cause an indicator light to turn ON (usually as a red light) belong to at least three categories:
| ▪Program syntax error | ... programming error |
| ▪Lubrication error | ... low lubrication |
| ▪Machine problem | ... various causes |
Other problems may also be the cause of an alarm.
Syntax error is an error that originates in the part program. This type of error can be easily detected by the control system - syntax error simply means that proper programming format was not followed. For example, the negative sign in -X100.0 is a syntax error, because only a letter can be the first character. On the other hand, X-100 is not a syntax error, because the format itself is correct, meaning 100 microns (metric) or 0.1 of an inch, depending on the selected units! Yes, decimal point IS very important.
Syntax error is an error caused by an illegal program input. This error CAN be detected by the control system
When you encounter this type of error in the program, the syntax can be wrong in several cases, such as:
▪First character is not a word (-X10.0 or 10.0X)
▪Letter O was programmed instead of digit 0 (MOO) (probably the most common program input error)
▪Digit 2 was programmed instead of letter Z (2-10.0) (a common error if program written by hand)
▪Space was programmed after the letter (X 10.0) (also a space between digits)
▪Letter not acceptable by the control was programmed (Y for a standard 2-axis lathe)
▪Correct but unavailable command or function (G02 X.. Y.. Z.. I.. J.. is wrong if helical interpolation is not available - same applies to other control options - check manual for the list of commands)
▪... other possibilities
Syntax error is not exclusive to part programs delivered to the CNC machine. Errors of this kind can also happen at the machine, for example, when using MDI mode (Manual Data Input) or even setting various offsets. Syntax has to be accurate and in accordance with the control standards.
Logical Errors
In the majority of cases, there is no special control feature to ‘catch’ logical errors. In comparison with syntax errors, logical errors are much more difficult to detect, as they consist of correct program format but wrong input data. For example, the earlier entry of X100 is as good as any. X100 and X100.0 are far apart. Quite a bit apart, in fact. X100 is equivalent to X0.1 in metric and to X0.01 in imperial units!
There is, however, one case, where the system alarm will work, even for a logical error. The subject is cutter radius offset, described in a chapter of its own. For now, if the control system detects that a cutter radius set at the control is larger than any inside radius of the contour, there will be alarm and the indicator light will flash red. In addition, an error message will appear on the screen.
The reason for such alarm is that the cutter radius offset uses a feature called ‘look-ahead’ type. During program run, the control will evaluate at least one block that is to be processed (next block) and checks if such cut is possible - if not, hence the alarm.
General alarm condition will also occur if there is a malfunction of the machine itself or some of its main elements. Usually, the error message will point towards the problem cause. One machine related alarm that has its own indicator light is the LUBE alarm.
Lubrication Alarm
Lube alarm - lubrication alarm - is the result of a situation when the machine slide lubrication supply is detected as being below certain level. This alarm will occur once in a while, for the simple reason that the CNC operator does not normally watch the level of lubricant in the storage container. In fact, there is not need to check how much lubricating oil is available - just wait for the alarm, then fill-up the container with appropriate lubricant. There will be no damage due to insufficient slide lubrication. The control will simply not allow it, as the possible damage could be very substantial.
Many CNC operators are sometimes puzzled why the lube alarm light comes on, when the lube oil container appears to have plenty of oil. Keep in mind that what the lube alarm really means is that the lubrication oil is being taken from a reserve. Although the oil container does seem to be fairly full, the machine has started lubricating its slides from its reserved supply. The natural question is ‘why so soon?’ - and yes, there is a simple explanation.
Most common machining operations typically take a very short time, usually only a few minutes to complete. Machining operations taking an hour or even several hours may not be common to small shops, but in certain industries they may be the norm. For example, three dimensional machining in mold work may use a single tool and let it cut for much longer than one hour. For example, what happens if a three hour cutting time experiences a lube alarm after two hours of machining? This is where the reserve comes into the picture.
Stopping machining before all cutting is completed, when the tool is just fine, is not only inefficient, it can cause various flaws to the machined part. In such cases, machining will not stop, when the lube alarm comes on. In fact, the machining will continue normally for the remaining time, until machining with this tool is fully completed. From the time of the first lube alarm appearance to the end of the cutting, the lubricating oil will be taken from the reserve in the container. That is the basic design about having a rather large reserve.
In summary, until it is interrupted by the program or by manual interference, the slide lubricant will be taken from the reserve the moment the lube alarm has occurred. Practically, it means that the lube alarm light will turn ON when oil level indicator reaches ‘low level’, and it will remain ON until the oil level in the reservoir is increased. If any machining takes place when the light comes on, the machining will be completed, as long as there is sufficient supply of lube oil. Having a rather large oil reserve guarantees that even a long machining sequence will be completed.
While the lube alarm is active (red light is ON), no further machining will be possible after the control system detects program tool change function M06, program stop function M00, optional program stop M01, or program end M30. In order to continue machining after these functions, the lube alarm must be eliminated by adding more lube oil to the reservoir.
When the LUBE alarm is ON, machining cycle will be completed, but program will not continue until the lubrication oil level is increased
