JP2001242700A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively and easily reduce irregular density in printing in a main scanning direction by an exposure device. SOLUTION: This device is provided with a developer regulating blade 6b regulating developer supplied by a developing roller 6b in a developing device so that developer supply distribution in the main scanning direction of the developing roller 6b may be dense in a part where exposure is small and sparse in a part where the exposure is large at the image forming point of light from the exposure device. Since a developing gap gets wider in the part where the exposure is small as shown by Figure 2 (b) than in the conventional case shown by Figure 2 (a), the carrying amount of the developer gets large and printing density is compensated. Since the developing gap gets narrower in the part where the exposure is large than in the part where the exposure is small, the carrying amount of the developer is restrained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus utilizing an electrophotographic system.

[0002]

2. Description of the Related Art An image forming apparatus using an electrophotographic method used for a facsimile or a printer generally has the following configuration. That is, in such an image forming apparatus, a charger, an exposure device, a developing device, and a transfer device are arranged around the photoconductor drum, and the surface (photoconductor surface) of the photoconductor drum charged through the charger is Exposure is performed according to image information by an exposure device to form an electrostatic latent image, the developing device develops the electrostatic latent image as a developer image, and the transfer device transfers the developer image to paper in a transfer area, and transfers the image. Is fixed by a fixing device, and the sheet is conveyed to the outside of the device. On the other hand, the photoreceptor surface after the transfer repeats the operation of removing the developer on the photoreceptor drum by the cleaning unit, passing through the charger again, and being charged.

As shown in FIG. 4, the exposure apparatus 20 includes a laser light source 2 such as a laser diode inside a housing.
1. A rotating mirror (polygon mirror) 22 that receives laser light 30 from the laser light source 21 and deflects and scans the laser light 30 in the main scanning direction, and scans traveling light from the rotating mirror 22 at a constant scanning speed in the main scanning direction. Lens system 23 composed of an fθ lens, a slit, etc., which corrects the laser light, a reflecting mirror 24 that reflects the laser beam scanned through the lens system 23 and guides the laser beam to the photosensitive surface of the photosensitive drum, and rotates the rotating mirror 22. A scanner motor 25 to be driven is arranged. The laser light modulated by the electric signal is emitted from the laser light source 21, and the emitted laser light 30 is converged by the lens system 23 so as to form an image on the photosensitive drum, and is deflected by the rotating mirror 22 to be deflected by the rotating mirror 22. In the main scanning direction to form a latent image on the photosensitive drum whose surface is charged by the charger.

[0004]

Incidentally, in such an image forming apparatus, the light output characteristic at the image forming point of the exposure device 20 is not uniform at the position in the scanning direction.
This is due to the relationship between the angle of incidence of the laser beam 30 on the rotating mirror 22 that scans the laser beam in the main scanning direction and the reflectance, and the exposure is performed by the exposure apparatus 20 configured as shown in FIG. The amount is high at the center of the image forming point and decreases toward the end as shown in FIG.

[0005] In other words, the exposure amount and the print density are in a relationship in which the higher the exposure amount, the higher the print density. Therefore, in the exposure apparatus having the characteristics shown in FIG.
The relationship between the exposure amount and the print density is as shown in FIG. 6, and when compared with the same exposure amount of the laser light source 21, the print density is higher at the center in the main scanning direction than at the ends, and Causes uneven density. In particular, there is a problem in that halftone printing in which the amount of exposure per unit area is small tends to be noticeable.

As a countermeasure for this, it may be considered that an exposure amount that saturates the print density may be used. However, such a method makes the dots and lines of the image thicker, lowers the resolution, and reduces the resolution of the halftone image. On the other hand, increasing the concentration is not very effective.

[0007] Means for coating a film for suppressing reflection in a place where the reflectivity of the surface of the deflecting mirror is high can be considered, but it is difficult to optimize the distribution of the film, and it becomes expensive.

Accordingly, an object of the present invention is to provide an image forming apparatus capable of easily and inexpensively reducing print density unevenness in the main scanning direction by an exposure device.

[0009]

According to the first aspect of the present invention, an electrostatic latent image is formed by traveling and scanning light in a main scanning direction by an exposure unit based on image data, and an electrostatic latent image is formed by a developing unit. In an image forming apparatus that forms an image by developing the image with a developer and transferring it to a sheet conveyed in the sub-scanning direction,
The developing unit develops such that the developer supply distribution in the main scanning direction is large for a portion with a small amount of exposure at an image forming point of light from the exposure unit and is small for a portion with a large amount of exposure. An image forming apparatus comprising a developer regulating unit for regulating a developer.

According to a second aspect of the present invention, the developing means includes a developer supply means for supplying a developer, and the developer regulating means comprises
The developer regulating unit is arranged in parallel with a predetermined interval to regulate the amount of the developer supplied to the developer supplying unit, and the interval between the developer supplying unit and the developer regulating unit is mainly 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is configured to change in a scanning direction.

According to a third aspect of the present invention, the developer regulating means includes:
3. The image forming apparatus according to claim 2, wherein at least the end in the main scanning direction draws a curve so that the distance between the developer supply unit and the developer regulating unit gradually increases toward the end. An image forming apparatus.

According to a fourth aspect of the present invention, there is provided the image forming apparatus according to any one of the first to third aspects, wherein the developer is a magnetic toner.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram of an image forming apparatus (here, a laser printer) according to the present embodiment.
A photosensitive drum 2 is arranged at a substantially central portion of the housing 1.
The photosensitive drum 2 is driven to rotate in one direction (clockwise in the figure) by a main motor (not shown), and an electrophotographic process mechanism is provided around the photosensitive drum 2 as an electrophotographic process mechanism. A charger 4 for uniformly charging a photosensitive layer on the surface, and an exposure apparatus (a configuration shown in FIG. 4) that irradiates a laser beam to the photosensitive layer charged by the charger 4 based on image information to form an electrostatic latent image (Same as shown) 2
0, a developing unit 6 for applying toner to the electrostatic latent image formed on the photosensitive layer to develop the image, a transfer unit 7 for transferring an image developed by the developing unit 6 to transfer paper conveyed on a conveyance path, A cleaning unit 8 for peeling off toner from the photosensitive drum 2;
A static elimination unit 9 for neutralizing the photosensitive drum 2 is arranged.

The developing section 6 includes a developer hopper 6a containing a toner (developer), a developing roller 6b for bringing the toner in the developer hopper 6a into contact with the photosensitive drum 2 while rotating and adhering thereto. An intermediate roller 6 that rotates while being in contact with the developing roller 6b and applies a developer to the developing roller 6b.
c, a developer regulating blade 6d as developer regulating means for regulating the amount of developer supplied from the developing roller 6b to the photosensitive drum 2. In the present embodiment, since the amount of the developer attracted to the developing roller 6b is regulated by scraping off the developer regulating blade 6d spaced apart from the developing roller 6b, a magnetic toner is used as the developer. I do.

The transfer section 7 is located below the photosensitive drum 2, and is moved toward the transfer section 7 from a paper feed section 10 provided on one side of the housing 1 by the operation of a pickup roller 11. Are transported one by one at a predetermined timing.

After the toner image on the photosensitive drum 2 is transferred by the transfer unit 7 to the conveyed sheet, the sheet is further fixed by the fixing unit 13. Then, the fixed paper is discharged to the outside of the housing by the discharge roller 14.

When a printing operation is performed by such an image forming apparatus, when a printing start signal is sent from a controller (not shown), the main motor of the apparatus is started, and the photosensitive drum 2 is activated.
Rotates in the direction of the arrow and simultaneously starts applying voltage to each member, and the charger 4 uniformly charges the surface of the photosensitive drum 2,
The fixing device 13 is heated by an internal heater.

The charged photoreceptor surface of the photoreceptor drum 2 then reaches an exposure area, and the recording device is exposed to laser light 30 by the exposure device 20 to form an electrostatic latent image on the photoreceptor drum 2. The photoconductor surface of the photoconductor drum 2 on which the electrostatic latent image is formed has a toner (toner) of the developing roller 6b in a developing area by a difference between a potential after exposure on the photoconductor drum 2 and a potential applied to the developing roller 6b. The developer is attracted onto the photosensitive drum 2 to form a toner image (developer image).

Toner (developer) on the developing roller 6b
The developer in the developer hopper 6a is transported to the vicinity of the developing roller 6b by the intermediate roller 6c, and a thin developer layer is formed on the developing roller 6b by the developer regulating blade 6d.

Thereafter, the developer image formed on the photosensitive drum 2 is conveyed to the transfer area, where the pick-up roller 1
The sheet is conveyed by the transfer unit 7 to the sheet conveyed from the bottom of the image forming apparatus by the transfer roller 1 and the conveying roller 14. The transferred developer image on the sheet is fixed by the fixing device 13, and the fixed sheet is discharged to the discharge tray 15 by the transport roller 14.

After passing through the transfer section 7, the photosensitive drum 2 is uniformly discharged from the photosensitive drum surface by the charge removing section 9 and passes through the cleaning section 8 to remove transfer residual toner on the photosensitive drum 2. Thereafter, the above operation is repeated.

