JP5581189B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic system in which a uniformly charged photosensitive drum is exposed based on image data to form an electrostatic latent image on the photosensitive drum, and the electrostatic latent image is developed with a developer. In particular, the present invention relates to a technique for suppressing an influence on image quality due to an edge effect and waste of toner. Here, the edge effect means that the toner amount per unit area of the image (pattern image) portion formed by a set of halftone dots and fine lines is larger than the toner amount per unit area of the filled image (solid image) portion. Say that.

Conventionally, an electrostatic latent image is formed on a photosensitive drum by exposing a uniformly charged photosensitive drum based on image data, and the electrostatic latent image is developed with a developer. An image forming apparatus is known. In this image forming apparatus, an edge effect in which the density of the edge portion of the image is darker than that of the central portion becomes a problem. FIG. 24 is a diagram for explaining the edge effect of the positively charged photoconductor as an example.
As shown in FIG. 24A, the photosensitive drum is charged uniformly with a positive charge from the charging device. On the other hand, a negative bias voltage is applied to the developing roller disposed opposite to the photosensitive drum, and toner having a positive charge adheres thereto. At this time, lines of electric force are generated from the photosensitive drum toward the developing roller, as shown in FIG.
Then, as shown in FIG. 24C, the photosensitive drum is exposed based on the image data by the exposure device, and the exposed portion is discharged to form an electrostatic latent image. As a result, the positively charged toner adhering to the developing roller moves to the discharge location on the photosensitive drum, and the electrostatic latent image is developed.
However, at this time, a part of the electric lines of force acting from the non-image forming area (blank area) of the photosensitive drum toward the developing roller goes around the image forming area or is charged to a positive potential in the non-image forming area. It is known that a repulsive force (developing repulsive force) that separates the toner works. As a result, the amount of toner adhering to the edge portion in the vicinity of the boundary between the image forming area and the non-image forming area is increased and the density is increased.
Specifically, as shown in FIG. 25, with the pixel number “31” as the center, “1 dot line”, “5 dot line”, “15 dot line”, “25 dot line”, “35 dot line”, Consider the case of forming each image pattern of “solid”. In this case, as shown in FIG. 26, the image forming area and the non-printing area are not present at both ends of “1 dot line”, “5 dot line”, “15 dot line”, “25 dot line”, and “35 dot line”. It can be seen that the developing electric field strength at the edge portion on the image forming region side from the boundary with the image forming region is larger than the developing electric field strength at the center (equivalent to the developing electric field strength of “solid”). For this reason, the amount of toner adhering to the edge portion increases. Here, the positive side of the developing electric field strength is the strength of the electric field from the developing roller of the developing device to the photosensitive drum.
On the other hand, for example, Patent Document 1 proposes that the density of the edge portion is made uniform by decreasing the amount of exposure light applied to the edge portion of the image in advance.

JP 2000-43315 A

By the way, it is known that the influence of the edge effect extends not only to the inside of the image forming area but also to the non-image forming area. Specifically, as shown in FIG. 26, when the electric field lines wrap around from the non-image forming area to the image forming area due to the edge effect and the development electric field strength at a part inside the boundary increases, The developing electric field strength of a part of the outer non-image forming area is lowered. As a result, there is a risk that the toner charged with the opposite polarity will be developed at a portion of the non-image forming area where the developing electric field strength is reduced. For this reason, the development of toner having the opposite polarity affects the image quality and waste of toner becomes a problem.
In order to prevent development of reverse polarity toner, it is conceivable to mix a reverse polarity external additive with the toner. In this case, however, it is necessary to mix a large amount of external additive with the toner. May hinder the performance required for the toner supplied by the printer.
Therefore, the present invention has been made in view of the above circumstances, and an object of the present invention is to suppress the influence on the image quality due to the edge effect and waste of toner even when no external additive is used. An object of the present invention is to provide an image forming apparatus capable of performing the above.

To achieve the above object, the present invention provides an exposure apparatus that exposes a uniformly charged photoreceptor to form an electrostatic latent image on the photoreceptor, and develops the electrostatic latent image with a developer. When the electrostatic latent image is formed by the exposure device, the developer is attached to an image forming region to which the developer is attached later. The outer edge region of the predetermined range on the non-image forming region side adjacent to the boundary with the non-image forming region is not subjected to the edge effect when the value after the change in the developing electric field strength of the outer edge region due to the edge effect is not affected. The image forming apparatus includes an outer edge exposure correction unit that irradiates with a predetermined exposure light amount so as to approximate the developing electric field strength of the non-image forming region.
As a result, adhesion of the reverse polarity developer to the outer edge region can be suppressed, and the influence on the image quality and waste of toner due to the edge effect can be suppressed. Therefore, it is not necessary to mix a large amount of external additive with the developer.
Here, it is preferable that the outer edge exposure correction unit irradiates a plurality of regions of the outer edge region with light of different exposure light amounts based on preset exposure correction information. Thereby, the developing electric field intensity can be appropriately adjusted for each of the plurality of regions in the outer edge region. For example, it is conceivable that the exposure correction information defines the amount of exposure light corresponding to the distance from the boundary so as to decrease stepwise as the distance from the boundary increases. This is because the influence of the edge effect decreases as the distance from the boundary increases.
Further, the exposure light intensity is such that the absolute value of the developing electric field intensity in the outer edge region is equal to or larger than the developing electric field strength in the region excluding the outer edge region in the non-image forming region, and the outer edge exposure correction unit is used. It is desirable that the predetermined value is set so as to be lower than the peak value of the developing electric field intensity in the outer edge region after the change due to the edge effect in the case of the absence. As a result, it is possible to prevent the developer charged to the normal polarity from adhering to the outer edge region due to the excessive exposure light amount.
It should be noted that the amount of exposure light may be 50% or less of the amount of light at the center of the image forming area. The predetermined range may be a range of 1 mm or less from the boundary.

