Title:
KEYBOARD SWITCH ASSEMBLY WITH IMPROVED HERMETICALLY SEALED DIAPHRAGM CONTACT STRUCTURE
United States Patent 3749859
Abstract:
A contact key for use in a keyboard arrangement is disclosed wherein one contact extends through a circuit board and a second contact comprises a curved plate or dome spring is positioned on one side of the circuit board and is depressable so that the center thereof can come in contact with the first contact to complete a circuit. In one form of the invention the first contact comrpsies a rivet while in another form it comprises a plated-through hole to the back of the circuit board. The second contact can include a dimple at the center thereof which comes in contact with the first contact when the plate is depressed. A plurality of these first contact members are placed in a circuit board and the second contacts can be supported by a conductive support, such as a shim or plated support having apertures corresponding to the position of the first contacts. If the contact support is in the form of the shim, it can comprise a plurality of sections interconnected by frangible tabs which are broken during assembly to separate the sections, the tabs being bent through holes in the circuit board and crimped against the back side to hold the shim in place and to provide connections for the respective sections to appropriate circuitry. In an embodiment having a plated contact support, the support can be provided with one or more raised bosses to support the contact plate above the first contact.
US Patent References:
PUSHBUTTON KEYBOARD SWITCH ASSEMBLY WITH IMPROVED OVER CENTER DIAPHRAGM CONTACT
Boulanger - August 1972 - 3684842
PUSHBUTTON DIAPHRAGM SWITCH WITH IMPROVED DIMPLE ACTUATOR AND/OR CAPACITANCE-TYPE SWITCH CONTACT STRUCTURE
Jackson - February 1972 - 3643041
PRINTED CIRCUIT KEYBOARD
Comstock - July 1971 - 3591749
Quick acting positive contact switch
Roper - November 1941 - 2262777
ELECTROMECHANICAL KEYBOARD INDEPENDENTLY OPERATED SWITCH MECHANISM WITH IMPROVED CONDUCTIVE RESILIENT ACTUATING MEANS
Berezowski - February 1972 - 3641286
PUSHBUTTON KEYBOARD SWITCH ASSEMBLY WITH IMPROVED OVER CENTER DIAPHRAGM CONTACT
Boulanger - August 1972 - 3684842
PUSHBUTTON DIAPHRAGM SWITCH WITH IMPROVED DIMPLE ACTUATOR AND/OR CAPACITANCE-TYPE SWITCH CONTACT STRUCTURE
Jackson - February 1972 - 3643041
PRINTED CIRCUIT KEYBOARD
Comstock - July 1971 - 3591749
Quick acting positive contact switch
Roper - November 1941 - 2262777
ELECTROMECHANICAL KEYBOARD INDEPENDENTLY OPERATED SWITCH MECHANISM WITH IMPROVED CONDUCTIVE RESILIENT ACTUATING MEANS
Berezowski - February 1972 - 3641286
Inventors:
Webb, Richard C. (Boulder, CO)
Webb, James R. (Boulder, CO)
Tyler, Tommy N. (Broomfield, CO)
Webb, James R. (Boulder, CO)
Tyler, Tommy N. (Broomfield, CO)
Application Number:
05/245577
Publication Date:
07/31/1973
Filing Date:
04/19/1972
View Patent Images:
Export Citation:
Assignee:
Colorado Instruments, Inc. (Broomfield, CO)
Primary Class:
Other Classes:
200/5A, 200/516, 200/302.200, 200/275
International Classes:
B41J5/12; B41J5/16; H01H13/70; B41J5/00; H01H13/52; H01H5/04
Field of Search:
200/159R,159B,166BH,167R,168G,5R,5A,16A
US Patent References:
| 3657492 | KEYBOARD APPARATUS WITH MOISTURE PROOF MEMBRANE | April 1972 | Arndt et al. |
Primary Examiner:
Scott J. R.
