JP6127783B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to a technique for improving image definition in an image forming apparatus.

  In an image forming apparatus using an electrophotographic system such as a printer or a copying machine, the surface of a photoconductor is uniformly charged, and then an electrostatic latent image is written by irradiating the photoconductor with a laser beam. Thereafter, toner is supplied onto the electrostatic latent image by the developing device to form a toner image. The toner image is transferred and fixed on the final medium.

  As an apparatus for irradiating a photosensitive member with laser light, an optical scanning apparatus including a light emitting unit that emits laser light and a rotating polygon mirror is known. Laser light emitted from the light emitting unit is reflected by a rotating polygon mirror. Due to the rotation of the polygon mirror, the irradiation position of the laser light changes in the axial direction (first scanning direction, main scanning direction) of the photosensitive member. In addition, the photoconductor rotates with the irradiation of the laser beam. Due to the rotation of the photosensitive member, the irradiation position of the laser light changes in the second scanning direction (sub-scanning direction) orthogonal to the first scanning direction. Therefore, a two-dimensional electrostatic latent image with a dot pattern is formed on the photoreceptor.

  Here, in an image forming apparatus capable of forming a full-color image, a plurality of image formations are performed in order to form toner images of respective colors (for example, yellow (Y), magenta (M), cyan (C), and black (K)). A unit is provided. A developing device provided in each image forming unit is usually provided with toner containers of different colors. However, it is possible to attach a toner container of the same color toner to all the developing devices. In this way, when the image forming apparatus only forms a monochrome image (single color image), the number of replacements of the toner container can be reduced.

  By the way, as an image forming apparatus, an apparatus capable of changing the definition (resolution) of an image to be formed is generally used. For example, there is one that can switch between a high-definition mode that forms an image at 1200 dpi and a normal-definition mode that forms an image at 600 dpi. When an image of 1200 dpi is formed by such an image forming apparatus, the interval between the laser light irradiation positions in the main scanning direction and the sub-scanning direction is halved as compared with the case of forming an image of 600 dpi. That is, each photoconductor is irradiated with laser light at a high density. Specifically, if it is 1200 dpi in an area for one pixel of 600 dpi, laser light is emitted for four pixels.

  The laser beam irradiation density in the main scanning direction is changed by changing the dot clock frequency (pulse rate) of the laser beam. If the dot clock frequency is doubled, the irradiation density in the main scanning direction is doubled. However, in this case, since the laser beam is irradiated at a high rate, the operation load of the light emitting unit that emits the laser beam increases.

  On the other hand, the laser beam irradiation density in the sub-scanning direction is changed by changing the rotation speed of the polygon mirror or the system speed (linear speed, paper passing speed). If the rotation speed of the polygon mirror is doubled without changing the system speed, the irradiation density in the sub-scanning direction is also doubled. However, in this case, the cost increases due to an increase in driving power of the polygon mirror. Even if the system speed is halved without changing the rotational speed of the polygon mirror, the irradiation density in the sub-scanning direction is doubled. However, in this case, there is a demerit that the time required for image formation increases.

  Incidentally, Patent Document 1 below describes an image forming apparatus capable of forming an image with a higher definition than the normal definition only when a black monochrome image is formed. In the image forming apparatus described in this document, one laser beam is applied to each of the four photoconductors for each color when forming a color image. On the other hand, at the time of forming a monochrome image, the optical paths of the three laser beams for irradiating the photosensitive member except for the black one in the four photosensitive members are changed so that all the laser beams are applied to one photosensitive member for black. Yes. According to such a technique, it is said that a high-definition monochrome image can be formed.

JP 2001-296492 A

  However, in the technique described in the above-mentioned document, it is necessary to greatly change the optical path of the laser beam irradiated to the photoconductor other than the one for black, so that it is necessary to arrange many mirrors in the optical scanning device. Become. This complicates the configuration of the optical scanning device and enlarges the optical scanning device.

  The present invention has been made in view of the above circumstances. That is, the problem is that a single color image with high definition can be obtained without excessively complicating the optical scanning device and without changing the system speed, the rotation speed of the polygon mirror, or the frequency of the dot clock. An object of the present invention is to provide an image forming apparatus capable of forming the above.

The image forming apparatus of the present invention, which has been made for the purpose of solving this problem, includes a photoconductor rotating about an axis, a charger for charging the surface of the photoconductor, a developing device for supplying toner onto the surface of the photoconductor, A plurality of image forming units, a light emitting unit that emits laser light, and a rotating polygon mirror, and the laser light emitted from the light emitting unit is reflected by the polygon mirror and is charged by a charger on the photosensitive member. An optical scanning device that irradiates the charged portion while scanning in the axial direction of the photosensitive member is provided. An electrostatic latent image is formed on each photosensitive member of a plurality of image forming units by irradiation of laser light, In an image forming apparatus that forms an image by superimposing toner images formed on an electrostatic latent image, a plurality of image forming units have toner containers of different colors attached to each developer. Normal color mode, and a multi-single color state in which toner containers of the same color toner are attached to all developing units, and a normal definition mode for forming an image with a first definition. A definition setting unit for selecting one of a plurality of definition modes including at least a high definition mode for forming an image with a second definition higher than the first definition, and a plurality of image forming units A multi-single-color high-definition mode control unit for performing image formation in the multi-single-color high-definition mode when the multi-color state is selected and the high-definition mode is selected in the definition setting unit; In the multi-single color high-definition mode, the irradiation position of the laser beam in the plurality of photoconductors belonging to the first group is the second of the plurality of photoconductors that does not belong to the first group. To those belonging to the group One pixel in the high-definition mode for one of the first scanning direction caused by the rotation of the polygon mirror and the second scanning direction caused by the rotation of the photoconductor with respect to the irradiation position of the laser beam. while a partial shift position, as definition of the definition for one of the scanning direction the in the normal definition mode, intends line toner image formed on the plurality of image forming units.

  According to the image forming apparatus of the present invention, toner images of the same color are formed on a plurality of photoconductors while being shifted by one pixel in the high-definition mode in the first scanning direction or the second scanning direction. An image is formed by superimposing toner images. Therefore, even if the toner image is formed with the definition in the shifted scanning direction as the definition in the normal definition mode, the definition in the scanning direction in the image in which the toner images are superimposed is the same in the high definition mode. It becomes the definition of. Accordingly, when the laser beam irradiation position is shifted in the first scanning direction due to the rotation of the polygon mirror, the definition in the first scanning direction can be improved without increasing the frequency of the dot clock of the laser light. . Also, when the laser beam irradiation position is shifted in the second scanning direction due to the rotation of the photoconductor, the rotation speed of the polygon mirror is increased without decreasing the system speed (rotation speed of the photoconductor). Therefore, the definition in the second scanning direction can be improved. In addition, in order to improve the definition, it is not necessary to change the optical path of the laser beam so that the laser beam is irradiated to a photoconductor that is different from the irradiation destination at the time of color image formation. There is nothing.

In the image forming apparatus according to the first aspect of the present invention, a plurality of photoconductors belong to the first group and the second group, respectively. In the multi-single color high-definition mode, the first group of photoconductors is further added. Among these, the irradiation position of the laser beam in the members belonging to the first small group and the members belonging to the first small group out of the second group of photosensitive members, the remainder not belonging to the first small group in the first group of photosensitive members. The first scanning is performed with respect to the irradiation position of the laser light in the second subgroup belonging to the second subgroup and the second group of photoconductors belonging to the second subgroup that does not belong to the first subgroup. The other scanning direction of the direction and the second scanning direction is shifted by one pixel in the high definition mode, and the definition in the other scanning direction is also the definition in the normal definition mode. Toner image formation with multiple image forming units And wherein the Ukoto. Since such a configuration, that have resolution for both the scanning direction of the first scanning direction and a second scanning direction is improved.

