Reed Switch

Abstract

A reed switch includes a housing with a pair of magnetically-responsive contacts mounted therein, which contacts are closed when an axially-movable magnetic actuator reaches a specified distance with respect to the contacts. A plunger is carried by the housing and moves the actuator toward and away from the contacts. Adjusting means are provided which operatively engage the magnet and the plunger for varying the initial distance of the magnet from the contacts. A cap is removably attached to the plunger and is constructed to conceal and protect the adjusting means.

Description

This invention is directed to a switch utilizing magnetically-responsive contacts which are actuated by a magnetic field.

It is an important object of the present invention to provide a reed switch which is actuated by depressing a button and which includes improved means for adjusting the amount by which the button must be depressed to cause actuation.

Another object of the invention is to provide a reed switch in which the adjusting means are concealed and protected so as to prevent inadvertent alteration of the setting during use.

Still another object is to provide a reed switch usable in conjunction with a number of other similar reed switches in a keyboard, which reed switches include concealed adjusting means to enable each switch to be actuated in response to the same amount of depression.

Yet another object is to provide a reed switch which includes concealed adjusting means to enable compensation for variations in the characteristics from one reed to another reed.

A further object is to provide a reed switch in which access to the adjusting means is gained by removing a push-button cap.

In summary, there is provided a reed switch comprising a housing having a wall with an opening therein, a pair of magnetically-responsive contacts in the housing and having opened and closed position conditions, the contacts being arranged to switch from one condition to the other condition when a magnetic field presented thereto reaches a predetermined value, a plunger disposed partly in the opening and slidably movable therein along a predetermined path adjacent to the contacts, a magnetic actuator including a movable portion operatively engaged by the plunger to be moved therewith along the predetermined path to vary the magnetic field presented to the contacts, an adjustment device operatively engaging the movable portion and the plunger for varying the initial distance of the movable portion from the contacts, and a cap removably attached to the plunger and constructed to conceal and protect the adjustment device.

The magnetic actuator may be a magnet which is movable along the predetermined path to close and open the contacts. Also, the plunger may consist of two separate sections, one section being provided with means to receive a snap-fitted cap and the other section being provided with means to limit outward movement of the plunger.

Further features of the invention pertain to the particular arrangement of the elements of the reed switch, whereby the above-outlined and additional operating features thereof are attained.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings, in which:

FIG. 1 is a view in longitudinal cross section of a reed switch incorporating the features of the present invention;

FIG. 2 is a view in longitudinal cross section taken along line 2--2 of FIG. 1;

FIG. 3 is a view in horizontal cross section of the reed switch of FIG. 1 taken along the line 3--3 thereof;

FIG. 4 is a view similar to the view in FIG. 2, but with the push-button cap depressed so as to close the switch contacts;

FIG. 5 is a view of the reed switch also similar to FIG. 2, with the cap removed and with a hex driver inserted to adjust the initial position of the magnet; and

FIG. 6 is a view in horizontal cross section taken along the line 6--6 of FIG. 5.

Referring now to the drawings, there is shown a reed switch 10 incorporating therein the features of the present invention. The reed switch finds particular use on a keyboard such as that employed in a computer input device or in a calculator. The reed switch 10 is of the push-button variety, that is, the switch includes an outwardly-biased button which is operative to close an electrical circuit as long as the button is depressed. The reed switch 10 is shown as being mounted on such a keyboard 11, the keyboard 11 having a hole 12 (FIG. 1) to accommodate a projection on the reed switch 10 as will be described. A threaded bolt is provided which passes through a suitably-formed hole in the reed switch 10 and passes through an opening in the keyboard 11 for engagement with a nut 14, thereby securely to retain the reed switch 10 in the selected location.

The reed switch 10 comprises a rectangular housing, which, in the form shown, is constructed of plastic. The housing 20 is rectangular in transverse cross section and has a wall 23 adjacent to one end thereof, a neck 21 being provided on the wall 23 and protruding outwardly therefrom. An opening 22 (FIG. 1) extends through the neck 21 and the wall 23, with the opposite end of the housing 20 being open. There is also provided a base 25 having a rectangular bottom wall 26 and four depending side walls 27, which side walls fit into and frictionally engage respectively the inside of the side walls of the housing 20. Formed on the bottom wall 26 and protruding outwardly therefrom is a projection 28 (FIG. 1) which fits into the hole 12 formed in the keyboard 11, thereby to prevent turning of the reed switch 10 as it is secured to the board 11 by means of the bolt 13 and the nut 14. Protruding inwardly in the same direction as the side walls 27 is a cylindrical post 29. After the parts are properly located within the housing 20, the base 25 is force fitted into the open end of the housing 20. In addition to the frictional engagement, it is preferable to use cement to insure a long lasting connection.

