Patent Publication Number: US-6907222-B2

Title: Method and apparatus of controlling an image input and a recording-medium supply of an image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the priority of Korean Patent Application No. 2002-73041, filed on Nov. 22, 2002, in the Korean Industrial Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   An aspect of the present invention relates to inputting an image into an exposure unit and supplying a recording medium to a transfer unit in an image forming apparatus such as a printer, a copier, and a facsimile, and more particularly, to a method and apparatus to control an image input and a recording-medium supply of an image forming apparatus. 
   2. Description of the Related Art 
   An electrophotographic image forming apparatus inputs an image, which is transferred from a host such as a PC, a workstation, or an input from an image input unit such as a copier into an exposure unit such as a laser scanning unit (LSU) or a light emitting diode (LED). The image forming apparatus forms the input image on a photosensitive body such as an electrostatic latent image, and changes the electrostatic latent image into a toner image via a developing unit. Meanwhile, the image forming apparatus accurately moves a recording medium, such as paper, via a recording-medium supply unit and a recording-medium movement adjusting unit, and transfers the above-mentioned toner image on the recording medium, thereby completing a printing operation. In this case, line synchronizing signals or horizontal synchronizing signals, which are line control signals output from the exposure unit, are used to input the image transferred from the host or input from the image input unit into the exposure unit. The line synchronizing signals or the horizontal synchronizing signals are the basis of a starting point per line on a printing image. The image forming apparatus counts the line control signals and controls the start and end of an image input into the exposure unit. Moreover, a timer in the image forming apparatus is used to control a supply time needed for the recording medium to be supplied from the recording-medium supplying unit to the transfer unit. Accordingly, the image input and the recording-medium supply are controlled in different manners. Therefore, in order to print a good-quality image, it is very important to precisely synchronize the time when the image is input into the exposure unit with the time when the recording medium is supplied to the transfer unit. This is particularly required to print a color image because equalizing each color image with each toner image and equalizing the coincident toner image with a recording medium determine printing image quality. 
   Generally, in order to place an image properly on a recording medium, a monochromatic image forming apparatus synchronizes line control signals outputted from an exposure unit with front end signals of the recording medium supplied from a recording-medium supply unit to control a time when an image is input into the exposure unit. However, since most color image forming apparatuses have a movement path of an image relatively longer than a movement path of the recording medium, the color image forming apparatus synchronizes line control signals with an image input time to control a time when a recording medium is supplied. Moreover, an image input time and a recording-medium supply time are synchronized by a rotation period of a developing unit or a transfer unit. 
   However, before a printing operation on a first page is completed, a printing operation may be performed on a second page, meaning, a printing operation may be repeatedly and simultaneously performed on two or more pages. This case usually occurs when a path through which the recording medium passes is long. However, even when a toner image of each color is overlapped on another toner image during a color image printing operation, a repeated printing operation may be performed. When the repeated printing operation is performed, if a counter that counts an image input time and a timer that calculates a recording-medium supply time are initialized when each printing operation starts, it cannot be checked whether the recording medium is exhausted from the image forming apparatus after the printing operation is completed. Thus, in order to check whether the recording medium is exhausted from the image forming apparatus, a counter or a timer used for a previous page should not be initialized. Therefore, in order to control the image input time and the recording-medium supply time during the repeated printing operation, a plurality of counters and timers to control the image input and the recording-medium supply should be used. The plurality of counters and timers are synchronized at various points in time. Thus, in order to control the plurality of counters and timers, the image forming apparatus ends up becoming complicated. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an aspect of the present invention to provide a method to control an image input and a recording-medium supply of an image forming apparatus via which demands on an image input and a recording-medium supply are synchronized by periodically generating a timer interrupt such that an image can be printed in a correct position on the recording medium even under a simple control. 
   Another aspect of the present invention provides an apparatus to control an image input and a recording-medium supply of an image forming apparatus in which the method to control the image input and the recording-medium supply of an image forming apparatus is implemented. 
   Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
   According to an aspect of the present invention, a method to control an image input and a recording-medium supply of an image forming apparatus is provided. The method comprises: periodically generating synchronized demands of an image input into the exposure unit and for a recording medium supply to the transfer unit, inputting the image into the exposure unit according to the synchronized demand on image input, and supplying the recording medium to the transfer unit according to the synchronized demand on recording-medium supply. The method further comprises: forming an electrostatic latent image via an exposure unit in response to an image input signal, changing the image in which the electrostatic latent image is formed into a toner image via a developing unit, and transferring the toner image on a recording medium to which the toner image is supplied via a transfer unit. 
