Patent Publication Number: US-2007103499-A1

Title: Color registration apparatus and method

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION  
      This application claims the benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 10-2005-0105470, filed on Nov. 04, 2005, in the Korean Intellectual Property Office, the entire disclosure of which is hereby incorporated by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a color registration operation performed in an electro-photographic printer such as a laser printer. More particularly, the present invention relates to a color registration apparatus which performs color registration without errors regardless of a concentration of a developing agent by determining the intensity of light irradiated onto a registration mark and the minimum intensity of sensed light necessary to identify the registration mark according to the concentration of the developing agent and a method for using the color registration apparatus.  
      2. Description of the Related Art  
      An electro-photographic printer such as a color laser printer includes four photoconductive drums, an exposing unit, a developing unit and a transferring belt. The four photoconductive drums respectively correspond to four colors such as yellow (Y), magenta (M), cyan (C) and black (K). The exposing unit radiates light onto each of the photoconductive drums, thereby forming an electrostatic latent image of an image to be printed.  
      The developing unit respectively develops the electrostatic latent image formed by the exposing unit for each color using a separate developing solution for each color. The transferring belt sequentially receives the images respectively developed on each of the photoconductive drums, superimposes these images to form a final color image, and then transfers the final color image onto paper.  
      Initial and final positions of the developed electrostatic latent images for the four colors are identically superimposed on the transferring belt to obtain a final color image identical to the desired color image. The exposure start timing for the photoconductive drums in the exposing unit should be accurately controlled in consideration of the transferring speed of the transferring belt to facilitate the accurate realization of a color image. The control of the exposure start timing is referred to as color registration.  
      An electro-photographic printer comprising a conventional color registration apparatus exposes, develops, senses a registration mark for each color and then performs color registration according to the time when each color is sensed before printing data.  
      The color registration apparatus radiates light of a predetermined emitting intensity onto the developed registration mark and senses a light of a predetermined intensity reflected from the developed registration mark, thereby sensing the developed registration mark.  
      The time when each color is sensed represents a time when the intensity of sensed light is greater than a predetermined threshold value. As the concentration of the developing agent decreases, the intensity of sensed light decreases.  
      Therefore, the conventional color registration apparatus cannot sense a developed registration mark when the concentration of a developing agent is too low which leads to erroneous performance of the color registration.  
      Accordingly, there is a need for an improved system and method for performing color registration without errors regardless of a concentration of a developing agent.  
     SUMMARY OF THE INVENTION  
      An aspect of exemplary embodiments of the present invention is to address at least the above problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of exemplary embodiments of the present invention is to provide a color registration apparatus to perform color registration without errors regardless of a concentration of a developing agent by determining the intensity of light irradiated onto a registration mark and the minimum intensity of sensed light necessary for identifying the registration mark according to the concentration of the developing agent.  
      An exemplary embodiment of the present invention provides a color registration method to perform color registration without errors regardless of a concentration of a developing agent by determining the intensity of light irradiated onto a registration mark and the minimum intensity of sensed light necessary for identifying the registration mark according to the concentration of the developing agent.  
      An exemplary embodiment of the present invention also provides a computer-readable recording medium on which a program for executing a color registration method is recorded. The program performs color registration without errors regardless of a concentration of a developing agent by determining the intensity of light irradiated onto a registration mark and the minimum intensity of sensed light necessary to identify the registration mark according to the concentration of the developing agent.  
      According to an aspect of an exemplary embodiment of the present invention, a color registration apparatus is provided. A mark forming unit forms a concentration mark. for each color and forms a registration mark for each color in response to a color registration control signal. A mark sensing unit senses the concentration mark by emitting a plurality of first emitted lights comprising different intensities and senses the registration mark by emitting second emitted lights. An examining unit compares the intensities of first sensed lights with a predetermined reference value and generates the color registration control signal in response to the comparison results. A calculating unit calculates the intensity of the second emitted light using the intensities of the plurality of first emitted lights and the intensities of the plurality of first sensed lights if the intensities of second sensed lights are greater than a predetermined value. A color registration unit performs color registration using the intensity of the second sensed light which is greater than a predetermined threshold value, wherein the first sensed light is a light reflected from the concentration mark, and the second sensed light reflected from the registration mark.  
      The threshold value may be previously determined between the predetermined value and the minimum intensity of the second sensed light. The predetermined threshold value may be an average value of the predetermined value and the minimum intensity of the second sensed light. The predetermined value may be the maximum intensity of light which can be sensed by the mark sensing unit.  
