Fig。 1 One embodiment of the in situ manufacturing system for aircraft structures [1]

which can perform a range of machining and manufacturing tasks [2]。 Primary and secondary rails (22 and 38, respec- tively—Fig。 2) are set approximately parallel and joined by a spanned or cross rail (50)。 The cross rail is securely mounted on the primary rail, which serves as the dimensional reference, but is more loosely mounted on the secondary rail so it will not foul if they are not parallel。 The tool  head

(12) is mounted on the cross rail and both are able to move to deliver X and Y axis movement。 The tool holder may support additional axes。 The system is mounted on an array of spacing pins (26) to keep it a uniform distance from the workpiece, and it is secured by vacuum cups (28)。 This system is designed for aircraft manufacture, but could be applied to a much wider range of tasks。 The system is computer controlled to perform manufacturing tasks with great accuracy; the controller can compensate for the shape of the workpiece when positioning tools if necessary。 This machine offers greater flexibility as its use of vacuum clamping makes it able to attach anywhere without being dependent on mounting features such as holes in the workpiece。 In addition, the flexible rail structure should enable it to work with a greater range of workpiece geometries。

2。1。2 SKM for maintenance

Also in relation to the aerospace industry, a maintenance system has been reported for temporary attachment to the surfaces of aircraft and similar structures, in order to apply positive pressure to them [3]。 This maintenance device, Fig。 3, is intended to aid with the application of adhesive composite patches to damaged aircraft skins and similar operations。 The system comprises a frame (12) equipped with a number of vacuum cups (17) which are connected by vacuum lines (34) to a vacuum pump (32) mounted in   the

Fig。 2 An example flexible rail machine tool for temporary attachment to workpieces [2]

frame。 When the vacuum is activated the force through the cups is sufficient to hold the system in place while it is applying pressure to the surface on which it is mounted by means of an inflatable pressure pad (26)。 The cups can be fitted with sensors (18) which monitor the vacuum and, through a controller, regulate the operation of the pump to maintain a constant vacuum。 A composite patch can be applied to a damaged surface and the positive pressure generator mounted over it。 The device can then apply pressure to the patch until the adhesive cures to ensure a good bond and surface finish。 This is a highly specialised system designed for a specific maintenance task and so is not very versatile, although the fastening system can be used to attach a variety of manufacturing and repair systems onto large parts with complex geometry such as aircraft, heavy machinery, pressure vessels, etc。

A range of specialist machines have been developed for in situ maintenance of marine engines and power systems as it is impractical, or in some cases almost impossible, to disassemble them and remove them from the ship for repair。 Several examples of these in situ machines are described below; the first is for maintenance of large piston engines。 This machine is designed for in situ re-conditioning of crank shafts and pins [4]。 This machine is intended for maintenance of large internal combustion engines such as marine diesels without the time and expense of removing the crank shaft and shipping it to a machine shop。 The design comprises a bracket system which temporarily attaches to the crank webs and supports a pair of orbital wheels with the machine tool mounted between them。 This system enables the machine tool to move in an orbital fashion around the workpiece while machining。 A number of variations on the basic design for machining parts of different sizes and configurations are described。 This is a fairly simple design for a specific range of re-conditioning tasks; however, the use of different embodiments of the system for different workpieces could suggest a lack of flexibility and versatility of the design。