JP2000334996A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make inconspicuous the banding caused by meshing of a gear located on the side closest to a latent image carrier by setting a specified formula for the diameter of a gear, or the like, in a moving force transmitting means. SOLUTION: Assuming the diameter of a gear located on the side closest to a latent image carrier in a moving force transmitting means is Dg (mm), the radius of curvature at the light beam irradiating position on the surface of a module M is Dp/2 (mm), the circle ratio is π, and the diameter in the surface moving direction of a region where the beam intensity in a beam spot on the surface is equal to 1/e of peak value is Lb (mm), formulas are satisfied. It has been known from experiments that conspicuity of banding has correlation with the Dp, Dg, Lb, and the like, in addition to the size of M. More specifically, banding can be made inconspicuous from the relation of the generation period Lg of banding (π×Dp×M/Dg) and the Lb (hereinafter, referred to as 1/e radius Lb). For that purpose, the 1/e radius Lb at the first term on the left side can be decreased or the Dp, Dg, M, and the like, at the second term on the left side can be decreased.

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 such as a facsimile machine, a copying machine, a printer, and the like. Beam irradiating means for carrying the latent image, visualizing means for visualizing the latent image, moving force transmitting means having a gear for transmitting moving force to the latent image carrier, and moving force The present invention relates to an image forming apparatus including a moving force applying unit that applies a moving force to the latent image carrier via a transmission unit.

[0002]

2. Description of the Related Art Conventionally, in a digital electrophotographic image forming apparatus, a surface of a photosensitive member as a latent image carrier is uniformly charged while moving endlessly, and then a laser diode (LD) is applied to the surface. A device that forms an electrostatic latent image by irradiating a light beam emitted from a light emitting diode (LED) or the like is known.

[0003] As a drive system of the photoconductor for realizing such endless movement, a DD motor drive system, a gear drive system and the like are known. The DD motor drive system rotates the photosensitive drum and the drive roller by a motor directly connected to a shaft of a photosensitive drum as a photosensitive body and a drive roller for stretching and driving a photosensitive belt similarly to the photosensitive body. It is a method to make it. The gear driving method transmits the driving force of the motor to the shaft of the photosensitive drum, the driving roller, and the like through a gear train as a moving force transmitting means or a combination of a gear pulley and a timing belt. In this method, the shaft of the photosensitive drum, the driving roller, and the like are rotationally driven at a peripheral speed different from the speed.

[0004] Among these driving methods, the DD motor driving method generally causes uneven rotation of the motor at each rotation of the motor or at predetermined intervals due to harmonic components of the drive power supply. Tends to occur.

Further, in the gear driving method, a shading difference called banding is likely to occur on an image position having a period of about 1 [mm] corresponding to a tooth pitch of a gear as a gear. This banding is mainly performed by moving force transmission means (drive transmission mechanism).
The gears and gear pulleys (hereinafter collectively referred to simply as "gears") located closest to the photosensitive member among the above members are caused by meshing with other members. For example, when the drive transmission mechanism is a gear train, banding due to the engagement of the intermediate gears is unlikely to occur due to the buffering action of the gap between the intermediate gears, but the final stage that directly transmits the driving force to the photoreceptor is provided. Does not exhibit such a buffering effect. For this reason, banding with a cycle corresponding to the number of teeth of the gear located closest to the photoconductor in the gear train easily occurs in the image. Further, even when the driving force transmission mechanism is a combination of a gear pulley and a timing belt, banding having a cycle corresponding to the number of teeth of the gear pulley located closest to the photoconductor is likely to occur in the image for the same reason.

Therefore, conventionally, a buffering member is provided on a gear located closest to the photoconductor, or a flywheel is provided on a rotating shaft of the photoconductor, so that banding caused by engagement of the gear with another member is provided. Measures have been taken to reduce the occurrence of spills.

However, such measures not only increase the cost but also cannot completely eliminate the fluctuation of the moving speed of the photosensitive member.

