Design and Smooth Position/Force Switching Control of a Miniature Gripper for Automated Microhandling

Automated microhandling tasks demand miniature grippers equipped with position and force sensors to execute reliable operations. This paper presents the design, implementation, and control of a piezoelectrically actuated compliant gripper with combined position and force monitoring/control capabilities. The gripper structure is devised based on a compliant rotary bearing mechanism with the displacement amplification lever, which endows a simplified architecture than the existing parallelogram-based ones. Moreover, the challenge of achieving a smooth transition between the position and force switching control is addressed by means of a new incremental control scheme. Precision control under the influence of hysteretic nonlinearity is guaranteed by a discrete sliding-mode control algorithm. The scheme is implemented with an field-programmable gate array (FPGA) platform. Experimental investigations are undertaken to verify the effectiveness of the gripper system by executing grasp-hold-release operations of a micro copper wire. The results confirm that the proposed incremental-based switching control outperforms conventional approach in terms of position/force regulation accuracy and operation time.