US 3911233 A
There is provided a keyboard switch for desk top electronic calculators in which a conductive member and a plurality of tubular resilient means are disposed between fixed electrode means formed on a printed circuit board and a plurality of key buttons, whereby the positive contacting action between the fixed electrode means and the conductive member by the operated key button and the self-restoration of the operated key button are ensured by the associated tubular resilient means.
Claims available in
Description (OCR text may contain errors)
United States Patent 1191 Nakamura et al. Oct. 7, 1975  KEYBOARD SWITCH FOR DESK TOP 2.848.920 8/1958 Lester 200/ I66 C ELECTRONIC CALCULATORS 3,304,386 2/1967 Shlesinger. Jr. 200/83 B 3,668,337 6/1972 Sinclair 200/5 A  Inventors: Shigeo Nakamura, Neyagawa; 3,742,157 6/1973 Leposavic 200/159 B Yutaka Takano, Katano; Masaki 3,743,798 7/1973 Pentecost 200/5 R Suzumura; Keizi Onishi, both of 3.773.998 11/1973 Seegar et al..... 200/159 B Moriguchi a" of Japan Klehm, J1 B  Assignee: Matsushita Electric industrial Co., Ltd., Osaka, Japan Primary Examiner-Robert K. Schaefer Assistant Examiner-William J. Smith [221 Filed 1973 Attorney, Agent, or Firm-Stevens, Davis, Miller &  Appl. No.: 389,436 Mosher  Foreign Application Priority Data Feb. 20, 1973 Japan 48-20938  ABSTRACT 2% 12:: There is prov1ded a keyboard switch for desk top elec- 1973 g 48 37336w] tronic calculators in which a conductive member and 1973 1a an 48 38403[U] a plurality of tubular resilient means are disposed bep tween fixed electrode means formed on a printed cir-  U S cl zoo/5 ZOO/159 ZOO/264 cuit board and a plurality of key buttons, whereby the  HOIH 13/52 positive contacting action between the fixed electrode  Fieid 159 B 5 A means and the conductive member by the operated ZOO/5 E 6 5 key button and the self-restoration of the operated key button are ensured by the associated tubular resilient  References Cited means UNITED STATES PATENTS 8 Claims, 17 Drawing Figures 2.025.981 12/1935 Getty 200/159 B i US. Patent OM1 sheet 1- 4- $911,233
FIG. lo FIG-lb PRIOR ART U.S. Patent 'Oct. 7,1975 Sheet2 on 3,911,233
US. Patent Oct.7,1975 Sheet3of4 3,911,233
US. Patent Oct. 7,1975 Sheet4 of4 3,911,233
KEYBOARD SWITCH FOR DESK TOP ELECTRONIC CALCULATORS The present invention relates to a keyboard switch which is of a compact and thin construction and which produces no chattering noise.
The size of desk top electronic calculators has been reduced and the calculators made more compact as a result of the miniaturization of their display and circuitry sections made possible by the miniaturization of electronic components through the development of integrated circuits or large scale integrated circuits. Particularly, in the field of desk top electronic calculators, the tendency has changed toward a general adoption of handy-type desk top electronic calculators which can be carried in ones pocket. In view of these circumstances, there has naturally existed a need for a keyboard switch of compact and thin structure which is used by the operator to enter the necessary information for continuous computational operations.
Further, there has been a general adoption of MOS elements for constructing desk top electronic calculator; these circuits have a high imput impedance and therefore it is possible to use a mechanical switch for entering signals whose contact resistance is very high.
The purpose of the present invention will be made apparent by considering the drawbacks of conventional switch structures of the above type with reference to the accompanying drawings, in which:
FIGS. 1a and 1b are a front sectional view and side sectional view of a prior art keyboard switch of the reed switch type;
FIG. 2 is a front sectional view of another prior art keyboard switch employing a metallic movable contact piece;
FIG. 3 is a front sectional view of still another prior art keyboard switch using a conductive plastic sheet;
FIG. 4 is an exploded perspective view showing an embodiment of a keyboard switch according to the present invention;
FIGS. 5a to 5d are partial sectional views of the keyboard switch of FIG. 4 which are useful for explaining the operation thereof;
FIGS. 6a to 6d are longitudinal and cross-sectional views showing various forms of the tubular resilient means used in the keyboard switch shown in FIG. 4;
FIG. 7 is a partial sectional view of another embodiment of the present invention;
FIG. 8 is a sectional view showing the tubular resilient means used in still another embodiment of the present invention; and
FIGS. 9a and 9b are a partial perspective view and partial sectional view showing a tubular resilient means formed integral with a sheet in still another embodiment of the present invention.
