Abstract:
An image scanning apparatus and method are provided. The image scanning apparatus scans an image of a document and converts the scanned image into digital data, and includes light sources that emit light. The apparatus includes a light guide unit that diffuses the light emitted by the light sources and a sensor unit that senses image data from the document by recognizing light reflected from the document by being diffused by the light guide unit. The apparatus includes a control unit that controls the turning on of the light sources. The control unit alternately turns on or off the light sources such that at least one of the light sources is turned on when at least one other light source is turned off.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related to and claims priority to Korean Patent Application No. 10-2011-0120930, filed on Nov. 18, 2011, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein. 
     BACKGROUND 
     1. Field 
     The embodiments discussed herein relate to an image scanning apparatus and a control method thereof. 
     2. Description of the Related Art 
     An image scanning apparatus is an apparatus that scans an original image such as a document, a picture or a film, and converts the scanned image into digital data. The digital data may be shown on a computer monitor or printed out by a printer and be generated as an output image. Such an image scanning apparatus may be a scanner, copier, facsimile, or an MFP (Multi Function Peripheral) where the functions of a scanner, copier and facsimile are integrated in one apparatus. 
     An image scanning apparatus uses a light source for emitting light for performing scanning. For example, cold cathode fluorescent lamps (CCFLs), xenon (Xe) lamps, or light-emitting diodes (LEDs) may be used as the light source. 
     Due to the risks posed to the environment by CCFLs or Xe lamps and the shortcomings of CCFLs or Xe lamps such as low efficiency and high power consumption, LEDs are becoming more widely employed as light sources for image scanning apparatuses. 
     The temperature of LEDs gradually increases as the LEDs emit light. Since the performance and lifetime of LEDs depend on the temperature of the LEDs, a heat dissipation plate may be provided in an image scanning apparatus using LEDs as light sources. The size of the heat dissipation plate may be determined by the amount of heat to dissipate from the LEDs. Accordingly, in the case of using high-performance LEDs, a large-size heat dissipation plate may be needed to adequately dissipate heat. However, the use of a large-size heat dissipation plate may lead to an increase in the manufacturing cost of an image scanning apparatus, and it is difficult to secure enough space for accommodating a large-size heat dissipation plate in an image scanning apparatus. 
     To address these problems, an array of a plurality of low-performance LEDs may be used as a light source for an image scanning apparatus. However, the low-performance LEDs may not be able to uniformly emit light, and also may contribute to an increase in the manufacturing cost of an image scanning apparatus. 
     SUMMARY 
     Additional aspects and/or advantages will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the invention. 
     An exemplary embodiment may address at least the above problems and/or disadvantages and other disadvantages not described above. 
     An exemplary embodiment provides an image scanning apparatus and a control method thereof. 
     According to an aspect of the exemplary embodiment, an image scanning apparatus is provided that scans an image of a document and converts the scanned image into digital data, the image scanning apparatus including, a plurality of light sources that emit light, a light guide unit that diffuses the light emitted by the light sources, a sensor unit that senses image data from the document by recognizing light reflected from the document by being diffused by the light guide unit, and a control unit that controls the turning on of the light sources, wherein the control unit alternately turns on or off the light sources such that at least one of the light sources is turned on when at least one other light source is turned off. 
     The control unit may control a turn-on duty of each of the light sources to be at least 50% or higher. 
     The control unit may control a frequency of each of the light sources to be within a range of about 50 kHz to about 200 kHz. 
     The light guide unit may include a first light guide and a second light guide. 
     The light sources may include at least one light source installed at one end of the first light guide and at least one light source installed at one end of the second light guide. 
     The light sources may include a first light source and a second light source. 
     The first light source may be installed at one end of the first light guide and the second light source may be installed at one end of the second light guide. 
     The control unit may control the first light source and the second light source to be alternately turned on. 
     The control unit may control the first light source and the second light source such that a turn-on period of the first light source and a turn-on period of the second light source partially overlap with each other. 
     The light sources may be light-emitting diodes (LEDs). 
     According to another aspect of the an exemplary embodiment, there is provided a control method of an image scanning apparatus which scans an image of a document and converts the scanned image into digital data, the control method including: emitting light by turning on a plurality of light sources; sensing image data from the document by recognizing light reflected from the document by being diffused; and converting the image data into digital data, wherein the turning on the light sources comprises alternately turning on or off the light sources such that at least one of the light sources is turned on when at least one other light source is turned off. 
     The turning on the light sources may also include controlling a turn-on duty of each of the light sources to be at least 50% or higher. 
     The turning on the light sources may also include controlling a frequency of each of the light sources to be within a range of about 50 kHz to about 200 kHz. 
