JP2001136354A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of reducing the variation of a light quantity without improving precision of correction data. SOLUTION: This image forming device 10 is provided with a timing generator 66, which outputs a line number to an adding and rounding circuit 68. A ROM 70 stores the optimal value of the light quantity correction data of each LED of an LED chip 60. The circuit 68 generates such plural correction data as to match with the optimal value of the light quantity correction data in the case of averaging from precise light quantity correction data stored in the ROM 70 and the value of the low-order 2 bits of a line number. An LED driver 62 corrects the light quantity of each LED by switching the plural generated correction data. Thus, the whole light quantity can be corrected precisely.

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, and more particularly, to an image forming apparatus that forms an image by exposing a photoreceptor by turning on an LED array in accordance with an image to be formed.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer, an electrostatic latent image is formed by exposing a photosensitive member in accordance with an image, and the electrostatic latent image is developed by toner development. An image is formed by transferring the toner image formed on the body to recording paper.

[0003] As a light source for forming an electrostatic latent image on a photosensitive member, a laser beam has been conventionally used.
In recent years, as shown in FIG. 7, LED chips 102 and LED chips 102 in which LED elements 100 are arranged in a row corresponding to each pixel are shown.
LED head 106 including a plurality of ED drivers 104
Has been used. The LED driver 104 is connected to each L
A current is supplied to the ED element 100 to light up according to an image.

However, in the LED head 106,
± 15% variation in light intensity of each LED due to manufacturing problems
To some extent.

In order to solve this problem, the LED driver is provided with a function of controlling the current value, and the correction value is used to control the current value of the current flowing through each LED. Has been proposed (see JP-A-8-39862).

In addition, the amount of light emitted from each LED element is irregularly changed by using a chaos generator, whereby each LED is
There has been proposed a technique for reducing unevenness in image density by alleviating a difference in light emission amount between elements (Japanese Patent Laid-Open No. 8-31).
0044).

[0007]

However, the technique described in Japanese Patent Application Laid-Open No. 8-39862 has a problem that it is difficult to improve the accuracy of correction data due to a problem in manufacturing an LED head. .

In the technique described in Japanese Patent Application Laid-Open No. 8-310044, even if the amount of light emitted from each LED element is irregularly changed, the variation in the average amount of light from each LED element is large to some extent. There is a problem that it is difficult to reliably reduce such factors.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problem, and has as its object to provide an image forming apparatus capable of reducing unevenness in light amount without increasing the accuracy of correction data.

[0010]

In order to achieve the above object, the invention according to claim 1 comprises a plurality of light emitting elements each emitting light at a predetermined light emission amount and arranged in a line in the main scanning direction. Scanning means for performing main scanning in the main scanning direction by light emission of a plurality of light emitting elements, and sub-scanning in a sub-scanning direction intersecting with the main scanning direction to perform a plurality of light emission in the main scanning direction in the sub-scanning direction; For each of the plurality of light-emitting elements, the amount of variation from the predetermined light-emitting amount is represented, and the total light-emitting amount when the sub-scan is performed a predetermined number of times substantially coincides with each other, and the correction determined for each of the predetermined number of times is performed. Storage means for storing data, and light amount correction means for correcting the light amount of each light emitting element by switching the correction data stored in the storage means according to the number of sub-scans when performing the sub-scanning. Is characterized by There.

The scanning means includes a plurality of light emitting elements arranged in a line in the main scanning direction. The light emitting element is, for example, L
An ED can be used, and a number corresponding to the resolution of an image to be formed can be provided. Each of these light emitting elements emits light at a predetermined light amount. The predetermined amount of light may be different depending on, for example, the variation of each light emitting element.

The scanning means makes the plurality of light emitting elements emit light, for example, to perform main scanning on the photosensitive member in the main scanning direction. Then, by rotating the photoreceptor, sub-scanning is performed in a sub-scanning direction that intersects with the main scanning direction, and a plurality of light emission in the main scanning direction are performed in the sub-scanning direction. That is, by sub-scanning one line at a time, for example, a latent image corresponding to an image can be formed on a photoconductor.

[0013] The storage means stores, for each of the plurality of light emitting elements, correction data determined for a predetermined number of times.
Each of the correction data represents a variation amount from a predetermined light emission amount, that is, a light amount correction value, and is determined such that the total light emission amount when sub-scanning is performed a predetermined number of times is substantially the same for each light emitting element. It should be noted that the predetermined number of times is set such that the total light emission amount can be made to substantially match with respect to each light emitting element with high accuracy if the number is large, and the total light emitting amount is completely matched with each light emitting element. Is preferred.

