GB2189458A - Compliant coupling mechanism - Google Patents

Abstract

A compliant mechanism 10 comprises a first coupling member 11 connected to a robot gripper 2, through a further compliant mechanism 100, and a second coupling member 12 connected directly to a robot arm 1. A spring 18 acts to align members 11, 12 co-axially along the Z-Z direction so that ball bearings 23 block respective openings 21 in member 12. If the gripper 2 is subjected to a substantial force, member 11 is displaced causing one or more ball bearings to be raised from their respective seatings. A monitoring system monitors the ingress or egress of air through the exposed openings and generates a control signal which, for example, is used to arrest further movement of the robot arm 1 and thus prevent damage to the gripper 2 and/or a component or tool carried thereby. <IMAGE>

Description

SPECIFICATION Compliant coupling mechanism This invention relates to a compliant mechanism for coupling a robotgrippertoa robotarm.

In some automated assembly and or processing operations the positional accuracy of a gripper in relation to a workpiece can be of critical importance.

Figure 1 ofthe accompanying drawings illustrates how both lateral and angular misalignment of a pin in relation to a hole could hinder insertion, and even cause jamming. A solution to the problem involves providing someform of compliant coupling mechanism which allows relative displacement of the gripper and arm in response to the prevailing forces. A known mechanism, shown in Figure 2, comprises two metal plates, one attached to the robotarm and the othertothe gripper. The platesare joined together by a pair of elastomeric shear pads each consisting of a stack of metal and rubber washers arranged alternately. The shear pads are set ata slight angle so asto allow, in effect, rotational and or lateral displacement of the gripper relativeto the arm.In some operational situations, however, especially in the case of accidental collision of parts, a coupling mechanism ofthis kind may not prevent damageto the gripper and or a component ora tool carried thereby. It is therefore an object of this invention to provide a compliant coupling mechanism which at least alleviates the above described problems.

Accordingly there is provided a compliant mechanism for coupling a robot gripper to a robot arm, the mechanism comprising a first member for coupling tothe arm, a second memberforcoupling to the gripper and resilient means effective to bias the first and second members towards preset relative positions, wherein one of said first and second members has an air inlet (or outlet) opening connectableto an air pressure, orairflow monitoring system and the other ofsaid first and second members is adapted to block said opening, to prevent ingress (or egress) of air, provided the first and second members assume preset relative positions, displacement of said first and second members from said preset relative positions allowing ingress (or egress) of air and causing the monitoring system to produce a response indicative ofthe displacement.

The monitoring system may generate a control signal effective to arrestfurther movement of the robot arm and so prevent damagetothe gripper and ora componentortool carried thereby.

In one embodiment ofthe invention said one member has a plurality of recessed openings and said other member is provided with a corresponding plurality of blocking members, preferably ball bearings, which seat against, and so block,the respective openings when the first and second members assume said preset relative positions.

In another embodiment, said opening is formed in a surface of the first member and said second member is adapted to abut said surface directly, and block the opening, whenever said first and second members are in said preset relative positions.

In orderthatthe invention may be carried readily into effect particular embodiments thereof are now described, byway of example only, by reference to the accompanying drawings ofwhich, Figure 1 illustrates lateral and angular misalignment of a pin in relation to a hole, Figure2 shows a know form of compliant coupling mechanism, Figure 3 shows a longitudinal cross-sectional view through a compliant coupling mechanism in accordance with the present invention, Figure 4 shows a side elevation view of the compliant coupling mechanism shown in Figure 3, and Figure 5 shows a different side elevation view, in direction of arrow B in Figure 3, of a partofthe compliant coupling mechanism.Referring now to the Figures 3 and 4 of drawings, a compliant mechanism shown generally at 10 couples a robot arm 1 to a robot gripper 2. In this particular example, the gripper comprises three independently, but simultaneously operable, suction heads 3,31,311 each dedicated to a specifictask. Itwill, however, be appreciated that any alternative form ofgripper, known to those skilled in the art, could be used.

Mechanism 10 has two main parts, namely a first coupling member 1 1 connected to gripper 2through a further (optional) compliant mechanism, shown generally at 100, and a second coupling member 12 connected directly to the arm. Mechanism 100, also in accord with the present invention, will be described in greater detail hereinafter.

Member 1 1 comprises a generally circular base plate 13 mounting a cylindrical wall 1 4formed with an annularflange 15, extending radially inwards, and member 12 comprises a disc 16 formed with a central boss 17 connected directly to the robot arm, as shown.

Disc 16 is confined in an enclosure bounded by the flange, wall and base plate, and a coil spring 18, which is located by respective upstanding formations 19,20 on the disc and base plate, acts to press the disc resiliently against the flange. The disc has a number of recessed openings 21 formed at regular intervals around the boss, and a network of internal passageways 22 connects the openings to an air-pressure monitoring system (not shown) via a central coupling. The openings are shaped and dimensioned to seat respective ball bearings (eg 23) mounted at corresponding positions in a facing surface240ftheflange.

