Abstract:
Radiation from a collimated linear source ( 7, 8 ) is directed partly into a light guide structure ( 6 ) and partly glancing over the surface of the light guide structure ( 6 ). The radiation ( 15, 20 ) travelling inside the light guide is coupled out by micro-optical structures to illuminate the underlying reflective or superlying transmissive LCD. Radiation ( 17 A,  17 B) travelling across the surface outside the light guide ( 6 ) is directed towards an array of light sensitive detectors. Interruption of this radiation by a pen ( 21 ) or a finger ( 21 ) is detected and the position of the interruption is deduced.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to an input and a display device provided with an output screen and means for determining a position of a pointing device relative to a position at the output screen, said means for determining comprising elongated radiation sources along two substantially non-parallel sides of the output screen for radiating radiation in beams to opposing sides of the output screen, which beams are substantially parallel to a surface of the output screen. 
     Such a device is known from European patent application EP-A2-0.365.232 wherein is disclosed an integrated liquid crystal display with an optical touch panel. The elongated radiation sources comprise one or several conventional light emitting diodes arranged to emit a continuous beam of light along it&#39;s length. Additional illumination means are provided for illuminating the output screen. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an input and display device in which the generation of the light used for various purposes is simplified. 
     An input and display device according to the invention thereto is characterized in that a lighting system for the output screen is provided, which lighting system comprises a substantially flat light guide and in that the elongated radiation sources comprise means stretching along two substantially non-parallel end sides of the flat light guide for coupling radiation into the flat light guide, which means for coupling radiation into the flat light guide have radiation output windows with tangential dimensions larger than the thickness dimension of the flat light guide, which tangential dimensions are in a direction substantially orthogonal to a surface of the flat light guide, which surface of the flat light guide is substantially parallel to the surface of the output screen, and which means for coupling radiation into the flat light guide protrude above an upper one of said surfaces and have portions of the radiation output windows protruding above the upper one of said surfaces. 
     Thereby it is achieved that with a single light emitting element, such as a lamp or a light emitting diode both the lighting system for the output screen and the elongated radiation sources are provided with radiation. 
     A preferred embodiment of an input and a display device according to the invention is characterized in that at least one of the means for coupling radiation into the flat light guide comprises an elongated piece of the same material of which the flat light guide is comprised, which elongated piece is rotated over 90° about a longitudinal axis of the elongated piece relative to the orientation of the flat light guide. 
     Thereby it is achieved that from a manufacturing point of view a single flat element can be manufactured and subsequently be cut into pieces, one larger piece forming the flat light guide and two smaller pieces forming the means for both coupling radiation into the light guide and for providing beams substantially parallel to a surface of the output screen. 
    
    
     BRIEF DESCRIPTION OF THE INVENTION 
     The invention will now be described in more detail referring to the accompanying drawings in which: 
     FIG. 1 shows an input and display device; 
     FIG. 2 shows a lighting system according to the invention; 
     FIG. 2 a  shows a further lighting system according to the invention; 
     FIG. 3 shows a way of manufacturing a lighting system and elongated radiation sources from a single slab of material, and 
     FIG. 4 shows an application of a lighting system with a transmissive liquid crystal display. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In FIG. 1 there is shown an example of a hand held pc, electronic agenda or personal digital assistant, all hereinafter referred to as hand held pc. The hand held pc  1  comprises an output screen  2 , a casing  3  and two substantially non-parallel sides  4  and  5 . The output screen  2  displays information for reading by an observer. Almost all hand held pc&#39;s use reflective liquid crystal displays (LCD) because of the low power requirements of such displays. For use of those products in dark environments, where there is insufficient ambient light, an auxiliary illumination is required. This can for instance be realized with a so-called front lighting system, consisting of a side illuminated light guide placed on top of the display. In the light guide micro-optical structures are present which give a preferential out-coupling of the light towards a display. The light guide is indicated in FIG. 1 by reference number  6  and in case of the use of reflective LCD&#39;s for the output screen  2  is on top of the output screen  2 , i.e. between the output screen  2  and the observer. It is known, for example from U.S. Pat. No. 5,506,929 to make use of two point-like light sources. The radiation emitted by the point-like light sources is coupled into two elongated light pipes. The light pipes are provided with optical micro-structures which cause the light in the light pipes to be directed into the direction of a flat light guide, such as flat light guide  6  (FIG.  1 ). 
