WO2002093599A1

WO2002093599A1 - A switch assembly

Info

Publication number: WO2002093599A1
Application number: PCT/AU2002/000588
Authority: WO
Inventors: Tino Fibaek; Andrew Bell
Original assignee: Fairlight Esp Pty Ltd
Priority date: 2001-05-11
Filing date: 2002-05-13
Publication date: 2002-11-21
Also published as: AUPR496101A0

Abstract

A switch assembly including a pushbutton key (40) having a first guide formation, a key surround (12) having a second complemental guide formation, an elastically deformable keymat (16), and locating means (62, 64) for locating the keymat relative to the surround, whereby the pushbutton key is arranged to travel reciprocally within the surround between a raised position and a depressed position, with the keymat being arranged to return the key to the raised position, and the first and second guide formations being arranged to restrict the key to a predetermined path throughout its reciprocal travel. The keymat typically includes a pushbutton key portion, an outer peripheral base (44) and an elastically deformable web (42) extending between the pushbutton key portion and the base, and constituting a return spring, for providing sprung movement between the pushbutton key portion and the base.

Description

A switch assembly

Field of the invention

This invention relates to a switch assembly, and in particular to a pushbutton switch assembly. Background of the invention

There are many different types of pushbutton switches. One highly popular and economical pushbutton switch array employs an elastically deformable silicone keymat formed with integrally moulded keys which protrude through apertures in an overlying fascia plate. Whilst economical to manufacture, the keys do not always have a quality "feel". Keymat- type switches are also more suited to mass produced articles where the matrix or array of switches remains identical across the range.

At the .high quality end of the market, sprung mechanical switches are utilised. Whilst these switches generally have a superior "feel", they usually have precision metal parts and require robot assembly, which adds to their cost. Summary of the invention

According to a first aspect of the invention there is provided a switch assembly including a pushbutton key having a first guide formation, a key surround having a second complemental guide formation, an elastically deformable keymat, and locating means for locating the keymat relative to the surround, whereby the pushbutton key is arranged to travel reciprocally within the surround between a raised position and a depressed position, with the keymat being arranged to return the key to the raised position, and the first and second guide formations being arranged to restrict the key to a predetermined path throughout its reciprocal travel.

Preferably, the first guide formation includes at least one face defined by an outer cylindrical side wall of the pushbutton key, and the second complemental guide formation includes at least one face defined by an inner cylindrical side wall ofthe surround.

Conveniently, the predetermined path is a rectilinear path which may be parallel to and preferably coaxial with central axes ofthe inner and outer cylindrical side walls. In a preferred form of the invention, mounting means extend from the key surround for enabling the switch assembly to be mounted mechanically to a base, which is typically a pcb, such that the keymat is located between the surround and the base.

The locating means typically comprise an outer peripheral channel defined in the keymat within which locating projections extending from a base ofthe surround are arranged to locate.

The mounting means preferably include non-conductive mounting lugs terminating in feet arranged to form an interference or click fit with complemental apertures defined in the pcb. The lugs conveniently extend through apertures defined in the keymat.

The keymat typically includes a pushbutton key portion, an outer peripheral base and an elastically deformable web extending between the pushbutton key portion and the base, and constituting a return spring, for providing sprung movement between the pushbutton key portion and the base.

The pushbutton key portion is preferably surmounted by a complemental pushbutton cap having outer cylindrical side walls of the type described above, and a skirt portion for holding the cap captive relative to the surround. The skirt portion may be eliminated to allow for in situ removal ofthe cap for relabelling purposes.

The underside of the pushbutton key portion conveniently carries at least one and typically two or four electrically conductive contacts typically in the form of carbon pips arranged to bridge a corresponding contact array on the pcb when the pushbutton key is in the depressed position.

The pushbutton key portion advantageously is translucent and defines a chamber for accommodating at least one illumination source which is typically in the form of an led or an led cluster. An opaque divider may be incorporated into the chamber to define two sub- chambers for accommodating separate illumination sources. The switch assembly is preferably unitary, in that it can be moved and repositioned independently, and does not form part of an integral switch matrix or array.

