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These are the software travel limits. Before moving, the control checks whether the destination falls inside the axis's permitted zone and, if it does not, stops before reaching the physical limit switch. It appears before the mechanical stop, with the axis still in good territory, and that is exactly what makes it a protection rather than a fault.
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 appeared after loss of parameters, battery or machine recovery.
Correct origin/program and reset after removing the axis from the limit.
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.
Every axis has its positive and negative limits stored in parameters, in machine coordinates. The control uses them in two ways: it checks the end point of the block before executing it, and it watches the position during the move. Because the check works in machine coordinates, it depends on the reference being established: with no reference return done, the control does not really know where it is and the software check cannot protect you, which is why many machines only enable it after homing. Besides each axis's travel limits, many machines have additional forbidden zones defined to protect the tool changer, the tailstock, the turret or an indexer. The practical consequence matters: when one of these trips, the coordinate the control calculated as the destination is outside, and that coordinate is the sum of the programmed point plus the work offset plus the tool offsets. Very often the program is correct and the sum is what is wrong. The other family of causes is different and more serious: if the limit parameters were lost or badly restored, after a dead battery or a recovery, the limits may be sitting at values that do not belong to this machine, in which case the protection is wrongly set and has to be re-established from builder data.
In order, from the fastest and cheapest check to the most expensive.
01First check that a reference return has been done
See whether the axes show their reference marks. If the machine has just been switched on and no reference return was done, do it by the normal procedure before going any further. Without reference, any conclusion about coordinates is worthless.
02Read the machine coordinate and compare it against the limit
Note the axis's current position in machine coordinates and what destination the block was asking for. If the destination is clearly outside, the problem is the sum of work offset and tool offsets. If the axis is at a perfectly normal position and it still trips, suspect the limits themselves or a forbidden zone defined by the builder.
03Check the active work offset and the tool offsets
G54 or whichever is active, with its values, plus the length and wear offsets of the tool that is loaded. An extra digit, a flipped sign or an H that does not match the T explain most cases. Compare against what is written on the job's setup sheet.
04Move off the limit in jog, in the right direction
Move slowly back into the permitted zone. With a soft limit you can normally move towards the good side with no further ceremony. If the machine will not move in any direction, do not force it: consult the builder's procedure, because every builder has its own.
05Rule out a builder-defined forbidden zone
If the alarm always appears near the tool changer, the tailstock or one particular area of the table, it is probably a protection zone defined by the machine builder rather than the general travel limit. It is documented in the machine manual, not in the control manual, and that is where to look for it.
06If the limits look wrong, do not touch them: call maintenance
If you suspect the limit parameters were lost, after a dead battery, a restore or an intervention, do not adjust them by eye. Wrongly set limits leave the machine with no travel protection and the next crash is into the hard stop. They are restored from the builder's backup, with the machine stopped and by maintenance.
The job is positioned outside the usable envelope: a badly measured work offset, or a part clamped where it does not fit with those tools. Confirm it by comparing the machine coordinate of the work offset against the machine's travels. It is solved by repositioning the setup or the offset.
The limits or the reference were not left as they were. It is confirmed because the problem is general rather than tied to one job. It needs the builder's documented parameters restored and the references re-established; that is maintenance work.
Tool length eats into the Z travel. Confirm it by adding tool length, setup height and part height and comparing against the stroke. Fix it by shortening overhangs or rethinking the setup, not by moving limits.
A machine parameter backup saved and dated, limits included, which is what saves your day after a dead battery. A setup sheet with work offsets, tool offsets and tooling recorded for each job. CAM simulation with the real machine model and the real setup height, which catches travel overruns before they reach the machine. Standardised setup heights. And the habit of homing every time the machine is switched on, with no exceptions, because without reference this protection does not exist.
Fanuc blocks movement because the axis exceeds stored stroke limits. It is an alarm from the Sobrecarrera area, and in the catalog it is listed as “Soft limit / stroke check”. On the machine you notice it like this: Alarm before reaching physical end, Movement blocked in one direction, Usually appears after a wrong origin or offset.
On the shop floor it almost always comes from one of these causes: G54/G55 wrong, Incorrect tool offset, Program out of tour, Poorly restored stroke parameters. Rule out the most likely one on your machine first, before touching parameters or swapping anything.
Correct origin/program and reset after removing the axis from the limit. Resetting without fixing the cause first only hides the problem: OT0300-OT0305 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: Check the active offset, Check the commanded coordinate, Only leave the limit in a safe direction. That alone will tell you whether it is the program or whether you need to raise a maintenance job.
With OT0300-OT0305 active, avoid this: Do not bypass safety devices, Do not manipulate energized electrical cabinet, Do not continue producing if the alarm reappears. Skipping any of these points is what turns a minor stop into an expensive breakdown.
If it appeared after loss of parameters, battery or machine recovery. 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 a stop alarm: the cycle will not continue until you fix the cause. It does not always mean serious damage, but it leaves the machine where it is and you have to check it before running again. Guidance reference. Always confirm the full text in the exact machine/control manual.
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