GB2278825A - Gripper. - Google Patents

Abstract

A gripper, for a non-symmetrical object e.g. a turbine blade, has a plurality of pneumatically operated grippers 11 and 12 arranged in opposing pairs at the points of a triangle. In use two jaws 3 and 4 come together, allowing grippers 11, 12 to touch the blade, the grippers are energised by a common air supply thereby eliminating side loads on the blade as it is gripped. <IMAGE>

Description

A MECHANICAL HAND The invention relates to a mechanical hand. In particular, the invention concerns a mechanical hand adapted to grasp objects such as an aeroengine aerofoil blade.

In an automated production process a mechanical hand which has to pick-up a rough or part-finished component and present it to a further work station must be able to cope with components of known nominal dimensions. The shape and size of the components can vary, within tolerance limits. For example, variations in the blade profile can result in the misalignment of the component relative to a receiving machine fixture. An objective of the present invention, therefore, is to eliminate this relative misalignment in the position of different components in the hand. This and other objectives will be evident in the following description.

According to the invention in its broadest form there is provided a mechanical hand comprising a plurality of grippers arranged in diametrically opposed pairs, and actuator means for moving the grippers of each pair in unison and with equal force between retain and release positions.

In one form of the invention the grippers are arranged in a two-dimensional triangular array, and the actuators are energised from a common source of pneumatic pressure. Other gripper arrays may be employed.

These and other features of the invention will be readily apparent from the following description of a preferred embodiment illustrated in the accompanying drawings, in which: Figure 1 is a side elevation of the mechanical hand, Figure 2 shows in schematic layout the pneumatic actuation system of the mechanical hand, Figure 3 is a detail of the padded ends of the grippers in plan view, Figure 4 is a view on section AA in Figure 3 showing the disposition of the grippers, and Figure 5 is a perspective view of the mechanical hand grasping an aerofoil blade.

Referring now to the drawings, the overall layout of the invention is illustrated in Figures 1 and 5. In all figures of the drawings like parts carry like references. The basic structure of the mechanical hand comprises a rectangular, fixed plinth 1 which may be carried for example at the distal end of a robot arm 2 (Figure 1). Two upstanding pedestals 3,4 are mounted on the upper surface of the plinth by means of a dovetail slide or the like, generally indicated at 5. The two pedestals are mounted on the same slide which extends across the width of the plinth whereby the pedestals may be moved towards and away from each other.

The confronting faces 6,7 of the pedestals 3,4 define a slot 8 into which an object to be grasped by the hand is received, see Figure 5. Preferably the lower parts of the pedestals, towards the plinth 1, are formed with shoulders 9,10 which project from faces 6,7 towards each other thereby limiting the closest approach of pedestals 3,4 and define the width of the slot 8.

The upper ends of the pedestals 3,4 remote from the plinth 1 are provided with gripping means which, when actuated, co-operate to grasp an object located within slot 8. In the particular embodiment illustrated each of the gripping means 11,12 comprises a plurality of pneumatically energised linear stroke actuators mounted inside the pedestals.

In the drawings the left hand pedestal 3 and the right hand pedestal 4 are each provided with three pneumatic actuators 14,16,18 and actuators 20,22,24 respectively.

Each of the actuators has an axially movable output member 26-36, at the end of which is attached a gripping pad or foot 38-48.

The two groups of three actuators are mounted in recesses 50,52 formed towards the upper ends of pedestals 3,4 and facing into the slot 8.

The actuators are all mounted with their axes parallel and each actuator in one pedestal is mounted co-axially with an opposing actuator in the opposite pedestal. The actuators thus form opposing pairs and are mounted and dimensioned so that the opposing gripping pads will grip an object between them. Thus, the actuators are arranged with the ranges of mutual extension in suitable juxtaposition. For example at full extension the ranges may overlap, just meet or fall sightly short depending on the thickness of the object.

In normal operation the pedestals 3,4 are initially retracted, and the component to be grasped protrudes into the slot 8.

The pedestals 3,4 are then moved towards each other to a predetermined distance apart. They are made to approach until the shoulders 9,10 abut. During this movement the actuators 14-24 are unpowered, with their power circuits vented to atmosphere so that movement of an actuator rod will not produce internal pressure within an actuator.

