JPH05153397A - Image generating device - Google Patents

Abstract

PURPOSE:To prevent the deterioration of picture quality caused by the fluctuation of the irradiated quantity of the laser light by dividing a scanning range of the axial direction set on the surface of a photosensitive matter, measuring the bright potential of each divided range, and correcting the image data based on these measured bright potentials. CONSTITUTION:The scanning range of the axial direction set on the surface of a photosensitive matter 21 is divided into plural parts. Then the bright potentials of these divided ranges are measured by the bright potential measurement means 41, 42 and 43 respectively. Based on these measured potentials, the image data are corrected. Thus the value of the image data is corrected so as to prevent such a case where the density and the gradation expression reproducibility are changed by the fluctuation of the irradiated laser light quantity caused to the axial direction of the matter 21. In such a constitution, it is possible to prevent the deterioration of picture quality due to the fluctuation of the irradiated laser light quantity.

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 an electrophotographic copying machine or a laser printer which is exposed by laser light.

[0002]

2. Description of the Related Art In an image forming apparatus such as an electrophotographic copying machine or a laser printer which is exposed by laser light, the surface of a photosensitive drum having a photoconductive layer on its surface is uniformly charged by a charger. After that, the surface of the photosensitive drum is selectively irradiated with laser light to perform exposure. The potential (hereinafter, referred to as a bright potential) at the place where the laser beam is irradiated on the surface of the photosensitive drum is related to the image density, the gradation reproducibility of the image, and the like, and therefore it is preferable that the potential is always constant.

However, the bright potential is not always constant due to the temperature dependence of the output of the laser beam and the contamination of the optical system due to the deterioration of the sensitivity of the photosensitive drum itself due to the exposure fatigue of the photosensitive drum. Therefore, at the center of the axial scanning range of the photoconductor drum, the surface potential sensor measures the potential of the surface of the photoconductor drum during laser irradiation (bright potential), and the bright potential is kept constant based on this measurement value. An image forming apparatus that controls the output of laser light has already been developed.

[0004]

By the way, in an image forming apparatus such as an electrophotographic copying machine or a laser printer which is exposed by a laser beam, the laser beam is sensitized by an optical system including a polygon mirror which is driven to rotate. The surface of the drum is scanned in the axial direction of the photosensitive drum. Since the optical path from the reflecting surface of the polygon mirror to the surface of the photoconductor drum differs depending on the axial position of the photoconductor drum, the irradiation amount of laser light on the surface of the photoconductor drum is constant over the entire axial scanning range of the photoconductor drum. I won't.

That is, the amount of light emitted by the laser light varies depending on the axial position on the surface of the photosensitive drum. In general, as shown in FIG. 5, the irradiation light amount for the end portions PF, PR of the axial scanning range of the surface of the photosensitive drum is smaller than the irradiation light amount for the central portion PM of the axial scanning range of the surface of the photosensitive drum. Therefore, in general, as shown in FIG. 6, the end portions PF, P of the axial scanning range of the surface of the photoconductor drum.
The bright potential for R is higher than the bright potential for the central portion PM of the axial scanning range on the surface of the photosensitive drum.

Therefore, in the central portion of the axial scanning range of the photosensitive drum, the surface potential sensor measures the surface potential (bright potential) of the surface of the photosensitive drum during laser irradiation, and the bright potential is determined based on the measured value. In the above-described conventional image forming apparatus that controls the output of the laser light so as to be constant, it is possible to make the bright potential constant in the central portion of the axial scanning range of the photoconductor drum, but the axis of the photoconductor drum surface is constant. There is a problem in that the bright potential cannot be made constant over the entire directional scanning range, and the image quality deteriorates.

It is an object of the present invention to provide an image forming apparatus capable of preventing deterioration of image quality due to variations in the irradiation light amount of laser light depending on the axial position of the surface of the photoconductor.

[0008]

An image forming apparatus according to the present invention is an image forming apparatus in which exposure is performed by a laser beam, and a bright potential is applied to each divided range in which an axial scanning range of a photosensitive member surface is divided into a plurality of areas. It is characterized by comprising bright potential measuring means for measuring each and image data correcting means for correcting image data based on the bright potential for each of the divided ranges measured by the bright potential measuring means.

