GB2329349A

GB2329349A - Control of mechanical manipulators

Info

Publication number: GB2329349A
Application number: GB9719178A
Authority: GB
Inventors: Colin Alfred Hawes; Ghassan Matar
Original assignee: GEODETIC TECHNOLOGY INTERNATIO; Geodetic Tech International Holdings NV
Current assignee: GEODETIC TECHNOLOGY INTERNATIO; Geodetic Tech International Holdings NV
Priority date: 1997-09-09
Filing date: 1997-09-09
Publication date: 1999-03-24
Also published as: WO1999012697A1; AU9084198A; GB9719178D0

Abstract

A computer controlled machine comprises a platform (7) suspended by three pairs of supportive legs (8) which are coupled to the platform at triangularly spaced-apart locations by means of universal joints (9), the two legs of each pair extending in divergent directions to spaced-apart locations in an overhead mounting (500). Each leg (8) is driven by a motor (10) to move the leg (8) in its own longitudinal direction. A laser rangefinder (600) mounted on the platform (7) enables the computer to monitor the position of the platform and construct a database of positional accuracy. The platform may mount a rotary cutting tool.

Description

IMPROVEMENTS RELATING TO MECHANICAL MANIPULATORS Field of the Invention: This invention concerns improvements relating to mechanical manipulators and is particularly, though not exclusively, concerned with mechanical manipulators of the kind described in WO-A-92/17313 the disclosure whereof is incorporated herein by reference.

Backqround of the Invention: We have pioneered the development of machines based upon the mechanical manipulator that is described in WO-A-92/17313 and which comprises a platform suspended by means of three pairs of supportive legs which are coupled thereto at triangularly spaced-apart locations by means of three universal joints each of which couples to one end of each of the two legs of a respective pair, the two legs of each pair extending from their respective universal joint in divergent directions to spaced-apart locations in an overhead mounting (which is preferably domed as described in International Patent Application No. PCT/GB97/01562) whereat each leg is drivingly engaged by a respective leg-drive motor arranged to move the leg in its own longitudinal direction whilst simultaneously accommodating the angular leg movement that results, the motors being gimbal-mounted or, more preferably, being mounted within spherical bearings for accommodating angular or pivotal movements of the legs. The platform position and orientation can be controlled by appropriate operation of the six leg drive motors and provides for the mounting thereon of a variety of working tools including mechanical cutters and drills for example, lasers, high-pressure fluid cutters, robotic components etc. Disclosed in WO-A-92/17313 for example is an arrangement wherein the platform has a rotary stage mounted thereon, a pivotal stage is mounted on the rotary stage and a spindle motor is mounted in the pivotal stage for driving a rotary cutter.

The system of WO-A-92/17313 further incorporates a computer control system which determines the operation of the various motor drives and other components of the system whereby the platform and a working tool carried by the platform can be manipulated with a precision which exceeds the standard levels of precision achieved by conventional X,Y,Z orthogonal axis machine tools. Shaft encoders and other feedback measurement systems are provided which enable the computer control system to operate with precision.

Notwithstanding the efforts that we have made to develop the system of WO-A-92/17313 so as to reduce to the absolute minimum positional errors that can arise on account of manufacturing tolerances in the component parts of the system and variations, for example temperature variations, in its operating environment, we have found that problems can arise in this regard. The scale of these problems is not such as to detract significantly from the many advantages of the system as compared to conventional X,Y,X orthogonal axis systems, but nonetheless we have addressed ourselves to this problem.

Obiects and Summary of the Invention: It is thus the principal object of the present invention to provide a means for overcoming or at least substantially reducing the abovementioned problem.

According to the present invention, we are proposing to incorporate one or more laser rangefinders into the system of a machine as aforementioned and to programme the machine to execute a routine whereby the platform of the machine is driven sequentially to a plurality of different positions, the laser rangefinder(s) serving to precisely measure each said position so as to enable a databank to be developed, for example by comparison of intended and actual positions, which can be utilized as a 3-dimensional space calibration factor during machine operation.

Laser rangefinders could be associated with the legs of the machine for determining the leg lengths on a more-or-less continuous basis during machine operation and providing corresponding feedback to the computer system. The laser rangefinder(s) provided in accordance with the teachings of the present invention would be additional to any such leg length determining laser rangefinders and would operate independently thereof, though the data from the leg length laser rangefinders could be utilized with the data from the platform positions laser rangefinder(s) in the generation of the abovementioned 3-dimensional space calibration factor.

