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MFG-MECH15-06 · Lesson 10 · 14 clock hours · lab

Preventive Maintenance: Inspection, Lubrication, and Battery Service

Objective. Students complete a scheduled preventive maintenance inspection on a FANUC robot following the manufacturer's checklist, including battery voltage check, grease-nipple identification, teach pendant cable inspection, and brake-release test.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed engineer or certified journey-level tradesperson or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.

Why Preventive Maintenance Matters

A FANUC robot is a precision electromechanical system. Bearings, grease, cables, batteries, and brake hardware all degrade with time and use. A structured preventive maintenance (PM) program catches problems before they become unplanned downtime, costly repairs, or safety hazards. FANUC publishes a maintenance manual that includes a PM schedule organized by interval — daily, monthly, quarterly, annually, and by operating hours. Following that schedule exactly, and recording every result, is the foundation of professional robot maintenance.

Safety Before You Touch Anything

All PM work begins with energy control. Apply lockout/tagout (LOTO) per OSHA 29 CFR 1910.147 before opening controller panels, touching internal components, or working near robot joints. Each energy source — mains power, pneumatics, any stored energy in capacitors — must be isolated and verified de-energized. After lockout, attempt to restart: if nothing moves and no indicator energizes, LOTO is effective.

For electrical measurements (battery voltage, fan continuity, E-stop chain), use NFPA 70E guidance: verify absence of voltage with a properly rated meter before contacting any conductor, and wear appropriate PPE (safety glasses, nitrile gloves rated for the voltage level, arc-flash PPE if required by a hazard assessment).

Robot cell perimeter guarding must remain in place during all PM work except specific tests that require controlled, supervised access. Follow ANSI/RIA R15.06 / ISO 10218 safeguarding requirements: if a safeguard must be bypassed temporarily, use an enabling device and follow the robot manufacturer's documented procedure.

Machine guarding (OSHA 1910.212): never reach into a robot work envelope without LOTO confirmed or a documented safe-speed enabling procedure.

The PM Checklist Walkthrough

The FANUC maintenance manual lists specific items to inspect at each interval. A PM log is not optional — it is the legal and quality record of work performed. Work through each item in order and record Pass, Fail, or Due (meaning the item is not due yet at this interval).

Typical checklist items include:

Battery Voltage Check and Replacement

FANUC controllers use backup batteries to retain program memory (teach points, system variables) when main power is off. When battery voltage drops below the manufacturer's threshold, the controller generates a low-battery alarm. If the battery fully discharges and power is removed, all stored programs and parameters may be lost.

Measuring battery voltage:

1. With the controller powered on (reducing risk of data loss), set your multimeter to DC voltage on an appropriate range.

2. Locate the battery connector in the controller cabinet — refer to the maintenance manual for exact location.

3. Touch meter probes to the correct terminals (observe polarity).

4. Record the reading and compare it to the manufacturer's specified nominal and minimum voltage.

Battery swap procedure:

FANUC specifies a maximum allowable power-off time during a battery swap. Keep replacement time shorter than this limit; the controller's capacitors maintain memory for that window. Steps: power on the controller, open the battery compartment, note the battery connector orientation, remove the old battery, install the compatible replacement, reconnect, close the compartment, verify the alarm clears. Document the battery type, lot, and date on the PM log.

Always use a compatible replacement battery specified by FANUC. Dispose of the old battery according to local regulations — lithium cells require proper disposal, not landfill.

Brake-Release and Axis-Drop Safety Test

FANUC robots use electromechanical brakes on each axis to hold position when servo power is removed. Over time, brake pads wear. The brake-release test verifies that brakes engage and release correctly and that the axis does not free-fall unexpectedly.

This test requires LOTO and physical support of the robot arm before any brake is released. If a brake releases on an unsupported axis, the arm will drop under gravity — potentially crushing a hand, damaging the robot, or breaking tooling. The brake-release fixture or support stand absorbs the load before the brake opens.

