Abstract
A palm-top machine tool, "Micro-lathe", has been developed and evaluated. The machine tool sizes 32 x 28 x 30 mm in volume and weighs about 98 g. It uses a pair of micro-sliders as key components, orthogonally stacked as X and Z slides. On the top of the Z slide, a spindle unit and a 1.2 W DC drive motor are mounted, while a cutting tool is fixed on a base. Each micro-slider uses a unique step-feed configuration driven by two embedded PZT actuators. The complete micro-lathe system is numerically controlled by a full closed-loop feedback servo system using newly developed micro-linear encoders with 62.5nm resolution after 400X interpolation. A servo control of the two micro-slides is done by a separate controller based on a single board computer. Total occupying desktop space is about 550 x 450 mm, including the lathe, a custom NC and electronics. The system resolution is 0.2μm. No overshoot is induced due to the minimized moving mass, the settling time is only ruled by the maximum velocity. In terms of frequency response, 20Hz of bandwidth for 10μm amplitude was achieved. Using diamond tools complex shaft shapes of 2 mm maximum diameter can be practically machined. Surface roughness on a cylindrical surface was better than 50 nmRa, or 500 nmRz.
