US2832867A - Polarized relay - Google Patents

Description

April 29, 1958 H. P. LUHN POLARIZED RELAY Filed June 1; 1954 4 Sheets-Sheet 1 HANS P. LU HN BY f [3W 8M, MZPW ATTORNEYS April 29, 1958 H P, LUQN 2,832,867

POLARIZED RELAY Filed June 1, 1954 4 Sheets-Sheet 2 FIG. 2

FIG. 3 4|0 4 47 45 SSH/4T0 as I 32 320 l 48 1 38 [I j I {I 50 I I 28 28a 49 i i I5 I I 150 5&3

INVENTOR. HANS P. Lu HN ATTORNEYS April 29, 1958 H. P. LUHN 2,832,867

POLARIZED RELAY Filed June 1, 1954 4 Sheets-Sheet 3 I FIG. 5

ATTORNEYS April 29, 1958 H. P; LUHN POLARIZED RELAY 4 Sheets-Sheet 4 Filed June 1. 1954 JNVENTOR. HANS P LUHN ATTORNEYS ilnited. States Patent POLARIZED RELAY Hans P. Luhn, Armonk, N. Y., assignor to International lllnsiness Machines Corporation, New "York, N, EL, a corporation of New York Application June 1, 1954, Serial No. 433,552

7 Claims. (Cl. 200-93) This invention relates to polarized relays of the type wherein permanent magnets are employed to hold the relay in either of its operating positions after the circuit is broken through the coil of the relay whose action opens and closes the contacts. Such relays are widely used in many and various instruments and apparatus wherein electric circuits must be rapidly and repeatedly opened and closed and positively held in position, notwithstanding the mechanical vibration, electrical disturbances and the like which are unavoidable in various types of apparatus in which such relays are employed.

One of the most important requisites of a relay of this character is speed of operation, for in many forms of apparatus such, for example, as electronic accounting machines the speed of operation of the relays is a limiting factor in the overall speed of operation of the machine.

The object of my invention is to provide a relay of this character which will operate at a high rate of operations per minute, will make a good electrical contact and will be maintained in its open or closed position notwithstanding the substantial mechanical vibration and electrical disturbances incidental to the operation of an electronic accounting machine.

A further object of the invention is to provide a relay of this character which is not subject to significant wear even over long periods of operation.

A further object of the invention is to provide a relay of this character which may be readily assembled in multiple units in a common frame or casing, and may be housed in a small space, and utilized in various circuits without disturbing the relays themselves or their mountings.

In the accompanying drawings I have disclosed a preferred embodiment of my improved relay in the form in which it is now made for commercial use. I have selected for illustration a unit containing eight two-way relays.

In the said drawings,

Fig. l is a vertical section of the unit taken on line 1l-l of Fig. and showing a relay and its supporting panel in front elevation and drawn to a greatly enlarged scale;

Pig. 2 is a vertical transverse section taken on line 2-2 of Pig, 1 and drawn to the same scale;

Fig. 3 is a similar section taken on line 3-3 of Fig. 1;

Fig. 4 is a plan view (drawn to a smaller scale) of the base of the relay unit but with the relays, panels and cover removed and the upper portion of the base broken away and shown in section;

Fig. 5 is a vertical section taken on line 5-5 of Fig. 4 and drawn to the same scale, with the relays and their supporting panels in position; and

Figs. 6 and 7 are face views of a supporting panel showing the front and rear sides before the relays are attached.

Referring to the drawings, 1 indicates the base of the unit which is of insulating material, preferably molded phenolic resin plastic, having formed therein a series of rectangular recesses 2 (Fig. 4) connected by slots 3 to receive the lower edge of the supporting panels 4 on which the relays 5 are mounted. The panels 4 are also made of plastic, and pressed into the surface of the panel on each side along the bottom edge are a series of contact strips copper, strips SlS6 (Fig. 1) being on the front of the panel, and strips S7-Sl2 on the rear (Fig. 7). These strips may be fused directly to the plastic when the panel is made, or otherwise attached, with their surfaces approximately flush with the surfaces of the panel.

A panel may be placed in any of the four rows of six holes 2 and slots 3 shown in Fig. 4. The panel is held in position by the frictional engagement of spring contact members two of which are mounted in each of the holes 2, as shown in Figs. 4 and 5. These contact members have spring fingers Flt-F6 which engage the respective contact strips Sll-S6 on the front side of the panel, and fingers 1 7-1 12 which engage the contact strips S7Sll.2 on the opposite side of the panel. These spring fingers serve both to hold the panel in upright position and also to make electrical connections with the respective copper strips S1-S12.

