OT0502

Review Program Code

Access the active program on the CNC control panel and check the coordinates for the affected axis (indicated by +n in the alarm). Look for any values that exceed the positive software limit set in the parameters.

Use the program check function on the control to simulate the tool path and identify the exact line causing the overtravel.

Ensure the machine is in a safe state before running any simulations to avoid unintended movement.

Compare with Software Limits

Navigate to the parameter settings (typically in the 1300 or 1320 series for FANUC controls) to confirm the positive software limit for the affected axis. Compare this value with the programmed coordinates.

Document the current limit settings before making any changes for future reference.

Incorrect parameter changes can cause further issues; proceed with caution.

Modify Program if Necessary

If the programmed coordinates exceed the limit, edit the program to stay within the defined range. Test the modified program in a dry run mode to ensure the issue is resolved.

Consider adding safety margins in the program to prevent future overtravel alarms.

Always back up the program before making edits to avoid data loss.

Access Parameter Settings

Using the CNC control panel, access the parameter menu (often under SYSTEM or PARAMETER mode) and locate the software limit parameters for the affected axis (e.g., Parameter 1320 for positive limit).

Refer to the machine’s parameter manual for the exact parameter numbers if unsure.

Do not alter parameters without proper documentation or authorization.

Verify Limit Values

Compare the current positive software limit value with the machine’s design specifications or previous settings. Check if the value is too restrictive compared to the physical travel range.

If a recent backup exists, compare current parameters with the backup to identify discrepancies.

Incorrect settings can lead to machine damage; ensure accuracy.

Adjust Parameters if Needed

If the limit is incorrectly set, adjust the parameter to a value within the machine’s safe operating range. After adjustment, perform a test move to confirm the alarm no longer triggers.

Make small incremental changes and test after each adjustment to avoid overcompensation.

Power cycle the machine after parameter changes to ensure they take effect.

Interview Operator

Ask the operator about the actions taken before the alarm occurred, focusing on manual jogging or reference point setting for the affected axis.

Check the operation log if available on the control system for a record of manual commands.

Ensure the machine is stopped during discussions to prevent accidental movement.

Check Manual Mode Settings

Verify if the machine was in manual mode (JOG or HANDLE) and if any rapid traverse or override settings were active that could have caused overtravel.

Look for override switches or settings above 100% that may have increased travel speed unexpectedly.

Do not attempt manual moves until the cause is identified.

Reset and Test

Return the axis to a safe position within the software limits using manual mode at a slow speed. Test with a small manual move to ensure the alarm does not reoccur.

Use the lowest jog speed setting to maintain control during testing.

Monitor the axis position display closely to avoid exceeding limits again.

Check Reference Point Status

On the CNC control, check if the reference point return (zero return) has been completed for the affected axis. Look for indicators or messages showing incomplete homing.

Some FANUC controls display a ‘Not Returned’ status if homing is incomplete.

Do not attempt automatic operation without a valid reference point.

Perform Zero Return

Manually initiate a zero return procedure for the affected axis using the control panel. Follow the machine-specific homing sequence as outlined in the operator’s manual.

Ensure no obstructions are in the axis path before starting the zero return.

Monitor for any unusual noises or resistance during homing.

Verify Position and Test

After homing, confirm the axis position matches the expected reference point on the control display. Perform a small programmed move to ensure the alarm does not trigger again.

Record the position data post-homing for future troubleshooting reference.

If homing fails repeatedly, there may be a hardware issue; stop and escalate.

Inspect Axis for Obstructions

Visually inspect the affected axis for any debris, tools, or mechanical obstructions that could prevent normal movement or affect position sensing.

Check for accumulated chips or coolant residue near the axis ways or sensors.

Power down the machine and lock out/tag out before physical inspection.

Check Position Feedback

Using the diagnostic screen on the FANUC control, monitor the position feedback from the encoder for the affected axis. Look for erratic or inconsistent readings during slow manual movement.

Compare feedback values with actual movement to detect discrepancies.

Avoid rapid movements during testing to prevent further damage.

Test Encoder or Sensor

If feedback is inconsistent, test the encoder or position sensor using a multimeter or diagnostic tool as per the manufacturer’s guidelines. Replace or repair if defective.

Consult the machine’s wiring diagram to locate encoder connections for accurate testing.

Sensor replacement requires technical expertise; escalate if unsure.