Light guide for illuminating the display or keyboard of a portable communication device

Abstract: A communication unit including a light guide for illuminate the display including a substantially transparent plate-formed element with reception means for receiving light from respective light sources and to guiding the light into the transparent plate-formed element of the light guide. The reception means includes light in-coupling surfaces facing towards respective light sources and being substantially parallel with the main surface of the light guide, and means, a lens and a diffuser, for dispersing the light substantially parallel with the main surface of the light guide to illuminate the display. The light guide has also means for illuminate the keyboard. These means includes that the keyholes have chamfered surfaces for reflecting the light in the light guide perpendicular to the surface of the light guide onto the keyboard. The light guide also incorporates a dome sheet attached to the light guide including a reflector sheet, flexibly attaching the keyboard to the light guide.

Description: The invention relates to communication units having a light guide for guiding light from a light source to illuminate a display. Light guides are also used to transfer light from a light source to illuminating the keyboard/keys. In mobile phones the light guide is placed between a printed circuit board and the display and/or the keyboard to transfer the light from a light source, e.g. an LED, to illuminate the display or/and the keyboard. This is e.g. shown in US 5 746 493, where a light guide is described having a plurality of light coupling recesses. Some of the light coupling recesses are placed between keyholes on the light guide, where the LEDs mounted on a printed circuit board sticks up, and transfer through the light guide light for illuminating mainly the keyboard and partly the display. On one side of the light guide are the light coupling recesses arcuately shaped to transmit light from the LED uniformly into the light guide. Another approach of illuminating a keyboard is shown is US 5 711 588, where the light is reflected on a cover, mounted over the keys of a keyboard assembly, into the keys. In this case a light guide is not needed, nor is there a need for a light source for each key on the keyboard. Yet another approach is shown in US 5 847 336, with one LED for each key to illuminate the keys directly. The LEDs are mounted on a flexible film, which is placed directly under the keyboard. Between this flexible film and the printed circuit board there is a dome sheet with domes that short-circuit a pair of electrical contacts on the printed circuit board, when pressing the keys. This approach is not used to illuminate the display, just the keyboard. Still another approach is described in US 5,708,428, where LEDs are embedded, by insert moulding, directly into the light guide. The light guide is placed between the keyboard and printed circuit board, having aperture for permitting the conductor on the bottom of each of the keys to contact respectively positioned contacts on the printed circuit board. Furthermore, JP 9287971 describes a device for guiding the light from a substantially linear light-emitting element into a photo-conducting plate, without increasing the thickness of the plate. To manage to transmit the light without having a thicker plate a lens is used more exactly a Fresnel lens. EP-A-0 414 366 discloses a light guide for illuminating a keyboard or keypad from behind, which comprises a transparent grid-like plate having an array of apertures each of which accommodates a key. The plate has an integral lens aligned with a reflector for directing light from an external source into the plane of the plate. Document US-A-5 130 897 discloses a light guide according to the preamble of claim 1. According to the invention there is provided a light guide according to claim 1. Preferred embodiments of the invention are set out in the dependent claims. The invention will be explained more fully below, by way of example, in connection with preferred embodiments and with reference to drawing, in which: Fig. 1-2 shows in a perspective view a preferred embodiment of the communication unit according to the invention. Fig. 3 schematically shows the essential parts of a telephone for communication with a cellular network. Fig. 4-5 shows in a perspective view a light guide. Fig. 6 shows a front view of the light guide, where several cross-sections has been indicated. Fig. 7 shows cross section A - A of the light guide. Fig. 8 shows cross section B - B of the light guide. Fig. 9 shows cross section C - C of the light guide. Fig. 10 shows a front view of the light guide, where cross section D - D has been indicated. Fig. 11 shows cross section D - D of the light guide. Fig. 12 shows in a perspective view the upper side of the light guide with a plastic dome sheet applied. Fig. 13 shows in a perspective view the lower side of the light guide with a plastic dome sheet applied. Fig. 14 shows in a perspective view the plastic dome sheet with a reflector