US 3725625 A
A switch, particularly useful as a keyboard switch, which comprises a casing containing two or more free-standing coil contacts and a longitudinally movable switch bar carrying a shorting plate which when depressed engages adjacent ends of the coil contacts to close an electrical circuit therebetween.
Claims available in
Description (OCR text may contain errors)
United States Patent 1 Pratt 1 1 Apr. 3, 1973  MECHANICAL PUSH-KBUTTON SWITCH WITH POINTED END COIL SPRING CQNTACT  Inventor: Albert R. Pratt, Weston, Mass.
 Assignee: Raytheon Mass.
221 Filed: Aug. 25, 1971 211 Appl.No.: 174,596
 US. Cl. ...200/159 R, 200/166 BA, 200/166 BH  Int. Cl. ..HOlh 13/52, HOlh H06  Field of Search ..200/ 166 BA, 200/16 A, 159 R, 166 BH.
200/166 C, 166 G, 5 C
 References Cited UNITED STATES PATENTS 2,845,608 7/1958 Short ..200/16 A X 3,141,936 7/1964 Boyle et a1 ..200/166 BA UX 2,806,907 9/ 1957 Mazzola ..200/5 C 3,207,862 9/1965 Robbins... ..200/16 A 2,490,020 12/ 1949 Enzler ..200/166 BH UX 2,183,892 12/1939 Pitsch .200/166 H UX 3,211,872 10/1965 Baer ..200/159 R Primary Examiner-Robert K. Schaefer Assistant Examiner-Robert A. Vanderhye Attorney1-larold A. Murphy et .al.
[ 5 7 ABSTRACT A switch, particularly useful as a keyboard switch, which comprises a casing containing two or more freestanding coil contacts and a longitudinally movable switch bar carrying a shorting plate which when depressed engages adjacent ends of the coil contacts to'close an electrical circuit therebetween.
3 Claims, 8 Drawing Figures PATENTEDAPRB ms SHEET 1 OF 2 MECHANICAL PUSI-IBUTTON SWITCH WITH POINTED END COIL SPRING CONTACT BACKGROUND OF THE INVENTION predetermined point, causes the magnetic field of the magnet to relocate to a position which causes the reeds to close and then, upon release of pressure from the keycap, to return to the open position.
The use of magnetics, however, results in many variables which complicate manufacture and end-use of these devices. For example, the pull-in and drop-out ratio of the reed is difficult to control, and the shape, size and permeability of the magnet are relatively difficult to produce. It has furthermore been found that in some matrices where many units are placed in close proximity to one another the magnetic forces of individual switches affect adjacent switches, thus requiring the use of expensive shielding. Such reed units also are prone to mechanical shock and vibration and thus require extreme care in handling and processing to prevent deterioration of the finished product. The reeds themselves are relatively expensive and are always in danger of being upset or destroyed by an outside magnetic influence.
Mechanical devices tried for the purpose have been found to be unsuitable for various reasons. In some mechanical devices the springs cause vibration in the contacts, resulting in undesired bounce. In some cases where a shorting bar is moved into engagement with a contact on the end of a spring, skidding occurs, resulting in inefficient contact between the two parts.
SUMMARY OF THE INVENTION The above and other disadvantages in known switches of the character described are overcome or avoided in the present invention wherein the switch includes in a casing two or more spaced freestanding coil contacts and a slidable bar carrying a shorting plate which, when the bar is depressed, engages both contacts to complete a circuit therethrough. Means is thus provided to allow overtravel of the bar and plate without deterioration to the contact resistance and at the same time acts as a cushion at the lower end of the switch stroke, which in turn tends to prevent contact bounce. The shorting bar, furthermore, has its surface adjacent the contacts roughened in such a manner that the contacts are prevented from skidding or sliding and thus the contact is maintained in an efficient manner. The present switch does not include magnetic means and is not influenced by adjacent switches or other electrical or magnetic devices, and is comparatively economical.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an enlarged axial sectional view of one embodiment of the invention; 1
FIG. 2 is an axial sectional view taken at 90 to FIG.
FIGS. 3 and 4 are horizontal sectional views taken along lines 3-3 and 4-4 respectively of FIG. 1 looking in the direction of the arrows;
FIG. 5 is an enlarged axial sectional view of a second embodiment of the invention;
FIG. 6 is an axial sectional view taken at to FIG. 5; and
FIGS. 7 and 8 are horizontal sectional views taken along lines 7-7 and 8-8 respectively of FIG. 5 looking in the direction of the arrows.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring more particularly to the drawings wherein like characters of reference designate like parts throughout the views, the switch shown in FIGS. 1-4 comprises a hollow casing 10 which may be made of any rigid dielectric material such as glass, plastic or ceramic. Casing 10 is closed at the bottom by a dielectric base 12 which is provided with a pair of diametrically spaced apertures through which extend respective elongated contacts 14 and 14a. One portion 1646a of each contact extends externally of the casing and base while a second portion 18-18a of each contact extends longitudinally within the casing. The contacts thus are fixedly mounted within the base in a predetermined spaced relation.