As the bright potential measuring means, for example,
The bright potential of the central portion of the axial scanning range of the surface of the photoreceptor,
Three surface potential detectors for respectively measuring the bright potentials at both ends of the axial scanning range of the surface of the photoconductor are provided, and each of the divided ranges is based on the bright potentials detected by the three surface potential detectors. What measures the bright potential of is used.

As the image data correction means, for example, multiplication coefficient calculation for obtaining image data correction multiplication coefficients for the respective divided ranges based on the bright potential for the respective divided ranges measured by the bright potential measuring means. Means for multiplying the image data corresponding to the division range by the image data correction multiplication coefficient for each division range obtained by the multiplication coefficient calculation means are used.

[0011]

The bright potential is measured for each of the divided areas obtained by dividing the axial scanning range of the surface of the photoconductor into a plurality of areas. Then, the image data is corrected based on the measured bright potential for each divided range.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a digital color copying machine will be described below with reference to the drawings.

FIG. 1 shows a schematic structure of a digital color copying machine.

The copying machine 1 includes a scanner section 1 and a printer section 2.
It consists of and. The scanner unit 1 includes an automatic document feeder (ADF) 11, a scanning reading unit 12, and a conveyance mechanism 13 thereof. The automatic document feeder 11 automatically supplies a document onto the contact glass 14. A shading reference plate 15 is arranged in front of the contact glass 14 in the scanning direction. The scanning reading unit 12 includes a document illumination lamp 16 that irradiates a document on the contact glass 14 with light, and the optical system 1 that reflects light reflected from the document.
It has a CCD line sensor 18 which receives light through 7. The output of the CCD line sensor 18 is the image processing unit 54.
(See FIG. 2), edited, and processed. Transport mechanism 1
3 is for reciprocating the scanning reading unit 12,
A motor 19 is included.

The printer unit 2 includes a photosensitive drum 21, a charging unit 22, a laser scan unit (LSU) 23, a developing unit 24, a transfer drum 25, a cleaning unit 26, a paper feeding unit 27, a conveying unit 28 and a fixing unit 29. I have it. The charging unit 22 uniformly charges the surface of the photoconductor drum 21. The laser scanning unit 23 has a laser light source, an optical system including a polygon mirror, and the like.
Electric signal (pixel signal) sent from the image processing unit 54
Is converted into an optical signal and output. As a result, the surface of the photoconductor drum 21 is selectively irradiated with the laser light and is exposed.

The developing section 24 makes the electrostatic latent image formed on the surface of the photosensitive drum 21 by the exposure noticeable as a toner image. The transfer drum 25 transfers the toner image onto the recording paper. The cleaning unit 26 removes the toner remaining on the surface of the photosensitive drum 21 after the transfer. The paper feeding unit 27 supplies recording paper to the transfer drum 25. The transport unit 28 transports the recording paper on which the toner image is transferred to the fixing unit 29. The fixing unit 29 fixes the toner image on the recording paper.

The developing section 24 is provided with four developing devices 31 to 34 in which toners of different colors are stored, and at the time of development, each developing device 31 to 34 performs a predetermined developing process around the photoconductor 21 in a predetermined order. It is made to position sequentially in a position. Transfer drum 2
Reference numeral 5 is rotated four times with respect to one recording sheet in order to sequentially perform development processing by each of the developing devices 31 to 34 on one recording sheet.

Three surface potential sensors 41, 42, 43 for detecting the surface potential of the photosensitive drum 21 are arranged between the exposure position and the developing position around the photosensitive drum 21. The surface potential sensors 41 and 43 are arranged close to the surface of the photosensitive drum 21 near both ends of the axial scanning range of the photosensitive drum 21. The surface potential sensor 42 is arranged near the surface of the photoconductor drum 21 near the center of the axial scanning range of the photoconductor drum 21.

FIG. 2 shows the electrical construction of the copying machine.

The copying machine is controlled by the main controller 50. The main control unit 50 includes a storage unit 51. Input devices such as the surface potential sensors 41, 42 and 43 are connected to the main controller 50. Further, the main controller 50 includes a drive circuit 5 for rotating the photoconductor drum 21.
2. Output devices such as a drive circuit 53 for the charging unit 22, an image processing unit 54, and a laser scan unit 23 are connected.