In an image forming apparatus that reproduces the density gradation of an image by adjusting the irradiation conditions of LDs and LEDs, banding may occur even if the moving speed of the photosensitive member is slightly changed for the following reasons. . That is, in general,
In an image forming apparatus using an LD or LED, an electrostatic latent image portion corresponding to a high-density portion of an image is formed by irradiating a photoreceptor with a light beam having an intensity capable of sufficiently attenuating its potential, Further, by modulating the intensity, the irradiation time, and the like to form an electrostatic latent image portion having an intermediate potential corresponding to a halftone portion or a highlight portion of the image, the density gradation of the image is adjusted. I have. However, if the movement speed of the photoconductor changes due to the meshing of the gears, a portion that is not irradiated to the photoconductor for a regular irradiation time occurs in a cycle of about 1 [mm]. If this portion is an electrostatic latent image portion having an intermediate potential as described above, potential unevenness occurs. On the other hand, the Fourier component (MTF) of the developing electric field formed in the developing area between the photoreceptor and the developing device as the visualizing means is:
The enhancement is performed at a period of about 1 [mm]. When the Fourier component is emphasized in this way, 1 [m
m], the potential unevenness occurring in the period before and after [m] is further emphasized. When the potential unevenness is enhanced in this way, the development unevenness in the developing process is enhanced, and banding occurs.

Further, it has been found that human visual detection sensitivity to density unevenness in a cycle of about 1 [mm] is extremely high. FIG. 5 is a graph showing the relationship between the spatial frequency (X-axis) of density unevenness appearing on an image and an allowable density difference (Y-axis) of the density unevenness with respect to a human. As shown,
There is a correlation between the spatial frequency of density unevenness and the human allowable density difference for the density unevenness. The human allowable density difference for the density unevenness that occurs in a cycle of the order of 1 [mm] is the density unevenness that appears in another cycle. Lower than for. For this reason, banding that occurs in a cycle of about 1 [mm] due to the gear tooth pitch is conspicuous even if the density difference is low.

[0010]

The inventors of the present invention have conducted intensive studies and have found that the conspicuousness of banding has a correlation with not only the spatial frequency of the banding but also the beam diameter on the surface of the photoreceptor. Specifically, the inventor of the present invention, within the beam spot on the photoreceptor surface,
It has been found that there is a correlation between the diameter of the region where the beam intensity is 1 / e of the peak value in the photoconductor moving direction (hereinafter referred to as the sub-scanning direction) and the banding easiness. Conventionally, as the beam diameter indicating the effective beam range within the beam spot on the surface of the photoconductor, the diameter in the sub-scanning direction of a region where the beam intensity within the beam spot is 1 / e ² has been generally used. However, according to the study of the present inventor, no clear correlation was recognized between the beam diameter and the conspicuousness of the banding, and the conspicuousness of the banding was determined by the fact that the beam intensity in the beam spot was 1 / the peak value. It has been found that there is a correlation with the beam diameter in the sub-scanning direction in the region of e. This is considered to suggest that the conventional definition of the beam diameter was inappropriate.

Further, the present inventor has made intensive studies and found that the conspicuousness of banding is also correlated with the thickness of the photosensitive layer on the surface of the photoreceptor and the degree of dirt on the non-image portion on the recording medium such as the degree of toner dust. I found something.

The present invention has been made in view of the above background, and an object of the present invention is to provide an image forming apparatus capable of making banding caused by meshing of gears less noticeable. is there.

[0013]

In order to achieve the above-mentioned object, a first aspect of the present invention is to provide a latent image carrier for carrying a latent image on a surface while moving in a predetermined direction, and a light beam for the surface. Beam irradiation means for irradiating the latent image by irradiating the latent image, visualizing means for visualizing the latent image, and moving force transmitting means having a gear for transmitting a moving force to the latent image carrier; A moving force applying means for applying a moving force to the latent image carrier via the moving force transmitting means, wherein the gear is located closest to the latent image carrier in the moving force transmitting means. Is Dg [mm], the module is M [mm],
And the radius of curvature of the surface at the light beam irradiation position is D
p / 2 [mm], the pi is π, and the diameter in the surface moving direction of the area where the beam intensity in the beam spot on the surface is 1 / e of its peak value is Lb [mm]. Where Lb / 0.06 + (π × Dp × M / Dg) / 2 <1
A conditional expression [mm] is provided.