   According to another aspect of the present invention, an apparatus to control image input and a recording-medium supply of an image forming apparatus is provided. The apparatus comprises an exposure unit to form an electrostatic latent image in response to an input image signal, a developing unit to change the image in which the electrostatic latent image is formed into a toner image, and a transfer unit to transfer the toner image on a recording medium to which the toner image is supplied. Moreover, the apparatus includes a synchronization signal generating unit which periodically generates each synchronization demand signal to input an image into the exposure unit and to supply a recording medium to the transfer unit, and to output each generated synchronization demand signal, an image input processing unit which inputs an image into the exposure unit in response to the synchronization demand signal for image input, and a recording-medium supply processing unit which supplies a recording medium to the transfer unit in response to the synchronization demand signal for recording-medium supply. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and/or other aspects and advantages of the invention will become apparent and more appreciated from the following description of the embodiments taken in conjunction with the accompanying drawings of which: 
       FIG. 1  is a flow chart to illustrate a method to control an image input and a recording-medium supply of an image forming apparatus according to the present invention; 
       FIG. 2  is a flow chart to illustrate operation  10  shown in  FIG. 1 ; 
       FIG. 3  is a flow chart to illustrate inputting an image into an exposure unit according to demands on synchronization of image input of operation  12  shown in  FIG. 1 ; 
       FIG. 4  is a flow chart to illustrate operation  58  shown in  FIG. 3 ; 
       FIG. 5  is a flow chart to illustrate another embodiment of operation  58  shown in  FIG. 3 ; 
       FIG. 6  is a flow chart to illustrate another embodiment of inputting an image into an exposure unit according to demands on synchronization of image input of operation  12  shown in  FIG. 1 ; 
       FIG. 7  is a flow chart to illustrate an embodiment of supplying a recording medium to a transfer unit according to demands on synchronization of image input of operation  12  shown in  FIG. 12 ; 
       FIG. 8  is a flow chart to illustrate an embodiment of operation  198  shown in  FIG. 7 ; 
       FIG. 9  is a flow chart to illustrate another embodiment of supplying a recording medium to a transfer unit according to demands on synchronization of image input of operation  12  shown in  FIG. 12 ; 
       FIG. 10  is a block diagram to illustrate an apparatus to control an image input and a recording-medium supply of an image forming apparatus in which the method to control an image input and a recording-medium supply of an image forming apparatus shown in  FIG. 1  is implemented; 
       FIG. 11  is a block diagram to illustrate a synchronization signal generating unit shown in  FIG. 10 ; 
       FIG. 12  is a block diagram to illustrate an image input processing unit shown in  FIG. 10 ; 
       FIG. 13  is a block diagram to illustrate a recording-medium supplying unit shown in  FIG. 10 ; and 
       FIG. 14  is a timing chart to illustrate an embodiment of operations performed in an interrupt generating unit shown in  FIG. 11 , a counting unit shown in  FIG. 12 , and a timing unit shown in FIG.  13 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Reference will now be made in detail to the present preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
   A method to control an image input and a recording-medium supply of an image forming apparatus according to one aspect of the present invention is shown in FIG.  1 . The method comprises the operations  10  and  12  of inputting an image into an exposure unit and supplying a recording medium to a transfer unit according to demands of an image input and demands for a recording-medium supply, which are periodically generated. 
   In operation  10  shown in  FIG. 1 , synchronized demands of an image input into an exposure unit and synchronized demands for a recording medium supply to a transfer unit are periodically generated. The demand on image input and the demand on recording-medium supply are generated at the same point in time. The synchronized demands are periodically generated. A generation period of the synchronized demands may be arbitrarily set, may be coincident with a rotation period of a developing unit in which the input image is changed into a toner image, or a rotation period of the transfer unit in which the toner image is transferred on the supplied recording medium. 
   An embodiment  10 A of operation  10  shown in  FIG. 1 , according to an aspect of the present invention, is shown in FIG.  2 . The embodiment  10 A comprises operations  30  through  34  of generating synchronized demands of image input and for recording-medium supply via a generated interrupt if a printing operation is required. 
   In operation  30 , it is determined whether a printing operation is required from a host such as a PC, a workstation, or from an image forming apparatus, such as a facsimile or a copier. If it is determined that the printing operation is not required, the embodiment  10 A proceeds to operation  12  of FIG.  1 . 
   However, if it is determined that the printing operation is required, in operation  32 , it is determined whether an interrupt is generated. If it is determined that the interrupt is not generated, the embodiment  10 A proceeds to operation  12  of FIG.  1 . 
   However, if it is determined that the interrupt is generated, in operation  34 , each synchronized demand of image input and for recording-medium supply is generated. The synchronized demands of image input and for recording-medium supply are simultaneously generated whenever the interrupt is generated. 
   After operation  10 , in operation  12 , the image is input into the exposure unit according to the synchronized demand of the image input, and demand for the recording medium is supplied to the transfer unit according to the synchronized demand on recording-medium supply. 
   An embodiment  12 A of inputting an image into an exposure unit according to demands on synchronization of image input of operation  12  shown in  FIG. 1  is shown in FIG.  3 . The embodiment  12 A comprises operations  50  through  58  of counting the number of line control signals, if image input is required, using an initialized counter, starting or stopping image input, and initializing the counter. The line control signals output from the exposure unit are line synchronizing signals or horizontal synchronizing signals, which are the basis of a starting point per line on a printing image. In the embodiment  12 A, since the number of line control signals is counted, counting the number of line control signals starts whenever the line control signals are generated. 
   In operation  50 , it is determined whether an image input is required. If the image input is not required, the embodiment  12 A proceeds to operation  54 . 
   However, if it is determined that image input is required, in operation  52 , an initialized counter found among one or more counters to count the number of line control signals output from the exposure unit starts counting the line control signals. Here, a sufficient number of counters have to be prepared so that an adequate number of counters can be initialized. 
   After operation  52 , in operation  54 , it is determined whether there is a counter that starts counting the line control signals. If there is no counter that starts counting the line control signals, after the above-mentioned operations are terminated, the embodiment  12 A repeats the above operations at a next line control signal generation time. 
   However, if it is determined that there is a counter that starts counting the line control signals, in operation  56 , the counter counts the line control signals. By counting the line control signals using the counter, the time to input the image into the exposure unit can be determined. 
   After operation  56 , in operation  58 , the image is input into the exposure unit or image input stops according to the number of counted line control signals and the counters which counted the line control signals are initialized. 
