Patent Publication Number: US-2013234991-A1

Title: Optimized hemi-ellipsoidal led shell

Description:
This application is a continuation-in-part of U.S. application Ser. No. 13/424,472, entitled OPTICAL TOUCH SCREEN WITH TRI-DIRECTIONAL MICRO-LENSES, filed on Mar. 20, 2012 by inventors Lars Sparf, Stefan Holmgren, Magnus Goertz, Thomas Eriksson, Joseph Shain, Anders Jansson, Niklas Kvist, Robert Pettersson and John Karlsson. 
     U.S. application Ser. No. 13/424,472 is a non-provisional of U.S. Provisional Application No. 61/564,124, entitled OPTICAL TOUCH SCREEN WITH TRI-DIRECTIONAL MICRO-LENSES, filed on Nov. 28, 2011 by inventors Lars Sparf, Stefan Holmgren, Magnus Goertz, Thomas Eriksson, Joseph Shain, Anders Jansson, Niklas Kvist, Robert Pettersson and John Karlsson. U.S. application Ser. No. 13/424,472 is also a continuation-in-part of PCT Application No. PCT/US11/29191, entitled LENS ARRANGEMENT FOR LIGHT-BASED TOUCH SCREEN, filed on Mar. 21, 2011 by inventors Magnus Goertz, Thomas Eriksson, Joseph Shain, Anders Jansson, Niklas Kvist, Robert Pettersson, Lars Sparf and John Karlsson. 
     PCT/US11/29191 is a non-provisional of U.S. Provisional Application No. 61/410,930, entitled OPTICAL TOUCH SCREEN SYSTEMS USING REFLECTED LIGHT, filed on Nov. 7, 2010 by inventors Magnus Goertz, Thomas Eriksson, Joseph Shain, Anders Jansson, Niklas Kvist, Robert Pettersson and Lars Sparf. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to molded plastic shells for light emitters and light detectors. 
     BACKGROUND OF THE INVENTION 
     Conventional light-emitting diodes (LEDs) include a semiconductor light source mounted on a substrate inside a molded plastic shell, which acts as a refractive intermediary between the relatively high index semiconductor and the low index open air. As such, the plastic shell distributes light from the semiconductor and forms the angular distribution of the light emission by acting as a lens. 
     In conventional LEDs, the plastic shells are cylindrical or hemispherical, providing similar light intensity distributions in both vertical and horizontal dimensions. 
     SUMMARY OF THE DESCRIPTION 
     Aspects of the present invention relate to novel shell design for light emitters, optimized to provide more radiant intensity in the forward direction than conventional cylindrical or hemispherical lenses. The novel shell design concentrates light distribution in the vertical dimension. 
     There is thus provided in accordance with an embodiment of the present invention a hemi-ellipsoidal light module that includes a substrate for placement on a printed circuit board, a light element mounted on the substrate, and a molded plastic shell encasing the light element and having a geometry of a partial semi-ellipse rotated through a semi-circle about an axis on the light element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be more fully understood and appreciated from the following detailed description, taken in conjunction with the drawings in which: 
         FIG. 1  is an illustration of a prior art light-based touch screen; 
         FIG. 2  is a simplified perspective view of a light emitter module mounted on a printed circuit board, in accordance with an embodiment of the present invention; 
         FIG. 3  is an illustration of distribution of light emitted by a light emitter module in a plane parallel to a screen surface, in accordance with an embodiment of the present invention; 
         FIG. 4  is an illustration of distribution of light emitted by a light emitter module in a plane parallel to a screen surface, in accordance with an embodiment of the present invention; 
         FIG. 5  is a simplified diagram of angular light intensity distributions for light emitted by a prior art light emitter module; 
         FIG. 6  is a simplified diagram of angular light intensity distributions for light emitted by a light emitter module in accordance with an embodiment of the present invention; 
         FIG. 7  is a simplified perspective view of a hemi-ellipsoidal plastic shell for a light emitter module, in accordance with an embodiment of the present invention; 
         FIG. 8  is a simplified diagram of a side view of a light emitter encased in the plastic shell of  FIG. 7 ; and 
         FIG. 9  is a simplified diagram of a top view of a light emitter encased in the plastic shell of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     Aspects of the present invention relate to a novel shell design for light-emitting diodes (LEDs). LEDs having the novel shell design are of advantage for use with many different applications. One such advantage relates to their use with light-based touch screens. 
