Application of Velocity Profile Generation and Closed-Loop Control in Step Motor Control System

Abstract

Step motors are widely used in motion control systems. The step motor controller must perform high-precision positioning and smooth movement operation. In motion systems applying velocity profile control, the velocity of the motor gradually increases or decreases, to avoid the negative effect caused by the sudden change in velocity. Previous research proposes several step motor controller designs, that contain several modules, including a velocity profile generator, step motor driver, and feedback counter. These controllers are able to perform precise positioning and provide smooth motion operation. However, because these controllers operate in an open-loop control so the synchronous condition can be lost when disturbances in load torque exist. This paper presents the application of closed-loop control in the step motor controller. The control algorithm is based on two mode operations: open-loop and closed-loop. The controller operates in open-loop mode when it remains synchronized, and switches to closed-loop mode when it loses synchronization. This paper presents an algorithm for generating various velocity profiles and closed-loop control algorithms. The experiment is performed on a 16-b DSP, to verify the performance of the design. The experimental results show a velocity profile of unsymmetrical shape and demonstrate effective closed-loop control in an actual step motor system.

A method to improve the accuracy of synchronous control systems

“…Velocity profiles are consecutively specified for the given tasks and express the desired acceleration and deceleration characteristics [11]- [13]. Each set of coefficients, expressing the desired characteristics of acceleration and deceleration, are computed and stored.…”

Implementation in Microcontrollers of an Algorithm for the Simple Generation of Speed Profiles in a Stepper Motor and Their Associated Kinematics

“…However, at high speeds, stepper motors may lose synchronization in the classical open-loop control [9]. Also, changes in load torque might produce step loss in control without feedback [10]. Bangji and coworkers proposed an algorithm for optimizing the open-loop control of stepper motors [11].…”

“…In stepper motors, the speed is proportional to the frequency and inversely proportional to the period of digital pulses or steps injected into the actuator [6], [8], [10], [12], [24]. Displacing the motor at the maximum speed can cause step loss and, of course, an error in angular positioning [10], [25], [26]. Additionally, the torque decreases as the velocity increases [27]- [29].…”

“…There are moments where the drastic change in acceleration in the trapezoidal profile generates a significant jerk with an impulse waveform, which produces unwanted vibrations [30], [38]- [42]. An alternative for reducing jerk is reached using an S-curve speed profile [10], [25], [26], [29], [30], [37]- [39], [42], [43] or patterns based on sinusoidal functions [30], [41]. Both profiles limit this variable, thereby reducing the residual vibrations.…”