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Circuits with dual commands
In some situations itmay be useful to have a second command in addition to the cycle start command, onewhich
permitsmaintenance or adjustment of the individual actuators once the sequence has stopped.
Figure 18
Pos. 1: Controlling a double-acting cylinder withBistable 5/2-way solenoid valve
.
Line 1:
when the
C.C.
(Continuous Cycle) button is pressed, the output signal reaches the closed End Cycle
F.C.
,
button. It passes through, arriving at, and energizing the coil of relay
X
. Contact
x
of this relay, connected in
parallel with the
C.C.
button, closes and latches the
C.C.
buttonwhich can now be released.
Line 2:
also contact
x
on this line closes and the signal reaches limit switch
a0
which by detecting the position
of the piston rod/piston at the negative end position, permits the signal to pass and energize solenoid
B1
of the
solenoid valve. The solenoid valve changes over and the piston rod/piston executes the positive stroke, reaching
position
a1
.With the release of the limit switch in position
a0
the contact opens and interrupts the passage of the
signal to solenoid
B1
. Even in the absence of this command, the bistable solenoid valve maintains the position
given by the last received signal.
Line3:
Onceposition
a1
has been reached, the corresponding limit switch is activated thereby closing the contact,
allowing the signal to energize solenoid
B2
. The solenoid valve changes over and the piston rod/piston executes
the negative stroke.
Once the position has been reached, limit switch
a0
re-activates, the signal is then free to pass (as the contact
X
is still closed), re-energizing solenoid
B1
, and the sequence repeats.With the release of switch limit
a1
, the signal
to solenoid
B2
is interrupted.
By pressing the EndCycle
F.C.
button, relay
X
de-energizes and opens contact
x
on
Line1
releasing the latch, the
cylinder can only be restarted if the
C.C.
button is pressed again.
Pressing the Single Cycle
C.S.
(
Line 2
) while the piston rod/piston is at end position
a0
causes solenoid
B1
to
energize.
The solenoid valve changes over, the piston rod/piston completes the positive stroke. Upon reaching limit switch
a1
, if the
C.S.
button is released, solenoid
B2
is energized to execute the negative stroke. Once the negative end
position has been reached, the cylinder stops.
In the event of a power failure the piston rod/pistonwould complete the current stroke and then stop. If it were in
the positive end positionwhen the power is restored, it would return immediately to its starting position as signal
a1
energizes solenoid
B2
.
Note
: The
C.S.
button can not be placed in parallel with contact
x
on
Line 1
and the
C.C.
button, as its activation
would drive the coil of the relay
X
, to energize, cancelling the single cycle function. (Ref. circuit in the box).
Figure 18
Pos. 2: Control of a double-acting cylinder with aMonostable 5/2-way solenoid valve
.
With this type of solenoid valve the
C.C.
and
C.S.
commands must be memorized for the duration of the positive
stroke.
Line 1:
by pushing and holding down the
C.C.
button, the signal reaches and passes through the contact of the
F.C.
buttonand energizes the coil of relay
X
thereby closing contact
x
. This contact, inparallel with the
C.C.
button
latches. The
C.C.
button can then be released.
Line 2:
also contact
x
on this line closes, the signal passes and reaches limit switch
a0
, which, by detecting the
position of the piston rod/piston at the negative end position, allows the signal to energize solenoid
B1
, the signal
also reaches the coil of relay
Y
on
Line 3
.
Line 3:
when the coil of relay
Y
energizes, its respective contact
y
closes. As contact
z
is closed, the signal once
again reaches the coil of relay
Y
and latches.
Line 4:
with solenoid
B1
on
Line 2
energized, the piston rod/piston initiates its movement towards limit switch
a1
, which, once reached, allows the signal to reach the coil of relay
Z
.
When contact
z
opens, the coil of relay
Y
is de-energized. Opening contact
y
and releasing the latch interrupts the
energizing of solenoid
B1
. The solenoid valve, due to the effect of the internal spring, returns to its rest position and
the piston rod/piston completes thenegative stroke.With the activation of the limit switch
a0
, the signal, still active
on
Line 2
, will once again reach solenoid
B1
and the coil of relay
Y
, and a new sequence begins.
By pressing the
F.C.
button, the coil of relay
X
de-energizes, the contact
x
on
Line 2
opens and interrupts the
energizing of solenoid
B1
and the coil of relay
Y
.
TheSingleCyclebutton
C.S.
(
Line2
) is inparallel with contact
x
and repeats the flow illustratedaboveby stopping
the cycle when the piston rod/piston reaches the negative end position again. For a new Single Cycle the
C.S.
buttonmust be pressed.
In the event of a power failure, the cylinder immediately returns to the start position. The restart is obtained by
pressing the
C.S.
or
C.C.
buttons.
6
204
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ELECTRO-PNEUMATICCIRCUITS