JP2004012665A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a photoreceptor unevenly rotates and banding occurs. <P>SOLUTION: The image forming apparatus is provided with a writing means 1 for scanning the photoreceptor 3 with light beams and forming a latent image, and a marking position reading sensor 5 for reading marks formed on the surface of the photoreceptor 3 in accordance with the scanning interval of the light beam, and the latent image is formed on the photoreceptor 3 by the writing means 1 in synchronism with a signal from the marking position reading sensor 5. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile.
[0002]
[Prior art]
In image forming apparatuses such as digital copiers and printers having writing means for writing image information on a photoreceptor by laser light from a laser light source, laser light output from a laser light source and irradiated on the photoreceptor is used. Scanning in the longitudinal direction of the photoconductor using a polygon mirror or the like, writing data corresponding to one line of image information on the photoconductor to form an electrostatic latent image, and rotating the photoconductor at a constant speed, An electrostatic latent image is sequentially formed, transferred to a transfer drum, and the electrostatic latent image on the transfer drum is developed to form an image (toner image) on the transfer drum. Transcribed to
[0003]
However, when actually writing image information on the photoconductor, vibrations from various drive system parts in the image forming apparatus, vibration during transfer paper transfer, vibration due to contact between the photoconductor and the transfer drum, etc. Rotational speed of the photoconductor varies due to the influence of vibrations generated from various factors.
[0004]
For this reason, the image formed on the photoreceptor (the latent image to be written) is affected by the vibration, so that the pitch between the scanning lines is not uniform, and the actual formed image has a sub-scanning direction (rotational direction of the photoreceptor). ) Uneven density appears. This phenomenon is called banding, and is a major cause of lowering the quality of a formed image.
[0005]
In order to suppress this banding, as a method of keeping the rotation speed of the photoconductor constant, a member having a large moment of inertia called a flywheel is added on the axis of the photoconductor to stabilize the rotation of the photoconductor, There is known a method for suppressing the rotational speed unevenness, which is used in many products. However, in order to stabilize the rotation of the photoconductor using the flywheel, the flywheel requires a mass of several tens of kilograms or more, which increases the weight of the entire apparatus. There are many problems such as a problem in safety and a problem in miniaturization of the entire device.
[0006]
In addition, as a method of stabilizing the rotation of the photoconductor without using a flywheel, a method of detecting and controlling the rotation speed of the photoconductor by a detector, a method of controlling a motor and a driving device described in Japanese Patent Application Laid-Open No. 10-323067 are disclosed. As described above, there is a method of detecting the position information of the photoconductor by an encoder and controlling the position of the photoconductor to realize constant rotation of the photoconductor.
[0007]
In addition to the rotation control of the photoreceptor, a method of controlling the optical system includes detecting the vibration of the entire optical system and canceling the vibration as in an optical scanning device described in JP-A-9-33848. There is a method of applying a vibration to an optical system to make a writing position of a beam constant.
[0008]
Japanese Patent Application Laid-Open No. H11-30895 discloses a drum driving device that drives a plurality of photoconductors in an image forming apparatus with dedicated motors. Japanese Patent Application Laid-Open No. H11-168894 describes a photosensitive drum driving structure in an image forming apparatus. Japanese Patent Application Laid-Open No. H8-110347 discloses that the rotational speed of a photoreceptor is detected by comparing the states at two different times of projected images of markings made at substantially constant intervals on the circumferential surface of the photoreceptor. An image forming apparatus for controlling rotation of a photoconductor is described.
[0009]
[Problems to be solved by the invention]
2. Description of the Related Art In image forming apparatuses such as digital copiers and printers, uneven rotation of a photoconductor occurs due to the influence of vibration of the machine itself or vibration caused by disturbance, and unevenness in a scanning line pitch of a laser beam when a latent image is formed on the photoconductor. And density unevenness called banding occurs in the formed image.
[0010]
As a method of suppressing the banding and improving the image quality, there is a method of controlling the rotation of the photoconductor. In this method, however, a processing device such as a DSP (Digital Signal Processor) is required to control the rotation of the photoconductor. Therefore, there is a problem that a control system needs to be changed for each machine.