In the first aspect, the other scanning direction is the first scanning direction. In the multi-single-color high-definition mode, the phase of the dot clock of the laser light applied to both the first small group of photoconductors is set as follows: It is desirable to shift by one clock cycle in the high definition mode with respect to the phase of the dot clock of the laser light applied to both the second small group photoreceptors. However, the dot clock of the laser beam itself is a period in the normal definition mode. With this configuration, the irradiation position of the first small group of photoconductors and the irradiation position of the second small group of photoconductors are shifted by one pixel in the high-definition mode in the first scanning direction. Because you can.

Alternatively , in the first aspect , the other scanning direction is the first scanning direction, and the optical scanning device includes a plurality of polygon mirrors. In the multi-single color high-definition mode, both of the plurality of polygon mirrors are included. A configuration in which the rotation phase of the one corresponding to the small group of photoconductors is shifted by an angle corresponding to the shift of one pixel in the high-definition mode with respect to the rotation phase of the one corresponding to the second small group of photoconductors. It is good. Even in this configuration, the irradiation position of the first small group of photoconductors and the irradiation position of the second small group of photoconductors are shifted by one pixel in the high-definition mode in the first scanning direction. Because it can.

In the first embodiment, the one scanning direction is a second scanning direction, the multi-single Irodaka on an optical path from the light emitting portion to the photoreceptor of at least one group of the first group and the second group The optical path changing member is arranged in the definition mode, and the optical path changing member changes the irradiation position on the first group of photoconductors in the multi-single color high definition mode to the irradiation position on the second group of photoconductors. On the other hand, it is desirable to shift by one pixel in the high definition mode in the second scanning direction. If comprised in this way, the irradiation position of the 1st group photoconductor and the irradiation position of the 2nd group photoconductor can be made into the position which shifted 1 pixel in the high definition mode about the 2nd scanning direction. Because.

In the image forming apparatus according to the second aspect of the present invention, the one scanning direction is the second scanning direction, and light from the light emitting unit to each of the photosensitive members of at least one of the first group and the second group. An optical path changing member disposed on the road in the multi-single-color high-definition mode, and the optical path-changing member determines an irradiation position on the first group of photosensitive members in the multi-single-color high-definition mode. The second scanning direction is shifted by one pixel in the high-definition mode with respect to the irradiation position on the photoconductor, and the amount of laser light applied to the first group of photoconductors is applied to the second group of photoconductors. The optical path changing member is disposed only on the optical path from the light emitting unit to each of the first photosensitive members, and in the multi-single color high-definition mode, the optical path changing member is less than the amount of laser light to be irradiated. By taking a different posture than in the degree mode, The irradiation position of the first group of photoconductors in the multi-color high-definition mode is higher in the second scanning direction than the irradiation position of the first group of photoconductors in the definition mode other than the multi-single-color definition mode. Ru der those shifted by one pixel in the definition mode.

There is a possibility that the light quantity of the laser light may be reduced by changing the optical path in the optical path changing member. For this reason, there is a need to leave room for an increase in the light amount of the laser light whose optical path is changed. There is much room for increasing the amount of light as the amount of laser light decreases. Thus in Rukoto be configured as described above, even if the amount of the laser beam by the optical path changing is insufficient, the laser characteristics by increasing the light intensity (light quantity stability and pulse width reduction resistance) improved if.

In the image forming apparatus according to the third aspect of the present invention, the one scanning direction is the second scanning direction, and on the optical path from the light emitting unit to each of the photosensitive members of at least one of the first group and the second group. In the multi-single color high-definition mode, the optical path changing member determines the irradiation position on the first group of photoconductors in the multi-single-color high-definition mode. The optical path length of the laser light irradiated to the first group of photoconductors is shifted from the irradiation position on the body by one pixel in the high-definition mode in the second scanning direction. It is less than the optical path length of the irradiated laser beam, and the optical path changing member is disposed only on the optical path from the light emitting portion to each of the first group of photoconductors. By taking a different posture than in the fineness mode , The irradiation position of the first group of photoconductors in the multi-single color high-definition mode with respect to the second scanning direction with respect to the irradiation position of the first group of photoconductors in the definition mode other than the multi-single-color definition mode. It may be shifted by one pixel in the high definition mode.

  The longer the optical path length of the laser beam from the light emitting part to the photoconductor, the higher the amount of laser beam already. Therefore, there is no room for future improvement. Therefore, if the optical path of a laser beam with a short optical path length that leaves room for an increase in the light amount is changed, even if the light amount of the laser light is insufficient due to the optical path change, the laser characteristics will be improved by increasing the light amount. Can do.

In the image forming apparatus according to the fourth aspect of the present invention, the one scanning direction is the second scanning direction, and on the optical path from the light emitting unit to each of the photosensitive members of at least one of the first group and the second group. In the multi-single color high-definition mode, the optical path changing member determines the irradiation position on the first group of photoconductors in the multi-single-color high-definition mode. The first scanning direction is shifted by one pixel in the high-definition mode in the second scanning direction with respect to the irradiation position on the body, and a reflecting mirror is disposed on the optical path of the laser light from the light emitting portion to the photosensitive member. The number of reflections of the laser light applied to the photosensitive member by the reflecting mirror is less than the number of reflections of the laser light applied to the second group of photosensitive members by the reflecting mirror, and the optical path changing member is moved from the light emitting unit to the first group. It is arranged only on the optical path to each photoconductor In addition, the multi-single-color high-definition mode takes a different attitude from the other fine-definition modes so that the irradiation position of the first group of photoconductors in the multi-single-color high-definition mode can be changed to the multi-single-color high-definition mode. The irradiation position of the first group of photoconductors in the definition mode other than the mode may be shifted by one pixel in the high definition mode in the second scanning direction.

  As the number of reflections of the laser beam from the light emitting unit to the photosensitive member increases, the light amount of the laser beam is already increased in consideration of a decrease in the light amount due to reflection. Therefore, there is no room for future improvement. Therefore, if the optical path of the laser beam with a small number of reflections, where there is room for increase in the amount of light, is changed, even if the laser beam quantity is insufficient due to the optical path change, the laser characteristics will be improved by increasing the light quantity. Can do.

  In the image forming apparatus of the present invention, a color information acquisition unit that acquires toner color information in a toner container attached to each developing device, and a plurality of images based on the color information acquired by the color information acquisition unit. A state determination unit that determines whether or not the forming unit is in a multi-single color state, and the definition setting unit always switches to a high-definition mode when the state determination unit determines that it is in a multi-single color state. It is desirable to choose. This is because with such a configuration, image formation with a single color can always be performed with high definition.

  According to the present invention, a single color image can be formed with high definition without making the optical scanning device excessively complicated and without changing the system speed, the rotation speed of the polygon mirror, or the frequency of the dot clock. There is provided an image forming apparatus that enables the above.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment. 2 is a schematic configuration diagram of an optical scanning device provided in the image forming apparatus. FIG. FIG. 3 is a sectional view taken along line III-III in FIG. 2. It is a block diagram showing a control system related to the exposure operation of the image forming apparatus. 6 is a flowchart illustrating processing during image formation performed by the image forming apparatus. FIG. 5 is a schematic diagram of a dot pattern when an image is formed with a resolution of 600 dpi. It is the schematic of a dot pattern at the time of forming an image with a resolution of 1200 dpi It is the schematic for demonstrating the positional relationship of the irradiation position of the laser beam to each photoconductor. FIG. 9 is a schematic diagram showing a dot pattern when an image is formed by attaching a toner container of the same color toner to each developing device and controlling the irradiation position of laser light to each photoconductor as shown in FIG. 8. 6 is a flowchart illustrating processing at the time of image formation performed by an image forming apparatus according to a modification. It is a schematic block diagram of the image forming apparatus which concerns on the other modification.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the best mode for embodying the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a diagram illustrating a configuration example of an image forming apparatus according to the present invention. An image forming apparatus 1 shown in FIG. 1 is an electrophotographic tandem digital color printer (hereinafter simply referred to as “printer”). Of course, in addition to the printer, the present invention can also be applied to a copier having a scanner or a multi-function machine having these functions combined.

