US1944578A - Means for adjusting field strength in electromagnetic devices - Google Patents

Description

Jan. 23, 1934. R. D. SLALMON 1,944,578

MEANS FOR ADJUSTING FIELD STRENGTH IN ELECTROMAGNETIC DEVICES Filed Feb. 25, 1931 REGINALD o. SALMON BY- ,1: .2/ .20 27 32 a ATTORNEY Patented Jan. 23, 1934 PATENT OFFICE MEANS FOR ADJUSTING FIELD STRENGTH IN ELECTROMAGNETIC DEVICES Reginald Dennis Salmon, Oroydon, England, assignor to Creed and Company, Limited, Groydon, England Application February 25, 1931, Serial No. 518,120, and in Great Britain March 26, 1930 6 Claims.

This invention relates to a method of and means for adjusting magnetic field strength in electromagnetic devices such as relays in which a permanent magnet is employed to provide a magnetic flux.

The object of the invention is to provide a simple means for readily varying the field strength of a polarized relay such as that disclosed more particularly in Patent No. 1,864,296, issued to F. G. Creed et al. on June 21, 1932, and also described on pages 256-251 of Telegraphy by T. E. Herbert, published by Sir Isaac Pitman & Sons, London, 1930. The invention is applicable, however, to other classes of apparatus as will be readily seen from the following description.

In polarized electromagnetic relays for example, a strong magnetic field results in firm contact pressure of the movable contact stops upon the fixed contact stops upon actuation of the relay armature. A disadvantage of a strong magnetic field is that a relatively heavy current is required to overcome this contact pressure and to eiiect the actuation of the movable armature from one stop position to another. If the field strength is reduced the relay is rendered more sensitive to weak actuating currents but this is accomplished at the expense of reduced contact pressure. In such relays, as in other cases, it is a great advantage to be able to adjust the effective field strength in a ready manner, by the simplest means possible. One method and means of adjusting the field strength of a relay is disclosed in the above-mentioned patent. The present invention involves an improved and novel method for more effectively controlling the field strength of a relay or similar apparatus.

The invention consists in a method and means for adjusting field strength in electromagnetic devices of the class referred to. It accomplishes this result by tilting a permanent magnet by means of an adjusting screw from off the faces of two soft iron pole pieces or fixed members of the magnetic circuit, each of these members being similarin shape and approaching each other so closely as to form a substantially closed magnetic circuit. The permanent magnet is therefore, held to these pole pieces by magnetic attraction. The tilting action exposes the faces of the pole pieces and causes a wedge-shaped air gap to be formed between the pole pieces and the formerly contiguous sides of the permanent magnet, one edge of each of the ends of the permanent magnet remaining in continuous contact with its immediately associated pole piece. In this manner an adjustable wedge shaped airgap is formed between the faces of the pole pieces and the surfaces of the permanent magnet previously contiguous to those faces.

Referring to the accompanying drawing:

Fig. 1 shows diagrammatically the method of semi-circular permanent magnet for the bar magnet indicated by numeral 12 in Figs. 1 and 2 of that mentioned patent. Further constructional details are also given in this mentioned patent. These details are not shown in the present application as it is not deemed neces- (0 sary to uselessly encumber the drawing with features which are not especially subservient to the complete operation of the apparatus involved in this application.

Figure 3 shows, in front elevation, a relay in which adjustment is effected in accordance with the present invention.

Figure 4 is a side elevation of the relay shown in Figure 3 with the cover thereof in section.

Referring first to Fig. 1, this shows in diagrammatic representation a pole piece 2 of magnetic material, such pole piece being one of a pair of pole pieces adapted to be permanently energized by a permanent magnet 1 placed in contact with their end faces. The permanent magnet, which is preferably of semi-circular shape, is held against the ends of the pole pieces solely by magnetic attraction. Other pole faces of the pole pieces co-operate with a moving armature of the magnet system in any suitable manner, for example as will be more fully hereinafter described in connection with Figs. 3 and 4.

Threaded in a suitable portion of the apparatus, here shown as bracket '7 attached to the casing 6 of the relay, is an adjusting screw/i which may conveniently be turned by head 5, the point of the screw bearing against the extended semi-circular U-shaped yoke portion of the permanent polarizing magnet 1.

By turning the adjusting screw 4 the magnet 1 can be tilted away from full contact with the pole piece faces 2 and 3 of the fixed members. This results in the formation of a thin wedge shaped air gap in the magnetic circuit which in turn causes a reduction in the magnetic flux in the latter. The edges of the poles at the further extremities of the magnet 1 will however be held in contact with the further edges of the end faces of the pole pieces by magnetic attraction, the contacting elements being reduced. from two contiguous surfaces to two contiguous lines. The attraction will also cause the magnet to follow screw 4 on retraction of the screw 4 in order to reduce the angle of the air-gap in the wedge shaped opening between the surfaces.

