H-infinity control of a flexible gantry robot arm using smart actuators

This paper presents new feedback actuators to achieve an accurate position control of a flexible gantry robot arm. The translational motion in the pla ne is generated by two d.c. motors and controlled by electro-rheological (E R) clutch actuators. The generated motion can be continuously controlled by controlling the intensity of electric fields imposed to the ER fluid domai ns of bi-directional rotating ER clutches. On the other hand, during contro l action of the translational motion, a flexible arm attached to the moving part produces undesirable oscillations due to its inherent flexibility. Th e oscillations are actively suppressed by employing feedback voltage to the piezoceramic actuator bonded on the surface of the flexible arm. Consequen tly, an accurate position control at the end-point of the flexible arm can be achieved. In order to accomplish this control target, the governing equa tions of the proposed system are derived and rewritten as transfer function s to design a robust H-infinity controller. The control electric fields to be applied to the ER clutch and the control voltage for the piezoceramic ac tuator are determined via the loop shaping design procedures (LSDP) in the H-infinity control technique. Control results of position regulating and tr acking are provided to evaluate the effectiveness of the proposed methodolo gy. (C) 1998 Elsevier Science Ltd. All rights reserved.