   An embodiment  58 A of operation  58  shown in  FIG. 3 , according to an aspect of the present invention is shown in FIG.  4 . The embodiment  58 A comprises operations  70  through  78  of starting or stopping image input and initializing counters. 
   In operation  70 , it is determined whether the number of line control signals counted by the counter corresponds to a number of line control signals used to start image input. The number of line control signals used to start image input is defined by whether, for example, an exposure unit employing a laser scanning unit (LSU) starts inputting an image into the exposure unit when a laser beam is scanned a predetermined times. The number is preset before the printing operation is performed. If it is determined that the number of counted line control signals does not correspond to the number of line control signals used to start image input, the embodiment  58 A does not proceed to operation  72  but proceeds to operation  74 . 
   However, if it is determined that the number of counted line control signals corresponds to the number of line control signals used to start image input, in operation  72 , image input starts. That is, the image is input into the exposure unit. 
   After operation  72 , in operation  74 , it is determined whether the number of counted line control signals corresponds to a number of line control signals used to stop an image input. The number of line control signals used to stop image input is, as described previously, defined by whether, for example, an exposure unit employing a laser scanning unit (LSU) stops input of an image into the exposure unit when a laser beam is scanned a predetermined times. The number is preset before the printing operation is performed. If it is determined that the number of counted line control signals does not correspond to the number of line control signals used to stop image input, after the above-mentioned operations are terminated, the embodiment  58 A performs the above-mentioned operations again at a next execution point in time. 
   However, if it is determined that the number of line control signals corresponds to the number of line control signals used to stop image input, in operation  76 , image input stops. That is, inputting the image into the exposure unit stops. 
   After operation  76 , in operation  78 , counters via which the number of line control signals was counted are initialized. The counters are initialized to count the number of line control signals used to print another recording medium. 
   Embodiment  58 B of operation  58  shown in  FIG. 3 , according to an aspect of the present invention, is shown in FIG.  5 . The embodiment  58 B comprises operations  90  through  122  of starting or stopping input of first through fourth color images required to form a desired color image, and initializing counted counters. When color images are printed, a four-time developing process of colors such as cyan (C), magenta (M), yellow (Y), and black (B) is performed to develop the color images. In this case, the first through fourth color images are input to repeat image input four times. Thus, when the number of printing colors is more than four, additional operations of starting and stopping input of color images are performed. 
   In operation  90 , it is determined whether the number of counted line control signals corresponds to a number of line control signals used to start input of the first color image of fourth color images required to form a desired color image. If it is determined that the number of counted line control signals does not correspond to the number of line control signals used to start input of the first color image, the embodiment  58 B proceeds to operation  94 . 
   However, if it is determined that the number of counted line control signals corresponds to the number of line control signals used to start input of the first color image, in operation  92 , input of the first color image starts. 
   After operation  92 , in operation  94 , it is determined that the number of counted line control signals corresponds to a number of line control signals used to stop input of the first color image. If it is determined that the number of counted line control signals does not correspond to the number of line control signals used to stop input of the first color image, the embodiment  58 B proceeds to operation  98 . 
   However, if it is determined that the number of counted line control signals corresponds to the number of line control signals used to stop input of the first color image, in operation  98 , input of the first color image stops. 
   After operation  96 , in operation  98 , it is determined whether the number of counted line control signals corresponds to a number of line control signals used to start input of the second color image. If it is determined that the number of counted line control signals does not correspond to the number of line control signals used to start input of the second color image, the embodiment  58 B proceeds to operation  102 . 
   However, if it is determined that the number of counted line control signals corresponds to the number of line control signals used to start input of the second color image, in operation  100 , input of the second color image starts. 
   After operation  100 , in operation  102 , it is determined whether the number of counted line control signals corresponds to a number of line control signals used to stop input of the second color image. If it is determined that the number of counted line control signals does not correspond to the number of line control signals used to stop input of the second color image, the embodiment  58 B proceeds to operation  106 . 
   However, if it is determined that the number of counted line control signals corresponds to the number of line control signals used to stop input of the second color image, in operation  104 , input of the second color image stops. 
   After operation  104 , in operation  106 , it is determined whether the number of counted line control signals corresponds to a number of line control signals used to start input of the third color image. If it is determined that the number of counted line control signals does not correspond to the number of line control signals used to start input of the third color image, the embodiment  58 B proceeds to operation  110 . 
   However, if it is determined that the number of counted line control signals corresponds to the number of line control signals used to start input of the third color image, in operation  108 , input of the third color image starts. 
   After operation  108 , in operation  110 , it is determined whether the number of counted line control signals corresponds to a number of line control signals used to stop input of the third color image. If it is determined that the number of counted line control signals does not correspond to the number of line control signals used to stop input of the third color image, the embodiment  58 B proceeds to operation  114 . 
   However, if it is determined that the number of counted line control signals corresponds to the number of line control signals use to stop input of the third color image, in operation  112 , input of the third color image stops. 
   After operation  112 , in operation  114 , it is determined whether the number of counted line control signals corresponds to the number of line control signals used to start input of the fourth color image. If it is determined that the number of input counted line control signals does not correspond to the number of line control signals used to start input of the fourth color image, the embodiment  58 B proceeds to operation  118 . 
   However, if it is determined that the number of counted line control signals corresponds to a number of line control signals used to start input of the fourth color image, in operation  116 , input of the fourth color image starts. 