As described above, the exposure device 20 has an uneven exposure amount distribution in the main scanning direction depending on the scanning position. Since the exposure amount and the print density have a relationship as shown in FIG. 6, the unevenness in the exposure amount causes unevenness in the print density.

The following principle is used to reduce the density unevenness. The amount of the developer applied from the developing roller 6b to the photosensitive drum 2 in the developing unit 6 varies depending on the distance between the developing roller 6b and the developer regulating blade 6d. FIG. 3 shows the relationship between the distance between the developing roller 6b and the developer regulating blade 6d and the print density at the center and the end in the main scanning direction. It is understood from FIG. 3 that when the distance (development gap) between the developing roller 6b and the developer regulating blade 6d is widened, the amount of the developer conveyed on the developing roller 6b increases, so that the print density increases. This indicates that the print density can be controlled by the development gap.

That is, conventionally, the developer regulating blade 6
FIG. 2D shows a shape d in which the distance between the developing roller 6b and the developer regulating blade 6d is constant regardless of the main scanning direction, as shown in FIG. 2A. In this way, the shape is such that the developing gap at the center is narrow and spreads out in a curve toward the end.

That is, based on the results shown in FIG. 5, the developing gap is increased as the exposure amount is smaller (the end in the main scanning direction), and the developing gap is increased as the exposure amount is larger (the center in the main scanning direction). The shape of the developer regulating blade 6d is determined so that is smaller than the portion where the exposure amount is small. In the case of the exposure apparatus 20 having an exposure amount distribution as shown in FIG.
In order to further increase the print density to 1.4, the size of the developing gap may be 0.24 mm at the center and 0.3 mm at the ends.

As a result, the developing gap is widened in a portion where the exposure amount is small (the end in the main scanning direction), so that the amount of the developer to be conveyed is increased and the print density is compensated. Since the developing gap is narrower (in the central portion in the scanning direction) than the portion where the exposure amount is small, the transport amount of the developer can be suppressed, so that the unevenness in the print density due to the uneven exposure amount can be reduced.

[0027]

As described above in detail, according to the present invention, the distribution of the developer supply in the main scanning direction is large for the portion where the exposure amount is small at the image forming point of the light from the exposure means, and By regulating the developer supplied by the developing means so as to reduce the density of the part with a large amount, the developing gap is widened for the part with a small amount of exposure, so the amount of the developer transported is increased and the print density is increased. Is compensated for, and the developing gap is narrower in the area with a large exposure than in the area with a small exposure, so that the transport amount of the developer is suppressed. Can be.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a view for explaining a developing gap between a developing roller and a developer regulating blade, and FIG.
FIG. 4B shows the present embodiment.

FIG. 3 is a graph showing a relationship between a development gap and a print density.

FIG. 4 is a diagram illustrating a configuration of an exposure apparatus.

FIG. 5 is a graph showing a relationship between a position in a main scanning direction (a traveling position of a laser beam) and an exposure amount ratio.

FIG. 6 is a graph showing a relationship between an exposure amount of a laser light source and a print density.

[Explanation of symbols]

 2 photoreceptor drum 6 developing unit 6b developing roller 6d developer regulating blade 7 transfer unit 20 exposure apparatus

Claims (4)

[Claims] 1. An electrostatic latent image is formed by traveling and scanning light in a main scanning direction by an exposure unit based on image data, and the electrostatic latent image is visualized by a developing unit by a developing unit and conveyed in a sub-scanning direction. In the image forming apparatus for forming an image by transferring the image on a printed sheet, the developing unit may be configured such that a developer supply distribution in a main scanning direction is less than a portion of the exposure amount at an image forming point of light from the exposure unit. An image forming apparatus, comprising: a developer regulating unit that regulates a developer so as to reduce the amount of the developer in a portion having a large amount of exposure. 2. The developer supply means for supplying a developer, wherein the developer regulation means is arranged in parallel with the developer regulation means at a predetermined distance from the developer supply means. 2. The apparatus according to claim 1, wherein an amount of the developer applied to the developer is regulated, and an interval between the developer supply unit and the developer regulating unit changes in a main scanning direction. The image forming apparatus as described in the above. 3. The developer regulating unit draws a curve at least at an end in the main scanning direction such that an interval between the developer supply unit and the developer regulating unit gradually increases toward the end. The image forming apparatus according to claim 2, wherein the image forming apparatus is configured as described above. 4. The image forming apparatus according to claim 1, wherein the developer is a magnetic toner.