US2550779A - Electromagnetic unit - Google Patents

Description

May 1, 1951 A. M. COHEN ELECTROMAGNETIC UNIT 3 Sheets-Sheet l Filed April 25, 1950 May 1, 1951 A. M. COHEN 2,550,779

ELECTROMAGNETIC UNIT Filed April 25, 1950 3 Sheets-Sheet 2 INVENTOR. 4677/0@ M. @QH/5N l wm- May 1, 1951 A, McoHEN 2,550,779

ELECTROMAGNETIC UNIT Filed April 25, 1950 3 Sheets-Sheet 3 JNVENTOR. 4277/0@ M Caf/7V Patented May 1, 1951 UNITED STATES PATENT OFFICE The Vpresent invention relates to a novel construction of an eleotromagnet having a movable armature, particularly adapted to be used for controlling linger-type circuit regulator. This application is a division or application Ser. No. 34,517, iiled lune 22, 1948 entitled Finger Type Circuit Regi* Circuit regulators, and particularly those of the type known as voltage regulators, have in the past taken a large number of forms. The present invention relates to that 'type of regulator commonly known as the linger type by reason of the fact that it employs a plurality of movable lingers each normally urged into electrical connection with a corresponding fixed Contact, the lingers being sequentially movable out of electrical engagement with their respective Xed contacts so as to vary the circuit constants of the circuit with which the regulator is associated. Finger type regulators as heretofore known have suffered from the disadvantage that they were either exceedingly large and heavy or else were highly susceptible to derangement and malfunctioning because ci vibrations or the position in which they were placed. In addition, those nger regulators which were not of relatively massive proportions were extremely fragile and hence di te undependable. As a result, the utilication or" finger type regulators has lagged con siderably behind regulators of other types. rlhis has been particularly true in military installations where dependability under all sorts of climatic condi ns and under extreme vibratory conditions, s as are experienced in tanks and aircraft, is a prime requisite. In addition, size and weight considerations are of extrem@ iinportance peticularly insofar as =porable and aircraft inst `llations are concerned. No linger type regulator has in the past been able to satisfy military reouirements and, the sise and Weight of prior art linger type regulators as used in industrial applications have made the units so expensive that they could not economically compete With alternative devices.

By means or an extensive redesign of linger type regu ors l have produced a unit which is i exceedingly small size yet which will operate .ccurately no nf er in what position it may be d nor to iv f atec forces it may be subjected. f exhibits outstanding relviy entire unit may be t g 1% inches high, 1% inches loog and 1% inoiles Wide. rhe inherent accuracy of my device is so great, even when subjected to ator.

which sistance to vibration. encompassed in a liousi' 26 Claims. (Cl. 175--345) to extreme vibratory action, that it has successfully passed all of the tests prescribed by the United States Army Air Forces and the United States nllrmy Signal Corps for circuit regulators, and in passing them has performed better than non-ringer type regulators formerly used for the same purpose. My device is the iirst linger type regulator capable of satisfying these requirements. Orders for substantial numbers of my regulators have already been made by the Armed Forces.

The greatly improved operation of my device is due to a number of specific design features which depart radically from similar prior art devices. Prior application Ser. No. 34,517, of which the instant application is a division, relates to the interconnection of the finger lifting member and the electromagnetically controlled armature, and to other related features. The instant application rela-tes more speciiieally to the mounting of said armature and the construction of the electromagnet which controls it.

Other novel features of my regulator shown but not claimed herein are claimed in my copending application, Ser. No. 49,726, filed September 17, i948, entitled Finger Type Circuit Regulator Contact assembly Ther-eier and Method of Making Same.

To design. a linger type regulator characterized by lightness, coinpactness, and inexpensiveness and at the same time accurate in all positions and when subjected to extreme vibratory iniiuences required a. complete rearrangement of the moving parts of the regulator, these zparts including the armature and the linger lifting member. lt was discovered that, for accurate control of the movable lingers, it was desirable that the linger lifting member be movable substantially in a straight line and that it engage the lingers by motion substantially at right angles thereto. It was further discovered that dashpot damping of these moving parts was an important factor in achieving proper operation. To mount the dashpot in line with the finger lifting member would result in a unit of excessive size. Since the plunger moves in the dashpot with very small clearance, on the order of a few ten-thousandths or an inch, it is essential that the plunger be urged as closely as possible in its direction of moverrient, since any material deviation from that direction or movement would cause the plunger to tend to bind in its cylinder and hence not only destroy the damping eiiect but pre ent the linger lifting member from moving at all. By the same token, if the finger lifting member were disposed in line with the armature, or, to put the matter another way, if the armature were movable in the same direction as the finger lifting member, the size of the unit w-ould be materially increased.

