Patent Publication Number: US-2011074738-A1

Title: Touch Detection Sensing Apparatus

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to a touch detection sensing apparatus, more particularly, to a touch detection sensing apparatus including an image capturing device and a reflection mirror. 
     BACKGROUND OF THE INVENTION 
     Currently, an image capturing device (camera) is used as a device for detecting a touch object on a touch screen. Generally, it uses two cameras disposed at corners of a detected screen to detect the touch object by means of Triangulation. This solution has the advantage of good applicability. However, for the solution that position coordinates of the touch object is obtained by image processing, it is necessary to use two cameras to obtain data required by the Triangulation, on the other hand, it requires high performance of a microprocessor for processing the images of the cameras. Thus production cost of such device is increased. The U.S. Pat. No. 7,274,356 discloses an apparatus in which a touch object is detected and located by a camera and two reflection mirrors that are disposed at an inner side of edges of a detected screen. In this solution, only one camera is used. However, two reflection mirrors are needed, and the two reflection mirrors should be disposed on the adjacent edges and an intersection of the two reflection mirrors form a non-reflection area. Therefore the structure of the apparatus is still complicated, which makes manufacture and installation of the apparatus difficult. 
     In addition, a field angle of the image capturing device (camera) in the touch detection sensing apparatus in the prior art is generally very large, and the field angle of each image capturing device can cover the whole detected screen. So the camera with a large field angle will have large distortion. Therefore, there exists the problem of large distortion and large location error in these touch detection sensing apparatuses. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the present invention, there is provided a touch detection sensing apparatus for detecting a position of a touch object on a detected screen, which has a simplified structure and comprises: a detected screen; an reflection mirror, which enables the detected screen to be imaged as a virtual image in the reflection mirror; an image capturing device, for capturing an image of the touch object on the detected screen and capturing an image of the virtual image of the touch object in the reflection mirror, wherein field of view of the image capturing device covers the whole detected screen and the whole image of the detected screen in the reflection mirror. The touch detection sensing apparatus further comprises: an image processing circuit for calculating the position of the touch object on the detected screen based on the image of the touch object and the image of the virtual image of the touch object in the reflection mirror captured by the image capturing device. 
     According to another aspect of the present invention, there is provided a touch detection sensing apparatus for detecting a position of a touch object on a detected screen, in order to reduce the distortion of an image capturing device and improve location accuracy of the apparatus, which comprises: a detected screen; two image capturing devices; and a reflection mirror; wherein each image capturing device has a small field angle so that its field of view does not cover the whole detected screen, and an overlapping of the fields of view of two image capturing devices, i.e. the total field of view of the two image capturing devices, covers the whole detected screen. The touch detection sensing apparatus further comprises an image processing circuit, wherein when the touch object appears in a common field of view of the two image capturing devices, the image processing circuit calculates the position of the touch object in the detected screen based on the images of the touch object captured by the two image capturing devices by using Triangulation; when the touch object appears in the field of view covered only by one image capturing device, the image processing circuit calculates the position of the touch object in the detected screen based on the image of the touch object and the image of the virtual image of the touch object in the reflection mirror captured by the one image capturing device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1   a  is a structure diagram of a touch detection sensing apparatus and its coordinate detection schematic diagram according to an embodiment of the present invention; 
         FIG. 1   b  is a schematic perspective view of the touch detection sensing apparatus shown in  FIG. 1   a;    
         FIG. 2  is another structure diagram of a touch detection sensing apparatus equivalent to  FIG. 1  and its coordinate detection schematic diagram; 
         FIG. 3  is a structure diagram of a touch detection sensing apparatus including two image capturing devices according to another embodiment of the present invention; 
         FIG. 4  is a structure diagram of an infrared light source comprising a plurality of light-emitting tubes; 
         FIG. 5  is a structure diagram of an infrared light source comprising a light-emitting tube and a concave lens; 
         FIG. 6  is a structure diagram of a touch detection sensing apparatus including two image capturing devices and two reflection mirrors according to another embodiment of the present invention; 
         FIG. 7  is a structure diagram of a touch detection sensing apparatus including two image capturing devices and two reflection mirrors according to another embodiment of the invention; and 
         FIG. 8  is a diagram of imaging a touch object and a virtual image of the touch object in a reflection mirror on a photosensitive chip of the image capturing device. 
     
