GB2273326A - An end effector for fitting to robotic or automation systems - Google Patents

Abstract

An end-effector for a manipulator wherein the end effector comprises two connected 2 bar linkages (50) mounted at 90 degrees to each other, such that both ends of each linkage is pivoted, one to a first plate adapted to be secured to a manipulator flange and the other to a second plate that is adapted to carry a piece of tooling. The resultant constrained structure describes a movement made up of the intersection of the two planes of movement possible by each 2 bar linkage. The movement so described is that of a straight line at the point of intersection between the planes. Thus a compliant movement of the tool, will always be in a straight line and any force applied to the tooling will remain constant throughout the compliant stroke. To enable omnidirectional movement, a counterbalance 60 is fitted on link 52 to compensate for the weight of tooling fitted. The counterbalance can be moved up and down the rod 62 to compensate for the weight of the tooling filled. Two air operated actuators 71 and 72 are shown. These will cause pressure to be exerted on the tooling as required for finishing or deburring applications. <IMAGE>

Description

Title: Robot End-Effector Description of Invention: This invention relates to an end-effector for use in conjunction with an automation system such as, but not exclusive , a manipulator, for example a robot, which is capable of applying a constant force.

So called manipulators are used to displace a tool at the end of the manipulator to effect tasks such as deburring and finishing.

These types of tasks fall into different categories of severity based on the complexity of shape being worked, the size and quantity of material that has to be removed and the quality of finish required. What is characteristic of these operations is that modification to the surface of the part being worked is of primary importance and has to be achieved with adequate material removal and minimal alteration ( none if possible) to the basic profile or shape of the part.

In such tasks material removal is achieved using one of two types of tools: hard and soft tools. With hard tools the profile of the tools are retained dimensionally over their effective life. However they present some drawbacks that inhibit their use.

Drawbacks such as chatter, gouging and micro-burr generation, to name but three. With soft tools, the tools are designed to slowly wear away and to overcome the drawbacks presented with hard tools. These tools however present a problem when applied to robotic automation, namely that the robot path parameters require changing to compensate for the natural wear of the tooling which prevents a consistent force from being applied between the tool and the part being worked..

It is proposed to produce an end effector capable of maintaining a constant force of interaction between the tooling and the workpiece. The end-effector will maintain a constant force while passively compensating for both the wear of the tooling and any slight errors in robot path movement. Thus the need for altering robot parameters is eliminated and programming is made far easier.

Known end effectors, have a tool fastened to a plate which is the central moving part of a 4-bar linkage. The tool is therefore constrained to move in an arc which is equal to the working length of the outer moving link of the 4 bar linkage. The outer links are also extended the other side of the fixed link and another plate is fitted to the ends forming a second 4-bar linkage conjugate to the first. This second plate will therefore move in an arc, the radius of which is determined by the length of the extension from the fixed link. This second plate is parallel to the tool plate but moves in the opposite direction. Weights are attached to this second plate to balance the tool and it's associate plate. Wherby balance is retained in all orientations.

A low-friction pneumatic actuator is fitted onto the linkage in such a manner that a defined force is applied to the tooling plate. However, since any point on the end of such a linkage moves in an arc relative to the link pivot points, when any radial component of force is applied to the linkage, away from.

the datum position, an additional force component is induced at the tooling. The effect of this additional component is to increase or decrease the desired force being applied through the linkage by the pneumatic actuator on the tooling plate, thus inhibiting the ability to apply a constant force as desired at all times.

This invention proposes a device that overcomes this fundamental problem by being capable of complying in a straight line, rather than an arc, enabling a constant force to be maintained.

According to one aspect of the invention we provide a basic linkage structure consisting of a 2 bar linkage, such that when one end of the linkage is pivoted the other open end of the linkage will describe a locus of points in a single plane.

According to a second aspect of the invention we provide an endeffector for a manipulator wherein the end effector comprises two 2 bar linkages (in this example) mounted at 90 degrees to each other, such that both ends of each linkage is pivoted, one to a first plate adapted to be secured to a manipulator and the other to a second plate that is adapted to carry a piece of tooling.

