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For microsteps No 3-5 the slow decay has the lowest deviation, but in the further step deviations under the mixed and fast decay modes, they are much lower, and only the slow decay mode has an increasing slippage at the second half of the full step (microsteps No 8-15 and 25-31).
Therefore, that phenomenon could be explained by the current decay mode change in the phase coils.
If the rotation direction is changed after the stop in the first half of the step, for the mixed current decay mode the calculated RMS value is equal to 1.
When the bridge operates under the fast decay mode, all the time, the coil current flows through the shunt resistor and could be measured accurately.
It could be corrected by lowering the supply voltage to 12 V (for continuous rotation linearization) or by using the fast current decay mode and changing the rotation direction after the stop if only there is initiated the first half of the step (for the final position fix).
To design a new controller it is significant to provide the accurate coil current measurements, thus the fast decay mode is preferable, and there has been determined no mixed decay mode benefit versus the fast decay.
Coil Supply Decay mode RMS connection voltage Series 24 V Mixed 3.
A3979 microstepping driver includes two full bridges with fixed off-time current regulators that have the ability to operate in slow, fast, or mixed decay modes.
There have been made the measurements using the lower power supply values 12 V and 8 V, and thus, much lower position deviation has been obtained, and no difference in positioning accuracy for different decay modes has been found.
The quantitative evaluation of the deviation for the diverse decay modes is provided by RMS calculation.