Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FLAT WEB COUPLI=;R FOR CMM'S
Background of the Invention:
Field of the Invention:
This invention relates generally to three dimensional coordinate measuring
machines (or CMM's). More particularly, this invention relates to a new and
improved coupler which compensates for misalignment between the moving
component and the measurement transducer used for transmission of the
rotational
motion to the rotational measurement transducers used in each coupler in the
CMM.
Without these couplers, significant forces in errors would occur in the
transducer
measurements.
Prior Art
It will be appreciated that everything in the physical world occupies volume
or
space. Position in a space may be defined by length, width and height which,
in
engineering terms, is often called an X, Y, Z coordinate. The X, Y, Z numbers
represent the dimensions of length, width and height or three dimensions.
Three-
dimensional objects are described in terms of position and orientation; that
is, not just
where an object is but in what direction it points. The orientation of an
object in
space can be defined by the position of three points on the object.
Orientation can
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also be described by the angles of alignment of the object in space. The X, Y,
and Z
coordinates can be most simply measured by l:hree linear scales. In other
words, if
you lay a scale along the length, width and height of a space, you can measure
the
position of a point in the space.
Presently, coordinate measurement machines or CMM's measure objects in a
space using three linear scales. FARO Technologies, Inc. of Lake Mary, Florida
(the
assignee of the present invention) has successfully produced a series of
electrogoniometer-type digitizing devices for the medical and industrial
fields.
Electrogoniometer-type devices of the type used for skeletal analysis and
surgery are
disclosed in U.S. Patent 4,670,851, 5,251,127 and 5,305,203, all of which are
assigned to the assignee hereof and incorporated herein by reference. Portable
CMM's, are now used for three dimensional measurement of objects for reverse
engineering, inspection, etc. An example of such a portable CMM system is
disclosed
in U.S. Patent 5,402,582, which is assigned to the assignee of the present
application,
and incorporated herein by reference. As shown in FIGURE 1, the three
dimensional
measuring system of the prior art generally comprises a coordinate measuring
machine (CMM) 10 composed of a manually operated multijointed arm 12 and a
support base or post 14, a controller or serial box 16 and a host computer 18.
It will
be appreciated that CMM 10 electronically communicates with serial box 16
which,
in turn, electronically communicates with hosl; computer 18. It should be
noted that
the number of transfer housings used is dependent on the number of degrees of
freedom that are needed to make the desired measurements required of the
individual
CMM.
As will be discussed in more detail hereinafter, CMM 10 includes transducers
(e.g., one transducer for each degree of freedom) which gather rotational
positioning
data and forward this basic data to serial box 16. The CMM 10 of the prior art
comprises a base connected to a measuring arrn which includes a plurality of
transfer
housings. With respect to these transfer housings, it will be appreciated that
the
transmission of rotational motion to a rotational measurement transducer
requires the
use of a coupler to compensate for misalignments between the moving component
and
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the measurement transducer. With reference to FIGURES 2 and 3, the transducer
80
of the prior art is mounted to a universal mounting plate 82 for mounting into
the
transfer casing 64. High accuracy rotational measurements using encoders
require
that there be no loads applied to the encoders and that motion of the transfer
casing be
accurately transmitted to the encoder despite small misalignments of the axis
of the
transfer casing and axis of the encoder.
Refernng now to FIGURES 2-4 of the: prior art, the two diaphragm coupler is
designated as item 84 in the FIGURES. Arrows designated as "A" in FIGURE 3
further highlight the space taken up by the prior art coupler 84 when
assembled within
arm 12. It should be noted that the transmission of rotational motion to a
rotational
measurement transducer requires the use of a coupler to compensate for
misalignments between the moving component and the measurement transducer. As
shown in FIGURES 2 and 3, the transducer 80 is mounted to a universal mounting
plate 82 for mounting into the transfer casing 64.
