Patent Publication Number: US-2011049241-A1

Title: Barcode Scanner

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This Application claims priority of Taiwan Patent Application No. 098129683, filed on Sep. 3, 2009, the entirety of which is incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a barcode scanner, and more particularly to a barcode scanner with reduced manufacturing costs and optical sensitivity. 
     2. Description of the Related Art 
     Barcode scanners have been widely employed in various fields. A conventional barcode scanner is mainly composed of a lens set and an imaging member. When the barcode scanner scans a barcode image, the barcode image is received by the lens set and the light beams thereof are imaged on the imaging member by refraction of the lens set. Scanning of the barcode image is thus achieved. 
     Nevertheless, as the lens set of the conventional barcode scanner comprises a plurality of glass lenses, manufacturing costs thereof are high. 
     Hence, there is a need for a barcode scanner with a lens set comprising a plurality of plastic lenses, reducing the overall manufacturing costs. 
     BRIEF SUMMARY OF THE INVENTION 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     An exemplary embodiment of the invention provides a barcode scanner comprising a lens set and an imaging member. The lens set receives a barcode image and comprises a first plastic lens, a second plastic lens, a diaphragm, a third plastic lens, and a low-pass filter sequentially arranged along an optical axis of the lens set. The first and third plastic lenses comprise convex lenses. The second plastic lens comprises a concave lens. The imaging member is separated from the lens set by a predetermined distance. The low-pass filter is disposed between the third plastic lens and the imaging member. The barcode image received by the lens set is imaged on the imaging member. 
     The second plastic lens comprises an aspheric concave lens, and the third plastic lens comprises an aspheric convex lens. 
     The first, second, and third plastic lenses are respectively provided with a first focal length, a second focal length, and a third focal length. The ratio of the first focal length to the second focal length ranges between −2 and −1. The ratio of the second focal length to the third focal length ranges between −1 and 0. 
     The ratio of the first focal length to the second focal length is −1.268. The ratio of the second focal length to the third focal length is −0.522. 
     The first, second, and third focal lengths are 6.713 mm, −5.294 mm, and 10.139 mm, respectively. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The 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 schematic view showing the inner structure of a barcode scanner of the invention; and 
         FIG. 2  is a schematic view showing operation of the barcode scanner, of the invention, scanning a barcode image. 
     
    
    
     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. 
     Referring to  FIG. 1 , a barcode scanner  100  comprises a lens set  110  and an imaging member  120 . 
     As shown in  FIG. 1  and  FIG. 2 , the lens set  110  can receive a barcode image BI and comprises a first plastic lens  111 , a second plastic lens  112 , a diaphragm  114 , a third plastic lens  113 , and a low-pass filter  115  sequentially arranged along an optical axis  0  of the lens set  110 . Moreover, the low-pass filter  115  may be a flat glass panel with a plating film. 
     The imaging member  120  is separated from the lens set  110  by a predetermined distance. Here, the low-pass filter  115  is disposed between the third plastic lens  113  and the imaging member  120 . Moreover, the barcode image BI received by the lens set  110  is imaged on the imaging member  120 . 
     In this embodiment, the first plastic lens  111  is a convex lens, the second plastic lens  112  is an aspheric concave lens, and the third plastic lens  113  is an aspheric convex lens. Moreover, the first plastic lens  111 , second plastic lens  112 , and third plastic lens  113  are respectively provided with a first focal length F 1 , a second focal length F 2 , and a third focal length F 3 . Specifically, the ratio of the first focal length F 1  to the second focal length F 2  ranges between −2 and −1 (i.e. −2&lt;F 1 /F 2 &lt;−1), and the ratio of the second focal length F 2  to the third focal length F 3  ranges between −1 and 0 (i.e. −1&lt;F 2 /F 3 &lt;0). More specifically, when the first focal length F 1 , second focal length F 2 , and third focal length F 3  are respectively 6.713 mm, −5.294 mm, and 10.139 mm, the ratio of the first focal length F 1  to the second focal length F 2  is −1.268 and the ratio of the second focal length F 2  to the third focal length F 3  is −0.522. Additionally, when a maximum distance TL (as shown in  FIG. 1 ) between the lens set  110  and the imaging member  120  is 13.883 mm and the numerical aperture of the diaphragm  114  is 3.705 mm, the focal length of the lens set  110  is 12 mm and a maximum imaging height MIH (as shown in  FIG. 2 ) on the imaging member  120  is 3 mm. Here, the distance between the barcode image BI and the first plastic lens  111  is 200 mm. 
     Moreover, the specifications of the first plastic lens  111 , second plastic lens  112 , and third plastic lens  113  of the lens set  110  are as follows. As shown in  FIG. 1 , the first plastic lens  111  has a first lens surface S 1  and a second lens surface S 2 , the second plastic lens  112  has a third lens surface S 3  and a fourth lens surface S 4 , and the third plastic lens  113  has a fifth lens surface S 5  and a sixth lens surface S 6 . The second lens surface S 2  is adjacent to the third lens surface S 3  and a minimum distance therebetween is 0.1 mm. The diaphragm  114  is disposed between the fourth lens surface S 4  and the fifth lens surface S 5 . Specifically, the first lens surface S 1  is a spherical surface while the second lens surface S 2 , third lens surface S 3 , fourth lens surface S 4 , fifth lens surface S 5 , and sixth lens surface S 6  are aspheric surfaces. Additionally, the curvature radiuses of the first lens surface S 1 , second lens surface S 2 , third lens surface S 3 , fourth lens surface S 4 , fifth lens surface S 5 , and sixth lens surface S 6  are 2.79 mm, 10.587 mm, 2.978 mm, 1.457 mm, −3.767 mm, and −2.428 mm, respectively. Here, the plus and minus signs denote different or opposite curvature directions. Furthermore, the maximum central thicknesses of the first plastic lens  111 , second plastic lens  112 , and third plastic lens  113  are 1.6 mm, 0.6 mm, and 1.08 mm, respectively. 
     Accordingly, when the barcode scanner  100  scans the barcode image BI, the barcode image BI is received by the lens set  110  and the light beams thereof are imaged on the imaging member  120  by refraction of the lens set  110  (as shown in  FIG. 2 ). Scanning of the barcode image BI is thus achieved. 
     In conclusion, as all the lenses of the lens set  110  of the barcode scanner  100  are composed of plastic, overall manufacturing costs thereof can be effectively reduced. Additionally, as the diaphragm  114  is disposed between the second plastic lens  112  and the third plastic lens  113 , optical sensitivity of the barcode scanner  100  or lens set  110  can be reduced, thereby enhancing assembly yield thereof. 
     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. 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.