Push Button Switches With Interlocking Diaphragm Contact

Abstract

A multiple push button assembly in which the buttons are arranged in a row. The buttons are normally biased outwardly relative to the panel in which they are supported, but when one of the buttons is pushed inwardly, it is latched and remains depressed until another button in the row is depressed. Movement of the other button releases the latch from engagement with the first button, allowing it to move outwardly to its initial position. Thus, only one button in the row remains depressed at a time. Latching of the buttons is accomplished by a thin, resiliently flexible band, which is mounted in longitudinal compression against a curved guide through which the buttons project. The band also serves as a contact element.

Description

BACKGROUND OF THE INVENTION

This invention relates to electrical switches, and more particularly to multiple, interlocking push button switches.

Multiple push button switch assemblies are often used as selector switches to permit one circuit to be selected from a group of circuits. Typically, a plurality of push buttons are arranged in a row extending across a panel. The buttons are spring biased toward a raised position, but one button at a time may be pressed into the panel to close a switch and thereby completing the electrical circuit associated with the button that has been depressed.

Various means have been proposed for interlocking the push button switches in such a way that the button that is being depressed becomes latched in a depressed position, while the button that was previously latched in a depressed position is released to return to a raised position. Conventional push button selector switches typically have spring biased latch bars or other devices for holding one button at a time in a depressed position, while allowing the remaining buttons to be in a raised position. In addition to the latch bar, switch contacts often are provided under each push button, so that the contacts may be closed when the button is depressed. Furthermore, individual springs are provided for each push button to bias the push buttons toward the raised position. All of these components are assembled in a housing behind the panel, and often the assembly requires hand labor to fit the components together. Also, due to the large number of components, it may not be possible to achieve a high production rate.

Another problem encountered with many types of conventional push button selector switches is that considerable energy is required to operate the push buttons. Typically, the buttons have a long stroke and a large force is required to apply the energy necessary to close one set of contacts and to release the mechanism latching the previously depressed button. Due to the need for a high energy input to operate the selector switches, it is not practical to use small buttons, or to shorten the stroke, although the present arrangements are burdensome to the user. In some selector switches considerable frictional drag resists displacement of the button, particularly at the time the latch engages the button to hold the button depressed. Rapid wear of the switch contacts or other components also may occur due to relative sliding movement.

SUMMARY OF THE INVENTION

In view of the defects of prior multiple push button switches, it is an object of this invention to provide a push button selector switch having relatively few components and which can be assembled with a minimum of hand labor.

Another object of this invention is to provide a push button selector switch which operate reliably and has a long service life, without substantial wear of its components.

A further object of this invention is to provide a push button selector switch in which the push buttons require substantially the same force to be depressed and the force does not noticeably increase at the time of latching.

These objects are accomplished in accordance with a preferred embodiment of the invention by a push button selector switch assembly having a curved guide surface on the interior wall of the housing and a plurality of push buttons spaced along a row that is concentric with the curvature of the wall. A thin resiliently flexible strip is slotted longitudinally, but remains joined at opposite ends. The slots divide the strip into tension bands and an operative band. The strip is inserted in the housing with the operative band positioned against the curved surface of the wall and the tension bands stretched over projections on the wall of the housing to induce the operative band to be compressed longitudinally and to buckle into a single lobe. The lobe projects toward the center of curvature of the wall and engages a contact plate with terminals spaced apart along the length of the plate. While one of the push buttons is being depressed, the lobe becomes aligned with that push button as it moves inwardly. Simultaneously the lobe is removed from the push button that was previously depressed, that push button springs outwardly to the raised position. If necessary, individual springs are provided at each push button to suppress any tendency for additional lobes to form. Thus, the operative band serves as part of the switch contact and closes a circuit when one of the push buttons is depressed to align the lobe with the selected contact.

DETAILED DESCRIPTION OF THE DRAWINGS

This preferred embodiment of the invention is illustrated in the accompanying drawings in which:

FIG. 1 is a top plan view of a switch assembly in accordance with this invention;

FIG. 2 is a side elevational view of the switch assembly;

FIG. 3 is a cross sectional view of the switch assembly along the line 3--3 in FIG. 1;

FIG. 4 is a cross sectional view of the switch assembly along the line 4--4 in FIG. 1;

FIG. 5 is a cross sectional view of the switch assembly along the line 5--5 in FIG. 4;

FIG. 6 is an exploded view of the switch assembly; and

FIG. 7 is a perspective view, partially in cross section, of the switch assembly.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

The switch assembly 2 of this invention is shown in FIG. 1 as mounted within an opening in a panel 4 by means of screws 6 which engage tapped holes in the housing 8 of the assembly 2.

