Image forming device

Abstract

To provide an image formation apparatus which suppresses unnecessary radiation noise while maintaining image quality.SOLUTION: An image formation apparatus includes storage means which stores pattern information which exhibits an exposure pattern as the pattern of an exposure area and a non-exposure area along a main scanning direction of a pixel and generation means which generates a driving signal for driving exposure means by using the exposure pattern exhibited by pattern information based on first image data. Therein, the pattern information exhibits a plurality of exposure patterns with respect to a first pixel, the non-exposure area does not continue on a boundary of adjacent two exposure patterns even when the same exposure patterns, among a plurality of exposure patterns of the first pixel are made adjacent to each other in a main scanning direction, even when different two exposure patterns are made adjacent to each other in a main scanning direction, and the generation means selects the exposure patterns from the plurality of exposure patterns at random or selects the exposure patterns according to a predetermined order from the plurality of exposure patterns, while continuously using a plurality of exposure patterns of the first pixel in a main scanning direction.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus such as a copying machine, a laser beam printer, or a facsimile machine, and more particularly to a technique for suppressing unwanted radiation noise emitted from an image forming apparatus. [Background technology]

[0002] In an image forming apparatus, it is required to maintain the quality of the image formed. On the other hand, in an image forming apparatus using electrophotography, a phenomenon called "sweeping" or "edge effect" may occur, in which toner excessively adheres to the edge portion of an electrostatic latent image formed on a photoconductor. "Sweeping" refers to a phenomenon in which toner excessively adheres to the edge portion of the electrostatic latent image that is on the rear side in the rotation direction of the photoconductor. "Edge effect" refers to a phenomenon in which toner excessively adheres to the edge portion around the electrostatic latent image. Patent Documents 1 and 2 disclose a configuration in which the sweeping and edge effect are suppressed by adjusting the amount of exposure by pulse width modulation. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2003-345076 A [Patent Document 2] JP 2000-343748 A Summary of the Invention [Problem to be solved by the invention]

[0004] The configurations disclosed in Patent Documents 1 and 2 can prevent toner from excessively adhering to the edge portions of the electrostatic latent image, but they generate unnecessary radiation noise (radiated electromagnetic waves) due to pulse width modulation.

[0005] The present invention provides an image forming apparatus that suppresses unnecessary radiation noise while maintaining image quality. [Means for solving the problem]

[0006] According to one aspect of the present invention, an image forming apparatus includes a photoconductor, an exposure unit for scanning and exposing the photoconductor in a main scanning direction to form an electrostatic latent image on the photoconductor, a development unit for developing the electrostatic latent image with a developer to form an image on the photoconductor, a storage unit for storing pattern information indicating an exposure pattern which is a pattern of exposed areas and non-exposed areas of a pixel along the main scanning direction, and a generation unit for generating a drive signal for driving the exposure unit using the exposure pattern indicated by the pattern information based on first image data, and the pattern information is , two exposure patterns, a first exposure pattern and a second exposure pattern indicates, the first exposure pattern is an exposure pattern in which the first pixel is divided into three regions along the main scanning direction, the first and third regions being the exposed region and the second region being the non-exposed region, and the second exposure pattern is an exposure pattern in which the first pixel is divided into two regions along the main scanning direction, the first region being the exposed region and the second region being the non-exposed region, The generating means generates the first pixel The above two When the exposure patterns are used consecutively in the main scanning direction, The above two The exposure pattern to be used is selected at random from the exposure patterns. Effect of the Invention

[0007] According to the present invention, it is possible to suppress unnecessary radiation noise while maintaining image quality. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating the configuration of an image forming apparatus according to an embodiment. [Diagram 2] FIG. 2 is an explanatory diagram of a jumping development method and a contact development method. [Diagram 3] 13A and 13B are diagrams showing an image in which an edge effect occurs and an image in which sweeping occurs. [Figure 4] FIG. 4 is a diagram showing an exposure amount control configuration according to an embodiment. [Diagram 5] FIG. 4 is an explanatory diagram of an exposure pattern of one pixel. [Figure 6] FIG. 4 is a functional block diagram of a CPU for generating a drive signal according to an embodiment. [Figure 7] 4A and 4B are diagrams showing an example of image data and an example of correction target pixels; [Figure 8]5 is an explanatory diagram of a process performed by an exposure amount adjustment unit. [Figure 9] 11A and 11B are diagrams showing examples of exposure patterns of pixels having the same pixel value that are consecutive in the main scanning direction; [Figure 10] 4 is a flowchart of an image forming process according to an embodiment. [Figure 11] FIG. 13 is a diagram illustrating a combination of exposure patterns of two adjacent pixels having the same pixel value according to an embodiment. [Figure 12] 5 is a flowchart of a process for generating a drive signal according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the embodiments will be described in detail with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims. Although the embodiments describe a number of features, not all of these features are essential to the invention, and the features may be combined in any manner. Furthermore, in the attached drawings, the same reference numbers are used for the same or similar configurations, and duplicated descriptions are omitted.