This image forming apparatus has an Lb / 0.06 +
A conditional expression of (π × Dp × M / Dg) / 2 <1 [mm] is provided. The present inventor has conducted intensive studies and found that by providing such a conditional expression, banding caused by meshing of a gear located closest to the latent image carrier in the moving force transmitting means can be made less noticeable. I found it.

According to a second aspect of the present invention, in the image forming apparatus of the first aspect, Lb / 0.05 + (π × Dp × M / Dg) /
A conditional expression of 1.5 <1 [mm] is provided.

This image forming apparatus has an Lb / 0.05 +
A conditional expression of (π × Dp × M / Dg) /1.5 <1 [mm] is provided. The inventor of the present invention has made intensive studies to provide such a conditional expression so that banding caused by meshing of the gear located closest to the latent image carrier in the moving force transmitting means can be more reliably made inconspicuous. I found that I got it.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, wherein the latent image carrier is a photosensitive member, the photosensitive layer on the surface of the photosensitive member is formed to have a thickness of 15 μm or less. It is characterized by the following.

In this image forming apparatus, the thickness of the photosensitive layer on the surface of the photosensitive member is 15 [μm] or less. The inventors of the present invention have made intensive studies and, by forming the thickness of the photosensitive layer in this manner, more clearly show banding caused by meshing of the gear located closest to the latent image carrier in the moving force transmitting means. I found that it can be difficult.

According to a fourth aspect of the present invention, there is provided a transfer means for transferring a visual image obtained by attaching an image forming substance to the latent image by the visualizing means to a recording medium, and forming an image on the recording medium. 4. The image forming apparatus according to claim 1, wherein the recording medium extends in a direction perpendicular to the non-image portion of two pixels in a direction corresponding to the surface movement direction. When two existing linear images are formed, a total of 20 lines with respect to a center line parallel to these linear images in the non-image portion.
The method is characterized in that the above-mentioned image forming substance is adhered to a portion of [%] or more.

In this image forming apparatus, a predetermined degree of dirt is generated on the center line of the non-image portion of the recording medium due to the adhesion of the image forming substance. Specifically, a stain is generated to such an extent that the image forming substance adheres to a portion of 20% or more of the center line.
The inventor of the present invention causes such a degree of dirt to occur on the center line of the non-image portion of the recording medium, so that the dirt occurs due to the engagement of the gear located closest to the latent image carrier in the moving force transmitting means. We have found that banding can be made less noticeable.

According to a fifth aspect of the present invention, there is provided an image data processing means for performing halftone processing on the image data, and irradiating the latent image carrier with the light beam based on the halftone processed data. In the image forming apparatus of the third aspect, the image data processing means is configured to perform halftone processing on the image data by an error diffusion method.

In this image forming apparatus, image data is subjected to halftone processing by an error diffusion method, so that a matrix shape of a density gradation portion, which is likely to occur in an image forming apparatus using, for example, a dither method as the halftone processing method. This reduces the so-called grainy feeling of the image due to the prominence.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a digital electrophotographic printer which is an image forming apparatus will be described below. First, an outline of the entire printer will be described. FIG. 1 is a schematic configuration diagram of a printer according to the present embodiment. In FIG. 1, 1 is a photosensitive drum as a latent image carrier, 2 is a charging charger 2 for uniformly charging a photosensitive layer on the surface of the photosensitive drum 1, 3 is an optical writing unit as beam irradiation means, 4 Denotes a developing device as a visualizing device, 5 denotes a primary transfer device as a transfer device, 6 denotes a secondary transfer roller also as a transfer device, 7
Denotes a static eliminator for neutralizing the photosensitive layer, and 8 denotes a cleaning blade for cleaning the photosensitive drum.

In this printer, a gear train as moving force transmitting means and a drum motor as moving force applying means, also not shown, are connected to a rotating shaft (not shown) projecting from the end surface of the photosensitive drum 1. I have. A photosensitive layer is coated on the surface of the photoreceptor 1 which is rotated in a direction indicated by an arrow (clockwise) in the figure through a gear train by the driving force of the drum motor. That is, in this printer, a gear driving method is used as a driving method of the photosensitive drum 1.

