This invention relates to an assembly method wherein a novel design of component carrier, used in conjunction with positional features within the components to be assembled, effects accurate assembly without the need for complex fixtures.

In current practice a common method of assembling components is to load two or more components into a fixture which clamps them in a required relative position; to fasten by welding, riveting, clinching, or the application of adhesive at each of the fastening points; and to release the clamps, and remove the assembly from the fixture.

This method requires a special purpose fixture for each assembly operation and hence it is extremely expensive to instal. It lacks versatility in that the fixture geometry has to reflect the component geometry and hence any change in component geometry may necessitate a new fixture. It is very labour intensive in that multi-stage assemblies involve multiple handling of components, and component loading and unloading are usually manual operations.

Our invention takes advantage of the fact that components can readily be brought into a desired position relative to each other by means of positional features incorporated within each of the components. It has many advantages in that it substantially reduces the need for fixturisation; it provides maximum access for assembly and fastening purposes; and it minimises component handling by providing an assembly process wherein each component is handled only once.

The positional features within each of the components to be assembled,

may be holes which, when engaged by location pins, automatically bring the components into the desired relative position. The pins can be mounted on an assembly fixture, or pins on one component can engage holes in a mating component. Location holes are a very effective way of achieving accurate alignment because they can be located immediately adjacent to functional features within the components and hence can give high positional accuracy.

However alignment can be achieved without the use of holes. For instance a male form of one component may nest in a female form of a mating component; or the component attachment means, usually a component gripper, may engage the outer profile of components in a way which permits only one alignment. In instances where it is important for the components to be brought into alignment prior to contact being established, non-contact methods such as optical means involving the use of lasers or cameras can be used to detect features or markings on the surface of components.

Usually the first component is fixed in position and the second component is floated into engagement with it by means of a component carrier. The component carrier incorporates a compensator mechanism which has the facility to allow limited positional and orientational adjustment of the second component. This is important because in practice both the first and second components may be subject to limited positional inaccuracies, and if there is no facility permitting positional and orientational adjustment of the second component, both components may be damaged as they come into engagement.

The compensator has the facility to counteract the effects of the mounted weight of the component attachment means and the component carried

thereby by bringing the attendant mounting forces and turning moments into either substantial equilibrium or a pre-determined directional bias. It provides the necessary force and turning moment to the component attachment means to counteract the effects of gravity so that minimal contact pressures on the components can effect any required positional and orientational adjustment.

Once the position and orientation in which the second component will be held at the pick-up station are determined, it is possible to determine the position and orientation which the component attachment means must assume to achieve engagement. Similarly, once the position and orientation of the first component are fixed, it is possible to determine the position and orientation which the second component must assume to achieve engagement. Hence it is possible to pre-programme the compensator mechanism to generate the forces and turning moments required to counteract the effects of gravity at the assembly and the component mounting station. The compensator also has the facility to provide programmed residual forces to propel the component attachment means into engagement with the second component, and the second component into engagement with the first component. The magnitude of the residual forces can be set to meet the twin requirements of speed of movement and gentleness of contact.

The compensator mechanism consists of a multiple axes mounting allowing freedom of movement along or around any or all of three mutually perpendicular axes. Movement along each axis is controlled by a fluid actuator cylinder which generates movement along linear bearings. Rotation about each axis is controlled by a fluid actuator generating movement around rotary bearings. In many applications it is not necessary to allow freedom of movement along and around all three axes,

and consequently some of the bearings and actuators can be omitted from the mechanism.

A convenient fluid for this purpose is air, in which case the fluid actuators can be air cylinders which can each be set to the air pressures required to balance out the effects of gravity at any predetermined position and orientation of the compensator and to provide any desired residual force.

In one version of our invention a first component is supported on vertical supports which hold it in a position where a second component can readily be brought into the correct relative position for assembly.

The second component is mounted on a component carrier which incorporates a compensator mechanism and a component attachment means, and is moved by a prime mover such as a robot. To transport the component from a storage magazine to the required assembly position the component carrier is rigidly clamped to the robot arm. Prior to arrival, fluid actuated cylinders are charged with the operating pressures required to counter-balance the effects of gravity and to provide a residual force in the direction necessary to bring the second component into engagement with the first component. The clamp can safely be released once the robot arm decelerates near the end of its travel because the component will be held in its forward-most position by the residual force generated by the compensator and by its own inertia. Hence as it is brought into contact with the first component it is free to float into the correct relative position under the guidance of the positional features.

