U.S. patent application number 13/006461 was filed with the patent office on 2011-07-21 for embedded arm strain sensors.
This patent application is currently assigned to FARO TECHNOLOGIES, INC.. Invention is credited to Paul C. Atwell, Burnham Stokes.
Application Number | 20110175745 13/006461 |
Document ID | / |
Family ID | 43736091 |
Filed Date | 2011-07-21 |
United States Patent
Application |
20110175745 |
Kind Code |
A1 |
Atwell; Paul C. ; et
al. |
July 21, 2011 |
EMBEDDED ARM STRAIN SENSORS
Abstract
A portable articulated arm coordinate measurement machine
(AACMM) can include a manually positionable articulated arm
portion, a measurement device attached to the first end, a
structural component of the AACMM, wherein the structural component
has an axial direction, at least three strain gage sensors, each
having a sensitive axis, coupled to the structural component,
wherein the sensitive axis of each strain gage sensor is oriented
approximately parallel to the axial direction, each strain gage
sensor is approximately intersected by a transverse plane
perpendicular to the axial direction, each strain gage sensor
produces an analog strain gage signal, and the strain gage sensors
are disposed to provide data sufficient to determine a bending
strain at any point residing on both the structural component and
the transverse plane and an electronic circuit that receives the
position signal and provides data corresponding to a position of
the measurement device.
Inventors: |
Atwell; Paul C.; (Lake Mary,
FL) ; Stokes; Burnham; (Lake Mary, FL) |
Assignee: |
FARO TECHNOLOGIES, INC.
Lake Mary
FL
|
Family ID: |
43736091 |
Appl. No.: |
13/006461 |
Filed: |
January 14, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61296555 |
Jan 20, 2010 |
|
|
|
Current U.S.
Class: |
340/665 ;
33/503 |
Current CPC
Class: |
G05B 19/406 20130101;
G01B 5/012 20130101; G05B 2219/40233 20130101; G05B 19/401
20130101; G01B 21/047 20130101; G05B 2219/37193 20130101; G05B
2219/40596 20130101; G05B 2219/24067 20130101; G05B 2219/45061
20130101; G01B 11/007 20130101 |
Class at
Publication: |
340/665 ;
33/503 |
International
Class: |
G08B 21/00 20060101
G08B021/00; G01B 5/008 20060101 G01B005/008 |
Claims
1. A portable articulated arm coordinate measurement machine
(AACMM) for measuring coordinates of an object in space,
comprising: a manually positionable articulated arm portion having
opposed first and second ends, the arm portion including a
plurality of connected arm segments, the plurality of connected arm
segments including an arm segment adjacent the first end, each arm
segment including at least one position transducer that produces a
position signal; a measurement device attached to the first end; a
structural component of the AACMM, wherein the structural component
has an axial direction; at least three strain gage sensors, each
having a sensitive axis, coupled to the structural component,
wherein the sensitive axis of each strain gage sensor is oriented
approximately parallel to the axial direction, each strain gage
sensor is approximately intersected by a transverse plane
perpendicular to the axial direction, each strain gage sensor
produces an analog strain gage signal, and the strain gage sensors
are disposed to provide data sufficient to determine a bending
strain at any point residing on both the structural component and
the transverse plane; and an electronic circuit that receives the
position signal and provides data corresponding to a position of
the measurement device.
2. The AACMM of claim 1 further comprising an analog-to-digital
converter circuit that converts some combination of the analog
strain gage signals into a plurality of digital strain gage
signals, wherein the electronic circuit receives the plurality of
digital strain gage signals.
3. The AACMM of claim 2 wherein the electronic circuit calculates
the magnitude and direction of maximum bending of the structural
component.
4. The AACMM of claim 3 wherein the electronic circuit uses the
digital strain gage signals from the at least three strain gage
sensors to modify the provided data corresponding to the position
of the measurement device.
5. The AACMM of claim 4 further comprising a capture signal,
wherein the position signal and the digital strain gage signals are
collected in response to the capture signal.
6. The AACMM of claim 4 further comprising parameters obtained from
a compensation procedure and stored in the electronic circuit,
wherein the parameters are obtained in part by a collecting of data
by the AACMM in response to movement of the arm segments.
7. The AACMM of claim 6, wherein the electronic circuit uses the
parameters and the calculated magnitude and direction of maximum
bending to modify the provided data corresponding to the position
of the measurement device.
8. The AACMM of claim 3 wherein the structural component has a
coefficient of thermal expansion and the strain gage sensor is
selected to match the coefficient of thermal expansion of the
structural component.
9. The AACMM of claim 3, further comprising a fourth strain gage
sensor.
10. The AACMM of claim 3 wherein the electronic circuit produces a
warning in response to the strain gage signals.
11. The AACMM of claim 10 wherein the warning is one of a visual
warning and an audible warning.
12. The AACMM of claim 10 wherein the warning is produced when the
bending strain has a value that falls outside pre-determined
limits.
13. A method for measuring strain in an articulated arm coordinate
measurement machine (AACMM) comprising the steps of: providing a
manually positionable articulated arm portion having opposed first
and second ends, the arm portion including a plurality of connected
arm segments, each attached to at least one bearing cartridge, the
plurality of connected arm segments including an arm segment
adjacent to the first end, each arm segment including at least one
position transducer that produces a position signal; a measurement
device attached to the first end; a structural component of the
articulated arm coordinate measurement machine, wherein the
structural component has an axial direction; at least a first
strain gage sensor disposed on the structural component, each
strain gage sensor producing an analog strain gage signal;
converting a combination of the analog strain gage signals into at
least one digital strain gage signal; sending the at least one
digital strain gage signal through at least one of the at least one
bearing cartridges to an electronic circuit that receives the
position signal and the at least one digital strain gage signal;
providing and storing data corresponding to a position of the
measurement device; and storing the at least one digital strain
gage signal.
