Digital Cam Switch Unit
Digitronic
CamCon DC30
Automationsanlagen GmbH
2.1. Delay time compensation
Every mechanical switching part (e.g. relays, magnetic valves) possesses a delay time, i.e. between
the triggering signal and the actual switching of the contacts passes a certain amount of time. Because
of that, problems can arise during procedures in which positionings are carried out in a moved system.
If such a process is driven with different speeds, different positionings will arise. One would have to
generate new (de)activation points for the switching signals for every speed in order to overcome this.
To explain the problem of the delay time compensation, the context shall be clarified using the
example of a packaging machine. During the process which is presented by the drawing, a dot of glue
is to be applied onto a precicely defined spot of a past going paber web.
magnetic valve
glue nozzle
drop
paper
Points where the glue
hits the paper at the
different speeds
.
paper track
encoder
CamCon
The system has the following parameters:
vp
-
Speed of the paper web
vT
-
Falling speed of the drop of glue
d
-
Distance between the glue nozzle and
the paper web
TMV - Delay time of the magnetic valve
This happens without delay time compensation:
As soon as the measuring system reaches a certain position, the CamCon sends out an impulse to the
magnetic valve. This opens the glue nozzle for a short time, out of which the drop of glue then shoots.
Between the placing of the impulse and the falling of the drop passes a certain time, which is mainly
based on the delay time of the magnetic valve TMV Another delay results in the time in which the drop
needs to cover the distance d between the glue nozzle and the surface of the paper.
This flight time can be calculated with:
tFlight =
d
vT
So a delay time of TMV results altogether. During this time,, the paper web moves a certain
distance further on. One could now decrease the position at which the magnetic valve is activated, so
that the drop of glue hits the same spot as during standstill. One gains a delay time compensation in
this way, which however can only function at one single speed of the paper. As soon as the speed of
the system and the paper web is e.g. doubled, the landing range of the drop of glue is moved again by
the distance x, so that it would, without delay time compensation, move to the rear by twice the
distance (2
⋅
x) altogether.
The automatic delay time compensation of the CamCon makes it now possible to operate with
processes with variable speeds. The CamCon gathers the speeds of the system continually and
adjusts the cams, which define the moments of switching, on line in dependence of the speed.
According to this, the outputs of the switching parts are being switched on or off earlier. The direction
of movement is of no importance.
Page: 6
Version from: 04.06.2002