Patent Publication Number: US-2023143276-A1

Title: Touchscreen

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a bypass continuation of co-pending PCT Patent Application No. PCT/IL2021/050799, filed Jun. 29, 2021, which is based upon and claims priority to Israeli Patent Application No. 275807, filed Jul. 1, 2020, the contents of each of which are incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     The present disclosed subject matter relates to touchscreens. More particularly, the present disclosed subject matter relates to a touchscreen having optical touch sensors arrays. 
     BACKGROUND OF THE INVENTION 
     Touch screens are commonly used as pointing sensors to provide a man-machine interface for computer driven systems. Several methods are known in the art for detecting and determining the location of touch events on the surface of the display screen. 
     Among the detection and determination methods, optical touch screen uses a number of infrared optical emitters (i.e., transmitters) and detectors (i.e., receivers) that are arranged around the periphery of the display screen to create a plurality of intersecting light paths. 
     US20090135162A1 to Sander B. F. Van De Wijdeven, et al., titled “ System and Method for Detecting the Location, Size and Shape of Multiple Objects That Interact With a Touch Screen Display”, discloses a system for detecting the location, size and shape of an object, or multiple objects, placed on a plane within the touch sensor boundaries of a touch screen. 
     SUMMARY OF THE INVENTION 
     It is an object of the present subject matter to provide, in accordance with a preferred embodiment, a touch screen (TS) apparatus comprising:
         a display;   a frame with at least a first edge, a second edge, a third edge and a fourth edge around the display, wherein the first edge and the second edge are positioned opposite each other, and the third edge and the fourth edge are positioned opposite each other;   at least a first sensor array and at least a second sensor array, wherein each of the sensor arrays has a plurality of light transmitters and a plurality of light sensors, and wherein the at least first sensor array and the at least second sensor array are disposed on the first edge and the second edge of the frame, respectively, wherein the transmitters of the first sensor array are facing the light sensors on the second sensor array positioned on two opposing edges of the frame; and   at least one physical obstacle, located on at least one of the third edge or the fourth edge, for reducing stray light scattered or reflected by said at least one of the third edge or the fourth edge and arriving to the light sensors,
 
wherein light from each of the light transmitters in one of the first sensor array and the second sensor array is directed along a direct light path to be detected by at least one light sensor of other sensor array, and wherein when at least one direct path between one of the light transmitters in one sensor array and at least one corresponding light sensor of the other sensor array is blocked, a touch event is detected , and a location of the touch event is determined based on a location of the direct path that is blocked.
       

     In accordance with another preferred embodiment of the present subject matter, said at least one physical obstacle is selected from a group of obstacles consisting of: a plurality of guards protruding from the edges, an optical filter tilted in respect to a surface of the display, and windows in a cover positioned in front of the light sensors. 
     In accordance with another preferred embodiment of the present subject matter, the guards are thin opaque sheets normal to the edge to which they are attached. 
     In accordance with another preferred embodiment of the present subject matter, the guards are placed between two adjacent light sensors or two adjacent light transmitters. 
     In accordance with another preferred embodiment of the present subject matter, the guards are normal to the cover. 
     In accordance with another preferred embodiment of the present subject matter, the guards have a length between 1 mm and 5 mm. 
     In accordance with another preferred embodiment of the present subject matter, the guards have a length between 3 mm and 4 mm. 
     In accordance with another preferred embodiment of the present subject matter, the cover further comprises a corresponding window positioned in front of each of the light transmitters for limiting spread of light transmitted by said light transmitters. 
     In accordance with another preferred embodiment of the present subject matter, the cover is configured to protect the arrays. 
     In accordance with another preferred embodiment of the present subject matter, the cover is in a right angle to the display. 
     In accordance with another preferred embodiment of the present subject matter, wherein the cover is tilted outwardly in respect to the display. 
     In accordance with another preferred embodiment of the present subject matter, the light transmitters are sequentially powered to transmit a burst of light pulses. 
     In accordance with another preferred embodiment of the present subject matter, the light transmitters are sequentially powered to transmit a burst of light pulses at power level higher than a power level that the transmitters are capable to be powered in continuous operation. 
     In accordance with another preferred embodiment of the present subject matter, the physical obstacle prevents the light sensor from saturation when the TS is operating while exposed to sunlight. 
     In accordance with another preferred embodiment of the present subject matter, the physical obstacle that prevents the light sensor from saturation when the TS is operating while exposed to sunlight is an optical filter for blocking light having wavelength shorter than the light transmitted by the light transmitters. 
     In accordance with another preferred embodiment of the present subject matter, an optical filter is placed in front of the light transmitters. 
     In accordance with another preferred embodiment of the present subject matter, the physical obstacle that prevents the light sensors from saturation when the TS is operating while exposed to sunlight is an optical filter for blocking light having wavelength shorter than the sensitivity wavelength of a night vision system. 
     In accordance with another preferred embodiment of the present subject matter, the light transmitters and the light sensors are organized in the sensor arrays in a single row. 
     In accordance with another preferred embodiment of the present subject matter, each of the sensor arrays comprises more light sensors than light transmitters. 
     In accordance with another preferred embodiment of the present subject matter, each of the sensor arrays is organized to have repeating groups comprising three light sensors and one light transmitter. 
     In accordance with another preferred embodiment of the present subject matter, the display comprises two halves: a left side screen and a right side screen. 
     In accordance with another preferred embodiment of the present subject matter, each of the two halves is a separate display. 
     In accordance with another preferred embodiment of the present subject matter, the sensor arrays that are positioned on opposite edges are identical. 
     In accordance with another preferred embodiment of the present subject matter, the sensor arrays are located above the surface of the display. 
     It is also provided, in accordance with another preferred embodiment of the present subject matter, a sensor array for detecting and locating a touch event on a touch screen (TS) having at least a first edge, a second edge, a third edge, and a fourth edge around a touch active surface, 
     wherein the first edge and the second edge are opposing each other, and the third edge and the fourth edge are opposing each other, and having at least a first sensor array and a second sensor array positioned on the first edge and the second edge, respectively, each of the sensor arrays comprising: 
     a plurality of light sensors organized in a light sensors&#39; row configured to be positioned adjacent to the touch active surface of the TS; and 
     a plurality of light transmitters organized in a transmitters&#39; row positioned adjacent to and above the light sensors&#39; row in respect to the touch active surface, 
     wherein light from at least one of the light transmitters of one of the sensor arrays forms at least one direct path of light that is detected by at least one light sensor in another sensor array oppositely positioned,
 
