System identification and microposition control of ionic polymer metal composite for three-finger gripper manipulation

Abstract

Smart materials have been widely used for control actuation. A robotic hand can be equipped with artificial tendons and sensors for the operation of its various joints, mimicking human hand motions. The motors in the robotic hand could be replaced with novel electro-active polymer (EAP) actuators. In the three-finger gripper proposed in this paper, each finger can be actuated individually so that dexterous handling is possible, allowing precise manipulation. To develop model-based control laws, an approximated linear model representing the electromechanical behaviour of the gripper fingers is introduced. Several chirp voltage signal inputs were applied to excite the IPMC (ionic polymer metal composite) actuators in the interesting frequency range of (0.62 Hz, 5 Hz) for 30 s at a sampling frequency of 250 Hz. The linear Box-Jenkins (BJ) model was well matched with the model obtained using a stochastic power spectral method. With feedback control, the large overshoot, rise time, and settling time associated with the inherent material properties were reduced. The motions of the IPMC fingers in the microgripper would be coordinated to pick, move, and release a macro- or micro-part. The precise manipulation of this three-finger gripper was successfully demonstrated with experimental closed-loop responses.