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XPS-Q8 Controller
XPSDocumentation V1.4.x (EDH0301En1060 — 10/17)
A Home switch (Figure 18) separates the entire travel in two areas: one has a high level
and the other has a low level. The most important part is the transition between the two
areas. Just by looking at the origin switch level, the controller knows already on which
side of the transition the positioner is and which direction to start the homing process.
The task of the home search process is to define one unique index pulse as the absolute
position reference. This is first done by finding the home switch transition and then the
very first index pulse (Figure 19).
Figure 19: Slow-Speed Origin Switch Search.
Labeling the two motion segments D and E, the controller searches for the origin switch
transition in D and for the index pulse in E. To guarantee the best repeatability possible,
both D and E segments must perform at a very low speed and without stopping in
between.
The homing process described above has a drawback. At low search speeds, the process
could take a very long time if the positioner happens to start from the one end of travel.
To speed things up, the positioner is moved fast until it is in the vicinity of the origin
switch and then performs the two slow motions, D and E, at half the home search
velocity. The new sequence is shown in Figure 20.
Figure 20: High/Low-Speed Home (Origin) Switch Search.
Motion segment B is performed at the pre-programmed home search speed. When the
home switch transition is encountered, the motion device stops (with an overshoot),
reverses direction and searches for the switch transition again, this time at half the speed
(segment C). Once the switch transition is encountered, it stops again with an overshoot,
reverses direction and executes D and E with one tenth of the programmed home search
speed.
In the case when the positioner starts from the other end of the home switch transition,
the routine is shown in Figure 21.
Figure 21: Home (Origin) Search from Opposite Direction.
The positioner moves at the home speed up to the home switch transition (segment A)
and then executes segments B, C, D and E as in figure 20.
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Motion Tutorial
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