Load behavior concerned PID control for two-mass servo systems

PID control closed on the motor position is the most common solution in commercial servomechanisms. If significant compliance exists between the motor and load, performance limitations emerge if the load position behavior is properly considered. Quantification of the loss of performance at increasing nominal bandwidth of the closed loop system is the main result of this paper. After describing a simple procedure for identification of the relevant physical parameters, the performance is expressed as the H_∞ norm of the transfer function from motor position setpoint to load position. A simple expression is given and experimentally assessed for this norm, in terms of inertial, elastic and damping parameters of the system, as well as of the nominal bandwidth of the closed loop system. Explicit formulas are finally given for load behavior concerned tuning of the PID controller.