Procedure outline:

1. Apply LOTO per 1910.147. Physically support J2 or J3 with the brake-release fixture.

2. Follow the FANUC manual procedure to briefly activate the manual brake-release button for the selected axis.

3. Observe controlled, slow descent (or no movement if the arm is already at a mechanical stop) — not a free-fall drop.

4. Release the button; confirm the brake re-engages.

5. Record observations in your lab log. Explain in writing why physical support is mandatory: without it, gravity acts on the full arm mass the instant the brake opens, creating an immediate crush hazard.

Documentation

A PM log with no skipped items, signed by the technician and verified by the instructor, is the deliverable for this lab. Date, technician name, robot serial number or asset tag, battery voltage reading with pass/fail notation, and brake-release observations must all appear. Incomplete logs indicate the work was not done — in industry, that is a compliance failure.

Key terms9

Preventive Maintenance (PM) scheduleA manufacturer-specified list of inspection, lubrication, and service tasks organized by time interval or operating hours to keep equipment reliable and safe.
Backup batteryA battery inside the robot controller that retains program memory, teach points, and system variables when main power is switched off; must be replaced before voltage drops below the manufacturer's minimum threshold.
Brake-release fixtureA mechanical support stand or jig that bears the weight of a robot arm segment before the axis brake is manually released, preventing uncontrolled arm drop.
Lockout/Tagout (LOTO)The energy-control procedure required by OSHA 29 CFR 1910.147 that isolates all hazardous energy sources and verifies de-energization before maintenance work begins.
E-stop chainThe series safety circuit connecting all emergency-stop devices (teach pendant, operator panel, fence interlocks); if any device opens the circuit, servo power drops immediately.
Controller air filterA foam or fiber filter on the robot controller cabinet intake that prevents dust from entering and must be cleaned or replaced on schedule to maintain adequate cooling airflow.
PM logThe written record of each checklist item inspected, its result (pass/fail/due), the technician's name, the date, and any corrective actions taken; serves as the quality and compliance record.
ANSI/RIA R15.06 / ISO 10218The industrial robot safety standard specifying safeguarding requirements, safe distances, and procedures for collaborative and traditional robot installations.
NFPA 70EThe standard for electrical safety in the workplace, covering arc-flash and shock boundaries, PPE selection, energized-work permits, and the requirement to verify absence of voltage before contact.