   After operation  116 , in operation  118 , it is determined whether the number of counted line control signals corresponds to a number of line control signals used to stop input of the fourth color image. If it is determined that the number of counted line control signals does not correspond to the number of line control signals used to stop input of the fourth color image, the embodiment  58 B proceeds to operation  122 . 
   However, if it is determined that the number of counted line control signals corresponds to the number of line control signals use to stop input of the fourth color image, in operation  120 , input of the fourth color image stops. 
   After operation  120 , in operation  122 , if input of all four images is terminated, the counted counters are initialized. 
   Embodiment  12 B of inputting an image into an exposure unit according to demands on synchronization of image input of operation  12  shown in  FIG. 1  is shown in FIG.  6 . The embodiment  12 B comprises operations  140  through  172  of inputting an image or stopping image input by counting line control signals using three counters and initializing the above-mentioned counters. Although three counters are shown in  FIG. 6 , a plurality of counters, preferably more than m (m is a positive integer greater than 1) can be provided. 
   In operation  140 , it is determined whether an image input is required. If the image input is not required, the embodiment  12 B proceeds to operation  156 . 
   However, if it is determined that the image input is required, in operation  142 , it is determined whether a first counter is initialized. If it is determined that the first counter is not initialized, the embodiment  12 B proceeds to operation  146 . 
   However, if it is determined that the first counter is initialized, in operation  144 , the first counter starts counting the line control signals. 
   If it is determined that the first counter is not initialized, in operation  146 , it is determined whether a second counter is initialized. If it is determined that the second counter is initialized, in operation  148 , the second counter starts counting the line control signals. 
   If it is determined that the second counter is not initialized, in operation  150 , it is determined whether a third counter is initialized. If it is determined that the third counter is not initialized, the embodiment  12 B proceeds to operation  154 , and an error that the initialized counters are in short supply is marked. 
   However, if it is determined that the third counter is initialized, in operation  152 , the third counter starts counting the line control signals. 
   After operations  144 ,  148 , and  152 , in operation  156 , it is determined whether the first counter starts counting the line control signals. If it is determined that the first counter does not start counting the line control signals, the embodiment  12 B proceeds to operation  162 . 
   However, if it is determined that the first counter starts counting the line control signals, in operation  158 , the number of line control signals is counted by the first counter. 
   After operation  158 , in operation  160 , an image is input or image input stops in response to the counted line control signals, and the counted first counter is initialized. Preferably, operation  160  comprises the same operations as those of the flow chart shown in  FIG. 4  or  FIG. 5  described previously. 
   If the first counter does not start counting the line control signals or after operation  160 , in operation  162 , it is determined whether the second counter starts counting the line control signals. If it is determined that the second counter does not start counting the line control signals, the embodiment  12 B proceeds to operation  168 . 
   However, if it is determined that the second counter starts counting the line control signals, in operation  164 , the number of line control signals is counted by the second counter. 
   After operation  164 , in operation  166 , an image is input or image input stops in response to the counted line control signals, and the counted second counter is initialized. Preferably, the operation  166  comprises the same operations as those of the flow chart shown in  FIG. 4  or  FIG. 5  described previously. 
   If the second counter does not start counting the line control signals or after operation  166 , in operation  168 , it is determined whether the third counter starts counting the line control signals. If it is determined that the third counter does not start counting the line control signals, after the above-mentioned operations are terminated, the embodiment  12 B repeats the above operations at a next execution point in time. 
   However, if it is determined that the third counter starts counting the line control signals, in operation  170 , the number of line control signals is counted by the third counter. 
   After operation  170 , in operation  172 , an image is input or image input stops in response to the counted line control signals, and the counted third counter is initialized. Preferably, the operation  172  comprises the same operations as those of the flow chart shown in  FIG. 4  or  FIG. 5  described previously. 
   An embodiment  12 C of supplying a recording medium to a transfer unit according to demands on synchronization of image input of operation  12  shown in  FIG. 12  is illustrated in FIG.  7 . The embodiment  12 C comprises operations  190  through  198  of supplying a recording medium to a transfer unit and adjusting a position of the recording medium by measuring a time using initialized timers, if recording medium supply is required. 
   In operation  190 , it is determined whether a recording-medium supply is required. If it is determined that the recording-medium supply is not required, the embodiment  12 C proceeds to operation  194 . 
   However, if it is determined that the recording-medium supply is required, in operation  192 , at least one initialized timer starts. 
   After operation  192 , in operation  194 , it is determined whether there is a timer that starts operating to measure a time. If there is no timer that starts operating, after the above-mentioned operations are terminated, the embodiment  12 C performs the above operations again at a next execution time. 
   However, if it is determined that there is a timer that starts operating, in operation  196 , measuring of a time is performed by the timer. 
   After operation  196 , in operation  198 , the recording medium is supplied to the transfer unit or movement of the recording medium is adjusted by the measured time, and the timer is initialized. 
   Embodiment  198 A of operation  198  shown in  FIG. 7  is illustrated in  FIG. 8  according to an aspect of the present invention. The embodiment  198 A comprises operations  210  through  220  of supplying a recording medium to a transfer unit, and adjusting a position of the recording medium by measuring a time using initialized timer and initializing the timer. 
   In operation  210 , it is determined whether a time measured by the timer corresponds to a time needed to supply the recording medium to the transfer unit. The time needed to supply the recording medium to the transfer unit is defined as the time in which the recording medium is supplied from a paper feeding apparatus (not shown) to the transfer unit. The time needed to supply the recording medium to the transfer unit is preset before a printing operation starts. If it is determined that the measured time does not correspond to the time needed to supply the recording medium to the transfer unit, the embodiment  198 A proceeds to operation  214 . 
