JP2004098593A - Image forming apparatus and registration correction method thereof - Google Patents

Abstract

An object of the present invention is to reduce a difference in scanning position between a plurality of beams scanning on an image carrier or to eliminate a difference in scanning line length (writing width) of each beam on the image carrier during one scan. An image forming apparatus capable of correctly forming a registration correction pattern and performing accurate registration correction.
An image forming apparatus detects a difference in scan length of each laser on a surface to be scanned during one scan between lasers by using a main scan scan length detection pattern, and generates a CLK generation circuit (804a, 804b). Is set to a predetermined frequency to correct the scanning length difference. Then, after correcting the difference in the scanning line length in each laser, registration correction is performed.
[Selection diagram] FIG.

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus using a multi-beam scanning optical system that scans an image carrier with beams respectively emitted from a plurality of light sources, and a registration correction method therefor.
[0002]
[Prior art]
Conventionally, as a device used as an optical writing means of an image forming apparatus such as a laser copying machine, a laser facsimile, a laser printer, etc., a laser beam from a laser light source is condensed as a light spot on a scanned surface such as a photoconductor. There is known a scanning optical system that performs optical scanning. In recent years, in order to increase the writing speed, a multi-beam scanning optical system that uses a plurality of laser beams to scan a plurality of lines in one scan has been realized. A color image is formed by multiple transfer of a visible image formed by each image forming unit onto a transfer material on a belt-shaped transfer material transporter or onto an intermediate transfer member. A multicolor image forming apparatus has been realized.
[0003]
[Problems to be solved by the invention]
Such a scanning optical system irradiates a rotary polygon mirror (polygon mirror) with a laser beam and exposes and scans the photosensitive member with the reflected light. Here, it is desirable to use a photoreceptor having a shape equidistant from the laser light source, that is, a shape drawing an arc from the reflection surface of the polygon mirror. However, for image formation after exposure, many image forming apparatuses employ a cylindrical photoconductor. The exposure speed on the photoconductor is not uniform due to the mismatch of the optical path length from the laser light source to the surface of the photoconductor due to the shape of the photoconductor. As a means for solving this, a complicated optical means called an f-θ lens is provided, and the f-θ lens is processed so as to make the exposure speed on the photosensitive member uniform.
[0004]
Further, in a multi-laser in which a plurality of laser light sources are arranged in the sub-scanning direction and the photoconductor is exposed with laser light from each laser light source, the exposure length between each laser light source and the photoconductor arranged in the sub-scanning direction is made equal. There is a need. However, in addition to optical and mechanical errors, the length of the scanning line (writing width) on the surface of the photoreceptor is changed due to a change in the optical system due to a rise in temperature or a change in the wavelength of the laser. If there is a difference in the writing width between the laser beams, there is a problem that, particularly, vertical line fluctuation occurs, which can significantly affect image degradation.
[0005]
FIG. 14 shows a state in which an image is formed when the scanning line length is different between the multi-lasers (in the case of two laser light sources). FIG. 14A shows the case where the scanning line length is the same. The dots formed by the two lasers (LD1 and LD2) are aligned on both the writing start side and the writing end side in the main scanning. FIG. 14B shows a case where the scanning line length of the LD2 is longer than the scanning line length of the LD1, and a dot shift occurs on both the writing start side and the writing end side in the main scanning.
[0006]
In such a multicolor image forming apparatus, a registration correction pattern is formed on a transfer material transporting body or an intermediate transfer body in order to match the registration of each color, and the pattern is read by a photo sensor, and the registration of each color is performed. The deviation of the optical path is detected, the image signal to be recorded is electrically corrected, and / or the folding mirror provided in the laser beam path is driven to correct the optical path length change or the optical path change.
[0007]
FIGS. 14C and 14D show examples of registration correction patterns. FIG. 14C shows the case where the scanning line length is the same, and FIG. 14D shows the case where the scanning line length is different. If there is a difference in the scanning length between a plurality of lasers, a pattern that should originally be as shown in FIG. 14C becomes a "rattle" line as shown in FIG. , It becomes impossible to accurately detect the registration deviation.
