Abstract:
A case has a front surface facing an image sensing area, a concave formed on the front surface, and an opening on the bottom of the concave. The case accommodates an area image sensor to image-sense the image sensing area through the opening, and an illumination device to illuminate the entire image sensing area. There are provided a photoelectric converting unit converting an output of the area image sensor into an electric image signal, and an output unit outputs an image signal converted by the photoelectric converting unit to an image processing device. The case also accommodates a lens to form an image of the image sensing area on the area image sensor with a depth of field so as to the image processing device obtain a resolution to enable analysis of a code symbol included in the image signal. A lens side limit position of the depth of field corresponds with the position of the front surface of the case.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is based on and claims the benefit of priority of Japanese Patent Application No. 2007-243127 filed on Sep. 19, 2007, the entire contents of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a code symbol reading apparatus, and more particularly, to a code symbol reading apparatus for infallibly and easily reading a code symbol of a commercial product in a wide range including peripheral positions of the apparatus. 
     2. Discussion of Related Art 
     As a code symbol reading apparatus which optically reads an image of a code symbol such as a barcode attached to a product and obtains a product code from the read image, an apparatus using an area image sensor such as a CCD image sensor is known. This code symbol reading apparatus extracts image information of a barcode as a subject from image data obtained with the CCD image sensor, analyzes the obtained image information and obtains code information of the barcode, i.e., a product code. 
       FIG. 4A  is a cross-sectional view schematically showing the structure of a conventional code symbol reading apparatus. The code symbol reading apparatus  200  has an approximately rectangular parallelepiped case  210  formed with a front cover member  211  which is provided on the image sensing area F side where a product is placed and which has an image sensing opening  213 , and a back cover member  212  which is engaged with the front cover member  211  and which is provided on the side opposite to the image sensing area side. 
     An image sensing device  220  to take image of the image sensing area F, an illumination board  230  to illuminate the image sensing area F and an image processing board  240  are provided in the case  210 . The image sensing device  220  image-senses a barcode attached to a product, and the image processing board  240  analyzes image data of the image-sensed barcode and outputs product data. 
     The image sensing device  220  has an image sensing board  221  including a CCD image sensor (not shown) as an area image sensor and a driving circuit (not shown) for the CCD image sensor, and an lens  222  to form an image of the image sensing area F on the CCD image sensor. The illumination board  239  is provided with an image sensing opening  232  of the lens  222  in its central portion. Plural LEDs (Light Emitting Diodes)  231  to emit illumination light to the image sensing area F are provided around the opening  232 . The image processing board  240  extracts a barcode portion from image data of a product outputted from the image sensing board  221 , analyses the barcode data and obtains a product code. 
     In this code symbol reading apparatus  200 , a front surface  211   a  is provided in a position closest to the image sensing area F side in the front cover member  211  of the case. A plate type transparent cover  250  is provided so as to cover the opening  213  on the rear side of the front surface  211   a . The image sensing opening  232  of the lens  222  is provided on the illumination board  230 , and the LEDs  231  are provided so as to be positioned inside the opening  213  on the image sensing area F side. Light from the LEDs  231  is emitted on an illumination area I including the image sensing area F. 
     A barcode of a product placed in the image sensing area F is image-sensed with the image sensing device  220 . Then the image processing board  240  extracts image data of the barcode from image data of the product obtained with the image sensing device  220 , then analyses the image data and obtains a product code. 
     As a code symbol reading apparatus having such area image sensor, Japanese Published Unexamined Patent Application No. 2005-025311 discloses a barcode reader having plural LEDs to emit illumination light on a barcode symbol and a CCD on which reflected light from the barcode symbol is image-formed via a light receiving lens. In the barcode reader, the respective LED emitting portions are covered with LED caps for light diffusion. The respective LED caps have a diffusion characteristic to diffuse the light emitted from the respective LEDs so as to form a uniform illumination distribution surface on the barcode symbol. 
