GB2105676A - Concentric gripper for industrial robots - Google Patents

Abstract

A gripper device for use with industrial robots and comprising at least two opposable pivotted arms 1, 1a is provided whereby cylindrical or like objects of varying diameter, such as billets in an automatic forging line, may be located in a constant position, e.g. concentrically about a given centre. Throughout their designed operating range, movement of the arms 1, 1a and/or jaws 3, 3a carried thereby is controlled by the cam slot mechanisms 9, 10 and 2, 15; 9a and 8a and 2a, 15 the profiles of which are predetermined so that the centres of inscribed circles enclosed by the co- operating operative surfaces of the jaws 3,3a remain at a fixed point. When a V-shaped jaw is provided it is arranged for the bisector of the angle thereof to pass through a fixed point during movement of the arm carrying the same. This is preferably achieved by pivotally connecting the jaw to its associated arm and adjusting the angular relationship of the jaw and arm during movement of the latter. The gripper may have three fingers, each mounting a roller and may be arranged to engage either inside or outside diameters of workpieces. <IMAGE>

Description

SPECIFICATION Concentric gripper for industrial robots This invention relates to grippers for use with industrial robots and handling machines.

With such grippers, and particularly those of the so-called linkage type which have pivotted arms, when required to handle objects of varying diameter difficulties arise in clamping or placing the objects in a constant position.

It is the object of this invention to ameliorate this difficulty.

According to this invention in a gripper device having at least two opposable pivotted arms carrying jaws or the like, the operative surfaces of the jaws are arranged to be moved towards and away from a fixed centre.

The jaws may comprise at least one V-shaped member and it is arranged that upon opening or closing movements of the arm carrying the same the bisector of the angle of the V-shaped operative surface of the jaw always passes through a fixed point. The second jaw of the gripper may be similarly formed and adapted for operation.

Alternatively the second jaw may comprise a flat operative surface in which event it is arranged that the centres of a series of inscribed circles enclosed by the cooperating V-shaped jaw and the flat jaw are always kept at the same point.

The invention is described below with reference to the accompanying drawings in which: Figure 1 is a diagrammatic representation of a linkage gripper illustrating the problem to be overcome by the invention, Figures 2 to 8 are diagrammatic representations of alternative forms of linkage gripper in accordance with the invention, Figure 9 is a perspective view of a linkage gripperofthe form indicated in Figure 3, Figures 10 and 11 are part sectional elevations of the gripper of Figure 9 showing the operative extremes thereof, Figures 12 to 15 are part sectional elevations of grippers employing the principles indicated in Figures 5 to 8 respectively, and Figure 1 2a is a section on the line A-A of Figure 12.

Throughout the drawings like parts have been given the same reference numerals, and in each of Figures 2 to 8 and 12 to 15 the grippers are shown in two positions by full and chain lines.

Referring to Figure 1 a linkage gripper is shown comprising an arm 1 pivotally mounted at 2 and at the free end of which a V-shaped jaw 3 is fixed.

The arm and jaw are movable between the positions indicated in full and chain lines by movement of a piston rod 4 which is transmitted to the arm 1 by a link 5 pivotally connected at its ends to the arm 1 and rod 4. It will be noted that when the jaw 3 is moved from the position shown in full lines in which it clamps workpiece 6 of relatively large diameter, to the position shown in chain lines in which it clamps a work-piece 7 of relatively small diameter, a considerable shift or offset occurs in the centre about which the workpieces are held, i.e. from the point 6a to the point 7a.

On this account ordinary linkage grippers cannot be employed for handling workpieces of varying or unpredictable diameter that have to be concentrically arranged as for example do billets in an automatic forging line.

Referring to Figure 2, in accordance with the invention a linkage gripper comprises a pair of arms 1, 1 a pivoted at 2, 2a respectively, to the free ends of which V-shaped jaws 3, 3a are pivotally secured. The arms are operated by a piston or like rod 4 via links 5, 5a. As the arms are opened or closed the attitude of the jaws 3, 3a is controlled so that the bisector of the angle of the jaws always passes through the same point, by means of adjusting links 8, 8a. These links are pivotally secured at one end to their respective jaw and at their other end are conveniently arranged to be located by, but free to slide in relation to, the pivots of the links 5, 5a to the arms 1, 1 a. As may be more clearly seen from subsequent figures of the drawings, e.g.Figures 9 to 11, a cam slot 9, 9a is formed in each of the links 5, 5a in which a cam follower 10, 1 Oa secured to each adjusting link 8, 8a is engaged.

