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Stepper Fundamentals Slide 28

This graph shows the actual operating waveforms implemented with an L6208 for a microstepping drive. Channels 2 and 3, the green and purple traces, are the output of the DAC for the two coils. Channel 4, the magenta trace, shows the current in the winding corresponding to the reference voltage on channel 2. Channel 1 shows the step clock input that controls the phase relationship of the bridge. In this example the sine wave is synthesized using 16 microsteps per step, dividing each 90° into sixteen 5.63° microsteps. This implementation uses an 8 bit DAC, actually a RC filter on a PWM output from a microcontroller, to generate the two reference voltages. As a rule of thumb, two additional bits are needed in the DAC above the number of microsteps to generate an acceptable sine wave. For the 16 microsteps shown here, a 6 bit DAC would be sufficient. With an 8 Bit DAC, an acceptable approximation can be created for the two sine waves for a 64 microstep application. Typically 1/16 to 1/32 microstepping can be achieved with most motors. How well the motor will follow the microsteppping waveform depends on its construction.

PTM Published on: 2011-12-14