Patent Publication Number: US-10782629-B2

Title: Image forming apparatus and method for controlling the same

Description:
BACKGROUND ART 
     An electrophotographic image forming apparatus, which a kind of image forming apparatus, irradiates light onto a rotating photoreceptor through an exposing unit to form an electrostatic latent image, supplies a toner to the photoreceptor on which the electrostatic latent image is formed to form a toner image on a surface of the photoreceptor, transfers the toner image of the photoreceptor to a transfer unit, again transfers the toner image to a printing medium, and presses and heats the image transferred to the printing medium through a fusing unit to form an image on the printing medium. 
     Since the exposing unit irradiates the light emitted from an internal light source to the photoreceptor through a light window, there is a risk that printing quality will be deteriorated due to pollution of the light window by the toner, dust, and the like. 
     Therefore, the image forming apparatus according to the related art may prevent the pollution of the light window by including a separate shutter unit closing the light window during a period in which the exposing unit is not operated and opening the light window when the exposing unit is operated. 
     In addition, the image forming apparatus according to the related art may form a color toner image on the printing medium, and generally overlaps toners of cyan (C), magenta (M), yellow (Y), and black (K) colors with one another to form the color toner image. 
     To this end, the image forming apparatus includes four developing units each including the toners of the cyan (C), magenta (M), yellow (Y), and black (K) colors, and overlaps the toners of the cyan (C), magenta (M), yellow (Y), and black (K) colors with one another through the developing units to transfer the color toner image to a transfer belt of the transfer unit and transfers the color toner image to the printing medium through the transfer belt to which the color toner image is transferred. 
     To form a high-quality color toner image, a precise control for overlapping toner images of the respective colors with one another at an accurate position is required. In the case in which color registrations of the color toner image output by the image forming apparatus according to the related art do not coincide with each other, the image forming apparatus according to the related art performs auto color registration (ACR) aligning the color toner image by forming predetermined measuring marks on the transfer belt of the transfer unit and then sensing the predetermined measuring marks through a separate sensor, to correct discrepancy between the color registrations. 
     The image forming apparatus according to the related art includes a separate shutter unit opening the sensor only during a period in which the ACR is performed to prevent the sensor from being polluted by the toner, dust, and the like, in the case in which it does not perform the ACR. 
     As described above, the image forming apparatus according to the related art separately includes the shutter unit for opening or closing the light window of the exposing unit and the shutter unit for opening or closing the sensor for performing the ACR, and drivers for driving the shutter unit for opening or closing the light window and the shutter unit for opening or closing the sensor are also separately configured, such that an entire structure of the image forming apparatus including the shutter units and a method for controlling the image forming apparatus become complicated. 
    
    
     
       DESCRIPTION OF DRAWINGS 
       Certain examples of the present disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a view schematically illustrating a structure of an image forming apparatus according to an example; 
         FIG. 2  is a perspective view illustrating an exposing unit, a sensing unit, and a shutter unit according to an example; 
         FIG. 3  is a side view of a motor, a first shutter part, and a second shutter part according to an example; 
         FIG. 4  is a perspective view illustrating the exposing unit and the first shutter part illustrated in  FIG. 2  according to an example; 
         FIG. 5  is an exploded perspective view of the exposing unit and the first shutter part illustrated in  FIG. 4  according to an example; 
         FIG. 6  is a view illustrating a state in which the first shutter part illustrated in  FIG. 4  closes a light window according to an example; 
         FIG. 7  is a view illustrating a state in which the first shutter part illustrated in  FIG. 4  opens the light window according to an example; 
         FIG. 8  is a perspective view illustrating the sensing unit and the second shutter part illustrated in  FIG. 2  according to an example; 
         FIG. 9  is an exploded perspective view of the sensing unit and the second shutter part illustrated in  FIG. 8  according to an example; 
         FIG. 10  is a view illustrating a state in which the second shutter part illustrated in  FIG. 8  closes sensors according to an example; 
         FIG. 11  is a view illustrating a state in which the second shutter part illustrated in  FIG. 8  opens the sensors according to an example; 
         FIG. 12  is a flowchart illustrating a method for controlling an image forming apparatus according to an example; 
         FIGS. 13A to 13C  are views illustrating operations of a shutter unit in a printing mode according to an example; and 
         FIGS. 14A to 14C  are views illustrating operations of a shutter unit in an auto color registration (ACR) mode according to an example. 
     
    
    
     DETAILED DESCRIPTION 
     Various examples will be described more fully hereinafter with reference to the accompanying drawings. The examples described hereinafter may be modified in many different forms. 
     The following examples may be variously modified without departing from the technical scope of the present disclosure, and these modifications are considered to fall within the technical scope of the present disclosure. In addition, to assist in the understanding of examples to be described below, components performing the same operations and related components in the respective examples will be denoted by the same or similar reference numerals throughout the accompanying drawings. Further, the accompanying drawings are not illustrated to scale, but sizes of some of components may be exaggerated to assist in the understanding of the present disclosure. 
       FIG. 1  is a view schematically illustrating a structure of an image forming apparatus according to an example. 
     Referring to  FIG. 1 , an image forming apparatus  1  may be implemented as a printer, a copier, a scanner, a facsimile, and the like, and may be a multi-function peripheral (MFP) in which functions of the printer, the copier, the scanner, and the facsimile, are complexly implemented through one apparatus. 
     As illustrated in  FIG. 1 , the image forming apparatus  1  may include a body  101 , a paper feeding unit  11 , an exposing unit  12 , a photoreceptor  13 , a developing unit  14 , a transfer unit  15 , a sensing unit  16 , a fusing unit  17 , a paper discharging unit  18 , and a cassette unit  19  disposed in the body  101 . In various examples, there may one or a plurality (e.g., four) of each of photoreceptors  13  and developing units  14  depending on a number of colors of toners used by the image forming apparatus  1 . 
     The paper feeding unit  11  may pick up printing media such as paper, or the like, on which an image is to be formed, loaded in the cassette unit  19  one by one, and inject the picked-up printing media into a transport path P. The paper feeding unit  11  may include a pick-up roller to pick up the paper one by one and a plurality of transport rollers disposed on the transport path P. 
     The cassette unit  19  may include a cassette body  191  separably coupled to a lower portion of the body  101 , a pick-up plate  192  on which the printing media are loaded, and a pick-up elastic member  193  elastically supporting the pick-up plate  192 . A plurality of printing media loaded in the cassette body  191  may be picked up one by one by the pick-up roller of the paper feeding unit  11  in a state in which they are supported by the pick-up plate  192 . 
     Although a case in which a single cassette unit  19  is separably coupled to the lower portion of the body  101  is illustrated by way of example in  FIG. 1 , the number of cassette units  19  may be plural, and the image forming apparatus  1  may further include a multipurpose tray coupled to a side surface or an upper portion of the body  101  and supplying the printing media into the body  101 . 
     The exposing unit  12  irradiates light including image information to the photoreceptor  13  to form an electrostatic latent image on a surface of the photoreceptor  13 , and the developing unit  14  supplies toners to the photoreceptor  13  on which the electrostatic latent image is formed to form toner images. 
     As an example, the developing unit  14  may include first to fourth developing units  141 ,  142 ,  143 , and  144 , and the first to fourth developing units  141  to  144  may include toners of cyan (C), magenta (M), yellow (Y), and black (K) colors, respectively. 
     The photoreceptor  13  may be implemented in a photoreceptor drum form. The photoreceptor  13  may include first to fourth photoreceptors  131 ,  132 ,  133 , and  134  respectively corresponding to the first to fourth developing units  141  and  144 . In addition, first to fourth charging rollers (not illustrated) respectively charging the first to fourth photoreceptors  131  to  134  may be disposed on outer peripheral surfaces of the first to fourth photoreceptors  131  to  134 . The first to fourth charging rollers may uniformly charge surfaces of the first to fourth photoreceptors  131  to  134  that rotate at a predetermined potential, respectively. 
