Patent Publication Number: US-2020285919-A1

Title: Image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-040218, filed Mar. 6, 2019, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to an image forming apparatus. 
     BACKGROUND 
     Image forming apparatuses, such as printers, copiers, and multi-functional peripherals (MFPs), using an electrophotographic process are known. Two different exposure systems called a laser optical system (also known as a LSU or laser scan unit) and a print head (also known as a solid head) are known as exposure means in the apparatuses. In a laser optical system, a photoconductive drum is exposed to a laser beam scanned by a polygon mirror. In a print head, the photoconductive drum is exposed to light from light emitting elements such as light emitting diodes (LEDs). 
     Since it is necessary to rotate the polygon mirror at high speed, the laser optical system consumes a lot of energy and also typically generates an operation sound audible during image formation processing. Furthermore, since a mechanism for scanning the laser beam and a lens group for focusing the scanning beam on the photoconductive drum are necessary, to the laser optical system tends to be a physically large unit. 
     Some print heads can be miniaturized because they have a structure in which light emitted from a plurality of light emitting elements is focused on a photoconductive drum using a small lens called a rod lens array. Since there are no moving parts, it can also achieve a quiet exposure process and less energy consumption. In addition to a print head using LEDs (or an arrangement of LED chips), a print head using organic light emitting diodes (OLEDs) has also been developed. 
     A print head using LEDs generally has LED chips arranged on a printed circuit board. OLEDs or organic electroluminescence (EL) elements are formed on a substrate using a photomask process, and these light emitting elements can be arranged with high precision. For example, the plurality of light emitting elements made relying on organic EL can be formed on a glass substrate. 
     A plurality of light emitting elements of the print head correspond to one line along a main scanning direction of the image forming apparatus, and each light emitting element emits light based on pixel information read from a page memory. That is, the light emission timing of each light emitting element of the print head is controlled based on the pixel information in image data. 
     The active light emitting element of the print head emits light according to the electric charge (potential) held in a capacitor, and an image is formed according to this light emission. When the light emission of the light emitting element is controlled based on original image data, stray or unintended light emission may be caused by the electric charge held in the capacitor. Unintended light emission may reduce image quality of printed images. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating an example of a positional relationship between a photoconductive drum and a print head in an image forming apparatus according to a first embodiment. 
         FIG. 2  is a diagram illustrating an example of a transparent substrate of the print head according to the first embodiment. 
         FIG. 3  is a diagram illustrating an example of light emitting element lines (two-line head) according to the first embodiment. 
         FIG. 4  is a diagram illustrating an example of a structure of the light emitting device according to the first embodiment. 
         FIG. 5  is a diagram illustrating an example of a circuit configuration including a DRV circuit for driving the light emitting element and a light emitting element that emits light by the DRV circuit according to the first embodiment. 
         FIG. 6  is a diagram illustrating an example of a head circuit block of the print head according to the first embodiment. 
         FIG. 7  is a diagram illustrating an example of the image forming apparatus including the print head according to the first embodiment. 
         FIG. 8  is a block diagram illustrating an example of a control system of the image forming apparatus according to the first embodiment. 
         FIG. 9  is a diagram illustrating an example of image data transfer (including transfer of additional null image data) in the image forming apparatus according to the first embodiment. 
         FIG. 10  is a diagram illustrating an example of image data transfer (not including transfer of additional null image data) in the image forming apparatus according to the first embodiment. 
         FIG. 11  is a diagram illustrating an example of an image formed based on the transfer of image data (including transfer of additional null image data) illustrated in  FIG. 9 . 
         FIG. 12  is a diagram illustrating an example of an image (tail image) formed based on the transfer of image data (not including the transfer of additional null image data) illustrated in  FIG. 10 . 
         FIG. 13  is a flowchart illustrating a first example of turn-off control (non-emission control) by the image forming apparatus according to the first embodiment. 
         FIG. 14  is a flowchart illustrating a second example of turn-off control (non-emission control) by the image forming apparatus according to the first embodiment. 
         FIG. 15A  is a diagram illustrating an example of a relationship between a sample/hold signal and a light emitting state of the light emitting element when the turn-off control according to the first embodiment is performed. 
         FIG. 15B  is a diagram illustrating an example of the relationship between the sample/hold signal and the light emitting state of the light emitting element when the turn-off control according to the first embodiment is performed. 
         FIG. 16A  is a diagram illustrating an example of a relationship between the sample/hold signal and the light emitting state of the light emitting element when the turn-off control is not performed. 
         FIG. 16B  is a diagram illustrating an example of a relationship between the sample/hold signal and the light emitting state of the light emitting element when the turn-off control is not performed. 
         FIG. 17  is a diagram illustrating an example of a circuit configuration including a DRV circuit for driving a light emitting element, a light emitting element that emits light by the DRV circuit, and a switch that switches a current supply to the light emitting element according to a second embodiment. 
         FIG. 18  is a diagram illustrating an example of a head circuit block of a print head according to the second embodiment. 
         FIG. 19  is a diagram illustrating an example of a relationship of a sample/hold signal, a capacitor potential, original image data D 1 , and additional null image data D 2 , a switch SW, and a light emitting state of the light emitting element when turn-off control according to the second embodiment is performed. 
         FIG. 20  is an example of a relationship between the sample/hold signal, the capacitor potential, the original image data D 1 , the switch SW, and the light emitting state of the light emitting element when the turn-off control according to the second embodiment is not performed. 
     
    
    
     DETAILED DESCRIPTION 
     One or more embodiments of the present disclosure are directed to providing an image forming apparatus that reduces unintended light emission of a light emitting element and provides improved reproducibility of an original image. 
     In general, according to an embodiment, an image forming apparatus includes a print head and a control circuit. The print head includes a plurality of light emitting elements arranged in a main scanning direction and a plurality of drive circuits corresponding to the plurality of light emitting elements, respectively. The control circuit is configured to add footer null image data after original image data corresponding to an image portion to be formed by one of the light emitting elements. The control circuit is configured to supply the original image data followed by the footer null image data to the print head, and cause the one of the light emitting elements to emit light in accordance with the original image data and then to be turned off in accordance with the footer null image data. 
