Evaluation of a monolithic piezoelectric drive unit for a miniature robot

In this paper, the evaluation of two different piezoelectric drive units developed for motion generation in a miniature robot is presented. The miniature robot is intended for high precision manipulation of microscale objects. The drive units have six drive elements integrated monolithically and each drive element is a three-axial multilayer piezoceramic actuator. This enables the robot to perform five-axial manipulation operations. Two inertial and two quasistatic walking mechanisms are evaluated. Due to the high level of miniaturisation the motion capacity of the drive elements is restrained. A fair step control is obtained for the inertial mechanisms while the quasistatic waveforms give a somewhat larger scatter. Walking mechanisms are expected to be advantageous at miniature scale, but the need for more complex motion patterns increases demands on design and fabrication. The height errors of the drive elements are believed to be the main reason for the larger variation in step length of the walking mechanisms. The inertial mechanisms appear to be affected by uncontrolled collisions between the drive elements and the moving body. With proper waveforms and optimised design all these undesired effects could be minimised and the second drive unit, which has an advantageous shape of the drive elements, demonstrates an improved behaviour.