[0010] First Embodiment FIG. 1 is a configuration diagram of an image forming apparatus 101 according to this embodiment. Photoconductor 1, which is an image carrier, is rotated in the direction of the arrow in the figure during image formation. Charging section 2 charges the surface of photoconductor 1 to a uniform potential. Exposure section 7 scans and exposes the charged surface of photoconductor 1 with light 72 based on image data to form an electrostatic latent image on photoconductor 1. The direction in which exposure section 7 scans photoconductor 1 with light 72 is called the main scanning direction. Note that exposure section 7 is driven by drive signal 71 output by image calculation section 9. Exposure control section 19 of image calculation section 9 adjusts exposure intensity by exposure section 7 to a target value using voltage Va.

[0011] The developing unit 3 includes a container 13 for storing toner, which is a developer, and a developing roller 14. The toner may be a non-magnetic one-component toner, a two-component toner, or a magnetic toner. The regulating blade 15 is provided to regulate the layer thickness of the toner supplied to the developing roller 14 to a predetermined value. The regulating blade 15 may 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 an area where the developing roller 14 and the photoconductor 1 are in close proximity or in contact with each other, and is an area where the toner is attached to the electrostatic latent image. The developing unit 3 attaches the toner to the electrostatic latent image formed on the photoconductor 1, and the toner is visualized as a toner image. The transfer unit 4 transfers the toner image formed on the photoconductor 1 to a recording material P. The fixing unit 6 applies heat and pressure to the recording material P to which the toner image has been transferred, thereby fixing the toner image to the recording material P.

[0012] The CPU 10 of the image calculation unit 9 is a control unit that controls the entire image forming apparatus 101. It is possible to configure the CPU 10 to execute all of the controls described below, or to configure the ASIC 18 to execute some of them. It is also possible to configure the ASIC 18 to execute all of the controls described below. The memory 11 is a storage unit that stores image data in the image memory 111 and holds the LUT 112. The LUT 112 is a lookup table that indicates various information related to image processing. The image calculation unit 9 receives image data transmitted from the host computer 8, and corrects the image data based on the information held by the LUT 112 to suppress the edge effect and the influence of sweeping, and to reduce toner consumption.

[0013] Next, the development method will be explained with reference to FIG. 2. FIG. 2(A) shows a development unit 3 that uses a jumping development method. In the jumping development method, the development roller 14 and the photoconductor 1 are not in contact with each other, and a gap 17 of a predetermined distance is provided. Then, an AC bias superimposed with a DC bias is used as the development bias output by the development roller 14. FIG. 2(B) shows the configuration of the development unit 3 that uses a contact development method. In the contact development method, the development roller 14 and the photoconductor 1 are brought into contact with each other. Then, a DC bias is used as the development bias output by the development roller 14.

[0014] Next, the principles of edge effect and sweeping, in which the amount of toner adhering to an electrostatic latent image increases at the edge of the electrostatic latent image, will be described. The edge effect is a phenomenon in which an electric field is concentrated at the boundary between the exposed area of ​​the photoconductor 1 and the other non-exposed area of ​​the electrostatic latent image, causing excessive toner to adhere to each edge of the electrostatic latent image. FIG. 3A shows a toner image 400 in which the edge effect has occurred. The arrow A in FIG. 3A indicates the conveying direction of the toner image, that is, the rotating direction of the photoconductor 1. Note that the image data on which the toner image 400 is based has the same pixel value for all pixels, that is, the toner image 400 is an image of uniform density. When the edge effect occurs, toner is concentrated and adheres to all edge areas 402a of the toner image 400. As a result, the density of the edge area 402a becomes higher than the density of the non-edge area 401a. The edge effect mainly occurs in a jumping development method in which there is a gap between the photoconductor 1 and the developing roller 14.

[0015] On the other hand, the sweeping is a phenomenon in which toner is concentrated at the rear end of the electrostatic latent image in the rotation direction of the photoconductor 1. FIG. 3B shows a toner image 410 in which the sweeping has occurred. The arrow A in FIG. 3B indicates the conveying direction of the toner image, that is, the rotation direction of the photoconductor 1. The image data on which the toner image 410 is based has the same pixel value for all pixels, that is, the toner image 410 is an image of uniform density. When the sweeping occurs, the amount of toner in the rear end region 402b of the toner image 410 increases. This is because, when the peripheral speed of the developing roller 14 is faster than that of the photoconductor 1, when the part of the developing roller 14 entering the developing area 16 passes the rear end region 402b in the developing area 16, the toner held in the part is concentrated and adhered to the rear end region 402b. As a result, the density of the rear end region 402b becomes higher than the density of the other region 401b.