Claims:
What is claimed is
1. An electrical normally-open contact switch comprising:
2. An electrical normally-open contact switch comprising:
3. An electrical normally-open contact switch comprising:
4. A keyboard having a plurality of normally open contact switches, said keyboard comprising:
5. A keyboard, as claimed in claim 4, wherein said contact support includes:
6. A keyboard, as claimed in claim 4, wherein said contact support includes:
7. A keyboard, as claimed in claim 6, wherein said shim comprises:
8. A keyboard, as claimed in claim 4, wherein:
9. A keyboard, as claimed in claim 4, wherein:
10. A keyboard, as claimed in claim 4, wherein:
11. A keyboard, as claimed in claim 4, wherein said insulative element further includes:
1. An electrical normally-open contact switch comprising:
2. An electrical normally-open contact switch comprising:
3. An electrical normally-open contact switch comprising:
4. A keyboard having a plurality of normally open contact switches, said keyboard comprising:
5. A keyboard, as claimed in claim 4, wherein said contact support includes:
6. A keyboard, as claimed in claim 4, wherein said contact support includes:
7. A keyboard, as claimed in claim 6, wherein said shim comprises:
8. A keyboard, as claimed in claim 4, wherein:
9. A keyboard, as claimed in claim 4, wherein:
10. A keyboard, as claimed in claim 4, wherein:
11. A keyboard, as claimed in claim 4, wherein said insulative element further includes:
Description:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electric signal device, and more particularly to a contact switch for use in a keyboard arrangement, including alpha-numeric keyboard arrangements, to cause the generation of binary signals that are suitable for direct entry into digital data transmission systems, displays and/or computers.
2. Description of the Prior Art
With the advent of the widespread use of electronic data processing systems, commonly known as computers, there is a need for a simpler, smaller, low cost and generally more satisfactory keyboard data entry system since keyboards form the machine/man interface in the data processing system. That is, the operator of the machine depresses keys on the keyboard to form binary or coded binary signals which are fed into the data processing machine. Currently, such interface equipment is formed by such devices as teletype machines, card keypunch units, electric typewriters, adding machines, and the like. However, these devices are not entirely satisfactory for various reasons.
The most common prior art apparatus for generating data from an array of keys is an electric switch that closes when a key is depressed. This is, each time the key in the keyboard array is depressed an associated switch closes. Closure of the switch causes a coded signal to be generated which uniquely defines the key that was depressed. The data bit pattern thus generated is fed into the data processing system. While apparatus of this nature is generally satisfactory, there are several disadvantages, the complexity of the keys and cost thereof being one significant factor.
It will be appreciated by those who have used them that prior art keyboards generally have several other undesirable features. For example, many keyboards are thick and not compact and have a relatively high profile, thus making them inconvenient and tiresome to reach. Furthermore, a relatively large keyboard increases the size of the data processing system beyond what is necessary for miniaturized circuitry now available. In addition, the action of the keys is frequently less rapid than desirable. Furthermore, simultaneous key depressions may not be detectable. Often the keys are rugged and not sealed so as to be immune from dust and dirt. Some keyboard systems are adversely subject to changes in temperature. Furthermore, many systems use more than a minimal amount of power, making them unuseful in battery operated environments.
SUMMARY OF THE INVENTION
In accordance with the present invention, an electrical normally open contact switch is provided which includes a first electrical contact, and a second contact formed as a resilient curved plate of electrically conductive material spaced from the first contact in a normally opened position and having a peripheral edge along at least a portion of which the second contact is supported and further includes means for connecting the first and second contacts in an electrical circuit, the switch completing the circuit upon deflection of the center of the plate from the normally open position to the closed position against the first contact when pressure is exerted against the center, the center snapping back to the normally open position upon removal of the pressure.
More particularly, the switch may be provided in a keyboard array and be mounted on a circuit board which has a plurality of spaced first electrical contacts which extend through the circuit board from a first side of the circuit board to a second side thereof and are electrically connected to selective circuits on the second side. A plurality of second contacts each formed as a curved resilient plate or dome spring are mounted on a contact support on the first side of the circuit board which contact support surrounds each of the first contacts and has an opening corresponding to the position of the first contact. The contact support is formed, in one embodiment, in separate sections interconnected by frangible tabs which are broken during assembly and crimped through appropriate holes in the circuit board and crimped against the other side. The selective sections can be connected, as by soldering to selective circuitry on the other side and each section is connectable to a separate potential to provide different circuit capabilities with different keys. It is understood that each switch completes a circuit upon deflection of the center of the plate from the normally open position to the closed position against the corresponding first contact when pressure is exerted against the center, the center snapping back to the normally open position upon removal of the pressure. In another embodiment, the contact support is formed by electroplating the keyboard and includes a layer of flexible material extending over the side of the circuit board on which the dome springs are supported, completely covering that side of the circuit board to keep moisture and foreign material out of the contacts but permitting deflection of the plate or dome spring contact. In addition, a plurality of depressable keys are positioned with one key above each of the second contacts, which keys are held in position with a grid or frame connected to the circuit board.
