a
focus shim 432, is screwed to a collimator barrel 434. Light from
the optical fiber 422, which in an embodiment is visible light such
as red light, launches from a small ferrule spot having a diameter
of a few micrometers and diverges to meet collimator lens elements
which, in an embodiment, include a singlet lens 436 held in place
by a singlet retaining ring 438 and a doublet lens 440 held in
place by a doublet retaining ring 442. In an embodiment, the
collimator barrel 434 is made of steel having a coefficient of
thermal expansion (CTE) relatively close to the CTE of the glasses
in the singlet and the doublet. The thickness of the glass and air
spaces are designed to make the quality of the collimation
insensitive to changes in temperature. In an embodiment, the
launch/collimator assembly 410 is aligned outside of the laser
tracker, with each launch/collimator assembly being essentially the
same as any other, thereby enabling replacement of a
launch/collimator assembly 410 in a laser tracker 10 with any other
launch/collimator assembly 410 without performing further
adjustments.
[0077] In an embodiment, alignment of the launch/collimator
assembly 410 takes place in stages. In a first stage, the first
lens 436 is centered within a bore of the collimator barrel 434. In
this step, three identical gage pins having the same diameter are
selected that provide a snug fit for the lens within the bore. The
singlet retaining ring 438 and three set screws 443 are placed
around the first lens 436 to hold it in place while epoxy is
applied through epoxy injection holes 444. After the epoxy has set,
the set screws 443 may be removed. In a second stage, the second
lens 440 is centered within the bore of the collimator barrel 434.
As above, three identical gage pins are used to roughly center the
lens 440, which is afterwards held lightly in place while a further
procedure is performed to center the second lens 440 with respect
to the first lens 436. In an embodiment, centering is done by
sending a plane wave of light through the doublet and singlet lens.
A photosensitive array is used to view the light passing through
the two lenses, and the position of the second lens adjusted to
minimize optical aberrations observed on the photosensitive array.
The doublet retaining ring 442 and three set screws 443 are
tightened before applying epoxy through the epoxy injection holes
444. In a third stage, the focus shim 432 is selected to place the
beam waist of the collimated beam of light at a predetermined
distance from the launch/collimator assembly 410. This may be done
by checking the diameter of the beam at a few different distances
from the launch/collimator assembly 410. In a fourth stage,
adjustment screws 446 are positioned to center the launched beam to
travel along the optical axis of the lens.
[0078] FIG. 17A shows two alignment holes 449 on the front of the
launch/collimator assembly 410. The alignment holes 449 mate with
alignment pins 451 of a combiner assembly 450 shown in FIG. 18. By
using alignment elements to enable consistent alignment of any
launch/collimator assembly 410 to a combiner assembly, replacement
of any launch/collimator assembly 410 with any other
launch/collimator assembly 410 is possible without realigning any
components within the laser tracker 10. Although a pin-and-hole
alignment method is described here, it should be appreciated that
any sort of repeatable alignment features may be used. Attachment
screws 458 are used to firmly fix the launch/collimator assembly
410 to the combiner assembly 450.
[0079] The combiner assembly 450 is used to combine the
launch/collimator assembly 410 with the position-detector assembly
460, and it is also used to combine different beams of light from
the position detector splitter 454 and the six-DOF splitter 456.
The position-detector assembly 460 includes a position detector 478
mounted on a position-detector circuit board 506. The position
detector 478 is a detector that converts light into electrical
signals and further provides secondary electrical signals that
enable determination of a position at which light strikes a surface
area of the position detector 478. Examples of position detectors
include a lateral effect detector, a quadrant detector, a
complementary metal-oxide-semiconductor (CMOS) array, and a
charge-coupled detector (CCD).
[0080] The position-detector assembly 460 is ordinarily used to
keep the outgoing beam of light 90 centered or nearly centered on a
moving retroreflector 95, thereby causing the returning beam of
light 92 to follow the same path as the outgoing beam of light 90.
A control system causes the tracker motor to steer the beam to keep
moving the beam toward the center of the position detector, thereby
enabling tracking of the retroreflector 95 with the laser tracker
10. In practice, when the outgoing beam is exactly centered on a
retroreflector, the returning beam may fall a little off a center
of the position detector 478. The position on the position detector
of the return beam when the outgoing beam is centered on the
retroreflector is referred to as the beam-retrace position.
[0081] The position detector assembly 460 is aligned by sending a
laser beam from the launch/collimator assembly 410 out of the
tracker to the center of a retroreflector and then aligning
elements of the position-detector assembly 460 to the returning
laser beam. In an embodiment, the position-detector assembly 460
includes a position-detector filter 462, an aspheric lens mount
464, an aspheric lens 466, an aspheric-lens retaining ring 468, a
pinhole 470, a pinhole retainer 472, a position-detector sensor
mount 474, a holographic diffuser 476, the position detector 478,
the position-detector circuit board 480, and a position-detector
clamping ring 482. The position-detector filter 462 blocks unwanted
light at wavelengths other than the wavelength launched by the
launch/collimator assembly 410. The aspheric lens 466 reduces the
size of the beam but does not focus it onto the position detector
478, which would result in measuring angle of returned light rather
than lateral offset of returned light. The pinhole is used to block
any unwanted ghost beams that might result, for example, from an
unwanted double reflection off an optical element within the laser
tracker 10. In an embodiment, the six-DOF splitter 456 has a
dichroic coating that passes one wavelength and reflects another
wavelength. For example, if the wavelength of the passed light is
640 nanometers (nm), which is red light, and the wavelength of a
projected six-DOF light is 940 nm, the dichroic beam splitter 456
for the geometry shown would reflect the 940 nm light and transmit
the 640 nm light.
[0082] In an embodiment, a launch-collimator assembly receives a
first light through a first optical fiber, launces it into free
space, and collimates the launched first light into a first beam of
light. The launch-collimator assembly is pre-aligned and
pre-collimated outside a coordinate measuring device, which might
be a laser tracker. The launch-collimator assembly is further
coupled through a first optical fiber to a distance meter operable
to measure a first distance to a target illuminated by the first
beam of light. The launch/collimator assembly is exchangeable in
the coordinate measuring device with any other launch/collimator
assembly without realignment of any elements within the coordinate
measuring device. In a further embodiment, the exchangeable nature
of the launch/collimator assembly is facilitated using mating
features of the launch/collimator assembly with elements internal
to the coordinate measuring device. In an embodiment, the mating
features are alignment pins and alignment holes. In a further
embodiment, the first beam of light is a visible beam of light such
as a red beam of light.
[0083] FIG. 19 is a block diagram of tracker electronics 500. In an
embodiment, fundamental circuit boards to obtain measurement data
include an azimuth encoder board 502, a zenith encoder board 504, a
position-detector board 506, an ADM module 600, an
analog-to-digital converter (ADC) board 510, and a payload digital
board 512. The azimuth encoder board 502 and the zenith encoder
board 504 process encoder read-head information from the azimuth
and zenith encoder boards, respectively, and communicate with the
azimuth motor board 503 and the zenith motor board 505,
respectively. The position detector board 506 determines position
at which light strikes the position detector 478. The ADM module
600 provides RF modulation and processing for the ADM system 1300.
The ADC board 510 digitizes signals from the ADM module 600 and the
position detector 478. The payload digital board 512 provides
electrical processing for the first locator camera 76 and the
second locator camera 78 and communicates with the camera processor
board 514. The payload digital board 512 also communicates with the
six-DOF light source driver 513. These fundamental circuit boards
described above communicate bidirectionally with a synchronization
(sync) board 517, which performs ADM calculations, processes
position detector data, synchronizes all tracker data to one kHz,
and performs an ADM Kalman filtering calculation at a 15 kHz
rate.
[0084] In an embodiment, the sync board 517 and the camera
processor board 514 both communicate with a real-time processor
board 516. The real-time processor board 516 further communicates
with a six-DOF active probe by providing a time stamp and
communicating over Ethernet. The real-time processor board 514
provides a real-time operating system. It is responsible for
azimuth, zenith, and ADM data acquisition; for establishing the
1-kHz control loop; for generating the 1-kHz sync latch; for
correcting the position detector readings; for generating a 32-bit
time stamp and attaching it to readings; for generating three-DOF
values; and for fusing readings from a six-DOF probe to obtain
six-DOF readings.
[0085] In an embodiment, the camera processor board 514 has a Linux
operating system. The camera processor board 514 performs camera
control, camera processing, gesture processing, SMR position
processing using two cameras, and Wi-Fi processing. The camera
processor board 514 attaches to a daughter board 515 that provides
Wi-Fi and Bluetooth (IEEE 802.15.1) for smart devices 560 such as
laptops, notepads, and smart phones. The camera processor board 514
also provides an interface for communicating with external
computers and networks by Ethernet and Wi-Fi. It should be
appreciated that many types of tracker electronics may be used to
perform the functions of the laser tracker 10. More or fewer
processing components may be used, and some processing may be
carried out by processors external to the laser tracker 10. Fewer
circuit boards may be used to accommodate the required circuit
components, or separated into further circuit boards. The term
processor is generally understood to include memory used to store
information and intermediate results.
