JP2764811B2 - Image forming device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus having a plurality of photoconductors, such as a digital color copying machine.

[Conventional technology]

In an image forming apparatus that forms a color image using a plurality of photoconductors, the causes of the positional deviation in the transfer paper feed direction (longitudinal registration) include each photoconductor mounting position and peripheral speed, the exposure position on the photoconductor, the transfer belt. There was a linear speed, etc., and it was configured to guarantee each with component accuracy and assembly accuracy.However, component costs and assembly costs increased,
Re-adjustment is required due to variations due to component replacement.

As a method for solving this problem, a method has been proposed in which a transfer sheet is detected by a sensor provided in front of each transfer position to obtain a write timing for each color (Japanese Patent Laid-Open No. 155870/1984).

Also, a device for forming a measurement pattern on each photosensitive member in a plurality of divided regions in the main scanning direction and simultaneously detecting the measurement pattern with a plurality of detection means to detect a positional shift amount (Japanese Patent Application Laid-Open No. Sho 62-242969).
Has also been proposed.

Further, from the same applicant as the present invention, a technique of forming an image on a transfer belt by shifting the pattern of each photoconductor and measuring a time difference between the patterns with a single sensor (Japanese Patent Application Laid-Open No. 63-73277,8)
Has also been proposed.

[Problems to be solved by the invention]

However, in the technology disclosed in Japanese Patent Application Laid-Open No. 59-155870, the displacement limit of the color image (about 0.15 mm) is guaranteed because of the variation in the sensor mounting position and the variation in the detection position of each sensor. Was difficult.

In JP-A-62-242969, there is a problem that the degree of alignment of a plurality of detection means affects detection accuracy, and furthermore, the use of a plurality of expensive detection elements such as CCDs increases the cost. There were drawbacks.

Also, in Japanese Patent Application Laid-Open No. 63-73277,8, there is room for improvement in that the displacement due to distance unevenness is detected because the positional displacement is detected by replacing it with a time difference.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned disadvantages of the prior art and to provide a simple configuration in an image forming apparatus that obtains one image by superimposing a plurality of images on a transfer sheet fed by a conveyor belt. An object of the present invention is to provide an image forming apparatus capable of reducing a shift of each image in a transfer paper transport direction.

[Means for solving the problem]

For this purpose, the present invention provides a photoconductor, a charging unit for uniformly charging the surface of the photoconductor, an exposure unit for projecting image light corresponding to recorded information onto the photoconductor, and an electrostatic latent image on the photoconductor. A plurality of recording apparatuses having a developing unit for developing the image and a transfer unit for transferring a visible image of the photoreceptor to the transfer paper are arranged, and the transfer paper is sequentially conveyed to each of the recording devices by the transfer belt to transfer the image in an overlapping manner. In an image recording apparatus, a pattern image signal generating means for forming a pattern image for measurement for each recording apparatus on a transfer belt, and a plurality of patterns formed between the patterns formed by the pattern image signal generating means. Measuring means for measuring the intervals of each pattern, comparison calculating means for comparing each measured value in each of the intervals by the measuring means, and calculating the amount of deviation of each pattern, and setting according to the output value from the comparing and calculating means Changeable Characterized in that a control unit of each image information generating timing.

[Action]

According to the present invention, a measurement pattern image for each recording device is formed on the transfer belt, and the width of the boundary between the two pattern images is measured from the width of the rectangular wave output of one sensor. It is determined whether or not it is appropriate, that is, whether or not there is a deviation.

〔Example〕

Hereinafter, the configuration and operation of the present invention will be described in detail based on an embodiment shown in the drawings.

First, FIG. 2 is a schematic diagram of a digital color image forming apparatus to which the present invention is applied.

FIG. 2 shows a color copying machine as an example of the image recording apparatus. The copier is a scanner 1 for reading originals.
An image processing unit 2 for electrically processing an image signal output as a digital signal from the scanner 1, and an image processing unit 2
And a printer 3 for forming an image on copy paper based on the image recording information of each color. The scanner 1 has a lamp 5 for scanning and illuminating the original on the original placing table 4, for example, a fluorescent lamp. The reflected light from the original when illuminated by the fluorescent lamp 5 is reflected by the mirrors 6, 7, 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, such as a red light, for each wavelength light. CCD11R, Green CCD
Light is incident on the CCD 11B for 11G and blue. CCD11R, 11G, 11B
Converts the incident light into a digital signal and outputs the digital signal. The output is subjected to necessary processing in the image processing unit 2 to record color information of each color, for example, black (hereinafter abbreviated as Bk) and yellow (abbreviated as Y). ), Magenta (abbreviated as M), cyan (C
(Abbreviated as) for each color.

