This page covers FANUC OT alarms related to overtravel conditions, soft limits, hard limits, interference detection, and travel pre-check errors. These alarms are commonly generated when an axis moves beyond an allowed machine travel range, enters a prohibited zone, reaches a hardware limit switch, or is judged in advance to exceed the allowable travel area.
These alarm references apply to FANUC Series 0i-Model D and FANUC Series 0i Mate-Model D.
In practical machine maintenance and operation, OT alarms are among the most familiar CNC alarms because they are directly related to axis travel limits and machine protection logic. Some OT alarms are triggered by parameter-defined soft limits, while others are caused by physical limit switches or interference protection functions. At REACO CNC, we supply FANUC CNC parts, FANUC robot parts, Mitsubishi automation parts, and repair services for customers worldwide.
What These FANUC OT Alarms Usually Indicate
This section of the FANUC alarm list mainly relates to machine travel boundaries. In practical terms, these alarms indicate that the axis position or commanded movement has gone beyond an allowed range, or that the control has detected a prohibited travel condition before or during movement.
Depending on the specific alarm, the cause may be a soft limit setting, a hard limit switch being activated, a turret interference condition, or a programmed endpoint falling inside a forbidden zone. Some alarms stop all axis feed in automatic operation, while others stop only the affected axis during manual operation. Because OT alarms are closely tied to machine protection, they should be reviewed carefully before attempting recovery.
Common Causes of FANUC Overtravel and Limit Alarms
Typical causes of OT alarms include incorrect machine position, reference return not completed correctly, travel limit parameter mismatch, limit switch activation, jog movement beyond the machine stroke, program coordinates beyond the allowed travel range, or interference between moving machine elements.
On turning machines and other specialized configurations, some OT alarms may also be related to chuck-tailstock barrier protection or turret interference logic. In addition, pre-check alarms may appear before actual movement begins if the CNC determines that the programmed destination would enter a prohibited limit zone. For this reason, both actual axis position and programmed motion should be reviewed when diagnosing OT alarms.
Full FANUC OT Alarm List: Overtravel and Limit Alarms
Table 1. Soft Limit Alarms
| Alarm Code | Alarm Message | Full Technical Content |
|---|---|---|
| OT0500 | Overtravel + direction (soft limit 1) | The positive-end stored stroke check 1 has been exceeded. |
| OT0501 | Overtravel - direction (soft limit 1) | The negative-end stored stroke check 1 has been exceeded. |
| OT0502 | Overtravel + direction (soft limit 2) | The positive-end stored stroke check 2 has been exceeded. [T] Alternatively, in chuck-tailstock barrier control, the axis entered the prohibited zone during positive-direction movement. |
| OT0503 | Overtravel - direction (soft limit 2) | The negative-end stored stroke check 2 has been exceeded. [T] Alternatively, in chuck-tailstock barrier control, the axis entered the prohibited zone during negative-direction movement. |
| OT0504 | Overtravel + direction (soft limit 3) | The positive-end stored stroke check 3 has been exceeded. |
| OT0505 | Overtravel - direction (soft limit 3) | The negative-end stored stroke check 3 has been exceeded. |
Table 2. Hard Limit Alarms
| Alarm Code | Alarm Message | Full Technical Content |
|---|---|---|
| OT0506 | Overtravel + direction (hard limit) | The positive-end stroke limit switch has been activated. This alarm is issued when the machine reaches the end of travel. When this alarm occurs, all axis feed stops in automatic operation. In manual operation, only the axis that generated the alarm stops feeding. |
| OT0507 | Overtravel - direction (hard limit) | The negative-end stroke limit switch has been activated. This alarm is issued when the machine reaches the end of travel. When this alarm occurs, all axis feed stops in automatic operation. In manual operation, only the axis that generated the alarm stops feeding. |
Table 3. Interference Alarms
| Alarm Code | Alarm Message | Full Technical Content |
|---|---|---|
| OT0508 | + Interference [T] | Axis n interfered with another turret during movement in the positive direction. |
| OT0509 | - Interference [T] | Axis n interfered with another turret during movement in the negative direction. |
Table 4. Travel Pre-Check Alarms
| Alarm Code | Alarm Message | Full Technical Content |
|---|---|---|
| OT0510 | Overtravel + direction (pre-check) | In the travel check before movement, the endpoint of the program block was inside the prohibited zone at the positive-end travel limit. Correct the program. |
| OT0511 | Overtravel - direction (pre-check) | In the travel check before movement, the endpoint of the program block was inside the prohibited zone at the negative-end travel limit. Correct the program. |
Practical Inspection Notes
When an OT alarm appears, the first practical check is usually to confirm the actual machine position and determine whether the alarm is caused by a real travel overrun, an incorrect coordinate condition, or a travel limit setting issue. If the machine has not completed reference return properly, the control may judge the axis position incorrectly, which can lead to overtravel conditions or prevent normal recovery.
For soft limit alarms, it is often necessary to review stroke limit parameters, machine coordinates, and whether the axis has moved outside the permitted stored travel range. For hard limit alarms, the physical limit switch, switch wiring, mechanical stop area, and actual machine position should be checked carefully. For interference and pre-check alarms, the machine program, axis destination, and protected machine zones should also be reviewed before restarting operation.
REACO CNC Support
REACO CNC supplies FANUC CNC parts, FANUC robot parts, Mitsubishi automation parts, and repair services for customers worldwide. If your machine is showing FANUC OT alarms related to overtravel, limit protection, or machine travel issues, we can support your spare parts sourcing and industrial repair requirements.
With 34 years of industry experience, REACO CNC supports global customers with worldwide shipping, tested industrial parts, and practical repair solutions for FANUC and Mitsubishi systems.
FAQ
What does a FANUC OT alarm usually mean?
It usually means an axis has exceeded a defined travel limit, reached a hardware limit condition, entered a prohibited area, or been judged likely to do so before movement starts.
What is the difference between soft limit and hard limit alarms?
Soft limit alarms are based on stored travel range settings inside the CNC, while hard limit alarms are triggered by physical stroke limit switches on the machine.
Why does the machine stop all axes on some OT alarms?
For hard limit alarms in automatic operation, the control stops all axis feed to protect the machine. In manual operation, only the axis that generated the alarm stops.
What does an OT pre-check alarm mean?
It means the CNC detected, before movement started, that the programmed endpoint would enter a prohibited travel zone. The program should be corrected.
Which machines does this reference apply to?
These alarm references apply to FANUC Series 0i-Model D and FANUC Series 0i Mate-Model D.
Reference Source: Beijing FANUC. This article is based on technical documentation provided by Beijing FANUC.
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