High-speed and high-precision tracking control of ultrahigh-acceleration moving-permanent-magnet linear synchronous motor

• The suitable control system for the ultrahigh-acceleration LSM has been introduced.
• The learning controller has been designed without the detailed dynamic model.
• The proposed control system shows the high tracking accuracy at high speed motions.

This paper describes the high-speed and high-precision tracking control of an ultrahigh-acceleration, high-velocity linear synchronous motor (LSM). The linear motor can produce a thrust force of more than 3000 N, an acceleration greater than 70 G (=686 m/s2), and move at a velocity of over 10 m/s. However, it has highly nonlinear characteristics, and it is difficult to provide an exact dynamic model for the controller design. Thus, a suitable controller that does not require a dynamic model in the design was selected and used for the high-precision tracking control of the linear motor. The design procedure for the suitable controller consists of two steps. In the first step, a two-degree-of-freedom controller with additional control elements was designed, and its performance was examined. The additional elements were used to suppress the negative influences characterizing permanent-magnet LSMs with cored electromagnets. The controller showed high tracking accuracy at low speed, but not at high speed. To overcome this problem, the controller was improved with a learning control element in the second step. The learning control element does not require a dynamic model in the design, and it is effective at reducing reproducible errors at high speed. The effectiveness of the controller was examined and demonstrated experimentally. The improved controller with the learning control element reduced the maximum tracking error to 1.62 μm in the sinusoidal reference motion at a frequency of 20 Hz and an amplitude of 10 mm.