JP2852019B2 - 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 a color 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 a superimposed 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 conveying means (for example, 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, methods described in JP-A-59-155870 and JP-A-62-242969 have been proposed. However, in these methods, if the image shift amount is calculated every time an image is formed, the paper feeding timing and the image writing timing are automatically corrected regardless of the magnitude thereof. The operation of the control system becomes unstable, which causes a malfunction, which causes a problem in operation reliability. SUMMARY OF THE INVENTION An object of the present invention is to provide a highly reliable image forming apparatus capable of appropriately correcting color misregistration by solving the above-mentioned drawbacks of the prior art. In order to achieve the above object, the present invention provides, for example, black, yellow, magenta,
A plurality of image forming means such as a recording device described later for forming an image of each color such as cyan; and a recording medium such as a recording sheet described later and a transfer belt for conveying the color image formed by the image forming means. With 1
The present invention is directed to an image forming apparatus that forms an image of each color on one recording medium in a superimposed manner. A recording medium is provided by the plurality of image forming means.
For measurement of each color sequentially formed on the transport means for transporting
A turn image is detected at one place on the transporting means , for example, one detecting means such as a sensor described later, and one detecting means for detecting one of the measuring pattern images which is a reference among the measuring pattern images for each color. Measuring means for measuring an interval between a pattern image (for example, a black measurement pattern image) and another measurement pattern image (for example, yellow, magenta, and cyan measurement pattern images), such as a counter described later; as for calculating a displacement amount of the measurement pattern image based on the measurement of the measuring means, for example a such computing means comparison operation circuit to be described later, it is set in advance and the displacement amount
Comparison means for comparing the allowable value, by the comparison means
As a result of the comparison, if the absolute value of the deviation amount is larger than the allowable value,
In this case, there is provided an adjusting means such as an image writing timing generating circuit which adjusts the image writing timing of the image forming means based on the shift amount. [0008] As described above, the present invention compares whether the deviation calculated by the calculation means is within a preset allowable value, and determines whether the deviation is outside the allowable value. The image writing timing of the image means is adjusted. Therefore, it is not necessary to adjust the image writing timing every time a measurement pattern image is formed, so that a control system such as an image writing timing circuit is stabilized, malfunction does not occur, and it is necessary to adjust the shift amount. Therefore, it is possible to reliably adjust the deviation amount, and it is possible to provide an image forming apparatus having excellent operation reliability. 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, for example, 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 printer section 3, four sets of recording devices 13C, 13M, 13Y, and 13Bk are arranged in a line in the example shown in 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 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
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 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 between 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
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. As shown in FIG. 7, the comparison operation circuit 30 calculates the amount of deviation from a preset value based on the counter value of the counter 29C. That is, if the clock frequency is MHz and 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 difference K _(C-CS) represents the amount of deviation of the pattern image between Bk and C from the set interval. 6 (a), when the image is displaced as shown in FIG. 6 (a), depending on the position of the pattern image, Feedback as it is, there is a risk that the amount of deviation will increase. FIG. 6B shows a shift on the image in the case of feedback (both figures are shown as horizontal lines for clarity of explanation. The pattern image 28 for measurement is not shown because it is outside the transfer paper). . Therefore, in the present invention, a position deviation allowable value e is set, and a count value Ke corresponding to the allowable value e is compared with an absolute value of a deviation amount count value K _(C-CS) from the sensor 27. , As a result, when Ke <| K _(C-CS) |
Changed image export timing. This will be described with reference to the flowchart shown in FIG. First, input the counter value K _C , and K _(C-CS)
Is calculated by the above equation, and the absolute value of the calculation result | K _(C-CS) |
And the allowable value Ke. As a result of comparison, | K _(C-CS) |
Is less than or equal to the allowable value Ke (| K _(C-CS) | ≦ Ke), the image writing timing is not changed, and the next measurement is prepared. |
If K _(C-CS) |> Ke, the shift amount exceeds the permissible value e, so that the processing shifts to calculation for changing the image writing timing. First, in order to know the shift direction of the image, it is determined whether the value of K _(C-CS) is positive or negative. If K _(C-CS) ≧ 0, it means that the cyan measurement pattern image 28C is formed at a position later than the preset position with respect to the reference black measurement pattern image 28Bk. Therefore, it is necessary to change (advance) the image writing timing of cyan C with respect to black Bk so as to fall within the deviation allowable value. Therefore seek clock change amount K _d from K _(C-CS) -Ke, when the image writing timing setting value K _gC of cyan C for black Bk (The initial value may be used for K _gC = M · t _c) , K ′ _gc = K _gC −K _d are obtained, and the newly calculated K ′ _gc is replaced with K _gC , thereby correcting the image shift amount and the shift direction in the next image formation. If K _(C-CS) ≧ 0, the cyan measurement pattern image 28C is formed at a position earlier than the preset position with respect to the reference black measurement pattern image 28Bk. Therefore, it is necessary to change (delay) the image writing timing of cyan C with respect to black Bk so as to fall within the deviation allowable value. Therefore | K _(C-CS) | seeking clock change amount K _d from _{-Ke, K 'gc = K gC} + K d with the new timing setting value K' may be changed to _gc. By a series of these arithmetic processing, the shift amount falls within the allowable value e at the maximum at the next image output. The same applies to the other corrections for M and Y. As described above, in the present embodiment, an example in which C, M, and Y 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 that can detect 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. According to the present invention, as described above, the deviation calculated by the calculating means is compared with a preset allowable value.
Only when the deviation is larger than the absolute value of the allowable value.
It has been configured to adjust the image writing timing of the image forming means. Therefore , a shift amount occurs in the measurement pattern image.
It is not necessary to adjust the image writing timing every time the image writing is started, so that the control system such as the image writing timing circuit is stable, malfunction does not occur, and the shift amount can be surely adjusted only when the shift amount needs to be adjusted. Accordingly, an image forming apparatus having excellent operation reliability can be provided. Further, in 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. According to a second aspect of the present invention, the recording medium comprises a recording sheet and an endless conveying means for sequentially conveying the recording sheet to the image forming means, and the pattern image for measurement is formed on the endless conveying means. The following advantages can be obtained. [0037] When the measurement pattern images of each color are formed on the recording sheet, they become obstructive on the recording sheet. Only the originally desired color image is formed. Also on the endless transport means
The measuring pattern image is detected by one detecting means, and
At one location on the endless transport means.
Need to tighten the mounting accuracy of the detection means.
Absent. [0038] In the recording sheet, wrinkles may be formed on the conveyance path from the formation of the measurement pattern image to its detection, but the endless conveyance means does not cause wrinkles, so the measurement pattern image is properly formed. The deviation amount can be accurately grasped. [0039] 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. [0040] In the case of transfer paper, since the paper quality and ground color vary depending on the type of transfer paper used, the formation of the measurement pattern image and its detection may not be performed properly. Since the apparatus has one endless conveyance means, the reproducibility is excellent without the aforementioned problems. As described in claim 4, if the measurement pattern images for each color are formed at intervals along the transport direction of the endless transport means, the shift amount of the recording sheet in the transport direction, that is, The shift amount in the sub-scanning direction can be easily corrected. If the pattern image for measurement is a linear pattern that intersects with the transport direction of the endless transport means, the pattern is clearly transmitted to the detection means when the pattern passes below the detection means. A peak appears and the pattern is detected reliably.