Hence, in the design here disclosed, the armature is pivotally mounted on the electromagnet which constitutes the armature moving mecha` nism and is disposed substantially perpendicular to the finger lifting member to which it is pivotally connected. Springs are active on the finger lifting member to bias it to a position out of engagement with the fingers, this feature Well known in prior art regulators, but in the design here disclosed, the springs so orient the linger lifting member that it assumes a position substantially perpendicular to the armature and to the lingers and maintains its angular relationship` to the fingers and to the dashpot throughout its range of movement. The plunger of the dashpot is fastened to the finger lifting member, and through it to the armature, by means of an angular connection so that as the finger lifting member moves, the angular connection moves the plunger of the dashpot in its permitted direction of movement, this eliminating any possibility of binding on the part of the plunger in its cylinder.

The armature is so mounted on the electromagnet that it may conveniently be adjusted With regard thereto so as to aid in the expeditious assembly of the unit and so as to achieve the most desirable operating characteristics. The mount-1 ing construction is such that the armature pivots frictionlessly about an axis, which axis shifts With the armature as the armature is adjusted on the magnet, so that calibration is facilitated.

The mounting is so designed that the armature will pivot about the same axis no matter in what position the unit may be placed nor to what accelerated forces it may be subjected. This is particularly important in aircraft installations Where the position of the aircraft with respect to gravitational pull may vary Within wide limits and where the extreme maneuvers carried out at high speed of which military aircraft must be capable exert large accelerative forces on the units contained Within the aircraft.

The prime object of the present invention is, therefore, to devise a ringer type regulator design which will permit the regulator to take up as small a space as possible and a much smaller space than any of the similar prior art devices and at the same time to cause the regulator to function with a high degree of accuracy under adverse conditions.

A further object of the present invention is to devise a novel armature mounting arrangement which will permit the armature to frictionlessly pivot about the nxed axis no matter in what position the unit may be placed nor to what accelerative forces it may be subjected.

It is yet another object of the present invention to devise such an armature mounting arrangement whieh is capable of adjustment on the electromagnet so that the armature may be expeditiously accurately positioned. with respect to the electromagnet, and in which the pivot axis moves with the armature so that calibration on account of displacement of the pivot axis is not necessary.

To the accomplishment of the foregoing objects such other objects as may hereinafter appear, the present invention relates to the construction of a ringer type electric regulator as defined in the appended claims and as described in this 4 specification, taken together with the accompanying drawings, in which:

Fig. l is a side view, partially in cross-section of one embodiment of the regulator of the present invention;

Fig. 2 is an end view thereof;

Fig. 3 is a top View thereof;

Fig. l is a side fragmentary View showing the armature mounted on the electromagnet;

Fig. 5 is a view taken along the line 5-5 of Fig. 4;

Fig. 6 is a cross-sectional View taken along the line i-i of Fig. 5.

Fig. 7 is a top view of the armature and the mounting member therefor;

8 is a cross-sectional view taken along the line f-8 of Fig. 5; and

Fig. 9 is an exploded view of a second embodiment of the present invention diifering from the iirst embodiment in manners not pertinent to the present invention.

The regulator here described comprises an inysulating plate 2, formed of any suitable insulating material, from which connection prongs 4 depend, so that the entire unit is adapted to be plugged into a suitable socket. A metal plate 6 is secured to the insulating base 2 as by means of eyelets S, and a casing It, shown in Fig. 1 in dotdash lines, is adapted to be secured to the plate G in any appropriate manner.