      According to another aspect of an exemplary embodiment of the present invention, a color registration method is provided. A concentration mark is formed for each color and the concentration mark is sensed for each color by emitting a plurality of first emitted lights comprising different intensities. A determination is made as to whether the intensity of first sensed light reflected from the concentration mark corresponding to a chromatic color is greater than a predetermined reference value. A registration mark is formed for each color when the intensity of the first sensed light is greater than the predetermined reference value and the intensity of second emitted light reflected from the registration mark is calculated to be greater than a predetermined value for all colors using the intensities of the plurality of first emitted lights and the intensities of the plurality of first sensed lights. The registration mark is sensed by emitting the second emitted light comprising the calculated intensity and performing color registration using information on the time when the second sensed light comprising the greater intensity than a predetermined threshold value is sensed.  
      According to still another aspect of an exemplary embodiment the present invention, a computer-readable recording medium is provided. A program is recorded on the computer-readable recording medium to facilitate the execution of a method for spatial predictive encoding of video data. According to an exemplary implementation of the method, a concentration mark is formed for each color and the concentration mark is sensed for each color by emitting a plurality of first emitted lights comprising different intensities. A determination is made as to whether the intensity of first sensed light reflected from the concentration mark corresponding to a chromatic color is greater than a predetermined reference value. A registration mark is formed for each color when the intensity of the first sensed light is greater than the predetermined reference value and the intensity of second emitted light reflected from the registration mark is calculated to be greater than a predetermined value for all colors using the intensities of the plurality of first emitted lights and the intensities of the plurality of first sensed lights. The registration mark is sensed by emitting the second emitted light comprising the calculated intensity and performing color registration using information on the time when the second sensed light comprising a greater intensity than a predetermined threshold value is sensed.  
      Other objects, advantages and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other exemplary objects, features and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:  
       FIG. 1  is a block diagram of a color registration apparatus according to an exemplary embodiment of the present invention;  
       FIG. 2  is a timing diagram illustrating the intensity of a first light and the intensity of a second light sensed by a mark sensing unit of  FIG. 1 ; and  
       FIG. 3  is a flowchart of a color registration method according to an exemplary embodiment of the present invention. 
    
    
      Throughout the drawings, the same drawing reference numerals will be understood to refer to the same elements, features and structures.  
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMETNS  
      The matters defined in the description such as a detailed construction and elements are provided to assist in a comprehensive understanding of the embodiments of the invention. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. Also, descriptions of well-known functions and constructions are omitted for clarity and conciseness.  
       FIG. 1  is a block diagram of a color registration apparatus according to an exemplary embodiment of the present invention. Referring to  FIG. 1 , the color registration apparatus includes a light intensity determining unit  110  for determining the intensity of emitted light, a mark forming unit  112 , a mark sensing unit  118 , an examining unit  120 , a calculating unit  122 , and a color registration performing unit  124 . The mark forming unit  112  includes an exposing unit  114  and a developing unit  116 .  
      An electro-photographic image forming apparatus such as a color laser printer may include the light intensity determining unit  110 , the mark forming unit  112  comprising the exposing unit  114  and the developing unit  116 .  
      The light intensity determining unit  110  determines the intensity of a first emitted light for sensing a concentration mark in the mark sensing unit  118 , which will be described later. The intensity of the first emitted light is transmitted to the mark sensing unit  118 .  
      The light intensity determining unit  110  may previously separately determine a plurality of intensities of first emitted lights. According to an exemplary implementation, if the light intensity determining unit  110  separately determines two sets of intensities of the first emitted lights, the determined intensities are denoted as PWM 1  and PWM 2 .  
      When the first lights PWM 1  and PWM 2  radiated onto a transferring belt are reflected before applying developing agents, the intensities of reflected lights sensed by the mark sensing unit  118  are denoted as BaseADC 1  and BaseADC 2 . The light intensity determining unit  110  determines the intensities PWM 1  and PWM 2  for detecting BaseADC 1  and BaseADC 2  when the developing agent is applied onto the transferring belt. In this operation, a mark sensor installed in the mark sensing unit  118  is controlled.  
      The mark forming unit  112  forms a concentration mark for each color and then forms a registration mark for each color in response to a color registration control signal. The concentration mark is used to determine a concentration of a developing agent and the registration mark is used to perform color registration.  
      The colors are assumed to be yellow (Y), magenta (M), cyan (C), and black (K). Y, M, and C are chromatic colors, and K is an achromatic color K. The electro-photographic image forming apparatus includes a photoconductive drum for each color.  