The inner portion 18-l8a of each contact carries a longitudinally extending spring 20-20a respectively which is fixed atone end to its respective contact portion 18-18a so that it provides a freestanding structure, the free or upper end of which may be engaged to compress the spring toward its fixed end.
In the upper end portion 22 of the casing there is provided an opening 24 within which an elongated switch bar 26 is slidably located. The upper end of bar 26 carries a push button 28 by which the bar may be depressed so as to move longitudinally within the cas-- ing. The opposite end of the bar 26 slides within an axial bore 30 which is aligned with opening 24 so that the movement of the bar will be constantly along the axis of the device.
The inner end portion 32 of bar 26 is of a size to comfortably slide within the bore 30 and to receive therearound a compression spring 34. One end of spring 34 normally rests upon a central portion of the inner surface of base 12. The other end of spring 34 abuts a shoulder 36 formed by an enlargement 38 of the bar, thus constantly urging the bar upwardly. The extent of upward movement of the bar is determined by a rubber stop 40 which is mounted on the bar and which is adapted, when the bar is moved upwardly to the full desired extent of travel, to engage the inner surface of casing end wall 22.
The enlarged portion 38 of the switch bar fixedly carries a transversely extending shorting plate 42 which is of a length to overlie the free ends of the spring contact members 20-20a. In the normal inoperative condition of the switch, the shorting plate 42 is located in predetermined spaced relation with the spring members. However, to perform a switching operation,'the push button 28 is manually depressed to move the switch bar 26 axially downward to a point where the shorting plate 42 engages the ends of the spring contact members 20-20a. Since the external terminal portions 16-16a of the contacts 14-14a are adapted to be suitably interconnected with associated circuitry, en-
gagement of the shorting plate 42 with the spring con- I tact members will close an electrical circuit through the i switch.
The downward movement of the switch bar 38 will, of course, be made in opposition to the normal forces exerted by the spring 34. It will be understood also that after the shorting plate 42 engages the ends of spring members 20 and 20a, the bar and plate will be allowed continued movement and will be additionally cushioned by spring members 20-20a. The extent of downward movement of the bar, however, will be restricted or limited by the engagement of a rubber cushion 44 on bar portion 32 with base 12. Upon release of pressure from the push button 28, spring 34 will function to return the parts to their normal inoperative positions as shown in FIG. 1 thus opening the switch.
In further accordance with this invention, the underside of the shorting bar is roughened or pitted to provide a nonsmooth surface, and the adjacent ends of the spring members 20 and 20a are made quite pointed so as to provide effective engagement between the plate and members without skidding -or sliding of the spring members along the surface of the plate. Such skidding has been found to sometimes cause chattering or similar undesirable switch operation. The roughened surfaces may be produced by any method such as by bombarding the surfaces with small glass beads.
While FIGS. 14 depict a switch of the character described which employs two contacts, the invention is readily adaptable to any additional number of contacts. In FIGS. 5-8 the switch disclosed is basically similar to the switch of FIG. 1 but includes a third contact 14b (see FIGS. 2 and 7) and a shorting plate 42a which is a circular disc so as to simultaneously engage all of the spring contact members 20, a and 20b. The additional contact 14b will, of course, include the spring member 20b and terminal portion 16b.
It is to be understood that the shorting plate 42a may terpreted as illustrative and not in a limiting sense.
1. A switch comprising a casing having a single central chamber, an actuator movable within the chamber and having a portion extending through a wall of the casing, at least two contacts disposed in spaced relation entirely within the chamber adjacent said actuator, one end portion of said contacts being immovably affixed to the casing, support means extending through the casing for individually connecting said one end portion of the contacts to external electrical circuitry, and conductive means on said actuator disposed to engage the opposite ends of said contacts when the actuator is moved, the abutting ends of the contacts and the adjacent surface of said conductive means being provided with means for preventing said ends of the contacts from sliding laterally in any direction along said surface of the conductive means.
2. A switch as set forth in claim 4 wherern said surface is irregular in texture, and said contacts each comprises a coiled compression spring, with one end thereof being relatively sharp for nonsliding engagement with said irregular adjacent surface of the conductive means.
3. A switch comprising a casing having a single central chamber, a switch bar within the chamber and extending through the casing, spring means within the casing adjacent one end of the bar for yieldably urging the bar in a direction outwardly of the casing, at least two elongated contacts disposed in spaced relation within the chamber adjacent and substantially parallel to said bar, a contact plate carried by said bar and extending radially therefrom in spaced overlying relation to said contacts, said contacts each comprising a coiled compression spring located entirely within the chamber andhaving one end rigidly fixed to the casing, conductive means extending through the casing for connecting the springs to external electrical circuitry, said bar being movable longitudinally against said spring means for positioning said contact plate in engagement with the adjacent ends of said compression springs, the abutting ends of said compression springs and the adjacent surface of said contact plate being provided with means for preventing said ends of the springs from sliding laterally in any direction along said surface of the plate.