JP2004317538A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that provides an output whose image uniformity is satisfactory, by detecting a difference in the speed of the surface of a photoreceptor, estimating misregistration of image data from the detected value, and correcting an arbitrary quantity of misregistration based upon a quantity of misregistration smaller than the magnitude of the smallest unit of resolution. <P>SOLUTION: The image forming apparatus which reproduces a requested image with requested resolution includes: a photoreceptor as an image carrier; an exposure means which exposes the photoreceptor according to image data; and a drive source which drives the photoreceptor. The image forming apparatus further includes: a detection means for detecting changes in the moving speed of the surface of the photoreceptor; a measurement means for measuring an amount of misregistration of the image data according to the detected quantity; and a means for altering a quantity of exposure that corresponds to the image data according to the quantity of misregistration. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as an electrophotographic copying machine or a printer.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus forms an image by charging, exposing, developing, transferring, and fixing processes, and after cleaning the photoreceptor surface after transferring (there may be no cleaning process), the next image is formed. The formation is repeated, and various proposals have been made in each step and in the entire apparatus.
[0003]
In particular, in digital electrophotography, which has become the mainstream in recent years, the accuracy of the optical signal writing position on the photoreceptor by a laser, LED, or the like in the exposure process is a major factor that determines the image quality level, and various configurations have been proposed. I have.
[0004]
On the other hand, the above-mentioned photosensitive drum is driven directly by a motor or driven by a drum gear. The drum gear has the same pitch circle as the circumference of the photosensitive drum, and is integrally attached to one end of the photosensitive drum. The driving force from the driving motor is finally transmitted to the photosensitive drum via a driving gear, the above-described drum gear meshing with the driving gear, and the like. At this time, the rotation of the photosensitive drum is smoothly performed by, for example, improving the processing accuracy of the tooth surfaces of the drive gear and the drum gear, and an image defect due to uneven rotation is prevented.
[0005]
[Problems to be solved by the invention]
However, according to the above-described image forming apparatus, even when the processing accuracy of the tooth surfaces of the drive gear and the drum gear is increased, the photosensitive drum slightly generates uneven rotation when the drive gear and the drum gear mesh with each other. Therefore, when a halftone image is output, banding corresponding to the gear pitch of the drum gear occurs. Here, the term “banding” refers to periodic shading in the transfer material feeding direction caused by the image forming apparatus main body.
[0006]
On the other hand, even when driven directly by a motor, an image position shift occurs due to a shift in the photosensitive member surface speed, and the uniformity of an output image is significantly reduced as banding.
[0007]
Conventionally, as a countermeasure against such banding, a high-performance high-torque motor is used so that the surface speed of the photoconductor is constant, a flywheel is arranged on a drum drive shaft, and as described above, Methods such as improving the mechanical accuracy of gears and the like have been used, but all of these methods are means for increasing costs and increasing the number of components.
[0008]
On the other hand, there is also a method of detecting the position shift amount by an encoder or the like and feeding it back to the image data. However, the correction amount of the shift amount at that time depends on the image resolution, and is 85 μm for a 300 dpi device. The minimum unit of the image resolution is a limit such as 42 μm for a 600 dpi device and 21 μm for a 1200 dpi device, and control can be performed only in units of this unit.
[0009]
However, image quality of recent image forming apparatuses has been improved, and sufficient image uniformity cannot be provided with a correction amount based on a discrete amount depending on a resolution unit.
[0010]
SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and its object is to detect a speed deviation on the surface of a photoreceptor, predict a position deviation of image data from the detected value, and to determine a size of a minimum unit of resolution. An object of the present invention is to provide an image forming apparatus capable of outputting an image with good image uniformity by correcting an arbitrary displacement amount from a smaller position displacement amount.
