Design and Development of a Novel Compliant Gripper With Integrated Position and Grasping/Interaction Force Sensing

This paper proposes a new compliant gripper with integrated position and force sensors dedicated to automated microassembly tasks. The uniqueness of the gripper is that it possesses a large gripping range with a bidirectional drive, and it is capable of detecting grasping force and environmental interaction forces in horizonal and vertical axes, respectively. This is enabled by a mechanism design based on a rotary flexure bearing. Moreover, a compliant mechanism with two-stage stiffness is designed to provide the force sensing with dual sensitivities and measuring ranges to accommodate the grasp of objects with different sizes and weights. Analytical models are derived to predict the grasping range, force sensing sensitivities, and ranges. These models are verified by conducting finite-element analysis simulations. A proof-of-concept prototype gripper is developed for experimental calibration and performance testing. Results reveal that the single set of strain-gauge force sensor is able to detect both grasping and interaction forces in an alternate manner. The dual-sensitivity, dual-range force sensor provides a solution to large-range gripper with finer and coarser force sensing in a small and large ranges, respectively. Note to Practitioners-Large-range compliant gripper is attractive in microassembly for grasping objects with a wide range of sizes. This paper reports on the design of such a compliant gripper which is able to execute pick-and-place operation of objects ranging between 0.15 and 4 mm. One gripper arm is driven to provide a bidirectional gripping motion, whose position is sensed by a metal strain gauge. To meet the requirement of force sensing for grasping different sized objects, a dual-sensitivity, dual-range force sensor is devised for the other arm of the gripper. It is responsible for measuring the grasp forces of smaller and larger objects in the two measuring ranges, respectively. In addition to the grasp force sensing, the force sensor is able to detect the in-plane and out-of-plane interaction forces in perpendicular axes. Such capability is useful to determine the exact moment when a contact is made between the gripper tip and the environment, so as to secure the operation in microassembly applications. The performance of the developed gripper prototype is verified through extensive experimental studies. Moreover, an automated pick-transport-place operation of a small screw is conducted to demonstrate the gripper capability in automated assembly application.