JP2009210697A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus for making possible even correction of density unevenness which formerly used to be at a level where correction was not possible by varying not only quantity of laser beam but also varying together developing high voltage value. <P>SOLUTION: The image forming apparatus 3 includes: a photoreceptor drum 112; a driving means 316 for carrying out rotational drive of the photoreceptor drum; an exposure means 108 for forming a latent image on the photoreceptor drum; and a high voltage output means 402 for outputting high voltage for charging the photoreceptor drum. By varying exposure amount by the exposure means and the high voltage output by the high voltage output means according to a rotational position of the photoreceptor drum, unevenness in sensitivity and unevenness in charging in the photoreceptor drum is reduced. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus having a function of reducing density unevenness in a sub-scanning direction of a photosensitive drum.

  In an electrophotographic image forming apparatus such as a copying machine or a printer, unevenness in sensitivity in the photosensitive drum with respect to exposure means (laser, etc.) and unevenness in density in the sub-scanning (paper feed direction) due to unevenness in charging when charging is performed with a high voltage potential. There is a problem of producing. In particular, in an amorphous silicon drum, this unevenness appears remarkably because it is manufactured by vapor deposition. Conventionally, the exposure output (laser light amount) of the laser is changed so as to reduce the unevenness, and the unevenness is reduced.

For example, Patent Document 1 discloses an image forming apparatus that can eliminate uneven density due to uneven charging of a charger.
Japanese Patent Laid-Open No. 9-179366

  However, when the laser light quantity is reduced, there is a problem that linearity cannot be obtained from a certain region and control is not effective. There is also a problem that increasing the amount of laser light leads to a reduction in the lifetime of the laser element. For this reason, the amount of laser light can be changed only within a certain range, and it has been difficult to increase the amount of unevenness reduction correction (shading). As a result, there has been a problem that a photoconductor drum having a large unevenness cannot be used from the time of a new product, and a photoconductor drum having a large variation with time in the unevenness characteristic is replaced early, resulting in an increase in running cost.

  The present invention has been made in order to solve the above-mentioned problems, and by correcting not only the amount of laser light but also the development high voltage value, it is possible to correct even density unevenness at a level that could not be corrected so far. An object is to provide a possible image forming apparatus.

  In order to achieve the above-mentioned object, the present invention comprises the following configurations (1) to (3).

  (1) To output a photosensitive drum, driving means for rotationally driving the photosensitive drum, exposure means for forming a latent image on the photosensitive drum, and a high-voltage output for charging the photosensitive drum. In the image forming apparatus having the high-voltage output unit, the sensitivity unevenness of the photosensitive drum and the exposure amount of the photosensitive unit are changed by changing the exposure amount of the exposure unit and the high-voltage output of the high-voltage output unit according to the rotational position of the photosensitive drum. An image forming apparatus that reduces uneven charging.

  (2) having density measuring means for measuring the density of the toner image formed from the latent image on the photosensitive drum, and the measured value of the density measuring means is smaller than the first threshold value, or the second If larger than the threshold value, both the exposure amount of the exposure means and the high voltage output of the high voltage output means are changed, and the measured value is greater than the first threshold value and greater than the second threshold value. The image forming apparatus according to (1), wherein when it is small, sensitivity unevenness and charging unevenness of the photosensitive drum are reduced by changing an exposure amount of the exposure unit.

  (3) a memory for storing profile data in the sub-scanning direction of the photosensitive drum constituted by the measured value of the toner image density obtained by the density measuring means, a home position mark on the photosensitive drum, A sensor for detecting the home position mark; an encoder provided on a rotating shaft of the photosensitive drum; a counter for counting a signal of the encoder; and a reset means for resetting the counter by a detection signal of the sensor. The image forming apparatus according to (2), wherein the profile data is called from the memory in accordance with an output value of the counter, and the high voltage output means outputs a high voltage output corresponding to the data.

  According to the present invention, regarding density unevenness correction in the sub-scanning direction, it is impossible to repair until now by changing the development high-pressure value in a region where the laser element lifetime or linearity cannot be obtained only by correcting the laser light amount. It is possible to correct even the density unevenness of the level. As a result, it is possible to use a drum that could not be used until now, or a drum that has been replaced at an early stage, and it is possible to provide an image forming apparatus with reduced running costs.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to examples.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  In the schematic front sectional view of the copying machine shown in FIG. 5, the reader unit 1 is provided at the upper part of the apparatus body 4 of the copying machine 3 and the printer unit 2 is provided at the lower part. In the printer unit 2, a sheet skew / horizontal misregistration correction conveyance device 5 is incorporated. The configuration of the reader unit 1 will be described.

