Suboptimal synthesis of a robust decentralized control for large-scale mechanical systems

For a large-scale nonlinear mechanical system, a set of nominal trajectories is prescribed together with a region of allowable parameter values. The system is viewed as a set of decoupled linear time-invariant subsystems and a local controller is synthesized for each subsystem neglecting, in the first step, nonlinear coupling among subsystems. An iterative procedure is established to choose unique linear local controllers which can accommodate all nominal trajectories and withstand parameter variation. If such controllers cannot be found a force feedback is implemented as a global control in order to compensate for the influence of nonlinear and variable coupling. An example of a six-degree-of-freedom industrial manipulator is presented.