The extension shaft 86 is utilized for ultimately connecting encoder 80 to the
transfer casing. Shaft 86 is attached to coupler 84 and to the end of Garner
62 at
threading 74 using socket head cap screws 88., 90. High accuracy rotational
measurements using encoders 80 require that there be no loads applied to the
encoders
and that rotational motion of the transfer casing be accurately transmitted to
the
encoder despite small misalignments of the axis of the transfer casing and
axis of the
encoder.
Although the coupler 84 used in the CMM systems of the prior art is well
suited for its intended purpose, there is always. a need to increase the
accuracy and
reduce the costs of these couplers used in CM:M systems. Therefore, there is a
perceived need to develop more accuracy and~'or less costly couplers used in
CMM
systems.
Summary of the Invention:
The above-discussed and other drawbacks and deficiencies of the prior art are
overcome or alleviated by the flat web coupler for CMM's of the present
invention.
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As discussed, the prior art coupler in U.S. Patent 5,402,582 compensated for
misalignments between the moving component and the measurement transducer.
Without these couplers, significant forces are produced which cause errors to
occur in
the transducer measurement. The prior art utilized a two diaphragm coupler to
transmit rotational motion between the transff,r case spindle and the
transducer. In
accordance with the present invention, the transducer is instead mounted on a
coupler
comprised of a relatively thin flat web and is directly connected to the
moving
transducer. The flat web coupler, therefore, provides a flexible mounting to
accommodate misalignment between the encoder and the transfer case while
providing an accurate transmission of rotational movement between the parts.
The
non-lubricated, flexible web coupler is comprised of non-wearing parts to
directly
connect the transfer casing to the measuring component making a significantly
more
reliable connection which accommodates misalignment while reducing shock
loads.
Additionally, this design further reduces the axial length of the transfer
case coupler
and encoder combination by employing the relatively thin web coupler of the
present
invention in relation to the coupler element of the prior art. Thus, this
allows the
overall length of the arms of the CMM to be significantly more compact.
The above-discussed and other features and advantages of the present
invention will be appreciated and understood lby those of ordinary skill in
the art from
the following detailed discussion and drawings.
Brief Description of the Drawings:
Refernng now to the drawings, wherein like elements are numbered alike in
the several FIGURES:
FIGURE 1 is a front diagrammatic view depicting a three dimensional
measuring machine (CMM) typical of the prior art including a coordinate
measuring
machine (CMM), a controller box and a host computer;
FIGURE 2 is an exploded, side elevation view of a transfer housing used in
the prior art CMM of FIGURE 1;
FIGURE 3 is a cross-sectional elevation view of two assembled transversely
oriented transfer housings of the prior art CMM of FIGURE l;
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FIGURE 4 is a view taken along the Nine 4-4 of FIGURE 2;
FIGURE 5 is a plan view of a flat web coupler in accordance with the present
invention;
FIGURE 6 is a side view of the flat web coupler in accordance with the
present invention of FIGURE 5;
FIGURE 7 is a cross sectional diagra mnatic view of a flat web coupler
showing a transfer casing and encoder;
FIGURE 8 is a view taken along line 8-8 in Figure 7 showing a flat web
coupler and a universal mounting plate; and
FIGURE 9 is a plan view of an alternative embodiment of a flat web coupler.
Description of the Preferred Embodiment:
Referring first to FIGURE 5 a flat web coupler 200 for use in CMM's in
accordance with the present invention will be discussed in detail as follows.
As seen
in FIGURE 5, flat web coupler 200 is basically of square configuration,
(preferably a
little over one inch square), symmetric about the two plan view axis defined
by
centerlines 412, 414. Flat web coupler 200 includes flex members 420, 421
joined by
links 422, 423 to central web 424 and are disposed on either side of
centerline 414 and
further includes flex members 425, 426 disposed on either side of centerline
412.