[0011]
SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of suppressing banding even when rotation of a photosensitive member cannot be controlled at a constant speed and uneven rotation of the photosensitive member occurs.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 includes a writing unit that scans a light beam on a photoreceptor to form a latent image, and that corresponds to a scanning interval of the light beam on the surface of the photoreceptor. A marking position reading sensor for reading the applied marking; and a latent image is formed on the photoconductor by the writing means in synchronization with a signal from the marking position reading sensor.
[0013]
According to a second aspect of the present invention, a writing unit for forming a latent image by scanning a light beam on a photoreceptor is provided integrally with a side surface of the photoreceptor so as to correspond to a scanning interval of the light beam. A disk having a marking, and a marking position reading sensor for reading the marking, wherein a latent image is formed on the photoconductor by the writing means in synchronization with a signal from the marking position reading sensor. .
[0014]
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the writing unit can simultaneously write a plurality of lines, and selects a writing line based on a signal from the marking position reading sensor. It is.
[0015]
According to a fourth aspect of the present invention, in the image forming apparatus according to the first or second aspect, the writing unit can write a plurality of lines at the same time, and selects one writing line by a signal from the marking position reading sensor. Or a plurality of lines are selected simultaneously.
[0016]
According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, rotation unevenness of the photoconductor is detected by measuring a signal interval from the marking position reading sensor, and based on the detection result. If the image to be written when the rotation unevenness of the photoconductor occurs is a solid color, writing of a plurality of lines is selected at the same time.
[0017]
According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, a direction in which the rotation unevenness of the photoconductor is shifted is determined based on a signal interval from the marking position reading sensor, and a plurality of selections are made based on the determination result. This determines line writing.
[0018]
According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, the marking line on the photosensitive member and a writing position by an actual light beam have a certain shift. Things.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
In addition to keeping the rotation speed of the photoreceptor stable by controlling the rotation of the photoreceptor, controlling the writing position on the photoreceptor surface even when the rotation of the photoreceptor itself is not constant when forming a latent image on the photoreceptor It is considered that banding can be suppressed if the pitch of each scanning line becomes uniform.
[0020]
Therefore, in the embodiment of the present invention, even when the rotation of the photoconductor cannot be controlled to a constant rotation, a plurality of light beams or optical paths are prepared in advance, and the photoconductor is read in accordance with the output of a sensor that reads a marking position on the photoconductor. By selecting a light beam or an optical path to irradiate the body surface, the scanning line interval at the time of forming a latent image on the photoconductor is made equal, or the scanning line interval at the time of forming a latent image on the photoconductor is reduced. Even in the case of deviation, banding during image formation is suppressed by painting with a plurality of light beams.
[0021]
FIG. 1A shows a configuration of an image forming apparatus according to an embodiment of the present invention.
In FIG. 1A, reference numeral 1 denotes a laser optical system as a writing unit for irradiating a photoconductor with a laser beam as a light beam and exposing the photoconductor to form an electrostatic latent image on the photoconductor. A controller as control means for controlling the laser optical system 1 and the like, 3 is a photosensitive drum as a photosensitive member, 4 is a transfer drum as an intermediate transfer member that contacts the photosensitive drum 3 at a primary transfer position, 5 is a photosensitive member A position detector serving as a marking position reading sensor for detecting a marking on the drum 3 to detect a rotation position of the photosensitive drum 3. A rotation control unit 6 controls the rotation of the photosensitive drum 3 so that the rotation of the photosensitive drum 3 is constant. Is a rotation control device.
[0022]
The photosensitive drum 3 is uniformly charged by a charging device (not shown), and is then exposed by the laser optical system 1 to form an electrostatic latent image.
The laser optical system 1 outputs a laser beam modulated by the image information signal based on the image information signal sent from the controller 2. As shown in FIG. 1B, the laser beam A is irradiated on the photosensitive drum 3 while being repeatedly scanned in the axial direction of the photosensitive drum 3 by scanning means such as a polygon mirror in the laser optical system 1, The surface of the photosensitive drum 3 is exposed by the laser light, and image information (image data) for each line is written.
[0023]
The photosensitive drum 3 is driven to rotate by a motor in the rotation control device 6, whereby image data is written line by line in the sub-scanning direction, and an electrostatic latent image is formed. The latent image charges formed on the photoconductor drum 3 are transferred to the transfer drum 4 by a transfer unit (not shown), and the latent image charges on the transfer drum 4 are developed and developed by a developing device (not shown). An image is formed. The toner image on the transfer drum 4 is transferred to transfer paper as a transfer material by a transfer unit (not shown), and is fixed on the transfer paper by a fixing device to form an image on the transfer paper.