sheet. According to a first aspect the communication unit according to the invention will be described with reference to a hand portable phone, preferably a cellular phone. A preferred embodiment of this phone is shown in fig. 1 and 2. The phone is shown in perspective with the front in fig. 1 and with the back fig. 2. As will be seen, the phone is provided with a front cover 2 having a window frame 3 encircling the protection window of the display assembly 1. The phone comprises a user interface having an on/off button 4, a keyboard/keypad 7, a battery 11, a display/LCD 1, an earpiece 21 and a microphone 22 (not shown in fig. 1 or 2). Fig. 3 schematically shows the most important parts of a preferred embodiment of the phone, said parts being essential to the understanding of the invention. The microphone 22 records the user's speech, and the analogue signals formed thereby are A/D converted in an A/D converter (not shown) before the speech is encoded in an audio part 20. The encoded speech signal is transferred to the controller 18 (physical layer processor), which e.g. supports the GSM terminal software. The controller 18 also forms the interface to the peripheral units of the apparatus, including RAM and ROM memories 17a and 17b, a SIM card 16, the display 1 and the keyboard 7 (as well as data, power supply, etc.). The controller 18 communicates with the transmitter/receiver circuit 19. The audio part 20 speech-decodes the signal, which is transferred from the controller 18 to the earpiece 21 via a D/A converter (not shown). The preferred embodiment of the phone of the invention is adapted for use in connection with the GSM network, but, of course, the invention may also be applied in connection with other phone networks. It could be cellular networks, various forms of cordless phone systems or in dual band phones accessing sets of these systems/networks. The controller 18 is connected to the user interface. Thus, it is the controller 18, which monitors the activity in the phone and controls the display 1 in response thereto. Therefore, it is the controller 18, which detects the occurrence of a state change event and changes the state of the phone and thus the display text. The user may cause a state change event, when he activates the keyboard 7 including the navigation key 10, and these type of events are called entry events or user events. However, the network communicating with the phone may also cause a state change event. These type of events and other events beyond the user's control are called non-user events. Non user events comprise status change during call set-up, change in battery voltage, change in antenna conditions, message on reception of SMS, etc. In fig. 4 is a light guide 30 for illuminating a display 1 or a keyboard 7 shown, which includes a substantially transparent plate-formed element. The transparent plate-formed element has reception means 35 for receive light from respective light sources (not shown) and to guide the light into the transparent plate-formed element of the light guide 30. The transparent plate-formed element comprises a first part 32 of the light guide being a back screen for a display and a second part 33 being a keyboard part. The light guide 30 could be made of a plastic material or other substantially transparent materials. The keyboard part includes a plurality of keyholes 34 and reception means 35. The reception means 35 includes a plurality of light in-coupling surfaces 35, which faces towards respective light sources (not shown). The light in-coupling surfaces 35 are substantially parallel with the main surface of the light guide 30 and transfers the light from a light source (not shown) located under each light in-coupling surface 35 into the light guide 30. The light in-coupling surfaces 35 have means for dispersing the light substantially perpendicular to the direction of the light source (not shown) to illuminate the display 1. The means for dispersing the light from the light source into the light guide 30 is a lens 37 and a diffuser 38 (see fig. 7). The lens 37 is preferably concave and the light source (not shown) could be an LED. In fig. 7 is shown that the lens 37 and the diffuser 38 are together almost not as thick as the light guide 30. The tangent of the central part of the lens is parallel with the surface of the light guide 30, which is closest to the light source (not shown). This means that the thickness of the light guide 30 does not have to be thicker than the diffuser/lens, which enables having a thinner light guide, 30 and less material. This light guide 30 is also more efficient since the lens 37 and the diffuser 38 transfer a very large portion of the light from the light source (not shown) to the light guide 30. In earlier known light guides, like the one shown in US 5 746 493, the light is transferred directly from the LED into the light guide, giving a larger energy loss. In this document LEDs are also used, which extends through the whole light guide increasing the possible lost of energy. The light guide 30 could also be used to illuminate the keyboard 7. The light transferred