An adaptive control method for dielectric elastomer devices

The future of Dielectric Elastomer Actuator (DEA) technology lies in miniaturizing individual elements and utilizing them in array configurations, thereby increasing system fault tolerance and reducing operating voltages. An important direction of DEA research therefore is real-time closed loop control of arrays of DEAs, particularly where multiple degrees-of-freedom are desirable. As the number of degrees-of-freedom increases a distributed control system offers a number of advantages with respect to speed and efficiency. A low bandwidth digital control method for DEA devices is presented in this paper. Pulse Width Modulation (PWM) is used as the basis for a current controlled DEA system that allows multiple degrees-of-freedom to be controlled independently and in parallel using a single power supply set to a fixed voltage. The amplitude and the duty cycle of the PWM signal control the current flow through a high speed, high voltage opto-coupler connected in series with a DEA, enabling continuous control of both the output displacement and speed. Controlling the current in real-time results in a system approaching a stable and robust constant charge system. Closed loop control is achieved by measuring the rate of change of the voltage across the DEA in response to a step change in the current input generated by the control signal. This enables the capacitance to be calculated, which in combination with the voltage difference between the electrodes and the initial dimensions, enables the charge, strain state and Maxwell pressure to be inferred. Future developments include integrating feedback information directly with the control signal, leaving the controller to coordinate rather than control individual degrees-of-freedom.