According to a further aspect of the invention, there is provided a switch assembly including a pushbutton key having a first guide formation, a key surround having a second complemental guide formation, an elastically deformable keymat, and locating means for locating and anchoring the keymat relative to the surround, whereby the pushbutton key is arranged to travel reciprocally within the surround between a raised position and a depressed position, with the keymat being arranged to return the key to the raised position, and the first and second guide formations being arranged guide the key throughout its reciprocal travel, wherein mounting formations extend from said key surround for enabling the switch assembly to be detachably mounted to a complemental array of apertures defined in said circuit board, with the keymat being sandwiched between said surround and said circuit board.

The invention extends to a switchboard including a circuit board populated with a plurality of switch assemblies ofthe type described above.

The invention still further provides a switchboard including at least one printed circuit board carrying a plurality of switch assemblies, each switch assembly including a pushbutton key having a first guide formation, a key surround having a second complemental guide formation, an elastically deformable keymat, and locating means for locating and anchoring the keymat relative to the surround, whereby the pushbutton key is arranged to travel reciprocally within the surround between a raised position and a depressed position, with the keymat being arranged to return the key to the raised position, and the first and second guide formations being arranged to restrict the key to a predetermined path throughout its reciprocal travel, and further including mechanical mounting means arranged to detachably engage with complemental apertures defined in the printed circuit board, said pushbutton key carrying at least one electrically conductive contact arranged to bridge a corresponding contact array on the circuit board when said pushbutton key is in said depressed position.

By the term "switchboard" is meant any circuit board populated with a plurality of pushbutton switch assemblies.

Brief description of the drawings

Figure 1 shows an exploded top perspective view of a first embodiment of a pushbutton switch assembly ofthe invention;

Figure 2 shows an exploded bottom perspective view ofthe pushbutton switch assembly of Figure 1;

Figure 3 shows an assembled top plan view ofthe switch assembly of Figures 1 and 2;

Figure 4 shows an assembled underplan view ofthe switch assembly of Figures 1 and 2; Figure 5 shows a cross sectional side view of the switch assembly along the line 5-5 of Figure 3;

Figure 6 shows a cross sectional side view along the line 6-6 of Figure 3;

Figure 7A shows a cross section similar to that of Figure 5 with the switch assembly in a raised position mounted in position on a pcb;

Figure 7B shows a cross section ofthe switch assembly in the lowered position;

Figure 8 shows an exploded top perspective view of a second embodiment of a pushbutton switch assembly ofthe invention; and

Figure 9 shows an exploded bottom perspective view of the switch assembly of Figure 8.

Detailed description of the embodiments

Referring first to Figures 1 and 2, a first embodiment of a pushbutton switch assembly 10 of the invention comprises a key surround 12, a pushbutton key cap 14, a keymat 16 and a divider 18. The key surround 12 is formed with upper side walls 20.1, 20.2, 20.3 and 20.4 having rounded corner edges 22, and defining an opening 24 having a central axis 26. The side walls 20.1-20.4 extends from corresponding base walls 24.1 to 24.4, with outer and inner respective shoulders or lands 27 and 28 extending between the upper and lower walls. A pair of locating legs 30 and 32 extend from opposite rounded corners 34 of the base walls, and terminate in projecting feet 36. Locating tabs 38 project from the midpoints of the lowermost edges of the base walls 24.1 to 24.4.

The keymat 16, which is injection moulded from a translucent elastomeric silicone rubber material, has a pushbutton key portion 40 from the base of which a sprung web or membrane 42 of reduced thickness extends, with the web terminating in an outer peripheral base 44. The pushbutton key portion 40 is substantially cubic in form, having an uppermost labelling surface 46 and four square cylindrical side faces 48, and defining a central axis of symmetry 26.1. The cap 14 is arranged to fit over the pushbutton key portion 40 in a snug complemental fit and is formed from a hard transparent plastics material such as a transparent scratch resistant acrylic, with the base of the cap terminating in a skirt 52. The cap has an axis of symmetry 26.2. An arrangement of four conductive carbon pips 54 are located on integral pillar formations 56 extending from the lowermost corners of the pushbutton key portion 40. The pips 54 serve as the switch contacts. The divider 18 is arranged to divide the cavity 58 defined with the pushbutton key portion 40 into sub-chambers 58.1 and 58.2 for housing indicator led's, and locates within slot formations 60. A peripheral channel 62 is defined within the base 44, and four locating apertures 64 are provided within the channel for receiving the corresponding four tabs 38. The corner apertures 66 receive the legs 30 and 32, as is clear from Figures 3-6. The channel and the locating and corner apertures in conjunction with the corresponding feet and tabs serve to anchor and locate the keymat firmly relative to the surround. Referring now to Figures 3-6, the assembled pushbutton switch assembly 10 can be hand assembled or can be assembled together on a relatively simple jig. The cap 14 is first inserted over the pushbutton key portion 40 to define in combination the pushbutton key. The assembled keymat and cap are then inserted from below into the opening 24, with the legs 30 and 32 extending through the corner apertures 66, the tags 38 passing through the intermediate apertures 64, and the lowermost edges of the side walls 24.1 to 24.4 locating snugly within the channel 62. The divider 18 is subsequently added by inserting it between the slot formations 60.