Worked examples4

1. A FANUC controller backup battery reads 2.85 V DC on a multimeter. The manufacturer's specification states nominal voltage is 3.6 V and the minimum acceptable voltage is 3.0 V. Is this battery within spec, and what action is required?
  1. Compare measured voltage to the minimum specification: 2.85 V < 3.0 V minimum.
  2. The measured voltage is below the manufacturer's minimum threshold, so the battery fails the PM check.
  3. Action required: replace the battery immediately using the swap procedure, keeping power-off time within the manufacturer's maximum allowable window to avoid memory loss.
  4. Record on the PM log: measured voltage = 2.85 V, spec minimum = 3.0 V, result = FAIL, battery replaced, date and technician signature.
Answer: The battery fails (2.85 V is below the 3.0 V minimum). Immediate replacement is required.
2. During a brake-release test on J2, a student measures that the arm descends 8 mm in 2 seconds when the brake button is held, then stops when the button is released. The support fixture is holding the arm. Is this result acceptable, and what should the student record?
  1. Confirm that the fixture was in place before the brake was released — this is the mandatory safety prerequisite.
  2. The arm moved a small amount (controlled descent) and stopped when the brake re-engaged. This indicates the brake releases and re-engages as designed.
  3. There was no free-fall drop, which would indicate a worn or failed brake.
  4. Record in the lab log: J2 brake-release test — controlled descent observed with fixture supporting arm; brake re-engaged upon button release; result PASS. Note why the fixture is mandatory: releasing a brake on an unsupported arm creates a gravity-driven crush hazard equal to the full mass of the arm segment.
Answer: Result is acceptable. The brake released and re-engaged correctly with no free-fall. The fixture was correctly in place. Record as PASS with the safety explanation.
3. A technician is scaling a 4–20 mA sensor signal to a robot controller analog input. The sensor output is 12 mA. The engineering range is 0 to 100 °C. What temperature does 12 mA represent?
  1. Identify the live zero and span: 4 mA = 0 °C (live zero), 20 mA = 100 °C (full scale). Span in mA = 20 − 4 = 16 mA. Span in °C = 100 − 0 = 100 °C.
  2. Calculate the fraction of span the measured signal represents: (12 mA − 4 mA) / 16 mA = 8 / 16 = 0.50.
  3. Apply that fraction to the engineering span: 0.50 × 100 °C = 50 °C.
  4. The sensor is reading 50 °C at 12 mA.
Answer: 12 mA corresponds to 50 °C.
4. During the controller air filter inspection, a technician notes the filter is visibly clogged with metal dust. They use shop compressed air directed inward (from outside the filter) to blow it out. Identify the error and state the correct technique.
  1. Error: blowing compressed air inward drives contamination deeper into the filter media and into the cabinet interior, potentially depositing conductive metal dust on circuit boards.
  2. Correct technique: direct the compressed air from the clean side outward (from inside the filter frame toward the dirty outside face) so contaminants are expelled away from the cabinet.
  3. If the filter is damaged, saturated with oil, or too clogged to clean effectively, replace it with a compatible spare rather than attempting to clean it.
  4. Record the action (cleaned or replaced) and the filter condition on the PM log.
Answer: The error is blowing air inward. Correct technique is to blow outward from the clean side, expelling debris away from the controller. Replace the filter if it cannot be adequately cleaned.
In class: PM checklist walkthrough: using the FANUC maintenance manual PM schedule, students work through each item (teach pendant connector seating, cable abrasion inspection, controller air filter cleaning, fan operation verification, E-stop chain continuity check) and record pass/fail/due for each item on the PM log. · Battery voltage check and replacement procedure: students use a multimeter to measure controller backup battery voltage, compare to the manufacturer's specification, and practice the battery swap procedure on a training spare — noting the maximum allowable power-off time during swap to avoid memory loss. · Brake-release and axis-drop safety test: with the robot supported by the brake-release fixture and LOTO applied, students briefly activate the manual brake-release button for J2 or J3, observe controlled descent, and explain in their lab log why proper support is mandatory before brake release.
Materials: FANUC robot cell, FANUC maintenance manual (PM schedule section), PM log form, multimeter, replacement battery (compatible type), controller air filter, brake-release fixture or support stand, nitrile gloves, lab log
Check: PM log submitted with all checklist items completed and signed. Battery voltage recorded with pass/fail compared to specification. Lab log brake-release entry explains support requirement. Instructor signs PM log. Pass = completed log with no skipped items plus correct battery comparison.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Safety — LOTO / FANUC CERT Technician
1. According to OSHA 29 CFR 1910.147, what must a technician verify immediately after applying lockout devices and before beginning PM work inside a robot controller?
Preventive Maintenance — FANUC CERT Technician
2. A FANUC controller backup battery reads 2.7 V DC. The manufacturer specifies a minimum acceptable voltage of 3.0 V. What is the correct immediate action?
Safety — ANSI/RIA R15.06 / FANUC CERT Technician
3. Why is a brake-release fixture or support stand mandatory before manually releasing a robot axis brake during a PM test?
Preventive Maintenance — FANUC CERT Technician
4. During PM, a technician notices the teach pendant cable has a visible kink near the connector where insulation is cracked. What is the correct action?
Preventive Maintenance — FANUC CERT Technician
5. A controller air filter is clogged with dust. A technician uses compressed air to clean it. In which direction should the air be directed for safe, effective cleaning?
Safety — Siemens SMSCP L1 / PMMI Electrical
6. Which NFPA standard governs electrical safety practices — including arc-flash boundaries, PPE selection, and verifying absence of voltage — that apply when measuring battery voltage inside a robot controller?
Instrumentation / Analog Signals — PMMI / Siemens SMSCP
7. A sensor using a 4–20 mA signal represents a range of 0 to 200 PSI. The controller reads 16 mA. What pressure does this represent?
Safety — FANUC CERT / ANSI Robot Safety
8. Which safety standard specifically addresses industrial robot safeguarding requirements, including safe distances and procedures for working near robot work envelopes?
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