GB2459723A

GB2459723A - Robotic end effector

Info

Publication number: GB2459723A
Application number: GB0817029A
Authority: GB
Inventors: Robin Greogory Read
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-04-30
Filing date: 2008-09-17
Publication date: 2009-11-04
Also published as: GB0807874D0; GB0817029D0

Abstract

An end effector for robotic arms to effect grip and manipulation of objects, such as in rehabilitation robotics or industries where direct contact between humans and objects is undesirable. Twin pairs of interlinked jaws close belts held in constant tension onto the object being grasped. The length of the belts within the jaws may be varied to improve grip. The belts may be both driven in the salve direction to brush or rotate an object, or contra-rotated to impart opposing turn on an object, for example to remove screw tops from containers. The belts may include angled notches which form claws as they pass end rollers, to enable small objects to be picked up. For heavier duty service, other materials such as chains and sprockets may be used instead of belts and pulleys. Sensors may be incorporated to enable proximity and/or slip sensing and automated control system response.

Description

ROBOTIC END EFFECTOR

This invention relates to a robotic end effector capable of gripping and manipulating objects of non-uniform shape.

End effectors are commonly used on robotic arms' to grasp objects so that they can be moved. They are often of simple construction comprising rigid jaws which close on the object, with limited capability to handle small, irregular shaped, fragile or compliant objects and are usually unable to perform manipulations other than grasping. Actions such as unscrewing the top off a bottle would require use of a second device in conjunction with such a simple end effector. Such end effectors are used in applications where the presence of human beings or their hands is either impractical or undesirable eg in medical, radioactive, subsea or outer space applications This invention provides an end effector comprising a chassis on which are mounted two pairs of interlinked jaws which can be pivoted by a drive mechanism and around each of which passes a belt or chain which can be driven in either direction independently of one another. The position of the belts or chains within the respective jaws can be altered under constant tension such that objects can be brushed by the belts or drawn into the jaws and grasped and manipulated by the belts.

Further features and advantages of the invention will be apparent from the following

description and the claims.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying Figure 1 which shows orthographic drawings of the end effector. In the following description and claims the word belts' is used to cover all flexible means of transmitting tension and/or imparting frictional, squeezing or wrapping forces including chains, wires, webbing, elastic bands etc Referring to Figure 1, the end effector comprises a two pairs of jaws 1 interlinked by gear teeth and mounted on a chassis 2. These jaws can be opened and closed by means of a motor 3 which transmits torque to both pairs of jaws by means of a gearbox 4 and gear trains 5. The gearbox 4 includes a differential arrangement, which transmits torque equally to the two pairs of jaws and which allows each pair to continue to close in the event that the other one has already met an irregularly shaped object being grasped.

Continuous belts pass around the jaws and a roller 6 on a linear axis device 7 which moves the roller 6 towards or away from the open end of the jaws by means of a motor 8. This allows the contact area between belts on the jaws and the object being grasped to be varied by the user or by the control system. As the jaws and/or linear axis device move, tension is maintained in the belts for example by means of an arrangement of weights and pulleys, a spring, a linear actuator and sensor arrangement, or similar means (not shown).

The belts can be driven in either direction by means of electric motor and pulley arrangements 9. This allows objects to be brushed without moving the position of the jaws or chassis by moving the belts/chains in the same direction, or objects to be contra-rotated once grasped between the belts eg to remove the screw top from a jam jar or bottle.

A typical sequence of operations to grasp an object is as follows: The jaws of the end effector are closed onto the object with the linear axis device positioning the belts forward in the jaws. The object is drawn into the jaws by retracting the linear axis device back towards the pivot points of the jaws. As the belts are attached to the linear axis device, the length of belt within the jaws increases and the contact area between the belts and the object being grasped also increases, thus firming up the grip on the object. When an adequate grip is achieved as gauged by the user or by the sensors! control system combination described below, movement of the linear axis device is ceased. Should the user wish to impart torque and/or (contra-)rotation to the object or parts thereof, the belts may be rotated in either or opposing directions. This enables actions such as screwing tops on or off containers, or nuts to be turned on bolts.

An additional advantage of the ability to move the belts relative to the jaws is that the point of wear can be altered enabling a longer lifetime before the point of contact becomes too worn for further use. This is useful if it is impractical or inconvenient to retrieve the end effector to perform maintenance on it eg in case it has become radio-active or is in an inaccessible location such as deep-sea or outer space.

Operation of the end effector can be facilitated by proximity sensors on the ends of the jaws, which provide a signal to the user or control system that an object is within a pre-set distance from the jaws -this signal can be used to warn the user or trigger response by the control system. Further sensors mounted on the jaws detect slippage of an object being lifted by the end effector relative to the jaws or belts-this signal can be used to warn the user or to trigger a (semi-)autonomous control system to adjust the position of the jaws and/or belts until slippage stops, thus enabling lifting with application of minimum force to the object being lifted. Both these features are attractive in applications where it is desirable to reduce the cognitive loading on the user, eg where the end effector is used on a robotic arm for handicapped people or where a partial or completely autonomous response is desirable to allow the user to devote attention to other aspects of the task being undertaken.

A schematic and a flow diagram illustrating how the controls described in the preceding paragraphs may operate are provided in Figures 2 and 3 respectively.

If the end effector is to be used in robust applications, chains and sprockets may replace the belts and pulleys whilst the other features of the design remain in essence the same.

Claims

CLAIMS1 An end effector comprising a chassis on which are mounted two pairs of interlinked jaws which can be pivoted by a drive mechanism and around each of which passes a belt or chain which can be driven in either direction independently of one another such that objects can be brushed by the belts or chains or grasped by the jaws and manipulated by the belts or chains.
2 An end effector as claimed in Claim 1 wherein means is provided to alter the position of the belts or chains within the respective jaws whilst maintaining tension in the belts or chains.
3 An end effector as claimed in Claims 1 and 2 whereby means is provided to maintain the tension in the belts or chains at a constant setting.
4 An end effector as claimed in any of the preceding Claims wherein means is provided to allow either pair ofjaws to continue to close when the other has already closed on an object.
An end effector as claimed in any of the preceding Claims wherein means is provided to apply equal closing force in each pair ofjaws.
6 An end effector as claimed in any combination of the preceding Claims wherein the belts contain angled notches or protrusions which form claws as they pass round the pivot on the end of the jaws.
7 An end effector as claimed in any combination of the preceding Claims equipped with sensors to detect immediate proximity of an object.
8 An end effector as claimed in any combination of Claims 1 to 6 and Claim 7 coupled to a control system which alerts the user of immediate proximity of an object to the jaws.
9 An end effector as claimed in Claim 8 in which the control system also triggers slowing down or cessation of movement of any part of the end effector towards the object concerned.
An end effector as claimed in any combination of Claims 1 to 9 equipped with sensors to detect slippage of an object being lifted relative to the jaws or belts or chains.
11 An end effector as claimed in Claim 10 coupled to a control system which alerts the user of slippage.
12 An end effector as claimed in Claim 11 in which the control system also triggers tightening of the jaws or belts or chains around the object until the sensors detect cessation of slip of the object concerned past the jaws.
13 An end effector substantially as described herein with reference to the accompanying drawings.
14 An end effector as claimed in preceding claims but including more than two pairs of jaws and associated belts or chains.