It is clear from Figures 5 and 6 how the assembled pushbutton switch defines a main central axis 70 comprising the coaxial axes 26, 26.1 and 26.2. The outer surface 52.1 of the skirt 52 abuts against the inner shoulder 28 defined within the surround to define the limit of upward movement of the pushbutton key. In the particular embodiment, the outer surface 52.1 is angled at approximately 100° relative to the outer surface 74 of the sidewall of the cap, resulting in point contact between an outer edge 28.1 of the shoulder 28 and the surface 52.1. Point contact between the engaging surfaces of the skirt and surround is desirable, compared to more intimate contact if the engaging surfaces were parallel, because it can prevent the switch from sticking. This adjusts the "feel" of the switch, in the sense that there is a "click-up/click- down" response.

The pushbutton is moveable from the" uppermost raised position illustrated in Figures 5 and 6 to a depressed position illustrated in Figure 7B in which the contact pips 54 bridge corresponding labyrinthine contacts 71 on the upper surface of the pcb 72. There is a small clearance 73 of about 0.1mm between the outer surfaces 74 of the side walls of the cap 14 and the inner surfaces 76 ofthe upper side walls 20.1 to 20.4 ofthe surround 12. This is sufficient to allow unrestricted movement in the direction of arrows 78, whilst at the same time ensuring that the path of travel of the pushbutton assembly 14 and 40 relative to the surround is essentially coaxial with the axis 70. The piston-and-cylinder-type relationship between the square cylindrical aperture 24 of the surround and the complemental square cylindrical outer surfaces 74 of the walls the cap 14 ensure that lateral deviation or wobble of the pushbutton assembly is kept to a minimum during both forward and reverse directions of travel. The switch accordingly has a relative long and guided travel 79 of typically 1-1.5mm, in line with the aforementioned more costly mechanical pushbutton switches. In Figure 7 A, the pushbutton switch assembly 10 is shown mounted in position on the pcb 72, with the outwardly angled legs 30 and 32 extending through corresponding pairs of circular apertures 79A drilled through the pcb, and each foot 36 locating in a removable click fit against the undersurface of the pcb 72. Repositioning of the switch is easily effected by squeezing the diagonally opposed feet towards one another to clear the passage of the feet through the apertures in the pcb. It will be appreciated that other types of demountable formations may be used, which typically rely on a snap or click fit. Led clusters 80 and 81 are mounted on the pcb 72 in such a way that they occupy different sub-chambers 58.1 and 58.2 defined by the divider 18, which is opaque. The pushbutton switch portion 40 ofthe keymat 16 is translucent, and the inner surfaces of the respective top and side walls 46 and 48 meet at a relatively small corner radius 82, thereby maintaining the uniform thickness of the upper wall 46 and allowing for even distribution of light through this wall.

The upper surface of the wall 46 may be provided with positive or negative text or graphics on a thin printed film which is interposed between the wall -46 and the underside ofthe cap 14. In this way, the switches may be manufactured in a "blind-until-ready" mode. Functionality can easily be changed merely by replacing the printed film. Mass produced uni- functional keys may also have insignia printed directly on the upper surface of the wall 46. In both cases, the protective cap 14 prevents wear of the insignia. In one version of the invention, the skirt 52 of the cap may be removed. For relabelling purposes, the cap can accordingly simply be pulled off the pushbutton key portion 40 without having to disassemble the switch or to remove the fascia plate. A new label, typically printed on clear plastic, can be fitted inside the cap and the cap can simply be replaced. Whilst certain of the "feel" qualities of the switch are lost due to this modification, the advantages of being able to relabel the switch in the field in many cases outweigh the loss of quality. To increase the security ofthe fit, locating formations can be provided on the inner surface of the cap and the outer surface of the pushbutton key portions to provide an interference fit. By virtue ofthe opaque divider 18, the led clusters 80 and 81 illuminate different halves of the pushbutton which may carry different indicia. The clusters may comprise different led elements, such as rgb led's, with variation in colour used to indicate different modes of operation. An important feature is that the led clusters are also able to provide different light levels. In particular, the led clusters may be off (indicating that the key is non-responsive), dim (indicative of the key being in the standby mode in which it is responsive to actuation) and on full, indicating that the key has been depressed and, depending on the colour of the light transmitted through the upper face of the pushbutton and the indiciae being illuminated, this indicates the particular function that the key is currently performing. A significant advantage of this feature when applied to individual switch assemblies is that the status and functionality of individual keys can readily be indicated and controlled, as opposed to a conventional keymat cluster in which the enabled key dim function extends to the entire cluster.