Mounted on the base 25 and extending upwardly therefrom is a pair of dry reeds, respectively consisting of elongated glass envelopes 30 and 30a, each being hermetically sealed and containing an inert gas. Encased in the envelope 30 is a pair of beams 31 which are in the form of very thin, narrow, metal strips that are directed toward one another and extend in a direction substantially parallel to the longitudinal axis of the housing 20. Respectively at the ends of the beams 31 are contacts 32 which are spaced from each other, that is, open, as shown in FIG. 2 or closed as shown in FIG. 4. The beams 31 respectively penetrate the ends of the envelope 30 and are connected to terminals 33 which protrude outwardly of the base 25. When the contacts 32 are oppositely magnetically poled so as to be attracted to each other, they will close. This occurs when they are exposed to a magnetic field of sufficient magnitude to overcome the rigidity of the beams 31. The beams 31 are constructed to possess the characteristic of a leaf spring so that, when their mechanical stiffness is overcome by the strength of magnetic attraction, the contacts 32 close.

The other envelope 30a similarly includes a pair of beams 31a which are in the form of very thin narrow metal strips that are directed toward one another and extend in a direction substantially parallel to the longitudinal axis of the housing 20. Respectively at the ends of the beams 31a are contacts 32a which are spaced from each other, that is, open, as shown in FIG. 2 or closed as shown in FIG. 4. The beams 31a respectively penetrate the ends of the envelope 30a and are connected to the terminals 33a which protrude outwardly of the base 25. When the contacts 32a are oppositely magnetically poled so as to be attracted to each other, they will close. This will occur when they are exposed to a magnetic field of sufficient magnitude to overcome the rigidity of the beams 31a. The beams 31a are constructed to possess the characteristics of a leaf spring so that, when their mechanical stiffness is overcome by the strength of the magnetic attraction, the contacts 32a close.

The reed switch 10 further comprises a plunger 40 including a first plunger portion 41 and a mating second plunger portion 50. The first plunger portion 41 includes a sleeve 42 also made of plastic in the preferred form and having a lateral wall 43 therein. The interior of the sleeve above the lateral wall 43 defines a recess 44. There is provided a depending tongue 46 on the lateral wall 43, which tongue extends along the diameter of the lateral wall 43 and is generally rectangular in transverse cross section. An access opening 45 extends through the lateral wall 43 and the tongue 46, which opening extends along the axis of the sleeve 42. On one end of the sleeve 42, the upper end as viewed in the FIGS. 1-6, there is a square flange 47 having a notch 48 (FIG. 3) in each of its four sides. The diameter of the sleeve 42 is slightly less than the inside diameter of the neck 21 to enable the sleeve freely to slide in the neck 21 along a predetermined path defined by the axis of the housing 20. The flange 47 is adapted to engage the outer end of the neck 21 so as to limit inward movement of the sleeve 42.

A second plunger portion 50 includes a dowel or peg 51 that has a diameter approximately equal to the inside diameter of the sleeve 42. The peg 51 carries a pair of depending arcuate legs 52 each having an angular extent of on the order of 90.degree. in the embodiment shown. The inside of each leg is round and is about 90.degree. in extent, so as to define between the legs 52 a channel 53 for a cylindrical magnet. The peg 51 has a diametrically-extending notch in the outer end thereof with a shape to receive the tongue 46 on the first plunger portion 41. There is provided a threaded opening 54 (FIG. 4) extending axially through the peg 51, with a screw 55 being provided therein. The screw 55 has a hex-shaped socket 56 in the outer end thereof in the embodiment shown. Finally, the laterally-disposed surfaces at the juncture of the peg 51 and the legs 52 define shoulders 57.

The second plunger portion 50 is disposed in the housing 20 with the peg being force fitted into the sleeve 42 so as frictionally to engage the same, with the tongue 46 being disposed or partly disposed in the complementary-shaped groove in the second plunger portion 50. With the plunger portions 41 and 50 thus interconnected, the shoulders 57 limit outward movement of the plunger 40 by engaging the wall 23.

