Note: Descriptions are shown in the official language in which they were submitted.
CA 02240876 1998-06-17
1
FAIL-SAFE ACTUATOR WITH TWO PERMANENT MAGNETS
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to solenoid actuators for valves and the like in
general
and in particular to an actuator for valves for control of fluid flow. More
particularly
still, it relates to a fail-safe actuator suitable for controlling flow of
toxic substances
or the like hazardous or corrosive fluids.
2. Prior
United States Patent No. 4,259,653 granted March 31, 1981 to McGonigal titled
"Electromagnetic Reciprocating Linear Actuator with Permanent Magnet Armature"
discloses a spring-less linear actuator, especially useful as a print wire
drive. A
permanent magnet armature is driven from a rest position on a pole piece by
magnetic
repulsion upon energization of a solenoid by a D.C. pulse. The armature is
fixed to
a print wire which rebounds from a printing medium, thereby returning the
permanent
magnet toward the rest position, where it is held, without bouncing, by the
magnetic
attraction between the armature and the pole piece of the solenoid, which is
now de-
energized.
CA 02240876 1998-06-17
United States Patent No. 5,546,063 granted August 13, 1996 to Hoffman ritled
"Magnetic Field Solenoid" discloses an electrical coil having a central
opening in
which is fixedly located a rod formed of a material of the type capable of
being
magnetized when in a magnetic field. A plunger is supported for movement
toward
and away from one end of the rod. A permanent magnet is supported by the
plunger.
In one embodiment the permanent magnet is located such that the plunger and
permanent magnet are held next to the coil when the coil is in a deactivated
condition.
When the coil is activated, the magnetic field produced by the coil repels the
permanent magnet and hence the plunger away from the coil. The polarity of the
permanent magnet can be reversed in position such that normally the permanent
magnet and hence the plunger are normally repelled away from the rod end when
the
coil is in a deactivated condition. When the coil is activated in a given
manner, the
magnetic filed of the coil pulls the magnet and hence the plunger next to the
coil. In
another embodiment two permanent magnets are attached to opposite ends of a
plunger
of the type unaffected by a magnetic field to form a push-pull type of
solenoid.
United States Patent No. 5,497,135 granted March 5, 1996 to Wisskirchen et al.
titled
"Bistable Electromagnet, particularly an Electromagnetic Valve" discloses a
bistable
electromagnet moved from one operating position into the other by a short
direct-
current pulse, the next pulse following in each case having the opposite
current
direction. The essential factor in this is a permanent magnet which is
arranged in the
core area and which holds the armature against the action of an armature
spring in one
CA 02240876 1998-06-17
3
operating position. An electromagnet constructed in this manner can be
produced
without tolerance calibration and requires less control power when the
permanent
magnet is carried freely movably between two end positions in the direction of
armature movement in a hollow space of the coil core. The coil core can be
constructed as a pot, at the bottom of which the permanent magnet is
magnetically
held whilst the permanent magnet is held in the other end position by a stop
in such
a manner that its side facing the armature is approximately flush with the
edge of the
pot.
The closest prior art known is United States Patent No. 4,534,537 granted
August 13,
1985 to Zukausky titled "Pilot Operated Valve Assembly" discloses a pilot
operated
valve assembly including a flexible diaphragm which selectively engages a
valve seat
to open and close a fluid passage through the valve. The diaphragm has a
plurality
of filtering apertures and an inward peripheral attaching projection. A
diaphragm
insert is fractionally received in the diaphragm. The diaphragm insert has a
pilot
supply aperture in fluid communication with a peripheral recess extending
inward from
a peripheral edge. The diaphragm filtering apertures are disposed in fluid
communication with the peripheral recess and the pilot supply aperture. The
insert
peripheral edge has a peripheral valley for receiving the peripheral
projection of the
diaphragm. The insert has a pilot outlet aperture which is selectively opened
and
closed by an armature assembly. A guide shell aligns the armature assembly
with the
pilot outlet aperture an defines a pilot reservoir with the diaphragm. This
United
CA 02240876 1998-06-17
4
States patent is incorporated herein by reference.
