Magnetically Operated Electrical Switch

Abstract

An electrical switch has a freely movable magnetic ball contact maintained in a first position out of engagement with at least one of a plurality of stationary electrical contacts by a permanent magnet. The ball contact is movable to a second position wherein it engages all of the contacts in response to magnetic influence exerted thereon by an iron rod carried by a reciprocally movable push button and disposed within a flux path of the magnet. The rod exerts greater magnetic influence on the ball contact than magnet during only an initial portion of push button travel toward a fully depressed position whereby to cause the ball contact to return to its first position in response to magnetic influence of the magnet before the push button reaches its fully depressed position.

Description

BACKGROUND OF THE INVENTION

This invention relates in general to electrical switches and deals more particularly with an improved magnetically operated electrical switch suitable for use as a keyboard switch or the like.

The switch of the present invention is particularly adapted for use as a keyboard switch on an electric typewriter, business machine, computer or like apparatus which requires single pulse switch output during each switching cycle. In a keyboard switch of the aforedescribed type, it is generally required that the electrical output of the switch be isolated from and wholly independent of the mechanical output of the operator. Thus, the operator controls the occurrence of switch pulse output but not the duration thereof. It is further desirable that such a switch have a tactile feedback characteristic to indicate to the keyboard operator, as by sharp reduction of key stroke pressure, that a character has been transmitted.

Accordingly, the general aim of the present invention is to provide an improved magnetically operated switch which possesses the aforedescribed desired operational characteristics and which is of simple durable construction for low cost manufacture.

SUMMARY OF THE INVENTION

In accordance with the present invention, an improved electrical switch is provided which comprises a plurality of stationary electrical contacts, a permanent magnet mounted in fixed position relative to the contacts, a movable switching part maintained by the magnet in one switching position out of engagement with at least one of the contacts, an operating part supported for movement relative to the contacts and magnet between first andd second positions, and a ferromagnetic element carried by the operating part and disposed within the magnetic influence of the magnet and in close proximity to the switching part when the operating part is in its first position and the switching part is in its one position. The ferromagnetic element exerts a greater magnetic attraction for the switching part than the magnet when the operating part is in its first position and during at least a portion of its travel toward its second position whereby the switching part moves with the operating part to another position wherein it engages each of the stationary contacts when the operating part is moved from its first position toward its second position.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an axial sectional view through an electrical switch embodying the present invention.

FIG. 2 is a sectional view taken along the line 2--2 of FIG. 1.

FIG. 3 is a sectional view taken generally along the line 3--3 of FIG. 2.

FIG. 4 is a fragmentary sectional view taken along the line 4--4 of FIG. 1.

FIG. 5 is a sectional view similar to FIG. 1 but shows the operating button in a partially depressed position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning now to the drawing, an electrical switch embodying the present invention and indicated generally at 10, comprises a switch housing designated generally by the numeral 12 supporting a plurality of spaced stationary contacts 14, 16 and 18 and a permanent magnet 20 associated with the contact 14. The illustrated switch 10 is particularly adapted for use as a keyboard switch and further includes an operating part or push button indicated generally at 22 which carries a ferromagnetic element 24. The push button is supported by the housing 12 for movement relative thereto and controls movement of a switching part or movable spherical contact 26 preferably made from steel and contained in the housing and within magnetic influence of the magnet 20. The movable magnetic ball contact 26 is maintained in one position out of electrical contact with at least one of the stationary contacts by the magnetic attraction of the magnet and is movable to another position wherein it is in electrical contact with each of the stationary contacts to establish electrical connection therebetween in response to movement of the operating part.

Considering now the housing 12 in further detail, it includes a hollow generally rectangular base 28 and a terminal board 30 secured to the base by threaded fasteners 32, 32 as best shown in FIG. 3. The base 28 has a reduced neck portion at its upper end which partially defines a generally rectangular bore 34 which extends through the base. A downwardly opening recess 36 in one side of the base communicates with the bore 34 as best shown in FIG. 2.