[0086] FIG. 20A is an isometric view of the ADM module 600 and the
ADC board 510 according to an embodiment. The ADC board 510 is
mounted over the ADM module 600, which at its top level includes an
ADM transceiver board 602. On a lower side of the ADM transceiver
board 602 is an upper shielded enclosure 604, which is a shielded
enclosure operable to shield sensitive circuit elements of the ADM
transceiver board 602 from RF electromagnetic interference. Below
the upper shielded enclosure 604 is a lower shielded enclosure 606,
which further includes a fiber-optic adapter 608. As shown in FIG.
20B, in an embodiment, the ADM module includes an ADM light source
640, an optional Faraday isolator 700, an optional temperature
control 701, a fiber-optic network 660, and ADM electronics 620. In
an embodiment, the ADM electronics 620 provides a bias current and
an electrical RF modulation to the ADM light source 640, which in
an embodiment is a visible laser such as a red laser. In an
embodiment, the ADM light source 640 is connected to the Faraday
isolator 700 by a first optical fiber 612, and the Faraday isolator
700 is connected to fiber-optic network 660 by a second optical
fiber 614. As discussed further below, in an embodiment, the
fiber-optic network 660 sends light to the fiber optic adapter 608
and also to the ADM electronics 620. A part of light returned from
a target 95 also passes back through the launch/collimator assembly
410 and the fiber-optic network 660 to reach the ADM electronics
620.
[0087] In an embodiment illustrated in FIG. 20B, a
collimator/launch assembly 410 includes a fiber-optic connector
682, which is attached to the optical fiber 422. The fiber-optic
connector 682 mates with the fiber-optic adapter 608. In addition
to the fiber-optic connector 682, the collimator/launch assembly
410 includes other launch/collimator components 684 as shown in
FIGS. 17A, 17B, 17C. Central optics assembly 400 includes
launch/collimator assembly 410, beam splitter 454, and
position-detector assembly 460.
[0088] Many types of light sources may be used in the laser tracker
10, including lasers, superluminescent diodes, LEDs, or other types
of light sources. If the light source 640 is a laser, it may be any
of several types of laser such as a semiconductor laser (also
referred to as a diode laser), a solid-state diode-pumped laser, or
a gas laser. For a light source 640 used in an ADM module 600 in
which distance is based on a phase determination, as described
below with respect to FIG. 23, measurements have typically been
carried out using a distributed feedback (DFB) semiconductor laser
because DFB lasers are designed to maintain a constant laser
wavelength and to produce a single longitudinal mode (as well as a
single transverse mode), thereby providing a stability to the
measurement of phase in the determination of the measured
distance.
[0089] It would be highly desirable for a laser tracker 10 to make
3D measurements and to further track a retroreflector target 95
using a single visible wavelength. Use of a single visible
wavelength eliminates potential problems from misalignment of
multiple-wavelength laser beams in propagating over large
distances. A further advantage is that a visible laser maintains a
smaller beam size when propagating over distance, which is helpful
when propagating to distant, small retroreflector targets. Another
potential advantage is a potential reduction in the manufacturing
cost of the laser tracker 10. However, DFB lasers are not readily
available with desirable modulation characteristics for ADM
measurements at visible wavelengths. An alternative to a DFB laser
is a Fabry-Perot laser, which is a type of semiconductor (diode)
laser. Such a laser does not include wavelength stabilizing
structures as in a DFB laser and so a Fabry-Perot laser ordinarily
generates multiple longitudinal modes. By providing a Fabry-Perot
laser with a relatively large drive current and by avoiding
conditions near mode-hop regions, it is possible for the
Fabry-Perot laser to emit one wavelength that is much larger than
emitted sideband wavelengths. The spacing of sideband wavelengths
depends on the length of a cavity in the active lasing region. For
a Fabry-Perot laser at visible wavelengths, sidebands might be
spaced at intervals of around 200 picometers from the main lasing
wavelength, for example.
[0090] To obtain the best ADM measuring performance of an ADM
module 600 using a Fabry-Perot laser, the size of the relatively
small emitted sideband wavelengths should be stabilized relative to
the main (largest) laser mode and the emitted wavelength of the
main laser mode should further be stabilized. A way to achieve
these objectives is to stabilize the temperature of the Fabry-Perot
diode laser 642. FIG. 20C show how this may be done by coupling a
temperature sensor 654 and a thermoelectric cooler (TEC) 656 to the
laser 642. In an embodiment, the temperature sensor 654 sends a
first electrical signal to electronics in the ADM module 600, which
in turn sends the TEC 656 a second electrical signal adjusted to
hold the temperature of the diode laser 642 at a constant value. An
added advantage of holding the diode laser 642 at a constant
temperature is that it may extend the lifetime of the diode laser
642 since lifetime of the diode laser 642 decreases with increasing
temperature.
[0091] Distance measurements by the ADM module 600 may be further
stabilized by controlling the level of the DC bias current applied
by to diode laser 642 to hold the output optical power of the diode
laser 642 at a constant level. In an embodiment, the DC bias and
the RF signal are combined in the ADM module 600 using a bias-tee
circuit that includes inductor and capacitor components. The
combined RF/DC signal 650 is applied to the diode laser 642. In an
embodiment, an electrical signal 652 from a back-facet monitor
photodiode of the diode laser 642 is fed to electronics in the ADM
module 600. This adjusts the level of the applied DC bias in the
combined RF/DC signal 650 to hold the optical output power from the
diode laser 642 at a constant level.
[0092] In an embodiment, the Fabry-Perot diode laser 642 includes
an active region 643 from which the emitted light 644 emerges. The
emitted light 644 passes through a lens 646, which might be a small
glass sphere, for example. Other types of lenses, including
non-spherical glass lenses and gradient-index lenses, may
alternatively be used. In an embodiment, back reflections are
minimized by coating the lens 646 with an antireflection coating.
The lens 646 focuses the light into a core of an optical fiber 612.
The optical fiber 612 may be a regular single-mode (SM) optical
fiber that supports the selected visible wavelength, or it may be a
polarization maintaining (PM), but still single-mode, optical
fiber. The light is focused by the lens 646 into a small spot of
approximately the same size as the core in the optical fiber 612.
For visible light, the core diameter may be around 4 micrometers.
Ordinarily laser light emitted by a Fabry-Perot laser 642 is
linearly polarized. Effort is required to align the linearly
polarized laser light to the polarization axis of a PM fiber. This
effort may be reduced by using a polarization-insensitive Faraday
isolator, which enables the light to be focused into a SM fiber
rather than a PM fiber, as explained with reference to FIGS. 21A,
21B. In some cases, it may be possible to eliminate the Faraday
isolator 700 altogether, as explained further below.
[0093] An integrated or packaged laser assembly 640 includes the
diode laser 642, the lens 646, the optical fiber 612, the
temperature sensor 654, the TEC 656, and the back-facet monitor
diode, which produces a signal 652. Initially, the packaged laser
assembly 640 includes a pigtailed optical fiber 612 at its output,
but this is connected to an input fiber from the Faraday isolator
700 to become a connected optical fiber 612. In an embodiment, the
pigtailed fibers of the packaged laser assembly 640 and the
pigtailed fibers of the next component (either the Faraday isolator
700 or the fiber network 660) are fusion spiced together.
Alternatively, the pigtailed fibers of the packaged laser assembly
and the pigtailed fibers of the next components may be connected by
mating a fiber-optic connector and a fiber-optic adapter. This
latter option is more bulky than the fusion-spliced option, but it
offers the possibility of easily exchanging a Fabry-Perot laser
after a few years of use. In an embodiment, an optical-fiber end
face 613 is not perpendicular to the optical fiber 612 but instead
is angled to the perpendicular, for example, by 8 degrees from
perpendicular. This angled back face minimizes the emitted light
644 that reflects off the fiber end face 613 and then passes back
to the diode laser 642, potentially causing destabilization of the
diode laser 642.
[0094] The purpose of the Faraday isolator 700 in FIG. 20B is to
minimize back-reflected light, for example, light that leaves the
laser tracker 10, reflects off the retroreflector 95, returns to
the tracker, passes through the optical fiber 612 and enters the
laser 642. In this document, the ratio of the optical power
reflected from a target to the optical power launched from an ADM
light source 640 is referred to as the back-reflection ratio.
Generally, the back-reflection ratio needed to destabilize a diode
laser depends on the particular laser but usually falls between one
part in one thousand (0.001) and one part in one hundred thousand
(0.00001). The required laser back-reflection ratio should be
maintained over rated operating temperatures of the laser tracker
10. Rated operating temperatures are those temperatures for which
specifications of the laser tracker 10 are applicable.
[0095] There are two ways to reduce the laser backreflection ratio:
(1) by providing isolation using an isolator and (2) by providing
optical loss over the round-trip path of the laser light from the
laser light source to the target and back to the laser light
source. These two ways of reducing laser backreflection ratio are
discussed further below in reference to FIGS. 20B, 21A, 21B,
22.
