JP2755569B2 - Image forming device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a plurality of image forming means for forming an image of each color, and a recording medium for forming an image by the image forming means. The present invention relates to an image forming apparatus, such as a digital color copying machine, for forming an image of each color in an overlapping manner on one recording medium. 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. [0004] As a method for solving this problem, for example, a method described in JP-A-59-155870 or JP-A-62-242969 has been proposed. However, these proposals do not take into account periodic fluctuations in the speed of the photoconductor and the transfer paper conveying means. Therefore, the actual image shift amount is affected by the periodic speed fluctuation of the photoconductor and the transfer paper conveying means, and is detected as being larger than the actual image shift amount, or conversely, being detected as being smaller than the actual image shift amount, As a result, there is a drawback that an image of constant quality cannot be obtained despite the provision of the shift amount adjusting means. SUMMARY OF THE INVENTION An object of the present invention is to provide a highly reliable image forming apparatus which can solve the above-mentioned drawbacks of the prior art and can appropriately adjust the image shift amount. 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. [0007] The recording device detects a measurement pattern image of each color formed on the transfer belt . For example, detection means such as a sensor described below, and detection by the detection means, among the measurement pattern images of each color, The distance between a specific measurement pattern image (eg, a black measurement pattern image) serving as a reference and another color measurement pattern image (eg, a yellow, magenta, and cyan measurement pattern image) is measured. A measuring means such as a counter, and an averaging means such as an averaging circuit described below, which averages the measurement results of the measuring means for each color, and a specific reference serving as a reference based on the averaged value . A calculating means for calculating a shift amount between the measurement pattern image and the measurement pattern image of another color, for example, an arithmetic circuit described later; The image writing timing of the recording apparatus to adjust, for example, and a such adjustment means described later image writing timing generating circuit, in the recording apparatus Te
A plurality of sets of measurement pattern images for each color, for example, four sets, are formed on the transfer belt , and the plurality of sets of measurement pattern images are respectively detected by the detection unit, and the image intervals are respectively measured by the measurement unit. , Wherein the measurement results are averaged by the averaging means. As described above, according to the present invention, a plurality of sets of measurement pattern images for each color are formed on a recording medium by an image forming means, and the plurality of sets of measurement pattern images are detected. The image interval is detected by the means, the image interval is measured by the measuring means, and the measurement result is averaged by the averaging means. For this reason, for example, the influence of the periodic speed fluctuation of the photosensitive member or the recording medium is reduced as much as possible by averaging.
Therefore, a value close to the actual image shift amount can be calculated, and the image writing timing can be adjusted based on the shift amount.
A highly reliable image forming apparatus can be obtained. Further, according to the present invention, one measurement pattern image serving as a reference among a plurality of measurement pattern images is determined, and the shift amount of the measurement pattern image of another color with respect to it is determined. The calculation error is small. 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 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 light emitting devices 12Bk, 12Bk,
It is sent to 12Y, 12M, and 12C. In the example shown in the figure, four sets of recording devices 13C, 13M, 13Y, and 13Bk are arranged in the printer unit 3 in a line. 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 photosensitive member 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 develops 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 28 (2
8Bk, 28Y, 28M, and 28C) sequentially pass below the sensor 27 as the transfer belt 21 moves.
Optically detected by the 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 variations in the position of each photoconductor 14, variations in the exposure position with respect to the photoconductor 14, and variations in the linear velocity of the photoconductor 14 and the transfer belt 21, 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
C, 28M, and 28Y are sequentially detected. The signal of the sensor 27 is sent to the counters 29C, 29M, and 29Y shown in FIG. 6, and the counters 29C, 29M, and 29Y are reset and start counting by the detection signal of the Bk pattern (28Bk). Next, the counter 29C stops counting in response to the detection signal of the C pattern (28C). The same applies to the other counters 29M and 29Y, so that the description for C will be given. Based on the counter value of the counter 29C, the amount of deviation from the preset value is calculated by the arithmetic circuit 31 (FIG. 8).
). In other words, the clock frequency is MHz,
Assuming that the counter value is K _C , the difference between the set value t _KC and the count value K _CS (= M · t _KC ) is calculated. K _(C-CS) = K _C -K _CS This K _(C-CS) represents a shift amount of the pattern image between Bk and C with respect to the set interval. Since it is also affected by speed fluctuations (periodic fluctuations with respect to the set linear velocity), when a shift on the image occurs as shown in FIG. If the feedback is performed as it is, there is a risk that the deviation amount may be increased. FIG. 6B shows a shift on the image when the feedback is performed.
They are shown as horizontal lines for clarity. The measurement pattern image is not shown because it is outside the transfer paper). With respect to the periodic speed fluctuation, the longer the period, the larger the deviation amount with respect to the same speed fluctuation rate.
Position shift due to the speed variation rate of the photoconductor is likely to occur. Therefore, in the present invention, as shown in FIG. 7, a plurality of sets of measurement pattern images are formed for one cycle of the photoconductor. In the example shown in the figure, the measurement pattern images (28Bk, 28C, 28M, 28
Y) are formed in four sets. The timing of outputting the Bk pattern (28Bk) is πD where D is the lightness of the photoconductor.
/ 4v ₁ and should be. Other measurement pattern images 28
The same applies to C, 28M, and 28Y. FIG. 8 is a control block diagram, and FIG. 9 is a flowchart of the control.
Y is a counter that counts the passage of each of the measurement pattern images 28C, 28M, and 28Y, 30 is an averaging circuit that averages the count values as described later, and 31 is a calculator that calculates the amount of deviation from the averaged count values. An arithmetic circuit 32 for adjusting the image writing timing based on the shift amount; and an LD modulation circuit 33 driven by the image writing timing generating circuit 32. As shown in FIG. 9, first, the count value Kc of the cyan measurement pattern image 28C is input, and then the count values Kc _{(1) to} Kc ₍₄₎ are averaged by the averaging circuit 30 according to the following equation. Be transformed into The averaging count value _{K c = {Kc (1)} + K
c ₍₂₎ + Kc ₍₃₎ + Kc ₍₄₎ ｝ / 4 The difference between this and the count value K _CS with respect to the set value t _KC , that is, the shift amount is calculated by the calculation circuit 31. [0034] The _{K (C-CS) = K} c-K CS this value, changes the black number K _gc for the image signal generation timing to the K _'gc (K _gc is the initial value, the t
Set to the count value for _C ). K ' _gc = K _gc -K _(C-CS) This makes it possible to adjust the image writing timing of the image writing timing generation circuit 32 in accordance with the amount of deviation, and from the next time the LD modulation circuit will be in a state where there is no positional deviation. 33 can be driven. Such control is similarly performed for M and Y. In the above embodiment, four sets of measurement pattern images are formed for one cycle of the photosensitive member, but the number of sets and the output timing can be set arbitrarily. In this embodiment, a reflection type sensor is used. However, any other means such as a transmission type 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 output of the pattern image is performed when each image is output (1
For each copy, various methods such as a method of outputting the image to the outside of the recording sheet area, a method of outputting the image for each set number of sheets, and a method of outputting the image in a fixed time are possible. The present invention according to claim 1 has the following features.
A plurality of sets of measurement pattern images for each color are formed on the transfer belt by the recording device , and the plurality of sets of measurement pattern images are respectively detected by the detection means, and the image intervals are respectively measured by the measurement means. Are averaged by the averaging means. Therefore, for example, the influence of the periodic speed fluctuation of the photosensitive member and the transfer belt is minimized by averaging, so that a value close to the actual image shift amount can be calculated, and the image writing timing is adjusted based on the shift amount. Therefore, a highly reliable image forming apparatus can be obtained. Further, according to the present invention, a measurement pattern image of a specific color to be a reference from among a plurality of measurement pattern images is determined, and a shift amount of a measurement pattern image of another color with respect to the measurement pattern image is determined. There is little error in quantity calculation. Thus, it is possible to provide an image forming apparatus having excellent operation reliability. In the present invention, the measurement pattern image is transferred.
Since it is formed on a belt, it has the following features. . When forming the measurement pattern image of each color on the transfer sheet, it is becomes obtrusive on the transfer sheet, such that there is no by forming the measurement pattern image on the transfer belt, originally on the transfer sheet Only the desired color image is formed. [0044] On transfer paper , wrinkles may be formed on the transport path until the measurement pattern image is formed and detected, but the transfer belt does not wrinkle, so the measurement pattern image is formed properly. The deviation amount can be accurately grasped. [0045] 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 . [0046] In the case of the transfer paper, since such paper quality and ground color depending on the type of the transfer sheet to be used is changed to different, although formation and its detection in the measurement pattern image not done properly, the transfer in one image forming apparatus 1 belt
Therefore, the reproducibility is excellent without the above-mentioned problem. As described in claim 2 , if the measurement pattern images for each color are formed at intervals along the transfer direction of the transfer belt , the shift amount in the transfer direction of the transfer paper , that is, the sub-scanning, The direction shift amount can be easily corrected. [0048] As according to claim 3, wherein, when the measurement pattern image is a linear pattern intersecting the transport direction of the transfer belt, is a clear peak in the detection means when the pattern is passed under the detecting means It has features such as appearing and reliable detection of the pattern.