and wherein when the touch active surface of the TS is touched by a touching object, the at least one direct path of light is blocked, the touch event is detected, and wherein the location of the touch event is determined based on the location of the at least one direct path of light that is blocked; and
         at least one physical obstacle located on at least one of the third edge or the fourth edge, for reducing stray light arriving to the light sensors,   wherein said stray light is light that is:
           emitted by a transmitter of the plurality of light transmitters of the first sensor array,   scattered or reflected by structure on at least one of the third edge or the fourth edge, and
 
detected by a light sensor on the second sensor array. In accordance with another preferred embodiment of the present subject matter, the touching object is an opaque object capable of blocking the at least one direct path of light.
   
               

     In accordance with another preferred embodiment of the present subject matter, the opaque object is  1 / 8 ″ or larger. 
     In accordance with another preferred embodiment of the present subject matter, the opaque object is detected when it touches any location on the active surface of the TS. 
     In accordance with another preferred embodiment of the present subject matter, the opaque object is selected from a group of objects consisting of finger, gloved finger, stylus. 
     In accordance with another preferred embodiment of the present subject matter, the TS and the touch active surface are rectangular. 
     In accordance with another preferred embodiment of the present subject matter, the sensor array comprises more light sensors than light transmitters. 
     In accordance with another preferred embodiment of the present subject matter, the light transmitters are oriented so that a light emitting area of at least one of the light transmitters is close to a light sensor. 
     It is yet another object of the present subject matter to provide a method of detecting a location of a touch event in a rectangular touch screen (TS) apparatus having a rectangular display divided to a first side and a second side located one aside the other, the rectangular display has at least a first edge, a second edge, a third edge, and a fourth edge such that the first edge and the second edge that opposes the first edge are longer than the third edge and the fourth edge that opposes the third edge; the TS further has at least a first sensor array and at least a third sensor array, positioned near the first side and the second side of the display, respectively, and along the first edge; at least a second sensor array and at least a forth sensor array, positioned near the first side and the second side, respectively, along the second edge; at least a fifth sensor array and at least a sixth sensor array, positioned near the first side along the third edge and near the second side along the fourth edge, respectively, wherein each one of the sensor arrays comprises light transmitters and light sensors;
         the method comprising:   a first sequence comprising:   concurrently activating in sequence, one at a time, the light transmitters in the first sensor array and in the third sensor array to transmit light towards light sensors in the second sensor array and the fourth sensor array, respectively, each along a direct light path; and   determining if at least one direct light path of the direct light paths between any of the light transmitters in the first sensor array and the light sensors in the second sensor array is blocked;   if during the first sequence, at least one direct light path is blocked, starting a third sequence wherein the third sequence comprising:   activating in sequence, one at a time, the light transmitters in the fifth sensor array to transmit light towards light sensors in the sixth sensor array;   determining which of the direct light paths is blocked; and   determining the location of the touch event based on the at least one direct light path that is blocked;
 
if the direct light path that is blocked is between a light transmitter that is activated in the third sensor array and a light sensor in the fourth sensor array, starting a fourth sequence comprising:
   activating is sequence, one at a time, the light transmitters in the fifth sensor array to transmit light towards light sensors in the sixth sensor array;   determining which of the direct light path or direct light paths are blocked; and   determining the location of the touch event based on the at least one direct light path that is blocked;
 
and
 
if during the first sequence no direct light path is determined to be blocked, starting a second sequence comprising:
   concurrently activating is sequence, one at a time, the light transmitters in the second sensor array and forth sensor array to transmit light towards light sensors in the first sensor array and the third sensor array, respectively; and   determining if a direct light path between any of the light transmitters in the second sensor array and the fourth sensor array and the light sensors in the first sensor array and the fourth sensor array, respectively, is blocked;
 
if during the second sequence:
 
a direct light path is blocked between a light transmitter in the second sensor array and a light sensor in the first sensor array, starting the third sequence;
 
if during the second sequence:
 
a direct light path is blocked between a light transmitter in the fourth sensor array and a light sensor in the third sensor array, starting the fourth sequence; and
 
if during the second sequence no direct light path is blocked, starting first sequence again.
       

     In accordance with another preferred embodiment of the present subject matter, the method further comprising: 
     if during the third sequence or the fourth sequence following the first sequence, at least one direct path is determined to be blocked from the light transmitters closer to the first sensor array or the third sensor array,
         starting the second sequence; and   updating the location of the touch event based on the direct light path that is blocked; and
 
if during the third sequence or a fourth sequence following the second sequence, a direct path is determined to be blocked from the light transmitter closer to the second sensor array or the fourth sensor array,
   starting the first sequence; and   updating the location of the touch event based on at least one direct light path that is blocked.       