In an alternative version of our invention, the robot arm is brought to rest before the clamp is released and the component is caused to float into engagement by the residual force provided by the compensator.

Where necessary detector systems can be mounted to monitor the position and orientation of the component attachment means as it approaches the second component, and likewise the position and orientation of the second component as it approaches the first component. Furthermore the detector system can be used to confirm that satisfactory engagement has been obtained in each case. For instance linear transducers mounted within the compensator can be used to monitor the position of the component attachment means when the programmed residual force has been attained. Alternatively proximity switches can be used to confirm that the component attachment means has come into successful engagement with the second component and that the second component has come into successful engagement with the first component.

Where multiple component assemblies are required, the first component may be mounted on a carrier which transports it to successive assembly stations at which one or more components are added to the assembly.

When the components are being brought together to be fastened, the fastener applicator can normally apply clamping force to augment the residual force provided by the compensator. In the case of a self-pierce rivet applicator, the clamping action can be applied through a rivet applicator delivery nose. This is a very effective means of clamping in that it acts on the area immediately around the point where the rivet is to be applied.

One suitable fastener applicator is the applicator described by way of example in our PCT patent application publication No. WO 94/02267, to which reference is directed for further information.

This utilises a compensated balance to accommodate positional and

orientation adjustment with respect to a workpiece (36) to which a fastener is to be applied, including compensator means (eg. 18,20,24,27,31 ,34) for counteracting the effects of the applicator mounted weight, by bringing the attendant mounting forces and turning moments into either substantial equilibrium, or a predetermined directional bias, whereby, upon encountering a workpiece, ultimate adjustment of the applicator position and orientation can be dictated by the workpiece position and orientation with minimal exertion thereupon and thereby with minimal contact damage thereto.

DESCRIPTION OF DRAWINGS

Our invention can readily be understood by reference to Figures 1 - 8.

Figs 1 , 2 and 3 show the use of positional features to bring components into a desired relative position.

Fig 4 shows a component carrier attached to a robot arm.

Fig 5 shows a typical example of five components to be assembled.

Fig 6 shows the first component mounted on support means.

Fig 7 shows a second component held in a desired position relative to the first component by a component carrier whilst being fastened by fastener applicators.

Fig 8 shows the final assembly of the five components with each of the required fasteners in position.

MODES OF CARRYING OUT THE INVENTION

Fig 1 shows component 1 containing a protruding position feature which engages with a mating recessed position feature in component 2 to bring the two components into a desired position relative to each other, as shown in assembly 3.

Fig 2 shows component 4 with positioning holes 5 and 6, and component 7 with positioning pins 8 and 9. The positioning pins 8 and 9 can engage holes 5 and 6 to bring the two components into a desired position relative to each other, as shown in assembly 10.

Fig 3 shows component 11 with positioning holes 12 and 13, and component 14 with positioning holes 15 and 16, and component carrier 17 containing positioning pins 18 and 19. Positioning pins 18 and 19 can engage holes 12 and 13 to bring components 11 and 14 into a desired position relative to each other as shown in assembly 20.

Fig 4 shows component 14 mounted on component carrier 17, which in turn is mounted on compensator 21, which in turn is mounted on robot arm 22. Compensator 21 is a multiple axes mounting allowing component

14 freedom to move along, or rotate about, each of three orthogonal axes

X, Y and Z. Movement along the X axis is accommodated by linear bearings 23 and is controlled by a fluid actuator cylinder 24. Movement along the Y axis is accommodated by linear bearings 25 and is controlled by a fluid actuator cylinder 26. Movement along the Z axis is accommodated by linear bearings 27 and is controlled by fluid actuator cylinder 28. Rotation about the X axis is accommodated by rotary bearings 29 controlled by fluid actuator cylinder 30. Rotation about the Y axis is accommodated by radial slot 31 controlled when force is applied

by fluid actuator cylinder 32. Rotation about the Z axis is accommodated by radial slot 33 controlled by fluid actuator cylinder 34.

Fig 5 shows component 35 to which are to be assembled components 36, 37, 38 and 39.

Fig 6 shows component 35 mounted on support means 40.

Fig 7 shows component 36 being held in a desired position relative to component 35 by component carrier 17 attached to robot arm 22. Once in position, component 36 can be fastened to component 35 by fastener applicators 41 and 42.

Fig 8 shows the five components 35, 36, 37, 38 and 39 fastened together to form assembly 43.