[0008]
SUMMARY OF THE INVENTION It is an object of the present invention to reduce the difference in scanning position between a plurality of beams that scan on an image carrier or to reduce the difference in the scanning line length (writing width) of each beam on the image carrier during one scan. An object of the present invention is to provide an image forming apparatus capable of correctly forming a registration correction pattern and performing accurate registration correction, and a registration correction method therefor.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention includes a plurality of image forming process units for executing image forming processes of different colors, wherein the plurality of image forming process units include beams respectively emitted from a plurality of light sources. An image forming apparatus comprising: a multi-beam scanning optical system for exposing and scanning a corresponding line on an image carrier; and a frequency variable clock generating means for generating a frequency variable clock for modulation driving for each light source. A correcting pattern forming means for forming a plurality of correcting patterns for detecting a scanning length in a main scanning direction on the image carrier through the multi-beam scanning optical system for each of the image forming process means; A correction pattern reading unit that reads the plurality of correction patterns, and a correction pattern reading unit that reads the plurality of correction patterns based on a result read by the correction pattern reading unit. Scanning length correction means for correcting the frequency of the frequency variable clock generated for each light source from the frequency variable clock generation means, and each color formed by the plurality of image forming process means after correcting the frequency of the frequency variable clock And a registration correction unit for performing registration correction for correcting the image shift.
[0010]
The plurality of image forming process means may include, as the image carrier, a first image carrier on which the electrostatic latent image is formed and an electrostatic latent image formed on the first image carrier. A second image bearing member to be used.
[0011]
The plurality of image forming process means may include, as the image carrier, a first image carrier on which the electrostatic latent image is formed and an electrostatic latent image formed on the first image carrier. And a second image carrier that carries and conveys the transfer material to be transferred.
[0012]
Further, when the number of beams emitted from the plurality of light sources is n, the driving speed of the first and second image carriers is set to 1 / n of that in normal image formation. .
[0013]
Further, the second carrier is formed of an endless belt.
[0014]
Further, the correction pattern reading means includes a light emitting element and a light receiving element for reading the correction pattern at a predetermined position.
[0015]
Further, in order to achieve the above object, the present invention includes a plurality of image forming process units for executing image forming processes of different colors, wherein the plurality of image forming process units are respectively emitted from a plurality of light sources. Image forming apparatus having a multi-beam scanning optical system for exposing and scanning a corresponding line on an image carrier with a beam, and a frequency variable clock generating means for generating a frequency variable clock for modulation driving for each light source A scanning start position detecting unit for detecting a scanning start position of a beam emitted from each of the plurality of light sources for each of the image forming process units; and a light emitting unit for emitting light from each of the plurality of light sources for each of the image forming process units. Scanning end position detecting means for detecting the scanning end position of the scanned beam, the detection result of the scanning start position detecting means, and the scanning end position. Scanning length correction means for correcting the frequency of the frequency variable clock generated for each light source from the frequency variable clock generation means based on the detection result of the position detection means, and after correcting the frequency of the frequency variable clock, And a registration correction unit for performing registration correction for correcting a shift of an image of each color formed by the image forming process unit.
[0016]
The plurality of image forming process means may include, as the image carrier, a first image carrier on which the electrostatic latent image is formed and an electrostatic latent image formed on the first image carrier. A second image bearing member to be used.
[0017]
The plurality of image forming process means may include, as the image carrier, a first image carrier on which the electrostatic latent image is formed and an electrostatic latent image formed on the first image carrier. And a second image carrier that carries and conveys the transfer material to be transferred.
[0018]
Further, when the number of beams emitted from the plurality of light sources is n, the driving speed of the first and second image carriers is set to 1 / n of that in normal image formation. .
[0019]
Further, the second carrier is formed of an endless belt.
[0020]
Further, in order to achieve the above object, the present invention includes a plurality of image forming process units for executing image forming processes of different colors, wherein the plurality of image forming process units are respectively emitted from a plurality of light sources. Image forming apparatus having a multi-beam scanning optical system for exposing and scanning a corresponding line on an image carrier with a beam, and a frequency variable clock generating means for generating a frequency variable clock for modulation driving for each light source A registration correction method, wherein a plurality of correction patterns for detecting a scanning length in a main scanning direction are formed on the image carrier through the multi-beam scanning optical system for each of the image forming process means. Forming a correction pattern, performing a correction pattern reading step for reading the plurality of correction patterns, and A scanning length correcting step of correcting a frequency of a frequency variable clock generated for each light source from the frequency variable clock generating means based on a result read by the frequency variable clock generating means, and after correcting the frequency of the frequency variable clock, the plurality of images. A registration correction step of performing a registration correction for correcting a shift of an image of each color formed by the forming process means.
