Design approaches for microstepping step motor controllers

The authors discuss design methods for microstepping controllers for motors with arbitrary torque characteristics. These characteristics often show pronounced effects of magnetic saturation which is desirable for obtaining higher torque at high slewing rates. For some stepping motors, particularly the variable reluctance type, the static torque curves depart considerably from the sinusoidal shape which is normally assumed in the calculation of currents for microstepping. It should be noted that manufacturers tend to classify motors with nearly sinusoidal torque characteristics as suitable for microstepping applications. This calls for distributed windings and larger than required airgaps which in turn leads to larger magnet volume. The authors describe methods of calculating/obtaining microstepping currents when motor torque characteristics depart from the ideal situation due to magnetic saturation, airgap geometry and mechanism of torque production with a view to using all stepping motors for microstepping using suitably designed controllers