[0011]
Another object of the present invention is to provide an image forming apparatus capable of outputting an image with good image uniformity by predicting image density unevenness from the detected value and changing the image forming conditions accordingly.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 is a device for duplicating a desired image in an image forming apparatus having a desired device resolution, a photoconductor as an image carrier, and a photoconductor according to image data. Detecting means for detecting a change in the moving speed of the surface of the photoreceptor, comprising: an exposing means for exposing the photoreceptor; a driving source for driving the photoreceptor; Means for changing the amount of exposure according to the image data in accordance with the amount of positional deviation, thereby comprising means for correcting the positional deviation of image data smaller than the image resolution.
[0013]
According to a second aspect of the present invention, in the first aspect of the present invention, the movement speed variation of the photoconductor surface is detected by a drive current of a drive source for driving the photoconductor.
[0014]
According to a third aspect of the present invention, in the first aspect of the present invention, the movement speed fluctuation of the photoreceptor surface is detected using an encoder.
[0015]
According to a fourth aspect of the present invention, in the first aspect of the invention, the movement speed fluctuation of the photoconductor surface is detected by using a laser Doppler measuring device.
[0016]
According to a fifth aspect of the present invention, in the first aspect of the present invention, the movement speed fluctuation of the photoconductor surface is detected using an optical scale sensor provided on the photoconductor surface.
[0017]
According to a sixth aspect of the present invention, as a device for duplicating a desired image in an image forming apparatus having a desired device resolution, a photoconductor as an image carrier, and an exposure unit for exposing the photoconductor according to image data, A drive source for driving the photoconductor, a detection unit for detecting a change in the moving speed of the surface of the photoconductor, and a unit for changing an image forming condition according to the detection amount.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an electrophotographic image forming apparatus will be described by taking a printer (a modified version of LBP-1760 manufactured by Canon) as an example.
[0019]
(Image forming device)
[Image processing step]
FIG. 1 shows a block diagram of the image processing step of the present invention.
[0020]
In FIG. 1, 1 is a host computer, 2 is a printer, 3 is a printer controller, 4 is a data processing and generating unit, 5 is a laser driver, and 6 is a semiconductor laser.
[0021]
Next, the operation of the above configuration will be described.
[0022]
The host computer 1 sends an image code to the printer 2. The printer 2 converts the image code into multi-valued image data by the printer controller 3, performs the processing described later on the multi-valued image data by the data processing and generation unit 4, which is a feature of the present invention, After the conversion, the signal is converted into a laser drive signal, and the laser driver 5 causes the semiconductor laser 6 to blink. The semiconductor laser 6 irradiates a photosensitive drum (not shown) and performs printing by an image forming apparatus described later. Here, in the present embodiment, the printer engine prints at an image resolution of 600 dots / inch (hereinafter abbreviated as dpi).
[0023]
In the case of a copying machine, the image data captured from the scanner is transmitted to the printer unit 2 as an image code.
[Device configuration]
FIG. 2 shows the device configuration. The photoconductor has a drum shape, and includes a charger 12 disposed around the photoconductor drum 11, an L exposed by an exposure device, a developing device 13, a transfer charger 14, a fixing device 15, and a cleaning device 16. . Here, the photosensitive drum 11, the charging device 12, and the developing device 13 are configured to be included in the integral type cartridge 17, but the configuration of the apparatus is not limited to this.
[Operation of the entire device]
Next, the operation of the entire apparatus will be described.
[0024]
The surface of the photosensitive drum 11 is uniformly charged by the charging roller 12 to which the voltage is applied. Thereafter, the photosensitive drum 11 is scanned while the semiconductor laser of the laser scanner is turned on in accordance with the image signal processed by the above-described image processing unit, and an electrostatic latent image is formed on the photosensitive drum 11.
[0025]
Next, the electrostatic latent image on the photosensitive drum 11 is visualized by frictionally charged toner supplied from the developing device 13. The developed toner image on the photosensitive drum 11 is transferred to the recording material P in the transfer section and finally fixed by the fixing section 15 to obtain a recorded image. Thereafter, the toner remaining after transfer is collected by a cleaner, and the surface of the photosensitive drum is used for the next image formation.