[0021]
Further, in order to achieve the above object, the present invention includes a plurality of image forming process units for executing image forming processes of different colors, wherein the plurality of image forming process units are respectively emitted from a plurality of light sources. Image forming apparatus having a multi-beam scanning optical system for exposing and scanning a corresponding line on an image carrier with a beam, and a frequency variable clock generating means for generating a frequency variable clock for modulation driving for each light source A registration correction method, wherein a scanning start position detecting step of detecting a scanning start position of a beam emitted from each of the plurality of light sources for each of the image forming process means, A scanning end position detecting step of detecting a scanning end position of each of the beams emitted from the light sources; A scanning length correction step of correcting a frequency of a frequency variable clock generated for each light source from the frequency variable clock generation means based on a detection result of the step and a detection result of the scanning end position detection step; and And a registration correction step of performing a registration correction for correcting a shift of an image of each color formed by the plurality of image forming process units after the frequency correction.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0023]
(1st Embodiment)
FIG. 1 is a longitudinal sectional view showing a main part of the image forming apparatus according to the first embodiment of the present invention. In this embodiment, a color image forming apparatus employing an electrophotographic method, a plurality of image forming units arranged in parallel, and employing an intermediate transfer method will be described.
[0024]
The color image forming apparatus includes an image reading unit 100 and an image output unit 101 as shown in FIG. The image reading unit 100 optically reads a document image, converts the read image into an electric signal, and sends the signal to the image output unit 101. The configuration of the image reading unit 100 is known, and a detailed description thereof will be omitted. The image output unit 101 includes an image forming unit 10, a paper feed unit 20, an intermediate transfer unit 30, a fixing unit 40, a cleaning unit 50, and a control unit 70.
[0025]
The image forming unit 10 includes four stations a, b, c, and d having the same configuration. In the image forming unit 10, photosensitive drums 11a, 11b, 11c, and 11d as image carriers are pivotally supported at the centers thereof, and are driven to rotate in the direction of arrows. Primary chargers 12a, 12b, 12c, 12d, optical systems 13a, 13b, 13c, 13d, optical systems 13a, 13b, 13c, 13d, folding mirrors 16a, 16b, 16c, 16d, developing devices 14a, 14b, 14c and 14d are arranged. The primary chargers 12a to 12d apply charges of a uniform charge amount to the surfaces of the photosensitive drums 11a to 11d. The optical systems 13a to 13d expose and scan the photosensitive drums 11a to 11d with the laser light modulated according to the recording image signal via the return mirrors 16a to 16d. Thereby, an electrostatic latent image is formed on the photosensitive drums 11a to 11d. The electrostatic latent image formed on each of the photosensitive drums 11a to 11d is visualized as a toner image by a developer (hereinafter, referred to as toner) of a corresponding color (yellow, cyan, magenta, black). Here, the toner of each color is stored in the developing devices 14a to 14d.
[0026]
On the downstream side of the image transfer areas Ta, Tb, Tc, and Td for transferring the visualized toner image to the intermediate transfer belt 31, the toner images are not transferred to the transfer material P by the cleaning devices 15a, 15b, 15c, and 15d. The toner remaining on the photosensitive drums 11a to 11d is scraped off to clean the drum surface. According to the process described above, image formation using each toner is sequentially performed.
[0027]
The paper supply unit 20 includes cassettes 21a and 21b and a manual tray 27 for storing the transfer material P, and pickup rollers 22a, 22b and 26 for feeding the transfer material P one by one from the cassettes 21a and 21 or the manual tray 27. A pair of paper feed rollers 23 and a paper feed guide 24 for transporting the transfer material P sent from each of the pickup rollers 22a, 22b and 26 to the registration rollers 25a and 25b. The registration rollers 25a and 25b The transfer material P is sent to the secondary transfer area Te in accordance with the image forming timing of the unit 10.
