JP2765627B2 - Image forming device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plurality of image forming means which are arranged in a row to form images of respective colors, and records the images along the arrangement direction of the image forming means. An endless conveying means for conveying the sheet, wherein the endless conveying means sequentially conveys the recording sheet to each image forming means to form an image of each color on one recording sheet in a superposed manner, for example, a digital color copying machine And other image forming apparatuses. 2. Description of the Related Art In an image forming apparatus such as a digital color copying machine for forming an image of each color on one recording sheet (for example, a transfer sheet) in such a manner as described above, the positional shift of each color, that is, the color Misalignment is a problem. The causes of the positional deviation (color deviation) include, for example, in the case of a digital color copying machine, the mounting position and peripheral speed of each photoconductor, the exposure position on the photoconductor, and the linear speed of the endless conveyance means (for example, a transfer belt). Etc. In order to avoid this displacement as much as possible, measures have been taken to increase the accuracy of each component and the accuracy of mounting the components. However, the cost of parts and assembly is high, and the productivity is low. In addition, there is a problem that readjustment is required due to a change with time of each component and variation due to component replacement. As a method for solving this problem, for example, as described in Japanese Patent Application Laid-Open No. 59-155870, a leading edge of a transfer sheet is provided by a sensor provided before each transfer position. Has been proposed to obtain the write timing of each color by detecting the color. However, in this case, it is difficult to guarantee the positional deviation limit (about 0.15 mm) of the color image due to the variation in the mounting position of the sensor and the variation in the detection position of each sensor. Further, for example, Japanese Patent Application Laid-Open No. 62-242969
As described in Japanese Patent Application Laid-Open Publication No. H11-264, a method has been proposed in which a measurement pattern image for each color is formed on transfer paper, and the writing timing of each color is corrected based on the amount of shift between the patterns. But in this case,. Since an unnecessary color measurement pattern image is formed on the transfer paper in addition to the originally desired color image, the measurement pattern image becomes annoying and is not preferable in image quality. [0006] In the case of transfer paper, wrinkles may be generated between the formation of the measurement pattern image and the detection, so that even if the bent angle measurement pattern image is formed, the amount of displacement may not be accurately grasped. [0007] If the measurement pattern image is formed only for adjusting the positional deviation, the transfer paper is wasted. [0008] Since the quality and ground color of the transfer paper vary depending on the type of transfer paper used, the pattern image for measurement may not be formed properly, or the pattern image for measurement may not be detected properly, resulting in problems with reproducibility. There is. SUMMARY OF THE INVENTION An object of the present invention is to provide a highly reliable image forming apparatus which solves the above-mentioned drawbacks of the prior art and can appropriately correct color misregistration. [0010] In order to achieve the above object, the present invention provides, for example, black, yellow, magenta,
It has multiple recording devices that form images of each color, such as cyan.
Then, the transfer paper is sequentially conveyed to each recording device by the transfer belt.
And an image forming apparatus for superimposing and transferring an image. [0011] Then the pattern image signal generating means for forming a measurement pattern image of each color on the transfer belt, detects the measuring pattern image for each color, and such detection means of the sensor to be described later for example, the detection Inspection by means
With knowledge, the reference of the measurement pattern image for each color and
A measurement pattern image of a specific color (for example, black
Pattern image) and measurement pattern images of other colors (example)
For example, yellow, magenta, cyan measurement pattern images
Image), such as a counter to be described later.
Measuring means and a reference based on the measurements of the measuring means.
The pattern image for measurement of a specific color and the pattern for measurement of other colors
Calculating means for calculating the amount of deviation from the image , for example, a comparison operation circuit described later, and the other means based on the amount of deviation .
