JPH09166897A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent banding on an image from standing out by reducing the gear pitch of a photoreceptor drum, and to prevent the occurrence of interference fringes (gradation of image density) due to the reduction of the gear pitch and the approach to a pitch based on the number of basic lines for forming a half tone. SOLUTION: Provided that d(mm) denotes the diameter of the photoreceptor drum 2, a(mm) denotes a gear pitch, that is, the moving distance of the photoreceptor drum 2 surface in accordance with the rotation of a tooth of the drum gears integrally rotated with the photoreceptor drum 2, (c) denotes the number of teeth of the drum gears, (1) denotes the number of basic lines for forming the half tone, ad b(mm) denotes a pitch based on the number of basic lines for forming the half tone, by establishing the following inequalities between the gear pitch (a) of the photoreceptor drum 2 and the pitch (b) based on the number of basic lines, b/a= 25.4/1}/ (d×π)/c}>1.277, and also, a <=1.51, or b/a= (25.4/1)}/ (d×π)/c}<0.752, also, a <=1.51, the occurrence of the banding and the interference fringes are prevented.

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 laser beam printer or an LED printer which scans an image carrier according to an image signal and outputs an image.

[0002]

2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus such as a digital copying machine or a laser beam printer is related to printing from an external information processing device (hereinafter referred to as "host device") such as a computer or a workstation. A command (print command, command that defines the print state of the printer, etc.) and coded characters and graphic information are received as data, and the formatter converts the code information into pixel information. At the time of conversion, an image image such as a photograph having density information is binarized by being subjected to image processing such as dither matrix.

Next, the electrophotographic engine portion prints based on the pixel information. The engine section includes, for example, an electrophotographic photosensitive member, a charging roller, a developing device, a cleaner and the like. The electrophotographic photosensitive member is formed on a drum-shaped base made of aluminum, nickel, or the like, and
It is configured by providing a photosensitive layer of C, amorphous Se, amorphous Si, or the like.

First, the surface of the above-mentioned drum type photoconductor (hereinafter referred to as "photosensitive drum") is uniformly charged by a charging roller. Next, the laser scanner raster-scans the image signal to expose the surface of the photosensitive drum. The laser scanner scans the blinking of the semiconductor laser with a polygon scanner, and forms an optical spot image on the surface of the photosensitive drum via an optical system and a folding mirror. This creates an electrostatic latent image. This electrostatic latent image is developed (visualized) by a developing device with toner attached by jumping development, two-component development, FEED development, or the like. In a digital image forming apparatus, image exposure and reversal development are often combined. That is, latent image formation is performed by image exposure in which electric charges in a portion where an image is formed (recorded) are removed by lighting (irradiation) of a laser, and development is performed by reversal development in which toner is attached to the portions where electric charges are removed. .

The toner image formed on the photosensitive drum by development is transferred to a transfer material. Transfer materials such as paper are stored in a paper feed cassette, and when a print signal is sent from the host device, they are fed one by one by a paper feed roller. The transferred transfer material is synchronized with the image signal by the timing roller, and the toner image is transferred by the transfer roller. The transfer roller is made of a conductive elastic body having a low hardness, and a bias electric field is applied while nipping and transferring the transfer material by a nip portion formed between the transfer roller and the photosensitive drum. As a result, the toner image on the photosensitive drum is electrostatically transferred to the surface of the transfer material.

The transfer material having an unfixed toner image on its surface is fixed on the surface by a fixing device, and then discharged onto a discharge tray by a discharge roller. On the other hand, the untransferred toner remaining on the photosensitive drum without being transferred to the transfer material is removed by the cleaning blade provided in the cleaner.

Regarding the control in the above-mentioned image forming apparatus, the light emission intensity and the light emission duty of the semiconductor laser of the laser scanner are controlled by the exposure control section. Also,
Bias of charging roller, bias of developing device,
The bias applied to the transfer roller is controlled by the high voltage control unit, the main motor and the scanner motor are controlled by the motor control unit, and the pressing force and temperature of the fixing device are controlled by the motor control unit.
The fixing control unit controls each. The operations of the paper feed roller and the timing roller are controlled by the paper feed controller.

