What the E0021 alarm means

The actual axis position lagged the commanded position beyond the allowed window; the servo stops the axis. We see this alarm constantly when servicing Nachi AW / FD series systems, and the first on-site pass usually pins down the cause.

Most common causes

  • Mechanical interference or collision
  • Brake not fully releasing
  • Worn reducer or gearing
  • Payload heavier than configured
  • Drive tuning degraded
Field note: Based on our handling experience the first cause is the most frequent — use it as your starting point.

Step-by-step field fix

  1. Remove any interference
  2. Check the axis brake release
  3. Inspect the reducer and drive train
  4. Verify payload and inertia settings
  5. Reduce speed on the failing move; if it persists, check drive tuning and encoder
Safety first: For NACHI e0021, this alarm family points at arm motion control: after a reset the arm can move unexpectedly, and anyone inside the working envelope is at strike and pinch risk. What you can check yourself first is Remove any interference; the arm working envelope handling is not a DIY job.

How we diagnose motion alarms on site

NACHI e0021 belongs to the motion & path family. On NACHI e0021 the failing stage is servo amplifier modules in the cabinet, assigned per axis on the AX-series / FD-series controllers - the gap between command and execution: trajectory planning, joint limits, singularities, following error and mechanical resistance. We start reading NACHI e0021 at the pendant error-code screen (E-series codes) with amplifier panel indicators.

The chain involved in NACHI e0021 runs: program command -> trajectory planner -> joint targets -> servo execution -> actual position feedback -> deviation compare.

First check whether NACHI e0021 only appears at one pose - A six-axis arm near wrist extension or near axis-5 zero has a Jacobian approaching singularity: tiny tool moves demand huge joint rates, and the controller either reports following error or the arm snaps through. When the report is alarms at one position and clean on another path, suspect the singular region first. The fix is not raising speed limits but routing around it: move the part, add an intermediate point, or pass the region in joint interpolation.

Field notes on this page cover NACHI e0021 (Servo Follow-Up Error (Following Error)); written by the Henghuan repair team, updated 2026-10-01.

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Related Motion & Path alarms

E0012 — Robot Cannot Reach Recorded Point E0022 — Deviation Error E0025 — Position Jump (Jump Position)
Same family: this code belongs to the Motion & path alarms family - the page collects all Motion & path-family codes we have handled, with the common inspection order and spares.
Other brands: we also keep field-fix libraries for Omron · ESTUN · INOVANCE and more — see the complete alarm code hub.

Frequently asked questions

QWhat does the NACHI e0021 alarm mean?

The actual axis position lagged the commanded position beyond the allowed window; the servo stops the axis. We see this alarm constantly when servicing Nachi AW / FD series systems, and the first on-site pass usually pins down the cause. NACHI e0021 sits in the motion & path family; on our work orders the highest-frequency trigger for this code is "Mechanical interference or collision".

QCan I clear a NACHI e0021 alarm myself?

Whether NACHI e0021 clears on its own depends on the outcome of "Remove any interference". Finish the flow with "Reduce speed on the failing move; if it persists, check drive tuning and encoder" to confirm NACHI e0021 - do not skip it. If that step is clean, the second most frequent cause on NACHI e0021 is "Brake not fully releasing". After clearing NACHI e0021, watch it for one shift. A second trip means stop and let an engineer arrive with the right test gear for the arm working envelope.

QFor motion alarms like NACHI e0021, can you triage remotely first?

The commonest causes we see on NACHI e0021 are "Mechanical interference or collision, Brake not fully releasing, Worn reducer or gearing", so we stock the van against those. For NACHI e0021 specifically, we carry mechanical and configuration items: grease, limit switches, drag-chain segments, encoder cables and the parameter sheets for common reducers. For NACHI e0021, motion alarms can often be narrowed remotely first, so an on-site visit is not always immediate. Before we roll, tell us what NACHI e0021 shows on the pendant error-code screen (E-series codes) with amplifier panel indicators and what the machine was doing - phone or video triage is free.

The notes on NACHI e0021 were summarized by the Henghuan Robotics repair team from on-site service. The alarm interpretation is our empirical summary for troubleshooting reference and may vary by controller and software version — please check Nachi documentation or contact us with questions. Henghuan is an independent service provider, not affiliated with or endorsed by Nachi.