Design & Development of Bipolar Microstepping Drive for Disc Rotor Type Stepper Motor

Abstract

A stepper motor is a device that translates an electrical signal to a change in po- sition of a shaft or other actuator. This is usually a linear translation or rotation. Unlike a conventional DC or AC motor, this is usually a discrete quantity, and occurs when a pulse or other signal is applied. While DC or AC motors are driven contin- uously, a stepper motor is driven generally by pulses. Apart from various types of stepper motors available, Disc rotor type stepper motor is receiving significant atten- tion from industries in the last decade. This motor offers many advantages such as higher torque at high speed, high torque to weight ratio - as rotor is compact com- pared to conventional stepper motor, very low moment of inertia - due to disc magnet rotor, high torque to inertia ratio - as inertia is low, low power consumption, ironless rotor and also with SiFe laminations in the stator, eddy current losses are minimized. They are extremely reliable and compact having better dynamic performance than other stepper motors. The report presents simulation, design and extensive analysis of microstepping drive for disc rotor type stepper motor. A new microstepping drive technique has been proposed over the conventional full step & half step driving tech- niques. Single stepping or turning a stepper motor at its rated step size, results in jerky movements. Microstepping is a technique used to smooth the motor's movement between full steps and to improve the step resolution of motor. Microstepping also improves the efficiency of the system because the current in the windings of the motor is manipulated in a controlled manner rather than being turn on and of abruptly. A microstepping technique known as high torque microstepping alternately varies the current in the two windings of a stepping motor. Microstepping is a relatively new stepper motor technology that controls the current in the motor winding to a degree that further subdivides the number of positions between poles. Microstepping is typ- ically used in applications that require accurate positioning and a fine resolution over a wide range of speed.