The profile of the cam slot of course governs the movement of the adjusting links upon operation of the gripper arms and the profile is predetermined to obtain the above mentioned control of the attitude of the jaws. In this instance in which the arms and jaws are symmetrical the profile of the cams 9 and 9a is the same. When, however, as indicated in Figure 3, a flat jaw 3b is provided in place of one V-shaped jaw the movement required of the flat jaw differs from that of the remaining Vshaped jaw. The requirement in this case is that throughout the designed range of movement of the gripper arms and jaws the centres of inscribed circles enclosed by the V-shaped and the flat jaw must remain at the same point.To effect the necessary coordinated movement of the arm 1a, and as may better be seen in Figures 9 to 1 , the link 5a is made fast with the piston rod 4 and is formed with a cam slot 9b in which a cam flower 1 Ob secured to the arm 1 a is engaged, the profile of the cam being predetermined to produce the required movement of the arm 1 a.

A modification of the gripper of Figure 2 is illustrated in Figure 4 in which only one compensating cam assembly is provided to govern the movement of one jaw, the cooperating jaw being biased as by a spring 11 so that the jaw 3a will compliantly match the movement of the controlled jaw 3. Necessarily this arrangement can only be employed in cases where the dimensions of the two arms and jaws are the same.

Referring now to Figures 9 to 11 , an engineered version of the gripper illustrated in Figure 3 is shown. Both of the arms 1 and 1 a are slotted to receive their respective operating links 5 and 5a, the link 5a being fast with the piston rod 4 and the link 5 being pivotally connected thereto at 12. The outer end of the link 5 is secured to the arm 1 by a pivot pin 13. The cam follower 1 Ob in the form of a rotatable pin spanning the arm 1 a is engaged in the cam slot 9b provided in the link 5a and the cam follower 10 comprising a similar rotatable pin secured in the adjusting link 8 is engaged in the cam slot 9 provided in the link 5.It will be noted that the adjusting link 8 is bifurcated to embrace the link 5 and at its inner end is provided with a slot 14 embracing the pivot pin 1 3 so as to locate the inner end of the link 8 whilst providing the required freedom of movement produced by the interaction of the cam follower 10 and the cam slot 9. In Figure 10 the arms and jaws are shown in their fuily closed position and in Figure 11 in their fully open position.

Referring now to Figures 5, 12 and 1 2a, an alternative cam mechanism is shown applicable to a gripper comprising a symmetrical pair of arms and V-shaped jaws. In this arrangement the jaws are fast with their respective arms and it is the attitude of the arms which is adjusted so that the bisector of the angle of the jaws remains driected towards the same point during their designed range of movement. The required freedom of movement of the arms is provided by slots 1 5 at their inner ends which embrace their respective pivot pins 2, 2a. The cam slots 9, 9a are not in this instance formed in the links 5, 5a but in adjacent support structure 16. This structure surrounds the lower ends of the gripper arms and the cam slots are conveniently duplicated in the structure to either side of the arms.The ends of the pivot pins by which the links 5, 5a are connected to the arms, as can best be seen in Figure 1 2a, are arranged to project from both sides of their respective arms to serve as cam followers 10, 1 Oa. The advantage of this arrangement is that it simplifies the design of the cam slots but on the other hand the arms need to be relatively longer than for example a gripper as illustrated in Figure 2 to pick up objects in the same size range.

An alternative construction of the arms of the gripper is illustrated in Figures 6 and 13.The basic cam mechanism is directly comparable with that of the gripper of Figures 5 and 12, the cam slots being formed in the support structure 16, but in this instance each arm is constituted by a parallelogram linkage 1 7 which acts to maintain the spacial orientation or attitude of the jaws constant during their designed range of movement, which movement of course takes palce in the same straight iine. With this arrangement workpieces of square or rectangular cross-section may readily be handled in addition to those ofcircularsection. Also the V-shaped jaws may be replaced by roller fingers which may then be arranged to engage either internal or external diameters of workpieces.Flat jaws may also be provided for handling square or rectangular cross section workpieces.