In one form of the invention the first contact is formed by a rivet extending through the circuit board from the first side to the second side and connected to selective circuits on the second side whereas in an alternative embodiment the first contact is formed as a plated through hole in the circuit board which plated through hole is also connected to selective circuits on the second side of the circuit board.
The contact support in one form of the invention is formed as a shim which is made up of separate sections connected together by frangible tabs which tabs may be broken during assembly so that they may be forced through holes in the circuit board and clenched to the back side to be soldered or otherwise connected into the circuits on the second side of the circuit board. This arrangement permits connection of different potentials to different sections of the contact support so that different keys may be used to perform different functions.
In an alternative embodiment the contact support is formed, as by electroplating, as a plated support on the circuit board which has a plurality of openings corresponding to the position of the respective first contacts and includes in one embodiment one or more bosses spaced around each opening for supporting the second contact or dome spring above the surface of the first contact. These bosses can be formed by means of an embossing punch which forms the bosses in the plated contact support after it is formed on the circuit board.
From the foregoing, it can be seen that a contact switch made in accordance with this invention is of simple and economic construction and will be reliable in operation. Additional advantages will become apparent from the description which follows, taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exploded, fragmentary, perspective view of a keyboard which illustrates a key comprising one form of the invention;
FIG. 2 is an enlarged vertical section, taken along line 2--2 of FIG. 1, showing an assembled key in normally open position;
FIG. 3 is an exploded, perspective view of a circuit board and contact support showing how the contact support is positioned on the circuit board and attached thereto;
FIG. 4 is an exploded, perspective view, similar to FIG. 1, but showing an alternative keyboard for a mini-computer;
FIG. 5 is an enlarged vertical section taken along line 5--5 of FIG. 4, showing an assembled key in normally open position;
FIG. 6 is a vertical section, similar to FIG. 5, but showing an alternative plate contact;
FIG. 7 is a fragmentary, perspective view of an alternative contact support having raised bosses;
FIG. 8 is a fragmentary, vertical section, showing the method of making the raised bosses of FIG. 7;
FIG. 9 is a fragmentary exploded perspective view showing a plate contact positioned on a still further alternative contact support having a single raised boss; and
FIG. 10 is a fragmentary vertical section taken along line 10--10 of FIG. 9 showing the position of the assembled switch of FIG. 9 in its normally open position.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In accordance with this invention, the keyboard B of FIG. 1 is of the type used for desk calculators or computer keyboards wherein numeric or alpha-numeric function controls are necessary. A series of keys K are mounted as shown on a conventional glass epoxy circuit board 2 which has a printed circuit on the lower side thereof. At the center of each key position a first contact 4 extends through the circuit board from the top side to the lower side where it is connected, as by soldering, to a circuit (not shown) as by a lead as shown in FIG. 2. Conveniently, the contact 4 may take the form of a rivet as shown which extends about 0.013 inches above the circuit board.
A shim 7, which has a thickness of about 0.010 inches, extends over substantially the entire upper surface of the circuit board and is provided with a series of openings or perforations 8 which are adapted to be received over the respective contacts 4. Conveniently, during assembly frangible tabs 9 can be broken by a tool (not shown) which separates shim 7 into separate segments and pushes the ends of tabs 9 through holes punched in circuit board 2 and crimps them against the lower side thereof so that the segments can be soldered or connected to circuitry on the lower side of the circuit board. Similarly, tabs 9' can be bent through holes in the circuit board to make connections to the other side thereof.
Each switch K includes a second contact 10 in the form of a plate or curved dome spring which in FIG. 1 is illustrated as being generally triangular shaped with depending legs. This dome spring is more fully described in commonly assigned co-pending U. S. application Ser. No. 175,941 to Wray C. Hansen, filed Aug. 30, 1971. Spring 10 can be deflected downwardly into contact with contact 4 by depressing the key K associated therewith. The key includes a cylinder 12 which is conveniently made of polyurethane and rests on top of spring 10 and is surrounded by a coil spring 14. The upper end of coil spring 14 is received in an actuator 16 which has a central recess 18 therefore. The actuator includes a body 20 with an upwardly projecting neck 22, the body having a plurality of semi-cylindrical legs 24 spaced therearound. The actuator is received in a generally cubic housing 26 having a body 28 with downwardly projecting legs 30 thereon which are adapted to be received in openings (not shown) in circuit board 2. The housing includes a lid 32 which has an open cylindrical collar 34 through which neck 22 of actuator 16 is adapted to project. The actuator is slidably mounted within body 28 whereby legs 24 are received in semi-cylindrical recesses 36 within the body. Conveniently, lid 32 is attached to body 28 by means of pins 38 which are received in openings 40 on the body of the housing.
