US3406267A

US3406267A - Proximity switch having a magnetic shield

Info

Publication number: US3406267A
Application number: US574395A
Authority: US
Inventors: James P Kohls
Original assignee: Jervis B Webb Co
Current assignee: Jervis B Webb Co
Priority date: 1966-08-23
Filing date: 1966-08-23
Publication date: 1968-10-15
Anticipated expiration: 1985-10-15
Also published as: BE702814A; JPS4945435B1; GB1188009A; DE1588952B1

Description

J- P. KO HLS PROXIMITY SWITCH HAVING A MAGNETIC SHIELD Oct, $5, 1968 2 Sheets-Sheet 1 Filed Aug. 215, 1966 1 |||l| /II//// I, I 1 ill llh I 1 1 1 F l G. 2

mvewron 4,415: Ao/as BY AZ 41.; 4 41 A TTORNEVS Oct. 15, 1968 J. P. KOHLS PROXIMITY SWITCH HAVING A MAGNETIC SHIELD 2 Sheets-Sheet 2 Filed Aug. 215, 1966 FIG.3

FIG.4

INVENTOR JAMES P AOl/ZJ A T TORNEVS United States Patent 3,406,267 PROXIMITY SWITCH HAVING A MAGNETIC SHIELD James P. Kohls, Detroit, Mich., assignor to Jervis B. Webb Company, a corporation of Michigan Filed Aug. 23, 1966, Ser. No. 574,395 Claims. (Cl. ZOO-61.41)

This invention relates to an improved construction for a proximity switch of the type employing a switch element having magnetically operable contacts mounted in a magnetic field formed by biasing and sensing magnets so that the relative position of the switch contacts will be changed when a ferromagnetic object is brought within the magnetic field.

The operating characteristics and sensitivity of a switch of this type are of course determined by the manner in which the switch is designed and manufactured, and these characteristics are set when the switch leaves the factory. When the switch is used, it must be mounted on some structure and if this structure is of iron or steel, then it is usually necessary to employ a mounting member of non-magnetic material in order to space the switch a minimum distance from the structure of magnetic material in order that the sensitivity and operating characteristics of the switch will not be affected thereby. Even after the switch has been installed, its operating characteristics can be affected by any change in the amount or positioning of surrounding magnetic material. These considerations have tended to reduce the reliability and usefulness of magnetic proximity switches in many possible industrial applications.

One object of the present invention is to provide a magnetic proximity switch of the type under discussion which can be mounted directly on structure of ferromagnetic material, and which is insensitive to the presence of ferromagnetic material beyond a location defined by a shield plate incorporated in the magnetic circuit of the switch.

Another object is to provide an improved arrangement for biasing the switch for a normally open or normally closed condition of the switch contact elements and for adjusting the sensitivity of the magnetic circuit of the switch to the presence of magnetic material to be detected, with the aforementioned shield plate forming part of the improved biasing arrangement.

A magnetic proximity switch constructed in accordance with the invention includes a non-magnetic case having a sensing face and a switch element with a pair of magnetically operable contacts mounted in a sensing magnetic field and in a biasing magnetic field. The sensing magnetic field is formed by a pair of sensing magnets mounted in the case in spaced relation to each other with one pair of opposite poles adjacent the sensing face, the magnetically operable contacts of the switch element being mounted in the field between the other pair of opposite poles. The biasing magnetic field is formed by a pair of biasing magnets positioned in the case with one pair of opposite poles adjacent the magnetically operable contacts of the switch element. A shield member of magnetic material is mounted in the case to form a closed flux path for the sensing and biasing magnetic fields, which closed flux path is spaced from the sensing face and shields both the sensing and biasing magnetic fields from the influence of extraneous magnetic material other than magnetic material to be detected adjacent the sensing face of the case.

In one preferred construction, the shield member is provided with a surface on which the biasing magnets are mounted for movement toward and away from each other to vary the biasing magnetic field relative to the magnetically operable switch contacts whereby the 3,406,267 Patented Oct. 15, 1968 normal position of the switch contacts can be varied and the sensitivity of the proximity switch to magnetic material adjacent the sensing face of the case can be adjusted.

Other features and advantages of the invention will appear from the following description of the representative embodiments disclosed in the accompanying drawings in which:

FIGURE 1 is a plan view of a switch with the cover of the case removed;

FIGURE 2 is a sectional elevation taken as indicated by the line 22 of FIG. 1 but showing the cover of the switch in place and the switch mounted on a structural member;

FIGURE 3 is a plan view similar to FIG. 1 showing an alternate construction; and

FIGURE 4 is a sectional elevation similar to FIG. 2 but taken on the line 4-4 of FIG. 3.

