FANUC Alarm, Message and Diagnosis Screens: Alarm History, P/S and Overtravel

Estimated reading time: 7 minutes

What Will You Learn in This Lesson?

In this lesson you will learn:

how to reach the FANUC alarm screen,
how to read the alarm number and description,
how to separate a CNC alarm from a machine alarm,
how to examine the alarm history,
how to evaluate operator messages,
how to use the basic diagnosis screens safely,
the checks to be made before and after RESET,
the intervention limits of the operator and the maintenance/service personnel.

This lesson does not teach parameter changing, PMC/Ladder editing or service work. The aim is for the operator to identify the alarm correctly and to act deliberately.

What Is an Alarm?

An alarm is a warning showing that the FANUC control or the machine does not allow a particular operation to continue.

When an alarm occurs, the control may:

stop program execution,
prevent axis movement,
not allow the spindle to run,
not accept the Cycle Start command,
display the relevant alarm number and description on the screen.

It is not enough to evaluate an alarm only as “the machine is not working”. The operator should first determine the following:

Was the alarm produced by the CNC or by the machine tool builder?
What is the alarm number and its full text?
During which operation did the alarm occur?
Which are the active program and sequence number?
Which physical condition on the machine changed?
Can a safe correction be made at operator level?
Is maintenance or service support needed?

Opening the Alarm Screen

On FANUC controls the alarm screen is mostly reached with one of the following function keys:

MESSAGE
MSG
ALARM
MESSAGE/ALARM

The following pages can then be selected with the soft keys:

ALARM
HISTORY
MSG
OPERATOR MESSAGE

On some FANUC 0i controls, pressing the MESSAGE key several times switches between the alarm, alarm history and operator message screens.

The alarm screen generally displays:

the alarm class,
the alarm number,
the alarm description,
the alarm list if there is more than one active alarm.

If there is more than one alarm on the screen, do not look only at the last line. The first alarm that occurred may be the cause of the others.

Record the Alarm Number and Text

Before trying to clear the alarm, the alarm number and the full description on the screen should be recorded.

An example record:

Alarm type:
Alarm number:
Full message on the screen:
Active program:
Active sequence number:
Operating mode:
The operation during which the alarm occurred:

If possible, a photograph of the screen should be taken. After a RESET or a power-off the active alarm may disappear from the screen and the fault investigation may become harder.

The alarm number alone is not always enough. The same number may carry a different meaning:

on different FANUC series,
on a lathe control and a milling control,
with different software options,
in the machine tool builder’s own alarm list.

For this reason the alarm number should be evaluated together with the alarm class and the description on the screen.

The Difference Between a CNC Alarm and a Machine Alarm

On a machine with a FANUC control, alarms can come from two main sources.

Alarms produced by the CNC

These are the conditions the FANUC control detects regarding the program, the axes, the servo, the spindle or the system.

Example alarm groups:

P/S or programming alarms
Overtravel alarms
Reference position alarms
Servo alarms
Spindle alarms
Communication and data input/output alarms
System alarms
Battery warnings

Alarms produced by the machine tool builder

These are the alarms the machine tool builder produces through the PMC program and the machine sensors.

Examples:

Insufficient hydraulic pressure
Low lubrication level
Low air pressure
Door open or not locked
Chuck clamping condition not satisfied
Turret not locked
Tool change not completed
Magazine position not suitable
Low coolant level

The number and the solution method of these messages are determined mostly by the machine tool builder, not by FANUC.

FANUC note: the FANUC alarm manual can explain a CNC alarm; for a machine-specific alarm the electrical, maintenance or alarm manual of the machine tool builder may be needed.

P/S and Programming Alarms

P/S is a group of errors related to the program or the programming operation.

This type of alarm can occur for the following reasons:

An invalid G or M code
A missing or incorrect address
An unsupported command
The cycle format written incorrectly
An invalid sequence number
An unsuitable combination of modal codes
A problem with the program memory or the editing operation
The subprogram called by the program not being found

The operator can follow this order:

Record the alarm number and message.
Determine the active O and N numbers.
Open the program block indicated by the alarm.
Examine the block together with the preceding lines.
Compare the command used with the relevant FANUC programming manual.
If a program change is needed, report it to the authorised person.
After the correction, check the program again in a controlled way.

Looking only at the line where the alarm was given may not be enough. The error may come from a modal state activated in an earlier block.

Overtravel and Movement Alarms

An overtravel alarm reports that an axis has reached or passed the permitted travel limit.

In this case the following should be checked:

the direction of movement,
the machine position,
the active coordinate system,
the tool and workpiece offsets,
the programmed target point.

The overtravel recovery method differs from machine to machine. On some machines there may be a special release button or a builder’s procedure.

Caution: do not use the overtravel switch, the limit release or a special recovery key without understanding it. Movement in the wrong direction can cause a mechanical collision. The procedure of the machine tool builder should be followed.

Servo and Spindle Alarms

A servo alarm may be related to the axis drive system and a spindle alarm to the spindle drive system.

Possible causes include:

Overload
Overcurrent
Overheating
A feedback error
A motor or drive problem
A communication problem
Mechanical binding
A power or connection problem

In this situation the operator should:

record the alarm number and the full description,
state during which movement the alarm occurred,
stop the machine safely if there is an unusual noise, smell or temperature,
not try the same movement again and again,
not interfere with the parameters or the drive settings,
inform the maintenance/service personnel.

Resetting a servo or spindle alarm repeatedly does not solve the underlying problem and can make the fault worse.

System Alarms

A system alarm may indicate a more serious condition such as the CNC hardware, software, memory or internal communication.

In this case the operator should:

record the alarm screen,
not carry out unnecessary key operations,
not change the parameter or system screens,
not apply random power on-off cycles,
contact authorised maintenance or FANUC service support.