     In accordance with another preferred embodiment of the present subject matter, the method further comprising: 
     if the touch event is no longer detected, returning to the first sequence. 
     In accordance with another preferred embodiment of the present subject matter, the method further comprising: 
     independently powering and controlling the first side of the display and the second side of the display by different power and control sub-systems. 
     In accordance with another preferred embodiment of the present subject matter, the display is a rectangular display divided to a first side and a second side located one aside the other, the rectangular display has four edges such that a first edge and an opposing second edge are longer than a third edge and an opposing forth edge, 
     and wherein the first and the second sensor arrays are located opposite each other along the first edge and an opposing second edge respectively near the first side of the display, the TS further comprising:
 
at least a third sensor array and at least a fourth sensor array along the first edge and an opposing second edge respectively near the second side of the display;
 
at least a fifth sensor array and at least a sixth sensor array, positioned near the first side along the third edge and near the second side along the fourth edge, respectively, wherein each one of the sensor arrays comprises light transmitters and light sensors.
 
     In accordance with another preferred embodiment of the present subject matter, in the first, the second, the third and the fourth sensor arrays the plurality of light transmitters and light sensors are organized in a single row. 
     In accordance with another preferred embodiment of the present subject matter, in the first, the second, the third and the fourth sensor arrays the light transmitters and light sensors are organized in repeated groups of one light transmitter and a plurality of light sensors. 
     In accordance with another preferred embodiment of the present subject matter, in the first, the second, the third and the fourth sensor arrays each group comprises one light transmitter and three light sensors. 
     In accordance with another preferred embodiment of the present subject matter, in the fifth and the sixth sensor arrays the plurality of light transmitters organized in a transmitters&#39; row positioned adjacent to and above the light sensors&#39; row in respect to the touch active surface. 
     In accordance with another preferred embodiment of the present subject matter, said at least one physical obstacle comprises, an optical filter placed in front of the light transmitters. 
     In accordance with another preferred embodiment of the present subject matter, said at least one physical obstacle comprises, an optical filter placed in front of the light sensors. 
     In accordance with another preferred embodiment of the present subject matter, the apparatus further comprising a third sensor array and a fourth sensor array disposed on the third edge and the forth edge of the frame, respectively, 
     wherein said at least one physical obstacle comprises four physical obstacles, respectively located on the first, second, third and fourth edge. 
     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosed subject matter belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosed subject matter, suitable methods and materials are described below. In case of conflict, the specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. 
     The features as indicated above can be combined individually or all together. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Some embodiments of the disclosed subject matter described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present disclosed subject matter only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the disclosed subject matter. In this regard, no attempt is made to show structural details of the disclosed subject matter in more detail than is necessary for a fundamental understanding of the disclosed subject matter, the description taken with the drawings making apparent to those skilled in the art how the several forms of the disclosed subject matter may be embodied in practice. 
       In the drawings: 
         FIG.  1    schematically illustrates a general view of a display unit, in accordance with some exemplary embodiments of the disclosed subject matter; 
         FIG.  2    schematically illustrates an exploded view of a frame and sensor arrays of a display unit, in accordance with some exemplary embodiments of the disclosed subject matter; 
         FIG.  3    schematically illustrates an element of the bottom left corner of  FIG.  2   , illustrating some details of the display unit frame, in accordance with some exemplary embodiments of the disclosed subject matter; 
         FIG.  4 A  schematically illustrates some details of the sensor arrays, in accordance with some exemplary embodiments of the disclosed subject matter; 
         FIG.  4 B  schematically illustrates the grouping of the LEDs and the corresponding light sensors in the arrays, in accordance with some exemplary embodiments of the disclosed subject matter; 
         FIG.  5 A  schematically illustrates the top-to-bottom and bottom-to-top touch detection sequences, in accordance with some exemplary embodiments of the disclosed subject matter; 
         FIG.  5 B (i) schematically illustrates inaccuracies in bottom-to-top touch location determination, in accordance with some exemplary embodiments of the disclosed subject matter; 
         FIG.  5 B (ii) schematically illustrating inaccuracies in top-to-bottom touch location determination, in accordance with some exemplary embodiments of the disclosed subject matter; 
         FIG.  6    schematically illustrates side to side touch location determination, in accordance with some exemplary embodiments of the disclosed subject matter; 
         FIG.  7 A  schematically illustrates distances of the vertical light paths from the surface of the touch screen, in accordance with some exemplary embodiments of the disclosed subject matter; 
         FIG.  7 B  schematically illustrates distances of the horizontal light paths from the surface of the touch screen, in accordance with some exemplary embodiments of the disclosed subject matter; 
         FIG.  8 A  schematically illustrates a cross section of a top or bottom array, in accordance with some exemplary embodiments of the disclosed subject matter; 
         FIG.  8 B  schematically illustrates an isometric view of the frame and covers of both types of arrays, in accordance with some exemplary embodiments of the disclosed subject matter; 
