US2897312A - Magnetostriction switch - Google Patents

Description

July 28, 1959 R. M. ZIEGLER, JR I 2,897,312

- MAGNETOSTRICTION SWITCH Filed June 3, 1957 FIG. I.

FIG.2.

INVENTOI? ROBERT M, Z/EGLER JR,

A TTORNE Y United States Patent Ofiiee 2,897,312 Patented July 28, 1959 MAGNETOSTRICTION SWITCH Robert M. Ziegler, Jr., Los Angeles, Calif., assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Application June 3, 1957, Serial No. 664,880

1 Claim. (Cl. 200-87) The present invention relates generally to switches, and more particularly to a magnetic switch.

In the prior art there are many types of switches, including electronic, mechanical and magnetic switches. Most of the switches that may be categorized as magnetic switches are commonly known as relays and utilize an electric signal to close a pair of contacts by moving a magnetic member such as an armature having one of the contacts secured thereto in the presence of a magnetic field. While this type of switch will suifice for many purposes, faulty operation often results when it is subjected to shock and vibration.

It is an object of the present invention to provide a switch responsive to magnetic signals that is not affected by shock and vibration over wide ranges of acceleration and frequency.

It is another object of the present invention to provide an electromagnetically operated switching device which is simple in structure, mechanically rugged and capable of operation over a wide temperature range.

In accordance with the present invention a switching device responsive to magnetic signals is provided which includes a bimetallic plate having the magnetostriction property of flexing in responsive to changes in magnetic flux to which the plate is subjected. A first portion of the plate is secured against movement to permit a second portion of the plate to move when the plate is flexed. A first contact is mounted on the second portion and adapted to move therewith. A second contact is maintained in a fixed spaced relation to the first or stationary portion of the bimetallic plate and in the path of the movement of the first contact. Means are provided for applying a magnetic flux to the bimetallic plate and thereby to flex the plate and cause the contacts to engage in response to an electric current flowing in the windings of the electromagnet.

The novel features which are believed to be characteristic of the invention both as to its organization and method of operation, together 'with the further objects and advantages thereof will be better understood from the following description considered in connection with the accompanying drawing in which:

Fig. l is a view taken in section of a device illustrating the principles of the present invention wherein the contacts are shown in their normal position;

Fig. 2 illustrates the same device as is shown in Fig. 1 with the contacts illustrated in their closed position; and

Fig. 3 is a plan view of bimetallic element as taken substantially as indicated by line 33, Fig. 2.

Referring now to the drawing, there is shown a switch which includes a bimetallic plate having the magnetostriction property of flexing in response to a changing magnetic field and secured between a pair of magnetic pole pieces 12 and 14. The pole pieces 12 and 14 have a rectangular cross-section as shown and are provided with suitable notches or grooves 20 and 22 cut on the faces 13 and thereof to receive a portion of the bimetallic plate 10.

The bimetallic plate 10 is preferably formed in the shape of a disc which is slightly preformed into a convex shape. The pole pieces 12 and 14 may be permanent magnets having opposite poles on the surfaces 13 and 15 thereof. The pole pieces or magnets 12 and 14 secure a first portion of the magnetostrictive plate 10 against relative movement therewith, apply an initial magnetic flux to the plate having lines of force parallel to the surfaces of the plate and provide a low reluctance path for additional magnetic flux that is applied to the plate as will be discussed later. Where it is not desired to apply an initial flux to the magnetostrictive plate, the pole pieces may be composed of any suitable magnetic material such as soft iron.

The bimetallic plate 10 is composed of elements 16 and 18 which are discs or plates of magnetostrictive material as illustrated, particularly in Fig. 3. The element 16 is a negative magnetostrictive material such as Nl-SPAN C and element 18 is a positive magnetostrictive material such as nickel. It is not necessary that the elements 16 and 18 be composed of negative and positive magnetostrictive materials respectively. It is only necessary that these elements be composed of magnetostrictive materials having different coefficients of magnetostriction so that the bimetallic plate 10 will flex when placed in a magnetic field. The discs or elements 16 and 18 may have a small thickness to provide the switch with a movable plate 10 having a small inertia. The small inertia of the plate 10 renders the switch immune to shock and vibration over a wide range of frequency and acceleration.

A housing 23 completely encloses the plate 10 and the pole pieces 12 and 14. This housing may be composed of a magnetic material such as soft iron to complete the magnetic flux path of the pole pieces 12 and 14 and the plate 10 and to shield the switch from external magnetic fields. This housing may have a circular or rectangular cross-section. An energizing winding 24 is secured within the housing 23 and surrounds the pole pieces 12 and 14 and the magnetostrictive plate 10. The winding 24 is energized from a suitable source of alternating or direct current potential (not shown) by the conductors 26 and 28.

A first switch contact 30 is mounted on the center of the magnetostrictive plate 10 and extends on both sides of the plate as is shown. This contact is electrically connected to an output terminal 32 by means of a pair of electrical conductors 34 and 36. The conductor 36 may comprise any conductive material that is relatively flexible so that it Will not break when the contact 30 is moved with respect to the conductor 34. A second switch contact 38 is mounted in the path of the movement of the first contact and is connected to another output terminal 40 by means of a conductor 42. A third switch contact 44 is also mounted in the path of the movement of the first contact and is connected to a third output terminal 46 by means of a conductor 48. The conductor 34 extends through an annular dielectric member 49 and the housing 23. The conductors 42 and 48 extend through an annular dielectric member 50 and the housing 23.