[0026]
[Example 1]
In the present embodiment, using the image forming apparatus described above, the drive current of the drive motor is detected, and the fluctuation of the position of the pixel is adjusted by feeding back the image exposure data.
[0027]
(Detection method)
FIG. 3 is a diagram showing the configuration of the motor driver unit 101 and the motor unit 102. In the figure, reference numeral 103 denotes a current detection resistor, and reference numeral 104 denotes a control unit of the image forming apparatus.
[0028]
The drive current of the motor can be detected by the current detection resistor 103 in FIG. FIG. 4 shows an example of the detected current waveform.
[0029]
Since the detected current changes depending on the load applied to the motor, the detected current can be regarded as a change in one rotation of the photosensitive drum 11 due to the eccentricity of the photosensitive drum 11 and a change in the speed. The waveform in FIG. 4 shows one rotation of the drum. Istd in the graph is a standard value of the drive current, and the speed at this time is the aiming speed of the image forming apparatus. As shown in FIG. 5, the speed (V) of the photosensitive drum 11 can be calculated from the drive current (I), and the speed deviation (ΔV) from the standard speed (Vstd) can be obtained.
[0030]
Further, as shown in FIG. 6, the shift amount (Δx) from the position where the image data is originally output can be calculated from the speed data. Here, the calculation process of current → speed → distance has been shown for the sake of simplicity. However, it is possible to directly calculate (distance) position data from the detected current data and further calculate light intensity data described below. However, there are few processing steps, which is advantageous in terms of time.
[0031]
In this manner, the change in the detected current of the motor is observed in a period of one cycle, and the image exposure intensity of the photosensitive drum 11 is adjusted as described below based on the result, thereby improving the image uniformity. be able to.
[0032]
(Image data processing method)
The exposure intensity of the image data is adjusted according to the fluctuation of the current of the photosensitive drum drive motor, and the image forming position is controlled.
[0033]
From the obtained detection current, the speed fluctuation amount of the photosensitive drum is calculated, and the displacement amount ΔV of the photosensitive drum surface speed Vn from the average speed Vave at each exposure position is obtained. The amount ΔX is calculated, and the exposure amount is modulated in accordance with the positional deviation amount. The relationship between the parameters is represented by the following equation. Here, the time t is the exposure time Vn = Vave + ΔVn of the image data to be varied.
ΔX = ΔVn × t
The position correction at this time was performed up to ΔX = 1 μm in this embodiment. The reason is that in the apparatus of the present embodiment, when ΔX is less than 1 μm, a good image is obtained to a level that cannot be recognized as image unevenness, but when ΔX is 1 μm or more, the image can be recognized as image unevenness.
[0034]
The modulation of the exposure amount of the image data will be described with reference to FIG.
[0035]
In the case of Vn = Vave (ΔV = 0), ΔX = 0, so that the position Pnm (n: main scanning position, m sub-scanning position) in FIG. In this case, an image is output with the exposure intensity based on the image data as it is.
[0036]
In the case of Vn> Vave (ΔVn> 0), since the photosensitive drum speed is faster than the original speed, ΔX is in a lagging direction, and the ideal pixel position needs to be earlier than the current position. FIG. ~ D. In order to correspond to the above, the multi-valued 256 gradations of the image exposure are converted to a. Is lit at an intensity of level 255, but b. Then, the multi-value level of the position Pnm is lowered (here, level 220), and a latent image of weak exposure is formed at a position P (n-1) m one scan earlier than that position (here, level 55). By forming such a latent image, an image can be formed above the current position. c. In, in order to further move the pixel forward, the intensity of Pnm is set to level 200, and the intensity of P (n-1) m is set to level 126.
[0037]
D. By setting the intensity of P (n-1) m and Pnm to level 179, a pixel can be formed at an intermediate position between P (n-1) m and Pnm. Further, when increasing the displacement amount, the exposure level of P (n-1) m is further increased, and Pnm is further decreased.
