Keyboard assembly with foldable printed circuit matrix switch array, and key actuator locking slide plate

Abstract

This invention provides a keyboard assembly for installation in an electronic system of the type having discrete devices such as integrated circuit chips which are electrically actuated by the manual movement of keys. More particularly, the keyboard assembly consists totally of a cover, keys, cam plate, guide plate, contact plate, contacts deposited on flat flexible cable, a spacer, a base plate, and the bolts, etc. for mounting it.

Description

BACKGROUND OF THE INVENTION

Conventional keyboards such as found on TouchTone telephones contain 101 parts including mounting screws, studs and nuts. In addition to these many parts the final assembly requires the bringing together of three major subassemblies. Further, all the work in both subassembly and final assembly must be done by skilled workmen, with such work including countless soldering operations. Obviously the cost of the many parts plus skilled labor is high. Further, as is well known, humans make mistakes which lead to high failure rates of the assembled keyboards.

It is therefore an object of this invention to provide a keyboard assembly having only a few inexpensive parts. As a corollary yet distinct feature, it is an object to provide a keyboard assembly which is extremely simple to assemble and as such, is not subject to misassembly.

Another object of the present invention is to provide a keyboard assembly which is virtually foolproof insofar as operative manipulation is concerned.

It is yet another object of the present invention to provide a keyboard assembly which is exceedingly reliable in operation.

These and other objects, novel features and advantages of the present invention will be readily apparent from the following detailed description of the preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of the keyboard assembly constructed in accordance with the preferred embodiment of the present invention; and

FIG. 2 is a view showing the contacts and circuits deposited on a flat flexible cable used in the keyboard assembly of FIG. 1.

FIGS. 3 and 4 are side sectional views of a portion of the keyboard of FIG. 1 subsequent to its assembly and illustrating a key in an unactuated condition (FIG. 3) and actuated, condition (FIG. 4).

DESCRIPTION OF THE PREFERRED EMBODIMENT

The several elements of the keyboard assembly have been exploded vertically to show the details of each element, the relationship of one element to another and also to illustrate the natural, uncomplicated method of assembling the elements to form the keyboard.

The lower most element in FIGS. 1, 3 and 4 is base plate 10 on which the other elements rest. This plate is preferably made from steel with a chromate conversion coating.

Base plate 10 is made with a pair of downturned tabs 14 which provide means for fastening the keyboard assembly to a telephone or other keyboard-using device (not shown) by bolts 16 one of which is shown positioned in an aperture in the one tab visible in the drawing.

The subassembly positioned directly over the base plate consists of an end of a strip of non-conductive flat flexible cable 18 folded back over itself. A spacer 20 is sandwiched inbetween.

Turning now to FIG. 2, the inside surface 22 of the cable 18 is displayed. This surface contains the circuitry for the keyboard. Reference numeral 24 points out the axis about which the cable is folded to provide the configuration seen in FIG. 1. The solid dots represent contacts 26 which are located on each side of the axis. The contacts are deposited on the cable via conventional methods in a symmetrical pattern such that when the cable is folded over, contacts on one side are in precise opposing registration with contacts on the other side. In some cases, one pair of opposing contacts constitute a switch while in other cases, two pair constitute one switch.

Conductors 30 connect contacts 26 to appropriate power sources, discrete devices, etc. (none of which are shown) which perform the necessary functions characteristic of the device to which the subject keyboard assembly is attached; e.g., a telephone. Circuits are closed by bringing one or more contacts on the one inside film surface into physical contact with one or more contacts on the opposite inside film surface.

The circles shown in FIG. 1 on cable 18 simply represent the location of some of the contacts 26 on the inside surface.

Although a number of non-conductive or insulative films are available from which flat flexible cable 18 can be made, a polyimide film sold under the trademark KAPTON by E. I. duPont de Nemours & Co. is preferred. The conductors generally consist of a deposition of a single layer of conductive material such as copper. The contacts preferably consist of a multilayered deposition having gold and other highly conductive metals therein. A preferred deposition consists of copper on the bottom, gold on top and nickel inbetween.