Referring to Figs. 1 and 2, the operation of the structure shown therein will be described. It is well known in the art that magnetostrictive material will contract or expand when placed in a magnetic field depending on whether the coefiicient of the magnetostriction is negative or positive. Hence, when the magnetostrictive plate 16 is placed in a magnetic field, a portion of the plate that is not restrained will bend or flex. In the structure shown in these figures, the magnetic field that is applied to the plate 10 is created by the permanent magnets 12 and 14 and also by the coil 24. The permanent magnets serve to determine the operating point on the magnetization curve of the magnetostrictive plate and thereby increase the sensitivity of the switch where the magnetic field created by the coil 24 aids the field created by the permanent magnets. When the coil 24 is de-energized, the flux applied to the .magnetostrictiveplat'e- 10 willre turn to the original'operating pointon the magnetization curve as determined ,.by the field strength created within the plate 10 by the permanent magnets.

In operatiomthe coil 24 is energized by a current of appropriate polarity from a suitable direct current source (not shown) and'connected to leads 26, 28 to create a magnetic field that aids the field created by the permanent magnets 12 and 14. The combined magnetic fields created by the coil 24'and the permanent magnets cause the disc 16to expand and the disc 18 to contract which results in internal stresses within the magnetostrictive plate 10. These stresses tend to flatten out the disc surfaces and result in a reversal of the structure of the plate 10 from convex'to concave. The switch contacts 30 and 38 are thereby. separated or opened and the contacts 30 and 44 are closed as is shown in Fig. 2. The coil 24 is now de-energized and the magnetostrictive plate 10 reverts to its original position as is shown in Fig. 1.

It is to be understood that the coil 24 may be energized from an alternating current source as well as a direct current source. Also, it is not necessary that permanent magnets be utilized as the pole pieces 12 and 14-of the switch disclosed in the drawing. These pole pieces may be made of any magnetic material that provides a low reluctance path for the flux generated by the coil 24. As pointed out before, by utilizing permanent magnets as the pole pieces 12 and 14, the switch is rendered more sensitive to the energizing current for the coil 24. The utilization of permanent magnets has one further advantage in that such magnets may be chosen to place the plate 10 in an initial magnetic field to bring the magnetization of this plate to a point near the knee of its magnetization curve. This decreases the time of the switching action of the plate 10 over that which results if the pole pieces 12 and 14 are not permanent magnets due to the fact that the magnetostriction effect is greatest during the steepest part of the magnetization curve or at the time when the rate of change of the magnetic field within the magnetostrictive material is the greatest. Hence, the utilization of permanent magnets or some other means such as a suitable electromagnet energized with a constant DC. current to place the magnetostrictive plate in an initial magnetic field renders the switch ofthe present invention very sensitive to the energizing current and also afiords a quick switching action.

While the embodiment of the switch disclosed in the drawing'utilizes the coil 24 to provide the magnetic field necessary to actuate the switch, it is to be understood that other means could be utilized to provide the magnetic field necessary for actuating the switch. For example,

permanent magnets could be rotated past the magnetostrictive' plate 10'to subject the plate 10 to a fluctuating magnetic field to cause the plate to switch from one position to the other position.

Where the switch will be subjected to varying temperatures, the magnetostrictive elements 16 and 18 may be chosen so that their temperature coeflicients are substantially the same to render the switch insensitive to such temperature changes. Also, it is not necessary that the switch contact 30 be secured tothe magnetostn'ctive plate 10. Itis only necessary that the movi-ngcontact 30 be actuated or moved by the plate 10 so'thata pair of contacts are opened or closed when the plate 10 is snappedfrom one position such as the position shown in Fig. 1, to another positionsuch as the position shown in Fig. 2. Also, the principles of the present invention could be utilized in a multi-contact switch wherein a magnetostrictive plate having the properties of fiexingin response to a changing. magnetic field is adapted to close or open a plurality of contacts.

There has thus been provided a fast acting magneticv switch which is simple in structure, mechanically rugged;

V and is not afiectedby shock and vibration over a wide tionship; an annular, bimetallic magnetostriction switch member disposed intermediate said faces of said'perma-- nent magnets; notches in said faces of said permanent magnets for receiving a peripheral edge of said switch member, said switch member being normally concave; acontact carried by a central area of said switch member;

a pair of fixed contacts positioned within said housing and'in coextensive axial alignment with said contact car'-' ried by said switch member; an electronragnet disposed within. said housing and about said'switch' member and said'permanent magnets; .and means electrically insulating said electromagnet from said permanent magnets, said permanent magnets serving to induce'a constant bias on said" switch member toward fiection thereof between said fixed contacts whereby, upon energization of said electromagnet, to efiect fiection of said switch member and movement of. said contact carried thereby from one of said fixed contacts to the other, deenergization of said electromagnet serving to permit return of. said. switch member to an'origi'nal posit-ion thereof.

References Cited in the file of-this patent UNITED STATES PATENTS 2,764,647 Leslie et a1; Sept; 25; 1956

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