    
    
     In the drawings, the same component or element is denoted by the same reference number, wherein the meanings of every reference number are: 
       101 : detected screen;  102 : camera (image capturing device);  103 : reflection mirror with a strip shape;  104 : touch object;  105 : virtual image of the touch object in reflection mirror;  106 : infrared light source;  107 : light directly from touch object to a vertex of the field angle θ of camera;  108 : light to the vertex of the field angle θ of camera reflected by reflection mirror and surface of touch object;  109 : virtual light of image in reflection mirror;  110 : reflection surface of reflection mirror;  111 : frame of detected screen;  112  to  115 : four edges of frame  111  of detected screen;  401 : motherboard for installing infrared light-emitting tube;  402 : infrared light-emitting tube;  501 : single infrared light-emitting tube;  502 : concave lens;  601 : effective pixel band of photosensitive chip in camera;  602 : a part of image of light directly irradiating touch object on photosensitive chip;  603 : image of virtual image of touch object reflected by reflection mirror on photosensitive chip. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Next, the embodiments of the present invention will be described in detail by way of example in conjunction with accompany drawings. 
     First Embodiment 
       FIGS. 1   a  and  1   b  show a structure diagram of a touch detection sensing apparatus according to an embodiment of the invention and a schematic diagram of performing coordinate detection respectively. In the embodiments shown in  FIGS. 1   a  and  1   b , the detected screen  101  is a touch area of a touch screen, that is, the detected screen  101  is an area of the touch screen for a user to perform touch operation. The image capturing device is a camera  102  which is installed (or disposed) at a corner of a surface of the detected screen  101 . In this embodiment, two edges forming the corner are two adjacent edges  112  and  113  of the detected screen  101 . The reflection mirror  103  is disposed on an edge (i.e. the edge  115 ) opposite to one edge (i.e. the edge  113 ) of the two edges. The length of the reflection mirror  103  at least equals to the length of the edge  115 . A reflection surface  110  of the reflection mirror  103  is towards the edge  113  opposite to the edge  115  where the reflection mirror  103  is located, i.e. towards an area within the frame  111 . That is to say, in  FIG. 1   a , the reflection surface  110  of the reflection mirror  103  is towards the direction indicated by the arrow  116 . The image processing circuit (not shown) is coupled to the camera  102  to obtain the image data captured by the camera  102 . 
       FIG. 1   a  also shows a coordinate system XOY, wherein the X axis and Y axis are in parallel with the edge  113  and  112  of the detected screen respectively, and the origin is the vertex of the field angle θ of the camera  102 , i.e. the central point of the lens equivalent to the objective lens of the camera  102 . Assume that there is a touch object  104  on the detected screen, its coordinate value in the coordinate system XOY is set as P(x, y), the horizontal length of the edges of the detected screen is set as L (i.e. the length of the edges  113 ,  115 ), and the height is set as H. According to optical reflection theory and analytic geometry theory, the following formulas can be obtained: 
       y 1 =xtgα
 
       2 y   2   +y   1   =xtgβ   
     
       
      
