One of the major problems in the development of robotics is the difficulty in designing a simple but effective gripping mechanism.

Current robotic grippers generally consist of crude two finger devices capable of no more than an uncontrolled open/close movement.

Normally these are pneumatically powered devices with no means to control the gripping force applied and no tactile sense to indicate success or failure ; their limited capabilities restrict them to the handling of only a very limited class of objects. One solution to this problem is to arrange for some form of"quick-change"mechanism whereby any one of perhaps six or more grippers can be selected, one for each different class of object to be handled. While this approach is possible in a highly structured environment such as, for example, electronic assembly lines, it is completely impracticable and inappropriate when faced with the complexity of the real world that exists away from the production line.

If robots are ever to become the universal work tool they were originally conceived to be, then something much better must be found.

An ideal model for a gripper is the human hand, capable as it is of grasping and manipulating a vast range of objects ranging from the very small and delicate to the very large and heavy; human fingers can adjust to the form of a huge range of objects and can apply the appropriate pressure to handle them in a secure way.

A number of attempts have been made to copy the human hand.

However, problems lie in the mechanical and computational complexity of such attempts. The resulting structures for example require six or more independent servo controlled actuators for each finger, and the computer power required to'coordinate all of these motions is formidable. These problems are likely to keep this class of gripper firmly confined to the research laboratory for the foreseeable future.

The present invention seeks to provide an apparatus for applying a controlled force (preferably a predetermined force) to an object. The apparatus may, for example, be used to grip an object by means of the controlled force. Additionally or alternatively, the apparatus may be used as a component part of a gripper comprising a plurality of such apparatuses.

Accordingly, a first aspect of the present invention provides an apparatus for applying a force to an object, comprising first and second fluid operated pressure transfer devices, a common supply of fluid thereto, and counteracting means arranged to oppose operation of the second device by the fluid, the first device being operable to apply a force to an object by pressurization of the fluid, until the pressure of the fluid reaches a minimum predetermined pressurization sufficient to overcome the opposition of the counteracting means whereupon the second device operates, thereby substantially preventing the further operation of the first device such that a controlled force, dependent upon the predetermined pressurization of the fluid, is applied to the object.

The controlled force applied to the object preferably is a predetermined force (dependent upon the predetermined pressurization of the fluid).

The invention has the advantage that the operation of the first pressure transfer device ceases upon the operation of the second pressure transfer device, and the second device operates only once the pressure of the fluid reaches a predetermined pressurization equivalent to a controlled (preferably predetermined) force applied to an object (by the first device). The invention therefore provides an elegant solution to the problem of how to apply a controlled force to an object.

In use, the pressurization of the fluid preferably increases due (at least in part) to resistance to the first pressure transfer device by the object to which a force is applied (by means of the first device).

Advantageously, the speed with which the first device operates may be controlled by the rate at which the fluid is pressurized.

Preferably the first and/or the second fluid operated pressure transfer devices comprise fluid operated pistons, bellows, diaphragms, rotary actuators, or the like. More preferably, operation of the first and/or the second fluid operated transfer device comprise movement thereof. In the description that follows, the pressure transfer devices will be described primarily in terms of them being pistons. It is to be understood, however, that at least in the broadest aspects of the invention, the term"piston"is intended to include substantially any pressure transfer device, and movement of a piston is intended to include the operation of any such device.

The counteracting means preferably comprises resilient means, for example a spring (especially a helical spring, and particularly a compression spring). The opposition of the counteracting means to the operation of the second pressure transfer device consequently preferably comprises the resilience of the resilient means.

Accordingly a second aspect of the invention provides an apparatus for applying a force to an object, comprising first and second fluid operated pistons, a common supply of fluid thereto, and resilient means arranged to oppose movement of the second piston by the fluid, the first piston being movable to apply a force to an object, by pressurization of the fluid, until the pressure of the fluid reaches a predetermined minimum pressurization sufficient to overcome the resilience of the resilient means whereupon the second piston moves, thereby substantially preventing the further movement of the first piston such that a controlled (preferably predetermined) force, dependent upon the predetermined pressurization of the fluid, is applied to the object.

The first fluid operated piston preferably is located in a double- sided first piston cylinder having a source/sink of the fluid on opposite sides of the piston. The common supply of the fluid supplies the fluid preferably to a rear side of the first cylinder, on a rear side of the first piston. A separate second source/sink of fluid preferably is located at a front side of the first cylinder, on a front side of the piston.

The second fluid operated piston preferably is located in a second piston cylinder, and the common supply of the fluid supplies the fluid preferably to a rear side of the second cylinder, on a rear side of the second piston.