One of the keyboard switches known in the art is the reed switch type in which, as shown in FIGS. 1a and 1b, a reed switch element 2 is attached to a printed circuit board 1 and a key button 4 which is guided by a frame 3 and the printed circuit board 1 to move vertically is provided with a magnet 5 and a spring 6 which restores the key button 4. A disadvantage of the reed switch type is that the size of the reed switch element 2 itself constitutes a limiting factor in the miniaturization of the keyboard switch and moreover a large stroke is required for the vertical movement of the key button 4 thus constituting another limiting factor in reducing the size and thickness of the keyboard switch. This reed switch type is also disadvantageous from the manufacturing cost point of view, since the reed switch element 2 itself is expensive to manufacture.
As a substitute for the reed switch type keyboard switch, another keyboard switch has been developed and used in which, as shown in FIG. 2, a metallic movable contact piece 9 is provided to cooperate with a fixed electrode 8 formed on a printed circuit board 7 and the movable contact piece 9 is actuated by a key button 12 fit in a frame 10 vertically movable through a spring 11.
Still another type of keyboard switch has been developed and used in which, as shown in FIG. 3, an insulating spacer 15 is disposed on fixed electrodes 14 formed 'on a printed circuit board 13 and a conductive plastic sheet 16 is placed on the insulating spacer 15, whereby the conductive plastic sheet 16 is pressed to contact with the fixed electrodes 14 by a keyboard switch 19 fit in a frame 17 through a spring 18.
These two types of keyboard switch are also disadvantageous in that since the movable contact piece 9 or conductive plastic sheet 16 is moved in a vertical direction with respect to the fixed electrode 8 or 14, the switch is turned on when the key button 12 or 19 is near the lowermost point of its downward movement with the result that a very small clearance is left after the turning on of the switch and therefore a positive depression of the key button must be maintained throughout the whole stroke to operate the switch. Moreover, when the key button 12 or 19 starts restoring from its lowermost position, the resiliency of the spring 11 or 18 and that of the movable contact piece 9 or conductive plastic sheet 16 oppose each other causing a resonance or bounce at the portions of their contact and thereby frequently inducing chattering which is a ruinous disadvantage for the keyboard switch.
In other words, these deficiencies have a direct effect on the operating quality of the key buttons by the operator, giving rise to erroneous operations with considerable deterioration in the reliability and durability of the desk top electronic calculator. Moreover, the use of such keyboard switches is costly since they generally require many component parts and much labor for their assembly.
The present invention contemplates the elimination of these deficiencies of the prior art devices, and it is therefore an object of the present invention to provide a keyboard switch which is of compact and thin structure and which thus greately contributes to the miniaturization of desk top electronic calculators.
It is another object of the present invention to provide a keyboard switch which operates with increased stability without chattering to ensure a greater reliability and durability of desk top electronic calculators.
It is still another object of the present invention to provide a keyboard switch which is simple in construction requiring a reduced number of component parts, inexpensive to manufacture and easy to operate.
The construction and features of the present invention will now be explained with reference to FIGS. 4 through 9.
Referring first to FIG. 4, the detailed construction of a keyboard switch according to an embodiment of the present invention will be described. In FIG. 4, numeral 20 designates a frame made for example of a synthetic plastic on which a fixed number of key buttons 21 are mounted and which is formed with a through hole 22 for each key button 21 to guide its vertical movement. A plurality of tubular resilient means 23 made of resilient synthetic plastic are disposed below the mounted key buttons 21, and positioning notches 24 for the tubular resilient means 23 are cut in the inner peripheral wall portions of the frame 20 and partition wall portions 25. Each of the key buttons 21 is also formed on its periphery with n'otches 26 for receiving the tubular resilient means 23 and it is further provided with a semispherical projection 27 on the central lower actuating surface thereof. Disposed below the tubular resilient means 23 is a flexible sheet 28 made of a material mixed with powder of conductive substance, for example, carbon black, and disposed below this conductive sheet 28 is an insulating spacer 30 which is made for example of a synthetic plastic of a predetermined thickness and which is formed with as many holes 29 as there are the key buttons 21 at the positions corresponding to the key buttons 21, which holes have a shape desired from the viewpoint of design. A substrate in the form of a printed circuit board 32 formed with fixed electrodes 31 by a printed-circuit technique is disposed below the insulating spacer 30 and this printed circuit board 32 is secured to the frame 20 with small screws 33 thereby securely holding therebetween the key buttons 21, the tubular resilient members 23, the conductive sheet 28 and the insulating spacer 30.
