GB2317157A - Gripper mechanism using electrorheological fluid - Google Patents

Abstract

A gripper mechanism comprises a deformable wall 4 preferably mounted between two supports 2,3, attached to a base 1 the supports being either pivotally mounted (5, 6, Fig 4) or flexible. An electrorheological fluid is located either within the deformable wall, preferably in a chamber formed by the wall, or situated adjacent to it. Through application of an electrical field across the electrorheological fluid by appropriate means, the electrorheological fluid is solidified and, hence, the deformable wall becomes rigid. In use, an item to be gripped is enveloped by the deformable wall and then the electrical field is applied. This causes the item to be gripped so it can be moved until it is required to be released. Removal of the electric field causes the electrorheological fluid to revert to a liquid state and the deformable wall loses its rigidity releasing the grip on the item. Further embodiments include coupling a plurality of such grippers together to give a more flexible gripping device or mounting two gripping mechanisms back to back to form an arm with a gripping element at each end.

Description

GRIPPER MECHANISM The present invention relates to a gripper mechanism for use, for example, in robot applications.

At present robots are fitted with specially designed end effectors to perform specified tasks and handling operations. With a change of application there is a need to change the gripper.

Industry is constantly confronted with issues of handling objects of various shapes and sizes. Tasks performed by robots are often lirnited by the ability of the gripper to accommodate a range of objects. Presently these problems are overcome by providing a range of grippers to perform different tasks. It is not always possible or convenient to have a variety of grippers readily available to overcome handling problems.

The present invention seeks to provide an improved gripper mechanism.

According to an aspect of the present invention, there is provided a gripper mechanism including a housing with at least one deformable wall, the housing including a space adjacent the deformable wall within or by which an electrorheological fluid is located; and means for applying a voltage across the electrorheological fluid to cause the fluid to solidify; the space and deformable wall being such that an item to be gripped can be substantially enveloped by the deformable wall.

The arrangement is such that the gripper mechanism can grip an item without the aid of any other means, such as an adjacent support, opposing gripper mechanism and so on.

Preferably, the deformable wall includes a chamber within which the electro rheological fluid is located. Preferably, the mechanism includes at least one movable member forming a wall of the housing and being coupled to the deformable wall; the movable member allowing deformation of the deformable wall into the space so as substantially to envelop an item to be gripped.

There is advantageously provided a pair of movable members on opposing sides of the deformable wall.

The movable member or members may be flexible or pivotably coupled to the housing.

According to another aspect of the present invention, there is provided a coupling mechanism including a plurality of gripper mechanisms coupled to one another.

In an embodiment, there are provided two gripper mechanisms facing away from one another, enabling opposing units to be coupled together.

A plurality of such double gripper units can provide an electrorheological link chain.

It can be said that the preferred embodiment provides a versatile auto wraparound robot gripper using electrorheological conformable elements.

This preferred versatile gripper uses an electrorheological fluid as a means of providing conformability. It can be used as a robot end effector or as an implement for handling both regular and irregular shaped objects.

In industrial applications where robots are used for handling, there are problems with conventional grippers which are often restricted in their handling function.

The preferred versatile gripper overcomes these shortcomings as it can be used for handling a variety of shapes and sizes of objects.

An embodiment of the present invention is described below, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional view of a preferred embodiment of gripper mechanism; Figure 2 is a cross-sectional view of the gripper mechanism of Figure 1 gripping an object of circular cross-section; Figure 3 is a cross-sectional view of the gripper mechanism of Figure 1 gripping an object of rectangular cross-section; Figure 4 is a cross-sectional view of another embodiment of gripper mechanism; Figure 5 shows two views of two coupling units each formed of two of the gripper mechanisms of Figure 4; and Figure 6 shows two views of a link chain formed for use as the fluid strip of the embodiments of Figures 1 or 4.

The preferred versatile gripper, which may be rectangular or trapezoidal in shape or of any other suitable shape, is mounted on a robot end effector (see Figure 1).

The primary elements of the gripper are two flexible self-closing flappers 2, 3 mounted on a base 1. On the gripping side, the flappers are linked by an electrorheological band 4.

As the object to be handled is approached by and interacts with the gripper, the band 4 conforms around the object making the flat spring-like flappers 2, 3 progressively bend inwards. When the ends of the flappers 2, 3 have closed to give maximum wrap, grasping is completed by energizing the electrorheological band 4.

