| Summary: | 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.
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