The reed switch 10 further comprises a magnet 60 which, in the form shown, is a solid cylinder, the magnet being axially magnetized so as to have the north and south poles at opposite ends. The diameter of the magnet 60 is slightly less than the distance between the legs 52 which define the channel 53. The magnet 60 is disposed in said channel 53 so as to be axially movable therein as will be described presently. In one form of the invention, there is sufficient frictional engagement between the legs 52 and the magnet 60 to retain the magnet 60 against the action of gravity. There is also provided a spacer 61 which is disposed against the lower end of the magnet 60 and a compression spring 62 between the lower end of the spacer 61 and the bottom wall 26 of the base 25, the post 29 being disposed within the spring 62. The spring urges the magnet 60 against the second plunger portion 50 so that the shoulders 57 thereon are resiliently urged against the wall 23 of the housing 20. It may be seen that, as the magnet is moved axially toward and away from the axial position of the contacts 32 and 32a, the magnetic field presented thereto varies. When the magnet reaches a certain position such that the magnetic field reaches a predetermined value, the contacts 32 and 32a close.

Lastly, the reed switch 10 comprises a cap 70 which has a top wall 72 with four depending, slightly inclined side walls 71. Formed in the top wall 72 is a depression 73 to accommodate the tip of a finger. On the interior of the top wall 72 is a set of four depending posts 74 adjacent to the corners thereof. On each of the side walls 71 is a ramp 75 having an inclined cam surface 76 and a laterally-disposed notch 77 near the upper end of each ramp 75. The four ramps 75 and the four notches 77 are respectively laterally aligned with the four notches 48 in the flange 47 of the first plunger portion 40.

In assembling the cap 70 on the first plunger portion 41, the ramps 75 on the cap 70 are respectively aligned with the notches 48 in the flange 47. The cap 70 is pushed downwardly to carry the plunger 40 down until further movement is prevented, which, in the embodiment shown, occurs when the spacer 61 strikes the post 29. Further force on the cap 70 will cause the ramps 75 thereon to ride down on the flange 47, with the cam surfaces 76 guiding the flange 47 until the sides thereof respectively snap into the notches 77. The notches 77 have therein the adjacent portion of the flange 47 so as to retain securely the cap 70 in position. Removal of the cap 70 is accomplished by forceably tilting the same until one side of the flange 47 is unseated from the associated notch 77, after which the other sides of the flange 47 naturally become unseated from their respective notches 77. The cap 70 may then be lifted to expose the recess 44 in the first plunger portion 41.

In use, the reed switch 10 is mounted on a keyboard 11 as previously explained with the sets of terminals 33 and 33a being electrically connected to their respective circuits. When it is desired to complete these electrical circuits, the user depresses the cap 70 which moves the plunger 40, consisting of the first and second plunger portions 41 and 50, downwardly, that is, toward the base 25, which, in turn, carries the magnet 60 downwardly against the action of the spring 62. When the magnet 60 reaches a predetermined axial position, that is, presents to the contacts 32 and 32a a magnetic field of a predetermined value, the contacts 32 and 32a close.

It has been found that one magnet may be stronger than another. Whereas a given displacement of the cap 70 would be required to close the contacts 32 and 32a with a stronger magnet, a greater displacement of the cap 70 would be required to close the contacts with a weaker magnet. Also, the reeds themselves vary in that it takes differing magnetic field strengths to effect closure of the contacts. For example, one reed may require a magnet intensity of 27 ampere turns to effect closure, whereas another reed may require 42 ampere turns to effect closure. Although a certain displacement of the cap 70 will close the contacts requiring the weaker magnetic strength, the contacts requiring a greater magnetic intensity would require a greater displacement of the cap 70. Particularly when a number of such reed switches 10 are mounted on a keyboard 11, such as in the case of a computer input or a calculator, it is desirable that the same displacement of each cap 70 will actuate the associated reed switch 10. The invention includes improved adjustment means to insure that this does occur. In the form shown, the adjustment means is the screw 55 in the threaded opening 54. When the lower end of the screw 55 is within the opening 54 or at least flush with the bottom surface of the peg 51 as shown in FIGS. 1 and 2, the magnet 60 will be resiliently urged by the spring 62 against that surface. In this position, as is most clearly shown in FIGS. 1 and 2, the initial distance of the magnet 60 from the contacts 32 and 32a would be a maximum. To reduce this initial distance, the screw 55 may be adjusted to its position shown in FIG. 5. To this end, there is provided a tool 80 having a handle 81 and a hexagonal shank 82. The shank 82 is inserted through the access opening 45 in the first plunger portion 41 and into the socket 56 of the screw 55. The tool 80 may be rotated to turn the screw 55 and adjust its axial height. If screwed downwardly, the magnet 60 is moved downwardly, that is, away from the plunger 40 and against the action of the spring 62. As the magnet 60 is moved downwardly, its initial distance from the contacts 32 and 32a is reduced.

