US3001107A

US3001107A - Electromagnetic structure

Info

Publication number: US3001107A
Application number: US760621A
Authority: US
Inventors: Chester R Rhodes
Original assignee: ELECTRO MECHANICAL SPECIALTIES
Current assignee: ELECTRO MECHANICAL SPECIALTIES; ELECTRO-MECHANICAL SPECIALTIES Co Inc
Priority date: 1958-09-12
Filing date: 1958-09-12
Publication date: 1961-09-19
Anticipated expiration: 1978-09-19

Description

Sept. 19, 1961 c. R. RHODES 3,001,107

ELECTROMAGNETIC STRUCTURE Filed Sept. 12, 1958 2 Sheets-Sheet 1 INVENTOR. CHESTER R. RHODES I AGENT Sept. 19, 1961 c. R. RHODES 3,001,107

ELECTROMAGNETIC STRUCTURE Filed Sept. 12,, 1958 2 Sheets-Sheet 2 FIG. 2.

INVENTOR. CHESTER R. RHODES liniteci States Patent 3,001,107 ELECTROMAGNETIC STRUCTURE Chester R. Rhodes, Whittier, Califi, assignor to Electro- Mechanical Specialties Co., Inc., Whittier, Califi, a corporation of California Filed Sept. 12, 1958, Ser. No. 760,621 Claims. (Cl. 317-189) My invention relates to means for producing motion by electricity through the intermediary of magnetic fields and particularly for producing rotation through a limited are such as required for relay, switching or similar contacting devices.

In devices of the class mentioned, small size and high torque are important desirable attributes. In devices of the prior art plural poles with individual windings have resulted in structures wasteful of space and various types of radially extending armatures have caused the magnetic forces developed to be applied to the motor elements at less than the position of maximum torque.

By greatly altering the magnetomotive-force-producing structure and the armature coacting with it I have been able to reach maxima of performance heretofore unvisioned in the attributes mentioned.

Briefly, in a typical embodiment, I provide one central coil upon a magnetic core having scalloped end disk pole pieces. I surround this structure with an armature having circumferentially disposed slats of magnetic material. These are positioned so as to give an overall magnetic circuit of relatively high magnetic reluctance by virtue of the armature being opposite the cut out portions of the scalloped pole pieces. When magnetomotive force is applied, as by passing an electric current through the coil, the armature moves to decrease the reluctance of the magnetic circuit. Decrease of reluctance is accomplished by rotation of'the armature until the slats are opposite the projecting portions of the pole pieces. When the magnetornotive force is no longer applied, the armature is returned to its high reluctance position by a restoring force, of which a spring or other resilient means is an example.

An object of my invention is to provide an electromagnetic structure having a high packing density of elements.

Another object is to provide a high-torque electromagnetic structure.

Another object is to provide an electromagnetic structure capable of rapid actuation.

Another object is to provide a dynamically balanced armature which may easily be adjusted as to magnetomotive function.

Another object is to provide a magnetomotive structure having a low reluctance in comparison with those offollowing detailed specification and upon examining the accompanying drawings, in which are set forth by way of illustration and example certain embodiments of my invention.

FIG. 1 shows a perspective view of the magnetic el ments of my electromagnetic structure,

FIG. 2 shows a sectional elevation view of a relay application of my electromagnetic structure,

assist? ice 1FIG. 3 shows a sectional split plan view of the above re ay,

FIG. 4 shows an elevation of a modification of the magnetic elements of FIG. 1,

FIG. 5 shows an elevation view of a differential electromagnetic structure,

FIG. 6 shows a sectional elevation view of an alternate embodiment,

FIG. 7 shows a plan view of a two pole alternate embodiment, and

FIG. 8 shows a sectional elevation view of the two pole alternate embodiment.

In FIG. 1, numeral 1 indicates the upper of two scalloped end disks of magnetic material. A suitable material is Armco ingot iron. Numeral 2 is the lower scalloped end disk, which is similarly formed and similarly oriented with respect to disk '1. The two disks are joined together by central cylindrical portion 3. Preferably,

portions

1, 2, and 3 are turned or otherwise ma chined from a single piece of magnetic material. Each scalloped disk constitutes a group of radially projecting poles.

