Image forming device

Abstract

In the present invention, an exposure unit 7 is capable of exposing a photosensitive drum 1 according to a plurality of exposure patterns #B to #E in which the positioning of ON time and OFF time in one pixel is different, and is provided with an exposure pattern setting unit 1302 for setting one exposure pattern out of the plurality of exposure patterns #B to #E for one pixel. The exposure pattern setting unit 1302 sets an exposure pattern in each pixel so that ON time or OFF time is continuous between a plurality of pixels continuous in a main scanning direction B. A signal generation unit 1303 generates a drive signal 71 according to the exposure pattern set by the exposure pattern setting unit 1302.

Description

Image forming device

[0001] The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that can reduce the amount of developer consumed.

[0002] In image forming apparatuses, a phenomenon known as "edge concentration" or "edge effect" occurs, in which the amount of toner increases at the edge portions of a toner image attached to an electrostatic latent image. This phenomenon can lead to problems such as increased toner consumption and excessive density in some parts of the formed image. By suppressing the increase in toner amount due to this phenomenon, it is possible to reduce toner consumption during image formation and optimize the density of the formed image. For example, Japanese Patent Application Laid-Open No. 2016-91009 discloses a configuration for suppressing the effects of edge concentration or "edge effect." Specifically, a correction area to be corrected is first determined based on the data value of a pixel and the data value of a pixel shifted a predetermined amount from the pixel in the sub-scanning direction or main scanning direction. Then, the exposure amount of each pixel in the determined correction area is corrected according to the distance from the edge, thereby suppressing the effects of edge concentration.

[0003] However, in the conventional configuration, depending on the amount of exposure correction, a phenomenon may occur in which the light source for exposing the photosensitive member cannot keep up with the light emission operation. If the light source cannot keep up with the on / off operation, the exposure amount may not be corrected to the intended amount.

[0004] The present invention has been made under these circumstances, and has as its object to expose a photosensitive member in consideration of the response of a light source.

[0005] In order to solve the above-mentioned problems, the present invention has the following configuration.

[0006] an exposure period for exposing the photosensitive member to light within one pixel, and a non-exposure period for not exposing the photosensitive member to light within one pixel; and a setting means for setting one of the exposure patterns for one pixel, the setting means setting the exposure pattern for each pixel so that the exposure period or the non-exposure period is continuous between a plurality of pixels that are consecutive in the main scanning direction.

[0007] According to the present invention, it is possible to perform exposure of a photosensitive member taking into consideration the response of a light source.

[0008] FIG. 1 is a diagram showing the configuration of an image forming apparatus according to the first and second embodiments.

[0009] FIG. 2 is an explanatory diagram of the developing method of the first and second embodiments.

[0010] FIG. 3 is an explanatory diagram of the principle of edge effect generation in the first and second embodiments.

[0011] FIG. 4 is a diagram showing images in which sweeping and edge effects occur in Examples 1 and 2.

[0012] FIG. 5 is an explanatory diagram of the principle of the occurrence of the sweep concentration in the first and second embodiments.

[0013] FIG. 6 is a diagram showing the configuration of the exposure unit in the first and second embodiments.

[0014] FIG. 7 is an explanatory diagram of a method for controlling the exposure amount of one pixel in the first and second embodiments.

[0015] FIG. 8 is a functional block diagram of the exposure control configuration of the first and second embodiments.

[0016] FIG. 9 is a diagram showing images formed based on image data in the first and second embodiments, and a diagram showing correction amount parameters.

[0017] FIG. 10 is a diagram showing an example of exposure accompanied by short exposure-off in the first and second embodiments.

[0018] FIG. 11 is a diagram showing an example of exposure with exposure-on for a short time in the first and second embodiments.

[0019] FIG. 12 is a functional block diagram of the generation unit according to the first and second embodiments.

[0020] FIG. 13 is a diagram showing an example of exposure pattern setting in which exposure-off periods are continuous in the first and second embodiments.

[0021] FIG. 14 is a diagram showing an example of exposure pattern settings in which the exposure-on time is continuous in the first and second embodiments.

[0022] FIG. 15 is a flowchart showing the exposure pattern setting process of the second embodiment.

[0023] FIG. 16 is a diagram showing an example of exposure pattern setting in the second embodiment.

[0024] Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. Note that the following embodiments are merely examples, and the present invention is not limited to the contents of the embodiments. Furthermore, in the following drawings, components that are not necessary for the description of the embodiments will be omitted. Note that in the following description, the rotation direction of the photosensitive drum is the sub-scanning direction, and the direction perpendicular to the rotation direction of the photosensitive drum (i.e., the sub-scanning direction) (the direction of the rotation axis of the photosensitive drum) is the main scanning direction. (Example 1) <Image forming apparatus>

[0025] FIG. 1 is a structural diagram of an image forming apparatus 101 according to a first embodiment. During image formation, a photosensitive drum 1, which is an image carrier, is driven to rotate in the direction of the arrow in FIG. 1 (clockwise). A charging unit 2 charges the surface of the photosensitive drum 1 to a uniform potential. An exposure unit 7, which serves as an exposure means, exposes the surface of the charged photosensitive drum 1 to light emitted from a light source and based on image data, thereby forming an electrostatic latent image on the photosensitive drum 1. The exposure unit 7 is driven by a drive signal 71 output by an image calculation unit 9. An exposure control unit 19 of the image calculation unit 9 adjusts the exposure intensity of the exposure unit 7 to a target value using a voltage Va.

[0026] The developing unit 3 includes a container 13 for storing toner as a developer and a developing roller 14 as a developer carrier. The toner may be non-magnetic single-component toner, two-component toner, or magnetic toner. A regulating blade 15 is provided to regulate the thickness of the toner layer supplied to the developing roller 14 to a predetermined value. The regulating blade 15 may also be configured to impart an electric charge to the toner. The developing roller 14 transports the toner to a developing area 16. The developing area 16 is the area where the developing roller 14 and the photosensitive drum 1 are in close proximity or contact with each other, and where toner adheres to the electrostatic latent image. As shown in FIG. 5 (described later), the start position of the developing area 16 is designated as a start position Ps, and the end position is designated as an end position Pe. The developing unit 3 applies toner to the electrostatic latent image formed on the photosensitive drum 1, visualizing it as a toner image. The transfer unit 4 transfers the toner image formed on the photosensitive drum 1 to a recording material P. The fixing unit 6 applies heat and pressure to the recording material P to fix the unfixed toner image Te transferred onto the recording material P to the recording material P.

[0027] The CPU 10 of the image calculation unit 9 is a control unit that performs overall control of the image forming apparatus 101. It is possible to configure the CPU 10 to perform all of the control described below, or to configure the ASIC 18 to perform some of the control. It is also possible to configure the ASIC 18 to perform all of the control described below. The memory 11 is a storage unit configured to store image data 111 transmitted from the host computer 8. The memory 11 also serves as a storage unit that stores an LUT 112. The LUT 112 is a lookup table that includes a correction width parameter and a correction amount parameter, which will be described later. In the first embodiment, the memory 11 collectively refers to a volatile memory and a nonvolatile memory, and may include multiple physically separate memories. The LUT 112, which indicates the correction width parameter and the correction amount parameter, may be stored in the memory 11 in advance (before shipment). The LUT 112 may also be stored in the memory of a process cartridge 21 including the photosensitive drum 1. In this case, when the cartridge is replaced, the CPU 10 reads out the LUT 112 stored in the memory of the replaced cartridge and stores it in the memory 11. <Developing Method>

[0028] There are two types of development methods: jumping development and contact development. FIG. 2(A) shows the configuration of the development unit 3 in the case of the jumping development method, and FIG. 2(B) shows the configuration of the development unit 3 in the case of the contact development method. In the jumping development method, the development roller 14 and the photosensitive drum 1 are not in contact with each other, but a gap 17 of a predetermined distance is provided. An AC voltage superimposed with a DC voltage is used as the development voltage output by the development roller 14. In the contact development method, the development roller 14 and the photosensitive drum 1 are brought into contact with each other. A DC voltage is used as the development voltage output by the development roller 14. In either method, the rotation directions of the photosensitive drum 1 and the development roller 14 are opposite to each other, that is, in the development area 16, the surfaces of the photosensitive drum 1 and the development roller 14 move in the same direction. <Sweeping and Edge Effect>

[0029] Next, we will explain the principles of the edge effect and sweeping phenomenon, in which the amount of toner adhering to an electrostatic latent image increases at its edges. The edge effect is a phenomenon in which an electric field concentrates at the boundary between the exposed area and the non-exposed area of ​​an electrostatic latent image formed on the photosensitive drum 1, causing excessive toner to adhere to each edge of the electrostatic latent image. Here, for example, assume that the image to be formed has a uniform density. As shown in FIG. 3 , electric field lines from the non-exposed areas 301 and 302 surrounding the exposed area 300 wrap around the edges of the exposed area 300, making the electric field strength at the edges of the exposed area 300 stronger than in the other areas of the exposed area 300. Therefore, more toner adheres to the edges of the exposed area 300 than in the other areas.

[0030] FIG. 4A shows a toner image 400 in which the edge effect has occurred. Arrow A in FIG. 4A indicates the transport direction of the toner image, i.e., the rotation direction of the photosensitive drum 1. Note that the image data from which the toner image 400 was created has the same pixel value, meaning that the toner image 400 is an image of uniform density. When the edge effect occurs, toner is concentrated and adheres to all edge regions 402a of the toner image 400. As a result, the density of the edge regions 402a becomes higher (darker) than the density of the non-edge regions 401a. Note that the edge effect mainly occurs in the jumping development method ( FIG. 2A ) in which there is a gap between the photosensitive drum 1 and the developing roller 14.

[0031] On the other hand, sweeping refers to the phenomenon in which toner concentrates at the trailing edge of a toner image in the direction of rotation of the photosensitive drum 1. In the contact development method, the peripheral speed of the developing roller 14 is set faster than that of the photosensitive drum 1 in order to maintain a predetermined toner thickness on the photosensitive drum 1. As shown in FIGS. 5A to 5C, in the development zone 16, the electrostatic latent image is developed with toner transported by the developing roller 14. Note that in FIG. 5, the toner is represented by a circle. Because the developing roller 14 rotates at a faster speed than the photosensitive drum 1, the relative positions of the two on their surfaces are constantly shifted. As shown in FIG. 5A, when the trailing edge 600a of the electrostatic latent image 600 enters the development zone 16, the toner on the developing roller 14 is located behind the start position Ps of the development zone 16 in the direction of rotation. However, because the rotational speed of the developing roller 14 is faster than the rotational speed of the photosensitive drum 1, as shown in Fig. 5B, the toner on the developing roller 14 overtakes the trailing edge 600a of the electrostatic latent image 600 by the time the trailing edge 600a of the electrostatic latent image 600 leaves the development area 16. Then, as shown in Fig. 5C, this toner on the developing roller 14 (the amount of toner that has been overtaken) is supplied to the trailing edge 600a of the electrostatic latent image 600, so that the amount of toner adhering to the trailing edge 600a of the electrostatic latent image increases (part 600b). This is the mechanism by which sweep concentration occurs.

[0032] Fig. 4B shows a toner image 410 in which concentration has occurred. Arrow A in Fig. 4B indicates the transport direction of the toner image, i.e., the rotation direction of the photosensitive drum 1. Note that the image data on which the toner image 410 is based has the same pixel value, meaning that the toner image 410 is an image of uniform density. When concentration occurs, toner is concentrated and adheres to the trailing edge region 402b of the toner image 410. As a result, the density of the trailing edge region 402b becomes higher (darker) than the density of the remaining non-trailing edge region 401b. <Control configuration of the exposure unit>

[0033] FIG. 6 shows the control configuration of the exposure unit 7. The exposure control unit 19 includes an IC 2003 including an 8-bit DA converter (DAC) 2021 and a regulator (REG) 2022. The IC 2003 adjusts the voltage VrefH output by the regulator 2022 based on an intensity adjustment signal (not shown) set by the CPU 10. The voltage VrefH serves as the reference voltage for the DA converter 2021. The IC 2003 sets input data 2020 for the DA converter 2021, which then outputs a voltage Va to the exposure unit 7. The VI conversion circuit 2306 of the exposure unit 7 converts the voltage Va into a current value Id and outputs it to the driver IC 2009. The driver IC 2009 controls the exposure intensity of the exposure unit 7 using the current value Id. In other words, the exposure control unit 19 can control the exposure intensity of the exposure unit 7 using the voltage Va. Furthermore, the driver IC 2009 switches the switch SW of the driver IC 2009 in response to the drive signal 71 output from the image calculation unit 9. The switch SW controls whether the current IL flows to the laser diode LD of the exposure unit 7 or to the dummy resistor R1, thereby controlling the ON (light emission) / OFF (extinction) of the laser diode LD. <Method of controlling the amount of exposure of one pixel>

[0034] FIG. 7 is an explanatory diagram of a method for controlling the exposure amount of one pixel by the exposure unit 7. FIGS. 7A to 7E each show one pixel, with the black area indicating the exposed area and the white area indicating the unexposed area. FIG. 7A shows a state in which the entire area within one pixel is exposed at a predetermined intensity. At this time, the pixel value of the pixel is assumed to be 255. Meanwhile, FIGS. 7B to 7E each show a state in which the exposure amount is 75% of that of FIG. 7A. Specifically, FIGS. 7B to 7E show a state in which 3 / 4 of the area of ​​one pixel is exposed at a predetermined intensity. At this time, the pixel value of the pixel is 255 × 0.75, which is 191 when rounded down to an integer.

[0035] In this way, in the first embodiment, the exposure period of each pixel is adjusted by turning on / off the switch SW of the driver IC 2009 of the exposure unit 7, and thus the amount of exposure is adjusted. In this case, the drive signal 71 is a PWM (pulse width modulation) signal. Note that in the first embodiment, a laser diode LD is used as the light source of the exposure unit 7, but the specific configuration of the light source is not limited to an LD; for example, an LED can also be used, and the number of light sources is not limited to one.

[0036] 7B to 7E all have 75% of the exposure amount of FIG. 7A, but the patterns within one pixel are different. Hereinafter, the period (area) within one pixel during which the light source emits light to expose the photosensitive drum 1 will be referred to as the exposure period (exposure area), and the period (area) during which the light source does not emit light and the photosensitive drum 1 is not exposed will be referred to as the non-exposure period (exposure area).

[0037] FIG. 7B shows a pattern in which the left side of a pixel is the exposure area, and the exposure period is located upstream in the main scanning direction within the pixel. FIG. 7C shows a pattern in which the right side of a pixel is the exposure area, and the exposure period is located downstream in the main scanning direction within the pixel. FIG. 7D shows a pattern in which the center of a pixel is the exposure area, and the exposure period is located at the center of the pixel in the main scanning direction within the pixel. FIG. 7E shows a pattern in which both ends of a pixel are the exposure areas, and the exposure periods are located at both ends of the pixel in the main scanning direction within the pixel. For the purposes of the following explanation, the exposure patterns for one pixel shown in FIGS. 7A to 7E are referred to as exposure pattern #A, exposure pattern #B, exposure pattern #C, exposure pattern #D, and exposure pattern #E, respectively. The exposure unit 7 can expose the photosensitive drum 1 to a plurality of exposure patterns #B to #D, which have different arrangements of exposure and non-exposure periods within a pixel, for a given pixel value. In the first embodiment, pixels where the edge effect or the sweeping effect occurs are identified, and the pixel values ​​of the identified pixels are corrected to suppress the edge effect or the sweeping effect.

[0038] 8 shows functional blocks for exposure control implemented by the CPU 10. For example, the CPU 10 implements the functional blocks shown in FIG.

[0039] Image data 111 (second image data) stored in memory 11 is input to image analysis unit 801. Setting unit 803 reads out LUT 112 stored in memory 11 and holds a correction width parameter 805 and a correction amount parameter 806 indicated by the LUT 112. The correction width parameter 805 is information for identifying pixels where convergence or edge effect occurs. Setting unit 803 outputs the correction width parameter 805 to image analysis unit 801. Based on the correction width parameter 805, image analysis unit 801 identifies pixels where convergence or edge effect may occur, i.e., pixels to be corrected, from the pixels of the image formed by the image data 111. Then, image analysis unit 801 outputs the image data 111 (first image data) and information 804 indicating the pixels to be corrected to generation unit 802.

[0040] In the first embodiment, the correction width parameter 805 indicates the pixel to be corrected and is expressed as the number of pixels from the edge of the area where toner adheres. For example, assume that the image formed by the image data 111 is the image 901 shown in FIG. 9A, and the correction width parameter 805 indicates "10." Note that the correction width parameter 805 (e.g., "10") does not depend on the size of the area 902 described below. In this case, the image analysis unit 801 identifies pixels within a 10-pixel range from the edge of the area 902 where toner adheres in the image 901 as the pixel to be corrected. Note that when correcting for sweeping, the pixel to be corrected is within a 10-pixel range from the edge on the trailing end side in the rotation direction of the photosensitive drum 1. On the other hand, when correcting the edge effect, the pixel to be corrected is within a 10-pixel range from all edges.

[0041] Returning to the description of FIG. 8 , the setting unit 803 notifies the generation unit 802 of a correction amount parameter 806. FIG. 9B shows an example of the correction amount parameter 806. In FIG. 9B , the correction amount parameter 806 is information indicating the relationship between the distance from the edge and the correction amount. In FIG. 9B , for example, a correction amount of 48 / 255 is used for a pixel that is 10 meters away from the edge. For example, a correction amount of 32 / 255 is used for a pixel that is 1 meter away from the edge. The generation unit 802 corrects the pixel value of the pixel to be corrected based on the information 804 indicating the pixel to be corrected output from the image analysis unit 801 and the correction amount parameter 806.

[0042] Note that if the pixel value of the correction target pixel is Y and the correction amount is "X / 255," the generation unit 802 sets the corrected pixel value of the correction target pixel to Y-(X×Y / 255). For example, assume that the correction target pixel is the first pixel from the edge, has a pixel value of 255, and the correction amount parameter 806 is as shown in FIG. 9B. In this case, the generation unit 802 sets the corrected pixel value of the correction target pixel to 255-(255×32 / 255)=223. The generation unit 802 generates the drive signal 71, which is a PWM signal, based on the corrected image data and outputs it to the exposure unit 7.

[0043] The values ​​of the correction width parameter 805 and the correction amount parameter 806 are set to appropriate values ​​depending on the characteristics of electrostatic latent image formation on the photosensitive drum 1 and the development characteristics of toner for the electrostatic latent image. If these characteristics change depending on the operating environment and the number of sheets used, the values ​​of the correction width parameter 805 and the correction amount parameter 806 for each condition such as the operating environment and the number of sheets used may be stored in the LUT 112, and appropriate values ​​may be selected and used depending on the conditions used. The values ​​of each parameter are determined in advance by experiment or simulation and stored in the memory 11. <Light Source Response>

[0044] As described with reference to FIG. 6 , the exposure unit 7 controls the switch SW of the driver IC 2009 based on a PWM signal (drive signal 71). Here, when the time during which the switch SW is set to the on or off state is short, the off / on operation of the switch SW may not be able to keep up with the control. Specifically, this occurs when the exposure involves off / on for such a short time that the response of the switching operation of the switch SW of the driver IC 2009 is not guaranteed, depending on the pixel value and the arrangement of the exposure pattern in the main scanning direction. Furthermore, even if the on / off operation of the switch SW can keep up with the control, the laser diode LD may not be able to respond to the on / off operation of the switch SW.

[0045] A specific example will be explained using Figures 10 and 11. Figures 10 and 11 show an example of an exposure pattern of a group of pixels corrected to pixel value Z by the exposure amount correction by the generation unit 802. These groups of pixels are lined up in the main scanning direction B. First, the off time and on time in the exposure period of one pixel depend on the pixel value. For example, if the pixel value is Z (Z is a value from 0 to 255), a period of Z / 255 of the exposure period of one pixel is on time, and the remaining period ((255 - Z) / 255) is off time. The off time per pixel for pixel value Z is T, and the on time is t. Note that Figure 10 shows an example where the off time is short, and Figure 11 shows an example where the on time is short.

[0046] In Figure 10A, all of the exposure patterns for each pixel are exposure pattern #B. At this time, on, off, on, off, ... are repeated in the main scanning direction B. At this time, the time during which the switch SW of the exposure unit 7 is in the off state is always T. Figure 10B shows an example in which the exposure patterns for each pixel are alternately repeated in the order of exposure pattern #C, exposure pattern #D, exposure pattern #C, ... in the main scanning direction B. At this time, the off times are repeated as T, T / 2, 3T / 2, ... in the main scanning direction B. In other words, the time during which the switch SW of the exposure unit 7 is in the off state in Figure 10B is at least T / 2 and at most 3T / 2.

[0047] In Figure 11 (A), all of the exposure patterns for each pixel are exposure pattern #C. At this time, off, on, off, on, ... are repeated in the main scanning direction B. At this time, the time during which the switch SW of the exposure unit 7 is in the on state is always t. Figure 11 (B) shows an example in which the exposure patterns for each pixel are alternately repeated in the order of exposure pattern #B, exposure pattern #E, exposure pattern #B, ... in the main scanning direction B. At this time, the on time is repeated as t, t / 2, 3t / 2, ... in the main scanning direction B. In other words, in Figure 11 (B), the time during which the switch SW of the exposure unit 7 is in the on state is at least t / 2 and at most 3t / 2.

[0048] In the pixel groups shown in FIGS. 10 and 11 , if the off time T or on time t based on the pixel value Z of each pixel is short enough to be outside the guaranteed response of the switch SW switching operation of the driver IC 2009, the exposure unit 7 cannot perform exposure according to the pixel value Z. Even if the off time T or on time t is within the guaranteed response of the switch SW switching operation, as shown in FIGS. 10B and 11B , depending on the exposure pattern, there may be locations where the off time is T / 2 and the on time is t / 2. These off times / on times may be outside the guaranteed response of the switch SW switching operation. In locations where the off times / on times are outside the guaranteed response, exposure according to the pixel value Z cannot be performed.

[0049] If the exposure unit 7 cannot perform exposure according to the pixel value Z, the exposure set by the generation unit 802 based on the correction amount parameter 806 is not performed. As a result, the correction of the exposure amount is not reflected in the actual exposure, and the sweeping and edge effect are not appropriately suppressed. Furthermore, in exposure involving off / on times that are outside the guaranteed response of the switch SW switching operation, the current IL described in FIG. 6 may overshoot when switching from a non-exposed area to an exposed area. Such excessive current may affect the durability of the exposure unit 7. In response to these issues, a process of Example 1 will be described below, which reduces the frequency of use of exposure involving off / on times in short periods that are outside the guaranteed response of the switch SW switching operation. <Process for reducing the frequency of use of exposure in short periods that are outside the guaranteed response>

[0050] In the first embodiment, the generation unit 802 sets an exposure pattern for each pixel so that the OFF or ON time is continuous between each pixel every two or three pixels in the main scanning direction. FIG. 12 shows functional blocks related to the exposure pattern setting performed by the generation unit 802. The generation unit 802 first corrects the pixel value of the correction target pixel using the correction unit 1301 (correction unit) as described above. The correction unit 1302 then outputs corrected image data 1304 to the exposure pattern setting unit 1302 (setting unit). The exposure pattern setting unit 1302 sets an exposure pattern for each pixel in the corrected image data 1304 so that the OFF or ON time is continuous between each pixel. The exposure pattern setting unit 1302 then outputs image data 1305 after exposure pattern setting to the signal generation unit 1303 (generation unit). The signal generation unit 1303 generates a drive signal 71, which is a PWM signal, in accordance with the pixel values ​​of the image data 1305 after exposure pattern setting and the exposure pattern setting, and outputs the drive signal 71 to the exposure unit 7.

[0051] 13 and 14 show examples of pixel groups for which exposure patterns have been set by the processing of Example 1. The pixel groups shown in these figures are part of the pixel group to be corrected by the generation unit 802. Note that Fig. 13 shows an example when the OFF time is short, and Fig. 14 shows an example when the ON time is short. Also, arrow B in both figures indicates the main scanning direction.

[0052] The group of pixels shown in Figure 13 all have the same pixel value, and an off-time of T is set per pixel by correcting the exposure amount based on the correction amount parameter 806. The exposure patterns for the pixels shown in Figure 13(A) are set in the main scanning direction B, such as exposure pattern #B, exposure pattern #C, ..., repeated every two pixels. The interval between these repetitions (in other words, the number of consecutive pixels) is called the exposure pattern setting interval. In Figure 13(A), the off-time T of exposure pattern #B and the off-time T of exposure pattern #C are consecutive, resulting in an off-time of 2T. The total off-time for the two pixels, which is the exposure pattern setting interval, is 2T.

[0053] In this way, by setting the exposure pattern so that the off-time T per pixel is continuous between pixels, exposure is performed for an off-time twice T every two pixels in the main scanning direction. Even if the off-time T per pixel is short enough that the driver IC 2009 switch SW switching operation is unresponsive, the off-time of the exposure unit 7 is twice T, thereby reducing the frequency of the unresponsive off-time. However, setting this exposure pattern does not change the average off-time for multiple pixels in the main scanning direction B. In FIG. 13A , where this exposure pattern setting is implemented, the off-time per two pixels is 2×T. Therefore, the exposure off-time per pixel is T, which matches the correction amount parameter 806, enabling appropriate correction.

[0054] The exposure patterns of the pixels shown in Fig. 13(B) are set in the main scanning direction as exposure pattern #B, exposure pattern #D, exposure pattern #C, ... with an exposure pattern setting interval of three pixels. In Fig. 13(B), the off-time T of exposure pattern #B and the off-time T / 2 of exposure pattern #D are consecutive, resulting in an off-time of 3T / 2. Furthermore, the off-time T / 2 of exposure pattern #D and the off-time T of exposure pattern #C are consecutive, resulting in an off-time of 3T / 2. The total off-time for the three pixels, which is the exposure pattern setting interval, is 3T.

[0055] In this way, by setting the exposure pattern so that the off-time T per pixel is continuous between pixels, two exposures are performed for every three pixels in the main scanning direction B, with the off-time being 1.5 times T. In this case, even if the off-time T per pixel is short enough that the driver IC 2009 does not respond to the switch SW switching operation, the off-time of the exposure unit 7 is 1.5 times T, thereby reducing the frequency of the off-time. The exposure pattern setting in FIG. 13B is configured to suppress the increase in off-time compared to the setting in FIG. 13A by setting the exposure pattern interval to three pixels. However, this exposure pattern setting does not change the average off-time for multiple pixels in the main scanning direction B. In FIG. 13B, when this exposure pattern setting is implemented, the off-time per three pixels is 2×(T+T / 2)=3×T. Therefore, the off-time per pixel is T, which matches the correction amount parameter 806, enabling appropriate correction.

[0056] Whether the exposure pattern setting interval is set to two pixels or three pixels is determined based on the response characteristics of the switching operation of the switch SW of the driver IC 2009 and the effect on image quality due to an increase in the off time. Alternatively, the setting interval may be determined based on the pixel value after the exposure amount is corrected.

[0057] The group of pixels shown in Fig. 14 all have the same pixel value, and an on-time of t per pixel has been set by correcting the exposure amount based on the correction amount parameter 806. The exposure patterns of the pixels shown in Fig. 14(A) are set at an exposure pattern setting interval of two pixels, such as exposure pattern #C, exposure pattern #B, ... in the main scanning direction B. In Fig. 14(A), the on-time t of exposure pattern #C and the on-time t of exposure pattern #B are consecutive, resulting in an on-time of 2t. The total on-time for the two pixels, which is the exposure pattern setting interval, is 2t.

[0058] In this way, by setting the exposure pattern so that the on-time t per pixel is continuous between pixels, an exposure is performed once for every two pixels in the main scanning direction B with an on-time twice t. Even if the on-time t per pixel is short enough that the driver IC 2009 switch SW switching operation is not responsive, the on-time of the exposure unit 7 is twice t, thereby reducing the frequency of the non-responsive on-time. However, even with this exposure pattern setting, the average on-time for multiple pixels in the main scanning direction B does not change. In FIG. 14A , where this exposure pattern setting is implemented, the on-time per two pixels is 2×t. Therefore, the on-time per pixel is t, which matches the correction amount parameter 806, enabling appropriate correction.

[0059] The exposure patterns of the pixels shown in Figure 14(B) are set in the main scanning direction B as exposure pattern #C, exposure pattern #E, exposure pattern #B, ... with an exposure pattern setting interval of three pixels. The on-time t of exposure pattern #C and the on-time t / 2 of exposure pattern #E are consecutive, resulting in an on-time of 3t / 2. Furthermore, the on-time t / 2 of exposure pattern #E and the on-time t of exposure pattern #B are consecutive, resulting in an on-time of 3t / 2. The total on-time for the three pixels, which is the exposure pattern setting interval, is 3t.

[0060] In this way, by setting the exposure pattern so that the on-time t per pixel is continuous between pixels, two exposures are performed for every three pixels in the main scanning direction B, with the on-time being 1.5 times t. In this case, even if the on-time t per pixel is short enough that the driver IC 2009 switch SW switching operation is not responsive, the on-time of the exposure unit 7 is 1.5 times t, thereby reducing the frequency of use of the non-responsive on-time. The exposure pattern setting in FIG. 14B is configured to suppress the increase in on-time compared to the setting in FIG. 14A by setting the exposure pattern interval to three pixels. However, even with this exposure pattern setting, the average on-time for multiple pixels in the main scanning direction B does not change. In FIG. 14B, when this exposure pattern setting is implemented, the on-time per three pixels is 2 × (t + t / 2) = 3 × t. Therefore, the on-time per pixel is t, which matches the correction amount parameter 806, enabling appropriate correction.

[0061] Whether the exposure pattern interval is set to two pixels or three pixels is determined based on the response characteristics of the switching operation of the switch SW of the driver IC 2009 and the effect on image quality due to an increase in the ON time. Alternatively, the setting interval may be determined based on the pixel value after the exposure amount is corrected.

[0062] In this way, the exposure pattern setting unit 1302 sets one exposure pattern out of the exposure patterns #B to #C for one pixel. The exposure pattern setting unit 1302 sets the exposure pattern for each pixel so that ON times (exposure periods) or OFF times (non-exposure periods) are continuous between multiple pixels that are continuous in the main scanning direction B. The signal generation unit 1303 generates the drive signal 71 in accordance with the exposure pattern set by the exposure pattern setting unit 1302.

[0063] The exposure pattern setting unit 1302 sets the exposure pattern so that when two pixels are consecutive pixels and the two pixels are a first pixel and a second pixel from upstream to downstream in the main scanning direction B, the on-time or off-time is consecutive between the first pixel and the second pixel. For example, in Fig. 13A, the exposure pattern setting unit 1302 sets the first pixel as exposure pattern #B (first exposure pattern) and the second pixel as exposure pattern #C (second exposure pattern), and exposure pattern #B and exposure pattern #C are repeated every two pixels in the main scanning direction B. For example, in Fig. 14A, the exposure pattern setting unit 1302 sets the first pixel as exposure pattern #C (first exposure pattern) and the second pixel as exposure pattern #B (second exposure pattern), and exposure pattern #C and exposure pattern #B are repeated every two pixels in the main scanning direction B.

[0064] The exposure pattern setting unit 1302 sets the exposure patterns so that the ON time or OFF time is continuous between the first pixel and the second pixel and between the second pixel and the third pixel, assuming that three pixels are a first pixel, a second pixel, and a third pixel from upstream to downstream in the main scanning direction B. For example, in FIG. 13B , the exposure pattern setting unit 1302 sets the first pixel to exposure pattern #B (first exposure pattern), the second pixel to exposure pattern #D (second exposure pattern), and the third pixel to exposure pattern #C (third exposure pattern). The exposure pattern setting unit 1302 repeats exposure pattern #B, exposure pattern #D, and exposure pattern #C every three pixels in the main scanning direction B. For example, in FIG. 14B , the exposure pattern setting unit 1302 sets the first pixel to exposure pattern #C (first exposure pattern), the second pixel to exposure pattern #E (second exposure pattern), and the third pixel to exposure pattern #B (third exposure pattern). The exposure pattern setting unit 1302 repeats exposure pattern #C, exposure pattern #E, and exposure pattern #B in the main scanning direction B for every three pixels.