     As illustrated in  FIG. 1 , the exposing unit  12  is disposed below the first to fourth photoreceptors  131  to  134  and irradiates the light including the image information to the charged first to fourth photoreceptors  131  to  134  to form electrostatic latent images on the outer peripheral surfaces of the first to fourth photoreceptors  131  to  134 . The exposing unit  12  may irradiate light including image information for each color of each toner to the first to fourth photoreceptors  131  to  134 . 
     The first to fourth developing units  141  to  144  may include first to fourth developing rollers  1411 ,  1421 ,  1431 , and  1441  facing the first to fourth photoreceptors  131  to  134 , respectively. The first to fourth developing rollers  1411  to  1441  may selectively be in contact with the first to fourth photoreceptors  131  to  134  on which the electrostatic latent images are formed, respectively, and rotate in a state in which they are in contact with the first to fourth photoreceptors  131  to  134 , respectively, to move the toners of the cyan (C), magenta (M), yellow (Y), and black (K) colors to the electrostatic latent images formed on the first to fourth photoreceptors  131  to  134 . 
     Therefore, visible toner images of the cyan (C), magenta (M), yellow (Y), and black (K) colors are formed on the surfaces of the first to fourth photoreceptors  131  to  134 . 
     The transfer unit  15  may include a transfer belt  151 , rotation rollers  1521  and  1522  to rotate the transfer belt  151 , and a transfer roller  153  facing the transfer belt  151  to form a nib through which the printing medium passes. 
     The rotation rollers  1521  and  1522  may rotatably support the transfer belt  151 , and the transfer belt  151  may rotate depending on rotation of the first and second rotation rollers  1521  and  1522 . For example, the first rotation roller  1521  may maintain tension of the transfer belt  151 , and the second rotation roller  1522  may rotate through a separate driver to rotate the transfer belt  151 . However, the rotation rollers  1521  and  1522  may further include a plurality of rotation rollers, in addition to the first and second rotation rollers  1521  and  1522 . 
     The transfer belt  151  may rotate in a state in which it is in contact with the first to fourth photoreceptors  131  to  134 , and the toner images of the first to fourth photoreceptors  131  to  134  may be sequentially transferred to the transfer belt  151 . 
     As an example, as illustrated in  FIG. 1 , as the transfer belt  151  rotates in a counterclockwise direction in  FIG. 1 , the toner images of the cyan (C), magenta (M), yellow (Y), and black (K) colors of the first to fourth photoreceptors  131  to  134  may be sequentially transferred to the transfer belt  151 . Therefore, a color toner image in which the toner images of the cyan (C), magenta (M), yellow (Y), and black (K) colors are overlapped with one another may be formed on the transfer belt  151 . 
     The color toner image formed on the transfer belt  151  may be transferred to the printing medium passing between the transfer belt  151  and the transfer roller  153 . 
     The sensing unit  16  may face the transfer belt  151  to sense the color toner image transferred to the transfer belt  151  and include one or more sensors (e.g.,  161 ,  162 , and  163  as illustrated in  FIG. 9 ). The sensors  161  to  163  configuring the sensing unit  16  may be image sensors such as an optical sensor, a complementary metal oxide semiconductor (CMOS) sensor, a charge coupled device (CCD) sensor, and the like. 
     In an example, the sensing unit  16  may be disposed between the first to fourth photoreceptors  131  to  134  and the transfer roller  153 , and as illustrated in  FIG. 1 , the sensing unit  16  may be disposed adjacently to the transfer belt  151 , and be disposed behind the fourth photoreceptor  134  in a rotation direction of the transfer belt  151 . 
     In a case in which the developing unit  14  is replaced, the image forming apparatus  1  performs a large amount of printing, the image forming apparatus is not operated for a long period of time, or the like, color registrations of the color toner image output by the image forming apparatus  1  may not coincide with each other. In this case, toners of the respective colors may not accurately overlap with one another such that quality deterioration (e.g., a boundary portion of the color toner image looks blurred, etc.) may occur. 
     To address such a problem, the image forming apparatus  1  may be operated in an auto color registration (ACR) mode for performing ACR. 
     As an example, predetermined measuring marks may be formed on the transfer belt  151  through the first to fourth photoreceptors  131  to  134  and the first to fourth developing units  141  to  144  and be sensed through the sensing unit  16 . 
     The measuring marks may include a plurality of measuring marks at which the toner images of the cyan (C), magenta (M), yellow (Y), and black (K) colors are marked to be independent from or overlapped with one another depending on predetermined widths and lengths. A controller (not illustrated) may sense widths, lengths, and the like, of the plurality of measuring marks through the sensing unit  16  to determine whether or not the measuring marks formed on the transfer belt  151  coincide with a reference. In a case in which the measuring marks formed on the transfer belt  151  correspond to a predetermined ACR correction condition, the controller may control the exposing unit  12 , the photoreceptor  13 , the developing unit  14 , or the transfer unit  15  to perform correction on the color toner image formed on the transfer belt  151  and the printing medium. 
     However, since a process of performing the ACR through the sensing unit  16  described above is similar to that of the related art, an overlapped description will be omitted. 
     The fusing unit  17  may include first and second fusing rollers  171  and  172 . In an example, the printing medium to which the color toner image is transferred is pressed and heated during a period in which it passes between the first and second fusing rollers  171  and  172  that rotate, such that the color toner image may be fused on the printing medium. 
     The paper discharging unit  18  may include first and second paper discharging rollers  181  and  182 . In an example, the printing medium on which the color toner image is fused by the fusing unit  17  may pass between the first and second paper discharging rollers  181  and  182  that rotate and be discharged to the outside of the image forming apparatus  1 . 
     The image forming apparatus  1  may include a shutter unit  10  to selectively expose (i.e., open or close) a light window (e.g.,  122  as illustrated in  FIG. 5 ) of the exposing unit  12  and the sensors  161  to  163  of the sensing unit  16 . 
     The shutter unit  10  may include a motor  100 , a first shutter part  200 , and a second shutter part  300 . In an example, the first and second shutter parts  200  and  300  may receive a driving force transferred from the motor  100  to selectively expose (i.e., open or close) the light window  122  and the sensors  161  to  163 , thereby reducing or preventing the window  122  and the sensors  161  to  163  from being polluted by pollutants such as the toners, dust, and the like. 
     Example structures of the exposing unit  12 , the sensing unit  16 , and the shutter unit  10  will be described below. 
       FIG. 2  is a perspective view illustrating an exposing unit, a sensing unit, and a shutter unit according to an example. 
     Referring to  FIG. 2 , a state in which the shutter unit  10  closes the light window  122  (see  FIG. 5 ) of the exposing unit  12  and the sensors  161  to  163  (see  FIG. 9 ) is illustrated. 
     The exposing unit  12  includes a light source (not illustrated) disposed in an exposing unit body  1200  and the light window  122  transmitting light emitted from the light source to the photoreceptor  13 . 
     The exposing unit  12  is disposed below the first to fourth photoreceptors  131  to  134  and may irradiate light including image information depending on the respective toner colors to the first to fourth photoreceptors  131  to  134 . 
     First to fourth light windows (e.g.,  1221 ,  1222 ,  1223 , and  1224  as illustrated in  FIG. 5 ) facing the first to fourth photoreceptors  131  and  134 , respectively, are disposed on an upper surface  1201  of the exposing unit body  1200 . 
     The exposing unit  12  may irradiate the light including the image information to the first to fourth photoreceptors  131  to  134  through the first to fourth light windows  1221  to  1224 , respectively, to form the electrostatic latent images on the first to fourth photoreceptors  131  to  134 . 