The calibration factor developed by use of laser rangefinding could be augmented by time and temperature considerations enabling multi-dimensional space, time and temperature corrections to be effected for example in order additionally to take due consideration of the length of time for which the machine has been operating and the temperature of the machine environment.

A machine according to the teachings of WO-A-92/17313 would conventionally have a knowledge based computer operating system incorporating characterisation files which enable the machine to "know" the positions of its six legs and how to drive them in order to move the platform to any desired position and orientation in 3-dimensional space. The laser rangefinder data developed in accordance with the teachings of the present invention could be employed to adjust the characterisation files of the computer operating system.

In the practice of the present invention it is envisaged that the laser rangefinder(s) might measure several thousand different positions of the machine platform within the working space of the machine during an autocalibration operation. There could be major autocalibration routines comprising many thousands of different platform positions and such routines might best be effected overnight or at other times when the machine was not being utilized, and there might additionally be minor routines comprising many fewer different platform positions, for example only a hundred or so, which could be effected during use of a machine for the purpose of checking the status of the machine calibration. Failure of a machine to pass such a minor test routine might be arranged to cause the machine automatically to go into a major autocalibration routine.

The laser rangefinder(s) might comprise spaced-apart laser emitters and detectors in which case one or more laser emitters might be provided on the platform and plural detectors might be provided within the envelope of the machine. Alternatively, combined emitter/detector type rangefinders might be utilized with reflectors provided at selected positions within the envelope of the machine. In either case, the routine that is performed to determine the status of the machine for calibration purposes would include determination by use of the laser rangefinder(s) of the positions of those components of the rangefinding system that are located within the envelope of the machine. Where more than one laser rangefinder is utilized, the laser outputs could be modulated for the purpose of enabling the data from one laser rangefinder to be discriminated from that from any other. Additionally, or alternatively, lasers providing different colour outputs could be utilised with filter discrimination.

Whilst the present invention will be described herein by reference to mechanical movement systems of the kind described in WO-A-92/17313, the invention has broader application and could be utilized with other mechanical movement systems such as the systems described in WO-A-91/03145, EP-A-O 534 585, EP-A-0 589 565 and US-A-5 388 935 for example.

The foregoing and other features of the present invention are set forth in the appended claims and will be described in the following by way of example with reference to the accompanying drawing.

Descrintion of the Drawing: The single figure of the accompanying drawing is an enlarged showing of Figure 2 of the drawings accompanying WO-A-92/17313, which has been modified to show the provision of laser rangefinding means in accordance with the teachings of the present invention.

Detailed Description of the Embodiment: A full description of the mechanical movement system that is shown in the accompanying drawing is provided in WO-A-92/17313 and only a brief description will be provided herein. The reference numerals employed in the following description correspond to those used in WO-A-92/17313.

A triangular platform 7 is suspended by three pairs of legs 8 from a bulkhead 500 which, as described in PCT/GB97/01562 aforementioned, is preferably of a domed construction. Each pair of legs 8 defines a support triangle for the platform 7 with the apex of each support triangle coupled to the platform 7 by means of a universal joint 9 and its opposed base defined by two spaced-apart drive motors 10 which are mounted in gimbals or equivalent spherical bearings in the bulkhead 500. The drive motors 10 each drivingly engage a respective one of the legs 8, for example by means of a recirculating ball screw arrangement, for moving the same in the direction of its length. The six leg drive motors 10 are individually controllable, by the computer operating system of the machine, to determine the lengths of the support legs 8 from the motors 10 to the platform 7 and thus to determine the spatial position and orientation of the platform 7 within the range of permitted movement of the universal joints 9 and the leg drive motor mountings.

To the underside of the platform 7 there is coupled a precision rotary indexing stage 11 which can be positioned in any selected one of a plurality of angular orientations with respect to the platform 7, the indexing stage 11 rotating in a plane parallel to that of the platform. The indexing stage 11 itself carries a further index stage 12 acting in a plane orthogonal to the plane of action of the stage 11, and a rotary effector 13 is coupled to the second index stage 12 for effecting rotation in a further orthogonal plane. The rotary effector 13 can for example be a spindle drive motor for rotating a cutting tool.

Further details of the above-described system are given in WO-A-92/17313 and will not be described herein.

