506

Check DIAGNOSIS > I/O screen for limit switch status. Navigate to SYSTEM > DIAGNOSIS > I/O and verify X: +OT (or corresponding axis) shows '1' indicating active limit switch contact. Note the axis number 'n' in the alarm message.

Reset alarm and enter MANUAL mode with feedrate override at 0%. Press RESET, then manually jog axis in negative direction using handwheel or slow jog (5-10%) to retract from limit switch until I/O signal clears.

If axis will not move in jog mode, enable Parameter 1815#0 (OTL) = 1 temporarily to allow overtravel release. Return to 0 after clearing limit.

Verify machine reference point is correct. Execute RETURN TO ZERO sequence from SYSTEM > MANUAL > REF RETURN. Check Parameter 1815 (reference point return direction) and Parameters 1850-1854 (stored stroke limits) match machine mechanical travel.

Check software limit parameters to prevent recurrence. Verify Parameter 1320-1327 (software overtravel +) and 1420-1427 (software overtravel -) are set correctly with margin inside hardware limits. Typical margin is 5-10mm from hardware switch position.

After retracting from limit, verify stored reference position. Check DIAGNOSIS > PARAMETER > ABSOLUTE POSITION screen (SYSTEM > CURRENT > ABSOLUTE). Compare to machine mechanical reference position. Re-establish reference point if discrepancy exists.

Loss of absolute position requires re-homing with dog and grid reference procedure per machine builder specifications.

Check all active work coordinate offsets. Navigate to OFFSET SETTING > WORK COORDINATE and verify G54-G59.3 offset values. Excessive positive offset values on the alarmed axis will shift allowable travel into hardware limit zone.

Verify External Workpiece Offset is not active. Check Parameter 1201#3 (EWZ) and if enabled, confirm G54.1 P1-P48 offsets in OFFSET SETTING screen are appropriate. Check for unintended G10 L2 offset programming in active program.

Review Parameter 1240 (reference counter) for battery-backed absolute position systems. If battery voltage is low (check DIAGNOSIS > STATUS > BATTERY), absolute position may drift. Replace CNC battery and re-establish reference point.

Battery replacement requires Parameter 1815#7 (APZ) verification and careful re-homing procedure to avoid positional errors.

Physically inspect hardware limit switch on positive end of alarmed axis. Verify switch actuator arm, roller, or proximity sensor is not damaged, bent, or blocked. Check mechanical alignment with trip dog or cam on axis carriage.

Lockout/Tagout required. Ensure machine power is isolated per safety procedures before inspecting limit switches.

Test limit switch circuit continuity. With CNC powered off, disconnect limit switch wiring at switch and measure continuity. Normally-closed switches should show 0Ω when not actuated. Check wiring from switch to CNC I/O board (typically X8 connector on 0i/16i/18i, JD1A on 30i/31i/32i systems).

Verify limit switch signals at PMC ladder. Access PMC > LADDER MONITOR (SYSTEM > PMC > LADDER) and locate limit switch input addresses (typically X0.0-X0.7 for axis limits). Manually actuate switch and confirm signal change. Check for proper NOT logic if NC switches used.