  The image forming apparatus 1 includes an image forming unit 2 that forms a toner image on a sheet (recording medium, final medium), and a paper feeding unit 80 disposed below the image forming unit 2. The paper feed unit 80 includes a paper feed cassette 81 in which the paper P is accommodated. Each sheet cassette 81 stores sheets P of different sizes in a stacked state. The paper P in the paper feed cassette 81 is sent to a secondary transfer area 25 described later by a paper feed roller 82 and the like.

  The image forming unit 2 includes an intermediate transfer belt 3. The intermediate transfer belt 3 is stretched around a driving roller 4 and a tension roller 5. The intermediate transfer belt 3 rotates counterclockwise as the driving roller 4 rotates. The tension roller 5 urges the intermediate transfer belt 3 from the inside toward the outside. Therefore, tension is always applied to the intermediate transfer belt 3.

  Below the intermediate transfer belt 3, four process units (corresponding to image forming units) 10Y, 10M, and 10C respectively corresponding to the colors of yellow (Y), magenta (M), cyan (C), and black (K). , 10K. The process units 10Y, 10M, 10C, and 10K are arranged in this order along the moving direction of the intermediate transfer belt 3. Each of the process units 10Y, 10M, 10C, and 10K performs the same function except that the color of the toner image formed during color image formation is different. Therefore, the configuration is the same. In the following description, the subscripts representing each color are omitted except when it is necessary to distinguish between yellow (Y), magenta (M), cyan (C), and black (K).

  Each process unit 10 has a photoreceptor 11. Around the photoconductor 11, a charger 12, a developing device 14, and a cleaning device 15 are arranged in order along the rotation direction during image formation (also referred to as a positive rotation direction, clockwise in the figure).

  The charger 12 is a scorotron, for example, and uniformly charges the surface of the photoreceptor 11.

  The developing device 14 converts an electrostatic latent image formed on the photoconductor 11 by an optical scanning device 30 described later into a visible image with toner. That is, a toner image is formed on the photoconductor 11. A toner container 17 is attached to each developing device 14Y, 14M, 14C, 14K. Each toner container 17 is provided with a chip component (storage unit) that stores information about the color of toner in the container. When a color image is to be formed by the image forming apparatus 1, toner containers 17Y, 17M, 17C, and 17K for toners of different colors (Y, M, C, and K) are provided in the developing units 14Y, 14M, 14C, and 14K. Install. This state is referred to as a normal color state of the process unit 10.

  However, instead of the toner container 17Y for Y toner, a toner container 17K for K toner can be attached to the developing device 14Y. Further, a toner container 17K for K color toner can be attached to the developing device 14M in place of the toner container 17M for M color toner. Further, a toner container 17K for K color toner can be attached to the developing device 14C in place of the toner container 17C for C color toner. A state in which the toner containers 17K of the same color (K color) toner are attached to all the developing devices 14Y, 14M, 14C, and 14K is referred to as a multi-single color state of the process unit 10. When the image forming apparatus 1 is not used for forming a color image, it is preferable to set the multi-single color state. It should be noted that any color toner container may be attached to all the developing devices 14. By doing so, it is possible to realize a multi-single color state that can be printed with the Y color, a multi-single color state that can be printed with the M color, and a multi-single color state that can be printed with the C color.

  The cleaning device 15 scrapes off residual toner remaining on the photoconductor 11 after the primary transfer.

  Further, as shown in FIG. 1, primary transfer rollers 20Y, 20M, 20C, and 20K for primary transfer are located at positions facing the respective photoreceptors 11Y, 11M, 11C, and 11K with the intermediate transfer belt 3 interposed therebetween. Is provided. The toner images of the respective colors formed on the photoreceptors 21Y, 21M, 21C, and 21K rotate counterclockwise in FIG. 1 by applying a bias potential to the primary transfer rollers 20Y, 20M, 20C, and 20K. The images are sequentially transferred and superimposed on the intermediate transfer belt 3. As a result, a superimposed toner image is formed on the intermediate transfer belt 3 by superimposing the toner images of the respective colors. The superimposed toner image becomes a color image when the image forming apparatus 1 is in the normal color state, and becomes a monochrome image when the image forming apparatus 1 is in the multi-single color state.

  Further, a secondary transfer roller 24 for secondary transfer is pressed against the portion of the intermediate transfer belt 3 supported by the driving roller 4. A nip portion between the secondary transfer roller 24 and the intermediate transfer belt 3 becomes a secondary transfer region 25. In the secondary transfer region 25, the toner image transferred onto the intermediate transfer belt 3 is transferred onto the paper P.

  A fixing unit 90 is provided above the secondary transfer region 25. The fixing unit 90 includes a heating roller 92 that has a hollow cylindrical shape and includes a heater 91 therein, and a pressure roller 93 that is pressed against the heating roller 92 and rotates. The toner image is fixed to the paper P when the paper P on which the toner image is transferred by the secondary transfer passes through the nip formed by the heating roller 92 and the pressure roller 93. The paper P after the toner image is fixed is discharged to a paper discharge tray 95.

  Next, the optical scanning device 30 will be described in detail. The optical scanning device 30 is disposed below the process unit 10. The optical scanning device 30 irradiates each of the photoconductors 11Y, 11M, 11C, and 11K after charging with a laser beam reflected by the polygon mirror 34 while changing its traveling direction by the reflecting mirror 45 and before development. is there. In FIG. 1, LY is a laser beam irradiated to the photoconductor 11Y, LM is a laser beam irradiated to the photoconductor 11M, LC is a laser beam irradiated to the photoconductor 11C, and LK is irradiated to the photoconductor 11K. The laser light to be shown is shown respectively. In the following description, it is described as laser light L unless it is particularly necessary to distinguish which photoconductor 11 is irradiated. By irradiating each laser beam L, an electrostatic latent image corresponding to image data to be formed is formed on each photoconductor 11.

  The laser beam LY is reflected by the two reflecting mirrors 45 and applied to the photoconductor 11Y. The laser beam LM is reflected by the two reflecting mirrors 45 and applied to the photoconductor 11M. The laser beam LC is reflected by the three reflecting mirrors 45 and applied to the photoconductor 11C. Further, the laser beam LK is reflected by a single reflecting mirror 45 and is applied to the photoconductor 11K.

  FIG. 2 is a diagram showing an outline of a detailed configuration of the optical scanning device 30. However, in FIG. 2, the reflecting mirror 45 is omitted. As shown in FIG. 2, the optical scanning device 30 includes a laser diode (an example of a light emitting unit) 31, a collimator lens 32, a slit 33, a polygon mirror 34, a scan start sensor 35, and two scanning lenses. 36a, 36 second subgroup.

  The laser diode 31 emits laser light (laser beam) L. The collimator lens 32 focuses the diffused laser beam L emitted from the laser diode 31 into parallel light. The slit 33 shapes the laser light L that has passed through the collimator lens 32. The laser light L that has passed through the slit 33 enters the polygon mirror 34.

  The polygon mirror 34 is a regular polygonal plate-like member, and each side surface thereof is a reflecting surface. The polygon mirror 34 rotates at a constant speed by driving a polygon motor 38 (see FIG. 4). As a result, the laser beam L reflected by the reflecting surface is scanned in the axial direction (main scanning direction, first scanning direction) of the photosensitive member 11. The rotational speed of the polygon motor 38 is controlled by the CPU 50 (see FIG. 4). The scanning for one line in the main scanning direction is performed while changing the scanning position in the sub scanning direction by the rotation of the photosensitive member 11. Therefore, a two-dimensional electrostatic latent image is formed on the photoreceptor 11.

  The laser beam L reflected by the polygon mirror 34 is emitted from the window portion 37 through two scanning lenses 36a and 36b (cylindrical lens and fθ lens). The window portion 37 is a portion in which a transparent plate (for example, a glass plate or an acrylic plate) is fitted in the opening.

