FAQ
TL;DR: In one documented case, 99% of similar servo drift issues traced to AC power noise; “use noise filter.” [Elektroda, Manoj Kumar, post #21673415]
Why it matters: This FAQ helps pick-and-place and motion-control engineers stop position drift that ruins placement accuracy and throughput.
Quick Facts
- Reported symptom: calibration at 85 mm drifting to 95 mm after continuous cycles. [Elektroda, Ankim Tandon, post #21673404]
- Environment steady: temperature stable in clean room; drift persisted. [Elektroda, Ankim Tandon, post #21673409]
- Observed mismatch: command vs received pulses on driver differed; ferrites added and AC/DC wiring isolated. [Elektroda, Ankim Tandon, post #21673409]
- Root-cause claim: “99percent – noise from AC power supply in the panel”; fix with an AC noise filter. [Elektroda, Manoj Kumar, post #21673415]
- Alternative causes: encoder fault or belt slip on actuator mechanics. [Elektroda, Zachary Pick, post #21673412]
What causes servo position to drift after many cycles on a pick-and-place machine?
Common triggers include AC mains noise coupling into pulse-train wiring, amplifier faults, or mechanical slip. One contributor reported 99% cases tied to panel AC noise. Adding an AC line noise filter resolved it. Inspect feedback integrity and mechanics after power quality checks. [Elektroda, Manoj Kumar, post #21673415]
How do I quickly test if AC power noise is the culprit?
Do a controlled run with an AC noise filter added to the panel supply. Keep pulse-train and power cables separated. If drift disappears, noise was the source. This mirrors a reported 99% noise-caused drift outcome and recommended filter remedy. [Elektroda, Manoj Kumar, post #21673415]
Can temperature changes explain the drift?
Temperature can affect sensors and mechanics, but one case showed stable temperature in a clean room while drift persisted. That points away from thermal causes and back to electrical noise or mechanics. “It could be temperature related...” is worth checking, but verify power noise first. [Elektroda, Rohit Dubla, post #21673405]
What is a servo encoder and why does it matter here?
A servo’s built‑in encoder reports shaft position to the drive. If the encoder is damaged, loose, or its coupling slips, commanded and actual positions diverge. On belt or linear actuators, an encoder can read fine while the belt slips, causing drift at the tool point. [Elektroda, Zachary Pick, post #21673412]
My command and received pulses don’t match—what should I check?
Treat it as signal integrity noise. Separate AC and DC runs, twist CW/CCW pairs, add ferrites, and verify shielding and grounding. One user noted mismatch and reduced interference by isolating AC/DC wiring and adding ferrites before continued monitoring. [Elektroda, Ankim Tandon, post #21673409]
Could the amplifier/drive be faulty?
Yes. A weak or failing amplifier stage can miscount or distort pulses, leading to drift. One report listed the amplifier among likely causes alongside AC noise, with the latter being far more common. Swap with a known-good drive to A/B test. [Elektroda, Manoj Kumar, post #21673415]
Is this a purely position-command issue or sensor-based control?
Even in position-command sequences, the servo relies on encoder feedback. Confusion arises when sequences are “position based,” yet actual position still comes from the encoder. Validate encoder health and mounting regardless of command mode. [Elektroda, Ankim Tandon, post #21673411]
What mechanical issues can mimic electrical drift?
Look for belt slip, loose couplings, worn pulleys, or weak springs in return mechanisms. If mechanics relax under load, the system returns to a shifted zero. Check and retension or replace suspect parts before retuning controls. [Elektroda, Zachary Pick, post #21673412]
How do I reduce pulse-train noise on CW/CCW lines?
Use twisted pairs, short cable runs, proper shields grounded at one end, and physical separation from AC power. Add ferrite beads and install an AC mains noise filter in the control panel. Re‑test placement repeatability. [Elektroda, Ankim Tandon, post #21673409]
Should I try PID control or tuning to fight drift?
If offset accumulates due to plant dynamics, a tuned PID can help. However, if noise or slip causes missed counts, tuning will not cure root causes. Fix power noise and mechanics first, then tune. [Elektroda, Justin Spencer Mamaradlo, post #21673413]
Edge case: can a weak power transistor cause drift?
Yes. A degrading power stage transistor or its driver can reduce torque or distort drive signals, allowing position error under load. Replace the weak device or the drive module and verify repeatability after repair. [Elektroda, Sambath Kumar, post #21673414]
What’s a fast 3‑step diagnostic to reproduce and isolate the drift?
- Log command vs received pulses over 500 cycles at nominal speed.
- Add AC mains noise filter and separate AC/DC cable trays; repeat the run.
- Swap in a spare drive or motor; retest to isolate electronics vs mechanics. [Elektroda, Ankim Tandon, post #21673409]
How big can the drift get during production?
One case documented a calibration at 85 mm shifting to 95 mm after continuous cycling. Ten millimeters is enough to ruin placements, so treat early warnings seriously and act before yield falls. [Elektroda, Ankim Tandon, post #21673404]
If temperature is stable and drift remains, what’s next?
Proceed to electrical and mechanical checks. Prioritize AC noise mitigation, verify pulse integrity, then inspect encoders and belts. This sequence matched a clean-room case where temperature was steady but pulses differed at the drive. [Elektroda, Ankim Tandon, post #21673409]
