U.S. patent number RE45,211 [Application Number 13/708,775] was granted by the patent office on 2014-10-28 for surface sensing device with optical sensor.
This patent grant is currently assigned to Renishaw PLC. The grantee listed for this patent is Renishaw PLC. Invention is credited to Kevyn Barry Jonas, Geoffrey McFarland.
United States Patent |
RE45,211 |
McFarland , et al. |
October 28, 2014 |
Surface sensing device with optical sensor
Abstract
A surface sensing device for use in position determining
apparatus has an elongate stylus (74) with a tip (82) for scanning
the surface of a workpiece to be measured. Lateral displacements of
the stylus tip are detected by a light beam which passes along the
stylus from a light source (66) to a retroreflector (78). This
reflects the beam back via a beamsplitter (70) to a position
sensitive detector (76). The stylus is mounted for longitudinal
displacement on a carriage (72). The longitudinal displacement is
measured by another light beam projected by the beamsplitter (70)
onto a second position sensitive detector (84).
Inventors: |
McFarland; Geoffrey
(Wotton-under-Edge, GB), Jonas; Kevyn Barry (Bristol,
GB) |
Applicant: |
Name |
City |
State |
Country |
Type |
Renishaw PLC |
Gloucestershire |
N/A |
GB |
|
|
Assignee: |
Renishaw PLC
(Wotton-Under-Edge, GB)
|
Family
ID: |
34640121 |
Appl.
No.: |
13/708,775 |
Filed: |
December 7, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
11918524 |
Oct 15, 2007 |
7847955 |
Dec 7, 2010 |
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Foreign Application Priority Data
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Apr 26, 2005 [GB] |
|
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0508388.6 |
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Current U.S.
Class: |
356/614; 33/559;
250/559.29 |
Current CPC
Class: |
G01B
5/012 (20130101); G01B 11/007 (20130101) |
Current International
Class: |
G01B
11/00 (20060101); G01B 5/00 (20060101); G01N
21/86 (20060101) |
Field of
Search: |
;356/614-616,622
;250/559.29,559.44,227.13,227.11,216 ;33/559,556,502-504 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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A-1051786 |
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May 1991 |
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CN |
|
A-1457422 |
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Nov 2003 |
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CN |
|
0 373 644 |
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Jun 1990 |
|
EP |
|
0 415 579 |
|
Mar 1991 |
|
EP |
|
0 566 719 |
|
Oct 1993 |
|
EP |
|
0 544 854 131 |
|
Sep 1996 |
|
EP |
|
0 544 854 |
|
Sep 1996 |
|
EP |
|
U-3-61505 |
|
Jun 1991 |
|
JP |
|
A-05-010745 |
|
Jan 1993 |
|
JP |
|
A-05-060542 |
|
Mar 1993 |
|
JP |
|
0 566 719 |
|
Oct 1993 |
|
JP |
|
A-07-167620 |
|
Jul 1995 |
|
JP |
|
A-11-304463 |
|
Nov 1999 |
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JP |
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A-2000-193449 |
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Jul 2000 |
|
JP |
|
A-2000-304529 |
|
Nov 2000 |
|
JP |
|
A-2002-503339 |
|
Jan 2002 |
|
JP |
|
A-2005-098936 |
|
Apr 2005 |
|
JP |
|
WO 2004/040232 |
|
May 2004 |
|
WO |
|
Other References
International Search Report issued in International Patent
Application No. PCT/GB2006/001534; mailed Jul. 4, 2006. cited by
applicant .
Dec. 19, 2011 Chinese Office Action issued in corresponding Chinese
Application No. 200680014249.1 (with translation). cited by
applicant .
SP25M Scanning Brochure. Renishaw PLC. cited by applicant .
SP25M Technical Paper. Renishaw PLC. cited by applicant .
SP600 Brochure. Renishaw PLC. cited by applicant .
SP600 Installation Guide. Renishaw PLC. cited by applicant .
SP600Q in-quill scanning probe, Renishaw PLC. cited by
applicant.