Either before or after the cap 70 is placed in position, the reed switch 10 is tested to determine the amount of displacement of the plunger 40 required to close the contacts 32 and 32a. As an example, assume that the test indicates that a particular reed switch 10 requires a displacement of .25 inches before the contacts 32 and 32a are closed, whereas predetermined specifications require that the contacts should close with a displacement of .225 inches. In that case, the cap 70 would be removed as previously explained, and the tool 80 inserted in the hex socket 56. The screw 55 would be rotated to move the magnet 60 downwardly, that is, reduce the initial axial distance between the magnet 60 and the contacts 32 and 32a. With the proper adjustment, the contacts 32 and 32a will close when the plunger 40 is displaced .225 inches. If the test, on the other hand, established that the plunger 40 had to be displaced .275 inches to close the contacts 32 and 32a, the screw 55 would be withdrawn partially to increase the initial distance between the magnet 60 and the contacts 32 and 32a and by an amount to cause closure at the selected .250 inch displacement. After the proper adjustment has been made, the cap 70 is replaced as previously described. The same procedure is effected in respect to each reed switch 10 in a multiple-switch system, so that all of the reed switches 10 mounted on a given keyboard or in a particular unit will be actuated by the same displacement of the cap 70. This procedure may be performed either at the manufacturing facility of the reed switches and/or at the user's plant. For example, after extended usage, it may be determined that the switch 10 should be readjusted to meet original specifications. Alternatively, after a certain amount of usage, it may be determined that a different displacement of the reed switch 10 would be desirable. Also, it may be found that the particular environment in which the reed switch 10 is used differs substantially from that in which the reed switch was adjusted such as, for example, humidity which would require a readjustment at the user's location. The user can perform the adjustment merely by removing the cap 70 as previously explained and utilizing the tool 80.

One very important advantage of the instant invention is that the adjusting means, consisting of the screw 55 in its threaded opening 54, is concealed and protected by the cap 70. Thus, inadvertent variation of the adjusting means during day-to-day operation is prevented. The user can make necessary adjustments easily and simply, yet at the same time have assurance that inadvertent variations will not occur.

Although the drawings illustrate the reed switch 10 as having two pairs of contacts 32 and 32a, it should be appreciated that any number of pairs of contacts may be utilized, limited by the available space within the housing 20. Of course, one pair of contacts with its attendant elements is also contemplated. Also, although the particular form illustrates a magnet 60 as being the actuating element, it can be appreciated that the magnet 60 may be fixed in position and a shield be provided around the magnet 60, which shield is axially movable so as to vary the magnetic field presented to the contacts 32 and 32a.

While there has been what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

Claims

1. A reed switch comprising a housing having a wall, an outwardly protruding neck on said wall and having an opening extending therethrough, a pair of magnetically responsive contacts in said housing and having open and closed conditions, a plunger including first and second mating plunger portions, said first plunger portion including a sleeve and a flange on the outer end of said sleeve, said sleeve being disposed in said neck and slidably movable therein along a predetermined path, said second plunger portion including a peg frictionally engaging in said sleeve and a shoulder on said sleeve, said shoulder being adapted to engage the inside of said wall of said housing to limit outward movement of said plunger, a magnet operatively engaged by said second plunger portion to be movable therewith along said predetermined path to vary the magnetic field presented to said contacts, a spring engaging said housing and said magnet resiliently to urge said shoulder against said wall, adjusting means operatively engaging said magnet and said second plunger portion for varying the initial distance of said magnet from said contacts, and a cap removably attached to said flange and constructed to conceal and protect

2. The reed switch set forth in claim 1, wherein said second plunger portion has an axially threaded opening extending therethrough, said adjusting means including a screw in said opening and engaging with said magnet for varying the initial distance of said magnet from said contacts.

3. The reed switch set forth in claim 1, wherein said first plunger portion includes a laterally extending wall having an access opening therethrough in axial alignment with the threaded opening in said second plunger portion, said access opening accommodating the shank of a tool to be

4. The reed switch set forth in claim 1, wherein said second plunger portion includes a pair of depending legs defining a guide for said

5. The reed switch set forth in claim 1, wherein said cap includes a top wall, four depending side walls, and two ramps respectively on opposite ones of the side walls, each of said ramps having adjacent the top wall thereof a notch, said ramps serving to guide said flange to said notches to be snap-fit thereinto.