     The first shutter part  200  opening or closing the first to fourth light windows  1221  to  1224  may be disposed on the exposing unit  12 . 
     The first shutter part  200  may include a first cover  210 , a first elastic member  220 , a first cam gear  230 , a first lever  240 , and a lever elastic member  250 . 
     The first cover  210  is disposed on the upper surface  1201  of the exposing unit body  1200  of the exposing unit  12  and may reciprocate to selectively open or close the first to fourth light windows  1221  to  1224 . The first elastic member  220  may connect the first cover  210  and the upper surface  1201  of the exposing unit body  1200  of the exposing unit  12  to each other to apply an elastic force to the first cover  210 . The first cam gear  230  may rotate by receiving a driving force transferred from the motor  100  to selectively push the first lever  240 , and the first lever  240  may push the first cover  210  to move the first cover  210  in a direction in which the first cover  210  opens the first to fourth light windows  1221  to  1224 . In addition, movement of the first lever  240  may be guided by a guide member  124  covering one side of the exposing unit  12 . 
     The second shutter part  300  may include a second cover  310 , a second elastic member (e.g.,  320  as illustrated in  FIG. 9 ), a second cam gear  330 , and a second shutter part body  340 . 
     The sensing unit  16  may be disposed in the second shutter part body  340  to face the transfer belt  151  disposed above, and the second cover  310  may cover an upper surface of the second shutter part body  340  to close the sensing unit  16 . The second cam gear  330  may rotate by receiving a driving force transferred from the motor  100  to selectively push the second cover  310 , such that the second cover  310  may selectively open or close the sensing unit  16 . 
     Example structures of the first and second shutter parts  200  and  300  will be described below. 
     As illustrated in  FIG. 2 , the first cam gear  230  of the first shutter part  200  and the second cam gear  330  of the second shutter part  300  may simultaneously receive the driving force transferred from the motor  100 , such that the first shutter part  200  and the second shutter part  300  may be simultaneously operated. 
       FIG. 3  is a side view of a motor, a first shutter part, and a second shutter part according to an example. 
     Referring to  FIG. 3 , a structure in which a driving force is transferred from the motor  100  to the first and second shutter parts  200  and  300  will be described. 
     As described above, the first and second shutter parts  200  and  300  may be operated by simultaneously by receiving a driving force transferred from a single motor  100 . 
     As an example, the motor  100  may include a motor body  110  and a driving shaft  120  coupled to the motor body  110  to rotate in a first rotation direction R 11  or a second rotation direction R 12 . 
     As illustrated in  FIGS. 2 and 3 , the first cam gear  230  may be disposed below the motor  100  and be engaged to rotate with the driving shaft  120 . The second cam gear  330  may be disposed above the motor  100  and be engaged to rotate with the driving shaft  120 . 
     The first cam gear  230  may include a first gear part  231  that may engage and rotate with the driving shaft  120 . The first gear part  231  may rotate depending on a rotation of the driving shaft  120  to rotate the first cam gear  230 . 
     The second cam gear  330  may include a one-way clutch gear  331  that may engage and rotate with the driving shaft  120 . The one-way clutch gear  331  may rotate depending on a rotation of the driving shaft  120  to rotate the second cam gear  330 . 
     The driving shaft  120  may include a driving gear  121  that may couple to and rotate with a front end portion. The first gear part  231  and the one-way clutch gear  331  may be engaged to rotate with the driving gear  121 . 
     As illustrated in  FIG. 3 , a rotation center  120 R of the driving shaft  120  may be perpendicular to rotation directions of the first and second cam gears  230  and  330 . In an example, the driving gear  121  may be a worm gear, and the first gear part  231  and the one-way clutch gear  331  engaged with the driving gear  121  may be spur gears. However, a gear structure illustrated in  FIG. 3  is an example. In other examples, the rotation center of the driving shaft  120  and shafts of the first and second cam gears  230  and  330  may be parallel with each other, and structures of the first gear part  231  and the one-way clutch gear  331  simultaneously engaged and rotating with the driving shaft  120  may be variously modified. 
     In an example, rotation directions of the first gear part  231  and the one-way clutch gear  331 , which rotate depending on the rotation of the driving shaft  120 , are opposite to each other. 
     As an example, as illustrated in  FIG. 3 , when the driving shaft  120  rotates in the first rotation direction R 11  around the rotation center  120 R, the first gear part  231  rotates in a fourth rotation direction R 22  (e.g., a counterclockwise direction in  FIG. 3 ), and the one-way clutch gear  331  rotates in a third rotation direction R 21  (e.g., a clockwise direction in  FIG. 3 ) opposite to the fourth rotation direction R 22 . 
     In addition, when the driving shaft  120  rotates in the second rotation direction R 12  opposite to the first rotation direction R 11 , the first gear part  231  rotates in the third rotation direction R 21 , and the one-way clutch gear  331  rotates in the fourth rotation direction R 22 . 
     The one-way clutch gear  331  may transfer the driving force to the second cam gear  330  only in a case in which it rotates in the fourth rotation direction R 22 , and block the driving force transferred to the second cam gear  330  in a case in which it rotates in the third rotation direction R 21 . Therefore, in a case in which the driving shaft  120  rotates in the first rotation direction R 11 , the first shutter part  200  may be operated, and the second shutter part  300  may be in a stand-by state in which it is not operated. 
     A rotation direction of the driving shaft  120  may be changed to either one of the first and second rotation directions R 11  and R 12 , such that only the first shutter part  200  may be independently driven or the first and second shutter parts  200  and  300  may be simultaneously driven. An example structure of the second cam gear  330  including the one-way clutch gear  331  and an example method for controlling the first and second shutter parts  200  and  300  will be described below. 
       FIG. 4  is a perspective view illustrating the exposing unit  12  and the first shutter part  200  illustrated in  FIG. 2  according to an example, and  FIG. 5  is an exploded perspective view of the exposing unit  12  and the first shutter part  200  illustrated in  FIG. 4  according to an example.  FIG. 6  is a view illustrating a state in which the first shutter part  200  illustrated in  FIG. 4  closes a light window  122  according to an example, and  FIG. 7  is a view illustrating a state in which the first shutter part  200  illustrated in  FIG. 4  opens the light window  122  according to an example. 
     Hereinafter, an example of the first shutter part  200  opening or closing the light window  122  of the exposing unit  12  will be described with reference to  FIGS. 4 to 7 . 
     As described above, the exposing unit  12  may include the exposing unit body  1200 , the light source (not illustrated) provided in the exposing unit body  1200 , and the first to fourth light windows  1221  to  1224  disposed on the upper surface  1201  of the exposing unit body  1200 . 
     The first to fourth light windows  1221  to  1224  may transmit the light emitted from the light source to the first to fourth photoreceptors  131  to  134 , and the exposing unit  12  may irradiate the light including the image information corresponding to the toner images of the cyan (C), magenta (M), yellow (Y), and black (B) colors to the first to fourth photoreceptors  131  to  134  through the first to fourth light windows  1221  to  1224 , respectively. 
     As the exposing unit  12 , a laser scanning unit (LSU) or a light emitting diode (LED) print head (LPH) may be used. The laser scanning unit may include a light source emitting light and a reflecting mirror that is rotatable, and reflect the light irradiated from the light source on the reflecting mirror that rotates, transmit the light through a light window, and irradiate the light to a photoreceptor. The LED print head may include an LED array to directly irradiate linear light to a photoreceptor. 
     As described above, the first shutter part  200  may include the first cover  210 , the first elastic member  220 , the first cam gear  230 , the first lever  240 , and the lever elastic member  250 . 
     The first cover  210  is movably disposed on the exposing unit  12 , that is, on the first to fourth light windows  1221  to  1224  to selectively expose (i.e., open or close) the first to fourth light windows  1221  to  1224 . 