The contact assembly generally designated I2 comp-rises a plaque ill at one end of Which a plurality of xed contacts l 6 are secured, these contacts in Figs. 1 3 being individually connected by means of the leads !8 to the appropriate one of the prongs Also secured to the plaque I4 are a plurality of resilient fingers Z, one for each fixed contact I6. The fingers 20 in the form here disclosed are formed of a resilient material which is a good conductor of electricity. The free ends 22 of the fingers 26 project out beyond the plaque It and the `ngers 2!) are normally urged into electrical connection with the xed contacts i6, thus dening movable contacts. A metal clamp 2li serves in the embodiment of Figs. 1 3 to secure the inner ends of the fingers 'Z' to the plaque lf2. A pair of mounting arms 25 are secured to the plaque Ed and are spaced from the plate ii by means of sleeves 28, the sleeves being appropriately positioned by passing over screws Si! extending upwardly from the insulating plate 2.

The electromagnet generally designated 32 which denes the armature moving mechanism comprises an energizing coil Sli wound around a .magnetizable core Se, the upper end of the core being secured within the magnetizable top plate 33 of the electromagnet 32. Magnetizable spacers ed are also secured at one end to the magnetic top plate $3 and at their other end have screw threaded projections l2 which pass through apertures i3 in the magnetizable bottom plate fie. The core 3b extends downwardly through an aperture it in the bottom plate M. Leads 48, which pass through apertures i9 in the bottom plate it, connect the coil 34 to appropriate prongs (i.

internally threaded spacers 5e and 52 are poitioned below the magnet bottom plate el! so as to receive the threaded projecting portions 42 of the magnetizable spacers 43S, thus maintaining the electromagnet 32 in assembled position. The spacers are considerably shorter than the spacers 5i?, the spacers 5Fl extending between the magnet bottom plate lili and the plate E and being secured in position by means of screws 54 extending through the insulating plate 2 and the spacers 52 being positioned between the contact assembly I2 and the magnet top plate 38 so as to be threadedly engageable with the screws 30. In this way, the contact assembly I2 and the electromagnet 32 are secured in position in the unit.

The armature 56 is in the form of a nat sheet of magnetizable material to the upper surface of which is secured a flexible sheet deiining the magnet mounting member 58, the mounting member 55 being in turn secured to the magnet bottom plate 44 between said plate 44 and the spacers 52. The armature mounting member 5S is so constructed that the armature 55 is pivotable about an axis parallel to the plane of the lower surface of the magnet bottom plate 4P. and parallel to a line between the axes of the spacers 552, as will be described later more in detail. The right hand portion of the armature 55, as viewed in Fig. l, is provided with an aperture B concentrically arrangeable with the downwardly pron jecting portion of the core B so that said pro- `iecting portion is receivable therein. The left hand portion of the armature 56 extends out beyond the electromagnet 32, and it is to that left hand portion of the armature 55 that the armature mounting member 58 is fastened as by means of rivets 52. The spacers 59 are provided with shoulders 13 which are adapted to engage with the extreme right hand portions of the armature 56 so as to limit its pivotal motion in a clockwise direction as viewed in Fig. 1.

The finger lifting member 65 is in the form of a sheet of non-conductive material having an in clined lower edge G8. The member 6 is mounted substantially perpendicular to the extending free ends 22 of the fingers 2D and is movable in a direction substantially perpendicular thereto so that as the member '65 is moved downwardly, its inclined lower edge 88 will sequentially make contact with the fingers 23 and thus move them one after the other out of electrical connection with the fixed contacts I6.

The extreme left hand portion 'iii of the arman ture mounting member 58 extends out beyond the armature '3 and is receivable in the aperture 12 in the finger lifting member 65 so as to be passable between the upper surface of said aperture 72 and the lug 1li formed therein. The portion 'l0 of the armature mounting member is nrovided with an aperture 16 through which the lug 'i4 is receivable, and by means of this lug and aperture connection the finger lifting member et is connected to the armature 5S so as to be pivotable with respective thereto as the armature is pivoted on the magnet bottom plate Ali.

In order to ensure that the finger lifting member maintains its proper position, so that the entire width of its inclined lower edge |58 will make contact with the ends 22 of the fingers 2Q. a pair of springs 8d are active thereon, one end of each of the springs being securable in apertures 82 in the member 65 and the other end of the springs being securable in notches 8l!- in the frame portions 86 which may be integral extensions of the magnet top plate 38. The frame portions St are preferably made relatively narrow so that they may, if desired, be manually bendable so as to vary the tension which the springs exert upon the finger lifting member 66.