     The turning on the light sources further may include controlling the light sources such that turn-on periods of the light sources do not overlap with each another. 
     The turning on the light sources may also include controlling the light sources such that turn-on periods of the light sources partially overlap with each another. 
     The light sources may be LEDs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and/or other aspects will be more apparent by describing certain exemplary embodiments with reference to the accompanying drawings, in which: 
         FIG. 1  illustrates an image scanning apparatus according to an exemplary embodiment; 
         FIG. 2  illustrates an example of the structure of the image scanning apparatus illustrated in  FIG. 1 , according to an exemplary embodiment; 
         FIG. 3  illustrates an example of the relationship between the turn-on duty of a light-emitting diode (LED) and the temperature of heat generated by the LED; 
         FIG. 4  illustrates a control method of light sources, according to an exemplary embodiment; 
         FIG. 5  illustrates a control method of light sources, according to an exemplary embodiment; 
         FIG. 6  illustrates an image scanning apparatus according to an exemplary embodiment; and 
         FIG. 7  illustrates an image scanning apparatus according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments are described in greater detail with reference to the accompanying drawings. 
     In the following description, the same drawing reference numerals are used for similar elements even in different drawings. The matters defined in the description, such as detailed construction and elements, are provided to assist in a comprehensive understanding of the exemplary embodiments. However, an exemplary embodiment can be carried out without those specifically defined matters. 
       FIG. 1  is a schematic diagram illustrating an image scanning apparatus according to an exemplary embodiment,  FIG. 2  illustrates an example of the structure of the image scanning apparatus illustrated in  FIG. 1 , according to an exemplary embodiment,  FIG. 3  illustrates an example of the relationship between the turn-on duty of a light-emitting diode (LED) and the temperature of heat generated by the LED, and  FIG. 4  illustrates a control method of light sources, according to an exemplary embodiment. 
     Referring to  FIG. 1 , an image scanning apparatus  1  includes a document table  20  on which a document  10  is placed and a frame  30  that is arranged so as to be reciprocally movable in directions indicated by a bidirectional arrow. 
     The document table  20  may be formed of a transparent material such that it can transmit light emitted from a light source unit  110 , as illustrated in  FIG. 2 , therethrough. 
       FIG. 2  illustrates a light guide unit  120  and a sensor unit  150  may be installed in a frame, e.g., frame  30 . The light guide unit  120  may evenly diffuse light emitted from the light source unit  110  toward the document  10 . The sensor unit  150  may sense image data from the document  10  by recognizing light that is reflected from the document  10  via diffusion. 
       FIG. 2  illustrates a light source unit  110  including a first light source  112  and a second light source  114 . The first light source  112  and the second light source  114  may be implemented as LEDs. 
     The light source unit  110  may be connected to and controlled by a control unit  170 . 
     The light guide unit  120  includes a first light guide  122  and a second light guide  124 . The first light source  112  may be installed at an end of the first light guide  122 , and the second light source  114  may be installed at an end of the second light guide  124 . The first light guide  122  and the second light guide  124  may be a predetermined distance apart from each other, and may be arranged in parallel with each other. 
     As illustrated in  FIG. 1 , a heat dissipation plate  190  may be installed in the frame  30 , facing a light source unit, e.g., the light source unit  110 . 
     The heat dissipation plate  190  may reduce heat emitted from the light source unit  110 . If the temperature of the light source unit  110  can be reduced, a large-size heat dissipation plate  190  may be no longer needed. In an exemplary embodiment, the heat dissipation plate  190  may be optional. 
     An exemplary operation of the image scanning apparatus  1  includes that in response to the document  10  being placed on the document table  20 , light may be emitted from the light source unit  110 , and the light may be evenly diffused over the document  10  by the light guide unit  120 . The sensor unit  150  may sense image data from the document  10  based on light reflected from the document  10 , and the image scanning apparatus  1  may convert the image data into digital data. 
     A relationship between the temperature of heat generated by an LED and the turn-on duty of the LED is illustrated in  FIG. 3 . Referring to  FIG. 3 , the temperature of heat generated by an LED is proportional, e.g., directly proportional to the turn-on duty of the LED. The performance and the properties of an LED (for example, brightness, color gamut, and lifetime) depend on the temperature of heat generated by the LED. A continuous use of a high-performance LED may inevitably lead to an increase in the temperature. Assuming that a 350 mA LED reaches a temperature of 100° C. after a continuous turning on of the LED, the temperature of the LED may be reduced to 50° C. by setting the turn-on duty of the LED to 50%. When an LED is turned on or off at intervals of 10 microseconds, i.e., when the LED is turned on for five microseconds and then turned off for five microseconds repeatedly, the temperature of the LED may decrease in inverse proportion to the turn-on duty of the LED. The temperature of the LED may also be reduced by reducing a current. In this example, however, the performance of the LED may deteriorate. To address this problem, a plurality of low-performance LEDs may be used, which, however, may result in an uneven emission of light and an increase in the manufacturing cost. 