With the construction described above, the operation of the keyboard switch will be explained with reference to FIGS. a to 5d.
FIG. Sashows the conditions in the keyboard switch when none of the key buttons is operated. When one of the key button 21 is depressed with a finger, the key button 21 is guided by the hole 22 in the frame to move downward so that, as shown in FIG. 5b, the tubular resilient means 23 is gradually pressed and deformed by the semi-spherical projection 27. Namely the tubular resilient means 23 is deformed through two steps, through the first step of which the cross section of said means takes the form of an ellipse and through the second step of which said means begins to deform downward due to its repellent force. Consequently the conductive sheet 28 disposed in close contact with the lower part of the tubular resilient means 23 is pressed into the corresponding hole 29 of the insulating spacer 30.
when this operation is continued, the tubular resilient means 23 is downwardly deformed by the semispherical projection 27 of the key button 21 so that the conductive sheet 28 is eventually brought into contact with the fixed electrodes 31 on the printed circuit board 32 as shown in FIG. 50 thereby closing the circuit.That is, the switch is turned on.
When the key button 21 is depressed further, the switch remains in the closed position as shown in FIG. 5d. The downward stroke of the key button 21 is so designed that the downward motion of the key button 21 is stopped at or before a position where the tubular resilie nt means 23 is completely depressed.
When the depression of the key button 21 is released, the deformed tubular resilient means 23 returns to its original form by its own resilient property and this restora tion causes the key button 21 to move upward and return to the position shown in FIG. 5a. The conductive sheet 28 depressed by the tubular resilient means 23 returns to its original position by its own resiliency along with the restoration of the tubular resilient means 23, thereby interrupting the contact between the conductive sheet 28 and the fixed electrodes 31 and turning the switch off.
Further, tubular resilient means 23 having various shapes may be employed. That is, it may be of cylindrical shape having the same wall thickness throughout its length as shown in FIG. 6a or of cylindrical shape with the wall thickness thicker on the key button side as shown in FIG. 6b. Alternatively, it may be formed to have a rectangular section as shown in FIG. or a trangular section as shown in FIG. 6d. Thus, the shape of the tubular resilient means 23 may be selected as described.
Furthermore, as shown in FIG. 7, a conductive tubular resilient means 34 prepared from a resilient synthetic plastic mixed with a powder of a conductive substance, e.g., carbon black to make it conductive may be used in place of the tubular resilient means 23 and the conductive sheet 28 thereby serving the purpose of two component parts with a single component part. Still furthermore, the tubular resilient means may be made partially conductive instead of making it entirely conductive.
The tubular resilient means 34 may also be formed, as shown in FIG. 8, with projections 35 on the lower side thereof to serve as spacers so that in assembling the tubular resilient means 34, each of the projections 35 having an insulating sheet attached on the bottom side thereof may be disposed on the printed circuit board 32 or the projections 35 may be integrally formed with the conductive tubular resilient means 34 in such a manner that only the projections are made nonconductive. Further, no care is needed for the determination of the insulating property of the projections 35, providing that the printed wiring of the printed circuit board is well-designed or patterned therefor to connect the fixed electrodes. Accordingly it is unnecessary to provide the nonconductive, i.e., insulating sheet, so that the overall portion of the projections can be made of the same material as the tubular means. The tubular resilient means constructed by either of these two methods may concurrently serve as a tubular resilient member, conductive sheet and insulating spacer.
Further, as will be seen from FIGS. 9a and 9b, a resilient insulating sheet 36 may be integrally formed with tubelike portions 37 and recessed portions 38 may be formed on the lower side of the insulating sheet 36 facing the fixed electrodes 31 on the printed circuit board 32 so that the tubelike portion 37 is located at the center of a thin portion 39 provided by the recessed portion 38 and at least the tubelike portions 37 become conductive. The insulating sheet 36 thus produced may concurrently serve as a tubular resilient member, conductive sheet and insulating sheet. I
The keyboard switch of the present invention constructed as above described can, by virtue of the use of tubular resilient means, have a sufficient clearance to permit the key button to move downward further even after the closing of the circuit. This well suits the mental feeling of a man and constitutes a factor which has an important effect on the operating quality of the keyboard switch, that is, the operating quality of the keyboard switch can be improved greatly.
Further, since the conductive sheet adapted to contact with the fixed electrodes is resilient, its engaging and disengaging operations, coupled with the elastic force of the tubular resilient, can provide a clearance for the movement of the key button and therefore the bounce at the contacting area can be absorbed to prevent the occurrence of chattering or resonance. The keyboard switch is thus free from misoperation and highly reliable and durable.