SUMMARY OF THE INVENTION
The present invention endeavours to provide a springless fail-safe
electromagnetic
actuator for valves or the like. What is meant by fail-safe is that should the
controlling electrical power fail, the actuator will revert to its unactuated
position by
virtue of the interaction of two permanent magnets. In the preferred
embodiment, one
of the two permanent magnets is fixed in position and the other is part of a
reciprocating actuator armature.
The electromagnetic actuator has two permanent magnets arranged along their
polar
axes, with the proximal poles having same polarity. The electromagnet
surrounds the
two permanent magnets and, when energized, overndes the repulsion between the
proximal poles and moves one permanent magnet toward the other fixed magnet.
Should the electromagnet fail, the actuator reverts to the unactuated position
without
need of a spring, gravity and so forth.
According to the present invention, an actuator comprises first and second
permanent
magnets arranged such that their proximal poles have the same polarity and
that an
electromagnet is arranged such that upon magnetization in a predetermined
manner its
magnetization causes a net force causing at least one of said proximal poles
to move
CA 02240876 1998-06-17
toward the other; whereby upon demagnetization or failure of said
electromagnet said
at least one of said proximal poles moves away from the other proximal pole.
According to another aspect of the present invention, an actuator comprising:
a
magnetizable yoke having a central aperture within which an armature made of
soft
5 iron reciprocates; a ring magnet proximal one end of said yoke and having
its central
aperture coextensive with the central aperture of said yoke; said armature
having a
first permanent magnet affixed to its end near said ring magnet; and said
armature
reciprocating between open and closed positions upon momentary magnetization
of
said yoke by means of an electrical pulse having predetermined polarity.
1D BRIEF DESCRIPTION OF THE DRAWINGS
The preferred embodiment of the present invention will now be described in
conjunction with the annexed drawing figures, in which:
Figure 1 shows a cross-section of an actuator according to the present
invention;
Figures 2a, 2b and 2c illustrate the operation of the actuator of Figure 1 in
the off
position, in the on-position and in the on-position immediately following
power
failure, respectively;
CA 02240876 1998-06-17
b
Figure 3 is a schematic representation of a swimming pool or the like
chlorination
system for use with a flow control valve using the actuator shown in Figure 1;
Figure 4 shows a cross-section of an actuator according to the present
invention for
pulsed on-off operations;
Figure 5 illustrates on-off pulses for operating the actuator of Figure 4;
Figure b shows the actuator of Figure 4 in the retracted {open) position;
Figure 7 shows an alternative embodiment to that shown in Figure 4 with only
one
magnet in the reciprocating armature;
Figure 8 shows the embodiment of Figure 7 in the retracted (open) position;
Figures 9a and 9b illustrate the principle of operation of the actuator of
Figures 7 and
8;
Figure 10 shows a variation on the embodiment of Figure 7;
Figure 11 shows the embodiment of Figure 10 in the retracted {open) position;
CA 02240876 1998-06-17
7
Figure 12 shows a variation of the embodiment shown in Figure 10; and
Figure 13 shows the embodiment of Figure 12 in the retracted (open) position.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to Figure 1 of the drawings, the solenoid actuated fluid value
controls the
flow of a liquid supplied via pipe 10 by means of a moving diaphragm 11 to
enable
the liquid to flow through pipe 12. The diaphragm 11 is controlled by the
solenoid
actuator, which comprises an extension armature 13 made of soft-iron and
forming the
extension of an armature permanent magnet 14, such that the entire armature
13/14
is capable of reciprocating movement, within the central cavity of a solenoid
15
enclosed in a surrounding soft-iron yoke 16, toward and away from another
permanent
magnet 17 have the same magnetic polarity (shown here is N for north). If the
permanent magnets 14 and 17 are poled as shown, then the solenoid 15 should be
energized (i.e. when the actuator is on) such that the end of the yoke 16 near
the
magnet 17 is poled S (south}, in order to over-ride the repulsive force
between the
magnets 14 and 17 and draw the armature 13/ 14 towards the magnet 17 and open
the
valve by removing the downward pressure on the diaphragm 11.
