| The laser industry and the contact lens industry are two of the first industries to accentuate the need for Fast Tool Servo systems (FTS). FTS's enable Diamond Turning Machines (DTM) to produce non-axisymmetric optics by moving the diamond cutting tool towards and away from the workpiece several times per one revolution of the spindle. During the course of this work, a new FTS system was developed capable of accurately translating the tool a total distance of 2 mm at a bandwidth of more than 140 Hz. The system consists of a flexure mechanism carrying the tool, a voice coil actuator, a custom-built voltage controlled current amplifier, a heterodyne laser interferometer system for position feedback, and a Digital Signal Processing (DSP) computer. The system was implemented and tested on a Precitech Nanoforrn 350 DTM. Despite an installed mass damper, residual inertia forces caused surface finish degradations on parts with large amplitudes. A modified Moore no. 3 jig bore base was used as a more rigid testbed significantly improving the surface finish. The performance of the FTS and, therefore, the surface finish of the machined parts could be enhanced further by damping the system and implementing feedforward control. The machined test parts were analyzed using both form and surface instruments. A cylindrical three lobed part with amplitude of +/-500 mum had a surface roughness value of approximately 40 nm Ra. The baseline cut with a rigid tool post but otherwise identical cutting conditions had a surface roughness value of approximately 20 nm Ra. |