The housing 8 includes a wall 10 which projects through the opening in the panel 4. A plurality of bores 12 are provided in the wall 10 at spaced intervals. The outer end of each bore has an enlarged portion 14 of substantially square cross section and a shoulder 16 is provided at the interior end of each enlarged portion 14. An elongated push button 18 is received in each of the bores 12. The push buttons 18 are square in cross section at the the outer end to conform to the shape of the portion 14 of the bore, while the inner end of each push button 18 is in the form of a shank 20 conforming to the shape of the bore 12. The push buttons 18 slide freely longitudinally within the bore 12.

The interior side of the wall 10 has a curved surface 22 (FIG. 6). The center of curvature of the surface 22 is in the plane of the center line of the push button 18. As shown in FIG. 1, the push buttons 18 extend substantially perpendicular to the surface 22 and the longitudinal axes of the push buttons 18 intersect approximately at the center of curvature of the surface 22. A thin resiliently flexible strip 24 is applied along the curved surface 22. The strip 24 may be formed of spring metal, such as beryllium copper alloy, and preferably has a thickness of less than one one hundredth of an inch. As shown in FIG. 6, the strip 24 has a pair of longitudinal slots 26 and 28 which divide the strip into a pair of elongated lateral sections 30 and a band 32 between the sections 30. The slots 26 and 28 terminate at opposite end portions 34 and are spaced from the ends of the strip. Thus, the sections 30 are integral with the band 32.

The end portions 34 are received in slots 36. The band 32 overlies the curved surface 22 and the sections 30 are received within lateral recesses 38. A pair of pegs 40 project upwardly from the wall 10 within the recesses 38 and the respective sections 30 engage the side of the pegs 30, as shown in FIG. 4. Since the pegs 40 hold the sections 30 outwardly from the curved surface 22, the tension in the sections 30 at each end tends to urge the ends of the strip 24 to remain against the outer side of the slots 36. Therefore, the strip is spaced from the inner side of the slots 36. In fact, the housing 8 may be changed to eliminate the inner side of the slots 36, if desired.

In FIG. 1, it is apparent that the length required for the sections 30 is greater than the arcuate length of the curved surface 22 because of the displacement of the sections 30 which is required by the pegs 40. The sections 30, however, are integrally joined with the band 32 which extends along the curved surface 22. To accommodate this difference in length, the tension in the sections 30 draws the end portions 34 of the strip 24 longitudinally toward each other, thereby causing the band 32 to flex into a lobe 42. The formation of the lobe in the band 32 and its characteristics are fully disclosed in the copending U.S. Pat. application of Donald F. Wilkes, Ser. No. 32,886; filed Apr. 29, 1970, the disclosure of which is incorporated herein by reference.

The differential between the length of the curved surface 22 and the length of the band 32 that is superimposed on the surface 22 determines the length of the lobe 42. Preferably, the lobe 42 has a length that is slightly less than twice the distance separating adjacent push buttons from each other. Thus, each end of the lobe 42 is located near the closest push buttons on either side of the depressed push button. It is important to note that one characteristice of the lobe 42 is that it is spring biased to remain in the lobe shape and resists forces tending to flatten the lobe.

The slot 28 in the strip 24 has a plurality of notches 43 corresponding to the locations of the bores 12. Each push button shank 20 has a transverse slot 44 in which the band 32 is received. The notches 43 have a width greater than the diameter of the shank 20, as shown in FIG. 7. Of course, the notches 43 may be omitted, so that the band has a continuous edge that extends through the slot 44 in the buttons 18, although the band would be more narrow in order to fit between the buttons 18 and the lower strip section 30. The housing 8 includes a channel opposite the curved surface 22 with a support surface 46 that is substantially concentric with the curved surface 22. A spring strip 48 is mounted on the surface 46 and has a plurality of spring fingers 50 which are aligned with each push button 18. The surface 46 has a transverse curvature, as shown in FIGS. 3 and 4, to allow clearance for transverse flexing of the strip 48 as the fingers 50 flex toward the surface 46. The distal ends of the fingers 50 are engaged by the inner ends of the respective push buttons 18. When the push buttons are extended, as shown in FIG. 3, the finger 50 associated with that push button is sufficiently flexed to apply spring bias urging the push button to remain in the extended position. Outward movement of the push button is limited by the band 32 which engages the inner side of the slot 44.

A contact board 52 is mounted in the housing 8 and has conductive contacts 54 superimposed on the surface of the board 52. The contacts 54 are connected with suitable circuit elements which are arranged in a row along a terminal portion 56 of the board which projects outwardly from the housing 8. The terminal portion is adapted to receive a conventional electrical connector. The contacts 54 may be formed as part of an overlay sheet which is bonded to the surface of the board 52 and subsequently, the contacts are insulated from each other by drilling holes 58 through the overlay and through the board. This technique simplifies the assembly procedure. Each of the contacts 54 extends over the edge of the board 52 and is aligned with the central axis of a push button 18, as shown in FIG. 5. Also, the edge of the board at each contact 54 slopes inwardly in a V-shape toward the center to serve as a detent for the lobe 42. The lobe 42 flexes outwardly against the contact 54 on the edge of the board 52, as shown in FIGS. 4 and 5 and the apex of the lobe 42 is retained at the center of the contact 54 by the shape of the edge.

