Table of Contents
Advertisement
Programming the Board
6.3.3
Position Acquisition via Shaft Encoder Edge Evaluation
A two-track incremental shaft encoder with zero-marking track can be connected to each channel (see
also chapter 2.5.1). The counting impulses and counting direction are determined from the signals of
the A and B tracks. This is done by evaluating the edges of the individual tracks.
The following figure illustrates this principle.
A track
B track
Counting pulses
Evaluation:
Counting dirction:
Figure 6.1
Shaft encoder edge evaluation
The counting direction is determined by the relationship of the A track to the B track. The number of
counting pulses depends on which type of edge evaluation was set in the mode registers of the
counters (see chapter 6.4.1).
•
Quadruple edge evaluation counts each edge on the A and the B tracks.
•
Double edge evaluation only counts the change in edge on the A track.
•
Single edge evaluation only counts the rising edge of the A track.
Note:
With single edge evaluation, the counter may drift off slowly in one counting direction (due to
operating mode) even the shaft encoder axis is at a standstill. This occurs when vibrations from the
plant cause the shaft encoder to always have an edge change on the A track.
The hysteresis function which can be activated in the mode registers of the counters (see also
chap. 6.3.11) can be used to counteract this behavior and suppress the first counting pulse after a
reverse in the direction of rotation. The following figure illustrates use of the hysteresis function.
30
4
4
4
4
4
2
2
2
1
Up
4
4
4
4
2
1
SMP16-SFT251
4
4
4
4
4
2
2
2
1
Down
©Siemens AG 2003, All Rights Reserved
(4)J31069-D2090-U001-A1-7618
4
Advertisement
Table of Contents