First, the photosensitive layer of the photosensitive drum 1 is uniformly charged when the photosensitive layer 1 passes through a position facing the charging charger 2 as the photosensitive drum 1 rotates. Next, when passing through a position facing the optical writing unit 3, a laser beam (not shown) of the optical writing unit 3 irradiates a light beam based on an image signal from an image processing unit (not shown). Carries an electrostatic latent image with a positive polarity charge, for example.

On the other hand, the developing device 4 contains a toner as an image forming substance, and is charged on the developing roller 4a in the direction of the arrow (counterclockwise) in FIG. Supported on. The developing roller 4 partially exposed from the opening of the developing device 4
A developing bias is applied to a by a bias applying unit (not shown), and by this application, a developing electric field (not shown) is formed between the photosensitive drum 1 and the developing roller 4a.

The primary transfer device 5 is driven by a driving device (not shown) to rotate in a counterclockwise direction in the figure, and the primary transfer roller 5b and the stretching rollers 5c and 5d, while being stretched by these three rollers. Similarly, it is constituted by a flexible intermediate transfer belt 5a, etc., which is driven to rotate counterclockwise. The primary transfer roller 5b is located on the downstream side of the developing device 4 in the rotation direction of the photosensitive drum 1.
A primary transfer nip is formed by abutting the photosensitive drum 1 via a. A primary transfer bias is applied to the primary transfer roller 5b by a bias applying unit (not shown), and a primary transfer electric field is formed in the primary transfer nip by this application. Further, the tension roller 5d contacts the secondary transfer roller 6 via the intermediate transfer belt 5a below the primary transfer device 5 to form a secondary transfer nip. A secondary transfer bias is applied to the secondary transfer roller 6 by a bias applying unit (not shown), and a secondary transfer electric field is formed in the secondary transfer nip by this application.

When the positive electrostatic latent image carried on the photosensitive layer passes through the developing position as the photosensitive drum 1 rotates, the toner charged to the negative polarity on the developing roller 4a becomes Moved and adhered by the influence of the developing electric field,
The toner image is formed by the adhesion to form a toner image. Then, when passing through the primary transfer nip, primary transfer is performed on the intermediate transfer belt 5a under the influence of the pressing force in the primary transfer nip and the primary transfer electric field.

In view of the timing of such a primary transfer, a paper feeder (not shown) transfers the transfer paper 11 as a recording medium.
To the secondary transfer nip. The toner image transferred onto the intermediate transfer belt 5a is
When passing through the secondary transfer nip with the rotation of, the toner image is secondarily transferred onto the transfer paper 11 under the influence of the pressing force in the secondary transfer nip and the secondary transfer electric field.

The transfer paper 11 on which the toner image has been secondarily transferred is
The sheet is sent into the fixing device 9. And in this fixing device,
After the toner image is fixed between the heating roller 9a and the pressure roller 9b by heating, the toner image is discharged to the outside of the printer.

The photosensitive layer having passed through the primary transfer nip is neutralized when passing through a position facing the static eliminator 7 as the photosensitive drum 1 rotates. Then, when passing through the position facing the cleaning blade 8, the untransferred toner remaining without being primary-transferred is mechanically scraped off and prepared for the next image formation.

In the printer having the above configuration, 1 [m] corresponding to the tooth pitch of a gear (hereinafter simply referred to as a gear) directly connected to the photosensitive drum rotating shaft in the gear train (not shown).
[m] banding is likely to occur on the image position of the period before and after. It has been found that banding that occurs at a period of about 1 mm due to the gear tooth pitch becomes conspicuous even if the density difference is low. If banding is generated at different periods, the banding can be made less noticeable. In a normal image forming apparatus, it is difficult to make the gear tooth pitch larger than the order of 1 [mm] due to the diameter of the photosensitive drum, the peripheral speed, and the like. Will do. However, there is a limit to reducing the gear tooth pitch, and there is also a cost problem such as the need to increase the strength of the gear.

Therefore, the inventor conducted an experiment on the conspicuousness of banding that occurs when the printer is set under various conditions as shown in Table 1 below.

