A novel three-finger IPMC gripper for microscale applications

摘要

Smart materials have been widely used for control actuation. A robotic hand can\nbe equipped with artificial tendons and sensors for the operation of its various joints\nmimicking human-hand motions. The motors in the robotic hand could be replaced with\nnovel electroactive-polymer (EAP) actuators. In the three-finger gripper proposed in this\npaper, each finger can be actuated individually so that dexterous handling is possible,\nallowing precise manipulation.\nIn this dissertation, a microscale position-control system using a novel EAP is\npresented. A third-order model was developed based on the system identification of the\nEAP actuator with an AutoRegresive Moving Average with eXogenous input (ARMAX)\nmethod using a chirp signal input from 0.01 Hz to 1 Hz limited to 7 ± V. With the\ndeveloped plant model, a digital PID (proportional-integral-derivative) controller was\ndesigned with an integrator anti-windup scheme. Test results on macro (0.8-mm) and\nmicro (50-μm) step responses of the EAP actuator are provided in this dissertation and its\nposition tracking capability is demonstrated. The overshoot decreased from 79.7% to 37.1%, and the control effort decreased by 16.3%. The settling time decreased from 1.79\ns to 1.61 s. The controller with the anti-windup scheme effectively reduced the\ndegradation in the system performance due to actuator saturation. EAP microgrippers\nbased on the control scheme presented in this paper will have significant applications\nincluding picking-and-placing micro-sized objects or as medical instruments.\nTo develop model-based control laws, we introduced an approximated linear\nmodel that represents the electromechanical behavior of the gripper fingers. Several chirp\nvoltage signal inputs were applied to excite the IPMC (ionic polymer metal composite)\nfingers in the interesting frequency range of [0.01 Hz, 5 Hz] for 40 s at a sampling\nfrequency of 250 Hz. The approximated linear Box-Jenkins (BJ) model was well matched\nwith the model obtained using a stochastic power-spectral method. With feedback control,\nthe large overshoot, rise time, and settling time associated with the inherent material\nproperties were reduced. The motions of the IPMC fingers in the microgripper were\ncoordinated to pick, move, and release a macro- or micro-part. The precise manipulation\nof this three-finger gripper was successfully demonstrated with experimental closed-loop\nresponses.