     FIG. 2 shows a preferred embodiment of a part of an input and display device according to the invention, in particular it shows the flat light guide  6  together with corresponding elongated radiation sources  7  and  8 . In the embodiment shown in FIG. 2 the elongated radiation sources  7  and  8  are identically of construction, so only one of them,  7 , will described in more detail. Elongated radiation source  7  comprises a point-like radiation source  9 , such as for example a light emitting diode. Radiation  10  emitted by the point-like radiation source  9  is emitted in the direction of a light pipe  11 . Light pipe  11  is disposed with a side  12  to an input side  13  of flat light guide  6 . Means to couple radiation  10  from radiation source  9  into light guide  11  are known as such, see e.g. U.S. Pat No. 5,506,929, to a person skilled in the art, and do not form a part of the present invention and therefore will not be further described in here. As is known in the art a surface  14  of the light guide  11  is provided with micro-optical surface structures which cause radiation  10  to be reflected in the direction of the arrow  15  into the flat light guide  6 . 
     A thickness dimension of the flat light guide  6  is indicated by “D”. A tangential dimension E of the light guide  11 , which is a dimension of the surface  12  in the same direction as the thickness dimension of the flat light guide  6  is larger than the dimension D. A portion  16  of the side  2  protrudes above the flat light guide  6 . The micro-optical structure on the surface  14  of the light guide  11  also directs light out of the surface  16 , i.e. the surface part  16  forms a radiation output window in a portion of the light guide  11  protruding above an upper surface of the flat light guide  6 . As indicated by arrows  17 A,  17 B, etc., substantially parallel, beams of radiation or emitted by the surface  16  of the light guide  11 . 
     A corresponding construction is shown in FIG. 2 as elongated radiation source  8 . The flat light guide  6 , which is known as such, for example from U.S. Pat. No. 5,506,929, directs the radiation  15  equally across its surface in the direction of arrow  18  to illuminate a reflective LCD schematically indicated by reference number  19 . 
     Along sides  20  and  21  of the flat light guide  6  detectors, which are known as such, are provided for detecting any of the light beams  17 A,  17 B, etc. to determine in two directions the location of a pointing device, schematically indicated by the reference letter P, such as a pen or a finger. The determination, based upon the locations of the ‘shadows’ of the pointing device on the detectors, of the exact position of the pointing device relative to a position at the output screen  19  is known to a person skilled in the art and does not form part of the present invention. 
     FIG. 2 a  shows a still more compact solution for inputting light into the light guide  11  and its corresponding structure of elongated radiation source  8 , indicated by the reference numeral  42 . In a corner between the light guides  11  and  42  a single radiation source  43  is located. Radiation source  43  is preferably point-like and radiates both in the direction of light guide  11  as well as in the direction of light guide  42 . 
     FIGS. 3A through 3D show an advantageous way of manufacturing a flat light guide  6  with a light pipe  11 . FIG. 3A shows a slab of material  21  which at an upper side  22  is provided with micro-optical structures  23 . As is well known to a person skilled in the art micro-optical structures  23 , which are at the surface  22  or inside the body of material  21  parallel to the surface  22 , operate to direct radiation which is present in the material  21  in a direction that does not differ too much from a horizontal direction into the direction of the arrow  24 . Line  25  indicates a position at which the slab  21  will be cut in two parts. After cutting the slab  21  is divided in two parts  26  and  27  as shown in FIG.  3 B. Thereafter part  27  is rotated about axis  28  (perpendicular to the plane of the drawing) in the direction of arrow  29 . Thereafter the situation is as shown in FIG.  3 C. It is to be noted that the optical micro-structure  23  now is present at the left hand side of element  27  as indicated by reference number  30 . As a consequence any light entering the piece of material  27  in a direction more or less parallel to the axis  28  will be directed by the optical micro-structure  30  to pass through surface  31  in the direction of the arrows  32  and  33 . The next phase is to fit part  27  in the orientation shown in FIG. 3C to the part  26 , the result of which is shown in FIG.  3 D. 
     FIG. 4 shows a further embodiment of the invention in which a transmissive LCD  19 ′ is illuminated from its back side  34 . A flat light guide  26 ′ is provided with optical micro-structure  23 ′ either at its lower surface or in the bulk of the material of the flat light guide  26 ′. As herein before in relation to FIG. 3 a part  27 ′ of a slab of material  26 ′ has been cut of. A micro-optical structure  30 ′ directs radiation into the direction of the arrows  32 ′ and  33 ′. Radiation in the direction of the arrow  32 ′ is directed by the micro-optical structure  23 ′ into the direction of the transmissive LCD  19 ′ as indicated by the arrow  35 . Radiation that passes through output windows in portion  27 ′ protruding above an upper surface of transmissive LCD  19 ′ passes over  19 ′ as, substantially parallel, beams that are substantially parallel surface  36  of transmissive LCD  19 ′.