Adjusting the image writing timing of the color recording device , for example, adjusting means such as an image writing timing generating circuit described later, provided at a position facing the measurement pattern image formed on the transfer belt, and the detecting means A cleaning unit, such as a cleaning unit described below, for removing the measurement pattern image after the detection from the transfer belt, is provided. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the present invention forms a measurement pattern image on an endless conveyance means as compared with a conventionally proposed method of forming a measurement pattern image on transfer paper. do it, . Since the pattern image for measurement is not formed on the recording sheet (for example, transfer paper), the pattern image for measurement is not obstructed as in the related art. [0013] Since the endless conveyance means does not wrinkle during conveyance unlike transfer paper, a measurement pattern image is appropriately formed, and the shift amount can be accurately grasped. [0014] Since the recording sheet is not used even when the measurement pattern image is formed only for adjusting the positional deviation, the recording sheet is not wasted. [0015] Since one image forming apparatus has one endless conveying means (for example, a transfer belt), the paper quality and ground color do not change variously depending on the type of transfer paper used, such as the transfer paper. Image formation and its detection are properly performed, and the reproducibility is excellent. Further, the present invention is provided at a position facing the measurement pattern image formed on the endless transport means,
Since there is a cleaning means for removing the measurement pattern image after detection by the detection means from the endless conveyance means, it is possible to surely erase the previous measurement pattern image for the next shift amount correction. It is not possible to mistakenly detect the previous measurement pattern image. From the above, an image forming apparatus having excellent operation reliability can be provided. Hereinafter, the structure and operation of the present invention will be described in detail based on an embodiment shown in the drawings. FIG. 1 is a schematic configuration diagram of a digital color copying machine as an example of an image forming apparatus. This copying machine has a scanner unit 1 for reading an original, and an image processing unit 2 for electrically processing an image signal output from the scanner unit 1 as a digital signal.
And a printer unit 3 that forms an image on transfer paper based on image recording information of each color from the image processing unit 2. The scanner section 1 has a lamp 5 for scanning and illuminating the original on the original placing table 4, for example, a fluorescent lamp. Light reflected from the original when illuminated by the lamp 5 is reflected by mirrors 6, 7, and 8 and is incident on the imaging lens 9. The image light is imaged on the dichroic prism 10 by the imaging lens 9 and split into light of three wavelengths, for example, red R, green G, and blue B, and a light receiver 11, for example, red light for each wavelength light. To the CCD 11R, the CCD 11G for green, and the CCD 11B for blue. Each of the CCDs 11R, 11G, and 11B converts incident light into a digital signal and outputs the digital signal. The output is subjected to necessary signal processing in the image processing unit 2, and recording color information of each color, for example, black (hereinafter abbreviated as Bk) ), Yellow (Y
, Magenta (abbreviated as M), cyan (abbreviated as C)
Are converted into signals for recording image formation of each color. FIG. 1 shows an example in which four colors of Bk, Y, M, and C are formed. However, a color image can be formed using only three colors. In that case, the number of recording devices can be reduced by one set compared to the example of FIG. The signal from the image processing unit 2 is input to the printer unit 3, and the laser beam emitting devices 12Bk, 12Bk,
It is sent to 12Y, 12M, and 12C. In the printer section 3, four sets of recording devices 13C, 13M, 13Y, and 13Bk are arranged in a line in the example of FIG. Since each recording device 13 is composed of the same member, the recording device 13C for cyan will be described for simplicity of description, and other colors will be omitted. For each color, the same portions are denoted by the same reference numerals, and in order to distinguish the configuration of each color, a reference numeral indicating each color is added to the reference numeral. The recording device 13C is a laser beam emitting device 12C.
And a photoconductor 14C, for example, a photoconductor drum. Around the photoreceptor 14C, a charging charger 15C, an exposure position by the laser beam emitting device 12C, a developing device 16C, a transfer charger 17C, and the like are arranged. The photoreceptor 14C uniformly charged by the charging charger 15C forms a latent image of a cyan light image by exposure by a laser beam emitting device 12C, and is developed by a developing device 16C to form a visible image. The transfer paper supplied from the paper supply unit 19, for example, one of the two paper supply cassettes by the paper supply roller 18, is sent to the transfer belt 21 by the registration roller 20 at a proper timing. The transfer paper conveyed by the transfer belt 21 is sequentially formed with the photosensitive members 14Bk, 14Y,
The transferred images are sequentially transferred to 14M and 14C, and a visible image is transferred onto transfer paper under the action of the transfer charger 17. The transfer paper is electrostatically attracted to the transfer belt 21 so that the transfer paper is conveyed with high accuracy at the speed of the transfer belt 21. Thereafter, the transfer paper is fixed by the fixing roller 22 and discharged by the discharge roller 23. FIG. 2 is a front view of the transfer belt portion. The transfer belt 21 is supported by a belt drive roller 24 and a driven roller 25, and moves in the direction A to convey the transfer paper. Further, the cleaning unit 26 allows the transfer belt 21 to be moved.
Then, the detected measurement pattern image 28 formed in the above is removed to prepare for the formation of the next measurement pattern image 28.
