AN4158 datasheet(9/34 Pages) STMICROELECTRONICS

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AN4158

Stepper motor basics

1.2

Microstepping

The driving methods considered in the previous section imply a constant current flowing into

the motor phases and the magnetic field being rotated by turning on/off and reversing the

currents.

Modulating the phase currents, the available positions of the stator magnetic field, and then

the intermediate positions between the subsequent steps, can be increased without any

theoretical limit. This driving method is called microstepping and the intermediate positions

are called microsteps.

As shown in Figure 4, in order to obtain a rotating magnetic field with constant module, the

two-phase current must be sinusoidal and with a phase difference of 90° (sine and cosine).

Figure 4. Microstepping phase currents

The currents applied to the motor phases are not actually continuous sinewaves, but

a sequence of samples of sinewaves generated using the formula of Equation 2, where

Nmicrostep is the microstepping resolution (defined by the number of samples composing

a sinewave quarter which is equivalent to a full step) and n is the incremental number

generating the sequence (some examples are shown in Table 8 on page 33). Different

microsteppings are identified according to their resolution (1/4 step, 1/8 step, etc.).

PhA

peak

PhA= I peak x sin(α)

PhB= I peak x cos(α)

PhB

AM15106v1

AN4158 Datasheet(PDF) 9 Page - STMicroelectronics