Piezoelectric tool actuator for precision machining on conventional CNC turning centers

A single axis piezo-based fast tool servo is presented for precision turning of local areas on conventional machine tools. The compact design features the use of solid flexures to transmit motion from a high voltage piezo stack actuator to the turning tool assembly. Analytical and finite element models of the flexures are presented, and the design process is outlined. The assembled actuator has a 38 micron stroke, 370 N/micron stiffness, and 3200 Hz natural frequency. A sliding mode controller is implemented which provides 200 Hz bandwidth and 20 nm tool positioning resolution by rejecting cutting force disturbances and piezoceramic nonlinearity during precision machining. Stepped, tapered, and convex micro profiles are machined to verify the control command is accurately reflected in the part form. Maximum surface roughness of 2.0 μg was achieved in machining 4340 steel with 35–40 HRC hardness, and 0.85 μg for 4320 steel with 58–62 HRC hardness.