The rubber web or membrane 42 that provides the return spring mechanism is significantly quieter than that of a mechanical switch, whilst still retaining a positive feel. This is particularly useful in the case of audio and medical applications. The deformation of the rubber web has three phases. Initially, depressed force is proportional to the downward movement ofthe pushbutton. At the point that the silicone membrane or web collapses, there is a relatively rapid movement of the pushbutton and corresponding reduction in the actuation force. At the point indicated in 7B where the pushbutton contact pips 54 connect with the corresponding contacts on the pcb, electrical connection is established, and the actuation force rises relatively rapidly, with virtually no further movement of the switch occurring. The combination of these three phases of actuation provide the switch with a good "feel", in conjunction with the wobble- limiting guide formations. The manner in which the base of the keymat is firmly located in position via its channel and leg apertures stabilises the keymat and minimises lateral deviation of the keymat and ensures that each switch assembly delivers a uniform response. In contrast, a keymat for a large array of keys provides differing responses in respect of corner, side and central keys. The relationship between the actuation force and the movement ofthe pushbutton key can be altered by addition in the hard plastics mouldings ofthe surround and the cap of click formations. These may be in the form of integral protrusions which are arranged to provide audible clicks at appropriate points in the movement as they pass one another. Referring now to Figures 8 and 9, a second embodiment of a pushbutton switch assembly 90 is shown comprising a surround 92, a cap 94 and keymat 96 having a pushbutton key portion 98. The key portion 98, the cap 94 and the corresponding aperture 100 through the surround have a racetrack-type profile as opposed to the square profile of the previous embodiment. In addition, only two carbon contact pips 54.1 are provided. Numerous different profiles can be utilised, including circular and rectangular profiles and variations thereof. A general proviso is that the profiles should have cylindrical side walls or other guide means for preventing sideways wobble ofthe pushbutton relative to the surround.

One advantage of the pushbutton switch assembly of the invention is that the components can readily be injection moulded into any required profile. A further significant advantage of an embodiment of the pushbutton switch assembly of the invention lies in its unitary construction and a manner in which it is mounted to a pcb. The switch assembly may be deployed in any desired position over the surface ofthe pcb, depending on the layout thereof, thereby facilitating design changes. The switches may be mounted directly to the pcb prior to full assembly, and in particular prior to addition of the console or fascia plate 102, thereby allowing for testing to take place during the assembly process. In particular, a single switch may be moved from one mounting location to another during the testing phase, and prior to programming. Once testing has been finalised, the apertures 104 in the fascia plate may be formed. In contrast, prior art silicone keymat switches provide for a predetermined array or matrix of switches in fixed juxtaposition with one another. Pre-testing is limited, and any change to the layout of a circuit requires expensive and time consuming remoulding ofthe entire keymat and fascia plate.

In an alternative less preferred version of the invention, a mini-cluster of switch assemblies in, say, a 2x1 or 2x2 matrix maybe provided, with the surround being one-piece and being formed with locating feet and tabs for each switch. The keymat may also be one-piece, with corresponding locating apertures and channels being provided to ensure that each key operates totally independently of adjoining keys. It will be appreciated by the person skilled in the art that numerous modifications and/or variations may be made to the present invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.

Claims

1. A switch assembly including a pushbutton key having a first guide formation, a key surround having a second complemental guide formation, an elastically deformable keymat, and locating means for locating and anchoring the keymat relative to the surround, whereby the pushbutton key is arranged to travel reciprocally within the surround between a raised position and a depressed position, with the keymat being arranged to return the key to the raised position, and the first and second guide formations being arranged to restrict the key to a predetermined path throughout its reciprocal travel.