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Primary Examiner: Nguyen; Sang
Attorney, Agent or Firm: Oliff PLC
Claims
The invention claimed is:
1. A surface sensing device for use in position determining
apparatus, comprising: an elongate stylus having a
workpiece-contacting stylus tip; an optical element at or near or
connected to the tip so as to be subjected to lateral displacements
of the tip; an optical transducer system which projects a light
beam along the stylus .[.between a the.]. .Iadd.between the
.Iaddend.optical element and a detector, thereby to measure said
lateral displacements of the tip; a mounting for the stylus
.[.the.]. .Iadd.of the .Iaddend.surface sensing device which
enables .Iadd.only .Iaddend.longitudinal displacement .Iadd.and
bending .Iaddend.of the stylus .Iadd.and constrains other movements
thereof.Iaddend., the mounting for the stylus disposed within a
housing of the surface sensing device, wherein the longitudinal
displacement of the stylus is at the mounting for the stylus within
the housing of the surface sensing device; and a displacement
measurement transducer arranged to measure said longitudinal
displacement of the stylus.
2. A surface sensing device according to claim 1, wherein the
stylus is bendable to permit said lateral displacements of the
tip.
3. A surface sensing device according to claim 1, wherein the
displacement measurement transducer arranged to measure
longitudinal displacement comprises a further light beam projected
onto a further detector.
4. A surface sensing device according to claim 3, including a
beamsplitter which derives both light beams from a common light
source.
5. A surface sensing device according to claim 1, wherein the
stylus is mounted on a longitudinally movable carriage.
6. A surface sensing device according to claim 5, wherein the
carriage is mounted for longitudinal movement on a pair of parallel
leaf springs or diaphragms.
7. A surface sensing device according to claim 1, wherein the
stylus has two portions, one of which is stiffer than the
other.
8. A surface sensing device according to claim 1, comprising a
probe, wherein the stylus is exchangeably attached to the
probe.
9. A surface sensing device according to claim 8, wherein the probe
comprises a longitudinally movable carriage, to which the stylus is
exchangeably attached, and wherein said displacement measurement
transducer is arranged to measure longitudinal displacement of the
carriage.
10. A surface sensing device according to claim 8, wherein the
exchangeable stylus adjusts the gain of the transducer system which
measures the lateral displacements of the stylus tip.
11. A surface sensing device for use in position determining
apparatus, comprising: an elongate stylus having a
workpiece-sensing stylus tip; the stylus having a relatively
flexible portion permitting bending of the stylus and a relatively
stiff portion, the relatively stiff portion being closer to the tip
than the relatively flexible portion: said tip being subjected to
lateral displacements caused by bending of the stylus; a transducer
system which measures lateral displacements of the tip, including
those caused by said bending of the stylus; a mounting for the
stylus in the surface sensing device which enables longitudinal
displacement of the stylus, the mounting for the stylus disposed
within a housing of the surface sensing device, wherein the
longitudinal displacement of the stylus is at the mounting for the
stylus within the housing of the surface sensing device; and a
displacement measurement transducer arranged to measure said
longitudinal displacement of the stylus.
12. A surface sensing device according to claim 11, wherein the
transducer system is optical.
13. A surface sensing device according to claim 12, wherein the
transducer system includes an optical element at or near or
connected to the tip so as to be subjected to the lateral
displacements of the tip, and a detector, and wherein the
transducer system projects a light beam between the optical element
and the detector.
14. A surface sensing device according to claim 11, wherein the
displacement measurement transducer for measuring longitudinal
displacement comprises a detector, and projects a light beam onto
the detector.
15. A surface sensing device according to claim 7, comprising a
probe, wherein the probe comprises a longitudinally movable
carriage, to which the stylus is exchangeably attached, and wherein
said displacement measurement transducer is arranged to measure
longitudinal displacement of the carriage.
16. A surface sensing device according to claim 11, comprising a
probe, wherein the stylus is exchangeably attached to the
probe.
17. A surface sensing device according to claim 16, wherein the
exchangeable stylus adjusts the gain of the transducer system which
measures the lateral displacements of the stylus tip.
.Iadd.18. A surface sensing device for use in position determining
apparatus, comprising: a probe housing; a longitudinally movable
carriage mounted within the probe housing; an elongate stylus
having a workpiece-sensing stylus tip; the longitudinally movable
carriage providing a mounting for the stylus, which enables
longitudinal displacement of the stylus at said mounting for the
stylus within the housing; the stylus being exchangeably attachable
to and detachable from the carriage; a displacement measurement
transducer in the probe housing arranged to measure said
longitudinal displacement; said stylus tip being subject to lateral
displacements; a transducer system located at least partially in
the exchangeable stylus, and arranged to measure said lateral
displacements of the tip..Iaddend.