   However, if it is determined that the time measured by the timer corresponds to the time needed to supply the recording medium to the transfer unit, in operation  212 , the recording medium is supplied to the transfer unit. That is, the recording medium is supplied from the paper feeding apparatus to the transfer unit. 
   After operation  212 , in operation  214 , it is determined whether the time measured by the timer corresponds to a time needed to adjust a movement of the recording medium. The time needed to adjust the movement of the recording medium is defined to make overlapping of a developed image on the recording medium supplied to the transfer unit coincident. The time to adjust the movement of the recording medium is preset before the printing operation starts. If it is determined that the measured time does not correspond to the time needed to adjust the movement of the recording medium, the embodiment  198 A proceeds to operation  218 . 
   However, if it is determined that the time measured by the timer corresponds to the time needed to adjust the movement of the recording medium, in operation  216 , movement of the recording medium is adjusted. Movement of the recording medium is adjusted by changing a movement speed of the recording medium or stopping the movement of the recording medium and restarting it. As a result, the developed image is placed accurately in a proper position on the recording medium. 
   After operation  216 , in operation  218 , it is determined whether the recording medium is exhausted from the transfer unit for a predetermined amount of time. Preferably, it is also determined whether the recording medium is exhausted from the image forming apparatus for the predetermined amount of time. If it is determined that the recording medium is not exhausted from the transfer unit, the above-mentioned operations are terminated, and then, the embodiment  198 A performs the above operations again at a next execution time. 
   However, if it is determined that the recording medium is exhausted from the transfer unit for the predetermined amount of time, in operation  220 , the timer is initialized. The timer is initialized to measure a time required to print another recording medium. However, for a simple control, the method according to an aspect of the present invention may omit operation  218  and perform operation  220  after operation  216 . 
   Another embodiment  12 D of supplying a recoding medium to a transfer unit according to demands on synchronization of an image input of operation  12  shown in  FIG. 12  is illustrated in FIG.  9 . The embodiment  12 D comprises operations  240  through  272  of supplying the recording medium to the transfer unit or stopping of recording-medium supply by measuring a time using three timers, and initializing the above-mentioned timers. Although three timers are shown in  FIG. 9 , a plurality of timers, preferably more than n (n is a positive integer greater than 1) can be provided. 
   In operation  240 , it is determined whether a recording-medium supply is required. If it is determined that a recording-medium supply is not required, the embodiment  12 D proceeds to operation  256 . 
   However, if it is determined that a recording-medium supply is required, in operation  242 , it is determined whether a first timer is initialized. If it is determined that the first timer is not initialized, the embodiment  12 D proceeds to operation  246 . 
   However, if it is determined that the first timer is initialized, in operation  244 , the first timer starts operating. 
   If it is determined that the first timer is not initialized, in operation  246 , it is determined whether a second timer is initialized. If it is determined that the second timer is not initialized, the embodiment  12 D proceeds to operation  250 . 
   However, if it is determined that the second timer is initialized, in operation  248 , the second timer starts operating. 
   If it is determined that the second timer is not initialized, in operation  250 , it is determined whether a third timer is initialized. If it is determined that the third timer is not initialized, the embodiment  12 D proceeds to operation  254 , and an error that initialized timers are in short supply, is marked, and the embodiment  12 D is terminated. However, if it is determined that the third timer is initialized, in operation  252 , the third timer starts operating. 
   After operations  244 ,  246 , and  252 , in operation  256 , it is determined whether the first timer starts operating. If it is determined that the first timer does not start operating, the embodiment  12 D proceeds to operation  262 . However, if it is determined that the first timer starts operating, in operation  258 , a time is measured by the first timer. 
   After operation  258 , in operation  260 , the recording medium is supplied to the transfer unit or movement of the recording medium is adjusted based on the measured time, and the first timer is initialized. Preferably, operation  260  comprises the same operations as those of the flow chart shown in  FIG. 8  described previously. 
   If it is determined in operation  256  that the first timer does not start operating or after operation  260 , in operation  262 , it is determined whether the second timer starts operating. If it is determined that the second timer does not start operating, the embodiment  12 D proceeds to operation  268 . However, if it is determined that the second timer starts operating, in operation  264 , a time is measured by the second timer. 
   After operation  264 , in operation  266 , the recording medium is supplied to the transfer unit or movement of the recording medium is adjusted based on the measured time, and the second timer is initialized. Preferably, operation  266  comprises the same operations as those of the flow chart shown in  FIG. 8  described previously. 
   If it is determined in operation  262  that the second timer does not start operating or after operation  266 , in operation  268 , it is determined whether the third timer starts operating. If it is determined that the third timer does not start operating, the above-mentioned operations are terminated, and then, the embodiment  12 D performs the above operations again at a next execution time. 
   However, if it is determined that the third timer starts operating, in operation  270 , a time is measured by the third timer. 
   After operation  270 , in operation  272 , the recording medium is supplied to the transfer unit, or movement of the recording medium is adjusted based on the measured time, and the third timer is initialized. Preferably, operation  272  comprises the same operations as those of the flow chart shown in  FIG. 8  described previously. 
   Hereinafter, the structure and operation of an apparatus to control an image input and a recording-medium supply of an image forming apparatus, according to an aspect of the present invention, in which the method to control image input and a recording-medium supply of an image forming apparatus according to one aspect of the present invention is implemented will be described with reference to the accompanying drawings. 