     First and second example embodiments will be described below with reference to drawings. An example of the configuration of a print head according to a first embodiment will be described with reference to  FIGS. 1 to 6 . An example of the configuration of an image forming apparatus (including a print head) according to the first embodiment will be described with reference to  FIGS. 7 and 8 . With reference to  FIGS. 9, 11, 13, 14, 15A, and 15B , an example of light emission control and turn-off control of a print head by a control unit of the image forming apparatus according to the first embodiment will be described. With reference to  FIGS. 10, 12, 16A, and 16B , an example of the light emission control of a print head by a control unit of the image forming apparatus according to the first embodiment will be described. 
     An example of the configuration of a print head according to a second embodiment will be described with reference to  FIGS. 17 and 18 . With reference to  FIG. 19 , an example of light emission control and turn-off control of a print head by a control unit of an image forming apparatus according to the second embodiment will be described. With reference to  FIG. 20 , an example of light emission control of a print head by a control unit of the image forming apparatus according to the second embodiment will be described. 
     The light emission control described in each of the first and second embodiments indicates light emission control of a light emitting element based on original image data (control of light emission and turn-off at a predetermined timing). The turn-off control described in each of the first and second embodiments indicates turn-off control of the light emitting element (control of turn-off at a predetermined timing) based on added null image data. Here, the null image data may refer to image data corresponding to an image portion in which each pixel has a maximum or minimum value of a gradation level so that no toner is formed for the pixel. Therefore, a blank image with no toner or substantially a negligible amount of toner is formed on a region of a sheet corresponding to such an image portion. In contrast, a non-blank image may refer to an image with toner of a conceivable amount that can be recognized by human eyes. 
     First Embodiment: Configuration of Print Head 
       FIG. 1  is a diagram illustrating an example of a positional relationship between a photoconductive drum and a print head in an image forming apparatus according to a first embodiment. For example, an image forming apparatus such as a printer, a copier, or a multifunction machine includes a photoconductive drum  111  illustrated in  FIG. 1 , and a print head  1  is disposed so as to face the photoconductive drum  111 . 
     The photoconductive drum  111  rotates in the direction of the arrow illustrated in  FIG. 1 . This rotation direction is referred to as a sub-scanning direction SD. The photoconductive drum  111  is uniformly electrostatically charged by a charger and is then exposed to light from the print head  1 , whereby the electrical potential of the exposed portion is lowered. That is, an electrostatic latent image can be formed on the photoconductive drum  111  by controlling the light emission of the print head  1 . Controlling the light emission of the print head  1  refers here to controlling the timing of light emission and turn-off (non-light emission) of the print head  1 . 
     The print head  1  includes a light emitting unit  10  and a rod lens array  12 . The light emitting unit  10  further includes a transparent substrate  11 . For example, the transparent substrate  11  is a glass substrate that transmits light. On the transparent substrate  11 , a plurality of light emitting element lines  13  made of a plurality of LED or OLED light emitting elements are formed.  FIG. 1  illustrates an example in which two lines, a first light emitting element line  13 L 1  and a second light emitting element line  13 L 2 , are formed in parallel to each other. In the first embodiment, a case where the print head  1  includes a plurality of light emitting element lines  13  will be described, but a case where the print head  1  includes only a single light emitting element line  13  is also contemplated. 
       FIG. 2  is a diagram illustrating an example of the transparent substrate constituting the print head according to the first embodiment. As illustrated in  FIG. 2 , two light emitting element lines  13  (the first light emitting element line  13 L 1  and the second light emitting element line  13 L 2 ) are formed in the central portion on the transparent substrate  11  along the longitudinal direction of the transparent substrate  11 . In the vicinity of the light emitting element line  13 , drive circuit lines  14  (a first drive circuit line  14 L 1  and a second drive circuit line  14 L 2 ) for driving (causing light to be emitted from) each light emitting element is formed. Hereinafter, a “drive circuit” is referred to as a “DRV”. 
     In  FIG. 2 , a DRV circuit line  14  for driving the light emitting elements is arranged on both sides of the two light emitting element lines  13 , but the DRV circuit lines  14  may instead be arranged on one side. 
     An integrated circuit (IC)  15  is disposed at one end of the transparent substrate  11 . The transparent substrate includes a connector  16 . The connector  16  is electrically connected to the print head  1  and a control system of a printer, a copier, or a multi-function machine. This connection enables power supply, head control, image data transfer, and the like. The transparent substrate  11  is attached with a substrate for sealing the light emitting element line  13 , the DRV circuit line  14  and the like so as not to be exposed to the outside air. If it is difficult to attach a connector to the transparent substrate, flexible printed circuits (FPC) may be connected to the transparent substrate and electrically connected to the control system. 
       FIG. 3  is a diagram illustrating an example of the light emitting element lines (two-line head) according to the first embodiment. As illustrated in  FIG. 3 , each light emitting element line  13  includes a plurality of light emitting elements  131  arranged along a main scanning direction MD perpendicular to the rotating direction (sub-scanning direction SD) of the photoconductive drum  111 . That is, the plurality of light emitting elements  131  forming the first light emitting element line  13 L 1  and the plurality of light emitting elements  131  forming the second light emitting element line  13 L 2  are parallel to the main scanning direction MD. 
     Each light emitting element  131  is, for example, a 20 μm square. An arrangement interval D 11  between adjacent light emitting elements  131 , for example, a pitch of about 42.3 μm for a resolution of 600 dpi. 
     The first light emitting element array  13 L 1  and the second light emitting element array  13 L 2  are arranged at an interval of distance D 12  along the sub-scanning direction SD. Furthermore, each light emitting element  131  in the first light emitting element line  13 L 1  and each light emitting element  131  in the second light emitting element line  13 L 2  are arranged at a predetermined offset pitch D 13  and thus shifted relatively along the main scanning direction MD. For example, the predetermined offset pitch D 13  is ½ of the arrangement interval D 11 . Thereby, the two light emitting element lines  13  are arranged in a staggered manner. 
     When the light emitting elements in the first and second light emitting element lines  13  emit light at the same timing, a staggered exposure pattern is formed on the photoconductive drum  111 . Assuming that the upstream side is the first line and the downstream side is the second line with respect to the moving direction of the photoconductive drum  111 , the control unit (e.g., a control unit  174  in  FIG. 8 ) causes the first light emitting element line  13 L 1  and the second light emitting element line  13 L 2  to emit light at different timings depending on the moving speed of the photoconductive drum  111  and the distance D 12 . That is, the control unit  174  delays the light emission timing of the second light emitting element line  13 L 2  with respect to the first light emitting element line  13 L 1  by a certain time according to the rotating speed of the photoconductive drum  111  and the separating distance D 12 . In other words, the control unit  174  outputs first light emitting element image data to the first light emitting element line  13 L 1  and second light emitting element image data to the second light emitting element line  13 L 2  at different timings depending on the rotating (moving) speed of the photoconductive drum  111  and the distance D 12 . Here, the first light emitting element image data and the second light emitting element image data correspond to image data for each line along the main scanning direction. As a result, a latent image can be formed on the photoconductive drum with a resolution of 1200 dpi. 