The light quantity correction means corrects the light quantity of each light emitting element by switching the correction data stored in the storage means in accordance with the number of sub-scans, that is, the correction data determined every predetermined number of times. I do. As a result, the total light emission amount of each light emitting element for each predetermined number of times substantially matches.

That is, even when the light emission amount of each light emitting element cannot be made to match each other as in the case where the accuracy of correction by the light amount correction means is low, the total light emission amount can be made substantially equal. Therefore, the light amount can be corrected with high accuracy for the entire image, and the vertical streak and the like of the image can be reduced at low cost.

The correction data determined for each of the plurality of light-emitting elements may be stored in advance in the storage means. Thus, light amount correction can be performed with a simple configuration.

According to a second aspect of the present invention, the predetermined number of times for each of the plurality of light emitting elements is adjusted such that an average of the correction data determined for each of the predetermined number of times matches predetermined target correction data. It is characterized by further comprising a calculating means for calculating each correction data.

The calculating means calculates the correction data for each of the plurality of light emitting elements such that the average of the correction data determined for each of the predetermined number of times coincides with the predetermined target correction data. I do. This calculation can be performed, for example, as follows.

First, the number of bits of the target correction data is set to n (n
Is an integer), and when the number of bits of the correction data by the light amount correction means is m (m is an integer, n> m), the predetermined number is 2
^(nm) . Then, the value indicated by the lower (nm) bits of the line number is added to the n-bit target correction data by 2
^The value divided by ^(nm) is added, and 2 ^(nm) pieces of correction data in which lower ^(nm) bits are further discarded are generated. The average value of the plurality of correction data generated in this way matches the target correction data.

As described above, since the correction data for each of the predetermined number of times is calculated and obtained, only the target correction data can be stored in the storage means even if each correction data is not stored in the storage means in advance. Therefore, the storage capacity of the storage unit can be reduced.

The calculating means calculates the correction data for each of the predetermined number of times by adding a predetermined random number to the target correction data and truncating predetermined low-order bits. You may make it.

The random number is, for example, lower (n-
m) Use a random number such that a value obtained by dividing a value indicated by bits by 2 ^(nm) is uniformly generated. Thereby, the average value of the generated plurality of correction data can be matched with the target correction data.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] A first embodiment of the present invention will be described below.

FIG. 1 shows the overall configuration of the image forming apparatus 10. As shown in FIG. 1, the image forming apparatus 10
Includes a photosensitive drum 12 for forming a latent image corresponding to digital image data of an image to be formed. The photosensitive drum 12 rotates in the direction of arrow A in FIG.

A charger (not shown) for uniformly charging the photosensitive drum 12 is provided around the photosensitive drum 12.
An LED head 14 for forming an electrostatic latent image on the photosensitive drum 12 by exposing the photosensitive drum 12 in accordance with an image; and for developing the electrostatic latent image formed on the photosensitive drum 12 with toner. And an intermediate transfer belt 18 to which a toner image formed on the photosensitive drum 12 is primarily transferred.

As shown in FIG. 2, the LED head 14
A plurality of Ls arranged in one row along a direction (main scanning direction) orthogonal to the rotation direction (sub-scanning direction) of the photosensitive drum 12
It comprises a plurality of LED chips 60 on which ED elements (not shown) are arranged.

The LED elements are provided by the number of pixels (dots) corresponding to the resolution (for example, 600 dpi) in the main scanning direction, and are driven by the LED driver 62. This L
Image data processed by the image processing circuit 64 is input to the ED driver 62.

The LED driver 62 includes an image processing circuit 64
Each LED element in the LED chip 60 is turned on in accordance with the image data output from. As a result, the photosensitive drum 12 is exposed line by line as shown in FIG. 3, and an electrostatic latent image corresponding to the image is formed.

A timing generator 66 and an addition / rounding circuit 68 are connected to the LED driver 62. The LED driver 62 includes, for example, an addition / rounding circuit 6.
The current supplied to each LED element can be controlled in 16 steps based on the light amount correction data of m bits (for example, 4 bits) output from 8.

The amount of current correction (correction resolution) per step is, for example, 2%. That is, when the light quantity correction data has a 4-bit configuration, for example, as shown in Table 1, each LED element has a range of -16% to + 14% by 2%.
The light quantity is corrected in steps.

[0031]

[Table 1]

The timing generator 66 is connected to an addition / rounding circuit 68. The addition / rounding circuit 68
It is connected to the ROM 70. The timing generator 66 outputs a clock signal, a line synchronization signal, and an LED emission signal to each LED driver 62, and outputs a line signal indicating a line number of a line to be written to the addition / rounding circuit 68.

