UBC Theses and Dissertations
Development of a piezoelectric tool actuator for precision turning Woronko, Andrew Stanley
Precision turning as an alternative to conventional finish machining operations of cylindrical components offers significant reductions in manufacturing cost and cycle time. In this thesis the development of a piezoelectric tool actuator for precision turning of shafts is presented. A review of research conducted in the areas of precision turning, piezoelectric actuator development, and micropositioning systems design is presented. Mounted to a conventional turning machine, the tool actuator overcomes the limitations of machine tool feed drives by providing precise control of the finishing depth of cut. In this manner part tolerances are achieved in one setup on a single machine, without the need for subsequent finishing operations. Design of the actuator system was driven by constraints on motion range and resolution, size, and structural properties. Tool motion is provided through the use of a high voltage piezoelectric translator housed within a monolithic solid flexure. A capacitive position sensor provides feedback of tool motion to the controller. In order to be practical in an industrial setting the actuator design is compact, and provides an interface for exchangeable tooling. The specifications of the actuator are 36 micron stroke, 370 N/micron stiffness, and 3200 Hz natural frequency (radial direction). A sliding mode control scheme was implemented to regulate tool position, and reject disturbances due to cutting forces and actuator non-linearity. The actuator was experimentally verified through machining tests in both laboratory and industrial sites. Results showed that positioning resolution of 20 nm is achievable in precision finishing, and that the commanded controller position was accurately reflected on the machine workpiece. Average surface roughness for 4340 steel (36-40 HRC) was less than 0.3 microns, and less than 0.15 microns for hardened 4320 steel (58-62 HRC).
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