The dashpot generally designated B8 comprises a cylinder 3Q which a piston 92 is slidable. The dashpot 38 is secured to the unit by means f screws S4 which pass through other frame portions also preferably integral extensions of the magnet top plate 38, these frame portions being separated so as to provide access to the adjusting screw S8 which controls the air escape from the dashpot 8B and hence determines the extent of itsdamping action. The plunger S2 of the dashpot 8S is secured to the nger lifting member G5 by engagement of the angular connection ESS, here shown as of L-shape, in the aperture |G| of the member 65, in which it may be secured by solder |53.

The detailed construction and functioning of the armature mounting may best be seen in Figs. 4 through 8. The .magnet bottom plate d4, which is end plate of the electromagnet 32, has a side M32 beyond which the left hand portion of the armature 5S projects. Centrally mounted adjacent the side |32 a stop mit having a shoulder |355 which projects out beyond. the side E32 and below the plate It, the stop ldd as here illustrated projecting downwardly from the magnet bottom end plate 44. The side H32 is provided with an inset portion it under the shoulder tilt and is also provided with inset portions lli on either side of the stop` |534, the purpose of which inset portions Hi8 and will become apparent hereinafter.

The armature mounting member 53 may be stamped or otherwise formed from a single thin sheet of flexible and preferably resilient material such as beryllium copper so that its various segments are integrally connected.. It will be noted that said sheet need not be of magnetic-able material. It comprises portions H2 having aper- 'ures H4, the apertures H4 being considerably larger than the externally threaded projecting portions t2 of the spacers d0, the portions H2 of the mounting member 53 receiving the proutesting portions i2 within. the apertures lift and being securable between the net bottom end plate Mand the spacers 52.

Integrally connected to the portions ||2 are strips H6 which are fastenable, by means of rivets E2, to the left hand end of the armature 55. The strips HE are so positioned with respect to the portions H2 that they pass over the inset portions Hi) of the magnet bottom end plate M.

Also a part of the magnet mounting member 58 are legs i2 which are adapted to be positioned over the portions |22 of the magnet end bottom plate dtbetiveen the inset portions iif thereof. The legs 23 terminate in aligned edges IE which. as will be seen most clearly from Eig. 3, constitute the axis about which the armature 5E pivots.

Connected to the left hand extremity,7 of the strips Ht is linger |25 optionally secured. to the armature 55 by means of rivet |25 and termin hating in an edge i3d preferably in line with the edges E24 of the legs |20. The end portion of the finger |2 is receivable beneath the shoulder Inti of the stop ldd., that shoulder being separated from the bottom surface of the magnet bottom end. plate 44 by a distance equal to the thickness of the finger |2i. The armature 5:3 is provided with an aperture |32 through which the stop is freely passable.

The embodiment of Fig. 9 differs from that Figs. l 2 and 3 in that the xed contacts i5 are individually bendable, are secured to the plarnie 4 by means of a metal clamp 2li', and are provided with a common lead t8. pian-ue iii is secured in the unit by the U-shaped mounting member 2t" and the ngers 2i) are individually secured tothe plaque i4 by the eyelets 65 and are provided with individual leads itv to the appropriate prongs 4.

By reason of the pivotal connection between the finger moving member 5S and the karmature 55 and because of the location and orientation of the springs SU, the nger lifting member e3 is caused to assume a position substantially perpendicular to the armature 5t and in line with the springs e6. As the armature 56 pivots by reason of the energization of the electromagnet 32, said energization causing attraction between the magnet bottom plate 44 and the right hand end of the armature 55, the nger lifting member B6 will be moved downwardly so as to bring its inclined lower edge E8 sequentially into engagement with the lingers 20, thus moving them one by one out of electrical connection with the corresponding nxed contacts i6. As this takes p-lace, the action of the springs Si) and the pivotal connection between the armature 56 and the nnger lifting member -66 causes the member 66 to maintain the same angular relation to the fingers 2@ and the stationary parts of the unit so that the entire width of the lower edge 68 bears directly upon the fingers 26, thus increasing the accuracy of the device. It will be clear that if the member 6e were to accurately maintain its angular relationship with the armature 56 as the latter pivots, the entire `width of the surface E3 would only be active upon the ngers for one position of the moving parts and that as the parts deviate from that position, the edges rather than the entire width of the surface t8 would be effective to move the lingers 26. Such a differential aotion would make for great dimculty in calibration and would render the device quite undependable, particularly if the fixed angular relationship between the ringer moving member (it and the armature 56 should be upset.