[0016] FIG. 4 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 the intensity adjustment signal 73 set by the CPU 10. The voltage VrefH becomes the reference voltage of the DA converter 2021. The IC 2003 sets the input data 2020 of the DA converter 2021, so that the DA converter 2021 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 with a current value Id and outputs it to the driver IC 2009. The driver IC 2009 controls the light emission intensity of the LD of the exposure unit 7, that is, the exposure intensity, by controlling the current IL flowing through the laser diode (LD) of the exposure unit 7 using the current value Id. Thus, 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 a switch (SW) of the driver IC 2009 in response to a drive signal 71 output from the image calculation unit 9. The SW controls ON / OFF of the light emission of the LD by switching whether the current IL flows to the LD of the exposure unit 7 or to the dummy resistor R1. Note that, in this embodiment, the LD emits light when the drive signal 71 is at a high level, but the LD may be configured to emit light when the drive signal 71 is at a low level.

[0017] Next, a description will be given of a plurality of exposure patterns for one pixel in this embodiment. In this embodiment, the exposure time (exposure section) in the main scanning direction of one pixel is adjusted by using pulse width modulation (PWM), thereby adjusting the amount of exposure. All of Figs. 5(A) to 5(D) show exposure patterns for achieving a 50% amount of exposure. In Figs. 5(A) to 5(D) and the figure showing the pixel row described later, the direction from left to right in the figure is the main scanning direction. In Fig. 5(A), one pixel is divided into two regions, the first region is the exposed region, and the second region is the non-exposed region. In the following description, the numbers such as the first and second increase along the main scanning direction. In other words, the numbers increase in order from the left side to the right side of the figure. In Fig. 5(B), one pixel is divided into two regions, the first region is the non-exposed region, and the second region is the exposed region. In Fig. 5(C), one pixel is divided into three regions, the first and third regions are non-exposed regions, and the second region is exposed region. In Fig. 5(D), one pixel is divided into three regions, the first and third regions are exposed regions, and the second region is non-exposed region.

[0018] FIG. 5 shows the case where the exposure amount is 50%, so the areas of the exposed area and the non-exposed area in one pixel are the same in each of FIG. 5(A) to FIG. 5(D). In this example, the number of divisions in the main scanning direction is a maximum of 3, but it can also be divided into four or more areas. Also, in FIG. 5(C) and FIG. 5(D), the lengths of the first and third areas in the main scanning direction are the same, but they may be different. In the following description, the exposure patterns of one pixel shown in FIG. 5(A), FIG. 5(B), FIG. 5(C), and FIG. 5(D) are denoted as patterns #A, #B, #C, and #D, respectively.

[0019] FIG. 6 is a functional block diagram of the CPU 10 for suppressing the edge effect or the sweeping and suppressing the unnecessary radiation noise. As already explained, the functional block shown in FIG. 6 can be realized by the ASIC 18 and the CPU 10 as a whole, or by the ASIC 18 alone. The LUT 112 (FIG. 1) holds correction pixel specification information, exposure correction information, and pattern information. The setting unit 602 notifies and sets the correction pixel specification information, exposure correction information, and pattern information held by the LUT 112 to the image analysis unit 601, the exposure adjustment unit 603, and the drive signal generation unit 604. The image data 605 transmitted from the host computer 8 and stored in the memory 11 is input to the image analysis unit 601. The image analysis unit 601 specifies a correction target pixel where the edge effect or the sweeping may occur from the pixels of the image formed by the image data 605 based on the correction pixel specification information, and notifies the specified correction target pixel to the exposure adjustment unit 603 together with the image data 605. Here, the image means an area where toner is continuously attached. In other words, one recording material P is not formed with one image, but one or more images may be formed on one recording material P depending on the toner attachment state. The correction pixel specifying information may indicate, for example, the range of pixels where edge effect or sweeping may occur, by the number of pixels from the edge pixel of the image. For example, if the correction pixel specifying information is "5", then in the area (image) where toner is continuously attached, five pixels from the edge are determined to be correction target pixels. Any parameter that can specify pixels where edge effect or sweeping may occur may be used as the correction pixel specifying information.