[0028]
The intermediate transfer unit 30 includes an intermediate transfer belt 31. The intermediate transfer belt 31 sandwiches the driving roller 32 that transmits drive to the intermediate transfer belt 31, a driven roller 33 that is driven by the rotation of the intermediate transfer belt 31, and a belt. , And is wound around the secondary transfer facing roller 34 facing the secondary transfer area Te. Among these rollers, a primary transfer plane A is formed between the driving roller 32 and the driven roller 33. The driving roller 32 is a metal roller having a surface coated with a rubber (urethane or chloroprene) having a thickness of several mm. The rubber coating prevents the intermediate transfer belt 31 from slipping. The drive roller 32 is driven to rotate by a pulse motor (not shown). Primary transfer chargers 35a to 35d are arranged in primary transfer areas Ta to Td where the respective photosensitive drums 11a to 11d face the intermediate transfer belt 31, and the primary transfer chargers 35a to 35d are located on the back side of the intermediate transfer belt 31. Is positioned at A secondary transfer roller 36 is disposed at a position facing the secondary transfer facing roller 34, and a nip between the secondary transfer roller 36 and the intermediate transfer belt 31 forms a secondary transfer area Te. The secondary transfer roller 36 is pressed with an appropriate pressure on the intermediate transfer member. Further, on the intermediate transfer belt 31 and downstream of the secondary transfer area Te, a cleaning unit 50 (a blade 51 and a waste toner box 52 for storing waste toner, including a blade 51) for cleaning the image forming surface of the intermediate transfer belt 31 is included. ) Is provided.
[0029]
The fixing unit 40 includes a fixing roller 41a having a heat source such as a halogen heater therein, a pressing roller 41b pressed against the fixing roller 41a (the roller may also have a heat source), and a fixing roller 41a. A guide 43 for guiding the transfer material P to a nip portion between the pressure roller 41b and the fixing heat insulating covers 46 and 47 for confining the heat of the fixing unit 40, the fixing roller 41a, and the pressure roller 41b. It comprises an inner discharge roller 44, an outer discharge roller 45 for further guiding the transfer material P to the outside of the apparatus, a discharge tray 48 on which the transfer material P is stacked, and the like.
[0030]
The control unit 70 includes a CPU (not shown) for controlling a mechanism in each unit, a motor drive board (not shown), and the like.
[0031]
Next, the operation of the apparatus will be described.
[0032]
When the image forming operation start signal is issued, first, the transfer material P is sent out one by one from the cassette 21a by the pickup roller 22a. Then, the transfer material P is guided between the paper feed guides 24 by the paper feed roller pair 23 and is conveyed to the registration rollers 25a and 25b. At this time, the registration rollers 25a and 25b are stopped, and the leading end of the paper strikes the nip. Thereafter, the registration rollers 25a and 25b start rotating at the timing when the image forming unit 10 starts forming an image. The rotation start timing is a timing at which the transfer material P and the toner image primarily transferred from the image forming unit 10 onto the intermediate transfer belt 31 exactly coincide with each other in the secondary transfer area Te.
[0033]
On the other hand, in the image forming section 10, when the image forming operation start signal is issued, the toner image formed on the most upstream photosensitive drum 11d in the rotation direction of the intermediate transfer belt 31 by the above-described process is changed to a high voltage. The primary transfer is performed on the intermediate transfer belt 31 in the primary transfer area Td by the applied primary transfer charger 35d. The primary-transferred toner image is transported to the next primary transfer area Tc. In this case, image formation is performed with a delay of the time during which the toner image is transported between the image forming sections, and the next toner image is transferred with the registration on the previous image. Hereinafter, the same steps are repeated, and finally, the toner images of four colors are primarily transferred on the intermediate transfer belt 31.
[0034]
Thereafter, when the transfer material P enters the secondary transfer area Te and comes into contact with the intermediate transfer belt 31, a high voltage is applied to the secondary transfer roller 36 in accordance with the passage timing of the transfer material P. Then, the four color toner images formed on the intermediate transfer belt 31 by the above-described process are transferred onto the surface of the transfer material P. Next, the transfer material P is accurately guided to the nip portion of the fixing roller 41a by the transport guide 43, and the toner image is fixed on the surface of the transfer material P by the heat and the nip pressure by the fixing roller 41a and the pressure roller 41b. Then, the transfer material P is conveyed by the inner and outer discharge rollers 44 and 45, discharged outside the apparatus, and stacked on the discharge tray 48.
[0035]
Next, an operation of forming an electrostatic latent image on each of the photosensitive drums 11a to 11d in the image forming unit 10 will be described. In the present embodiment, there are four stations in the image forming unit 10, and these stations have the same configuration. Therefore, one of them will be described here. FIG. 2 is a diagram schematically illustrating one configuration of the stations provided in the image forming unit 10 of the image forming apparatus in FIG.
[0036]
In each station of the image forming unit 10, as shown in FIG. 2, an image signal sent from an external device such as the image reading unit 100 or a computer (not shown) is sent to the image writing timing control circuit 201. The image writing timing control circuit 201 generates a laser lighting signal according to the image signal. This laser lighting signal is sent to the laser drive control circuit 202, and the laser drive control circuit 202 modulates and drives the laser diode 207 according to the laser light signal. In the present embodiment, two laser chips 207a and 207b are arranged at a predetermined interval in the laser diode 207 such that dots are formed at a predetermined pitch in the sub-scanning direction. The laser light emitted from the laser diode 207 is reflected by a polygon mirror 204 driven by a polygon motor 203 to rotate in the direction of the arrow, and the reflected light is subjected to fθ correction by an f-θ lens 205 before being returned to the return mirror 16 (return mirror 16). The light is reflected by the mirrors 16a to 16d) and scans on the photosensitive drum 11 (corresponding to the photosensitive drums 11a to 11d). As a result, an electrostatic latent image corresponding to the image signal is formed on the photosensitive drum 11.
[0037]
A BD sensor 206 is provided in the vicinity of the scanning start position of one line of the laser light, and the output of the BD sensor 206 is a signal when detecting the start of the line scanning of the laser light. It is input to the write timing circuit 201.
[0038]
Next, a registration correction operation between each color required for the image forming apparatus of the multiple transfer system will be described. FIG. 3 is a schematic diagram of the vicinity of photosensors 60 and 61 as pattern image detecting means for detecting a pattern image for registration correction in the image forming apparatus of FIG.
[0039]
As shown in FIG. 3, the intermediate transfer belt 31 is wound around a driving roller 32 and rotates in the direction of arrow B by the driving force transmitted from the driving roller 32. The intermediate transfer belt 31 is made of an elastic material such as rubber or elastomer as a raw material, and its Young's modulus in the circumferential direction is 1 × 10 ⁷ Pa or more. The thickness of the intermediate transfer belt 31 is desirably 0.3 mm to 3 mm from the viewpoint of securing thickness accuracy and strength and realizing flexible rotational driving. Further, the resistance of the intermediate transfer belt 31 can be adjusted to a desired resistance value (volume resistance value of 1 × 10 3) by adding a conductive agent such as metal powder (carbon or the like). ¹¹ Ωcm or less is desirable).
[0040]
Further, photo sensors (pattern image detecting means) 60 and 61 constituted by light emitting and light receiving elements are provided. The photosensors 60 and 61 are located between the drive roller 32 and the photosensitive drum 11a located at the most downstream in the belt advancing direction among the plurality of photosensitive drums 11a to 11d, and the registration formed on the intermediate transfer belt 31. The correction pattern image is configured to be read. The photo sensors 60 and 61 are disposed at both ends of the intermediate transfer belt 31, respectively.
[0041]
Before performing the copy operation, a registration correction pattern image 301 is formed on the intermediate transfer belt 31 at a predetermined timing, and the pattern image 301 is read by the photosensors 60 and 61. Then, based on the read pattern image 301, a registration shift on the photosensitive drums 11a to 11d corresponding to each color is detected, an image signal to be recorded is electrically corrected, and / or a laser beam is The folding mirrors 16a to 16d provided in the optical path are driven to correct the optical path length change or the optical path change.
[0042]
There are various patterns in the registration correction pattern image. For example, a first line segment arranged at a predetermined angle to a process direction B which is a moving direction of the intermediate transfer belt 31 as shown in FIG. 4B and a pattern formed of a second line segment symmetrically arranged with a virtual line perpendicular to the process direction B interposed therebetween, or a process direction B which is a moving direction of the intermediate transfer belt 31 as shown in FIG. And a pattern composed of a second line segment parallel to a direction (main scanning direction) orthogonal to the process direction B and a first line segment arranged with a pattern.
