FANUC Maintenance & Troubleshooting of CNC Robots 4 — Questions and Answers
Question 1: A FANUC robot joint fails to move and displays SRVO-006 (Hand Broken). In a typical configuration, what triggers this alarm?
- The teach pendant is in HOLD state
- An end-of-arm tooling overload signal or broken-tool detection I/O input is active (Correct answer)
- The payload setting exceeds rated capacity
- The joint temperature sensor detected overheating
Correct answer: An end-of-arm tooling overload signal or broken-tool detection I/O input is active
SRVO-006 is triggered by an active signal on the configured hand-broken detection I/O input, which is typically wired to a tool crash sensor or pneumatic pressure switch.
Question 2: When performing FANUC joint mastering using the Master/Cal fixture method, the robot joints must be positioned at:
- Their software joint limit positions
- The zero-degree reference position defined by the mastering fixture marks (Correct answer)
- Full positive travel on all axes simultaneously
- The stored HOME position in the TP program
Correct answer: The zero-degree reference position defined by the mastering fixture marks
Fixture mastering requires aligning each joint to its physical zero-degree mark (witness line or tooling hole) so the pulse coder reference matches the mechanical zero position.
Question 3: During FANUC controller maintenance, the technician notices the SRAM battery alarm is active. What is the immediate risk if power is cycled without replacing the battery first?
- The servo amplifiers will be permanently damaged
- All SRAM-stored data (programs, mastering, system variables) will be lost (Correct answer)
- The robot will execute its last TP program automatically on power-up
- The teach pendant display will become corrupted
Correct answer: All SRAM-stored data (programs, mastering, system variables) will be lost
SRAM is volatile memory backed only by the controller battery; if power is cycled with a dead battery, all programs, mastering data, and system variables stored in SRAM are permanently erased.
Question 4: A FANUC robot axis moves in the wrong direction compared to taught positions after a motor replacement. The technician should:
- Swap two motor phase wires to reverse direction
- Check and correct the axis direction parameter ($DIR_PARAM) or perform re-mastering (Correct answer)
- Invert the encoder cable polarity
- Increase the servo gain to compensate
Correct answer: Check and correct the axis direction parameter ($DIR_PARAM) or perform re-mastering
Wrong-direction movement after motor replacement typically indicates the replacement motor has a different encoder phase or the axis direction parameter needs to be verified and corrected, followed by re-mastering.
Question 5: In FANUC CNC robotics, what is the purpose of the 'Torque Limit' instruction (TL[n]) in a TP program?
- It sets a maximum speed for the next motion instruction
- It limits the servo torque to protect workpieces or tooling during specific motion segments (Correct answer)
- It activates the regenerative braking mode for energy savings
- It adjusts the payload weight compensation algorithm
Correct answer: It limits the servo torque to protect workpieces or tooling during specific motion segments
TL[n] temporarily reduces the servo torque output to a percentage of maximum, used to prevent workpiece damage, detect obstructions, or protect tooling during force-sensitive operations.
Question 6: A FANUC robot's wrist joint (J4/J5/J6) cable unit requires replacement. After the replacement, which additional maintenance task is MANDATORY before returning the robot to production?
- Replacement of all three wrist servo amplifiers
- Full TCP (Tool Center Point) calibration and wrist joint mastering (Correct answer)
- Re-teaching of all I/O wiring in the controller
- Complete FROM memory initialization
Correct answer: Full TCP (Tool Center Point) calibration and wrist joint mastering
Replacing the wrist cable unit disturbs the wrist joint mechanical assembly, requiring re-mastering of the affected axes and TCP recalibration to ensure positional accuracy.
Question 7: What FANUC diagnostic utility allows a technician to run a motion test on a single axis without executing a TP program, typically used to isolate servo faults?
- MANUAL FCTRL (Functional Test)
- JOG mode with individual joint selection on the teach pendant (Correct answer)
- CYCLE START in step mode
- DCS position monitor test
Correct answer: JOG mode with individual joint selection on the teach pendant
Using Jog mode on the teach pendant with JOINT coordinate frame selected allows individual axis motion without a TP program, isolating whether a servo fault is axis-specific.
FANUC Maintenance & Troubleshooting of CNC Robots 4
A FANUC robot joint fails to move and displays SRVO-006 (Hand Broken).
In a typical configuration, what triggers this alarm?