Neck 22 of actuator 16 includes an X-shaped element 42 at the upper end thereof adapted to receive a button of key element 44. In operation, when button 44 is depressed, it forces actuator 16 downwardly against coil spring 14 and cylinder 12 and when a sufficient amount of pressure is applied the dome or curved spring 10 rapidly collapses bringing the center thereof into contact with rivet 4 to complete a circuit connection. Upon release of finger pressure on button 44, the spring 10 quickly snaps back to its arched position over rivet 4. Advantageously, this key K is non-teasable and provides finger touch feedback. Also, the arrangement provides a relatively low profile and is rugged and consumes low power and is readily manufactured at low cost. Advantageously, the dome spring 10 is approximately 0.005 inches in thickness and is spaced from rivet 4 approximately 0.0025 inches. It will be further understood that body 28 may be so dimensioned as to constrain dome 10 from lateral movement. The relative differences in diameter of the dome and body have been exaggerated for clarity of illustration.
An alternative keyboard B' is disclosed in FIG. 4 which has particular application in pocket-size or mini-calculators of the battery-operated type which can be carried in the pocket or alternatively can be connected to a conventional power source. This keyboard includes a circuit board 46 made of conventional materials which has a plurality of plated-through holes 48, one of which can be seen in FIG. 5, each of which serves as a first contact for the switch in key K' and is connected by a lead 50 to suitable portions of a printed circuit on the bottom side of the circuit board. A contact support 52 is formed on the top side of circuit board 46 as shown in FIGS. 4 and 5, as by electroplating, upon which a second contact such as a dome spring or plate 54 is mounted as in the previous embodiment the contacts 48 extending through holes or perforations 53 therein. Advantageously, the plated-through holes and the contact support can be formed at the same time to a thickness of say 0.004 inches and a portion of the contact surface of the plated-through hole can be etched away, such as 0.002 inches to provide sufficient clearance for the dome spring to "snap through" when it makes contact. In this embodiment, a spacer or cage 56 is provided having a plurality of openings 58 corresponding to the position of dome spring 54 and is adapted to hold the dome spring in proper orientation with respect to the plated-through holes 48. To protect the contacts from moisture, dirt and other foreign matter, a thin plastic sheet 60, such as Mylar, is placed over the spacer 56 and the dome spring 54 and conveniently has an adhesive on the contacting side.
Above each dome spring and above sheet 60 is an actuating key, such as key 62 which has a depending finger 63 for depressing dome spring 54, the keys being held in position by a frame or grid 64 which extends thereover as shown in FIG. 4 and is attached to the mini-calculator to hold the same in place.
An alternative embodiment is shown in FIG. 6 wherein a circuit board 46' has a plated-through hole 48' therein which is connected to selective circuits (not shown) by means of a lead 50'. A dome spring 66 is supported on a contact support 52' and is held in position by a spacer or cage 56', a plastic sheet 60' extending across the spacer and the dome spring 66 to provide a sealed unit. In this embodiment, the dome spring 66 is provided with a dimple 68 at the center thereof which provides a downwardly extending projection to provide point contact the edge of a plated-through hole 48' when the spring is depressed, as by finger 63' of key 62', the latter being held in position by a frame 64'.
In the embodiments of FIGS. 5 and 6 the plated-through holes and the contact supports are formed by electroplating, but then the top of the plated-through hole must be etched away so that it is spaced below the contact space a distance on the order of 0.002 inches. In the alternative embodiments shown in FIGS. 7-10 this additional etching procedure is not required. To avoid this, a plated support 52" which is formed on circuit board 46" is provided with a plurality of raised bosses 70, such as three, for supporting a dome spring 72 above a plated hole contact 48". Conveniently, these bosses can be approximately 0.002 inches above the surface of support 52" and thereby support dome spring 72 at a suitable height to allow sufficient deflection of the center thereof to bring it into contact with contact 48". The raised bosses may be formed in the contact support 52" by positioning an embossing die 74 over the contact support and striking the bottom of the circuit board with an embossing punch 76, as shown in FIG. 8. Thus, the etching step can be omitted.