The conformable band 4 consists of electrorheological fluid contained in a highly elastomeric tube with deformable or elastic conductive electrodes. The unique attribute of the electrorheological fluid is that it virtually transforms from a liquid to a solid when subjected to high dc voltage (4kv/mm gap) but the currents of less than milli amps per square centimetre and power consumed are very low.

Once activated, the gripper can be used to move the object until it is required to be released. Releasing of the grip on the object is achieved by removal of voltage to the electrorheological fluid, which then reverts to the liquid state, thus loosing its rigidity. The band 4 will then resume its original shape under the influence of spring flappers 2, 3.

By using composite (electrorheological springs as flappers), pre-grip forces can be controlled to suit the physical characteristics of the object to be handled.

A modified version of this gripper (see Figure 4) can have pivoted links with electrorheological clutch pins 5, 6. The band 4 can be replaced with an electrorheological chain link 7 (see Figure 6). This arrangement will provide a stronger and more accurate grip than the 'spring flaps'.

This type of gripper is simple to operate and function and does not require a complex control system. Its simplicity enables its use in industry, aerospace, under sea, hazardous environment and medical applications.

This type of gripper can prove useful for handling hazardous materials and be able to operate in hostile environments. When used on spacecraft robots, multi grippers of this type could be used for grasping onto regular or irregular shaped structures (see Figure 5). Thus it could help build structures in space. A gripper at either end of a robot arm may be used for docking spacecraft together. On the ground it could be used for stabilizing or gripping of rockets prior to launch (response time of Electro-rheological times is in milliseconds).

A robot arm with grippers at either end as shown in Figure 5, can be used in spacecraft applications, in which the mechanism initially grips onto the parent craft with one gripper and then clasps with the second gripper onto the second craft to be docked with (see Figure 5 showing two robot arms with grippers at both ends). The approach speed of the gripper and the controlled grasp can be such that any undesirable stresses can be avoided on the space ship during or after docking.

Its dexterity and conformability will allow the gripper to perform multiple tasks as compared to other dedicated gripper designs. As explained above, the grasp is self-acting and easy to control. Its strength is varied by varying the electrical field to the electrorheological fluid, thus controlling the force to which the object may be exposed. Collision damage due to the flexible nature of the gripper is minimized since, when not activated, the flappers 2, 3 will swing freely or with the chain type could be folded or anchored safely.

Although one gripper could handle multiple shapes and a range of object sizes there is a limit in its physical capacity which can be overcome in the chain link type as the links could be selectively activated.

The gripping mechanism can be modified and its applications widened to make its use in handling food, meat and fish products. It could have much wider application in the agricultural industry where the objects like vegetables and fruits could be handled with ease.

With multiple ERF bands the gripper can be programmed to have a variable stiffness. This is achieved by varying the actuating voltage that causes the change in the viscosity simultaneously resulting in stiffness change that can be matched to the object being handled.

multi-bands in the gripper can be selectively activated to take up the shape of the object or maintain the shape of the gripper when operating in different planes.

The selective variation allows the device to be used for handling solid or hollow objects with unstructured features, stiffness or surface texture.

Claims (8)

1. A gripper mechanism including a housing with at least one deformable wall, the housing including a space adjacent the deformable wall within or by which an electrorheological fluid is located; and means for applying a voltage across the electrorheological fluid to cause the fluid to solidify; the space and deformable wall being such that an item to be gripped can be substantially enveloped by the deformable wall.

2. A gripper mechanism according to claim 1, wherein the deformable wall includes a chamber within which the electrorheological fluid is located.

3. A gripper mechanism according to claim 1 or 2, including at least one movable member forming a wall of the housing and being coupled to the deformable wall; the movable member allowing deformation of the deformable wall into the space so as substantially to envelope an item to be gripped.

4. A gripper mechanism according to claim 3, including a pair of movable members on opposing sides of the deformable wall.

5. A gripper mechanism according to claim 3 or 4, wherein the or each movable member is flexible or pivotably coupled to the housing.

6. A coupling mechanism including a plurality of gripper mechanisms according to any preceding claim, coupled to one another.

7. A coupling mechanism according to claim 6, including two gripper mechanisms facing away from one another.

8. A gripper mechanism substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.