The switch construction disclosed in FIGS. 1 and 2 includes a case 10 of cast aluminum or other suitable non-magnetic material having a central bafiie 11 which divides the interior of the case into two compartments. One compartment 12 includes

bosses

13 and 14 for mounting bolts 15 which also retain a cover plate 16, and receives the structural and

electrical leads

17 and 18 respectively for the switch. The other compartment 19 receives the Various components of the switch and its magnetic circuits which are mounted generally adjacent the sensing face 20 of the case.

The switch components include a switch element 22 of the encapsulated reed type having a pair of magnetically

operable contact elements

24 and 25 mounted in a sensing magnetic field and in biasing magnetic field. The sensing magnetic field is formed by a pair of

sensing magnets

26 and 28 which are mounted in the case in spaced relation to each other with the north pole of magnet 26 adjacent the sensing face 20 and the south pole of magnet 28 adjacent the sensing face. These sensing magnets are preferably of barium ferrite, a material of low permeability so that the flux from these sensing magnets is greatly increased by the presence of a ferromagnetic object 30 adjacent the sensing face 20. The switch element 22 is mounted adjacent the

sensing magnets

26 and 28 with the magnetically

operable contacts

24 and 25 of the switch element in the field between the other pair of poles of the sensing magnets.

Biasing magnets

32 and 34 are mounted along the side of the switch element 22 opposite from the sensing magnets, and a spacer strip 36 of nonmagnetic material is preferably installed intermediate the biasing magnets and switch element. Relative polarity of the biasing to the sensing magnets is opposite as indicated-4n other words a north pole of a biasing magnet opposes a south pole of a sensing magnet and vice versa.

A shield plate 40 of ferromagnetic material is mounted in the case with the

biasing magnets

32 and 34 resting on one face 41 thereof, and is held in position by a spacer 42, which may be a length of plastic tubing inserted between the other face of the plate and the bafiie 11 of the case. The shield plate 40 forms a closed flux path, extending parallel to the sensing face, for the fields of both the biasing and sensing magnets and hence prevents or limits the distance to which the biasing and sensing magnetic fields can extend inwardly from the sensing face. Any extraneous magnetic material which does not extend toward the sensing face beyond a plane slightly spaced from the inner face 44 of the plate 40 will not affect the sensing and biasing magnetic fields. This is illustrated in FIG. 2 wherein the switch is shown attached by mounting bolts 15 directly to a ferromagnetic structural member 46, the end 48 of which does not extend beyond the plane referred to above. Therefore, this structural member, or any other object which does not project beyond this plane will not affect the desired operating characteristics of the switch, which may be set when the switch is manufactured as illustrated by the construction of FIGS. 1 and 2, or which may be varied in use as illustrated by the construction in FIGS. 3 and 4.

In the construction of FIGS. 1 and 2, the switch is assembled by inserting the

sensing magnets

26 and 28 into pockets provided inthe case, and the switch element 22, spacer 36,

biasing magnets

32 and 34, shield plate 40, and spacer tube 42 are all slipped into position. With the various parts so assembled, the

biasing magnets

32 and 34 are mounted for movement toward and away from each other on the surface 41 of the plate 40. As the

biasing magnets

32 and 34 are moved toward each other, the biasing magnetic field becomes increasingly predominant in its effect upon the

switch contact elements

24 and 25, and as the biasing magnets are moved away from each other the field of the sensing magnets becomes predominant.

For example, if it is desired to have the switch contacts 24 and normally open and to close in the presence of a ferromagnetic object at a distance of one-half inch from the sensing face 20 of the case, this setting is obtained as follows: The object 30 is placed one-half inch away from the sensing face and the biasing magnets are moved together so that the distance separating them is zero. A continuity check should show that the switch contacts are closed. The biasing magnets are then gradually moved apart until the switch contacts open and then close. The object 30 is removed, brought back to the desired one-half inch spacing and the switch contacts should close. The switch is then potted by filling the compartment 16 of the case with a suitable plastic material.

This adjustment of the normal position of the switch contacts and the sensitivity thereof to a change from normal posit-ion as the result of the presence of a magnetic object adjacent the sensing face of the case is obtained by varying the length of the flux path of the biasing magnetic field through the

biasing magnets

32 and 34, the shield member and the magnetically

operable switch contacts

24 and 25. In the construction shown, the length of the flux path is varied by means of adjusting the relative position of the biasing magnets along the face 41 of the shield plate, and while this is preferable because of the simplicity of construction, the flux path length could obviously also be changed by varying the position of the shield plate.

The proximity switch construction shown in FIGS. 3 and 4 is similar except that means are provided for adjusting the position of the

biasing magnets

32 and 34 at any time during the life of the switch, no potting compound being placed in the switch compartment 16 of the case and the adjusting means being accessible externally of the case. A spring is placed between the biasing magnets and normally urges them apart, while positioning

screws

52 and 53, each extending through a threaded boss 54 in the case, enable the biasing magnets to be moved in opposition to the force of the spring 50. Since no potting compound is used, all the components of the switch except the biasing magnets may be fixed in position in the case by cementing or other suitable means. A tongue and

groove connection

56, 57 is employed between the

biasing magnets

32 and 34 and the shield plate 40, the biasing magnets being urged against the face of the shield plate by a combination spacer and retainer member 58.

