GB2192607A - Gripper for a robotic arm - Google Patents

Abstract

A gripper has a pair of jaws (12) pivoted together about a pin 14 and adjustable by rotation of a rod (40) threadedly engaged in bushes (48) received in the jaws. Assembly of the gripper is simplified by the gripper housing having a base (36) with a groove to guide the pivot pin, a first support plate (100) carrying a bearing (105) for one end of the rod (40) and mounting a drive motor (52), and a second plate (112) carrying the bearing (106) for the other end of the rod (40) and displaceable for adjusting the mesh between gears (54,56) fast with the drive shaft and rod (40), the bearings being self-aligning and permitting axial displacement of the rod therein. <IMAGE>

Description

SPECIFICATION Gripper for a robotic arm This invention relates to a gripper for a robotic arm, and in particular the present specification discloses improvements and modifications to the gripper described in our copending International Patent Application No.

PCT/GB86/00123, whereby manufacture and assembly of the gripper are facilitated.

In the embodiment of the invention specifically described herein, the gripper jaws, an electric motor and the drive mechanism coupling the motor shaft to the jaws for the jaws to be opened and closed in response to actuation of the motor, are all easily assembled together and mounted as a pre-assembled unit onto a gripper housing or base and secured thereto, e.g. by fasteners such as screws.

A full understanding of the improved gripper will be had from the following detailed description which is given with reference to the accompanying drawings in which: Figure I is a top plan view of the gripper, the jaw tips being omitted; Figure 2 is a section taken along the line Y-Y of Fig. 1; Figure 3 is a front view of the gripper; Figure 4 is a side view of the gripper; and Figure 5 is a scrap section showing a tip fitted to a gripper jaw.

The fundamental construction of the illustrated gripper is the same as that described in the above mentioned application No.

PCT/GB86/00123, and reference is made to that application for a detailed description of the basic form of the gripper and its operation. As a matter of convenience the same reference numerals are used herein to denote parts corresponding to those identified by those numerals in the earlier International application. For the purposes of the present specification it is sufficient to explain that the gripper has a pair of jaws 12 interconnected adjacent their inner ends by a pivot pin 14, a protruding end of which is guided for linear displacement in a groove 50 provided in the gripper housing 36 when the jaws are opened and closed by rotation of a screw rod 40 having sections 41a, 41b of oppositely handed thread engaged with cylindrical bushes 48 located in openings in the respective grippers 12.The rotation of the rod 40 is produced by a motor 52 through a pair of meshing gears 54, 56 respectively fitted to the output shaft of the motor and to a projecting end of the rod 40. At their free ends the jaws 12 carry pivotal tips 20 (Fig. 5) adapted to enable articles of various shapes and sizes to be held by the gripper.

In the modified and improved gripper embodying the present invention, the housing or base 36 comprises an open-topped injection moulding formed with the guide groove 50 in the upper surface of its bottom wall. The top of the base is covered by a main support plate 100 which is secured to the base by six screws 102. At one end the plate 100 has a down turned tongue 104 with a hole into which is fitted a self-aligning bearing 105. The end of the rod 40 opposite the gear 56 is journalled in the bearing 105 which allows the rod to float in its axial direction. An up-turned flange 108 is provided on the plate 100 at its end opposite the tongue 104 and the electric motor 52 and its gear box are secured on this flange by screws 110 which pass through holes in the flange. The screws 110 also serve to clamp against the flange 108 a planar mounting plate 112.A second self aligning bearing 106 is inserted in a hole in a lower end portion of the plate 112 and a part of the rod 40 intermediate the threaded section and the gear 56 is journailed in this bearing. The output shaft of the gear box projects through holes in the flange 108 and plate 112 and has an end portion of D cross-section onto which the gear 54 is fitted with a push fit. The gear 56 is similarly fitted onto an end portion of the rod 40 having a D cross-section. The motor 52 is shown equipped with an encoder device 58 to enable the speed and position of the gripper jaws to be controlled by microprocessor.