In accordance with the teachings of the present invention at least one laser rangefinder comprising an integrated laser emitter and detector 600 is provided on the upper surface of the platform 7. Furthermore, the computer operating system of the machine includes at least one route selectable by an operator and/or automatically operable in certain circumstances, for example after the machine has been operated continuously for a predetermined time period, such routine causing the machine to position the platform 7 sequentially in a plurality of predetermined positions and by use of the laser rangefinder(s) to measure the accuracy of such positions thereby to build up a database providing a 3-dimensional correlation between the intended position of the platform 7 and the actual position to which it is moved. The resulting database enables the knowledge-based operating system of the machine, which maintains machine characterisation files regarding its calibration status, to be compensated for the purpose of ensuring that all machine movements of the platform 7 are effected to the requisite degree of accuracy, for example to within 10-5 metres of accuracy or better.

The laser rangefinder 600 that is provided on the platform 7 will for the most part be arranged to measure the position of the platform relative to the underside of the bulkhead 500, but other datum positions for platform position measurements could be provided within the envelope of the machine.

Claims

CLAIMS:

1. A mechanical movement system wherein a means defining a base for further movement is mounted for movement with substantial freedom in translation and rotation by means of a plurality of legs the effective length and angular orientation whereof are controllably adjustable, and wherein at least one laser rangefinder is provided for monitoring the position of said base defining means in the course of a routine wherein the base defining means is controllably moved to a plurality of predetermined positions.

2. A system as claimed in claim 1 wherein the means defining a base for further movement comprises a platform having three pairs of supportive legs coupled thereto at triangularly spaced-apart locations by means of three universal joints each of which couples to one end of each of the two legs of a respective pair, and the two legs of each pair extend from their respective universal joint in divergent directions to spaced-apart locations in a mounting whereat each leg is drivingly engaged by controllable leg drive means for moving the leg in its own longitudinal direction, the leg drive means associated with each leg being mounted so as to be capable of accommodating angular movement of its respective leg.

3. A system as claimed in claim 2 wherein the triangularly spaced-apart locations whereat the three pairs of supportive legs couple to the platform are equilaterally spaced apart, and the locations in the mounting whereat the legs are drivingly engaged by the leg drive means are arranged in a hexagon wherein the spacing between the respective locations for the two legs of each pair of legs are uniform as between the three pairs of legs, and the spacings between the adjacent legs of different pairs of legs are uniform.

4. A system as claimed in claim 2 or 3 wherein the leg drive means comprise motors drivingly engaged with the legs, for example electric motors driving the legs by means of recirculating ball screw couplings with the legs.

5. A system as claimed in claim 2 or 3 or 4 wherein the leg drive means are mounted in the mounting by universal joint means.

6. A system as claimed in claim 5 wherein said universal joint means mounting the leg drive means comprise ball and socket means.

7. A system as claimed in claim 6 wherein said ball and socket means mounting the leg drive means comprises a spherical ball within which is housed the leg drive means.

8. A system as claimed in any of claims 2 to 7 wherein the universal joints coupling the ends of respective pairs of the legs to the platform comprise ball and socket means.

9. A system as claimed in any of claims 2 to 8 including means coupled to said platform and providing for movement additional to the platform movement arising out of movements of the legs.

10. A system as claimed in claim 9 wherein said means for providing said additional movement is adapted and arranged to provide rotational movement in a plane parallel to a plane defined by the platform.

11. A system as claimed in claim 10 wherein said means for providing rotational movement in a plane parallel to a plane defined by the platform comprises a motor driven member rotatably mounted with respect to the platform.

12. A system as claimed in any of claims 9 to 11 including yet further means coupled to said additional movement providing means and providing for a different degree of movement to that provided by said additional movement providing means.

13. A system as claimed in claim 12 wherein said yet further movement providing means is arranged to provide rotational movement in a plane generally transverse to the plane defined by the platform.

14. A system as claimed in claim 13 wherein said yet further movement providing means comprises a motor driven pivotal arrangement.

15. A system as claimed in claim 14 wherein said pivotal arrangement comprises a motor adapted to provide rotational movement about an axis transverse to the pivot axis.

16. A system as claimed in claim 15 wherein a tool-holder is arranged to be rotated by said motor.

17. A system as claimed in any of the preceding claims wherein said plurality of legs suspend the said means providing a base for further movement from a plurality of overhead positions.

18. A system as claimed in any of the preceding claims adapted and arranged for use as a machine tooling apparatus.

19. A system as claimed in any of the preceding claims in combination with a computer system controlling the operation of the system.

20. A system as claimed in claim 19 wherein said computer system is adapted and arranged to cause movement of said base defining means to a plurality of predetermined positions, to check the accuracy of said positions with said laser rangefinder(s) and to construct a database for use in subsequent positioning operations.