      The mark forming unit  112  includes the exposing unit  114  and the developing unit  116 . The exposing unit  114  scans light onto the photoconductive drums to form electrostatic latent images according to the concentration marks or the registration marks.  
      The developing unit  116  develops the electrostatic latent image for each color formed by the exposing unit  114  using a separate developing agent for each color. The transferring belt sequentially receives the electrostatic latent images respectively developed on each of the photoconductive drums.  
      The mark sensing unit  118  senses the concentration marks or registration marks formed by the mark forming unit  112 . Specifically, the mark sensing unit  118  radiates a first light comprising a predetermined intensity onto each of the concentration marks, and senses lights reflected from the concentration marks, thereby sensing the concentration marks.  
      Similarly, the mark sensing unit  118  radiates a second light comprising a predetermined intensity onto each of the registration marks, and senses lights reflected from the registration mark, thereby sensing the registration marks.  
      When the mark sensing unit  118  senses the concentration marks, a plurality of first lights comprising different predetermined intensities may be radiated onto each of the concentration marks. The mark sensing unit  118  may radiate lights comprising one of the plurality of intensities separately determined by the light intensity determining unit  110  to facilitate the sensing of the concentration marks.  
      For this purpose, the mark sensing unit  118  receives the intensities of the first emitted lights from the light intensity determining unit  110 .  
      For example, after the mark sensing unit  118  emits the first light comprising the intensity PWM 1  to sense a concentration mark, the mark forming unit  112  forms a new concentration mark and then the mark sensing unit  118  emits the second light comprising the intensity PWM 2  to sense the new concentration mark.  
      When the first lights PWM 1  and PWM 2  which have been radiated onto a transferring belt are reflected, the intensities of reflected lights sensed by the mark sensing unit  118  are denoted as ADC 1  and ADC 2 .  
      The examining unit  120  compares the intensities ADC 1  and ADC 2  of the first sensed lights, which are reflected from the formed concentration marks, with a predetermined reference value, and generates a registration control signal in response to the comparison results. The generated registration control signal is input into the exposing unit  114 .  
      If the mark sensing unit  118  emits a plurality of first lights comprising different intensities onto the concentration marks, the mark sensing unit  118  senses a plurality of lights reflected from the concentration marks. Then, the examining unit  120  separately compares the intensity of each of the sensed lights with the predetermined reference value.  
      For example, when the intensity of the first sensed light is from one of the concentration marks corresponding to Y, M, or C, the examining unit  120  estimates whether the intensity of the first sensed light is greater than the predetermined reference value. When the examining unit  120  estimates that the intensity of the first sensed light is greater than the predetermined reference value, the examining unit  120  generates a registration control signal.  
      Otherwise, when the intensity of the first sensed light is from the concentration mark corresponding to K, the examining unit  120  estimates whether the intensity of the first sensed light is less than the predetermined reference value. When the examining unit  120  estimates that intensity of the first sensed light is less than the predetermined reference value, the examining unit  120  generates a registration control signal.  
      The operations of the examining unit  120  may be performed for all colors. Thus, the examining unit  120  generates a registration control signal when the intensity of the first sensed light is greater than the predetermined reference value for Y, M, and C, or when the intensity of the first sensed light is less than the predetermined reference value for K.  
      The exposing unit  114  of the mark forming unit  112  operates in response to the generated registration control signal.  
      The calculating unit  122  calculates the intensities of second emitted lights by using the intensities of the first emitted lights and the intensities of the first sensed light. When second lights are radiated, the intensities of second sensed lights are greater than predetermined values for all colors.  
      The intensity of the second sensed light is denoted as PWM 3 , and the predetermined value is denoted as ADC 3 . ADC 3  may be a maximum intensity of light sensed by the mark sensing unit  118 . ADC 3  is determined according to the hardware characteristics of the mark sensing unit  118 .  
      The calculating unit  122  may operate when the examining unit  120  estimates that the intensities of the first sensed lights are greater than the predetermined reference value for Y, M, and C, or the intensities of the first sensed lights are less than the predetermined reference value for K.  
      For example, the calculating unit  122  may calculate the intensity PWM 3  using intensities PWM 1 , PWM 2 , LowADC 1 , and LowADC 2 . LowADC 1  denotes the lowest intensity of the first sensed lights when a light comprising the intensity PWM 1  is emitted onto the concentration mark. LowADC 2  denotes the lowest intensity of the first sensed light when a light comprising the intensity PWM 2  is emitted onto the concentration mark.  
