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The axis has fallen too far behind the position the control commanded while it was moving. The CNC compares commanded position against encoder feedback every cycle, and when that difference exceeds the limit allowed in motion, it cuts out. It is one of the most useful alarms the machine has: it almost always warns you of a real mechanical problem before something breaks.
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.
If it repeats in the same area, or there is noise, stiffness, heating or a crash history.
Reset after removing obvious load/obstacle; If it comes back, stop the machine.
It can be displayed with specific axis and additional diagnostics on servo screen.
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.
On every interpolation cycle the CNC generates a commanded position for the axis and reads the real position from the encoder. The difference between the two is the following error, and it is not a defect: in motion it always exists, because the position loop needs that error to generate a velocity command. Under normal conditions it is stable and proportional to the feed rate. The control stores a limit for how much following error it tolerates in motion and compares against it every cycle; when the real error exceeds it, the control concludes the axis has lost control of its trajectory and trips SV0411. What makes this alarm tricky is that following error grows for two opposite reasons. On one hand, because the axis is harder to move than the drive can compensate for: a dry way, a stiff slide, a damaged ball screw, packed chips, a brake that did not release, a tool jammed in the material. The drive demands more current, the motor cannot keep up and the real position falls behind. On the other hand, because the loop is badly tuned or badly sized for what is being asked of it: low gain, programmed acceleration beyond what the axis can deliver, or servo parameters that do not match that motor after some intervention. The screen symptom is identical, but the diagnosis is completely different, and that is what you have to separate before touching anything: an axis that always fails in the same physical zone is mechanical; an axis that fails anywhere as soon as you ask for more speed is tuning or cutting load.
In order, from the fastest and cheapest check to the most expensive.
01Note the axis, the position and what it was doing
Which axis the alarm names, what machine coordinate it was at, whether it was in rapid or in cutting feed, and whether it was cutting material or moving in air. Those four facts separate the two big families of causes. In rapid, in air and always at the same point: mechanical. Only under cutting load: process or tooling.
02Rule out the obvious in that area: chips, obstruction, workholding
With the machine stopped and following safe procedure, look for chips packed into the ways, into the way covers or between the slide and a stop, for a wrench or a part left in the travel path, or for workholding that is fouling. A torn bellows letting chips reach the way produces exactly this picture, getting worse week by week.
03Check that axis's lubrication
Reservoir level, pump actually cycling, and whether there is an oil film on the ways. Lubrication is the number one mechanical cause of this alarm and the cheapest to fix. An empty reservoir for two days leaves the slide stiff, and if it stays that way it ends up scoring a way or a screw, which is no longer cheap.
04Jog the axis slowly in a clear area and listen
With the area clear and the feed rate low, run the axis end to end on the handwheel or in jog. Look for tight spots, ball noise, squeal or repeating vibration. If it is always stiff over the same stretch and free elsewhere, you have located the fault. If it moves smoothly end to end, the problem is not gross mechanics.
05Look at the axis load on the servo diagnostic screen
The control shows load percentage and following error per axis; the screen and the diagnostic number change between series, so look it up in the maintenance manual as the servo monitor or servo diagnostics. Compare the failing axis against a healthy axis on the same machine making the same move. A clearly higher load in air confirms abnormal mechanical resistance.
06If none of that shows up, it is a maintenance job
Loop gains, acceleration times, error limits and motor parameters are for maintenance, with a backup taken first and real knowledge of the machine. Same for the encoder, the feedback cable and the amplifier. Never raise the error limit just to keep producing: that fixes nothing, it only removes the protection that was stopping the axis from destroying itself.
Localised damage: a pitted ball screw, a nut with backlash, a scored way or chips packed into that stretch. Confirm it by jogging the axis slowly through that zone and feeling the stiffness, and by watching the load rise right there on the servo monitor. It needs mechanical work; forcing it makes the damage worse fast.
Cold, thick oil, or lubrication that takes time to distribute. Confirm it by warming the axes up in air before producing: if that makes it disappear, the picture is clear. Check the oil type and viscosity against what the builder specifies, and the flow rate at each point.
The process is asking for more than the axis can give: excessive feed or depth, a worn tool that pushes instead of cutting, an entry at full engagement with no ramp. Confirm it by repeating the same move in air, where it does not fail, and by dropping the feed to 50 % on the real pass, where it also does not fail. Fix it in the program and in the tooling, not in the servo parameters.
Lubrication first: level checked every shift and the distributors inspected as part of the maintenance plan, because one blocked port leaves a slide dry without the reservoir level dropping. Bellows and way covers replaced as soon as they tear, since they are what keeps chips out of the ways. Warm the axes up in air at start-up in cold shops. Enter material on a ramp or in an arc, not plunging at full engagement. And control tool wear by time or part count, so you never reach the point where the tool pushes instead of cutting.
The axis does not follow the commanded position within the allowed tolerance. It is an alarm from the Servo / ejes area, and in the catalog it is listed as “Excessive servo error”. On the machine you notice it like this: Alarm during movement, The shaft may sound hard or lag behind, Usually appears under load or in one particular area.
On the shop floor it almost always comes from one of these causes: Mechanical jam, Guides without lubrication, Incorrect servo gain/parameters, Faulty encoder or cable. Rule out the most likely one on your machine first, before touching parameters or swapping anything.
Reset after removing obvious load/obstacle; If it comes back, stop the machine. Resetting without fixing the cause first only hides the problem: SV0411 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 axis and position where it occurs, Check visible lubrication and absence of chips/shock, Try a slow move in manual only if it is safe. That alone will tell you whether it is the program or whether you need to raise a maintenance job.
With SV0411 active, avoid this: Do not force the axis repeatedly, Do not raise error limits to continue producing, Do not reach into the movement area. Skipping any of these points is what turns a minor stop into an expensive breakdown.
If it repeats in the same area, or there is noise, stiffness, heating or a crash history. 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. It can be displayed with specific axis and additional diagnostics on servo screen.
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