The resilient means which opposes movement of the second piston by the fluid preferably is located on the opposite, front side, of the second piston, thereby to oppose the movement of the second piston in a direction from the rear to the front of the second cylinder (which would otherwise happen by means of the (common) supply of the fluid to the rear of the cylinder).

A cut-off valve (or the like) preferably is located between the second source/sink of the fluid and the front side of the first cylinder.

The cut-off valve preferably is open when the fluid supplied by the common supply of fluid has a pressure below the predetermined pressurization of the fluid. This preferably is achieved by the cut-off valve being open when the resilient means is in its relaxed state, i. e. when the pressurization of the fluid supplied by the common supply is insufficient to overcome the resilience of the resilient means. The cut- off valve preferably is closed when the fluid supplied by the common supply reaches a pressure at least as great as the predetermined pressurisation of the fluid. This is preferably due to the cut-off valve being closed when the resilient means is in a non-relaxed state due to the pressurization of the fluid having overcome the resilience of the resilient means. Preferably the resilient means is compressed when in its non-relaxed state.

When the cut-off valve is closed, further movement of the first piston preferably is substantially prevented because the fluid present in the first cylinder in front of the first piston preferably has no means of escape. The fluid preferably is substantially incompressible, i. e. the fluid preferably is a liquid. The fluid preferably comprises a hydraulic fluid.

The fluid supplied by the common supply may be the same as, or different to, that from the second source/sink, but preferably it is the same. The fluid supplied by the common supply preferably therefore is a liquid (i. e. a hydraulic fluid). Alternatively, the fluid supplied by the common supply may comprise a pneumatic gas.

The cut-off valve preferably is operated directly by movement of the second piston. For example, a piston rod of the second piston may extend across a fluid conduit which connects the front side of the first cylinder with the second source/sink of fluid, the piston rod including an aperture which forms part of the fluid conduit when the resilient means is in its relaxed state, but which becomes out of alignment with the conduit, thereby blocking the conduit, when the resilient means is in its non-relaxed state.

In some particularly preferred embodiments of the invention, the predetermined force can be varied by means of a third source/sink of fluid located at the front side of the second cylinder on a front side of the second piston (i. e. on the opposite side of the second piston to that of the common supply of fluid). By varying the pressure of fluid supplied by the third source/sink, the pressure of the fluid supplied by the common supply that is required to move the second piston, thereby closing the shut-off valve and preventing the further movement of the first piston, is also varied. A relatively high pressure of fluid supplied to the third source/sink requires a relatively high pressurization of the fluid supplied by the common supply before further movement of the first piston is prevented, and this relatively high pressurization is transferred as a relatively high force applied to the object. Conversely, a relatively low pressure of fluid supplied to the third source/sink of fluid is transferred as a relatively low force applied to the object. In this way, the force applied to the object by the apparatus can be controlled.

The fluid supplied from the third source/sink of fluid may be the same as, or different to, that from the common supply and/or the second source/sink (but preferably it is the same as both). The fluid supplied from the third source/sink preferably therefore is a liquid (i. e. a hydraulic fluid). Alternatively, the fluid supplied from the third source/sink may comprise a pneumatic gas.

The apparatus preferably includes a resilient part (for example a spring, preferably a compression spring, especially a helical spring) arrange to oppose the operation (e. g. the movement) of the first piston, the resilient part having a lower resilience than that of the resilient means, so that the first piston operates at a lower pressurization of the fluid from the common supply than does the second piston.

Advantageously the apparatus includes a contact member by which the first piston applies a force to an object. The contact member preferably is connected to the first piston (and preferably is directly connected thereto). The contact member may advantageously be an extension of a piston rod of the first piston, for example.

The contact member may include manipulation means by which the object may be manipulated by the contact member (and hence by the apparatus). The manipulation means may for example comprise a hook or a bearing mount, or a suction pad, or substantially any means by which an object may be manipulated.

A third aspect of the invention comprises a mechanism for gripping an object, comprising a plurality of apparatuses according to the first or second aspect of the invention.

In the gripping mechanism according to the third aspect of the invention, the common supply of fluid to the first and second pressure transfer devices of each apparatus preferably is arranged in parallel with that of each of the other apparatuses. That is, the common supplies of fluid preferably have a common supply.

Preferably each apparatus includes a resilient part as described above. Consequently, the order in which the first pistons of the mechanism operate as the fluid from the common supplies is pressurized, is predetermined by the relative resiliences (opposing strengths) of the resilient parts.

Advantageously, the relative strengths of the predetermined forces applied to an object by the respective apparatuses of the mechanism may be predetermined by the relative resiliences of the resilient means of the respective apparatuses. The relative resiliences of the resilient means of the respective apparatuses advantageously also determines the order in which the first pistons (and hence the contact members, where present) are prevented from further operation.

