Revised motor winding smooths stepper operation

By Design News Staff -- Design News, September 24, 2006

Most stepper motor applications require smooth motion. To achieve extremely smooth movement, some engineers alter the voltage, current, and more often, the microstep setting. These changes frequently require an extensive trial-and-error process that may or may not result in better performance. A patent-pending design from Lin Engineering known as R-winding provides an alternative for providing smooth motion in lower torque applications. The benefits of the R-winding are most apparent in stepper motors that use half stepping, however, studies have shown smoother motion even during 64 × microstepping.

Bipolar step motors have two phases. To half-step these motors, current passes through each phase in a sequence called One-Phase ON and Two-Phase ON. Using One-Phase ON and Two-Phase ON, different magnetic fluxes develop a step hysteresis. The unevenness in every other step causes jittery and unsmooth movement.

The R-winding shifts the phase currents, sending current to both phases under all conditions. Forcing the motor to the Two-Phase ON position at all times eliminates the One-Phase ON position and maintains the same magnetic path through the entire range of half-stepping. As a result, the settling time characteristic and the holding torque of each step are identical. The even oscillations from step to step provide smoother, quieter step motor operation.

The semiconductor industry could provide one of the initial applications for the R-winding. During the semiconductor manufacturing process, a lead screw connected to a step motor moves the wafer. Smooth movement is critical for accurate optical inspection. If too much vibration exists, there is a possibility the scanning will cause inaccurate readings.

CONTACT: Mindy Lin at mcheng@linengineering.com or 408-919-0200 ext. 224

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