Precision Grasping With Variable Compliance Using Force Sensing Resistors
The ability to precisely control the applied force and deformation of a grasped object is the focus of this paper. A simple mechanical end effector system with parallel grippers was developed to study compliance effects in precision grasping. A servo gripper was instrumented with force and position sensors, associated circuitry, hardware, and visual indicators; moreover, the sensors and servo motor were connected to a microcontroller that interfaced with a laptop computer. A closed-loop position control system was embedded within a force control system. Springs of varying, known stiffness were grasped to characterize and calibrate the force control system. Compliance effects of the servo gripper were observed and measured while grasping these springs under several discrete control conditions. Experimental data were compared to reduced order theoretical models for validation. A control scheme was successfully developed to precisely grasp and hold objects of varying size, shape, stiffness, and orientation, using the real-time data to establish correction factors for compliance and sensor drift. It was demonstrated that these effects can be minimized by modifying the motor control signals using the presented force and position feedback scheme.