High gain acceleration feedback for robots with revolute, flexible joints is investigated. The robot is an open kinematic chain with revolute joints. Joints are modeled as linear torsional springs and the joint damping is small: drives are attached at the joints. For fixed theta and with the nonlinear terms considered as disturbances, the transfer function from drive torque to motor angle has only finite zeros, while the transfer function from drive torque to link angle has some infinite zeros. If the joint damping is zero, only infinite zeros appear in this transfer junction. High gains in the acceleration feedback loop from the link angles can be destabilizing due to the presence of these infinite zeros. Stabilizing control laws for the fast dynamics are obtained when using acceleration feedback. Two solutions are proposed. Assuming joint torque can be measured, a joint torque control law can stabilize the fast dynamics: or a compensator can be designed to directly stabilize the fast dynamics in the acceleration feedback loop.
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