     As described above, the control unit  174  controls the light emission timings (image data transfer timings) of the plurality of light emitting element lines  13 , whereby the image density can be increased. In the case of two light emitting element lines  13 , the density of the image can be increased to twice the density of the light emitting elements  131  per line, and in the case of n light emitting element lines  13  (n≥3, n being an integer), the density of the image can be increased by n times the density of the light emitting elements  131  per line. 
       FIG. 4  is a diagram illustrating an example of a structure of the light emitting device according to the first embodiment. In  FIG. 4 , the substrate used for sealing is omitted. For example, the light emitting element  131  is an organic electroluminescence (EL). As illustrated in  FIG. 4 , the light emitting element  131  includes a hole transport layer  131   a,  a light emitting layer  131   b,  and an electron transport layer  131   c  and is sandwiched between and in contact with an electrode (+)  132   a  and an electrode (−)  132   c  insulated by an insulating layer  132   b.  In the first embodiment, for example, the light emitting layer  131   b  is an organic EL. The electrode (−)  132   c  has a structure that reflects the light emitted from the light emitting layer  131   b.  With this structure, light emitted from the light emitting layer  131   b  is output to the transparent substrate  11  side. 
       FIG. 5  is a diagram illustrating an example of a circuit configuration including a DRV circuit for driving the light emitting element and a light emitting element that emits light by the DRV circuit according to the first embodiment. The DRV circuit includes transistors  141  and  143 , each of which may be a low-temperature polysilicon thin film transistor, and a capacitor  142 . The capacitor  142  is connected between a channel electrode and a gate electrode of the transistor  143 . A sample/hold signal S 1  becomes “L” level when the light emission intensity of the light emitting element  131  connected to a DRV circuit  140  is changed. When the sample/hold signal S 1  becomes “L” level, the voltage of the capacitor  142  changes according to the voltage of a light emission level signal S 2 . That is, the capacitor  142  holds a charge that changes according to image data including a plurality of image lines. 
     When the sample/hold signal S 1  becomes “H”, the voltage of the capacitor  142  is held. Even if the voltage of the light emission level signal S 2  changes, the voltage level of the capacitor  142  does not change. A current corresponding to the voltage held in the capacitor  142  flows through the light emitting element  131  connected to a signal line I of the DRV circuit  140 . That is, the light emitting element  131  emits light according to the potential of the capacitor. A predetermined light emitting element  131  is selected from the plurality of light emitting elements  131  included in the light emitting element line  13  by the sample/hold signal S 1 , and light emission intensity is determined by the light emission level signal S 2 , and the light emission intensity can be maintained. 
       FIG. 6  is a diagram illustrating an example of a head circuit block of the print head according to the first embodiment. As illustrated in  FIG. 6 , the light emitting unit  10  includes a head circuit block including the IC  15 , and the IC  15  includes a light emitting element address counter  151 , a decoder  152 , a D/A (digital to analog) conversion circuit  153 , a light amount correction memory  154 , and the like. The light emitting element address counter  151 , the decoder  152 , the D/A conversion circuit  153 , and the light amount correction memory  154  supply signals (e.g., sample/hold signal S 1  and emission level signal S 2 ) for controlling the light emission intensity and ON and OFF of each light emitting element  131  to the DRV circuit  140  and the like. 
     As illustrated in  FIG. 6 , the light emitting element  131  is connected to each DRV circuit  140 . Each individual DRV circuit  140  supplies an individual current to each individual light emitting element  131 . The D/A conversion circuit  153  is connected to the first DRV circuit line  14 L 1  connected to the first light emitting element line  13 L 1 . Similarly, the D/A conversion circuit  153  is connected to the DRV circuit line  14 L 2  connected to the second light emitting element line  13 L 2 . 
     The light amount correction memory  154  stores correction data D 3  corresponding to the current passed through each light emitting element  131 . A horizontal synchronization signal S 4  and an image data write clock C are input to the light emitting element address counter  151  via the connector  16 . The horizontal synchronization signal S 4  resets the count value of the light emitting element address counter  151 . The light emitting element address counter  151  outputs a light emitting element address signal S 5  synchronized with the image data write clock C. 
     The light amount correction memory  154  receives the original image data D 1  and the light emitting element address signal S 5  output from the light emitting element address counter  151 . The light emitting element address signal S 5  output from the light emitting element address counter  151  is input to the decoder  152 . The decoder  152  outputs the sample/hold signal S 1  corresponding to the light emitting element  131  specified by the light emitting element address signal S 5 . The light amount correction memory  154  outputs correction data D 3  corresponding to the light emitting element  131  specified by the light emitting element address signal S 5  based on the original image data D 1 . The correction data D 3  output from the light amount correction memory  154  is input to the D/A conversion circuit  153 . The D/A conversion circuit  153  outputs the voltage of the light emission level signal S 2  based on the correction data D 3 . The voltage of the light emission level signal S 2  is sampled and held in the capacitor  142  of the DRV circuit  140 . Sample hold on the capacitor  142  is performed periodically. 
     First Embodiment: Configuration of Image Forming Apparatus 
       FIG. 7  is a diagram illustrating an example of the image forming apparatus including the print head according to the first embodiment.  FIG. 7  illustrates an example of a quadruple tandem type color image forming apparatus, but the print head  1  of the first embodiment can also be applied to a monochrome image forming apparatus. 
     As illustrated in  FIG. 7 , for example, the image forming apparatus  100  includes an image forming unit  102 -Y that forms a yellow (Y) image, an image forming unit  102 -M that forms a magenta (M) image, an image forming unit  102 -C that forms a cyan (C) image, and an image forming unit  102 -K that forms a black (K) image. The image forming units  102 -Y,  102 -M,  102 -C, and  102 -K form yellow, cyan, magenta, and black images, respectively and transfer the images to a transfer belt  103 . As a result, a full color image is formed on the transfer belt  103 . 
