Robust compensation of optimal control for manipulators

In a suboptimally controlled manipulator arm, friction torque variations cause trajectory deviations and performance deterioration. On the other hand, the on-line computation of nonlinear terms in the suboptimal controller is time consuming or requires large memory space when table look-up techniques are used. In order to obtain robustness against variations in open loop dynamics and decrease nonlinear couplings in suboptimal control systems for manipulators with quadratic performance indices, in addition to full state feedback, it is necessary to introduce feedback associated with the derivatives of the state variables. This additional feedback may be implemented as minor compensating loops embedded within the suboptimal controller by analog devices. As an example, torque compensation and acceleration compensation for MIT arm are considered and yield a simple linear controller with improved robustness.