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A
B
a0
a1
b1
a1
a0
b0
b1
b0
I.C.
F.C.
RESET
EM.
_A
+
B_
+
1 2 3
1 4
I.C.
b0
a0
a1
a1
Fig. 61
The EM command does not always generate the same effect; based on the circuit in which it is engaged, it is
possible for the piston rod/piston of the actuator to reach the end position, in contrast to situations where it is
preferable to return to the cycle start position or an alternative position. In this example you break the cycle and
bring the cylinders to the start cycle position, in a sequence that avoids any eventual mechanical interference.
We develop the following sequence:
A+ / B – / C+ / A – / B+ / C –
Figure 62
Required condition in the case of EM
: the piston rod/piston of cylinders
A
and
B
must be the first to return, and
only upon the arrival of their respective end positions is the piston rod/piston of cylinder
C
able tomove.
Analysis of the circuit:
when the system is stationary the pilot port of the 5/2-way valve is connected to the outlet of the EM valve, this
5/2-way valve has outlet 2 active and feeds the3/2-way valve, which in this phase is closed. By operating the
I.C.
button, and assuming no other commands intervene, the 3/2-way opens and the cycle starts.
While operating the
F.C.
button the3/2-way valve closes, the limit switch
c0
is no longer fed, the sequence reaches
the last phase and stops. Activating the EMwill pilot the 5/2-way valve which exhausts outlet 2, interrupting the
air supply of the 3/2-way valvewhile pressurizing outlet 4, which, via the
OR
function:
• places the 3/2-way valve in the closed position,
• operates the valve in order tomake the piston rod/piston of cylinder
A
return,
• operates the valve in order tomake the piston rod/piston of cylinder
B
return.
In the presence of the output signal from the limit switches
a0
and
b1
and due to the effect of the
AND
function,
we have confirmation that both cylinders have reached the desired position and it is possible to operate the valve
in order to allow the return of the piston rod/piston of cylinder
C
.
By releasing themechanical latch of the EM valve, air supply is restored to the 3/2-way valve and the sequence
can be restartedwith the
I.C.
command.
5
164
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CIRCUIT TECHNIQUE