     The image forming unit  102 -Y includes a charging charger  112 -Y, a print head  1 -Y, a developing device  113 -Y, a transfer roller  114 -Y, and a cleaner  116 -Y around a photoconductive drum  111 -Y. The image forming units  102 -M,  102 -C, and  102 -K have the same configuration. 
     In  FIG. 7 , the configuration of the image forming unit  102 -Y that forms a yellow (Y) image is given a suffix symbol “-Y”. The configuration of the image forming unit  102 -M that forms a magenta (M) image is given a suffix symbol “-M”. The configuration of the image forming unit  102 -C that forms a cyan (C) image is given a suffix symbol “-C”. The configuration of the image forming unit  102 -K that forms a black (K) image is given a suffix symbol “-K”. 
     The charging chargers  112 -Y,  112 -M,  112 -C, and  112 -K uniformly charge the photoconductive drums  111 -Y,  111 -M,  111 -C, and  111 -K, respectively. The print heads  1 -Y,  1 -M,  1 -C, and  1 -K each expose the respective photoconductive drums  111 -Y,  111 -M,  111 -C,  111 -K using light emission from light emitting elements  131  of the first light emitting element line  13 L 1  and the second light emitting element line  13 L 2  in each respective print head and form electrostatic latent images on the photoconductive drums  111 -Y,  111 -M,  111 -C, and  111 -K. The developing device  113 -Y supplies yellow toner, the developing device  113 -M supplies magenta toner, the developing device  113 -C supplies cyan toner, the developing device  113 -K supplies black toner to the electrostatic latent image portions of the respective photoconductive drums  111 -Y,  111 -M,  111 -C, and  111 -K. 
     The transfer rollers  114 -Y,  114 -M,  114 -C, and  114 -K transfer the toner images formed (developed) on the photoconductive drums  111 -Y,  111 -M,  111 -C, and  111 -K to the transfer belt  103 . Cleaners  116 -Y,  116 -M,  116 -C, and  116 -K remove (clean) the toner remaining on the photoconductive drums  111 -Y,  111 -M,  111 -C, and  111 -K and enter a standby state for the next image formation process. 
     A first size (e.g., a small size) paper P 1  is stored in a paper cassette  117 - 1  which is paper supply means. A second size (e.g., a large size) paper P 2  is stored in a paper cassette  117 - 2  which is a paper supply means. In this context, paper is an example of an image forming medium. 
     The toner image is transferred from the transfer belt  103  to the paper P 1  or P 2  from the paper cassette  117 - 1  or  117 - 2  taken out by a transfer roller pair  118  as transfer means. The paper P 1  or P 2  to which the toner image has been transferred is then heated and pressed by a fixing roller  120  of a fixing unit  119 . The toner image is firmly fixed on the paper P 1  or P 2  by heating and pressing by the fixing roller  120 . By repeating the above process operation, the image forming operation is continuously performed. 
       FIG. 8  is a block diagram illustrating an example of a control system of the image forming apparatus according to the first embodiment. As illustrated in  FIG. 8 , an image forming apparatus  100  includes an image reading unit  171 , an image processing unit  172 , an image forming unit  173 , a control unit  174 , a read only memory (ROM)  175 , a random access memory (RAM)  176 , a nonvolatile memory  177 , a communication I/F  178 , a control panel  179 , page memories  180 -Y,  180 -M,  180 -C, and  180 -K, a color misregistration sensor  181 , a mechanical control driver  182 , an image data transfer control unit  183 , and an image data bus  184 . The image data transfer control unit  183  can provide the null image data addition. The image forming unit  173  includes image forming units  102 -Y,  102 -M,  102 -C, and  102 -K. 
     The ROM  175 , the RAM  176 , the nonvolatile memory  177 , the communication I/F  178 , the control panel  179 , the color misregistration sensor  181 , the mechanical control driver  182 , and the image data transfer control unit  183  are connected to the control unit  174 . 
     The image reading unit  171 , the image processing unit  172 , the control unit  174 , and the page memories  180 -Y,  180 -M,  180 -C, and  180 -K are connected to the image data bus  184 . Each of the page memories  180 -Y,  180 -M,  180 -C, and  180 -K outputs Y, M, C, or K original image data D 1 . The image data transfer control unit  183  is connected to the page memories  180 -Y,  180 -M,  180 -C, and  180 -K, and the Y original image data D 1  from the page memory  180 -Y, the M original image data D 1  from the page memory  180 -M, the C original image data D 1  from the page memory  180 -C, and the K original image data D 1  from the page memory  180 -K are input. The print heads  1 -Y,  1 -M,  1 -C, and  1 -K are connected to the image data transfer control unit  183  corresponding to each original image data D 1 . The image data transfer control unit  183  inputs each original image data D 1  to the print heads  1 -Y,  1 -M,  1 -C, or  1 -K corresponding to each original image data D 1 . 
     The control unit  174  is configured with one or more processors and controls operations such as image reading, image processing, and image formation in accordance with various programs stored in at least one of the ROM  175  and the nonvolatile memory  177 . The control unit  174  performs light emission control in accordance with various programs stored in at least one of the ROM  175  and the nonvolatile memory  177 . The light emission control is timing control of light emission and turn-off (non-light emission). 
     The control unit  174  outputs a print head enable signal ES to each print head  1  of the image forming unit  173 , and also outputs the transfer control signals of the original image data D 1  and additional null image data D 2  to the image data transfer control unit  183 , and controls the light emission of the print head  1  based on the original image data D 1  and the additional null image data D 2 . Alternatively, the control unit  174  may output the print head enable signal ES to each print head  1  of the image forming unit  173 , and also output the transfer control signals of the original image data D 1  to the image data transfer control unit  183 , and control the light emission of the print head  1  based on the original image data D 1 . 
     The control unit  174  inputs the image data of test patterns on the page memories  180 -Y,  180 -M,  180 -C, and  180 -K and forms the test pattern. The color misregistration sensor  181  detects the test patterns formed on the transfer belt  103  and outputs detected signals to the control unit  174 . The control unit  174  can recognize the positional relationship between the test patterns of the respective colors from the input of the color misregistration sensor  181 . Further, the control unit  174  selects the paper cassette  117 - 1  or  117 - 2  for feeding a paper on which an image is to be formed, through the mechanical control driver  182 . 