Connections with the desired external circuits are made through these spring fingers Fl--Fl2, and conventional type circuit plugs a may be received in recesses 7' in the bottom of base 1 and have their connecting portions in engagement with conventional receptacle tubes, 8 associated with the respective contact members which support the fingers Fl-Fl2.

Connections on each panel 4 may be made between. various parts of the relays 5 and the contact strips S1S6= on one side and 87-812 on the opposite side in any de--- sired manner, for example, by employing conventional insulated wires each soldered or otherwise connected at one end to the respective contact strips, and at their oppo site ends to the appropriate part of the relay. Preferably, however, such connections are made in part by means of conventional insulated wires, and in part by means of.

the metallic strips shown in Figs. 6 and 7 which are: formed as extensions of certain of the contact strips; Si-Si2, and which are fused flush into the respective surfaces of panel 4.

Thus, referring to Fig. 6, contact S2 has a metallic extension 9 which branches to the opposite sides of the plate and terminates in two metallic contact mounts 10 and 11 for two of the fixed contacts (to be described) of one of the relays These mounts are connected by means of hollow rivets, used in assembling the relay structure, to be referred to later, with contact mounts 10a. and 11a on the opposite side of the panel (Fig. 7 A third contact mount 12 at the top front of the panel supports a third fixed relay contact and is similarly connected to a mount 312a on the opposite side of the panel, and this mount is connected through an extension 13 with contact strip SS. Similarly, contact strips S3 and S6 have extensions which terminate in mounts l4 and 15 for other parts of the relay. Also contact strips Sh and S12 have extensions terminating in similar mounts 14a and 15a.

There are three coils on each side of each panel, the three coils together forming two independently operated two-way relays both of which may be actuated to one of their two positions at the same time, or one to one position and the other to the opposite position, so that each panel provides four separate relays. In the arrangement shown there are two separate panels (Fig. 5) making a total of twelve relays enclosed by a cover 18, the lower edge of which is received on base 1, occupying an overall space approximately two inches by two and one-quarter inches, and two and three-quarter inches high.

Figs. 1-3 show the construction of the individual relays. The two operating coils of the front relay are indicated at .19 and 2G, and the reset coil at 21, this being the middle coil. The corresponding coils and other parts of the relays on the back of the panel are indicated by reference numerals with the subscript a, and no further description will be given. The three coils are alike, that is, they contain the same number of turns of the same gage wire and they are mounted in parallel relation on vertical cores Z2, 23 and 24 which are connected together at the top by means of a yoke member 25. The lower ends of the cores are of a T-shape as shown in Fig. 1, these T-shaped ends forming pole pieces 26, 27 and 28 which are spaced from one another to leave two air gaps between neighboring pole pieces.

The movable part of each relay consists of a swncn member or rocker, these rockers being designated as 29 and 39, respectively. Each rocker is of insulating material such as plastic and has a hub portion 31 with a tubular downward extension 32, and a slender upper portion 33 terminating in a T-shaped head 34. Hub portion 31 has a trunnion mounted on a suitable bearing stud 35 which may be press-fitted into an aperture in the lower end of an extension 36 of yoke member between the coils. The rockers are retained on studs in any suitable manner as by means of snap rings 37.

A small elongated cylindrical permanent magnet 38 is mounted within the tubular extension 32 of each of the switch members or rockers 29 and 30 and the lower ends of these permanent magnets extend into operative relation with their associated pole pieces at the lower ends of the core members 22, 23 and 24. Thus the lower end of permanent magnet 38 of rocker 29 extends into the air gap between the ends of the T- shaped pole pieces 26 and 28 whereas the permanent magnet 38 of rocker 30 extends into the air gap between the pole pieces 27 and 28.

The fixed contact members of the relays are shown at 39, 4t) and 41, these preferably comprising geometrically similar stampings each having a base portion 42 which fits against the flat face of panel 4 from which a horizontal flange 43 is bent outwardly from the lower edge. The opposite ends of this flange are bent upwardly at an angle of about 45 and the outside horizontal edges or corner portions 44 of such portions constitute the portions of the fixed contacts which are engaged by the movable contact members of the relay.