The members 66 will move, as the armature 56 pivots, substantially inthe plane of its orientation. The motion will not be exactly in that plane because of the fact that the extending end 10 of the armature mounting member 58, to which the finger lifting member 66 is directly connected, describes an arc. However by reason of the limited degree of pivoting of which the armature 56 is capable, the motion of the nger lifting member 65 is planar for all practical purposes and is in the plane in which the member 66 is oriented. Hence, engagement between the fingers 26 and the lower surface 68 of the member 66 is direct and positive, with only an infinitesimal and wholly inconsequential sliding movement over the ringer 26. In addition, since the motion of the member 66 is in the saine direction as the permissible motion of the plunger 92 of the clashpot 38, the tWo may be directly connected ywithout any danger of binding in the dashpot 88. The deviation of the motion of the member 66 from true planar motion is so slight as to be imperceptible to the plunger 92 of the dashpot 88, particularly when the connector |66 is even slightly resilient.

The magnet mounting member 58 is interposed between the armature 56 and the magnet bottom end plate i4 so that the armature and the magnet end plate are separated by the thickness of the mounting member 56. Since the legs 29 terminate short of the side |62 of the magnet bottom plate 44, the biasing tension exerted by the springs t6 will cause the armature 5t to pivot about the edges 24 of the legs lila. Since those edges are in line, they denne an axis about which 8 the armature is pivotable. If the electromagnet 32 be energized, the armature 56 will be caused to pivot in a counter-clockwise direction as viewed in Fig. 1, this pivoting still taking place about the same axis. The stop 164 is active upon the finger |26 so as to prevent the armature 56 from moving away from the magnet bottom plate 44, thus rendering the pivoting motion of the armature independent of the position of the unit and also independent of any accelerative forces to which the unit may be subjected. In the event that, because of a substantial change in direction of motion of the unit, as when the unit is contained within an aircraft making a high speed turn, the armature 56 is urged away from the magnet end plate 44 the actual pivoting action of the armature 55 may be exerted about the edge E36 of the finger |26 as that edge is retained in position by th-e shoulder H16 on the stop 64, but, since the edge |36 is preferably in line with the edges 124 of the legs H26', the armature 56 will still pivot about the same axis.

In assembling the unit, the armature 56 is nrst secured to its mounting member 53, by means of the rivets 62 and H28, and the portions H2 of the mounting member 58 are then placed in position on the magnet end plate 44, the projecting portions i2 of the spacers 46 being received within the apertures H4. Since these apertures H4 are considerably larger than the projecting portions 42 of the spacers 46, the armature mounting member 58, and with it the armature 56, is slidable Within limits over the magnet bottom plate 44. The armature 56 is therefore adjusted until its aperture 66 is rendered concentric with the core 36 of the electromagnet S2. This may readily be accomplished by the use of a ring gauge dimensioned to fit between the exterior of the core 36 and the interior of the aperturey 66. When proper positioning has been thus achieved and maintained, the spacers 52 may then be tightened, thus fixedly securing the armature 56 in its proper position. It will be noted that any shifting of the armature 56 to bring it into proper position with respect to the core 3% is accompanied by a corresponding shift of the pivot axis about which the armature 56 will pivot, since the axis is dened by the edges i253 and 36 of the legs |26 and the nger i265 and said legs and nger are rigidly attach-ed to and consequently move with the armature 56 as it is moved.

The importance of achieving proper relationship between the armature 56 and the electromagnet 32 is apparent from the fact that the magnetic iiux generated by the coil 34 passes upwardly through the core 36, through the magnet top plate 38 and thence through the magnetic spacers 43 to the magnet bottom plate 44. The ilux then tends to pass from the interior of the aperture l5 in the magnet bottom plate 44 back to the core 36, but the large air gap inhibits this flow. Most of the flux passes to the armature 55 and of the flux which does go to the armature 56 most of it enters the armature near the pivot point thereof where the air gap is least. From there, the flux jumps the air gap between the interior of the aperture 66 in the armature 56 and the core 35, since this air gap is considerably less than the air gap between the interior of the aperture i6 and the core 3S. As the armature pivots in a counter-clockwise direction, the ux distribution will change because of the greater proximity of the extreme right hand end of the armature 56 to the magnet bottom plate 44 and because the projecting tip of the core 36 is receivable within the aperture 69. If the aperture El! is properly positioned with respect to the core 36, a straight line relationship between the magnetic pull and the position assumed by the armature 5t will result over a large proportion of the permissible movement of the armature 553.

