Experimental investigation of stiffness control for a robotic manipulator

grantor: University of TorontoImpedance control is a strategy for controlling both the position of a robotic manipulator, and the forces it exerts on its environment. Stiffness control is the simplest form of impedance control. An approach to stiffness control, using force feedback, is implemented on a 2 degree-of-freedom manipulator. The two joints are actuated by brushless d.c. motors connected to a harmonic drive gear. A wrist mounted force/torque sensor provides the measured forces and torques at the same rate as the control cycle: 500 Hertz. Experimental results demonstrate the use of force feedback for overcoming complicated friction and dynamic effects for geared manipulators. However, the effect of joint compliance limits the ability of the controller to realize the desired Cartesian stiffness. The inner loop based approach to force control is implemented for comparison with stiffness control. It relies on the position servo to reject disturbances, rather than on force feedback. However, filtering limits the bandwidth of the outer force control loop. Thus two practical approaches to force control have been demonstrated, which are suitable for implementation on manipulators using harmonic drive gears.M.A.Sc