     The first cover  210  may include a first plate  211  having a quadrangular shape corresponding to a shape of the upper surface  1201  of the exposing unit body  1200 , and first to fourth openings  212  (i.e.,  2121 ,  2122 ,  2123 , and  2124 ) formed in the first plate  211  and corresponding, respectively, to the first to fourth light windows  1221  to  1224 . 
     The first cover  210  may reciprocate in a first close direction  210   a  in which it closes (i.e., covers) the first to fourth light windows  1221  to  1224  and a first open direction  210   b  in which it opens (i.e., exposes) the first to fourth light windows  1221  to  1224 , on the upper surface  1201  of the exposing unit body  1200 . 
     When the first cover  210  moves in the first close direction  210   a , the first to fourth openings  2121  to  2124  of the first cover  210  and the first to fourth light windows  1221  to  1224  are disposed to be misaligned with each other, as illustrated in  FIG. 6 . Therefore, the first to fourth light windows  1221  and  1224  are covered and closed by the first cover  210 . 
     When the first cover  210  moves in the first open direction  210   b , the first to fourth openings  2121  to  2124  of the first cover  210  and the first to fourth light windows  1221  to  1224  face each other, as illustrated in  FIG. 7 . Therefore, the first to fourth light windows  1221  to  1224  are opened through the first to fourth openings  2121  to  2124 . 
     The first cover  210  may include at least one sliding protrusion  2111  extended in a direction parallel with a moving direction. A sliding groove  1211  corresponding to the sliding protrusion  2111  may be provided in the upper surface  1201  of the exposing unit body  1200 . 
     The sliding protrusion  2111  of the first cover  210  may be slidably inserted into the sliding groove  1211 . Therefore, the first cover  210  may be reciprocated between the first close direction  210   a  and the first open direction  210   b.    
     The structures of the sliding protrusion  2111  of the first cover  210  and the sliding groove  1211  of the exposing unit  12  described above may be replaced by each other, and may be replaced by various structures that may guide the reciprocation of the first cover  210 . 
     The first elastic member  220  may apply an elastic force to the first cover  210  so that the first cover  210  moves in the first close direction  210   a.    
     As an example, one end of the first elastic member  220  may be connected to a hooked part  213  formed at one side of the first cover  210 , and the other end of the first elastic member  220  may be connected to a hooked part  123  formed on the upper surface  1201  of the exposing unit body  1200 . Therefore, the first elastic member  220  may pull the first cover  210  in the first close direction  210   a . Accordingly, the first elastic member  220  may be a tension spring. In this case, the hooked part  123  of the exposing unit  12  may be disposed toward the first close direction  210   a  as compared with the hooked part  213  of the first cover  210 . 
     In addition, the first plate  211  may include a hole  2131  into which the hooked part  123  of the exposing unit  12  may be inserted. The first elastic member  220  may apply the elastic force to the hooked part  213  of the first cover  210  in the hole  2131  of the first plate  211 . 
     Therefore, the first elastic member  220  may apply the elastic force to the first cover  210  in the first close direction  210   a  opposed to the first open direction  210   b  so that the first cover  210  maintains a state in which it closes the first to fourth light windows  1221  to  1224 . 
     The first cam gear  230  may include the first gear part  231  engaged with and rotating the driving shaft  120  and a first cam  232  coupled to the first gear part  231 . 
     As described above, the first cam gear  230  may rotate in the third rotation direction R 21  and the fourth rotation direction R 22  opposed to the third rotation direction R 21  through the first gear part  231  engaged with the driving shaft  120 . The first cam  232  may also rotate in the third and fourth rotation directions R 21  and R 22 . The first gear part  231  and the first cam  232  may be formed integrally with each other. 
     As illustrated in  FIGS. 4 to 7 , the first cam  232 , which may be an edge cam protruding in a direction parallel with a shaft, may rotate using a cross section of a cylinder cut in an oblique direction as a contour curved line. In addition, the first cam  232  may be a disk cam. Since the edge cam and the disk cam that may be used as the first cam  232  are similar to those according to the related art, a detailed description therefor will be omitted. 
     The first lever  240  may reciprocate in a length direction in a state in which one end  241  thereof is in contact with the first cam  232  and another end  242  thereof is in contact with the first cover  210 . 
     The first lever  240  may have a shape of a bar extended in a direction parallel with a shaft of the first cam gear  230 . The first lever  240  may reciprocate depending on the rotation of the first cam  232  on the upper surface  1201  of the exposing unit body  1200  to push the first cover  210  in the first open direction  210   b.    
     As an example, the first lever  240  may reciprocate in a direction perpendicular to a moving direction of the first cover  210 , and may reciprocate in a first direction  240   a  in which it pushes the first cover  210  in the first open direction  210   b  and a second direction  240   b  opposed to the first direction  240   a.    
     The first lever  240  may be disposed so that one end  241  thereof is in contact with the first cam  232  on one end portion of the upper surface  1201  of the exposing unit body  1200 , and may be slid along an inner side surface of the guide member  124  covering one side of the exposing unit body  1200 , such that the reciprocation of the first lever  240  in the first and second directions  240   a  and  240   b  may be guided. 
     The lever elastic member  250  may apply an elastic force to the first lever  240  so that the first lever  240  moves in the second direction  240   b . The lever elastic member  250  may have one end connected to a hooked part  1241  of the guide member  124  and another end connected to a hooked part  243  of the first lever  240  to pull the first lever  240  in the second direction  240   b . In an example, the lever elastic member  250  may be a tension spring. In this case, the hooked part  1241  of the guide member  124  may be disposed toward the second direction  240   b  as compared with the hooked part  243  of the first lever  240 . 
     The guide member  124  may include a hole  1242  in which the hooked part  243  of the first lever  240  may be inserted and move. The lever elastic member  250  may apply the elastic force between the hooked part  243  of the first lever  240  and the hooked part  1241  of the guide member  124 . 
     One end  241  of the first lever  240  may press the first cam  232  in the second direction  240   b  in a state in which it is in contact with the first cam  232  by the elastic force of the lever elastic member  250 . 
     The first cover  210  may include an inclined part  214 . In an example, the inclined part  214  may be formed by protruding a portion of one end portion of the first cover  210  adjacent to the first lever  240  in the first close direction  210   a . The first lever  240  may reciprocate in the first and second directions  240   a  and  240   b  in a state in which the other end  242  thereof is in contact with the inclined part  214 . When the first lever  240  moves in the first direction  240   a , the other end  242  of the first lever  240  may push the inclined part  214  to move the first cover  210  in the first open direction  210   b.    
     In addition, the first cam  232  may include a first portion  232 L having the lowest phase and a second portion  232 H having the highest phase on the basis of the first direction  240   a.    
     The first portion  232 L and the second portion  232 H correspond to portions of the contour curved line of the first cam  232  in contact with one end  241  of the first lever  240 . The first portion  232 L and the second portion  232 H are disposed at an interval of 180° on the basis of a rotation center of the first cam  232 . 
     One end  241  of the first lever  240  in contact with the first cam  232  may be in alternate contact with the first portion  232 L and the second portion  232 H depending on the rotation of the first cam  232 . When the first cam  232  rotates by 180° in the third rotation direction R 21  or the fourth rotation direction R 22  in a state in which one end  241  of the first lever  240  is in contact with the first portion  232 L, one end  241  of the first lever  240  is in contact with the second portion  232 H. 
     As an example, as illustrated in  FIG. 6 , when one end  241  of the first lever  240  is in contact with the first portion  232 L, the first lever  240  moves in the second direction  240   b  by the elastic force of the lever elastic member  250 . Therefore, the first cover  210  moves in the first close direction  210   a  to close the first to fourth light windows  1221  to  1224 . 