[Table 1]

Then, the banding is easily noticeable due to the size of the gear tooth pitch (module M) and twice the radius of curvature at the light beam irradiation position on the latent image carrier (= the diameter of the photosensitive drum 1). Dp), gear diameter (Dg),
It was found that there is also a correlation with the beam diameter (Lb) in the region where the peak value of the beam intensity is 1 / e.

FIG. 2 shows the banding occurrence period Lg (π × Dp × M / Dg) and the beam diameter Lb (hereinafter, 1 / e) in the region where the beam intensity is 1 / e under the conditions of Table 1 above.
(referred to as e-diameter Lb). In the graph of FIG. 2, the straight line A corresponds to the equation Lb / 0.06 + Lg
/ 2 = 1 [mm], and the equation Lb / 0.05 +
A solution of (π × Dp × M / Dg) /1.5=1 [mm] is shown. Further, ×, Δ, and ○ indicate the evaluation results of the conspicuousness of banding, respectively. As shown in the figure, it can be seen that banding is less noticeable in a region below the straight line A. Further, in the area below the straight line B, it can be seen that the banding becomes more inconspicuous.

In order to make the solution of each of the above equations smaller than 1 [mm] to make banding less noticeable, the 1 / e diameter Lb of the first term on the left side of each equation may be reduced, or the second term of the left side may be reduced. The diameter Dp of the photosensitive drum, the diameter Dg of the gear, the module M of the gear, and the like may be reduced.

Conventionally, as the beam diameter, the diameter in the sub-scanning direction of a region where the peak value of the beam intensity is 1 / e ² (hereinafter referred to as 1 / e ² diameter) has been generally used. According to the experiment, no clear correlation was recognized between the 1 / e ² diameter and the conspicuousness of banding. For example, when a predetermined LD optical system is used and the parameters of the LD optical system are shifted from the optimal conditions to change the beam intensity distribution of the beam spot, even if the 1 / e ² diameter changes, the banding becomes noticeable. It didn't change much. Further, even if the LED optical system is used as the optical system instead of the LD and the 1 / e ² diameter is changed by changing the size of the light emitting portion of the LED, the amount of change in banding conspicuousness due to this change is measured. It was small enough to be included in the error.

On the other hand, when a plurality of LD optical systems having different parameters are used and an experiment is performed under the parameter condition of minimizing the 1 / e ² diameter in each optical system, the 1 / e diameter Lb of each optical system and the banding And a good correlation was recognized. Further, in the LED optical system, a combination of an LED array having a number of LEDs and lenses corresponding to the number of dots formed in the main scanning direction and a self-fox lens array is used, and a beam intensity distribution from each LED is used. There is a technical limit to unifying the two. For this reason, the 1 / e ² diameter and the 1 / e diameter Lb vary among the LEDs, but no correlation was observed for the 1 / e ² diameter with respect to the conspicuousness of banding. A good correlation was observed for the e-diameter Lb. That is, regardless of whether the optical system of the optical writing unit was an LD or an LED, a good correlation was recognized between the 1 / e diameter Lb and the banding easiness.

The reason why a good correlation is recognized between the 1 / e diameter Lb instead of the 1 / e ² diameter and the conspicuousness of banding is not clear, but the following is related. it is conceivable that. That is, as shown in FIG. 3, the 1 / e diameter Lb has a peak beam intensity of about 36.8.
[%] Or more, where the change in the beam intensity distribution curve is sharp (the change in the amount of light with respect to the change in the measurement point is large). On the other hand, the 1 / e ² diameter is an area where the beam intensity is about 13.5 [%] or more of the peak value, and is an area where the beam intensity distribution curve becomes a tail. Here, when the parameters of the optical system are slightly changed, the 1 / e diameter Lb is not changed much, but 1 / e.
/ E will be greatly changed for the ² diameter. In particular, when the beam spot is narrowed down by the LD optical system, this tendency becomes strong. This is because, as a result of the interference of LD light, a second peak called a so-called side lobe is formed near the peak value of the beam intensity distribution curve, and this peak raises the trailing portion of the beam intensity distribution curve, and 1 / e ² This is considered to be because the diameter is largely changed. The beam portion having the intensity of the foot portion does not contribute much to the formation of the electrostatic latent image, and the electrostatic latent image is formed by optical writing exclusively with the beam portion within the 1 / e diameter Lb. , This 1 / e diameter L
As b increases, the amount of light written to adjacent pixels also increases. vice versa. As the 1 / e diameter decreases, the amount of light written to adjacent pixels decreases. Then, it is considered that the banding density difference caused by the fluctuation in the speed of the photosensitive drum becomes small, and the banding becomes less noticeable.