The image processing section 54 includes the CCD line sensor 1
8 output is A / D converted, and shading correction processing is performed on the multi-valued pixel data after A / D conversion, and the photoconductor drum 21.
The correction process, the color correction process, the color conversion process, the density process, the multi-valued process, and the like for the variation of the laser irradiation light amount due to the axial position on the surface are performed. The pixel data output from the image processing unit 54 is sent to the laser scan unit 23, converted into an optical signal, and output.

In the above-described structure, a pixel data correction multiplication coefficient for the variation of the laser irradiation light amount depending on the axial position on the surface of the photosensitive drum 21 is created every time the power of the copying machine is turned on or when the copying operation is started. A multiplication coefficient creating process is performed.

In this process, first, the photosensitive drum 21 is rotationally driven and the surface of the photosensitive drum 21 is charged to a predetermined potential by the charging section 22. Then, the laser scanning unit 23 scans the surface of the photosensitive drum 21 with laser light. When the laser light is scanned, the absolute value of the potential at the scanning position becomes smaller.

Thereafter, the rotation of the photosensitive drum 21 causes
When the portion of the surface of the photoconductor drum 21 scanned by the laser beam reaches a potential measurement position of each of the surface potential sensors 41, 42, 43, the photoconductor drum 21 is detected based on each of the surface potential sensors 41, 42, 43. Surface potential of surface (bright potential)
Is measured and stored.

FIG. 3 shows detection values S1, S2 and S of the surface potential sensors 41, 42 and 43 for the potential measurement positions P1, P2 and P3 on the surface of the photosensitive drum 21.
3 shows an example. Generally, the amount of irradiation light on the center of the axial scanning range on the surface of the photosensitive drum 21 is larger than the amount of irradiation light on the end of the axial scanning range on the surface of the photosensitive drum 21, so that the axial scanning of the surface of the photosensitive drum 21 is performed. The absolute value of the bright potential (corresponding to S2) at the potential measurement position P2 at the center of the range corresponds to the absolute value (S1 or S3) of the bright potential at the measurement position P1 or P3 at the end of the surface of the photosensitive drum 21. ) Becomes smaller. In the example of FIG. 3, S2
<S3 <S1.

Next, each surface potential sensor 41, 42, 43
Of the detection values S1, S2 and S3 of (1), the largest detection value Smax (the one having the largest absolute value of the bright potential) is selected. In this example, S1 is selected as Smax. Then, the deviations a1, a2, and a3 of the detected values S1, S2, and S3 with respect to Smax are calculated, respectively. That is, the calculation of the following formula 1 is performed.

[0027]

## EQU00001 ## a1 = Smax-S1 a2 = Smax-S2 a3 = Smax-S3

Next, by referring to the multiplication coefficient table which is prestored in the storage unit 51 and comprises the data of the multiplication coefficient J for the deviation a, the multiplication coefficients J1, J2 and J3 for the respective differences a1, a2 and a3 are respectively calculated. It is read and stored in the storage unit 51. As shown in FIG. 4, the multiplication coefficient J for the deviation a stored in the multiplication coefficient table becomes 1 when the deviation a is 0,
The larger the deviation a, the smaller the multiplication coefficient J. Therefore, in this example, the magnitude relationship among the multiplication coefficients J1, J2, and J3 is J1 = 1>J3>J2> 0. In this way, the multiplication coefficients J1, J2 and J3 are stored in the storage unit 51.
The current multiplication coefficient creation process ends by being stored in.

During the copying operation, the image processing unit 54 corrects the multivalued pixel data after the shading correction.
That is, multi-valued pixel data for each one line is divided into three blocks B1, B2 and B3 corresponding to the positions of the surface potential sensors 41, 42 and 43. Here, the block B1 is located at the position of the surface potential sensor 41, and the block B1
2 corresponds to the position of the surface potential sensor 42, and the block B3 corresponds to the position of the surface potential sensor 43. Then, the multi-valued pixel data in the block B1 is multiplied by the multiplication coefficient J1, the multi-valued pixel data in the block B2 is multiplied by the multiplication coefficient J2, and the multi-valued pixel data in the block B3 is multiplied by the multiplication coefficient J3. As a result, the multi-valued pixel data is corrected.

In this example, the multivalued pixel data in the block B2 corresponding to the central portion of the axial scanning range of the photosensitive drum 21 corresponds to the block B1 corresponding to the end of the axial scanning range of the photosensitive drum 21, It is made smaller at a rate larger than that of the multivalued pixel data in B3. That is, the greater the laser irradiation light amount in the axial scanning range of the photoconductor drum 21,
That is, the smaller the absolute value of the bright potential, the smaller the multi-valued pixel data corresponding to that position is.

