GB2341203A

GB2341203A - Flat web coupler for coordinate measurement systems

Info

Publication number: GB2341203A
Application number: GB9914718A
Authority: GB
Inventors: Simon Raab; John Bodjack; Allen Sajedi
Original assignee: Faro Technologies Inc
Current assignee: Faro Technologies Inc
Priority date: 1998-09-01
Filing date: 1999-06-23
Publication date: 2000-03-08
Also published as: ITTO990621A1; CA2281230A1; FR2782791B3; GB9914718D0; JP2000074691A; DE19941025A1; FR2782791A1; IT1310109B1

Abstract

A flat web coupler (200) for use with a multi joint manually positional measuring arm of a three-dimensional coordinate measurement system, comprises a web portion (424) and flexing members (420, 421) joined by links (422, 423) to the web portion via spring portions (427), to accurately translate rotational motion between a transfer coupling and a measurement device while accommodating misalignment between the components. In addition, the flat web coupler of the present invention is relatively thin thereby minimizing the space required within the arm for its mounting as well as the weight and moment created by the coupler and transferred to the arm.

Description

2341203 FLAT WEB COUPLER FOR CNIM'S 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.

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 also be described by the angles of alignment of the ob ect in 0 j space. The X, Y, and Z coordinates can be most simply measured by three 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-ty evices of the type used ped i for skeletal analysis and surgery are disclosed in U.S. Patent 4,670,851, 5,251,127 and 5,3 305,203 3, all of which are assigned to the assignee hereof Portable CMNI'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 host 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.,--, 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 arm which includes a plurality of transfer housings. With respect 2 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 the measurement transducer. With reference to FIGURES 2 and 33, 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 misalicr gnments of the axis of the transfer casing and axis of the encoder.

Referring 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 33 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 n- dsalignnients 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 tansfer 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 carrier 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 CMNI systems. Therefore, there is a perceived need to develop more accuracy and/or less costly couplers used in CMM systems.

The above-discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by the flat web coupler for CIMM's of the present invention. As 0 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 transfer case spindle and the transducer. In accordance with the present invention, the 15 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 ZO the transfer casing to the measuring component making a significantly more reliable

4 connection which accommodates misalignment while reducing shock loads. Additionally, this design filrther 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 arins 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 by those of ordinary skill in the art from the following detailed discussion and drawings.

Brief Description of the DraD n g:

Referring now to the drawings, wherein like elements are numbered aae in the several FIGURES:

FIGURE I is a front diagrammatic view depicting a three dimensional measuring machine (CMM) typical of the prior art including a coordinate measuring machine (CW, 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 33 is a cross-sectional elevation view of two assembled transversely oriented transfer housings of the prior art CMM of FIGURE 1;

FIGURE 4 is a view taken along the line 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 diagrammatic 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), syrnmetric 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.

lle 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 out side radii as shown 6 1 typically at point 430 are preferably.060 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 transferring torque and rotational movement as will be more fully explained herein below. It should be further noted that the aforementioned 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 shown 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 when assembled within arm 12 (Fig. 3)). The preferred material of the embodiment is 301 or 302 fall work hardened stainless steel which provides extraordinary strength for 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 7 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 cap screws 90. Mounting tabs 404, 406, which have cap screw mounting holes 408, 410 C7 are preferably spaced on centerline 412 at 1.63 3 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.

Referring 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 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 J3) and 7, it 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 J3) 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 CY 0 well as decreased forces transmitted to the encoders. The result is an increase in accuracy of 8 transferring 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.

Claims

What is claimed is:

9 CLAIM 1. A flat web coupler comprising: a web portion; and a plurality of flex members depending from the web portion.
CLAIM 2. A flat web coupler as set forth in claim 1 wherein the flat web coupler is generally planar.
CLAIM 3. A flat web coupler as set forth in claim I wherein the flex members are comprised of spring portions arranged in circuitous paths.
CLAIM 4. A flat web coupler as set forth in claim I wherein the flex members include mounting holes disposed therein.
CLAIM 5. A flat web coupler as set forth in claim I wherein the flat web coupler is comprised of a metallic material, a plastic material or a fiber reinforced composite material.

I.
CLAIM 6. A flat web coupler connecting a rotating member to a measurement device, the flat web coupler comprising: a web portion; a first pair of flex members depending from the web portion connecting to the rotating member; and a second pair of flex members depending from the web portion connecting to the measurement device.
CLAIM 7. A flat web coupler as set forth in claim 6 wherein the flat web coupler is generally planar.
CLAIM 8. A flat web coupler as set forth in claim 6 wherein the flex members are comprised of spring portions arranged in circuitous paths.
CLAIM 9. A flat web coupler as set forth in claim 6 wherein the flex members include mounting holes disposed therein.
CLAIM 10. A flat web coupler as set forth in claim 6 wherein the flat web coupler is comprised of a metallic material, a plastic material or a fiber reinforced composite material.
11 CLAIM 11. A flat web coupler as set forth in claim 6 wherein the second pair of flex members is connected to the web portion by a pair of links.
CLAIM 12. A flat web coupler as set forth in claim 6 wherein the second pair of flex members are attached to a mounting plate.
CLAIM 13 3. A flat web coupler as set forth in claim 6 wherein the rotating member is a transfer coupling of a multijointed arm.
CLAIM 14. A flat web coupler as set forth in claim 6 wherein the measurement device is an encoder of a multijointed arm.
CLAIM 15. A flat web coupler for use in a multijointed arm translating rotational movement of a rotating member to a measurement device, the flat web coupler comprising:

web portion; first pair of flex members depending from the web portion connecting to the rotating member; and a second pair of flex members depending from the web portion connecting to the measurement device.

12 CLAIM
16. A flat web coupler as set forth in claim 15 wherein the flat web coupler is generally planar.
CLAIM 17. A flat web coupler as set forth in claim 15 wherein the first pair and second pair of flex members are comprised of spring portions arranged in circuitous paths.
CLAIM 18. A flat web coupler as set forth in claim 15 wherein the first pair and second pair of flex members include mounting holes disposed therein.
CLAIM 19. A flat web coupler as set forth in claim 15 wherein the flat web coupler is comprised of a metallic material, a plastic material or a fiber reinforced composite material- CLAIM
20. A flat web coupler as set forth in claim 15 wherein the second pair of flex members connected to the web portion by a pair of links.

CLAIM
2 1. A flat web coupler as set forth in claim 15 wherein the second pair of flex members are attached to a mounting plate.
CLAIM 22. A flat web coupler as set forth in claim 15 wherein the rotating member is a transfer coupling of a multijointed arm.
CLAIM 23. A flat web coupler as set forth in claim 15 wherein the measurement device is an encoder of a multijointed arm.
CLAIM 24. A flat web coupler substantially as any one embodiment herein described with reference to Figs. 59 of the accompanying drawings.

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