Patent Publication Number: US-2013241882-A1

Title: Optical touch system and optical touch position detecting method

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of Taiwan Patent Application No. 101109283, filed on Mar. 19, 2012, the entirety of which is incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an optical touch system and an optical touch position detecting method, and in particular relates to an optical touch system and an optical touch position detecting method adopting a camera provided with two lenses to detect a touch position. 
     2. Description of the Related Art 
     Touch techniques applied in displays include not only embedding a capacitive or inductive touch panel in to a display device, but also disposing a camera provided with an image sensor to the periphery of the display device to optically detect touch positions. 
     In a conventional optical touch technique, two cameras are used and disposed at different corners of the touch surface such that the fields of view (FOV) of the two cameras both cover the entire touch surface. The touch position of a touch object at the touch surface is determined by the intersection point of the lines passing through the touch object and the two cameras. 
     As shown in  FIG. 1 , camera  101  and  102  are disposed at two corners of the touch area  103  such that the fields of view of the two cameras  101  and  102  both cover the entire touch area  103 . A linear light source  104  and a retro-reflector  105  are further disposed at the boundary of the touch area  103 . The retro-reflector  105  is located along three edges of the touch area  103  and is capable of reflecting any incident light beam back along its incident direction. Therefore, when the linear light source  104  lightens the entire touch area  103 , the light beams are reflected by the retro-reflector  105  to the cameras  101  and  102 . In this case, when a touch object touches the touch area  103  to produce a touch point  107 , the touch object blocks the reflecting light beams of the directions through the touch point  107  and the cameras  101  and  102 , and accordingly the cameras  101  and  102  respectively obtain a dark point at a position on the pixel array of an image sensor provided via the cameras  101  and  102 . Finally, a processor  106  acquires the directions of the touch point  107  with respect to the cameras  101  and  102  and calculates the real position of the touch point  107 , according to the positions of the dark points on the pixel arrays of the image sensors. 
     In addition, the conventional optical touch techniques also include a structure wherein a camera and a mirror are disposed at the periphery of the touch surface. 
     As shown in  FIG. 2 , a camera  201  is disposed at a corner of a touch area  203  such that the field of view of the camera  201  covers the entire touch area  203 . Further, a linear light source  204  and a mirror  205  are disposed along the edges of the touch area  203 . Because the camera  201  and the mirror image of the camera  201  are located at the symmetry positions with respect to the mirror  205 , this configuration is substantially equal to a two-camera configuration. The linear light source  204  lightens the entire touch area  203  and the mirror  205  reflects light beams to the camera  201 . When a touch object touches the touch area  203  to produce a touch point  207 , the touch object blocks the light beams of the two directions reflected from the mirror  205  to the camera  201 , and accordingly the camera  201  obtains two dark points at two positions on the pixel array of an image sensor provided via the camera  201 . Finally, a processor  206  acquires the direction of the touch point  207  with respect to the camera  201  and calculates the real position of the touch point  207 , according to the two positions of the two dark points on the pixel array of the image sensor provided via the camera  201 . 
     However, no matter if the configuration has two cameras and a retro-reflector or a camera and a mirror, in the conventional art the camera is always a structure provided with a lens and an image sensor. Therefore, the purpose of the invention is providing an optical touch system and an optical touch position detecting method different from the conventional art. The optical touch system and the optical touch position detecting method according to the invention use a camera provided with two lenses and an image sensor to detect touch positions. 
     BRIEF SUMMARY OF THE INVENTION 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     The invention provides an optical touch system for detecting a position of a touch object on a touch area, including: at least one active light source for lightening the touch area; a camera having two lenses and an image sensor to capture two images of the touch object on the image sensor through the two lenses; and a processor for calculating the position of the touch object according to the positions of the two images of the touch object on the image sensor, wherein the camera is disposed at the periphery of the touch area such that fields of view of the two lenses both cover the entire touch area. 
     In the above optical touch system, the positions of the two images on the image sensor correspond to two angle parameters, wherein the angle parameters are values of an angle between a predetermined reference line and a line passing the position of the touch object and one of the two lenses. A two-dimensional coordinate system is used to define the position of a point on the touch area with a coordinate, and the processor uses the two angle parameters and the coordinates of the two lenses to calculate the coordinate of the touch object. 
     In the above optical touch system, the predetermined reference line is parallel with the x-axis of the two-dimensional coordinate system and the processor calculates the coordinate (x, y) of the touch object according to the following equations: 
       ( y−y   1 )/( x−x   1 )=tan θ 1 ;
 