     The image data transfer control unit  183  is configured with a line memory and transfers the additional null image data D 2  to the light emitting elements of the print heads  1 -Y,  1 -M,  1 -C, and  1 -K in accordance with instructions from the control unit  174  based on the original image data D 1  sent from the page memories  180 -Y,  180 -M,  180 -C, and  180 -K and a null image data addition control signal S 6  from the control unit  174 . For example, the image data transfer control unit  183  adds the additional null image data D 2  to the original image data D 1  based on the null image data addition control signal S 6  and outputs the original image data D 1  and the additional null image data D 2  to the print heads  1 -Y,  1 -M,  1 -C, or  1 -K. The additional null image data D 2  is data for turning off the light emitting element  131 . Alternatively, the image data transfer control unit  183  may transfer the original image data D 1  to the light emitting elements of the print heads  1 -Y,  1 -M,  1 -C, and  1 -K (not transferring the additional null image data D 2 ). 
     The ROM  175  stores various programs necessary for the control of the control unit  174 . The various programs include a print head emission control program. The light emission control program is a program for controlling the timing of light emission and turn-off (non-light emission). 
     The RAM  176  temporarily stores data necessary for control by the control unit  174 . The nonvolatile memory  177  stores updated programs, various parameters, and the like. The nonvolatile memory  177  may store some or all of various programs. 
     The mechanical control driver  182  controls the operation of a motor or the like necessary for printing in accordance with instructions from the control unit  174 . The communication I/F  178  outputs various information to the outside and inputs various information from the outside. For example, the communication I/F  178  functions as an acquisition unit that acquires image data including a plurality of image lines, and the image forming apparatus  100  prints image data acquired via the communication I/F  178  by a print function. The control panel  179  receives operation inputs from a user or a service person (maintenance technician). 
     The image reading unit  171  optically reads an image of a document, functions as an acquisition unit that acquires image data including a plurality of image lines, and outputs the image data to the image processing unit  172 . The image processing unit  172  performs various types of image processing (including correction) on the image data input via the communication I/F  178  or the image data from the image reading unit  171 . The page memories  180 -Y,  180 -M,  180 -C, and  180 -K store image data processed by the image processing unit  172 . The control unit  174  edits the image data on the page memories  180 -Y,  180 -M,  180 -C, and  180 -K so as to match the printing position and the print head. The image forming unit  173  forms an image based on the image data D 1  (in other words, original image data D 1  transferred by the image data transfer control unit  183 ) stored in the page memories  180 -Y,  180 -M,  180 -C, and  180 -K. That is, the image forming unit  173  forms an image corresponding to the light emission (light emission and turn-off state) of the light emitting element  131  based on the original image data D 1  or the original image data D 1  and the additional null image data D 2 . The image forming unit  173  includes the print heads  1 -Y,  1 -M,  1 -C, and  1 -K. 
     First Embodiment: Light Emission Control of Print Head 
       FIG. 9  is a diagram illustrating an example of image data transfer (including transfer of additional null image data D 2 ) in the image forming apparatus according to the first embodiment. The control unit  174  outputs the print head enable signal ES for switching the operation of the print head  1  between enabled and disabled based on the timing of image formation to the print head  1  or outputs the null image data addition control signal S 6  and an image data transfer control signal to the image data transfer control unit  183 . The null image data addition control signal S 6  is a control signal for adding null image data before and after the original image data. As a result, as illustrated in  FIG. 9 , during the valid period of the print head enable signal ES, the image data transfer control unit  183  outputs the additional null image data D 2  at the beginning (hereinafter may be referred to as “header null image data”), the original image data D 1  including the last line from the one line following the additional null image data D 2  at the beginning, and the additional null image data D 2  after the last line (hereinafter may be referred to as “footer null image data”). The original image data may include image data portion corresponding to a blank image. 
     The null image data addition control signal S 6  may be a control signal for adding null image data after the original image data. In this case, during the valid period of the print head enable signal ES, the image data transfer control unit  183  outputs the original image data D 1  including one line to the last line and the additional null image data D 2  after the last line. 
     In an embodiment, a time period to transmit the header null image data D 2  and/or the footer null image data D 2  may be equal to a time period to transmit one line of the original image data D 1 . Further, in an embodiment, a data transmission rate to transmit the header null image data D 2  and/or the footer null image data D 2  may be equal to a data transmission rate to transmit the one line of the original image data D 1 . In an embodiment, therefore, a length (data size) of the header null image data and/or the footer null image data may be equal to a length (data size) of one line of the original image data. 
     The control unit  174  may output the null image data addition control signal S 6  to the image data transfer control unit  183  when the last line of the original image data is other than null (e.g., corresponds to a blank image data), and the control unit  174  may not output the null image data addition control signal S 6  to the image data transfer control unit  183  if the last line is null. 
     The light emitting element  131  is turned off according to the additional null image data D 2  at the beginning, is turned on or off according to the original image data including the last line from the one line following the additional null image data D 2  at the beginning, and is turned off according to the additional null image data D 2  after the last line. 
       FIG. 10  is a diagram illustrating an example of image data transfer not including transfer of additional null image data D 2  in the image forming apparatus according to the first embodiment. The control unit  174  outputs the print head enable signal ES for switching the operation of the print head  1  between enabled and disabled based on the timing of image formation to the print head  1  or outputs the image data transfer control signal to the image data transfer control unit  183 . As a result, as illustrated in  FIG. 10 , during the valid period of the print head enable signal ES, the image data transfer control unit  183  outputs the original image data D 1  including one line to the last line. Since the null image data is not added before and after the original image data output from the image data transfer control unit  183 , the light emitting state of the light emitting element  131  is not confirmed before and after the original image data. When the light emitting element  131  emits light according to the original image data of the last line, the light emitting element  131  is gradually turned off due to the influence of the electric charge held in the capacitor  142  thereafter. 
       FIG. 11  is a diagram illustrating an example of an image formed based on the transfer of image data (including transfer of additional null image data D 2 ) illustrated in  FIG. 9 . As illustrated in  FIG. 11 , when the print head enable signal ES changes in the order of disable, enable, disable corresponding to the paper transport direction (sub-scanning direction SD), and null image data is added after the original image data (after the last line), after the original image data, the light emitting element  131  is confirmed to be turned off, and the original image corresponding to the acquired image data can be reproduced accurately. When null image data is added before and after the original image data (before one line and after the last line), the light emitting element  131  is confirmed to be turned off before and after the original image data, and the original image corresponding to the acquired image data can be reproduced more accurately. 
