Nonlinear Control for Constraint-tuning Modified-mode Ultrasonic Actuating Linear Stage

A proportional-integral-derivative-based (PID based) sliding mode control (SMC) was applied to the linear stage driven by a constraint-tuning modified-mode (CTMM) ultrasonic actuator. Based upon the driving variation of voltage amplitude and the preload on the CTMM ultrasonic actuator, nonlinear phenomena, such as frequencies shifting in electromechanical resonance and the dead zone in moving response, could be suppressed almost completely by the PID based SMC controller with output biases. Using system identification technique, an approximate second-order model of the linear stage could be obtained for the equivalent control term of the PID based SMC controller. Through an estimated model error, the design of the switching control term was used to compensate for the shifting property of resonant frequencies under electromechanical coupling. A target-command-shaping function matched the responding speed of the system during tracking experiments. Experimental results demonstrate that the SMC controller has the capacity for noise rejection to control the slider’s position in bilateral tracking motions. Its resolution is sufficient to approach micrometer-level accuracy.