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Stepper Fundamentals Slide 10

An idealized half step sequence of current in the two windings is shown here. The sequence is characterized by the current being positive for 3 steps, zero for one step, negative for three steps and zero for one step. The two coil currents are, as in the previous slide, shifted 90° with respect to each other and reversing the sequence would shift one of the two current waveforms by 180°. This simple sequence is generated by switching the currents on or off and controlling the direction of current flow in the coils so that the magnitude of a current when it is on is always the same. This page illustrates that for every other step, the current in one of the two windings is zero. Since the magnitude of the resulting magnetic vector is equal to the vector sum of the vectors generated by the two coils, the magnitude when both coils are energized will be larger, by a factor of the square root of 2, than when only one of the two coils is energized. This variation leads to a ripple in the torque, since the torque is proportional to the magnitude of the magnetic vector.

PTM Published on: 2011-12-14