The fixed contact members 39, 4'0 and 41 are assembled in pairs on opposite sides of the panel 4 in engagement with the respective contact mounts 16, 11 and 12 on the front and 10a, 11a and 12a on the rear. They are then attached to the panel by means of hollow rivets or eyelets 45. To facilitate assembly the contact members are preferably provided with pairs of lugs 46 which rest upon the top edge of the panel.

The movable contact members of each switch member 29 and 30 are preferably formed of so-called brush wire. The wire is fairly stiff, quite resilient and highly conductive. Each movable contact member is preferably made of a number of separate wires but for simplicity only one is shown on each side of the rocker in the sample selected for illustration. These two wires are indicated at 47 and 48. Except at their lower ends these wires are normally straight, but are held in slightly bent position when mounted on the switch members.

At their lower ends they are bent to form in effect fiat hooks 49 whereby the wires may be fixedly supported in an aperture in a fixed metal flange or step 50 projecting from the short outer leg of a metal clip 51 which is U- shaped in plan view but has an inner leg 52 which is longer than its outer leg. This clip is attached by means of a hollow rivet 53 to mount 14 on the face of panel 4. The contact wires 47 and 48 for switch member 30 are similarly fixed at their lower ends in a similar U-shaped clip 54 which is attached to mount 15 by means of hollow rivet 55. It will be understood that the construction is similar on the rear side of the panel, the U-shaped members there being designated by the subscript a and attached against the respective mounts 14a and 15a (Fig. 7).

Wires 47 and 48 extend upwardly from their supporting aperture in the metal step 50 and are sprung outwardly and received in grooves in the bulging hub 31 of the switch member. Their upper end portions project through apertures 56 in the T-shaped head 34, being held in position e apertures and by the hub grooves. Wires 47 and 48 extend a sufficient distance above the head 34 to engage the fixed contact members 39, 40 or 41 when the switch members are rocked in one direction or the other and complete an electric circuit therewith. Apertures 56 are preferably slightly larger than the wires 47 and 48 so as to allow the wires to ride loosely therein. The construction provides a slight wiping contact of the wires with the fixed contact members which is suflicient to keep the contacts clean without undue wear.

For illustrative purposes the switch members 29 and 3G in Fig. 1 have been shown in mid position, but it will be understood that in actual operation the permanent ma nets 38 will always be in contact with one of their adjacent pole pieces so that the contact wires 47 and 43 will be swung either to the left or right and one of these wires will engage its adjacent fixed contact member. In other words the switches are of the single pole two-way type.

The operation of the double relay shown in Fig. 1 will now be referred to and in this discussion it will be assumed that the lower end of each of the two permanent magnets 38 has north magnetic polarity, and it will be further assumed that the north pole of the magnet for each of the switch members 29 and 30 is in contact, respectively, with the pole piece 26 of the core of the left hand coil 19, and the pole piece 27 of the core of the right hand coil 29. Thus switch member 29 has been rocked to electrically connect the clip 51 with the central stationary contact 41 through its wire 48, and switch member 30 has been rotated to connect clip 54 with central stationary contact 41 through its Wire 47.

Assume now that operating coil 19 is energized in a direction to produce a north magnetic pole in its pole piece 26. There is a path for the south magnetic flux extending from the upper end of this coil through yoke 25 and center core 24 to pole piece 28, thus forming a south pole in this pole piece. The resultant interaction of the electromagnetic and permanent magnet fields will be to cause the permanent magnet of switch 29 to shift from pole piece 26 of the left-hand core into engagement with pole piece 28 of the center core. This moves the upper end of switch member 29 to the left thereby disconnecting wire 48 from the central stationary contact 41 and engaging wire 47 with the left-hand fixed contact 39. Accordingly, the connection of clip 51 is shifted from contact 41 to contact 39.

This Will not affect the position of switch member 30 Whose permanent magnet 38 remains in engagement with pole piece 27 of the right-hand operating coil However, should it be desired to actuate switch member 30 the energization of operating coil 2% in a direction to cause pole piece 27 to have north magnetic polarity will result in the permanent magnet of switch member 3ft moving to the left into engagement with the center pole piece 23. Thereby the connection of clip 54 is shifted from central stationary contact 41 through wire to the right-hand stationary contact 46 which is now engaged by wire 48. I

Only a momentary or instantaneous energization of coils 19 and 20 is required to produce the shifting of the switch members 29 and 30 as described, inasmuch as they will be held in the positions to which they have been shifted by the magnetic attraction of their respective permanent magnets 38. These magnets each remain in engagement with pole piece 2% after the current has been cut ofi through operating coils 19 and 20 because of the south magnetic poles which will be induced in the pole piece 28 by each of the permanent magnets 38 through the closed magnetic paths from the upper ends of magnets 38, which paths are comprised by the studs 35, the yoke extensions 36, the yoke and the center core 24.