The photosensitive drum described above is driven by a drum gear. The drum gear is formed so that its pitch circle is the same as the peripheral length of the photosensitive drum, and is integrally attached to one end of the photosensitive drum. The driving force from the driving motor is finally transmitted to the photosensitive drum via the driving gear, the above-mentioned drum gear meshing with the driving gear, and the like. At this time, the photosensitive drum is smoothly rotated by, for example, improving the processing accuracy of the tooth surfaces of the drive gear and the drum gear to prevent image defects due to uneven rotation.

[0009]

However, according to the above-mentioned image forming apparatus, when the photosensitive drum is improved in the machining accuracy of the tooth surfaces of the drive gear and the drum gear, when the drive gear and the drum gear mesh with each other. , Rotational irregularity occurs slightly. Therefore, when a halftone image is output, banding corresponding to the gear pitch of the drum gear occurs. Here, the banding is a periodic unevenness of light and shade in the transfer material feeding direction caused by the main body of the image forming apparatus.

As one of the measures to prevent this,
For example, a proposal has been made in which a pulley is used instead of a drum gear, and the pulley is driven by a rubber belt or the like to eliminate banding at the time of outputting a pattern image. However, in this case, because of the belt drive,
Since slipping is likely to occur and wear due to durability is large, uneven rotation of the photosensitive drum occurs in a sense different from the above.

As another preventive measure, it may be considered to reduce the module of the drum gear to reduce the gear pitch. To reduce the module m, which is a value obtained by dividing the diameter dmm of the gear pitch circle by the number of teeth z, for example, if the diameter d of the pitch circle is not changed, the number of teeth z may be increased.
The banding interval generated for each gear pitch when the pattern image is output becomes smaller as the gear pitch of the drum gear becomes smaller, so that it becomes less noticeable to human vision.

By the way, since the gear pitch of the conventional drum gear is sufficiently larger than the pitch of the basic matrix for expressing the gradation, interference fringes (light and shade of the image density, which are generated when the gear pitch and the image pitch are close to each other). )There was no. However, if the module m of the drum gear is made smaller to make the banding less noticeable and the gear pitch is made smaller, this gear pitch becomes sufficiently close to the pitch of the basic matrix for gradation expression.
Interference fringes may occur on the image surface due to interference.

[0013]

According to the present invention for solving the above-mentioned problems, an image carrier, a scanning means for scanning the image carrier according to image data, and a drive source for driving the image carrier. An image forming apparatus having a gear for transmitting power from a driving source to the image carrier, a moving pitch of the image carrier corresponding to a gear pitch of the gear is a [mm], and a basic matrix for gradation expression Where the pitch is b [mm], a ≦ 1.51 and b / a <0.752, or
It is characterized in that a ≦ 1.51 and b / a> 1.277 are satisfied.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 is a schematic configuration diagram of an electrophotographic printer as an example of an image forming apparatus according to the present invention.

First, the structure and operation of the entire image forming apparatus will be briefly described with reference to FIG.

In the figure, reference numeral 1 is a process cartridge, which is constructed by integrally incorporating an electrophotographic photosensitive member 2 as an image bearing member, a charging roller 3, a developing device 4 and a cleaner 5 into a cartridge container. The electrophotographic photosensitive member 2 includes an OPC, amorphous Se, and amorphous Si on a cylindrical substrate formed of aluminum, nickel, or the like.
And the like, and a drum type as a whole.

A drum type electrophotographic photosensitive member (hereinafter referred to as "photosensitive drum") 2 is driven by an arrow R by a driving means (not shown).
It is rotated in one direction, and its surface is uniformly charged by the charging roller 3. Next, the laser scanner 6 raster scans the image signal to expose the surface of the photosensitive drum 2. The laser scanner 6 scans the blinking of the semiconductor laser with a polygon scanner, and forms an optical spot image on the surface of the photosensitive drum 2 via an optical system and a folding mirror 7. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 2. This electrostatic latent image is developed (visualized) by the developing device 4 with toner attached by jumping development, two-component development, FEED development, or the like. In these developments, the toner 4b is carried on the surface of the developing roller 4a, the layer thickness is further regulated by the regulating blade 4c, and then the developing roller 4a is rotated in the direction of arrow R4 and conveyed to the developing position facing the photosensitive drum 2. By doing. In a digital image forming apparatus, image exposure and reversal development are often combined. That is, latent image formation is performed by image exposure in which electric charges in a portion where an image is formed (recorded) are removed by lighting (irradiation) of a laser, and development is performed by reversal development in which toner is attached to the portions where electric charges are removed. .