       y 
       1 
       +y 
       2 
       =H+y 
       0  
      
     
     In the above formulas, y 0  is a distance from an edge of the detected screen opposite to the reflection mirror to the coordinate axis in parallel with the reflection mirror, in  FIG. 1   a , y 0  is the distance between the upper edge  113  of the detected screen and X axis; α is an angle between the light  107  reflected directly from the surface of the touch object  104  to the vertex of the field angle θ of the camera and X axis; β is an angle between the light  108  reflected from the touch object to the vertex of the field angle θ of the camera by the reflection mirror and X axis. It can be known from the optical theory of photography or camera that the angles α and β can be obtained by detecting the position of the image of the touch object on a photosensitive chip in the camera and by utilizing the position where the virtual light  109  emitted by the virtual image  105  is imaged in the photosensitive chip in the camera. Thus, the three unknown numbers x, y 1  and y 2  (wherein y 1 =y) can be calculated by solving a three-variable linear equations that comprises the above three formulas. Additionally, in  FIG. 1   a , x 0  is a distance between an edge  112  of the detected screen and Y axis, and x 0  and y 0  may be zero or a value that is small but bigger than zero. x 0  and y 0  are the distance parameters between the detected screen  101  and the camera  102 , and are known, so the coordinate value of the touch object  104  in the detected screen can be acquired. Here, the touch object  104  is approximately a point. 
     A person skilled in the art can appreciate that the expressions “installed at a corner” or “disposed at a corner” can be interpreted as installed or disposed at somewhere adjacent to the corner, i.e. x 0  and y 0  are zero or are a positive value that is small but bigger than zero. 
       FIG. 2  shows a variation of the first embodiment. It differs from  FIG. 1  in that the reflection mirror  103  is installed on the edge  114  instead of on the edge  115 . The principle of detecting and solving the coordinate value is same as that of  FIG. 1 , and is not described here. 
     Second Embodiment 
     To accommodate various complex illumination environments and display contents, based on the first embodiment, an infrared light source, such as the infrared light source  106  in  FIG. 1   a , can be disposed on the edges of detected screen, wherein luminous surface of the infrared light source is towards the detected screen, i.e. towards the area within the frame. The image capturing device is photosensitive to the infrared light. The infrared light source is used here as the infrared light is invisible for human eyes. If the infrared light source is only used for illumination, an infrared color filter (not shown) can be added on a light path of the camera so that the infrared light can transmit, thereby eliminating interference from ambient light. As shown in  FIG. 1   a , four infrared light sources are disposed on the frame  111  of the detected screen  101 , such as at four corners. There are two kinds of structure for the infrared light source. The first is, as shown in  FIG. 4 , that each infrared light source comprises a plurality of infrared light-emitting tubes  402  arranged in parallel, typically, they are installed on a motherboard  401  in a sector to get a large illumination scattering angle. The second is, as shown in  FIG. 5 , that each infrared light source comprises one infrared light-emitting tube  501  and, if necessary, a concave lens  502  is disposed in front of the luminous surface of the infrared light-emitting tube to enlarge the scattering angle of the infrared light-emitting tube to obtain the uniform light. 
     In addition, the above infrared light source can be replaced with other light sources. 
     Third Embodiment 
     In the structure shown in  FIG. 1   a , if the field angle θ of the camera is small, the distance between the camera and the screen is required to be large to ensure the whole detected screen is within the field of view of the camera. This will increase installation size of the system, but can obtain the uniform location accuracy on the whole screen. If the camera is required to be close to the detected screen to reduce the installation size, the field angle θ of the camera is approaching or even larger than 90 degrees. It can be known from  FIGS. 3 and 1   a  that when the touch object is very close to the vertical edge at the left side, the angles α and β are very close, so when the angles change a little, their tangent value will vary significantly, at this time, the distortion of lens of the camera will also be very large, thus it is not easy to get a good detection accuracy. In order to get better and uniform detection accuracy, based on the first or second embodiment, another camera  102  is added at the corner adjacent to the camera  102 , as shown in  FIG. 3 . Now the reflection mirror  103  is disposed on the edge opposite to the edge of the detected screen between the two cameras, that is, the reflection mirror is disposed on the edge  115  which is not the edge forming the corner where the cameras are disposed. With this structure, it is easy to get the uniform detection accuracy on the whole screen by setting each camera to work in its own optimal accuracy. That is, in  FIG. 3 , the field angle of each camera covers the whole detected screen, but the image processing circuit only utilize the image of the touch object and the image of the virtual image of the touch object in the reflection mirror captured within a part of field of view of each camera to calculate the position of the touch object, so as to prevent the calculation error from being too large and avoid inaccuracy in the position when the angles α and β are close to 90 degrees. The part of field of view of each camera utilized by the image processing circuit when calculating the position of the touch object is referred to as an effective field of view. 
     As a variation of the embodiment, it is not necessary for each camera to have a large field angle. The field of view of each camera may only cover a portion of the detected screen, but the overlapping of the fields of view of the two cameras would cover the whole detected screen. When the touch object appears in a common field of view of the two image capturing devices, the image processing circuit calculates the position of the touch object on the detected screen based on the image of the touch object captured by the two image capturing devices by using the known Triangulation. When the touch object appears in the field of view covered only by one image capturing device, similar to the first embodiment, the image processing circuit calculates the position of the touch object in the detected screen based on the image of the touch object and the image of the virtual image of the touch object in the reflection mirror captured by the one image capturing device. In this way, the problem of high image distortion can be overcome and the location accuracy on the whole screen can be improved, because each image capturing device has a relatively small field angle. 