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 illustrating a relative positional shift state of an image on a transfer sheet. FIG. 7 is a control block diagram of the digital color copying machine. FIG. 8 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 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

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁶ , DB name) G03G 13/01 G03G 15/01 G03G 21/00 370-502 G03G 21/16

Claims (1)

(57) [Claims] A plurality of image forming means for forming an image of each color, each color image to be imaged by the plurality of image forming means 1
An image forming apparatus for forming an image by superimposing images on one recording medium , comprising: conveying means for conveying the recording medium by the plurality of image forming means.
The measurement pattern images of each color sequentially formed on the
And one detection means for detecting at one place on the feed means, the detection by said detection means, one measurement pattern image and other color measurement pattern image as a reference of the measurement pattern image of each color comparing means for comparing the measuring means for measuring the interval, and calculating means for calculating a shift amount in the measurement pattern image based on the measurement of the measuring means, and a preset allowable value and the amount of deviation between, As a result of the comparison by the comparing means, the absolute value of the deviation
An image forming apparatus, comprising: an adjusting unit that adjusts an image writing timing of the image forming unit based on the shift amount when the value is larger than an allowable value . 2. 2. The carrier according to claim 1, wherein
Stage is an endless conveying means for sequentially conveying the recording medium to the plurality of image forming means, and characterized in that the measurement pattern image of each color is configured to be formed on endless conveying means Image forming apparatus. 3. 2. The image forming apparatus according to claim 1, wherein a shift direction of the measurement pattern image is also calculated by the calculation unit, and an image writing timing of the image forming unit is adjusted based on the shift amount and the shift direction. An image forming apparatus comprising: 4. 2. The image forming apparatus according to claim 1, wherein the measurement pattern images for each of the colors are formed at intervals along a conveyance direction of a recording medium. 5. Claim 1 or Claim 4
9. The image forming apparatus according to claim 1, wherein the measurement pattern image is a linear pattern that intersects a recording medium conveyance direction. 6 . 2. An image forming apparatus according to claim 1, wherein said image forming apparatus is a digital color copying machine.