Coacting with the scalloped end disks are a plurality of slats or peripheral members 4, 5, 6, 7. A lower disk 8 is shown in FIG. 1 towhich each of the slats are fastened. This is of non-magnetic material and may conveniently be fabricated of a suitable structurally stable insulator; of which diall phthalate, Myclex, aluminum oxide, etc. are examples. This use of an insulator allows elements of the relay, switch, or other device to be actuated by my motor to be mounted directly upon a structurally necessary member of the motor. This results in simplicity.

The upper disk of the armature has not been shown in FIG. 1 so that the scalloped piece 1 could be shown in detail. However, in this embodiment this piece is the same as the lower disk 8. This results in a double-ended structure which is highly coordinated between motor and contacting elements. That is, a second group of relay or switch'contacts can be fastened upon the upper disk, resulting in a highly desirable saving in space and structural elements.

The several slats 4, 5, 6, 7 are shown assymetrically located with respect to the open parts of the scallops on end disks 1 and 2. The armature assembly is journaled at the center of the upper and lower disks, is thus free to revolve and envelopes the stationary elements. When a magnetomotive force is applied to the stator, as electrically by a coil carrying current wound around cylinder 3, it is apparent that a force is exerted upon the armature in the direction to rotate the slats into close proximity to the protruding portions of the scalloped end disks and so to greatly reduce the reluctance of the overall magnetic path. Upon the cessation of the magnetomo'tive force the armature is normally returned to its initial position by a restoring force, such as a spring of some form or a permanent magnet. In practical embodiments it is convenient to place a stop 9, in the form of a pin, in the lower armature disk positioned in one scallop of end disk 2. This positively limits the rotation of the armature in the armature of my device may be made stationaryand the inner magnetic system to rotate,

The completed structure of one embodiment of my motor is shown in connection with the relay of FIGS. 2 and 3. A central core '12 of magnetic material has scalloped

end disks

13 and 14, upper boss '15 and lower tubular extension 16. This is preferably one piece of material. A coil of insulated wire 17 is wound around core 12 between

end disks

13 and 14. vWhen energized with electric current this coil provides the magnetomotive force to actuate the relay.

Surrounding this structure is an armature composed of bottom disk 18, top disk 19, and plural slats, of which a two, 20 and 21, are seen in FIG. 2. The bottom disk is preferably fabricated of the same matcrial'as lower disk 18, although it may be fabricated from a non-magnetic material such as brass. Disk 18 is provided with a bronze sleeve bearing 23 and disk 19 with asimilar bearing 24. These journal the armature structure around b'osses 15 and 16 of core 12. 'Oilite may be used as the bronze material to obviate lubrication maintenance.

The significance of the magnetic structure is revealed at the left hand side of FIG. 3, where the scallops of end disk 14 are seen.

Coactive slats

21 and 25, of magnetic material, and lower disk-18 are seen to be disposed so that energization of coil 17 causes rotation of the armature in the direction of the arrow 26. This motion takes place because the magnetic reluctance between the rotating and stationary magnetic structures is reduced thereby.

A six pole relay is shown, thus' the rotation required is less than 30, i.e., about 24,-for the contacts shown in the right hand portion of FIG. 3. A plurality of spheres 26 are shown, each with a group of three contacts; 27 28 for the separate throws of the switch and 29 for the common pole. With the rotation previously noted in the direction 2 6 spheres 26 will be rotated between the two

contacts

27 and 28 in each instance. A spring 39, fastened under tension-adjusting screw 31 "at the top of the the same time the circumferential extremities of the sealloped pole, as 1 in FIG. 1, are made sufliciently long so that as the slats of FIG. 4 come close to the extremities of the upper pole they are not yet close to the corresponding extremity 'on the lowerpole, namely 41 and 42in FIG. 4. Accordingly, the magnetic reluctance is further decreased by further rotation and such rotation takes place. Theextremities are sufficiently long so that the top of the slat does not pass beyond the extremity, circumferentially, before the bottom of the slat has come fully opposite its corresponding extremity. By employing relatively narrow slats on an angle as shown in FIG. 4 a maximum operating arc of perhaps 55 for atom pole structure and 110 for a two pole structure can be reached. It will be understood that for most uses to which my motor may be put this is a greater throw than required.

The two pole modification is accomplished hy merely omitting two opposite poles from end disk 1. as maybe conveniently seen in FIG. 1 and increasing the circumferential width of the two extremities remaining.