      The intensity of light sensed by the mark sensing unit  118  is proportional to the intensity of emitted light. That is, the intensity of the first sensed light is proportional to the intensity of the first emitted light, and the intensity of the second sensed light is proportional to the intensity of the second emitted light. Equations 1 and 2 may be derived from this relationship. The calculating unit  122  may calculate the intensity PWM 3  using Equations 1 and 2.  
                 (       PWM   ⁢           ⁢   2     -     PWM   ⁢           ⁢   1       )     ⁢     :     ⁢     (       LowADC   ⁢           ⁢   2     -     LowADC   ⁢           ⁢   1       )       =       (       PWM   ⁢           ⁢   3     -     PWM   ⁢           ⁢   1       )     ⁢     :     ⁢     (       ADC   ⁢           ⁢   3     -     LowADC   ⁢           ⁢   1       )               (   1   )                 PWM   ⁢           ⁢   3     =           (       PWM   ⁢           ⁢   2     -     PWM   ⁢           ⁢   1       )     *     (       ADC   ⁢           ⁢   3     -     LowADC   ⁢           ⁢   1       )           LowADC   ⁢           ⁢   2     -     LowADC   ⁢           ⁢   1         +     PWM   ⁢           ⁢   1               (   2   )             
 
      The mark sensing unit  118  emits light comprising the intensity PWM 3  and senses the registration mark. Accordingly, some of the intensities of the second sensed lights of Y, M, C, and K are greater than the predetermined value ADC 3 .  
      The color registration performing unit  124  senses the registration mark for each color formed by the mark forming unit  112 , and performs color registration using information relating to the time when the registration mark for each color is sensed. Specially, the color registration performing unit  124  performs color registration using information relating to the time when the intensity of the second sensed light, which is greater than a sensed predetermined threshold value.  
      The threshold value may be previously determined using the predetermined value ADC 3  and the minimum intensity of the second sensed light. The threshold value may be an average value of the predetermined value ADC 3  and the minimum intensity of the second sensed light. The second sensed light comprising the minimum intensity may be reflected from the registration mark corresponding to K.  
      The registration marks of Y, M, and C are separately developed using a corresponding chromatic developing agent, but the registration mark corresponding to K is generally not developed using only an achromatic developing agent. If the registration mark corresponding to K is developed using only the achromatic developing agent, the reflection ratio is too low which reduces the mark sensing unit&#39;s  118  ability to sense the reflected lights. Accordingly, inversion portions of the registration mark corresponding to K are developed using the achromatic developing agent, and mark forming portions of the registration mark are developed using the chromatic developing agent.  
      When the registration mark corresponds to K, lights comprising low intensities are sensed at the portions developed using the achromatic developing agent, and lights comprising relatively high intensities are sensed at the portions developed using the chromatic developing agent. The high intensity of the sensed light is greater than the predetermined value ADC 3 .  
      The minimum intensity of the second sensed light may be obtained by Equation 3.  
               BlackADC   ⁢           ⁢   3     =           (       PWM   ⁢           ⁢   3     -     PWM   ⁢           ⁢   1       )     *     (       BlackADC   ⁢           ⁢   2     -     BlackADC   ⁢           ⁢   1       )           PWM   ⁢           ⁢   2     -     PWM   ⁢           ⁢   1         +     BlackADC   ⁢           ⁢   1               (   3   )             
 
 where BlackADC 3  denotes the minimum intensity of the second sensed light reflected from the registration mark corresponding to K. 
 
      Meanwhile, BlackADC 1  denotes an average value of the intensities of the first sensed light when the emitted light comprising the intensity PWM 1  is reflected from the concentration mark corresponding to K. BlackADC 2  denotes an average value of the intensities of the first sensed light when the emitted light comprising the intensity PWM 2  is reflected from the concentration mark corresponding to K.  
      According to an exemplary implementation, the threshold value may be an average value of BlackADC 3  and ADC 3 .  
      The color registration performing unit  124  performs color registration using information relating to the time when the intensity of the sensed second light is greater than the threshold value.  
       FIG. 2  is a timing diagram illustrating the intensity of a first sensed light and the intensity of a second sensed light sensed by a mark sensing unit  118  of  FIG. 1 . The reference numerals  210  and  230  denote BaseADC 1  and BaseADC 2 , respectively.  