from the diffuser substantially parallel to the surfaces of the light guide 30 is reflected at the keyholes 34 by a chamfered surface 39 in the keyholes 34. The chamfered surface 39 reflects the light in the light guide 30 perpendicular to the surface of the light guide 30 onto the keyboard 7. The light in-coupling surfaces 40 closest to the first part 32 being a back screen for a display 1 has means to ensure that a maximum of the light from the light source (not shown), e.g. LED, is transferred into the first part 32 of the light guide 30. The light source (not shown) is located under said light in-coupling surface 40, mounted on a printed circuit board (not shown). These means are a diffuser 42 that stretches to one end of the lens 43, transferring the light from the lens to be substantially transferred into the first part. The light guide 30 comprises an upper side turning towards the keyboard 7 and the display 1 and a lower side turning towards a printed circuit board (not shown). In fig. 12 and 13 is a light guide 30 shown having a plastic dome sheet 50 attached on to one side of the light guide 30, the lower side of the light guide. The plastic dome sheet 50 is provided with metal domes 51 on the side not attached to the light guide, which are affected by pressing the keys 8 to short-circuit a circuit/switch, corresponding to each key 8, on a printed circuit board (not shown). The dome sheet 50 is also provided with a plurality of holes 52 through which the light reaches the light in-coupling surfaces 35 on the light guide, otherwise the light from the light sources (not shown) would not pass through the plastic dome sheet 50. The part of the plastic dome sheet 50 that covers the first part 32, being the back screen for the display 1, includes a reflector sheet 53 for improved the illumination of the display. In fig. 14 is sown the plastic dome sheet 50 with the reflector sheet 53. The plastic dome sheet 50 is glued onto the light guide 30 with an adhesive. This adhesive is also applied to the plastic dome sheet 50 surfaces that covers the keyholes 34 to flexibly attach the keyboard 7 to the light guide 30. The keyboard 7 is therefore, when the phone is disassembled, attached to the light guide 30 and there are fewer loose parts. The keyboard 7 is also easily replaced if necessary. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the claims.

Claims: A light guide (30) for illuminating a display (1) or a keyboard (7) including: a substantially transparent and substantially planar element with reception means (35) for receiving light from respective light sources and for guiding the light into the element, wherein the reception means (35) includes: light in-coupling surfaces substantially parallel to the plane of the light guide and arranged to receive the light from the respective light sources; and means (37, 38) for dispersing the light substantially parallel to the plane of the light guide, the light guide further including a plastic dome sheet (50), characterised in that : the plastic dome sheet (50) is attached to one side of the light guide and is provided with through holes (52) for allowing the light from the light sources to reach the element, the plastic dome sheet further comprising a reflector sheet (53). A light guide according to claim 1, wherein the domes (51) of the plastic dome sheet are metal domes to enable completion of a circuit on a printed circuit board on which the domes are arranged to be received. A light guide according to claim 1 or 2, further comprising means for flexibly attaching the keyboard (7) to the dome sheet (50). A light guide according to claim 3, wherein said flexible attaching means comprises an adhesive that holds each key (8) of the keyboard onto the plastic dome sheet (50). A light guide according to any one of the preceding claims, wherein the means for dispersing the light comprises a lens (37) and a diffuser (38), and wherein the element comprises keyholes (34) for receiving the keys (8) of the keyboard (7), wherein the keyholes have chamfered surfaces for reflecting the light in the light guide perpendicular to the plane of the light guide. A light guide according to any one of the preceding claims, wherein the light guide comprises a keyboard supporting portion (33) and a display supporting portion (32), the reflective sheet (53) being arranged to cover the display supporting portion (32). A light guide according to claim 6, wherein the in-coupling surfaces on the keyboard supporting portion (33) closest to the display supporting portion (32) have means for transferring light into the display supporting portion (32) of the light guide. A light guide according to claim 7, wherein said light transferring means comprises a diffuser that stretches to one end of a lens, transferring the light from the lens into the display supporting portion (32). A communication unit including a light guide according to any one of the preceding claims.

Inventors: MESSEL ALTE, MESSEL, ALTE
Applicants: NOKIA CORP, NOKIA CORPORATION
Application year: 2000
Main classification: H01H13
IPC codes: H01H13, H04M1