  The laser beam L that has passed through the window portion 37 is reflected by the galvanometer mirror 40 and irradiated onto the photosensitive member 11. The galvanometer mirror (an example of an optical path changing member) 40 is provided with an electromagnet, and the tilt angle of the mirror can be changed in the direction of arrow a shown in FIG. 3 by changing the magnitude of the current flowing through the electromagnet. is there. The tilt angle of the galvanometer mirror 40 is controlled by the CPU 50 (see FIG. 4). When the tilt angle of the galvanometer mirror 40 is changed, the irradiation position of the laser beam L on the photosensitive member 11 changes in the sub-scanning direction (second scanning direction, paper passing direction). In this embodiment, the galvanometer mirror 40 is disposed only on the optical path of the laser light LK and the optical path of the laser light LY, and is not disposed on the optical path of the laser light LM and the optical path of the laser light LC. The galvanometer mirror 40 takes different postures in a multi-single-color high-definition mode described later and other definition modes. The posture taken in the definition mode other than the multi-single color high-definition mode is called the standard posture, and the posture taken in the multi-single color high-definition mode is called the changed posture. The irradiation position on the photoconductor 11K and the photoconductor 11Y when the galvanometer mirror 40 is set to the changed posture is the sub-scanning direction with respect to the irradiation position on the photoconductor 11K and the photoconductor 11Y when the galvanometer mirror 40 is set to the standard posture. Is a position shifted by one pixel in the high definition mode.

  The galvanometer mirror 40 may be disposed at a position where the laser light L before being reflected by the reflecting mirror 45 is reflected, or may be disposed at a position where the laser light L after being reflected by the reflecting mirror 45 is reflected. Also good. Furthermore, it may be arranged in place of the reflecting mirror 45.

  Further, as shown in FIG. 2, the scan start sensor 35 is disposed in the vicinity of one end of the photoconductor 11. This is because the laser beam L reflected by the polygon mirror 34 is incident on the scan start sensor 35 at a timing before being irradiated onto the photoconductor 11. The scan start sensor 35 is a light detection sensor such as a photodiode, and emits an SOS signal when the laser light L is incident. Thereby, the scanning start timing when the laser beam L is scanned onto the photosensitive member 11 is detected.

  Subsequently, an exposure-related control system of the image forming apparatus 1 of the present embodiment will be described. This control system is configured as shown in FIG. The optical scanning device 30 in FIG. 4 includes a laser diode drive circuit 56, a polygon motor 38, and a PLL control circuit 62 in addition to those shown in FIG.

  The laser diode drive circuit 56 is a circuit that drives the laser diode 31. The polygon motor 38 is a motor that rotationally drives the polygon mirror 34. The PLL control circuit 62 is a circuit that rotates the polygon motor 38 at a constant speed.

4 includes the CPU 50, the storage device 51, the crystal oscillator 52, the dot clock generation circuit 53, the image data synchronization circuit 54, the light emission control circuit 55, the crystal oscillator 60, and the polygon clock generation. A circuit 61, a galvano mirror driving unit 63, and a photosensitive member driving unit 64 are provided. Of these, the CPU 50 and the storage device 51 may be shared with a control system other than the exposure relationship. The CPU 50 controls the overall operation of the control system. The storage device 51 stores various programs and data necessary for control.

  The dot clock generation circuit 53 is a circuit that generates a dot clock (pixel clock) based on the oscillation signal of the crystal oscillator 52. The image data synchronization circuit 54 is a circuit that sends an image data signal to the laser diode drive circuit 56 in synchronization with the dot clock supplied from the dot clock generation circuit 53. The image data synchronization circuit 54 also receives an SOS signal from the scan start sensor 35. Here, the image data is supplied from an external device such as a personal computer if it is a printer, or from a built-in scanner if it is a copier.

  The light emission control circuit 55 is a circuit that controls the light amount of the laser diode 31. Therefore, the light emission control circuit 55 has a function of causing the laser diode 31 to emit light with a desired amount of light via the laser diode drive circuit 56. Specifically, a light emission control signal is sent to the laser diode drive circuit 56. The light emission control circuit 55 receives the dot clock from the dot clock generator 24, the light amount detection signal from the laser diode 31, and the SOS signal from the scan start sensor 35.

  Thereby, the laser diode drive circuit 56 drives the laser diode 31 in accordance with the light emission control signal from the light emission control circuit 55 or the image data signal from the image data synchronization circuit 54.

  The polygon clock generation circuit 61 is a circuit that generates a polygon clock based on the oscillation signal of the crystal oscillator 60. The PLL control circuit 62 rotates the polygon motor 38 in accordance with the polygon clock. That is, the polygon motor 38 outputs an FG signal, which is a pulse signal synchronized with the rotation, to the PLL control circuit 62. The PLL control circuit 62 controls the polygon motor 38 so that the frequency of both signals becomes the same while comparing the polygon clock and the FG signal. As a result, the polygon motor 38 is rotated at a normal rotation speed. The lock detection signal input from the PLL control circuit 62 to the CPU 50 is output when it is determined that the polygon clock and the FG signal are rotating at a desired rotation speed.

  Further, the CPU 50 controls the tilt angle of the galvano mirror 40 via the galvano mirror driving unit 63. The galvanometer mirror driving unit 63 includes an electromagnet for changing the tilt angle of the galvanometer mirror 40. Further, the CPU 50 controls the rotational speed of the photoconductor 11 via the photoconductor drive unit 64. The photoconductor drive unit 64 includes an electric motor for driving the photoconductor 11. Further, the CPU 50 can acquire information on the color of the toner in the toner container 17 attached to each developing device 14 (color information) from each toner container 17. The color information is stored in a storage unit provided in the toner container 17. Based on this color information, the CPU 50 determines whether the process unit 10 is in the normal color state or the multi-single color state.

  Here, the image forming apparatus 1 of the present embodiment has a normal definition mode in which an image is formed with a first definition (here, 600 dpi resolution) and a second definition (here, 1200 dpi) higher than this. It is possible to take a high-definition mode in which image formation is performed at (resolution). The image forming apparatus 1 is set to the normal definition mode by default. Note that the image forming apparatus 1 may have a configuration capable of taking a definition mode other than the normal definition mode and the high definition mode. In this embodiment, the definition of the image forming apparatus 1 (selection of the normal definition mode or the high definition mode) can be performed by a user operating an operation unit (for example, a touch panel). .

  Next, the operation of the image forming apparatus 1 during image formation will be described based on the flowchart shown in FIG. As shown in FIG. 5, when forming an image, the CPU 50 first acquires setting information of the image quality mode (information of the set definition mode) (step S001), and whether or not it is set to the high definition mode. (S002). When the high definition mode is not set (NO in S002), since the normal definition mode is set, image formation is performed with the normal definition. That is, the image formation at the normal definition is performed without changing the system speed, the dot clock frequency (pulse rate), and the optical path of each laser beam L at the setting for image formation at 600 dpi (S003). S004). Here, the change of the optical path of the laser light L means the change of the irradiation position of the laser light L by changing the tilt angle of the galvano mirror 40 or the phase of the dot clock. Note that the irradiation position of the laser beam L on each photoconductor 11 in the normal definition mode is the position of the dot 70 shown in FIG.

  On the other hand, when the high-definition mode is set (YES in S002), the color information of the toner in the toner container 17 attached to each developing device 14 is acquired (S005), and the multi-single color state is set. It is determined whether or not (S006). If the normal color state is set instead of the multi-single color state (NO in S006), a color image is formed with high definition. Therefore, the system speed and the frequency of the dot clock are changed from the settings at the time of image formation at 600 dpi (S007), and high-definition image formation is performed (S009).