     Conventional light-based touch screens operate by emitting light beams across a touch screen from two adjacent edges, and detecting whether the light beams are blocked from reaching detectors at the two opposite edges. In this regard, reference is made to  FIG. 1 , which is an illustration of a prior art light-based touch screen.  FIG. 1  shows LEDs  50 , which emit invisible infrared light, aligned along two adjacent edges of a display. Across from LEDs  50  are corresponding photodiode (PD) light receivers  60 , which receive the light emitted by LEDs  50 . However, when an object  70  touches the display, it blocks light emitted by one or more specific LEDs  50  from reaching their corresponding PDs  60 . As such, object  70  is detected when light is not detected by the corresponding PDs  60 . Since the PDs are arranged along two dimensions of the display, the blocked PDs on each edge suffice to determine the spatial location of object  70  on the display. 
     In some embodiments of the present invention, wide light beams cover the entire screen, and this enables very precise touch coordinate calculation. These embodiments are described in detail in applicant&#39;s co-pending application Ser. No. 13/424,472, entitled OPTICAL TOUCH SCREEN WITH TRI-DIRECTIONAL MICRO-LENSES, the contents of which are hereby incorporated by reference in their entirety. 
     Reference is made to  FIG. 2 , which is a simplified perspective view of a light emitter module  100  mounted on a printed circuit board (PCB)  310 , in accordance with an embodiment of the present invention. 
     Light emitter module  100  includes a light emitting semiconductor  105  mounted on a substrate  115  and encased in a molded plastic shell  125 . 
     Reference is made to  FIG. 3 , which is an illustration of distribution of light emitted by light emitter module  100  in a plane parallel to a screen surface  240 , in accordance with an embodiment of the present invention.  FIG. 3  shows a side view of light emitter module  100 , encased in a molded plastic shell  260  and mounted on PCB  310 . An angular spread, denoted by h, is narrow, directing light beams  220  substantially parallel to screen surface  240 . 
     Reference is made to  FIG. 4 , which is an illustration of distribution of light emitted by light emitter module  100  in a plane parallel to screen surface  240 , in accordance with an embodiment of the present invention.  FIG. 4  shows a top view of light emitter module  100  mounted on PCB  310 ; i.e., the view in  FIG. 4  is looking down onto screen surface  240 . The angular emission, denoted w, is wide, and spreads light beams  230  across a wide angle to cover a large area of screen surface  240 . Light emitter module  100  includes a semiconductor light source  105 , a substrate  115 , and molded plastic shell  260 . 
     Together,  FIGS. 3 and 4  show that embodiments of the present invention generate a narrow angular emission in the height dimension of an emitter ( FIG. 3 ); i.e., perpendicular to the screen surface, and maintain a wide lateral angular emission, parallel to the screen surface ( FIG. 4 ). 
     Reference is made to  FIG. 5 , which is a simplified diagram of angular light intensity distributions for light emitted by a prior art light emitter module  50 .  FIG. 5  shows light emission for an emitter having a hemispherical plastic shell  250 .  FIG. 5  shows top and side views of light emitter module  50  with hemispherical plastic shell  250 . Above each emitter view is a normalized intensity graph showing relative radiant intensity vs. angular displacement. The outermost semi-circle represents a maximum light intensity detected by a light detector at any point across a 180° arc surrounding the light source. The maximum intensity is normalized to 1.0. The inner semicircles represent lower relative light intensities; e.g., 80%, 60%, of the maximum. A half-intensity angle, θ 1/2 , is used to characterize how far in degrees from the on-axis perspective a particular LED&#39;s luminous intensity drops to 50%. On the left side of  FIG. 5  the top view of light emitter module  50  shows that light is distributed across a wide arc covering a large area of the screen, characterized by a large half-intensity angle  360 . Similarly, on the right side of  FIG. 5  the side view of emitter  50  shows that light is distributed across a wide range of heights above the screen surface, characterized by a large half-intensity angle  370 . The minor difference between distributions across vertical and horizontal axes is due to the shell being wider than it is high. 
