What causes FANUC alarm 511?

A programmed move commands the tool to travel past the negative software travel limit on the affected axis. Incorrect work offset (G54-G59) or tool length offset is shifting the actual endpoint into the forbidden zone. A typo or wrong sign in the NC program sends the axis in the negative direction further than allowed. The soft travel limits (parameters 1320/1321) are set too conservatively and do not match the actual machine travel. Absolute vs incremental mode confusion causes the calculated endpoint to land outside the allowed travel range.

How do I fix FANUC alarm 511?

1. Note which axis N is triggering the alarm, then check the program block that was being pre-checked and verify the commanded endpoint coordinate makes sense for the part setup. 2. Check the active work offset (G54-G59) on the offset page and confirm the origin is set correctly. A wrong offset can shift all moves into the forbidden area. 3. Check tool length offsets if the alarm is on the Z axis. A missing or incorrect tool length offset can cause the pre-check to calculate a position well below the limit. 4. Manually jog the axis to its negative limit and compare the actual position to the soft limit values in parameters 1320 and 1321. Adjust parameters only if the machine physically allows more travel and it is safe to do so. 5. Review the program for incorrect sign usage or absolute vs incremental mode errors near the flagged block. Correct the coordinate value and restart the program.

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FANUC Controller

Overtravel/Limit · Basic · 15-30 minutes

Alarm 511

Fanuc Alarm 511 - OVER TRAVEL: -n (PRE-CHECK)

Fanuc Alarm 511 OVER TRAVEL -n (PRE-CHECK) occurs when stroke limit check (parameter 1320#0=1) detects the programmed endpoint of a move command will exceed the software over-travel limit in the negative direction of the specified axis before motion begins. This is a preventative alarm that stops execution when the commanded position is beyond the stored travel limit defined in parameters 1320-1326.

FANUCOvertravel/LimitBasic15-30 minutes

511

Fanuc Alarm 511 - OVER TRAVEL: -n (PRE-CHECK)

Z- Overtravel

Root Cause Summary

Fanuc Alarm 511 OVER TRAVEL -n (PRE-CHECK) occurs when stroke limit check (parameter 1320#0=1) detects the programmed endpoint of a move command will exceed the software over-travel limit in the negative direction of the specified axis before motion begins. This is a preventative alarm that stops execution when the commanded position is beyond the stored travel limit defined in parameters 1320-1326.

Safety

Only jog in opposite direction of overtravel
Only jog in the opposite direction of overtravel.
Before jogging, ensure the path is clear of obstructions to prevent further collisions.
Be aware of potential pinch points during axis movement.
If the machine requires power cycling, follow the manufacturer's recommended shutdown procedure.
If troubleshooting involves accessing the machine's electrical cabinet, ensure the power is disconnected and locked out/tagged out by qualified personnel.
Do not bypass or disable safety limit switches. These are critical for preventing machine damage and personal injury.
Consult the machine's documentation before making any changes to parameters or settings.
Only jog in the direction opposite to the overtravel to prevent further damage.
Ensure no personnel or objects are in the machine's path before operating.

Causes and Fixes

1
Press RESET to clear alarm. Review the NC program block displayed on screen and identify the axis number (n) and commanded position that triggered the alarm.
2
Navigate to SYSTEM > PARAM and check parameter 1326 (stored stroke limit 2 minus for axis n). Compare this limit value with the programmed endpoint position in the flagged block.
3
If the programmed position is incorrect, edit the NC program to move the endpoint within the valid travel range. If the limit is incorrect, verify machine mechanical limits then adjust parameter 1326 accordingly.
Changing parameter 1326 requires parameter write enable (PWE) and must match actual machine physical travel limits to prevent crash
4
Verify parameter 1320#0 (stored stroke check) = 1 is intentional. Set work coordinate system (G54-G59) zero positions properly using SYSTEM > CURRENT POS to ensure programmed positions align with actual machine envelope.

DIY Feasiblehigh confidence

Call a technician if:

·Software limit parameters require changes beyond operator authority
·Reference return mechanism fails mechanically
·Encoder or position feedback system suspected faulty

Prevention

Always verify work offsets after setup
Include software limit checks in program verification
Maintain regular reference return procedures
Use program simulation before running new programs

Common Mistakes

Confusing negative direction limits with positive values
Forgetting to account for work offset in limit calculations
Setting software limits equal to mechanical limits without safety margin
Ignoring reference position status before running programs

Related Alarms

510 512 513 500 501

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