Preferably, therefore, the relative resiliences of the resilient means of the mechanism determines the order in which the first pistons (and the contact members, where present) are locked in place with respect to the object to be gripped.

For those apparatus embodiments in which the pressurization of the fluid from the common supply required to prevent further operation of the first piston can be controlled by means of a third source/sink of fluid, advantageously the relative strengths of force applied and/or the relative order in which the first pistons may be locked in place, can be controlled by controlling the pressurization of the fluid from the third source/sink.

The gripping mechanism may comprise at least one digit having one or more of the apparatuses associated therewith. The (or each) apparatus preferably is arranged such that operation of its first device causes the digit to bend and thus to grip an object. Preferably the (or each) digit comprises a plurality of articulated sections. Each section preferably is connected to a neighbouring section by a joint by which the sections may be rotated with respect to each other. Each joint preferably has an associated apparatus wherein operation of the first pressure transfer device of the apparatus causes such rotation. The mechanism may advantageously comprise a plurality of such digits arranged to grip an object in a manner similar to that of a human hand.

A fourth aspect of the invention comprises a robot including at least one apparatus or gripping mechanism according to the invention.

Embodiments of the invention will now be described, by way of example, with referred to the accompanying figures, of which: Figures 1 to 4 are schematic cross-sectional views of an embodiment of an apparatus according to the invention; Figure 5 is a schematic view of an embodiment of a gripping mechanism according to the invention; and Figure 6 shows two views of part of another embodiment of a gripping mechanism according to the invention.

Figure 1 shows, schematically and in cross-section, an embodiment of an apparatus 1 according to the invention. The apparatus comprises a first fluid operated pressure transfer device 3 in the form of a first double-sided piston located in a first cylinder 5, and a second fluid operated pressure transfer device 7 in the form of a second double-sided piston located in a second cylinder 9. A common supply 11 of fluid supplies hydraulic fluid (or alternatively pneumatic gas) to the rear sides F2 and V2 of the first and second double-sided pistons, respectively.

A resilient part 13 in the form of a helical compression spring provides a relatively weak opposition to the forward movement (right to left as drawn) of the first piston 3 when the fluid supplied by the common supply 11 is pressurised. A relatively stronger opposition to the forward movement (again right to left as drawn) of the second piston 7 due to pressurisation of the common supply of fluid is provided by a resilient means 15 in the form of a stronger helical compression spring. The piston rod 17 of the second piston has an aperture there through and forms a cut-off valve 18 in a conduit 19 between the front side Fl of the first cylinder 5 and a second source/sink 21 of fluid. A third source/sink 23 of fluid is connected to the front side V1 of the second cylinder 9. A forward extension 25 of the piston rod 27 of the first piston 3 comprises, together with an end portion 29, a contact member by which a force may be applied to an object (for example to grip the object) by movement of the first piston. The end portion 29 may be a manipulation means by which the object may be manipulated.

For example, an alternative end portion 31 in the form of a bearing mount, is illustrated. (Alternatively, a suction pad could for example be used.) The apparatus shown in Figure 1 operates as shown in Figures 2 to 4. As indicated in Figure 2, fluid from the common supply 11 is pressurised, thereby pushing the first piston 3 forward against the resilience of the resilient part 13, and consequently the contact member 25 is moved towards an object 33. At this stage the second piston 7 does not move because the pressure of the fluid from the common supply 11 is insufficient to overcome the resilience of the resilient means 15. Consequently, as the first piston 3 moves forward, fluid filling the front side F1 of the first cylinder 5 is pushed out of the first cylinder via the conduit 19 to the second supply/sink 21 of fluid.

Once the contact member 25 contacts the object 33 as shown in Figure 3 (and the object offers some resistance to the contact member), the pressure of the fluid supplied by the common supply 11 increases, thereby increasing the force applied to the object by the contact member. The applied force increases until a predetermined minimum pressurisation of the fluid from the common supply is reached, that is sufficient to overcome the resilience of the resilient means 15. At this stage, the resilient means 15 is compressed by the forward movement of the second piston 7, and the cut-off valve 18 is closed as shown in Figure 4.

Once the cut-off valve 18 is closed, the fluid (which is preferably a liquid, i. e. a hydraulic fluid) present in the front side F1 of the first piston can no longer escape. Due to the substantially incompressible nature of the fluid, no further forward movement of the first piston is possible, and hence a controlled force (and preferably a predetermined force) is thereby applied to the object. While the fluid from the common supply is pressurised above the resilience of the resilient means, the contact member 25 is consequently locked in place. Subsequent release of the fluid pressure from the common supply causes the resilient part 13 to move the contact member 25 back, away from the object (and also causes the resilient means 15 to open the cut-off valve once more).

The apparatus is then back to its starting condition.

