FANUC Reference Return and Position Screens: ABS, REL, MACHINE, JOG and HANDLE

Estimated reading time: 6 minutes

What Will You Learn in This Lesson?

In this lesson you will learn:

reference return with REF/ZRN,
the ABS, REL, ALL and MACHINE position screens,
manual axis movement with JOG and HANDLE,
axis and direction of movement selection,
handwheel steps,
the use of JOG feedrate and Rapid Override,
the basic screen differences between a lathe and a vertical machining centre.

The aim is not to teach axis theory, but to show how the machine position is displayed on a FANUC control and how manual movements are managed.

What Is the Reference Position?

The reference position is a fixed machine position determined by the machine tool builder. The FANUC control uses this position to keep track of the axis movements and the machine coordinates.

The reference position can be used for the following purposes:

To verify the machine coordinate system
To make sure the axes are recognised correctly by the control
To create a safe position for tool change or turret movement
To make sure the software travel limits work correctly
To help the positions in the program to be evaluated correctly

The reference position and the workpiece zero are not the same.

Reference position: a fixed position belonging to the machine.
Workpiece zero: the start of machining, determined by the operator or the programmer according to the part to be machined.

Although the machine reference does not change, different workpiece zeros can be used for different jobs.

Reference Return with REF / ZRN

On machines with a FANUC control, the reference return mode may be shown under different names:

REF
ZRN
ZERO RETURN
HOME

The general order of checks for a reference return is as follows:

A safety check is carried out around the machine.
The position of the tool, the part, the chuck, the fixture or the table is examined.
REF/ZRN mode is selected.
The axis to be sent to reference is determined.
The reference return direction required by the machine is selected.
The axis movement and the position screen are followed.
The reference completed indicator is checked.

These steps show the general FANUC logic. The reference direction and the axis order are determined by the machine tool builder.

Caution: there is no single order valid for every machine in the form of “this axis is always sent first”. On a lathe the turret being close to the chuck, or on a milling machine the tool being inside the part or the fixture, can make the reference movement dangerous.

Is a reference return needed at every power-on?

This depends on the position detection system used.

On machines with incremental position encoders, a reference return may be needed after the power is switched on.
On machines with absolute position encoders, the control can retain the axis position even while the power is off.
After battery loss, loss of the reference data or certain alarms, the reference setting may need to be made again.

APZ/APC, grid shift and reference parameters are not operator level subjects. In the case of such an alarm, maintenance or service personnel should be contacted.

Opening the FANUC Position Screen

Position information is generally opened with the POS function key on the MDI keyboard.

Different position views can then be selected using the soft keys at the bottom of the screen:

ABS
REL
ALL
HNDL
OPRT

Do not look for a separate key for the machine coordinate. On most FANUC 0i class controls there is no independent MACHINE soft key on the POS screen; the machine position is shown inside the ALL (overall) screen together with the other position data. On some series and machine tool builder configurations there may be a separate machine position page.

The name of the screen and the order of the soft keys may differ according to the FANUC series.

ABS – Absolute Position

The ABS screen shows the current position of the axes according to the active workpiece coordinate system.

This screen is used to:

compare the current position with the coordinates in the program,
see where the tool is relative to the workpiece zero,
follow the axes during automatic operation,
check tool or workpiece measuring operations.

On a lathe control mostly X and Z values are seen; on a vertical machining centre the X, Y and Z values are seen.

When the active workpiece coordinate or an offset is changed, the value on the ABS screen may change even though the tool has not moved physically. This is because the reference of the position shown on the screen has changed.

REL – Relative Position

The REL screen allows the operator to treat a point they need as a temporary start and to follow the amount of movement from there.

The relative position can be used to:

check the distance between two points,
follow the amount of manual movement,
take a temporary measurement,
help the operator during tool setting.

Zeroing the REL value does not change the machine reference or the workpiece zero. It only changes the display of the relative screen.

Common mistake: thinking that zeroing the REL screen defines the workpiece zero. REL is a temporary indicator that helps the operator; it does not replace the normal workpiece coordinate system.

MACHINE – Machine Position

The MACHINE screen shows the position of the axis in the machine coordinate system. On most FANUC 0i controls this value is reached through the ALL screen.

This position is evaluated according to:

the reference point of the machine,
the machine travel limits,
the tool change or turret positions,
the fixed machine points determined by the builder.

Changing a tool or workpiece offset does not normally change the MACHINE value. This is because the tool has not moved physically and the machine coordinate is the same.

This feature is one of the easiest ways to tell the ABS and MACHINE screens apart:

ABS shows the position according to the active work coordinate.
MACHINE shows the position according to the machine’s own coordinate.

ALL – Combined Position Screen

The ALL screen shows more than one item of position information on the same page.

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

Absolute position
Relative position
Machine position
Distance to go
Active program and sequence number
Feedrate and spindle information

The operator can examine the general movement status of the machine without switching between different screens.