A further alternative embodiment is shown in FIGS. 9 and 10 wherein a circuit board 46'" has a contact support 52'" plated thereon which includes a single boss 70' which boss is twice as high as boss 70 at FIGS. 7 and 8. Thus a dome spring 72' is supported at one edge by the contact support 52'" and at the other edge by raised boss 70' to position dome spring 72' a sufficient distance above plated hole 48'" which is connected to suitable circuitry, as by welding, by means of lead 50". The dome springs 72' are held in position by spacer or cage 56" and are covered by flexible layer 60". Each dome spring is deflected by a finger 63" on a key 62" to make contact with plated-through hole 48'". Conveniently, as in previous embodiments, the keys are positioned by a frame 64". With this arrangement, it is necessary only to make one boss, and this is advantageous because it is some times difficult to find three equally spaced positions around a contact support which can be engaged by the embossing punch without disturbing the printed circuitry on the bottom side of the circuit board.
The dimensions described are exemplary only and may be varied for particular applications as required. In this regard, a spacing between the center contact and the dome spring of 0.010 and 0.020 inches has been found to be satisfactory.
From the foregoing, the advantages of this invention are readily apparent. A keyboard for use with calculators is shown in one embodiment wherein the printed circuit board has a shim with openings surrounding contacts in the circuit board which shim is divided into portions that are connected by frangible tabs that are broken during assembly to attach the shim to the circuit board and provide electrical connections thereto. In addition, a dome or curve spring is provided above each contact which is supported by the shim and which is depressable to deflect the center thereof into engagement with its associated contact to complete a circuit. The first contact is formed as a rivet in one embodiment.
In an alternative embodiment a keyboard is provided for a mini-calculator wherein the contacts extending through the circuit board are formed as plated-through holes which are surrounded by a contact support on the side of the circuit board opposite the circuit and supports curved or dome spring contacts which are positioned by means of a spacer, the entire contact assembly being sealed against moisture and foreign matter by means of a plastic adhesive layer, such as Mylar, which extends across the spacer and the dome springs. The dome springs are deflected selectively by keys positioned thereabove within a frame. The dome spring in a further alternative embodiment includes a dimple at the center thereof which is engageable with the plated-through hole. In a still further alternative embodiment the contact support is formed with one or more bosses which support the dome spring above the contact to avoid the necessity of etching the plated-through hole so that in its position below the contact hole the contact support a sufficient distance to provide suitable deflection of the dome springs.
The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the field and scope of this invention.
1. Field of the Invention
This invention relates to an electric signal device, and more particularly to a contact switch for use in a keyboard arrangement, including alpha-numeric keyboard arrangements, to cause the generation of binary signals that are suitable for direct entry into digital data transmission systems, displays and/or computers.
2. Description of the Prior Art
With the advent of the widespread use of electronic data processing systems, commonly known as computers, there is a need for a simpler, smaller, low cost and generally more satisfactory keyboard data entry system since keyboards form the machine/man interface in the data processing system. That is, the operator of the machine depresses keys on the keyboard to form binary or coded binary signals which are fed into the data processing machine. Currently, such interface equipment is formed by such devices as teletype machines, card keypunch units, electric typewriters, adding machines, and the like. However, these devices are not entirely satisfactory for various reasons.
The most common prior art apparatus for generating data from an array of keys is an electric switch that closes when a key is depressed. This is, each time the key in the keyboard array is depressed an associated switch closes. Closure of the switch causes a coded signal to be generated which uniquely defines the key that was depressed. The data bit pattern thus generated is fed into the data processing system. While apparatus of this nature is generally satisfactory, there are several disadvantages, the complexity of the keys and cost thereof being one significant factor.
It will be appreciated by those who have used them that prior art keyboards generally have several other undesirable features. For example, many keyboards are thick and not compact and have a relatively high profile, thus making them inconvenient and tiresome to reach. Furthermore, a relatively large keyboard increases the size of the data processing system beyond what is necessary for miniaturized circuitry now available. In addition, the action of the keys is frequently less rapid than desirable. Furthermore, simultaneous key depressions may not be detectable. Often the keys are rugged and not sealed so as to be immune from dust and dirt. Some keyboard systems are adversely subject to changes in temperature. Furthermore, many systems use more than a minimal amount of power, making them unuseful in battery operated environments.