  Specifically, the system speed is set to 1/2 of 600 dpi. This doubles the definition in the sub-scanning direction (paper passing direction). The dot clock frequency is doubled. This doubles the definition in the main scanning direction (axial direction of the photoconductor 11). The optical path of each laser beam L is not changed. By performing such setting changes and forming an image, it is possible to form an image with a resolution of 1200 dpi as shown in FIG. In the case of 1200 dpi shown in FIG. 7, four dots 71 are formed in the region for one pixel of 600 dpi shown in FIG. That is, four pixels are formed.

  If it is determined in step S006 that the state is the multi-single color state (YES in S006), a monochrome image is formed with high definition (image formation is performed in the multi-single color high-definition mode). Therefore, the optical path of the laser beam L is changed from the setting in the normal definition mode (S008), and image formation with high definition is performed (S009). Note that the system speed and the dot clock frequency are not changed as set in the normal definition mode (S008).

  Image formation in the multi-single color high-definition mode is performed as follows. That is, as shown in FIG. 8, the irradiation positions of the laser beams LK and LY on the photoconductor 11K and the photoconductor 11Y (which belong to the first group among the plurality of photoconductors 11) are set as the photoconductor 11M and the photoconductor 11C (multiple In the high-definition mode in the sub-scanning direction (second scanning direction) with respect to the irradiation position of the laser beams LM and LC in the photosensitive member 11 of the photosensitive member 11 belonging to the second group which is a residue not belonging to the first group. The position is shifted by one pixel. Specifically, the attitude of the galvanometer mirror 40 is changed from the standard attitude to the changed attitude. Thereby, the irradiation position of the first group of photoconductors 11K and 11Y is shifted by one pixel in the high-definition mode downstream in the sub-scanning direction with respect to the irradiation position of the second group of photoconductors 11M and 11C. And

  At the same time, the laser beam LY on the photoreceptor 11Y (the first group of photoreceptors belonging to the first small group) and the photoreceptor 11C (the second group of photoreceptors belonging to the first small group). , LC are irradiated with the photosensitive member 11K (the first group of photosensitive members belonging to the second small group that does not belong to the first small group) and the photosensitive member 11M (second group of photosensitive members). 1 in the high-definition mode in the main scanning direction (first scanning direction) with respect to the irradiation position of the laser beams LK and LM in the second subgroup that does not belong to the first subgroup. The position is shifted by pixels. More specifically, the phase of the dot clocks of the laser beams LY and LC irradiated to both the first small group photoconductors 11Y and 11C is set to the laser beams LK and LM irradiated to both the second small group photoconductors 11K and 11M. Is delayed by one clock cycle in the high definition mode. Thereby, the irradiation position of the first small group photoconductors 11Y and 11C is shifted by one pixel in the high-definition mode in the main scanning direction with respect to the irradiation position of the second small group photoconductors 11K and 11M. And

  In this way, the irradiation positions of the laser beams LY, LM, LC, and LK to the respective photoreceptors 11 are determined, and the definition in the main scanning direction and the sub-scanning direction is defined as the definition (600 dpi) in the normal definition mode. Toner images of the same color (K color) are formed on the photoreceptors 11Y, 11M, 11C, and 11K. In FIG. 8, in order to explain the positional relationship of the toner images formed on each photoconductor 11, the dot patterns of the toner images on each photoconductor 11 are collectively shown. In this embodiment, it is assumed that the irradiation position of the photoconductor 11M in the multi-single color high-definition mode is not different from that in the normal definition mode. The four K color toner images formed in such a positional relationship are superimposed on the intermediate transfer belt 3 by primary transfer, and then superimposed on the paper P by secondary transfer. Therefore, as shown in FIG. 9, the superimposed image is a monochrome image of K color with high definition (1200 dpi).

  As described above, according to the image forming apparatus 1 of the present embodiment, the system speed (the rotational speed of the photoconductor 11), the rotational speed of the polygon mirror 34, and the frequency of the dot clock are not changed without changing the setting of the normal definition mode of 600 dpi. , 1200 dpi high-definition monochrome images can be formed. If the definition is improved by such a method, it is assumed that an image forming apparatus (specification of system speed, rotation speed of the polygon mirror 34, dot clock, etc.) capable of forming an image only with a resolution of 600 dpi. Even if the image forming apparatus cannot change the frequency, a monochrome image can be formed with a resolution of 1200 dpi.

  Here, as the laser beam L whose irradiation position on the photoconductor 11 is changed in the sub-scanning direction by the galvanometer mirror 40, it is desirable to select a laser beam that leaves as much room as possible for increasing the amount of light. This is because the amount of light may be reduced by reflection at the galvanometer mirror 40. Therefore, it is desirable to select the laser light L that can improve the laser characteristics (light quantity stability and pulse thinness) by increasing the light quantity as necessary. Specifically, it is preferable to select two of the plurality of laser beams L from those having a small light amount. The amount of laser light L is set differently depending on the color of the toner and the degree of novelty. Alternatively, it is preferable to select two of the plurality of laser beams L from those having a short optical path length. This is because the light with a long optical path length has already increased, and there is relatively little room to increase the light intensity. Alternatively, it is preferable to select two from those having a small number of reflections by the reflecting mirror 45 (those having a small number of reflections from the emission to the photosensitive member 11). This is because the number of reflections is large because the light quantity has already been increased, and there is relatively little room to increase the light quantity. In the present embodiment, the number of reflections of the laser beam LY is 2, the number of reflections of the laser beam LM is 2, the number of reflections of the laser beam LC is 3, and the number of reflections of the laser beam LK is 1 (see FIG. 1). ). Therefore, LK and LY are selected as the laser light L that changes the irradiation position in the sub-scanning direction. Incidentally, the laser beam LY and the laser beam LM may select either because of the number of reflection is the same. That is, when selecting two from the ones with the small number of reflections, either one may be selected from the ones with the same number of reflections. The same applies to selection based on the light amount and the optical path length. The CPU 50 increases the amount of laser light emitted from the laser diode 31 via the light emission control circuit 55 and the laser diode drive circuit 56 (see FIG. 4).

  As described in detail above, the image forming apparatus 1 according to the present embodiment provides high-definition toner images of the same color (K color) on the plurality of photoconductors 11Y, 11M, 11C, and 11K in the main scanning direction and the sub-scanning direction. The image is formed by shifting by one pixel at a resolution (1200 dpi) in the degree mode, and the toner images are overlapped with each other (see FIG. 9). Therefore, even if a toner image is formed with the definition in both the main scanning direction and the sub-scanning direction as the definition (600 dpi) in the normal definition mode, both the scans in the image in which the toner images are superimposed are performed. The directional definition is the definition (1200 dpi) in the high definition mode. Accordingly, it is possible to improve the definition in the main scanning direction without increasing the frequency of the dot clock of the laser beam L as it is in the normal definition mode. Further, the definition in the sub-scanning direction can be improved without decreasing the system speed (rotational speed of the photoconductor 11) and without increasing the rotational speed of the polygon mirror 34. Further, the change in the optical path of the laser light L for realizing the improvement in definition can be as small as one pixel in the high definition mode. Therefore, the optical scanning device 30 is not unnecessarily complicated.

  In addition, embodiment mentioned above is only a mere illustration, and does not limit this invention at all. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, in the above-described embodiment, the image is formed in the multi-single color high-definition mode when the multi-single-color state is set and the high-definition mode is set. That is, even in the multi-single color state, if the normal definition mode is set, image formation with high definition has not been performed. On the other hand, when the color information of the toner in each toner container 17 is acquired and it is determined that the multi-single color state is based on the color information, the high-definition mode is always selected, and the multi-single color height is selected. You may comprise so that the image formation in a definition mode may be performed. With this configuration, the processing load on the CPU 50 can be reduced by the fact that image formation in the multi-single color state is always performed in the high definition mode.