[0020] The exposure adjustment unit 603 corrects the pixel value of the correction target pixel indicated by the image data 605 based on the exposure correction information, and outputs the corrected image data 605 to the drive signal generation unit 604. The exposure correction information indicates the correction amount of the exposure of the correction target pixel. As an example, the exposure correction information can be an amount indicating a reduction rate of the exposure. The drive signal generation unit 604 generates the drive signal 71 based on the image data 605 corrected by the exposure adjustment unit 603 and the pattern information. The pattern information is information indicating a plurality of exposure patterns for one pixel for each pixel value except the maximum value and the minimum value. For example, when the maximum pixel value is 255, the pattern information for the exposure amount of 50%, that is, the pixel value of 128, can be two or more of those shown in FIG. 5(A) to FIG. 5(D). The maximum value and the minimum value are excluded because the entire region of the pixel is exposed in the case of the maximum value, and the entire region of the pixel is not exposed in the case of the minimum value. In other words, there is only one exposure pattern for the maximum value and the minimum value of the pixel.

[0021] FIG. 7(A) shows an example of image data 605. In FIG. 7(A), the pixel value of the pixel is shown at the pixel position of the image formed by the image data 605. In the following description, the pixel value of the maximum density is 255. Therefore, when the pixel value is 255, the exposure amount is 100%, and the entire area of ​​the pixel is exposed. In the image data 605 of FIG. 7(A), toner is continuously attached to 45 pixels located in the 2nd to 10th columns from the left in the 3rd to 7th rows from the top of the figure. In other words, these 45 pixels form one image. For example, it is assumed that the sweeping is suppressed, and the correction pixel specification information is "2". In addition, the rotation direction of the photoconductor 1 is the direction from the bottom to the top of FIG. 7. In this case, the image analysis unit 601 determines that the pixel columns of two rows from the bottom edge to the top are correction target pixels among the 45 pixels that make up the image. FIG. 7(B) shows the correction target pixels in this case. In FIG. 7B, pixels to be corrected are indicated by "1", and pixels not to be corrected are indicated by "0".

[0022] The exposure adjustment unit 603 corrects the pixel value of the correction target pixel by the exposure correction information. FIG. 8(A) shows the pixel value of the pixel column in the sixth row from the top of FIG. 7(A) including the correction target pixel. FIG. 8(B) shows the pixel value after correction by the exposure adjustment unit 603 when the exposure correction information of the correction target pixel in FIG. 8(A) is 50%. FIG. 8(C) shows the pixel value after correction by the exposure adjustment unit 603 when the exposure correction information of the correction target pixel in FIG. 8(A) is 25%. In this manner, the exposure adjustment unit 603 corrects the image data 605 based on the exposure correction information. The correction amount of the exposure indicated by the exposure correction information can be made different depending on the distance from the edge of the pixel. Furthermore, the correction amount of the exposure indicated by the exposure correction information can be made different depending on the pixel value. Furthermore, the correction amount of the exposure indicated by the exposure correction information can be made different depending on the distance from the edge of the pixel and the pixel value of the pixel.

[0023] The driving signal generating unit 604 generates the driving signal 71 based on the image data 605 corrected by the exposure amount adjusting unit 603 and the pattern information. FIG. 9 is an explanatory diagram of the driving signal 71 for the portion of FIG. 8B where nine pixel values ​​"128" are consecutive. FIG. 9A shows a case where only pattern #C is used for nine consecutive pixels. FIG. 9B shows a case where only pattern #D is used for nine consecutive pixels. As shown in FIG. 9A and FIG. 9B, if the same exposure pattern is used continuously when the same pixel value is consecutive in the main scanning direction, the exposed area and the non-exposed area will be regularly repeated. In other words, the driving signal 71, which is PWM, becomes a signal in which a high level (corresponding to the exposed area) and a low level (corresponding to the non-exposed area) are regularly repeated, and the frequency component corresponding to this regular repetition becomes stronger, making it easier for unnecessary radiation noise to occur. Therefore, in this embodiment, as shown in FIG. 9C or FIG. 9D, the driving signal 71 is made not to be a regularly repeated signal. In Fig. 9(C), pattern #A and pattern #D are used. Note that whether pattern #A or pattern #D is to be used for a given pixel can be selected / determined, for example, randomly. Similarly, in Fig. 9(D), pattern #B and pattern #D are used randomly.

[0024] As shown in FIG. 9(C), when pattern #A and pattern #D are used, the non-exposed regions of two consecutive pixels are not continuous, whether pattern #A is continuous, pattern #D is continuous, pattern #A is followed by pattern #D, or pattern #A is followed by pattern #D. The lengths of the non-exposed regions of pattern #A and pattern #D are the same. Therefore, even if the exposure pattern to be used is randomly selected from pattern #A and pattern #D, the non-exposed regions of two adjacent pixels in the main scanning direction are not continuous, and therefore the length of the non-exposed region in the main scanning direction is constant. Image quality can be maintained by making the length of the non-exposed region in the main scanning direction constant in the part where the same pixel value is continuous. The same is true when pattern #B and pattern #D are used, as shown in FIG. 9(D).

