Microstepping Control of a Stepper Motor for Precise Positioning

Abstract

Stepper motors are widely used in mechatronic systems for positioning,because they move in precise discrete steps and can be commanded to aposition without a feedback sensor, but the size of the step limits how finelythey can be positioned and can cause jerky motion and vibration;microstepping is a technique that divides each step into many smaller ones for finer, smoother positioning. This study examines the microstepping control of a stepper motor for precise positioning and how it achieves finer resolution than ordinary stepping. A stepper motor was driven by microstepping, in which the currents in the two motor windings are varied gradually, in steplike increments following a sine and a cosine, rather than switched fully on and off, and the resulting positioning was examined. By holding the two winding currents at intermediate values, in proportions between those of adjacent full steps, the motor was made to take up intermediate positions between the full-step positions, so that each full step was divided into a number of finer microsteps, greatly increasing the resolution of positioning. The gradual change of the currents also smoothed the motion, reducing the jerkiness and vibration of ordinary full stepping, in which the abrupt switching of the windings moves the rotor in sudden jumps. Microstepping thus improved both the fineness and the smoothness of positioning, at the cost of a more complex drive that must control the winding currents to graded levels rather than simply switching them, and with some reduction in the precision and torque of each individual microstep. The study shows that microstepping markedly improves the resolution and smoothness of stepper-motor positioning, and it discusses how it works and the trade-offs it entails. KEYWORDS: Stepper motor, Microstepping, Precise positioning, Motioncontrol, Resolution, Winding currents, Mechatronics, Actuator, Vibrationreduction