  In addition, the image forming apparatus 1 of the above embodiment can form a high-definition color image of 1200 dpi. On the other hand, an image that cannot form a 1200 dpi high-definition color image, that is, a monochrome image that can form an image with a high-definition of 1200 dpi may be used. In this case, the CPU 50 performs the processing shown in the flowchart in FIG. That is, the CPU 50 first acquires the color information of the toner in each toner container 17 (S101), and determines whether or not the image forming apparatus 1 is in a multi-single color state (S102). If not in the multi-single color state, the system speed, the dot clock frequency, and the optical path of the laser light L are not changed from the initial settings (S103), and a color image is formed with a resolution of 600 dpi (S104).

  On the other hand, if the image forming apparatus 1 is in the multi-single color state (YES in S102), the image quality mode setting information is acquired (S105), and it is determined whether or not it is in the high definition mode (S106). If the mode is not the high-definition mode (NO in S106), a monochrome image is formed with a resolution of 600 dpi without changing the system speed, the dot clock frequency, and the optical path of the laser light L from the initial settings (S103). (S104). On the other hand, in the high definition mode (YES in S106), the optical path of the laser light L is changed (S107) without changing the system speed and the dot clock frequency, and the multi-single color high definition is obtained. The image is formed in the mode, that is, a monochrome image is formed with a high definition of 1200 dpi (S108).

  In the above embodiment, the optical scanning device 30 provided with one polygon mirror 34 exposes the four photoconductors 11Y, 11M, 11C, and 11K. On the other hand, as shown in FIG. 11, it is good also as a structure provided with several optical scanning device 76Y, 76M, 76C, 76K corresponding to each process unit 75Y, 75M, 75C, 75K. The configuration of each of the optical scanning devices 76Y, 76M, 76C, and 76K is the same as that shown in FIGS. That is, each of the optical scanning devices 76Y, 76M, 76C, and 76K has the polygon mirror 34, respectively. The plurality of optical scanning devices 76Y, 76M, 76C, and 76K correspond to “optical scanning devices” in the claims.

  In such a configuration, the CPU 50 sets the rotational phase of the polygon mirror 34 corresponding to the photoconductors 11Y and 11C (both first small group photoconductors) to the photoconductors 11K and 11M (both second small groups). The irradiation position of the first small group of photoconductors 11Y and 11C and the first irradiation position of the photoconductors 11Y and 11C of the first small group are shifted by an angle corresponding to the shift of one pixel in the high-definition mode. The irradiation positions of the two small groups of photoconductors 11K and 11M may be shifted by one pixel in the high-definition mode in the main scanning direction. Specifically, the CPU 50 shifts the rotational phase of the polygon mirror 34 included in the optical scanning device 76M from the rotational phase of the polygon mirror 34 included in the optical scanning device 76C, thereby irradiating the photoconductor 11C with the laser light LC. Is shifted by one pixel in the high-resolution mode in the main scanning direction with respect to the irradiation position of the laser beam LM on the photoconductor 11M (see FIG. 8). Further, by shifting the rotational phase of the polygon mirror 34 included in the optical scanning device 76K and the rotational phase of the polygon mirror 34 included in the optical scanning device 76Y, the irradiation position of the laser beam LY on the photosensitive member 11Y is determined. Is shifted by one pixel in the high-resolution mode in the main scanning direction with respect to the irradiation position of the laser beam LK on (see FIG. 8). However, the rotational phases of the polygon mirrors 34 of the optical scanning device 76M and the optical scanning device 76K are matched, and the rotational phases of the optical scanning device 76C and the polygon mirror 34 of the optical scanning device 76Y are matched. In this way, the irradiation position of the laser light L can be shifted in the main scanning direction without shifting the phase of the dot clock of the laser light L as in the above embodiment.

  The plurality of optical scanning devices 76Y, 76M, 76C, and 76K are not provided corresponding to the process units 75Y, 75M, 75C, and 75K, but one corresponding to the two photoconductors 11Y and 11C belonging to the first small group. A polygon mirror and a polygon mirror corresponding to both the second small group of photoconductors 11K and 11M may be provided. Also in this case, by shifting the rotational phase of these polygon mirrors, the irradiation position of the first small group of photoconductors 11Y and 11C and the irradiation position of the second small group of photoconductors 11K and 11M are shifted in the main scanning direction. be able to.

  Further, the laser beam L emitted from the laser diode 31 may be a single beam or a plurality of beams.

  Moreover, in the said embodiment, although the galvanometer mirror 40 which changes the optical path by reflecting light was used as an optical path change member, the refractive element (for example, plane glass) which changes the optical path by refracting light is used. May be.

  Further, the optical path changing member may be disposed on the optical paths of all the laser beams LY, LM, LC, and LK. In this case, in the multi-single color high-definition mode, all the optical path changing members are changed to the changed posture. An optical path changing member disposed on the optical path of the laser beams LK and LY to the first group of photoconductors 11K and 11Y, a laser beam LM to the laser beams LM and LC of the second group of photoconductors 11M and 11C, The changing posture is different from that of the optical path changing member arranged on the LC optical path. As described above, when each optical path changing member takes the changing posture, the irradiation positions of the photoconductor 11K and the photoconductor 11Y in the multi-single color high-definition mode are subordinate to the irradiation positions of the photoconductor 11M and the photoconductor 11C. The position is shifted by one pixel in the high definition mode in the scanning direction.

  Further, the optical path changing member is in the retracted position retracted from the optical path of the laser beam L in the definition mode other than the multi-single color high definition mode (corresponding to the standard posture when in the retracted position). In the definition mode, it may be at the optical path changing position that has advanced on the optical path of the laser beam L (when it is at the optical path changing position, it corresponds to the changing posture). In this case, when the optical path changing member is disposed only on the optical paths of the laser beams LK and LY, the irradiation positions of the laser beams LK and LY when the optical path changing member is at the optical path changing position are determined by the optical path changing member. The position is shifted by one pixel in the high-definition mode in the sub-scanning direction with respect to the irradiation positions of the laser beams LK and LY at the retracted position. On the other hand, when the optical path changing member that takes the retracted position and the optical path changing position is arranged on the optical paths of all the laser beams LY, LM, LC, and LK, the optical path changing member is in the optical path changing position. The irradiation positions of the first group of photoconductors 11K and 11Y are shifted by one pixel in the high-definition mode in the sub-scanning direction with respect to the irradiation positions of the second group of photoconductors 11M and 11C. To be.

  In addition, the optical path changing member is arranged only on the optical paths of the laser beams LK and LY or on the optical paths of all the laser beams LY, LM, LC, and LK. It does not need to consist of separate members arranged on the road. That is, it may consist of one member.

  Further, the change in the posture of the optical path changing member (change in the posture between the standard posture and the changed posture) is not limited to changing the inclination angle, but may change the position by parallel movement or the like.

  The acquisition of the color information from the toner container 17 by the CPU 50 may not be a configuration in which the CPU 50 acquires the color information stored in the storage unit of the toner container 17. That is, the appearance (shape, color, etc.) of each toner container 17 differs depending on the color of the toner, and the CPU 50 acquires color information by optically or mechanically reading the appearance of the toner container 17. You may comprise.

  Further, the CPU 50 may not be able to acquire the toner color information (color information) in the toner container 17 attached to each developing device 14 from the toner container 17. In this case, the image formation in the multi-single color high resolution mode may be performed based on the input operation by the user. Alternatively, it may be configured such that information on whether it is in the normal color state or the multi-single color state is written in the storage device 51 based on an input operation by the user, and is read out by the CPU 50 as appropriate.

  When the definition in the main scanning direction and the sub-scanning direction is both 1200 dpi, in the main scanning direction, the phase of the dot clock of the laser light L irradiating the photoreceptors 11Y and 11C in the first small group and the second small group. In the sub-scanning direction, the system speed is halved or the polygon mirror 34 is rotated while the dot clock phase of the laser light L irradiated to the photoconductors 11K and 11M is changed to high definition. High definition may be achieved by doubling the speed. Further, in the main scanning direction, the dot clock frequency may be doubled to achieve high definition, while in the sub-scanning direction, the galvano mirror 40 may be provided with high definition by changing the tilt angle.

