In addition to the reduction of space, material and energy requirements, the miniaturisation of this system should further minimise environmental impact by reducing coolant and other fluid usage。 Re-configuration of workshop facilities should also be made easier。 The ability to perform multiple machining operations on the same machine without needing to reposition the workpiece is intended to improve product accuracy。 The article goes on to describe the development and successful testing of the machine tool。 The construction of a gantry-type four-axis miniature machine tool (Fig。 14) has also been reported [21] using a combination of low thermal expansion materials an Invar 36 frame on a granite base。 The machine has three linear

axes with motion generated by linear motor stages and one rotational axis with motion generated by a goniometer。 The travel ranges are 25 mm in the linear axes and 20° in the rotational axis。 The machine can be equipped with a brushless DC spindle for micro machining or an air turbine spindle for micro grinding。 The system is capable of being computer controlled。 The machine has been installed on an active vibration damping table to isolate it from external vibrations。 Experiments have shown that this machine tool is capable of producing parts of acceptable accuracy。 Research is ongoing with this system to identify uncertain- ties and error sources in the machining process。 This machine is currently a research tool, but could form the

Fig。 14  Example of four-axis miniature machine  tool[21]

basis for a portable multi-axis machining system for processing small features。

A five-axis PC controlled micro machine tool has been developed for production of three-dimensional micro components such as impellers and other fluid flow devices [22]。 The machine has a column-type architecture, Fig。 15, with three linear and two rotational axes。 The tool is driven by an air-powered spindle, which was selected because its light weight would reduce stress on the rotational stage on which it is mounted。 The system was constructed from commercially available stages, spindle and control card in order to minimise cost。 The movement ranges are 20 mm in X and Y, 30 mm in Z and 360° in both rotary axes。 The capability of the machine was tested by producing micro walls and a micro impeller。 This system offers a compact and low-cost tool with high versatility for producing micro fluid flow devices。

In a further development of the micro machining concept, Japanese researchers built an experimental micro factory [16, 23]。 The project started with a lathe measuring (32 ×25× 30 mm); further development saw the creation of a micro milling machine and micro press which were assembled into a micro factory along with a transfer arm and two fingered manipulator。 The factory was first assembled on a desktop, and subsequently as a portable factory built into a suitcase with a total mass of 34 kg。 The system is manually operated by joysticks with CCD cameras  providing  feedback  via  an  LCD  display。  As  it

Fig。 15  Five-axis micro machine tool  [22]

stands, this is an impressive demonstration of miniaturisa- tion, but lacks practical use; the subsequent development of CNC equipment may offer more industrial potential。

A novel micromachining cell has been devised around a hexagonal base with exchangeable machining modules mounted on three opposing sides [24]。 The base incorpo- rates a vibration damping system, workpiece manipulation robot (i。e。 transfer arm) and a flexible modular controller。 It can be integrated with a conveyer system to supply workpieces。 A range of machining and inspection modules enable quick configuration for a variety of manufacturing tasks。 All modules have a standard base with alignment feature, vacuum clamp and electrical connection to fit the machining cell。 The controller can detect which modules are installed and adapt accordingly。