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Piezoelectric tool actuator for precision turning

University of British Columbia

High precision machining has the potential of increasing the efficiency of machining operations and lowering costs in the manufacturing of many machined parts. This thesis investigates the use of a piezoelectric tool/actuator designed for the precision turning of cylindrical shafts. The piezo tool actuator has four fundamental components. The piezo stack element delivers a dynamic displacement range of 40 μm when 0 to -1000V voltage is applied. The piezo element is placed in a mechanical housing with leaf springs, which amplifies the displacement range to 62um. The piezo element is activated by an amplifier which delivers a maximum 150W and 0- 1000 V voltage. The digital control law runs on a PC/DSP which has 5KHz loop frequency. The tool position is measured using a laser displacement sensor with 0.1 μm accuracy, and the workpiece surface is monitored using another laser sensor which has 1 μm resolution. The piezo tool actuator is mounted on a standard CNC turning center turret, and is intended to be used in precision positioning of cutting tool within one micrometer during finish turning of shafts. The mathematical model of each component in the dynamic system is identified. The piezoelectric hysteresis is modeled using a time-delay model, and the actuator's transfer function is identified experimentally by analytically indicating the source of dynamics. Several digital control methodologies are developed for the actuator based upon the model generated. Pole placement, zero phase error tracking, and state feedback control with a disturbance observation model have been developed and cutting tests performed to evaluate their suitability for precision turning. The mathematical model and experimental trials indicate that one to two micrometer displacement can be best achieved using a feed-forward controller with state feedback disturbance observer and rejection. The ability of the system in tracking highly dynamic position commands is also demonstrated by turning elliptical shafts. The identified bandwidth of the actuator is found to be about 500Hz, but the displacement ranged rapidly drops to ~12 μm at the peak frequency Higher dynamic bandwidth and surface finish accuracy can be obtained if the mechanical system is more rigidly designed, and the amplifier has more power to drive the piezoelectric element at higher actuation frequencies.

Thesis/Dissertation

application/pdf

2009-06-16

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http://hdl.handle.net/2429/9290

Mechanical Engineering

University of British Columbia

UBCV

DSpace