GETTING THE SMOOTHEST LOW-SPEED MOTION POSSIBLE WITH SUB-MICROSTEPPING
Figure 2 shows a linearly interpolated 10-microstep waveform. The space between each step change in current is now linearly “filled in” with 32 sub-microsteps to give the motor an effective 320 microstep smoothness. A normal 320-microstep drive requires a 3.2 MHz step pulse frequency to get 3,000 RPM from the motor. The GM215 and G214 require only a 0.1 MHz step pulse frequency to get the same speed while operating at 10 microstep.
Figure 3 shows the individual sub-microsteps over a small range of the Figure 4 waveform. Each cycle of the yellow trace is the 10-microstep input step pulse. There are 16 sub-microsteps seen per input period; the other phase winding's sub-microsteps are interleaved for a total of 32 sub-microsteps.
The GM215's FPGA measures every step input period and then divides the measured time period by 16. The result goes to a timing circuit that produces exactly 16 evenly spaced pulses over the span of every input pulse period. The G214 will change the level of sub-microstepping based on the resolution setting for best performance. With a maximum resolution of 256 microstep it will operate smoothly at all resolution settings because of this feature without any rough stepping at lower resolutions.