Patent Publication Number: US-2012032921-A1

Title: Optical touch system

Description:
This application claims the benefit of Taiwan application Serial No. 99126383, filed Aug. 6, 2010, the subject matter of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates in general to an optical touch system, and more particularly to an optical touch system with high accuracy. 
     2. Description of the Related Art 
     The touch screen which provides an instinctive way of operation has now been widely used in various electronic products, such as portable electronic device, desktop computer or ATM. According to the principles of sensing, the touch screen can be divided into resistive touch screen, capacitive touch screen, ultra-sonic touch screen and optical touch screen. Let the optical touch screen be taken for example. When an object such as the user&#39;s finger or a stylus is placed in the touch region, the light emitted from the light source will be blocked by the object. Based on the image received by the sensor, the touch point coordinate of the object in the touch region can thus be obtained. 
     However, as the technology advances, the demand for multi-touch technology also grows. However, the conventional method for determining the touch point coordinate according to the image received by the sensor and the measured angle cannot meet the requirement of the multi-touch technology. Thus, how to increase the accuracy of determining the touch point coordinate has become an imminent task to the industry. 
     SUMMARY OF THE INVENTION 
     The invention is directed to an optical touch system, which increases the accuracy of determining a touch point coordinate according to angle information and distance information between a touch point and a sensing module. 
     According to a first aspect of the present invention, an optical touch system including a first light source, a second light source, a sensing module and a processing module is provided. The lighting timing of the second light source differs with that of the first light source by a phase. The sensing module is for capturing a sensing image related to a touch point on a panel, and receiving a first bounce light of the touch point corresponding to the first light source and a second bounce light of the touch point corresponding to the second light source. The processing module is for obtaining an angle information according to the sensing image, calculating a phase difference between the first bounce light and the second bounce light to obtain a distance information, and determining a coordinate corresponding to the touch point according to the angle information and the distance information. 
     The above and other aspects of the invention will become better understood with regard to the following detailed description of the preferred but non-limiting embodiment(s). The following description is made with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an optical touch system according to a preferred embodiment of the invention; 
         FIG. 2  shows a first light source, a second light source and a sensing module according to a preferred embodiment of the invention; and 
         FIG. 3  shows a diagram of timing wave-patterns of a first light source, a second light source, a first sensor and a second sensor according to a preferred embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention provides an optical touch system, which increases the accuracy of determining a touch point coordinate according to the information of the angle at the touch point and the information of the distance from the touch point to the sensing module, wherein the angle information is obtained by the sensing module and the distance information is obtained from the calculation of the phase difference between different bounce lights. 
     Referring to  FIG. 1 , an optical touch system according to a preferred embodiment of the invention is shown. The optical touch system  100  is for determining a touch point coordinate on a panel  110 . A touch region  115  can be defined on the panel  110  by a number of optical elements such as light guide bars and reflectors. The optical touch system  100  includes a first light source  120 , a second light source  125 , a sensing module  130  and a processing module  140 . The first light source  120  and the second light source  125  have the same lighting frequency (such as 100 MHz), but the lighting timing of the first light source  120  differs with that of the second light source  125  by a phase. 
     In the exemplification below, the lighting timing of the first light source  120  differs with that of the second light source  125  by 180 degrees, but such exemplification is not for limiting the invention. Referring to  FIG. 2 , a first light source  120 , a second light source  125  and a sensing module  130  according to a preferred embodiment of the invention is shown. In  FIG. 2 , the first light source  120  such as emits a P polarized light, and the second light source  125  such as emits an S polarized light, wherein the P polarized light and the S polarized light are two polarized light components perpendicular to each other. The sensing module  130  includes a first filter  142 , a second filter  144 , a first sensor  152  and a second sensor  154 . The first filter  142  is for receiving a reflected P polarized light (the first bounce light), and the second filter  144  is for receiving a reflected S polarized light (the second bounce light). The above effect can be achieved by using light sources of different wavelengths accompanied by a band-pass filter. 
     The sensing module  130  captures a sensing image related to a touch point A on a panel  110 . The processing module  140  obtains an angle information corresponding to touch point A according to the sensing image. Referring to  FIG. 3 , a diagram of timing wave-patterns of the first light source  120 , the second light source  125 , the first sensor  152  and the second sensor  154  according to a preferred embodiment of the invention is shown. As indicated in  FIG. 3 , the first sensor  152  and the second sensor  154  perform exposure at a fixed frequency (such as 100 MHz), so that the control burden of the entire optical touch system is reduced. 
     After the light emitted from the first light source  120  is reflected through the touch point A, the first bounce light returns in a time difference  6 . Then, the first bounce light is received by a lens assembly of the sensing module  130  and then focused on the first sensor  152 , which accordingly analyzes the strength of the first bounce light. After the light emitted from the second light source  125  is reflected through touch point A, the second bounce light also returns in the same time difference  6 . Then, the second bounce light is received by a lens assembly of the sensing module  130  and then focused on the second sensor  154 , which accordingly analyzes the strength of the second bounce light. 
     The processing module  140  calculates the ratio of the strength of the first bounce light to the strength of the second bounce light to obtain the phase difference between the first bounce light and the second bounce light. For example, let the lighting frequency (such as 100 MHz) of the first light source  120  be the same with that of the second light source  125 , but the lighting timing of the first light source  120  differs with that of the second light source  125  by 180 degrees. Suppose the ratio of the strength of the first bounce light to the strength of the second bounce light is 8.333:1.667, the processing module  140  calculates the phase difference between the first bounce light and the second bounce light as: 1.667/(8.333+1.667)×10 −8 =1.667×10 −9 . The processing module  140  can further multiplies the phase difference 1.667×10 −9  with the light speed to obtain a proceeding optical path of 50 cm. In other words, the information of the distance from the touch point A to the sensing module  130  is a half of the optical path and equal to 25 cm. 
     After the angle information and the distance information are obtained, the processing module  140  combines the angle information and the distance information to accurately determine a coordinate corresponding to the touch point A. 
     Since the aberration of the optical lens results in optical distortion to the relation between view angle and image height, the optical touch system  100  of the present embodiment of the invention can apply image processing to the images formed on the first sensor  152  and the second sensor  154  so as to calibrate the error caused by optical distortion. Furthermore, phase difference occurs between the images formed on the first sensor  152  and the second sensor  154  due to the difference in optical paths. The phase difference is caused by the errors occurring during the manufacturing and the assembly of the elements. The optical touch system  100  can dispose a reflective plate at a suitable distance, and compare the measured phase difference to the theoretical phase difference to obtain a base error on which system calibration is based. 
     The optical touch system disclosed in the above embodiments of the invention has many advantages exemplified below: 
     The optical touch system of the invention increases the accuracy of determining a touch point coordinate according to the angle information of the touch point and the information distance from the touch point to the sensing module, wherein the angle information is obtained by the sensing module and the distance information is obtained from the calculation of the phase difference between different bounce lights. The optical touch system of the invention has high accuracy, and meets the requirement of the multi-touch technology. 
     While the invention has been described by way of example and in terms of the preferred embodiment (s), it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.