     In many cases, in the conventional code symbol reading apparatus, for the purpose of cost reduction, the lens  222  is a fixed focus lens. In this case, in accordance with barcode position in the image sensing area F, an image obtained by image sensing may become a so-called “out-of-focus” image. From a viewpoint of resolution, as shown in  FIG. 4B , in such blurred image, the resolution is a maximum in a focus position P 1  of the lens, and becomes lower in the vicinity of the focus position. 
     Upon analysis of code symbol image by the image processing board  240 , when image data as the subject of processing is in a resolution equal to or lower than a predetermined value d, analysis cannot be performed and a product code cannot be outputted. Accordingly, the barcode reading range is a predetermined area (depth of field A 1 ) between a lens side limit Pc 1  and a limit Pf 1  opposite to the lens side positioned with the focus position P 1  therebetween. Generally, as the depth of field A 1 , the focal distance of the lens  222  or the like is selected such that a product can be easily placed. That is, the depth of field A 1  is selected for the optimum placement of product in the focus position P 1 . 
     In an area out of the depth of field A 1 , an outer area B 1  of the limit Pf 1  opposite to the lens side and an inner area C 1  from the inside of the lens side limit Pc 1  to the surface of the front cover member  211 , as the resolution of image data is low, the barcode of a product placed in these areas cannot be read. On the lens side limit Pc 1  side, the lens side limit Pc 1  of the depth of filed A 1  is away from the case  210 . When a product is placed in a position closer to the case  210  than the lens side limit Pc 1 , the barcode of the product cannot be analyzed. 
     When a barcode attached to the product cannot be read with such code symbol reading apparatus, an operator places the product in the image sensing area of the code symbol reading apparatus again to perform barcode reading. However, in the conventional code symbol reading apparatus, the depth of field A 1  of the image sensing device in the image sensing area is not clear. Accordingly, in some cases the operator cannot place the product in the depth of field A 1  of the image sensing device again, and reading cannot be performed. 
     As long as the apparatus can infallibly perform barcode reading when the product is placed in a position close to the case of the code symbol reading apparatus in such retry, barcode reading can be performed only by allowing the operator to place the product in a position in close vicinity to the code symbol reading apparatus. Accordingly, a code symbol reading apparatus which infallibly performs barcode reading when a product is placed in a position close to the case of the apparatus is needed. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention has been made in consideration of the above situation, and provides a code symbol reading apparatus for infallibly and easily reading a code symbol of a product within a wide range including peripheral positions of the apparatus. 
     According to embodiment of the present invention, a code symbol reading apparatus includes a case having a front surface facing an image sensing area, a concave formed on the front surface, and an opening on the bottom of the concave, an area image sensor provided inside the case to image-sense the image sensing area through the opening, an illumination device provided inside the case without interference to the scope of image sensing by the area image sensor to illuminate the entire image sensing area, a photoelectric converting unit converting an output of the area image sensor into an electric image signal, an image processing device extracting an image signal of a code symbol from the image signal converted by the photoelectric converting unit, and analyzing the extracted image signal, and outputting a product code, and a lens provided inside the case to form an image of the image sensing area on the area image sensor with a depth of field so as to the image processing device obtain a resolution to enable analysis of a code symbol included in the image signal. A lens side limit position of depth of field corresponds with the position of the front surface of the case. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the present invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  is an outer appearance perspective view showing an example of a barcode scanner according to an embodiment of the present invention; 
         FIG. 2A  is a cross-sectional view schematically showing the structure of a code symbol reading apparatus according to the embodiment of the present invention; 
         FIG. 2B  is a graph showing the resolution of image data; 
         FIG. 3A  is a cross-sectional view schematically showing the structure of a code symbol reading apparatus according to the embodiment of the present invention; 
         FIG. 3B  is a graph showing the resolution of image data; 
         FIG. 4A  is a cross-sectional view schematically showing the structure of the conventional code symbol reading apparatus; 
         FIG. 4B  is a graph showing the resolution of image data; 
         FIG. 5A  is a cross-sectional view schematically showing the structure of a code symbol reading apparatus as a premise of the present invention; 
         FIG. 5B  is a graph showing the resolution of image data; 
         FIG. 6A  is a cross-sectional view schematically showing the structure of another code symbol reading apparatus as a premise of the present invention; and 
         FIG. 6B  is a graph showing the resolution of image data. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First, a code symbol reading apparatus as a premise of the present invention will be described based on  FIGS. 5A and 5B  and  FIGS. 6A and 6B . In these figures, constituent elements corresponding to those shown in  FIG. 4A  have the same reference numerals and detailed explanations thereof will be omitted. 