     In this embodiment, the field angle or effective field angle of each image capturing device can be set as shown in  FIG. 7 . 
     Fourth Embodiment 
       FIG. 6  is a structure diagram of a touch detection sensing apparatus according to another embodiment of the present invention. The touch detection sensing apparatus is used to detect the position of the touch object on a rectangular detected screen  101 , and comprises the detected screen  101 , two cameras  102 , the image processing circuit, and two reflection mirrors  103 , and optionally, the infrared light sources  106 . The length of each of the reflection mirrors  103  at least equals to the length of the corresponding edge of the rectangular detected screen  101 . The two cameras  102  are disposed on two opposite short edges of the detected screen  101  respectively, that is to say, the field of view of each of the two image capturing devices (cameras  102 ) does not cover the whole detected screen  101 , but the whole detected screen  101  is within the total field of view of the two cameras  102 , that is, a portion of the detected screen  101  is within both fields of view of the two cameras  102 , and other portions are within the respective fields of view of the two cameras  102 . The two reflection mirrors  103  are installed on two opposite edges adjacent to the edges where the cameras  102  are disposed respectively, and the reflection surfaces of the reflection mirrors  103  are towards the detected screen  101 , i.e., in this embodiment, the reflection mirrors  103  are disposed on two opposite long edges of the detected screen  101  respectively. 
     As shown in  FIG. 6 , when the touch object may be within the both fields of view of the two cameras, as the touch object Q shown in  FIG. 6 , the image processing circuit can calculate the position of the touch object by using the known Triangulation. 
     In another case where the touch object is only within the field of view of one camera, as the touch object P shown in  FIG. 6 , the position of the touch object is calculated by using the same method as the first embodiment, that is, the image processing circuit calculates the position of the touch object based on the image of the touch object P and the image of the virtual image of the touch object P in the upper reflection mirror  103  captured by the left camera  102 . 
     Obviously, when the touch object is only within the field of view of one camera and is close to the lower reflection mirror, the image processing circuit calculates the position of the touch object based on the image of the touch object P and the image of the virtual image of the touch object P in the lower reflection mirror  103  captured by the camera  102 . 
     As a variation of the embodiment, the positions of the image capturing devices are not changed, and the reflection mirrors can be disposed on the two edges where the image capturing devices are disposed, that is, the reflection mirrors and the image capturing devices are disposed on the same edges of the detected screen. 
     Fifth Embodiment 
       FIG. 7  illustrates a structure diagram of a touch detection sensing apparatus according to another embodiment. As shown in  FIG. 7 , the touch detection sensing apparatus differs from the touch detection sensing apparatus in the fourth embodiment shown in  FIG. 6  in that the installation position of the image capturing devices and reflection mirrors is different. In  FIG. 7 , two image capturing devices (cameras  102 ) are disposed at two adjacent corners of the detected screen  101 , and two reflection mirrors  103  are disposed on two opposite edges that are not common for the two adjacent corners where cameras  103  are disposed. 
     When the touch object is within the both fields of view of the two cameras, the image processing circuit can calculate the position of the touch object by using the known Triangulation. When the touch object is only within the field of view of one camera, the position of the touch object is calculated by using the same method as the first embodiment. 
     In comparison with the fourth embodiment, this embodiment can greatly reduce the field angle of the image capturing device, thereby obtaining the smaller distortion and further improving the location accuracy for the touch object. 
     Other Variations 
     Since the touch detection sensing apparatus is used to detect whether there is the touch object in proximity to the surface of the detected screen, in the above embodiments, the system only needs the image data of a narrow strip on the photosensitive chip inside the camera. As shown in  FIG. 8 , the angles α and β can be calculated only by selecting a line array  601  formed by pixels on the photosensitive chip with surface array structure and detecting the positions of the image  602  formed by directly illuminating the touch object and the image  603  formed by the reflection of the reflection mirror on the line array. Thus, in the above embodiments, the surface array photosensitive chip inside the camera can be replaced by a photosensitive chip with line array structure. 
     In addition, the detected screen  101  may also be in other shapes. In the case where the two reflection mirrors are installed in opposite to each other, the two image capturing devices may also be disposed on different planes in parallel with the detected screen  101 . The negative effects due to the opposite installation of two reflection mirrors with the surfaces opposite to each other can be reduced. The image capturing device in the above embodiments is the camera, but it can be replaced with other image capturing devices to capture the image of the touch object. 
     The touch detection sensing apparatus described in the above embodiments may be disposed on a plasma television monitor or a computer monitor, or disposed in front of or behind a projection screen of a projector, or integrated into a touch screen, or used in other touch systems. 
     The embodiments of the present invention are described above only by way of example. The present invention is not limited to the specific details and the illustrative embodiments disclosed herein in its broader aspects. Therefore, various variations can be derived without departing from the spirit and scope of the general inventive concept and its equivalent description, which is defined by the appended claims.