The inset portions lit of the side m2 of the magnet top plate 44 project inwardly beyond the pivotal axis of the armature 56 so that the strips H8 are permitted to bend freely above the plane of the lower surface of the magnet bottom plate 44 as the armature pivots. The pivotal action is therefore frictionlesg and unimpeded throughout the eiective motion of the armature.

B y the above described arrangement of fixed and moving parts, I have devised a ringer type regulator which is capable of being encompassed in an exceedingly small space, which utilizes a minimum number of parts, which is extremely simple to assemble and adjust, and which may be manufactured at a small fraction of the oost of prior art structures comparable in operation. The device of my invention is exceedingly accurate and capable of operation over long periods of time and under adverse conditions of climate, placement and vibration without loss of dependability. By the arrangement here described, a compact unit is developed the moving parts of which are so spatially and directionally related as to ensure a maximum of positive and predictable operation and a minimum of deviations from normal operation.

The mounting 58 for the armature 5e is extremely inexpensive, since it is stamped from a single thin sheet of appropriate material, and provides for frictionless pivoting motion of the armature. By reason of its construction, the axis about which the armature pivots remains the same no matter in what position the unit is placed nor to what accelerative forces it is subjected. The armature is easily adjustable in its mounted position so as to achieve the best magnetic eiects, and the adjustment of the armature with regard to the electromagnet automatically adjustsi the position of the axis of pivoting so that no further compensation need be made therefor. The unit is composed of a minimum number of parts, all easily fabricatable on a mass production basis to commercial tolerances and quickly and simply assemblable into the finished unit without requiring the use of any equipment more complicated than a conventional ring gauge.

AIt wil be apparent that many deviations may be made in the details here disclosed without departing from the spirit of the invention as dened in the following claims.

I claim:

l. An electromagnet-armature combination comprising a frame, an energizing coil mounted therein, a magnetizable core xedly secured in said coil and having a tip extending out from one end thereof, a magnetizable bottom plate on said frame overlying said coil end and having an aperture larger than said core tip through which said tip passes and beyond which it projects, and an armature pivotally mounted on said frame below said bottom plate so as to extend over the aperture therein, said armature having an aperture larger than said core tip and concentric there- With and smaller than the aperture in said bottemplate.

2. An electromagnet-armature combination comprisinga frame, an energizing coil mounted therein, a magnetizable core ilxedly secured in said coil and having a tip extending out from one end thereof, a magnetizable bottom plate on said frame overlying said coil end and having an aperture larger than said core tip through which said tip passes and beyond which it projects, and an armature separated from and pivotally mounted on said bottom plate so as to extend over the aperture therein, said armature having an aperture larger than said core tip and concentric therewith and smaller than the aperture in said bottom plate; 4

3. An electromagnet-armature combination comprising a trame, a magnetizable top plate therein, a magnetizable core secured to said top plate, an energizing coil surrounding said core, a magnetizable bottom plate on said frame at the opposite end of said coil from said top plate, said core having a tip and said bottom plate having an aperture larger than said core tip through which said core tip passes and beyond which it projects, and an armature pivotally mounted on said frame below said bottom plate and below all other magnetizable components of said combination so as to extend over the aperture therein, said armature having an aperture larger than said core tip and concentric therewith and smaller than the aperture in said bottom plate.

4t. electromagnet-armature combination comprising a frame, a magnetizable top plate therein, a magnetizable core secured to said top plate, an energizing coil surrounding said core, a magnetizable bottom on said frame at the opposite end of said coil from said top plate, said core having a tip and said bottom plate having an aperture larger than said core tip through which said core tip passes and beyond which it projects, and an armature separated from and pivotally mounted on said bottom plate and below all other magnetizable components of said combination so as to extend over the aperture therein, said armature having an aperture larger than said core tip and concentric therewith and smaller than the aperture in said bottom plate.