By the way, in the image forming apparatus, the degree of the influence of the edge effect and the range in which the influence of the edge effect reaches vary depending on various conditions. Therefore, it is conceivable that the outer edge exposure correction means changes the predetermined range and the exposure light amount according to the following various conditions. Thereby, correction suitable for each of the various conditions can be performed.
First, it is conceivable that the outer edge exposure correction means changes the predetermined range and the exposure light amount according to the width of the electrostatic latent image.
Further, the outer edge exposure correction means changes the predetermined range and the amount of exposure light according to one or both of the material of the photosensitive member and the separation distance of the photosensitive member and the developing device. Is also possible.
Further, it is conceivable that the outer edge exposure correction means changes the predetermined range and the amount of exposure light in accordance with the charging potential of the photoconductor and the developing bias of the developing device.
Further, the outer edge exposure correction means may be any one of a pattern image that forms one image forming region by intermittently arranging halftone dots or fine lines, and a solid image in which an image is formed on continuous pixels. It is conceivable that the predetermined range and the amount of exposure light are changed depending on whether or not there is.
In addition, it is conceivable to further include correction content changing means for selecting an arbitrary predetermined range or the exposure light amount from a plurality of the predetermined ranges or the exposure light amount set in advance.

The present invention also includes an exposure device that exposes a uniformly charged photoconductor to form an electrostatic latent image on the photoconductor, and a developing device that develops the electrostatic latent image with a developer. An image forming region to which a developer is attached later by the developing device and a non-image forming region to which the developer is not attached when forming an electrostatic latent image by the exposure device Development of the image forming region when the value after the change of the developing electric field strength of the inner edge region due to the edge effect is not subjected to the edge effect, the inner edge region of the predetermined range adjacent to the boundary with the image forming region side An inner edge exposure correction unit that irradiates with light having a predetermined exposure light amount so as to approximate the electric field intensity is provided, and the inner edge exposure correction unit performs the inner edge region based on preset exposure correction information. It is intended to irradiate with light of different exposure light quantity into a plurality of regions in configured as an image forming apparatus according to claim.
This makes it possible to individually perform corrections suitable for a plurality of areas in the inner edge area to appropriately suppress the amount of developer adhering to the inner edge area. The waste of the agent can be suppressed.
For example, it is conceivable that the exposure correction information defines the amount of exposure light corresponding to the distance from the boundary such that the exposure correction information gradually decreases as the distance from the boundary decreases. This is because the influence of the edge effect increases as the boundary is approached.
Further, the exposure light amount is such that the absolute value of the developing electric field strength in the inner edge region is equal to or larger than the developing electric field strength in a region excluding the inner edge region in the image forming region, and the inner edge exposure correction unit is not used. It is desirable that the predetermined value is set so as to be lower than the peak value of the developing electric field strength in the inner edge region after the change due to the edge effect. Accordingly, it is possible to prevent the density from being lowered and the image from being thinned by preventing the development electric field strength in the inner edge region from becoming too low.
Note that the exposure light quantity may be 50% or more and 100% or less of the light quantity at the center of the image forming area. The predetermined range may be a range of 1 mm or less from the boundary.

By the way, in the image forming apparatus, the degree of the influence of the edge effect and the range in which the influence of the edge effect reaches vary depending on various conditions. Therefore, it is conceivable that the inner edge exposure correction means changes the predetermined range and the exposure light amount according to the following various conditions. Thereby, correction suitable for each of the various conditions can be performed.
First, it is conceivable that the inner edge exposure correction means changes the predetermined range or the amount of exposure light according to the width of the electrostatic latent image.
Further, the inner edge exposure correction means changes the predetermined range and the exposure light amount according to one or both of the material of the photoconductor and the separation distance of the photoconductor and the developing device. Can be considered.
Further, it is conceivable that the inner edge exposure correction means changes the predetermined range and the amount of exposure light according to the charging potential of the photosensitive member and the developing bias of the developing device.
Further, the inner edge exposure correction means may be any one of a pattern image that forms one image forming region by intermittently arranging halftone dots or fine lines, and a solid image in which an image is formed on continuous pixels. It is conceivable that the predetermined range and the amount of exposure light are changed depending on whether or not there is.
Note that it may be possible to further include correction content changing means for selecting an arbitrary predetermined range or the exposure light amount from a plurality of the predetermined ranges or the exposure light amount set in advance.

According to the present invention, it is possible to suppress the adhesion of the reverse polarity developer to the outer edge region, and it is possible to suppress the influence on the image quality and waste of the toner due to the edge effect. Further, it is not necessary to mix a large amount of external additive into the developer.
On the other hand, according to the present invention, it is possible to suppress the adhesion of the developer to the inner edge region, and it is possible to suppress the influence on the image quality and waste of toner due to the edge effect.

1 is a block diagram showing a schematic configuration of a color printer X according to an embodiment of the present invention. 1 is a block diagram showing a schematic configuration of an image forming unit 3 of a color printer X according to an embodiment of the present invention. 1 is a block diagram showing a schematic configuration of an optical scanning device 33 of a color printer X according to an embodiment of the present invention. The figure which shows an example of the exposure correction information which correct | amends the outer side of an edge part. FIG. 5 is a diagram showing an example of a developing electric field intensity when the exposure correction information of FIG. 4 is used. The figure which shows an example of the exposure correction information which correct | amends the outer side of an edge part. The figure which shows an example of the image development electric field intensity at the time of using the exposure correction information of FIG. The figure which shows the difference in the development electric field strength by the difference in a relative dielectric constant. The figure which shows an example of the exposure correction information which correct | amends the outer side of an edge part. FIG. 10 is a diagram showing an example of a developing electric field intensity when the exposure correction information of FIG. 9 is used. The figure which shows the difference in the development electric field strength by the difference in a solid image and a pattern image. The figure which shows an example of the exposure correction information which correct | amends the outer side of an edge part. The figure which shows an example of the image development electric field intensity | strength at the time of using the exposure correction information of FIG. The figure which shows an example of the exposure correction information which correct | amends the inner side of an edge part. The figure which shows an example of the image development electric field intensity at the time of using the exposure correction information of FIG. The figure which shows an example of the exposure correction information which correct | amends the inner side of an edge part. The figure which shows an example of the image development electric field strength at the time of using the exposure correction information of FIG. The figure which shows the difference in the development electric field strength by the difference in a relative dielectric constant. The figure which shows an example of the exposure correction information which correct | amends the inner side of an edge part. The figure which shows an example of the image development electric field strength at the time of using the exposure correction information of FIG. The figure which shows the difference in the development electric field strength by the difference in a solid image and a pattern image. The figure which shows an example of exposure correction information. The figure which shows an example of the image development electric field intensity | strength at the time of using the exposure correction information of FIG. The figure for demonstrating the edge effect. The figure which shows an example of conventional exposure information. The figure which shows an example of the image development electric field strength at the time of using the exposure information of FIG.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.
The color printer X according to the present embodiment is merely an example of the image forming apparatus according to the present invention, and other than this, a copier, a facsimile machine, a multifunction peripheral, and the like also correspond to the image forming apparatus according to the present invention. In this embodiment, a color-compatible image forming apparatus having a plurality of optical scanning devices 33 described later will be described. However, a monochrome-compatible image forming device having only one optical scanning device 33 may be used.