SUMMARY OF THE INVENTION
In accordance with the present invention, an electrical normally open contact switch is provided which includes a first electrical contact, and a second contact formed as a resilient curved plate of electrically conductive material spaced from the first contact in a normally opened position and having a peripheral edge along at least a portion of which the second contact is supported and further includes means for connecting the first and second contacts in an electrical circuit, the switch completing the circuit upon deflection of the center of the plate from the normally open position to the closed position against the first contact when pressure is exerted against the center, the center snapping back to the normally open position upon removal of the pressure.
More particularly, the switch may be provided in a keyboard array and be mounted on a circuit board which has a plurality of spaced first electrical contacts which extend through the circuit board from a first side of the circuit board to a second side thereof and are electrically connected to selective circuits on the second side. A plurality of second contacts each formed as a curved resilient plate or dome spring are mounted on a contact support on the first side of the circuit board which contact support surrounds each of the first contacts and has an opening corresponding to the position of the first contact. The contact support is formed, in one embodiment, in separate sections interconnected by frangible tabs which are broken during assembly and crimped through appropriate holes in the circuit board and crimped against the other side. The selective sections can be connected, as by soldering to selective circuitry on the other side and each section is connectable to a separate potential to provide different circuit capabilities with different keys. It is understood that each switch completes a circuit upon deflection of the center of the plate from the normally open position to the closed position against the corresponding first contact when pressure is exerted against the center, the center snapping back to the normally open position upon removal of the pressure. In another embodiment, the contact support is formed by electroplating the keyboard and includes a layer of flexible material extending over the side of the circuit board on which the dome springs are supported, completely covering that side of the circuit board to keep moisture and foreign material out of the contacts but permitting deflection of the plate or dome spring contact. In addition, a plurality of depressable keys are positioned with one key above each of the second contacts, which keys are held in position with a grid or frame connected to the circuit board.
In one form of the invention the first contact is formed by a rivet extending through the circuit board from the first side to the second side and connected to selective circuits on the second side whereas in an alternative embodiment the first contact is formed as a plated through hole in the circuit board which plated through hole is also connected to selective circuits on the second side of the circuit board.
The contact support in one form of the invention is formed as a shim which is made up of separate sections connected together by frangible tabs which tabs may be broken during assembly so that they may be forced through holes in the circuit board and clenched to the back side to be soldered or otherwise connected into the circuits on the second side of the circuit board. This arrangement permits connection of different potentials to different sections of the contact support so that different keys may be used to perform different functions.
In an alternative embodiment the contact support is formed, as by electroplating, as a plated support on the circuit board which has a plurality of openings corresponding to the position of the respective first contacts and includes in one embodiment one or more bosses spaced around each opening for supporting the second contact or dome spring above the surface of the first contact. These bosses can be formed by means of an embossing punch which forms the bosses in the plated contact support after it is formed on the circuit board.
From the foregoing, it can be seen that a contact switch made in accordance with this invention is of simple and economic construction and will be reliable in operation. Additional advantages will become apparent from the description which follows, taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exploded, fragmentary, perspective view of a keyboard which illustrates a key comprising one form of the invention;
FIG. 2 is an enlarged vertical section, taken along line 2--2 of FIG. 1, showing an assembled key in normally open position;
FIG. 3 is an exploded, perspective view of a circuit board and contact support showing how the contact support is positioned on the circuit board and attached thereto;
FIG. 4 is an exploded, perspective view, similar to FIG. 1, but showing an alternative keyboard for a mini-computer;
FIG. 5 is an enlarged vertical section taken along line 5--5 of FIG. 4, showing an assembled key in normally open position;
FIG. 6 is a vertical section, similar to FIG. 5, but showing an alternative plate contact;
FIG. 7 is a fragmentary, perspective view of an alternative contact support having raised bosses;
FIG. 8 is a fragmentary, vertical section, showing the method of making the raised bosses of FIG. 7;
FIG. 9 is a fragmentary exploded perspective view showing a plate contact positioned on a still further alternative contact support having a single raised boss; and
FIG. 10 is a fragmentary vertical section taken along line 10--10 of FIG. 9 showing the position of the assembled switch of FIG. 9 in its normally open position.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In accordance with this invention, the keyboard B of FIG. 1 is of the type used for desk calculators or computer keyboards wherein numeric or alpha-numeric function controls are necessary. A series of keys K are mounted as shown on a conventional glass epoxy circuit board 2 which has a printed circuit on the lower side thereof. At the center of each key position a first contact 4 extends through the circuit board from the top side to the lower side where it is connected, as by soldering, to a circuit (not shown) as by a lead as shown in FIG. 2. Conveniently, the contact 4 may take the form of a rivet as shown which extends about 0.013 inches above the circuit board.