The flex members include spring portions 427 comprised of narrow strips of
material shaped in circuitous paths. The inside radii at the end of the spring
portions
427 are preferably .020 inches as shown typically at point 429 and the outside
radii as
shown typically at point 430 are preferably .0(SO inches. Other radii and
groove
lengths are sized to suit so long as consideration is given to minimizing
stress and
maintaining flexibility in the flat web coupler 200. The clearance hole 431 in
the
center of flat web coupler 200 is preferably .500 inch in diameter to provide
sufficient
clearance for extension shaft 222 (Fig. 7). The flex members maximize the
ability of
the flat web coupler 200 to deflect in and out of the plane defined by
centerlines 412,
414 while accurately transfernng torque and rotational movement as will be
more
fully explained herein below. It should be further noted that the
aforementioned
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dimensions may easily be altered as required without in any way departing from
the
spirit and scope of the invention.
Reducing the length of the coupling is of particular importance to the present
invention, and as shown in FIGURE 6 the thickness represented by arrows 428 of
the
flat web coupler 200 in the embodiment showm is preferably .020 inches thick.
It is
partly this relatively thin cross sectional thickness that allows for the
reduction in the
space taken up by the prior art coupler 84 whf.n assembled within arm 12 (Fig.
3).
The preferred material of the embodiment is ?~O1 or 302 full work hardened
stainless
steel which provides extraordinary strength fc~r such a narrow thickness 428.
Of
course, any other suitable material may be substituted which meet the strength
and
deflection parameters which are required for satisfactory performance of web
coupler
200 such as other high strength metals as well as some plastic and fiber
reinforced
composite materials.
The flat web coupler 200 shown in Figure 5 is next shown mounted to an
encoder 280 in Figure 7 via attachment to universal mounting plate 201 as
shown in
Figure 8. In the embodiment shown cap screw receivers 400, 402 are preferably
spaced on a center line 414 of 1.024 inches from one another and mount flat
web
coupler 200 to encoder 280 via socket head ca.p screws 90. Mounting tabs 404,
406,
which have cap screw mounting holes 408, 410 are preferably spaced on
centerline
412 at 1.63 inches apart from one another for .engaging flat web coupler 200
to
universal mounting plate 201 via socket head cap screws 204 and nuts 205. In
turn,
universal mounting plate 201 mounts encoder 280 to transfer casing 264 via
flat web
coupler 200 by using socket head cap screws 287 through mounting holes 288. In
this
way, any small misalignments between the axis of the transfer casing 264 and
the axis
of the encoder 280 are compensated for easily by deflection of the spring
portions 427
while rotational movement is accurately transmitted between the transfer
casing and
the encoder.
Refernng now to Figure 9 an alternative embodiment of flat web coupler is
shown generally as 250. In this embodiment a flat web coupler similar to the
earlier
described embodiment is combined with a universal mounting plate. The
advantage
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of this particular embodiment is that mounting tabs 404, 406 and cap screws
204 are
eliminated and replaced by tab portions 251, 252 which connect spring portions
427
to mounting plate portion 253.
With reference to FIGURES 3 and 7, i.t can be readily seen how substantial
space is saved by substituting the flat web coupler 200 represented by arrow
"B"
(FIGURE 7) in accordance with the present invention for the prior art coupling
84
(FIGURE 3) represented by arrow "A". This savings in space reduces the
movement
arm and overall mass of the individual transfer casing, thereby producing
inherent
cost savings, a reduction in mass as well as decreased forces transmitted to
the
encoders. The result is an increase in accuracy of transfernng rotational
movement
between the transfer casing 264 and the encoder 280 by utilizing the new flat
web
coupler 200 in place of the prior art coupling 84 while maintaining the
ability to
compensate for misalignment between the two components.
While preferred embodiments have been shown and described, various
modifications and substitutions may be made thereto without departing from the
spirit
and scope of the invention. Accordingly, it is to be understood that the
present
invention has been described by way of illustrations and not limitation.
What is claimed is:
