Low order robust dynamic compensation for a spherical wrist motor

The position and force control problem for a spherical wrist motor using a low-order dynamic compensator in observer canonical form is investigated. The compensator is designed by an approximate loop transfer recovery technique to ensure the loop properties at the plant input. The approximate loop transfer recovery formulation is extended to account for the nonlinearities in the control problem by including a penalty on the plant nonlinearities in the quadratic performance index. This approach accounts for the system nonlinearities during the design process, without increasing the dimension of the optimization problem. The resulting closed-loop system provides near-linear behavior of the nonlinear system. The performance of this design technique is evaluated through nonlinear simulations of the manipulator response