       FIG. 12  is a diagram illustrating an example of an image (referred to as a tail image) formed based on the transfer of image data without additional null image data D 2  as illustrated in  FIG. 10 . As illustrated in  FIG. 12 , since the print head enable signal ES changes in the order of disable, enable, disable corresponding to the paper transport direction (sub-scanning direction SD), and null image data is not added before and after the original image data (before one line and after the last line), before and after the original image data, the light emission state of the light emitting element  131  becomes unconfirmed, and the original image corresponding to the acquired image data may not be accurately reproduced. For example, a tail image may be formed in a case where the light emission of the light emitting element  131  is gradually turned off after the last line of original image data. 
       FIG. 13  is a flowchart illustrating a first example of turn-off control (non-emission control) by the image forming apparatus according to the first embodiment. The control unit  174  configured by one or more processors or the like outputs the original image data D 1  including a plurality of image lines to the IC  15  (connected to a plurality of DRV circuits  140 ) and controls the light emission of the plurality of light emitting elements  131  according to the original image data D 1  including the plurality of image lines. This light emission control is to control the light emission or turn-off of the plurality of light emitting elements  131  according to the original image data D 1 . In addition, the control unit  174  performs a turn-off control C 1  for turning off the plurality of light emitting elements  131  before controlling the light emission of the plurality of light emitting elements  131  according to the original image data D 1  including the plurality of image lines. Further, the control unit  174  controls the light emission of the plurality of light emitting elements  131  according to the last line included in the original image data D 1 , and then executes a turn-off control C 2  for turning off the plurality of light emitting elements  131 . In general, the turn-off control C 1  is not essential in this context. 
     For example, when the control panel  179  receives a print start instruction from the user, the control unit  174  detects this print start (ACT  101 , YES) and executes the turn-off controls C 1  (ACT  102 , ACT  103 ) and C 2  (ACT  106 , ACT  107 ). 
     For example, the control unit  174  outputs the null image data addition control signal S 6  to control the transfer of the null image data (ACT  102 ), enables the light emission control by the print head enable signal ES (ACT  103 ), and outputs an image data transfer control signal to control the transfer of the original image data D 1  (ACT  104 ). That is, the control unit  174  executes the turn-off control C 1  for turning off the plurality of light emitting elements  131  before outputting the original image data D 1  to the plurality of DRV circuits  140  to control the light emission of the plurality of light emitting elements  131 . Thereafter, the control unit  174  outputs the original image data D 1  to the plurality of DRV circuits  140  and controls the light emission of the plurality of light emitting elements  131  according to the original image data D 1 . 
     After controlling the light emission of the plurality of light emitting elements  131  according to the last line included in the original image data D 1 , the control unit  174  controls the transfer of the null image data by outputting the null image data addition control signal S 6  (ACT  106 ) and disables the light emission control by the print head enable signal ES (ACT  107 ). In other words, the control unit  174  outputs the original image data D 1  to the plurality of DRV circuits  140  to control the light emission of the plurality of light emitting elements  131 , and then executes the turn-off control C 2  for turning off the plurality of light emitting elements  131 . 
     In the above description, the case where the image data transfer control unit  183  adds null image data based on the null image data addition control signal S 6  has been described, but null image data may be added in the page memories  180 -Y,  180 -M,  180 -C, and  180 -K. 
       FIG. 14  is a flowchart illustrating a second example of turn-off control (non-emission control) by the image forming apparatus according to the first embodiment. For example, when the control panel  179  receives a print start instruction from the user, the control unit  174  detects this print start (ACT  201 , YES) and executes the turn-off controls C 1  (ACT  202 , ACT  203 ) and C 2  (ACT  206 , ACT  207 ). 
     For example, the control unit  174  outputs the null image data addition control signal S 6  to control the transfer of the null image data (ACT  202 ), enables the light emission control by the print head enable signal ES (ACT  203 ), and outputs an image data transfer control signal to control the transfer of the original image data D 1  (ACT  204 ). That is, the control unit  174  executes the turn-off control C 1  before outputting the original image data D 1  to the plurality of DRV circuits  140  to control the light emission of the plurality of light emitting elements  131 . Thereafter, the control unit  174  outputs the original image data D 1  to the plurality of DRV circuits  140  and controls the light emission of the plurality of light emitting elements  131  according to the original image data D 1 . 
     After controlling the light emission of the plurality of light emitting elements  131  according to the last line included in the original image data D 1 , when the last line is other than null (ACT  205 , NO), the control unit  174  outputs the null image data addition control signal S 6  to control the transfer of the null image data (ACT  206 ) and disables the light emission control by the print head enable signal ES (ACT  207 ). When the last line is null (ACT  205 , YES), the control unit  174  disables the light emission control by the print head enable signal ES (ACT  207 ). In other words, the control unit  174  outputs the original image data D 1  to the plurality of DRV circuits  140  to control the light emission of the plurality of light emitting elements  131 , and then executes the turn-off control C 2  when the last line is other than null, and does not execute the turn-off control C 2  when the last line is null. 
     In the above description, the case where the image data transfer control unit  183  adds null image data based on the null image data addition control signal S 6  has been described, but null image data may be added in the page memories  180 -Y,  180 -M,  180 -C, and  180 -K. 
       FIGS. 15A and 15B  are diagrams illustrating an example of the relationship between the sample/hold signal and the light emitting state of the light emitting element when the turn-off control according to the first embodiment is performed. As illustrated in  FIG. 15A , in response to the print head enable signal ES being disabled, the light emitting element  131  is turned off (ACT  300 ), and then the print head enable signal ES is enabled, but the light emitting element  131  continues to be turned off by adding the null image data before the region corresponding to the original image data D 1  (by the turn-off control C 1 ) (ACT  301 ). Subsequently, in the region corresponding to the original image data D 1 , the light emitting element  131  repeats light emission by the light emission control according to the original image data D 1  (ACT  302 ) (ACT  303 ) (ACT  304 ). Subsequently, the light emitting element  131  is turned off by adding the null image data after the region corresponding to the original image data D 1  (by the turn-off control C 2 ) (ACT  305 ). Thereafter, the print head enable signal ES is disabled, and the light emitting element  131  continues to be turned off (ACT  306 ). 
