Heidenhain TNC 620 (81760x-01) ISO programming User Manual download pdf (Page 86)

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Programming: Fundamentals, file management

3.1 Fundamentals

TNC 620 | User's Manual for DIN/ISO Programming | 3/2014

3.1 Fundamentals

Position encoders and reference marks

The machine axes are equipped with position encoders that

usually equipped with linear encoders, rotary tables and tilting axes

with angle encoders.

When a machine axis moves, the corresponding position encoder

generates an electrical signal. The TNC 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

TNC when they are crossed over. From that signal the TNC can

re-establish the assignment of displayed positions to machine

positions. For linear encoders with distance-coded reference

marks, the machine axes need to move by no more than 20 mm,

for angle encoders by no more than 20°.

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.

Reference system

A reference system is required to define positions in a plane or in

space. The position data are always referenced to a predetermined

point and are described through coordinates.

The Cartesian coordinate system (a rectangular coordinate system)

is based on the three coordinate axes X, Y and Z. The axes are

mutually perpendicular and intersect at one point called the datum.

A coordinate identifies the distance from the datum in one of these

directions. A position in a plane is thus described through two

coordinates, and a position in space through three coordinates.

Coordinates that are referenced to the datum are referred to

as absolute coordinates. Relative coordinates are referenced to

any other known position (reference point) you define within the

coordinate system. Relative coordinate values are also referred to

as incremental coordinate values.

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Heidenhain TNC 620 (81760x-01) ISO programming User Manual Page 86

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