Control of voice coil actuator with application to cam turning

Direct drive actuation has the potential to improve quality and increase productivity. In camshaft manufacturing, the use of non-circular turning can reduce and eventually eliminate the need in cam lobe grinding. Direct actuation is fundamental in this application, as the required tool velocity and acceleration are beyond the capabilities of conventional machine tool drives. The goal of this research is development of practically effective control algorithms for a voice coil direct drive by applying acceleration feedback and data based tracking control.; High dynamic stiffness must be established by the drive control system to minimize effects of external processes. Acceleration measurement contains information closer to the disturbance source than position measurement and, therefore, can be utilized to increase system stiffness. A systematic approach to the design of local acceleration feedback is proposed. The local feedback structure is added to the primary position feedback system to shape its disturbance response, while preserving the input-output mapping for tracking. High-gain feedback control, like the repetitive control for high accuracy tracking, results in a system that is susceptible to limit cycle oscillations induced by dry friction. The local acceleration feedback provides a five-fold increase in drive stiffness and suppresses limit cycle oscillations.; Tracking designs involve inversion of system dynamics. This research considers a “model-free” tracking algorithm for stable LTI systems subject to periodic references and disturbances. An input signal chosen from practical considerations is used to excite the system in an identification experiment to determine its response. The data from the experiment is then used to construct the system inverse for application in an iterative learning scheme. The inverse is formed through basis function expansions utilizing bases generated by uniform time shifting of the input and the output signals. The condition identifying functions suitable for construction of the expansion bases and the expression for the dual basis generating function are developed. It is shown experimentally that features of the reference signals can be exploited to reduce the number of control calculations.; Cam machining results demonstrate that voice coil drives can be successfully used in industrial turning applications.