[0096] FIG. 21A is a schematic representation of a
polarization-dependent Faraday isolator 700A. The term
"polarization-dependent" means that the polarization of the light
entering the Faraday isolator 700A must be linearly polarized in a
specified direction. In an embodiment, the input optical fiber 612A
is fusion spliced to the optical fiber from the ADM light source
640 as described previously. Light leaving the optical fiber 612A
diverges as a cone of light 712A, arrives at collimating lens 702A,
and becomes collimated light 713A. When traveling away from the
light source, an outgoing light beam 717A passes through input
polarizer 703, passes through Faraday rotator 705, passes through
output polarizer 704, arrives at collimating lens 706A, converges
as a cone of light 715A, and passes into optical fiber 614A, which
in an embodiment is fusion spliced to the input optical fiber 614
of the fiber-optic network 660.
[0097] The polarization state 724 of the light after passing
through the input polarizer 703 is shown in a representation 723 of
the polarization states, which in 723 are shown in a plane
perpendicular to the "paper." A coordinate system 720 applied to
the Faraday isolator 700A shows that the light propagates along the
z axis, with the optical components lying in the x-y plane. A
coordinate system 722 shows the plane x-y in which the polarization
states are shown in the representation 723, with x pointing into
the paper and y pointing upward. In the example shown in FIG. 21A,
the input polarizer 703 is oriented so that the light passing
through it is linearly polarized in the y direction in a
polarization state 724. In an embodiment, the Faraday rotator 705A
includes a Faraday-rotator crystal surrounded by permanent magnets.
In passing through the Faraday rotator 705A, the polarization
rotates 45 degrees in a clockwise direction, ending in a
polarization state 726 aligned to a polarization direction of the
output polarizer 704. Hence, for ideal polarizer and Faraday
rotator components, there is no loss in optical power for light
traveling in a forward direction
[0098] A returning beam of light 718A may be decomposed into two
polarization states, one aligned to the polarization direction of
the output polarizer 704 and transmitted by the polarizer 704 to
end in a polarization state 730. The other polarization state is
perpendicular to the polarization state of the output polarizer 704
and is blocked from reaching the ADM light source 640. Light in the
polarization state 730 passes through the Faraday rotator 705A and
continues to rotate clockwise, ending in the polarization state
728, thereby being blocked by the input polarizer 703. Hence, an
ideal Faraday isolator 700A completely blocks the returning beam of
light 718A from reaching the ADM light source 640.
[0099] FIG. 21B is a block representation of a
polarization-insensitive Faraday isolator 700B, which is a type of
Faraday isolator capable of accepting light in any polarization
state at the input to the Faraday isolator 700B. This property is
convenient because it saves the effort and expense of aligning the
linearly polarized laser light from the ADM light source 640 to a
PM fiber and to align the output of the PM fiber to the input
polarizer 703 in FIG. 21A. In an embodiment, an input optical fiber
612B is fusion spliced to the optical fiber 612 from the ADM light
source 640. Light leaving the optical fiber 612B diverges as a cone
of light 712B, arrives at a collimating lens 702B, and becomes
collimated light 713B. When traveling away from the light source
640, an initial outgoing light beam 740B passes through a
birefringent beam displacer 708 aligned to separate light into two
orthogonal polarization states 771 and 781 that travel in two
different beam paths. An outgoing light 742 travels in an upper
channel 762, and an outgoing light 744 travels in a lower channel
760, respectively. The outgoing beams of light 742, 744 have
polarization states 770, 780 respectively. These polarization
states are shown in 770, 780 rotated perpendicular to the plane of
the paper according to the coordinate systems 767, 766
respectively, with the meaning of the coordinate systems understood
in relation to a coordinate system 765 aligned to components of the
Faraday isolator 700B, with z being a direction of propagation.
[0100] The outgoing light 742 passes through a Faraday rotator
705B, which rotates it to a polarization state 772, and then
through a half-wave plate 710, which rotates the light to a
polarization state 773. The outgoing light 744 passes through
Faraday rotator 705B, which rotates it to a polarization state 782,
and then through the half-wave plate 710, which rotates the light
to a polarization state 783. Light in the polarization state 773
passes through birefringent beam displacer 709 in the upper channel
762. Light in the polarization state 783 is in the lower channel
760 and passes through the birefringent beam displacer 709 to join
the beam in the upper channel in a common outgoing light beam 746,
which is a collimated beam of light 714B. A collimating lens 706B
sends a converging cone of light 715B into an optical fiber
614B.
[0101] The returning beam of light traveling in the reverse
direction may be decomposed into two polarization states, which are
separated by the birefringent beam displacer 709 into returning
light 748 in the upper channel 762 and returning light 750 in the
lower channel 760. The returning light 748 passes the birefringent
beam displacer 709, ending in a polarization state 774. It passes
the half-wave plate 710 to end in polarization state 775 and the
Faraday rotator 705 to end in polarization state 776. In passing
through the birefringent beam displacer 708, it continues to travel
in a straight path and encounters a beam block surface 752, which
prevents the returning beam from reaching the ADM light source 640.
In the lower channel, the returning light 750 passes the
birefringent beam displacer 709, ending in a polarization state
784. It passes the half-wave plate 710, ending in a polarization
state 785, and the Faraday rotator 776, ending in the polarization
state 786. In passing through the birefringent beam displacer 708,
it continues to travel in a straight path and encounters a beam
block surface 752, which prevents the returning beam from reaching
the ADM light source 640.
[0102] Several types of fiber-optic networks 660 are possible in
the ADM module 600. Three representative fiber-optic networks are
described in FIGS. 8A, 8B, 8C of U.S. Pat. No. 8,537,376, the
contents of which are incorporated by reference. FIG. 22 in the
present application is a schematic representation of the
fiber-optic network 660 according to an embodiment. The fiber-optic
network 660 includes a first fiber coupler 666 and a second fiber
coupler 672 connected together by an optical fiber 668, which may
result from fusion-splicing together of pigtailed fibers from the
two couplers 666, 672.
[0103] A portion of light exiting the first fiber coupler 666
passes through fibers 662, 663 to a reference detector 630 (FIG.
23) in a reference channel of the ADM module 600. Another portion
of the light exiting the first fiber coupler 666 passes through the
optical fiber 668 and on to the second fiber coupler 672. A portion
of the light continues through an optical fiber 674 to a
low-reflection termination 675. Another portion of the light
continues through an optical fiber 607 out of the fiber-optic
network 660. On a return path through the fiber-optic network 660,
light passes in a reverse direction through the optical fiber 607
into the second fiber coupler 672. A portion of the returned light
passes through an optical fiber 664 to a measure detector 631 (FIG.
23) in a measure channel. Another portion of the light passes
through the second fiber coupler 672 and through the optical fiber
668 into the first fiber coupler 666. A portion of the light in the
first fiber coupler passes through the optical fiber 669 to a
low-reflection termination 670. Another portion of the light passes
back through the optical fiber 614.
[0104] As an example of a change in optical power from the laser
642 to the retroreflector 95 and back to the laser 642, suppose the
laser 642 has a coupling efficiency into the optical fiber 612 of
70 percent, the Faraday isolator 700 has a coupling efficiency of
70 percent, the first fiber coupler 666 passes 98 percent of
remaining optical power to the second fiber coupler 672, the second
fiber coupler passes 10 percent of remaining optical power to the
launch/collimator assembly 410, the beam splitters 454, 456 have a
combined transmittance of 95 percent, and the retroreflector 95
returns 75 percent of incident optical power. Further suppose that
the Faraday isolator 700 has an isolation of -30 dB, which is a
fractional return of optical power of 0.001. For these conditions,
the fraction of optical power returned to the laser 642 relative to
the launched power from the laser is
(0.7)(0.7)(0.98)(0.1)(0.95)(0.75)(0.95)(0.1)(0.98)(0.7)(0.7)(0.001)=1.6.t-
imes.10.sup.-6=-58 dB. Suppose that testing demonstrates that the
diode laser 642 remains stable for back-reflected light as large as
-28 dB. In this case, it might be possible to remove the Faraday
isolator altogether and increase the optical loss slightly. Without
the Faraday isolator 700, for the conditions given above, the
fraction of optical power returned to the laser 642 relative to the
launched power from the laser is
(0.7)(0.98)(0.1)(0.95)(0.75)(0.95)(0.1)(0.98)(0.7)=0.0032=-25 dB.
In this case, an increase in the system round-trip loss by 3 dB (a
fractional factor of 2) somewhere in the system might be included
to reduce the back-reflected optical power to -28 dB, thereby
eliminating the need for the Faraday isolator 700. On the other
hand, if testing demonstrated that the diode laser 642 remains
stable for back-reflected light as large as -40 dB, the Faraday
isolator 700 would need to provide at least 15 dB of isolation to
maintain stable laser operation. If the laser tracker 10 were
designed to meet its specifications over rated operating
temperatures from 0 to 50.degree. C., and if the isolation of the
Faraday isolator 700 were found to fall by 15 dB for a change in
temperature of 15.degree. C., then a temperature control system 701
would be needed to hold the temperature range within +15.degree. C.
One way to do this would be to include a heater blanket in the
temperature control system. In this case, the heater blanket might
be set to a baseline temperature of 40.degree. C., with a minimum
temperature (with no current applied to the heater blanket) of
25.degree. C. and with maximum temperature (with maximum current
applied to the heater blanket) of 55.degree. C. In this case, the
ambient air temperature (outside the laser tracker 10) would fall
between 0 and 50.degree. C. In this example, the temperature
control system 701 would include three elements: a heater blanket,
a temperature sensor, and a control circuit, the control circuit
operable to set current to the heater blanket to keep the
temperature of the Faraday isolator 700 as close to 40.degree. C.
as possible.