A shim 7, which has a thickness of about 0.010 inches, extends over substantially the entire upper surface of the circuit board and is provided with a series of openings or perforations 8 which are adapted to be received over the respective contacts 4. Conveniently, during assembly frangible tabs 9 can be broken by a tool (not shown) which separates shim 7 into separate segments and pushes the ends of tabs 9 through holes punched in circuit board 2 and crimps them against the lower side thereof so that the segments can be soldered or connected to circuitry on the lower side of the circuit board. Similarly, tabs 9' can be bent through holes in the circuit board to make connections to the other side thereof.
Each switch K includes a second contact 10 in the form of a plate or curved dome spring which in FIG. 1 is illustrated as being generally triangular shaped with depending legs. This dome spring is more fully described in commonly assigned co-pending U. S. application Ser. No. 175,941 to Wray C. Hansen, filed Aug. 30, 1971. Spring 10 can be deflected downwardly into contact with contact 4 by depressing the key K associated therewith. The key includes a cylinder 12 which is conveniently made of polyurethane and rests on top of spring 10 and is surrounded by a coil spring 14. The upper end of coil spring 14 is received in an actuator 16 which has a central recess 18 therefore. The actuator includes a body 20 with an upwardly projecting neck 22, the body having a plurality of semi-cylindrical legs 24 spaced therearound. The actuator is received in a generally cubic housing 26 having a body 28 with downwardly projecting legs 30 thereon which are adapted to be received in openings (not shown) in circuit board 2. The housing includes a lid 32 which has an open cylindrical collar 34 through which neck 22 of actuator 16 is adapted to project. The actuator is slidably mounted within body 28 whereby legs 24 are received in semi-cylindrical recesses 36 within the body. Conveniently, lid 32 is attached to body 28 by means of pins 38 which are received in openings 40 on the body of the housing.
Neck 22 of actuator 16 includes an X-shaped element 42 at the upper end thereof adapted to receive a button of key element 44. In operation, when button 44 is depressed, it forces actuator 16 downwardly against coil spring 14 and cylinder 12 and when a sufficient amount of pressure is applied the dome or curved spring 10 rapidly collapses bringing the center thereof into contact with rivet 4 to complete a circuit connection. Upon release of finger pressure on button 44, the spring 10 quickly snaps back to its arched position over rivet 4. Advantageously, this key K is non-teasable and provides finger touch feedback. Also, the arrangement provides a relatively low profile and is rugged and consumes low power and is readily manufactured at low cost. Advantageously, the dome spring 10 is approximately 0.005 inches in thickness and is spaced from rivet 4 approximately 0.0025 inches. It will be further understood that body 28 may be so dimensioned as to constrain dome 10 from lateral movement. The relative differences in diameter of the dome and body have been exaggerated for clarity of illustration.
An alternative keyboard B' is disclosed in FIG. 4 which has particular application in pocket-size or mini-calculators of the battery-operated type which can be carried in the pocket or alternatively can be connected to a conventional power source. This keyboard includes a circuit board 46 made of conventional materials which has a plurality of plated-through holes 48, one of which can be seen in FIG. 5, each of which serves as a first contact for the switch in key K' and is connected by a lead 50 to suitable portions of a printed circuit on the bottom side of the circuit board. A contact support 52 is formed on the top side of circuit board 46 as shown in FIGS. 4 and 5, as by electroplating, upon which a second contact such as a dome spring or plate 54 is mounted as in the previous embodiment the contacts 48 extending through holes or perforations 53 therein. Advantageously, the plated-through holes and the contact support can be formed at the same time to a thickness of say 0.004 inches and a portion of the contact surface of the plated-through hole can be etched away, such as 0.002 inches to provide sufficient clearance for the dome spring to "snap through" when it makes contact. In this embodiment, a spacer or cage 56 is provided having a plurality of openings 58 corresponding to the position of dome spring 54 and is adapted to hold the dome spring in proper orientation with respect to the plated-through holes 48. To protect the contacts from moisture, dirt and other foreign matter, a thin plastic sheet 60, such as Mylar, is placed over the spacer 56 and the dome spring 54 and conveniently has an adhesive on the contacting side.