In normal operation of the robot arm, spring 19 acts to align members 11,12 coaxiallyalongthe Z-axis direction (shown as line ZZ in the drawing) so that the ball bearings are all seated firmly against, and so block, the respective openings. However, if the gripper is subjected to a substantial force, due to a collision, for example, acting along, and or transversely of, the Z-axis direction, member 11 is displaced with respectto member 12causing one or more of the ball bearings to be raised from their respective seatings. In the case of a monitoring system operating at a reduced pressure, air enters the system via the exposed openings producing a detectable increase of pressure.In response, the monitoring system generates a control signal which, in this example, is used to arrestfurther movement ofthe robot arm and so prevent damage to the gripper and or a component ortool carried thereby.

Alternatively, the control signal could be used to initiate a search routinewherebythe robot arm is manoeuvred in accordance with a prearranged search pattern in such awayasto relievetheforce acting on the gripper. It will be appreciated that, alternatively,itwould bepossibletoemploya monitoring system operating at an elevated pressure and in that case air can escape from the system via the exposed opening(s) to produce a detectable decrease of pressure. Alternatively it would be possible to monitor flow, ratherthan pressure, ofair in the system.

As described hereinbefore, gripper 2 is coupled to compliant mechanism 10 through a further compliant mechanism 100. The suction heads, 3,31, 311 are arranged in side-by-side fashion on a common support plate 101 mounted pivotally in a shallow, generally U-shaped yoke 102. Plate 101 is supported on opposite sides by respective bearings 103,1031 which allow the plate to tilt, relative to the yoke,aboutan axisWorthogonal to ZZ. Theyoke is fitted with a rectangularframe member 104, shown most clearly in Figure 5, and a flat finger 105, formed as an extension of plate 101, is pressed resiliently against an inner surface 106 ofthe frame member by a coil spring 107.The frame member has an internai passageway 108 which connects an opening 109, formed in surface 106, to afurtherairpressure monitoring system (not shown in the drawings). In the illustrated position, finger 105 abuts surface 107 to block opening 109. However, should the gripper be subjected to a substantial transverse force, sufficienttoovercomethe resilience of spring 106, plate 101 can rock relative to the yoke causing the finger two move away from the opening. As in the case of mechanism 10, the further air pressure monitoring system responds by producing a control signal effective to arrestfurther movement of the robot arm, though, as described herein before, the control signal could alternatively be used to initiate a search rountine.

Mechanism 10 is connected fixedly two mechanism 100 by a cylindrical shaft 24 attached centrally to a circular plate 25. Pneumatic lines (eg 26) servicing the suction heads are housed in a central supply duct in the robot arm, independently of any gripper drive mechanism, and so sufficient lengths of line are stowed in an annular space S, enclosed by a protective cover 27, to accommodate a desired rotation of the gripper about the Z-axis-typical Iy through an angle up to 720 . The cover, to which the pneumatic lines are anchored, is mounted on shaft 24 through a ball race 28, and is prevented from rotating with the gripper by a rod 29 which is free to slide in runners 30 mounted on the robot arm, in response to changes of axial position. Rod 19 is coupled to the coverthrough a lever arm 31 and a ball and socketjoint 32 to accommodate pivotal displacent of the gripper and the associated compliant mechanisms. Itwill be appreciated that mechanisms 10 and 100 operate independently of one another, and although the described arrangement incorporates both mechanisms, alternative arrangements could may incorporate a single mechanism only.

Claims (5)

1. Acompliantmechanismforcouplingarobot gripperto a robotarm,the mechanism comprising a first memberfor coupling to the arm, a second memberforcouplingtothegripperand resilient means effective to bias the first and second members towards preset relative positions, wherein one of said first and second members has an airinlet (or outlet) opening connectable to an air pressure, or airflow monitoring system and the other of said first and second members is adapted to block said opening,to prevent ingress (or egress) of air, provided the first and second members assume said preset relative positions, displacement of said first and second members from said preset relative positions allowing ingress (or egress) of air and causing the monitoring system to produce a response indicative of the displacement.

2. Acompliantmechanism according to Claim 1 wherein said one member has a plurality of recessed openings and said other member is provided with a corresponding plurality of blocking members which seat against, and so block, the respective openings when the first and second members assume said preset relative positions.

3. A compliant mechanism according to Claim 2 wherein said blocking members are ball bearings.

4. Acompliantmechanism according to Claim 1 wherein said opening is formed in a surface ofthe first member, and said second member is adapted to abut said surface directly, and so biockthe opening, whenever said first and second members are in said preset relative positions.

5. A compliant mechanism substantially as hereinbefore described by reference to the accompanying drawings.