Use micro-stepping techniques to smooth operation of step motors

Over the last two decades, stepping motors (or step motors) have increasingly been applied in electronic-control applications throughout all segments of the electronics industry. Its simplicity of design has made the stepping motor an ideal choice in applications where size, weight and low power consumption are primary requisites.

Indeed, the rotor, which is the only moving part of a stepping motor has, unlike typical DC motors, no windings, commutator or brushes. The rotor is held at its position solely by the action of the magnetic flux between stator and rotor. But stepping motors need a special, repeating sequence of pulses to generate a more or less smooth rotation. Every pulse sequence results in the turning of the rotor with a fixed known angle. The position of the rotor can easily be calculated by knowing the starting position of the rotor and the number of pulses (as long as the maximum loading is not exceeded).

To make the rotation of the rotor smoother (i.e., to make the angular steps smaller), a technique of mini- or micro-stepping technique can be applied. This article will detail a micro-stepping design technique that improves the precision of the rotor movement and smoothes out the motion of stepping motors.

Micro-stepping
Micro-stepping is a technique based on two-phase-on operation, which provides for the subdivision of each full step into a number of "sub steps" of equal size. In contrast with the two-phase, full step mode where the two currents of two poles have to be kept equal, the currents are deliberately made unequal in the design technique detailed below. By correctly choosing and controlling the relative amplitudes of the currents, the rotor equilibrium position can be made to lie anywhere between the step positions for each of the two separate phases.

In terms of input control for stepping motor driver, two groups can be named: clock-in type controllers that include the complete sinus stepping function internally, and phase input controllers, which need all controlling signals from an MCU.