Switch Pushbutton-type Digit Keyboard Switch With Leaf Spring Contract And Actuator Biasing Means On Common Conductive Frame

Abstract

An array of pushbuttons, e.g., as used for digit selection in a telescommunication system, are recived in apertures of a cylindrical housing above a printed-circuit board. A metallic disk overlying that board, partly cut away in the region of the pushbuttons, is integral with a set of leaf-spring contacts respectively associated with these pushbuttons. Each contact has a relatively broad prong with an upbent extremity, bearing from below under pressure upon a lug of the associated pushbutton, and a pair of narrow parallel tongues bent down with reference to that prong and terminating in hooked extremities which engage a corresponding contact area on the printed-circuit board upon depression of the contact by the pushbutton.

Description

FIELD OF THE INVENTION

Our present invention relates to a keyboard switch for the selective closure of a multiplicity of circuits with the aid of a corresponding number of pushbuttons, e.g., for the transmission of digital frequencies to make a call in a telecommunication system.

BACKGROUND OF THE INVENTION

Conventional keyboard switches of this description generally employ two sets of springs, i.e., a set of restoring springs tending to hold the pushbuttons in their unactuated or elevated positions and a set of leaf-spring contacts which act as circuit closers upon the depression of the associated pushbuttons against the force of their respective restoring springs. It is usually also necessary to provide fixed abutments for limiting the depression strokes of the pushbuttons.

OBJECTS OF THE INVENTION

The general object of our present invention is to provide a simplified keyboard construction which eliminates the need for two separate spring sets as described above.

A more particular object is to provide a set of elements combining the functions of restoring and contact springs as well as of the abutments referred to.

SUMMARY OF THE INVENTION

A keyboard according to our invention comprises a printed-circuit board on a support, e.g., on the bottom of a substantially cylindrical housing, one of whose faces (referred to hereinafter as the upper face) is provided with a multiplicity of contact areas which are respectively included in the circuits to be selectively closed. An array of resilient contact elements are interposed between this board and respective pushbuttons movably mounted on the support, e.g., in apertures formed in the top of the housing, each of these contact elements being a leaf spring with a fixed end and a movable end. The movable end of each leaf spring is split into an upbent prong and one or more relatively downwardly bent tongues, the prong bearing under pressure (i.e., with a certain bias) upon the overlying pushbutton; the tongue or tongues are normally spaced from the corresponding contact area but are engageable therewith upon depression of the pushbutton to displace the prong toward the printed-circuit board (PCB).

In an advantageous embodiment the leaf springs are integral with a conductive frame in the shape of a disk overlying the PCB, the disk being partly cut away around the leaf springs in the region of the contact areas in order to prevent possible short circuits. The prong engaging the pushbutton should be considerably wider than any of the associated tongues acting as circuit closers, its width preferably exceeding the combined width of the tongues.

In this way, any depression of a pushbutton against the biasing force of the contacting prong entrains the associated tongue or tongues into engagement of the corresponding contact area during the downstroke; with the aforedescribed relative dimensioning of the tongues and the prong, the reaction force of the tongues is small compared with the biasing force exerted by the prong upon the descending pushbutton and may be chosen independently of that reaction force to exert the right contact pressure for closure of the circuit.

According to a further feature of our invention, each pushbutton is provided with a lug engaging an angled tip of the coacting prong in line with the working extremity of the adjoining tongue, this tip being pressed flat against the PCB in a fully depressed position of the pushbutton with the leaf spring curving away from the board surface between its fixed end and the tip. The tip of the prong thus acts as a positive stop preventing any further depression of the pushbutton and limiting the deformation of the leaf spring as well as the contact pressure exerted by the tongue extremity upon the printed face.

BRIEF DESCRIPTION OF THE DRAWING

The above and other features of our invention will now be described in detail with reference to accompanying drawing in which:

FIG. 1 is an exploded perspective view (with parts broken away) of a keyboard switch according to our invention;

FIG. 2 is a top plan view of the keyboard switch of FIG. 1;

FIG. 3 is a cross-sectional view taken on the line III--III of FIG. 2; and

FIG. 4 is a plan view of a spring assembly forming part of the keyboard switch of FIGS. 1 - 3.

SPECIFIC DESCRIPTION

The keyboard switch shown in the drawing comprises a cylindrical housing 1 of insulating material provided at its top with a multiplicity (here 12) of generally rectangular apertures 26, surrounded by tubular bosses 25, accommodating respective pushbuttons 2. The pushbuttons are of upwardly tapering configuration and are provided at their lower ends with shoulders 12 limiting their upward displacement.

Housing 1 is closed at its bottom by a lid 10, which may be metallic, whose raised rim 10' supports a printed-circuit board 8 seated in a rabbet 16 at the lower edge of the inner housing wall. A disk 3 of resilient metal of good electrical conductivity, such as beryllium copper, is clamped in position between the rabbet 16 and the board 8. The assembly is completed by nonillustrated screws traversing holes 11 in the lid 10 and engaging inner threads of several posts 13 which integrally depend from the top of the housing and having reduced lower extremities passing through holes 14 and 14' in board 8 and disk 3.