     When the first cam  232  starts to rotate in the third rotation direction R 21  or the fourth rotation direction R 22  in the state in which one end  241  of the first lever  240  is in contact with the first portion  232 L, the first cam  232  presses one end  241  of the first lever  240  in the first direction  240   a  to push the first lever  240  in the first direction  240   a . Therefore, the other end  242  of the first lever  240  presses the inclined part  214 , such that the first cover  210  is pushed in the first open direction  210   b.    
     As illustrated in  FIG. 7 , when the first cam  232  rotates by 180° in the state in which one end  241  of the first lever  240  is in contact with the first portion  232 L, one end  241  of the first lever  240  is in contact with the second portion  232 H to push the first cover  210  in the first open direction  210   b . Therefore, the first cover  210  may open the first to fourth light windows  1221  to  1224 . 
     In addition, when the first cam  232  again rotates by 180° in a state in which the first cover  210  is opened, the first cover  210  may close the first to fourth light windows  1221  to  1224 , as illustrated in  FIG. 6 . 
     As described above, in a standby mode of the image forming apparatus  1 , the first cover  210  maintains a state in which it closes the first to fourth light windows  1221  to  1224  by the elastic force of the first elastic member  220 . 
     When a printing mode starts, the first cover  210  opens the first to fourth light windows  1221  to  1224  through the rotation of the first cam  232 , and the exposing unit  12  may irradiate the light to the first to fourth photoreceptors  131  to  134  to form the electrostatic latent images. When the printing mode ends, the first cam  232  may again rotate to close the first to fourth light windows  1221  to  1224  through the first cover  210 . 
     The first to fourth light windows  1221  to  1224  may be opened through the first cover  210  only at the time of an operation of the exposing unit  12  and may be closed through the first cover  210  in the standby mode, such that pollution of the first to fourth light windows  1221  to  1224  due to the toners, and the like, may be reduced or prevented. 
     In addition, although an example in which the first shutter part  200  has a structure in which the first lever  240  reciprocates in the first and second directions  240   a  and  240   b  through the rotation of the first cam gear  230  to push the first cover  210  in the first open direction  210   b  is illustrated by way of example in  FIGS. 4 to 7 , the first shutter part  200  may also have a structure in which the first cam  232  of the first cam gear  230  rotates to directly push the first cover  210  in the first open direction  210   b , without separately using the first lever  240 . 
       FIG. 8  is a perspective view illustrating the sensing unit  16  and the second shutter part  200  illustrated in  FIG. 2  according to an example,  FIG. 9  is an exploded perspective view of the sensing unit  16  and the second shutter part  300  illustrated in  FIG. 8  according to an example,  FIG. 10  is a view illustrating a state in which the second shutter part  300  illustrated in  FIG. 8  closes sensors  161  to  163  according to an example, and  FIG. 11  is a view illustrating a state in which the second shutter part  300  illustrated in  FIG. 8  opens the sensors  161  to  163  according to an example. 
     Hereinafter, an example of the second shutter part  300  selectively exposing (e.g., opening or closing) the sensors  161  to  163  of the sensing unit  16  will be described with reference to  FIGS. 8 to 11 . 
     The sensing unit  16  may include one or more sensors  161  to  163  that may face the transfer belt  151  to sense the color toner image transferred to the transfer belt  151  and the measuring marks for the ACR, and may include first to third sensors  161 ,  162 , and  163  as illustrated in  FIG. 9 . 
     The first to third sensors  161  to  163  may be disposed at predetermined intervals in a width direction of the transfer belt  151 , perpendicular to the rotation direction of the transfer belt  151 . Therefore, the first to third sensors  161  to  163  may sense the color toner image and the measuring marks formed on the transfer belt  151  that rotates. 
     The first to third sensors  161  to  163  may be disposed to face the transfer belt  151  to perform the ACR, and may sense the measuring marks formed on the transfer belt  151  at the time of an operation in the ACR mode. Since a structure of the first to third sensors  161  to  163  may be the same as or similar to those according to the related art, a description therefor will be omitted. 
     The second shutter part  300  may include the second cover  310 , the second elastic member  320 , the second cam gear  330 , and the second shutter part body  340 . 
     The first to third sensors  161  to  163  may be disposed in the second shutter part body  340 , and may be exposed to face the transfer belt  151  on the upper surface of the second shutter part body  340 . 
     The second shutter part body  340  may include a body housing  341  of which one side is opened and a body housing cover  342  covering the body housing  341 . 
     In addition, as illustrated in  FIG. 9 , the first to third sensors  161  to  163  are disposed in the body housing  341 , and the body housing cover  342  is coupled to the body housing  341 , such that the first to third sensors  161  to  163  may be disposed in the second shutter part body  340 . 
     Sensing portions (upper portions) of the first to third sensors  161  to  163  are disposed to be exposed at predetermined intervals on an upper surface of the body housing  341 . 
     The second cover  310  is movably disposed on the body housing  341 , that is, on the first to third sensors  161  to  163  to open or close the first to third sensors  161  to  163 . 
     The second cover  310  may have a shape of a plate corresponding to a shape of the upper surface of the body housing  341 . The second cover  310  may be extended in a length direction of the upper surface of the body housing  341  in which the first to third sensors  161  to  163  are sequentially disposed, and may be extended from one end  311  in contact with the second cam gear  330  toward another end  312 . 
     The second cover  310  may reciprocate in a second close direction  310   a  in which it covers (i.e., closes) the first to third sensors  161  to  163  and a second open direction  310   b  in which it exposes (i.e., opens) the first to third sensors  161  to  163 , on the body housing  341  in which the first to third sensors  161  to  163  are disposed. 
     As an example, as illustrated in  FIG. 9 , the second cover  310  may include at least one guide protrusion  313  protruding downward. In addition, the at least one guide protrusion  313  may include first to third guide protrusions  3131 ,  3132 , and  3133 . 
     The body housing  341  may include a guide hole  3411  formed in the upper surface thereof and corresponding to the guide protrusion  313 . The guide hole  3411  may include first to third guide holes  34111 ,  34112 , and,  34113  into which the first to third guide protrusions  3131  to  3133  may be inserted, respectively. 
     The first to third guide holes  34111  to  34113  may be long holes formed in the same shape in the upper surface of the body housing  341 , and the first to third guide protrusions  3131  to  3133  may be inserted and slid into the first to third guide holes  34111  to  34113 , respectively, to guide the reciprocation of the second cover  310 . 
     As an example, the first to third guide holes  34111  to  34113  may have a shape of a long hole extended in a width direction of the body housing  341  on the upper surface of the body housing  341 . 
     For example, the second cover  310  may close the first to third sensors  161  to  163  in a state in which the first to third guide protrusions  3131  to  3133  are respectively in contact with one end of the first to third guide holes  34111  to  34113 . In addition, the first to third guide protrusions  3131  to  3133  may move to the other ends of the first to third guide holes  34111  to  34113  along the first to third guide holes  34111  to  34113 , such that the second cover  310  may open the first to third sensors  161  to  163 . 
     Since the second cover  310  may be pressed and move in a length direction of the second cover  310  through the second cam gear  330 , the first to third guide holes  34111  to  34113  may have a shape of a long hole inclined at a predetermined angle in the length direction of the second cover  310  for the purpose of smooth reciprocation of the second cover  310 . 
     In an example, since the second close direction  310   a  and the second open direction  310   b  in which the second cover  310  reciprocates correspond to the shape of the first to third guide holes  34111  to  34113 , the second close direction  310   a  and the second open direction  310   b  may be inclined at a predetermined angle in the length direction of the second cover  310  depending on the shape of the first to third guide holes  34111  to  34113 . However, the shape of the first to third guide holes  34111  to  34113  may be variously modified. The second close direction  310   a  and the second open direction  310   b  in which the second cover  310  reciprocates to open or close the first to third sensors  161  to  163  may also be modified. 