         FIG.  9 A (i) schematically illustrates the use of covers and filters to reduce interference of sunlight with the operation of the display unit, in accordance with some exemplary embodiments of the disclosed subject matter; 
         FIG.  9 A (ii) schematically illustrating the use of tilted filters to deflect reflected light away from the ST, in accordance with some exemplary embodiments of the disclosed subject matter; 
         FIG.  9 B  schematically illustrates spectral filtering of sunlight, in accordance with some exemplary embodiments of the disclosed subject matter; and 
         FIG.  10    schematically demonstrates the spectral computability of the display unit with night vision goggles, in accordance with some exemplary embodiments of the disclosed subject matter, 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Before explaining at least one embodiment of the disclosed subject matter in detail, it is to be understood that the disclosed subject matter is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The disclosed subject matter is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting. The drawings are generally not to scale. For clarity, non-essential elements were omitted from some of the drawings. 
     The terms “comprises”, “comprising”, “includes”, “including”, and “having” together with their conjugates mean “including but not limited to”. The term “consisting of” has the same meaning as “including and limited to”. 
     The term “consisting essentially of” means that the composition, method or structure may include additional ingredients, steps and/or parts, but only if the additional ingredients, steps and/or parts do not materially alter the basic and novel characteristics of the claimed composition, method or structure. 
     As used herein, the singular form “a”, “an” and “the” include plural references unless the context clearly dictates otherwise. For example, the term “a compound” or “at least one compound” may include a plurality of compounds, including mixtures thereof. 
     Throughout this application, various embodiments of this disclosed subject matter may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed subject matter. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. 
     It is appreciated that certain features of the disclosed subject matter, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the disclosed subject matter, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination or as suitable in any other described embodiment of the disclosed subject matter. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements. 
     Similar elements may be marked with letters following the same numeral. A numeral followed by the letter/s “x” or “Xx” refers to any or all of the same type of elements. 
     Referring to  FIG.  1    schematically illustrating a general view of a display unit, in accordance with some exemplary embodiments of the disclosed subject matter. 
     The touch screen (TS)  110  comprises: 
     A rectangular display having a long dimension (X) and a short dimension (Y). It should be understood that the terms used herein “Y”, “Y”, “left”. “right”, “top”, “bottom”, etc. are for convenient only and do not intend to define direction relative to the gaze of the user or the earth gravity. The current subject matter may be used for example with a maneuvering airplane where the directions up and down may change, or if the display is installed such that its long dimension is vertical or oblique, and similarly, if the system undergoes symmetry reversal such as reflection, minoring or rotation. It is now defined that TS has a right side screen  111  and a TS left side screen  112 . The display can be a rectangular single display, two side by side displays meeting at adjacent edges  113 . Optionally, the adjacent edges or S 113  can be covered by a mullion. The TS can be physically or logically divided to a larger array of “sided” such as an additional “central screen” in between the right side screen  111  and the TS left side screen  112 . 
     The right side screen  111  and the left side screen  112  are “night vision system” (NVIS) compatible (to be detailed later in this document). Screens  111  and  112  are within a TS frame  120  and are having: a right side section  121 , a left side section  122 , a top right section  131 , bottom right section  132 , a top left section  141 , and a bottom left section  142 . 
     TS frame  120  houses touch detection and location arrays as well as guard protrusions  199  (shown better in  FIG.  3   ) to reduce light bypassing an object touching the screen from arriving to the sensors and interfering with the operation of the touch detection and location arrays. 
     Light arriving to the sensors and interfering with the operation of the touch detection and location arrays can be light that is generated by a light source such as a LED in one touch detection and location array and traveled not in the direct optical path between that light source to a light sensor in another detection and location array. The interfering light takes an indirect path, such as being reflected or scattered by an element of the TS or other structures nearby. In the text below, light arriving to the sensors and interfering with the operation of the touch detection and location arrays taking the above indirect path or paths may be named as “scattered light”. Some details of scattered light will be discussed in reference to  FIG.  2   , 
     In contrast, the “direct optical path” of light that is generated by a light source in one touch detection and location array and travels in the direct optical path between that light source to a light sensor in another detection and location array will be referred in the text simply as “path” or “direct path”. 
     Optionally, guard protrusions  199  are of different shapes or lengths. For example, guard protrusions  199  on the sides of the TS can be of different length than the guard protrusions  199  on the top and/or the bottom of the ST. Optionally, guard protrusions  199  are missing on one or few edges of the ST. 
     It should be noted that exemplary embodiments of the current subject matter are configured to be used with different sizes of touchscreens, for example large TS may be used. For example, a width of TS  110  can be over to 50 cm 
     Referring now to  FIG.  2    schematically illustrating an exploded view of the frame and sensor arrays of a display unit, in accordance with some exemplary embodiments of the disclosed subject matter. 
     The TS frame  120  accommodates touch sensors that will be comprehensively disclosed later on in this document. The frame is further provided with connecting members  201  for connecting the TS frame  120  to the support structure (shown in  FIG.  3   ). 
