Ultra-precision Machining

Machine for Ultra-precision Machining (Photo: Fraunhofer IPT)
Machine for Ultra-precision Machining (Photo: Fraunhofer IPT)

Ultra Precision (UP) Machining is about producing parts with the highest requirements in terms of geometric accuracy and surface­quality. Applications are found in optics for microscopes, lasers, fiber optics, displays, reflectors, etc.

Most UP machines on the market rely on analog amplifiers to achieve the high surface qualities. The Fraunhofer IPT in Aachen, in cooperation with Triamec, has now succeeded for the first time in achieving comparable results with Triamec's clocked, digital high-end amplifiers, but with significantly lower energy consumption and at lower costs.

Detail of free-form surface processing (Photo: Fraunhofer IPT)
Detail of free-form surface processing with fast tool servo (Photo: Fraunhofer IPT)

Various multi-axis systems with air bearings, hydrostatic bearings, gantries and fast tool servos have been realized. Windows PCs with Beckhoff TwinCAT and the CNC extension from ISG are used as the control system, which enables the very specific production programs to be implemented efficiently. The Triamec Servo Drives are transparently embedded in the TwinCAT system via Tria-Link.

The CNC target data generation rate is currently 5kHz. The set values are interpolated to 10kHz in the TwinCAT system and sent to the servo drives as P,V,A triplets (position, speed and acceleration values). There they are further interpolated to 50kHz for position control.

Encoder auto-calibration is also used here very successfully - the air-bearing axes are now hardly audible when driving.

For the large air-bearing portals, special algorithms were developed in Tama, so that both motors share the load correctly and the portal moves perfectly evenly.

The system is so successful that the Fraunhofer IPT in Aachen has already equipped a wide variety of machines with it.