The resultant structure constrains the movement of the second plate to a path that describes the intersection of the two planes of movement allowed by each 2 bar linkage. The movement so described is that of a straight line at the point of intersection between the planes. Thus a compliant movement of the tool, will always be in a straight line relative to the manipulator.

It will be appreciated that by using this basic 2 bar linkage with other orientations and with movements at the joints being either pivots or ball joints, a variety of constant force and other devices requiring controlled compliant movements can be obtained.

According to a third aspect of the invention, low pressure air is used to load the plate to which the tooling is attached with a desired level of force. Since the compliant movement of the tool will now be in a straight line, a constant force is always exerted.

A final aspect of the invention provides for the unit being able to operate in any orientation. This is achieved by balancing any tooling weight by a counterbalance. Thus enabling a constant force to be applied in any orientation.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Fig 1. Shows a side view of the end effector connected to the manipulator with tooling fitted.

Fig 2. Shows a top sectional view through an end-effector of the invention shown and counterbalance. ( the tooling has not been shown) Fig 3. Illustrates the basic 2 bar linkages and the mounting arrangements used in this case.

Referring to the drawing, there is shown in fig 1 and 2 an endeffector 10 mounted onto an arm of a manipulator 11. The arm 11 is a manipulator of the type which permits tranlational, linear and rotation movements of the arm, hence allowing any end effector 10 fitted to move in a trajectory desired to achieve a desired position of work.

Such manipulators are well known and hence further discription of the manipulator is not required.

The end effector 10 (in fig 1) comprises a first part 14 which is adapted to be fixed to an end plate 12 of the manipulator 11 by by bolt 13 ( all bolts required not shown), the first part 14 is a formation which includes flanges 15 and 16 perpindicular to axis A and another set of flanges 17 and 18 parallel to axis B.

Although shown as part of the first part 14, flanges 15,16,17 and 18 may be seperate parts secured to 14 by a variety of fixing methods.

The end effector comprises a second part 20 which is a formation similar to the first part 14. This second part is the tool carrying part of the end effector and is adapted to carry a plate 31 to which is fitted the tool required 32 - in the present example a pneumatic motor 33 with a soft tool 34.

The second part 20 is a formation with 2 side flanges 21 and 22 parallel to axis B onto which are mounted , via shielded bore races 26 on either flange, an axle 27 onto which is mounted the bottom linkage 40 ( see also fig 3). The axle 27 is retained in position using a nut 28 or other suitable retention method. Thus link arm 41 can pivot relative to the second part flanges 21 and 22. The bottom linkage 40 comprises two sets of links 41 and 42 which are connected to the second part 20, through link 41 being mounted onto the axle 27. Link 42 is connected to 41 by an axle 43 and via shield bore races 44 and is prevented from moving from side to side by retention pin 46. Thus link 42 will pivot relative to link 41 about the axis D. Hence the bottom linkage 40 will pivot about axis C.

The first part 14 has the top linkage 50 mounted nearly the same way with the linkage part 52 connected via axle 53 to the flange 16, 15 of the first part using a series of bearings ( not shown) as for linkage 41 and the linkage part 51 connected to part 52 via the axle 54 via bearings and retaing nuts, not shown, as for 41 & 42. This enables the top linkage to pivot about axis F.

The linkage arm 42 is also connected to the flange ends 17, 18 via shielded bore races and an axle 48 retained by a series of nuts as per 49, although other methods of retention may be used.

This enables link 42 to pivot about axis E.

The linkage arm 51 of 50 is also connected to the part 20 via arrangements similar to that connecting link 42 to part 14. i.e the extended arms of link 52, 55 and 56 ( in fig 2) which are duplicated the other side are connected to part 20, via a shield bore race and a rod or axle retained by nuts on either side This constraint arrangement of linkages will result in movements that will be in a straight line in parallel to the axis B shown.