First, a schematic configuration of the color printer X according to the embodiment of the present invention will be described with reference to FIG.
As shown in FIG. 1, the color printer X is connected to a display / operation unit 1 such as a liquid crystal display and a touch panel for displaying and inputting various information in the color printer X via a communication network such as a LAN. The image processing unit 2 that performs various image processing on the image data of the document input from the information processing apparatus that is not shown, and the toner on the paper based on the image data of the document input from the image processing unit 2 An image forming unit 3 that forms an image (developer image), a paper transport unit 4 that transports the paper to the image forming unit 3, and a toner image formed on the paper by the image forming unit 3 is melt-fixed on the paper A fixing device 5 for controlling the color printer X, and a control unit 6 for comprehensively controlling the color printer X. The control unit 6 includes a CPU, ROM, RAM, and the like as arithmetic means, and the CPU executes various processes according to a predetermined control program stored in the ROM.

Here, the image forming unit 3 and the paper transport unit 4 will be described with reference to FIG.
As shown in FIG. 2, the image forming unit 3 includes a plurality of image forming units 3M, 3C, 3Y, 3K corresponding to the colors magenta (M), cyan (C), yellow (Y), and black (K). have. On the other hand, the paper transport unit 4 includes a plurality of transport rollers 41, a transport belt 42, a drive roller 43, and a stretching roller 44. By driving the drive roller 43 and causing the transport belt 42 to travel, The sheets are conveyed in the order of the image forming units 3M, 3C, 3Y, 3K.
The image forming units 3M, 3C, 3Y, and 3K are configured in substantially the same manner, and include a photosensitive drum 31, a charger 32, an optical scanning device (exposure device) 33, a developing device 34, a cleaner 35, a static eliminator 36, and the like. It has. The developing device 34 has a developing roller to which a negative bias voltage is applied, and supplies positively charged toner attached to the developing roller to the photosensitive drum 31. The photoreceptor drum 31 is a photoreceptor using amorphous silicon (a-Si) having a relative dielectric constant ε≈12.
In each of the image forming units 3M, 3C, 3Y, and 3K configured as described above, the photosensitive drum 31 is uniformly charged with a positive charge from the charger 32. Then, the surface of the photosensitive drum 31 that is uniformly charged is irradiated with laser light based on image data from the optical scanning device 33, and only the portion exposed to the laser light is discharged, whereby an electrostatic latent image is discharged. Is formed. Next, the electrostatic latent image formed on the photosensitive drum 31 is developed with positively charged toner supplied from the developing roller of the developing device 34 (reversal development).
After that, the toner images formed on the photosensitive drums 31 of the image forming units 3M, 3C, 3Y, and 3K are sequentially superimposed and transferred onto the paper transported by the paper transport unit 4. A color image is formed on the paper. Of course, the toner images formed on the photosensitive drums 31 of the image forming units 3M, 3C, 3Y, and 3K may be transferred to an intermediate transfer belt and transferred from the intermediate transfer belt to a sheet.
Note that the toner remaining on the photosensitive drum 31 without being transferred onto the sheet is removed by the cleaner 35, and thereafter, the photosensitive drum 31 is discharged by the static eliminator 36.

Next, the optical scanning device 33 will be described with reference to the schematic diagram of FIG.
As shown in FIG. 3, the optical scanning device 33 includes a laser light source 11 having a laser diode for irradiating a laser beam, and a main scanning on the photosensitive drum 31 with the laser beam emitted from the laser light source 11. A polygon mirror (rotating polygon mirror) 12 that scans in the direction, an fθ lens 13 that forms an image of the laser beam scanned by the polygon mirror 12 on the surface of the photosensitive drum 31, and the laser beam emitted from the polygon mirror 12. A laser beam detection sensor 14 provided at a predetermined position on the scanning path is provided.
Further, the optical scanning device 33 controls the presence or absence of light emission of the laser light from the laser light source 11 and the light emission intensity based on the input image data, thereby generating an electrostatic latent image corresponding to the image data on the photoconductor. An exposure control circuit 15 formed on the drum 31 and a laser driver 16 that drives the laser light source 11 in accordance with a control instruction from the exposure control circuit 15 are provided. The exposure control circuit 15 can change the amount of exposure light by the laser light source 11 by adjusting the magnitude of the current flowing through the laser light source 11, for example.

The color printer X configured as described above is characterized in that the light emission intensity of the laser light source 11 is adjusted by executing an outer edge exposure correction process described later by the exposure control circuit 15. This point will be described in detail below.
Specifically, the exposure control circuit 15 includes an image forming area to which toner is attached later by the developing device 34 and a non-image forming area to which developer is not attached when an electrostatic latent image is formed by the optical scanning device 33. Development of the non-image forming area when the value after the change of the developing electric field strength of the outer edge area due to the edge effect is not affected by the edge effect, in the outer edge area of the predetermined range adjacent to the boundary of the non-image forming area Outer edge exposure correction processing is performed in which exposure is performed with a predetermined exposure light amount so as to approximate electric field strength (that is, development electric field strength in a region excluding the outer edge region in the non-image forming region). Here, the exposure control circuit 15 when executing the outer edge exposure correction process corresponds to the outer edge exposure correction means. The outer edge exposure correction process may be executed by the image processing unit 2 or the control unit 6. In this case, the image processing unit 2 or the control unit 6 corresponds to an outer edge exposure correction unit. To do.