FIG. 2 shows an example in which four colors of Bk, Y, M and C are formed.
A color image can be formed using only 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 3,
The laser beams are sent to the laser beam emitting devices 12Bk, 12C, 12M, and 12Y of the respective colors.

In the example of the figure, the printer 3 has four recording devices 13Y, 13M,
13C and 13Bk are arranged side by side. Since the recording devices 13 are made of the same components, the recording device for C will be described for simplicity of description, and other colors will be omitted. In addition, 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 has a photoconductor 14 outside the laser beam emitting device 12C.
C, for example, having a photosensitive drum.

The photoconductor 14C includes a charging charger 15C, an exposure position by the laser beam emitting device 12C, a developing device 16C, and a transfer charging device 17C.
C and the like are provided similarly to a known copying apparatus.

Photoconductor 14C uniformly charged by charging charger 15C
Forms a latent image of a cyan light image by exposure with a laser beam emitting device 12C, and develops the latent image with 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 at the same timing by the registration rollers 20 with the leading ends thereof aligned. The transfer paper conveyed by the transfer belt 21 is a photosensitive member 14Bk, 14
The images are sequentially sent to C, 14M, and 14Y, and a visual image is transferred under the action of the transfer charger 17. The transferred paper is transferred to the fixing roller 22.
And is discharged by the discharge roller 23.

The transfer paper can be accurately conveyed at the speed of the transfer belt by being electrostatically attracted to the transfer belt 21.

FIG. 3 is a front view of the transfer belt unit. Transfer belt 21
Is supported by the belt drive roller 24 and the driven roller 25, and A
To transfer the transfer paper. Further, the toner adhering to the belt is removed by the cleaning unit 26. A reflection type sensor 27 is provided on the downstream side of the photoconductor 14 in the belt moving direction as a pattern image detecting unit.

The detecting means is provided in the driving roller portion of the transfer belt to prevent the influence of the transfer belt from fluttering, and to always keep the distance between the transfer belt and the transfer belt constant.

 FIG. 1 is a system block diagram according to the embodiment.

The system controller 30 controls each module of the scanner 1, the image processing unit 2, and the printer 3. The control contents include display control of the operation panel 31 and key input processing, transmission of a start signal to the scanner 1 and the printer 3, transmission of a scaling ratio designation signal, and image processing unit 2 according to the mode set on the operation panel 31. Sends image processing mode designating signals (color conversion, masking, trimming, mirroring, etc.) to the system, and controls the entire system using abnormal signals from each module and operating status signals (Wait, Ready, Busy, Stop, etc.) Do.

The scanner 1 scans the original at a scanning speed that matches the scaling factor specified by the start signal from the system controller 30, reads the original image with a reading element such as a CCD,
Image processing is performed in synchronism with S-LSYNC (horizontal synchronization signal), S-STROBE (image clock), and FGATE (vertical synchronization signal) from the image processing unit 2 as 8-bit image data for each of R, G, and B. Send to Part 2.

The image processing unit 2 performs image processing such as γ correction, UCR (under color removal), and color correction on the 8-bit R, G, and B image data sent from the scanner 1, and performs Y, M, C, and Bk image processing. The image data is converted into 3-bit image data and sent to the printer 3. Further, in accordance with a command from the system controller 30, editing processing such as scaling processing, masking, trimming, color conversion, and mirroring is performed.

Further, a buffer memory for outputting the image data of Y, M, C, and Bk shifted by the photosensitive drum interval of the printer 3 is provided.

The printer 3 outputs a laser beam in accordance with image data of Y, M, C, and Bk each transmitted from the image processing unit 2 in synchronization with P-LSYNC (horizontal synchronization signal) and P-STROBE (image clock). The light emitting device is modulated, and a copy image is obtained on transfer paper by an electrophotographic process.

 FIG. 4 shows an example of the detection pattern of the present invention.

In each recording device, the pattern images visualized by the signal from the pattern image signal generating means outside the transfer paper area are respectively transferred to the transfer belt 21, and each of the images is a (as shown in FIG. 4). mm). The pattern images 28Bk, C, M, and Y sequentially pass through the sensor 27 according to the movement of the belt, and are detected by the sensor 27. The image interval a is a numerical value that can be arbitrarily selected by setting the exposure timing for each recording device in advance.

In the color copying machine shown in FIG.
It is necessary to shift the transmission of the image data of each color from the photosensitive drums of the respective colors by the distance.

FIG. 5 is a block diagram showing a configuration of a buffer memory for that purpose and a configuration of a pattern image signal generating means.

FIG. 6 is a timing chart showing the operation of the block diagram of FIG. 5 (the timing chart of waveforms indicated by 〜).

In the color copying machine of the present embodiment, since the recording devices are arranged in the order of Bk, C, M, and Y, the image data of Bk is output as it is after being processed by the image processing unit 2, and C, M,
Y image data is different from Bk image data
The output is delayed by t _DC , t _DM , and t _DY .