When the lobe 42 is aligned with a particular push button, as shown in FIG. 4, the push button is held depressed by the spring force in the band 32 engaging the inner side of the slot 44, and the spring force of the band 32 is sufficient to overcome the spring bias of the finger 50 which bears against the end of the push button. At each location where a push button is extended, as shown in FIG. 3, the band 32 is supported by the surface 22 and the full force of the finger 50 maintains the push button in its extended position. The force of the spring finger 50 is also transmitted through the slot 44 to urge the band 32 to remain against the curved surface 22. Any tendency for the band 32 to form multiple lobes is suppressed by the continuous spring bias of the fingers 50 applied against the band 32. This spring bias at one of the extended push buttons is relieved by depressing the push button to uncouple the connection between the spring 50 and the band 32 through the slot 44. The width of the slot 44 is greater than the thickness of the band 32, so that as the push button moves inwardly, the inner side of the slot becomes spaced from the band 32 and spring force is no longer applied to the band 32. At this point, the band portion adjacent the push button that is being depressed, does not need to overcome the force of the spring 50 in order to form a lobe, as do the band portions adjacent all of the other push buttons, except the one with which the band lobe 42 is already aligned. Consequently, the band lobe has a preference for forming at the push button that has been depressed sufficiently to relieve the force of the spring 50. Continued inward movement of the push button 18 causes the outer side of the slot 44 to engage the band 32 to urge it to move away from the surface 22. When sufficient force is applied to the push button, the lobe 42 progresses from its initial position into alignment with the push button that is being depressed. In doing so, the band portion 32 snaps from the position shown in FIG. 4 to the position shown in FIG. 3 to return the push button that previously was depressed outwardly to the position shown in FIG. 3. Also, the lobe disengages from the contact 54 at the previous location and engages the contact 54 at the new location. In accordance with conventional techniques, the band 32, which is electrically conductive, may be used as a common contact element and the individual contacts 54 may be connected through external circuits with the band 32.

Referring to FIGS. 3 and 4, it will be noted that the push buttons 18 engage the band near the upper edge of the band 32, while the switch contacts 54 are adjacent the lower edge of the band. The reasons for this arrangement are to obtain maximum contact pressure and to avoid the need for precise adjustment of the spring force applied by the fingers 50. The spring finger 50 applies a force outwardly on the button 18 when the button is depressed (FIG. 4), while the band lobe 42 applies a force inwardly by engaging the side of the slot 44. Although the force of the lobe 42 is greater than the force of the finger 50 on the button 18 so that the button remains depressed, the resultant inward force exerted by the lobe at the upper edge of the band is diminished by the spring 50. The effect of the spring 50, however, is progressively reduced across the width of the lobe 42, and at the edge of the band that engages the contact 54, the effect is negligible.

In operation, the push button switch initially has one of the buttons depressed, and the band portion 32 associated with the depressed push button is flexed away from the curved surface in a lobe 42 that engages the contact 54 to close the electrical circuit between the contact 54 and the band 32. When it is desired to open the switch associated with the depressed button and to close the switch associated with a second button, the second button is merely depressed, which causes the first push button to pop out to its extended position and the band lobe 32 latches the second push button in a depressed position and closes the electrical switch by engagement with the contact 54. It should be noted that the lobe 42 does not engage the switch contacts as it moves from one position to another along the curved surface 22. The lobe 42 at least partially collapses and reforms as controlled by the movement of the push buttons 18.

The lobe suppression spring bias that is supplied by the strip 48 and fingers 50, may also conveniently be supplied by compression springs inserted between the enlarged end of the buttons 18 and the shoulders 16, or by other suitable spring means. It has been found that the lobe suppression spring bias is not necessary, if the radius of curvature of the guide surface 22 is sufficiently small, or there are relatively few buttons positioned close to each other. The elimination of the suppression spring bias does not adversely affect the operation of the switch in these switch assemblies, since the curvature of the guide surface is the primary means for holding the band against the guide surface, except the portion that forms the lobe.

