US3699293A

US3699293A - Key switch for chatterless switching

Info

Publication number: US3699293A
Application number: US60028A
Authority: US
Inventors: Peter Portugall
Original assignee: International Standard Electric Corp
Current assignee: Alcatel Lucent NV
Priority date: 1969-08-04
Filing date: 1970-07-31
Publication date: 1972-10-17
Anticipated expiration: 1989-10-17
Also published as: GB1259567A; DE1939642A1; FR2056556A5; DE1939642B2

Abstract

A normally open key switch for chatterless switching. The switching element is a silicone rubber part containing granular silver-plated, copper particles which normally lies in a loose relationship over a pair of separate contact plates. A compression member applies a deforming force to the switching element when the switch is actuated, causing a great decrease in effective resistivity of the switching element. The compression member is independently resiliently linked to the actuating button, permitting some button overtravel and thereby isolating the switching element from the full actuating force applied to the button.

Description

United States Patent Portugall [1 3,699,293 [451 Oct. 17, 19 72 [54] KEY SWITCH FOR CHATTERLESS SWITCHING [72] lnventor: Peter Portugal], Fischbach, Germany [73] Assignee: International Standard Electric Corporation, New York, NY.

[22] Filed: July 31, 1970 [21] App1.No.: 60,028

[58] Field of Search ..200/166 C, 166 H, 46, 86 R; 252/511, 512

[56] References Cited UNITED STATES PATENTS 3,194,860 7/1965 Ehrreich et al. ....252/511 UX 3,509,296 4/1970 Harshman et al ..200/46 Germany ..-.P 19 39 6420 Schenck ..200/166 H 2,430,829 11/1947 Sepavich ..200/166 C X 2,752,558 6/1956 Kane ..200/166 C X 2,867,043 1/1959 Jarret et a1. ..200/166 C X Primary Examiner-H. 0. Jones I Attorney-C. Cornell Remsen, Jr., Walter J. Baum, Paul W. l-lemminger, Percy P. Lantzy and Thomas E,

Kristofferson [57] ABSTRACT A normally open key switch for chatterless switching.

Theswitching element is a silicone rubber part containing granular silver-plated, copper particles which normally lies in a loose relationship over a pair of separate contact plates. A compression member applies a deforming force to the switching element when the switch is actuated, causing a great decrease in effective resistivity of the switching element. The compression member is independently resiliently linked to the actuating button, permitting some button overtravel and thereby isolating the switching element from the full actuating force applied to the button.

10 Claims, 1 Drawing F igure /2III ill/i PATENTEDncr 1 1 1912 INVENTOR PE TER pvRr -(GALL BY Miy ATTORNEY KEY SWITCH FOR CHATTERLESS SWITCHING The present invention relates to a key switch for chatterless switching. Such types of switches are particularly required in the field of high-frequency engineering. As examples relating thereto, there are to be mentioned the key switches for subsequently arranged transistors or Schmitt-triggers requiring a chatterless switching.

Various arrangements have already become known for avoiding the contact bouncing or chattering in electrical switching apparatus. Once such proposal provides for the insertion of flexible or silicone intermediate members between the contact parts and the switching part for damping the switching operations, in which a damping is achievable with the aid of a flexible deformation work (DAS) l 052 510. To all of the conventional arrangements employing a damping element, it is common that during the switching only a part of the appearing oscillating energy is suppressed, so that sufficient damping cannot be achieved.

With respect to write-in keyboards, such as the input machines of computers, it is known to provide contactless pushbutton switches which, in contrast to the switching equipments employing classic contacts perform a chatterless switching, because these contacts are replaced by contactless components. To this end there are provided, for example, Hall-Generators, Field Plates, or Lamp Type Photo Cell Combinations (radio mentor, 2, 1969, pp. 066 to 067). Such types of contactless keying arrangements, however, are rather expensive in their construction owing to the required contactless components.

By the present invention it is possible, with the aid of simple means, to overcome these disadvantages and to provide a key switch likewise avoiding contact bouncings or chatterings. According to the invention this is accomplished in that the contact part electrically connecting or disconnecting the stationary contact parts, is designed as a flexible silicone member filled with metal particles which, in particular, are in contact with one another and which, upon actuation of the key, by deforming the silicone part, are capable of being brought into a surface contact with the stationary contact parts, acting in the sense of establishing an electrical connection between these contact parts.

Flexible parts of electrically conductive silicone are already known (U.S. Pat. No. 3 140 142, Plastic RF- Shielding Forms based on new Conductive Filler by J.E.Ehrreich and Nimoy, Chomerics, Inc., Cambridge 39, 1963, originally presented at the Fifth National Symposium on Radio Frequency Interference, Philadelphia, Pa., June 4/5, 1963).