.Iadd.19. A surface sensing device according to claim 18, wherein
the exchangeable elongate stylus is bendable to permit said lateral
displacements of the stylus tip..Iaddend.
.Iadd.20. A surface sensing device according to claim 18, wherein
the transducer system for measuring the lateral displacements of
the stylus tip includes a detector and projects a light beam along
the exchangeable elongate stylus to the detector..Iaddend.
.Iadd.21. A surface sensing device according to claim 20, wherein
the transducer system for measuring the lateral displacements of
the stylus tip comprises an optical element at or near or connected
to the stylus tip so as to be subjected to lateral displacements of
the stylus tip; and the light beam is projected between the optical
element and the detector of the transducer system..Iaddend.
.Iadd.22. A surface sensing device according to claim 20, wherein
the detector of the transducer system for measuring the lateral
displacements of the stylus tip is located in the probe
housing..Iaddend.
.Iadd.23. A surface sensing device according to claim 20, wherein
the displacement measurement transducer in the probe housing for
measuring said longitudinal displacements of the exchangeable
stylus comprises a further light beam projected onto a further
detector..Iaddend.
.Iadd.24. A surface sensing device according to claim 23, including
a beamsplitter which derives both light beams from a common light
source..Iaddend.
.Iadd.25. A surface sensing device according to claim 18, wherein
the displacement measurement transducer in the probe housing for
measuring said longitudinal displacements of the exchangeable
stylus comprises a light beam projected onto a
detector..Iaddend.
.Iadd.26. A surface sensing device according to claim 18, wherein
the carriage is mounted for longitudinal movement on a pair of
parallel leaf springs or diaphragms..Iaddend.
.Iadd.27. A surface sensing device according to claim 18, wherein
the exchangeable stylus is configured to adjust the gain of the
transducer system arranged to measure the lateral displacements of
the stylus tip..Iaddend.
.Iadd.28. A surface sensing device according to claim 27,
configured such that the stylus is exchangeable for alternative
styli by automatic stylus changing apparatus..Iaddend.
.Iadd.29. A surface sensing device according to claim 18, wherein
the stylus is exchangeably attachable to and detachable from the
carriage via a kinematic mount..Iaddend.
.Iadd.30. A surface sensing device according to claim 29, wherein
the stylus is magnetically attracted into the kinematic
mount..Iaddend.
.Iadd.31. A surface sensing device according to claim 18,
configured such that the stylus is exchangeable for alternative
styli by automatic stylus changing apparatus..Iaddend.
Description
BACKGROUND
1. Technical Field
The present invention relates to a surface sensing device for use
in position determining apparatus such as, for example, a
coordinate measuring machine (CMM), a scanning machine, a machine
tool or a measuring robot.
2. Related Art
Such machines are used for measuring workpieces, and typically
comprise an arm other member which is movable in three directions
X, Y and Z relative to a table on which the workpiece is supported.
Movements of the movable arm or other member in each of the X, Y
and Z directions are measured by transducers on the machine, so
that the position of the movable member relative to a datum
position can be determined.
The surface sensing device with which the invention is particularly
concerned is an analogue or measuring probe, having an elongate
stylus with a workpiece-contacting tip. In use, it may be mounted
on an articulating head for use in a high speed scanning operation,
such as described in our U.S. Pat. No. 5,040,306. The head is
mounted on the movable member of the machine, and has motors or
actuators capable of orienting the axis of the probe stylus about
two orthogonal axes of rotation. Transducers associated with these
rotatable axes determine the direction of orientation.
During a scanning operation, the machine and/or the head cause the
stylus tip to move over the surface of the workpiece, in accordance
with instructions from the machine controller, to gather data about
the profile of the workpiece surface. From the signals provided by
the transducers of the machine and the head, and from a knowledge
of the dimensions of the probe stylus, the positions of points on
the surface being scanned can be estimated. However, this would
only have the required accuracy if the stylus were made
sufficiently rigid, which is impractical.
Our U.S. Pat. No. 6,633,051 (corresponding to International Patent
Application No. WO 00/60310) shows such a probe. It includes a
relatively flexible, hollow stylus, which bends laterally under the
forces of contact between the stylus tip and the workpiece surface,
and under inertial forces while accelerating. An optical system is
provided which measures the lateral displacement of the stylus tip
caused by such bending. This is then combined with the measurements
from the transducers of the machine and the head.