[0043]
Such a pattern image for registration correction is read by photosensors 60 and 61 including light emitting elements such as LEDs and phototransistors, and light receiving elements. The two photosensors 60 and 61 are arranged at a predetermined distance in a direction (main scanning direction) orthogonal to the process direction, and a registration correction pattern image is formed so as to pass over the photosensor. Is done. FIG. 5 is a diagram schematically illustrating the manner in which the photosensors 60 and 61 detect the registration correction pattern 301 on the intermediate transfer belt 31. The intermediate transfer belt 31 is made of a material whose reflectance of light (for example, infrared light) emitted by the LEDs 201 in the photosensors 60 and 61 is larger than that of the pattern image 301. The pattern can be detected based on the difference in reflectance.
[0044]
FIG. 6 is a diagram schematically showing a state in which the phototransistor 202 receives light reflected by the LED 201 from the pattern image 301 or the intermediate transfer belt 31. FIG. 7 shows how the phototransistor 202 receives reflected light. FIG. 8 is a diagram illustrating a light receiving circuit that converts the signal into an electric signal. FIG. 8 is a diagram illustrating a principle of calculating a main scanning magnification using a pattern.
[0045]
As shown in FIG. 7, when the phototransistor 202 detects the reflected light from the intermediate transfer belt 31, a large amount of photocurrent flows through the phototransistor 202 because the amount of the reflected light is large, and current-voltage conversion is performed by the resistor 407. And amplified by the resistors 402 to 404 and the operational amplifier 401. When the phototransistor 202 detects the reflected light from the pattern image 203, a small amount of photocurrent flows through the phototransistor 202 as compared with the reflected light from the intermediate transfer belt 31 because the amount of reflected light from the pattern image 203 is small. Similarly, current-voltage conversion is performed by the resistor 407, and the current is amplified by the resistors 402 to 404 and the operational amplifier 401. FIG. 6A shows a state in which the light receiving circuit detects the reflected light in the order of the intermediate transfer belt 31 → the pattern image 301 → the intermediate transfer belt 31. A threshold level 601 is set by the variable resistor 406 between the intermediate transfer belt detection level and the pattern image detection level. That is, the pattern detection output 602 can be created by comparing the current-voltage converted value with the threshold level 601 by the comparator 405.
[0046]
In this manner, the pattern image detection output 602 is read, and a registration shift is detected from the pattern image interval or the like. Then, an electrical correction is applied to the image signal to be recorded according to the detection result of the registration deviation, and / or the folding mirror 16 provided in the laser beam optical path is driven to change the optical path length or the optical path. The change is corrected.
[0047]
In the present embodiment, correction is performed by detecting the difference in the length (writing width) of the scanning line of each laser on the surface to be scanned during one scanning between lasers using the registration correction pattern image. It is. In the present embodiment, a case where scanning is performed with two laser beams for each photosensitive drum will be described.
[0048]
A method for detecting a difference in scanning line length between beams will be described. First, the transfer belt 31 is driven to rotate, and the main scanning length detection pattern is written by the laser chip 207a, and this is detected by the photo sensors 60 and 61. Subsequently, a main scanning length detection pattern is written by the laser chip 207b, and this is detected by the photo sensors 60 and 61. At this time, the rotational drive speed of the intermediate transfer belt 31 and the photosensitive drum 11 (11a to 11d) is reduced to half of that during normal printing, so that even with writing by one laser, the normal scanning pitch can be maintained without an interval. Become. When n lasers are provided, the same effect can be obtained by setting the rotational drive speed of the intermediate transfer belt 31 and the photosensitive drum 11 to 1 / n of that in normal printing.
[0049]
As a pattern for detecting a shift in the main scanning direction, there is a pattern as shown in FIG. 4A or 4B or the like, which is formed on the near side and the far side in the main scanning direction and detected. Thus, the difference in the scanning length in the main scanning direction can be detected.
[0050]
For example, in the case of forming and detecting the pattern of FIG. 4A, as shown in FIG. 8, assuming that the time from the detection of the first line segment 1001 to the detection of the second line segment 1002 is T1, The distance from the intersection of the one line segment 1001 and the second line segment 1002 to the position where the sensor passes in the main scanning direction is proportional to T1, and the angle between the first line segment 1001 and the second line segment 1002 is 90. If it is degrees, the above distance is a distance corresponding to T1 / 2. If the scan length of the main scan is different, the position where the pattern is formed is different, so that the distance corresponding to T1 / 2 is different.
