Note: Descriptions are shown in the official language in which they were submitted.
~145870
This invention relates to a lighted telephone dial of the
pushbutton type, with illumination by means of a plurality of light
emitting diodes (LEDs) with a flat light-guide plate, the buttons being
illuminated or glowing.
Various arrangements exist for illuminating dials, generally
including incandescent lamps mounted below the dial, or lamps of LEDs
mounted in the pushbuttons. Two main disadvantages of such systems are
the power requirements, and, in the case of incandescent lamps, space,
particularly when mounted below the dial. With the present development to
thinner dial assemblies, use of incandescent lamps is no longer possible.
The present invention provides a pushbutton dial assembly in
which the buttons are illuminated by light transmitted laterally via a
light-guide plate from a small number of LEDs, less than the number of
buttons, the guide-plate having apertures through which the buttons pass,
light being transmitted across from the plate to each button. Each button
is translucent and glows, being readily visible in the dark.
This invention will be readily understood by the following
description of certain embodiments, by way of example, in conjunction
with the accompanying drawings in which:-
Figure 1 is an exploded perspective view of a form of
pushbutton assembly incorporating the invention;
Figure 2 is a bottom plan view of one form of light-guide
plate;
Figure 3 is a cross-section on the line 3-3 of Figure 2;
Figure 4 is a side view in the direction of arrow A in
Figure 2;
Figure 5 is a side view of one form of an encapsulated LED
11~5~0
for use in the light-guide plate;
Figure 6 is a top plan view of the encapsulated LED of
Figure 5;
Figure 7 is a side view of another form of an LED positioned
in a recess in a light-guide plate;
Figures 8 and 9 are plan views of one form of lead frame for
use in supplying electric power to the LEDs, in the manufactured form
and final form respectively.
As illustrated in Figure 1, a pushbutton dial assembly
comprises, in a sandwich form, a printed circuit board (PCB) 10 having
thereon a conductor pattern 11 defining a plurality of switch positions
12, each position comprising a plurality of contact areas 13. On the PCB
10 is positioned a switch member 14 holding a plurality of spring contact
switches 15. In the example the switches are in strips of four and each
switch has a domed portion 16 and cantilevered contact members 17. The
switches are as described in U.S. patent no.l 4,029,916lissued June 14,
1~77, the disclosure of which is included herein by reference.
Over the switch member 14 and switches 15 is positioned a
thin flexible membrane 20. On the membrane rests a pushbutton member 21
which has a plurality of cantilevered pushbuttons 22. The pushbuttons
have a narrow clearance on three sides 23 and connected to the main member
by a hinge portion on the fourth side. This arrangement is also described
in the above-mentioned U.S. patent no. 4,029,916.
Pesting on the pushbutton member 21 is a light-guide plate
25. Plate 25 has a plurality of apertures 26, one for each pushbutton 22
and the pushbuttons extend up through the apertures. The form of
light-guide plate 25 will be described in more detail in conjunction with
l~S870
Figures 2, 3 and 4, but as seen in Figure 1 the plate 25 has recesses 27
for reception of LEDs and shaped grooves 28 which act as reflectors. Over
the light-guide plate 25 fits a bezel 30 having a plurality of apertures
31, an aperture for each pushbutton.
Various ways of holding the assembly together can be used.
As an example, protrusions molded on the back or under surface of the
bezel 30 can be passed through holes in the other members and the
protrusions molded over on the back or undersurface of the PCB 10. Some
means must be provided for supplying electric power to the LEDs in the
recesses 27. Leads can be brought out to one or more edges and connected
to the PCB or a lead frame can be positioned between the pushbutton member
21 and the light-guide plate 25, the LEDs mounted on the lead frames.
Figures 2, 3 and 4 illustrate in more detail the light-guide
plate 25. The plate is of transparent plastic material, for example an
acetyle copolymer, two examples of which are "Celion" acetyle copolymer by
Celanese Co. Ltd., and V52 by Rhome & Hass. The particular material
chosen in addition to being readily molded, is selected to have as high a
transmission value as possible for the emission wavelength of the LEDs.
Basically the light-guide plate 25 is a flat plate with the
plurality of apertures 26. The example of Figures 2, 3 and 4 is for what
can be termed a normal or conventional sized pushbutton dial. The
apertures 26 are arranged in four rows and three columns being
individually identified as 26a to 26Q. Four recesses 27a to 27h are
provided. The recesses 27 are positioned at intersections to rows and
columns. Thus, in the top two rows, in Figure 2, a recess 27a is formed
at the intersection between apertures 26a, 26b, 26d and 26e, and a further
recess 27b at the intersection between apertures 26b, 26c, 26e and 26f.
