Heidenhain iTNC 530 (340 420) Manuel d'utilisateur télécharger pdf (Page 62)

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34 4 Fundamentals of NC, File Management, Programming Aids, Pallet Management

4.1 Fundamentals

Position encoders and reference marks

The machine axes are equipped with position encoders that register

the positions of the machine table or tool. Linear axes are 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 the axes

pass over them. From the 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 (datum) you define within the coordinate system.

Relative coordinate values are also referred to as incremental

coordinate values.

X (Z,Y)

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Heidenhain iTNC 530 (340 420) Manuel d'utilisateur Page 62

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