Technology Option F01
08.2012
6SE7087-6QX70 (Version AN) Siemens AG
9-52
Compendium Motion Control
SIMOVERT MASTERDRIVES
9.4.10
Linear axis with absolute encoder when the traversing range is
greater than the display range of the encoder.
The following chapter describes the procedure when the traversing
range of a linear axis is greater than the traversing range of the
absolute encoder.
Absolute encoders have a limited display range. For example, on
multiturn encoder EQN1325 up to 4096 encoder revolutions can be
counted. This is sufficient for most applications. However, if the
traversing range of the linear axis is greater than the display range of
the encoder, an encoder overflow occurs. The position of the axis can
no longer be uniquely determined.
This problem is explained in the diagram below:
Absolute encoder
position
Linear axis position
A
B
Encoder
overflow
When the encoder overflows, the absolute encoder starts counting from
zero again. The position of the linear axis is position A, but position B is
output by the absolute encoder.
Function block "Starting position absolute encoder" function diagram
[327] ([333]) ensures the correct functioning of the position acquisition
even if the encoder overflows.
The function block is integrated as shown in the function diagram. The
block is handled in exactly the same way as that of the rotary encoder
(section "9.4.9"), only configuration U813 (U798) has to be
parameterized to xxx1 = linear axis.
Maximum 15 encoder overflows can be tracked. When the range is
exceeded, a fault is displayed at binector B565 (B566).
Position tracking is set such that the overflow counter lies within the
valid range 0 to 15. Underflows below zero must be prevented. The
following commissioning procedure must therefore be followed:
The linear axis is traversed to the end stop, so that the smallest
possible position actual value results. The overflow counter is then set
to zero via U812 (U797) and the converter is switched off and on again.
Basic problems
NOTE
Handling