       ( y−y   2 )/( x−x   2 )=tan θ 2 ,
 
     wherein (x 1 , y 1 ) is the coordinate of a first lens of the two lenses, θ 1  is the angle parameter with respect to the first lens, (x 2 , y 2 ) is the coordinate of a second lens of the two lenses, and θ 2  is the angle parameter with respect to the second lens. 
     In the above optical touch system, the angle parameter θ 1  corresponds to a pixel position within an image range of the first lens on the image sensor, and the angle parameter θ 2  corresponds to a pixel position within an image range of the second lens on the image sensor, wherein the angle parameters θ 1  and θ 2  are determined by the two pixel positions of the two images formed on the image sensor through the first lens and the second lens. 
     According to an embodiment of the invention, the active light source is disposed on the camera and provides light with enough intensity such that the light omitted from the active light source can be reflected by the touch object to the camera. 
     According to an embodiment of the invention, the optical touch system further includes: at least one retro-reflector disposed at the periphery of the touch area, wherein the light omitted from the active light source is reflected by the retro-reflector such that the image background captured by the image sensor is a bright background. 
     According to an embodiment of the invention, the active light source is an infrared light emitting diode or an infrared light diode, and the image sensor is capable of detecting infrared light images. 
     The invention also provides an optical touch position detecting method, including: using a camera provided with two lenses and an image sensor to receive images of a touch object; and calculating the position of the touch object according to the positions of two images of the touch object formed on the image sensor through the two lenses. 
     In the above optical touch position detecting method, the positions of the two images on the image sensor correspond to two angle parameters, wherein the angle parameters are values of an angle between a predetermined reference line and a line passing the position of the touch object and one of the two lenses. 
     The above optical touch position detecting method further includes using a two-dimensional coordinate system to define the position of a point on the touch area with a coordinate, and using the two angle parameters and the coordinates of the two lenses to calculate the coordinate of the touch object. 
     In the above optical touch position detecting method, the predetermined reference line is parallel with the x-axis of the two-dimensional coordinate system and the coordinate (x, y) of the touch object is calculated according to the following equations: 
       ( y−y   1 )/( x−x   1 )=tan θ 1 ;
 
