FANUC Maintenance & Troubleshooting of CNC Robots 3 — Questions and Answers
Question 1: Alarm SRVO-047 (HVAL Alarm) appears on a FANUC robot. What does this indicate?
- High ambient temperature in the controller cabinet
- High voltage detected in the servo amplifier DC bus
- Hardware velocity exceeded the axis speed limit (Correct answer)
- Hard stop contact on a limit switch
Correct answer: Hardware velocity exceeded the axis speed limit
SRVO-047 HVAL (Hardware Velocity Alarm) triggers when an axis velocity exceeds the maximum hardware speed limit, often caused by runaway servo or loose encoder coupling.
Question 2: When using FANUC's Dual Check Safety (DCS), a 'Position/Speed Check' violation alarm does NOT reset automatically after clearing. What must the technician do?
- Replace the DCS safety board
- Perform a DCS configuration backup and restore
- Cycle power and confirm the robot is within the safe zone before resuming (Correct answer)
- Delete the DCS parameters and reconfigure from scratch
Correct answer: Cycle power and confirm the robot is within the safe zone before resuming
DCS safety alarms require the robot to be physically moved into a safe position and a deliberate operator action (power cycle + confirmation) before the safety system resets.
Question 3: A FANUC R-30iB controller shows a PRIO-155 alarm (User alarm). Where would a maintenance technician find the custom description text for this alarm?
- In the ALARM History detail screen
- In the TP program UALM[ ] configuration under MENU > SETUP > Alarm (Correct answer)
- In the SYSVAR $UALM_MSG variable array
- In the controller's error log CSV export
Correct answer: In the TP program UALM[ ] configuration under MENU > SETUP > Alarm
User alarms (PRIO-155) are configured through MENU > SETUP > Alarm, where each UALM[n] entry can have a custom description string assigned by the programmer.
Question 4: To back up FANUC robot programs and system parameters to a USB drive, which image type preserves ALL data including mastering and calibration?
- TP-only backup (.TP files)
- ASCII backup (.LS files)
- IMAGE backup (SYSIMAGE.IMG) (Correct answer)
- Controller Configuration backup (.DG files)
Correct answer: IMAGE backup (SYSIMAGE.IMG)
An IMAGE backup (SYSIMAGE.IMG) creates a complete bit-for-bit copy of the FROM/SRAM memory including mastering data, calibration, system variables, and all programs.
Question 5: A FANUC robot's cycle time has gradually increased over several months. After checking programs, what maintenance item most likely contributes to this degradation?
- Outdated teach pendant firmware
- Mechanical wear increasing joint friction and reducing achievable speed (Correct answer)
- Too many TP programs stored in memory
- An expired robot license key
Correct answer: Mechanical wear increasing joint friction and reducing achievable speed
As harmonic drives and bearings wear, increased friction forces the servo system to reduce speed to stay within torque limits, gradually increasing cycle time.
Question 6: Which FANUC system variable should a technician check to verify the remaining battery voltage for SRAM memory backup?
- $BATT_VOLT (Correct answer)
- $PARAM_SVOLTA
- $MOR_CFG.$BATTERY
- $SCR.$BATT_ALM_LVL
Correct answer: $BATT_VOLT
$BATT_VOLT stores the current measured voltage of the controller's SRAM backup battery, allowing technicians to confirm battery health without external measurement.
Question 7: A FANUC CNC robot produces chatter marks on a machining workpiece only at certain path segments. The most appropriate first diagnostic step is to:
- Replace the spindle motor immediately
- Review the path using FANUC's Fine Motion or Servo Tuning screen to identify velocity oscillation (Correct answer)
- Increase feed rate to pass through the resonant frequency zone
- Disable look-ahead function in the CNC parameters
Correct answer: Review the path using FANUC's Fine Motion or Servo Tuning screen to identify velocity oscillation
Servo Tuning / Fine Motion monitoring displays velocity, torque, and positional error in real time, allowing identification of the specific motion segment causing oscillation before making hardware changes.
FANUC Maintenance & Troubleshooting of CNC Robots 3
Alarm SRVO-047 (HVAL Alarm) appears on a FANUC robot.
What does this indicate?