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 an explanatory diagram showing a state of relative displacement of an image. FIG. 7 is an explanatory diagram showing a state in which a plurality of sets of measurement image patterns are formed for one cycle of the photoconductor in the digital color copying machine. FIG. 8 is a control block diagram of the digital color copying machine. FIG. 9 is a control flowchart in 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 (measurement means) 30 Averaging circuit (averaging means) 31 Comparison operation circuit (Calculation means) 32 Image writing timing generation circuit (timing signal generation means) 33 LD modulation circuit (pattern image signal generation means) A Transport direction a Image interval

Continued on the front page (58) Fields surveyed (Int.Cl. ⁶ , DB name) G03G 13/01 G03G 15/01-15/01 117

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
In an image forming apparatus that performs superimposed transfer, a detection unit that detects a measurement pattern image of each color formed on a transfer belt by the recording device ; Measuring means for measuring an interval between a measuring pattern image of a specific color and a measuring pattern image of another color; averaging means for averaging the measurement results of the measuring means for each color; based on the value, and calculating means for calculating a shift amount between the specific color measuring <br/> titration, pattern image and other color measurement pattern image as a reference, of the recording apparatus on the basis of the shift amount and an adjusting means for adjusting the image writing timing, the measurement pattern image of each color on the transfer belt by the recording device is a plurality of sets formed, before the plurality of sets of measurement pattern image, respectively Detected by the sensing unit to measure each image interval by the measuring unit, the image forming apparatus characterized by being configured to average the results of the measurement by said averaging means. 2 . 2. The image forming apparatus according to claim 1, wherein the measurement pattern images of the respective colors are formed at intervals along a transfer direction of the transfer belt . 3 . In mounting Claims first Kouki, an image forming apparatus, wherein the measurement pattern image is a linear pattern intersecting the transport direction of the transfer belt. 4 . 3. The image forming apparatus according to claim 2 , wherein there is one detecting means for detecting the measurement pattern image for each color. 5 . 2. An image forming apparatus according to claim 1, wherein said image forming apparatus is a digital color copying machine.