[0024]
In the present embodiment, in the above operation, the photosensitive drum 3 rotates at a constant speed, but vibration from other parts of the apparatus or vibration due to external disturbance is transmitted to the photosensitive drum 3, Due to the influence, the rotation of the photosensitive drum 3 becomes uneven.
[0025]
As shown in FIG. 2, an image on the photosensitive drum 3 is provided on a marking area (an end on which no latent image is formed) 3b other than the photosensitive surface (latent image forming area for forming a latent image) 3a on the photosensitive drum 3. At the same pitch (interval of 0.042 mm in the case of 600 dpi) of a proper scanning line pitch at the time of formation (at the time of formation of an electrostatic latent image), a mark (mark) 7 as rotation position information is provided on the photosensitive drum 3 by a laser. The position detector 5 which is provided corresponding to the writing position (scanning line) by light and is installed at a fixed position is located at the marking area 3b on the rotating photosensitive drum 3 as shown in FIG. By irradiating a light beam B such as a laser beam and detecting the return light C, the marking 7 on the photosensitive drum 3 is detected to detect the rotational position of the photosensitive drum 3. The marking 7 may be added to a disk integrally provided on the side surface of the photosensitive drum 3, and the position detector 5 may detect the marking 7 to detect the rotational position of the photosensitive drum 3.
[0026]
The position detector 5 irradiates the marking 7 on the photosensitive drum 3 with the light beam B and monitors the reflected light C to generate a position detection signal having a waveform as shown in FIG. 4 is binarized by comparing a position detection signal indicated by a broken line with a threshold value to obtain a rectangular wave as indicated by a solid line in FIG.
[0027]
In the laser optical system 1, a write start signal generator (not shown) that detects the rotational position of the polygon mirror is used. As shown in FIG. A write start signal is generated so as to synchronize with the start of writing.
[0028]
In this embodiment, when a laser beam is irradiated from the laser optical system 1 onto the photosensitive drum 3 to form a latent image on the photosensitive drum 3, as shown in FIG. It is possible to output a plurality of laser beams R1 to R5 at intervals smaller than the position where the laser beam scans the three surfaces (interval between scanning lines), and the controller 2 outputs one laser beam from the plurality of laser beams R1 to R5. The laser optical system 1 is selected such that the laser light is selected (one laser light is selected or a plurality of laser lights are selected simultaneously) and the selected laser light is irradiated onto the photosensitive drum 3. Control.
[0029]
As a method of selecting the laser light emitted from the laser optical system 1 to the photosensitive drum 3 by the controller 2, a method of blocking the optical path such as a shutter on the optical path through which the laser light passes in the laser optical system 1 is described. A method of selecting a laser beam that reaches the surface of the photosensitive drum 3 by providing an object and controlling the shield to move from the optical path by the controller 2 is used.
[0030]
In order to control the laser beam, the controller 2 measures the amount of deviation between the write start signal from the write start signal generator and the position detection signal from the position detector 5 to determine the position detection signal based on the write start signal. Is measured, and the selection control of the laser beam is realized by the following procedure.
Laser light for forming a latent image on the photosensitive drum 3 is scanned in the longitudinal direction of the photosensitive drum 3 by rotation of a polygon mirror or the like in the laser light optical system 1 as shown in FIG. Therefore, scanning is performed at regular intervals in the rotation direction of the polygon mirror. Here, when the speed of the rotation of the photosensitive drum 3 itself does not change, the trajectories (scanning lines) of the laser light scanned on the surface of the photosensitive drum 3 are at equal intervals. When the rotation unevenness occurs, the gap between the scanning lines on the surface of the photosensitive drum 3 is shifted.
[0031]
The write start signal generator generates a write start signal as shown in FIG. 5 by generating a write start signal at the start of laser beam line scanning by detecting the rotation position of the polygon mirror. On the other hand, the position detector 5 irradiates a light beam such as a laser beam to a marking 7 provided on a portion other than the photosensitive surface of the photosensitive drum 3 and detects a return light thereof, and the like. The upper write position is detected to generate a position detection signal as shown in FIG.
