Two-Degrees-of-Freedom Control of DC Servo Motor by Means of Passive Adaptive Control

Abstract

DC servo motor has been widely used for industrial robot manipulators. The dynamics of a robot manipulator varies largely; in particular, the inertia varies by changing the attitude and grasping objects. Nevertheless, conventional servo controllers (e.g. proportional controller) has not been taking large parameter variations into account, because these variations at the motor shaft appear negligible by the high ratio gear. However the high ratio gear has also the demerits, such as friction, deflection, backlash and so on, therefore for better and faster performance of a robot manipulator, the number and ratio of the gears tend to be decreased and the perfection of this effort may reach a direct drive arm. In such a system, the servo controller should play a role by itself to reduce the sensitivity against the parameter variations and the disturbance.In this paper, the insensitive servo controller to suppress the influence of the parameter variations on the desirable transient response is realized by applying the two-degrees-of-freedom configuration. The significant feature of the two-degrees-of-freedom configuration is that the system sensitivity function and the system transfer function can be independently determined. Here, the two-degrees-of-freedom control system of DC servo motor is based on the new insensitive compensator, which is called the passive adaptive controller; that is combined with a conventional position servo controller.The method to realize the two-degrees-of-freedom control system in a discrete type of system is also derived by taking attention to the one sampling delay due to the calculation time, and the stabilizing condition is shown.Experimental results show that the proposed control system is valid and robust from the view point of the sensitivity reduction against the parameter variations and the torque distur-bance.