As shown in FIG. 2, in order to make banding less noticeable, the 1 / e diameter Lb is reduced, the photosensitive drum diameter Dp, the gear diameter Dg, and the gear module M Etc. should be reduced. However, 1
In order to reduce the / e diameter Lb, for example, it is necessary to increase the lens system of the LD optical system or to decrease the emission wavelength of the LD. However, these not only increase the cost but also increase the sensitivity. 30 [μ] stably on the drum
[m] or less, it is extremely difficult to realize a 1 / e diameter Lb. If the diameter Dp of the photosensitive drum is too small, the distribution of each unit around the photosensitive drum 1, such as the charging charger 2, the optical writing unit 3, the developing device 4, the primary transfer device 5, the charge removing device 7, and the cleaning blade 8, will be described. Therefore, there is a limit in reducing the diameter Dp. Further, the diameter Dg of the gear is limited by the size of the apparatus. Particularly, in the case of an image forming apparatus of a so-called Dratandem system in which a plurality of photosensitive drums are arranged in parallel around an intermediate transfer belt, The diameter Dg of this gear is greatly restricted by the distance between the photosensitive drums. Further, if the size of the gear module M is too small, not only the cost is increased, but also a problem occurs in the strength. Therefore, the lower limit of the module M is substantially about 0.5 [mm]. Considering the above, the 1 / e diameter Lb and the lower limit of the module M are set to 30 [μm] and 0.5 [mm], respectively, depending on the size of each unit disposed on the photosensitive drum. It is desirable to reduce the diameter Dp of the photosensitive drum and the diameter Dg of the gear to make the solution of each of the above equations smaller than 1 [mm].

According to the experiment of the present inventor, by forming the thickness of the photosensitive layer of the photosensitive drum 2 to 15 μm or less, the same effect as when the 1 / e diameter Lb is reduced is recognized. Was done. It is considered that the reason why such an effect is exerted is to reduce the diffusion of charges in the photosensitive layer by reducing the thickness of the photosensitive layer. Further, since the thickness of the photosensitive layer is thin, the MTF emphasized region of the developing electric field is shifted to a period shorter than 1 [mm], so that small dots and thin lines can be developed with sufficient density. Are also considered involved.

The present inventor has conducted the following experiment. As a result, the 1 / e diameter Lb in the sub-scanning direction, the thickness of the photosensitive layer, and the speed fluctuation due to the meshing of the gears of the photosensitive drum 1 are found. Even in the case of the same, it was found that the banding could be made less noticeable when a proper amount of toner dust was generated in the non-image area of the transfer paper 11. That is, as shown in FIG.
For each of the pixel rows L1, L2, L3, L4 extending in the main scanning direction (the horizontal direction in the drawing) on the transfer paper 11, a line image is formed on L1 and L4, and L2 and L3 are defined as non-image portions. (In practice, repetition of forming a line image via a non-image portion composed of two pixel columns) was performed. Then, a 200-fold microphotograph of the transfer paper 11 was taken, a center line AA ′ was drawn between pixels in the non-image portion, and the ratio of toner applied on the center line AA ′ due to toner dust was measured. . As a result of repeatedly performing such a measurement while changing the degree of occurrence of toner dust, banding becomes conspicuous when toner dust that adheres to a portion of 20% or more of the center line AA ′ occurs. It turned out to be difficult. It is not clear why banding is less noticeable,
It is considered that if a certain amount of toner does not exist in the non-image portion between the line images, the outline line of the non-image portion stands out.