A sixth part 60, the counterbalance, comprises weight 61 fitted onto a rod 62 which is fitted itself on the link 52, a screw fitting is shown although alternative methods could be used. The counterbalance can be moved up and down the rod 62 and secured into position to compensate for the weight of the tooling fitted.

Two air operated actuators 71 and 72 are shown connected between the first part 14 and the bottom part 20. This actuator will cause pressure to be exerted on the tooling as required by the manipulator. Its form and type may vary depending on the applications requirement.

The end effector may be used as follows:- see fig 3 With a 2 bar linkage made up of parts 51 and 52 connected to another 2 bar linkage made up of parts 41 and 42, mounted in the arrangement shown and configured into a design as described above, movement in a straight line along a Z axis (as described in fig 3) will be always achieved by applying a force component through the balanced actuating system , consisting of pneumatic actuators71 and 72, between the first part 14 and the bottom part 20, a constant force will be exerted between the soft tool and a component being operated upon.

To enable operation in any orientation, the weight of the tooling carried needs to be counterbalanced at all times. This is done by adjusting the counterbalance 60 connected via part 50 to part 40, to compensate for the tooling carried 32. Alternative counterbalance approaches can be use but the end requirement would interact with the linkage in the manner similar to that described.

Various modifications may be made without departing from the scope of the invention. For example, the actuators 71 and 72 may be replaced by a single or multiple arrangement of actuators They may be operated using pneumatics, hydraulics or electrical means.

In another arrangement, the position of the 2 bar linkage can be altered to obtain a different direction of compliance and possibly force (see fig 3). Thus devices capable of generating a constant force with compliance in a variety single or multiple directions can be generated.

Also the tooling arrangement shown could be altered whereby a tool is carried not only as shown but also at 90 degrees to that shown by say being on the side of the unit.

The features disclosed in the foregoing description or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, or a class or group of substances or compositions, as appropriate, may, seperately or in any combination of such features, be utilised for realiosing the invention in diverse forms thereof.

Claims (9)

1. Title: A Constant Force End-Effector

   CLAIMS 1. An end-effector made up of linkage structure consisting of a 2 bar linkage, such that when one end of the linkage is pivoted the other open end of the linkage will describe a locus of points in a single plane.
2. 2. An end-effector for a manipulator wherein the end effector comprises two 2 bar linkages (in this example) mounted at 90 degrees to each other, such that both ends of each linkage is pivoted, one to a first plate adapted to be secured to a manipulator and the other to a second plate that is adapted to carry a piece of tooling.

   The resultant structure constrains the movement of the second plate to a path that describes the intersection of the two planes of movement allowed by each 2 bar linkage. The movement so described is that of a straight line at the point of intersection between the planes. Thus a compliant movement of the tool, will always be in a straight line relative to the manipulator.
3. 3. An end effector according to claim 1 and 2, wherein the use of this basic 2 bar linkage but with other orientations and with movements at the joints being either pivots or ball joints, a variety of constant force planes can be obtained.
4. 4. An end effector substancially as hereinbefore described with reference to and as shown in the accompanying drawings.
5. 5. An end effector according to claims 1,2 and 3 wherein a linkage arrangement is used consisting of more than 2 bar linkages, but which adopt a similar method of constraint to secure movements in only one plane.
6. 6. An end effector so defined by a linkage arrangement in any one of the preceding claims, wherein means are provided to apply a pneumatic or other pressure actuation methods to exert a force onto a tool fixed to a plate attached to the linkage. Thus enabling a level of force to be applied by the tool.. Since the compliant movement of the tool will now be in a straight line, a constant force is always exerted throughout the compliant movement.
7. 7. An end effector according to any one of the preceding claims, wherin the end-effector is mounted onto a fixed surface rather than a manipulator on one plate and carries tooling on the other.
8. 8. An end-effector being able to operate in any orientation. This is achieved by balancing any tooling weight by a counterbalance.

   Thus enabling a constant force to be applied in any orientation.
9. 9. Any novel feature or novel combination of features disclosed herein and/or shown in the accompanying drawings.