~4S870
Two further recesses 27c and 27d are positioned at similar intersections
between apertures 269, 26h, 26; 26k, and 26n 26i, 26k and 26Q
respectively. Thus, with four rows, each adjacent four apertures in the
top two rows are positioned around a recess 27 and each adjacent four
apertures in the bottom two rows are positioned around a recess 27. Thus
light emitted from the LEDs can travel inbetween the rows and between the
columns.
Grooves 28 are formed near the edges of the plate and act to
reflect light from the LEDs around the apertures 26. Thus, as seen in
Figure 2, each groove has one or more inward projections 35 having
rearwardly inclined inner surfaces 36. Behind the projections 35 are
inclined surfaces 37 which reflect light sideways along groove portions
38. The projections 35 are aligned with the recesses 27 and thus also the
LED's. While two grooves 28 are shown at each edge, these can be extended
to form a single groove at each edge.
Between each adjacent pair of recesses 27, at the top and
bottom of the plates, is a recess 39 and also further recesses 40 midway
between each central pair of recesses 27. These recesses 39 and 40 are of
a somewhat rectangular or diamond plan form and act to reflect light
sideways, the recess 39 reflecting light towards the apertures 26 of the
central column and the recesses 40 reflecting light sideways between rows.
Light is transmitted through all of plastic material, directly from the
LEDs and via reflection by grooves 28 and recesses 39 and 40, and thus
light is transmitted to all round the periphery of each aperture 26. At
the peripheries of each of the apertures 26, light is emitted across the
small gap between aperture periphery and the pushbuttons 22.
The pushbuttons 22 are of translucent or "milky" material
~L~45870
which "glows" as a result of the light being transmitted to it. The
material of the pushbutton member 21 is selected to be this translucent
form but also be easily moldable and have flexibility for the hinged
portions hingedly connecting the pushbuttons to the member. One such
material is a polycarbonate having a "milky" translucent colour.
Identifying numbers or emblems are formed on the top surface of each
pushbutton by a suitable process, as by printing filling shaped recesses
with coloured ink or plastic.
When the bezel 30, which is opaque, is in position the
light-guide plate cannot be seen. In the dark, or in a dim light, the
pushbuttons appear to glow, appearing separate and individual and readily
identifiable.
In Figures 2, 3 and 4 are shown spigots or projections 41
projecting from the rear face of the plate 25. These can pass through
holes in the pushbutton member 21, diaphragm 20, switch member 14 and PCB
10, being rivetted or molded over to form an assembly to which the bezel
30 can be attached. This is an alternative arrangement to that described
above and illustrated in Figure 1.
Figures 5 and 6 illustrate one form of encapsulated LED for
positioning in the recesses 27. An LED is shown at 50, with a power
limiting resistor at 51. Only the LED may be provided in the
encapsulation, the resistor being provided elsewhere, for example on the
PCB 10. Leads 52 provide for connection of electric power. The shape of
the encapsulation 53, is such as to fit closely in the recesses 27. A
reflecting top surface 54 is provided, the surface defined by a rotation
of an arcuate surface about the central axis. The arcuate surface may be
a true arc, or have a parabolic curve, or some other form. By this means,
~5~370
light emitted from the top surface of the LED is reflected sideways into
the light-guide plate.
Figure 7 illustrates an alternative form of encapsulated
LED. The LED 55, is encapsulated in an epoxy resin 56, and has two
contacts or leads 57. The encapsulated LED is positioned in a recess 27
and in this example, the recess has a conical top surface 5a. This
surface 58 reflects the light from the LED, which is surface emitting,
laterally into the light oxide plate 25. Instead of being conical, the
surface 58 can be made arcuate~ or approximating thereto.
Figure 8 illustrates a lead frame, conveniently of sheet
aluminum, stamped or etched from sheet or ribbon. Initially, to hold the
individual sections together for handling and storage case, bridge members
are provided. Thus, in Figure 8, one section of the frame extends to the
right of the chain dotted line 60, and indicated generally at 61, while
the other section, 62, extends to the left of the dotted line 60. However
two small sections 63 also form part of section 61. The LED positions are
indicated at 64. The bridge members are indicated at 65. Apertures for
the pushbuttons are indicated at 65.
The encapsulated LED's are attached to the lead frame by
spot welding the leads of the LED's to the lead frames. This is seen in
Figure 9, the LED's for example as in Figure 7, indicated at 56, the leads
57 welded to the lead frame. Once the LED's have been attached the bridge
members 65 are removed, also as seen in Figure 9. Finally, two
electrically conducting bridges or connections are made to electrically
connect sections 63 to section 61, these connections being indicated by
dotted lines 68. One way of making such connections is by first
positioning shsrt lengths of adhesive tape over the intervening parts of
1~458~0
section 62 and then soldering leads over the tape from sections 63 to
section 61. Connection is made to the lead frame by leads 69. The lead
frame is shown in its position in Figure 1, although other ways of
providing a power supply can be used, for example a conductive pattern on
the rear surface of the light guide-plate.