  The reader unit 1 includes an original table glass 101 on which an original is stacked, an original pressure plate 102 that presses the stacked original from above, a light source 103 that irradiates an image surface of the original, and a mirror base 133 that loads the light source 103 and scans the original. Is provided. Further, a plurality of mirrors 104 and a lens 105 for guiding reflected light from the image surface, and photoelectric conversion / image processing for performing various image processing on the obtained electric signal by photoelectrically converting the reflected light from the original by the CCD. The unit 106 is also provided. The photoelectric conversion / image processing unit 106 has an image processing function for performing A / D conversion, shading correction, masking correction, scaling, LOG conversion, and the like on the photoelectrically converted electrical signal. The operation of the reader unit 1 will be described.

  The user places the document on the platen glass 101 with the image surface facing downward, and presses it against the platen glass 101 with the document pressure plate 102 from above. The mirror stage 133 moves while illuminating light with the light source 103 to scan the image surface of the document. The reflected light image from the image plane is imaged on the CCD of the photoelectric conversion / image processing unit 106 via the plurality of mirrors 104 and the lens 105, and is photoelectrically converted into an electric signal here. The image signal that has become an electrical signal is subjected to various image processing and then sent to the next printer unit 2. The configuration of the printer unit 2 will be described.

  The printer unit 2 includes a laser driving unit 304 that converts an image signal from the reader unit 1 into a signal for driving a laser, a laser element 108, and a polygon scanner 109 that scans the surface of the photosensitive drum 112 with laser light. . Further, an image forming unit (image forming unit) 6 including the photosensitive drum 112, a fixing device 120 disposed on the most downstream side in the transfer direction of the transfer material, and the like are also provided.

  The image forming unit 6 includes a photosensitive drum 112 that is rotatably supported in the direction of the arrow, and a primary charger 113 that is disposed in almost the order along the rotation direction and uniformly charges the surface of the photosensitive drum 112. A developing device 110 for developing the electrostatic latent image on the photosensitive drum 112 is installed. Further, a transfer charger 119 that transfers the toner image on the photosensitive drum 112 to a transfer material, a cleaner 116 that removes transfer residual toner, a cleaner blade 117, an auxiliary charger 115 that performs charge removal, and a pre-exposure that removes residual charge. The lamp 114 is configured.

  Further, the developing device 110 is provided with a developing roller 111. The developing roller 111 is configured to develop a toner image on the photosensitive drum 112 by rotating in the opposite direction to the photosensitive drum 112. The pre-fixing belt 118 conveys the transfer material onto which the toner image has been transferred to the fixing device 120. The fixing device 120 heats and presses the transfer material while conveying the transfer material by rotation of the fixing rollers 121 and 122 to fix the toner image on the transfer material. The conveyance roller 123 discharges the transfer material after fixing to a paper discharge tray 126 outside the apparatus main body 4.

  The sheet feeding / conveying unit 124 has a transfer material conveying path, and includes a lower sheet feeding cassette 127, an upper sheet feeding cassette 128, a lower sheet feeding roller 129, an upper sheet feeding roller 130, conveying rollers 131 and 132, and the like. Yes. The operation of the printer unit 2 will be described.

  The sheet feeding / conveying section 124 supplies the transfer material P from the cassettes 127 and 128 to the sheet skew / horizontal registration error correcting and conveying apparatus 5 described later. The upstream sheet conveyance roller pair 141a, 141b, the skew correction roller pair 142a, 142b, and the horizontal registration error correction roller pair of the sheet skew / horizontal registration error correction conveying device 5 convey the transfer material P to the image forming unit 6.

  The photoconductive drum 112 and the transfer charger 119 of the image forming unit 6 transfer the toner image formed on the photoconductive drum to a straightened transfer material. The pre-fixing belt 118 sends the transfer material on which the toner image is transferred to the fixing device 120. The fixing device 120 fixes the toner image on the transfer material. Finally, the transport roller 123 discharges the transfer material on which the toner image is fixed to the paper discharge tray 126. The control relationship of the copying machine 3 will be described.