[0105] In an embodiment, a coordinate measuring device 10 includes
a first light source 640, a Faraday isolator 700, and a fiber-optic
network 660. The coordinate measuring device may be a laser
tracker. The first light source 640 emits a first light. In an
embodiment, the first light source 640 includes a Fabry-Perot
laser, a lensing system, a first optical fiber, and a
thermoelectric (TE) cooler. The Fabry-Perot laser produces visible
light at a first wavelength. The lensing system couples the
produced first light into the first optical fiber, which is a
single-mode optical fiber. The TE cooler holds the Fabry-Perot
laser at a constant temperature. The Faraday isolator passes first
light traveling in a forward direction but blocks the first light
traveling in a reverse direction toward the light source. The
Faraday isolator includes an input optical fiber coupled to the
first optical fiber. The Faraday isolator further includes an
output optical fiber. The fiber network receives the first light
from the output optical fiber and passes a first portion to a
launch-collimator assembly that launches the first portion of the
first light into free space and collimates the launched first light
into a first beam of light. As stated above, the coordinate
measuring device may be a laser tracker. In this case, the
coordinate measuring device includes a first motor and a second
motor to steer the beam, a first angle measuring device and a
second angle measuring device to determine the direction of the
first beam of light, a distance meter that measures distance to a
retroreflector, and a processor that determines 3D coordinates of
the retroreflector. In an embodiment, the laser tracker may further
include a position detector. In an embodiment, the first light is
used by the distance meter to determine distance and by the
position detector to keep the first beam of light locked on the
retroreflector. In an embodiment, the first light is visible light
such as red light.
[0106] FIG. 23 is a block diagram of components of an ADM 1300
according to an embodiment. The ADM 1300 includes the ADM light
source 640, the ADM electronics 620, the ADC board 510, and a
processor 639. The processor 639 may include one or more computing
elements within the tracker electronics 500 and may further include
one or more external computing elements outside the laser tracker
10. In the embodiment illustrated in FIG. 23, the ADM 1300
determines distance based on a calculated phase of electrically
modulated light. In alternative embodiments, an absolute distance
meter may be based on other operating principles such as a pulsed
time-of-flight approach or a frequency-modulation continuous wave
(FMCW) approach.
[0107] In an embodiment, the ADM electronics 620 includes a
frequency reference 621 that provides a highly stable reference
signal at a specified frequency. In an embodiment, the frequency
reference 621 is an oven-controlled crystal oscillator (OCXO)
generating a stable and accurate sinusoidal or square-wave signal.
In an embodiment, the frequency reference 621 generates a frequency
of 20 MHz that is accurate and stable to within 4 Hz. The frequency
reference 621 is provided to a synthesizer 623 that generates
signals at a radio frequency (RF) f.sub.RF, a local-oscillator (LO)
frequency f.sub.LO, and a sampling frequency f.sub.SAMP.
[0108] In an embodiment, the ADM light source 640 is a Fabry-Perot
laser that emits visible light, such as red light. In alternative
embodiments, another type of laser such as a distributed feedback
(DFB) laser is used. The synthesizer 623 sends an electrical signal
626, which includes a modulation signal and a DC bias current, to
the ADM light source 640. In an embodiment, the modulation signal
may be sinusoidal, rectangular, or alternatively shaped signal
having at least one fundamental modulation frequency f.sub.RF. The
ADM light source 640 emits light 627 modulated at the modulation
frequency f.sub.RF. In an embodiment, the optical power of the ADM
light source 640 is modulated at the modulation frequency f.sub.RF.
This type of modulation is referred to as intensity modulation.
Some of the modulated light 627 passes through the optical fibers
662, 663 (FIG. 22) and arrives as an optical signal 628 at a
reference detector 630 that converts the optical signal 628 to an
electrical signal having a fundamental modulation frequency
f.sub.RF. In an embodiment, the electrical signal passes from the
reference detector 630 to conditioning electronics 632 that
provides a conditioned electrical signal to a mixer 634. The
synthesizer 623 sends a local-oscillator (LO) port of the mixer 634
an electrical signal 624 having the LO frequency f.sub.LO. In
response, the mixer 634 produces a signal having an intermediate
frequency (IF) f.sub.IF equal to a difference in the LO and RF
frequencies. The output of the mixer 634 may include additional
frequencies besides f.sub.IF. The output of the mixer 634 passes
through conditioning electronics 636, which may include an
electrical filter that removes unwanted frequencies. The signal
from the conditioning electronics 636 passes to the ADC board 510,
which samples the IF signal 638A at the sampling frequency
f.sub.SAMP to obtain a collection of sampled values. In an
embodiment, the intermediate frequency is 120 kHz and the sampling
rate is 15 kHz, so that 8 sampled values are obtained for each
cycle of the IF signal 638A. In an embodiment, a processor 639 uses
an algorithm to extract the phase of the IF signal 638A from the
sampled values.
[0109] Another part of the modulated light 627 is projected out of
the laser tracker 10, strikes the retroreflector 95, and returns to
the laser tracker 10. A part of the reflected light passes through
the optical fiber 664 (FIG. 22) and arrives as an optical signal
629 at a measure detector 631 that converts the optical signal 629
to an electrical signal having the fundamental modulation frequency
f.sub.RF. The electrical signal passes from the measure detector
631 to conditioning electronics 633 that provides a conditioned
electrical signal to a mixer 635. The synthesizer 623 sends the
mixer 635 an electrical signal 624 having the LO frequency
f.sub.LO. In response, the mixer 635 produces a signal having an
intermediate frequency (IF) f.sub.IF equal to a difference in the
LO and RF frequencies. The output of the mixer 635 may include
additional frequencies besides f.sub.IF. The output of the mixer
635 passes through conditioning electronics 637, which may include
an electrical filter to remove unwanted frequencies. The signal
from the conditioning electronics 637 passes to the ADC board 510,
which samples the IF signal 638B at the sampling frequency
f.sub.SAMP to obtain a collection of sampled values. In an
embodiment, the intermediate frequency is 120 kHz and the sampling
rate is 15 kHz, so that 8 sampled values are obtained for each
cycle of the IF signal 638B. In an embodiment, the processor 639
uses an algorithm to extract the phase of the IF signal 638B from
the sampled values, using methods known in the art. In an
embodiment, the processor 639 uses the determined phases for the IF
signals 638A, 638B to determine a distance (the result) to the
target.
[0110] In an embodiment, when a the light from the ADM light source
640 is first sent to the retroreflector 95, the frequency f.sub.IF
is rapidly cycled among a plurality of different frequencies,
thereby enabling determination of an unambiguity range for the
retroreflector 95. Thereafter, the tracking of the retroreflector
95 by the laser tracker is relatively rapid, say 1000 measurements
per second, thereby enabling the laser tracker 10 to keep track of
the current unambiguity range occupied by the retroreflector 95
using a single modulation frequency f.sub.RF as the retroreflector
95 is moved. If the beam of light to the retroreflector 95 is
broken, the ADM 1300 again rapidly cycles through the plurality of
frequencies to re-establish the unambiguity range. In this
discussion, the term unambiguity range R.sub.U is understood to be
R.sub.U=c/(2f n), where c is the speed of light in vacuum, f is the
modulation frequency f.sub.RF, and n is the index of refraction of
the air through which the beam of light from the ADM light source
640 travels to the retroreflector 95. In an alternative embodiment,
the target 95 is not a retroreflector but is a diffusely scattering
surface. In this case, since measured distances to a surface can
abruptly change as the beam of light is moved transversely, the
light from the ADM 1300 may simultaneously include a plurality of
modulation frequencies to continually determine a present
unambiguity range. A typical number of such simultaneous modulation
frequencies is three to six.
[0111] A method for extracting phase from an ADM is described in
U.S. Pat. No. 7,352,446, the contents of which are incorporated by
reference. It should be understood that phase extraction may also
be obtained using electrical architectures different than that of
FIG. 23. An example of such an alternative electrical architecture
is described in U.S. Pat. No. 9,157,987, the contents of which are
incorporated by reference. It should further be appreciated that
many alternative types of absolute distance meters are possible and
may be used in place of the ADM 1300.
[0112] In an embodiment, the laser tracker 10 is a six-DOF laser
tracker that uses a six-DOF launch 800 and a six-DOF probe 900 to
determine six degrees-of-freedom of the six-DOF probe 900. In an
embodiment, the six-DOF probe 900 includes a tactile probe 910
capable of measuring with a probe tip 916 object features not
directly accessible by the beam of light 90 from the laser tracker
10. In other words, the retroreflector 940 may be in a direct
line-of-sight of the beam of light 90, while an object feature
measured by the probe tip 916 is hidden from view. In other
embodiments, the tactile probe 910 is replaced by another type of
six-DOF probe such as a six-DOF line scanner, a six-DOF area
scanner, a six-DOF indicator, a six-DOF sensor, or a six-DOF
projector. Examples of such six-DOF probes are given in U.S. Pat.