The central part of disk 3 is cut away or stamped out to expose an underlying portion of the upper face of board 8 provided with a multiplicity of contact areas 7, one for each pushbutton 2. Extensions 7' of these contact areas are connected to leads passing through the dielectric board 8 and continuing on its underside to respective loads not shown; voltage to energize these loads is applied to the rim of disk 3 through a nonillustrated connection.

Within the cut-away part of disk 3 there are left standing a multiplicity of contact elements in the form of leaf springs 21 integral with one another and with the rim of the disk, there being one such spring for each pushbutton. Each spring 21 comprises a relatively wide prong 4 and a pair of substantially narrower tongues 5 parallel thereto, the tongues and the prong branching off the body of the spring along a transverse line indicated at 22 in FIG. 4. This body decreases in width from the line 22 to its end 23 at which it is fixed to the remaining stationary disk structure. As best seen in FIG. 3, the spring body is bent upwardly (out of the plane of the disk) at the end 23 and arches past the branching point to a line 24 near the free end of the spring at which the prong 4 is upwardly angled to form a flat tip 20. This tip bears from below upon a lug 9 on the underside of the associated pushbutton 2 which is thereby biased into its top position in which its shoulder 12 abuts the underside of the boss 25 guiding this pushbutton.

As illustrated for the pushbutton 2a in FIG. 3, a depression of that button against the spring force flattens the corresponding tip 20a against the upper face of board 8 to stop the descent. FIG. 3 also clearly shows that the free extremity of each tongue 5 is formed into a generally V-shaped hook 6 lying at a level below that of tip 20 in the unoperated (open-circuit) position of the pushbutton; in this position the tongues 5 diverge downwardly from the prong 4 so that hooks 6 engage the associated contact area 7 early in the downstroke of the actuated pushbutton. The final contact pressure between hooks 6 and area 7 is constant and independent of the pressure exerted by the finger of the user upon the associated pushbutton.

As clearly shown in the drawing, the width of prong 4 exceeds the combined width of tongues 5 (naturally, the number of these tongues is not limited to two) and is nearly equal to the width of the spring body at its junction 23 with the framework of disk 3. The tongues 5 are laterally offset from this junction 23 whereas the tip 20 is in line with that junction so that its engagement with the surface of PCB 8 does not cause any twisting of the leaf spring 21 about its longitudinal axis. Owing to the absence of such twisting, the tongues 5 act with equal pressures upon the associated contact area 7.

In order to increase the flexibility of the leaf spring, its body 27 is advantageously provided with a cutout 19 in the form of a longitudinal slot terminating in the vicinity of the line 22, the width of this slot increasing progressively in the direction toward that line. Thus, despite the trapezoidal shape of the spring body between its limits 22 and 23, its effective width (measured only along its solid portions) remains nearly constant within these limits.

In order to insure the correct alignment of the springs 21 with the associated contact areas, disk 3 is integrally formed with a pair of tangs 18 receivable in holes 17 of PCB 8. Holes 15 (only one shown) in lid 10 accommodate nonillustrated conductors serving as extensions of the leads which traverse the board 8.

Claims

We claim:

1. A keyboard switch for the selective closure of a multiplicity of circuits, comprising:

a support;

a printed-circuit board on said support having a face provided with a multiplicity of contact areas respectively included in the circuits to be selectively closed;

a conductive frame on said support;

a multiplicity of pushbuttons on said support spacedly overlying said face with limited mobility perpendicular thereto; and

an array of resilient contact elements on said frame interposed between said board and respective pushbuttons for completing any of said circuits under the control of the associated pushbutton, each of said contact elements being provided with a fixed end and a movable end, said movable end being split into an upbent prong bearing under pressure upon the associated pushbutton and relatively downwardly bent tongue means alongside said prong normally spaced from the corresponding contact area but engageable therewith upon displacement of said prong toward said board by depression of said associated pushbutton.

2. A keyboard switch as defined in claim 1 wherein said contact elements are leaf springs and said frame is a disk integral with said leaf springs overlying said board, said disk being partly cut away around said leaf springs in the region of said contact areas.

3. A keyboard switch as defined in claim 2 wherein said tongue means comprises a plurality of parallel tongues which together are substantially narrower than said prong.

4. A keyboard switch as defined in claim 3 wherein said tongues terminate in hooked extremities pointing toward the corresponding contact area.

5. A keyboard switch as defined in claim 3 wherein said prong has an upwardly angled tip in line with said extremities, each pushbutton being provided with a lug engaging the tip of the associated prong for pressing said tip flat against said board in a fully depressed position of the pushbutton with said leaf spring curving away from said board between said tip and said fixed end.

6. A keyboard switch as defined in claim 3 wherein said leaf spring broadens from said fixed end to a transverse line intermediate its ends along which said prong and said tongues branch off the body of the leaf spring, said fixed end being in line with said prong but laterally offset from said tongues.

7. A keyboard switch as defined in claim 6 wherein said body is provided with a longitudinal slot terminating in the vicinity of said transverse line.

8. A keyboard switch as defined in claim 7 wherein said slot widens progressively in the direction toward said transverse line.

9. A keyboard switch as defined in claim 2 wherein said board and said disk are provided with coacting formations for positively aligning said leaf springs with said contact areas.

10. A keyboard switch as defined in claim 1 wherein said support comprises a housing with apertures in its top for the guidance of said pushbuttons and with a detachable lid at its bottom carrying said board.