       ( y−y   2 )/( x−x   2 )=tan θ 2 ,
 
     wherein (x 1 , y 1 ) is the coordinate of a first lens of the two lenses, θ 1  is the angle parameter with respect to the first lens, (x2, y2) is the coordinate of a second lens of the two lenses, and θ 2  is the angle parameter with respect to the second lens. 
     In the above optical touch position detecting method, the angle parameter θ 1  corresponds to a pixel position within an image range of the first lens on the image sensor, and the angle parameter θ 2  corresponds to a pixel position within an image range of the second lens on the image sensor, wherein the angle parameters θ 1  and θ 2  are determined by the two pixel positions of the two images formed on the image sensor through the first lens and the second lens. 
     According to the optical touch system and the optical touch position detecting method of the invention, a camera provided with two lenses and an image sensor is used, and an active light source is disposed on the camera to lighten a touch object such that the camera receives reflected light from the touch object for detecting the touch position of the touch object. Therefore, the invention provides a new optical touch system and optical touch position detecting method different from the conventional art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  is a configuration diagram showing a conventional optical touch system. 
         FIG. 2  is a configuration diagram showing another conventional optical touch system. 
         FIG. 3  is a configuration diagram showing an optical touch system in accordance with an embodiment of the invention. 
         FIG. 4  is a diagram for explaining the angle acquiring method of the optical touch system in accordance with the embodiment of the invention. 
         FIG. 5  is a diagram for explaining the angle acquiring method of the optical touch system in accordance with the embodiment of the invention. 
         FIG. 6  is a diagram for explaining the angle acquiring method of the optical touch system in accordance with the embodiment of the invention. 
         FIG. 7  is a configuration diagram showing an optical touch system in accordance with another embodiment of the invention. 
         FIG. 8  is a configuration diagram showing an optical touch system in accordance with another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
       FIG. 3  is a configuration diagram showing an optical touch system in accordance with an embodiment of the invention. As shown in  FIG. 3 , the optical touch system of the embodiment comprises a camera  301 , an active light source  302  and a processor  303 . The camera  301  has two lenses L 1  and L 2  and an image sensor S. The camera  301  is disposed at a corner of a touch area  304 , such that the fields of view of the lenses L 1  and L 2  can both cover the entire touch area  304  and the touch object can be completely imaged on the image sensor S through any one of the lens L 1  and lens L 2 . The active light source  302  is fixed on the camera  301  to lighten the touch object located on the touch area  304 . The touch object reflects the light beam omitted from the active light source  302  to the camera  301 . The processor  303  is used for calculating the position of the touch point  305  of the touch object. 
     Next, a touch position detecting method applied to this optical touch system is described. As shown in  FIG. 3 , every point on the surface of the touch area  304  is defined by a two-dimensional coordinate system. It is supposed that the position of the touch point is (x, y), the intersection point of the field of view of the lens L 1  (the center point of the lens L 1  in  FIG. 3 ) is (x 1 , y 1 ), and the intersection point of the field of view of the lens L 2  (the center point of the lens L 2  in  FIG. 3 ) is (x 2 , y 2 ). Further, it is supposed that the angle between a line passing through the touch point  305  and the lens L 1  and an edge of the touch area  304  (the length of the rectangular touch area  304  in this embodiment) is θ 1 , and the angle between a line passing through the touch point  305  and the lens L 2  and the same edge of the touch area  304  is θ 2 . Therefore, according to the trigonometric function, the following linear Equations are obtained. 
       ( y−y   1 )/( x−x   1 )=tan θ 1   (1)
 
       ( y−y   2 )/( x−x   2 )=tan θ 2   (2)
 
