the M02 function in the program, with almost identical results. In case of M02, the tape did not rewind to its beginning, in case of M30, the tape was forced to rewind.
Today, there is no physical tape used as a program source anymore, but both functions are still available in virtually all Fanuc control systems. M30 function is the normal standard, but M02 function is still supported, mainly for compatibility with old programs. The word ‘rewind’ takes on a new meaning, and is now interpreted as ‘return to the top of program’.
Many modern controls treat M02 the same as M30 and will rewind (return) to the program beginning (top)
Errors / Alarms / Faults
When checking the status indicator lights, make sure all light bulbs are functioning properly
This comment applies to all indicator lights but it is even more important for the group that shows red lights. Seeing red - that is, a red status indicator light on the Operation Panel - is generally not a good situation. It indicates that something has gone wrong either in the part program itself or during actual machining.
This is the third common group of lights that indicate a certain condition or situation. Usually, there are at least two indicator lights on every control system:
| ▪Alarm | ... general alarm or error condition |
| ▪Lube | ... machine slides lubrication alarm |
The first light is often called just ‘Alarm’ - this is a non-descriptive name that covers all kind of alarms. Also worth note is that some controls use other words, like ‘Error’ or ‘Fault’ with the same meaning. Fanuc controls generally use the word ‘Alarm’. Regardless of the definition, the results are the same. Typical alarms that will 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,