The ROM 70 stores in advance light amount correction data (optimum values) of predetermined n bits (n> m, for example, 6 bits) of each LED element. The light amount correction data is determined so that the light amounts of the light emitted from the respective LED elements match. An example of 6-bit light quantity correction data is shown below as an example.

[0034]

[Table 2]

The adding / rounding circuit 68 adds the light amount correction data of each LED element read from the ROM 70 to the lower order (n) of the line number output from the timing generator 66.
-M) The value indicated by bits (for example, 2 bits) is 2
^The m-bit light quantity correction data is generated by adding the value divided by ^(nm) and further truncating the lower (nm) bits. That is, the n-bit correction data is rounded to m
Generate bit correction data.

Each LED driver 62 supplies a current having a current value corrected by the light amount correction data to the LED element. The addition / rounding circuit 68 and the ROM 70 are LE
It may be provided inside the D head 14.

An example of the light quantity correction data rounded by the addition / rounding circuit 68 when m = 4 and n = 6 is shown below.

[0038]

[Table 3]

As shown in Table 3, for example, when the 6-bit light amount correction data (optimum value) of the first pixel stored in the ROM 70 is 9.75, the correction amount is + 3.5%. Then, when a value obtained by dividing the value indicated by the lower two bits of the line number by 2 ^(nm) is added to the 6-bit light quantity correction data, the light quantity correction data on the Mth line is 9.7.
5, the light quantity correction data of the (M + 1) th line is 10.00, M
The light amount correction data for the +2 line is 10.25, the light amount correction data for the M + 3 line is 10.50, and the light amount correction data for the M line is 9 (correction amount = + 2%) by cutting off the lower two bits. , M + 1, M + 2,
The light amount correction data of the M + 3 line is 10 (correction amount = + 4
%), And each is rounded to 4-bit light amount correction data.

The average of these light quantity correction data is 9.75 (correction amount = + 3.5%). That is, 2
^{When the (nm)} line is taken as one group, the average light amount in the group matches the optimum correction data.

The number of correction data for each LED is determined as follows. For example, in general, the human eye
It is said that it is very insensitive to a density change of 0.2 mm pitch or less, so that the repetition period of the correction data may be 0.2 mm or less on the image.

For example, when the resolution in the sub-scanning direction is 600 dpi as described above, the line interval is about 0.042 mm.
Thus, 0.2 mm ÷ 0.042 mm = 4.76, and the repetition period of the correction data may be set to four lines or less.

In the above example, the fluctuation in the amount of light per line is at most 2%. However, when the resolution in the sub-scanning direction is 600 dpi, the fluctuation in density occurs at a pitch of 0.042 mm. .

In consideration of the light quantity fluctuation in units of four lines, the density unevenness is 0.042 mm × 4 = 0.168 mm pitch, which is close to the 0.2 mm pitch which is easily visible to human eyes. Since the variation is 0.5% or less, it becomes more difficult for human eyes to understand as compared with the case where each pixel is corrected for the amount of light with one correction data.

The photosensitive drum 12 is controlled by the LED head 14.
The electrostatic latent image formed thereon is developed by the rotary developing device 16.

The rotary developing device 16 includes a yellow developing device 34 for developing toner of each color of yellow (Y), magenta (M), cyan (C), and black (K), a magenta developing device 36, and a cyan developing device. Device 38,
A black developing device 40 is provided, and by rotating the rotary developing device 16 in the direction of arrow B in FIG. 1 by 90 degrees, the developing device that performs the developing process of each color is switched.

The intermediate transfer belt 18 is an endless belt,
By a driving force of the driving roll 42, the driving roller 42 circulates a predetermined orbit in a predetermined direction (the direction of arrow C in FIG. 1). The intermediate transfer belt 18 is in contact with the photosensitive drum 12, and a transfer roll 47 is provided at the contact portion. Further, around the intermediate transfer belt 18, a transfer device 44,
A cleaner device (not shown) is installed.
, A fixing device 46 is provided on the left side of the transfer device 44.

The paper tray 4 is provided at the bottom of the image forming apparatus 10.
8 are provided. The paper 50 placed on the paper tray 48 is sent out to the transport path R, and is transported along the transport path R by the transport roll 52. During this conveyance, the paper 50 is conveyed to the transfer position of the transfer device 44, and the toner image transferred to the intermediate transfer belt 18 is transferred to the paper 50.