14. The method according to claim 13 for measuring strain in an
articulated arm coordinate measurement machine (AACMM), further
comprising the step of providing a second strain gage sensor on the
structural component and a third strain gage sensor on the
structural component, wherein the first, second, and third strain
gage sensors produce analog strain gage signals; converting some
combination of the analog strain gage signals into a plurality of
digital strain gage signals; sending the plurality of digital
strain gage signals through at least one of the at least one
bearing cartridges to the electronic circuit, wherein the
electronic circuit stores the digital strain gage signals.
15. The method according to claim 14 for measuring strain in an
articulated arm coordinate measurement machine (AACMM), further
comprising the steps of: coupling the first, second, and third
strain gage sensor, each having a sensitive axis, to the structural
component, wherein the sensitive axis of each strain gage sensor is
oriented approximately parallel to the axial direction; disposing
each strain gage sensor on the structural component to be
approximately intersected by a transverse plane perpendicular to
the axial direction of the structural component; and disposing the
first, second, and third strain gage sensor to provide data
sufficient to determine a bending strain at any point residing on
both the structural component and the transverse plane.
16. The method according to claim 15 for measuring strain in an
articulated arm coordinate measurement machine (AACMM), further
comprising the step of calculating the magnitude and direction of
maximum bending of the structural component.
17. The method according to claim 16 for measuring strain in an
articulated arm coordinate measurement machine (AACMM), further
comprising the step of using the plurality of digital strain gage
signals to modify the provided data corresponding to the position
of the measurement device.
18. The method according to claim 17 for measuring strain in an
articulated arm coordinate measurement machine (AACMM), further
comprising the steps of providing a capture signal; and collecting
the position signal and the digital strain gage signals in response
to the capture signal.
19. The method according to claim 18 for measuring strain in an
articulated arm coordinate measurement machine (AACMM), further
comprising the step of obtaining parameters from a compensation
procedure, wherein the parameters are obtained in part by the
collecting of data by the articulated arm coordinate measurement
machine in response to movement of the arm segments.
20. The method according to claim 19 for measuring strain in an
articulated arm coordinate measurement machine (AACMM), further
comprising the step of using the parameters and the calculated
magnitude and direction of maximum bending of the structural
element to modify the provided data corresponding to the position
of the measurement device.
21. The method according to claim 15 for measuring strain in an
articulated arm coordinate measurement machine (AACMM), further
comprising the step of selecting a coefficient of thermal expansion
for each strain gage sensor to match a coefficient of thermal
expansion of the structural component.
22. The method according to claim 14 for measuring strain in an
articulated arm coordinate measurement machine (AACMM), further
comprising the step of producing a warning in response to the
strain gage signals.
23. The method according to claim 22 for measuring strain in an
articulated arm coordinate measurement machine (AACMM), wherein the
warning is one of a visual warning and an audible warning.
24. The method according to claim 16 for measuring strain in an
articulated arm coordinate measurement machine (AACMM), further
comprising the step of producing a warning in response to the
strain gage signals when the bending strain has a value that falls
outside pre-determined limits.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit of provisional
application No. 61/296,555 filed Jan. 20, 2010, the content of
which is hereby incorporated by reference in its entirety.
BACKGROUND
[0002] The present disclosure relates to a coordinate measuring
machine, and more particularly to a portable articulated arm
coordinate measuring machine having strain gage sensors configured
to measure strain in structural components of the portable
articulated arm coordinate measuring machine.
[0003] Portable articulated arm coordinate measuring machines
(AACMMs) have found widespread use in the manufacturing or
production of parts where there is a need to rapidly and accurately
verify the dimensions of the part during various stages of the
manufacturing or production (e.g., machining) of the part. Portable
AACMMs represent a vast improvement over known stationary or fixed,
cost-intensive and relatively difficult to use measurement
installations, particularly in the amount of time it takes to
perform dimensional measurements of relatively complex parts.
Typically, a user of a portable AACMM simply guides a probe along
the surface of the part or object to be measured. The measurement
data are then recorded and provided to the user. In some cases, the
data are provided to the user in visual form, for example,
three-dimensional (3-D) form on a computer screen. In other cases,
the data are provided to the user in numeric form, for example when
measuring the diameter of a hole, the text "Diameter=1.0034" is
displayed on a computer screen.
[0004] An example of a prior art portable articulated arm CMM is
disclosed in commonly assigned U.S. Pat. No. 5,402,582 ('582),
which is incorporated herein by reference in its entirety. The '582
patent discloses a 3-D measuring system comprised of a
manually-operated articulated arm CMM having a support base on one
end and a measurement probe at the other end. Commonly assigned
U.S. Pat. No. 5,611,147 ('147), which is incorporated herein by
reference in its entirety, discloses a similar articulated arm CMM.
In the '147 patent, the articulated arm CMM includes a number of
features including an additional rotational axis at the probe end,
thereby providing for an arm with either a two-two-two or a
two-two-three axis configuration (the latter case being a seven
axis arm).