      Reference numerals  212 ,  214 ,  216 , and  218  indicate the intensities of the first sensed lights when the emitted lights comprising the intensity PWM 1  are reflected from the concentration marks corresponding to Y, M, C, and K, respectively  
      Reference numerals  232 ,  234 ,  236 , and  238  indicate the intensities of the first sensed lights when the emitted lights comprising the intensity PWM 2  are reflected from the concentration marks corresponding to Y, M, C, and K, respectively.  
      Reference numeral  250  denotes the intensity of the sensed light when the emitted lights comprising the intensity PWM 3  onto the transferring belt are reflected. Reference numeral  260  denotes the predetermined value ADC 3 . Reference numeral  270  denotes the minimum intensity of the second sensed light BlackADC 3  reflected from the registration mark corresponding to K. Reference numeral  290  denotes the threshold value.  
       FIG. 3  is a flowchart of a color registration method according to an exemplary embodiment of the present invention. Color registration is performed in steps  310  through  338  without errors regardless of a concentration of a developing agent by determining the intensity of light irradiated onto a registration mark and the minimum intensity of sensed light necessary to identify the registration mark according to the concentration of the developing agent.  
      The light intensity determining unit  110  determines the intensities PWM 1  and PWM 2  in step  310 . The determined value of the intensity PWM 1  is transmitted to the mark sensing unit  118  in step  312 . The mark forming unit  112  forms a first concentration mark in step  314 . The mark sensing unit  118  emits light comprising the intensity PWM 1  onto the first concentration mark and senses the first concentration mark in step  316 .  
      The determined value of the intensity PWM 2  is transmitted to the mark sensing unit  118  in step  318 . The mark forming unit  112  forms a second concentration mark in step  320 . The mark sensing unit  118  emits light comprising the intensity PWM 2  onto the second concentration mark and senses the second concentration mark in step  322 .  
      The examining unit  120  estimates whether the intensity of the second sensed light reflected from the concentration mark corresponding to Y, M, or C is greater than a predetermined reference value. The examining unit  120  estimates whether the intensity of the second sensed light reflected from the concentration mark corresponding to K is less than a predetermined reference value in step  324 .  
      When the intensity of the second sensed light reflected from the concentration mark corresponding to Y, M, or C is greater than a predetermined reference value, and when the intensity of the second sensed light reflected from the concentration mark corresponding to K is less than a predetermined reference value, the calculating unit  122  searches for the lowest intensity LowADC 1  of the first sensed light sensed in response to the intensity PWM 1  and the lowest intensity LowADC 2  of the first sensed light sensed in response to the intensity PWM 2  in step  326 .  
      Then, the calculating unit  122  calculates the intensity PWM 3  using the intensities PWM 1 , PWM 2 , LowADC 1 , LowADC 2 , and ADC 3  in step  328 , calculates BlackADC 3  using the intensity PWM 3  in step  330 , and determines a threshold value in step  332 .  
      The value of the intensity PWM 3  is transmitted to the mark sensing unit  118 , and the determined threshold value is transmitted to the color registration performing unit  124  in step  334 . The mark forming unit  112  forms a registration mark for each color in step  336 .  
      The mark sensing unit  118  senses the registration mark by emitting a light comprising the intensity PWM 3 . Color registration is performed when the intensities of the second sensed light, which are greater than the threshold value, are sensed in step  338 .  
      The exemplary embodiments of the present invention may be written as computer programs and may be executed in general-use digital computers that execute the programs using a computer readable recording medium. Examples of the computer readable recording medium include magnetic storage media (for example, ROM, floppy disks, and hard disks among others), optical recording media (for example, CD-ROMs, and DVDs among others), and storage media such as carrier waves (for example, transmission through the internet). The computer readable recording medium may also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. Functional programs, codes, and code segments for realizing the exemplary embodiments of the present invention may be easily modified by those of ordinary skill in the art.  
      As described above, the color registration apparatus and method according to the exemplary embodiments of present invention may perform color registration without errors regardless of a concentration of a developing agent by determining the intensity of light irradiated onto a registration mark. The minimum intensity of sensed light necessary to identify the registration mark is identified according to the concentration of the developing agent.  
      The color registration apparatus and method according to the exemplary embodiments of the present invention may determine the intensity of light irradiated onto a registration mark and the minimum intensity of sensed light necessary to identify the registration mark according to the concentration of a developing agent using the results of sensing concentration mark twice, thereby reducing the time for preparing the color registration and the amount of developing agents for the color registration.  
      While the present invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims and their equivalents.