     When the second cover  310  moves in the second close direction  310   a , the second cover  310  closes the first to third sensors  161  to  163  as illustrated in  FIG. 10 , and when the second cover  310  moves in the second open direction  310   b , the second cover  310  opens the first to third sensors  161  to  163  as illustrated in  FIG. 11 , such that the first to third sensors  161  to  163  may face the transfer belt  151 . 
     Referring to  FIG. 9 , the second elastic member  320  may apply an elastic force to the second cover  310  so that the second cover  310  moves in the second close direction  310   a.    
     As an example, one end of the second elastic member  320  may be connected to a hooked part  314  disposed at a lower side of the second cover  310 , and the other end of the second elastic member  320  may be connected to a hooked part  3412  of the body housing  341 . Therefore, the second elastic member  320  may pull the second cover  310  in the second close direction  310   a . Accordingly, the second elastic member  320  may be a tension spring. In this case, the hooked part  3412  of the body housing  341  may be disposed toward the second close direction  310   a  as compared with the hooked part  314  of the second cover  310 . 
     The body housing  341  may include a hole into which the hooked part  314  of the second cover  310  may be inserted. The second elastic member  320  may apply the elastic force to the hooked part  314  of the second cover  310  in the hole of the body housing  341 , and the hooked part  314  of the second cover  310  may move in the hole depending on movement of the second cover  310 . 
     The second elastic member  320  may apply the elastic force to the second cover  310  in the second close direction  310   a  opposed to the second open direction  310   b  so that the second cover  310  maintains a state in which it closes the first to third sensors  161  to  163 . 
     The second cam gear  330  may include the one-way clutch gear  331  to engage and rotate with the driving shaft  120  and may include a second cam  332  coupled to the one-way clutch gear  331 . 
     The one-way clutch gear  331  may include a second gear part  3311  to engage and rotate with the driving gear  121  of the driving shaft  120 , and a one-way bearing  3312  coupled to the second gear part  3311 . 
     The second gear part  3311  may rotate in the third rotation direction R 21  when the driving shaft  120  rotates in the first rotation direction R 11 , and may rotate in the fourth rotation direction R 22  when the driving shaft  120  rotates in the second rotation direction R 12 . 
     The one-way bearing  3312  may connect the second gear part  3311  and the second cam  332  to each other, and may block a transfer of the driving force to the second cam  332  when the second gear part  3311  rotates in the third rotation direction R 21  and transfer the driving force to the second cam  332  when the second gear part  3311  rotates in the fourth rotation direction R 22 . In an example, a structure of the one-way clutch gear  331  including the one-way bearing  3312  may be the same as or similar to that according to the related art. 
     When the second gear part  3311  rotates in the third rotation direction R 21 , the transfer of the driving force to the second cam  332  may be blocked by the one-way bearing  3312 , such that the second cam  332  does not rotate. In addition, when the second gear part  3311  rotates in the fourth rotation direction R 22 , the driving force may be transferred to the second cam  332  through the one-way bearing  3312 , such that the second cam  332  may rotate in the fourth rotation direction R 22 . 
     In an example, the one-way clutch gear  331  may block the transfer of the driving force to the second cam  332  when the driving shaft  120  rotates in the first rotation direction R 11 , and may transfer the driving force to the second cam  332  when the driving shaft  120  rotates in the second rotation direction R 12 . 
     The second cam  332  may have a structure similar to that of the first cam  232 . In an example, the second cam  332  may be an edge cam protruding in a direction parallel with a shaft. 
     The second cam  332  may include a first portion  332 L having the lowest phase and a second portion  332 H having the highest phase on the basis of a protruding direction. 
     The first portion  332 L and the second portion  332 H of the second cam  332 , which are portions of a contour curved line of the second cam  332  in contact with one end  311  of the second cover  310 , are disposed at an interval of 180° on the basis of a rotation center of the second cam  332 . 
     One end  311  of the second cover  310  in contact with the second cam  332  may be in selective contact with the first portion  332 L and the second portion  332 H of the second cam  332  depending on the rotation of the second cam  332 . When the second cam  332  rotates by 180° in the fourth rotation direction R 22  in a state in which one end  311  of the second cover  310  is in contact with the first portion  332 L, one end  311  of the second cover  310  may be in contact with the second portion  332 H. 
     As an example, as illustrated in  FIG. 10 , when one end  311  of the second cover  310  is in contact with the first portion  332 L of the second cam  332 , the second cover  310  moves in the second close direction  310   a  by the elastic force of the second elastic member  320  to close the first to third sensors  161  to  163 . 
     When the second cam  332  starts to rotate in the fourth rotation direction R 22  in the state in which one end  311  of the second cover  310  is in contact with the first portion  332 L, the second cam  332  presses one end  311  of the second cover  310  in the second open direction  310   b  to push the second cover  310  in the second open direction  310   b.    
     When the second cam  332  rotates by 180° in the state in which one end  311  of the second cover  310  is in contact with the first portion  332 L, one end  311  of the second cover  310  may be in contact with the second portion  332 H, such that the second cover  310  may open the first to third sensors  161  to  163 , as illustrated in  FIG. 11 . 
     When the second cam  332  again rotates by 180° in the fourth rotation direction R 22  in a state in which the second cover  310  is opened, the second cover  310  may close the first to third sensors  161  to  163 , as illustrated in  FIG. 10 . 
     In the image forming apparatus  1  according to an example, the second cover  310  may maintain a state in which it closes the first to third sensors  161  to  163  by the elastic force of the second elastic member  320  in the standby mode or during a period in which printing is performed in the printing mode, and when the ACR mode starts, the second cover  310  may open the first to third sensors  161  to  163  through the rotation of the second cam  332  to perform the ACR. When the ACR mode ends, the first to third sensors  161  to  163  may be again closed through the second cover  310 . 
     The first to third sensors  161  to  163  may be opened through the second cover  310  only at the time of an operation, that is, only when the ACR mode is performed, such that pollution of the first to third sensors  161  to  163  due to the toners, dust, and the like, may be reduced or prevented. 
       FIG. 12  is a flowchart illustrating a method for controlling an image forming apparatus according to an example,  FIGS. 13A to 13C  are views illustrating operations of a shutter unit in a printing mode according to an example, and  FIGS. 14A to 14C  are views illustrating operations of a shutter unit  10  an ACR mode according to an example. 
     Hereinafter, an example of a method for controlling an image forming apparatus  1  will be described on the basis of operations in which the light window  122  and the sensing unit  16  are opened or closed by the shutter unit  10  with reference to  FIGS. 12 to 14C . 
     The first shutter part  200  opening or closing the first to fourth light windows  1221  to  1224  and the second shutter part  300  opening or closing the first to third sensors  161  to  163  are together engaged with the driving shaft  120  of the motor  100  to receive the driving force transferred from the motor  100 . 
     The first cam gear  230  and the second cam gear  330  engaged and rotating with the driving shaft  120  may have the same gear ratio such that a rotation angle of the first cam gear  230  and a rotation angle of the second cam gear  330  depending on the rotation of the driving shaft  120  may be the same as each other. 
     As illustrated in  FIG. 12 , the image forming apparatus  1  may be operated in a printing mode for forming an image on a printing medium and an ACR mode for correcting a color toner image. 
     A controller (not illustrated) controlling the image forming apparatus  1  may control rotation directions and rotation angles of the driving shaft  120  of the motor  100  depending on operations in the printing mode and the ACR mode to control the first and second shutter part  200  and  300 . 
     Referring to  FIG. 12 , a printing mode for forming an image on a printing medium and an ACR mode for aligning the toner image transferred to the transfer belt  151  of the transfer unit  15  may be selected in operation  51 . 