Above each dome spring and above sheet 60 is an actuating key, such as key 62 which has a depending finger 63 for depressing dome spring 54, the keys being held in position by a frame or grid 64 which extends thereover as shown in FIG. 4 and is attached to the mini-calculator to hold the same in place.
An alternative embodiment is shown in FIG. 6 wherein a circuit board 46' has a plated-through hole 48' therein which is connected to selective circuits (not shown) by means of a lead 50'. A dome spring 66 is supported on a contact support 52' and is held in position by a spacer or cage 56', a plastic sheet 60' extending across the spacer and the dome spring 66 to provide a sealed unit. In this embodiment, the dome spring 66 is provided with a dimple 68 at the center thereof which provides a downwardly extending projection to provide point contact the edge of a plated-through hole 48' when the spring is depressed, as by finger 63' of key 62', the latter being held in position by a frame 64'.
In the embodiments of FIGS. 5 and 6 the plated-through holes and the contact supports are formed by electroplating, but then the top of the plated-through hole must be etched away so that it is spaced below the contact space a distance on the order of 0.002 inches. In the alternative embodiments shown in FIGS. 7-10 this additional etching procedure is not required. To avoid this, a plated support 52" which is formed on circuit board 46" is provided with a plurality of raised bosses 70, such as three, for supporting a dome spring 72 above a plated hole contact 48". Conveniently, these bosses can be approximately 0.002 inches above the surface of support 52" and thereby support dome spring 72 at a suitable height to allow sufficient deflection of the center thereof to bring it into contact with contact 48". The raised bosses may be formed in the contact support 52" by positioning an embossing die 74 over the contact support and striking the bottom of the circuit board with an embossing punch 76, as shown in FIG. 8. Thus, the etching step can be omitted.
A further alternative embodiment is shown in FIGS. 9 and 10 wherein a circuit board 46'" has a contact support 52'" plated thereon which includes a single boss 70' which boss is twice as high as boss 70 at FIGS. 7 and 8. Thus a dome spring 72' is supported at one edge by the contact support 52'" and at the other edge by raised boss 70' to position dome spring 72' a sufficient distance above plated hole 48'" which is connected to suitable circuitry, as by welding, by means of lead 50". The dome springs 72' are held in position by spacer or cage 56" and are covered by flexible layer 60". Each dome spring is deflected by a finger 63" on a key 62" to make contact with plated-through hole 48'". Conveniently, as in previous embodiments, the keys are positioned by a frame 64". With this arrangement, it is necessary only to make one boss, and this is advantageous because it is some times difficult to find three equally spaced positions around a contact support which can be engaged by the embossing punch without disturbing the printed circuitry on the bottom side of the circuit board.
The dimensions described are exemplary only and may be varied for particular applications as required. In this regard, a spacing between the center contact and the dome spring of 0.010 and 0.020 inches has been found to be satisfactory.
From the foregoing, the advantages of this invention are readily apparent. A keyboard for use with calculators is shown in one embodiment wherein the printed circuit board has a shim with openings surrounding contacts in the circuit board which shim is divided into portions that are connected by frangible tabs that are broken during assembly to attach the shim to the circuit board and provide electrical connections thereto. In addition, a dome or curve spring is provided above each contact which is supported by the shim and which is depressable to deflect the center thereof into engagement with its associated contact to complete a circuit. The first contact is formed as a rivet in one embodiment.
In an alternative embodiment a keyboard is provided for a mini-calculator wherein the contacts extending through the circuit board are formed as plated-through holes which are surrounded by a contact support on the side of the circuit board opposite the circuit and supports curved or dome spring contacts which are positioned by means of a spacer, the entire contact assembly being sealed against moisture and foreign matter by means of a plastic adhesive layer, such as Mylar, which extends across the spacer and the dome springs. The dome springs are deflected selectively by keys positioned thereabove within a frame. The dome spring in a further alternative embodiment includes a dimple at the center thereof which is engageable with the plated-through hole. In a still further alternative embodiment the contact support is formed with one or more bosses which support the dome spring above the contact to avoid the necessity of etching the plated-through hole so that in its position below the contact hole the contact support a sufficient distance to provide suitable deflection of the dome springs.
The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the field and scope of this invention.