The application of the invention to an electromagnetic relay similar to that described fully in said Patent No. 1,864,296 previously referred to, is shown in Figs. 2, 3 and 4. Magnetic pole pieces 2 and 3 having oppositely facing upper extremities 21, 22 and similarly facing lower extremities 23, 24 are moulded into a carrier 8 of insulating material. The pole pieces 2 and 3 are, therefore, [-shaped. The upper and lower extremities of these pole pieces form two polar gaps in which an armature rocks on an horizontal axis on pivots fixed to the carrier 8 at a position 25 mid-way between the two gaps. Opposite ends 26 and 27 of the armature move from one side to the other in the upper and lower gaps respectively. The armature carries an extension 28 on the extremity of which a contact 11 is adapted to play between contact screws 12 and 13 as actuated by the armature. An actuating coil or coils 14 surrounding the armature, but separated therefrom, is or are clamped to the carrier 8 by suitable means. The carrier 8 with the pole pieces 2 and 3, coils 14 and the pivoted armature form a unit which is pivotally mounted by pivot 9 to a vertical standard 29 formed of moulded insulating material in one piece with a base portion 30. The vertical standard 29 carries extensions 31, 32 in which the contact screws 12 and 13 respectively are mounted. The base portion 30 carries a bias adjusting screw 10 with the point of the screw engaging an extension (not shown) of the carrier 8 to move it on pivot 9 against spring means (also not shown) whereby the magnetic bias of the relay can be readily adjusted, as is fully explained in said U. S. Patent No. 1,864,296.

The pole pieces 2 and 3 are magnetized to 0pposite magnetic poles by a permanent magnet 1 which is held only by magnetic attraction of the extremities of the magnet 1 to horizontal exposed end faces 31 and 32 of the pole pieces 3 and 2 respectively. The bow-shaped mid-portion of permanent magnet 1 extends in a forward direction and is engaged on its upper surface by an adjusting screw 4. This screw 4 is rotatably supported at its upper end in a bracket 33 fixed to a circular casing 6 of the relay and threaded at its lower end in a second bracket 7 also fixed to casing 6. The casing 6 is provided with a cover 34 hinged at 35 to permit ready access to the contact screws 12 and 13, and to a head 5 of the adjusting screw 4.

It will be seen that the magnetic circuit or circuits in the above described relay forms or form what is known as a balanced armature movement. In accordance with the direction of current in the coil or coils 14 the direction of flux along the armature and the distribution of the magnetic flux from the permanent polarizing magnet 1 is altered in the upper and lower gaps in which the ends of the armature oscillate.

The contact 11 is thus actuated from one to the other of contact screws 12, 13 and is held against the respective screw owing to the permanent magnetic flux from magnet l causing the attraction of the ends 26, 27 of the armature to the nearer pole faces in the two polar gaps respectlvely.

The relative attraction to the nearer pole face of the armature when in one position as compared with that in the other can be adjusted by varying the position of carrier 8 by screw 10, as previously mentioned. The total force by which the armature is held in either position, disregarding any force due to the actuating coil 14, can be adjusted in the present arrangement by screw 4. In Figs. 3 and 4 screw 4 is shown tilting permanent magnet 1 on the horizontal faces 31, 32 of the pole pieces 3 and 2 against the magnetic attraction of the magnet to the pole pieces. The wedge-shaped air gap, which is best seen in Fig. 4, introduced into the magnetic circuit, reduces the total flux in the pole pieces and thus increases the sensitivity of the relay. If screw 4 is turned by head 5 to raise the screw, the air gap is reduced as magnetic attraction causes magnet 1 to follow the screw 4. The total flux in the magnetic circuit is increased and results in a correspondingly greater pressure of the movable contact 11 on either contact stop 12 or 13. As previously mentioned, however, this necessitates a heavier current through the actuating coils 14 to eifect the actuation of the armature to the opposite position.

The screw 4 provides a ready and simple method by which this adjustment can be made and it will be seen that if the end of screw 4 bears on a smooth portion of the upper surface of magnet 1 the bias adjusting screw 10 can be altered without affecting in any appreciable manner the adjustment due to screw 4.

Although the invention is particularly applicable to electromagnetic relays it will be appreciated by those familiar with the art that it is also applicable to other electromagnetic devices in which it is desirable to provide means for readily varying the field strength produced by a permanent magnet in those devices.

What is claimed is:

1. In an electromagnetic device such as a polarized relay, means for adjusting field strength comprising in combination, relatively fixed pole pieces having exposed faces, a permanent magnet held on to said faces by magnetic attraction, and an adjusting screw bearing against an extension of said magnet to tilt it against said magnetic attraction on said faces to introduce a wedge shaped air gap therebetween.

2. In an electromagnetic device such as a polarized relay, two relatively fixed pole pieces each having an exposed face, a semi-circularly shaped permanent magnet held by each pole thereof to one of the exposed faces of said pole pieces respectively, and an adjusting screw bearing against the yoke portion of said permanent magnet.

3. An electromagnetic polarized relay comprising in combination, two pole pieces, a carrier of moulded insulating material in which said pole pieces are imbedded, leaving an exposed face on each, a semi-circularly shaped permanent magnet held by the magnetic attraction of each pole thereof to one of the exposed faces of said pole pieces and substantially at right angles to said carrier of insulating material, and an adjusting screw bearing against the laterally extending yoke portion of said permanent magnet.

4. An electromagnetic device such as a polarized relay, comprising a pair of pole pieces, a permanent magnet having, and rotatable about, an edge in contact with said pole pieces, and means for rotating said magnet about said edge.

5. Electro-magnetic apparatus of the type herein described, comprising two oppositely arranged [-shaped pole pieces, a carrier of moulded tion two [-shaped pole pieces, a support of moulded insulating material for said pole pieces, each of said pole pieces having an exposed surface, a permanent magnet each pole of which is held to one of the exposed surfaces of the pole pieces by the magnetic attraction of said magnet, and an adjusting screw for tilting said magnet against the magnetic attraction on said faces to introduce a wedge-shaped air gap therebetween.

REGINALD DENNIS SALMON.

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