The toner image formed on the surface of the photosensitive drum 2 by development is transferred to a transfer material. Transfer materials such as paper are
It is housed in the paper feed cassette 8, and when a print signal is sent from the host device, the paper is fed by the paper feed roller 9 one by one. The fed transfer material is the timing roller 1.
When 0, the toner image is synchronized with the image signal, and the transfer roller 11 transfers the toner image. The transfer roller 11 is made of a conductive elastic body having a low hardness, and a bias electric field is applied while nipping and transferring the transfer material by a nip portion formed between the transfer roller 11 and the photosensitive drum 2. As a result, the toner image on the surface of the photosensitive drum 2 is electrostatically transferred to the surface of the transfer material.

The transfer material having an unfixed toner image on its surface has the toner image fixed on its surface by a fixing device 12, and thereafter is discharged to a paper discharge tray 14 by a paper discharge roller 13. On the other hand, the transfer residual toner remaining on the photosensitive drum without being transferred to the transfer material is removed by the cleaning blade provided in the cleaner 5.

Regarding the control in the above-mentioned image forming apparatus, the light emission intensity and the light emission duty of the semiconductor laser of the laser scanner are controlled by the exposure controller 16. Further, the bias applied to the charging roller 3, the bias applied to the developing roller 4a, and the bias applied to the transfer roller 11 are controlled by the high-voltage control unit 17, and the main motor and the scanner motor are controlled by the motor control unit 18.
The pressing force and temperature of the fixing device 12 are controlled by the fixing control unit 19, respectively. The operation of the paper feed roller 9 and the timing roller 10 is controlled by the paper feed controller 20.

Here, when the process cartridge 1 is mounted in the main body of the apparatus, the photosensitive drum 2 is driven by the drum gear 21 provided on the main body side via the drum flange 23. The drum gear 21 is driven by a motor 22.

In this embodiment, the diameter of the pitch circle of the drum gear is increased, and the number of teeth of the drum gear is increased to make the module of the drum gear smaller.
As a result, the gear pitch of the photosensitive drum 2 is shortened and the banding interval is shortened. By doing this,
Banding is obscured. Here, the gear pitch of the photosensitive drum 2 refers to the distance traveled by one point on the surface of the photosensitive drum 2 when the drum gear rotates by its circular pitch (pitch circle divided by the number of teeth). Shown).

Table 1 shows the relationship between the gear pitch and the banding of the image forming apparatus in this embodiment.

[0025]

[Table 1]

In Table 1 above, the banding level was evaluated by using a pattern in which a horizontal line of 1 dot and 2 spaces and 1 dot were arranged in a zebra shape as shown in FIG. 3 at a resolution of 600 dpi, and uneven density corresponding to the gear pitch was obtained. It was judged by whether it was visually noticeable. From the results of Table 1, the gear pitch is 1.51 mm or less, preferably 0.81 mm or less,
It can be seen that the occurrence of image unevenness due to the drum drive gear is reduced by more preferably setting it to 0.49 mm or less. Here, the gear pitch was fixed at a module of 0.5, and the outer diameter of the gear was changed to change the number of teeth, and the gear pitch was changed accordingly.

As can be seen from Table 1 above, by reducing the gear pitch of the image bearing member, the moving distance due to the rotation of one tooth of the drum gear is reduced, so that the banding interval is shortened and it becomes difficult to visually identify. In addition, rotation unevenness caused by driving by gears causes rotation unevenness due to meshing errors between gears, but the meshing area is reduced by reducing the module, and it becomes difficult to pick up the influence of the above meshing errors due to the tooth surface shape of the gear. The banding level is also improved by the effect. Rotational unevenness due to meshing of gears becomes better as the tooth flank accuracy of the gears is improved, but it is well known that it is difficult to obtain an ideal tooth flank shape in reality. This point is also easily improved by reducing the module as in the present embodiment, so that there is an advantage that banding is effective and gears are easily manufactured.