   An apparatus to control an image input and a recording-medium supply of an image forming apparatus according to one aspect of the present invention is shown in FIG.  10 . The apparatus comprises the method to control an image input and a recording-medium supply of an image forming apparatus shown in  FIG. 1 , according to one aspect of the present invention. The apparatus includes a synchronization signal generating unit  300 , an image input processing unit  320 , and a recording-medium supply processing unit  340 . 
   In order to perform operation  10 , the synchronization signal generating unit  300  shown in  FIG. 10  generates each synchronization demand signal to input an image into an exposure unit and to periodically supply a recording medium to a transfer unit, and outputs each generated synchronization demand signal. For example, the synchronization signal generating unit  300  receives a printing required signal through an input terminal IN 1 , generates each synchronization demand signal to input the image into the exposure unit and to periodically supply the recording medium to the transfer unit, outputs the generated synchronization demand signals to input the image into the image input processing unit  320 , and outputs the generated synchronization demand signals to supply the recording medium to the recording-medium supply processing unit  340 . 
   Embodiment  300 A of a synchronization signal generating unit  300  shown in  FIG. 10 , according to an aspect of the present invention, is illustrated in FIG.  11 . The embodiment  300 A comprises a printing requirement sensing unit  400 , an interrupt generating unit  410 , an image synchronizing signal generating unit  420 , and a recording-medium synchronization signal generating unit  430 . 
   In order to perform operation  30 , the printing requirement sensing unit  400  senses whether a printing operation is required, and outputs the result of sensing. For example, the printing requirement sensing unit  400  receives a printing required signal through an input terminal IN 3  and outputs the result of sensing to the interrupt generating unit  410 . 
   In order to perform operation  32 , the interrupt generating unit  410  periodically generates an interrupt in response to the result of sensing, and outputs the generated interrupt. An interrupt generation period may be arbitrarily generated for each predetermined amount of time or may be coincident with a rotation period of a developing unit (not shown) in which the input image is changed into a toner image, or a rotation period of a transfer unit (not shown) in which the toner image is transferred on the supplied recording medium. For example, the interrupt generating unit  410  periodically generates an interrupt in response to the result of sensing to detect whether or not a printing required signal is transmitted from the printing requirement sensing unit  400  and outputs the periodically-generated interrupt to the image synchronization signal generating unit  420  and the recording-medium synchronization signal generating unit  430 , respectively. In this case, the interrupt generating unit  410  outputs a signal requiring sensing of printing requirement again to the printing requirement sensing unit  400 . 
   In order to perform operation  34 , the image synchronization signal generating unit  420  generates the synchronization demand signal for image input in response to the generated interrupt, and outputs the generated synchronization demand signal. For example, the image synchronization signal generation unit  420  generates an image input synchronization demand signal periodically in response to the interrupt transmitted from the interrupt generating unit  410  and outputs the periodically-generated image input synchronization demand signal to the image input processing unit  320  through an output terminal OUT 3 . 
   Also, in order to perform operation  34 , the recording-medium synchronization signal generating unit  430  generates a synchronization demand signal for recording-medium supply in response to the generated interrupt, and outputs the generated synchronization demand signal. For example, the recording-medium synchronization signal generating unit  430  periodically generates a recording-medium supply synchronization demand signal in response to the interrupt transmitted from the interrupt generating unit  410  and outputs the periodically-generated recording-medium supply synchronization demand signal to the recording medium supply processing unit  340  through an output terminal OUT 4 . 
   Meanwhile, in order to perform operation  12 , the image input processing unit  320  inputs an image into an exposure unit (not shown) in response to a synchronization demand signal for image input. For example, the image input processing unit  320 , which receives line control signals from the exposure unit through an input terminal IN 2 , generates a signal used to start or stop image input in response to the synchronization demand signal for image input transmitted from the synchronization signal generating unit  300  and outputs the generated signal through an output terminal OUT 1 . 
   An embodiment  320 A of an image input processing unit  320  shown in  FIG. 10 , according to one aspect of the present invention, is illustrated in FIG.  12 . The embodiment  320 A comprises an image-input requirement sensing unit  500 , an initialization counter sensing unit  510 , a counting unit  520 , a counting controlling unit  530 , an image-input adjustment signal generating unit  540 , and an image input unit  550 . 
   In order to perform operation  50 , the image-input requirement sensing unit  500  senses whether image input is required, and outputs the result of sensing. For example, the image-input requirement sensing unit  500  receives a synchronization demand signal for image input through an input terminal IN 4 , and outputs the result of sensing to the initialization counter sensing unit  510 . 
   In order to perform operation  52 , the initialization counter sensing unit  510  senses whether there is an initialized counter among the counters provided in the counting unit  520 , and transmits the synchronization demand signal for image input. For example, the initialization counter sensing unit  510  senses a first counter  522  that is initialized among first through m-th counters (m is a positive integer greater than 1) provided in the counting unit  520  in response to the synchronization demand signal for image input received from the image-input requirement sensing unit  500 , and transmits the synchronization demand signal for input of an image into the initialized first counter  522 . The first counter  522  may be set to ‘1’ in response to the synchronization demand signal transmitted by the initialization counter sensing unit  510 . 
   In order to perform operation  56 , the first through m-th counters are provided in the counting unit  520 , and the counters count the number of line control signals. For example, because the first counter  522  of the counting unit  520  having a plurality of counters is set to “1” in response to the synchronization demand signal for image input transmitted from the initialization counter sensing unit  510 , the first counter  522  counts the number of line control signals input through an input terminal IN 5 . 
