Preventive and Predictive Maintenance Practices

Preventive and Predictive Maintenance Practices

Maintenance strategy determines whether a plant reacts to failures or prevents them. In a mechatronic or robotic system — where mechanical, electrical, pneumatic, and control elements all depend on each other — the right strategy saves money, protects workers, and keeps production running.

Three Maintenance Strategies

Corrective maintenance (CM) means you fix a system after it has already failed. A conveyor belt snaps, a robot servo alarm fires, or a pneumatic valve sticks — and production stops. CM is unavoidable for truly random failures, but relying on it alone leads to unplanned downtime, rushed repairs, and safety hazards from makeshift fixes.

Preventive maintenance (PM) uses a fixed schedule — based on elapsed time (hours, days, months) or operating cycles — to inspect, clean, lubricate, and replace components before they fail. PM tasks are drawn directly from the equipment manufacturer's maintenance manual. A FANUC robot, for example, specifies grease replenishment intervals for each joint axis in its maintenance documentation. Following those intervals, rather than guessing, is the correct approach. PM is predictable and easy to plan, but it can result in replacing parts that still have usable life, and it does not account for machines that are worked harder or in harsher environments than the baseline.

Predictive maintenance (PdM) monitors the actual condition of equipment and schedules service only when measurements indicate approaching failure. Common PdM techniques include:

• Vibration analysis — accelerometers detect changes in bearing or gear vibration signatures before mechanical failure occurs.
• Thermal imaging (infrared thermography) — an IR camera reveals hot spots in electrical panels, motor windings, and coupling assemblies that indicate loose connections, overload, or lubrication breakdown.
• Oil analysis — fluid samples from gearboxes and hydraulic systems are tested for metal particles, viscosity change, and contamination that signal internal wear.
• Current signature analysis — trending the current draw of a motor over time can reveal developing mechanical or electrical problems.

PdM maximizes component life and avoids unnecessary replacements, but it requires instruments, trained technicians, and data-management systems. It works best for high-value or high-consequence assets.

In practice, most facilities use all three strategies together: CM for minor incidental failures, PM for routine wear items on a manufacturer-defined schedule, and PdM for critical equipment where early warning pays for the monitoring cost.

Building a PM Schedule

A PM schedule is a table that lists every maintainable component, the specific task, the interval, the accept/reject criterion, and any parts that must be stocked. The source for intervals and criteria must always be the manufacturer's maintenance documentation — not guesswork or habit. When you choose to adjust an interval (for example, shortening a lubrication interval because the robot operates in a wet environment), you must document the reason and the section of the manual that was your starting point.

A well-formed PM table row looks like this:

| Component | Task | Interval | Accept/Reject Criterion | Parts to Stock |

|---|---|---|---|---|

| Axis 1 gearbox | Inspect for grease leakage; re-grease per manual volume | Per robot manual schedule | No visible leakage; correct grease quantity applied | Manufacturer-specified grease |

| Air filter-regulator (FRL) | Drain bowl, inspect element, check regulated pressure | Daily / shift start | Bowl clear; element not cracked; pressure at setpoint | Filter element, bowl seal |

Every accept/reject criterion must be specific enough that any technician reading it reaches the same pass/fail decision. "Looks okay" is not acceptable; "no visible cracks, pressure within ±5 PSI of setpoint" is.

Safety Requirements for Maintenance Work

All maintenance activities — PM and PdM alike — must be performed under the correct hazard controls.

Lockout/Tagout (LOTO): Before any maintenance that requires removing a guard, reaching into a danger zone, or making contact with moving parts or electrical components, you must follow OSHA 29 CFR 1910.147 — the Control of Hazardous Energy standard. De-energize the machine, isolate every energy source (electrical, pneumatic, hydraulic, gravity), apply your personal lock and tag, and verify the absence of energy before proceeding. This procedure is non-negotiable.

Electrical safety: When work must be performed near energized circuits (for example, taking thermal images with the panel door open), follow NFPA 70E. This includes determining the arc-flash boundary and incident energy level, wearing the appropriate arc-rated PPE, and — whenever possible — working in a de-energized state with an energized-work permit if de-energization is truly infeasible.

Machine guarding: Temporary removal of guards during PM must be followed by immediate reinstallation and verification before restart. OSHA 1910.212 and NFPA 79 govern guarding requirements for industrial machinery.

Robot safety: For any work on or near industrial robots, apply ANSI/RIA R15.06 / ISO 10218. Even a robot in teach mode can move unexpectedly. Use restricted-speed modes, enable safeguards, and never assume a robot is safe because it appears stopped.

Why This Matters for Your Career

The BLS reports that electro-mechanical and mechatronics technicians maintain and troubleshoot automated equipment working alongside engineers. Employers expect you to read a maintenance manual, extract the correct intervals, and build a schedule that prevents costly downtime — not just respond after a machine has already stopped producing.