13.3 Robotics & Automated Equipment

Task D-15 (Services robotics and automated equipment) is the smallest task on the exam at one question, but it is one that many candidates guess at. The millwright's role in a robot cell is mechanical: install and level the base, service the reducers and drivetrain, replace cable dress and end-of-arm tooling, diagnose mechanical backlash and vibration, and work safely inside the safeguarded space.

Robot Configurations

Specification terms: payload (mass at the wrist including tooling), reach (maximum distance to the tool centre point), repeatability (ability to return to the same taught point, typically 0.02–0.1 mm), and degrees of freedom (independent axes of motion).

Drivetrain, Encoders and Mastering

Each axis is driven by an AC servo motor through a very high ratio, very low backlash reducer:

• Harmonic drive (strain wave gearing) — a flexible spline deforming inside a rigid circular spline. Ratios of 50:1 to 160:1 in a compact package with essentially zero backlash. Common on wrist axes.
• Cycloidal / RV reducer — eccentric cycloidal discs rolling in a pin housing. Very high shock-load capacity and stiffness; used on the heavy base, shoulder and elbow axes.

Both are grease- or oil-lubricated with manufacturer-specific lubricant on a defined interval or hour count. Substituting an ordinary EP grease is a common and expensive mistake, because these reducers require specialty low-torque-ripple lubricants.

Encoders report axis position. Absolute encoders with battery backup retain position through a power cycle; incremental encoders must be homed on every start. When an encoder battery dies, the robot loses its position reference and must be re-mastered.

Mastering (zeroing / calibration) aligns each axis's encoder count to the physical zero position marked on the casting — either witness marks, a dial-indicator fixture, or a mastering pin. Any repair that separates a motor from its reducer, replaces a timing belt, or disturbs an axis requires re-mastering. Skipping it means every taught point in every program is now wrong, which is both a scrap and a collision hazard.

Millwright Preventive Maintenance Tasks

Backlash measurement is the key mechanical health check: lock the axis brake, apply a specified torque in each direction at the arm, and measure the movement at the tool centre point with a dial indicator. Growing backlash means reducer wear and a rebuild or replacement.

Brake testing matters on any axis that can fall. Servo brakes are fail-safe (spring-applied, electrically released). A weak brake on a shoulder axis lets the arm drop when power is removed — which is exactly why an arm must be supported before any drive component is removed.

Safeguarding: CSA Z434

In Canada, industrial robot systems are governed by CSA Z434 (Industrial Robots and Robot Systems), which adopts the international ISO 10218-1/-2 requirements. Provincial OHS regulations make compliance mandatory. The exam expects the concepts, not clause numbers.

The Safeguarded Space

The restricted space is the portion of the maximum space the robot can reach after limiting devices are set; the operating space is the portion actually used by the program; the safeguarded space is the area protected by the perimeter guarding. Access is controlled by:

• Fixed perimeter fencing with interlocked gates that command a protective stop when opened.
• Presence-sensing devices — safety light curtains, area scanners, pressure-sensitive mats — placed at a calculated safety distance based on approach speed and total system stopping time.
• Mechanical axis limits (hard stops) and software limits to restrict the working envelope.
• Emergency stops at the controller, at the teach pendant, and at each access point.

Teach Mode

Work inside the safeguarded space with the robot energized is only allowed in teach (manual reduced-speed) mode:

1. Motion is limited to 250 mm/s at the tool centre point.
2. The teach pendant must hold a three-position enabling device: motion is permitted only in the middle position. Releasing it (fear reaction) or squeezing it fully (startle reaction) both stop motion.
3. The person in the cell holds the pendant and exclusive control; the mode selector is key-switched and the key stays with them.
4. No other person may enter the cell, and automatic mode cannot be selected from inside the safeguarded space.

Full Lock-Out for Mechanical Work

Teach mode is not an energy-isolation state. Before mechanical disassembly, the millwright must:

• Lock out and tag the electrical supply and verify zero energy at the controller.
• Isolate and bleed pneumatic and hydraulic supplies to grippers and clamps.
• Support the arm mechanically — with a crane, sling or purpose-built stand — before removing a motor, brake or gearbox, because the servo brake is the only thing holding it.
• Block or discharge the counterbalance. Large articulated arms use a heavy spring cartridge or a gas cylinder to offset gravity on the shoulder axis. That stored energy will launch components if the balancer is unbolted while loaded — this is a documented cause of fatalities, and the manufacturer's balancer removal procedure must be followed exactly.

Automated Equipment Beyond the Robot

Robot cells sit inside a controlled system. The millwright interfaces with:

• Programmable logic controllers (PLCs) — the cell's sequence controller. A millwright is not expected to program one, but must understand that an input from a proximity sensor (inductive for metal, capacitive for non-metal), a photoelectric sensor, or a limit switch tells the PLC that a mechanical condition has been met, and that a mechanically misadjusted sensor target is a mechanical fault, not a controls fault.
• Servo and stepper positioning axes on gantries and indexers — ball screws, linear guides, and timing belts that need preload, alignment and lubrication.
• Vision systems whose accuracy depends on a rigidly mounted camera; loosening or bumping a camera bracket destroys calibration.
• Safety relays and interlocks — never bypassed, jumpered or defeated for troubleshooting convenience.