SRVO-036

Identify the faulting axis from alarm details

Press RESET to clear the alarm, then press ALARM → F1 (DETAIL) to view the alarm history. Note which axis number (1-6) is listed in the alarm detail. This is the joint requiring investigation.

The alarm detail screen shows the exact axis number and may include the position error value at timeout, which helps gauge severity.

Perform manual axis movement test

With servo power OFF, manually rotate the faulting axis through its full range of motion. Feel for binding, rough spots, excessive play, or grinding sensations. Compare the feel to adjacent axes. Loose joints will have noticeable play before the brake engages.

Ensure all personnel are clear and E-stop is accessible. Large robots may require two people to safely move axes manually.

Inspect joint mechanical components

Visually inspect the faulting joint for loose mounting bolts, worn harmonic drive components, leaking grease, or damaged seals. Check motor mounting bolts, encoder mounting, and any external cable connections to the joint. Torque critical fasteners to specification if loose.

J3 (elbow) and J4 (wrist roll) are most prone to wear on high-duty-cycle applications. Listen for unusual grinding or clicking during powered slow-speed movement.

Check for payload mounting issues

Verify that any end-of-arm tooling or payload is securely mounted to the robot flange. Loose tooling can cause oscillation at stop positions. Check all tool mounting bolts and clamps for proper torque.

Improperly secured payloads can shift during motion and cause injury or equipment damage.

Monitor axis settling behavior during motion

Execute a slow test program with the faulting axis. Watch the axis as it comes to each stop position. Look for visible oscillation (back-and-forth movement) or slow drift before settling. Note whether the behavior is consistent or intermittent.

Reduce override to 5-10% and use a program with simple point-to-point moves to isolate the settling behavior without acceleration effects.

Review current servo gain parameters

Navigate to MENU → SYSTEM → Variables → $GAIN_SERVO[GP:1,axis]. Note the current gain values. Compare to factory defaults or known-good backup values. Check $SERVO parameters for the faulting axis including GN1 (position loop gain), GN2 (velocity loop gain), and damping parameters.

Factory default gains are stored in the controller and can be referenced from MENU → MAINTENANCE → Servo → Servo Setup. Take screen photos before making changes.

Reduce servo gains incrementally if oscillation observed

If oscillation is visible, reduce the position loop gain (GN1) by 10-20% for the faulting axis. Navigate to MENU → SYSTEM → Variables → $GAIN_SERVO and modify the value. Test motion after each change. If drift is the issue rather than oscillation, gains may need slight increase instead.

Incorrect servo tuning can cause instability, excessive motor heating, or damage. Document original values before changes and make small incremental adjustments only.

Perform servo optimization if available

For R-30iB controllers with servo tuning software, run the automatic servo optimization routine: MENU → MAINTENANCE → Servo → Servo Setup → F5 (OPTIMIZE). Select the faulting axis and execute. This performs automatic tuning based on actual system response.

Optimization should be run with actual production payload mounted. Results vary significantly based on inertia. Save gain sets for different tooling configurations if you frequently change end effectors.

Verify damping and filter parameters

Check servo damping parameters at MENU → SYSTEM → Variables → search for $DMF (digital motor filter) and $DAMPNG parameters. Excessive filtering can slow settling time. Insufficient damping allows oscillation. Verify values match application requirements and payload inertia.

Higher payload inertia typically requires increased damping. J4-J6 wrist axes with long tooling often need damping adjustment when tooling changes.

Review in-position check parameters

Navigate to MENU → SYSTEM → Variables and search for $MOR_GRP.$IN_POS_CHK (in-position checking enable). Verify it is set appropriately. Then check $MOR_GRP.$INPOS_TIME (timeout duration in milliseconds) and $MOR_GRP.$INPOS_TOLER (position tolerance in degrees/mm per axis).

Default timeout is typically 500ms. Default tolerance is usually 0.02-0.05 degrees for rotary axes. These can be viewed as an array with separate values per axis.

Check position error at alarm occurrence

When the alarm occurs, check the actual position error magnitude. Press ALARM → F1 (DETAIL) immediately after the alarm. Some controller versions display the position error value that exceeded tolerance. Compare this to the tolerance parameter to see how far outside the window the axis was.

If the position error is only slightly larger than tolerance (within 2x), widening the tolerance is often the appropriate fix. If error is much larger, a mechanical or tuning issue is more likely.