[0025] For this reason, in this embodiment, two exposure patterns indicated by the pattern information are selected so that the non-exposure area of ​​the pixel exposed first and the non-exposure area of ​​the pixel exposed later are not continuous even when they are continuous in the main scanning direction. Fig. 9(C) is an example in which the pattern information indicates pattern #A and pattern #D, and Fig. 9(D) is an example in which the pattern information indicates pattern #B and pattern #D.

[0026] In FIG. 9C and FIG. 9D, two exposure patterns are selected for a pixel, but three or more exposure patterns can be selected. That is, the number of exposure patterns for each pixel indicated by the pattern information can be multiple (two or more). Note that, regardless of the order in which the exposure patterns of a pixel are consecutively arranged in the main scanning direction, multiple exposure patterns are selected so that non-exposed areas do not continue at the boundaries of the exposure patterns. Also, the length in the main scanning direction of the non-exposed areas of the multiple exposure patterns of a pixel is fixed. Note that the pattern information is provided for each pixel value except for the maximum pixel value and the minimum pixel value, 255 and 0 in this example. Furthermore, a configuration can be adopted in which multiple exposure patterns for multiple consecutive pixels of the same pixel value in the main scanning direction are added to the pattern information. In this case, the exposure pattern to be applied is randomly selected from the multiple exposure patterns corresponding to the number of consecutive pixel values ​​according to the number of consecutive pixel values ​​of the same pixel value to generate the drive signal 71. In any case, by making the drive signal 71 such that the high level and the low level do not regularly repeat, it is possible to reduce unnecessary radiation noise.

[0027] FIG. 10 is a flowchart of the image forming process according to this embodiment. When the CPU 10 receives image data 605 from the host computer 8, it determines whether or not the exposure adjustment is necessary in consideration of the device state, etc., in S10. If the exposure adjustment is not necessary, the CPU 10 generates a driving signal 71 based on the image data 605 in S13, and forms an image based on the driving signal 71 in S14. On the other hand, if the exposure adjustment is necessary, the CPU 10 determines a correction target pixel based on correction pixel specification information in S11. Then, the CPU 10 corrects the exposure based on the exposure correction information in S12, more specifically, corrects the pixel value of the correction target pixel. Then, the CPU 10 generates a driving signal 71 based on the corrected image data 605 in S13, and forms an image in S14. Next, the CPU 10 determines whether the image formation is completed in S15, and repeats the process from S10 until the image formation is completed.

[0028] As described above, in this embodiment, pattern information indicating a plurality of exposure patterns is stored in advance in the image forming apparatus for pixels of each pixel value except the maximum value and the minimum value. The exposure pattern of a pixel is a pattern of an exposed area and a non-exposed area along the main scanning direction. Although the plurality of exposure patterns for the same pixel are different, the total area of ​​the exposed area is the same value according to the pixel value of the pixel. Also, the length in the main scanning direction of the non-exposed area of ​​the plurality of exposure patterns of the pixel with the same pixel value is constant. Here, in this embodiment, the plurality of exposure patterns for a certain pixel are selected so that the non-exposed area does not continue at the boundary of the exposure patterns, even if two of the same exposure patterns are arranged in the main scanning direction or two arbitrary different exposure patterns are arranged in the main scanning direction. Then, when the exposure patterns of the same pixel are used continuously in the main scanning direction, the exposure pattern to be used is selected randomly from the plurality of exposure patterns of the pixel. This configuration can suppress unnecessary radiation noise. Also, by selecting a plurality of exposure patterns for a certain pixel so that the non-exposed area does not continue at the boundary of the exposure patterns, the length of the non-exposed area in the main scanning direction does not change, and image quality can be maintained.

[0029] For example, when the same pixel value occurs consecutively, the exposure pattern to be applied from among the multiple exposure patterns may be selected randomly for the entire image data after correction by the exposure adjustment unit 603. Also, when the same pixel value occurs consecutively, the exposure pattern to be applied from among the multiple exposure patterns may be selected randomly for the pixel to be corrected. In any case, it is possible to suppress unnecessary radiation noise with an inexpensive configuration and reduce edge effects or sweeping, thereby improving image quality and suppressing unnecessary toner consumption.

[0030] In this embodiment, when the exposure patterns of the same pixel are used consecutively in the main scanning direction, the exposure pattern to be used is selected randomly from the multiple exposure patterns of the pixel. However, when the exposure patterns of the same pixel are used consecutively in the main scanning direction, the selection order (predetermined order) may be determined in advance, and the exposure pattern to be used may be selected according to this selection order. This selection order is determined in advance so as to suppress unwanted radiation noise, and may be, for example, one of the pieces of information held by the LUT 112.

[0031] Second Embodiment Next, the second embodiment will be described with a focus on the differences from the first embodiment. In the first embodiment, the multiple exposure patterns indicated by the pattern information were set so that no non-exposed regions would be continuous no matter how they were connected in the main scanning direction. In this embodiment, such a restriction is not imposed. That is, in this embodiment, the multiple exposure patterns of a pixel indicated by the pattern information are allowed to include at least one set (two) of exposure patterns that would result in continuous non-exposed regions if connected in the main scanning direction. In the following, this embodiment will be described as an example in which the pattern information indicates three exposure patterns, patterns #A, #B, and #D in FIG. 5, for a pixel with an exposure amount of 50%.

[0032] 11(A) to 11(I) show possible combinations of exposure patterns that can be applied to two pixels with 50% exposure that are consecutive in the main scanning direction when the pattern information indicates patterns #A, #B, and #D. As shown in FIG. 11(A), if pattern #B is applied after pattern #A, the non-exposed area will be consecutive. Note that, as shown in FIG. 11(B) to FIG. 11(I), the non-exposed area is not consecutive in other combinations. In this embodiment, when pixels with the same pixel value are consecutive, the CPU 10 randomly selects an exposure pattern to be applied to the pixel from three exposure patterns, and then determines whether the selected exposure pattern is consecutive with the non-exposed area of ​​the exposure pattern of the previous pixel. Note that the previous pixel means the pixel that is exposed immediately before in the main scanning direction. If the non-exposed area is consecutive, the CPU 10 reselects the exposure pattern of the pixel.

[0033] The flow chart of the image forming process according to this embodiment is the same as that of FIG. 10, but in the process of generating the drive signal 71 in S13, the CPU 10 performs a process for preventing non-exposure regions from continuing between pixels when pixels of the same pixel value are consecutive in the main scanning direction. FIG. 12 is a flow chart of the process performed by the CPU 10 when the same pixel value is consecutive in the process of generating the drive signal 71 in S13 of FIG. 10. In S20, the CPU 10 randomly selects an exposure pattern for the determination target pixel from patterns #A, #B, and #D. Note that the first determination target pixel is the second pixel when pixels of the same pixel value are consecutive. In S21, the CPU 10 determines whether the non-exposure region of the determination target pixel by the exposure pattern selected in S20 is consecutive with the non-exposure region of the previous pixel of the same pixel value. If they are consecutive, the CPU 10 repeats the process from S20 until the non-exposure regions are no longer consecutive. If the non-exposed region of the pixel to be determined is not continuous with the non-exposed region of the previous pixel, the CPU 10 judges whether the process for the last pixel in the continuous region has been completed in S22. If the process for the last pixel has not been completed, the CPU 10 changes the pixel to be determined to the pixel to be exposed next, and repeats the process from S20 until the process for the last pixel has been completed. The process of FIG. 12 is executed every time a portion in which pixels with the same pixel value are continuous occurs.

[0034] Fig. 9(E) shows an example of a drive signal 71 determined by the process of Fig. 12 when the pattern information indicates three exposure patterns, patterns #A, #B, and #D. Fig. 9(E) shows an example of a drive signal 71 for a portion of Fig. 8(B) where nine consecutive pixel values ​​of "128" occur. Even if pattern #B is selected after pattern #A (Fig. 11(A)), reselection is performed (S21 in Fig. 12), so that there are no consecutive non-exposed regions at the boundaries of the exposure patterns.

[0035] As described above, in this embodiment, when the multiple exposure patterns indicated by the pattern information are connected in the main scanning direction, the non-exposed areas may be continuous at the boundary between the exposure patterns. Therefore, when the exposure patterns of the same pixel are connected in the main scanning direction, the CPU 10 randomly selects an exposure pattern under the condition that the non-exposed areas are not continuous at the boundary between the two exposure patterns. For example, when pixels of the same pixel value are continuous in the main scanning direction, the CPU 10 randomly selects an exposure pattern for the second and subsequent pixels, and then determines whether the non-exposed area of ​​the selected exposure pattern is continuous with the non-exposed area of ​​the previous pixel. If the non-exposed area is continuous, the random selection of the exposure pattern for the pixel is repeated until it is no longer continuous. With this configuration, it is possible to maintain image quality and suppress unnecessary radiation noise, similar to the first embodiment, while suppressing the effects of sweeping and edge effects.