The optical system comprises a light beam which passes along the
hollow stylus. The beam is then reflected by an optical component
at or near the tip, to pass back along the stylus. Lateral
displacement of the stylus tip causes a lateral or tilting
displacement of the returned beam, which is measured by a position
sensitive detector.
The probe shown in U.S. Pat. No. 6,633,051 is capable of measuring
only lateral displacements of the stylus tip.
SUMMARY
The present invention provides a surface sensing device for use in
position determining apparatus, comprising: an elongate stylus
having a workpiece-sensing stylus tip; an optical element at or
near or connected to the tip so as to be subjected to lateral
displacements of the tip; an optical transducer system which
projects a light beam between the optical element and a detector,
thereby to measure said lateral displacements of the tip; wherein
the stylus is mounted in the surface sensing device for
longitudinal displacement; and means are provided for measuring
said longitudinal displacement.
In some preferred embodiments, the means for measuring the
longitudinal displacement of the stylus is optical.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic representation of an articulating head
with a surface sensing device;
FIGS. 2A and 2B are a cross-section of a first embodiment of
surface sensing device;
FIG. 3 is a cross-section of a second embodiment of surface sensing
device; and
FIGS. 4,5,6 and 7 show alternative stylus assemblies for such
devices.
DETAILED DESCRIPTION OF EMBODIMENTS
Preferred embodiments of the invention will now be described by way
of example, with reference to the accompanying drawings.
Referring now to FIG. 1 there is shown an articulating probe head.
The head comprises a first housing part 10 adapted for attachment
to a position determining apparatus (not shown), and which contains
a motor or actuator 12 to provide rotation of a shaft 14 about a
first axis Z. Attached to the shaft 14 is a second housing part 16
which contains a second motor or actuator 18 to provide rotation of
a second shaft 20 about a second, orthogonal axis X. Attached to
the second shaft 20 for rotation therewith is a housing 24 which
includes a support for a surface sensing device comprising a probe
22 and a stylus assembly 26. Angular transducers are associated
with the axes X and Z, to measure the rotary motion and provide
feedback to a controller.
FIGS. 2A and 2B show the probe 22 and stylus assembly 26. The probe
22 is exchangeably attached to the housing or support 24 of the
head via a known kinematic mount 28, into which it is attracted
magnetically in known manner, so as to be easily removable and
exchangeable. Likewise, the stylus assembly 26 is exchangeably
attached to the probe 22 via a kinematic mount 30, into which it is
similarly attracted by magnets. As well known, the kinematic mounts
ensure that the probe and stylus are positioned in a precisely
repeatable manner, enabling precise, repeatable measurements. The
probe and stylus can be exchanged for alternative probes or styli,
by automatic probe/stylus changing apparatus as described in U.S.
Pat. No. 5,327,657 and European Patent No. EP 566719 (both of which
are incorporated herein by reference).
The probe 22 includes a carriage 32 which is movable vertically (in
the orientation seen in the drawings), i.e. in the longitudinal
direction of the stylus. The stylus 26 is attached to this carriage
32 via the kinematic mount 30. The carriage 32 is mounted to the
relatively fixed structure 33 of the probe 22 via two horizontally
extending planar leaf springs or diaphragms 34, which permit the
vertical movement but constrain lateral movements in X and Y
directions.
The stylus assembly 26 includes an elongate hollow tubular stylus
36, made of carbon fibre. This is slightly flexible (resiliently)
in the lateral X,Y directions and its stiffness and weight are
designed to give good dynamic performance under high speed scanning
conditions. It has a stylus tip 38 which contacts the workpiece
during such scanning. Rather than being hollow, the stylus 36 could
if desired be made of a solid transparent material such as a
suitable glass.
During scanning movements, the stylus tip 38 will undergo vertical
movements, permitted by the planar springs 34. It will also undergo
lateral X,Y movements permitted by bending of the stylus 36. The
probe 22 contains transducers to measure these movements, which
will now be described.
The probe 22 includes a laser diode or other light source 40. This
produces a beam of light which is collimated or brought to a focus
by a lens 42. The laser diode is mounted on an adjustable clamp for
alignment purposes, such that in conjunction with the lens 42 the
light beam passes axially along the hollow stylus 36. Both the
laser diode 40 and the lens 42 are provided on the fixed structure
33 of the probe 22.
