Position control of a 3 DOF piezohydraulic parallel micromanipulator

This paper focuses on the open-loop and closed-loop position control of a tripod-like joint-free parallel micromanipulator that is composed of three piezohydraulic actuation systems. The micromanipulator is controlled in open-loop using a general inverse kinematics model presented earlier for a tripod manipulator having ball and pin joints. Open-loop control is sufficient in many applications but when high accuracy and high speed are required, closed-loop control must be applied. The closedloop control of the micromanipulator is organized in multiple levels. The first level compensates non-linearities of the actuation systems and the second level controls the position of the end-effector. Level three is a supervisory level and level four tackles automatic operations. Level two, i.e. the position feedback controller, consists essentially of two single input/single output (SISO) proportional-integral (PI) controllers and an incremental form of the inverse kinematics model. The experimental results show that the position feedback control efficiently eliminates drift and vibration of the end-effector.