Active Sensing Using Miniature Gripper Driven by Piezoelectric Bimorph Actuators : Identification of Mass and Stiffness of Minute Flexible Objects

Abstract

This paper is a study on the identification of physical parameters of flexible minute objects by the active sensing using a two-fingered miniature gripper. The gripper is consisting of two flexible fingers actuated by piezoelectric bimorph strips, which ride respectively on translation stages driven by fine ball screws. A semi-conductor strain gauge is bonded on the surface of one finger to measure the vibration of the coupled finger-grasped object system. First, the two fingers are shifted laterally until they come in contact with the object and hold it. Then, one piezo-actuator of gripper is driven by a step input voltage so that the two fingers shake the grasped object. The first natural frequencies of symmetric and antisymmetric modes of the coupled system are read through the spectral density analysis of the strain gauge output, from which the mass and stiffness of the grasped object are determined uniquely. The proposed identification method is studied theoretically and its effectiveness is verified experimentally by using a sponge rubber block and a salmon roe.