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9 April 2010 Closed loop control of a rotational joint driven by two antagonistic dielectric elastomer actuators
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Dielectric elastomers are a subclass of electronic EAPs able to produce large deformations (and thus mechanical work) when an external electric field is applied. While the intrinsic compliance of this kind of polymeric actuators have been always addressed as major benefit with respect to traditional electromagnetic motors, unable to fully capture the capabilities and mechanical properties of biological muscles, their polymeric nature poses peculiar challenges in controlling a system which is subject to nonlinearities, hysteresis and viscous creep behavior. In this paper we explore the controllability properties of a simple rotational joint driven by two dielectric elastomer actuators arranged in an antagonistic configuration. A number of sensors are used to obtain information about the state of controlled system: the angular position of the joint is measured by an angular encoder, custom-designed tension sensors are used to monitor the tension of the two driving tendons and linear encoders provide accurate measurements of the displacements generated by the two actuators. Using this feedback information, a control algorithm has been implemented on a microcontroller unit in order to independently activate the two actuators, allowing a closed loop control of both the angular position of the joint (position control) and the tensions of its tendons (force control). A description of the developed control strategy and its performances under different load conditions are discussed in this paper.
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Marco Randazzo, Matteo Fumagalli, Giorgio Metta, and Giulio Sandini "Closed loop control of a rotational joint driven by two antagonistic dielectric elastomer actuators", Proc. SPIE 7642, Electroactive Polymer Actuators and Devices (EAPAD) 2010, 76422D (9 April 2010);

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