[0005] What is needed is an apparatus and method that can measure
strain associated with AACMMs.
SUMMARY OF THE INVENTION
[0006] Exemplary embodiments include a portable articulated arm
coordinate measurement machine (AACMM) for measuring coordinates of
an object in space, including a manually positionable articulated
arm portion having opposed first and second ends, the arm portion
including a plurality of connected arm segments, the plurality of
connected arm segments including an arm segment adjacent the first
end, each arm segment including at least one position transducer
that produces a position signal, a measurement device attached to
the first end, a structural component of the AACMM, wherein the
structural component has an axial direction, at least three strain
gage sensors, each having a sensitive axis, coupled to the
structural component, wherein the sensitive axis of each strain
gage sensor is oriented approximately parallel to the axial
direction, each strain gage sensor is approximately intersected by
a transverse plane perpendicular to the axial direction, each
strain gage sensor produces an analog strain gage signal, and the
strain gage sensors are disposed to provide data sufficient to
determine a bending strain at any point residing on both the
structural component and the transverse plane and an electronic
circuit that receives the position signal and provides data
corresponding to a position of the measurement device.
[0007] Further exemplary embodiments include a method for measuring
strain in an articulated arm coordinate measurement machine (AACMM)
including providing a manually positionable articulated arm portion
having opposed first and second ends, the arm portion including a
plurality of connected arm segments, each attached to at least one
bearing cartridge, the plurality of connected arm segments
including an arm segment adjacent to the first end, each arm
segment including at least one position transducer that produces a
position signal; a measurement device attached to the first end; a
structural component of the articulated arm coordinate measurement
machine, wherein the structural component has an axial direction;
at least a first strain gage sensor disposed on the structural
component, each strain gage sensor producing an analog strain gage
signal, converting a combination of the analog strain gage signals
into at least one digital strain gage signal, sending the at least
one digital strain gage signal through at least one of the at least
one bearing cartridges to an electronic circuit that receives the
position signal and the at least one digital strain gage signal,
providing and storing data corresponding to a position of the
measurement device and storing the at least one digital strain gage
signal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] 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:
[0009] FIG. 1, including FIGS. 1A and 1B, are perspective views of
a portable articulated arm coordinate measuring machine (AACMM)
having embodiments of various aspects of the present invention
therewithin;
[0010] FIG. 2, including FIGS. 2A-2D taken together, is a block
diagram of electronics utilized as part of the AACMM of FIG. 1 in
accordance with an embodiment;
[0011] FIG. 3, including FIGS. 3A and 3B taken together, is a block
diagram describing detailed features of the electronic data
processing system of FIG. 2 in accordance with an embodiment;
[0012] FIG. 4 illustrates a schematic view of the AACMM of FIG. 1
showing bending of a component of the AACMM;
[0013] FIG. 5 illustrates view of exemplary strain gage sensors
disposed on structural components of the AACMM; and
[0014] FIG. 6 is a flowchart of a method for detecting strain in
accordance with exemplary embodiments.
DETAILED DESCRIPTION
[0015] Exemplary embodiments include systems and methods for
measuring strain on arm segments of a portable articulated arm
coordinate measuring machine either to compensate measurement
results to improve accuracy or to alert the operator of the need
for corrective action.
[0016] FIGS. 1A and 1B illustrate, in perspective, a portable
articulated arm coordinate measuring machine (AACMM) 100 according
to various embodiments of the present invention, an articulated arm
being one type of coordinate measuring machine. As shown in FIGS.
1A and 1B, the exemplary AACMM 100 may comprise a six or seven axis
articulated measurement device having a measurement probe housing
102 coupled to an arm portion 104 of the AACMM 100 at one end. The
arm portion 104 comprises a first arm segment 106 coupled to a
second arm segment 108 by a first grouping of bearing cartridges
110 (e.g., two bearing cartridges). A second grouping of bearing
cartridges 112 (e.g., two bearing cartridges) couples the second
arm segment 108 to the measurement probe housing 102. A third
grouping of bearing cartridges 114 (e.g., three bearing cartridges)
couples the first arm segment 106 to a base 116 located at the
other end of the arm portion 104 of the AACMM 100. Each grouping of
bearing cartridges 110, 112, 114 provides for multiple axes of
articulated movement. Also, the measurement probe housing 102 may
comprise the shaft of the seventh axis portion of the AACMM 100
(e.g., a cartridge containing an encoder system that determines
movement of the measurement device, for example a probe 118, in the
seventh axis of the AACMM 100). In use of the AACMM 100, the base
116 is typically affixed to a work surface.
[0017] Each bearing cartridge within each bearing cartridge
grouping 110, 112, 114 typically contains an encoder system (e.g.,
an optical angular encoder system). The encoder system (i.e.,
transducer) provides an indication of the position of the
respective arm segments 106, 108 and corresponding bearing
cartridge groupings 110, 112, 114 that all together provide an
indication of the position of the probe 118 with respect to the
base 116 (and, thus, the position of the object being measured by
the AACMM 100 in a certain frame of reference--for example a local
or global frame of reference). The arm segments 106, 108 may be
made from a suitably rigid material such as but not limited to a
carbon composite material for example. A portable AACMM 100 with
six or seven axes of articulated movement (i.e., degrees of
freedom) provides advantages in allowing the operator to position
the probe 118 in a desired location within a 360.degree. area about
the base 116 while providing an arm portion 104 that may be easily
handled by the operator. However, it should be appreciated that the
illustration of an arm portion 104 having two arm segments 106, 108
is for exemplary purposes, and the claimed invention should not be
so limited. An AACMM 100 may have any number of arm segments
coupled together by bearing cartridges (and, thus, more or less
than six or seven axes of articulated movement or degrees of
freedom).