SRAM, BOOT SYSTEM, card replacement and system restore operations are outside beginner operator training.

Battery Warnings

There may be batteries used for different purposes on a FANUC control:

the battery that protects the CNC memory,
the absolute position encoder battery,
other backup batteries connected to the machine.

When a low battery alarm is seen, it should be determined which battery the alarm belongs to. The program and offset backup should not be delayed, and the battery replacement should be carried out by an authorised person according to the relevant manual.

If some batteries are replaced in the wrong power state:

the programs and offsets,
the reference position data,
the absolute position data

may be lost.

Continuing to use the machine by only resetting a low battery alarm carries the risk of data loss.

Operator Messages

An operator message does not always mean a CNC fault. The machine tool builder may produce a message to tell the operator about a missing working condition on the machine.

Examples:

Close the door
Clamp the chuck
Check the air pressure
Move to the tool change position
Top up the coolant
Check the chip conveyor

When an operator message is seen:

The message should be read in full.
The required condition should be checked physically.
The safety system should not be disabled.
After the condition is satisfied, it should be watched whether the message clears.

If the message continues, the sensor, the switch or the PMC condition should be examined by maintenance personnel.

Alarm History

The alarm history shows a list of the alarms that have occurred previously.

Depending on the control, the following information may be present:

the alarm number,
the alarm description,
the date and time of occurrence,
the order in which the alarm occurred,
additional status information on some systems.

The alarm history is useful in the following situations:

investigating intermittent faults,
seeing whether the same alarm repeats,
determining which alarm the fault started with,
passing information between operator shifts,
providing a past record for maintenance personnel.

An alarm appearing in the history should not be thought to be active now. The active alarm screen and the alarm history should be evaluated separately.

Common mistake: deleting the alarm history in order to solve the problem. Clearing the history does not remove the fault and may lose evidence that is important for maintenance.

Basic Diagnosis Screens

On FANUC controls, basic diagnosis information can mostly be reached from SYSTEM, DGNOS, DIAGNOSIS, PMC or the special maintenance screens of the machine tool builder.

At operator level, the diagnosis screens should be used only to read information.

Information that may be displayed:

The state of the input and output signals
The Cycle Start or Feed Hold signal
The state of the door and safety switches
The reference completed information
The axis ready state
The spindle ready state
Machine lock or similar panel selections
The machine tool builder’s special status indicators

A signal being 0 or 1 does not by itself mean “faulty” or “healthy”. Whether the signal should normally be on or off must be verified with the electrical diagram and the machine tool builder’s explanation.

What can the operator do on the diagnosis screen?

The operator can:

open the screen,
display the page requested by maintenance personnel,
report the state of a signal,
take a photograph of the screen,
explain the condition in which the alarm occurred.

The operator should not:

change PMC data,
interfere with Keep Relay or timer values,
enable parameter writing,
edit the Ladder,
force safety signals,
use the service password.

Checks to Make Before RESET

When an alarm occurs, instead of pressing RESET immediately:

Verify that the movement has stopped safely.
Record the alarm number and the full text.
Note the active program and the N block.
Examine the physical state of the machine.
Check the door, chuck, tool, turret, magazine or pressure conditions.
Determine whether the alarm is at operator level.
Inform the maintenance personnel if necessary.
Do not restart the program before the cause of the alarm has been removed.

Checks to Make After RESET

After the cause of the alarm has been safely removed and RESET has been applied:

Verify that the alarm has really cleared.
Check whether there is a new or secondary alarm.
Verify the active operating mode.
Determine at which block the program stopped.
Examine the axis positions.
Check the active tool and offsets.
Check the state of the spindle and the auxiliary functions.
Do not start the program directly from where it stopped.
Determine a safe restart point.
Watch the first movements with Single Block and low percentage settings.

The program restart operation will be covered in detail in Lesson 10.

The Operator and Service Boundary

What can be done at operator level

Recording the alarm
Checking the program block
Verifying the door and clamping conditions
Carrying out daily checks such as oil, air or coolant
Applying the operator procedure in the operation manual
Taking a backup of the programs and offsets
Giving the correct alarm information to the authorised person

Operations that require maintenance or service

Changing parameters
Enabling PWE
Making a PMC/Ladder intervention
Forcing signals
Changing servo or spindle settings
Setting APZ/APC and reference parameters
Changing the grid shift
Carrying out SRAM or BOOT SYSTEM operations
Replacing a drive or a control board
Overriding the safety circuits

Short Summary

The alarm number and full text should be recorded before the alarm is cleared.
A CNC alarm and a machine tool builder’s machine alarm do not come from the same source.
In a P/S alarm, the relevant block and the earlier modal states should be checked.
Overtravel recovery should be carried out according to the machine tool builder’s procedure.
RESET should not be applied repeatedly for servo, spindle and system alarms.
The alarm history helps to investigate repeating and intermittent faults.
Diagnosis screens should be used by the operator only to read information.
It should not be assumed that the program will safely continue from the same point after RESET.
Parameter, PMC, servo and system interventions are a maintenance/service matter.

Test Yourself

Which information should be recorded before RESET when an alarm occurs?
What is the difference between a CNC alarm and a machine tool builder alarm?
If there is more than one active alarm, why is the first alarm that occurred important?
In a P/S alarm, why may it not be enough to look only at the line where the alarm was given?
Why should overtravel recovery not be applied from memory?
Why is it risky to try the same movement again and again in a servo alarm?
What is the difference between the alarm history and the active alarm screen?
What risks are there with a low battery alarm?
Does a 0 or 1 value on the diagnosis screen show a fault by itself?
Why should the program not be restarted directly after RESET?
Which diagnosis operations can the operator carry out?
Which operations should be left to maintenance or service personnel?