  Further, in the main scanning direction, the phase of the dot clock of the laser light L applied to the first small group of photoconductors 11Y and 11C and the phase of the dot clock of the laser light L applied to the second small group of photoconductors 11K and 11M. The high definition (1200 dpi) may be obtained by changing the value, while the normal definition (600 dpi) may be maintained in the sub-scanning direction. Further, the fine definition (1200 dpi) may be achieved by changing the tilt angle of the galvanometer mirror 40 in the sub-scanning direction, while the normal definition (600 dpi) may be maintained in the main scanning direction.

  In each of the above cases, in order to increase the definition in the main scanning direction, the phase of the dot clock of the laser light L applied to the first small group of photoconductors 11Y and 11C and the second small group of photoconductors 11K and 11M Instead of changing the phase of the dot clock of the laser light L to be irradiated, a plurality of polygon mirrors 34 are provided, and the rotation phase of the plurality of polygon mirrors 34 corresponding to the first small group of photoreceptors 11 is changed to the second small group. Alternatively, the rotational phase of the photoconductor 11 may be shifted by an angle corresponding to the shift of one pixel in the high definition mode.

  In the above embodiment, the photoconductor 11K and the photoconductor 11Y are the first group of photoconductors, the photoconductor 11M and the photoconductor 11C are the second group of photoconductors, and the photoconductor 11Y and the photoconductor 11C are the first small group. The photoconductor 11K and the photoconductor 11M are described as the second small group of photoconductors. However, the photoconductor 11Y and the photoconductor 11C are the first group of photoconductors, and the photoconductor 11K and the photoconductor 11M are the first. The two groups of photoreceptors, the photoreceptor 11K and the photoreceptor 11Y may be regarded as a first small group of photoreceptors, and the photoreceptor 11M and the photoreceptor 11C may be regarded as a second small group of photoreceptors.

  In the above embodiment, the definition in the normal definition mode is 600 dpi and the definition in the high definition mode is 1200 dpi, but the definition in each mode may be other values.

  In the above-described embodiment, the laser light LY and LC dot clocks of the laser beams LY and LC irradiated to both the first small group of photoconductors 11Y and 11C are set to the laser light LK and the second small group of photoconductors 11K and 11M. The phase of the LM dot clock was delayed by one clock cycle in the high definition mode. On the other hand, the phase of the dot clock of the laser beams LY and LC irradiated to both the first small group photoconductors 11Y and 11C is changed to the laser beams LK and LM irradiated to both the second small group photoconductors 11K and 11M. The dot clock phase may be advanced by one clock cycle in the high definition mode.

  Further, in the above embodiment, the irradiation position of the first group of photoconductors 11K and 11Y is changed with respect to the irradiation position of the second group of photoconductors 11M and 11C by changing the attitude of the galvanometer mirror 40 from the standard attitude. Thus, it is configured to shift by one pixel in the high-definition mode downstream in the sub-scanning direction. On the other hand, by changing the posture of the galvano mirror 40 from the standard posture to the changed posture, the irradiation positions of the first group of photoconductors 11K and 11Y are changed with respect to the irradiation positions of the second group of photoconductors 11M and 11C. It may be configured to shift by one pixel in the high definition mode upstream in the sub-scanning direction.

  In the above embodiment, the irradiation position of the photoconductor 11M (second group second subgroup photoconductor) in the multi-single-color high-definition mode is set to the same position as in the normal-definition mode. On the other hand, the irradiation position of the photoconductor 11M (the second small group of photoconductors) in the multi-single color high definition mode may be changed to a position different from that in the normal definition mode. In this case, only one of the main scanning direction and the sub-scanning direction may be changed, or both the main scanning direction and the sub-scanning direction may be changed.

  In the above-described embodiment, the image forming apparatus 1 that forms a color image using four color toners has been described. However, an image forming apparatus that can use five or more color toners may be used. In this case, it is possible to perform image formation in the multi-single color high-definition mode in the embodiment by using four toners of the five or more colors as the same color, or in the embodiment in which all the toners are the same color. In the multi-single color high-definition mode, image formation may be performed. When all the toners have the same color, the fifth and subsequent toners may overlap with any one of the Y, M, C, and K positions shown in FIG.

  In the case of an image forming apparatus capable of using five or more colors of toner, “all developing units” in claim 1 is not a developing unit corresponding to all of five or more colors, This means all the developing devices corresponding to the four colors. The “definition setting unit”, “multi-single color high-definition mode control unit”, “color information acquisition unit”, and “state determination unit” in the claims are configured by the CPU 50 of the present embodiment. is there.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 2 ... Process unit (image forming unit)
DESCRIPTION OF SYMBOLS 11 ... Photoconductor 12 ... Charger 14 ... Developing device 17 ... Toner container 30 ... Optical scanning device 31 ... Laser diode (light emission part)
34 ... Polygon mirror 38 ... Polygon motor 40 ... Galvano mirror (light path changing member)
45 ... Reflector 50 ... CPU

Claims (8)