In Figures 7 and 14 a gripper is shown comprising three arms or fingers 20a, 20b, 20c each mounting a roller 21, the fingers being arranged to converge on or diverge from the same point. The two pivotted arms 20a and 20b are operated via the links 5, 5a which are fast with the piston rod 4 through the interaction of the cam following pins 10, 1 Oa secured to the arms with the cam slots 9, 9a formed in the links. The third finger 20c in effect comprsies an extension of the piston rod. A gripper in this form may also readily be arranged to engage either inside or outside diameters of workpieces.

In Figures 8 and 15 a modification of the gripper of Figures 7 and 14 is shown in which the cam slots 9, 9a controlling the movement of the arms 20a and 20b are not provided in the links 5, 5a but rather are formed in duplicate in the support structure as in the embodiments of Figures 5/12 and 6/13, but with the variation that the pivot pins, the ends of which serve as cam followers, slide in slots 22 formed in the arms 20a and 20b, in addition to slots 9, 9a formed in the support structure 1 6. The third finger comprises a roller 21 conveniently mounted on the pin 1 2 by which the links 5, 5a are secured to the piston rod 4.

In order to improve the mechanical efficiency of the cam mechanisms the rotatable pins serving as the cam followers are preferably mounted in ball bearings, and in order to save weight the arms and links of the grippers are conveniently made of aluminium alloy. The operative working surfaces of the jaws, fingers and/or rollers or the like forming operative gripping surfaces may if necessary be made of steel, particularly if they are required to clamp hot components.

It will be noted that while the grippers of this invention may be employed to handle objects or workpieces of a variety of forms they are designed to be of most use in handling workpieces of right cylindrical form, be they of circular or regular polygonal cross-section. The cylinders of the piston rods described as operating the grippers will of course themselves constitute a part of an industrial robot or handling machine and be movable between any number of chosen stations at which the grippers of the invention may be relied upon concentrically to locate, place or hold workpieces.

Claims (16)

1. A gripper device having at least a pair of opposable pivotted arms carrying jaws or the like in which the operative surfaces of the jaws or the like are arranged to be moved towards and away from a fixed centre.

2. A device as claimed in Claim 1 in which the jaws comprise at least one V-shaped member and it is arranged that upon opening and closing movements of the arm carrying the same the bisector of the angle of the V-shaped operative surface of the jaw always passes through a fixed point.

3. A device as claimed in Claim 2 in which one jaw comprises a flat operative surface arranged so that the centres of a series of inscribed circles enclosed by the co-operating operative surfaces of the V-shaped jaw and the flat jaw are always kept at the same point.

4. A device as claimed in Claim 2 or 3 in which the or each V-shaped jaw is pivotally connected to its associated arm.

5. A device as claimed in Claim 1 in which the jaws or the like comprise a pair of rollers, flat surfaces or V-shaped members arranged so that the centres of inscribed circles enclosed by the cooperating operative surfaces of the said rollers, flat surfaces or V-shaped members remain at a fixed point throughout their designed range of movement.

6. A device as claimed in any one of the preceding claims in which the arms of the said pair of arms are formed by links operatively interconnected to constitute or act as parallelogram linkages.

7. A device as claimed in any one of the preceding claims in which movements of the jaws or the like and/or the arms are controlled by cam slot mechanisms.

8. A device as claimed in any one of the preceding claims in which a third arm is provided adapted to be reciprocated to bring a jaw or the like carried thereby into operative relationship with the other two jaws or the like.

9. A gripper device constructed, arranged and adapted to operate substantially as herein described with reference to Figure 2.

1 0. A gripper device constructed, arranged and adapted to operate substantially as herein described with reference to Figure 3.

1 A gripper device constructed, arranged and adapted to operate substantially as herein described with reference to Figure 4.

12. A gripper device constructed, arranged and adapted to operate substantially as herein described with reference to Figures 5, 12 and 1 2a

1 3. A gripper device constructed, arranged and adapted to operate substantially as herein described with reference to Figures 6 and 1 3.

14. A gripper device constructed, arranged and adapted to operate substantially as herein described with reference to Figures 7 and14.

1 5. A gripper device constructed, arranged and adapted to operate substantially as herein described with reference to Figures 8 and 1 5.

16. A gripper device constructed, arranged and adapted to operate substantailly as herein described with reference to Figures 9, 10 and 11.