Nominal characteristics trajectory following control as practical controller: A review

Nominal Characteristic Trajectory Following (NCTF) control has been introduced and employed in positioning system since last two decades. It is well known with its practical and easy design procedure, which is independent of friction characteristics. Thus, designer does not need to consider the friction characteristic of a mechanism and it is a valuable controller approach in industry. Besides the straightforward design procedure, the NCTF controls are capable to achieve promising results in positioning and continuous motions and high robust performance as the end objective. The NCTF controller is comprehensive, comprising of a Nominal Characteristic Trajectory (NCT) and a PI compensator, which is free from exact modeling and parameter identification. There are three generations of the growth of NCTF controls, where it started as conventional NCTF control that emphasizes the motion of point-to-point. Then the NCTF control was improved in continuous motion where it has been named as Continuous Motion (CM) NCTF control. In order to enhance its motion accuracy and overshoot reduction characteristics, the acceleration element was added in the control structure, and namely Acceleration-Reference Continuous Motion (AR-CM) NCTF control. Although the control structure becomes slightly complicated, however, the design procedures of the three NCTF controls remain practical and easy. The usefulness of the NCTF controls have been clarified using the mechanisms with and without friction which in translation and rotary motions. The NCTF controls successfully demonstrated promising motion performances than the classical PID, PI-D and PDDO controllers in point-to-point, tracking and contouring motions.