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Memories technique
Using this technique it is possible to control the air supply of the limit switches.
We use the same sequence as in the previous section.
A+ / B+ / A – / C – / B – / C+
1
2
3
4
5
6
The limit switches that generate blocking signals as stated above, are
a0
and
c1
.
Once the blocking signals have been identified, the sequence is divided into groups. Each group comprises a set
of letters, which represent their respective cylinders, within the group the same letter
must not appearmore than
once
.
By subdividing groups in the sequencewe have:
A+ / B+ /
A – / C – / B –
/
C+
A+ / B+ /
C+ the limit switches of this groupwill be fed by a line labelled
U1
A – / C – / B – the limit switches of this groupwill be fed by a line labelled
U2
A 5/2-way memory valve has been introduced to the circuit. The respective outlets
U1
and
U2
, alternating feed
the limit switches of the cylinders of their respective groups.
Figure 84
Phase 1
:
A+
The last movement was the piston rod/piston of cylinder
C
activating limit switch
c1
.
This limit switch is fed by
LineU1
in this active Phase, its output supplies air to the
I.C.
commandwhich permits
the piloting of themain valve of cylinder
A
and the positive stroke of its piston rod/piston.
U1 * c1 * I.C.
=
A+
Phase 2
:
B+
Having advanced to the positive end position, limit switch
a1
is activated and fed by
LineU1
. Its outlet allows the
piloting of themain valve of cylinder
B
and the positive stroke of its piston rod/piston.
U1 * a1
=
B+
Phase 3
:
A –
As per the subdivisionof thegroups, the last operationof thefirst group is reachingposition
B+
. The limit switch
b1
which detects this position is fed by the
LineU1
; its outlet, via signal
S2
, pilots thememory valvewhich enables
LineU2
and disables
LineU1
.
LineU2
pilots themain valve of cylinder
A
and its piston rod/piston completes the negative stroke.
U1 * b1
=
S2
=
U2
=
A –
Phase 4
:
C –
Limit switch
a0
activates upon the completion of stroke
A
–
, its output pilots themain valve of cylinder
C
allowing
the negative stroke of its piston rod/piston.
U2 * a0
=
C –
Phase 5
:
B –
Limit switch
c0
activates upon the completion of stroke
C
–
, its output pilots themain valve of cylinder
B
allowing
the negative stroke of its piston rod/piston.
U2 * c0
=
B –
5
178
CAMOZZI
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CIRCUIT TECHNIQUE