Now, if it should be desired to throw switches 29 and 311 in the opposite direction, that is, back to their original positions, this can be done simultaneously by energizing the center or reset coil 21 in the direction to cause pole piece 28 to have north magnetic polarity. The flux issuing from the top of coil 21 has a divided path to the left and right through yoke 25 in both directions, and then downwardly through cores 22 and 23 to the respective pole pieces 26 and 27, thereby producing south magnetic poles in both of these pole pieces (coils 19 and 21 not being energized). Hence a repulsion is produced between the north pole of each of the permanent magnets 38 of the respective switches 29 and 30, and the pole faces of pole piece 28, and simultaneously an attraction is produced between such permanent magnets and the adjacent south poles. In the case of switch 29 this is pole piece 26, and in the case of switch 39 it is pole piece 27.

The two switches will be held in their respective positions just described by means of their permanent magnets. Only an instantaneous energization of reset coil 21 is required. In the reset position of switch 29, clip 51 will be disconnected from stationary contact 39, wire 47 moving out of engagement therewith, and a connection will be established to stationary contact 41 through wire 68. Similarly, switch will be disconnected from stationary contact 40, wire 43 of this switch leaving contact therewith, and will be connected with stationary contact 4-1, since wire 47 will engage this contact.

The switch members 29 and 30 will be held or locked, by the action of their respective permanent magnets 38, in the positions to which they are actuated, regardless of the direction of actuation.

Neither permanent magnet will be de-magnetized because when any of the three operating coils 1%, 20 or 21 is energized, there is always a magnetic flux path of low reluctance in parallel with the flux path of the respective permanent magnets 38 so that the flux produced by the coil which is energized will follow such path of low reluctance instead of endeavoring to de-magnetize the permanent magnet. For example, when the reset coil 21 is energized in such a way as to produce a north pole in pole piece 28, the flux issuing from the top of center core 24. has return paths through yoke member 25 and the outer cores 22 and 23 to the pole pieces 26 and 27, with only a relatively small air gap between these pole pieces and the lower ends of the permanent magnets 36; consequently any de-magnetizing effect on these permanent magnets by flux attempting to pass through the yoke extensions 36 is small and ineffective.

It will be understood that the connections between the various operating coils 19, 20 and 21 on one side of the panel 4, and 19a, 20a and 21a on the opposite side may be made to the contact strips S1S12 as required for the intended use of the relays. This also applies to the connections between clips 51 and 54 and 51a and 54a (which connect to the movable switch contact members) and the stationary contact members 39, 4t and l1, and 3%, 411a and 41a. As shown in the drawings, clip 51 is connected to contact strip S3 through the clip mount 14 and a contact extension. Similarly, clip 54- is connected through its mount 15 to contact strip S6. Likewise, on the opposite side of the panel, clips 51a and 54a are connected with contact strips S9 and S12 through the respective mounts 14a and 15a and contact strip extensions.

Also, as shownin the drawings, one terminal of each of the six operating coils 19, 20 and 21, and 19a, 20a and 21a is connected to a common contact strip S10 on the back of the panel. As mentioned previously, the conductors used for this purpose (not shown) consist preferably of ordinary flexible insulated wires, and the three wires leading from rear coils 19a, 20a and 21a are to be soldered to the upper end of contact strip S10. The conductors leading from front coils 19, 20 and 21 are to be soldered to a member 57 on the front side of the panel which is secured in place by means of two eyelets, one of which, makes electrical connection with the upper end of rear contact S10. In this way one lead of each of the six coils is commoned on the single contact strip S10.

It will be understood that the opposite leads of the six coils are connected to other of the contact strips. For example, the opposite terminal of coil 19 is connected through a wire conductor (not shown) to the upper end of contact strip S1, while the corresponding lead from coil 21? is connected to contact strip S5. in like manner the free terminal of reset coil 21 is connected to contact strip S4. The opposite terminal of rear reset coil 21a is also connected to contact S4 (through eyelet 59) so that in the relay illustrated the switch members on both sides of the panel are reset simultaneously. The opposite erminals of the other two rear coils 19a and 26a may be connected to the remaining free contact strips 37 and S11, respectively.