No. 9,151,830, the contents of which are incorporated by
reference.
[0113] In an embodiment illustrated in FIGS. 6A-6G, the tactile
probe 910 includes a stylus 912 and a stylus extension 918, the
stylus 912 further including the probe tip 916 and a stem 914. In
an embodiment, the tactile probe 910 is screwed into a threaded
hole 921 coupled to a frame-handle 920 that serves as a handle and
that further encloses a retroreflector 940 and six-DOF sensor
elements including a position-detector assembly 950 and a
roll-detector assembly 960. An upper button 922 and a lower button
924 provide an operator a way to start and stop 3D measurements. In
an embodiment, three indicator lights 926 provide status
information to the operator.
[0114] In an embodiment, the position-detector assembly 950
includes a first lens 952, a spacer plate 953, a second lens 954, a
position detector 955, and a first circuit board 956. In an
embodiment, the roll-detector assembly 960 includes polarization
assemblies 962 and reference assemblies 964. By determining a
position at which incoming light from the laser tracker 10 strikes
the position detector 955, the pitch and yaw angles of the six-DOF
probe 900 may be determined. In an embodiment, this determination
is made by a processor in the six-DOF probe 900. The polarization
assemblies 962 each includes a diffuser-polarizer plate 966
followed by a second circuit board 968 having an optical detector.
Each diffuser-polarizer plate 966 includes a linear polarizer that
in addition diffuses incoming light. The reference assemblies 964
includes the second circuit board 968 having an optical detector,
but the reference assemblies 964 do not include polarizers. Each of
the four linear polarizers in the four polarization assemblies 962
is rotated to a different one of four relative angles .theta., 45,
90, and 135 degrees. In an embodiment, the light is linearly
polarized in a known direction relative to the laser tracker. By
measuring the optical power passed through each of the four
polarization assemblies 962 and correcting the observed level by
the optical power observed in the reference assemblies 964, a roll
angle of the six-DOF probe 900 may be determined by a processor. In
an embodiment, the processor is included in the six-DOF probe, for
example, in the third circuit board or the fourth circuit board. A
port 928 of the six-DOF probe 900 is operable to receive signals
from a cable arriving from the laser tracker port A or from the
auxiliary box 1150 port A. The signal arriving through the port 928
provides the six-DOF probe 900 with 24 VDC power, a synchronization
signal from the laser tracker 10, a 32-bit time stamp, and a 100-Mb
Ethernet channel. In an alternative embodiment, the DC power is
provided by a battery internal to the six-DOF assembly, with the
synchronization, time stamp, and Ethernet signals transmitted
wirelessly, for example, over Wi-Fi (IEEE 802.11).
[0115] FIG. 16B shows the general position of the six-DOF launch
800 within the payload assembly 70. FIGS. 24A, 24B show the six-DOF
launch 800 in isometric and exploded views, respectively. The
six-DOF launch 800 includes a fiber-optic adapter 804 operable to
receive a fiber connector. In an embodiment, the fiber connector is
configured receive a multimode fiber operable to carry light from a
940-nm LED light source. The fiber-optic adapter 804 is attached to
the focus barrel 806 with a retainer nut 802. The focus barrel 806
attaches to a focus standoff 808, which in turn attaches to a
fold-mirror mount 810 that holds a fold-mirror assembly 812. The
fold-mirror mount further supports a collimating lens 814 and lens
retainer 816. In an embodiment, the collimated 940-nm light is
approximately 32 millimeters in diameter.
[0116] The collimated light passing through the collimating lens
814 further passes through a second Risley prism 820 and a first
Risley prism 824. The two Risley prisms are attached to the optics
body 828, with a flexure retainer 818 securing the Risley prisms
820, 824 to the optics body 828 and with the Risley prisms further
separated from adjacent elements by spacers 822 and 826. The light
arriving in optics body is folded by 90 degrees by the dichroic
six-DOF beam splitter 456. Each Risley prism assembly includes a
window having a slight wedge and a rotation mechanism that allows
the wedged window to be rotated into a desired position. By
adjusting the positions of the wedged windows in the first and
second Risley prisms, an incoming beam of light can be adjusted to
a desired direction. In this case, the Risley prisms are adjusted
to align the beam from the six-DOF launch 800 with the beam from
the ADM light source 640. In an embodiment described above, the
light projected by the six-DOF launch 800 is generated by a LED
that is linearly polarized and has a wavelength of 940 nm. In an
embodiment, the 940-nm light is modulated at a relatively low
frequency, detected at the six-DOF probe 900 by the optical
detectors of the roll-detector assembly 960 and the
position-detector assembly 950, and then filtered to remove
background light not modulated at the modulation frequency applied
by the six-DOF launch. In addition, optical filters may be used in
the optical path to remove background light outside the projected
wavelength, which in an embodiment is 940 nm. In an embodiment,
electrical processing within the six-DOF probe is carried out by
electronics 550 in a six-DOF active probe board(s), as shown in
FIG. 19. In an embodiment, within tracker electronics 500, the
payload digital board 512 communicates with a light-source driver
sub-board 513 to obtain a desired modulation in the optical signal
sent from the six-DOF launch 800. In an embodiment, the light from
the six-DOF launch 800 reflects off the dichroic six-DOF beam
splitter 656, combining with light from the ADM light source 640 to
form the outgoing light 90. In an embodiment, the modulation of the
light from the six-DOF launch is linked in time to the 1-kHz
synchronization signal from the sync board 517 and to the 32-bit
time stamp. In an embodiment, the real-time processor board 516
accepts electrical signals from the six-DOF probe 900 to fuse
six-DOF data. This board further uses the fused six-DOF data to
determine the 3D coordinates of the probe tip 916. In other
embodiments, the real-time processor board 516 uses the fused
six-DOF data to determine 3D coordinates of a surface using a
six-DOF line or area scanner probe 900 in place of the tactile
probe 910.
[0117] FIGS. 16C, 16D show front and isometric views, respectively,
of some optical and electrical components that may be seen when
covers of the payload assembly 70 are removed. FIGS. 16C, 16D show
the launch/collimator assembly 410, the optics housing 452, the
six-DOF fold mirror 830, the first Risley assembly 824, the second
Risley assembly 820, and the payload digital board 512. In an
embodiment, the payload digital board 512 includes a flex circuit
that allows a portion of it to be bent by 90 degrees. These figures
also show a first locator camera 76 and a second locator camera 78,
each attached to the optics housing 452 and to the payload digital
board 512. Each of the first and second locator cameras 76, 78
includes a camera mount 850, one or more infrared LEDs 852, camera
baffle 856, camera lens 854, and photosensitive array 855. In an
embodiment, camera cover windows 857 (FIG. 7) are attached in front
of the camera baffles 856. In an embodiment, the front surface of
the camera mount 850 and its attached components, including the one
or more LEDs 852, the camera baffles 856, and the camera cover
windows 857 are angled with respect to the optical axes of the
first locator camera 76 and the second locator camera 78. This
relative angle prevents ghost reflections from camera cover windows
857 from reaching the photosensitive arrays 855. In an embodiment,
the angle of tilt of the camera mount and its attached components
is at least 10 degrees. In some cases, the camera cover window is
coated to provide an optical filter that blocks unwanted optical
wavelengths outside desired wavelengths, which might be the
wavelength of the LEDs, for example. In other instances, the
optical coating if any may pass both visible light and infrared
light at the LED wavelength. In an embodiment, the LEDs 852 emit at
a wavelength of 850 nm. In other embodiments, light sources 852 are
not LEDs but another type of light.
[0118] The locator cameras 76, 78 may be used to locate one or more
retroreflectors 95 in an environment. A stereo-camera pair on a
payload assembly is described in U.S. Pat. No. 8,670,114, the
contents of which are incorporated by reference. In an embodiment,
the light sources 852 flash at regular intervals. The flashing
lights are picked up in images on the photosensitive arrays 855,
with each illuminated retroreflector captured in the images as
single spots of light. The flashing of the lights helps to
distinguish retroreflectors 95 from background objects. However, in
some cases, the flashing light of the light sources 852 may create
a glint, which is a bright specular reflection from a region of the
environment having an exactly correct orientation to create the
specular reflection.
[0119] In an embodiment, a processor is used to help eliminate
glints that might be mistaken for retroreflectors. In an
embodiment, the processor matches retroreflectors in a first image
of the first locator camera and a second image of the second
locator camera. The retroreflectors illuminated by the flashing
light sources 852 of the first locator camera 76 are seen as
retroreflector spots in the first image. The retroreflectors
illuminated by the flashing light sources 852 of the second locator
camera 78 are seen as retroreflector spots in the second image. In
an embodiment, the matching of the retroreflectors in the first
image and the second image is based at least in part on a
shape-and-context matching of retroreflector spots in the first
image and the second image. In addition, the matching is based at
least in part on an area-context-matching of background objects in
the first image and the second image. The area-context-matching is
based on identification and matching of natural features in the
first and second images.