   In order to perform operation  58 , the counting controlling unit  530  senses whether the number of counted line control signals corresponds to the number of line control signals used to start image input, outputs the first result of sensing, senses whether the number of counted line control signals corresponds to the number of line control signals used to stop image input, outputs the second result of sensing, and initializes the counter which has counted the number of line control signals in response to the second result of sensing. For example, the counting controlling unit  530  senses whether the number of line control signals counted by the first counter  522  corresponds to the number of line control signals used to start image input, outputs the first result of sensing to the image input adjustment signal generating unit  540 , senses whether the number of line control signals counted by the first counter  522  corresponds to the number of line control signals used to stop image input, and outputs the second result of sensing to the image input adjustment signal generating unit  540 . Also, the counting controlling unit  530  initializes the first counter  522  in response to the second result of sensing. 
   The image input adjustment signal generating unit  540  generates an image-input start signal in response to the above-mentioned first result of sensing, generates an image input stop signal in response to the above-mentioned second result of sensing, and outputs the generated image-input start signal and the image input stop signal. For example, the image input adjustment signal generating unit  540  generates the image-input start signal and the image-input stop signal in response to the first result and the second result sensed by the counting controlling unit  530 , and outputs the generated image-input start signal and the generated image-input stop signal to the image input unit  550 . 
   The image input unit  550  starts and stops input of an image into the exposure unit in response to the generated image-input start signal and the image-input stop signal. For example, the image input unit  550  starts or stops input of an image into the exposure unit through an output terminal OUT 5  in response to the image-input start signal and the image-input stop signal received from the image input adjustment signal generating unit  540 . 
   Meanwhile, in order to perform operation  12 , the recording-medium supply processing unit  340  supplies the recording medium to the transfer unit in response to synchronization demand signal for recording-medium supply. For example, the recording-medium supply processing unit  340  generates a signal to supply the recording medium to the transfer unit in response to the synchronization demand signal for recording-medium supply transmitted from the synchronization signal generating unit  300 , and outputs the generated signal through an output terminal OUT 2 . 
   An embodiment  340 A of a recording-medium supplying unit  340  shown in  FIG. 10 , according to an aspect of the present invention, is illustrated in FIG.  13 . The embodiment  340 A includes a recording-medium supply requirement sensing unit  600 , an initialization timer sensing unit  610 , a timing unit  620 , a timing controlling unit  630 , a recording-medium supply signal generating unit  640 , a recording-medium supplying unit  650 , a recording-medium adjustment signal generating unit  660 , a recording-medium movement adjusting unit  670 , and a recording-medium exhaust sensing unit  680 . 
   In order to perform operation  190 , the recording-medium supply requirement sensing unit  600  senses whether recording-medium supply is required, and outputs the result of the sensing. For example, the recording-medium supply sensing unit  600  receives a synchronization demand signal for recording-medium supply through an input terminal IN 6 , and outputs the result of sensing to the initialization timer sensing unit  610 . 
   In order to perform operation  192 , the initialization timer sensing unit  610  senses whether there is an initialized timer among the timers provided in the timing unit  620 , and transmits the synchronization demand signal for recording-medium supply to the initialized timer. For example, the initialization counter sensing unit  610  senses a first timer  622  initialized among first through n-th timers (n is a positive integer greater than 1) provided in the timing unit  620  in response to the synchronization demand signal for recording-medium supply received from the recording-medium supply requirement sensing unit  600 , and transmits the synchronization demand signal for supplying of a recording medium to the initialized first timer  622 . The first timer  622  may be set to ‘1’ in response to the synchronization demand signal transmitted by the initialization timer sensing unit  610 . 
   In order to perform operation  196 , the first through n-th timers are provided in the timing unit  620 , and the timing unit  620  measures a time from the timers in response to the transmitted synchronization demand signal for recording-medium supply. 
   In order to perform  198 , the timing controlling unit  630  senses whether the measured time corresponds to a timer for supplying a recording medium to a transfer unit, outputs the third result of sensing, senses whether the measured time corresponds to a time to adjust movement of the recording medium, outputs the fourth result of sensing, and initializes a timer by which the time is measured in response to the signal transmitted from the recording-medium exhaust sensing unit  680 . For example, as described previously, when the first timer  622  starts measuring a time, the timing controlling unit  630  senses whether the time measured by the first timer  622  corresponds to the time needed to supply the recording medium to the transfer unit, and outputs the third result of sensing to the recording-medium supply signal generating unit  640 . Also, the timing controlling unit  630  senses whether the time measured by the first timer  622  corresponds to the time needed to adjust movement of the recording medium, and outputs the fourth result of sensing to the recording-medium movement adjustment signal generating unit  660 . Also, the timing controlling unit  630  initializes the first timer  622  in response to the signal transmitted from the recording-medium exhaust sensing unit  680 . 
   The recording-medium supply signal generating unit  640  generates a recording-medium supply signal in response to the third result sensed by the timing controlling unit  630 , and outputs the generated recording-medium supply signal. For example, the recording-medium supply signal generating unit  640  generates the recording-medium supply signal in response to the third result of sensing and outputs the generated recording-medium supply signal to the recording-medium supplying unit  650 . 
   The recording-medium supplying unit  650  feeds the recording medium from a recording-medium supplying apparatus, and supplies the recording medium to a transfer unit in response to the transmitted recording-medium supply signal. That is, the recording-medium supplying unit  650  feeds the recording medium from the recording-medium supplying apparatus through an output terminal OUT 6 , and supplies the recording medium to the transfer unit in response to the recording-medium supply signal transmitted from the recording-medium supply signal generating unit  630 . 