[0018] The probe 118 is detachably mounted to the measurement probe
housing 102, which is connected to bearing cartridge grouping 112.
A handle 126 is removable with respect to the measurement probe
housing 102 by way of, for example, a quick-connect interface. The
handle 126 may be replaced with another device (e.g., a laser line
probe, a bar code reader), thereby providing advantages in allowing
the operator to use different measurement devices with the same
AACMM 100. In exemplary embodiments, the probe housing 102 houses a
removable probe 118, which is a contacting measurement device and
may have different tips 118 that physically contact the object to
be measured, including, but not limited to: ball, touch-sensitive,
curved and extension type probes. In other embodiments, the
measurement is performed, for example, by a non-contacting device
such as a laser line probe (LLP). In an embodiment, the handle 126
is replaced with the LLP using the quick-connect interface. Other
types of measurement devices may replace the removable handle 126
to provide additional functionality. Examples of such measurement
devices include, but are not limited to, one or more illumination
lights, a temperature sensor, a thermal scanner, a bar code
scanner, a projector, a paint sprayer, a camera, or the like, for
example.
[0019] As shown in FIGS. 1A and 1B, the AACMM 100 includes the
removable handle 126 that provides advantages in allowing
accessories or functionality to be changed without removing the
measurement probe housing 102 from the bearing cartridge grouping
112. As discussed in more detail below with respect to FIG. 2, the
removable handle 126 may also include an electrical connector that
allows electrical power and data to be exchanged with the handle
126 and the corresponding electronics located in the probe end.
[0020] In various embodiments, each grouping of bearing cartridges
110, 112, 114 allows the arm portion 104 of the AACMM 100 to move
about multiple axes of rotation. As mentioned, each bearing
cartridge grouping 110, 112, 114 includes corresponding encoder
systems, such as optical angular encoders for example, that are
each arranged coaxially with the corresponding axis of rotation of,
e.g., the arm segments 106, 108. The optical encoder system detects
rotational (swivel) or transverse (hinge) movement of, e.g., each
one of the arm segments 106, 108 about the corresponding axis and
transmits a signal to an electronic data processing system within
the AACMM 100 as described in more detail herein below. Each
individual raw encoder count is sent separately to the electronic
data processing system as a signal where it is further processed
into measurement data. No position calculator separate from the
AACMM 100 itself (e.g., a serial box) is required, as disclosed in
commonly assigned U.S. Pat. No. 5,402,582 ('582).
[0021] The base 116 may include an attachment device or mounting
device 120. The mounting device 120 allows the AACMM 100 to be
removably mounted to a desired location, such as an inspection
table, a machining center, a wall or the floor for example. In one
embodiment, the base 116 includes a handle portion 122 that
provides a convenient location for the operator to hold the base
116 as the AACMM 100 is being moved. In one embodiment, the base
116 further includes a movable cover portion 124 that folds down to
reveal a user interface, such as a display screen.
[0022] In accordance with an embodiment, the base 116 of the
portable AACMM 100 contains or houses an electronic data processing
system that includes two primary components: a base processing
system that processes the data from the various encoder systems
within the AACMM 100 as well as data representing other arm
parameters to support three-dimensional (3-D) positional
calculations; and a user interface processing system that includes
an on-board operating system, a touch screen display, and resident
application software that allows for relatively complete metrology
functions to be implemented within the AACMM 100 without the need
for connection to an external computer.
[0023] In accordance with an embodiment, the base 116 of the
portable AACMM 100 contains or houses an electronic data processing
system that includes two primary components: a base processing
system that processes the data from the various encoder systems
within the AACMM 100 as well as data representing other arm
parameters to support three-dimensional (3-D) positional
calculations; and a user interface processing system that includes
an on-board operating system, a touch screen display, and resident
application software that allows for relatively complete metrology
functions to be implemented within the AACMM 100 without the need
for connection to an external computer.
[0024] FIG. 2 is a block diagram of electronics utilized in an
AACMM 100 in accordance with an embodiment. The embodiment shown in
FIG. 2 includes an electronic data processing system 210 including
a base processor board 204 for implementing the base processing
system, a user interface board 202, a base power board 206 for
providing power, a Bluetooth module 232, and a base tilt board 208.
The user interface board 202 includes a computer processor for
executing application software to perform user interface, display,
and other functions described herein.
[0025] As shown in FIG. 2, the electronic data processing system
210 is in communication with the aforementioned plurality of
encoder systems via one or more arm buses 218. In the embodiment
depicted in FIG. 2, each encoder system generates encoder data and
includes: an encoder arm bus interface 214, an encoder digital
signal processor (DSP) 216, an encoder read head interface 234, and
a temperature sensor 212. Other devices, such as strain sensors,
may be attached to the arm bus 218.