One reflection sensor 27 is provided on the downstream side of the photoconductor 14 in the belt moving direction as a pattern image detecting unit. As shown in the figure, the cleaning unit 26 and the sensor 2
Reference numerals 7 are provided on the transfer path of the transfer belt 21 so as to be substantially opposite to each other. In this way, the fine-powder toner scattered during the operation of the cleaning unit 26 does not adhere to the detection surface of the sensor 27 and the detection sensitivity does not decrease, and the reliability of the sensor 27 is maintained for a long time. it can. The operation will be described with reference to FIGS. The measurement pattern images 28 sequentially visualized by the signals from the pattern image signal generating means outside the transfer paper area in each recording device 13 are transferred to the transfer belt 21 and are each a (mm) as shown in FIG. ). Each of the measurement pattern images 28Bk, 28Y, 28M, and 28C is a linear pattern extending in a direction substantially orthogonal to the transport direction of the transfer belt 21. Then, the measurement pattern image 28Bk,
28 </ b> Y, 28 </ b> M, and 28 </ b> C sequentially pass below the sensor 27 as the transfer belt 21 moves, and are optically detected by the sensor 27. The image interval a is set in advance for each recording device 13.
Is a numerical value that can be arbitrarily set by setting an exposure timing for the transfer belt 21.
₂ (mm / sec), the detection time difference between the measurement pattern images 28Bk, 28Y, 28M, and 28C for each color is a
/ V ₂ (sec). FIG. 4 illustrates the setting of the image interval a. The length from the exposure position to the transfer position for each photoconductor 14 is l ₁ (mm), the linear speed of the photoconductor is v ₁ (mm / sec), the distance between the photoconductors is l ₂ (mm), and the linear speed of the transfer belt is v ₂ (m
m / sec), the time required from exposure to transfer t
₁ becomes the same value as the photosensitive member 14, when the _{t 1 = l 1 / v 1} (sec) Time to move between each photoconductor and _{t 2, t 2 = l 2} / v 2 (sec) i.e., amm If it is desired to form a pattern 28 at intervals, based on the Bk signal generation timing from the pattern image signal generating _{means, t c = (l 2 +} a) / v 2 (sec) t M = 2 (l 2 + a) / V ₂ (sec) t _Y = 3 (l ₂ + a) / v ₂ (sec). However, in practice, due to the variation in the position of each photoconductor 14, the variation in the exposure position with respect to the photoconductor 14, and the variation in the linear velocity of the photoconductor 14 and the transfer belt 21, the measurement data transferred onto the transfer belt 21 is used. The interval between the pattern images 28 is shifted with respect to a, which also appears as a color shift in the superimposed image on the transfer paper. FIG. 5 is an example showing the output of the sensor 27. Measurement pattern images 28Bk, 28
Y, 28M, and 28C are sequentially detected. The signal of the sensor 27 is sent to the counters 29Y, 29M, and 29C shown in FIG. 6, and the counters 29Y, 29M, and 29C are reset and start counting by the detection signal of the Bk pattern (28Bk). Next, the counter 29Y stops counting in response to the detection signal of the Y pattern (28Y). The same applies to the other counters 29M and 29C, so that Y will be described. As shown in FIG. 6, the amount of deviation from a preset value is calculated by the comparison operation circuit 30 based on the counter value of the counter 29Y. That, MHz clock frequency, when the counter value is K _Y, calculates the difference between the set value t count value for _{KY K YS (= M · t} KY). [0035] K _{Y -} by _YS = K _Y -K _YS this value, changes the number of clocks K _gY for the image signal generation timing (in the initial state is set to the count value corresponding to the above-described t _Y). K ′ _gY = K _gY −K _{Y −YS} (K _gY = M · t _Y , K ′ _gY will be replaced with K _gY ). The recording device 1 can be changed in accordance with the corrected image writing timing.
The 3Y LD modulation circuit 32 is driven. The same applies to other M and C. As described above, in the present embodiment, an example in which Y, M, and C are respectively adjusted based on Bk has been described. In this embodiment, a reflection sensor is used. However, any other means such as a transmission sensor capable of detecting an image may be used. It is also possible to use a means such as a timer that can measure the timing instead of the counter. The correction of the writing timing by the pattern output may be performed for each copy, may be performed for each set number of sheets, or may be performed once after the main switch is turned on, and may be performed at an arbitrary interval as needed. The present invention according to claim 1 has the following features.