As metal parts there are used, for example, silverplated copper particles in granular form having a diameter ranging between 10 and 100 um (U.S. Pat. No; 3 203 488). The proportion of the filler in the binding agent is, in this case, about 76 to 84 parts by weight. Such an electrically conductive silicone has a density of about 3.2 to 3.7 g/cm", a tensile stress of about 12 kg/cm and a specific resistance of 0.01 ohm. cm when loaded with about 1 kg/cm. It is already known to use such a silicone as sealing, packing or connecting material in the field of high-frequency, in particular microwave engineering'As an example, there should be mentioned the sealing or packing of waveguides in the fields of microwave engineering.

Moreover, there are also known contact-making devices consisting of a flexible or silicone material upon the loading of which several contact strips of metal or an electrically conductive rubber arranged in the inside thereof in cavity-like recesses, are closed by way of being pressed upon one another, and are reopened upon being released (DAS 1 017 255 and DAS l 060 455). These contact-making elements, of course, are only used for releasing electrical switching processes; they are unsuitable, however, for avoiding the disadvantageous contact bouncing or chattering, because in that case there are provided bouncing contact elements. Accordingly, such types of contact-making elements, in the most favorable case, act as flexible or silicone damping bodies in which the bouncing or chattering energy is more or less converted into a fulling or felting work.

In distinction thereto, in the key switch according to the invention, bouncing contact parts are avoided, because the closure of the stationary contact parts is effected in this case, upon loading the flexible or silicone member, i.e., upon actuation of the key, the metal parts arranged in the inside thereof, which are of a smaller mass, by deforming the flexible or silicone part, are brought into a surface contact with the stationary contact parts. In so doing, however, the stationary contact parts are closed simultaneously with the loading of the flexible or silicone part, without delay for lapse of a bouncing or chattering period. Accordingly there will not be a repeated lifting of the movable contact part off the opposite contact.

A particularly simple construction for a key switch according to the invention will result when the flexible or silicone part, in the normal position, is already in a loose surface contact with the stationary contact parts. This is possible because, without a loading of the flexible or silicone part, the electrical connection between the stationary contact parts is a high resistance connection. Fixing of the silicone part with respect to the stationary contact parts is appropriately effected by a ring-shaped holding body loosely relatedto the edge thereof. A particular effect will result when stationary contact parts are designed as printed circuit conductors. In this way there is provided a larger surface contactand, consequently, enhanced conductivity. As external connections there may be used in this case contact pins, or the like projecting towards the outside, which are in electrical connection with the printed circuit conductors.

The key switch according to the invention can be further improved when taking care that the force as exerted by the actuating member, does not act upon the flexible or silicone part directly, but via a resiliently supported intermediate member. Since in this case both the actuating member and the intermediate member, largely independent of one another, develop spring characteristics of their own, it can be achieved that the loading of the silicone part, upon actuation of the key, and within a certain range of deviation, can be kept almost constant and low. One advantageous embodiment relating thereto is to, be seen in that the intermediate member is displaceably supported at an extension of the actuating member under the action of a coil spring surrounding both the extension and the intermediate member. For holding the intermediate member in its normal position there is approximately used a flange arranged at the free end of the extension, on which the intermediate member may rest with one shoulder.

A single axial cross-section drawing illustrates a typical structure for the invention. With reference to the accompanying drawing, there will now be described in detail one example of embodiment of a key switch according to the invention.

The key switch as shown in a the axial sectional view comprises a key button 2 which is acted upon by a reset spring designed as a helical compression spring 1, with this key button 2 being longitudinally displaceable and supported within a housing 3. The helical compression spring 1 is supported, on one hand, on the base plate 3 of the housing 3 and, on the other hand, on a flange 2', of the key button 2. In this way there is achieved a long spring path providing a progressive spring action. By the flange 2", in cooperation with one edge of the housing 3" surrounding said flange, the key button 2 is prevented from dropping out.

To one extension 2" of the key button 2 projecting into the inside of the housing, there is mounted a piston-shaped member 4, or is appropriately shaped thereto, serving to hold and guide resiliently mounted intermediate member 5. To this end the intermediate member is provided with a guide bore or opening 5, having a shoulder 5" within said guide opening. The intermediate member thereby rests against the flangelike part 4' of the member 4 in the normal position of the key. Under the action of a coil spring 6 embracing the extension 2" of the key button 2 and the intermediate member 5, this intermediate member is capable of being displaced by a certain amount along the piston-shaped member 4. In so doing, the coil spring 6, compresses, resting on a shoulder 2" of the key button 2 and, on a shoulder 5" of the intermediate member 5. The two spring elements, i.e., the helical spring 1 and the coil spring 6 may thus become effective within a certain range of axial movement essentially range independent of one another. In particular, it is possible in this way to achieve a specially soft spring characteristic at a relatively small spring path. It is of importance, in this case, that the oppositely arranged flexible or silicone part 7 is not directly subjected to the force e'xerted by the key button 2.