The ALL screen is particularly useful during automatic operation. However, since the fields are shown smaller, the dedicated screen may be preferred when reading a precise value.

Position Display on Lathes and Milling Machines

On a FANUC lathe

The basic axes are mostly:

X: the position in the diameter direction
Z: the position in the length direction

For incremental movements in the program, FANUC lathe systems frequently use the addresses:

U: incremental movement in the X direction
W: incremental movement in the Z direction

Whether the X value is displayed as a diameter or as a radius may depend on the control setting and the machine configuration. The display format of the machine should be verified before use.

On a FANUC milling machine / vertical machining centre

The basic position screens mostly contain the axes:

On machines with a fourth axis, an additional rotary axis such as A, B or C may also be displayed.

The aim of this lesson is not to teach the axis directions, but to enable the operator to select the correct axis and follow the movement on the position screen.

Manual Movement with JOG

In JOG mode the axis moves as long as the direction key on the operator panel is pressed.

The general order of use is:

JOG mode is selected.
It is confirmed that the area of movement is safe.
If necessary, the JOG feedrate is set to a low value.
The plus or minus direction key of the relevant axis is pressed.
The movement is followed on the ABS, REL or MACHINE screen.
The key is released when the desired position is approached.

On some panels the axis selection and the direction selection are separate controls. On others there are direct axis-direction keys such as X+, X-, Z+ and Z-.

JOG feedrate and manual rapid movement

The JOG movement speed may be affected by the following controls:

JOG Feed selector
Feed Override
Manual rapid movement button
Rapid Override

Manual rapid movement can be much faster than normal JOG movement. It should not be used while the tool is close to the part.

Common mistake: looking only at the value on the screen when the wrong direction has been selected. During the movement both the physical axis and the position screen should be watched.

Precise Movement with HANDLE

In HANDLE mode the axis is moved with the manual handwheel or MPG.

The general order of use is:

HANDLE mode is selected.
The axis to be moved is selected.
The appropriate handwheel step is determined.
The handwheel is turned by a small amount.
The physical movement and the position screen are checked together.
Once it is confirmed to be safe, the movement is continued.

The handwheel steps are mostly ×1, ×10 and ×100. These indicate the multiplier of the movement produced by each pulse. The actual amount of movement depends on the input unit of the control and the machine configuration.

The lowest suitable step should be used when approaching the part or the fixture.

Caution: turning the handwheel quickly does not always mean that the axis will move at the same speed at the same moment. The pulses may continue to be processed by the control. For this reason approach movements should be made slowly and in small steps.

Rapid Override

Rapid Override is used to select a certain percentage of the permitted maximum speed of rapid movement.

For example, the following options may be seen on the panel:

F0
25%
50%
100%

The F0 value is a low rapid movement level determined by the machine tool builder; it may not mean zero speed.

Using a low Rapid Override during the first check, a reference return or a program trial gives the operator more time to watch the movement. However, this control alone is not a guarantee of safety.

Rapid Override and Feed Override are different from each other:

Rapid Override: affects rapid movements.
Feed Override: affects cutting or programmed feed movements.

The movements affected and the percentages may differ according to the configuration of the machine tool builder.

An Example Check Exercise

To check the current position of an axis and the amount of manual movement:

Open the POS screen.
Examine the ABS and MACHINE values.
Switch to the REL screen.
Zero the relative value of the appropriate axis.
Select HANDLE mode.
Determine the correct axis and a low step.
Turn the handwheel by a small amount.
Check the amount of movement on the REL screen.
Confirm that the MACHINE value changes with the physical movement.

This exercise should only be carried out on a machine that is in a safe condition, where training authorisation has been given, and in accordance with the operating instructions of the machine.

Short Summary

The reference position is a fixed position belonging to the machine; it is not the workpiece zero.
The direction and axis order of the REF/ZRN operation may differ from machine to machine.
ABS shows the position according to the active workpiece coordinate.
REL can be used for temporary measurement and for following movement.
MACHINE shows the physical position of the axis in the machine coordinate.
ALL gathers more than one item of position information on the same screen.
JOG provides continuous manual movement with the direction key.
HANDLE provides precise movement with the handwheel.
The handwheel step and the Rapid Override should be checked before moving.
Even though the axis names differ on lathes and milling machines, the basic logic of the FANUC position screens is common.

Test Yourself

What is the difference between the reference position and the workpiece zero?
According to which coordinate system is the value on the ABS screen displayed?
Does zeroing the REL screen change the workpiece zero?
Why does the MACHINE value not normally change when an offset is changed?
What advantage does the ALL screen give the operator?
What is the basic difference in use between JOG and HANDLE?
Why should the handwheel step be checked before moving?
What is the difference between Rapid Override and Feed Override?
Why does the F0 option not necessarily mean zero speed?
Why should the reference return order be verified from the machine manual?