A platform for micropositioning based on piezo legs

In this paper, we describe the development and prototype testing of a platf orm for micropositioning having three legs made of piezo tubes. Each piezo tube has four outer electrodes and one common inner electrode on its walls. By appropriate polarization of outer(s) electrode(s) with respect to the i nner electrode, due to the inverse piezo effect, the tube wall will change its longitudinal dimension and the tube will bend in the corresponding dire ction. The platform motion is performed by successive slow bending and quic k stretching of the tubes (i.e., legs), At this stage of development, the p latform is connected by five wires to a power supply and a PC. The range of platform motion is limited only by the length of the wires connecting it t o the power source. Electronic circuits for generating appropriate voltage Signals are designed to be as simple as possible. This enabled the complete electronics and microcontroller for motion control to be placed onboard. T he microcontroller is capable of realizing all operations needed for the mo tion execution and the communication with PC (containing the information ab out motion direction and step amplitude) can be done using a standard RS-23 2 interface. It was experimentally verified that, though being of a simple design, the platform allows a positioning accuracy which is below 0.2 mum. Even more accurate positioning (below 0.1 mum) can be achieved in the "only bending" mode by simultaneous bending of all legs in a desired direction a nd without executing the legs' stretching. The platform capability to accom plish controlled complex motion using different motion velocities was demon strated. Using a joystick, translation and rotation are easily achievable a nd the motion can be controlled in real time. Platform loading capacity all ows some additional devices like a gripper, or any another device for a par ticular application to be mounted onboard. This enables the platform's pote ntial use in a wide variety of applications. (C) 2001 Elsevier Science Ltd. All rights reserved.