Referring back to FIGS. 1, 3 and 4 and the subassembly, it was noted above that a spacer 20 is sandwiched between the folded portion of cable 18. This spacer is preferably made from polyester and contains a plurality of holes 28 FIGS. 3 and 4 which are in alignment with opposing contacts 26. These holes or openings allow a contact 26 to be pushed through the spacer 20 and into physical contact with an opposing contact. In the absence of a biasing force on a contact, the spacer electrically and physically isolates opposing contacts one from the other.

A switch plate 32, positioned over the cable-spacer subassembly, contains two kinds of members having spring characteristics; three commoning members 34 seen along one side of the plate and a plurality of switch members 36 spaced throughout the surface of the plate. While only four switch members are shown, it is to be understood that there are as many switch members as are keys; i.e., one switch member for each key.

The commoning members 34 consist of a strip of metal stampe out from the plate on three sides. The strip is bent upwardly into an L-shape to form arm 38 and elbow 39. The commoning members may be rotated over a short arc with the point of rotation or hinge line being across the strip at its point of attachment to the plate. This hinge line is indicated generally by reference numeral 40.

The switch members 36 are also stamped out of the contact plate and formed into limbs 41 extending obliquely upwardly. Although each member is one piece, there are three functional parts. Two fingers 42 on each member are formed and bent obliquely downwardly. The free ends of each finger, curved up slightly to form a smooth surface, engages the outside insulative surface of the underlying flexible cable 18 with the point of contact immediately overlying a contact 26. In this manner, each switch member; i.e., the two fingers, contacts two contacts 26.

The fingers 42 are connected directly to the switch member proper 44 which moves about the hinge line located at the member's point of attachment with the plate. This hinge line is indicated generally by reference numeral 46.

An overload spring 48 extends forwardly between the two fingers and moves about a hinge line located at its attachment with the spring member proper. This hinge line is indicated generally by reference numeral 50.

The edges of the switch plate 32 have been turned up to form vertical walls 52. These walls provide ridgity to the plate as well as providing a raised platform on which the overlying guide plate rests in the assembly.

The material preferably used in making switch plate 32 is either pre-tinned steel or stainless steel. As is now evident, the material must be resilient and capable of having spring characteristics such that when they are moved, they tend to return to their original position.

The overlying guide plate 54 has three long narrow slots 56 up through which the arms 38 of commoning switch members 34 project in the assembled keyboard. Interiorly, the guide plate has as many openings 58 as there are keys. These openings, being in alignment with the switch members below, receive the lower part of the keys so as to guide such in their vertical movements. A vertical stud 60, located at one end of the guide plate, is provided to guide and align the movement of the overlying cam plate.

Guide plate 54 is preferably made from glass-filled VALOX, a polyester sold under that tradename by General Electric Company.

Cam plate 62 rests on guide plate 54 and in like manner, has three long, narrow slots 64 through which arms 38 project. The plate further has a plurality of openings 66, these being in alignment with openings 58 and switch members 36. One wall of openings 66 is beveled to provide a camming surface as generally indicated by reference numeral 68.

A stud receiving slot 70 is located on one end of the cam plate.

As with guide plate 54, the preferred material used in making cam plate 62 is glass-filled VALOX.

Keys 62, although integral, have an upper and lower section with laterally projecting rims 74 dividing the two. One side wall of the lower section is provided with a beveled camming surface 76. The length of the lower section below the camming surface is such that when assembled, the bottom surface of the key is on the top of overload springs 48 on switch members 36. The length of the lower section in the direction parallel to slot 70 is less than the length of opening 66.

The top surface of the upper section provides an area for key designation symbols.

Preferably keys 72 are molded from acrylonitrile-butadiene-styrene resins (i.e., `ABS`).

The last element of the keyboard assembly is cover plate 78. The plurality of openings 80 thereon are sized to receive the upper section of keys 72. The under surface of each opening is recessed as generally indicated by reference numeral 82, to receive rim 74 on the keys. Vertical walls 84, surrounding each opening 80, provide support for keys 72. Cover plate 78 is preferably molded from ABS.