The stationary contacts 14, 16 and 18 are supported on the terminal board 30 and have terminal portions which extend downwardly therethrough for connection in an external circuit or, if desired, to a printed circuit associated with the terminal board. The contact 14 comprises a generally rectangular plate which is disposed within the base and has its marginal side edges received and supported in opposing slots 38, 38 formed in the base as best shown in FIG. 2. The contact 14 forms a partition or dividing wall between the recess 36 and the bore 34 and defines a continuation of one wall of the rectangular bore 34, as best shown in FIG. 1. A pair of bent mounting clips 40, 40 struck from the contact 14 support the magnet 20 within the recess 36. The contacts 16 and 18 are generally cylindrical and project upwardly from the terminal board generally within a plane through the bore axis. Each of the contacts 16 and 18 has a generally conical upper end portion to provide a contact surface for electrical contact engagement with the ball contact 26. The contacts 16 and 18 are spaced from each other and from the contact 14. It should be noted that the contact 16 is of somewhat greater length than the contact 18 and extends for a slightly greater distance above the terminal board 30 than the contact 18.

The push button or key is preferably molded from plastic or like material and has a button portion 42 and an integral hollow shank 44 which depends from the button portion. The shank has a generally rectangular cross sectional configuration which complements the cross-sectional configuration of the bore 34 in which it is slidably received. At its lower end, the shank 44 has a downwardly opening slot 46 formed in the wall thereof adjacent the contact 14. The ferromagnetic element 24 comprises an iron rod which extends transversely through the lower end of the shank portion 44 between the contact 14 and the contacts 16 and 18. The end portions of the rod 24 project from opposite sides of the shank 44 and into a downwardly opening slot 48 formed in the base 28. The end portions of the rod cooperate with the upper wall of the slot 48 to retain the push button 22 in assembly with the housing 12 and function as a stop to limit its upward travel relative to the housing. The push button 22 is biased to a projected or first position, indicated by full lines in FIG. 1, by a compression spring 50 which surrounds the neck portion of the base 28 and acts between the base and the button portion 42. The push button 22 is manually movable against bias of the spring 30 to a fully depressed or second position indicated by broken lines in FIG. 1.

The spherical or ball contact 26 is disposed in the housing 12 within the magnetic influence of the magnet 20 and more specifically within the hollow shank 44 and above the iron rod 24. The magnet is preferably of the type which includes a plurality of poles arranged in alternate series. The illustrated magnet 20 has three alternate poles arranged substantially as indicated in FIG. 1. It should be further noted that when the push button 22 is in its projected position, the ferromagnetic rod 24 is disposed in close proximity to and preferably in contact with the ball contact 26, substantially as shown in FIG. 1.

When the push button 22 is in its projected position, the ball contact 26 is maintained in a generally central position relative to the magnet 20 and in electrical contact with the contact 14 by the magnetic attraction of the magnet. However, when the ball contact 26 is in the latter position, as it appears in FIG. 1, it is out of electrical contact with the stationary contact 16 and 18, as best shown in FIG. 3. When the push button 22 is in its projected position, the rod 24 is generally adjacent the ball contact 26 and within the magnetic influence of the magnet 20 and acts as a temporary magnet to exert further magnetic influence upon the ball 26. During initial movement of the push button 22 from its projected toward its depressed position, the rod 24 exerts a substantially greater influence upon the ball contact 26 than the magnet 20. Thus, the ball contact 26 moves downward with the push button and toward the stationary contacts 16 and 18 in rolling or sliding engagement with the contact 14. Due to the height differential between the contacts 14 and 16 relative to the base 30, the ball contact 26 establishes electrical contact with the stationary contact 16 before it engages the contact 18. However, the ball contact 26 ultimately attains another position, in response to continued downward movement of the push button 22, wherein it is in simultaneous engagement and electrical contact with all of the stationary contacts, as indicated in full lines in FIG. 5 and in broken lines in FIG. 3. The ball contact 26 attains the latter "make" position before the push button 22 is fully depressed and is restrained against further downward movement by the stationary contacts. When the ball contact 26 makes contact with all of the stationary contacts, the rod 24 is still within the magnetic influence of the magnet 20 and continues to be attracted to the ball contact. As the rod 24 continues to move downward and away from the ball contact 26, its influence on the ball contact sharply decreases. In the illustrated switch 10 an almost immediate reversal of magnetic influence occurs when the rod separates from the ball contact. More specifically, as the rod 24 moves out of engagement with and away from the ball contact 26, the latter contact comes under the greater influence of the magnet 20 which causes it to break contact and return to its initial or full line position in FIG. 1 before the push button 22 attains its fully depressed or broken line position in FIG. 1.