[0036] In this embodiment, when exposure patterns of the same pixel are used consecutively in the main scanning direction, the selection order (predetermined order) may be determined in advance, and the exposure pattern to be used may be selected according to this selection order. This selection order is determined so that the length of the non-exposure area in the main scanning direction does not change, that is, so that the non-exposure area does not continue at the boundary of the exposure pattern. Furthermore, this selection order is determined so as to suppress unnecessary radiation noise.

[0037] [Other embodiments] The present invention can also be realized by a process in which a program for implementing one or more of the functions of the above-described embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program. The present invention can also be realized by a circuit (e.g., ASIC) that implements one or more of the functions.

[0038] The invention is not limited to the above-described embodiments, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0039] 1: photoconductor, 7: exposure unit, 3: development unit, 11: memory, 604: drive signal generation unit

Claims

1. A photoconductor; an exposure unit for scanning the photoconductor in a main scanning direction to expose the photoconductor to light, thereby forming an electrostatic latent image on the photoconductor; a developing means for developing the electrostatic latent image with a developer to form an image on the photoreceptor; a storage means for storing pattern information indicating an exposure pattern which is a pattern of exposed and non-exposed areas of pixels along the main scanning direction; a generating means for generating a drive signal for driving the exposure means using an exposure pattern indicated by the pattern information based on first image data; Equipped with The pattern information indicates two exposure patterns, a first exposure pattern and a second exposure pattern, for a first pixel; the first exposure pattern is an exposure pattern in which the first pixel is divided into three regions along the main scanning direction, a first region and a third region are the exposed region, and a second region is the non-exposed region; the second exposure pattern is an exposure pattern in which the first pixel is divided into two regions along the main scanning direction, the first region being the exposed region and the second region being the non-exposed region; an exposure pattern generating unit that generates an exposure pattern for the first pixel from the two exposure patterns when the two exposure patterns are used consecutively in the main scanning direction;

2. A photoconductor; an exposure unit for scanning the photoconductor in a main scanning direction to expose the photoconductor to light, thereby forming an electrostatic latent image on the photoconductor; a developing means for developing the electrostatic latent image with a developer to form an image on the photoreceptor; a storage means for storing pattern information indicating an exposure pattern which is a pattern of exposed and non-exposed areas of pixels along the main scanning direction; a generating means for generating a drive signal for driving the exposure means using an exposure pattern indicated by the pattern information based on first image data; Equipped with The pattern information indicates two exposure patterns, a first exposure pattern and a third exposure pattern, for a first pixel; the first exposure pattern is an exposure pattern in which the first pixel is divided into three regions along the main scanning direction, a first region and a third region are the exposed region, and a second region is the non-exposed region; the third exposure pattern is an exposure pattern in which the first pixel is divided into two regions along the main scanning direction, the first region being the non-exposed region and the second region being the exposed region; an exposure pattern generating unit that generates an exposure pattern for the first pixel from the two exposure patterns when the two exposure patterns are used consecutively in the main scanning direction;

3. A photoconductor; an exposure unit for scanning the photoconductor in a main scanning direction to expose the photoconductor to light, thereby forming an electrostatic latent image on the photoconductor; a developing means for developing the electrostatic latent image with a developer to form an image on the photoreceptor; a storage means for storing pattern information indicating an exposure pattern which is a pattern of exposed and non-exposed areas of pixels along the main scanning direction; a generating means for generating a drive signal for driving the exposure means using an exposure pattern indicated by the pattern information based on first image data; Equipped with the pattern information indicates a plurality of exposure patterns for a first pixel; an exposure pattern generation means for randomly selecting an exposure pattern to be used from the multiple exposure patterns of the first pixel when the multiple exposure patterns of the first pixel are to be used consecutively in the main scanning direction, and when the non-exposure area of ​​the randomly selected exposure pattern is consecutive with the non-exposure area of ​​the exposure pattern determined to be used immediately before in the main scanning direction, repeating the random selection from the multiple exposure patterns of the first pixel until the non-exposure area is no longer consecutive with the non-exposure area of ​​the exposure pattern determined to be used immediately before in the main scanning direction.

4. the plurality of exposure patterns of the first pixel are three exposure patterns including a first exposure pattern, a second exposure pattern, and a third exposure pattern; the first exposure pattern is an exposure pattern in which the first pixel is divided into three regions along the main scanning direction, a first region and a third region are the exposed region, and a second region is the non-exposed region; the second exposure pattern is an exposure pattern in which the first pixel is divided into two regions along the main scanning direction, the first region being the exposed region and the second region being the non-exposed region; 4. The image forming apparatus according to claim 3, wherein the third exposure pattern is an exposure pattern that divides the first pixel into two regions along the main scanning direction, the first region being the non-exposed region and the second region being the exposed region.