     As in the case of the code symbol reading apparatus described in  FIG. 4A , the code symbol reading apparatus  200  shown in  FIG. 5A  has the case  210 , the image sensing device  220 , the illumination board  230 , the image processing board  240  and the transparent cover  250 . The difference from the code symbol reading apparatus described in  FIG. 4A  is that the focal distance of the lens  222  is shorter than that of the lens in  FIG. 4A , and a focus position P 2  is closer to the front cover member  211  of the case  210 . Further, in this code symbol reading apparatus  200 , a lens side limit Pc 2  of a depth of field A 2  corresponds with the position of the front surface  211   a  of the front cover member  211 . Accordingly, barcode reading can be performed even when a product is placed in a position close to the case  210 . However, as the focal distance of the lens  222  is short, the depth of field A 2  is narrow due to the characteristic of the lens as shown in  FIG. 5B , and the operability of the apparatus is low. 
       FIG. 6A  is a cross-sectional view schematically showing the structure of another code symbol reading apparatus as a premise of the present invention. The code symbol reading apparatus  200  shown in  FIG. 6A  has the case  210  formed with the front cover member  211  having the opening  213  and the back cover member  212 , the image sensing device  220 , the illumination board  230 , the image processing board  240  and the transparent cover  250 . The image sensing device  220  has the same specifications as those of the image sensing device in  FIG. 4A , and the position of the illumination board  230  is the same as that of the illumination board in  FIG. 4A . The difference from the code symbol reading apparatus in  FIG. 4A  is that the position of the image sensing board  221  is changed, and a lens side limit Pc 3  of a depth of field A 3  corresponds with the position of the front surface  211   a  of the front cover member  211 . That is, in the code symbol reading apparatus  200  in  FIG. 6A , the image sensing device  220  is positioned away from the front cover member  211  so as to ensure the wide depth of field A 3 . However, in this code symbol reading apparatus  200 , it is necessary to provide a large opening  232  at the center of the illumination board  230  and provide the LEDs  231  around the opening  232 . Accordingly, an area D where light is not emitted on the central portion of the illumination area I occurs around the front cover member  211 . When a product is placed in the area D, as it is not irradiated with illumination light, its barcode cannot be image-sensed. 
     In view of the problems shown in  FIGS. 5A and 5B  and  FIGS. 6A and 6B , a best mode of the code symbol reading apparatus according to the present invention will be described based on  FIG. 1 ,  FIGS. 2A and 2B  and  FIGS. 3A and 3B . In the present embodiment, an upright type barcode scanner is employed as an example. 
       FIG. 1  is an outer appearance perspective view showing an example of a barcode scanner according to the embodiment of the present invention. A barcode scanner  10  is upright-installed on an upper surface of a checkout stand  11  (or a counter table) on which a shopping basket or the like containing products is placed. The barcode scanner  10  has a pair of posts  13  having a guide groove  12 , a code symbol image sensing apparatus  100  upward/downward movably guided along the guide grooves  12 , a display unit  16  and a keyboard  17  provided above the code symbol image sensing apparatus  100 . The code symbol image sensing apparatus  100  optically reads a barcode as a code symbol attached to a product. The code symbol image sensing apparatus  100  is installed such that its opening  113  is directed to face the image sensing area side where a product with a barcode is placed. 
     Further, the barcode scanner  10  is connected to a computer  170  as an image processing device which analyzes image data of a barcode of a product obtained with the code symbol image sensing apparatus  100  and outputs a product code, via a network. 
