Digital Redesign of a Stepping-Motor Driver in the Presence of Computational Delays and Disturbances

Abstract

A method of digital redesign that can take computational delays and disturbances into account is presented and applied to an industrial analog driver for stepping motors. The method is based on the so-called Plant-Input-Mapping (PIM) method, which guarantees the stability for any non-pathological sampling interval and is extended to the case where computational delays are present. The delay, which does not have to be integral multiple of the sampling period, is considered to be a part of the plant so that adverse effects of the delay on the digital controller performance can be taken into account. Since the effects of disturbances in the motor should also be dealt with in the driver, modifications to the PIM are incorporated such that the characteristics from the disturbance to the plant-input can be adjusted without affecting those from the reference input. The performance of the resulting PIM method is investigated experimentally and found to be very close to that of the analog original, which cannot be recreated using the commonly used Tustin’s method at a sampling rate suitable for commercial production.

Experimental Verification of a Practical Digital Driver With Switched Gain-Tuning for Five-Phase Stepping-Motors

“…Drivers for such five-phase motors are designed, therefore, to achieve high performance, which tend to make the driver more complex and its implementation more costly. A large number of research papers have appeared for modeling stepping-motors and designing their drivers [3][4][5][6][7][8][9][10][11][12][13]. They often assume, however, that the angular position and speed can be measured, requiring the use of external sensors and making the system closed-loop.…”

“…Furthermore, control settings can be adjusted only by changing appropriate circuit elements off-line. Digital current regulators are designed by discretizing this otherwise superb analog regulator such that stability is guaranteed by using the Plant-Input-Mapping method in [11][12][13]. However, further improvement on the performance was found to be extremely difficult.…”

“…The power spectrum of the reference signal r under the condition of maximum-power setting possible with the present set of equipment revealed that an upper limit of the frequency components contained in the reference-current signal is about 100 Hz. Figure 3 is a block diagram of the analog current regulator considered in our previous studies [11][12][13], where…”