[0120] In an embodiment, the first locator camera 76 and the second
locator camera 78 together provide image information in the visible
spectrum and at the infrared wavelength of the flashing LEDs. In an
embodiment, this image information is combined into a single
composite image in which markers representing the LEDs are
superimposed on the image of background objects in the visible
spectrum. In an embodiment, the markers that indicate positions of
the LEDs are shown in a bright color that is easily seen. In an
embodiment, the single composite image including background objects
and LED markers is presented on a display for a user to view. Such
a display might be a computer monitor or a display of a smart
device, for example.
[0121] In an embodiment, the tracker may steer its beam of outgoing
light 90 to a retroreflector based on the first image and the
second image. In an embodiment, this steering of the beam
automatically occurs whenever there is a beam break in tracking the
beam of light with the retroreflector 95. In other embodiments, the
beam is steered to a retroreflector based on a gesture given by an
operator. In other embodiments, the beam is steered to each of a
collection of retroreflectors according to an inspection plan.
[0122] A problem that may occur in outdoor environments is that, on
the first image and the second image, background objects
illuminated by sunlight are relatively bright compared to
retroreflectors illuminated by the infrared lights 852. In an
embodiment, this problem is avoided by using one of the two locator
cameras to preferentially capture a visible image of background
objects and using the other of the two locator cameras to
preferentially capture an infrared image of the illuminated
retroreflectors. In an embodiment, a first locator camera assembly
includes a first camera and one or more first flashing lights
having a first infrared wavelength greater than 700 nm. The first
camera includes a first lens corrected for both visible and first
infrared wavelengths. The second locator camera assembly includes a
second camera having a second lens, a second photosensitive array,
and one or more flashing lights at a second infrared wavelength
greater than 700 nm. The second locator camera also includes a
second optical filter that passes the second infrared wavelength
and blocks visible wavelengths. The second optical filter may be
incorporated into a camera cover window 857 or it may be directly
incorporated into the second lens by coating the second lens with
an optical coating having optical filtering properties. The second
lens is corrected for the second infrared wavelength. In an
embodiment, the first infrared wavelength and the second infrared
wavelength are the same. A processor is operable to capture
background objects in a first image of the first camera and to
capture illuminated retroreflectors in a second image of the second
camera. The brightly illuminated retroreflectors in the second
image may be matched to the more dimly illuminated retroreflectors
in the first image. In an embodiment, a composite image is created
of background objects at visible wavelengths and markers added to
represent retroreflectors illuminated at infrared wavelengths. In
an embodiment, the exposure times of the first and second cameras
are set to different values according to the relative brightness of
background objects and illuminated retroreflectors.
[0123] In the previous embodiment, one of the locator cameras
included a lens corrected for both visible wavelengths and an
infrared wavelength of the flashing lights 852. In some cases,
lenses are not corrected for both wavelength ranges. In these
cases, it may not be possible to obtain a clear image showing both
background objects at visible wavelengths and retroreflectors
illuminated at infrared wavelengths. This lack of clarity may make
it difficult to carry out the matching of retroreflectors in the
first locator camera and the second locator camera by using
shape-and-context matching and area-context-matching as described
above. A way around this problem is to adjust the distance between
the camera lens and the photosensitive array to bring the visible
images into clear focus on one camera and to bring the infrared
illuminated retroreflectors into clear focus on the other camera.
In an embodiment, a first locator camera assembly includes first
flashing lights at a first infrared wavelength and a first camera.
The first camera includes a first lens and a first photosensitive
array, with a first separation distance between the first lens and
the first photosensitive array adjusted to bring infrared
wavelengths into focus in a first image. A second locator camera
assembly includes second flashing lights at a second infrared
wavelength and a second camera. The second camera includes a second
lens and a second photosensitive array, with a second separation
distance between the second lens and the second photosensitive
array adjusted to bring visible wavelengths into focus in a second
image. In the second image, the illuminated retroreflectors will
still be visible but not as clearly as in the first image. However,
there is enough information in the first image and the second image
to enable matching of the retroreflectors within the fields of view
of the cameras.
[0124] There is a tradeoff in selecting locator cameras having a
wide field-of-view (FOV) or a narrow FOV. A wide FOV gives the
possibility of capturing retroreflectors of a wide region, while a
narrow FOV gives the possibility of rapidly locking onto a
retroreflector target after it has been found. A way around this
tradeoff is to select a different FOV for each of the two locator
cameras. In an embodiment, a first locator camera assembly includes
a first camera and first flashing lights at a first infrared
wavelength. The first camera has a first FOV. A second locator
camera assembly includes a second camera and second flashing lights
at a second infrared wavelength. The second camera has a second FOV
smaller than the first FOV by at least a factor of two.
[0125] A potential problem is ghost reflections from the camera
cover windows 857. The camera cover windows 857 may be optical
filters. Ghost reflections occur when light striking the camera
cover windows reflects backwards off one of the window surfaces and
then forward off a second of the window surfaces. The doubly
reflected ghost beam may strike a photosensitive array, creating an
illuminated spot in the image where there should be none. A way
around this problem is to tilt the camera mount 850 to a large
enough angle to cause the ghost beam to miss the photosensitive
array. In an embodiment, a first locator camera assembly includes
first flashing lights and a first camera. The first camera includes
a first cover window, a first lens, and a first photosensitive
array. In an embodiment, the first cover window is tilted to a
first angle large enough to prevent first ghost beams from the
first cover window from reaching the first photosensitive array. A
second locator camera assembly includes second flashing lights and
a second camera. The second camera includes a second cover window,
a second lens, and a second photosensitive array. The second cover
window is tilted to a second angle large enough to prevent second
ghost beams from the second cover window from reaching the second
photosensitive array. In an embodiment, the first cover window and
the second cover window are tilted by at least ten degrees.
[0126] According to one or more embodiments, a coordinate measuring
device is provided. The coordinate measurement device includes a
light source operable to emit a first light, the first light being
visible light having a first wavelength. A launch-collimator
assembly is operable to receive the first light through a first
optical fiber, to launch the first light into free space, and to
collimate the launched first light into a first beam of light. The
launch-collimator assembly being pre-aligned and pre-collimated
outside of the coordinate measuring device. The launch-collimator
assembly being further coupled through the first optical fiber to a
distance meter operable to measure a first distance to a target
illuminated by the first beam of light, the launch/collimator
assembly being exchangeable in the coordinate measuring device with
any other launch/collimator assembly without realignment of any
elements within the coordinate measuring device. The coordinate
measurement device further includes a first motor and a second
motor that are operable to direct the first beam of light to a
first direction, the first direction determined by a first angle of
rotation about a first axis and a second angle of rotation about a
second axis, the first angle of rotation produced by the first
motor and the second angle of rotation produced by the second
motor. A first angle measuring device is provided that is operable
to measure the first angle of rotation and a second angle measuring
device operable to measure the second angle of rotation. The
coordinate measurement device further includes a processor operable
to determine three-dimensional (3D) coordinates of the target based
at least in part on the measured first angle of rotation, the
measured second angle of rotation, and the measured first
distance.
[0127] In accordance with one or more embodiments, the first light
of the coordinate measurement device is red light. In an
embodiment, the coordinate measuring device further includes a
position-detector assembly, wherein the launch-collimator assembly
and the position-detector assembly are coupled to a combiner
assembly, the combiner assembly being operable to direct the first
light from the launch-collimator assembly out of the coordinate
measuring device to the target. In an embodiment, the combiner
assembly of the coordinate measurement device is further operable
to receive returned first light from the target, the combiner
assembly sending a first portion of the returned first light to the
first optical fiber in the launch-collimator assembly and a second
portion of the returned first light to the position-detector
assembly. In an embodiment, the position-detector assembly of the
coordinate measurement device includes a position detector
responsive to the first wavelength of light, the position detector
having a position-detector surface, the position detector providing
a first signal indicative of a position of the second portion of
the returned first light on the position-detector surface. In still
another embodiment, the position detector of the coordinate
measurement device is selected from the group consisting of: a
lateral-effect detector, a quadrant detector, a complimentary
metal-oxide-semiconductor (CMOS) array, and a charge-coupled device
(CCD) array.
[0128] In accordance with one or more embodiments, the distance
meter of the coordinate measurement device is an absolute distance
meter. In accordance with an embodiment, the elements of the
position detector assembly of the coordinate measurement device are
aligned to the combiner assembly based at least in part on the
second portion of the returned first light. In an embodiment, the
position detector assembly of the coordinate measurement device
further includes a lens and a pinhole. In an embodiment, the target
of the coordinate measurement device is a retroreflector. In still
a further embodiment, the coordinate measurement device further
includes a control system, the control system operable to direct
the first beam of light to a center of the target based at least in
part on the first signal.
[0129] In accordance with an embodiment, the coordinate measuring
device further comprises a dichroic beam splitter configured to
direct the first beam of light to the target and a second beam of
light to the target, the second beam of light being a collimated
beam of light having a second wavelength, the second beam of light
having a larger diameter than the first beam of light. In
accordance with an embodiment, the launch/collimator assembly
coordinate measurement device mates or couples to the combiner
assembly of the coordinate measurement device through the coupling
of alignment pins to alignment holes. In still another embodiment,
the alignment pins on the combiner assembly mate with alignment
holes on the launch/collimator assembly.