[0026] Also shown in FIG. 2 are probe end electronics 230 that are
in communication with the arm bus 218. The probe end electronics
230 include a probe end DSP 228, a temperature sensor 212, a
handle/LLP interface bus 240 that connects with the handle 126 or
the LLP 242 via the quick-connect interface in an embodiment, and a
probe interface 226. The quick-connect interface allows access by
the handle 126 to the data bus, control lines, and power bus used
by the LLP 242 and other accessories. In an embodiment, the probe
end electronics 230 are located in the measurement probe housing
102 on the AACMM 100. In an embodiment, the handle 126 may be
removed from the quick-connect interface and measurement may be
performed by the laser line probe (LLP) 242 communicating with the
probe end electronics 230 of the AACMM 100 via the handle/LLP
interface bus 240. In an embodiment, the electronic data processing
system 210 is located in the base 116 of the AACMM 100, the probe
end electronics 230 are located in the measurement probe housing
102 of the AACMM 100, and the encoders are located in the bearing
cartridge groupings 110, 112, 114. The probe interface 226 may
connect with the probe end DSP 228 by any suitable communications
protocol, including commercially-available products from Maxim
Integrated Products, Inc. that embody the 1-Wire.RTM.
communications protocol 236.
[0027] FIG. 3 is a block diagram describing detailed features of
the electronic data processing system 210 of the AACMM 100 in
accordance with an embodiment. In an embodiment, the electronic
data processing system 210 is located in the base 116 of the AACMM
100 and includes the base processor board 204, the user interface
board 202, a base power board 206, a Bluetooth module 232, and a
base tilt module 208.
[0028] In an embodiment shown in FIG. 3, the base processor board
204 includes the various functional blocks illustrated therein. For
example, a base processor function 302 is utilized to support the
collection of measurement data from the AACMM 100 and receives raw
arm data (e.g., encoder system data) via the arm bus 218 and a bus
control module function 308. The memory function 304 stores
programs and static arm configuration data. The base processor
board 204 also includes an external hardware option port function
310 for communicating with any external hardware devices or
accessories such as an LLP 242. A real time clock (RTC) and log
306, a battery pack interface (IF) 316, and a diagnostic port 318
are also included in the functionality in an embodiment of the base
processor board 204 depicted in FIG. 3.
[0029] The base processor board 204 also manages all the wired and
wireless data communication with external (host computer) and
internal (display processor 202) devices. The base processor board
204 has the capability of communicating with an Ethernet network
via an Ethernet function 320 (e.g., using a clock synchronization
standard such as Institute of Electrical and Electronics Engineers
(IEEE) 1588), with a wireless local area network (WLAN) via a LAN
function 322, and with Bluetooth module 232 via a parallel to
serial communications (PSC) function 314. The base processor board
204 also includes a connection to a universal serial bus (USB)
device 312.
[0030] The base processor board 204 transmits and collects raw
measurement data (e.g., encoder system counts, temperature
readings) for processing into measurement data without the need for
any preprocessing, such as disclosed in the serial box of the
aforementioned '582 patent. The base processor 204 sends the
processed data to the display processor 328 on the user interface
board 202 via an RS485 interface (IF) 326. In an embodiment, the
base processor 204 also sends the raw measurement data to an
external computer.
[0031] Turning now to the user interface board 202 in FIG. 3, the
angle and positional data received by the base processor is
utilized by applications executing on the display processor 328 to
provide an autonomous metrology system within the AACMM 100.
Applications may be executed on the display processor 328 to
support functions such as, but not limited to: measurement of
features, guidance and training graphics, remote diagnostics,
temperature corrections, control of various operational features,
connection to various networks, and display of measured objects.
Along with the display processor 328 and a liquid crystal display
(LCD) 338 (e.g., a touch screen LCD) user interface, the user
interface board 202 includes several interface options including a
secure digital (SD) card interface 330, a memory 332, a USB Host
interface 334, a diagnostic port 336, a camera port 340, an
audio/video interface 342, a dial-up/cell modem 344 and a global
positioning system (GPS) port 346.
[0032] The electronic data processing system 210 shown in FIG. 3
also includes a base power board 206 with an environmental recorder
362 for recording environmental data. The base power board 206 also
provides power to the electronic data processing system 210 using
an AC/DC converter 358 and a battery charger control 360. The base
power board 206 communicates with the base processor board 204
using inter-integrated circuit (I2C) serial single ended bus 354 as
well as via a DMA serial peripheral interface (DSPI) 356. The base
power board 206 is connected to a tilt sensor and radio frequency
identification (RFID) module 208 via an input/output (I/O)
expansion function 364 implemented in the base power board 206.
[0033] Though shown as separate components, in other embodiments
all or a subset of the components may be physically located in
different locations and/or functions combined in different manners
than that shown in FIG. 3. For example, in one embodiment, the base
processor board 204 and the user interface board 202 are combined
into one physical board.
[0034] FIG. 4 depicts an exaggerated view of bending in the first
arm segment 106. Bending and twisting of components of the AACMM
100 (e.g., the first and second arm segments 106, 108) can result
from the forces due to gravity, the counter balance spring, or
handling of the AACMM 100 by the operator. If the kinematic model
calculations performed by the base processor board 204 do not take
these forces into account, it may not account fully account for
bending or twisting of the arm segments when calculating the
coordinates of a point. By directly measuring the bending strains
of the arm, the effects of the forces applied to the AACMM 100 can
be included in the kinematic model calculations, thereby improving
the measurement accuracy of the AACMM 100.
