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The axis is stopped and the real position still drifts further from the commanded one than is tolerated. This is different from excessive error in motion: here nobody is asking for movement, so if the position moves, something is moving it or something is not holding it. It nearly always points at the brake, at an external force, or at the feedback.
For reference only: alarms change with the manufacturer, the control and the machine PLC. Check the full code in the official manual before doing anything. Legal notice.
Always: indicates a servo/brake/encoder problem.
Reset only after removing load; If it returns, stop diagnosis.
Choose the manual matching your control series, software version and machine builder. A support portal is a starting point; it does not establish applicability to every model.
When an axis finishes a move, the position loop does not switch off: the control keeps commanding the same position and the servo keeps generating the torque needed to hold it. Following error at standstill should be practically nil, which is why the limit the control applies in this situation is far tighter than the one for motion. If the difference exceeds that limit with the axis stopped, the control concludes it has lost the ability to hold position and cuts out. The routes there are clear. One: an external force is overcoming the servo, such as the weight of a head whose holding brake is not gripping or has not engaged, the pressure of a jammed tool, or workholding pushing. Two: the axis is holding position mechanically but the feedback moves or drifts, because of an encoder problem or a loose encoder coupling, and the control sees movement where there is none. Three: the servo has insufficient torque because the excitation has degraded or the amplifier is limiting. And four, the one that shows up on vertical axes: the brake applies while the servo is still excited, or releases before the servo takes control, and in that small timing mismatch the axis drops a few millimetres. The important consequence is a safety one: a vertical axis that does not hold position is a physical hazard, not just a quality problem.
In order, from the fastest and cheapest check to the most expensive.
01Identify the axis and assess the risk before anything else
If it is a vertical axis, assume it can drop. Do not put your hands in and do not stand under the head, and do not disable anything. If the axis has already dropped onto the part, the recovery has its own procedure in the machine manual and often has to be done with maintenance.
02Check for an obvious external force
A tool jammed in the material, a part that moved and is pushing, a clamping system pressing against the axis, debris from a crash. If something is pushing, it has to be removed before drawing any conclusions about the servo.
03Pay attention to when it appears
At the end of a move, every time. After the machine has been stopped for a while. Right when excitation is cut at end of program or by emergency stop. Only on the vertical axis. Each of those patterns points at a different culprit, and the information costs nothing to collect.
04See whether the axis physically moves
With the machine safely stopped and using a visual reference or a dial indicator if one is to hand, check whether the axis really moved or whether only the number on screen changed. If it moved physically, it is the brake or a force. If it did not move and the number did, it is feedback.
05Do not touch the limits or the parameters
Widening the standstill error tolerance so the alarm does not trip leaves the machine without the only protection that was warning you an axis is not holding. On a vertical axis that is a direct risk to people. It is not done.
06Brake, encoder and amplifier: maintenance
Checking the holding brake, its actuation timing, the state of the encoder coupling or the amplifier's behaviour are maintenance tasks with the machine locked out and, on vertical axes, with the head supported or mechanically secured as the builder specifies.
A holding brake that does not grip, or a timing mismatch between the brake and the servo excitation. It is confirmed because the axis physically drops a few millimetres. It is a maintenance job and it is a safety priority.
Feedback: encoder, a loose coupling or a cable. Confirm it against a physical reference. It is a maintenance diagnosis; in the meantime do not produce on that machine, because the dimensions are not trustworthy.
External force or mechanical damage from the crash. Confirm it by removing the cause and checking whether the axis holds position again. After a crash it is also worth checking geometry and couplings before going back into production.
Holding brake checks on vertical axes inside periodic maintenance, which is the check that prevents the most dangerous case. Encoder couplings inspected after any work on an axis. Cutting parameters that do not lead to jammed tools, and wear control. Inspection after any crash, however slight it looks. And never leaving the machine with a tool engaged in the material at the end of the shift.
Fanuc detects difference between commanded and actual position greater than the limit with the axis stopped. It is an alarm from the Servo / ejes area, and in the catalog it is listed as “Excessive position error at stop”. On the machine you notice it like this: Alarm with stopped axis, Appears after braking or when clamping, It can go with sound or shaft vibration.
On the shop floor it almost always comes from one of these causes: Faulty servo brake, External force on the axis, Encoder drifting, Incorrect gain/tolerance parameters. Rule out the most likely one on your machine first, before touching parameters or swapping anything.
Reset only after removing load; If it returns, stop diagnosis. Resetting without fixing the cause first only hides the problem: SV0410 trips again and, in the meantime, you keep working with the machine in bad shape.
With the machine stopped and in a safe state, start with these checks: Identify the affected axis, Check that there is no external load, Check servo diagnosis. That alone will tell you whether it is the program or whether you need to raise a maintenance job.
With SV0410 active, avoid this: Do not raise limits to silence, Do not machine if the axis does not maintain position, Do not work on an energised brake. Skipping any of these points is what turns a minor stop into an expensive breakdown.
Always: indicates a servo/brake/encoder problem. If you are not sure how far it goes, stop the machine and report it: a repeat alarm always works out cheaper than a crash.
It is critical: there is a real risk of damage to the machine, the tool or a person. Leave the machine stopped, do not keep resetting it to see if it goes away, and call maintenance before producing again. Guidance reference. Always confirm the full text in the exact machine/control manual.
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