Motion segment B is performed at high speed, with the pre-
programmed home search speed. When the home switch transition is
encountered, the motion device 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 motion device starts from the other side of the
home switch transition, the routine will look like (
Figure 5.25).
All home search routines are run so that the last segment, E, is
performed in the position direction of travel.
origin switch
ED
C
motion
encoder
index pulse
A
B
Figure 5.25: Home (Origin) Search from Opposite Direction
The ESP300 moves at high speed up to the home switch transition
(segment A) and then executes B, C, D and E.
CAUTION
The home search routine is very important for the positioning
accuracy of the entire system and it requires full attention from
the controller. Do not interrupt or send other commands during
its execution, unless it is for emergency purposes.
5.5 Encoder
PID closed-loop motion control requires a position sensor. The most
widely used technology by far are incremental encoders.
The main characteristic of an incremental encoder is that it has a 2-bit
gray code output, more commonly known as quadrature output
(
Figure 5.26).
5-22 Section 5 – Motion Control Tutorial
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