To explain the interaction between the yoke 16 and the magnets 14 and 17, we
refer
to Figures 2a, 2b and 2c. In Figure 2a, the solenoid is off and the valve is
closed,
CA 02240876 1998-06-17
g
because the two magnets 14 and 17 repel each other and the yoke 16 acquires
polarities as shown, reinforcing the repulsion. The net force is forward the
diaphragm
11 as indicated by the arrow 19. To turn the actuator on, the solenoid 15 is
energized
and the yoke 16 acquires the polarity as shown in Figure 2b. The over-riding
magnetic field of the yoke 17 attracts the north pole of the armature magnet
14
towards (and in spite of) the magnet 17 and the pressure on the diaphragm 11
is
released as indicated by the arrow 20.
Now what happens should the power energizing the solenoid 15 fluid, is that
the yoke
16 immediately looses its strong magnetization and, as shown in Figure 2C,
reverts
to its previous polarization as in Figure 2A. The result is that a net force
on the
armature 13/ 14 as shown by arrow 21 is produced, which moves the diaphragm l
l to
shut the fluid flow. Note that this fail-safe action does not depend on
springs (which
could break), nor does it depend on the action of gravity, so that the
actuator of the
present invention has no preferred orientation in space.
Shown in Figure 3 is a chlorination arrangement for a swimming pool, which
used a
modified valve manufactured by Eaton Corporation (designated DW-163). T'he
actuator of the DW-163 valve was modified according to Figure 1 of the
drawings,
with the solenoid having a coil resistance of approximately 274 Ohms energized
by a
27 Volts DC. The permanent magnets used were Neodymium short rod magnets of
Master Magnetics Inc. (Castle Rock, Colorado, U.S.A.) designated NEO-27. The
CA 02240876 1998-06-17
9
magnets have a high resistance to demagnetization of -10 Koe and are 0.25
inches long
and 0.187 inches in diameter.
Turning now to the alternative embodiment shown in Figure 4, the solenoid
shown is
operable by momentary pulses only and does not require sustained power in the
valve
opened position, which is desirable in some applications. The solenoid as
shown in
Figure 4 is activated to open the valve by the pulse shown in Figure Sa and
activated
to close the valve by the opposite polarity pulse shown in Figure Sb. The
solenoid
actuator now comprises three parts: an intermediate soft-iron armature 40
having two
cylindrical permanent magnets 41 and 42 at its ends. The solenoid actuator
reciprocates within the central cavity of a solenoid 43 within soft-iron
toroidal yoke
44, which is shaped like a squared C in axial cross-section as shown. A ring
magnet
45 having the same diameter as the cylindrical yoke 44 surrounds a fluid
enclosure 46
of the valve with a gap 47 between the ring magnet 45 and the yoke's 44 end
near the
magnet 41.
Assuming that the valve was in the open position as shown in Figure 6 and a
pulse as
shown in Figure Sb is applied to the solenoid 43, repulsing the magnet 41 and
attracting 42 thereby moving the reciprocating actuator (40/41 /42) to the
position as
shown in Figure 4 and remains in that position after the Figure Sb pulse has
ended due
to a static force in the direction of the arrow 48 because of the interaction
between the
magnet 41 and the ring magnet 45. To open the valve by moving the actuator
CA 02240876 1998-06-17
(40/41 /42) to the position illustrated in Figure 6, a positive going pulse as
shown in
Figure Sa is applied momentarily to the solenoid 43, which magnetizes the yoke
44
in the reverse polarity to that produced by the Figure Sb negative going
pulse. Thus
the magnet 42 into the position shown in Figure G away from the yoke's 44 gap
49
5 edges, depending on how the edges of the gap 49 are poled as either of the
pulses in
Figures Sa and Sb is momentarily applied.
