A proportional integral derivative (PID) controller is one of controllers that are widely used in industrial fields of a control systems sector. The PID controller has a simple structure that includes proportional, integral, and derivative parts. The gains of the PID controller have a definite physical meaning, but there are numerous gains of the PID controller to be adjusted by an engineer, and it is difficult to make sure whether or not the a final gain correspond to an optimal gain. Particularly, designing PID gains required for controlling a multi-variable nonlinear system such as a robot requires a tremendous amount of time and efforts.
Many researches and techniques related to a design of gains of the PID controller for obtaining performance satisfying expectations have been presented. For example, a Ziegler-Nichols method is well-known in this field. This method is simple and can easily adjust PID gains, but does not provide satisfied performance in a nonlinear system. Generally, many researches show that the PID controller shows a proper level of performance in a linear system, but performance in a nonlinear system is difficult to estimate or frequently insufficient. Moreover, selecting a PID controller for a multi-variable nonlinear system is a very difficult task.
Particularly, in the case of conventional PID control techniques, when abrupt change occurs in the system dynamics, control performance may decrease or a stability problem may occur. Such a PID controller generally has a constant gain.
The background art of the present invention is disclosed in Korean Patent Laid-Open Publication No. 1992-0018544 (disclosed on Oct. 22, 1992).