GB2238663A

GB2238663A - Electrical push-button switch

Info

Publication number: GB2238663A
Application number: GB9025835A
Authority: GB
Inventors: Alan Dewhurst
Original assignee: DEWHURST PLC
Current assignee: DEWHURST PLC
Priority date: 1989-11-28
Filing date: 1990-11-28
Publication date: 1991-06-05
Also published as: GB8926839D0; GB9025835D0; CA2030698A1

Abstract

An illuminated electrical push-button switch for use in lift controls comprises a spring biased pushbutton having an opaque disc 11 mounted on a light transmitting moulding 10 which has a cylindrical portion 23 slidable in a circular section channel 48 of a frame 19. A clearance 18 formed at least part way round the cylindrical portion 23 of the pushbutton is illuminated by a light source 3. Locating means which may be in the form of at least one registration member on the pushbutton cooperating with a slot in the frame 19 accurately locates the disc 11 - and therefore any indicia or legend on the disc's surface - at the correct angular position relative to the frame 19 and maintain it in that position during operation. <IMAGE>

Description

Electrical Push-Button Switch The present invention relates to electrical push-button switches and more particularly to illuminated switches.

Push-button switches are well known and have a number of uses. In recent times, it has become customary for lift or elevator controls to be by way of illuminated switches, the illumination indicating that the depression of the pressel of the push-button switch has been registered. It has also become common to have vandal proof or weather proof push-button switches with wear or weather resistant surfaces eg. of metal.

Illumination by means of a "halo" of light appearing in the gap between the periphery of the pressel and the surrounding bezel has been described in our UK patent no. 1456391. It is also now usual to have indicia or a legend provided on the surface of the pressel. The surface can be cut so that the indicia is illuminated from the back in addition to or as an alternative to the "halo" illumination. A problem arises when the pressel is of circular configuration as it is important that the legend on the surface of the pressel is in a precise position with respect to the body of the push-button switch so that when a number of push-button switches are arranged in rows and/or columns there is an accurate alignment of the legends.

The present invention provides an electrical push-button switch, comprising: a frame having a channel of circular crosssection; at least one pair of electrical switch contacts; a pressel depressable against spring bias to switch the contacts, the pressel having a disc-shaped opaque surface layer provided on a light-transmissive moulding, the moulding having a cylindrical portion which is slidably movable in the channel relative to the frame, with a clearance at least part way round said portion, whereby the clearance may be illuminated by a light source disposed at the rear of the pressel; locating means for accurately maintaining the opaque surface layer at a pre-determined angular position relative to the frame.

Preferably, the push-button is illuminated and the surface of the pressel is flush with the surrounding plate.

In order that the present invention be more readily understood, an embodiment thereof will now be described by way of example by reference to the accompanying drawings in which: Fig. 1 shows a sectional view of an electrical push-button switch according to the present invention; Fig. 2 shows a side view of the electrical push button switch according to the present invention; Figs. 3(a) to (d) respectively show side, frontal, sectional elevation and rear views of a pressel of the push-button switch according to the invention; and Fig.- 4 shows (a) top and (b) sectional elevation views of a co-operating frame within which the pressel of Fig. 3 is arranged to slide.

A detailed description of an illuminated electrical push-button switch is not given in the present application in its entirety, and attention is directed to our UK patent no. 1456391 for full details of the construction and how illumination is achieved.

The principle difference between the construction shown in our earlier patent and the present construction is that the face plate of the pressel is circular rather than generally square.

Referring now to Figs. 1 and 2, the switch apparatus shown comprises a stainless steel frame 19 having an aperture provided with a metal rim 2 and a pressel comprising a stainless steel disc 11 and a main body part 10 of transparent plastics material, which may be coloured as desired, on which the disc 11 is mounted.

The disc 11 fits in the aperture left by the rim 2 with a clearance 18. A light bulb 3 mounted behind the main body part 10 illuminates the main body part and hence the clearance 18 through a margin on the main body part 10 provided by two-peripheral shoulders 13 and 15 on the main body part 10. The frame 19 rim 2 and disc 11 are all of metal, and hence are not light transmissive; the effect for an observer when the bulb 3 is illuminated is of an illuminated border or halo around the disc 11. As shown in Fig. 1, the main body part 10 has a peripheral skirt 23 on which the shoulders 13 and 15 are formed.

The surfaces of the skirt 23 are smooth apart from the shoulders 13 and 15, so that the skirt guides the light to the shoulder 13, where it escapes.

The light bulb 3 is mounted in a housing 24 which bears on its sides electrical switch elements 26 and 28 having plungers 30 and 32 by which the switch elements may be actuated. The main body part 10 has lugs 34 and 36 projecting laterally therefrom, with studs projecting from the lower sides thereof (as seen in Fig. 2) for engaging and depressing the plungers 30 and 32 on depression of the push button, to actuates the switch elements. Compression coil springs encircling the plungers 30 and 32 normally bias the push button to the position shown in Figs. 1 and 2.

The rim 2 is preferably chromium plated metal and is partly embedded in a support of plastics material 46 which can be formed by injection mounting. The housing 24 and support member 46 are secured to the back of the frame 19 by studs 50 and 52 which are welded to the back of the frame 19.

The support 46 also provides a channel 48 in which the skirt 23 slides with a clearance between 0.003 inches and 0.009 inches when the button is centered in the rim 2.