FIG. 4 shows the “1 dot line”, “5 dot line”, “15 dot line”, “25 dot line”, “35 dot line”, “solid” shown in FIG. ”Shows an example of exposure correction information in which the exposure light quantity after correction in the case where each image pattern is formed at a resolution of 600 dpi. Here, in the exposure correction information shown in FIG. 4, the exposure light quantity corresponding to each pixel is set to “1”, and the light quantity corresponding to the image forming area when the influence of the edge effect is ignored, corresponding to the non-image forming area. This is shown as a ratio when the amount of light to be emitted is “0”.
As shown in FIG. 4, in the color printer X, a range of 5 pixels (predetermined range) on the non-image forming area side from the boundary between the image forming area and the non-image forming area is set as the outer edge area. . The amount of exposure light in the outer edge region is set to a different value for each pixel (region) corresponding to the distance from the boundary so as to decrease stepwise as the distance from the boundary increases. ing. In the example shown in FIG. 4, the exposure light amount of the pixel closest to the boundary in the outer edge region is “0.27”, and thereafter, as the distance from the boundary increases, “0.20”, “0.13”. ”,“ 0.07 ”, and“ 0.07 ”. That is, unlike the exposure light amount shown in FIG. 25, a minute amount of light is irradiated to the outer edge region.

Here, it is desirable that the amount of exposure light in the outer edge region is 50% or less of “1” which is the amount of exposure light in the central portion of the image forming region. This is because the developing electric field strength in the image forming area, which is increased by the edge effect, is about twice or less and equal to or more than that of the solid image, and the amount of increase is 50% of the developing electric field strength in the center of the image forming area. This is because it is considered that it is optimal to correct the developing electric field intensity in the outer edge region of the non-image forming region that is affected by the edge effect of the same level, in the same range.
Further, the range of the outer edge region is not limited to the range of 5 pixels from the boundary. However, when the resolution is 600 dpi (0.042 mm per pixel), 5 to 6 pixels (0.2 mm to 0.3 mm). It is desirable that the outer edge region be in a range of about). Of course, when it is known from an experiment conducted in advance that the range in which the edge effect occurs is 10 dots from the boundary, the 10-dot range may be used as the outer edge region. However, it is desirable that the predetermined range of the outer edge region is a range of 0 to 1 mm or less from the boundary.

Then, the exposure control circuit 15 controls the emission intensity of the laser light from the laser light source 11 in the optical scanning device 33 based on the exposure correction information set in advance as shown in FIG.
FIG. 5 shows the development when the laser light emission intensity of the laser light source 11 is controlled in accordance with the exposure correction information shown in FIG. 4 and an electrostatic latent image is formed on the photosensitive drum 31. The developing electric field strength acting on the photosensitive drum 31 from the device 34 is shown.
As described above, the electric field lines in the non-image forming area wrap around the image forming area due to the edge effect on the photosensitive drum 31 (see FIG. 24), so that the developing electric field strength in a predetermined range of the non-image forming area is obtained. (See FIG. 26).
On the other hand, when the optical scanning device 33 performs exposure based on the exposure correction information shown in FIG. 4, the exposure light amount corresponding to the outer edge region of the non-image forming region is higher than “0” in advance. Therefore, as shown in FIG. 5, the developing electric field strength in the outer edge region after being lowered by the edge effect approximates the developing electric field strength in the non-image forming region when not receiving the edge effect. Become. In particular, the amount of exposure light in the outer edge region is set so that a plurality of pixels (regions) in the outer edge region are irradiated with light having different amounts of exposure light. Can be obtained.
As a result, it is possible to suppress adhesion of reverse polarity toner to the outer edge region affected by the edge effect, and to suppress the influence on the image quality and waste of the toner. Further, as shown in FIG. 5, the potential difference (contrast) inside and outside the boundary is reduced as compared with the case shown in FIG. 26, and the edge effect is weakened. Therefore, development on the image forming region side of the boundary due to the edge effect is performed. The increase in electric field strength is also reduced.
Furthermore, as shown in FIG. 5, the exposure light intensity corresponding to the image pattern of 5 dot lines or more shown in FIG. 4 is such that the absolute value of the developing electric field intensity in the outer edge region is the outer edge in the non-image forming region. The development electric field strength is higher than the development electric field strength in the region excluding the region, and lower than the peak value of the development electric field strength in the outer edge region after the change due to the edge effect when the exposure control process is not executed by the exposure control circuit 15. It is predetermined. Therefore, for an image pattern of 5 dot lines or more, it is possible to reliably prevent development of toner charged to a normal potential in the outer edge region.

By the way, when an image pattern of 1 dot line is formed, if exposure is performed with light having the same exposure light amount as that of forming an image pattern of 5 dot lines or more, the correction is too strong as shown in FIG. There is a possibility that the developing electric field strength in the outer edge region becomes too high. In this case, the positively charged toner may be developed in the outer edge region.
Therefore, it is conceivable that the exposure control circuit 15 changes the exposure light amount and the predetermined range of the outer edge region according to the width (size) of the image to be formed. Specifically, as shown in FIG. 6, when the formed image is “1 dot line”, the exposure control circuit 15 sets only three pixels from the center pixel “31” as the outer edge region. In addition, the amount of exposure light in the outer edge region is also smaller than that when an image pattern of “5 dot lines” or more is formed. For example, the exposure light amount of the pixel closest to the boundary of “1 dot line” is the same as the exposure light amount of the third pixel from the boundary when “5 dot line” is formed.
As a result, as shown in FIG. 7, with respect to “1 dot line”, the developing electric field strength of the outer edge region is set to other regions in the non-image forming region as in the case of an image having a size of “5 dot lines” or more. Can be adjusted to the same level. Further, as shown in FIG. 7, the exposure light amount shown in FIG. 6 is such that the absolute value of the developing electric field strength in the outer edge region is equal to or larger than the developing electric field strength in the region excluding the outer edge region in the non-image forming region. Yes, and predetermined so as to be lower than the peak value of the developing electric field intensity in the outer edge region after the change due to the edge effect when the exposure control circuit 15 does not execute the exposure correction process. Therefore, it is possible to prevent the toner charged to a normal potential from being developed in the outer edge region. It is also conceivable to change only one of the exposure light amount and a predetermined range of the outer edge region.

