Distance-Coded Reference Marks - Siemens SINUMERIK 840C Installation Instructions Manual

11.92
10.4.5
Corresponding data
NC MD 240*
NC MD 284*
NC MD 396*
NC MD 564*
NC MD 1300*
NC MD 1304*
NC MD 1808* bit 2
NC MD 1808* bit 3
NC MD 1808* bit 4
DB32 DW (K) bit 12
Machine data 240* (reference point value) is of no significance to the referencing movement,
but continues to described the reference point for the leadscrew error compensation table
(= position to which no offset is applied).
Description of function
In the case of linear scales with distance coded reference marks which have a reference mark
track and an incremental track running parallel to each other, neither a cam play has to be
evaluated, nor a certain point (reference point) approached when referencing the axes. The
distance between any two reference points is always different. The absolute position of the
axis in the machine system can thus be determined by crossing two reference marks and
measuring the distance between those two marks. The absolute position is sent to the NC: the
actual position has now been determined.
The direction and position from which the reference marks are crossed is of no significance. A
reference point cam is no longer necessary.
In operating mode REFPOINT, the travel direction (referred to the machine system) is
determined by the direction key (+/-) which is pressed on start.
In operating modes AUTOMATIC and MDI AUTOMATIC, a reference point can be taken from a
part program with the G74 command. As the G74 command contains no information regarding
direction, the reference point approach direction defined in machine data MD 564*, bit 0, is
taken (see also FUNCTIONAL DESCRIPTIONS Section).
Reference point approach is executed at creep speed (MD 284*).
If the reference point approach does not produce successful results within double the "Basic
distance between reference marks" (MD 1300*), because, for example, the zero mark tracks
are faulty, the axis is brought to a halt with alarm 132* ("Control loop hardware").
The function "Distance coded reference marks" does not affect the reference point approach
with position encoders already in use.
© Siemens AG 1992 All Rights Reserved
SINUMERIK 840C (IA)
More user manuals on

Distance-coded reference marks

Reference point value, reference point for leadscrew error
compensation
Reference point creep speed
Absolute encoder offset
bit 0 Reference point approach direction (only required for G74)
Basic distance between coded reference point marks
External pulse multiplication
Encoder absolute system opposite to machine system
Absolute offset valid
Measuring system 1 distance coded
Signal "REFERENCE POINT REACHED"
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10 Axis and Spindle Installation
10.4.5 Distance-coded reference marks
10–43