     Reference is made to  FIG. 6 , which is a simplified diagram of angular light intensity distributions for light emitted by a light emitter module  100  in accordance with an embodiment of the present invention.  FIG. 6  shows light emission for an emitter having a plastic shell according to the present invention.  FIG. 6  shows top and side views of light emitter module  100  encased in plastic shell  260  formed as a partial semi-ellipse rotated through a semi-circle. Above each emitter view is a normalized intensity graph showing relative radiant intensity vs. angular displacement. On the left side of  FIG. 6  the intensity graph above the top view of emitter  100  shows that light is distributed across a wide angle and therefore covers a wide wedge of the screen characterized by a large half-intensity angle, θ 1/2 ,  380 , similar to that of hemispherical plastic shell  250  of  FIG. 5 . This is because the lateral cross-section of plastic shell  260  is a semi-circle. However, the intensity graph above the side view of light emitter module  100  on the right side of  FIG. 6  shows that light is distributed within a substantially narrower range of heights than the emitter of  FIG. 5 , characterized by a small half-intensity angle  390 . This focused intensity is a result of plastic shell  260  being formed as a partial semi-ellipse along the height of light emitter module  100 ; i.e., along the dimension perpendicular to the screen surface. By narrowing the total radiation within a narrow range of angular displacements, the absolute radiant intensity is greater than that in  FIG. 5 . 
     Together,  FIGS. 5 and 6  illustrate the difference in light distribution between a prior art emitter with a hemispherical plastic shell, and an emitter according to the teachings of the present invention whose plastic shell is formed as a partial semi-ellipse rotated through a semi-circle. 
     Reference is made to  FIG. 7 , which is a simplified perspective view of a hemi-ellipsoidal plastic shell for a light emitter module  100 , in accordance with an embodiment of the present invention. As shown in  FIG. 7 , the longitudinal cross-section of the plastic shell is a partial semi-ellipse  120 , and the lateral cross-section of the plastic shell is a semi-circle  160 . When LEDs  100  of  FIG. 7  are used in optical touch screens as shown in  FIG. 1 , and as described in applicant&#39;s co-pending application Ser. No. 13/424,472, entitled OPTICAL TOUCH SCREEN WITH TRI-DIRECTIONAL MICRO-LENSES, they optimize use of available light for touch detection vis-à-vis conventional LEDs having cylindrical or hemispherical plastic shells. 
     Reference is made to  FIG. 8 , which is a simplified diagram of a side view of a light emitter that incorporates the shell of  FIG. 7 . As shown in  FIG. 8 , a light emitting semiconductor surface  110  is encased in a shell having a partial semi-elliptical cross-section  120  with a focal point  130  located at a distance  140  behind semiconductor surface  110 . This shell projects the light emitted from the semiconductor surface into an essentially collimated vertical field  150 , corresponding to the right-hand graph in  FIG. 6 . 
     Reference is made to  FIG. 9 , which is a simplified diagram of a top view of a light emitter that incorporates the shell of  FIG. 7 . As shown in  FIG. 9 , the shell has a semi-circular cross-section  160  and evenly distributes the emitted light over a wide angular range  170 , corresponding to the left-hand graph in  FIG. 6 .  FIG. 9  shows how all points on the semiconductor surface  110  contribute light to a wide angular range. 
     Together,  FIGS. 8 and 9  show that the shell has a three-dimensional geometry of partial semi-ellipse  120  rotated through semi-circle  160  about an axis on light emitting semiconductor surface  110 . 
     Although the above discussion relates to LED modules, it will be appreciated by those skilled in the art that the shell of  FIG. 7  may also be used with photodiode detectors. 
     In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made to the specific exemplary embodiments without departing from the broader spirit and scope of the invention as set forth in the appended claims. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.