Robot Anatomy: Mechanical and Electrical Systems
Objective. Students label all major mechanical and electrical components of a FANUC 6-axis robot and explain the function of each axis, servo drive, controller module, and teach pendant.
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.
Robot Anatomy: Mechanical and Electrical Systems
Before you jog a single joint or write a single program line, you need to know the machine you are working with. A FANUC 6-axis industrial robot is a tightly integrated system of mechanical structures, electric drives, and electronic controls. Understanding each part — what it is, where it is, and what it does — is the foundation of safe, competent robot operation and maintenance.
Safety First: LOTO Before You Touch
Any time personnel enter the robot work envelope or open the controller cabinet for inspection, the robot must be de-energized and locked out under OSHA 29 CFR 1910.147 (Control of Hazardous Energy — Lockout/Tagout). Isolate the main disconnect on the controller cabinet, apply your personal lock and tag, and verify zero energy by attempting a power-on. Follow NFPA 70E electrical safety practices: confirm the absence of voltage with a calibrated meter before touching any conductors. Machine guarding requirements under OSHA 1910.212 and robot-specific safeguarding under ANSI/RIA R15.06 / ISO 10218 must be in place whenever power is restored. Never bypass or defeat the E-stop chain or light curtains.
The Six Axes: Motion and Naming
A FANUC 6-axis articulated robot has six rotary joints, each called an axis and numbered J1 through J6. Think of the robot as a mechanical arm:
- J1 — The base rotates the entire arm left and right (rotation about a vertical axis).
- J2 — The lower arm pivots forward and backward from the base.
- J3 — The upper arm pivots up and down relative to J2.
- J4 — The wrist roll rotates the forearm about its own long axis.
- J5 — The wrist pitch tilts the end of the arm up and down.
- J6 — The wrist yaw (or flange rotation) spins the tool mounting flange.
Each axis has a defined software limit in the positive (+) and negative (−) direction, measured in degrees. The robot's control system prevents motion beyond these limits under normal operation.
Mechanical Components
Structural links — Cast iron or aluminum castings that form the base, lower arm, upper arm, and wrist. They carry loads without flexing.
Servo motors — Each axis is driven by a dedicated AC servo motor mounted at or near its joint. The motor converts electrical energy into controlled rotary motion.
RV (Rotate Vector) reducers and harmonic drives — These precision gearboxes reduce the high speed, low torque of the servo motor to the low speed, high torque needed to move the arm accurately. RV reducers are common on J1–J3 (heavier loads); harmonic drives appear on the smaller wrist axes J4–J6. These components define the robot's mechanical stiffness and repeatability.
Brakes — Each servo motor includes a spring-applied, electrically released brake. When power is off, the brake holds the axis in position. During the physical tour, you will locate the brake-release connectors — important because manually releasing a brake on a loaded axis can cause sudden, unexpected motion. Use extreme caution and only release brakes per the maintenance manual procedure.
End-of-arm tooling (EOAT) flange — The J6 mounting plate accepts grippers, welding torches, or other tools. It carries the tool center point (TCP) that the robot's frame math references.
Electrical Drive System
Servo amplifiers (drives) — Located inside the controller cabinet, each servo drive takes DC bus power and converts it to precisely timed three-phase AC current to run its servo motor. On an R-30iB controller you will typically see a servo amplifier rack with individual drive modules, one per axis (some multi-axis modules combine J4–J6). Each drive communicates with the main CPU via a high-speed serial link and receives encoder feedback from the motor.
Pulse coder (encoder) — Mounted on the back of each servo motor, the pulse coder sends position and speed feedback to the servo drive. This feedback loop is what gives the robot repeatable, precise positioning.
DC bus / power supply module — Converts incoming AC line voltage (typically 480 V three-phase in US industrial installations) to the DC bus voltage that feeds the servo drives. This module also manages regenerative braking energy returned by decelerating motors.
Controller Architecture
The R-30iB (or equivalent) controller cabinet contains:
- Main CPU board — Runs the FANUC operating system, executes robot programs, manages motion planning, and coordinates all modules.
- I/O PCB (I/O terminal blocks) — Provides discrete digital inputs and outputs (DI/DO) that connect the robot to external devices such as conveyors, sensors, grippers, and safety relays. During the tour you will trace wiring from field devices to these terminal blocks.
- E-stop safety relay chain — A hardwired safety circuit, separate from the CPU, that cuts servo power immediately when any E-stop button or safety device opens. Tracing this chain — from the teach pendant E-stop mushroom through the safety relay module to the servo amplifier enable signal — is a required lab activity.
- Teach pendant (TP) — The hand-held programming and jogging interface. It includes an LCD/touch screen, a deadman (enabling device) that must be held in the middle position for robot motion in manual mode, an E-stop mushroom button, and function keys. The TP communicates with the main CPU over a serial or Ethernet link.
- Cooling fans and thermal management — Cabinet fans maintain safe operating temperature for electronics.
Safeguarding Devices in the Cell
Light curtains — Electro-sensitive safety devices that create an invisible detection plane at the cell entrance. Breaking the beam opens the E-stop chain. Governed by ANSI/RIA R15.06.
Safety fence and interlocked gates — Physical barriers with door switches wired into the safety relay chain.
ROBOGUIDE — FANUC's offline simulation software, used in this program to program and visualize robot motion before running live hardware. It mirrors real controller behavior.
Putting It Together
A block diagram of the robot system flows like this: AC line power → power supply module → DC bus → servo drives → servo motors → joints → robot links → TCP. Simultaneously, the main CPU sends motion commands to the drives, receives encoder feedback, monitors I/O, and communicates with the teach pendant. Safety devices feed into a hardwired E-stop chain that can cut servo power independently of the CPU. Knowing this architecture lets you trace a fault logically: no motion on J3? Check the J3 drive module, its enable signal, the pulse coder cable, and the motor brake.
Key terms10
Materials: FANUC robot (R-2000 series or equivalent), FANUC controller (R-30iB or equivalent), FANUC maintenance manual for the cell robot, component-matching card set (instructor-prepared), lab notebooks, block-diagram worksheet
Check: Completed block diagram and worksheet checked by instructor; students must correctly identify all six axes, the teach pendant, E-stop chain, and at least four controller modules with function descriptions. Pass = 80% accuracy.
Practice check8
Answer each question, then check it. Nothing is recorded; this is your own practice.