The push button switch assembly of this invention has surprizingly few components, which are easily assembled. The spring strip 24, for example, is formed in one piece and the longitudinal compression of the band 32 to form the lobe 42 is quite simply provided by passing the tension sections 30 over the pegs 40 to draw the opposite ends of the band section toward each other. When assembled in this manner, the spring strip 24 is self-supporting and there is no need for clamps or other fasteners in order to apply the compressive longitudinal stresses in the band 32. In most switch applications, the physical dimensions and relationship would require the differential in length between the sections 30 and the band 32 to be of the order of less than 0.005 of the nominal length of the band. In some switch assemblies, the length differential may be as small as 0.002 times the length of the band. Furthermore, the differential must be held with a tolerance of the order of one-quarter of the design value to assume reliable operation. Conventional means for introducing and maintaining these differentials, such as by clamping the ends of the band in the housing, are entirely unsatisfactory. However, in accordance with this invention the required length differential is readily obtained and the band 32 is easily installed in the housing.

The contacts 54 may be formed by various economical methods, instead of being laminated on a contact board as disclosed in this application. For example, the contacts may be deposited by known methods on the edge of a board and leads from the contacts to a terminal strip may be etched on the surface of the board by conventional printed circuit techniques. There are many other alternative methods available which would permit the economical preparation and assembly of the contacts 54 in position to be engaged by the lobe 42.

Another important feature of the switch assembly of this invention is that there is substantially no relative movement between the edge of the contacts 54 and the band lobe 42. The band moves substantially perpendicular to the edge of the contacts 54 as the lobe forms and collapses. The absence of relative sliding motion between the band and the contacts results in almost complete absence of wear between these surfaces. At the same time, the flexing of the band in the lobe 42 assures a firm electrical connection between these elements.

While this invention has been illustrated and described in accordance with a preferred embodiment, it is recognized that variations and changes may be made therein without departing from the invention as set forth in the claims.

Claims

What is claimed is:

1. A multiple push button switch assembly comprising:

wall means having a guide surface and having a plurality of bores therein spaced longitudinally along said surface,

a thin resiliently flexible band extending along said surface,

means longitudinally compressing said band thereby flexing a portion of said band into a lobe projecting away from said surface,

urging means yieldably urging said band toward said surface,

a plurality of push buttons in said bores, said push buttons and said band being interconnected for coordinated movement, and

contact means spaced from said surface, said contact means being in position for engagement by said band lobe.

2. The multiple push button switch assembly according to claim 1, including spring means yieldably biasing said push buttons to move said band toward said surface, thereby assisting said urging means in suppressing a tendency for multiple lobe formation.

3. The multiple push button switch assembly according to claim 2 wherein said band has opposite longitudinal edges, said push buttons being interconnected with said band adjacent one of said edges and contact means being in position to be engaged by said band adjacent the other of said edges, whereby the effect of said spring means on contact pressure at said contact means is minimized.

4. The multiple push button switch assembly according to claim 2 wherein said push buttons have a slot through which said band extends, said slot having a width substantially greater than the thickness of said band, whereby when one of said buttons is being depressed, said slot relieves the bias of said spring means on said band to allow a lobe to form at said one button.

5. The multiple push button switch assembly according to claim 1 including an elongated thin resiliently flexible strip, said strip having a pair of longitudinal slots therein dividing said strip into a plurality of sections that are integral with each other, said band being a first one of said sections, said band compressing means including means providing a differential in length between at least one other of said strip sections and said band as measured with respect to said guide surface to urge opposite end portions of said band toward each other, thereby imposing compressive stresses in said band.

6. The multiple push button switch assembly according to claim 5 wherein said guide surface has a longitudinal curvature, said differential providing means includes a projection on said wall means spaced outwardly from said guide surface and said other strip sections engaging said projection.

7. The multiple push button switch assembly according to claim 10 wherein said push buttons project through said wall means substantially radially with respect to said curved surface, base means adjacent said wall means, said base means including an arcuate channel having a support surface concentric with said curved surface, and including a resiliently flexible spring member having a support portion and a plurality of spring fingers, said support portion being mounted on said support surface with said fingers projecting outwardly from said support surface and engaging said push buttons continuously to urge said push buttons outwardly relative to said wall means.

8. The multiple push button switch assembly according to claim 1 wherein said contact means is provided on base means adjacent said wall means, said contact means includes a plurality of contact elements spaced apart from each other along said base means, said base means being in position to be engaged by said band lobe portion, while the remaining portion of said band is spaced from said base means, said contact elements having detent surfaces to guide said lobe into alignment with said contact elements.

9. The multiple push button switch assembly according to claim 8 wherein said band is electrically conductive and forming a contact element cooperating with the contact elements on said base means.

10. The multiple push button switch assembly according to claim 1, wherein said surface has a longitudinal curvature, said urging means including means holding said band resiliently flexed toward said guide surface, said bores being spaced circumferentially along said surface.

11. The multiple push button switch assembly according to claim 1 wherein said bores extend substantially perpendicular to said guide surface, said push buttons being moveable in said bores substantially perpendicular to said surface.