6 NC Machine Data (NC MD), NC Setting Data (NC SD) 10.94
6.4 Axis-specific MD 1 (axial data 1)
Reference point shift
244*
Default value Lower input limit Upper input limit Units
0 - 99 999 999 99 999 999 units (MS)
Active on
NC Stop
Reference point shift is used to shift the reference points of the measuring system. Instead of
mechanical shifting or rotating of the measuring equipment (and thus of the "deceleration"
cam), the reference point can be shifted electrically by up to ±9 999 units.
The reference point shift path is traversed at the cutoff speed (NC MD 284*), which must
already have been reached at the operating cam (also see Section Axis (Analog) and Spindle
Installation for details on reference point approach).
The reference point shift is also effective in conjunction with automatic reference point
approach (NC MD 560*, bit 6).
Without reference point shift, the reference point is 2000 units behind the first zero mark after
the operating cam has become free again.
If the entry in NC MD 244* is positive, the axis travels the specified number of units beyond
the normal reference point (2000 units beyond the zero mark) in a positive direction.
If the entry in NC MD 244* is negative, the axis, after overrunning the zero mark, travels to
the value represented by the difference between 2000 units and the input value. In the event
of a reference point shift of more than approximately 2000 units, the axis reverses its direction
of travel (backlash on reversal).
Reference point pulse = zero marker from encoder
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MD 244* = 0
MD 296*
Ref. point
Velocity
Ref. cam
Ref. point pulse
Path
2000 units
V
S
MD 284*
6–44 © Siemens AG 1992 All Rights Reserved 6FC5197- AA50
SINUMERIK 840C (IA)
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