Considering the structure of FIG. 4 in detail, the circumferential width of the extremities on end disks 41 and 42 are greater than on the previous disks 1 and 2 in FIG.

1. The

slats

44, 45, 46, 47 are all slanted with respect to the end disks. This slant may be anything from a few degrees to perhaps 15. Normally insulated, or at l'ea'st

non-magnetic disks

48 and 49 hold the slats and are .journaled top and bottom upon bosses extending from viously described.

rotating structure and to the stationary structure in boss 15 provides the restoring torque to return the magnetic structure to a high reluctance position; Mechanical or equivalent stops are convenient tolimit the rotation to .prescribed'limits and stop 9 in "FIG. 1 is illustrative.

In this relay embodiment the insulating member in ternal connections byhook

terminals

31, 32; the former connecting to the

outer contacts

27, 28 and the latter to the inner contacts 29. The terminals are integral parts in glass inserts 33 of a metal header 34, which latter forms the lower enclosure of the relay. The contacts may be structurally and electrically connected 'to the terminals by silver soldering. Two additional terminals, of which one, 35, is shown in FIG. 2, are employed to connect the two ends of coil 17 to external circuits.

The header-insulating member assembly is fastened to core 12 by central screw "36. This screw is threaded into the lower tubular extension 16 of core 12 and may be locked in place'by a setting plastic over the head thereof. An outer case or housing 37 is provided to enclose the device and may be fastened to header 34'by soldering for a hermeticallysealed unit. The magnetic 'slats,as 21, may be fastened to end

disks

18 and 19 by flat'he'ad screws 38. I The above-described motors have straight slats and are adapted for use where the operating arc is;nominal,

such as 40,? or less fora four pole (slat) armature and 80 for a two pole armature.

It is'possible to increase theoperatin'g are considerably by placing the slats on an angle as shown in FIG. 4. At

In FIG. 5, scalloped end disks 51 and 52 are as before. Disk 53 is of the same diameter as these disks, but is without scallops and is located centrally between the other two. A central core '54 extends all the way between the scallope disks. cuits involved and is the element upon which coils 55 and 56 are wound. As indicated by the arrows on

connections

57 and 58 the coils are wound in opposite directions. The coils are normally of the same number of turns, but may vary 'widely in characteristicsto accommodate unusual electrical circuit conditions. As an example of the latter, one coil may be 'of only a few turns to produce a magnetomotive force proportional to current While the other may be of many turns to produce a magnet'ornotive force proportional to voltage.

The central disk 53 serves as a return magnetic path between each of the coil magnetomotive forces. It will be understood that currents, when flowing, now in op'p'osite directions in each of coils 55 and 56, creating opposing magnetomotive forces. In each slat the force will tend to turn the slat in one direction in the upper half of the slat and in the opposite direction in the lower half. Which current produces the greater magnetomotive force .will

cause the armature to turn in that direction. Thisis the result necessarily sought in a differential relay.

In addition to or instead of the windings of

coils

55 and 56 being difierent for special purposes, the spacing between disks 51, 52 and 53 may be varied by about to illustrate an alternate form of restoring spring so that (39) shown in FIG. 2. The alternate spring 60' takes the form of a torsional-spring housed in an axial hole 6'1 in central core'54. A length of music wire eight to twelve thousands of an inch in diameter is suitable for the spring. This is fastened rigidly to the core structure at This core completes the magnetiocirt the bottom thereof by virtue of a small loop in the wire being tightened under set screw 62. The upper armature disk 63 holds plural slats of. magnetic material as shown in any of the prior figures, and which slat 64 is illustrative. The lower armature disk and other slats have not been shown in FIG. 5 for simplicity in illustration.

A new element 65 fastens the music wire to the upper armature disk 63 in an adjustable manner regarding torsional tension. The top of the torsion wire, said top identified as 60', is bent to the left in initial fabrication. It fits in a shallow slot on the under side of element 65 toward the left thereof. Screws 66 are positioned in arcuate *slots in element 65 and thread into threaded holes in upper disk 63; The proper torsional tension on wire 60 is obtained by rotating element 65 as necessary and then securing it by tightening the fastening screws 66.

The torsional type spring described above may be considered the best type for the differential relay shown in FIG. 5. The counter-torque of such a spring is equal in both direction from the position of zero torque.