[0032]
As shown in FIG. 8, the controller 2 determines the amount of shift between the write start signal from the write start signal generator and the position detection signal from the position detector 5 as a clock faster than the period of the position detection signal and the write position signal. Measure using. The controller 2 controls the shield in accordance with the amount of deviation (clock deviation) between the measured write start signal and the position detection signal, and controls the plurality of lasers emitted from the laser optical system 1 to the photosensitive drum 3. An optical path of one or more laser beams is selected from the light beams R1 to R5 (one laser beam is selected or a plurality of laser beams are selected at the same time). This makes it possible to adjust the writing position when the scanning interval of the laser beam (rotation of the polygon mirror) and the speed on the surface of the photosensitive drum 3 are shifted, and the writing position can be adjusted on the photosensitive drum 3 surface. It is possible to scan with laser light. The controller 2 controls the laser optical system 1 so that a plurality of writing laser beams, which are simultaneously irradiated from the laser optical system 1 to the photosensitive drum 3, are modulated by the same image signal.
[0033]
For example, when the position detection signal is delayed with respect to the write start signal as shown in FIG. 8, when the reference laser beam is the laser beam R3 as shown in FIG. The shield is controlled by selecting the laser beam R4 or R5, which is the delay side in the rotation direction of the drum 3, according to the delay time of the position detection signal with respect to the write start signal (the amount of the clock shift). Thereby, even when the speed of the rotation of the photosensitive drum 3 itself varies, the scanning interval of the laser beam on the surface of the photosensitive drum 3 can be kept constant.
[0034]
Here, the controller 2 determines the direction of deviation of the rotation unevenness of the photosensitive drum 3 from the deviation of the interval between the position detection signals from the position detector 5 (the deviation of the position detection signal with respect to the write start signal measured as described above). Then, based on the determination result, the writing line is determined to be the laser beam R1, R2 or R4, R5 according to the direction of the deviation of the rotation unevenness of the photosensitive drum 3, and the delay time of the position detection signal with respect to the writing start signal (see the above description). One of the laser beams R1 and R2 or one of the laser beams R4 and R5 is selected in accordance with the clock shift amount).
[0035]
In this case, the controller 2 sets a certain deviation between the position detection signal (the detection position of the position detector 5) and the actual writing position by the laser optical system 1, and the position detection signal is delayed with respect to the writing start signal. However, as shown in FIG. 6, when the reference writing light is the laser light R3, the laser light R1 or R2 is selected according to the delay time of the position detection signal with respect to the writing start signal (the amount of the clock shift). The distance between the scanning lines may be kept constant by controlling the shield. .
[0036]
Further, the laser optical system 1 is configured to be able to simultaneously select and output a plurality of laser beams when scanning one line, and the controller 2 detects image information to be written on the photosensitive drum 3 in advance with the laser beams. In advance, it is determined whether or not a plurality of laser beams are simultaneously irradiated from the laser optical system 1 onto the surface of the photosensitive drum 3 according to the writing state of the line before the scanning line to be written on the photosensitive drum 3 at present. To control the shield.
[0037]
For example, the controller 2 detects the uneven rotation of the photosensitive drum 3 by measuring the shift of the interval between the position detection signals from the position detector 5 (the shift of the position detection signal with respect to the writing start signal) as described above, If the detection result indicates that the rotation unevenness of the photosensitive drum 3 occurs, the image information of the previous line is solid image information, and the image information of the line to be written is also image information to be written. In the case of (filled image information), in addition to the writing laser light of the line to be written on the photosensitive drum 3 at present, the laser light on the photosensitive drum 3 rotation direction side of a plurality of prepared laser lights is simultaneously. The shield is controlled so as to irradiate the photosensitive drum 3. This makes it possible to suppress white spots between scanning lines. The controller 2 controls the laser optical system 1 so that a plurality of writing laser beams that are simultaneously irradiated from the laser optical system 1 to the photosensitive drum 3 are modulated by the same image signal.
[0038]
As described above, according to the present embodiment, the marking 7 is applied to the disk on the surface of the photosensitive member 3 or the disk on the side surface of the photosensitive member 3 for each line of writing and scanning, and the marking 7 is used as a position detector as a marking position reading sensor. 5, a latent image is formed on the photoconductor 3 by the laser optical system 1 as a writing means in synchronization with the position detection signal from the position detector 5, so that when the latent image is formed on the photoconductor, Even if the rotation of the photoconductor cannot be controlled to a constant speed and the rotation of the photoconductor is uneven, the writing position on the photoconductor surface can be controlled to make the pitch of each scanning line uniform, thereby suppressing banding. And high-quality image output is possible.