5. An electromagnet-armature combination, said electromagnet comprising a magnetizable top plate, al magnetizable core secured thereto and having a tip, an energizing coil surrounding said core, and a magnetic bottom plate secured to said top plate by magnetizable supports positioned outside said coil, said bottom plate having an aperture larger than said core tip through which said core tip passes and beyond which it projects, and said armature being separated from said bottom plate and pivotally mounted thereon and below all other magnetizable components of said combination, said armature having an aperture larger than said core tip and concentric therewith and smaller than the aperture in said bottom plate.

6. The electromagnet-armature combination of claim l in which said armature is adjustably rnted on said frame so as to be movable in any direction in plane perpendicular to the axis of said core and nxable in adjusted position, thereby facilitating the concentric arrangement of core tip and armature aperture.

7. The electromagnet-armature combination of claim 2 in which said armature is adjustably mounted on said trame so as to be movable in any direction in a plane perpendicular to the axis ci said core and xable in adjusted position, thereby facilitating the concentric arrangement of core tip and armature aperture.

8. The electromagnet-armature combination of ii claim 3 in which said armature is adjustably mounted on said frame so as to be movable in any direction in a plane perpendicular to the axis of said core and xable in adjusted position, thereby facilitating the concentric arrangement of said core tip and armature aperture.

9. The electromagnet-armature combination of claim 4 in which said armature is adjustably mounted on said frame so as to be movable in any direction in a plane perpendicular to the axis of said core and nxable in adjusted position, thereby facilitating the concentric arrangement of said core tip and armature aperture.

10. The electromagnet-armature combination of claim 5 in which said armature is adjustably mounted on said frame so as to be movable in any direction in a plane perpendicular to the axis of said core and rlxable in adjusted position, thereby facilitating the concentric arrangement of said core tip and armature aperture.

11. An electromagnet-armature combination comprising an electromagnet and an armature, said electromagnet comprising a magnetizable top plate, a magnetizable core secured thereto and having a tip, an energizing coil surroundingr said core, and a magnetic bottom plate secured to said top plate, said bottom plate having an aperture larger than said core tip through which said core tip passes and beyond which it projects; said armature being xed to a sheet of material and having an aperture larger than said core tip and concentrically arrangeable therewith and smaller than the aperture in said bottom plate, said sheet being adjustably securable on said bottom plate so as to facilitate said concentric arrangement.

12. An electrcmagnet-armature combination comprising an electromagnet and an armature, said electromagnet comprising a magnetizable top plate, a magnetizable core secured thereto and having a tip, an energizing coil surrounding said core, and a magnetic bottom plate secured to said top plate by magnetizable supports positioned outside said coil, said bottom plate having an aperture larger than said core tip through which said core tip passes and beyond which it projects, said armature being fixed to a sheet of material and having an aperture larger than said core tip and concentrically arrangeable therewith and smaller than the aperture in said bottom plate, said sheet being adjustably securable on said botto-m plate so as to facilitate said concentric arrangement.

13. An electroma-gnet-armature combination comprising an electromagnet and an armature, said electromagnet comprising a magnetizable top plate, a magnetizable core secured thereto and having a tip, an energizing coil surrounding said core, and a magnetic bottom plate secured to said top plate, said bottom plate having an aperture larger than said core tip through which said core tip passes and beyond which it projects, -said armature being mounted on a sheet of material having an edge so as to pivot on said edge, said armature having an aperture larger than said core tip and concentrically arrangeable therewith and smaller than the aperture in said bottom plate, said sheet being movable over said bottom plate to a limited degree and securable thereon in adjusted position so as to facilitate said concentric arrangement.

14. An electromagnet-armat-ure combination comprising an electromagnet and an armature, said electromagnet comprising a magnetizable top plate, a magnetizable core secured thereto i2 and having a tip, an energizing coil surrounding said core, and a magnetic bottom plate secured to said top plate by magnetizable supports posi tioned outside said coil, said bottom plate having an aperture larger than said core tip through which said core tip passes and beyond which it projects, said armature being mounted on a sheet of material having an edge so as to pivot on said edge, said armature having an aperture larger than said core tip and concentrically arrangeable therewith and smaller than the aperture in said bottom plate, said sheet being movable over said bottom plate to a limited degree and securable thereon in adjusted position so as to facilitate said concentric arrangement.