A beamsplitter 44 is also provided on the fixed structure, to
receive the light beam emitted by the lens 42. It passes 50% of the
light down the stylus 36. Near the stylus tip 38, a lens 46 and a
mirror surface 50 (provided on a glass cylinder 48) act as a
retroreflector, to return the light beam back along the length of
the stylus 36. 50% of the returned beam is reflected through
90.degree. by the beamsplitter 44, onto a two-dimensional position
sensitive detector 52 (which is located on the fixed structure 33
of the probe). This arrangement is similar to that described in
U.S. Pat. No. 6,633,051. Any of the other arrangements described in
U.S. Pat. No. 6,633,051 could be used instead, and that
specification is hereby incorporated by reference.
When the stylus tip 38 is deflected laterally in X or Y directions,
the retroreflector (optical element) 46,50 causes the returned beam
to be laterally displaced by a corresponding amount in the
corresponding directions X,Y. This is detected by the position
sensitive detector 52. In the embodiment of FIGS. 2A and 2B, the
optical transducer system includes the laser diode or other light
source 40, lens 42, beamsplitter 44 and detector 52. Alternatively,
with some of the arrangements shown in U.S. Pat. No. 6,633,051, the
lateral displacement of the stylus tip 38 could cause a tilting
displacement of the returned beam, which again is measured in the X
and Y directions by the position sensitive detector 52.
The distance and the focus of the mirror/lens combination 46,50 may
be adjustable. This enables adjustment of the "gain" of the probe,
i.e. matching the amount of displacement of the returned beam at
the detector 52 depending on the length of the stylus and the
resulting amount by which the stylus tip 38 is displaceable
laterally.
The other 50% of the beam emitted by the laser diode 40 and lens 42
is reflected laterally towards a second position sensitive detector
54. This is also mounted on the fixed structure 33 of the probe.
However, between the beamsplitter 44 and the position sensitive
detector 54, the beam passes through a lens 56 which is mounted on
the vertically-movable carriage 32. Thus, the vertical position of
the beam on the detector 54 is deflected, depending upon the
vertical position of the carriage 32. Since the stylus assembly 26
is rigid in the longitudinal direction, the output of the detector
54 is a direct measure of the longitudinal position (Z) of the
stylus tip 38. The response of the detector 54 to a given amount of
vertical movement may be amplified by an appropriate choice of lens
56.
The position sensitive detector 54 could merely be a
one-dimensional detector. However, it is more convenient to use a
two-dimensional detector, the same as the detector 52, simply
ignoring the output for the other dimension.
The outputs of the detectors 52,54 therefore give a direct
indication of the three-dimensional position of the stylus tip 38,
relative to the housing 24 of the articulating head. This can be
combined in a known manner with the outputs of transducers in the
head and of the machine, in order to determine the tip position
during a scanning operation.
Other detectors can be used as the position sensitive detectors,
e.g. a CCD or other camera chip, or a quad cell.
FIG. 3 shows a cross-section through an alternative embodiment. A
probe 60 is mounted on an articulating head 62, and has an
exchangeable, kinematically mounted stylus assembly 64. A laser
diode or other light source 66, lens 68 and beamsplitter 70 are
mounted on the relatively fixed structure of the probe, and produce
light beams in a similar manner to FIG. 2A. In the embodiment of
FIG. 3, the optical transducer system includes the laser diode or
light source 66, the lens 68, the beamsplitter 70 and a position
sensitive sensor 76. The stylus assembly 64 is mounted on a
vertically-movable carriage 72 via two parallel planar leaf springs
or diaphragms 63, also as in FIG. 2A.
One of the light beams passes down a hollow tubular stylus 74 of
the stylus assembly 64, and is retroreflected back up the stylus
and directed by the beamsplitter 70 to an X,Y position sensitive
detector 76. Again, this is similar to FIGS. 2A and 2B, except that
this time the retroreflector (optical element) is formed by a GRIN
lens 78 with a mirrored back surface 80. This arrangement measures
the X,Y deflections of the stylus tip 82, as previously. In this
embodiment, contrary to the previous embodiment, the vertical (Z)
movement of the carriage 72 (and thus of the stylus tip 82) is
measured by a position sensitive detector 84 which is mounted on
the vertically-movable carriage 72.