     In the present embodiment, an operator places a product contained in the shopping basket in a position in front of the opening  113  of the code symbol image sensing apparatus  100  such that the apparatus optically reads a barcode as a code symbol attached to the product. Then the code symbol image sensing apparatus  100  transmits image data of the read barcode to the computer  170  as an image processing device. The computer  170  analyzes the image data of the barcode to obtain a product code, and transmits the product code to its upper apparatus. Then the upper apparatus performs product registration based on the product code. 
       FIG. 2A  is a cross-sectional view schematically showing the structure of the code symbol reading apparatus according to the embodiment of the present invention. The code symbol image sensing apparatus  100  has a case  110  formed with a front cover member  111  provided on the image sensing area F side where a product is placed and a back cover member  112  engaged with the front cover member  111  and provided on the side opposite to the image sensing area side. 
     The front cover member  111  is provided with a front surface  111   a  in a position closest to the image sensing area F side in the case. A concave  160  toward an area opposite to the image sensing area side from the front surface  111   a  is formed in the central portion of the front surface  111   a . The concave  160  has a quadrangular pyramid wall in which its cross-sectional area is reduced toward its back portion, and an opening  113  is provided in the deepest position of the concave  160 . Further, a plate transparent cover  150  is provided on the back cover member  112  of the opening  113  so as to cover the opening  113 . 
     An image sensing device  120  to image-sense the image sensing area F and an illumination board  130  as an illumination device to illuminate the image sensing area F are provided in the case  110 . The image sensing device  120  has an image sensing board  121  as a photoelectric converting unit, including a CCD image sensor (not shown) as an area image sensor and a driving circuit (not shown) for the CCD image sensor to convert an image to an electric signal, and an lens  122  to form an image of a barcode of a product placed in the image sensing area F. The illumination board  130  is provided on the side of the opening  113  opposite to the image sensing area, and an image sensing opening  133  is provided in the central portion of the illumination board  130 . The illumination board  130  is provided with plural LEDs  131 . The LEDs  131  are provided to surround the opening  133  inside the opening  113  and outside the image sensing area. Light emitted from the LEDs  131  is emitted to the illumination area I wider than the image sensing area F. 
     Further, the code symbol image sensing apparatus  100  has an output unit  180  to transmit an image signal of a barcode outputted from the image sensing board  121  to the computer  170  as an image processing device. The computer  170  analyzes the transmitted image signal of the barcode to obtain a product code and transmits the product code to its upper apparatus. 
     As described above, the reading area where barcode analysis by the image processing device is possible is an area where the resolution of an image obtained with the image sensing device  120  is equal to or higher than the predetermined value d. As shown in  FIG. 2B , the reading area is an area (depth of field A) between a lens side limit Pc and a limit Pf opposite to the lens side with the focus point P therebetween. The depth of field A is determined based on the specifications of the image sensing device  120  such as a device pitch of the CCD image sensors and the focal distance of the lens  122 , and the position of the image sensing device  120  in the case  110 . 
     In the present embodiment, the depth of field A is set such that the position of the lens side limit Pc approximately corresponds with the position of the front surface  111   a  of the front cover member  111 . Further, in the present embodiment, the depth of field A is set such that it is a sufficiently wide area including the position of the front surface  111   a  of the case  110  (i.e., the lens side limit Pc). Note that the sufficiently wide area corresponds to a range where the operator can place a product without being especially conscious of the depth of field A of the image sensing device. In the present embodiment, the distance from the position of the front surface  111   a  (i.e., the lens side limit Pc) to the limit Pf opposite to the lens side is about 150 mm, the distance from the focus position P to the limit Pf opposite to the lens side is about 100 mm, and the distance from the focus position P to the lens side limit Pc is about 50 mm. 
     Further, the positional relation between the lens side limit Pc and the front surface  111   a  is determined based on the focal distance of the lens  122  and the position of the image sensing device  120  in the case  110 . In the present embodiment, the distance from the end surface of the lens  122  to the focus position P is about 110 mm. The shape and the depth of the concave  160  are selected, in consideration of the positions of the image sensing device  120  and the illumination board  130 , so as not to disturb image sensing with the image sensing device  120  and illumination with the illumination board  130 . 
