SRVO-004

Visual inspection of all safety gates

Walk the entire safety perimeter and verify all gates, doors, and access panels are fully closed and latched. Check for gates that appear closed but haven't engaged the interlock switch completely - they may need to be opened and re-closed firmly.

Do not bypass or override safety interlocks. Ensure the robot cell is clear of personnel before restoring servo power.

Check safety I/O status on teach pendant

From the teach pendant: Press MENU > I/O > Digital > Filter by 'FENCE' or check DI signals starting around DI[9]-DI[16] (typical fence inputs). Look for the specific input showing OFF (0) state. Note the input number for further diagnosis.

On dual-check safety systems, you'll see pairs of inputs (FENCE1/FENCE2). Both must be ON for the alarm to clear. If only one is OFF, check that specific switch.

Verify gate latch and strike alignment

Check that gate latches are properly aligned with their strike plates. Worn hinges or loose mounting can cause gates to sag, preventing proper switch actuation even when the gate appears closed. Adjust gate position or replace worn hardware as needed.

Use a flashlight to look for shiny wear spots on latch hardware - this indicates misalignment or excessive play in the mechanism.

Reset alarm and restore servo power

After confirming all gates are secure and I/O shows all fence inputs ON: Press and hold SHIFT, then press RESET on the teach pendant. If alarm clears, enable servo power by pressing and holding the deadman switch to detent position, then press FCTN > Enable (or FWD+Deadman for cyclic enable).

Verify the work area is clear and announce 'ENABLING SERVO POWER' before restoring power to the robot.

Test switch actuation mechanically

With the gate closed, manually press the interlock switch actuator (plunger or roller) to verify it moves freely and clicks audibly. If no click or binding is felt, the switch mechanism may be failed. Check for physical damage, debris, or corrosion on the switch body.

Do not force stuck switches - replace them. Forcing can cause internal contact damage or safety mechanism failure.

Verify switch actuation with gate movement

Slowly close the gate while watching the digital input status on teach pendant (MENU > I/O > Digital > appropriate input). The input should transition from OFF to ON at a specific gate position (typically 2-3 inches before full close). If it doesn't change or is erratic, the switch position needs adjustment or replacement.

Mark the actuation point with tape - this helps identify if the switch position drifts over time during routine checks.

Check switch mounting and adjustment

Verify the interlock switch is securely mounted with no loose bolts. Check that the gate striker or actuator cam aligns properly with the switch roller/plunger within the manufacturer's specified travel distance (typically 4-6mm total travel). Adjust mounting brackets if needed to achieve proper actuation.

Most safety switches require the actuator to travel beyond initial contact - check the switch datasheet for 'operate point' vs 'release point' specifications.

Test switch continuity at terminal strip

With robot servo power OFF and LOTO applied, use a multimeter to check switch continuity at the controller terminal block. Gate closed should show continuity (0 ohms) across the normally-closed contacts. Open gate should show open circuit. If readings are incorrect, trace wiring or replace the switch.

Apply proper Lockout/Tagout procedures before testing electrical circuits. Verify zero voltage before touching any terminals.

Review switch replacement history

Check maintenance logs for this gate's switch replacement history. Safety switches have a rated lifecycle (typically 100,000-500,000 operations). High-traffic gates may need preventive replacement annually. Consider upgrading to monitored safety switches with diagnostic feedback if failures are recurring.

Install a mechanical counter on frequently-used gates to track operations and schedule predictive maintenance before failure occurs.

Identify fence circuit configuration

From teach pendant: MENU > SYSTEM > Config > Safety Config (password required). Review the fence input configuration. Navigate to MENU > I/O > I/O Config and note which DI inputs are assigned to *FENCE, *SFSPD, or safety chain signals. Check connection diagrams for your specific controller configuration (typically in FANUC Operator's Manual Section 3).

Take a photo of the I/O Config screen and safety circuit diagram for your records - this saves time during future troubleshooting.

Inspect controller terminal connections

Open the controller cabinet door and locate the fence input terminals (typically on JD1A or JD1B connector blocks, inputs XI9-XI16 range). Check for loose wire terminals, corrosion, or burn marks. Gently tug each wire to verify secure connection. Tighten any loose terminals to manufacturer torque specs (typically 0.5-0.6 Nm for signal terminals).

Even with servo power OFF, live voltage may be present in the controller cabinet. Verify your facility LOTO procedures before accessing internal components.