Again therefore, the outputs of the detectors 76,84 provide a
direct measurement of the movement of the stylus tip 82 in X,Y and
Z directions, relative to the head 62
Other arrangements can be envisaged in order to measure the stylus
tip movements. For example, the movement in the Z direction could
be measured by strain gauges mounted on the planar springs which
permit the vertical movement of the carriage 32 (FIG. 2A) or 72
(FIG. 3). Or another transducer can be provided to measure the
vertical movement between the carriage and the fixed structure. Or
the distance along the light beam passing through the stylus can be
measured interferometrically, or by the time of flight of the light
beam.
Other arrangements of the beamsplitter 42 or 70 and the detectors
52,54 or 76,84 can be envisaged. For example, in FIG. 3, the
beamsplitter 70 and detector 76 could both be mounted on the
movable carriage 72, in order to measure the X,Y movements. The
detector 84 would then be mounted on the relatively fixed structure
of the probe, so that the vertical movements of the beamsplitter 70
cause the light beam to move vertically on the detector 84 and thus
measure the vertical movements of the stylus tip 82.
In another embodiment, instead of providing a retroreflector, the
laser diode or other light source 40 may be located at the bottom
end of the stylus 36 with a lens 120, as shown in FIG. 7. Or it may
actually be in the stylus tip 38. It then directs a light beam up
the stylus to the beamsplitter. Electrical connections to the laser
diode may be provided integral y in the side wall of the
stylus.
Alternatively in FIG. 7, the detector 52 may be located at the
bottom end of the stylus or in the stylus tip, optionally without
the lens 120, to receive light from a light source positioned
within the probe body as in FIG. 2A. This has the advantage that
the arrangement detects only lateral movement of the stylus tip, as
required, and is insensitive to tilting of the stylus.
The above embodiments have included a stylus tip which contacts the
workpiece during a scanning operation. However, the invention is
also useful with a non-contacting tip, which senses the workpiece
surface using a non-contact transducer, e.g. capacitively,
inductively or optically. The detectors 52,54 or 76,84 then measure
stylus deflections caused e.g. by inertial forces during the
accelerations of the scanning movement or drooping under
gravity.
In the above embodiments, FIGS. 2B and 3 show a stylus extension 86
which mounts the stylus tip 38,82 to the end of the stylus 36,74.
This may be longer than shown where longer styli are required for a
particular measurement task. The stylus extension may be made
stiffer than the stylus 36,74 so that most bending occurs in the
stylus 36,74. Or it may have a similar stiffness. In either case,
the bending measured in the stylus 36,74 is proportional to the
bending of the total assembly of the stylus and extension.
FIG. 4 shows another embodiment of the stylus assembly, which may
replace the stylus assemblies 26,64 in FIGS. 2B and 3. A hollow,
relatively flexible stylus 88 has a stylus tip 90, as previously.
Within the stylus 88 is a relatively stiff rod 92. At one end 94
this is attached at or near the stylus tip 90. The other end 96 is
free.
At the free end 96 of the rod is located a retroreflector 98 of any
suitable design. This reflects the light beam from and to the
beamsplitter 44,70 as in previous embodiments. Since the rod 92 is
relatively stiff, the movement of its free end 96 follows the
movement of the tip 90 as the stylus 88 bends.
Alternatively, as shown in FIG. 5, there may be an X,Y transducer
comprising a first element 100 on the free end 96 of the rod 92,
and a second element 102 on the fixed structure of the probe. This
X,Y transducer may be capacitive, inductive (e.g. eddy current) or
an optical encoder.
FIG. 6 shows an alternative stylus assembly. It has a stylus 104
which is mounted on a planar spring or diaphragm 106. Thus,
effective bending of the stylus assembly is provided by the bending
of the planar spring 106 (as shown in broken lines) instead of
relying on the bending of the stylus 104 itself. Another
alternative would be to weaken the tubular stylus 104 by local
perforations near its mounting point, in order to allow it to bend
while retaining stiffness in the Z direction.
The upper end of the stylus 104 is provided with a suitable
retroreflector e.g. comprising a lens 108 and mirror 110. This
returns a light beam from and to the beamsplitter 44,70 as in the
previous embodiments. If the lens 108 is omitted, the beam can
still be returned in the same way, but will be tiltingly displaced
instead of laterally displaced.
* * * * *