[0039]
In addition, by preparing a plurality of laser beams, selecting one or more optical paths of the laser beams from the laser beams and performing writing on the photoconductor surface, controlling the writing position of the laser beam on the photoconductor. The laser beam scanning interval on the photoreceptor surface can be kept constant, or the omission of each scanning line can be eliminated, so that latent images can be formed without unevenness between line pitches and high quality with less banding. Image output is possible.
[0040]
In addition, the number of laser light lines used for writing is controlled in accordance with the state of formation of the latent image on the photoconductor (rotational unevenness of the optical body, presence / absence of solid image information, direction of deviation of the rotational unevenness of the photoconductor). Thus, banding can be suppressed even when the rotation of the photoconductor is not constant, without causing a dropout for each scanning line.
[0041]
In addition, when the laser beam to be written on the photoreceptor 3 is selected after the position of the marking 7 is detected, if the position detection is delayed compared to the writing timing, the amount of delay cannot be determined. By shifting the position by a fixed time, even if position detection is delayed, it is possible to cope with the amount of delay, control of the writing position is possible, and the interval between scanning lines can be kept constant, and banding can be prevented. It is possible to form a small number of images.
[0042]
【The invention's effect】
As described above, according to the present invention, banding can be suppressed even when the rotation of the photosensitive member cannot be controlled to a constant speed and uneven rotation of the photosensitive member occurs, and high-quality image output can be achieved. .
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention and a diagram showing a part of the embodiment.
FIG. 2 is a diagram showing a developed surface of the photosensitive drum of the embodiment.
FIG. 3 is a waveform chart showing a position detection signal of a position detector in the embodiment.
FIG. 4 is a waveform chart for explaining a position detector in the embodiment.
FIG. 5 is a waveform chart showing a write start signal of the embodiment.
FIG. 6 is a schematic diagram showing a photosensitive drum and a laser optical system according to the embodiment.
FIG. 7 is a diagram illustrating the same embodiment.
FIG. 8 is a timing chart showing operation timings of the embodiment.
[Explanation of symbols]
Reference Signs List 1 laser optical system 2 controller 3 photosensitive drum 4 transfer drum 5 position detector 6 rotation control device 7 marking

Claims (7)

Writing means for forming a latent image by scanning a light beam on a photoreceptor, and a marking position reading sensor for reading a marking provided on the surface of the photoreceptor in accordance with a scanning interval of the light beam. An image forming apparatus, wherein a latent image is formed on the photoconductor by the writing unit in synchronization with a signal from the marking position reading sensor. Writing means for scanning a light beam on a photoreceptor to form a latent image, a disc having markings provided integrally on a side surface of the photoreceptor and corresponding to a scanning interval of the light beam; An image forming apparatus comprising: a marking position reading sensor for reading a marking; and a latent image is formed on the photoconductor by the writing unit in synchronization with a signal from the marking position reading sensor. 3. The image forming apparatus according to claim 1, wherein the writing unit is capable of writing a plurality of lines at the same time, and selects a writing line based on a signal from the marking position reading sensor. 3. The image forming apparatus according to claim 1, wherein the writing unit is capable of simultaneously writing a plurality of lines, and selects one writing line or a plurality of lines simultaneously according to a signal from the marking position reading sensor. An image forming apparatus comprising: 5. The image forming apparatus according to claim 4, wherein a rotation interval of the photosensitive member is detected by measuring a signal interval from the marking position reading sensor, and the rotation unevenness of the photosensitive member is generated based on the detection result. An image forming apparatus characterized in that, when an image to be written at the time of writing is a solid color, writing of a plurality of lines is selected at the same time. 6. The image forming apparatus according to claim 5, wherein a shift direction of the rotation unevenness of the photoconductor is determined from a signal interval from the marking position reading sensor, and writing of a plurality of lines to be selected is determined based on the determination result. Characteristic image forming apparatus. 7. The image forming apparatus according to claim 1, wherein a line between the marking on the photoconductor and a writing position by an actual light beam has a certain shift. .

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