5. A photoconductor; an exposure unit for scanning the photoconductor in a main scanning direction to expose the photoconductor to light, thereby forming an electrostatic latent image on the photoconductor; a developing means for developing the electrostatic latent image with a developer to form an image on the photoreceptor; a storage means for storing pattern information indicating an exposure pattern which is a pattern of exposed and non-exposed areas of pixels along the main scanning direction; a generating means for generating a drive signal for driving the exposure means using an exposure pattern indicated by the pattern information based on first image data; Equipped with the pattern information indicates a plurality of exposure patterns for a first pixel; the plurality of exposure patterns of the first pixel are selected such that the non-exposed region does not continue at a boundary between two adjacent exposure patterns, even if the same exposure patterns of the plurality of exposure patterns of the first pixel are adjacent in the main scanning direction or two different exposure patterns are adjacent in the main scanning direction; the generating means randomly selects an exposure pattern to be used from the plurality of exposure patterns when the plurality of exposure patterns for the first pixel are used consecutively in the main scanning direction; an exposure pattern for each of the first pixels, the non-exposed regions of the first and second exposure patterns each having an equal length in the main scanning direction;

6. A photoconductor; an exposure unit for scanning the photoconductor in a main scanning direction to expose the photoconductor to light, thereby forming an electrostatic latent image on the photoconductor; a developing means for developing the electrostatic latent image with a developer to form an image on the photoreceptor; a storage means for storing pattern information indicating an exposure pattern which is a pattern of exposed and non-exposed areas of pixels along the main scanning direction; a generating means for generating a drive signal for driving the exposure means using an exposure pattern indicated by the pattern information based on first image data; Equipped with the pattern information indicates a plurality of exposure patterns for a first pixel; the generating means randomly selects an exposure pattern to be used from the plurality of exposure patterns under a condition that, when the plurality of exposure patterns for the first pixel are used continuously in the main scanning direction, the non-exposed region is not continuous at a boundary between two adjacent exposure patterns in the main scanning direction; an exposure pattern for each of the first pixels, the non-exposed regions of the first and second exposure patterns each having an equal length in the main scanning direction;

7. a specifying means for specifying a correction target pixel among pixels of an image formed using the second image data; a correction unit that corrects a pixel value of the correction target pixel indicated by the second image data to generate the first image data; 7. The image forming apparatus according to claim 1, further comprising:

8. 8. The image forming apparatus according to claim 7, wherein the correction target pixel is a pixel determined to have an edge effect or a sweep effect.

9. A photoconductor; an exposure unit for scanning the photoconductor in a main scanning direction to expose the photoconductor to light, thereby forming an electrostatic latent image on the photoconductor; a developing means for developing the electrostatic latent image with a developer to form an image on the photoreceptor; a storage means for storing pattern information indicating an exposure pattern which is a pattern of exposed and non-exposed areas of pixels along the main scanning direction; a generating means for generating a drive signal for driving the exposure means using an exposure pattern indicated by the pattern information based on first image data; Equipped with the pattern information indicates a plurality of exposure patterns for a first pixel; the plurality of exposure patterns of the first pixel are selected such that the non-exposed region does not continue at a boundary between two adjacent exposure patterns, even if the same exposure patterns of the plurality of exposure patterns of the first pixel are adjacent in the main scanning direction or two different exposure patterns are adjacent in the main scanning direction; the generating means randomly selects an exposure pattern to be used from the plurality of exposure patterns when the plurality of exposure patterns for the first pixel are used consecutively in the main scanning direction; The image forming apparatus according to the present invention is characterized in that the first pixel is a pixel whose pixel value is neither a maximum value nor a minimum value among pixels represented by the first image data.

10. A photoconductor; an exposure unit for scanning the photoconductor in a main scanning direction to expose the photoconductor to light, thereby forming an electrostatic latent image on the photoconductor; a developing means for developing the electrostatic latent image with a developer to form an image on the photoreceptor; a storage means for storing pattern information indicating an exposure pattern which is a pattern of exposed and non-exposed areas of pixels along the main scanning direction; a generating means for generating a drive signal for driving the exposure means using an exposure pattern indicated by the pattern information based on first image data; Equipped with the pattern information indicates a plurality of exposure patterns for a first pixel; the generating means randomly selects an exposure pattern to be used from the plurality of exposure patterns under a condition that, when the plurality of exposure patterns for the first pixel are used continuously in the main scanning direction, the non-exposed region is not continuous at a boundary between two adjacent exposure patterns in the main scanning direction; The image forming apparatus according to the present invention is characterized in that the first pixel is a pixel whose pixel value is neither a maximum value nor a minimum value among pixels represented by the first image data.

11. 9. The image forming apparatus according to claim 7, wherein the first pixel is a pixel of the correction target pixels whose pixel value is neither a maximum value nor a minimum value.

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