[0035] Referring to FIG. 5, strain gage sensors 500 are attached to
a structural part 510, which may include arm segments 106, 108,
bearing cartridge groupings 110, 112, 114, or other mechanical
components of AACMM 100. The strain gage sensors 500 may be
adhesively bonded, for example with epoxy, or otherwise suitably
connected to the structural part 510. The particular mounting
configuration of the strain gage sensors 500 in four quadrants on
the structural part 510, which is cylindrically shaped in this
instance, is particularly favorable as it provides a way to
distinguish between two types of strain seen in the arm segments of
AACMMs--bending strain and axial strain--and in addition determines
the direction of bending of the arm segment. For the arm segments
of FIG. 5, the strain gage sensors 500 can be mounted on the outer
surface, the inner surface, or embedded within the material of
structural part 510.
[0036] The axial direction of a beam is the long axis of the beam.
Transverse directions are perpendicular to the axial direction.
Forces may be applied to a beam in axial and transverse directions.
Strain .epsilon. is defined as the ratio of the change in length dL
to the corresponding length L: .epsilon.=dL/L. Axial strain in a
beam results from a stretching or contraction of the beam along the
axial direction--that is, without bending. Bending strain in a beam
results from bending of the beam, as illustrated in FIG. 4. Bending
strain may result from applying a force to the beam along a
transverse direction or by applying a force to the beam along the
axial direction, but off the neutral axis of the beam. For a
straight, cylindrically symmetric beam, the neutral axis runs along
the center of the cylinder.
[0037] If a first strain gage sensor is placed on top of a beam and
a second strain gage sensor is placed on the bottom of a beam, it
is possible to distinguish bending strain from axial strain for any
forces that lie in a vertical plane passing through the strain gage
sensors and the neutral axis. For example, if the strain measured
by both the upper sensor and lower sensor decrease by the same
amount, then the strain along the vertical cross section is
compressive and entirely axial. On the other hand, if the strain in
the upper sensor is positive by a particular amount and the strain
in the lower sensor is negative by the same amount, then the upper
portion of the beam has stretched and the lower portion of the beam
has contracted, and the strain along the vertical cross section is
entirely bending strain. By placing two strain gage sensors 180
degrees apart on a beam, it is possible to calculate the amount of
bending strain and axial strain from the readings of the two strain
gage sensors.
[0038] For the AACMM 100, each arm segment 106, 108 has the ability
to swivel around its long axis. Consequently, the forces applied to
one of the arm segments (e.g., by the counterbalance spring) may be
in any direction. To predict the effect of forces or strains on one
of the arm segments 106, 108, it is not enough to place two strain
gage sensors 180 degrees apart on the arm segment. Rather, to find
the axial and bending strains at an arbitrary point on the cross
section of an arm segment, at least three strain gages sensors 500
must be properly placed on the arm segments. In an embodiment, the
arm segments 106, 108 are cylindrical tubes, with three strain gage
sensors 500 placed on the outer surface of one of the arm segments.
The three strain gage sensors are separated by 120 degrees and
aligned approximately with a plane perpendicular to the axial
direction. With this configuration, the three strain gage sensors
500 provide enough information to calculate axial and bending
strains at arbitrary positions around the tube at the plane of the
cross section. The three strain gage sensors 500 do not have to be
placed 120 degrees apart, but not all placements of the three
strain gages provide the desired information. For example, two of
the three strain gage sensors cannot be placed 180 degrees apart as
this provides information on axial and bending strain for only one
plane--the plane that contains the neutral axis and the two strain
gages sensors that are 180 degrees apart.
[0039] In an embodiment, structural components include arm segments
106, 108 that have the form of cylindrical tubes. Three or more
strain gage sensors 500 on the outer surfaces of the cylindrical
tubes are placed so that the strain gage sensors are intersected by
a plane perpendicular to the axial direction. With this
arrangement, the bending strain can be calculated for each point
that resides on both the structural component and the transverse
plane. By selecting positions on the outside of the tube (at the
position of the transverse plane) for which the bending strains
have the extreme positive and extreme negative values, the
direction and magnitude of the bending can be calculated. By
combining the direction and magnitude of the bending for each of
the structural elements with the readings of the transducers (e.g.,
angular encoders), the overall displacement of the measurement
device can be calculated in the local frame of reference of the
AACMM 100. The displacement might be, for example, the displacement
of the probe tip of the probe 118 as a result of the forces applied
to the arm segments.
[0040] The strain gage sensors 500 may be resistive, acoustic,
capacitive, inductive, mechanical, optical, piezo-resistive, or
semi-conductive. In an embodiment, the strain gage sensor 500 is
resistive, with a metal foil form that is bonded to an elastic
backing (e.g., thin polyimide). The metal in the foil may be
self-temperature-compensated (STC) constantan alloy. The
self-temperature-compensation is achieved through proper processing
of the constantan alloy, especially through cold working, so that
the constantan gage wire has very low thermally induced strain over
a wide range of temperatures. In an embodiment, structural parts
510 include the arm segments 106, 108, which are hollow tubes made
of carbon-fiber composite having low CTE. The metal in the foil of
the strain gage sensor is constantan alloy (or other alloy)
selected to have a similar low CTE. The foil pattern may be a
zig-zag pattern of parallel lines such that a small amount of
stress in the direction of the parallel lines multiplies the strain
over the effective length of the foil pattern. The direction of the
parallel lines is said to be the sensitive direction of the strain
gage sensor. The parallel lines in the foil pattern of strain gage
sensors 500 are placed parallel to the axial direction of the
structural part 510. In an embodiment, the accuracy of a strain
reading of an STC strain gage is further improved by applying a
correction factor based on a curve or a polynomial equation
provided by the manufacturer of the STC strain gage.