15. An electromagnetic unit comprising an electromagnet, an armature mounting member, and an armature mounted thereon so as to be pivotable, said magnet comprising an end plate having a side and having astop projecting from said plate adjacent said side, said armature comprising a portion adapted to overlie said end plate and a portion extending out past said side, said armature having an aperture in which said stop is receivable, and said mounting `member being of resilient material secured to said end plate and to the extending portion of said armature, positioned between said plate and armature, and having an edge overlying said plate, said stop having a shoulder separated from said top plate by a distance approximately equal to the thickness of said mounting member, and a nger on said mounting member received beneath said shoulder and terminating in an edge, whereby said armature will frictionlessly pivot about said edges of said mounting member in any position of said unit.

16. The electromagnetic unit of claim 15, in which the side of said end plate is inset under the shoulder of said stop and in Which the edge of the nger of the mounting member terminates in line with but laterally separated from the edge of said mounting member overlying the non-inset portion of said end plate, whereby said armature will pivot about the same axis in any position of said unit.

17. The electromagnetic unit of claim 15, in which the side of said end plate is inset on either side of said stop so that portions of said mounting member are iree to bend below the surface of said end plate as said armature pivots.

18. The electromagnetic unit of claim 15, in which the side of said end plate is inset under the shoulder of said stop, in which the portion of the mounting member received beneath said shoulder terminates in line with but laterally separated from the edge of Said mounting member overlying the non-inset portion of said side, and in Which the side of said end plate is inset on either side of said stop so that portions of said mounting member are free to bend below the surface of said end plate as said armature pivots, whereby said armature will pivot about the same axis in any position of said unit.

19. The electromagnetic unit of claim 15, in which said mounting member' is adjustably securable to said end plate so that said armature may be adjustably positioned with respect to said electromagnet.

2). An electromagnetic unit comprising an electromagnet, an armature mounting member, and an armature mounted thereon so as to be pivotable, said magnet comprising an end plate having a side, a stop having a shoulder projecting from said plate adjacent said side, said-arma-` ture comprising a portion adapted to overle said end plate and a portion extending out past said side, said armature having an aperture in which said stop is receivable, and said mounting member being of resilient material secured to said top plate between said plate and said armature, said mounting member comprising parts securable to said end plate, legs overlying said end plate and terminating in edges about which the armature may pivot, strips extending past the side of said end plate and securable to said armature, and a finger securable to said armature and receivable beneath the shoulder of said stop, said shoulder being separated from said top plate by a distance approximately equal to the thickness of said finger, whereby said armature will frictionlessly pivot about the edges of said legs or finger of said mounting member in any position of the unit.

21. The electromagnetic unit of claim 20, in which the side of said end plate is inset under the shoulder of said stop and in which the edge of the finger of the mounting member is in line with the edges of said legs.

22. The electromagnetic unit of claim 29, in Which the side of said end plate is inset on either side of said stop so that the strips of said mounting member are free to bend below the surface of said end plate as said armature pivots.

23. The electromagnetic unit of claim 20, in which the side of said end plate is inset under the shoulder of said stop, in which the edge of the linger of the mounting member terminates in line with the edges of the legs of said mounting member, and in which the side of said end plate is inset on either side of said stop so that the i4 strips of vsaid mounting member are free to bend below the surface of said end plate as said armature pivots.

24. The electromagnetic unit of claim 20, in which said mounting member is adjustably seourable to said end plate, so that said armature may be adjustably positioned with respect to said electromagnet.

25. The unit of claim 20, in which said mounting member is an integral sheet of resilient nonmagnetic material.

26. The unit of 'claim 20, in which said mounting member extends out past said armature and is provided with an aperture, said aperture being adapted to secure an additional element to said armature.

ARTHUR M. COHEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 189,584 Stroh Apr. 17, 1877 688,554 Skirrow Dec. 10, 1901 1,906,027 Wahl Apr. 25, 1933 1,914,909 Creveling June 20, 1933 1,994,671 Slawik Mar. 19, 1935 2,390,796 Kovalsky Dee. 11, 1945 2,458,247 Bryan Jan. 4, 1949 FOREIGN PATENTS Number Country Date 566,778 Great Britain Jan. 12, 1945

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