Therefore, the value of the pixel data (density level) is corrected so that the density and gradation expression reproducibility do not change due to the variation of the laser irradiation light amount (variation of the bright potential) with respect to the axial position of the photosensitive drum 21. Therefore, it is possible to prevent the image quality from being deteriorated due to the variation in the laser irradiation light amount with respect to the axial position of the photosensitive drum 21.

The corrected multi-valued pixel data is subjected to color correction processing,
After being subjected to color conversion processing, density processing, multi-valued processing, etc., it is output from the image processing unit 54. Then, the image processing unit 54
Output is sent to the laser scanning unit 23 and converted into an optical signal.

In the above embodiment, the surface potential sensors 41, 42, 43 are arranged at three positions in the axial direction of the photosensitive drum 21, and the multiplication coefficient is obtained for each of these three positions. As will be described below, the multiplication coefficients at more positions may be obtained.

That is, the axial scanning range of the photosensitive drum 21 is divided into four or more ranges, and the surface potential sensor is arranged in each divided range. Then, the multiplication coefficient for each divided range is obtained based on the detection value of each surface potential sensor. During the copying operation, the multi-valued pixel data for one line is divided into a plurality of blocks corresponding to each division range, and the multiplication coefficient for the division range corresponding to the multi-valued pixel data in each block is multiplied. By doing so, the image data for each line can be divided into finer blocks, and the correction accuracy is improved.

Further, the axial scanning range of the photosensitive drum 21 is divided into four or more ranges, and detection value data for each divided range is created by an interpolation method or the like based on the above three detection values S1, S2 and S3. Alternatively, the multiplication coefficient for each divided range may be obtained using these detected value data. Also in this case, since the multi-valued pixel data for each line can be divided into finer blocks, the correction accuracy is improved.

Further, the axial scanning range of the photosensitive drum 21 is divided into four or more ranges, and each division is made based on the multiplication coefficients J1, J2 and J3 obtained based on the above three detection values S1, S2 and S3. The multiplication coefficient for each range may be obtained by an interpolation method or the like. Also in this case, since the multi-valued pixel data for each line can be divided into finer blocks, the correction accuracy is improved.

[0037]

According to the present invention, it is possible to prevent the image quality from being deteriorated due to the variation in the irradiation light amount of the laser light depending on the axial position of the photosensitive member surface.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a configuration of a digital color copying machine.

FIG. 2 is an electrical block diagram showing an electrical configuration of a copying machine.

FIG. 3 is a detection value S of each surface potential sensor 41, 42, 43.
It is a graph which shows an example of 1, S2, S3.

FIG. 4 is a graph showing a relationship between a deviation a and a multiplication coefficient J.

FIG. 5 is a graph showing a laser irradiation light amount characteristic with respect to an axial position of a photosensitive drum.

FIG. 6 is a graph showing a bright potential characteristic with respect to an axial position of a photosensitive drum.

[Explanation of symbols]

 21 Photoreceptor Drum 22 Charging Section 23 Laser Scanner Units 41, 42, 43 Surface Potential Sensor 50 Main Control Section 51 Storage Section 54 Image Processing Section

Claims (3)

[Claims] 1. An image forming apparatus which is exposed by a laser beam, and a bright potential measuring device for measuring a bright potential for each of a plurality of divided areas in which an axial scanning range of a surface of a photoconductor is divided. An image forming apparatus comprising: an image data correction unit that corrects image data based on the bright potential for each of the divided ranges measured by the bright potential measuring unit. 2. The bright potential measuring means for measuring the bright potential of the central portion of the axial scanning range of the photosensitive body surface and the bright potential of both ends of the axial scanning range of the photosensitive body surface, respectively. The image forming apparatus according to claim 1, further comprising three surface potential detectors, wherein the bright potentials in the respective divided ranges are measured based on the bright potentials detected by the three surface potential detectors. apparatus. 3. The image data correcting means calculates multiplication coefficient for image data correction for each divided range based on the bright potential for each divided range measured by the bright potential measuring means. And a multiplication means for multiplying the image data corresponding to the division range by the multiplication coefficient for image data correction for each division range obtained by the multiplication coefficient calculation means. Image forming device.