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origin switch
E
D
motion
encoder
index pulse
Figure 6.4-4 — Slow-Speed Origin Switch Search
So far, we can label the two motion segments D and E. During D the control-
ler is looking for the origin switch transition and during E for the index
pulse. To guarantee the best accuracy possible, both D and E segments are
performed at a very low speed and without a stop in-between.
The routine described above could work but has one problem. Using the
low speeds, it could take a very long time if the stage happens to start from
the opposite end of travel. To speed things up, we can have the stage move
fast in the vicinity of the origin switch and then perform the two slow mo-
tions, D and E. The new sequence is shown in Figure
6.4-5.
origin switch
E
D
C
encoder
index pulse
B
motion
Figure 6.4-5 — High/Low-Speed Origin Switch Search
Motion segment B is performed at high speed, with the pre-programmed
home search speed. When the origin switch transition is encountered, the
stage stops (with an overshoot), reverses direction and looks for it again,
this time with half the velocity (segment C). Once found, 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 stage starts from the other side of the origin switch
transition, the routine will look like Figure
6.4-6.
origin switch
E
D
C
motion
encoder
index pulse
A
B
Figure 6.4-6 — Origin Search From Opposite Direction
The ESP system moves at high speed up to the origin switch transition
(segment A) and then executes B, C, D and E.
All
home search
routines are run so that the last segment, E, is performed in
the positive direction of travel.
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