The paper presents a new parallel micromanipulator that is composed of three piezohydraulic actuation systems. The basic elements of the actuation system are a piezoelectric actuator, a bellows and hydraulic oil. The use of the flexible bellows results in a new type of parallel structure, where the joints are integrated into actuator links. The joint-free tripod-like micromanipulator is controlled using a real-time control software that is based on a multi-level architecture. Control is organised in four levels for nonlinearity compensation, position feedback control, supervision and tackling of automatic operations. The micromanipulator presented provides an exceptional combination of submicrometer resolution, large work space, miniature size and advanced control.

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. Open-loop control is sufficient in many applications but when high accuracy and high speed are required, closed-loop control must be applied. The closed-loop control of the micromanipulator is organized in multiple levels. The first level compensates nonlinearities 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.

This paper describes a new miniaturized actuation system designed especially for parallel link micromanipulators; the system is mechanically designed to form a very compact structure when used in parallel configuration. It consists of a monolithic unimorph type of piezoelectric actuator, an electro-deposited bellows, a tank and hydraulic fluid. The displacement of the piezoelectric element is hydraulically magnified and converted to the displacement of the bellows. The piezohydraulic actuator provides movement from a micrometer level up to a maximum displacement of 500 /spl mu/m.