     Sensor arrays are also provided to the frame while each array of sensors comprises light transmitters (LEDs) and light sensors (to be detailed in  FIGS.  3 - 6 ,  8 A -B). Right array  221  and left array  222  are similar or optionally identical. Right array  221  and left array  222  are provided on both sides, and top right array  231 , bottom right array  232 ; top left array  241 , and bottom left array  242  are correspondingly provided, forming an inner frame. Top right array  231 , bottom right array  232 ; top left array  241 , and bottom left array  242  are similar or optionally identical. 
     It should be noted that the arrays are arranged and works as opposing couples:  421  with  242 ;  231  with  232 ; and  221  with  222 . That is, light emitted by one array is to travel via a direct path to its opposing counterpart when the screen is not touched. Light traveling via an indirect path, for example by reflection or scattering by the frame or another (not the opposing) array, may provide enough light to the sensors, thus preventing detection of the blocking of the direct path. For example, light emitted from array  241  may be reflected or scattered towards array  242  by array  222  or the frame or other structure in front or near array  221 . Similarly, light from array  222  may be reflected or scattered towards array  222  by any of arrays  231 ,  232 ,  241 , and  242 , or the frame or other structure in front or near these arrays. Guards  199  strongly reduces the reflected or scattered light via these indirect paths. Additionally, as will be seen in reference to  FIG.  9 A (ii), tilting the covers  250  and or filters  810  further reduces the reflected light via these indirect paths. 
     Guards  199  (which may be seen in more details in  FIGS.  3  and  8 B ) may be made as thin sheets, for example metal, or opaque material, attached or part of the frame  120 , or parts of or attached to other parts of the cover  250 . The sheets do not block the direct paths from transmitters to receivers, but prevents light arriving at oblique angles from arriving at, reflecting from, or scattering from elements such as: the cover, the frame, filters, the receivers, and the transmitters. 
     A cover  250  is configured to cover and protect the arrays and to reduce the risk of sensing errors due to stray LED light reflections and blinding by sunlight. To reduce the risk of sensing errors, the cover further comprises guards  199  (to be seen in  FIGS.  3 , and  8 A -B), a filter, and windows  820   x  for allowing light to exit from the LEDs and arrive to the light sensors (to be detailed in  FIGS.  3 ,  8 A -B and  9 A-B). 
     Optionally, cover  250  is at a right angle to the surface of the TS  100 . This reduces the width of the frame and allows larger display size to fit into the confined space. Alternatively, cover  250  is tilted outwardly in respect to the surface of TS  100 , such that LED light not absorbed by a light sensor is predominantly reflected away from the TS surface. 
     In an exemplary embodiment, for example as seen here, the electro-optical elements of arrays  241 ,  231 ,  221 ,  232 ,  242 , and  222  are above the surface of the display(s) used with the TS. Optionally, the entire printed board circuit (PCB) of the array are above the surface of the display(s) used with the TS. 
     Referring now to  FIG.  3   , schematically illustrates an element of the bottom left corner shown in  FIG.  2   , illustrating some details of the display unit frame, in accordance with some exemplary embodiments of the disclosed subject matter. 
     The bottom left section  142  of TS frame  120  is having a rim  320  that can facilitate in stabilizing the hand of the user during touching the screen. 
     All sections of the TS frame (sections  122  and  142  are shown in  FIG.  3   ) comprise windows  820   x.  Guards  199  protrude from the frame inwardly. Optionally, guards  199  are located between any two adjacent windows  820   x  along the edge of the frame. However, a guard can be located at larger intervals. In the depicted example, guards  199  are normal to the cover. 
     Guards  199  may be between 1 to 5 mm long, for example between 3 to 4 mm long, such that they minimally interfere with the visually useful surface of the TS display and its touch active surface. 
     Optionally, guards  199  protrude into the active surface of the display used with the TS. Optionally, the frame is constructed such that the entire length of guards  199  is over the active surface of the display used with the TS. 
     Referring now to  FIG.  4 A  schematically illustrating some details of the sensor arrays, in accordance with some exemplary embodiments of the disclosed subject matter. 
     Each array of sensors comprises LEDs  410  and light sensors  420  in repeated order. However, the configuration of the LEDs and the light sensors are not identical:
         a) In the side arrays  222  and  221 , the LEDs  410  and the light sensors  420  are arranged in two rows, wherein the LEDs  410  are positioned above the light sensors  420  (further from the surface of the display). Preferably but not necessarily, one LED  410  is placed above every second light sensor  420 . As can clearly be seen in the enlargement  460  of a segment of the array  222 , the LEDs  410  are oriented with their long side adjacent to the light sensor such that their light emitting area  411  is closer to the light sensor  420 .
           This arrangement of sensors facilitates increased resolution of the screen, and detection of a user&#39;s touch close to the screen (as will be detailed in  FIGS.  6  and  7 B ). However, this arrangement should be viewed as a non-limiting example as exact configuration may depend on the dimensions of the LED and light sensor&#39;s components and their connections to the printed board circuit (PCB).   
           b) In the top and bottom arrays ( 232 ,  231 ,  241 ,  242 ), the LEDs  410  and light sensors  420  are positioned in one row. The LEDs  410  are preferably separated by three light sensors  420 ; the LEDs  410  are oriented with their long side vertical such as to minimize the gap between two light sensors  420  residing on both sides of the LED, as can be seen in corresponding enlargement  470 . This arrangement allows increased resolution, and detection of a touch close to the screen as detailed in  FIGS.  5  and  7 A ).
           However, this arrangement should be viewed as a non-limiting example as exact configuration may depend on the dimensions of the LED and light sensor&#39;s components and their connections to the PCB.
 