In order to form a measurement pattern image on a transfer belt , compared to a conventionally proposed method of forming a measurement pattern image on a transfer paper, the following method is used. Since the measurement pattern image on the transfer paper is not formed, it does not become unsightly conventional measurement pattern image as. [0040] Since the transfer belt does not wrinkle during transfer unlike transfer paper, a measurement pattern image is appropriately formed, and the shift amount can be accurately grasped. [0041] Even if a pattern image for measurement is formed only for adjustment of misalignment, no transfer paper is used,
There is no waste of transfer paper . [0042] Transfer bell in one image forming apparatus
DOO et or is one, it without change to a variety such as paper quality and ground color depending on the kind of the transfer sheet to be used, therefore the formation and its detection in the measurement pattern image properly carried out, reproducibility Are better. [0043] The present invention is provided in a position facing the measuring pattern image formed on the transfer belt, a cleaning means for removing from the transfer belt measured pattern image after being detected by the detection means Because
The previous measurement pattern image can be reliably erased for the next shift amount correction, and the previous measurement pattern image is not erroneously detected. Thus, an image forming apparatus having excellent operation reliability can be provided. As described in the second aspect, if the measurement pattern images for each color are formed at intervals along the transport direction of the transfer belt , the shift amount in the transport direction of the transfer paper , that is, the sub-scanning, The direction shift amount can be easily corrected. Also,
The width of the cleaning means may be small. As described in claim 3, if the detecting means and the cleaning means are provided on the transfer path of the transfer belt so as to be substantially opposite to each other, the cleaning means is in operation. The fine powdery toner scattered on the detection unit does not adhere to the detection surface of the detection unit, and the detection sensitivity does not decrease, so that the reliability of the detection unit can be maintained for a long time.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram of a digital color copying machine to which the present invention is applied. FIG. 2 is a front view of a transfer belt unit in the digital color copying machine. FIG. 3 is a partially enlarged plan view of a transfer belt portion in the digital color copying machine. FIG. 4 is an image interval a in the digital color copying machine.
It is a figure for explaining setting of. FIG. 5 is a diagram showing an output of a sensor in the digital color copying machine. FIG. 6 is a control block diagram of the digital color copying machine. [Description of Signs] 12Bk, 12Y, 12M, 12C Laser beam emitting devices 13Bk, 13Y, 13M, 13C Recording devices 14Bk, 14Y, 14M, 14C Photoconductors 15Bk, 15Y, 15M, 15C Charging chargers 16Bk, 16Y, 16M, 16C Developing devices 17Bk, 17Y, 17M, 17C Transfer charger 21 Transfer belt 27 Sensor (detection means) 28Bk, 28Y, 28M, 28C Measurement pattern image 29 Counter (counting means) 30 Comparison calculation circuit (calculation means) 31 Image writing timing generation Circuit (timing signal generating means) 32 LD modulation circuit (pattern image signal generating means) A transport direction a image interval

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Claims (1)

(57) [Claims] It has multiple recording devices that form images of each color ,
The transfer paper is sequentially conveyed to each recording device by the belt and the image is
An image forming apparatus for superimposing transfer, and the pattern image signal generating means for forming a measurement pattern image of each color on the transfer belt, detection means for detecting the measurement pattern image for each color, the detection by the detection means And the putter for measurement for each color
Pattern image for measurement of a specific color that is a reference in the
Measurement to measure the distance between the pattern image for measurement and other colors
Means and measurement of a specific color as a reference based on the measurement of the measuring means
Means for calculating the amount of shift between the pattern image for use and the pattern image for measurement of another color; adjusting means for adjusting the image writing timing of the recording apparatus for the other color based on the amount of shift; and the transfer belt An image forming apparatus comprising: a cleaning unit that is provided at a position facing a measurement pattern image formed thereon and that removes the measurement pattern image detected by the detection unit from the transfer belt. 2. 2. The image forming apparatus according to claim 1, wherein the measurement pattern image for each color is formed along a transfer direction of a transfer belt . 3. 2. An image forming apparatus according to claim 1, wherein said detecting means and said cleaning means are provided on the transfer path of the transfer belt at a distance substantially opposite to each other. 4. 2. An image forming apparatus according to claim 1, wherein said image forming apparatus is a digital color copying machine.