Minimization of Dissipated Energy in Position Control System Considering the Friction of Gears

This paper discusses on optimal current and velocity functions which minimize the dissipated energy of a servo system with a reduction gear train. Coulomb friction of the gears is represented by the efficiency of the gears and assumed to be proportional to the absolute value of the current of a motor. The optimal functions can be obtained from an optimal control theory by introducing a zero cross time tc, when the current is changed from positive to negative. As the dissipated energy can be given as a function of tc, the optimal zero cross time tc* minimizing the energy can be represented by a simple function of the efficiency of the gears. This method is expanded into the case including the viscous friction in addition to the Coulomb friction. The influence of the viscous frictional coefficient upon the optimal zero cross time tc* is examined by simulations. The expression of the Coulomb and the viscous frictions is verified by experiments using planetary gears with a DC motor.