  In the control block diagram of FIG. 2, all the copying machines 3 are controlled in a centralized manner by the CPU 306.

  The CPU 306 mainly controls driving of each load in the copying machine 3, information collection analysis of sensors, and data with the operation unit 305, that is, the user interface in addition to the image processing unit 107 and the laser driving unit 304 described above. The role of exchange.

  Further, the CPU 306 stores a ROM (not shown) in which programs for executing various sequences related to the image forming sequence described above are stored, and rewritable data that needs to be temporarily or permanently stored. RAM is connected. In the RAM, for example, a high voltage set value for the high voltage control unit, various data, and image formation command information from the operation unit 305 are stored.

  The operation unit 305 obtains information such as the copy magnification and density setting value set by the user, as well as the state of the image forming apparatus, such as information on the number of images formed, whether or not images are being formed, occurrence of jamming, Data for showing the location to the user is sent out.

  The CPU 306 is configured to drive each load in the copying machine and to collect and analyze sensor information. In various places inside the apparatus, a motor 316, a DC load 317 such as a clutch / solenoid, and various sensors 315 such as a photo interrupter and a micro switch are arranged. In other words, the various sensors 315 monitor the operation of conveying the transfer material and driving each unit by appropriately driving the motor 316 and each DC load 317.

  Therefore, the CPU 306 controls each motor 316 via the motor driver 307 by the motor control unit based on the signals from the various sensors 315, and simultaneously operates the DC load 317 such as a clutch / solenoid by the DC load control unit 311. The formation is proceeding smoothly.

  In addition, the CPU 306 sends various high voltage control signals to a high voltage control unit (not shown), so that it is suitable for the primary charger 113, the auxiliary charger 115, the transfer charger 119, and the developing roller 111, which are various chargers constituting the high voltage unit. A high pressure is applied.

  Further, the CPU 306 inputs the output signal of the thermistor inside the fixing device 120 and controls the driving of the fixing heater, and the temperature of the fixing device 120 is adjusted so that the fixing device 120 has an optimum temperature necessary for fixing the toner image. It also manages.

  Next, shading in the sub-scanning direction that is characteristic of the image forming apparatus of the present embodiment will be described.

  In FIG. 1, 400 is a density sensor which is a density measuring means for measuring the toner image density of a test density pattern on the drum, 401 is a memory for storing the measured value, and 306 is the CPU, which corresponds to the density in the memory. The high voltage output device 402 and the laser 406 are adjusted. 407 is a home position mark indicating the home position of the drum, 405 is a home position sensor for detecting the position, 404 is an encoder provided on a rotating shaft for detecting the amount of rotation of the drum, and 403 counts encoder signals. It is a counter.

  The adjustment mode will be described with reference to FIG. In the adjustment mode, a pattern for density detection is printed on the drum, the density profile data at each position in the sub-scanning direction of the drum is measured by an optical density sensor (not shown), and the laser light quantity (exposure) at each rotational position is measured. Amount) and development high pressure value. In this embodiment, an encoder code wheel that outputs 800 pulses per round is used. In the sub-scanning unevenness correction on the drum, a profile is acquired for every 10 encoder pulses in order to correct for each area obtained by dividing the circumference of the drum into 80 parts.

  The adjustment mode is started at F21. At F22, the drum home position is started at the same time as the drum is driven to rotate. When the drum home position is detected in F23, density pattern printing is started in F24. At the same time, the output value Ec of the encoder is reset at F25, and the count of the encoder is started at F26. In F27, 0 is input to the natural number m. In F28, the encoder count value Ec is compared with m * 10. Initially, since m = 0 and they match, the process proceeds to F29 in order to derive the set value of area 0. The area is an area divided into 80 in the sub-scanning direction of the drum, and is from 0 to 79 areas. In F29, the density of the pattern in region 0 is measured. The measured concentration is compared at F30. In this copying machine, the maximum solid density is 1.6. The print pattern density is 0.8. If it is determined that the density is higher than 1.2 (second threshold) at F30, that is, the density is very high, the laser in the region 0 is set so that the laser light amount is decreased by (1.2−0.8) * A at F31. Set the light intensity value. If the amount of laser light is lowered below that, the laser linearity is lost. Here, A is a constant unique to the apparatus. Next, the amount that cannot be compensated only by the amount of laser light is corrected by F32. That is, correction is performed by changing both the laser light quantity and the development high voltage value. In F32, the high pressure value in region 0 is set so as to lower the development high pressure value by an amount obtained by multiplying the value exceeding the density 1.2 by the constant B. If it is determined in F33 that the density is lower than 0.4 (first threshold value), the laser light amount is set to increase by (0.8−0.4) * A in F34. If the laser light quantity is increased at this time, the lifetime of the laser becomes shorter than the lifetime of the main body. Thereafter, the setting value is determined so as to increase the development high pressure value by (0.4−measured density) * B at F35. When the measured density is 0.4 or more and 1.2 or less, only the light amount of the laser is changed in F36. Next, it is detected at F37 whether m has reached 79. If it is less than 79, m + 1 is substituted for m in F38, and the control from F28 to F37 is repeated. If 79, the adjustment mode is terminated at F39. The adjustment mode described above determines the laser on the drum from 0 to 79 and the high pressure setpoint.

  Next, control when performing normal printing using this value will be described with reference to FIG. Printing operation is started at F1. At F2, the drum home position is detected at the same time as the drum starts to rotate. When the drum home position is detected in F3, the encoder count value Ec is reset in F4 by the detection signal, and the encoder count is started in F5. In F6, 0 is substituted for the natural number n. n is a number representing the same region as m described above. If the F7 encoder count value Ec and n * 10 are the same, exposure and high pressure output are performed with the laser light quantity and the development high pressure value for the region n in F8. If n is not 79 in F9, n + 1 is substituted for n in F10 and the control from F7 to F9 is repeated. When n = 79 in F9, it is determined whether or not printing is finished in F11. If printing is not finished, the control from F3 to F11 is repeated. When printing is completed, printing is terminated at F12.

  By performing the above control, it is possible to provide an image forming apparatus capable of correcting density unevenness in the sub-scanning direction over a wide range.

1 is a configuration diagram according to an image forming apparatus of an embodiment. Control block diagram according to image forming apparatus of embodiment Flowchart of print density control in adjustment mode of image forming apparatus of embodiment Flowchart of print density control in normal print mode of image forming apparatus of embodiment Schematic sectional view of the image forming apparatus of the embodiment

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reader part 2 Printer part 3 Copier 4 Apparatus main body 6 Image forming part 103 Light source 106 Photoelectric conversion / image processing part 107 Image processing part 108 Laser element (corresponding to exposure means)
110 Developing Device 112 Photosensitive Drum 113 Primary Charger 116 Cleaner 120 Fixing Device 304 Laser Driving Unit 305 Operation Unit 306 CPU
307 Motor driver 311 DC load control unit 315 Various sensors 316 Motor (corresponding to driving means)
317 Clutch / solenoid 320 Cardboard detection unit 400 Density sensor 401 Memory 402 High voltage output device (corresponding to high voltage output means)
403 Counter 404 Encoder 405 HP sensor 406 Laser 407 Home position

Claims (3)

A photosensitive drum, and driving means for rotationally driving the photosensitive drum;
Exposure means for forming a latent image on the photosensitive drum;
In an image forming apparatus having a high voltage output means for outputting a high voltage output for charging the photosensitive drum,
By changing the exposure amount of the exposure unit and the high voltage output of the high voltage output unit according to the rotational position of the photosensitive drum,
An image forming apparatus characterized by reducing unevenness in sensitivity and unevenness in charging of the photosensitive drum. Density measuring means for measuring the density of a toner image formed from a latent image on the photosensitive drum;
When the measured value of the density measuring means is smaller than the first threshold value or larger than the second threshold value, both the exposure amount of the exposing means and the high voltage output of the high voltage output means are changed,
By changing the exposure amount of the exposure means when the measured value is larger than the first threshold value and smaller than the second threshold value,
The image forming apparatus according to claim 1, wherein unevenness in sensitivity and unevenness in charging of the photosensitive drum is reduced. A memory for storing profile data in the sub-scanning direction of the photosensitive drum constituted by the measured value of the toner image density obtained by the density measuring means;
A home position mark on the photosensitive drum;
A sensor for detecting the home position mark;
An encoder provided on a rotating shaft of the photosensitive drum;
A counter that counts the encoder signal;
Resetting means for resetting the counter by a detection signal of the sensor;
The image forming apparatus according to claim 2, wherein the profile data is called from the memory in accordance with an output value of the counter, and the high voltage output unit outputs a high voltage output corresponding to the data.

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