A plurality of image forming units each including a photoconductor rotating around an axis, a charger for charging the surface of the photoconductor, and a developer for supplying toner onto the surface of the photoconductor;
A light emitting unit that emits laser light; and a rotating polygon mirror; the laser light emitted from the light emitting unit is reflected by the polygon mirror; An optical scanning device for irradiating while scanning in the axial direction of the photosensitive member,
An image forming apparatus that forms an electrostatic latent image on each photosensitive member of the plurality of image forming units by irradiating a laser beam, and forms an image by superimposing toner images formed on the electrostatic latent image. In
The plurality of image forming units includes a normal color state in which toner containers of different colors are attached to each developing device, and a multi-single color in which toner containers of the same color are attached to all the developing devices. Can take the state,
One of a plurality of definition modes including at least a normal definition mode for forming an image with a first definition and a high definition mode for forming an image with a second definition higher than the first definition. A definition setting section for selecting
When the plurality of image forming units are in the multi-single color state and the high-definition mode is selected in the definition setting unit, image formation in the multi-single-color high-definition mode is performed. A multi-single color high-definition mode control unit,
In the multi single color high definition mode,
Laser at the irradiation position of the laser beam in a plurality of belonging to the first group, those of multiple belonging to the second group is a residual that does not belong to the first group among the plurality of photosensitive bodies of the plurality of photoreceptor In the high-definition mode, one of the first scanning direction caused by the rotation of the polygon mirror and the second scanning direction caused by the rotation of the photoconductor with respect to the light irradiation position is determined. While making the position shifted by pixels,
Both the definition in the one scanning direction and the other scanning direction are defined as the definition in the normal definition mode ,
The irradiation position of the laser beam in the first group of photoreceptors belonging to the first small group and the second group of photoreceptors belonging to the first small group is defined as the first group of photoreceptors. Of the second group that belong to the second small group that does not belong to the first small group, and those that belong to the second small group that does not belong to the first small group among the photosensitive members of the second group In the other scanning direction of the first scanning direction and the second scanning direction with respect to the irradiation position of the laser beam in the above, the position is shifted by one pixel in the high-definition mode,
An image forming apparatus that forms toner images in the plurality of image forming units. The image forming apparatus according to claim 1 ,
The other scanning direction is the first scanning direction;
In the multi-single-color high-definition mode, the phase of the dot clock of the laser light that irradiates both the first small group photoconductors is the phase of the dot clock of the laser light that irradiates both the second small group photoconductors In contrast, the image forming apparatus is characterized by being shifted by one clock cycle in the high-definition mode. The image forming apparatus according to claim 1 ,
The other scanning direction is the first scanning direction;
The optical scanning device includes a plurality of the polygon mirrors,
In the multi-single color high-definition mode, the rotational phase of the polygon mirrors corresponding to the first small group photoconductors is changed to the rotational phase of the polygon mirror corresponding to the second small group photoconductors. On the other hand, the image forming apparatus is characterized by shifting by an angle corresponding to a shift of one pixel in the high definition mode. An image forming apparatus according to any one of claims 1 to 3 , wherein
The one scanning direction is the second scanning direction;
An optical path changing member disposed in the multi-single color high-definition mode on an optical path from the light emitting unit to each of the photosensitive members of at least one of the first group and the second group;
The optical path changing member is arranged such that the irradiation position on the first group of photoconductors in the multi-single color high-definition mode is the high-definition in the second scanning direction with respect to the irradiation position on the second group of photoconductors. An image forming apparatus that is shifted by one pixel in the mode. A plurality of image forming units each including a photoconductor rotating around an axis, a charger for charging the surface of the photoconductor, and a developer for supplying toner onto the surface of the photoconductor;
A light emitting unit that emits laser light; and a rotating polygon mirror; the laser light emitted from the light emitting unit is reflected by the polygon mirror; An optical scanning device for irradiating while scanning in the axial direction of the photosensitive member,
An image forming apparatus that forms an electrostatic latent image on each photosensitive member of the plurality of image forming units by irradiating a laser beam, and forms an image by superimposing toner images formed on the electrostatic latent image. smell Te,
The plurality of image forming units includes a normal color state in which toner containers of different colors are attached to each developing device, and a multi-single color in which toner containers of the same color are attached to all the developing devices. Can take the state,
One of a plurality of definition modes including at least a normal definition mode for forming an image with a first definition and a high definition mode for forming an image with a second definition higher than the first definition. A definition setting section for selecting
When the plurality of image forming units are in the multi-single color state and the high-definition mode is selected in the definition setting unit, image formation in the multi-single-color high-definition mode is performed. A multi-single color high-definition mode controller;
On the optical path from the light emitting unit to the photosensitive member belonging to the first group of the plurality of photosensitive members, the first group and the remaining second group not belonging to the first group, the multi-single color height An optical path changing member arranged in the definition mode,
The amount of laser light applied to the first group of photoconductors is less than the amount of laser light applied to the second group of photoconductors;
The optical path changing member is in the pre-SL multi single color high definition mode by taking the different postures and at other resolution mode, the first group in the multi-single color high definition mode photoreceptor With respect to the irradiation position of the first group of photoconductors in the definition mode other than the multi-single color definition mode, the irradiation position depends on the first scanning direction caused by the rotation of the polygon mirror and the rotation of the photoconductor. der which shifted one pixel in the high resolution mode for the second scanning direction of the second scanning direction due to is,
In the multi single color high definition mode,
The irradiation position of the laser beam on the photosensitive member belonging to the first group is one pixel in the high-definition mode in the second scanning direction with respect to the irradiation position of the laser beam on the photosensitive member belonging to the second group. While making the shifted position,
The definition in the second scanning direction is defined as the definition in the normal definition mode.
An image forming apparatus that forms toner images in the plurality of image forming units . A plurality of image forming units each including a photoconductor rotating around an axis, a charger for charging the surface of the photoconductor, and a developer for supplying toner onto the surface of the photoconductor;
A light emitting unit that emits laser light; and a rotating polygon mirror; the laser light emitted from the light emitting unit is reflected by the polygon mirror; An optical scanning device for irradiating while scanning in the axial direction of the photosensitive member,
An image forming apparatus that forms an electrostatic latent image on each photosensitive member of the plurality of image forming units by irradiating a laser beam, and forms an image by superimposing toner images formed on the electrostatic latent image. smell Te,
The plurality of image forming units includes a normal color state in which toner containers of different colors are attached to each developing device, and a multi-single color in which toner containers of the same color are attached to all the developing devices. Can take the state,
One of a plurality of definition modes including at least a normal definition mode for forming an image with a first definition and a high definition mode for forming an image with a second definition higher than the first definition. A definition setting section for selecting
When the plurality of image forming units are in the multi-single color state and the high-definition mode is selected in the definition setting unit, image formation in the multi-single-color high-definition mode is performed. A multi-single color high-definition mode controller;
On the optical path from the light emitting unit to the photosensitive member belonging to the first group of the plurality of photosensitive members, the first group and the remaining second group not belonging to the first group, the multi-single color height An optical path changing member arranged in the definition mode,
The optical path length of the laser light applied to the first group of photoconductors is less than the optical path length of the laser light applied to the second group of photoconductors,
The optical path changing member is in the pre-SL multi single color high definition mode by taking the different postures and at other resolution mode, the first group in the multi-single color high definition mode photoreceptor With respect to the irradiation position of the first group of photoconductors in the definition mode other than the multi-single color definition mode, the irradiation position depends on the first scanning direction caused by the rotation of the polygon mirror and the rotation of the photoconductor. der which shifted one pixel in the high resolution mode for the second scanning direction of the second scanning direction due to is,
In the multi single color high definition mode,
The irradiation position of the laser beam on the photosensitive member belonging to the first group is one pixel in the high-definition mode in the second scanning direction with respect to the irradiation position of the laser beam on the photosensitive member belonging to the second group. While making the shifted position,
The definition in the second scanning direction is defined as the definition in the normal definition mode.
An image forming apparatus that forms toner images in the plurality of image forming units . A plurality of image forming units each including a photoconductor rotating around an axis, a charger for charging the surface of the photoconductor, and a developer for supplying toner onto the surface of the photoconductor;
A light emitting unit that emits laser light; and a rotating polygon mirror; the laser light emitted from the light emitting unit is reflected by the polygon mirror; An optical scanning device for irradiating while scanning in the axial direction of the photosensitive member,
An image forming apparatus that forms an electrostatic latent image on each photosensitive member of the plurality of image forming units by irradiating a laser beam, and forms an image by superimposing toner images formed on the electrostatic latent image. smell Te,
The plurality of image forming units includes a normal color state in which toner containers of different colors are attached to each developing device, and a multi-single color in which toner containers of the same color are attached to all the developing devices. Can take the state,
One of a plurality of definition modes including at least a normal definition mode for forming an image with a first definition and a high definition mode for forming an image with a second definition higher than the first definition. A definition setting section for selecting
When the plurality of image forming units are in the multi-single color state and the high-definition mode is selected in the definition setting unit, image formation in the multi-single-color high-definition mode is performed. A multi-single color high-definition mode controller;
On the optical path from the light emitting unit to the photosensitive member belonging to the first group of the plurality of photosensitive members, the first group and the remaining second group not belonging to the first group, the multi-single color height An optical path changing member arranged in the definition mode,
A reflecting mirror is disposed on the optical path of the laser beam from the light emitting unit to the photoconductor;
The number of reflections of the laser light applied to the first group of photosensitive members by the reflecting mirror is less than the number of reflections of the laser light applied to the second group of photosensitive members by the reflecting mirror,
The optical path changing member is in the pre-SL multi single color high definition mode by taking the different postures and at other resolution mode, the first group in the multi-single color high definition mode photoreceptor With respect to the irradiation position of the first group of photoconductors in the definition mode other than the multi-single color definition mode, the irradiation position depends on the first scanning direction caused by the rotation of the polygon mirror and the rotation of the photoconductor. der which shifted one pixel in the high resolution mode for the second scanning direction of the second scanning direction due to is,
In the multi single color high definition mode,
The irradiation position of the laser beam on the photosensitive member belonging to the first group is one pixel in the high-definition mode in the second scanning direction with respect to the irradiation position of the laser beam on the photosensitive member belonging to the second group. While making the shifted position,
The definition in the second scanning direction is defined as the definition in the normal definition mode.
An image forming apparatus that forms toner images in the plurality of image forming units . An image forming apparatus according to any one of claims 1 to 7 , comprising:
A color information acquisition unit for acquiring information on the color of toner in a toner container attached to each of the developing devices;
A state determination unit that determines whether or not the plurality of image forming units are in the multi-single color state based on the color information acquired by the color information acquisition unit;
The image forming apparatus, wherein the definition setting unit selects the high-definition mode whenever the state determination unit determines that the multi-single color state is present.

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