In the non-limiting example, each side arrays have  35  light sensors and  17  LEDs.
 
In the non-limiting example, each top or bottom arrays have  33  light sensors and  11  LEDs.
   
               

     It should be noted that other arrangements of arrays with different ratios between the number of LEDs and the light sensors are possible without limiting the scope of the disclosed subject matter. 
     Referring now to  FIG.  4 B , schematically illustrating the grouping of the LEDs and the corresponding light sensors in the arrays, in accordance with some exemplary embodiments of the disclosed subject matter. 
     In this figure, the emission area of operating LED  410   o  in top left array  241  (better seen in enlargement  470 A) and the active area of the corresponding three operating light sensors  420   o  (seen in enlargement  470 B) in the opposite location in bottom left array  242  are seen in hatched coloring. It should be noted that in this non-limiting example, the operating sensors  420   o  are adjacent to one side of the non-operating LED  410   n  that is directly opposite to the operating LED  410   o.    
     It should be noted that in this document, “operating LED” or “activated LED” is a LED that emits a burst of IR pulses at a preset frequency. 
     In this document, “probed light sensor”, “operating light sensor” or “activated light sensor” is a light sensor that transmits its state: “detecting the LED light” or “light from the LED is blocked” to the controller controlling the TS unit. The light sensor may be energized and operational while not active, for example to performs tasks such as light background subtraction, temperature compensation, and automatic gain control. 
     Similarly, in this figure, the emission area of operating LED  410   o  in array right  221  (shown in enlargement  460 B) and the active area of the corresponding three operating light sensors  420   o  (shown in enlargement  460 A) in the opposite location in left array  222  are seen in hatched coloring. Note that in this non-limiting example, the operating light sensors  420   o  are adjacent, below, and on both sides of the non-operating LED  410   n  that is directly opposite to the operating LED  410   o.    
     Referring now to  FIG.  5 A , schematically illustrating the top-to-bottom and bottom-to-top touch detection sequences, in accordance with some exemplary embodiments of the disclosed subject matter. 
       FIG.  5 A  illustrates the initial touch screen detection and determination of “X” coordinate  530 . To reduce cluttering of the figure, only some of the components are marked. 
     In activated mode, the top (and bottom) arrays are constantly scanning for a “touch event” in which an object such as a finger, gloved finger, or a stylus interrupts at least one light path  501  between a LED  541 X,  542 X and a corresponding light sensor  542 Xx,  541 Xx. 
     The operation is first illustrated for a “top-to-bottom” scan, wherein LEDs  541 A,  451 B,  541 C . . .  541 X are activated one after the other in sequence. During activation of LEDs  541 A, as an example, the corresponding light sensors  542 Aa,  542 Ab and  532 Ac are also activated (in the sense that their state is considered by the controller in order to determine the location of a touch event). 
     If touch event was not detected, LEDs  541 A and  531 A and their corresponding light sensors are deactivated and the next LEDs  541 B and  531 B and their corresponding light sensors (not marked) are activated. Next, LEDs  541 C is activated together with the corresponding (not marked) light sensors, and so on. 
     In the exemplary non-limiting example, both TS right side screen  111  and a TS left side screen  112  are concurrently scanned For example, the detection sequence can start with top-to-bottom scan in the X direction  530  by activating LEDs  541 A and the corresponding light sensors  542 Aa,  542 Ab and  542 Ac; and at the same time, activating LED  531 A and the corresponding light sensors  532 Aa,  532 Ab, and  532 Ac. 
     Note that in this example of a concurrent top-to-bottom scanning, a distance of one half of the total width of the TS between the two active LEDs and the two group of active light sensors is maintained, thus reducing the risk of light scattered from one active LED arriving at a light sensor associated with the other activated LED, possibly causing missing a touch event. Yet the full scan time is reduced to one half of the time required in consecutive scanning of the two halves of the display. It should be noted that the number of concurrently activated LEDs can be more than two for further reducing the full scan time. 
     If the top-to-bottom scan is completed without detecting a touch event, a bottom-to-top scan begins by activating LED  542 A and  532 A and their corresponding light sensors. The bottom-to-top scan continues by sequentially activating the next LED  541 X and  531 X and their corresponding light sensors unless a touch was detected. 
     The sequence of top-to-bottom scan and bottom-to-top scan repeats until a touch event is detected. 
     Referring now to  FIG.  5 B (i), schematically illustrating a detection of a touch event and the inaccuracies in bottom-to-top touch location determination, in accordance with some exemplary embodiments of the disclosed subject matter. 
     For example, when a touch event by a small stylus  595  occurs near the bottom array (in this example array  242 ), all light paths  501  from the nearby LED  542 C are blocked. In the depicted example, all three corresponding light sensors  542 Ca,  542 Cb, and  542 Cc report reduced or no light direct detection. 
     In a bottom-to-top scan, the distances between light paths  501  near the bottom array  232  is only slightly smaller than the distance between adjacent LEDs  542 X. 
     From the depicted example, it is shown that the system thus cannot resolve the situation wherein the touching object is in position  595 A,  595 Bb or  595 C as all these positions blocks paths from LED  542 C and only from LED  542 C. Thus, X coordinate inaccuracy  597  exists in the determination of the location of the touching object. 
     Additionally, if the touching object is substantially smaller than the distance  580  between adjacent LEDs, it may avoid being detected if it is position so as not to block any path  501 . For example, the TS can be constructed to assure detection and location determination if the screen is touched by an object having minimal dimensions of width (in the X direction) and length (in the Y directions) larger than ⅛″ (3.175 mm) Different minimal dimensions can be achieved by selecting the maximal separation between adjacent light sensors and LEDs. 
     For this reason, when a touch occurs near the bottom array, a top-to-bottom scam is advantageous as in this case, the distances between light paths near the bottom array is comparable to the distance between (the more closely packed) light sensors  542 Xx. 
     Referring now to  FIG.  5 B (ii), schematically illustrating inaccuracies in top-to-bottom touch location determination, in accordance with some exemplary embodiments of the disclosed subject matter. 
     In the depicted example seen here, a touch event occurs near the bottom array (in this example array  242 ). In this example, only two light paths  501  from the top LED are blocked, and the two corresponding bottom light sensors report reduced or no light detection. 
     From the depicted example, it can be seen that the system thus, cannot resolve the situation wherein the touching object is in position  590   a,  or  590   c  as same paths  511  are blocked in these two positions. However, in this case, the X coordinate inaccuracy  598  in the determination of the location of the touching object is substantially smaller than the distance between two adjacent LEDs. Similarly, only if the touching object is substantially smaller than the distance  599  between adjacent light sensors (which is smaller than the distance  580  between adjacent LEDs) it may avoid being detected. 