[0130] In accordance with one or more embodiments, the
launch-collimator assembly of the coordinate measurement device
includes a plurality of optical lens elements, including a first
and second optical elements. The first of the optical lens elements
being fixed in place in the launch-collimator assembly. The second
of the plurality of optical lens elements being centered to the
first of the optical lens elements by sending a plane wave of light
through the combination of elements and adjusting the centering to
minimize aberrations as viewed on a photosensitive array. A
distance of the first optical fiber to the plurality of optical
lens elements being set using a shim, a thickness of the shim
selected to place a beam waist of the first beam of light at a
preferred distance from the launch-collimator assembly.
[0131] In accordance with one or more embodiments, another
coordinate measuring device is provided. The coordinate measurement
device having a light source operable to emit a visible first light
having a first wavelength. The coordinate measurement device
further having a launch-collimator assembly that is operable to
receive the first light through a first optical fiber, to launch
the first light into free space, and to collimate the launched
first light into a first beam of light. The launch-collimator
assembly being pre-aligned and pre-collimated outside the
coordinate measuring device. The launch-collimator assembly being
further coupled through the first optical fiber to an absolute
distance meter operable to measure a first distance to a target
illuminated by the first beam of light. The coordinate measurement
device further includes a first motor and a second motor operable
to direct the first beam of light to a first direction, the first
direction determined by a first angle of rotation about a first
axis and a second angle of rotation about a second axis, the first
angle of rotation produced by the first motor and the second angle
of rotation produced by the second motor. The coordinate
measurement device further includes a first angle measuring device
operable to measure the first angle of rotation and a second angle
measuring device operable to measure the second angle of rotation.
The coordinate measurement device further includes a
position-detector assembly having a position detector responsive to
the first wavelength of light, the position detector having a
position-detector surface, the position detector providing a first
signal indicative of a position of the second portion of the
returned first light on the position-detector surface. The
coordinate measurement device still further includes a combiner
assembly coupled to the launch-collimator assembly and the
position-detector assembly, the combiner assembly operable to send
the first beam of light to the target, to receive a returned first
beam of light from the target, to send a first portion of the
returned first beam of light through the launch-collimator assembly
into the optical fiber and on to the absolute distance meter, and
to send a second portion of the returned first beam of light to the
position-detector assembly. The coordinate measurement device also
includes a processor operable to determine three-dimensional (3D)
coordinates of the target based at least in part on the measured
first angle of rotation, the measured second angle of rotation, and
the measured first distance.
[0132] In accordance with an embodiment, the target is a
retroreflector target. In accordance with an embodiment, the
coordinate measurement device further includes a control system,
the control system operable to direct the first beam of light to a
center of the retroreflector target based at least in part on the
first signal.
[0133] In accordance with one or more embodiments, another
coordinate measuring device is provided. The coordinate measurement
device includes a light source operable to emit a first light, the
light source including a Fabry-Perot laser, a lensing system, a
first optical fiber, and a thermoelectric cooler, the Fabry-Perot
laser operable to produce visible light at a first wavelength. The
lensing system being operable to couple the produced first light
into the first optical fiber. The first optical fiber being a
single-mode optical fiber and the thermoelectric cooler being
operable to hold the Fabry-Perot laser at a constant temperature.
The coordinate measurement device also includes a fiber network
operable to receive the first light from the output optical fiber
and to pass a first portion of the first light to a
launch-collimator assembly. The launch-collimator assembly being
operable to launch the first portion of the first light into free
space and to collimate the launched first light into a first beam
of light. The coordinate measurement device further including a
first motor and a second motor operable to direct the first beam of
light to a first direction, the first direction determined by a
first angle of rotation about a first axis and a second angle of
rotation about a second axis, the first angle of rotation produced
by the first motor and the second angle of rotation produced by the
second motor. The coordinate measurement device further includes a
first angle measuring device operable to measure the first angle of
rotation and a second angle measuring device operable to measure
the second angle of rotation. The coordinate measurement device
further includes a distance meter operable to measure a first
distance to a target illuminated by the first beam of light. The
coordinate measurement device also includes a processor operable to
determine three-dimensional (3D) coordinates of the target based at
least in part on the measured first angle of rotation, the measured
second angle of rotation, and the measured first distance.
[0134] In accordance with an embodiment, the coordinate measuring
device further includes a Faraday isolator operable to pass the
first light traveling in a forward direction away from the light
source and to block the first light traveling in a reverse
direction toward the light source. The Faraday isolator including
an input optical fiber coupled to the first optical fiber, the
Faraday isolator further including an output optical fiber, the
output optical fiber being a single-mode optical fiber. In an
embodiment, a bias current sent to the Fabry-Perot laser is
adjusted to emit light at a constant average optical power. In
another embodiment, the optical power losses from the Fabry-Perot
laser to the target and back to the Fabry-Perot laser are large
enough are large enough to prevent destabilization of the
Fabry-Perot laser over a range of rated operating temperatures of
the coordinate measuring device.
[0135] In accordance with an embodiment, a combination of isolation
from the Faraday isolator and optical power losses from the
Fabry-Perot laser to the target and back to the Fabry-Perot laser
is large enough to prevent destabilization of the Fabry-Perot laser
over a range of rated operating temperatures of the coordinate
measuring device. In accordance with an embodiment, a temperature
control device is brought into contact with the Faraday isolator.
The temperature control device operable to control the temperature
of the Faraday isolator, thereby increasing the isolation of the
Faraday isolator over the range of rated operating temperatures. In
accordance with an embodiment, the Faraday isolator includes a
Faraday rotator having a Faraday-rotator crystal and a magnet, the
magnet positioned to immerse the Faraday-rotator crystal in a
magnetic field. In accordance with an embodiment, the Faraday
isolator is a polarization-independent Faraday isolator including a
first birefringent beam displacer, the Faraday rotator, a half-wave
plate, and a second birefringent beam displacer. In accordance with
an embodiment, the first optical fiber is not a
polarization-maintaining optical fiber and the input optical fiber
is not a polarization-maintaining optical fiber.
[0136] In accordance with one or more embodiments, the target is a
retroreflector. In accordance with one or more embodiments, the
distance meter is an absolute distance meter (ADM). In accordance
with an embodiment a first portion of the first returned light from
the target passes through the launch-collimator assembly to the
ADM.
[0137] In accordance with one or more embodiments, the coordinate
measurement device further includes an ADM module, the ADM module
being an integrated unit that includes the first light source, the
Faraday isolator, the fiber network, and radio-frequency (RF)
electronics, the RF electronics used to modulate the Fabry-Perot
laser and to process electrically-detected optical signals passing
through the fiber network, the ADM module further including an
optical-fiber adapter for coupling the fiber network to the
launch-collimator assembly.
[0138] In accordance with an embodiments, another coordinate
measuring device is provided. The coordinate measurement device
including a housing and a light source operable to emit a first
beam of light. A first motor and a second motor are provided that
are operable to direct the first beam of light to a first
direction, the first direction determined by a first angle of
rotation about a first axis and a second angle of rotation about a
second axis. The first angle of rotation produced by the first
motor and the second angle of rotation produced by the second
motor. The coordinate measurement device further includes a first
angle measuring device operable to measure the first angle of
rotation and a second angle measuring device operable to measure
the second angle of rotation. The coordinate measurement device
further includes a distance meter operable to measure a first
distance to a target illuminated by the first beam of light. The
coordinate measurement device further includes a shock-absorber
assembly coupled to a lower portion of the housing, the
shock-absorber assembly operable to reduce mechanical shock to the
coordinate measuring device when the coordinate measuring device is
brought into contact with an external element that supports the
housing. The coordinate measurement device also includes a
processor operable to determine three-dimensional (3D) coordinates
of the target based at least in part on the measured first angle of
rotation, the measured second angle of rotation, and the measured
first distance.
[0139] In accordance with an embodiment, the external element of
the coordinate measuring device is a mandrel. In accordance with an
embodiment the mandrel is attached to a stand. In accordance with
one or more embodiments, the shock-absorber assembly of the
coordinate measuring device includes a retractable surface that,
when brought into contact with the external element, retracts
toward the interior of the housing through compression of a damper
material.
[0140] In accordance with one or more embodiments, another
coordinate measuring device is provided. The coordinate measuring
device including a housing and a light source operable to emit a
first beam of light. The coordinate measuring device includes a
first motor and a second motor operable to direct the first beam of
light to a first direction, the first direction determined by a
first angle of rotation about a first axis and a second angle of
rotation about a second axis. The first angle of rotation produced
by the first motor and the second angle of rotation produced by the
second motor. The coordinate measuring device further includes a
first angle measuring device operable to measure the first angle of
rotation and a second angle measuring device operable to measure
the second angle of rotation. The coordinate measuring device
further includes a distance meter operable to measure a first
distance to a target illuminated by the first beam of light. The
coordinate measuring device further includes a first locator camera
assembly that is affixed to the housing, the first locator camera
assembly including a first camera and one or more first flashing
lights. The coordinate measuring device further includes a second
locator camera assembly affixed to the housing, the second locator
camera assembly including a second camera and one or more second
flashing lights. The coordinate measuring device also includes a
processor operable to determine three-dimensional (3D) coordinates
of the target based at least in part on the measured first angle of
rotation, the measured second angle of rotation, and the measured
first distance, the processor further operable to match
retroreflectors in a first image of the first locator camera and a
second image of the second locator camera, the matching based at
least in part on a shape-and-context matching of retroreflector
spots in the first image and the second image and on an
area-context-matching of background objects in the first image and
the second image, the retroreflector spots in the first image
produced by illumination of the retroreflectors by the first
flashing lights, the retroreflector spots in the second image
produced by illumination of the retroreflectors by the second
flashing lights, the processor further operable to provide a third
image that includes both the background objects and markers
indicating the matched retroreflectors.
