Incorrect Direction Detection During Reversal
Keshia.Jing 2026-10-15 15:03:18 72 Views1 Replies
Hello everyone. I am experiencing occasional step loss with my closed-loop stepper motor during reversals, which leads to an accumulation of positioning errors.
Upon checking the A, B, and Z signals from the encoder, I discovered a slight phase deviation between the Z-phase and the A/B-phases at the exact moment of reversal. This causes the driver to misinterpret the counting direction, treating forward-rotation pulses as reverse-rotation pulses and subtracting them from the position count.
Although the Z-phase is intended for zero-position (homing) purposes, this phase deviation is interfering with the reversal logic.
Readjusting the encoder's mounting angle has led to some improvement, but it has proven difficult to eliminate the issue entirely.
Could you please advise on the allowable phase deviation for encoder A/B/Z signals? Furthermore, does the driver incorporate any specific mechanism to verify the direction of rotation during a reversal?
Any advice or guidance would be greatly appreciated.
hi，
The direction determination should never rely on Z. The phase of the orthogonal encoder A/B inherently determines the direction (A leads B = positive, vice versa negative), and Z is only used for zero position/return zero capture. If Z is pulled along and incorporated into the counting direction determination during reversal, the positive pulse will be wrongly reduced —— First, confirm that Z is removed from the "running count/direction determination" path and only left for return zero.
The "phase deviation" of A/B/Z during reversal is more likely caused by insufficient filtering/debouncing or Z being too close to the A/B edges (due to insufficient setup time); adding a common-phase filter (50-100ns RC or the internal filter window of the driver) to the encoder input usually eliminates this.
Allowable deviation: The authoritative value depends on your driver + encoder datasheet's electrical timing (transition/misalignment specifications); the general experience is that Z must not be sampled within the tolerance band of A/B edges.
If the driver firmware allows it, increase the direction determination dead zone/hysteresis (several tens of ms) during reversal; do not sample immediately at the reversal edge.
Jason.Miao 