The silicone part 7 rests with metal particles as aforesaid incontact with one another, and is seated with a loose surface contact on the stationary contact parts 8 which are designed as printed circuit conductors. As outer or external connections of these circuit conductors there are provided the connecting pins 8 which are led through the insulating base plate 3' of the key housing 3. For fixing in position the silicone part 7 with respect to the stationary contact parts 8 there is provided a ring-shaped holding body 9 loosely applied or lying on the edge or rim portion of the silicone part, with this ring-shaped holding body 9 being mounted to the base plate 3.

The mode of operation of the key switch according to the invention is as follows:

By actuating key button 2 in opposition to the spring action of the helical compression spring 1, via the spring force of the coil spring 6, the intermediate member 5 is pressed on to the flexible or silicone part 7, thus deforming the latter slightly. In so doing, the

metal particles of part 7 pierce the surface thereof and come into surface contact with the stationary contact parts 8. In this way, between the connecting pins 8', there is established a low-ohmic (approx. 20 ohms) electrical connection which is suitable for tripping of electrical switching processes (operations).

Upon releasing the key button 2, the latter is returned to normal owing to the resetting force of the helical compression spring 1. In the course of this, the intermediate member 5 with the aid of the flanged part 4, if lifted off the flexible or silicone contact part 7, so that the latter reassumes its normal shape. Owing to the rubber-flexible properties of the contact part 7, the metal particles which, when being loaded, are lying at the surface, are simultaneously moved inwardly, so that between the stationary contact parts 8 there is established a high-ohmic (over 1 megohm) electrical connection, thus practically interrupting the passage of current.

What is claimed is:

1. A key switch for chatterless switching, comprising:

a pair of stationary contact parts;

a switching element including a body of elastic material containing a fill of electrically conductive particles, said switching element being arranged to normally lie relatively loosely over at least portions of both of said stationary contact parts, thereby to provide only relatively small electrical conductivity between said stationary contact parts through said switching element;

first operating means including a first mechanical member and a first resilient member, said first mechanical member being arranged to move against the restoring force of said first resilient member in response to an externally applied operating force;

a second mechanical member disposed adjacent said switching element and arranged to depress said switching element against at least portions of both of said stationary contact parts in response to a second force;

means including a second resilient member connected between said first and second mechanical members whereby said second force is generated and transmitted from movement of said first mechanical member through said resilient member so that said second force is substantially only the restoring force of said second resilient member.

2. Apparatus according to claim 1 in which said elastic material comprises an elastic silicone material.

3. Apparatus according to claim 1 in which said electrically conductive particles are silver-plated copper.

4. Apparatus according to claim 3 in which said electrically conductive particles range in size substantially between 10 and microns in diameter.

5. Apparatus according to claim 1 in which said switching element consists of a body of silicone elastic material filled with silver-plated copper particles in the range of 10 to 100 microns in diameter and in which the portion of said particles is between 76 and 84 parts by weight to one part of said silicone material.

6. Apparatus according to claim 5 including restraining means cooperating with said first resilient member for determining the initial position of said first mechanical member in the absence of said externally applied operating force.

7. Apparatus according to claim 6 further defined in that said second resilient member applies substantially no depressing force against said second mechanical member when said first mechanical member is in said initial position.

8. Apparatus according to claim 6 further defined in that said second resilient member applies only negligible depressing force against said second mechanical member when said first mechanical member is in said initial position.

9. Apparatus according to claim 8 further defined in said first and second mechanical members are spaced such that movement of said first mechanical member produces said second force substantially only as a func-

Claims

1. A key switch for chatterless switching, comprising: a pair of stationary contact parts; a switching element including a body of elastic material containing a fill of electrically conductive particles, said switching element being arranged to normally lie relatively loosely over at least portions of both of said stationary contact parts, thereby to provide only relatively small electrical conductivity between said stationary contact parts through said switching element; first operating means including a first mechanical member and a first resilient member, said first mechanical member being arranged to move against the restoring force of said first resilient member in response to an externally applied operating force; a second mechanical member disposed adjacent said switching element and arranged to depress said switching element against at least portions of both of said stationary contact parts in response to a second force; means including a second resilient member connected between said first and second mechanical members whereby said second force is generated and transmitted from movement of said first mechanical member through said resilient member so that said second force is substantially only the restoring force of said second resilient member.

4. Apparatus according to claim 3 in which said electrically conductive particles range in size substantially between 10 and 100 microns in diameter.

5. Apparatus according to claim 1 in which said switching element consists of a body of silicone elastic material filled with silver-plated copper particles in the range of 10 to 100 microns in diameter and in which the proportion of said particles is between 76 and 84 parts by weight to one part of said silicone material.

9. Apparatus according to claim 8 further defined in that said first and second mechanical members are spaced such that movement of said first mechanical member produces said second force substantially only as a function of the restoring force of said second resilient member and substantially independent of the restoring force of said first resilient member over a predetermined amount of movement of said first mechanical member.

10. Apparatus according to claim 9 in which said switch is substantially in the shape of a circular cylinder, said first and second mechanical members are placed to move substantially translationally along the axis of said cylinder, and said first and second resilient members are helical springs having their axes along said cylinder axis.