What the D# (-1021) alarm means

The indicated motor has been driven hard for too long; the servo system disabled power to protect the motor and amplifier from overheating. We are very familiar with this alarm on Omron SmartController (ACE / Viper / Cobra) systems — usually the first on-site inspection is enough to confirm the cause.

Most common causes

  • Motion speed/acceleration too high for the cycle
  • Cycle time shortened without retuning the trajectory
  • Payload increased without updating the program
  • Hot cabinet raising motor temperature
Field note: Our ticket data shows the first cause is by far the most common — start there to avoid dead ends.

Step-by-step field fix

  1. Turn high power back on
  2. Reduce the speed and/or acceleration of the motion that was in progress
  3. Repeat the failed motion and monitor whether it completes
  4. Review the duty cycle: add waits or slow the overall cycle
  5. Check cabinet cooling if the alarm is frequent
Safety first: For OMRON d-1021, this alarm family involves the DC bus, which sits at several hundred volts and stays charged for minutes after power-off - touching terminals is a shock hazard. What you can check yourself first is Turn high power back on; the DC bus and power stage handling is not a DIY job. On OMRON d-1021: checking incoming voltage at the disconnect and looking at breakers and fuses is fine to do yourself; opening the cabinet to touch bus terminals or pulling power modules needs a qualified electrician.

How we diagnose drive alarms on site

OMRON d-1021 belongs to the drive & power stage family. On OMRON d-1021 the failing stage is integrated drive units (amplifier and supply in one housing) on the OMRON robot controllers (including SCARA and cobot companions) - the fault sits on the energy chain: mains input, rectification, DC bus, braking resistor, inverter power devices and the drive board. We start reading OMRON d-1021 at controller status indicators and the software error list (letter prefixes RC / SW / V / M / D / A / E).

The chain involved in OMRON d-1021 runs: three-phase mains -> rectifier -> DC bus (bus capacitors) -> brake chopper / braking resistor -> inverter (IGBT) -> motor.

Bottom line up front: Motion speed/acceleration too high for the cycle is the first suspect for OMRON d-1021, but read it along the energy chain: Any link on this chain dropping voltage shows up at the end as a drive alarm, so order matters. We measure the mains first: more than 3% phase imbalance is enough to sag the bus under load, and plenty of bus over/under-voltage alarms are actually a grid problem wearing a robot costume. Mains fine, then the bus capacitors - bulged cases, weeping electrolyte or a lifted vent mean replacement; capacitance down 20% or more cannot hold the bus during braking. Last, the braking resistor: healthy values sit in the tens of ohms depending on rating, and an open or drifted resistor trips regenerative overvoltage directly.

Field notes on this page cover OMRON d-1021 (Duty Cycle Exceeded (Joint N)); written by the Henghuan repair team, updated 2026-10-01.

Blocked by this alarm? We can help you analyze it over the phone

Give us the alarm code, the robot model and what it was doing when the alarm hit. Our engineers run these diagnostics daily, and remote diagnosis by phone or video is free.

Get a Free Remote Diagnosis See Repair Services

Hotline: +86-20-39029800 · WhatsApp: +86-188-1886-2860

Related Drive & Power Stage alarms

24 — 24V Supply Fault A# — Amplifier Fault (Joint N) h# — High Temperature — Amplifier (Joint N) hV — High Voltage Bus Fault
Same family: this code belongs to the Drive & power stage alarms family - the page collects all Drive & power stage-family codes we have handled, with the common inspection order and spares.
Other brands: we also keep field-fix libraries for ESTUN · INOVANCE · EFORT and more — see the complete alarm code hub.

Frequently asked questions

QWhat does the OMRON d-1021 alarm mean?

The indicated motor has been driven hard for too long; the servo system disabled power to protect the motor and amplifier from overheating. We are very familiar with this alarm on Omron SmartController (ACE / Viper / Cobra) systems — usually the first on-site inspection is enough to confirm the cause. OMRON d-1021 sits in the drive & power stage family; on our work orders the highest-frequency trigger for this code is "Motion speed/acceleration too high for the cycle".

QCan I clear a OMRON d-1021 alarm myself?

Whether OMRON d-1021 clears on its own depends on the outcome of "Turn high power back on". Finish the flow with "Check cabinet cooling if the alarm is frequent" to confirm OMRON d-1021 - do not skip it. If that step is clean, the second most frequent cause on OMRON d-1021 is "Cycle time shortened without retuning the trajectory". After clearing OMRON d-1021, watch it for one shift. A second trip means stop and let an engineer arrive with the right test gear for the DC bus and power stage.

QFor drive/power alarms like OMRON d-1021, what spares do you bring on site?

The commonest causes we see on OMRON d-1021 are "Motion speed/acceleration too high for the cycle, Cycle time shortened without retuning the trajectory, Payload increased without updating the program", so we stock the van against those. For OMRON d-1021 specifically, we stock the van along the energy chain: braking resistors, bus capacitors, input fuses, drive-board supply parts and the common power modules for the brand. For OMRON d-1021, drive alarms usually stop the whole line, so they sit at the front of our dispatch queue. Before we roll, tell us what OMRON d-1021 shows on controller status indicators and the software error list (letter prefixes RC / SW / V / M / D / A / E) and what the machine was doing - phone or video triage is free.

This page on OMRON d-1021 is based on the field experience of the Henghuan Robotics repair team. Alarm explanations are our own summary for troubleshooting reference and may differ across controller and software versions — if unsure, verify against Omron documentation or reach out to us. Henghuan is an independent service provider with no affiliation or endorsement by Omron.