Abstract
Precise positioning and repeatability of movement for stepper motors require designing a robust control system. To achieve that, an analytical model of a four-phase variable reluctance stepper motor is presented. A proposed open-loop driving circuit is designed to control the motion of a variable reluctance stepper motor. The driving circuit has an ability to drive the motor into two-step angles, i.e. a full step (15^{circ }) and a half step (7.5^{circ }). The direction of movement can be either into clockwise or counterclockwise direction. The operation of the variable reluctance stepper motor in an open-loop control circuit has demonstrated disadvantages of an oscillation and a relatively high settling time. Therefore, a closed-loop control circuit has been introduced using fuzzy logic control to overcome the oscillation problem and to obtain on a precise positioning within a reasonable settling time. The fuzzy logic control is used to improve and enhance the behaviour of the step position response based on oscillatory response and hence to reduce the overshoot significantly. The comparisons between the open- and closed-loop circuits are presented to demonstrate the disparity between both control circuits. The simulation results of the open-loop and the closed-loop circuits show that the time responses have been improved using different loads conditions. The simulation experiments are conducted and investigated using MATLAB–SIMULINK software package.
Highlights
Stepper motors have various motion control applications in many systems such as industrial machines and electronics
A development of the variable reluctance (VR) stepper motor is needed to cope with the current limitations that imply with the operation of such type of motors
This circuit is used to ensure that the range of the current angle which will be compared with the reference value (15◦), is always between ‘0’ and ‘15◦’, because the Fuzzy logic control (FLC) is designed using this range
Summary
Stepper motors have various motion control applications in many systems such as industrial machines and electronics. It is noticeable that the angle management has four inputs, i.e. the direction signal (DS), step angle (R), clock, and rotor angular position (θ ) This circuit is used to ensure that the range of the current angle which will be compared with the reference value (15◦), is always between ‘0’ and ‘15◦’, because the FLC is designed using this range. In order to obtain an improvement in the step response of the VR stepper motor, i.e. the overshoot and settling time in the position angular response, the simulation results of the closed-loop control circuit are presented. To make the driving circuit more intelligent, we added a privilege of rotation in opposite direction in case the input angle (An) is greater than ‘180◦’ so that the final position can be reached faster.
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