     As illustrated in  FIG. 15B , in response to the print head enable signal ES being disabled, the light emitting element  131  is turned off (ACT  400 ), and then the print head enable signal ES is enabled, but the light emitting element  131  continues to be turned off by adding the null image data before the region corresponding to the original image data D 1  (by the turn-off control C 1 ) (ACT  401 ). Subsequently, in the region corresponding to the original image data D 1 , the light emitting element  131  is turned on (ACT  402 ), turned off (ACT  403 ), and turned on (ACT  404 ) by the light emission control according to the original image data D 1 . Subsequently, the light emitting element  131  is turned off by adding the null image data after the region corresponding to the original image data D 1  (by the turn-off control C 2 ) (ACT  405 ). Thereafter, the print head enable signal ES is disabled, and the light emitting element  131  continues to be turned off (ACT  406 ). 
       FIGS. 16A and 16B  are diagrams illustrating an example of the relationship between the sample/hold signal and the light emitting state of the light emitting element when the turn-off control is not performed. As illustrated in  FIG. 16A , since the light emitting element  131  is turned off in response to the print head enable signal ES being disabled (ACT  500 ), and then the print head enable signal ES is enabled, and the null image data is not added before the region corresponding to the original image data D 1 , the light emitting state of the light emitting element  131  is turned on or off depending on the previous light emitting state (ACT  501 ). In other words, the light emission of the light emitting element  131  is unconfirmed until the original image data D 1  is input. Subsequently, in the region corresponding to the original image data D 1 , the light emitting element  131  repeats light emission by the light emission control according to the original image data D 1  (ACT  502 ) (ACT  503 ) (ACT  504 ). Since null image data is not added after the region corresponding to the original image data D 1 , the electric charge held in the capacitor  142  gradually decreases, and the light amount of the light emitting element  131  correspondingly decreases (ACT  505 ). Thereafter, the print head enable signal ES is disabled, and the light emitting element  131  is turned off (ACT  506 ). 
     As illustrated in  FIG. 16B , since the light emitting element  131  is turned off in response to the print head enable signal ES being disabled (ACT  600 ), and then the print head enable signal ES is enabled, and the null image data is not added before the region corresponding to the original image data D 1 , the light emitting state of the light emitting element  131  is turned on or off depending on the previous light emitting state (ACT  601 ). In other words, the light emission of the light emitting element  131  is unconfirmed until the original image data D 1  is input. Subsequently, in the region corresponding to the original image data D 1 , the light emitting element  131  is turned on (ACT  602 ), turned off (ACT  603 ), and turned on (ACT  604 ) by the light emission control according to the original image data D 1 . Since null image data is not added after the region corresponding to the original image data D 1 , the electric charge held in the capacitor  142  gradually decreases, and the light amount of the light emitting element  131  correspondingly decreases (ACT  605 ). Thereafter, the print head enable signal ES is disabled, and the light emitting element  131  is turned off (ACT  606 ). 
     Second Embodiment: Configuration of Print Head 
     In a second embodiment, description of parts common to the first embodiment will be omitted as appropriate, and description will be focused on parts different from the first embodiment. In the first embodiment, the case where null image data is added and the turn-off control is executed has been described, but in the second embodiment, the turn-off control is executed by turning off the current supply to the light emitting element  131  instead of adding the null image data. Further, in the second embodiment, also in the light emission control of the light emitting element  131  based on the original image data D 1 , the light emission control corresponding to the blank image included in the original image data D 1  is turned off by turning off the current supply to the light emitting element  131 . 
       FIG. 17  is a diagram illustrating an example of a circuit configuration including a DRV circuit for driving a light emitting element, a light emitting element that emits light according to the DRV circuit, and a switch that switches a current supply to the light emitting element according to a second embodiment. In the circuit illustrated in  FIG. 17  and the circuit illustrated in  FIG. 5 , the same elements are denoted by the same reference numerals. 
     The circuit configuration illustrated in  FIG. 17  includes a switch SW. The switch SW switches between supply and non-supply of current supply to the light emitting element  131  according to switching signals (ON/OFF signals). That is, the switch SW switches between whether or not to supply a current to the light emitting element  131  (current supply is turned on or off). When the switch SW is closed by a light emission ON signal S 31 , a current flows through the light emitting element  131  and the light emitting element  131  emits light. When the switch SW is opened by a light emission OFF signal S 32 , no current flows through the light emitting element  131  and the light emitting element  131  is turned off. 
       FIG. 18  is a diagram illustrating an example of a head circuit block of the print head according to the second embodiment. As illustrated in  FIG. 18 , the light emitting unit  10  includes a head circuit block including the IC  15 , and the IC  15  includes a light emitting element address counter  151 , a decoder  152 , a D/A conversion circuit  153 , a light amount correction memory  154 , a light emission ON/OFF instruction circuit  155 , and the like. The light emitting element address counter  151 , the decoder  152 , the D/A conversion circuit  153 , the light amount correction memory  154 , and the light emission ON/OFF instruction circuit  155  supply signals (sample/hold signal S 1 , emission level signal S 2 , light emission ON signal S 31 , and light emission OFF signal S 32 ) for controlling the light emission intensity and ON and OFF for each light emitting element  131  to the DRV circuit  140  and the like. 
     As illustrated in  FIG. 18 , the light emitting element  131  is connected to each DRV circuit  140 , and a switch SW is connected to each light emitting element  131 . Each individual DRV circuit  140  supplies an individual current to each individual light emitting element  131  when the individual switch SW is closed, the individual DRV circuit  140  does not supply a current to its respective individual light emitting element  131  in a when the individual switch SW is opened. 
     The light emission ON/OFF instruction circuit  155  receives a horizontal synchronization signal S 4 , a light emitting element address signal S 5 , original image data D 1 , and additional null image data D 2 . The light emission ON/OFF instruction circuit  155  determines ON or OFF of each light emitting element  131  according to the input light emitting element address signal S 5 , original image data D 1 , and additional null image data D 2 . The light emission ON/OFF instruction circuit  155  determines the light emission (ON) of the light emitting element  131  based on image data (for example, black image data) other than the null image data included in the original image data D 1 . The light emission ON/OFF instruction circuit  155  determines whether to turn off (OFF) the light emitting element  131  based on the null image data included in the original image data D 1  or the additional null image data D 2 . 