Each of the several elements in the keyboard assembly have holes on two (cable 18) or four corners. These holes, along with suitable bolts (not shown), provide one means for securing the several elements together.

The assembly step of the keyboard illustrated in FIG. 1 simply requires stacking the several elements in the order shown and securing such together. FIG. 3 is a cross-sectional elevational view of an assembled keyboard. In addition to showing the assembly, FIG. 3 shows the keyboard in an unactuated condition.

As indicated above, the film or flexible cable 18 is folded back on itself to bring contacts 26 on one surface into a direct alignment with the contacts on the now opposing surface. Spacer 20, of an insulating material, provides the means for separating the two. Openings 28 in the spacer are also in direct alignment with the opposing contacts.

Attention is drawn to the position of switch member 36 and commoning member 34. Particularly of interest are the portions thereof which rest or bear on the upper outside surface of film 18. The members are preloaded or stressed upwardly so that the force bearing downwardly is negligible. With respect to commoning member 34, attention is also directed to the position of its arm 38 with respect to the wall defining opening 64 in cam plate 62. In this regard, attention is directed to the positioning of beveled surface 76 on key 72 and the wall defining opening 66.

Cam plate 62 is positioned on guide plate 54 so that stud 60 bears against the front end of slot 70.

As noted above, the bottom surface of each key 72 rests on top of a switch member 36.

FIG. 4 illustrates the actuated condition of the assembled keyboard.

In depressing a key 72, cam plate 54 is moved forward by the camming action of the two abutting beveled surfaces 68-76. The forward movement pushes arm 38 of commoning members 34 forward and downward in an arc so that the elbow 39 pushes down on cable 18. This pressure pushes one contact into electrical engagement with an opposing contact 26.

Concurrently, the key is pushing down on a switch member 36, the point of contact therewith being the overload spring 48. Initially the entire spring member arcs downwardly, the hinge point for the movement being at hinge line 46. The downward travel is transferred through fingers 42 to cable 18 and contacts 26 positioned below the fingers. The pressure pushes the contact through an opening in spacer 20 and into physical and electrical contact with an opposing contact on the other side thereby closing a circuit.

Additional downward pressure on key 72 is taken up by the overlaod spring 48 bending at hinge line 50. This prevents overflexing of cable 18.

When pressure is released from a key, the resiliency of the switch member restores it to its normal position and the reactive force exerted by arm 38 of commoning switch 34 returns cam plate 62 to its initial position.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as some modifications will be obvious to those skilled in the art.

Claims

What is claimed is:

1. A keyboard assembly comprising:

a. a flat flexible cable with a portion thereof folded back over on itself and having contacts deposited on both facing surfaces, contact on one surface being directly across from contacts on the other surface;

b. means for connecting the contacts into electrical circuits;

c. a layer of insulating material positioned between the two contact-carrying surfaces and having holes therethrough, said holes being in registration with opposing contacts;

d. a switch plate overlying the folded over cable and containing a plurality of resilient switch members comprising an elongated limb extending obliquely upwardly and a pair of fingers, one on either side of the limb, extending obliquely downwardly with the free end of each finger being adjacent an outside surface of the folded over cable and in direct alignment with a contact located on the inside surface, said plate further containing a plurality of commoning members comprising an L-shaped strip of material having a vertical arm and an elbow, said elbow being adjacent an outside surface of the folded over cable and in direct alignment with a contact located on the inside surface;

e. a slidable cam plate positioned over and spaced from the switch plate, said cam plate having a plurality of slots into which the vertical arms extend and a plurality of openings in alignment with each of the switch members;

f. a plurality of movable keys each having a bottom surface adjacent the free end of the limb on the switch member and a beveled surface on one side so that as one of the keys are depressed, the bottom surface thereof pushes downwardly on the limb whereby the two free ends on the fingers pushes the cable forcing the underlying aligned contacts into electrical engagement through a hole in the layer of insulating material, said beveled surface concurrently pushing on and laterally sliding the cam plate such that the arms of the commoning members extending through the slots are rotated about the point of attachment with the switch plate so that the elbows drive the underlying contacts into electrical engagement through the holes in the insulating layer.