[0065] These configurations allow the frequency of exposure, which involves short periods of off / on time during which the driver IC 2009 switch SW does not respond, to be reduced without changing the correction amount based on the correction amount parameter 806. This allows for both increased frequency at which exposure amount correction is reflected and correction with an appropriate correction amount. Therefore, it is possible to further suppress an increase in the amount of toner due to the sweeping effect and edge effect, thereby enhancing the effect of reducing toner consumption in image formation.

[0066] Moreover, the frequency of overshooting of the current IL can be reduced by reducing the frequency of exposure that involves off / on times outside the guaranteed response of the switch SW switching operation of the driver IC 2009. This reduces the impact of excessive current on the durability of the exposure unit 7 while maintaining an appropriate correction amount.

[0067] As described above, according to the first embodiment, it is possible to perform exposure of the photosensitive member while taking into consideration the response of the light source.

[0068] In the first embodiment, the exposure pattern for each pixel is set so that the OFF time or ON time continues between pixels at each exposure pattern setting interval in the main scanning direction. In this case, since a locally increased OFF time / ON time is set every two or three pixels, an OFF / ON pattern may be visible in the formed image at a cycle of two or three pixels. In the second embodiment, a configuration for setting an appropriate exposure pattern according to the OFF time / ON time will be described. In the second embodiment, the exposure pattern setting and the exposure pattern setting interval are determined based on the response characteristics of the switch SW switching operation of the driver IC 2009. In the description of the second embodiment, components common to the first embodiment will be omitted, and the differences from the first embodiment will be mainly described.

[0069] In the second embodiment, first, the following thresholds for the off time and the on time are defined based on the response characteristics of the switch SW switching operation of the driver IC 2009. First threshold: Lower limit of the off time to which the switch SW switching operation responds Second threshold: Lower limit of the on time to which the switch SW switching operation responds These thresholds are stored in the memory 11 or calculated by a program stored in the memory 11.

[0070] In the second embodiment, the exposure pattern setting unit 1302 of the generation unit 802 determines, for each pixel of the corrected image data 1304, whether to set an exposure pattern that makes the OFF time / ON time between each pixel continuous, and the exposure pattern setting interval, using the first threshold value and the second threshold value.

[0071] 15 is a flowchart showing the processing of the exposure pattern setting unit 1302 in Example 2. In step (hereinafter, abbreviated as S) 1601, the exposure pattern setting unit 1302 acquires or calculates the first and second thresholds. The exposure pattern setting unit 1302 acquires information about the first and second thresholds stored in the memory 11, or acquires the first and second thresholds calculated by a program stored in the memory 11.

[0072] In S1602, the exposure pattern setting unit 1302 calculates the off time T and on time t of each pixel in the corrected image data 1304. As described in the first embodiment, if the pixel value of the corrected image data 1304 is Z (Z is a value from 0 to 255), then within the exposure period of one pixel, a period of Z / 255 is the on time, and the remainder is the off time. Note that the exposure period of one pixel uses information stored in the memory 11.

[0073] In S1603, the exposure pattern setting unit 1302 determines whether or not the exposure pattern setting described in Example 1 is required. Here, the exposure pattern setting unit 1302 compares the off time T and the on time t with a first threshold and a second threshold, respectively, and determines whether the off time / on time are within the guaranteed response range of the switch SW switching operation. That is, the exposure pattern setting unit 1302 determines whether the off time T calculated in S1602 is smaller than the first threshold and whether the on time t is smaller than the second threshold.

[0074] Specifically, if the exposure pattern setting unit 1302 determines that the OFF time T is less than the first threshold or the ON time t is less than the second threshold for each pixel of the corrected image data 1304, the process proceeds to S1604. In this case, the exposure pattern setting unit 1302 sets an exposure pattern in which the OFF time / ON time is continuous between two or three pixels. If the exposure pattern setting unit 1302 determines in S1603 that the OFF time is equal to or greater than the first threshold or the ON time is equal to or greater than the second threshold, the process proceeds to S1607. In this case, the exposure pattern setting unit 1302 does not set an exposure pattern in which the OFF time / ON time is continuous, but sets one of exposure patterns #B to #E in exposure pattern setting 1607, and then ends the process. In the second embodiment, all the exposure patterns are the same, but they may be arbitrarily selected from multiple exposure patterns, or may be exposure patterns according to another exposure pattern setting (not shown) stored in the memory 11.

[0075] If it is determined in S1603 that exposure pattern setting is to be performed, the exposure pattern setting unit 1302 selects an exposure pattern setting interval in S1604. Here, the exposure pattern setting unit 1302 determines whether the OFF / ON times for the switch SW switching operation are responsive when the exposure pattern setting interval is set to 3 pixels. As described in the first embodiment, if the exposure pattern setting interval is set to 3 pixels, the OFF time of the exposure unit 7 is 3T / 2 and the ON time is 3t / 2. If the OFF time 3T / 2 is less than the first threshold or the ON time 3t / 2 is less than the second threshold, even if the exposure pattern setting interval is set to 3 pixels, the time will not be within the guaranteed response time for the switch SW switching operation. Therefore, in S1604, the exposure pattern setting unit 1302 determines whether 3T / 2 is less than the first threshold or whether 3t / 2 is the second threshold. If the exposure pattern setting unit 1302 determines in S1604 that 3T / 2 is less than the first threshold value or 3t / 2 is less than the second threshold value, the process proceeds to S1605. In S1605, the exposure pattern setting unit 1302 sets an exposure pattern with an exposure pattern interval of 2 pixels to obtain a larger OFF time / ON time, and then ends the process.

[0076] If the exposure pattern setting unit 1302 determines in S1604 that the OFF time 3T / 2 is equal to or greater than the first threshold value or that the ON time 3t / 2 is equal to or greater than the second threshold value, the process proceeds to S1606. In S1606, the exposure pattern setting unit 1302 sets an exposure pattern with an exposure pattern interval of 3 pixels, since setting the exposure pattern interval to 3 pixels makes it possible to achieve an exposure OFF / ON time within the guaranteed response of the switch SW switching operation, and then ends the process. <Specific example of a pixel group processed in Example 2>

[0077] A specific example of the processing and the pixel group after the processing according to Example 2 will be described below. In the following specific example, it is assumed that the exposure period of one pixel is 100 nsec, the first threshold is 20 nsec, and the second threshold is 30 nsec.