     It should be noted that the touching object can obstruct light sensor corresponding to more than one LED. In the exemplary embodiment, valid touch event is defined as obstructing a group of adjacent light sensors, and a multiple simultaneous spatially separated touch events are reported as an illegal event. In each case, the coordinate of the touch is determined by the centroid of the group of obstructed light sensors. 
     From  FIGS.  5 B (i) and  5 B(ii), it is clear that a better resolution is generally achieved for a touch event closer to the light sensors or at the zone in the center of the TS in the Y direction  531 . 
     Combining the information from both top-to-bottom and bottom-to-top scan thus can increase the resolution in some cases, as demonstrated in  FIG.  5 B (ii) in which light from a LED  542 C is blocked when the touching object is in position  590   a,  but not when the touching object is in position  590   c.    
     Thus, whenever a touch event is detected, the X coordinate is preferably reported after: a) both top-to-bottom and bottom-to-top scans were performed, or b) it was determined that the touch event occurred close enough to the active light sensors. An exception to this rule may be established, for example, in cases of a very fast response, requiring a touch event on an icon displayed on the TS, which is large enough so that accurate coordinate determination is not critical. 
     Referring now to  FIG.  6    schematically illustrating side-to-side scan for touch location determination in the Y direction, in accordance with some exemplary embodiments of the disclosed subject matter. 
     Once a touch was detected in the sequence depicted in  FIG.  5 B  (for example as in  5 B(i) or  FIG.  5 B (ii)), the system enters a mode of X and Y coordinates determination. 
     At this stage, the right side screen  111  or left side screen  112  that were touched, are known. A side-to-side scan, for determining the Y coordinate  531  is then commenced for the touched side of the TS. 
     In  FIG.  6   , it is assumed that the touch event  591  is detected in the left side  112  of the TS. Symmetric scan commences if the right side  111  was touched. 
     In the depicted example, since touch was detected on the left side  112  of the TS, LEDs  410 Rx in the right array  221  are activated one after the other in sequence. For example  410 Ra, followed by  410 Rb,  401 Rc etc. Each time a LED is activated, the state of the corresponding light sensors on the left array  222  are probed (as detailed in  FIG.  4 B ), and report their state: “detecting the LED light” or “light from the LED is blocked” to the controller controlling the TS. For example, light sensors  420 La,  420 Lb and  420 Lc are associated with LED  410 Ra, light sensors  420 Lb,  420 Lc and  420 Ld are associated with LED  410 Rb, etc. 
     Optionally, the Y coordinate  531  of the touch is determined by the centroid of the group of obstructed light sensors. If the touch was detected using the activation of the LEDs in the array (bottom or top array) that is closer to the touch, a “horizontal scan” (that is a “top-to-bottom”, or a “bottom-to-top” scan) is performed, activating the array having its LEDs further away from the touch in order to decrease the inaccuracy in the determination of the X coordinate  530  (as detailed in  FIGS.  5 B (i) and  5 B(ii)). The resolution is determined by the distance  790  between adjacent light sensors. 
     Alternatively, determination of the coordinates is reported after at least all “top-to-bottom”, “bottom-to-top” and the appropriate “side-to-side” scans were completed. 
     Location of the touch in the two dimensions X and Y (2D) is done by combining the results of the determined X value and Y value. 
     Scanning sequence continues to determine: 
     a) movement of the touching object, and 
     b) termination of the touch event by lifting the touching object. 
     Once the touch event has been terminated, the system reverts to stand-by state, repeatedly performing top-to-bottom and bottom-to-top scans until the next touch event is detected. 
     Referring now to  FIG.  7 A , schematically illustrating a horizontal cross section of the TS, showing distance of the vertical light paths from the surface of the touch screen, in accordance with some exemplary embodiments of the disclosed subject matter. 
     Since the LEDs  410  and the light sensors  420  in top and bottom arrays  231 ,  241 ,  232 ,  242  are in one row (see enlargement  470  in  FIG.  4 A ), the vertical light paths  501 Vt (from top to bottom) and  501 Vb (from bottom to top) are essentially in parallel to, and in close proximity to the surface of the TS displays  111  and  112 . This prevents false detection of a touch events if an object comes close to, but not close enough to the surface of the TS. 
     Referring now to  FIG.  7 B , schematically illustrating distances of the horizontal light paths from the surface of the touch screen, in accordance with some exemplary embodiments of the disclosed subject matter. 
     In this situation, LEDs  410  and the light sensors  420  in side arrays  221 ,  222  are in two rows (see enlargement  760  in  FIG.  4 A ), wherein the LEDs  410  are further away from the surface of the TS right side screen  111  and left side screen  112 . Thus, light paths  501 R (from right to left) and  501 L (from left to right) are slightly slopped in respect to the surface of the TS screens. 
     Thus, it is optionally advantageous to use the right-to-left light paths  501 R for determination of a touch on the left side  112 . Additionally, the resolution determined by the closer and closely packed light sensors is better as was demonstrated in  FIG.  6   . 
     The opposite is applied for using the left-to-right light paths SOIL for determination of a touch on the right side screen  111 . 
     Optionally, when the touch event is near the centerline  113  (for example when the X coordinate is between a preset values, for example ¼ to ¾ or between ⅓ to ⅔ or the total width of the TS screen), both right-to-left and left-to-right scans are performed and the Y coordinate is determined from the results of both scans. 
     Referring now to  FIG.  8 A  schematically illustrating a cross section of a top or bottom array, in accordance with some exemplary embodiments of the disclosed subject matter. 
     A cross section of the TS frame  120  through one of the top or bottom arrays  231 ,  241 ,  232 , or  242  is shown. Only elements that are not yet discussed will be explained in the description of the figure. 
     A PCB  801  carries electronic components  802  that drive and control the array of LEDs  410  and light sensors  420  is shown. Cover  250  comprises LED holes  820 L, each hole is aligned with the light emitting area  411  of a LED  410  to allow the light of the LED to pass in the direction of its corresponding light sensor  420  in the opposing sensor array. The holes might also inhibit light from the LED to spread in angles that are larger than needed and interfere with the operation of light sensors not associated with that specific LED. 
     Cover  250  further comprises sensor holes  820 S, each hole is aligned with the active area of a light sensor  420  to allow the light of the corresponding LED in the opposing sensor array to pass in the direction of the light sensors  420 . The holes might also inhibit ambient light from the cockpit or the sun, or light from an LED if not associated with that light sensor, from arriving at the active area of the light sensor. Guards  199  are seen to protrude from cover  250 . 