[0038]
On the other hand, when Vn <Vave (ΔVn <0), the speed of the photosensitive drum is slower than the original speed, and therefore ΔX is in the direction of increasing the speed, and the ideal pixel position needs to be slower than the current state. Concerning the formation of the pixel, the position of the pixel can be delayed by increasing the exposure amount of P (n + 1) m with respect to the position of Pnm and simultaneously decreasing the exposure amount of Pnm.
[0039]
In the description so far, the case where the image data represents one dot with a saturated density is taken as an example. However, in actual image formation, an intermediate gradation is also used, and in that case, each of the pixel of interest and its neighboring pixels is used. The exposure adjustment is performed by substantially multiplying the original exposure intensity based on the image data of the pixel by the ratio for correcting the positional deviation. However, in order to further increase the image position accuracy, it is preferable that the characteristic displacement amount in the configuration of the image forming apparatus to be used is grasped in advance and stored as data.
[0040]
(Operation of the device)
FIG. 8 shows the flow of the operation of the apparatus of this embodiment.
[0041]
In the apparatus of the embodiment described above, the above-described detection is performed in advance as a pre-process before image formation, and an image exposure light amount distribution data table is created based on the detected current, and stored in the storage device. Thereafter, when processing and creating image data in the process of forming an image, the exposure intensity of each image data is determined with reference to the stored data table. By processing and outputting an image in this manner, an image with good image uniformity could be output.
[0042]
In particular, in the present embodiment, since no new device is added as a detecting device, an image forming method with good image uniformity can be provided without a significant increase in cost.
[0043]
[Example 2]
In this embodiment, an encoder is used as a method for detecting the photosensitive drum surface speed.
[0044]
(Detection method)
FIG. 9 shows an example in which an encoder is attached.
[0045]
As shown in FIG. 9, a rotary encoder 201 is attached to the drive shaft of the photosensitive drum 11, and the speed of the photosensitive drum 11 is sequentially detected, whereby the speed fluctuation on the surface of the photosensitive drum 11 can be constantly detected. Thus, it is possible to provide an image forming method in which the image uniformity is always better than that of the first method.
[0046]
A small, high-speed, and inexpensive encoder is ideally used.
[0047]
(Operation of the device)
FIG. 10 shows a flow of the operation of the apparatus of this embodiment.
[0048]
Based on the output from the encoder, high-speed arithmetic processing is performed using a DSP (Digital Signal Processor), and the exposure amount is adjusted by directly controlling the laser driver to generate an image.
[0049]
In the present embodiment, the method of detecting the surface speed using an encoder was used. A method using an optical scale sensor that detects the speed by reading is exemplified, and an optimal sensor can be used according to the image forming apparatus.
[0050]
[Example 3]
The present embodiment particularly relates to a cartridge type image forming system having a built-in memory for data storage. Banding is often unique to a cartridge. Therefore, at the time of inspection after assembling the cartridge, speed fluctuation data for one rotation of the photosensitive drum is measured, the information is stored in a memory in the cartridge, and the main body controls the image exposure intensity based on the information. In the present embodiment, a jig capable of measuring only the rotation of the cartridge and measuring the drive current of the motor for the fluctuation of the speed of the photosensitive drum is separately prepared, and a data table of the light amount distribution is created.
[0051]
FIG. 11 shows the flow of the operation of the apparatus of this embodiment.
[0052]
Thereby, the banding unique to each cartridge can be improved without making a major change to the main body.
[0053]
[Example 4]
The photosensitive drum surface speed detection method of the present embodiment uses the detection method by the encoder used in the second embodiment, and adjusts the fluctuation of the image density by changing the developing bias as the change of the image forming condition.