[0141] In accordance with an embodiment, the processor of the
coordinate measuring device is operable to provide the third image
to a display. In accordance with an embodiment, the processor of
the coordinate measuring device is further operable to select one
of the matched retroreflectors as the target, to direct the first
beam of light to the selected target, and to determine the 3D
coordinates of the selected target.
[0142] In accordance with one or more embodiments, another
coordinate measuring device is provided. The coordinate measuring
device including a housing and a light source operable to emit a
first beam of light. The coordinate measuring device includes a
first motor and a second motor operable to direct the first beam of
light to a first direction, the first direction determined by a
first angle of rotation about a first axis and a second angle of
rotation about a second axis. The first angle of rotation produced
by the first motor and the second angle of rotation produced by the
second motor. The coordinate measuring device includes a first
angle measuring device that is operable to measure the first angle
of rotation and a second angle measuring device operable to measure
the second angle of rotation. The coordinate measuring device
includes a distance meter operable to measure a first distance to a
target illuminated by the first beam of light. The coordinate
measuring device further includes a first locator camera assembly
affixed to the housing, the first locator camera assembly including
a first camera and one or more first flashing lights having a first
infrared wavelength greater than 700 nanometers, the first camera
including a first lens and a first photosensitive array, the first
camera being corrected for both visible and first infrared
wavelengths. The coordinate measuring device further includes a
second locator camera assembly affixed to the housing, the second
locator camera assembly including a second camera and one or more
second flashing lights having a second infrared wavelength greater
than 700 nanometers, the second camera including a second filter, a
second lens and a second photosensitive array, the second filter
being operable to pass the second infrared wavelength and to block
visible wavelengths, the second camera being corrected for the
second infrared wavelength. The coordinate measuring device also
includes a processor operable to determine three-dimensional (3D)
coordinates of the target based at least in part on the measured
first angle of rotation, the measured second angle of rotation, and
the measured first distance, the processor further operable to
capture background objects in a first image of the first camera and
to capture illuminated retroreflectors in a second image of the
second camera, the captured illuminated retroreflectors being
within a field-of-view of second camera, the processor further
operable to provide a third image of both the background objects
and the illuminated retroreflectors.
[0143] In accordance with an embodiment, the first exposure time of
the first camera is selected based on a quality of the first image
at the first infrared wavelength and the second exposure time of
the second camera is selected based on a quality of the second
image at the visible wavelengths.
[0144] In accordance with one or more embodiments, another
coordinate measuring device is provided. The coordinate measuring
device including a housing and a light source operable to emit a
first beam of light. The coordinate measuring device including a
first motor and a second motor operable to direct the first beam of
light to a first direction, the first direction determined by a
first angle of rotation about a first axis and a second angle of
rotation about a second axis. The first angle of rotation produced
by the first motor and the second angle of rotation produced by the
second motor. The coordinate measuring device includes a first
angle measuring device operable to measure the first angle of
rotation and a second angle measuring device operable to measure
the second angle of rotation. The coordinate measuring device
further includes a distance meter operable to measure a first
distance to a target illuminated by the first beam of light. The
coordinate measuring device further includes a first locator camera
assembly affixed to the housing, the first locator camera assembly
including a first camera and one or more first flashing lights, the
first flashing lights operable at a first infrared wavelength
longer than 700 nanometers, the first camera having a first lens
and a first photosensitive array, a first separation distance
between the first camera and the first photosensitive array being
selected to permit a first image to be obtained in focus for the
first infrared wavelength. The coordinate measuring device further
includes a second locator camera assembly affixed to the housing,
the second locator camera assembly including a second camera and
one or more second flashing lights, the second flashing lights
operable at a second infrared wavelength longer than 700
nanometers, the second camera having a second lens and a second
photosensitive array, a second separation distance between the
second camera and the second photosensitive array being selected to
permit a second image to be obtained in focus for the visible
wavelengths. The coordinate measuring device also includes a
processor operable to determine three-dimensional (3D) coordinates
of the target based at least in part on the measured first angle of
rotation, the measured second angle of rotation, and the measured
first distance, the processor further operable to provide a third
image of both the background objects and the illuminated
retroreflectors.
[0145] In accordance with one or more embodiments, another
coordinate measuring device is provided. The coordinate measuring
device including a housing and a light source operable to emit a
first beam of light. The coordinate measuring device includes a
first motor and a second motor operable to direct the first beam of
light to a first direction, the first direction determined by a
first angle of rotation about a first axis and a second angle of
rotation about a second axis. The first angle of rotation produced
by the first motor and the second angle of rotation produced by the
second motor. The coordinate measuring device includes a first
angle measuring device operable to measure the first angle of
rotation and a second angle measuring device operable to measure
the second angle of rotation. The coordinate measuring device
further includes a distance meter operable to measure a first
distance to a target illuminated by the first beam of light. The
coordinate measuring device further includes a first locator camera
assembly affixed to the housing, the first locator camera assembly
including a first camera and one or more first flashing lights, the
first flashing lights operable at a first infrared wavelength
longer than 700 nanometers, the first camera having a first lens
and a first photosensitive array, the first locator camera having a
first field of view. The coordinate measuring device further
includes a second locator camera assembly affixed to the housing,
the second locator camera assembly including a second camera and
one or more second flashing lights, the second flashing lights
operable at a second infrared wavelength longer than 700
nanometers, the second camera having a second lens and a second
photosensitive array, the second locator camera having a second
field of view smaller than the first field of view by at least a
factor of two. The coordinate measuring device also includes a
processor operable to determine three-dimensional (3D) coordinates
of the target based at least in part on the measured first angle of
rotation, the measured second angle of rotation, and the measured
first distance, the processor further operable to match
retroreflectors in a first image of the first locator camera and a
second image of the second locator camera, the processor further
operable to provide a third image that includes both the background
objects and the matched retroreflectors.
[0146] In accordance with one or more embodiments, another
coordinate measuring device is provided. The coordinate measuring
device includes a housing and a light source operable to emit a
first beam of light. The coordinate measuring device includes a
first motor and a second motor operable to direct the first beam of
light to a first direction, the first direction determined by a
first angle of rotation about a first axis and a second angle of
rotation about a second axis. The first angle of rotation produced
by the first motor and the second angle of rotation produced by the
second motor. The coordinate measuring device further includes a
first angle measuring device operable to measure the first angle of
rotation and a second angle measuring device operable to measure
the second angle of rotation. The coordinate measuring device
further includes a distance meter operable to measure a first
distance to a target illuminated by the first beam of light. The
coordinate measuring device further includes a first locator camera
assembly affixed to the housing, the first locator camera assembly
including a first camera and one or more first flashing lights, the
first flashing lights operable at a first infrared wavelength
longer than 700 nanometers, the first camera having a first cover
window, a first lens and a first photosensitive array, the first
cover window being tilted to a first angle, the first angle being
large enough to prevent first ghost beams from reflections of the
first cover window from reaching the first photosensitive array.
The coordinate measuring device further includes a second locator
camera assembly affixed to the housing, the second locator camera
assembly including a second camera and one or more second flashing
lights, the second flashing lights operable at a second infrared
wavelength longer than 700 nanometers, the second camera having a
second cover window, a second lens and a second photosensitive
array, the second cover window being tilted to a second angle, the
second angle being large enough to prevent second ghost beams from
reflections of the second cover window from reaching the second
photosensitive array. The coordinate measuring device also includes
a processor operable to determine three-dimensional (3D)
coordinates of the target based at least in part on the measured
first angle of rotation, the measured second angle of rotation, and
the measured first distance, the processor further operable to
match retroreflectors in a first image of the first locator camera
and a second image of the second locator camera, the processor
further operable to provide a third image that includes both the
background objects and the matched retroreflectors.
[0147] In accordance with an embodiment, the first angle is at
least 10 degrees. In accordance with an embodiment, the first cover
window of the coordinate measuring device is a first optical filter
that is configured to pass at least one of the first infrared
wavelength and visible wavelengths.
[0148] Terms such as processor, controller, computer, DSP, FPGA are
understood in this document to mean a computing device that may be
located within an instrument, distributed in multiple elements
throughout an instrument, or placed external to an instrument.
[0149] While the invention has been described in detail in
connection with only a limited number of embodiments, it should be
readily understood that the invention is not limited to such
disclosed embodiments. Rather, the invention can be modified to
incorporate any number of variations, alterations, substitutions or
equivalent arrangements not heretofore described, but which are
commensurate with the spirit and scope of the invention.
Additionally, while various embodiments of the invention have been
described, it is to be understood that aspects of the invention may
include only some of the described embodiments. Accordingly, the
invention is not to be seen as limited by the foregoing
description, but is only limited by the scope of the appended
claims.
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