SRVO-072

Identify the affected axis

Check the alarm detail on the teach pendant under MENU > ALARM > F5 [DETAIL]. Note the specific axis number (J1-J6) generating the SRVO-072 alarm. Record the complete alarm history to identify if this is an intermittent or persistent fault.

If the alarm appears intermittently, check the alarm log timestamps (MENU > ALARM > F3 [HIST LOG]) to correlate with specific robot motions or environmental conditions like temperature changes.

Verify encoder feedback signals

Navigate to MENU > SYSTEM > F1 [TYPE] > Variables and check $POSN_FB[x] (position feedback) and $VEL_FB[x] (velocity feedback) for the affected axis. Compare values during slow jogging against expected encoder counts. Erratic or frozen values confirm encoder failure.

Enable deadman switch and use T1 mode at reduced speed (25% override) when jogging to verify feedback.

Check encoder cable and connections

Power down the robot controller completely. Inspect the encoder cable from the motor to the axis control board. Check connectors CN5A (motor side) and the corresponding axis connector on the servo amplifier for corrosion, bent pins, or loose connections. Measure cable continuity if physical damage is suspected.

Perform BZERO (cabinet zero) lockout procedure before accessing internal cabinet connections. Verify all E-stop circuits are engaged.

Replace the pulse coder

If diagnostics confirm encoder failure, replace the pulse coder assembly for the affected axis. After replacement, access MENU > SYSTEM > Variables and set $MCR.$SPC_RESET to TRUE (1) to reset the serial pulse coder data. This clears the encoder initialization flag.

Before removing the old encoder, record the current position from $POSN_FB and take a photo of any alignment marks. Some motors have witness marks for encoder alignment during reinstallation.

Re-master the axis and verify accuracy

After power cycling, perform single-axis mastering via MENU > SYSTEM > Master/Cal > F1 [SINGLE]. Use the Quick Master procedure if available, or master to mechanical reference. Verify mastering by jogging to known reference positions or tool calibration points and checking repeatability within ±0.02mm.

After mastering, run a slow test program with known positions and verify position error using $POS_ERR[x]. Values should remain under 0.05mm during motion. Use MENU > STATUS > POS_ERR to monitor real-time.

Check battery voltage and alarm history

Review alarm history (MENU > ALARM > F3 [HIST LOG]) for recent BATT-007 (low voltage) or BATT-011 (battery disconnected) alarms. Check current battery voltage via MENU > SYSTEM > Variables > $BATTERY_VOLTAGE. Voltage below 3.0V indicates immediate replacement needed.

Battery replacement must occur within 30 minutes of controller shutdown to prevent position data loss. Have replacement battery ready before powering down.

Replace controller battery if low

With controller powered ON, replace the battery pack (A98L-0031-0025 or equivalent for R-30iA/B). After replacement, monitor for 24 hours to ensure SRVO-072 does not reoccur. Battery issues may cause intermittent encoder data corruption.

Battery replacement should be performed every 2 years as preventive maintenance, even if no alarms are present. Log replacement dates in the controller's maintenance schedule.

Reset serial pulse coder data

If battery was depleted for extended period, encoder absolute position data may be corrupted. Set $MCR.$SPC_RESET to TRUE via MENU > SYSTEM > Variables. This forces the encoder to reinitialize on next power-up. Power cycle the controller completely (full shutdown, wait 30 seconds, restart).

On R-30iB controllers with absolute encoders, you can verify encoder battery status separately via system variable $SERIAL_ENC[x].$BATT_ALARM for each axis.

Re-master all axes after battery replacement

After battery replacement and power cycle, perform full robot mastering. Use MENU > SYSTEM > Master/Cal > F2 [ALL]. Follow the standard mastering procedure using zero position references or master tool. Verify all axes return to known positions accurately.

Do not operate the robot in production until all axes are properly mastered and accuracy is verified. Unmastered positions can cause collisions or part quality issues.

Inspect motor and encoder housing for contamination

Power down completely and inspect the motor housing and encoder assembly for the affected axis. Look for oil leakage from motor seals, coolant ingress, grinding dust, or metallic debris. Check encoder cable glands and motor shaft seals for integrity. Contamination often appears as residue around the encoder cover.

Lockout/tagout the robot and controller before inspecting motor assemblies. Ensure all stored energy is dissipated and brakes are engaged.

Check for mechanical damage or collision history

Review alarm history for COLL-001 (collision detect) or SRVO-050 (overload) alarms on the same axis. Inspect motor mounting bolts and encoder coupling for looseness or damage. Check motor shaft runout with dial indicator if collision is suspected - runout over 0.05mm can damage encoder optical components.

If robot experienced a collision, even if encoder appears intact, the optical disk may be cracked or misaligned internally. This often shows as intermittent SRVO-072 alarms during specific axis positions.