Because of the double-ended aspect of my motor and the double switching structure that may thus be accom- .modated, not only may these extra contacts be used to switch extra circuits, but also may be placed in parallel to carry twice the current or may be placed in series to be effective at twice the voltage.

A miniature size relay motor according to my invention may develop 6 /2 ounce-inches of torque. A magnetomotive force of 430 ampere turns is possible with my structure in this size. In devices of the prior art only between 150 and 200 ampere turns can be accommodated in a relay of the same size. My increase is due to excellent use of space.

FIG. 6 shows the magnetic structure for an alternate construction of my relay that may be of the singleended type.

A cup-shaped element 70 of magnetic material is provided with a central core '71. The latter is essentially the same as the prior core 3, etc. While the whole magnetic structure may be made of one piece it is more convenient in fabrication to employ two pieces, 70 and 71, and attach the two by means of a screw 72. Scalloped pole piece 73 is preferably integral with core 71 and has the same shape and function as that shown at 1 in FIG. 1, etc.

The upper armature disk of prior embodiments now becomes an inverted cup 74 of either insulating or nonmagnetic material. Attached thereto by insert molding, for example, are

armature pole pieces

75, 76, etc. There is one pole for each scallop of piece 73. As before, the armature rotates about a boss 77. j Restoring means are not shown, but the equivalent of any previously shown, positions the armature with the pole pieces thereof at the open scallops of poles on piece 73, and asymmetrically with respect to the openings of the scallops. Accordingly, when solenoid coil 78 is energized the structure is so magnetomechanically related that the armature rotates in the direction of the nearest projection of each scallop. This gives a desired motion to alternately connect one set of contacts or the other on a double-throw multiple-pole relay or switch.

This embodiment has the advantageof allowing small airgaps both above and below the

armature pole pieces

75, 76, etc. The gap between these and the periphery of cup 70 may be as small as two thousandths of an inch, as may also be the gap to scalloped pole piece 73.

The embodiment of FIG. 6 may be made double ended by merely extending the cylindrical portion of the armature piece 74 downward beyond the bottom of cup 70. This allows switching components to be mounted on a subsequently attached lower disk.

A still further embodiment is shown in FIGS. 7 and 8; This embodiment is similar to that of FIG. 6 in being of fundamentally single ended construction, but

it partakes of the earlier embodiments in that slats of magnetic material are utilized on the rotor.

A magnetic cup 80, of form similar to 70 in FIG. 6, is employed as the stator. It is provided with a center core 81, which has a surmounting scalloped pole piece 83. A screw 82 secures the core to the cup. It will be noted, particularly in FIG. 7, that a two pole piece 83 is shown. An upper armature disk 84, of insulating or non-magnetic material, is pivoted on boss-bearing 85 and is secured thereto by washer 86 and screw 87. Two

slats

88 and 89 of magnetic material are molded into or otherwise rigidly fastened to armature disk 84 on opposite sides thereof. These extend down below the upper end of cup 80 and make a lap magnetic joint therewith. An air gap of a few thousandths of an inch is included for mechanical clearance from this element and a corresponding amount at the extremities of the scalloped pole piece 83.

In FIGS. 7 and 8 the slats are shown in the actuated (minimum reluctance) position. It will be seen that when the slats are in the non-actuated position, asymmetrical-1y related to the open parts of the scallops, the magnetic reluctance of the entire magnetic path involved is relatively large. The slats are attractedto the position shown upon energization of coil 90 by the flow of electric current therein.

It will be noted that coil 90 is extended the full length of core 81 and that this is not possible in the embodiment of FIG. 6. As in FIG. 6, this embodiment may be made double-ended by extending the cylindrical portion of the non-magnetic armature material 84 to enclose cup 80. V

A two pole embodiment is shown in FIGS. 7 and 8, but any number of poles, even one, may be employed. Normally, the range would be from two to perhaps eight. Similarly, any of the embodiments illustrated may be constructed with any number of poles.

In view of the several embodiments of my disclosure it will be appreciated that numerous modifications may be had by combining a portion of one structure with a portion of another.

In FIG. 6, for example, the inclined slats of FIG. 4 woildfibecome non-radially shaped magnetic members 75 an 7 The circular spring of FIG. 2 and the torsional sprin of FIG. 5 may be interchanged as the restoring means in any of the figures.

A permanent magnet 91 placed opposite a scalloped portion of the stator end disk, as shown in FIG. 1, may be employed to provide non-mechanical restoring means. Two such magnets placed symmetrically on opposite sides of the structure may also be used, as well as four, etc.