FIG. 7 is an explanatory diagram for setting the delay times t _DC , t _DM , and t _DY of the image data.

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 (mm / sec)
Duration t ₁ to the transfer from the exposure when the respective photosensitive body with the same value _{t 1 = l 1 / v 1} (sec) Time to move between each photoconductor and _{t 2, t 2 = l 2} / v 2 (Sec) That is, in order to form each color image at the same position on the transfer paper, t _DC = l ₂ / v ₂ (sec) t _DM = 2l ₂ / v ₂ (sec) t _DY = 3l ₂ / v ₂ (sec).

As shown in FIG. 5, the circuit configurations of C, M, and Y are the same, so that Bk and C will be described.

The rise of the vertical synchronizing signal FGATE sent from the scanner 1 is detected by the rise detection circuit 40. Since each input of Bk, C, M, and Y and FGATE are input at the same time, the output of the rise detection circuit 40 is a signal indicating the start of image writing of Bk. The output of the rise detection circuit 40 is input to the Bk pattern signal generation means 41, and outputs a detection pattern. That is, in the case of Bk, the tip of the image and the pattern
It becomes the same for the 21 moving directions (FIG. 4).

The output of the rise detection circuit 40 is input to the reset terminal of the address counter C42a via the OR gate, and resets the address counter C42a. According to the count value of the address counter C42a, the input image data of C is stored in a buffer memory C43a.

On the other hand, the output of the address counter: C42a is compared by the comparator: C44a with the set value of the address setter: C45a, and when the output of the address counter: C42a matches the set value of the address setter: C45a, the comparator: C44a Outputs a match signal.
This match signal is output to the buffer memory: reset terminal of C43a.
Input via R gate, address counter: C4
The output of 2a is reset to "0" and the buffer memory: C
Access the address 0 of 43a. After reading the already stored image data, the buffer memory C43a writes the newly input image data at the same address.

Here, if the set value of the address setting device: C45a is set to the drum interval (t _DC ) between Bk and C, Bk and C on the transfer paper are set.
Images can be formed by aligning the images.

The coincidence signal of the comparator: C44a is also input to the delay device: C46a, which triggers the delay device: C46a, and outputs a detection pattern by the pattern signal generation means: C47a after a fixed time from the coincidence signal of the comparator: C44a. .

Since the coincidence signal of the comparator C44a is output at the same time as the leading edge of the image of C, the detection pattern of C is output from the leading edge of the image with a delay of the delay time (t _pc ) by the delay device C46a.

Here, the delay time of the delay device: C46a is a (mm)
If the time required for the movement is set, a C detection pattern can be created with a delay of a (mm) from the leading end of the image as shown in FIG.

The same applies to M and Y. Address setter: Set value of M45b = t _DM Address setter: Set value of Y45c = t _DY delay device: Set time of M46b = t _PM = 2a / v ₂ delay device: Y46c If the setting time = t _PY = 3a / v ₂ , the leading edge of the image can be made coincident with each color, and at the same time, the detection pattern can be output with a (mm) pitch as shown in FIG.

Here, when the image positions of Bk, C, M, and Y are shifted on the transfer paper due to the variation in the position of each photosensitive member, the variation in the exposure position with respect to the photosensitive member, and the variation in the linear speed of the photosensitive member and the transfer belt, it is detected. The pattern for use also shifts accordingly, and by measuring the interval between the detection patterns, the amount of positional shift of the image can be detected.

FIG. 8 shows an embodiment of the pattern detection circuit according to the present invention.

In the figure, the output current of the phototransistor Ph of the reflection type sensor 27 is converted into a voltage by the resistor R2 (the waveform of the portion is shown in FIG. 9 (a)), and the DC component is cut by the capacitor C2 and only the AC component is taken out. [Partial waveforms are shown in FIG. 9 (b)]. This signal is a voltage follower AM
It becomes an input to the inverting amplifier AMP2 via P1 and is amplified to an appropriate voltage level (partial waveform is shown in FIG. 9 (c)). The output of AMP2 is connected to resistors R8 and R by comparator COMP1.
Compared with the threshold voltage _VTH determined by 9, a rectangular wave output is obtained (the waveform of the portion is shown in FIG. 9 (d)).

By measuring the width of this rectangular wave output (white line width), the interval (white line width) between the detection patterns 28Bk, 28C, 28M, and 28Y transferred to the transfer belt 21 can be known.

FIG. 10 is a configuration diagram of the reflection type sensor 27. As shown in the figure, the sensor 27 can detect a state in a range of 3 to 4 mm on the transfer belt 21. Therefore, as shown in FIGS. 11 (a) and 11 (b), at the boundary between the two patterns 28Bk and 28C, the interval changes depending on the amount of displacement, and the reflected light from the white background changes.