While preferred embodiments have been described above in detail, it will be understood that numerous modifications might be resorted to without departing from the scope of the invention as defined in the following claims.

I claim:

1. A magnetic proximity switch including a nonmagnetic case having a sensing face and a switch element with a pair of magnetically operable contacts mounted in a sensing magnetic field and in a biasing magnetic field; characterized by the sensing magnetic field being formed by a pair of sensing magnets mounted in the case in spaced relation to each other with one pair of opposite poles adjacent the sensing face, the magnetically operable contacts of the switch element being mounted in the field between the other pair of opposite poles; the biasing magnetic field being formed by a pair of biasing magnets positioned in the case with one pair of opposite poles adjacent the magnetic ally operable contacts of the switch element; a shield member of magnetic material mounted in the case to form a closed flux path for the sensing and biasing magnetic fields, which closed flux path is spaced from the sensing face and shields both the sensing and biasing magnetic fields from the influence of extraneous magnetic material other than magnetic material to be detected adjacent the sensing face of the case.

2. A magnetic proximity switch as claimed in claim 1 further characterized by means for varying the length of the flux path of the biasing magnetic field through the biasing magnets, the shield member, and the magnetic operable switch contacts.

3. A magnetic proximity switch as claimed in claim 2 wherein the shield member and biasing magnets are mounted for movement relative to each other and to the magnetically operable switch contacts.

4. A magnetic proximity switch as claimed in claim 1 wherein the shield member is provided with a surface on which the biasing magnets are mounted for movement toward and away from each other to vary the biasing magnetic field relative to the magnetically operable switch contacts whereby the normal position of the switch contacts can be varied and the sensitivity of the proximity switch to magnetic material adjacent the sensing face of the case can be adjusted.

5. A magnetic proximity switch according to claim 4 further characterized by means accessible externally of the case for adjusting the position of the biasing magnets relative to each other.

6. A magnetic proximity switch as claimed in claim 5 wherein the means for adjusting the relative position of the biasing magnets includes a spring normally urging the biasing magnets apart, and positioning means extending through the case for moving the biasing magnets together in opposition to the force of the spring.

7. A magnetic proximity switch according to claim 1 wherein the sensing magnets are each of low permeability.

8. A magnetic proximity switch according to claim 1 wherein the shield member is a plate extending parallel to the sensing face of the case wit-h the sensing magnets, switch element and biasing magnet being mounted between one face of the plate and the sensing face of the case.

9. A magnetic proximity switch according to claim 8 wherein the biasing magnets of each mounted on the said one face of the plate forming the shield member for movement toward and away from each other.

10. A magnetic proximity switch as claimed in claim 9 further characterized by adjusting means extending through the case for varying the position of at least one of the biasing magnets relative to the magnetically operable contacts of the switch element.

' References Cited UNITED ROBERT K. SCHAEFER, Primary Examiner.

M. GINSBURG, Assistant Examiner.

Claims

1. A MAGNETIC PROXIMITY SWITCH INCLUDING A NON-MAGNETIC CASE HAVING A SENSING FACE AND A SWITCH ELEMENT WITH A PAIR OF MAGNETICALLY OPEARBLE CONTACTS MOUNTED IN A SENSING MAGNETIC FIELD AND IN A BIASING MAGNETIC FIELD; CHARACTERIZED BY THE SENSING MAGNETIC FIELD BEING FORMED BY A PAIR OF SENSING MAGNETS MOUNTED IN THE CASE IN SPACED RELATION TO EACH OTHER WITH ONE PAIR OF OPPOSITE POLES ADJACENT THE SENSING FACE, THE MAGNETICALLY OPERABLE CONTACTS OF THE SWITCH ELEMENT BEING MOUNTED IN THE FIELD BETWEEN THE OTHER PAIR OF OPPOSITE POLES; THE BIASING MAGNETIC FIELD BEING FORMED BY A PAIR OF BIASING MAGNETS POSITIONED IN THE CASE WITH ONE PAIR OF OPPOSITE POLES ADJACENT THE MAGNETICALLY OPERABLE CONTACTS OF THE SWITCH ELEMENT; A SHIELD MEMBER OF MAGNETIC MATERIAL MOUNTED IN THE CASE TO FORM A CLOSED FLUX PATH FOR THE SENSING AND BIASING MAGNETIC FIELDS, WHICH CLOSED FLUX PATH IS SPACED FROM THE SENSING FACE AND SHIELDS BOTH THE SENSING AND BIASING MAGNETIC FIELDS FROM THE INFLUENCE OF EXTRANEOUS MAGNETIC MATERIAL OTHER THAN MAGNETIC MATERIAL TO BE DETECTED ADJACENT THE SENSING FACE OF THE CASE.