Robotic End-Effector Impedance Control Without Expensive Torque/Force Sensor

Abstract

A novel low-cost impedance control structure is<br> proposed for monitoring the contact force between end-effector and<br> environment without installing an expensive force/torque sensor.<br> Theoretically, the end-effector contact force can be estimated from the<br> superposition of each joint control torque. There have a nonlinear<br> matrix mapping function between each joint motor control input and<br> end-effector actuating force/torques vector. This new force control<br> structure can be implemented based on this estimated mapping matrix.<br> First, the robot end-effector is manipulated to specified positions, then<br> the force controller is actuated based on the hall sensor current<br> feedback of each joint motor. The model-free fuzzy sliding mode<br> control (FSMC) strategy is employed to design the position and force<br> controllers, respectively. All the hardware circuits and software<br> control programs are designed on an Altera Nios II embedded<br> development kit to constitute an embedded system structure for a<br> retrofitted Mitsubishi 5 DOF robot. Experimental results show that PI<br> and FSMC force control algorithms can achieve reasonable contact<br> force monitoring objective based on this hardware control structure.