PID control of rigid robots actuated by brushless DC motors

In this note we are concerned with PID control of rigid robots equipped with brushless DC (BLDC) motors when the electric dynamics of these actuators is taken into account. We show that a PID controller suffices to achieve local stability whereas an adaptive PD controller yields stability and global convergence to the desired link positions. We show that the effect of the adaptive part can be rendered arbitrarily small and, hence, virtually the PD controller suffices to achieve the reported global results. We present a theoretical justification for the torque control or current control strategy commonly used in practice to control BLDC motors.