The width of the shoulder 13 is nominally 0.23 inches which prevents the disc 11 touching the rim 2 and is sufficiently wide to provide a readily visible halo.

The clearance between the edge of the shoulder 13 and the rim 2 is less than 0.025 inches to prevent the insertion of most common objects and in the preferred embodiments is between 0.006 inches and 0.012 inches when the button is centered in the rim 2. The maximum clearance between the disc 11 and the rim 2 is less than 0.050 inches to prevent the insertion of the majority of the more robust common objects and to minimize damage by fire, the heat sink effect of the metallic parts being of advantage in this respect By way of comparison, the disc 11 is, for example, approximately 1 inch in diameter in the preferred embodiment.

Although the shoulder 13 and 15 are shown encircling the disc 11 and this is currently preferred at least the shoulder 13 could extend only part way round the disc, the clearance between the disc and the rim 2 being correspondingly reduced on one or more sides.

Turning now to Fig. 3 of the drawings, the pressel comprises a cylindrical main body part 10 made of coloured transparent plastics material. An opaque circular disc 11 is provided on the top surface of the member 10. Tabs 12, only one of which is shown in the drawing, serve to fix the disc 11 onto the surface of the member 10. A legend (the numeral "1" in Fig. 3(b)) can be cut into the external surface of the disc 11.

The legend may be cut either completely through the disc so as to expose the coloured plastics material or can simply be cut partially through the disc.

Turning now to Fig. 4 this shows the construction of a frame within which the pressel shown in Fig. 3 fits and is arranged to slide. Fig. 4(b) shows a sectional veiw at BB1 in Fig. 4(a). The frame 19 provides a circular cylindrical portion which is arranged to house the circular cylindrical portion of the main body part 10 of the pressel. The cylindrical portion 20 of the frame is provided with one or more slots 21 whose use will be described in more detail later. The diameter of the bore of the cylindrical section 20 is very slightly larger than the external diameter of the cylindrical part 10 of the pressel to permit smooth operation thereof.

It will be appreciated that due to the clearances, there is the possibility that the pressel will not be located accurately in the cylindrical bore of the portion 20 and for this reason guide means are provided to ensure accurate angular positioning of the disc 11 on the pressel with respect to the body of the frame of the push-button. This is achieved by having one or more registration members 14 on the pressel. The registration member(s) may comprise members attached to the rear surface of the disc 11 prior to moulding the coloured transparent plastics material. The registration member 14 is formed by one or both tabs 12 having a portion which projects beyond the periphery of the opaque disc 11 and moulding the pressel around the projecting portion.

The tabs 12 may be unitary as shown in Fig.

3(c) w may be made from a plurality of parts. Although it is more difficult to manufacture, the tabs 12 may project through the moulded cylindrical side of the wall of the pressel.

The registration member is arranged to project from the cylindrical side wall of the part 10 at a level below that of a shoulder 15 (Fig. 3) and to co-operate with the slot 21 in the frame member 19.

The number and disposition of registration members can be varied depending on the actual use.

Claims

CLAIMS:

1. An electrical push-button switch, comprising: a frame having a channel of circular crosssection; at least one pair of electrical switch contacts; a pressel depressable against spring bias to switch the contacts, the pressel having a disc-shaped opaque surface layer provided on a light-transmissive moulding, the moulding having a cylindrical portion which is slidably movable in the channel relative to the frame, with a clearance at least part way round said portion, whereby the clearance may be illuminated by a light source disposed at the rear of the pressel; locating means for accurately maintaining the opaque surface layer at a pre-determined angular position relative to the frame.

2. An electrical push-button switch according to claim 1, wherein: said locating means includes one or more registration members provided on said pressel.

3. An electrical push-button switch according to claim 2, wherein: said locating means includes, for each registration member, a slot in the wall of said channel which is parallel to the length of elongation of said channel, each slot being slightly larger in width than its respective registration member to permit sliding movement of said registration member therein.

4. An electrical push-button switch according to claim 3, wherein: said one or more slots are provided at predetermined positions in the wall of said channel whereby said disc is maintained in said pre-determined angular position relative to said frame during operation of said pressel.

5. An electrical push-button switch according to any of claims 2 to 4, wherein: said one or more registration members comprise a tab fixedly attached to the rear of the opaque surface layer and projecting beyond the periphery of the opaque surface layer.

6. An electrical push-button switch according to any of the preceding claims, wherein: said opaque surface layer includes a legend provided thereon by cutting wholly or partially through the layer.

7. An electrical push-button switch according to any of the preceding claims, wherein: said moulding comprises a transparent coloured plastics material.

8. An electrical push-button switch according to any of the preceding claims, wherein: the frame includes a ledge adjacent the channel, and the pressel includes a shoulder which normally engages the ledge to impede of foreign matter through the clearance.

9. An electrical push-button switch according to any of the preceding claims, wherein: the pressel includes a further peripheral shoulder adjacent the opaque surface layer.

10. An electrical push-button switch according to any of the preceding claims, wherein: the opaque surface layer and/or a face plate of the frame are made of steel.

11. An electrical push-button switch according to any of the preceding claims, further including: a mounting for a source of light to be disposed at the rear of the pressel.

12. An electrical push button switch substantially as hereinbefore described with reference to Figures 1 to 4 of the accompanying drawing.