     Because of the fixed positions of the lenses L 1  and L 2 , x 1 , y 1 , x 2 , and y 2  are known constants. Therefore, as long as θ 1  and θ 2  are acquired, the position (x, y) of the touch point  305  can be derived from the above equations. The acquiring method for θ 1  and θ 2  is described below. 
       FIGS. 4-6  are diagrams for explaining the angle acquiring method of the optical touch system in accordance with the embodiment of the invention.  FIG. 4  shows fields of view FOV of the lenses L 1  and L 2  and their image ranges on the image sensor S. Assume that the image sensor S has 1280 pixels (pixel number 0˜1279) and the image ranges of the lenses L 1  and L 2  are both 800 pixels. Therefore, the image range of the lens L 1  and the image range of the lens L 2  are overlapped. Also refer to  FIG. 6 , the image range R 1  of the lens L 1  on the image sensor S is a range including 0 th ˜799 th  pixels, and the image range R 2  of the lens L 2  on the image sensor S is a range including 480 th ˜1279 th  pixels. 
     As shown in  FIG. 5 , fields of view FOV of the lenses L 1  and L 2  must both cover the entire touch area  304 . Namely, the lenses L 1  and L 2  are both capable of detecting at least touches at point A and at point C. Here, for easy understanding, assume that fields of view FOV of the lenses L 1  and L 2  are both equal to a range from point A to point C. When a touch object touches point A, the light beams omitted from the active light source  302  are reflected by the touch object to the camera  301 . Therefore, because of the touch at point A, two bright points are produced on the image sensor S by light beams passing through the lenses L 1  and L 2 . As shown in  FIG. 6 , the two bright points are located at the 0 th  pixel and the 480 th  pixel, respectively, wherein the bright point located at the 0 th  pixel is the image I 1  through the lens L 1  and the bright point located at the 480 th  pixel is the image I 2  through the lens L 2 . On the other hand, when a touch object touches point C, two bright points are located at the 799 th  pixel and the 1279 th  pixel, respectively, wherein the bright point located at the 799 th  pixel is the image I 1  through the lens L 1  and the bright point located at the 1279 th  pixel is the image I 2  through the lens L 2 . 
     From the above description it is known that for a lens, the touch object located at different angle positions is imaged to different corresponding pixel positions of the image sensor S. The angle θ 1  between the line passing through the touch point  305  and the lens L 1  and the edge of the touch area  304  corresponds to a pixel position between the 0 th  and the 799 th  pixel on the image sensor S. The angle θ 2  between the line passing through the touch point  305  and the lens L 1  and the edge of the touch area  304  corresponds to a pixel position between the 480 th  and the 1279 th  pixel on the image sensor S. This characteristic is used to depict a curve diagram showing the relation between the pixel position on the image sensor S and the angle position of the touch object. Then two pixel positions of the images of the touch object on the image sensor S are used to derive the angles θ 1  and θ 2 , which are angles between the touch point  305  and the edge of the touch area  304  with respect to the lenses L 1  and L 2 , respectively. 
     Finally, the values of the angles θ 1  and θ 2  are used to substitute the variables θ 1  and θ 2  in the above equations (1) and (2) to derive the position (x, y) of the touch point  305 . 
     According to the above embodiment, the optical touch system of the invention uses a camera provided with two lenses and an image sensor to detect touch positions. However, various kinds of configurations can be applied in the optical touch system of the invention. As shown in  FIG. 7 , the camera  301  is not limited to be disposed at a corner of the touch area  304 . As long as fields of view FOV of the two lenses L 1  and L 2  cover the entire touch area  304 , the camera  301  can also be disposed, for example, at the upper edge of the touch area  304 . 
     Furthermore, in the optical touch system in accordance with the above embodiment, the touch object reflects the light omitted from the active light source  302  to the camera  301 , and the processor  303  calculates the touch position by detecting the pixel positions of the bright points on the image sensor. However, as shown in  FIG. 8 , a retro-reflector  306  can be disposed along two edges of the touch area  304 , opposite to the camera  301 . In this way, the retro-reflector  306  reflects light beams from all direction to the camera  301  such that the image sensor S is totally bright. When a touch object touches the touch area  304 , the touch object blocks the reflected light beams from specific directions and therefore two dark points are generated in the bright background in the image sensor S. Accordingly, the method which detects dark points in the bright background is contrary to the before-mentioned method which detects bright points in the dark background. 
     The optical touch system and the optical touch position detecting method are described above. However, different touch objects have different characteristics such as different thicknesses. In this case, before a normal touch operation, the touch object can touch at least one specified reference point on the touch area in advance for angle calibration. In this way, the calculation for touch position becomes more accurate during normal touch operations. 
     According to the optical touch system and the optical touch position detecting method of the invention, a camera provided with two lenses and an image sensor is used, and an active light source is disposed on the camera to lighten a touch object such that the camera receives reflected light from the touch object for detecting the touch position of the touch object. Therefore, the invention provides a new optical touch system and optical touch position detecting method different from the conventional art. 
     While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements. For example, the active light can be an infrared light emitting diode or an infrared light diode. In this case, the image sensor must be capable of detecting infrared light images. Moreover, the lens L 1  or L 2  is described as a single lens in the embodiment, but the lens L 1  or L 2  can be a lens group consisting of a plurality of lenses.