[0078] 16 shows an example of pixel groups in image data 1305 after exposure pattern setting by the exposure pattern setting unit 1302. All of these pixel groups are pixels whose pixel value was 255, corrected in accordance with the correction parameters shown in FIG. 9B. Arrow B indicates the main scanning direction. (Pixel group corresponding to distance 1 from the edge)

[0079] 9B, for the pixel group corresponding to a distance of 1 from the edge, the correction amount is 32 / 255, so 32 / 255 of the exposure period of one pixel is the off time. In other words, the off time T of each pixel is T = 100 nsec × 32 / 255 ≈ 12.55 nsec. In this case, because the off time T is less than the first threshold, an exposure pattern is set in which the off time / on time is continuous between each pixel.

[0080] Furthermore, 3T / 2 is approximately 18.82 nsec, which is also less than the first threshold. Therefore, exposure patterns are set with an exposure pattern setting interval of 2 pixels. As a result, the exposure patterns are set in the order exposure pattern #B, exposure pattern #C, ... are repeated in the main scanning direction B (pixel group corresponding to distances 2 and 10 from the edge).

[0081] As shown in FIG. 9B, the correction amount for the pixel groups corresponding to distances 2 and 10 from the edge is 48 / 255, so 48 / 255 of the exposure period for one pixel is the off time. In other words, the off time T for each pixel is T = 100 nsec × 48 / 255 ≈ 18.82 nsec. Since the off time T is less than the first threshold, an exposure pattern is set in which the off time / on time periods are continuous between each pixel. Since 3T / 2 ≈ 28.24 nsec is greater than the first threshold, an exposure pattern is set with an exposure pattern setting interval of three pixels. As a result, the exposure patterns are set in a repeated order in the main scanning direction B: exposure pattern #B, exposure pattern #D, exposure pattern #C, etc. (Pixel group corresponding to distance 6 from the edge)

[0082] For the pixel group corresponding to a distance of 6 from the edge, as shown in FIG. 9B, the correction amount is 207 / 255, so 207 / 255 of the exposure period for one pixel is the off time. In other words, 48 / 255 of the exposure period for one pixel is the on time. Therefore, the on time t for each pixel is t = 100 nsec × 48 / 255 ≒ 18.82 nsec. Since the on time t is less than the second threshold, an exposure pattern is set in which the off time / on time is continuous between each pixel. Furthermore, 3t / 2 ≒ 28.24 nsec, which is also less than the second threshold. Therefore, an exposure pattern is set with an exposure pattern setting interval of two pixels. As a result, the exposure patterns are set in a repeated order in the main scanning direction B, with exposure pattern #C, exposure pattern #B, etc. (Pixel groups corresponding to distances 5 and 7 from the edge)

[0083] As shown in FIG. 9B, the correction amount for the pixel groups corresponding to distances 5 and 7 from the edge is 191 / 255, so the off-time is 191 / 255 of the exposure period for one pixel. In other words, the on-time is 64 / 255 of the exposure period for one pixel. Therefore, the on-time t for each pixel is t = 100 nsec × 64 / 255 ≒ 25.1 nsec. Since the on-time t is less than the second threshold, an exposure pattern is set in which the off-time / on-time is continuous between each pixel. Since 3t / 2 ≒ 37.65 nsec is greater than the second threshold, an exposure pattern is set with an exposure pattern setting interval of three pixels. As a result, the exposure patterns are set in a repeated order in the main scanning direction B: exposure pattern #C, exposure pattern #E, exposure pattern #B, etc. (Pixel groups corresponding to distances 3 and 9 from the edge)

[0084] For the pixel groups corresponding to distances 3 and 9 from the edge, as shown in FIG. 9B, the correction amount is 80 / 255, so the off time is 80 / 255 of the exposure period for one pixel. In other words, the on time is 175 / 255 of the exposure period for one pixel. Therefore, the off time T of each pixel is T = 100 nsec × 80 / 255 ≒ 31.37 nsec, and the on time t is t = 100 nsec × 175 / 255 ≒ 68.63 nsec. In this case, the off time T is equal to or greater than the first threshold, and the on time t is equal to or greater than the second threshold. Therefore, for these pixel groups, an exposure pattern setting that consecutively alternates the off time and on time between each pixel is not performed, and an arbitrary exposure pattern is set in S1607. All pixels corresponding to distances 3 and 9 are set to exposure pattern #E. However, for pixels corresponding to distances 3 and 9, any of exposure patterns #B to #E shown in Figure 7 may be used, and all may or may not be the same exposure pattern. (Pixel groups corresponding to distances 4 and 8 from the edge)

[0085] Similarly, for pixel groups corresponding to distances 4 and 8 from the edge, the off-time T is equal to or greater than the first threshold, and the on-time t is equal to or greater than the second threshold. Therefore, no exposure pattern setting is implemented that makes the exposure off-time / on-time continuous between pixels. The arbitrary setting of the exposure pattern is the same as for distances 3 and 9.

[0086] As described above, since there is no need to increase the off time / on time at distances 3, 4, 8, and 9, the frequency of image degradation can be reduced by excluding these areas from the application of the exposure pattern setting implementation of Example 1.

[0087] 16 shows pattern setting for the case where there is an edge in the sub-scanning direction as in FIG. 4B. The same applies to the case where there is an edge in the main scanning direction, and whether or not to implement exposure pattern setting that makes the OFF / ON times between each pixel continuous is determined depending on the result of comparing T with the first threshold value or t with the second threshold value. When implementing exposure pattern setting that makes the OFF / ON times between each pixel continuous, the exposure pattern setting interval is determined depending on the result of comparing 3T / 2 with the first threshold value or 3t / 2 with the second threshold value, and an exposure pattern is set for each exposure pattern setting interval.

[0088] According to the second embodiment, when the switching operation of the switch SW of the driver IC 2009 is responsive, it is possible to prevent image quality degradation by minimizing the off time / on time. Furthermore, even in areas where an increase in the off time / on time is required, preventing an excessive increase in the off time / on time leads to suppression of image quality degradation. Therefore, in the second embodiment, it is possible to achieve both an improved effect of reducing toner consumption and suppression of image degradation.

[0089] As described above, according to the second embodiment, it is possible to perform exposure of the photosensitive member while taking into consideration the response of the light source.

