Robust tracking control of an ironless linear motor with continuous motion nominal characteristic trajectory following controller

Permanent magnet linear motors (PMLM) are widely used in high precision machineries. With the removal of the transmission elements, the positioning performances of PMLM are easily affected by parameter variations and external disturbances. Various control approaches were proposed, yet it was noticed that majority of these controllers have complex design procedures, and require accurate model parameters of the PMLM, including the nonlinearities of the system. Therefore, in this paper, a Continuous Motion-Nominal Characteristic Trajectory Following (CM-NCTF) controller is proposed as a practical controller for tracking control of an ironless permanent magnet linear motor (IPMLM). The design procedure of CM-NCTF controller is straightforward, and does not require one to go through the hassle of determining the plant model parameters. The proposed controller is made up of two major parts: A Nominal Characteristic Trajectory (NCT) and a proportional-integral (PI) compensator. The NCT is constructed based on the actual response of the system, where the characteristics of the system are measured. The PI compensator works to reduce the motion difference between the NCT and system, thus ensuring the system motion follows the constructed trajectory. The tracking performance under mass variation of the proposed controller is examined experimentally and validated theoretically. Comparative evaluation is also done with a proportional-integral-derivative (PID) controller. Results showed that the designed CM-NCTF controller is indeed robust towards mass changes, while possessing a simple design procedure comparable to PID controller, and does not require the exact plant model parameters.