In this manner the external operating circuits may be connected with the operating coils of the relay, and the external circuits which are to be made and broken by the four two-way switches 29, 30 and 29a, 30a may be connected with the contacts of these four switch members. It will be understood that the external connections to the operating coils and the switches of the relay may be made in other ways, but the mounting of the relays in pairs on the front and rear of panels such as panel 4, and having the contact strips at the bottom which make contact with the external circuits through the fingers F1- F12 on the base 1 as shown in Figs. 4 and 5, afford a means for mounting the relays in an extremely compact form.

. Furthermore, the mounting of the relays on such supporting panels provides a construction which lends itself well to manufacture of the relays in large quantities and at minimum cost, and the assembling of the parts by means of rivets, preferably of the eyelet type to reduce weight and use of metal, eliminates all screw threaded connections, or connections of any other type which are likely to be loosened by vibration.

A particular example of the present construction which possesses such advantages is illustrated in the manner of attachment of the relays to panel 4. The panel is provided with a series of keyhole-shaped apertures 60. Each of these has an enlarged circular upper portion and a narrower slotted lower portion and the apertures are positioned in the panel at approximately the bottom of the two relay structures.

in assembling the relays on panel 4 a rodlike support 61 (Fig. 3) is slipped into each of the three apertures 60. These rodlike supports 61 are screw-machine-made parts made from a section of metallic rod such as brass having a diameter which may easily be inserted in the upper circular portions of apertures 60. Such supports are grooved centrally as indicated by numeral 62 and again near each end as shown at 63 and 64. In placing a support 61 in one of the apertures the central grooved portion 62 is received in the lower slotted portion of the aperture, the width of the groove 62 fitting the thickness of the panel.

After a support 61 has been placed in each of the three keyhole-shaped apertures 60, a pair of relays is presented to the panel. These relays will have been previously assembled by placing the coils on the respective cores 22, 23 and 24, the pole pieces 26, 27 and 28 being formed integrally with the lower ends of the cores, and then riveting'the upper ends of the cores to the cross yoke member 25 at the three places indicated in Fig. l, The studs with the two switch members 2? and 30 can be mounted in position on the lower ends of the yoke extensions 36, either before or after the yoke is attached.

With the reiays thus assembled a slot 65, which extends upwardly a slight distance from the central lower edge of each of the pole pieces 26, 27 and 23, is fitted into the groove 63 of each of the supports 62 on the front side of the panel, and the relay on the rear side of the panel is similarly rested in the slots 65 at the rear ends of the supports 61. Thereupon the yoke members 25 and 25a of the two relays are held against the opposite faces of the panel and two eyelets 65 are applied through two apertures 56 previously formed in panel 4.

in the foregoing specification I have described in detail the preferred form of my improved relay as designed for quantity production but it is to be understood that the structure disclosed may be variously modified without loss of advantage. For example, the movable contacts could be at the lower ends of the strips 47, 48 with c0- operating contact faces formed on the parts, 26, 27 and 23.

it will also be understood that such variations in the arrangement and construction of the parts of the relay structure may be made without departing from the scope of the invention as set forth in the appended claims.

I claim:

1. An electromagnetic latch relay comprising an operating coil and a reset coil having parallel cores connected at one end by a yoke, said cores having pole faces at their opposite ends forming an air gap, a pivotally mounted armature having a hub portion with a permanent magnet attached on one side of said hub and a contact supporting portion on the opposite side of said hub and approximately in line with the axis of said permanent magnet, said magnet having one end disposed in said air gap, stationary contact members positioned adjacent the opposite end of said armature at the sides thereof, a fixed support adjacent the free end of said permanent magnet, a pair of resilient wires forming the movable contact members of the relay, said wires being mounted on and in substantially parallel relation to said armature and being attached at one end to said fixed support, the opposite end portions of'said wires being attached to said armature contact supporting portion and being movable thereby into and out of engagement with said stationary contact members.

