Siemens SINUMERIK 840C - Manual (Page 859)

12 Functional Descriptions 07.97
12.11.2 ENDAT absolute encoder (SW 5.2 and higher)
12.11.2.4 Special features for large traversing ranges
For the linear absolute scale LC 181, the traversing range is predefined
through the length of the built-on scale.
An overflow of the absolute value of the encoder EQN 1325 occurs after 4096 revolutions.
This means that the calculated position value is unambiguous only over the specified ranges:
• Rotary axis, encoder on load: 4096 load revolutions
• Rotary axis, encoder on motor: 4096 motor revolutions
• Linear axis, encoder on motor: 4096* eff. spindle pitch
With a linear axis having an effective spindle pitch of 10 mm, a traversing range of -20.48 to
+20.48 m is covered.
Since it is practically impossible to put the zero point of the encoder in exactly the same
position as the zero point of the machine, overflow of the absolute value encoder can occur
with large traversing ranges. The NC recognizes this overflow and corrects it appropriately.
The complete traversing range can therefore always be utilized. In as from SW 6, the
functionality ”Range extension with ENDAT absolute encoder” (see Section 12.11.3) can also
be used for larger traversing ranges.
Restrictions with rotary axes
The following restriction applies for rotary axes with absolute encoders in endless operation up
to SW 5:
• If the encoder is fitted to the motor the gear ratio to the load must be n:1 (n motor
revolutions on 1 load revolution). Only powers of 2 are allowed for n.
In the standard case (encoder : load = 1 : 1) there are no restrictions for endlessly operated
rotary axes.
In as from SW 6, any gears can be used with the functionality ”Range extension with ENDAT
absolute encoder”.
• If a rotary axis does not fulfill the specified conditions, it must be
referenced after every endless operation.
• With MD 1808*, bit 6; Singleturn absolute encoder, you can
parameterize whether the actual value is to be determined in the
range of 1 or 16 load revolutions on POWER ON or after ”Park”.
12–84 © Siemens AG 1992 All Rights Reserved 6FC5197- AA50
SINUMERIK 840C (IA)