Hybrid position and force control of a robot arm equipped with joint torque sensors

A force/torque sensor, which is usually mounted at the wrist of a robot arm, is often used to implement force control. However, this sensor is very expensive and can only measure the forces and moments acting at the end-effector, so it cannot detect collisions occurring at parts other than the end-effector. To deal with these problems, we developed a robot arm in which joint torque sensors are installed at each joint instead of a force/torque sensor. With these torque sensors, hybrid position/force control can be conducted without a force/torque sensor. Experiments were conducted in which a robot arm draws a symbol on a board using a marker attached at the end-effector. These experiments show that position and force control are possible in any direction by using a robot arm with a torque sensor at each joint.