As a variation on the configuration shown in Figures 4 and 6, it is passible
to reverse
the polarities of the two cylindrical magnets 41 and 42, in which case the
free ("N ")
end of the magnet 41 would exit beyond the "N" end of the ring magnet 45 in
the
10 actuator's open position. In the closed position, the free end of the
magnet 41 would
be retracted between the south pole and the central plane of the ring magnet
45, which
again would produce a static force keeping the actuator in that position after
cessation
of the closing pulse.
For the embodiment of Figure 4, the preferred components are as follows:
RING MAGNET (45): Neodymium NR788405325-27 (The Magnet
Source, California)
OD: 0.788 in ID: 0.405 in Thick: 0.325 in
ARMATURE CYLINDRICAL
MAGNETS (41, 42): Neodymium ND283N-27
DIAM: 0.25 in LENGTH 0.25 in
SOFT IRON ARMATURE
CORE (40): DIAM: 0.25 in LENGTH: 0.$4 in
CA 02240876 1998-06-17
11
TOTAL ARMATURE {41, 42,
45) LENGTH: 1.34 in (3.42 cms)
ARMATURE DISPLACEMENT: Greater than 1/ in depending on relative lengths
of the armature and the solenoid (the position of
the gap 49)
SOLEN01D (43): Same as 15 in Figure 1
SOLENOID ACTIVATION
PULSE: Discharge of 400uf capacitor at 100volts; or
Manual momentary pulse ~a 200-300 mA
MEASURED STATIC FORCE
IN "CLOSED" POSITION: 2LBS (40 LBSISQ IN, FOR 1/ ORIFICE)
Where lower forces are acceptable, the magnet 42 may be dispensed with, as
shown
in Figures 7 and 8.
Figure 7 corresponds to Figure 4, and Figure 8 to Figure 6. The only
difference is
that the magnet 42 has been replaces by a softiron armature 50, which is
connected
to non-magnetic armature 5I , the other end of which is connected to the
magnet 41.
In order to open the valve, a pulse as in Figure 5a is applied to the solenoid
43, which
faces the softiron armature 50 to close the yoke 44 gap 49, the magnets 41 and
45
repel and the magnet 41 is attracted to the yoke 44, pushing the softiron
armature 50
to one side of the yoke 44 gap 49, as shown in Figure 8.
In order to close the valve a pulse as in Figure 5b is applied to the solenoid
43 and
the reverse of the above description ensues, with the magnet 41 now partially
inside
CA 02240876 1998-06-17
12
the ring magnet 45. The result is a static force keeping the valve in the
closed
posirion, as explained by means of Figures 9a and 9b. Figure 9a shows the
equilibrium position for the magnet 41 inside the ring magnet 45. Thus, when
the
magnets are in the positions shown in Figure 9b, which corresponds to the
their
position in Figure 7, the magnet 41, being displaced from the equilibrium
position,
is subject to a light attractive force in the direction of the arrow 48. The
valve
remains closed without power being applied.
Figure 10 - 13 show variations on the construction shown in Figures 7 and 8,
where
the positions of the softiron armature 50 and the magnet 41 have been
interchanged.
Thus, in Figures 10 and 11, the valve remains closed (Figure 10) due to a high
repulsive force between the magnets 41 and 45; while it remains open (Figure
11)
when the magnets are in the equilibrium position.
In Figure 12, the valve is closed due to the attractive force between the
magnets 41
and 45; which in Figure 13, the armature magnet 41 is pushed away from the
ring
magnet 45.
In all of the embodiments of Figures 4 - 13 only pulsed operation is required.