     Accordingly, in the code symbol reading apparatus  100  according to the present embodiment, it is possible to place a product within a wide range including a position in close vicinity to the position of the front surface  111   a  and read a code symbol. Further, as the image sensing area F is included in the illumination area I of the illumination board  130 , an area not irradiated with light from the illumination board  130  does not occur in the image sensing area F. Further, in the present embodiment, the case  110  has the concave  160  and the transparent cover  150  is provided on the opening  113  formed in the back of the concave  160 , the probability of contact between a product and the case  110  is low. That is, upon reading of code symbol, the probability of breakage of product is low. 
     In the present embodiment, an image signal of a barcode outputted form the image sensing device  120  is transmitted via the network to the computer  170  as an image processing device then a product code is analyzed. Further, as described later in  FIGS. 3A and 3B , the image processing device may be integrated with the image sensing device  120  and provided in the case  110 . 
       FIG. 3A  is a cross-sectional view schematically showing the structure of the code symbol reading apparatus according to the embodiment of the present invention. In this figure, constituent elements corresponding to those shown in  FIG. 2A  have the same reference numerals, and detailed descriptions thereof will be omitted. As in the case of the code symbol reading apparatus shown in  FIG. 2A , a code symbol reading apparatus  400  according to the present embodiment has the case  110  having the front surface  111   a  and the concave  160  provided with the opening  113 , the image sensing device  120 , the illumination board  130  and the transparent cover  150 . 
     The image sensing device  120  and the illumination board  130  are provided in the case  110 . The image sensing device  120  has the same specifications as that of the above-described image sensing device  120 . The illumination board  130  is provided in the same position as that of the above-described illumination board  130 . The difference from the code symbol reading apparatus shown in  FIG. 2A  is that an image processing board  140  as an image processing device is provided in the case  110 . The image processing board  140  analyzes an image signal of a barcode from an image signal outputted from the image sensing board  121  of the image sensing device  120  and outputs a product code. 
     According to the code symbol reading apparatus  400  of the present invention, when the operator causes the code symbol reading apparatus  400  to read a barcode of a product, the operator stands inside the checkout stand  11  and takes out products one by one from a shopping basket placed on the upstream side of the apparatus in the lane. When a barcode is attached to a product, the operator points the barcode at the opening  113  of the code symbol reading apparatus  400  such that the barcode is read with the image sensing device  120 . An image of the product read with the image sensing device  120  is sent to the computer  170  or the image processing board  140  as an image processing device. Then the image of the barcode is analyzed and a product code is outputted. Then the obtained product code is outputted to the upper apparatus, thereby product registration is performed. 
     When a product is placed within the depth of field A of the image sensing device, a barcode attached to the product is image-sensed with the image sensing device  120 . Thereafter, when the image of the barcode is analyzed by the image processing device and outputted to the upper apparatus, a checkout sound indicating the completion of reading is emitted from the barcode scanner  10 . The operator checks the sound, and puts the product in a shopping basket placed on the downstream side in the lane. 
     On the other hand, when the barcode cannot be read due to some reason, the operator again points the barcode attached to the product at the opening  113  of the code symbol reading apparatus  400 , so as to perform reading. At this time, the operator presses the product against a position closer to the opening  113  of the front cover member  111  than the position at the previous time, i.e., in the same position as that of the front surface  111   a . Then, the product can be placed in the depth of field A of the image sensing device, and the barcode can be infallibly read. That is, upon barcode reading, the concave  160  and the front surface  111   a  of the front cover member  111  are target positions for barcode reading. 
     Further, even when reading cannot be performed at once since a barcode is wrinkled or the barcode is small, the barcode can be infallibly read only by placing the product in close vicinity to the front cover member  111  of the code symbol reading apparatus  400 . As a result, the operator can feel a sense of assurance, and the apparatus can be easily used. 
     Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of appended claims, the invention may be practiced otherwise than as specifically described herein.