The sheet 50 on which the image has been transferred is fixed to the fixing device 46.
And is subjected to a fixing process. The sheet 50 on which the image has been fixed on the surface by the fixing process is transported along the transport path R by the transport rolls 54 and discharged to the outside.

Next, the operation of the first embodiment will be described.

In FIG. 1, the photosensitive drum 20 rotating in the direction of arrow A is charged by a charging device in the same manner, and an electrostatic latent image of the first color (for example, yellow) is first formed on the photosensitive drum 12 by the LED head 14. Formed.

More specifically, image data is output from the image processing circuit 64 to each LED driver 62. Further, a line signal indicating a line number is output from the timing generator 66 to the addition / rounding circuit 68. The addition / rounding circuit 68 reads n-bit (for example, 6-bit) light amount correction data of each LED element (each pixel) from the ROM 70, and adds the read light amount correction data to the lower part of the line signal output from the timing generator 66 (see FIG. nm)
A value obtained by dividing a value represented by a bit (for example, 2 bits) by 2 ^{(nm )} is added, and the lower (nm) bits are further rounded down.

That is, the n-bit light quantity correction data stored in the ROM 70 is rounded to generate m-bit light quantity correction data. Then, the m-bit light amount correction data is output to the corresponding LED driver 62.

An example of the correction data of the Nth pixel calculated as described above when m = 4 and n = 6 is shown below.

[0055]

[Table 4]

As shown in Table 4, when the original correction data (optimum value) is 13.25, a value obtained by dividing the value indicated by the lower 2 bits by 2 ^(nm) is added thereto, and the lower 2 bits are further added. The average of the four pieces of correction data generated by truncation has the same value as the original correction data. That is, LED
Even when the correction accuracy of the driver 62 is low, the entire light amount can be corrected with high accuracy.

Each of the LED drivers 62 sequentially switches the correction data 1 to 4 thus generated as shown in FIG. 4, and supplies a current of a current value corrected by the switched correction data to each LED element. .

FIG. 4 shows a case where the correction data of the Nth pixel is switched as an example. As shown in FIG. 4, when a line synchronization signal is output from the timing generator 66, the LED driver 62 switches the correction data. Then, when the LED light emission signal is output from the timing generator 66, a current having a current value corrected by the correction data is supplied to each LED to light each LED.

The electrostatic latent image formed on the photosensitive drum 12 is developed by a yellow developing device 34 with yellow toner. The developed yellow toner image is
The image is transferred to the intermediate transfer belt 18 by the transfer roller 47. The toner image remaining on the photosensitive drum 12 without being transferred is removed by a cleaner device, and the photosensitive drum 12 is discharged by a discharge lamp (not shown).

The photosensitive drum 12 is charged again by the charging device in the same manner, and the second color (for example, magenta) image is formed. In this way, a total of four color toner images are sequentially transferred to the intermediate transfer belt 18 up to the third color (for example, cyan) and the fourth color (for example, black). 4
When the transfer of the color toner image to the intermediate transfer belt 18 is completed, a color image is formed on the surface of the intermediate transfer belt 18.

The color image formed on the surface of the intermediate transfer belt 18 is transferred by the transfer device 44 onto the sheet 50 conveyed from the sheet tray 48 along the conveyance path R. The paper 50 on which the color image has been transferred is
Heating roll 5 transported to a predetermined fixing temperature
6 and the pressure roll 58, the color image is fixed on the sheet 50. As a result, a desired color image is formed on the sheet 50.

As described above, even when the correction accuracy of the LED driver 62 is low, the light amount correction of each pixel is performed by switching a plurality of correction data that match the target correction data when averaged. Accuracy can be corrected. [Second Embodiment] Next, a second embodiment of the present invention will be described.

FIG. 5 shows a schematic configuration of an image forming apparatus 10 ′ according to the second embodiment. The same parts as those of the image forming apparatus 10 shown in FIG. 2 are denoted by the same reference numerals, and detailed description thereof will be omitted.

As shown in FIG. 5, the image forming apparatus 10 ′
Has a random number generation circuit 72. The random number generation circuit 72 generates a random number as described below and outputs the generated random number to the addition / rounding circuit 68.

[0065]

[Table 5]

That is, instead of outputting the line number from the timing generator 66 as described in the first embodiment, the random number generation circuit 72 divides, for example, the value indicated by the lower two bits of the line number by 2 ^(nm) . Generate a random number in which the calculated value appears uniformly.

Thus, as in the first embodiment, 2
The average of the correction data for each ^(nm) line has the same value as the original correction data. That is, even when the correction accuracy of the LED driver 62 is low, the entire light amount can be corrected with high accuracy.