[0054]
(Change in developing bias)
The developing method of LBP-1760 used in the embodiment is one-component non-contact jumping development, and a developing bias in which an AC voltage is superimposed on a DC voltage is used. In this embodiment, the developability is most affected. The density is adjusted by changing the DC voltage. The developing bias is adjusted to the development acceleration side where the pixels are isolated and the density is seen to be light, and conversely, the development bias is adjusted to the development suppression side where the pixels are dense and the density looks dark. As a result, the uniformity of the obtained image density is improved, and good image output can be performed.
[0055]
(Operation of the device)
FIG. 12 shows a flow of the operation of the apparatus of this embodiment.
[0056]
In the present embodiment, the image forming conditions are changed by changing the developing bias.However, the charging potential is adjusted by changing the charging bias, the adjustment is performed by changing the intensity of the image exposure, or It is also effective to make adjustments by combining a plurality of these.
[0057]
【The invention's effect】
As is apparent from the above description, according to the present invention, the speed deviation of the photoconductor surface is detected, the position deviation of the image data is predicted from the detected value, and the position displacement smaller than the size of the minimum unit of resolution is detected. By correcting an arbitrary displacement amount from the amount, it is possible to provide an image forming apparatus capable of outputting an image with good image uniformity without image unevenness called banding.
[0058]
In addition, it is possible to provide an image forming apparatus capable of outputting an image with good image uniformity without image unevenness called banding by estimating image density unevenness from the detected value and changing image forming conditions according to the image density unevenness. it can.
[Brief description of the drawings]
FIG. 1 is a block diagram of an image processing step.
FIG. 2 is a schematic sectional view of the image forming apparatus.
FIG. 3 is a schematic diagram around a motor.
FIG. 4 is a graph of a detection current according to the first embodiment.
FIG. 5 is a graph of speed according to the first embodiment.
FIG. 6 is a graph of a position according to the first embodiment.
FIG. 7 is an explanatory diagram of exposure light amount data and image output according to the first embodiment.
FIG. 8 is an explanatory diagram of a flow of an operation of the apparatus according to the first embodiment.
FIG. 9 is an explanatory diagram of a part of the device according to the second embodiment.
FIG. 10 is an explanatory diagram of a flow of an operation of the apparatus according to the second embodiment.
FIG. 11 is an explanatory diagram of a flow of an operation of the apparatus according to the third embodiment.
FIG. 12 is an explanatory diagram of a flow of an operation of the apparatus according to the fourth embodiment.
[Explanation of symbols]
Reference Signs List 11 photosensitive drum 12 charger 13 developing device 14 transfer charger 15 fixing device 16 cleaning device L light exposed by exposure device

Claims (6)

An apparatus for duplicating a desired image with an image forming apparatus having a desired device resolution,
A photoconductor that is an image carrier, an exposure unit that exposes the photoconductor in accordance with image data, and a driving source that drives the photoconductor, and a detection unit that detects a movement speed variation of the photoconductor surface, An image having a size smaller than the image resolution is provided by having a calculation unit that calculates a displacement amount of image data according to the detection amount, and a unit that changes an exposure amount according to the image data according to the displacement amount. An image forming apparatus comprising: means for correcting a data displacement. 2. The image forming apparatus according to claim 1, wherein a change in the moving speed of the photosensitive member surface is detected by a drive current of a drive source for driving the photosensitive member. 2. The image forming apparatus according to claim 1, wherein a change in the moving speed of the surface of the photoconductor is detected using an encoder. 2. The image forming apparatus according to claim 1, wherein the fluctuation of the moving speed of the surface of the photoconductor is detected by using a laser Doppler measuring device. 2. The image forming apparatus according to claim 1, wherein a change in the moving speed of the photosensitive member surface is detected using an optical scale sensor provided on the photosensitive member surface. An apparatus for duplicating a desired image with an image forming apparatus having a desired device resolution,
A photoconductor that is an image carrier, an exposure unit that exposes the photoconductor in accordance with image data, and a driving source that drives the photoconductor, and a detection unit that detects a movement speed variation of the photoconductor surface, An image forming apparatus, comprising: means for changing an image forming condition according to the detection amount.

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