2. An electromagnetic latch relay comprising an operating coil and a reset coil having parallel cores connected at one end by a yoke, said cores having pole faces at their opposite ends forming an air gap, a pivotally mounted armature of insulating material having a hub portion with a permanent magnet attached on one side of said hub and a movable contact supporting portion on the opposite side, said permanent magnet having one end disposed in said air gap, a pair of resilient wires disposed on opposite sides of said armature and projecting beyond both ends thereof, a stationary support substantially in axial alignment with said armature, said support having said wires fixed thereto at one end, and stationary contac members positioned to be engaged by the sides of the opposite projecting portion of. said wires respectively, said wires frictionally engaging the hub portion and the ovable contact supporting portion of the armature and bein held in operative position by their own resilience.

an electromagnetic latch relay comprising an operatand a reset coil having parallel cores connected c end by a yoke, said cores having pole faces at osite ends forming an air gap, 21 nivotailv mounted armature of insulating material having a hub portion with a permanent magnet attached on one side of said hub and a movable contact supporting portion on the opposite side thereof terminating in a T.-shaped head,

said permanent magnet having one end disposed in said air gap, a pair of resilient wires disposed on opposite sides of said armature and forming the movable contact members of the relay, a contact support mounted in stationary position centrally with respect to said pole faces, said wires being attached at one end to said support and having their opposite end portions projecting through apertures in said T-shaped head, the central portion of said wires being sprung outwardly and frictionally engaging the opposite sides of said hub to-hold the wires in position on the armature, and stationary contact members positioned to be engaged by the sides of said respective wires.

4. An electromagnetic latch relay comprising three coils having parallel cores connected at one end by a yok the cores having pole faces at their opposite ends forming two air gaps, said yoke having extensions directed towards said air gaps and terminating intermediate the ends of said coils, armatures pivoted at the ends of said extensions for rocking movement parallel with the surfaces of the extensions, each armature carrying a permanent magnet projecting beyond the extension and into the corresponding air gap, movable contact means carried by each of said armatures, and stationary contact means cooperating therewith, the momentary energizing of either of said outer coils causing its adjacent armature to move into engagement with one of its adjacent pole faces thereby closing the armature contact means against one of its cooperating stationary contacts, and the momentary energizing of the middle coil causing said armature to engage its opposite adjacent pole face and the other armature to hold a symmetrical position therewith, the permanent magnet of each armature having a substantially continuous magnetic flux path through its associated yoke extension to said yoke and therethrough to the cores of said coils, the flux from said permanent magnets producing magnetic poles in the pole faces of said cores which are of opposite polarity to the permanent magnet poles within the air gaps thereby holding said permanent magnets in engagement with the pole faces against which they have een moved by the energizing of any of said coils and thereby latching the armatures in such corresponding positions until such time as a coil is reenergized.

5. An electromagnetic relay comprising an operating coil and a reset coil having parallel cores connected at one end by a yoke, said cores having pole faces at their opposite ends forming an air gap, a pivotally mounted armature having a hub with a permanent magnet portion on one side of said hub and a contact supporting portion on the opposite side of said hub, said permanent magnet having one end disposed in said air gap, stationary contact members positioned adjacent the opposite end of said armature, and movable contacts carried by said contactsupporting portion and cooperating with said stationary contact members.

6. An electromagnetic relay comprising two operating coils having parallel cores connected at one end by a yoke, a rocker armature, means for pivoting said armature for rocking movement between said cores, said armature having a permanent magnet mounted thereon between said pivot and one end of the armature, movable contact members comprising a pair of spring metal wires attached to said armature and extending parallel therewith on opposite sides thereof and projecting beyond one end of said armature, means for anchoring in fixed position the ends of said wires which project beyond the end of said armature so as to maintain the armature normally in mid-position between the two cores, and stationary contact members arranged to cooperate with said wires,

. one of said members being engaged by the side of one of said wires when the armature is rocked in either direction.

7. A polarized relay comprising two coils having cores terminating in spaced poles, a middle coil arranged bet tween said two coils, said middle coil having a core disposed centrally between the cores of the two outer coils and forming with the poles of said cores two pairs of spaced poles, two rocker armatures arranged on opposite sides of said middle coil with the outer ends of their permanent magnets disposed between said respective pairs of poles so that the two rocker armatures may be simultaneously operated by energizing the middle coil and separately operated by energizing the respective outer coils.

References Cited in the file of this patent UNITED STATES PATENTS 10 Nicholson Jan. 12, 1909 Chippen May 29, 1917 Leighton Mar. 22, 1927 Atherton Aug. 19, 1930 Lum Mar. 24, 1936 Koenig Aug. 3, 1948 Merkel Dec. 28, 1948 FOREIGN PATENTS Sweden Apr. 10, 1945 Great Britain Oct. 18, 1945 Germany Jan. 5, 1943

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