     An exemplary control method of a light source unit, e.g., light source unit  110  of the image scanning apparatus  1  is described. 
     In a case in which the light source unit  110  needs to be turned on for performing image scanning on the document  10 , the control unit  170  may alternately turn on the first light source  112  and the second light source  114  such that a turn-on period of the first light source  112  and a turn-on period of the second light source  114  do not overlap with each other. For example, if the first light source  112  and the second light source  114  both have a current of 500 mA, the control unit  170  may drive the first light source  112  and the second light source  114  with a current of 500 mA. Since the current of the light source unit  110  is inversely proportional to the temperature of heat generated by the light source unit  110 , the control unit  170  may alternately turn on the first light source  112  and the second light source  114  over the course of image scanning, to reduce the temperature of heat generated by the light source unit  110 . For example, referring to  FIG. 4 , the control unit  170  may control the second light source  114  to be turned off while the first light source  112  is turned on, and may control the first light source  112  to be turned off while the second light source  114  is turned on. For example, the first light source  112  and the second light source  114  may be turned on or off alternately, and the turn-on duty cycle of the first light source  112  and the second light source  114  may be set to 50%. If the turn-on duty cycle of the first light source  112  and the second light source  114  are both below 50%, i.e., if the first light source  112  and the second light source  114  are turned off for more than 50% of a total light source turn-on period for performing image scanning, the light source unit  110  may undesirably appear to flicker. 
     For example, the first light source  112  and the second light source  114  may be implemented as LEDs. Alternatively, cold cathode fluorescent lamps (CCFLs) or xenon (Xe) lamps may be used as the first light source  112  and the second light source  114 . In the latter example, however, the first light source  112  and the second light source  114  may respond very slowly. Therefore, the first light source  112  and the second light source  114  may be implemented as LEDs, and particularly, high-performance LEDs. 
     The control unit  170  may control the first light source  112  and the second light source  114  such that a uniform amount of light can be incident upon the sensor unit  150 . When an irregularity in the amount of light incident upon the sensor unit  150  is greater than 20%, the quality of an image may deteriorate. Accordingly, the control unit  170  may control the light source unit  110  such that any irregularity in the amount of light incident upon the sensor unit  150  is less than 20%. 
     Due to an improper turning or off of the first light source  112  and the second light source  114 , a period during which no light is incident upon the sensor unit  150  may be encountered. In this example, the amount of light incident upon the sensor unit  150  may decrease. Alternatively, in a case in which the first light source  112  and the second light source  114  are turned on or off at a low frequency, the sensor unit  150  may determine the light source unit  110  as flickering, which adversely affects the quality of an image. To prevent the light source unit  110  from flickering, the control unit  170  may control the frequency of the light source unit  110 . The higher the frequency of the light source unit  110 , the less likely the sensor unit  150  is to perceive a flicker. Thus, the control unit  170  may control the frequency of the light source unit  110  to be maintained within the range of about 50 kHz to about 200 kHz in consideration of the sensing speed of the sensor unit  150  and the response speed of the light source unit  110 . 
     A control method of an image scanning apparatus, according to an exemplary embodiment is described with reference to  FIG. 5 . 
       FIG. 5  illustrates a control method of an image scanning apparatus, according to an exemplary embodiment. The exemplary embodiment illustrated in  FIG. 5  is similar to the exemplary embodiment illustrated in  FIG. 4 , and thus, is described, focusing mainly on differences with the exemplary embodiment illustrated in  FIG. 4 . 
     Referring to  FIG. 5 , the control unit  170  may control the turning on of the first light source  112  and the second light source  114  such that a turn-on period of the first light source  112  and a turn-on period of the second light source  114  can partially overlap with each other, as indicated by bidirectional arrows. In this example, the overlap period between the turn-on period of the first light source  112  and the turn-on period of the second light source  114  may be appropriately set between 0% and 100% in accordance with a target temperature. 
     In the exemplary embodiment illustrated in  FIG. 5 , the control unit  170  may control the turn-on duty cycle of the first light source  112  and the second light source  114  to be within the range of 50% to 100%. 