     The light emission ON/OFF instruction circuit  155  outputs the light emission ON signal S 31  for closing the switch SW connected to the DRV circuit  140  to the switch SW by the determination of the light emission of each light emitting element  131 . Accordingly, a current flows through the light emitting element  131 , and the light emitting element  131  emits light. The light emission ON/OFF instruction circuit  155  outputs the light emission OFF signal S 32  for opening the switch SW connected to the DRV circuit  140  to the switch SW by the determination of the turn-off of each light emitting element  131 . Accordingly, regardless of the electric charge held in the capacitor  142 , no current flows through the light emitting element  131 , and the light emitting element  131  is turned off. When the light emitting element  131  is emitting light, the light emitting element  131  is immediately turned off when the switch SW is opened. In other words, the turn-off can be immediately determined regardless of the electric charge held in the capacitor  142 . When each light emitting element  131  emits light, a current corresponding to the correction data D 3  stored in the light amount correction memory  154  flows. 
     Second embodiment: Light Emission Control of Print Head 
       FIG. 19  is a diagram illustrating an example of a relationship between a sample/hold signal, a capacitor potential, original image data D 1  and additional null image data D 2 , a switch SW, and a light emitting state of the light emitting element when turn-off control according to the second embodiment is performed. 
     As illustrated in  FIG. 19 , in response to the print head enable signal ES being disabled, the light emitting element  131  is turned off (ACT  700 ), and then the print head enable signal ES is enabled, but by adding null image data before the region corresponding to the original image data D 1  (by the turn-off control C 1 ), the light emission ON/OFF instruction circuit  155  outputs the light emission OFF signal S 32  according to the additional null image data D 2  to the switch SW, the switch SW is opened by the light emission OFF signal S 32 , and the light emitting element  131  continues to be turned off (ACT  701 ). 
     Subsequently, in the region corresponding to the original image data D 1 , the light emitting element  131  is turned on, turned off, and turned on by light emission control according to the original image data D 1  (ACT  702 ) (ACT  703 ) (ACT  704 ). In this case, the light emission ON/OFF instruction circuit  155  outputs the light emission ON signal S 31  to the switch SW in accordance with image data (for example, black image data) other than the null image data included in the original image data D 1 , the switch SW is closed by the light emission ON signal S 31 , and the light emitting element  131  emits light according to the potential of the capacitor  142  (ACT  702 ) (ACT  704 ). The light emission ON/OFF instruction circuit  155  outputs the light emission OFF signal S 32  to the switch SW according to the null image data included in the original image data D 1 , the switch SW is opened by the light emission OFF signal S 32 , and the light emitting element  131  is turned off (ACT  703 ). 
     By adding null image data after the region corresponding to the original image data D 1  (by the turn-off control C 2 ), the light emission ON/OFF instruction circuit  155  outputs the light emission OFF signal S 32  to the switch SW according to the additional null image data D 2 , the switch SW is opened by the light emission OFF signal S 32 , and the light emitting element  131  is turned off (ACT  705 ). Thereafter, the print head enable signal ES is disabled, and the light emitting element  131  continues to be turned off (ACT  706 ). 
       FIG. 20  is an example of a relationship between the sample/hold signal, the capacitor potential, the original image data D 1 , the switch SW, and the light emitting state of the light emitting element when the turn-off control according to the second embodiment is not performed. As illustrated in  FIG. 20 , since the light emitting element  131  is turned off in response to the print head enable signal ES being disabled (ACT  800 ), and then the print head enable signal ES is enabled, and the null image data is not added before the region corresponding to the original image data D 1 , the potential level of the capacitor  142  and the modified state of the switch SW depend on the previous light emission state, and the light emission state of the light emitting element  131  is also turned on or off depending on the previous light emission state (ACT  801 ). In other words, the light emission of the light emitting element  131  is unconfirmed until the original image data D 1  is input. 
     In the region corresponding to the original image data D 1 , the light emitting element  131  is turned on, turned off, turned on by light emission control according to the original image data D 1  (ACT  802 ) (ACT  803 ) (ACT  804 ). In this case, the light emission ON/OFF instruction circuit  155  outputs the light emission ON signal S 31  to the switch SW in accordance with image data (for example, black image data) other than the null image data included in the original image data D 1 , the switch SW is closed by the light emission ON signal S 31 , and the light emitting element  131  emits light according to the potential of the capacitor  142  (ACT  802 ) (ACT  804 ). The light emission ON/OFF instruction circuit  155  outputs the light emission OFF signal S 32  to the switch SW according to the null image data included in the original image data D 1 , the switch SW is opened by the light emission OFF signal S 32 , and the light emitting element  131  is turned off (ACT  803 ). 
     Since null image data is not added after the region corresponding to the original image data D 1 , the switch SW remains closed by the original image data D 1  immediately before, the electric charge held in the capacitor  142  gradually decreases, and the light amount of the light emitting element  131  correspondingly decreases (ACT  805 ). Thereafter, the print head enable signal ES is disabled, and the light emitting element  131  is turned off (ACT  806 ). 
     According to the first and second embodiments described above, it is possible to provide an image forming apparatus that prevents unintended light emission of a light emitting element and provides excellent reproduction of an original image. The control unit  174  controls light emission of a plurality of light emitting elements  131  according to at least the last line of the plurality of image lines included in the original image data D 1 , and then executes the turn-off control C 2  on the plurality of light emitting elements  131 . Thus, even in a case where unintended electric charges remain in the capacitor  142 , the light emitting elements  131  can be turned off reliably and immediately after the image formation of the last line. 
     The control unit  174  can execute the turn-off control C 2  by outputting a control signal for adding the additional null image data D 2  after the last line. The light emitting element  131  is turned on according to image data other than null in the original image data D 1 , turned off according to null image data in the original image data D 1 , and further turned off according to additional null image data D 2 . Alternatively, as illustrated in  FIG. 17 , a switch SW may be provided in the circuit to execute the turn-off control C 2 . The current supply to the light emitting element  131  can be cut off by opening the switch SW by the light emission OFF signal corresponding to the null image data in the original image data D 1  or the additional null image data D 2 . Further, the control unit  174  may execute the first turn-off control when the last line is other than null and may not execute the first turn-off control when the last line is null. Thereby, unnecessary operations can be reduced. 
     The control unit  174  of the image forming apparatus may execute the turn-off control C 1  on the plurality of light emitting elements  131  before controlling the light emission of the plurality of light emitting elements  131  by outputting the image data to the plurality of DRV circuits  140 . Thereby, even in the case where unnecessary electric charges remain in the capacitor  142  due to the previous image formation, the light emitting element  131  can be turned off reliably before the image of the line at the beginning is formed. The turn-off control C 1  can be executed in the same manner as the turn-off control C 2 . 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiment described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.