However, if the gear module is simply reduced, the tooth flank strength of the gear is reduced and the gear is scraped, so that it cannot withstand long-term use. Therefore, unlike the present embodiment, the outer diameter of the gear is made larger than the outer diameter of the photosensitive drum, and the number of teeth of the driving gear is increased, so that the module of the gear is not extremely lowered (0.4 to 0.6 (Preferably) The gear pitch can be reduced, and at the same time, the load applied to one tooth of the gear can also be reduced, so from the viewpoint of strength,
There is an advantage that the module can be made relatively small (for example, a drive gear having the same outer diameter as the photosensitive drum requires a module of 0.8 or more).

However, by shortening the gear pitch of the photosensitive drum 2, the gear pitch and the pitch of the basic number of lines (line pitch in the paper feeding direction) for forming the halftone become close to each other, and the interference between the two occurs. Streaks occur. Here, the basic line number of the printer is the number of lines when the image data (multi-valued information) having density information sent from the external input device is binarized by the formatter of the image forming apparatus. The formatter of the forming apparatus usually has one or more basic lines.

Specifically, 8 bits from an external information processing device (personal computer, workstation, etc.)
When the printer receives the image data having the density information of, the halftone is reproduced by the halftone processing method (for example, dither processing, error diffusion method, etc.) that the printer has in advance. For example, a printer having a resolution of 600 dpi has 8 bits.
If the density information of is processed by an 8 × 8 dither matrix, the basic number of lines at this time becomes 75 lines. Here, when the pitch of the photosensitive drum drive gear 21 of the printer is 0.4 mm (the outer diameter of the photosensitive drum 2 is φ30 mm, the outer diameter of the drive gear 21 is φ117 mm, and the number of gear teeth is 235, the driving is about 0 mm). The photosensitive drum can be driven with a gear pitch of 0.4 mm), and the line pitch formed by the basic number of lines is 0.339 mm, which is very close to the pitch interval. .

Table 2 shows the occurrence of interference fringes due to the basic number of lines for forming the halftone and the gear pitch of the photosensitive drum 2. In this table, a laser beam printer with a resolution of 600 dpi was used, and the size of the dither matrix and the pitch of the photosensitive drum drive gear were changed to verify the occurrence of interference fringes. For example, when a 4 × 4 dither matrix is formed, the number of lines is 150, which is 8 × 8.
If the dither matrix is, the number of lines is 75.

[0032]

[Table 2]

In Table 2 above, ○ indicates that no interference fringes are generated, Δ indicates that interference fringes are slightly generated but is within the allowable level, and × indicates that interference fringes are generated and exceeds the allowable level. .

The gear pitch a (m) of the photosensitive drum 2 in Table 2
m) is the diameter of the photosensitive drum 2 and c is the number of teeth of the large gear 21.
Is expressed as a = (d × π) / c.

Further, as shown in FIG. 4a, when the screen angle is 0 °, the line number l in the sub-scanning direction (recording material feeding direction) is when the size of the dither matrix is n × n and the resolution is r. , L = r / n. In FIG. 4a, an 8 × 8 dither matrix is shown. If the resolution of the printer is 600 dpi, the line number l is l = 600/8 = 75.
(Line). When a screen angle (angle θ formed by the center line of dot growth with respect to the main scanning direction orthogonal to the paper feed direction A) is provided, the line number l ′ is the distance in the paper feed direction = the number of dots as shown in FIG. 4b. n times n multiplied by cos θ
It is indicated by a numerical value obtained by dividing the resolution r by cos θ (the number of lines l ′
= R / (n × cos θ)). However, also in this case, as shown in the results of Table 2, it can be seen that the occurrence of interference fringes is determined by the relationship between the pitch in the paper feed direction and the photosensitive drum gear pitch. Therefore, even when the screen angle θ is taken into consideration, it is understood that the numerical value represented by the number of lines 1 = r / n × cos θ should satisfy a predetermined relationship with the drum gear pitch.