My motor has been illustrated in FIGS. 2 and 3 as driving a relay type device. It will be appreciated that it may also be employed to drive rotary switches, various indicators, perform servo functions and be otherwise applied where a less than full turn rotary motion is required.

"In the several figures the armature may be held stationary and the stator made to rotate as long its provision is made for retaining connection to the energizing coil (as 78 in FIG. 6). Brushes and slip rings have already been suggested for this purpose. Where a fractionof a turn is involved in the functioning of the motor a pair of flexible leads may be employed instead.

While particular thicknesses of the magnetic and other elements have been shown it will be understood that such may be altered, as for example, a considerably greater thickness to scalloped end disks 1 and 2 in FIG. 1.

I The proportions of the embodiments of my devices may also be altered. Any may be made tall and slim, -or short and wide.

"electro-magnetomotive-force-producing means to produce magnetic flux in said core, 'said wound means having an axial length along said core approximately twice theexternal diameter of said wound means, a rotatable armature, and only slat members of magnetic material equal in number to the number of said ipoles, said slat members mounted upon said armature'radially beyond said poles; said members and said poles related to rotatesaid armature to the lowest reluctance position therebetween upon said el'eetro-magnetomotive-force-producing means being energized.

2. An electromagnetic motor comprising a magnetic core, two disks having only radially projecting poles formed by aligned radially shallow scallops, said disks connected to'the extremities of said core to form a structure twice'as long as the diameter of'said disks, electromagnetomotive-force-producing means upon said core, a rotatable armature enveloping said disks, thin'circumferentially-shaped membersof magnetic material equal in number to the number of said poles, said members mounted upon said, armature, a restoring means to locate said armature at a position of high reluctance between said members and said poles; said members and saidpoles structurally related to allow free rotation of said armature to a position of low magnetic reluctance upon said electro-magnetom-otive-forceproducing:means being energized.

3. An electromagnetic motor comprising a central cylindrical magnetic core, at least one disk "having a plurality of uniformly spaced exclusively radially projecting poles symmetrically magnetically connected to said core, said poles formed by radially shallow scallops in a said disk, magnetomotiveeforce-producing means employing'eleetrical wire, said magnetomotive-forceaproducing means surrounding said core, a rotatable armature surrounding said disk, the same plurality ofuniformly spaced thin members as said.. -projecting1poles of magnetic material peripherally mounted upon said armature, the axial length of the core-arm'aturestructure exceeding twice the diameter thereof, and magnetic restoring means torotate said armature to a position of high magneticreluctance of said members with respect to said poles; said members and said poles magneto-mechanically related to rotate said armature to a position of minimum reluctance when said magnetomotive-force-producing means is electrically energized.

-4; Anpelectromagnetic motor comprising a magnetic core having disksof magnetic material with onlyv radially projecting poles formed by more than two radially shallow scallops in each said disk, the length of said core being approximately twice the pole'diameter-of said disks, an armature surrounding the previously recited structure,

said armature journaled for rotation about said core, a non-magnetic stop,.and radially thin elements of magnetic material attached to said armature, said core magnetically related to rotate the elements of said armature to substantial circumferential coincidence with said poles upon ener ization o f said magnetomdt ive force producing means, the amount of said'rotafion being limited by said stop.

5. Anelectromagnetic motor comprising a magnetic core having only aligned circular e'n'd disks of magnetic material and radially shallow scallops, -a coil of wire wound around said core, the axial length of said coil'be ing in excess of 2 /2 times itsexternal diameter, an arma ture surrounding the recited --structure, said armature journaled upon said core 'andhaving only slats of magnetic material aligned between said end disks and insulating disks for supporting said slats, a spring attached to said armature and coaxially to said core to position said slats opposite said scallops in said end disks, said armature rotatable upon energization of said coil to bring said slats to a position of low reluctance with respect to the parts of said end disks between said scallops.

6. An electromagnetic motor comprising a magnetic core having two end disks of magnetic material, more than three radially shallow scallops in each said disk aligned between said disks, a multilayer solenoid coil having a length twice its diameter wound upon said core between said end disks, an armature-surrounding the previously recited structure, said armature having two disks of insulating material journaled upon said core and more than three slats of magnetic material exclusive ly laterally extendingbetween said insulating disks, and a spring coiled coaxiallywith respect to said core to posi" tion said slats opposite said scallops of said end disks; said armature adapted for rotation upon electrical energization of said coil to bring said slats to a low magnetic reluctance position within the magnetic circuit fully symmetrically away from the depression of saidscallops.

