Synthesis of compliance-independent robot control system (eliminates the effect of non-zero mechanical shaft compliance)

The authors describe a method of synthesizing a robot control system comprising an adaptive/self-tuning control loop within position and velocity negative feedback loops whereby the effects due to a finite mechanical shaft/gearing stiffness (the nonzero compliance effects) are forced to zero providing for a compliance-independent control. The system consists of an innermost positive feedback loop within an inner negative feedback loop, the two loops being closed within velocity and position negative feedback loops. Since the innermost positive feedback loop is of unity loop gain it forces a parameter-free operation, implying adaptive/self-tuning properties, as no knowledge of the parameters of the plant is required. In addition, a current-free operation is provided as no current through the plant need be sensed and processed, which minimizes measurement noise. Because of the virtually infinite gain margin imposed in the inner negative feedback loop, stabilization means are required. In this system in this work, they have been provided by closing outer loops (velocity and position) through a stabilizing circuit synthesized for desired phase/gain margin. In addition to providing compliance independence, the system provides independence of the load torque disturbances as well as a zero-order dynamics, all of these within physical limitations of a physical system.<>