Rotor oscillation damping of a stepping motor by sliding mode control

Stepping motors are used mainly in OA and FA systems due to the merits of their digital driving behavior using switching devices. They are driven by closed-loop control in systems where special performance such as prevention of out-of-synchronism or a high-speed drive is required. It is well known that rotor oscillation is one of the principal problems in the switched drive of a stepping motor, and nowadays several methods for damping this oscillation have been suggested in which the switching sequence is changed in some manner. In such methods, the excitation time of the stator windings must be tuned appropriately, or the effect of damping is insufficient and oscillation may be even amplified in some circumstances. To resolve this problem, adaptive methods for tuning of the excitation time have been developed. However, they suffer the disadvantage that they require a tuning period for the excitation time to attain the optimal value at the beginning of control or when the machine parameters are varied by changing the driving condition. The authors have developed a new method for rotor oscillation damping of a stepping motor in a closed-loop system. It is based on a sliding mode control technique and is designed to be robust to variation of rotor inertia which significantly affects the oscillatory characteristic. In this method, a lower-order dynamical model, obtained by reaching a sliding mode where the angle-torque characteristic of the motor is bound to a certain linear function, is made non-oscillatory by pole assignment over a certain region of varying rotor inertia. Applying this method to an experimental system, rotor oscillation is damped excellently in the cases of single-step and low-speed multi-step drive. On the other hand, it is shown deceleration is needed near the last step in the case of a high-speed drive. © 1998 Scripta Technica, Electr Eng Jpn, 126(1): 42–51, 1999