[0041] The strain gages 500 may be placed in a Wheatstone bridge
circuit, which may, for example, be located on a circuit board near
temperature sensor 212. In one embodiment arrangement, the strain
gage sensor 500 provides one resistance in the four resistor
network. The other three resistances are provided by fixed
resistors having resistances that change very little with
temperature. In an alternative embodiment, two strain sensors
separated by 180 degrees provide two resistances in the four
resistance network of the Wheatstone bridge. The Wheatstone bridge
may be configured in a three wire network to remove the effects of
parasitic resistances of wires run from the electronics to the
strain gage sensors 500. In an embodiment, the signal from the
Wheatstone bridge is sent to an analog-to-digital converter
circuit, where the analog signal from the Wheatstone bridge is
converted into a digital strain gage signal. All of the digital
strain gage signals are put onto the arm buses 218.
[0042] Although the discussion so far has considered the effect of
strains on beams, and particularly on cylindrically shaped beams
such as arm segments 106, 108, strain gage sensors 500 may be used
to find the strains in other structures. If the particular
structure being considered is not symmetrical about the axial
direction, then it may be necessary to perform a further analysis
to properly interpret the meaning of the strain gage readings. For
example, in a complicated structural component, finite element
analysis (FEA) performed on a computer using a detailed CAD model
of the particular structure may be used to find the axial and
bending strains based on the readings of four strain gages. In such
cases, four or more strain gages, rather than three, may be
required.
[0043] The readings obtained from the strain gages may be used
either to improve the accuracy of AACMM 100 measurements or to give
an alarm to the operator to indicate that corrective action needs
to be taken. For the best accuracy, strain gage readings are
correlated to the encoder readings. This may be done by capturing
the strain gage readings at the same instant as the encoder
readings. In an embodiment, the readings may be captured by all of
the sensors in the AACMM 100, including the strain gages and
encoders, in response to a capture signal sent over a bus within
the arm buses 218. For example, the strain gage sensors 500 may
provide strain data to correct the position of AACMM 100 in real
time (e.g., .about.1000 points per second) without operator
intervention.
[0044] Data from the strain gage monitoring system can also be used
to provide direct feedback to the operator, either in the form of
audible or visual warnings. Such warnings may be issued when the
strain gage readings, especially for bending strain, deviate from
established (expected) values by more than a pre-determined value.
These warnings may be supplemented by application software designed
to teach and refine measurement techniques. In exemplary
embodiments, visible warnings can include a visual display 520 of
the structural parts 510, showing a color or gray scale 530 to
represent the severity of the strain.
[0045] To obtain a simple but effective kinematic model for the
AACMM 100 that accounts for the effects of bending strain and axial
strain, it may be helpful to use FEA to observe the effects of
forces on the AACMM 100. An example of such an FEA is shown in the
upper inset 520 of FIG. 5. In this inset, differing amounts of
strain (or stress) are indicated by the gray-scale values. In the
instance shown, the greatest concentration of strain is at the
region 530. As a further refinement, experiments may be conducted
to measure the force applied by the counterbalance spring as a
function of the orientation of the arm segments in space. These
force values may be used to improve the FEA analysis.
[0046] The main purpose of FEA is to assist in establishing a
relatively simple, but accurate, form for the kinematic model of
AACMM 100. Once the form of the kinematic model has been
established, a large amount of data is collected and fit to the
model. An optimization method is used to select the best numerical
parameter values for the model. The combined steps of collecting
data and solving for the optimum parameter values is called
compensation or calibration. The collecting of data may include
measuring the coordinates of a probe fixed in a nest while arm
segments are moved into a variety of orientations. Since the
coordinate value should be constant for a probe tip that does not
move, the parameter values may be selected to minimize the
difference in probe readings for the different orientations of the
arm segments. The collecting of data may also include measuring the
distance between points on one or more artifacts of known
length.
[0047] As stated hereinabove, the strain gage sensor 500 may be
placed on the outer surface, the inner surface, or embedded within
the material of structural part 510. In the latter case, the strain
gage sensors 500 may be embedded in the carbon fiber of the tubes
510 that connect the joints. In the fabrication process, the carbon
fiber fabric is typically wound on a mandrel and the strain gage
sensors 500 may be installed prior to completing the final wrap,
thus protecting the strain gage sensors 500 and embedding them into
the part. By placing the strain gage sensors 500 at opposite ends
of the arm tube 510, and ninety degrees apart (i.e., orthogonally
arranged) on the circumference of the tube 510, tube deformation
can be fully characterized in the area of the strain gages, near
the bond joints of mating components where the greatest deformation
occurs, as shown in the stress diagram of FIG. 5.
[0048] FIG. 6 is a flowchart of a method 600 for measuring strain
in accordance with exemplary embodiments illustrating that the
AACMM 100 can continuously measure strain at block 610, make
appropriate corrections to the AACMM 100 arm model at block 620,
and display the measurements at block 630 continuously for so long
as the operator elects to measure and display at block 640.
[0049] Technical effects and benefits include the ability to
continuously measure strains on the structural parts 510 of the
AACMM 100. As such, the operator can know if the AACMM 100 is
undergoing any strains during a measurement to take into account
the strain during the measurement or to take corrective
actions.