From the results shown in Table 2, the number of lines for halftone formation is l
The relationship between the line pitch b and the drum gear pitch a determined by b is b / a <0.752 ... or b / a> 1.277.
Is satisfied, more preferably b / a ≦
It can be seen that interference fringes that occur during halftone image formation can be prevented by satisfying 0.741 or b / a ≧ 1.323. This relationship is represented by the number of lines 1 for forming a halftone image, the number of teeth of the drum gear c, and the diameter of the photosensitive drum d (25.4 /
l) / [(d × π) / c] <0.752, or (25.
4 / l) / [(d × π) / c]> 1.277, more preferably (25.4 / l) / [(d × π) /
c] ≦ 0.741, or (25.4 / l) / [(d ×
It can be seen that it is necessary to satisfy π) / c] ≧ 1.323.

(Embodiment 2) The electrophotographic printer used in this embodiment is the same as that in Embodiment 1.

In the present embodiment, the gear pitch (frequency f1) of the photosensitive drum 2 and the basic line number (frequency f2) for forming the halftone do not satisfy the expression of the first embodiment, and an interference fringe is generated. In such a case, once the image forming apparatus is configured, the gear pitch of the photosensitive drum 2 cannot be changed. By converting into a basic line number for this purpose, it is possible to obtain a high-definition image in which banding is not conspicuous without losing the gradation and density of the image.

From Table 2, when the resolution is 600 dpi and the gear pitch of the photosensitive drum 2 is 0.9 mm, the basic line number for forming a halftone is the closest to the basic line number for forming a halftone of 75 [lines / inch]. Number (in this case 100 [l
ines / inch]). When the basic number of lines for forming the halftone is 100 [lines / inch], the number of gradations is 36, but the gradation is high (the density difference in the high image density portion is not so great). There is also
Since interference fringes due to the gear pitch of the photosensitive drum 2 and the basic line number for forming the halftone do not occur, 75 [lines]
/ Inch], a higher-definition output image can be obtained.

(Embodiment 3) The electrophotographic printer used in this embodiment is the same as that of the above-described Embodiment 1.

In the present embodiment, the gear pitch (frequency f1) of the photosensitive drum 2 and the basic number of lines (frequency f2) for forming the halftone do not satisfy the above equation, and the gear pitch of the photosensitive drum 2 is intermediate. When the interference fringes due to the basic number of lines for forming the halftone are generated, the gear pitch of the photosensitive drum 2 is unchanged as in the second embodiment. Therefore, the basic number of lines for forming the halftone is converted to At this time, the resolution is converted so that the gradation is not changed before and after the conversion.

From Table 2, when the resolution is 600 dpi and the gear pitch of the photosensitive drum 2 is 0.9 mm, the basic line number for forming halftones is closest to the basic line number for forming halftones of 75 [lines / inch]. Number (in this case 100 [l
ines / inch]). When the number of basic lines for forming halftones is 100 [lines / inch], the resolution is 800d in order to maintain the number of gradations at 64.
pi.

Therefore, it is possible to obtain a high-definition output image in which the number of gradations is not reduced.

[0044]

As described above, according to the present invention,
By reducing the gear pitch of the image carrier, banding can be improved, and regarding the interference fringes that easily occur by reducing the gear pitch,
This can be prevented by selecting a combination of the gear pitch and the basic number of lines in which interference fringes are unlikely to occur, and a higher-definition image can be output.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present invention.

FIG. 2 is a schematic configuration diagram of an image carrier and a large gear of the image forming apparatus according to the present invention.

FIG. 3 is a diagram showing an image pattern for explaining the present invention.

FIG. 4 is a diagram showing an image pattern for explaining the present invention.

[Explanation of symbols]

 1 Process Cartridge 2 Image Carrier (Photosensitive Drum) 3 Charging Roller 4 Developer 5 Cleaner 6 Laser Scanner 8 Paper Feed Cassette 9 Paper Feed Roller 10 Timing Roller 11 Transfer Roller 12 Fixing Roller 16 Exposure Controller 17 High Voltage Controller 18 Motor Control Part 19 Fixing control part 20 Paper feed control part

Claims (1)

[Claims] 1. An image carrier, a scanning means for scanning the image carrier according to image data, a drive source for driving the image carrier, and a gear for transmitting power from the drive source to the image carrier. In the image forming apparatus having the above, when the moving pitch of the image carrier corresponding to the gear pitch of the gear is a [mm] and the pitch of the basic matrix for gradation expression is b [mm], a ≦ 1.51 and b /
a <0.752, or a ≦ 1.51 and b / a>
An image forming apparatus characterized by satisfying 1.277.