FIGS. 12 (a) and 12 (b) show detected waveforms corresponding to FIGS. 11 (a) and 11 (b). In FIG. 11, A is the sensor 27.
Shows the detection range.

13 and 14 show another embodiment. The pattern on the belt 21 is formed, for example, in the order of black, blue, black, (28Bk, 28C, 28Bk) as shown in FIG. One sensor 27
, A waveform as shown in FIG. 14 is obtained. In this case, since the two waveforms have different sizes, the blue (C pattern 28C) is formed slightly later than the black (Bk pattern 28Bk) (that is, the positions of Bk and C do not coincide). I understand. Therefore, the timing for forming blue (C pattern 28C) may be advanced until the two waveforms have the same magnitude.

Thus, in this method, the width (or height) of two waveforms is compared, rather than comparing the width of the waveform with a reference.

The above description has been made with reference to the apparatus shown in FIG. 2 in which four sets of recording apparatuses are arranged. Of course, the image forming apparatus shown in FIG. The present invention is also applicable to the case of the image forming apparatus shown in FIG.

In FIG. 15, reference numeral 50 denotes a paper feed cassette, 51 denotes a photosensitive drum, 52 denotes a charging charger, 53 denotes an optical system, 54 denotes a Y, M, C developing device, 55 denotes a transfer drum, 56 denotes a transport belt, and 57 denotes a transfer belt. Is a fixing device, and 58 is a paper discharge tray.

The present invention is applicable not only to a color image forming apparatus but also to a case where a plurality of images are formed by a recording apparatus of the same color. For example, there is a case where a plurality of originals are read separately by a scanner using the apparatus shown in FIG. 15, and are synthesized on the same recording paper or an image stored in an image memory is synthesized.

Further, although a photoreceptor is not used, the present invention can be similarly applied to a color printing machine (a two- to four-color offset machine, rotary press) having the same configuration.

In the present invention, the measuring means is the system controller 30.
Has that function.

〔The invention's effect〕

As described above, according to the present invention, a plurality of intervals formed between the respective patterns are measured by the measuring means, and the respective measured values at the respective intervals are compared by the comparing and calculating means. Since the amount is calculated and each image information generation timing is changed so that each measured value at each interval becomes the same, there is no need for a plurality of sensors and there is no need to set a set value for the measured value. As a result, spatially high-accuracy positional deviation detection with a small time error can be performed.

[Brief description of the drawings]

FIG. 1 is a system block diagram according to an embodiment of the present invention.
FIG. 2 is a schematic view of a digital color image forming apparatus to which the present invention is applied, FIG. 3 is a front view of a transfer belt portion, FIG. 4 is a view showing an example of a detection pattern, and FIG. FIG. 6 is a timing chart of each part of the circuit, FIG. 7 is an explanatory diagram for setting a delay time of image data, and FIG. 8 is an embodiment of a pattern detection circuit according to the present invention. Figures 9 (a), (b), (c),
(D) is a waveform diagram of each part in FIG. 8, FIG. 10 is a configuration diagram of the sensor, and FIGS. 11 (a) and (b) show how a boundary between two patterns according to the first embodiment is detected. Fig. 12 (a),
(B) is a detection waveform diagram, FIG. 13 is a diagram showing a state of detecting a boundary of a pattern according to the second embodiment, FIG. 14 is a detection waveform diagram thereof, FIG. 15 and FIG. FIG. 10 is a configuration diagram illustrating another image forming apparatus to which the image forming apparatus is applied. 27 ... Detection means, 28Bk, 28C, 28M, 28Y ... Measurement pattern image, 41,47 ... Pattern image signal generation means, 30 ...
System controller, 60... Comparison operation means, 21... Transfer belt.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI H04N 1/46 H04N 1/12 Z

Claims (1)

(57) [Claims] A photoconductor, a charging unit for uniformly charging the surface of the photoconductor, an exposure unit for projecting image light corresponding to recorded information onto the photoconductor, and a developing unit for developing an electrostatic latent image on the photoconductor. Means,
An image recording apparatus in which a plurality of recording devices having transfer means for transferring a visible image of a photoreceptor onto transfer paper are arranged, and the transfer paper is sequentially conveyed to each of the recording devices by a transfer belt and the image is overlaid and transferred, wherein a transfer belt is provided. A pattern image signal generating means for forming a pattern image for measurement for each recording device above, and a measurement for measuring a plurality of intervals formed between the respective patterns formed by the pattern image signal generating means. Means for comparing each measurement value in each of the intervals by the measurement means, and calculating a shift amount of each pattern; and generating each image information which can be changed in accordance with an output value from the comparison operation means. An image forming apparatus comprising: timing control means.