     The image forming apparatus  1  may be generally operated in the printing mode for forming an image on the printing medium. 
     In a case in which the developing unit  14  is replaced, the image forming apparatus  1  performs a large amount of printing, or the image forming apparatus  1  is not operated for a long period of time, the image forming apparatus  1  may be operated in the ACR mode. 
     The controller may sense that the developing unit  14  is replaced, the image forming apparatus  1  performs the large amount of printing, or the image forming apparatus  1  was in the standby mode for the long period of time to automatically select the ACR mode. In addition, the ACR mode may be performed before a start of the printing mode, after an end of the printing mode, or during printing. 
     In the image forming apparatus  1  in a standby mode state, as illustrated in  FIGS. 13A, 13C, 14A, and 14C , one end  241  of the first lever  240  is in contact with the first portion  232 L of the first cam  232 , and one end  311  of the second cover  310  is in contact with the first portion  332 L of the second cam  332 . Therefore, the first cover  210  and the second cover  310  may stand by in a state in which the first cover  210  closes the first to fourth light windows  1221  to  1224 , and the second cover  310  closes the first to third sensors  161  to  163 . 
     When a printing mode starts from the standby mode, the controller may rotate the driving shaft  120  of the motor  100  in the first rotation direction R 11  in operation S 21 . 
     The controller may rotate the driving shaft  120  in the first rotation direction R 11  to rotate the first cam gear  230  in the fourth rotation direction R 22 . 
     The first cover  210  of the first shutter part  200  may open the first to fourth light windows  1221  to  1224  of the exposing unit  12  through the driving force of the driving shaft  120 , and the driving force of the driving shaft  120  transferred to the second shutter part  300  is blocked, such that the second shutter part  300  maintains a position at which the second cover  310  closes the first to third sensors  161  to  163  in operation S 31 . 
     As an example, the first cam gear  230  may rotate in the fourth rotation direction R 22  due to the rotation of the driving shaft  120  in the first rotation direction R 11 , such that one end  241  of the first lever  240  in a state in which it is in contact with the first portion  232 L of the first cam  232  is pushed in the first direction  240   a . The other end  242  of the first lever  240  moving in the first direction  240   a  may push the inclined part  214  of the first cover  210 , such that the first cover  210  moves in the first open direction  210   b.    
     As illustrated in  FIG. 13B , the first cam gear  230  rotates by 180° in a state of  FIG. 13A , such that one end  241  of the first lever  240  is in contact with the second portion  232 H of the first cam  232 , and the first cover  210  opens the first to fourth light windows  1221  to  1224 . 
     The controller may control the motor  100  so that the driving shaft  120  does not rotate during a period in which the printing is performed, thereby maintaining a state in which the first to fourth light windows  1221  to  1224  are opened. 
     When the driving shaft  120  rotates in the first rotation direction R 11 , the one-way clutch gear  331  of the second cam gear  330  may rotate in the third rotation direction R 21 . 
     In a case in which the one-way clutch gear  331  rotates in the third rotation direction R 21 , the one-way clutch gear  331  blocks the driving force transferred to the second cam  332  through the one-way bearing  3312 , such that the second cam  322  does not rotate, but stands by. 
     As illustrated in  FIG. 13B , even though the first cam  232  rotates by 180° due to the rotation of the driving shaft  120  in the first rotation direction R 11 , the second cam  332  does not rotate, but may maintain a position in the standby mode. Therefore, the second cover  310  maintains a state in which it closes the first to third sensors  161  to  163 . 
     The image forming apparatus  1  performs the printing in operation S 41 . 
     In a case in which the image forming apparatus  1  is operated in the printing mode, the first to fourth light windows  1221  and  1224  are opened through the first cover  210 , such that the electrostatic latent images may be formed on the first to fourth photoreceptors  131  to  134 . 
     In a case in which the image forming apparatus  1  is operated in the printing mode, the transfer of the driving force to the second shutter part  300  is blocked through the one-way clutch gear  331 , such that the second cover  310  may maintain the state in which it closes the first to third sensors  161  to  163 . Therefore, the first to third sensors  161  to  163  that are not operated in the printing mode are maintained in a state in which they are closed by the second cover  310 , such that pollution of the first to third sensors  161  to  163  due to pollutants such as the toners, and the like, may be effectively reduced prevented. 
     When the printing mode ends, the controller rotates the driving shaft  120  in the first rotation direction R 11  in operation S 51 . 
     The first cover  210  closes the first to fourth light windows  1221  to  1224  through the driving force of the driving shaft  120 , and the driving force of the driving shaft  120  transferred to the second shutter part  300  is blocked, such that the second cover  310  maintains a position at which it closes the first to third sensors  161  to  163  in operation S 61 . 
     As an example, the first cam gear  230  rotates in the fourth rotation direction R 22  due to the rotation of the driving shaft  120  in the first rotation direction R 11 , such that one end  241  of the first lever  240  in a state in which it is in contact with the second portion  232 H of the first cam  232  is released from being pressed from the first cam  232 . 
     The first lever  240  moves in the second direction  240   b  by the elastic force of the lever elastic member  250 , and the first cover  210  moves in the first close direction  210   a  by the elastic force of the first elastic member  220 . 
     As illustrated in  FIG. 13C , the first cam gear  230  again rotates by 180° in a state of  FIG. 13B , such that one end  241  of the first lever  240  is in contact with the first portion  232 L of the first cam  232 . Therefore, the first cover  210  closes the first to fourth light windows  1221  to  1224 . 
     When the driving shaft  120  rotates in the first rotation direction R 11 , the one-way clutch gear  331  of the second cam gear  330  rotates in the third rotation direction R 21 , and the driving force transferred to the second cam  332  is blocked through the one-way bearing  3312 , such that the second cam  332  does not rotate. 
     As illustrated in  FIG. 13C , even though the first cam  232  again rotates by 180° due to the rotation of the driving shaft  120  in the first rotation direction R 11 , the second cam  332  does not rotate, but may maintain a position in the standby mode. Therefore, the second cover  310  maintains a state in which it closes the first to third sensors  161  to  163 . 
     The controller controls the motor  100  so that the driving shaft  120  does not rotate after the first to fourth light windows  1221  to  1224  are closed by the first cover  210  due to an end of the printing mode, such that the image forming apparatus  1  may enter the standby mode in a state in which the first to fourth light windows  1221  to  1224  and the first to third sensors  161  to  163  are closed. 
     When the ACR mode starts, such as from the standby mode of the image forming apparatus  1 , the controller rotates the driving shaft  120  of the motor  100  in the second rotation direction R 12  in operation S 22 . 
     The controller may rotate the driving shaft  120  in the second rotation direction R 12  to rotate the first cam gear  230  in the third rotation direction R 21 . 
     Through the driving force of the driving shaft  120 , the first cover  210  of the first shutter part  200  moves to open the first to fourth light windows  1221  to  1224  of the exposing unit  12 , and the second cover  310  of the second shutter part  300  moves to open the first to third sensors  161  to  163  in operation S 32 . 
     As an example, the first cam gear  230  rotates in the third rotation direction R 21  due to the rotation of the driving shaft  120  in the second rotation direction R 12 , such that one end  241  of the first lever  240  in a state in which it is in contact with the first portion  232 L of the first cam  232  is pushed in the first direction  240   a . The other end  242  of the first lever  240  moving in the first direction  240   a  pushes the inclined part  214  of the first cover  210 , such that the first cover  210  moves in the first open direction  210   b.    
     As illustrated in  FIG. 14B , the first cam gear  230  rotates by 180° in a state of  FIG. 14A , such that one end  241  of the first lever  240  is in contact with the second portion  232 H of the first cam  232 , and the first cover  210  opens the first to fourth light windows  1221  to  1224 . 