By virtue of its construction, assembly of the gripper is simplified and can be done by unskilled labour. The gripper jaws 12 with their bushes 48 are initially assembled together with the rod 40 and their pivot pin 14.

Because the pin is guided in the groove 50 of the gripper base, the initial position of the bushes 48 on the threaded sections of the rod 40 is not critical. The bearings 105, 106 are fitted into the plates 100, 112 and the ends of the rod 40 are inserted into the respective bearings. The plate 112 and the motor 52 are then secured to the flange 108 with the screws 110, but the screws are left untightened for the moment. The gears 54, 56 are pushed onto their respective shafts and by displacement of the plate 112 relative to the flange 108 the mesh between the two gears is adjusted and the screws 110 are then tightened to fix the position of the plate 112. It may be noted that the holes in the plate 112 through which the screws 110 pass are slotted to enable this positional adjustment of the plate.Furthermore, it may be noted that displacement of the plate 112 is not restrained by the rod because the self-aligning bearings 105, 106 permit around 5 angular adjustment of the rod, and the bushes 48 are free to float up and down in the gripper jaws.

The sub-assembly of the gripper jaws 12, motor 52 and the drive coupling carried on the plates 100, 112 is assembled as a unit with the base 36 by lowering it through the open top of the base so that the end of the pivot pin 14 engages in the groove 50, and then securing the plate 100 firmly to the base with screws 102. Due to the fact that the screws 102 are all inserted from above the latter step is well suited to automatic assembly.

From the foregoing it will be appreciated that the procedure for assembly of the gripper is uncomplicated and does not require any accurate setting up.

Referring to Fig. 5, there is shown one of the gripper jaws 12 with a tip 20. The tip is biased towards a predetermined position about its pivot axis by a leaf spring 120 of generally U-shape. This spring has the advantage over the coil spring as described in application No. PCT/GB86/00123 that it can be easily fitted onto the pivot pin after the tip 20 has been attached to the jaw. Thus, the assembly of the gripper is further facilitated.

Claims (12)

1. A gripper for a robotic arm, comprising a pair of jaws having inner ends connected by a pivot and received in a housing, and a rod having screw-threaded sections engaged with bushes carried by the respective jaws whereby rotation of the rod causes the jaws to open and to close, the housing inciuding a base arranged to guide the pivot for linear movement during opening and closing movements of the jaws, and bearing supports secured to the base and carrying respective bearings journalling opposite ends of said rod and permitting axial displacement of the rod therein.

2. A gripper as claimed in claim 1, wherein the bearings~are self-aligning bearings.

3. A gripper as claimed in claim 1 or 2, wherein the bearing supports comprise first and second plates, the first plate being secured to the second plate and to the base.

4. A gripper as claimed in claim 3, wherein a drive motor for rotating the rod is mounted on the first plate.

5. A gripper as claimed in claim 4, wherein the motor is secured by screw fasteners to a flange of the first plate, said screw fasteners also securing said second plate to the flange.

6. A gripper as claimed in claim 4 or 5, wherein the motor is arranged to rotate the rod through a pair of gears, the mesh between the gears being adjustable by displacement of the second plate relative to the first plate and motor.

7. A gripper as claimed in claim 4, 5 or 6, wherein the motor, the first and second plates, the jaws and the rod are mountable on the base of the housing as a pre-assembled unit.

8. A gripper as claimed in any one of claims 3 to 7, wherein the first plate is secured -to the- base by a plurality of screw fasteners all inserted in a direction generally parallel to the pivot axis.

9. A gripper as claimed in any one of claims 3 to 8, wherein the bearings are fitted into holes in the respective plates.

10. A gripper as claimed in any one of the preceding claims, wherein the bushes are cylindrical and have their axes substantially parallel to the pivot axis, the bushes being movable axially relative to the jaws to enable angular adjustment of the rod.

11. A gripper as claimed in any one of the preceding claims, wherein each of the jaws carries a pivotal tip, and a generally U-shaped leaf spring is fitted on to a pivot pin mounting the tip to bias the tip to a predetermined position relative to the jaw.

12. A gripper for a robotic arm substantially as herein described with reference to the accompanying drawings.