Therefore, even when the correction accuracy of the LED driver 62 is low, the light amount correction of each pixel is performed by switching a plurality of correction data that match the target correction data when averaged. Corrections can be made. [Third Embodiment] Next, a third embodiment of the present invention will be described.

FIG. 6 shows a schematic configuration of an image forming apparatus 10 ″ according to the third embodiment. The same parts as those of the image forming apparatus 10 shown in FIG. Detailed description is omitted.

The difference between the image forming apparatus 10 shown in FIG. 2 and the image forming apparatus 10 ″ shown in FIG. 6 is that the image forming apparatus 10 ″ shown in FIG.
That is, the correction data is output from the ROM 70 to the LED driver 62.

The ROM 70 previously stores a plurality of correction data shown in Table 3, that is, a plurality of correction data that coincides with the target correction data when averaged. Output to Therefore, it is possible to perform highly accurate light quantity correction with a simple configuration.

In the above-described embodiment, a case has been described where a plurality of correction data is determined for each LED such that the average value thereof is equal to the target correction data. The light amounts may be matched.

[0073]

As described above, according to the present invention,
Even when the accuracy of the correction data of the light amount correction by the light amount correction means is low, the correction data is switched according to the number of sub-scans to correct the light amount of each light emitting element, so that the overall correction accuracy is improved. This has the effect that vertical streaks and the like of the image can be reduced at low cost.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an image forming apparatus according to a first embodiment.

FIG. 2 is a schematic block diagram of the image forming apparatus according to the first embodiment.

FIG. 3 is a diagram for explaining image formation.

FIG. 4 is a timing chart for explaining switching of correction data.

FIG. 5 is a schematic block diagram of an image forming apparatus according to a second embodiment.

FIG. 6 is a schematic block diagram of an image forming apparatus according to a third embodiment.

FIG. 7 is a diagram showing a schematic configuration of an LED head.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Photoreceptor drum 14 LED head 16 Rotary developing device 18 Intermediate transfer belt 60 LED chip 62 LED driver 64 Image processing circuit 66 Timing generator 68 Addition and rounding circuit 70 ROM 72 Random number generation circuit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) G03G 15/04 111 G03G 21/00 372 5C072 21/14 H04N 1/04 103E 5C074 H04N 1/036 1/19 (72) Inventor Ken Kato 2274 Hongo, Ebina-shi, Kanagawa Prefecture Fuji Xerox Co., Ltd.Ebina Office (72) Inventor Masaki Hachisuka 2274 Hongo, Ebina-shi, Kanagawa Prefecture Fuji Xerox Co., Ltd.Ebina Office (72) Inventor Aikawa 2274 Hongo, Ebina, Ebina-shi, Kanagawa Prefecture (72) Inventor Yoichi Imamura 2274, Hongo, Ebina-shi, Kanagawa, Japan DA32 ED04 EE01 EE07 EF09 ZA07 2H0 30 AA02 AD17 BB02 BB13 BB24 BB42 2H076 AB22 AB42 AB55 AB66 EA01 5C051 AA02 CA08 DB02 DB09 DE03 DE12 DE30 EA00 5C072 AA03 BA15 FA16 FB18 FB27 UA01 UA11 WA03 5C074 AA02 BB04 DD01 DD16

Claims (3)

[Claims] A plurality of light-emitting elements each emitting a predetermined amount of light and arranged in a line in the main scanning direction, wherein the plurality of light-emitting elements emit light in a main scanning direction and emit light in a main scanning direction; A scanning unit that performs sub-scanning in the sub-scanning direction intersecting with and performs light emission in the main scanning direction a plurality of times in the sub-scanning direction; and for each of the plurality of light-emitting elements, represents a variation amount from the predetermined light emission amount, and A storage unit storing the correction data determined for each of the predetermined number of times while the total light emission amount when the sub-scanning is performed for the predetermined number of times substantially coincides with each other. An image forming apparatus comprising: a light amount correcting unit configured to switch the correction data stored in the storage unit in response to the light amount of each of the light emitting elements. 2. The correction data for each of the predetermined number of times for each of the plurality of light emitting elements such that the average of the correction data for each of the predetermined number of times matches a predetermined target correction data. The image forming apparatus according to claim 1, further comprising a calculating unit that performs a calculation. 3. For each of the plurality of light-emitting elements, the calculating means adds a predetermined random number to the target correction data and cuts off a predetermined lower-order bit to thereby correct the correction data for each of the predetermined number of times. 3. The image forming apparatus according to claim 2, wherein the calculation is performed.