   The recording-medium adjustment signal generating unit  660  generates a recording-medium movement adjustment signal in response to the fourth result sensed via the timing controlling unit  630 , and outputs the generated recording-medium movement adjustment signal. For example, the recording-medium adjustment signal generating unit  660  generates the recording-medium movement adjustment signal in response to the fourth result of sensing, and outputs the generated recording-medium movement adjustment signal to the recording-medium movement adjusting unit  670 . 
   The recording-medium movement adjusting unit  670  adjusts movement of the recording medium to the transfer unit in response to the generated recording-medium movement adjustment signal. The recording-medium movement adjusting unit  670  makes the position of a toner image coincident with a front end of the recording medium before the toner image is transferred on the recording medium to compensate a difference caused by recording-medium supply performed by the recording-medium supplying unit  650  during a color image printing operation. For example, the recording-medium movement adjusting unit  670  varies the speed of the recording medium in the transfer unit through an output terminal OUT 7  or stops and starts supplying the recording medium in response to the recording-medium movement adjustment signal transmitted from the recording-medium adjustment signal generating unit  660  so the position of the toner image is coincident with the front end of the recording medium. 
   The recording-medium exhaust sensing unit  680  senses whether the recording medium is exhausted from the transfer unit, and outputs the result of the exhaust sensing to the timing controlling unit  630 . For example, the recording-medium exhaust sensing unit  680  receives a signal which indicates whether the recording medium finishes the printing operation through an input terminal IN 7  and is exhausted from the transfer unit, senses the signal, and outputs the result of the exhaust sensing to the timing controlling unit  630 . As a result, the timing controlling unit  630  initializes a timer by which time is measured, in response to the result of exhaust sensing transmitted from the recording-medium exhaust sensing unit  680 . 
   An embodiment of operations performed in an interrupt generating unit  410  shown in  FIG. 11 , a counting unit  520  shown in  FIG. 12 , and a timing unit  620  shown in  FIG. 13 , according to an aspect of the present invention, is illustrated in FIG.  14 . 
   Referring to  FIG. 14 , a first interrupt INT 1 , a second interrupt INT 2 , a third interrupt INT 3 , a fourth interrupt INT 4 , and a fifth interrupt INT 5  are generated by the interrupt generating unit  410  at a predetermined period. 
   The counting unit  520  includes a first counter, a second counter, and a third counter. Each counter performs a first color image input operation, a second color image input operation, a third color image input operation, and a fourth color image input operation to print a color image. 
   The timing unit  620  includes a first timer, a second timer, and a third timer. Each timer performs a recoding-medium supply operation, a recording-medium movement adjustment operation, and a recording-medium exhaustion operation. 
   If the first interrupt INT 1  is generated, a printing operation is performed on a first page of an image to be printed, and if the second interrupt INT 2  is generated, a printing operation is performed on a second page of the image to be printed. After that, whenever an interrupt is generated, the above-mentioned printing operations are performed. 
   If the first interrupt INT 1  is generated, the first counter and the first timer start operations, and if the second interrupt INT 2  is generated, the second counter and the second timer start operations, and if the third interrupt INT 3  is generated, the third counter and the third timer start operations. In this case, a section a is a time which corresponds to the number of line control signals preset to start the above-mentioned image input, and a section c corresponds to a time preset to supply the above-mentioned recording medium. Since the sections a and c are maintained at a regular time interval whenever an interrupt is generated, image input and recording-medium supply of an image forming apparatus can be easily performed. 
   The number of first through m-th counters provided in the counting unit  520  is more than a number obtained, when one-time interrupt is generated, by adding 1 (the above-mentioned one-time interrupt) to the number of interrupts generated from a time when one counter starts counting to a time when the counter is initialized. For example, as shown in  FIG. 12 , if the first interrupt is generated, the first counter starts counting, and after the second interrupt is generated, the first counter stops counting and is initialized. That is, since the first counter is initialized only if a time which corresponds to a section b has passed, 2, which is a number obtained by adding 1 (first interrupt INT 1 ) to the one-time interrupt INT 2  occurring in the section b, is the minimum number of counters to be provided in the counting unit  520 . The reason for this is to prevent lack of initialized counters required to print a next page when less than two counters are provided in the counting unit  520 . 
   The number of first through n-th timers provided in the timing unit  620  is more than a number obtained, when one-time interrupt is generated, by adding 1 (the above-mentioned one-time interrupt) to the number of interrupts generated from a time when one timer starts measuring of a time to a time when the timer is initialized. For example, as shown in  FIG. 12 , if the first interrupt is generated, the first counter starts measuring of a time, and after the third interrupt is generated, the first counter stops measuring of a time and is initialized. That is, since the first timer is initialized only if a time which corresponds to a section d has passed, 3, which is a number obtained by adding 1 (first interrupt INT 1 ) to the two-time interrupts INT 2  and INT 3  occurring in the section d, is the minimum number of counters to be provided in the timing unit  620 . The reason for this is to prevent lack of initialized timers required to print a next page when less than two timers are provided in the timing unit  620 . 
   Accordingly, the method and apparatus to control image input and recording-medium supply of an image forming apparatus allow demands on image input and recording-medium supply per page to be synchronized such that an image can be printed in a correct position on a recording medium even under simple control. Moreover, the method and apparatus improve reliability of image printing control, and the image forming apparatus can be easily designed. 
   Although a few embodiments of the present invention 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 spirit and scope of the invention as defined by the appended claims and their equivalents.