7. An electromagnetic motor comprising a magnetic core having plural disks of magnetic material with only radially projecting poles, magnetomotive-iorce-producing means upon said core, and an armature surrounding said I radially projecting poles and iournaled for rotatiomsaid armature having slats of magnetic material extending between said plural disks, said slats disposed at an angle 1 to said poles such that when one end of one slat is circumferentially abreast of one said pole the other endof the same slat does not have an equivalent position with a pole of another of said plural disks.

8. .An electromagnetic motorcomprising a cylindrical magnetic core having plural disks of magnetic material with aligned exclusively radially projecting poles, magnetomotive-force-producing means surrounding said core, an armature surrounding said radially projecting poles, said armature journaled for rotation, and slats of magnetic material attached to said armature extending between said plural disks equal in number to the number of said aligned poles, said slats disposed at an angle to said aligned poles such that when one end of one slat is circumferentially abreast of one said pole the other end of the same slat has not assumed an equivalent position with the pole aligned with the first said pole, said motor thus having a rotational capability in excess of half the circumferential pitch betweensaid poles.

9. A diiferential electromagnetic motor comprising a magnetic core having disks of magnetic material, one

said disk centrally disposed on said core and one also near each end, the enddisks having radially projecting poles,

' opposed magnetomotive-force-producing means surrounding said core on opposite sides of the central disk, and an armature journaled for rotation surrounding said radial- 1y projecting poles, said armature having elements'of magsurrounding said core on opposite sides of the central disk, an armature journaled for rotation surrounding said radially projecting poles, said armature having thin 'cir- 'cumferentially disposed members of magnetic-material extending between said end disks equal in number toith'e posed magnetomotive-force-producing means surrounding said core on opposite sides of the central disk, an armature journaled for rotation, said armature surrounding said radially projecting poles, said armature having .slats of magneticmaterial extending between said end disks equal in number to the number of said aligned poles, and a torsional spring in said axial hole fastened to said armature to angularly restore the same to a position away from said aligned poles, said slats attracted to said aligned poles proportional to the resultant -magnetic field produced by said opposed magnetomotive-force-producing means from a non-attracted position determined by the mechanical characteristics of said torsional spring.

12. An electromagnetic motor comprising a magnetic core and a surrounding cup of magnetic material, magnetomotive-force-producing means between said core and said cup, radially projecting poles of magnetic material surmounting saidcore and said cup, and an armature of non-magnetic material pivoted for rotation having radial members of magnetic material disposed between said cup and said disk, said radial members circumferentially attracted toward said poles upon energization of said magnetomotive-force-producing means.

13. An electromagnetic motor comprising a central magnetic core and a surrounding cup of magnetic material, magnetomotive-force-producing means resident between said core and said cup, a disk of magnetic material having radially projecting poles surmounting said core and said cup, an armature of non-magnetic material pivoted for rotation above said disk, and'radial members 10 of magnetic material attached to said armature and closely circumferentially disposed between said cup and said disk, restoring means to position said radial members away from said poles for attraction circumferentially toward said poles upon energization of said magnetometive-force-producing means.

I4. An electromagnetic motor comprising a magnetic core, a cup of magnetic material attached to said core, a scalloped disk oppositely attached to said core, electromagnetomotive-force-producing means surrounded by the recited elements, and a rotatable armature surrounding the recited elements, said armature having members of magnetic material disposed intermediate with respect to said scalloped disk and said cup, to rotate said armature to a low reluctance position when said electro-magnetomotive-force-producing means is energized.

15. An electromagnetic motor comprising a central magnetic core, a cup shaped member of magnetic material attached to one end of said core, a scalloped disk attached to the other end of said core, electro-magnetomotive-force-producing means in between the recited elements, said armature having peripheral members of magnetic material regularly disposed with respect to said scalloped disk and adjacent to said cup, and means to restore said armature to a high reluctance position as against the attractive force between said disk and said peripheral members to rotate said armature to a low reluctance position when said electro-magnetomotive-forceproducing means is energized.

References Cited in the file of this patent UNITED STATES PATENTS