However, when the length of the non-image portion in the sub-scanning direction is equal to or less than 130 μm and the toner is present on the center line of the non-image portion at a rate exceeding 20%, , One width 65 in the white line of the non-image part
[Μm] or more of the toner from the line image
It was found that the line image appeared blurred and the sharpness of the image was reduced. Specifically, the length of the pixel in the sub-scanning direction (the center distance between the pixels) is set to L, and the operation of forming one line image on one end column of n pixel columns extending in the main scanning direction is repeated. In this case, it was found that when an image was formed under the condition of L × (n−1) <130 [μm], the sharpness of the image was reduced. Therefore, when the length of the non-image portion in the sub-scanning direction becomes 130 [μm] or less,
It is necessary to control the amount of toner dust so that the toner is present at a rate of 20% or less on the center line of the non-image portion. For example, when a line image as shown in FIG. 4 is formed at a resolution of 600 [dpi], the length L of the pixel in the sub-scanning direction is 25400 ÷ 600 = 42.3.
[Μm]. In such a case, 20
If the toner adheres at a rate exceeding [%], the thickness of the white line becomes 42.3 × (3-1) = 84.6 [μm].
It becomes smaller than 30 [μm], and the sharpness of the image decreases. For example, when two line images are formed at a resolution of 1200 [dpi], the length L of the pixel in the sub-scanning direction is 25400２５1200 = 21.2.
[Μm]. Therefore, when the operation of forming a line image at one end of three pixel columns is repeated as shown in FIG. 4, the thickness of the white line is 21.2 × (3-1) = 4.
2.4 [μm] is smaller than 130 [μm]. However, even when the operation of forming a line image at one end of the 4, 5, 6, and 7 pixel columns is repeated, the thickness of the white lines is 63.6, 84.8, 106.0, and 127.2, respectively.
[Μm], which is smaller than 130 [μm]. In such a case, in any one of the operations of forming a line image at one end of the 3, 4, 5, 6, and 7 pixel columns, the toner is applied onto the center line at a rate of 20% or less on the center line. If it is attached, it is possible to avoid a decrease in the sharpness of the image.

The degree of toner dust generation is adjusted, for example, by adjusting the fluidity of the toner (developer) by mixing with an additive, adjusting the toner particle diameter, adjusting the electrical resistance of the intermediate transfer belt, and adjusting the diameter of the photosensitive drum. (In the case of a photosensitive belt, the curvature at the beam irradiation position on the belt surface) adjustment,
The adjustment can be made by adjusting the size of the transfer electric field region in the primary transfer nip and the secondary transfer nip.

Next, a method of processing image data for expressing density gradation will be described. Conventional image data processing methods for density gradation expression, which have been used in electrophotographic image forming methods, include a dither method and an error diffusion method.

This dither method expresses a gradation in units of a matrix. Specifically, a matrix consisting of a plurality of basic pixels is set, and a density threshold is set for each basic pixel, and a basic pixel portion in which image data indicates a density higher than the threshold is regarded as an image portion. A basic pixel portion having a density lower than the threshold value is regarded as a non-image portion (background portion). In such a dithering method, a dot concentration type matching the developing characteristic peculiar to the electrophotographic method is often used as a method of setting the threshold value of the density. In the dot concentration type, since the photosensitive layer region having the intermediate potential is reduced, banding due to the potential variation in the region of the intermediate potential caused by the speed variation of the photoconductor is unlikely to occur. However, there is a drawback that the shape of the matrix of the density gradation expression is remarkably recognizable as roughness of the image.

On the other hand, the error diffusion method is a processing method widely used in an ink-jet method or the like, and accumulates the density of pixels to be formed over a plurality of pixels, and keeps the density constant every time the density level exceeds a threshold value. This is a method of forming dots of several levels in size and density. In this error diffusion method, the dot interval in a low-density image portion increases, and the dot interval in a high-density image portion decreases. For this reason, if the dots are invisible, almost all of them are independent, and a good image without a feeling of roughness can be obtained. However, contrary to the dither method, since a latent image in an intermediate area is formed around each dot, there is a disadvantage that banding is easily generated.