As the pedestals are moved together the gripping pads 38-48 make contact with the component. Continued movement produces no internal actuator forces and, providing the actuators have low internal resistance, no residual forces are set up which could displace the component. Then, when the actuators are energised the object is gripped firmly and without subsequent displacement within the hand.

So that the actuators grip the object in a stable manner they are disposed in a suitable array. In the embodiment being described the three actuators in each pedestal are disposed in a two-dimensional triangular array. From the drawings, especially Figure 4, it will be seen that two of the actuators are mounted side by side at the same height above the plinth 2 with the third mounted between and slightly below. The number and disposition of the actuators has been found suitable for grasping an aeroengine blade by the aerofoil section. It will be appreciated that three is not an exclusive number. There may be more, or even fewer, actuators and these may be mounted in other patterned arrays.

It has already been mentioned above that the actuators 14-24 are pneumatically operated and preferably energised from a common source. Figure 2 illustrates the pneumatic circuit of the embodiment. Each of the actuators is connected through a supply line 54-64 respectively to a common source of pneumatic pressure, in this case distribution manifold 66. The manifold in turn receives a pressure input through a connecting pipe 68 which is connected to a compressor (not shown).

The commonality of the pressure source ensures that all actuators exert equal pressures, and that the forces exerted by the paired actuators are matched and balanced. This will help to ensure that an initial orientation of the object held by the actuator gripping means is maintained.

Isolating valves 70-80 are connected in supply lines 54-64, one in each line. When the valves are operated to their isolating positions they trap pneumatic pressure in the actuators 14-24. This simultaneous action will maintain individually the gripping forces exerted by the actuators on the object and should ensure that no unintended motion of the object takes places.

In addition to maintaining the clamping force the isolating valves by trapping a volume of air (or pneumatic fluid) in the actuator and the intervening length of supply line also introduces a degree of resilience to the actuator. Each pair of actuators thus will tend to self-relocate should any minor displacements occur.

Alternative means of energising the actuators may be employed. For example, the pneumatic pressure system may be replaced by an hydraulic pressure system, or by electrically energised solenoid actuators. Hydraulic fluid was not preferred for the described embodiment due to the undesirable effects leaked hydraulic fluid might have on contact with the type of objects being handled.

The mechanical hand of the invention is useful in a robot cell for the manufacture of aeroengine aerofoil blades. In the manufacturing process a rough or forged cast blade blank has its locating root machined at a first station. The blade is then loaded into a holding magazine for presentation at a second station at which the aerofoil section is machined to final form in one operation. During this operation the blade is held by the previously finished root portion. The mechanical hand described finds application in receiving the blade from the holding magazine, grasping it by the aerofoil section and presenting it to a root holding fixture in a correct, predetermined orientation ready for a further machining operation.

Claims (10)

1 A mechanical hand comprising a plurality of grippers arranged in opposing pair, and actuator means for moving at least one of said grippers of each pair in unison and with equal force between retain and release positions.

2 A mechanical hand as claimed in claim 1 wherein the pairs of grippers are arranged in opposing two-dimensional arrays.

3 A mechanical hand as claimed in claim 2 wherein the pairs of grippers are disposed at the points of a triangular array.

4 A mechanical hand as claimed in any preceding claim wherein the grippers comprise linear stroke actuators.

5 A mechanical hand as claimed in claim 4 wherein the actuators are energised by pneumatic pressure.

6 A mechanical hand as claimed in claim 4 or claim 5 wherein the actuators are energised from a common source.

7 A mechanical hand as claimed in claim 6 wherein each actuator is connected to the common source of pneumatic pressure through pressure isolating means.

8 A mechanical hand as claimed in any preceding claim further comprising a body formed with a slot or recess within which an object to be grasped by the hand is received in use, and the grippers are disposed in confronting pairs on opposite sides of said slot or recess.

9 A mechanical hand as claimed in claim 8 wherein the slot in the body includes a base member which carries a pair of co-planar members, spaced apart by a distance sufficient to receive an object therebetween and the grippers are disposed towards the distal ends of the co-planar members.

10 A mechanical hand substantially as hereinbefore described with reference to the accompanying drawings.