[0050] As will be appreciated by one skilled in the art, aspects of
the present invention may be embodied as a system, method, or
computer program product. Accordingly, aspects of the present
invention may take the form of an entirely hardware embodiment, an
entirely software embodiment (including firmware, resident
software, micro-code, etc.) or an embodiment combining software and
hardware aspects that may all generally be referred to herein as a
"circuit," "module" or "system." Furthermore, aspects of the
present invention may take the form of a computer program product
embodied in one or more computer readable medium(s) having computer
readable program code embodied thereon.
[0051] Any combination of one or more computer readable medium(s)
may be utilized. The computer readable medium may be a computer
readable signal medium or a computer readable storage medium. A
computer readable storage medium may be, for example, but not
limited to, an electronic, magnetic, optical, electromagnetic,
infrared, or semiconductor system, apparatus, or device, or any
suitable combination of the foregoing. More specific examples (a
non-exhaustive list) of the computer readable medium would include
the following: an electrical connection having one or more wires, a
portable computer diskette, a hard disk, a random access memory
(RAM), a read-only memory (ROM), an erasable programmable read-only
memory (EPROM or Flash memory), an optical fiber, a portable
compact disc read-only memory (CD-ROM), an optical storage device,
a magnetic storage device, or any suitable combination of the
foregoing. In the context of this document, a computer readable
storage medium may be any tangible medium that may contain, or
store a program for use by or in connection with an instruction
execution system, apparatus, or device.
[0052] A computer readable signal medium may include a propagated
data signal with computer readable program code embodied therein,
for example, in baseband or as part of a carrier wave. Such a
propagated signal may take any of a variety of forms, including,
but not limited to, electro-magnetic, optical, or any suitable
combination thereof. A computer readable signal medium may be any
computer readable medium that is not a computer readable storage
medium and that can communicate, propagate, or transport a program
for use by or in connection with an instruction execution system,
apparatus, or device.
[0053] Program code embodied on a computer readable medium may be
transmitted using any appropriate medium, including but not limited
to wireless, wireline, optical fiber cable, RF, etc., or any
suitable combination of the foregoing.
[0054] Computer program code for carrying out operations for
aspects of the present invention may be written in any combination
of one or more programming languages, including an object oriented
programming language such as Java, Smalltalk, C++, C# or the like
and conventional procedural programming languages, such as the "C"
programming language or similar programming languages. The program
code may execute entirely on the user's computer, partly on the
user's computer, as a stand-alone software package, partly on the
user's computer and partly on a remote computer or entirely on the
remote computer or server. In the latter scenario, the remote
computer may be connected to the user's computer through any type
of network, including a local area network (LAN) or a wide area
network (WAN), or the connection may be made to an external
computer (for example, through the Internet using an Internet
Service Provider).
[0055] Aspects of the present invention are described with
reference to flowchart illustrations and/or block diagrams of
methods, apparatus (systems) and computer program products
according to embodiments of the invention. It will be understood
that each block of the flowchart illustrations and/or block
diagrams, and combinations of blocks in the flowchart illustrations
and/or block diagrams, may be implemented by computer program
instructions.
[0056] These computer program instructions may be provided to a
processor of a general purpose computer, special purpose computer,
or other programmable data processing apparatus to produce a
machine, such that the instructions, which execute via the
processor of the computer or other programmable data processing
apparatus, create means for implementing the functions/acts
specified in the flowchart and/or block diagram block or blocks.
These computer program instructions may also be stored in a
computer readable medium that may direct a computer, other
programmable data processing apparatus, or other devices to
function in a particular manner, such that the instructions stored
in the computer readable medium produce an article of manufacture
including instructions which implement the function/act specified
in the flowchart and/or block diagram block or blocks.
[0057] The computer program instructions may also be loaded onto a
computer, other programmable data processing apparatus, or other
devices to cause a series of operational steps to be performed on
the computer, other programmable apparatus or other devices to
produce a computer implemented process such that the instructions
which execute on the computer or other programmable apparatus
provide processes for implementing the functions/acts specified in
the flowchart and/or block diagram block or blocks.
[0058] The flowchart and block diagrams in the Figures illustrate
the architecture, functionality, and operation of possible
implementations of systems, methods, and computer program products
according to various embodiments of the present invention. In this
regard, each block in the flowchart or block diagrams may represent
a module, segment, or portion of code, which comprises one or more
executable instructions for implementing the specified logical
function(s). It should also be noted that, in some alternative
implementations, the functions noted in the block may occur out of
the order noted in the Figures. For example, two blocks shown in
succession may, in fact, be executed substantially concurrently, or
the blocks may sometimes be executed in the reverse order,
depending upon the functionality involved. It will also be noted
that each block of the block diagrams and/or flowchart
illustration, and combinations of blocks in the block diagrams
and/or flowchart illustration, may be implemented by special
purpose hardware-based systems that perform the specified functions
or acts, or combinations of special purpose hardware and computer
instructions.
[0059] While the invention has been described with reference to
example embodiments, it will be understood by those skilled in the
art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this invention, but that the invention will include
all embodiments falling within the scope of the appended claims.
Moreover, the use of the terms first, second, etc. do not denote
any order or importance, but rather the terms first, second, etc.
are used to distinguish one element from another. Furthermore, the
use of the terms a, an, etc. do not denote a limitation of
quantity, but rather denote the presence of at least one of the
referenced item.
* * * * *