An increase resistance to the downward movement of the push button or key 22 is felt at the instant the ball contact 26 establishes simultaneous electrical contact with the stationary contacts 14, 16 and 18 and separates from the rod 24. Further, a sharp reduction in key stroke pressure is felt at the instant that the ball leaves the magnetic influence of the rod 24 and returns to its initial position under the magnetic influence of the magnet 20. This tactile feedback is highly desirable in a keyboard switch, since it enables a keyboard operator to sense when a character has been transmitted by a key.

The switch 10 provides a single pulse output during each complete switching cycle. It will be apparent that after the push button 22 has been depressed a sufficient distance to cause the ball contact 26 to make and then break and return to its centralized position on the magnet 20, the switch cannot again be operated until the push button 22 has returned to its projected position to bring the rod 24 into adjacent relation with the ball contact 26 and within the magnetic influence of the magnet 20.

It will be further noted that the switch 10 may be connected in circuit so that it is first conditioned to establish two circuit paths through the terminals associated with the stationary contacts 14 and 16 and then establish a common path to ground through the terminals 18. Thus, the switch may be employed to provide simultaneous output at the two terminals 14 and 16.

Claims

1. An electrical switch comprising a plurality of electrical contacts spaced from each other, a permanent magnet mounted in fixed position relative to said electrical contacts, a magnetic switching part disposed within the magnetic influence of said magnet and maintained in one switching position by the magnetic attraction of said magnet, said switching part in said one position being out of electrical contact with at least one of said electrical contacts and being movable to another position wherein it is in electrical contact with each of said electrical contacts, an operating part supported for movement relative to said electrical contacts and said magnet between first and second positions, a ferromagnetic element carried by said operating part and disposed within the magnetic influence of said magnet and in close proximity to said switching part when said operating part is in its first position and said switching part is in said one position, said ferromagnetic element exerting a greater magnetic attraction for said switching part than said magnet when said operating part is in its first position and during at least a portion of the travel of said operating part from its first toward its second position, said switching part being movable from its one to its other position with said operating part when the latter part is moved from

2. An electrical switch as set forth in claim 1 wherein said ferromagnetic element exerts greater magnetic attraction for said switching part than said magnet during only the initial portion of the travel of said operating part from its first toward its second position, said switching part attains its other position in response to movement of said operating part from its first toward its second position before said operating part attains its second position, said magnet exerts greater attraction for said switching part than said ferromagnetic element after said switching part attains its other position and said switching part moves from its other position to its one position in response to magnetic attraction of said magnet during the final portion of the travel of said operating part

3. An electrical switch as set forth in claim 1 wherein said electrical contacts comprise three stationary contacts, said switching part passes through an intermediate position wherein it is in electrical contact with two of said contacts in traveling from its one to its other position, and said switching part remains in electrical contact with said two contacts during its movement from said intermediate position to its other position in response to movement of said operating part from its first toward its

4. An electrical switch as set forth in claim 3 wherein said switching part

5. An electrical switch as set forth in claim 4 wherein said ferromagnetic

6. An electrical switch as set forth in claim 2 wherein said switch includes a hollow housing which has a bore, said electrical contacts comprise stationary contacts fixedly mounted in said housing, said operating part comprises a push button which has a hollow shank slidably received in said bore, and said switching part is disposed generally

7. An electrical switch has set forth in claim 6 wherein said switching

8. An electrical switch as set forth in claim 7 wherein one of said stationary contacts partially defines said bore, said shank has a slot therein adjacent said one stationary contact, and said ball engages said

9. An electrical switch as set forth in claim 8 wherein said one stationary contact comprises means for supporting said magnet in fixed position in

10. An electrical switch as set forth in claim 7 wherein said ferromagnetic

11. An electrical switch as set forth in claim 1 wherein said switch includes means for biasing said operating part in one direction toward its first position and said ferromagnetic element comprises means for limiting

12. An electrical switch as set forth in claim 11 wherein said switch includes a housing which has a slot therein, said operating member is supported by said housing for movement relative thereto, and said ferromagnetic element comprises a rod received in said slot.