     An optical filter  810  (to be further discussed in  FIGS.  9 A and  9 B ) is placed between the sensor holes  820 S and the light sensor  420 . In the depicted embodiment, the optical filter  810  is in the form of a strip placed in front of the entire array and is also used for protecting the array from dust and moisture. The filter  810  is a long pass optical filter designed to be substantially transparent at the wavelength of the LEDs, while blocking large portions of the sun&#39;s visible and near IR radiation (shown in  FIG.  9 B ). 
     Referring now to  FIG.  8 B  schematically illustrating an isometric view of the frame and covers of both types of arrays, in accordance with some exemplary embodiments of the disclosed subject matter. The isometric view shows the cover on both types of top/bottom and side arrays. 
     The single row of holes  820 L and  820 S are seen in front of the (hidden) top/bottom arrays  231 ,  241 ,  232 , or  242 ; while bottom row of light sensors holes  820 S and a top row of LED hole  820 L are shown in front of the (hidden) side arrays  221  or  222 . 
     Optionally, the cover  250  is the filter  810  itself, and the holes  820 X are gaps in opaque paint applied to the filter. 
     In the depicted example seen in this figure, along the top or bottom edges ( 231 ,  241 ,  232 ,  242 ) the distances between the center of windows  820 L and the adjacent  820 S is the same as the distances between two adjacent windows  820 S. The centers of the corresponding optical elements (LEDs  410  and light sensors  420 ) are similarly equally spaced. 
     In the depicted example seen in this figure, along the side edges ( 221 ,  222 ) a LED window  820 L is located above each light sensor window  820 S. The corresponding optical elements (LEDs  410  and light sensors  420 ) are similarly equally spaced. 
     It should be noted that the spacing of the windows and the optical elements can be selected to provide the necessary touch location resolution and the minimal size of touching stylus. For example, LED window  820 L can be located at other position than directly above a light sensor window  820 S, for example, above the gap between two adjacent light sensor windows  820 S. 
     Referring now to  FIG.  9 A (i) schematically illustrating the use of covers and filters to reduce interference of sunlight with the operation of the display unit, in accordance with some exemplary embodiments of the disclosed subject matter. 
     It can be seen how the use of filter  810  (to be more detailed in  FIG.  9 B ) reduces the interference of ambient or sun light  901  from the sun  900  with the operation of light detector  420 . Additionally, cover  250  can also reduce the interference of ambient or sun light  901  from the sun  900  with the operation of light detector  420  as window  820  may act to limit the angular acceptance range of light detector  420 , blocking at least some of sun light  901 . 
     Referring now to  FIG.  9 A (ii) schematically illustrating the use of tilted filters to deflect reflected light away from the ST, in accordance with some exemplary embodiments of the disclosed subject matter. 
     By optionally tilting filter  810  and/or cover  250  by an angle  998 , light  501   x  is reflected  999  in a direction away from the TS, thus reducing the probability of reflected light arriving to, and interfering with the operation of a light sensors. Angle  998  can be for example 45 degrees, however other values may be used. 
     Referring now to  FIG.  9 B  schematically illustrating spectral filtering of sunlight, in accordance with some exemplary embodiments of the disclosed subject matter. The original spectrum of sunlight  930 , the attenuated spectrum of sunlight  930 A, the transmission curve  940  of filter  810 , the spectral response  950  of light sensor  420  are plotted against wavelength in nanometers. The graph is not to scale. 
     As can be seen, most of the radiation  930  from the sun is rejected by the combination of filter transmission  940  and light sensor spectral response  950 . 
     In a non-limiting embodiment, the filter used is an RG-1000 long-pass colored glass filter. Alternatively, a plastic filter is used. Optionally, the filter is antireflection coated to increase its transmission and/or reduce reflection of LED light. Optionally, plastic filter can be made to form structural element or elements of the frame and/or the cover. 
     It should be noted that in bright daylight, and specifically in high altitudes, and/or fast maneuvering airplane, the sunlight may saturate the light detectors such that no change of signal is produced when the screen is touched. Additionally, temperature of the display, when mounted in a cockpit can very over a wide range, for example between −30° C. to +85° C. The sensitivity of the light sensors is affected by temperature and this can cause errors due to inability to sense the touch or saturation. 
     To overcome the risk of light sensor saturation, sunlight filtering is used. Additionally, each LED is powered in strong, short bursts (optionally well above the capability of continuous powering of the LED) in order to achieve good signal to noise ratios. The light sensors use “tuned detection” in which the light signal is AC coupled and is sensitive to the fast variations caused by the train of pulses emitted by the LED and less sensitive to the slow variations in ambient light. Optionally, the light signal is electronically filtered at the frequency range of train of train of pulses emitted by the LED. 
     However, using high power LED light increases the risk of LED light bounces or scattered off around an intentional light obstacle such as a stylus or a finger such that a valid touch may be undetected. Guards  199  reduce this risk by limiting the range of angles that light may exit the LED and/or the acceptance angle that light may reach the light sensors. 
     Referring now to  FIG.  10    schematically demonstrating the spectral compatibility of the display unit with night vision system in accordance with some exemplary embodiments of the disclosed subject matter. 
     In some embodiments, TS unit  100  is used while the user is wearing night vision system 
       FIG.  10    plots the long wavelength edge of We acceptance spectra  1021  of an NVIS the emission peak  960  of LED  419 , and the attenuation spectra  940 A of a long pass filter. 
     The nominal emission peak  960  of LED  419  is well outside the acceptance spectra  1021  of the NVIS. However, it should be noted that LED emission may have a short wavelength tail  1025 . Additionally, there are manufacturing variations among LED, for example LED with nominal peak of 1050 nm may have +/−50 nm spread in peak wavelength. Additionally, peak wavelength may shift with temperature. Since NVIS are highly sensitive, it may be advantageous to use an attenuation long wavelength filter to keep the LED light, from blinding the NVIS. The attenuation spectrum  940 A of the filter used in front of the LED may be the same or different than the attenuation spectrum  940  of the filter used in front of the light sensors. 
     It should be noted that the disclosed subject matter uses at least one, and optionally a plurality of components and methods to improve the operation. These can be grouped to two general groups:
         a) Mechanical obstacle comprising at least one of: guard protrusions  199 , filters  810 , and windows  820 .   b) Electro-optical components and methods comprising at least one of: powering the LEDs in strong short bursts, and operating the light sensors in tuned detection, performing light background subtraction, temperature compensation, and automatic gain control.       

     Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention.