Research On Open-loop Performance Optimization And Closed-loop Control For Two-phase Hybrid Stepper Motor

Stepper motor is a kind of servo systems applied widely in the industry, because of itsinherent defects and the insufficient of traditional control mode, there are some problems thatcannot be ignored in the application. For example, it will be out of step very easy when itstarts in an open-loop way, the stability is poor when it is locked-rotor or at low speed, thequick response ability and the ability to resist load disturbance are not good enough when it isat high speed and so on. And to some extent the stepping motor servo system is constrained inthe industrial applications. Therefore, it is of profound significance for control system ofstepper motor to find an efficient control method.This article puts forward a modified exponential velocity curve to deal with the problemthat it is easy to lose step when it starts in an open-loop way. Based on the analysis ofoperation characteristics of the stepper motor and the studies of the stepper motor speed curve,this paper improves the exponential velocity curve. The modified velocity curve not onlykeeps the advantages of the original exponential velocity curve, but also makes it easy toimplement in the industrial application. And it is approved to be effective through simulationand experimentation.This paper uses the sliding mode variable structure control method to improve theanti-disturbance performance of the hybrid stepper motor. And the control method is paidattention by the broad scholars because of its strong robustness. The development of computercontrol technology provides a good opportunity for the method to develop, and therapid development and improvement of DSPIC and ASIC also make the method have moreexcellent performance in the motor speed control system or position control system. However,the system will chatter by using this method. Therefore, the problem how to weaken thechattering should be attached by the researchers. One of the ways to weaken the chattering isto use the reaching law method. The method can improve the dynamic characteristics of thesliding mode motion to weaken the chattering. The article analyzes some typical mathematicalmodels and characteristics of reaching law, and it provides the improved exponent reachinglaw, which is switching gain exponential reaching law with time-varying, for the largerchattering which happens near the sliding surfaces and the poor convergence in the sliding-mode field. This improved exponent reaching law method adds the time-varyingcorrection factor based on the original fixed switching gain. And that makes the switchinggain in the sliding mode motion stage with the state of the system is reduced and the decayto zero, so that it can weaken the chattering and improve the convergence and movementquality of the system.At last, this article studies the stepper motor control system by simulation andexperimentation, and the result suggests that, compared with the traditional PI controller, thestepper motor control system based on the sliding mode algorithm is with the fast responseand the high robustness. Moreover, the experiment also confirms that the modifiedexponential reaching law method can weaken the chattering effectively and make the systemconverges to the origin reliably.