Further, the use of the resilience of the tubular resilient means and the conductive sheet to provide the necessary restoring force for the key button has the effect of eliminating the use of any coil spring or the like as in the conventional keyboard switches and therefore simplifying the structure.
Still further, since the thickness of the component parts, i.e., the tubular resilient means, conductive sheet, insulating spacer, printed circuit board, etc. needs not be greater than that required to ensure their mechanical strength and functions, the -thickness of these component parts can be generally minimized. For example, the entire thickness of one keyboard switch according to the present invention can be made 7.0 mm by using tubular resilient means of 2.5 mm in diameter and selecting the stroke of the vertical movement of the key buttons at 1.5 mm, thereby reducing the size and thickness of the entire structure to the maximum possible extent that would not cause any inconvenience to the operation of the keyboard switch by the operator.
Further, it should be appreciated that the keyboard switch according to the present invention, by virtue of a reduction in the number of component parts and the use of a component part combining the functions of a tubular resilient member and conductive sheet in one or combining the functions of a tubular resilient means, conductive sheet and insulating spacer in one, can ensure a reduction in the number of component parts and an increased productivity owing to the simplified assemblying with resultant considerable reduction in the manufacturing cost.
It should also be appreciated that by virtue of the use of tubular resilient means, there is no large variation in the operating force through the entire range of the key button stroke, that is, the variation in the pressing force according to the amount of the deformation of the tubular resilient means is small as compared with a coil spring or the like and therefore any large variation in the pressing force during the operation of the key button can be eliminated thereby ensuring an excellent operating quality.
In conclusion, the keyboard switch in accordance with the present invention, by virtue of the aforesaid advantages, has a significant industrial value.
What we claim is:
l. A key board switch comprising a key button supporting frame supporting a plurality of key buttons movable vertically, horizontally disposed tubular resilient means positioned under at least two key buttons for interrupting vertical movement of said buttons and urging the same upwardly, printed substrate means positioned having plural pairs of fixed electrodes corresponding to said buttons under said resilient means, conductive resilient sheet means positioned between said resilient means and said substrate means for protecting said electrodes from dirt and dust, insulating spacer means provided between said substrate means and said conductive sheet means and having a thickness and apertures respectively corresponding to said pairs of electrodes for allowing deformations of parts of LII said sheet means and tubular means through the corresponding apertures to make parts of said conductive resilient sheet means be in contact with the corresponding pairs of fixed electrodes to shortcircuit the same, said key buttons having means for causing by downward actuations thereof said deformations of the conductive resilient sheet means and the tubular resilient means against their resilient forces, said resilient forces enabling the respective means to release said deformations with release of said downward actuation of the key buttons to open the shortcircuited electrodes, and said tubular resilient means having the resilient force for causing a good feeling upon the actuation of said key buttons and absorbing undesired possible actuations to said conductive sheet means other than those caused by the actuations of the key buttons.
2. A key board switch as claimed in claim 1 wherein said conductive resilient sheet means comprises continuous sheet-shaped conductive portions provided at parts of said tubular resilient means which are located .opposite to said pairs of fixed electrodes.
3. A key board switch comprising:
a. a plurality of key buttons each having an actuating surface;
b. means for supporting said key buttons for independent movement in a direction normal to the actuating surfaces thereof;
c. an elongated conductive hollow resilient member extending along said key buttons adjacent said actuating surfaces;
d. an insulating substrate having a plurality of pairs of spaced contacts affixed to a surface thereof, each of said pairs of contacts being spaced from the actuating surface of a corresponding key button, said resilient member being interposed between the actuating surface of said key buttons and said pairs of contacts; and
e. insulating spacing means located on said substrate between each of said pairs of contacts and between the surface of said substrate and said resilient member, displacement of one of said key buttons toward said insulating substrate deforming said resileint means toward the pair of contacts associ ated with the depressed button while being prevented by said spacing means from being deformed toward pairs of contacts associated with buttons which have not been depressed.
4. A key board switch as defined by claim 3 wherein said elongated hollow resilient member has a cylindrical cross-section.
5. A key board switch as defined by claim 4 wherein the thickness of the wall of said resilient member is thickest on the side facing the actuating surface of said key button.
6. A key board switch as defined by claim 3 wherein said elongated hollow resilient member has a rectangular cross-section.
7. A key board switch as defined by claim 3 wherein said elongated hollow resilient member has a triangular cross-section.
8. A key board switch as defined by claim 3 wherein said insulating spacing means comprises a sheet having openings therein above each of said pairs of contacts and said conductive resilient member is formed integrally with said sheet.