Therefore, an error diffusion method is employed as a method of processing image data for expressing density gradation, and the above-described requirements for the above-described equations, the thickness of the photosensitive layer, or the degree of occurrence of toner dust are provided. This makes it possible to obtain an image without roughness while making banding less noticeable.

The present invention is a new technical idea born from the above study, and can be applied to conventional electrophotography to form an image with less noticeable banding.

In the embodiment, the image forming apparatus having the gear train as the moving force transmitting means has been described. However, for example, an image forming apparatus having at least a moving force transmitting means having a gear, such as a gear pulley and a timing belt as gears. The present invention can be applied to any forming apparatus.

Although an image forming apparatus having a photosensitive drum as a latent image carrier has been described, the present invention is applicable to other image forming apparatuses having a latent image carrying drum and a latent image carrying belt. In an image forming apparatus having a latent image carrying belt, the radius of curvature of the latent image carrying belt at the light beam irradiation position may be Dp.

[0052]

According to the first, second, third, fourth or fifth aspect of the present invention, the banding caused by the engagement of the gear located closest to the latent image carrier in the moving force transmitting means is less noticeable. There is an excellent effect that you can.

In particular, according to the second, third or fourth aspect of the present invention, the banding caused by the meshing of the gear located closest to the latent image carrier in the moving force transmitting means is more reliably made inconspicuous. There is an excellent effect that can be.

In particular, according to the fifth aspect of the present invention, the roughness of the image is reduced, so that the gear located closest to the latent image carrier in the moving force transmitting means can be engaged while reducing the roughness. There is an excellent effect that banding caused by the above can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a printer according to an embodiment.

FIG. 2 shows a banding generation cycle Lg (π × Dp × M /
Dg) is a graph showing the relationship between 1 / e diameter Lb.

FIG. 3 is a graph showing a beam intensity distribution curve.

FIG. 4 is an enlarged view showing a line image on a transfer sheet.

FIG. 5 shows a spatial frequency (X) of density unevenness appearing on an image.
Axis) and the allowable density difference of the density unevenness with respect to humans (Y axis)
The graph which shows the relationship with.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charger 3 Optical writing unit 4 Developing device 5 Primary transfer device 6 Secondary transfer roller 7 Static elimination device 8 Cleaning blade 9 Fixing device

Claims (5)

[Claims] 1. A latent image carrier for carrying a latent image on a surface while moving in a predetermined direction, a beam irradiation means for irradiating the surface with a light beam to carry the latent image, Visualizing means for visualizing, a moving force transmitting means having a gear for transmitting a moving force to the latent image carrier, and applying a moving force to the latent image carrier via the moving force transmitting means And a diameter of the gear located closest to the latent image carrier in the moving force transmitting means.
g [mm], the module is M [mm], and the radius of curvature at the light beam irradiation position on the surface is Dp / 2 [m].
m], the pi is π, and the diameter in the surface movement direction of a region where the beam intensity in the beam spot on the surface is 1 / e of its peak value is Lb [mm]. An image forming apparatus characterized by satisfying the conditional expression shown in Expression 1. Lb / 0.06 + (π × Dp × M / Dg) / 2 <
1 [mm] 2. The image forming apparatus according to claim 1, wherein the following conditional expression is satisfied. Lb / 0.05 + (π × Dp × M / Dg) / 1.
5 <1 [mm] 3. The image forming apparatus according to claim 1, wherein said latent image carrier is a photosensitive member, wherein a thickness of a photosensitive layer on a surface of said photosensitive member is formed to be 15 [μm] or less. Image forming device. 4. A transfer device for transferring a visual image obtained by attaching an image forming substance to the latent image by the visualizing device onto a recording medium, and forming an image on the recording material. 2. The image forming apparatus according to claim 2, wherein two non-image portions of two pixels extend in a direction orthogonal to the recording medium in a direction corresponding to the surface movement direction. An image forming apparatus comprising, when a linear image is formed, adhering the image forming substance to 20% or more of the non-image portion with respect to a center line parallel to the linear image. . 5. An image data processing means for performing halftone processing on image data, and irradiating the latent image carrier with the light beam based on the halftone processed data.
The image forming apparatus according to claim 1, wherein the image data processing means is configured to perform halftone processing on the image data by an error diffusion method.