Recovering an Axis That Hit a Hard Stop

Stop and secure the cell

Confirm the robot is fully stopped and apply lockout/tagout before any physical inspection near the impacted axis. Keep everyone clear of the arm, since a joint resting against a stop can still hold stored energy in the drive train.

Caution: Treat the axis as loaded until you have confirmed it is at rest and drive power is isolated.

Read the alarm log before touching anything

Note the active alarm. SRVO-005 Robot overtravel means the axis has moved beyond a hardware limit switch, and the manual notes the *ROT overtravel signal is processed inside the mechanical unit rather than at the end-effector connector. If SRVO-050 Collision Detect also latched, the servo software saw an abnormally high disturbance torque, which is a second sign of a real impact.

Understand the three travel layers

FANUC limits each major axis with software soft limits set on the Axis Limits screen, a hardware overtravel input, and a physical mechanical stopper. The manual is explicit that mechanical stoppers and limit switches work together with the software joint range, and that the stoppers must be adjusted to match the software settings. Knowing which layer the axis reached tells you how hard the hit was.

Inspect the hard stop and axis housing

With power still locked out, inspect the hard stop, the axis casting, and the reducer area for cracking, deformation, a loosened or dislodged stopper, or displaced grease. Compare the stopper against its documented position, because a stopper knocked out of alignment no longer matches the software soft limit.

Caution: A cracked or shifted mechanical stopper is a safety-critical part. Do not return the robot to service until a qualified technician has assessed or replaced it.

Check cabling and connectors at the base

Inspect the robot connection cables and the RMP1 and RP1 connectors at the base for bent pins, cuts, or kinks that the impact may have caused. A damaged overtravel or feedback line can turn a one-time hit into recurring faults later.

Open the overtravel release screen

On the teach pendant, reach the overtravel release screen where the [OT release] and [System OT release] items appear. This is the documented path for releasing an axis that is sitting in the overtravel state, the same screen used at installation when the J2 and J3 axes ship pressed against their hard stops.

Release the axis from overtravel

Select the OT release item to release each robot axis from the overtravel state. Hold down the SHIFT key and press the alarm release key to reset the alarm condition, then, still holding SHIFT, jog the axis to bring it back into the movable range. Move slowly and watch the joint clear the stop before building any speed.

Caution: This temporary release exists to let you jog off the stop under control. Correct the cause of the impact first, and never wire out or short the overtravel signal to keep running.

Jog off the stop at reduced speed

Keep the pendant in a manual reduced-speed mode and jog the axis away from the stop in the correct direction. If the alarm re-latches immediately, you are likely jogging further into the stop, so reverse the jog direction and try again.

Release the brake only if the axis will not jog

If a joint stays pinned and cannot be jogged, the manual allows releasing the brake on the manual brake control screen, or using the brake release unit in an emergency such as a person pinched by the robot. Support the arm first, because a released brake lets a gravity-loaded joint drop or spring up.

Caution: A released holding brake removes the only thing keeping a de-energized joint in place. Block and support the arm and keep hands clear before releasing any brake.

Check for mastering or pulse loss

Review the log for a battery-zero-alarm SRVO-062 (BZAL) or a pulse-mismatch condition, either of which points to lost position data. The manual ties a BZAL or pulse-mismatch alarm to needing mastering, so a hard hit that also disturbed feedback may leave the axis without valid absolute position.

Re-establish the pulse if it was lost

If SRVO-075 Pulse not established is present, the absolute position of the Pulsecoder cannot be set yet. Reset the alarm and jog the affected axis until the alarm stops recurring, which lets the Pulsecoder establish a stable absolute count before you attempt any mastering.

Verify or restore mastering on the Master/Cal screen

Open the Master/Cal screen through MENU, SYSTEM, then F1 [TYPE] and Master/Cal, with $MASTER_ENB set to 1 or 2. Depending on the failure, use Quick Master for a battery-loss-style position loss, or Single Axis or Fixture Position Master when a Pulsecoder was disturbed, following the mechanical-unit manual for the reference position.

Caution: Mastering sets the robot zero. An incorrect master shifts every taught point, so verify against a known reference before running programs.

Calibrate and confirm position

After mastering, select 7 CALIBRATE on the Master/Cal screen, or cycle controller power, since calibration runs at every power-up. Confirm the screen reports the robot as calibrated and that the current joint angles read as expected for the pose it is in.

Measure for mechanical damage

Use a dial indicator to check the impacted joint for new backlash or misalignment, comparing against baseline values if you recorded them earlier. A joint that reads more play than before the hit points to reducer or bearing damage that a mastering pass will not fix.

Verify payload and load settings

Confirm the load setting on the controller still matches the actual tooling and part. The manual warns that wrong payload data causes vibration and mis-detection of collision, so a stale load setting can make the recovered axis fault again during testing.

Run a low-speed function test

In a manual reduced-speed mode, cycle the axis through its range and listen for noise, vibration, or resistance that was absent before the impact. Watch the position and overtravel status on the monitor screen while you move, and stop at once if a collision or overtravel indication returns.

Recheck the Axis Limits and stopper agreement

Open MENU, 6 SYSTEM, F1 [TYPE], Axis Limits and confirm the lower and upper joint limits are the intended values in degrees. Cycle controller power to enable any change, and confirm the mechanical stopper position still agrees with the software limit so the soft limit stops the axis before the hard stop again.

What can go wrong: overtravel will not clear

If the axis stays in overtravel after the release-and-jog sequence, you are usually jogging toward the stop, or the joint has not yet moved back inside the software range. Reverse the jog direction, and if the alarm persists with the axis clearly inside range, inspect the overtravel switch and its wiring rather than forcing the drive.

What can go wrong: collision detect keeps latching

Repeated SRVO-050 Collision Detect alarms during recovery point to real mechanical load, not a nuisance trip. Check whether the joint is still binding on the stop, whether the brake actually released, and whether the load settings are valid before trying to move again.

Caution: Do not raise the collision detection threshold to push past a recurring alarm. Find and remove the mechanical cause first.

Investigate why the impact happened

Determine the root cause, such as a program taught outside the intended range, a failed soft-limit setting, or a bad frame, and correct it before releasing the cell. A repeated hard-stop impact compounds mechanical damage, so the fix has to hold before production resumes.