It will be appreciated that by supplying a fluid pressure to the front side V1 of the second cylinder 9 via the third source/sink of fluid 23, the pressure of fluid from the common supply 11 required to compress the resilient means 15 and hence close the cut-off valve 18 and lock the contact member 25 in place can be controlled.

Consequently, supplying, and controlling the pressure, of fluid to the front side of the second cylinder provides a means of controlling the force applied to the object, in addition to the control conferred by the predetermined resilience of the resilient means.

Figure 5 is a schematic view of an embodiment of a gripping mechanism 35 according to the invention. The mechanism 35 comprises three apparatuses 1 arranged to grip an object 33. The apparatuses 1 are arranged such that the common supply 11 of fluid to each apparatus is in parallel with that of each other apparatus, such that the common supplies 11 themselves have a common supply 37.

Additionally, the second source/sink 21 of fluid of each apparatus 1 is in parallel with that of each other apparatus, all of them having a common second source/sink 39. Consequently, the order in which the contact members 25 of the respective apparatuses move towards the object 33 may be determined by the relative resiliences of the resilient parts 13 of the apparatuses. Also, the relative strengths of the controlled forces applied by the respective contact members, and the order in which the contact members are locked in place, may be determined by the relative resiliences of the resilient means 15 of the apparatuses. Optional connections to the third source/sink 23 of fluid for each apparatus are not shown, but could be included if variable force control were required.

Figure 6 shows two views of one digit 41 of a"hand-type" gripping mechanism according to the invention (which comprises a plurality of such digits). The digit 41 comprises a plurality of articulated sections 43, each section being connected to a neighbouring section by a joint (J1, J2, J3, respectively) by which the sections may be rotated with respect to each other in order that the digit (and hence the mechanism as a whole) may grasp an object 33. Each joint has an associated apparatus (Al, A2, A3, respectively) arranged such that the forward movement (as described earlier) of the first piston 3 of the apparatus causes the angle between the sections connected by the joint to decrease-i. e. causes the digit to bend, thereby to grasp an object.

Similarly to the mechanism shown in Figure 5, the respective fluid supplies of the apparatuses are arranged in parallel, and hence the relative resiliences of the respective resilient parts 13 and the relative resiliences of the respective resilient means 15 of the apparatuses can be arranged in order to determine the order in which the joints rotate, and the order in which they lock in place. For example, if the relative strengths of the resilient parts 13 are arranged in the order A3>A2>A1, then the apparatuses will operate in the order Al, A2, A3 and consequently the joints will bend in the order J1, J2, J3 (as indicated by views (a) and (b). If the relative strengths of the resilient means 15 are arranged in the order A3>A2>A1, then the apparatuses will lock in the order Al, A2, A3 and consequently the joints will lock in the order J1, J2, J3.

It will be appreciated that the embodiments of the invention described herein are illustrative, and other embodiments will fall within the scope of the invention. For example, each double-sided piston/cylinder may instead be two separate piston/cylinders. The pistons may be replaced by other types of pressure transfer devices, for example bellows, diaphragms (especially rolling diaphragms) rotary actuators, etc. The two pressure transfer devices of each apparatus may be separate parts rather than two integral parts. Gripping mechanisms according to the invention may include a floating wrist mechanism, for example that could be locked in place in the same way as a contact member of an apparatus as described above.

The apparatus and/or gripping mechanism according to the invention may be robotically controlled. Accordingly, a fourth aspect of the invention provides a robot comprising an apparatus and/or a gripping mechanism according to the invention.

A particular application for the invention is an assembly-line, for example a motor vehicle assembly-line. The apparatus is particularly suited to the robotic manipulation and/or fitting of windows to motor vehicles, for example. In robotic glazing, the glass is conventionally manipulated by the use of suction cups. Since different sizes and shapes of window normally need to be handled, the position of the suction cups conventionally tends to be a compromise. Additionally, the glass normally has significant flexibility, with the result that pushing the glass into place with a uniform force from each suction cup can be problematic, leading to fitting problems. The present invention may solve these problems by providing a robot that utilizes apparatuses and/or gripping mechanisms in accordance with the invention to grip the glass (especially the periphery of a window) with a controlled force.

Advantageously, such a robot in accordance with the invention may adapt to handle a range of objects.

Other robotic applications for the invention are envisaged, such as (for example) underwater exploration, space, underground, extreme temperature environments, chemical/biological hazard environments, radioactive material handling, use with explosives, forestry work, construction work, etc.

The invention is also salable, from sizes smaller than the human hand to much larger sizes, for example gripping mechanisms with a span of one metre or more (e. g. manipulated by large machinery such as tractors or mechanical excavators).

It will be appreciated that although the invention has been described in relation to certain specific embodiments, variations therefrom may be made without departing from the invention as defined in the claims.