Further, depending on the material (relative dielectric constant) of the photosensitive drum 31 and the separation distance (gap) between the photosensitive drum 31 and the developing roller of the developing device 34, the vicinity of the boundary between the image forming area and the non-image forming area. The magnitude of the edge effect generated at the edge portion is different.
Specifically, referring to FIG. 8, even when an image pattern of the same 35 dot lines is formed, the material of the photosensitive drum 31 is an OPC (organic photoconductor) having a relative dielectric constant ε≈3. It can be seen that the influence of the edge effect differs depending on whether or not a is a-Si (amorphous silicon) having a relative dielectric constant ε≈12.
Therefore, the exposure light amount and the predetermined range of the outer edge region corresponding to the case where the material of the photosensitive drum 31 is OPC and the case of a-Si are determined in advance, and the exposure control circuit 15 Based on the predetermined correspondence between the material of the photosensitive drum 31 and the exposure light quantity, the exposure light quantity of light applied to the outer edge area of the non-image forming area and a predetermined range of the outer edge area are changed. It is possible to make it.
Specifically, when the material of the photosensitive drum 31 is a-Si, the exposure light amount and the predetermined range (5 pixels) of the outer edge region determined by “Correction 1” shown in FIG. When the material of the photoconductive drum 31 is OPC, the exposure light quantity and the predetermined range (4 pixels) of the outer edge area determined by “Correction 2” shown in FIG. 9 are adopted. That is, when the material of the photosensitive drum 31 is OPC having a relative dielectric constant lower than that of a-Si, the amount of exposure light is lower than that of a-Si and the outer edge region is also narrowed.
As a result, as shown in FIG. 10, even when the material of the photosensitive drum 31 is OPC, the developing electric field strength in the region near the outside of the boundary can be made uniform. The case where the material of the photosensitive drum 31 is a-Si is shown in FIG. It is also conceivable to change only one of the exposure light amount and a predetermined range of the outer edge region.

Similarly, depending on the separation distance between the photosensitive drum 31 and the developing roller of the developing device 34, the amount of electric lines of wrap around from the non-image forming area to the image forming area changes, and the edge effect differs. Therefore, it is conceivable that the exposure control circuit 15 changes the predetermined range and the amount of exposure light in the outer edge area of the non-image forming area in accordance with the set value of the separation distance. Specifically, since the degree of the edge effect decreases as the separation distance increases, the predetermined range of the outer edge region may be narrowed and the exposure light quantity may be decreased as the separation distance increases. Of course, the predetermined range of the outer edge area of the non-image forming area and the amount of exposure light may be changed according to both the material of the photosensitive drum 31 and the separation distance between the photosensitive drum 31 and the developing roller.
The magnitude of the edge effect generated at the edge portion near the boundary also changes depending on the charging potential of the photosensitive drum 31, the developing roller developing bias of the developing device 34, and the like. Therefore, it is conceivable that the exposure control circuit 15 changes the outer edge region and the amount of exposure light according to the charging potential of the photosensitive drum 31 and the developing bias of the developing roller of the developing device 34. When the light amount of the laser light source 11 in the optical scanning device 33 is corrected by density correction or the like, the outer edge region and the exposure light amount may be changed according to the corrected light amount.

Furthermore, even if the widths of images constituting one image forming area are the same, the image is a solid image (filled image) in which images are formed on continuous pixels, or a set of halftone dots or thin lines. The magnitude of the edge effect generated at the edge near the boundary also changes depending on whether the pattern image is formed.
Here, FIG. 11 shows the development electric field intensity in each of the case where the 35 dot lines are formed by the solid image and the case where the 35 dot lines are formed by the pattern image in which one dot line is intermittently arranged at an interval of one pixel. Is shown. As shown in FIG. 11, the edge effect occurs both in the case where the 35 dot lines are formed by the solid image and in the case where the 35 dot line is formed by the pattern image. The pattern image is smaller than the solid image.
Therefore, when the exposure light quantity and the outer edge area shown in “Correction 1” in FIG. 12 are adopted in both cases, the outer edge area is formed when a 35 dot line is formed by the pattern image as shown in FIG. Since the value after the correction of the developing electric field intensity becomes too strong, there is a possibility that the toner charged to a normal potential in the outer edge region is developed.
Therefore, it is desirable that the exposure control circuit 15 changes the predetermined range of the outer edge region and the amount of exposure light depending on whether the image is the pattern image or the solid image. Specifically, “correction 2” shown in FIG. 12 is adopted in the case of the pattern image, and “correction 1” shown in FIG. 12 is adopted in the case of the solid image. That is, the correction amount may be smaller in the case of the pattern image than in the case of the solid image. Specifically, in the example shown in FIG. 12, “correction 1” has a predetermined range of 5 pixels, whereas “correction 2” has a predetermined range of 3 pixels. The light amount of the pixel closest to the boundary of “Correction 2” is the same as the light amount of the third pixel from the boundary of “Correction 2”.
As a result, as shown in FIG. 13, even when 35 dot lines are formed by the pattern image, the developing electric field strength in the outer edge region can be corrected in the same manner as in other regions.

  Further, the exposure control circuit 15 selects arbitrary exposure correction information from a plurality of exposure correction information in which a predetermined range of the outer edge region and an exposure light amount are set in accordance with a user operation on the display / operation unit 1. Accordingly, it is conceivable to arbitrarily select a predetermined range of the outer edge region and an exposure light amount. At this time, the display / operation unit 1 and the exposure control circuit 15 for performing the selection correspond to correction content changing means. Of course, a configuration in which the display / operation unit 1 can arbitrarily input the predetermined range of the outer edge region and the amount of exposure light can be considered as another embodiment.

