Introduction and fundamentals | Fundamentals
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HEIDENHAIN | MANUALplus 620 | User's Manual | 12/2017
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 assignment, 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 control
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.), and a maximum of 20° for angle encoders.
If incremental position encoders are without reference marks,
fixed reference positions have to be traversed after switch-on.
The control knows the exact distance between these reference
positions 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
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