2. A switch assembly according to claim 1 wherein the pushbutton key has an outer cylindrical side wall, said first guide formation includes at least one face defined by the said outer cylindrical side wall, said key surround has a cylindrical side wall, and said second complemental guide formation includes at least one inner face defined by said cylindrical side wall.

3. A switch assembly according either one of the preceding claims wherein said predetermined path is a rectilinear path substantially coaxial with the central axes defined by the inner and outer cylindrical side walls.

4. A switch assembly according to any one of the preceding claims including mounting formations extending from said key surround for enabling the switch assembly to be mounted to a base such that said keymat is located between said surround and said base.

5. A switch assembly according to claim 4 wherein said mounting formations include non-conductive mounting legs terminating in feet arranged to form an interference or click fit with complemental apertures defined in. said base.

6. A switch assembly according to claim 5 wherein said legs extend through apertures defined in said keymat, and form part of said locating means.

7. A switch assembly according to any one of the preceding claims wherein said locating means includes an outer peripheral channel defined in said keymat within which locating projections extending from a base of said surround are arranged to locate.

8. A switch assembly according to any one of the preceding claims wherein said keymat includes a pushbutton key portion, an outer peripheral base and an elastically deformable web extending between said pushbutton key portion and said base, said web constituting a return spring for providing sprung movement between said pushbutton key portion and said base.

9. A switch assembly according to claim 8 wherein said pushbutton key includes a pushbutton cap arranged to fit over said pushbutton key portion, whereby an upper wall of said cap is transparent for protecting underlying switch labelling insignia.

10. A switch assembly according to claim 9 wherein said pushbutton key includes a skirt portion for holding said cap captive relative to a stop formation within said surround.

11. A switch assembly according to claim 9 wherein said cap is detachably mounted to said pushbutton key portion, and can be demounted therefrom without having to remove said surround, for enabling the switch assembly to be relabelled with different insignia.

12. A switch assembly according to any one claims 8 to 11 wherein an underside of said pushbutton key portion carries at least one electrically conductive contact arranged to bridge a corresponding contact array on the base when said pushbutton key is in said depressed position.

13. A switch assembly according to claim 12 wherein said pushbutton key portion carries at least one and preferably two electrically conductive contact pips.

14. A switch assembly according to any one of claims 8 to 13 wherein said pushbutton key portion is substantially translucent and defines a chamber for accommodating at least one illumination source.

15. A switch assembly according to claim 14 wherein said chamber includes a divider defining two sub-chambers for accommodating separate and differently coloured illumination sources.

16. A switch assembly according to claim 10 wherein an engaging surface of said skirt portion that engages said stop formation within said surround is inclined with respect to a corresponding engaging surface of said surround, whereby an edge comer of said stop formation establishes point contact with said skirt portion.

17. A switch assembly according to any one of the preceding claims wherein said switch assembly can be moved and repositioned independently, and does not form part of an integral switch matrix or array.

18. A switch assembly including a pushbutton key having a first guide formation, a key surround having a second complemental guide formation, an elastically deformable keymat, and locating means for locating and anchoring the keymat relative to the surround, whereby the pushbutton key is arranged to travel reciprocally within the surround between a raised position and a depressed position, with the keymat being arranged to return the key to the raised position, and the first and second guide formations being arranged guide the key throughout its reciprocal travel, and wherein mounting formations extend from said key surround for enabling the switch assembly to be detachably mounted to a complemental array of apertures defined in said circuit board, with the keymat being sandwiched between said surround and said circuit board.

19. A switchboard including at least one circuit board populated with a plurality of switch assemblies according to any one of claims 1 to 18, and an overlying fascia plate or console having switch openings defined therein through which the pushbutton keys project.

20. A switchboard including at least one circuit board carrying a plurality of switch assemblies, each switch assembly including a pushbutton key having a first guide formation, a key surround having a second complemental guide formation, an elastically deformable keymat, and locating means for locating and anchoring the keymat relative to the surround, whereby the pushbutton key is arranged to travel reciprocally within the surround between a raised position and a depressed position, with the keymat being arranged to return the key to the raised position, and the first and second guide formations being arranged to restrict the key to a predetermined path throughout its reciprocal travel, and further including mechanical mounting means arranged to detachably engage with complemental apertures defined in the circuit board, said pushbutton key carrying at least one electrically conductive contact arranged to bridge a corresponding contact array on the circuit board when said pushbutton key is in said depressed position.