Incidentally, in the color printer X, as shown in FIG. 26, it is known that the absolute value of the developing electric field intensity in a predetermined range from the boundary to the image forming area side is increased by the edge effect. As a result, the density of the edge portion in the vicinity of the boundary becomes high, and the influence on the image quality and the waste of toner become problems.
Hereinafter, a description will be given of a configuration in which the influence on the image quality and the waste of toner can be suppressed by reducing the developing electric field strength within a predetermined range from the boundary to the image forming area.
Specifically, the exposure control circuit 15 includes an image forming area to which toner is attached later by the developing device 34 and a non-image forming area to which developer is not attached when an electrostatic latent image is formed by the optical scanning device 33. Development of the image forming area when the value after the change of the developing electric field strength of the inner edge area due to the edge effect is not affected by the edge effect, in the inner edge area of the predetermined range adjacent to the boundary of the image forming area An inner edge exposure correction process is performed in which exposure is performed with a predetermined exposure light amount so as to approximate the electric field intensity. Here, the exposure control circuit 15 when executing the inner edge exposure correction process corresponds to the inner edge exposure correction means. The inner edge exposure correction process may be executed by the image processing unit 2 or the control unit 6. In this case, the image processing unit 2 or the control unit 6 corresponds to an inner edge exposure correction unit. To do. It is also conceivable as another embodiment that both the outer edge exposure correction process and the inner edge exposure correction process are executed.

FIG. 14 shows the “1 dot line”, “5 dot line”, “15 dot line”, “25 dot line”, “35 dot line”, “solid” shown in FIG. ”Shows an example of exposure correction information in which the exposure light quantity after correction in the case where each image pattern is formed at a resolution of 600 dpi. Here, in the exposure correction information shown in FIG. 14, the exposure light amount corresponding to each pixel is set to “1”, and the light amount corresponding to the image forming region when the influence of the edge effect is ignored, corresponding to the non-image forming region. This is shown as a ratio when the amount of light to be emitted is “0”.
As shown in FIG. 14, in the color printer X, a predetermined range on the image forming area side from the boundary between the image forming area and the non-image forming area is set as an inner edge area. The amount of exposure light in the inner edge region is set to a different value for each pixel (region) corresponding to the distance from the boundary so as to decrease stepwise as the distance from the boundary decreases. ing. In the example shown in FIG. 14, the exposure light amount of the pixel closest to the boundary in the inner edge region is “0.73”, and thereafter “0.80”, “0.87” as the distance from the boundary increases. ”,“ 0.93 ”, and“ 0.93 ”. That is, the exposure light amount in the inner edge region is set to be lower than the exposure light amount shown in FIG.

Here, it is desirable that the exposure light amount in the inner edge region is 50% or more and 100% or less of “1” that is the exposure light amount in the central portion of the image forming region. This is because the development electric field strength in the inner edge region, which is increased by the edge effect, is about twice or less and equal to or more than that of the solid image, and the increase amount is 50% of the development electric field strength in the central portion of the image forming region. It is because it is% to 100%.
The range of the inner edge region is not limited to a range of 5 pixels from the boundary. However, when the resolution is 600 dpi (0.042 mm per pixel), the range is 5 to 6 pixels (0.2 mm to 0.3 mm). It is preferable that the inner edge region be in a range of about). Of course, when it is known from an experiment conducted in advance that the range in which the edge effect occurs is 10 dots from the boundary, the 10-dot range may be used as the inner edge region. However, it is preferable that the predetermined range of the inner edge region is a range of 0 to 1 mm or less from the boundary.

Then, the exposure control circuit 15 controls the emission intensity of the laser light from the laser light source 11 in the optical scanning device 33 based on the exposure correction information set in advance as shown in FIG.
Here, FIG. 15 shows the development when the light emission intensity of the laser light from the laser light source 11 is controlled according to the exposure correction information shown in FIG. 14 and an electrostatic latent image is formed on the photosensitive drum 31. The developing electric field strength acting on the photosensitive drum 31 from the device 34 is shown.
As described above, the electric field lines in the non-image forming area wrap around the image forming area due to the edge effect on the photosensitive drum 31 (see FIG. 24), so that the developing electric field strength in a predetermined range of the image forming area. Becomes higher (see FIG. 26).
On the other hand, when the optical scanning device 33 performs exposure based on the exposure correction information shown in FIG. 14, the amount of exposure light corresponding to the inner edge area of the image forming area is lower than “1” in advance. As shown in FIG. 15, the development electric field strength in the inner edge region after being increased by the edge effect is equal to the development electric field strength in the central portion of the image forming region (development without receiving the edge effect). Electric field strength). In particular, since the exposure light amount of the inner edge region is set so that a plurality of pixels (regions) in the inner edge region are irradiated with light of different exposure light amounts, an appropriate developing electric field strength is set in each pixel. Can be obtained.
As a result, the amount of toner adhering to the inner edge region affected by the edge effect can be suppressed, and the influence on image quality and waste of toner can be suppressed. Further, as shown in FIG. 15, the potential difference (contrast) inside and outside the boundary is reduced as compared with the case shown in FIG. 26, and the edge effect is weakened. Therefore, the boundary on the non-image forming region side of the boundary due to the edge effect is reduced. The amount of decrease in the development electric field intensity is also reduced.
Further, as shown in FIG. 15, the exposure light intensity corresponding to the image pattern of 5 dot lines or more shown in FIG. 14 is such that the absolute value of the developing electric field intensity in the inner edge region is the inner edge region in the image forming region. The development electric field strength in the region excluding the region is higher than the peak value of the development electric field strength in the inner edge region after the change due to the edge effect when the exposure control circuit 15 does not execute the exposure correction process. It is determined. Accordingly, it is possible to prevent the density of the edge portion near the boundary from becoming too low for an image pattern of 5 dot lines or more.

