Tracing the Cause of a Following-Error Fault

Read the actual position error on the pulse screen

On the teach pendant open STATUS, Axis, then press [TYPE] and select PULSE. The Position Error column shows the servo delay in pulses, meaning the lag of the actual pulse count behind the command pulse for each joint J1 through J6.

Caution: A small position error is normal servo lag during motion. Treat only a large or growing value on the flagged axis as the fault signature.

Record the axis and compare the magnitude

Note which joint carries the excess error and how large it is relative to the others. The Machine Pulse and Motion Command columns on the same screen let you see whether the command was still advancing while the actual pulses stalled.

Rule out a physical collision or obstruction first

Inspect the axis path for a crash, cable snag, fixture interference, or tip stick that would resist motion. The servo software raises SRVO-050 Collision Detect when it estimates an excessively large disturbance torque, and a real collision is the first cause to confirm or clear.

Caution: Keep all personnel clear of the axis before any motion. Do not assume the alarm is a false trip until you have physically checked for interference.

Confirm the payload setting matches the real load

Wrong payload data causes vibration and mis-detection of collision, because collision detection and gravity compensation both depend on it. Press MENU, 0 NEXT, 6 SYSTEM, then [TYPE] and select Motion to reach the MOTION PERFORMANCE list of payload schedules 1 through 10.

Check the detailed payload values

Move the cursor to the active schedule and press DETAIL to open MOTION/PAYLOAD SET. Verify PAYLOAD in kg, PAYLOAD CENTER X, Y, Z in cm, and PAYLOAD INERTIA X, Y, Z in kgfcms^2 against the tooling data sheet, where X, Y, Z follow the default tool coordinate system.

Verify the armload setting

Press ARMLOAD to reach MOTION/ARMLOAD SET and confirm the weight of equipment mounted on the J2 base and J3 arm, which is gear mounted on the arm rather than on the faceplate. Missing armload entries make the dynamic model underestimate the true load.

Review program acceleration and ACC override

Heavy acceleration and rapid motion are listed causes of an estimated disturbance spike. If the program uses ACC override above 100, reduce it, since the SRVO-050 remedy calls out ACC override over 100 as a trigger.

Look at reverse moves and singularity passes

Rapid reverse motion that uses CNT termination and linear motion near a singularity, where axes swing at high speed, both drive the disturbance estimate up. Modify or slow those segments if the error tracks to one of them.

Read the disturbance torque per axis

Open the STATUS, Axis, DISTURB screen ([4 STATUS / Axis / DISTURB]). It shows Current, Max (Allowed), and Min (Allowed) disturbance torque in amps for each joint, so you can see how close the flagged axis ran to its allowed band.

Understand the collision-detect alarm level

The controller posts a disturbance-excess warning when torque passes the allowed value, and cuts servo power with SRVO-050 when it passes the alarm level. That alarm level is the Max allowed value plus 0.3 times the amplifier max current on the upper side, and the Min allowed value minus the same margin on the lower side.

Caution: The 0.3 times max current term is a margin against false trips. Do not raise the allowed values to silence a genuine collision, since that defeats a safety-critical stop.

Check for an overload current condition

If the axis instead posts SRVO-046 OVC, the internally calculated root-mean-square current exceeded the permissible value, a protection against thermal damage to the motor and amplifier. Its causes include overload, added friction from continuous very slow motion, and external force on the robot.

Caution: SRVO-046 requires a power cycle to release. Correct the load or duty cause before restarting, and do not simply reset and run.

Inspect motor, encoder, and brake cabling

Check the motor power cable and the brake cable for damage or an intermittent connection, both listed causes of a collision-detect trip. A brake that fails to release, or a mis-set brake number, loads the axis as if it hit an obstruction.

Check mechanical resistance and drivetrain wear

Increased friction from low temperature, a worn reducer, and a failing balancer are all listed contributors to a high disturbance estimate. With the axis powered and stopped, visually inspect the reducer, balancer, and drivetrain for leaks, damage, and wear. If a backlash measurement is needed, refer it to a qualified maintenance technician, since checking backlash can require releasing the axis brake.

Caution: Any backlash or brake check that could release a brake must follow lockout/tagout or the manufacturer-approved brake-check procedure. Block or support the axis against gravity before any brake is released, because a released brake can let the axis drop. Do not release brakes without proper support and authorization.

Verify the supply voltage to the controller

Insufficient torque from low supply voltage appears under both the collision-detect and overload causes. Measure the input voltage and confirm it matches the controller specification before blaming the mechanics. Measuring live input voltage inside the cabinet is a qualified-technician task using proper live-work practice; do not attempt it untrained.

Recover the robot from a collision safely

Once personnel are clear and the cause is understood, release SRVO-050 by holding SHIFT and RESET, releasing RESET while still holding SHIFT, then pressing a jog key to move the axis away from the collision. Move at reduced speed and only far enough to relieve the interference.

Caution: Route any repeated or unexplained collision-detect faults to a qualified maintenance technician. Never clear and rerun a collision or overload alarm without removing the cause first.

Test the corrected fault under full load

Run the program at production speed with the real payload and watch the Position Error and DISTURB screens. Confirm the servo delay stays small and the disturbance torque holds inside its allowed band.

Document the root cause and corrective action

Record the axis, the measured position error and disturbance torque, the identified cause, and the fix in the maintenance log. Note the correct payload schedule number so the next technician can confirm it quickly.

What can go wrong: the alarm returns at the same point

A fault that repeats at one program location usually points to that motion segment, not a random fault. Recheck acceleration, ACC override, and the singularity or reverse-CNT geometry at that point, and confirm the payload schedule active there is correct.

Caution: Do not edit the disturbance allowed values to push past a repeatable trip. Fix the motion or the load that causes it.

What can go wrong: overload only after slow motion

SRVO-046 OVC can appear after long stretches of very slow motion, which raises mechanical friction and heats the motor. Insert a medium-to-high-speed move into the program so the axis does not run only at crawl speed, as the OVC remedy directs.

What can go wrong: threshold was widened to mask a real fault

If a previous technician raised the DISTURB allowed values, a genuine collision or drivetrain fault can hide until it causes damage. Compare the allowed values against the measured normal disturbance for the program and restore a proper margin.

Caution: Widening the collision threshold to stop nuisance alarms removes real protection. Tune it only during commissioning, after the mechanical cause is ruled out, and never to hide an active fault.