     According to the exemplary embodiment illustrated in  FIG. 5 , it is possible to appropriately set the turn-on duty of a light source within a given range and thus to reduce the temperature of the light source. For example, if the turn-on duty cycle of the first light source  112  and the second light source  114  are both set to 80%, the temperature of the light source unit  110  may be reduced by 20%. Alternatively, if the turn-on duty cycle of the first light source  112  and the second light source  114  are both set to 60%, the temperature of the light source unit  110  may be reduced by 40%. Therefore, according to the exemplary embodiment illustrated in  FIG. 5 , it is possible to appropriately control the amount by which the temperature of the light source unit  110  should be reduced in consideration of the capability of the heat dissipation plate  190 . In addition, by appropriately adjusting the turn-on duty cycle of the first light source  112  and the second light source  114  with the aid of the control unit  170 , it is possible to make the heat dissipation plate  190  optional or reduce the size of the heat dissipation plate  190 . 
     In the exemplary embodiment illustrated in  FIG. 5 , as in the exemplary embodiment illustrated in  FIG. 4 , the control unit  170  may control the frequency of the light source unit  110  to be maintained within the range of about 50 kHz to about 200 kHz to prevent the light source unit  110  from flickering. 
     An image scanning apparatus according to an exemplary embodiment is described with reference to  FIG. 6 . 
       FIG. 6  illustrates an image scanning apparatus according to an exemplary embodiment. The configuration of the image scanning apparatus illustrated in  FIG. 6  is similar to the configuration of the image scanning apparatus  1  illustrated in  FIG. 1 , and thus, the image scanning apparatus illustrated in  FIG. 6  is described, focusing mainly on the differences with the image scanning apparatus  1  illustrated in  FIG. 1 . 
     Referring to  FIG. 6 , the image scanning apparatus includes a light source unit  210 , a light guide unit  220 , and a control unit  270 . 
     The light source unit  210  includes a first light source  212  and a second light source  214 . The first light source  212  and the second light source  214  may be installed at either end of the light guide unit  220 . 
     The first light source  212  and the second light source  214  may be connected to the control unit  270 . 
     The control unit  270  may alternately turn on the first light source  212  and the second light source  214  such that a turn-on period of the first light source  212  and a turn-on period of the second light source  214  do not overlap with each other, as described above with reference to  FIG. 4 , or may alternately turn on the first light source  212  and the second light source  214  such that the turn-on period of the first light source  212  and the turn-on period of the second light source  214  partially overlap with each other, as described above with reference to  FIG. 5 . 
     To prevent the light source unit  210  from flickering, the control unit  270  may control the frequency of the light source unit  210  to be maintained within the range of about 50 kHz to about 200 kHz. 
     Since the light guide unit  220  includes only one light guide, it is possible to reduce the size of the light guide unit  220  and the manufacturing cost of an image scanning apparatus. 
     An image scanning apparatus according to an exemplary embodiment is described with reference to  FIG. 7 . 
       FIG. 7  illustrates an image scanning apparatus according to another exemplary embodiment. The configuration of the image scanning apparatus illustrated in  FIG. 7  is similar to the configuration of the image scanning apparatus  1  illustrated in  FIG. 1 , and thus, the image scanning apparatus illustrated in  FIG. 7  is described, focusing mainly on the differences with the image scanning apparatus  1  illustrated in  FIG. 1 . 
     Referring to  FIG. 7 , the image scanning apparatus includes a light source unit  310 , a light guide unit  320 , and a control unit  370 . The light source unit  310  includes a first light source  312 , a second light source  314 , a third light source  316 , and a fourth light source  318 . 
     The first light source  312 , the second light source  314 , the third light source  316 , and the fourth light source  318  may all be connected to the control unit  370 . 
     The light guide unit  320  includes a first light guide  322  and a second light guide  324 . 
     The first light source  312  and the second light source  314  may be installed at either end of the first light guide  322 . 
     The third light source  316  and the fourth light source  318  may be installed at either end of the second light guide  324 . 
     For example, the control unit  370  may turn off the second light source  314  and the fourth light source  318  when turning on the first light source  312  and the third light source  316 , and may turn on the second light source  314  and the fourth light source  318  when turning off the first light source  312  and the third light source  316 . Alternatively, the control unit  370  may turn off the second light source  314  and the third light source  316  when turning on the first light source  312  and the fourth light source  318 , and may turn on the second light source  314  and the third light source  316  when turning off the first light source  312  and the fourth light source  318 . That is, the control unit  370  may control the turning on or off of the light source unit  310  such that the light sources installed at one end of the light guide unit  320  are turned off when the light sources installed at the other end of the light guide unit  320  are turned on. 
     The control unit  370  may control the turning on or off of the light source unit  310  such that turn-on periods of the first light source  312 , the second light source  314 , the third light source  316 , and the fourth light source  318  partially overlap with one another. 
     To prevent the light source unit  310  from flickering, the control unit  370  may control the frequency of the light source unit  310  to be maintained within the range of about 50 kHz to about 200 kHz. 
     Although a few embodiments have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.