Operation Manual

HEIDENHAIN CNC PILOT 640 45

1.7 Fundamentals

Position encoders and reference marks

The machine axes are equipped with position encoders that register

the positions of the slide or tool. When a machine axis moves, the

corresponding position encoder generates an electrical signal. The

control evaluates this signal and calculates the precise actual position

of the machine axis.

If there is a power interruption, the calculated position will no longer

correspond to the actual position of the machine slide. To recover this

association, incremental position encoders are provided with

reference marks. The scales of the position encoders contain one or

more reference marks that transmit a signal to the control when they

are crossed over. This enables the CNC PILOT to re-establish the

assignment of the displayed position to the current machine position.

For linear encoders with distance-coded reference marks, you only

need to move each axis a maximum of 20 mm (0.8 in.) for these, and

a maximum of 20° for angle encoders.

If incremental encoders are without reference marks, fixed reference

positions have to be traversed after switch-on. The control knows the

exact distance between these reference points and the machine

datum (see figure).

With absolute encoders, an absolute position value is transmitted to

the control immediately upon switch-on. In this way the assignment

of the actual position to the machine slide position is re-established

directly after switch-on.

Axis designations

The cross slide is referred to as the X axis and the saddle as the Z

axis.

All X-axis values that are displayed or entered are regarded as

diameters.

Lathes with Y axis: The Y axis is perpendicular to the X axis and Z axis

(Cartesian system).

When programming paths of traverse, remember to:

 Program a positive value to depart the workpiece.

 Program a negative value to approach the workpiece.

X (Z,Y)

Zref

Xref

Z

Z+

Y+

X

X+