By the way, when an image pattern of 1 dot line is formed, if exposure is performed with light having the same amount of exposure light as that of forming an image pattern of 5 dot lines or more, the correction is too strong as shown in FIG. There is a possibility that the developing electric field strength in the inner edge region becomes too low. In this case, there is a possibility that the toner that is normally charged in the inner edge area is developed. On the other hand, when an image pattern of 5 dot lines is formed, the developing electric field strength at the central portion is particularly high due to the edge effect from both.
Therefore, it is conceivable that the exposure control circuit 15 changes the exposure light amount and the predetermined range of the inner edge region according to the width (size) of the image to be formed.
Specifically, as shown in FIG. 16, when the formed image is “1 dot line”, the exposure control circuit 15 determines the exposure light amount of the pixel closest to the boundary as “5 dot line”. The value is larger than that in the case where the above image pattern is formed.
Further, as shown in FIG. 16, when the formed image is “5 dot lines”, the exposure control circuit 15 sets the exposure light quantity of the inner edge region to an image pattern of “15 dot lines” or more. The value is smaller than that in the case where the is formed.

As a result, as shown in FIG. 17, with respect to “1 dot line”, the developing electric field strength of the inner edge region is set to be different from that of other regions in the image forming region as in the case of an image having a size of “5 dot line” or more. Can be adjusted equally. Further, as shown in FIG. 17, the exposure light intensity shown in FIG. 16 is such that the absolute value of the development electric field strength in the inner edge region is greater than or equal to the development electric field strength in the region excluding the inner edge region in the image forming region. The predetermined value is set to be lower than the peak value of the developing electric field intensity in the inner edge region after the change due to the edge effect when the inner exposure correction process is not executed by the exposure control circuit 15. Therefore, it is possible to prevent the density of the inner edge region from becoming too low.
Further, as shown in FIG. 17, with respect to “5 dot lines”, the amount of decrease in the developing electric field intensity in the inner edge region can be increased compared to an image having a size of “15 dot lines” or more. The amount of toner adhering to the inner edge region affected by the effect can be suppressed, and the influence on the image quality and the waste of toner can be suppressed. It is also conceivable to change the predetermined range of the inner edge region instead of the exposure light quantity or together with the exposure light quantity.

Further, depending on the material (relative dielectric constant) of the photosensitive drum 31 and the separation distance (gap) between the photosensitive drum 31 and the developing roller of the developing device 34, the vicinity of the boundary between the image forming area and the non-image forming area. The magnitude of the edge effect generated at the edge portion is different.
Specifically, referring to FIG. 18, even when an image pattern of the same 35 dot lines is formed, the material of the photosensitive drum 31 is OPC (organic photoconductor) having a relative dielectric constant ε≈3. It can be seen that the influence of the edge effect differs depending on whether or not a is a-Si (amorphous silicon) having a relative dielectric constant ε≈12.
Therefore, the exposure light quantity and the predetermined range of the inner edge region corresponding to the case where the material of the photosensitive drum 31 is OPC and the case of a-Si are determined in advance, and the exposure control circuit 15 Based on the correspondence between the predetermined material of the photosensitive drum 31 and the exposure light quantity, the exposure light quantity of light radiated to the inner edge area of the image forming area and a predetermined range of the inner edge area are changed. It is possible.
Specifically, when the material of the photosensitive drum 31 is a-Si, the exposure light quantity determined by “Correction 1” shown in FIG. 19 is adopted, and the material of the photosensitive drum 31 is OPC. Employs the exposure light quantity determined in “Correction 2” shown in FIG. That is, when the material of the photosensitive drum 31 is OPC having a relative dielectric constant lower than that of a-Si, the amount of exposure light is lower than that of a-Si, and the inner edge region is also narrowed.
As a result, as shown in FIG. 20, even when the material of the photosensitive drum 31 is OPC, the developing electric field strength in the region near the inside of the boundary can be made uniform. Note that the case where the material of the photosensitive drum 31 is a-Si is shown in FIG. It is also conceivable to change the predetermined range of the inner edge region instead of the exposure light quantity or together with the exposure light quantity.

Similarly, depending on the separation distance between the photosensitive drum 31 and the developing roller of the developing device 34, the amount of electric lines of wrap around from the non-image forming area to the image forming area changes, and the edge effect differs. Therefore, it is conceivable that the exposure control circuit 15 changes the predetermined range of the inner edge area of the image forming area and the amount of exposure light according to the set value of the separation distance. Specifically, since the degree of the edge effect decreases as the separation distance increases, the predetermined range of the inner edge region may be narrowed and the exposure light quantity may be increased as the separation distance increases. Of course, the predetermined range of the inner edge area of the image forming area and the amount of exposure light may be changed according to both the material of the photosensitive drum 31 and the separation distance between the photosensitive drum 31 and the developing roller.
The magnitude of the edge effect generated at the edge portion near the boundary also changes depending on the charging potential of the photosensitive drum 31, the developing roller developing bias of the developing device 34, and the like. Therefore, it is conceivable that the exposure control circuit 15 changes the inner edge region and the amount of exposure light according to the charging potential of the photosensitive drum 31 and the developing bias of the developing roller of the developing device 34. When the light amount of the laser light source 11 in the optical scanning device 33 is corrected by density correction or the like, the inner edge region and the exposure light amount may be changed according to the corrected light amount.

Furthermore, even if the widths of images constituting one image forming area are the same, the image is a solid image (filled image) in which images are formed on continuous pixels, or a set of halftone dots or thin lines. The magnitude of the edge effect generated at the edge near the boundary also changes depending on whether the pattern image is formed.
Here, FIG. 21 shows the development electric field strength in each of the case where the 35 dot lines are formed by the solid image and the case where the 35 dot lines are formed by the pattern image in which one dot line is intermittently arranged at an interval of one pixel. Is shown. As shown in FIG. 21, the edge effect occurs in both the case where the 35 dot lines are formed by the solid image and the case where the pattern image is formed. The pattern image is smaller than the solid image.
Therefore, if the exposure light quantity and inner edge area shown in “Correction 1” in FIG. 22 are adopted in both cases, the inner edge area is formed when a 35 dot line is formed with the pattern image as shown in FIG. The value after the correction of the developing electric field strength becomes too low, and there is a possibility that a sufficient density cannot be obtained.
Therefore, it is desirable that the exposure control circuit 15 changes the predetermined range of the inner edge region and the amount of exposure light depending on whether the image is the pattern image or the solid image. Specifically, “correction 2” shown in FIG. 22 is adopted in the case of the pattern image, and “correction 1” shown in FIG. 22 is adopted in the case of the solid image. That is, the correction amount may be smaller in the case of the pattern image than in the case of the solid image.
As a result, as shown in FIG. 23, even when 35 dot lines are formed by the pattern image, the developing electric field strength in the inner edge region can be corrected in the same manner as other regions.