     When the driving shaft  120  rotates in the second rotation direction R 12 , the first cam gear  230  rotates in the third rotation direction R 21 , and at the same time, the one-way clutch gear  331  of the second cam gear  330  rotates in the fourth rotation direction R 22 . 
     In a case in which the one-way clutch gear  331  rotates in the fourth rotation direction R 22 , the one-way bearing  3312  transfers the driving force to the second cam  332 , such that the second cam  332  also rotates in the fourth rotation direction R 22 . 
     One end  331  of the second cover  310  in a state in which it is in contact with the first portion  332 L of the second cam  332  is pushed in the second open direction  310   b , such that the second cover  310  moves in the second open direction  310   b.    
     As illustrated in  FIG. 14B , the second cam gear  330  rotates by 180° in a state of  FIG. 14A , such that one end  311  of the second cover  310  is in contact with the second portion  332 H of the second cam  332 , and the second cover  310  thus opens the first to third sensors  161  to  163 . 
     The controller controls the motor  100  so that the driving shaft  120  does not rotate during a period in which the ACR mode progresses. Therefore, the first to fourth light windows  1221  to  1224  are maintained in an open state. 
     In the ACR mode, the exposing unit  12  may form electrostatic latent images for predetermined measuring marks on the first to fourth photoreceptors  131  to  134  through the first to fourth light windows  1221  to  1224 , and may form predetermined measuring marks for the ACR on the transfer belt  151 . 
     The image forming apparatus  1  performs the ACR in operation S 42 . 
     The first to third sensors  161  to  163  are opened, such that the first to third sensors  161  to  163  may sense the measuring marks formed on the transfer belt  151  and thus perform alignment and correction on the color toner image. 
     When the ACR mode ends, the controller rotates the driving shaft  120  in the second rotation direction R 12  in operation S 52 . 
     Through the driving force of the driving shaft  120 , the first cover  210  moves in the first close direction  210   a  to close the first to fourth light windows  1221  to  1224 , and the second cover  310  moves in the second close direction  310   a  to close the first to third sensors  161  to  163  in operation S 62 . 
     As an example, the first cam gear  230  rotates in the third rotation direction R 21  due to the rotation of the driving shaft  120  in the second rotation direction R 12 , such that one end  241  of the first lever  240  in a state in which it is in contact with the second portion  232 H of the first cam  232  is released from being pressed from the first cam  232 . 
     The first lever  240  moves in the second direction  240   b  by the elastic force of the lever elastic member  250 , and the first cover  210  moves in the first close direction  210   a  by the elastic force of the first elastic member  220 . 
     As illustrated in  FIG. 14C , the first cam gear  230  again rotates by 180° in a state of  FIG. 14B , such that one end  241  of the first lever  240  is in contact with the first portion  232 L of the first cam  232 , and the first cover  210  thus closes the first to fourth light windows  1221  to  1224 . 
     When the driving shaft  120  rotates in the second rotation direction R 12 , the one-way clutch gear  331  of the second cam gear  330  rotates in the fourth rotation direction R 22 , and the driving force is transferred to the second cam  332  through the one-way bearing  3312 , such that the second cam  332  also rotates in the fourth rotation direction R 22 . 
     As illustrated in  FIG. 14C , the first and second cams  232  and  332  again rotate by 180° due to the rotation of the driving shaft  120  in the first rotation direction R 12 , such that the first to third sensors  161  to  163  are closed. 
     The controller may control the motor  100  so that the driving shaft  120  does not rotate after the first to fourth light windows  1221  to  1224  and the first to third sensors  161  to  163  are closed due to an end of the ACR mode, thereby allowing the image forming apparatus  1  to enter the standby mode. 
     As described above, in the image forming apparatus  1  according to an example, the first and second shutter parts  200  and  300  are connected together to the driving shaft  120  of the motor  100 , and the driving force is transferred from the motor  100  to the first and second shutter parts  200  and  300 , such that the first and second shutter parts  200  and  300  may be driven using only the single motor  100 . Therefore, the image forming apparatus  1  including the first and second shutter parts  200  and  300  may have a compact structure. 
     The second shutter part  300  may selectively rotate the second cam  332  depending on a rotation direction of the driving shaft  120  through the one-way clutch gear  331  to selectively open the first to third sensors  161  to  163 . 
     The image forming apparatus  1  may select a printing mode of maintaining a state in which the first to fourth light windows  1221  to  1224  are opened or closed and the first to third sensors  161  to  163  are closed and may select an ARC mode in which the first to fourth light windows  1221  to  1224  and the first to third sensors  161  to  163  are simultaneously opened or closed by only a simple control that changes the rotation direction of the driving shaft  120 , and be operated in the selected mode. 
     The first and second cam gears  230  and  330  may have the same gear ratio, such that they simultaneously rotate at the same rotation angle, and may thus indirectly sense an open or close state of the first cover  210  through the first to third sensors  161  to  163 . 
     As an example, the first cam gear  230  and the second cam gear  330  may have the same gear ratio, such that the rotation angle of the first cam gear  230  and the rotation angle of the second cam gear  330  may be the same as each other. 
     An amount of light sensed by the first to third sensors  161  to  163  becomes a maximum or a minimum when the first to third sensors  161  to  163  are opened or closed by the second cover  310  due to the rotation of the driving shaft  120  in the second rotation direction R 12 . 
     The controller may decide that a point in time in which an amount of light sensed by the first to third sensors  161  to  163  becomes maximum or minimum is a point in time in which the first to fourth light windows  1221  to  1224  are opened or closed by the first cover  210 . 
     In an example, in the operation in the ACR mode, the controller may decide that a point in time in which an amount of light introduced into the first to third sensors  161  to  163  becomes maximum is a point in time in which the first to third sensors  161  to  163  and the first to fourth light windows  1221  to  1224  are opened. Therefore, the controller may control the motor  100  so that the driving shaft  120  stops, thereby performing the ACR mode. 
     As the driving shaft  120  rotates in the second rotation direction R 12  due to an end of the ACR mode, the controller may decide that a point in time in which an amount of light sensed by the first to third sensors  161  to  163  becomes minimum is a point in time in which the first to third sensors  161  to  163  and the first to fourth light windows  1221  to  1224  are closed. Therefore, the controller may control the motor  100  so that the driving shaft  120  stops, thereby allowing the image forming apparatus  1  to enter the standby mode, or may change the rotation direction of the driving shaft  120  into the first rotation direction R 11 , thereby starting the printing mode. 
     The shutter unit  10  may accurately decide whether the first to fourth light windows  1221  to  1224  are opened or closed by the first cover  210  and the first to third sensors  161  to  163  are opened or closed by the second cover  310  through the sensing unit  16  without using a separate sensor for sensing states of the first and second covers  210  and  310 . 
     Since the shutter unit  10  may perform the driving and the control on the first and second shutter parts  200  and  300  in the printing mode and the ACR mode through the single motor  100 , the pollution of the first to fourth light windows  1221  to  1224  and the first to third sensors  161  to  163  may be effectively reduced or prevented by using the shutter unit  10  having a simple structure. 
     An entire size of the image forming apparatus  1  including the shutter unit  10  may be reduced, a structure of the image forming apparatus  1  may become compact, and a cost required for manufacturing the image forming apparatus  1  may be efficiently reduced. 
     Although diverse examples have been individually described hereinabove, the respective examples are not necessarily implemented singly, but may also be implemented so that configurations and operations thereof are combined with those of one or more other exemplary embodiments. 
     Although examples of the present disclosure have been illustrated and described hereinabove, the present disclosure is not limited to the examples described above, but may be variously modified by those skilled in the art to which the present disclosure pertains without departing from the scope and spirit of the disclosure as claimed in the claims. These modifications should also be understood to fall within the technical spirit and scope of the present disclosure.