[0090] In the present invention, the exposure patterns used to make the exposure off time or on time continuous between each pixel are not limited to the exposure patterns #B to #E shown in Figure 7, and other exposure patterns may be used.

[0091] The present invention can also be realized by supplying a program that realizes one or more of the functions of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program.The present invention can also be realized by a circuit (e.g., an ASIC) that realizes one or more of the functions.

[0092] As described above, in other embodiments, exposure of the photosensitive member can be performed taking into consideration the response of the light source.

[0093] The disclosure of this embodiment includes the following configurations: (Configuration 1)

[0094] an exposure period is a period during which the light source emits light to expose the photoconductor within one pixel, and a non-exposure period is a period during which the light source does not emit light and the photoconductor is not exposed; and an image forming apparatus for forming an image on a recording material, comprising: a photoconductor on which an electrostatic latent image is formed; a generating unit for generating a drive signal based on a pixel value of each pixel indicated by image data; and an exposure unit having a light source whose light emission is controlled based on the drive signal, and exposing the photoconductor to light emitted by the light source by scanning the photoconductor along a main scanning direction to form the electrostatic latent image; wherein the exposure unit is capable of exposing the photoconductor according to a plurality of exposure patterns in which the arrangement of the exposure period and the non-exposure period within one pixel differs; and the image forming apparatus further comprises a setting unit for setting one of the plurality of exposure patterns for one pixel, wherein the setting unit sets the exposure pattern for each pixel so that the exposure period or the non-exposure period is continuous between a plurality of pixels consecutive in the main scanning direction; and the generating unit generates the drive signal according to the exposure pattern set by the setting unit. (Configuration 2)

[0095] The image forming apparatus according to Configuration 1, wherein the setting unit sets a first exposure pattern for the first pixel and a second exposure pattern for the second pixel such that the exposure period or the non-exposure period continues between the first pixel and the second pixel when the plurality of consecutive pixels are two pixels and the two pixels are a first pixel and a second pixel from upstream to downstream in the main scanning direction. (Configuration 3)

[0096] The image forming apparatus according to the second aspect of the present invention, wherein the setting unit repeats the first exposure pattern and the second exposure pattern every two pixels in the main scanning direction.

[0097] The image forming apparatus of configuration 1, wherein the setting means sets a first exposure pattern for the first pixel, a second exposure pattern for the second pixel, and a third exposure pattern for the third pixel so that the exposure period or the non-exposure period is continuous between the first pixel and the second pixel, and between the second pixel and the third pixel, when the consecutive pixels are three pixels and the three pixels are a first pixel, a second pixel, and a third pixel from upstream to downstream in the main scanning direction.

[0098] According to the present invention, there is provided an image forming apparatus capable of exposing a photosensitive member in consideration of the response of a light source.

[0099] The present invention is not limited to the above-described embodiments, and various modifications and variations can be made without departing from the spirit and scope of the present invention. Therefore, the following claims are appended to apprise the public of the scope of the present invention.

[0100] This application claims priority based on Japanese Patent Application No. 2024-027524, filed February 27, 2024, the entire contents of which are incorporated herein by reference.

Claims

1. An image forming apparatus that forms an image on a recording material, comprising: a photosensitive member on which an electrostatic latent image is formed; a generating means that generates a drive signal based on the pixel value of each pixel indicated by image data; and an exposure means that has a light source whose light emission is controlled based on the drive signal and that exposes the photosensitive member by scanning the photosensitive member along the main scanning direction with light emitted by the light source to form the electrostatic latent image; wherein, when a period during which the light source emits light to expose the photosensitive member within one pixel is defined as an exposure period, and a period during which the light source does not emit light and the photosensitive member is not exposed is defined as a non-exposure period, the exposure means is capable of exposing the photosensitive member according to a plurality of exposure patterns in which the arrangement of the exposure period and the non-exposure period within one pixel differs; and the image forming apparatus comprises a setting means that sets one of the plurality of exposure patterns for one pixel, wherein the setting means sets the exposure pattern for each pixel so that the exposure period or the non-exposure period is continuous between a plurality of pixels that are consecutive in the main scanning direction, and the generating means generates the drive signal according to the exposure pattern set by the setting means.

2. The image forming apparatus according to claim 1, wherein the setting means sets a first exposure pattern for the first pixel and a second exposure pattern for the second pixel so that the exposure period or the non-exposure period continues between the first pixel and the second pixel when the consecutive pixels are two pixels and the two pixels are a first pixel and a second pixel from upstream to downstream in the main scanning direction.

3. The image forming apparatus according to claim 2, wherein said setting means repeats said first exposure pattern and said second exposure pattern every two pixels in said main scanning direction.

4. The image forming apparatus of claim 1, wherein the setting means sets a first exposure pattern for the first pixel, a second exposure pattern for the second pixel, and a third exposure pattern for the third pixel so that the exposure period or the non-exposure period is continuous between the first pixel and the second pixel, and between the second pixel and the third pixel, when the consecutive pixels are three pixels and the three pixels are a first pixel, a second pixel, and a third pixel from upstream to downstream in the main scanning direction.

5. An image forming apparatus according to claim 4, wherein said setting means repeats said first exposure pattern, said second exposure pattern and said third exposure pattern every three pixels in said main scanning direction.

6. The image forming apparatus according to claim 1, wherein said setting means selects the number of said plurality of consecutive pixels according to the exposure period or the non-exposure period within said one pixel.

7. An image forming apparatus as described in claim 1, wherein the setting means sets the exposure pattern for each pixel so that the exposure period or the non-exposure period is continuous between multiple pixels that are consecutive in the main scanning direction when the non-exposure period within one pixel is less than a first threshold value or the exposure period is less than a second threshold value.

8. An image forming apparatus as described in any one of claims 1 to 7, comprising: a correction means for correcting pixel values ​​of pixels in an area where toner adheres according to the distance from an edge of the area when the image data is first image data; and a storage means for storing information for identifying pixels to be corrected, which are pixels that are the subject of correction by the correction means, and information relating the distance from the edge to the amount of correction of the pixel value, wherein the correction means corrects input second image data based on the information stored in the storage means to generate the first image data.

9. An image forming apparatus as described in claim 1, wherein the multiple exposure patterns include a pattern in which the exposure period is located upstream in the main scanning direction within the single pixel, a pattern in which the exposure period is located downstream in the main scanning direction within the single pixel, a pattern in which the exposure period is located in the center in the main scanning direction within the single pixel, and a pattern in which the exposure period is located on both ends in the main scanning direction within the single pixel.

Images