  Further, the exposure control circuit 15 selects arbitrary exposure correction information from a plurality of exposure correction information in which a predetermined range of the inner edge region and an exposure light amount are set in accordance with a user operation on the display / operation unit 1. Accordingly, it is conceivable to arbitrarily select a predetermined range of the inner edge region and an exposure light amount. At this time, the display / operation unit 1 and the exposure control circuit 15 for performing the selection correspond to correction content changing means. Of course, a configuration in which the predetermined range of the inner edge region and the amount of exposure light can be arbitrarily input by the display / operation unit 1 is also conceivable as another embodiment.

X ... Color printer (an example of an image forming apparatus)
DESCRIPTION OF SYMBOLS 1 ... Display / operation part 11 ... Laser light source 12 ... Polygon mirror 13 ... f (theta) lens 14 ... Laser light detection sensor 15 ... Exposure control circuit 16 ... Laser drive circuit 2 ... Image processing part 3 ... Image formation part 3M, 3C, 3Y, 3K: image forming unit 31 ... photosensitive drum 32 ... charger 33 ... optical scanning device (exposure device)
34 ... Developing device 35 ... Cleaner 36 ... Static eliminator 4 ... Paper transport unit 5 ... Fixing device 6 ... Control unit

Claims (14)

An image forming apparatus comprising: an exposure device that exposes a uniformly charged photoconductor to form an electrostatic latent image on the photoconductor; and a developing device that develops the electrostatic latent image with a developer. There,
When forming the electrostatic latent image by the exposure device, a predetermined range on the non-image forming region side adjacent to a boundary between an image forming region to which the developer is attached later and a non-image forming region to which the developer is not attached by the developing device A predetermined exposure light quantity so that the value after the change of the developing electric field strength of the outer edge region due to the edge effect is approximated to the developing electric field strength of the non-image forming region The outer edge exposure correction means for irradiating with the light of
The outer edge exposure correcting means images constituting one of the image forming region, a pattern image dot or fine line Ru is Rikatachi formed by the Rukoto are intermittently arranged, images in consecutive pixels forming is der thereby changing the predetermined range and / or the amount of exposure depending on which of the solid image is is, towards the case where the images constituting one of the image forming region is the pattern image However, the image forming apparatus changes the predetermined range and / or the amount of exposure light so that the correction amount by the outer edge exposure correction unit is smaller than that in the case of the solid image . The image forming apparatus according to claim 1, wherein the outer edge exposure correction unit irradiates a plurality of areas of the outer edge area with different amounts of exposure light based on preset exposure correction information. 3. The image formation according to claim 1, wherein the exposure correction information defines an exposure light amount corresponding to a distance from the boundary so that the exposure correction information gradually decreases as the distance from the boundary increases. apparatus. Wherein the outer edge exposure correction means, the image forming apparatus according to any one of claims 1 to 3, intended for changing the predetermined range and / or the amount of exposure according to the width of the electrostatic latent image. Wherein the outer edge exposure correcting means in any one of claims 1-4 wherein is charged potential of the photosensitive member and / or in accordance with the developing bias of the developing device intended for changing the predetermined range and / or the amount of exposure light The image forming apparatus described. To any of a plurality of preset in the predetermined range and / or the select any of the predetermined range and / or the amount of exposure light from the exposure light amount becomes further comprising a correction changing means according to claim 1 to 5 The image forming apparatus described. The exposure light amount, image forming apparatus according to any one of claims 1 to 6 50% or less of the light amount in the center portion of the image forming region. Wherein the predetermined range, the image forming apparatus according to any one of claims 1 to 7 which is the range 1mm from the edge. An image forming apparatus comprising: an exposure device that exposes a uniformly charged photoconductor to form an electrostatic latent image on the photoconductor; and a developing device that develops the electrostatic latent image with a developer. There,
When forming an electrostatic latent image by the exposure device, a predetermined range on the image forming region side adjacent to a boundary between an image forming region to which a developer is attached later by the developing device and a non-image forming region to which the developer is not attached A predetermined exposure light amount so that the value after the change of the developing electric field strength of the inner edge region due to the edge effect is approximated to the developing electric field strength of the image forming region when the edge effect is not received. It has inner edge exposure correction means to irradiate with light,
The inner edge exposure correction means irradiates a plurality of areas of the inner edge area with different amounts of exposure light based on preset exposure correction information,
Said inner edge exposure correcting means images constituting one of the image forming region, a pattern image dot or fine line Ru is Rikatachi formed by the Rukoto are intermittently arranged, images in consecutive pixels forming is der thereby changing the predetermined range and / or the amount of exposure depending on which of the solid image is is, towards the case where the images constituting one of the image forming region is the pattern image but Monodea Ru images forming device wherein changing the predetermined range and / or the exposure light amount as the correction amount by the inner edge exposure correction means compared with the case the a solid image is reduced. The image forming apparatus according to claim 9 , wherein the exposure correction information defines an exposure light amount corresponding to a distance from the boundary such that the exposure correction information gradually decreases as the distance from the boundary decreases. The image forming apparatus according to claim 9, wherein the inner edge exposure correction unit changes the predetermined range and / or the amount of exposure light according to a width of the electrostatic latent image. Wherein the inner edge exposure correcting means in any one of the photosensitive member charge potential and / or the development in response to said developing bias device a predetermined range and / or the one in which changing the exposure light quantity claims 9-11 The image forming apparatus described. To any of a plurality of preset in the predetermined range and / or said any of said predetermined range and / or correction changing means for selecting the amount of exposure light from the exposure light amount, further comprising comprising a claims 9-12 The image forming apparatus described. The image forming apparatus according to any one of claims 9 to 13 , wherein the exposure light quantity is 50% or more and 100% or less of a light quantity at a central portion of the image forming area.