[0051]
Next, a method of calculating the difference in main scanning line length between laser beams will be described. FIG. 9A shows a pattern image 901 written with the laser chip 207a and read by the photosensors 60 and 61, and FIG. 9B shows a pattern image written with the laser chip 207b and the photosensors 60 and 61. A reading 902 is shown. Here, T1, T2, T3, and T4 in the figure represent the transit time between the lines of the pattern. T1 / 2 is compared with T3 / 2, and the difference between the writing start positions of the laser beams is T2 / 2 and T4 / T4. By comparing the two, the difference between the write end positions of the laser beams can be calculated. That is, (T1-T3) / 2 + (T2-T4) / 2 is the scanning length difference between the laser beams.
[0052]
Next, a method for correcting a difference in scanning line length between laser beams will be described.
[0053]
FIG. 10 is a diagram schematically showing a detailed configuration of the image writing timing control circuit 201 and the laser drive control circuit 202 of FIG.
[0054]
The semiconductor laser 207 includes two laser chips (LD) 207a and 207b and a photodiode (PD) 207c as shown in FIG. Each of the laser chips 207a and 207b is modulated and driven by the laser drive control circuit 202. The laser light from each of the laser chips 207a and 207b is received by the photodiode 207c, and the output of the photodiode 207c is input to the laser drive control circuit 202. The laser drive control circuit 202 has two laser drive current circuits 202a and 202b. Each of the laser drive current circuits 202a and 202b controls the laser drive current of the corresponding laser chip 207a and 207b according to the output of the photodiode 207c. Control.
[0055]
The image writing timing control circuit 201 has FIFOs (First In First Out) 803 a and 803 b composed of line memories. The FIFOs 803 a and 803 b receive an external image signal and output a timing signal from the read timing generation circuit 805. The reading of the image signal is started based on this. Here, the read timing generation circuit 805 generates the timing signal based on the BD signal. In addition, the read clock of each pixel is output from the CLK generation circuits 804a and 804b configured by a known frequency synthesizer circuit for fine adjustment. A timing signal from the read timing generation circuit 805 is input to the CLK generation circuits 804a and 804b, and a clock synchronized with this timing is output. Further, since the image size (writing width) of the main scanning can be changed according to the frequency of the CLK output from the CLK generating circuits 804a and 804b, the frequency defining this image size is set to the difference between the scanning line lengths of the lasers. By performing the fine adjustment according to the above, it is possible to correct the scanning length between the laser beams of the respective laser chips 207a and 207b to be the same. Image data read from each of the FIFOs 803a and 803b is input to pulse width modulation units 802a and 802b, and the pulse width modulation units 802a and 802b modulate the input image data into pulse width data having a predetermined width. This pulse width data is input to the corresponding laser drive current circuits 202a and 20b as a laser lighting signal for determining the laser lighting time.
[0056]
As described above, the difference between the scanning lengths of the laser beams on the photosensitive drum surface during one scan between the laser beams is detected using the main scanning length detection pattern, and the predetermined length is detected by the CLK generation circuits 804a and 804b. By setting the frequency, the scanning length difference can be corrected.
[0057]
In the present embodiment, in order to perform accurate registration correction, first, a difference in scanning line length between a plurality of laser beams is corrected, and then registration correction is performed. Thus, a CPU (not shown) performs registration correction according to the flowchart shown in FIG. FIG. 11 is a flowchart showing a procedure of registration correction in the image forming apparatus of FIG.
[0058]
When the registration correction operation is started, as shown in FIG. 11, first, at step S1, the transfer belt 31 is driven to rotate, and then at step S2, a main scanning line length correction pattern is formed. Then, in step S3, the patterns are read by the photosensors 60 and 61, the correction amount is calculated, and the frequency of the CLK generation circuits 804a and 804b is set.
[0059]
Next, in step S4, a pattern (registration pattern) for registration correction is formed, and the pattern is read by the photosensors 60 and 61. Subsequently, in step S5, a correction amount is calculated, and registration correction is performed. Then, in step S6, the rotation drive of the intermediate transfer belt 31 is stopped, and the registration correction operation ends.
[0060]
As described above, since the registration pattern is formed after the scanning line length of each laser beam is corrected, accurate registration correction can be performed.
[0061]
(2nd Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 12 is a vertical cross-sectional view schematically illustrating a main configuration of an image forming apparatus according to a second embodiment of the present invention.
[0062]
In the first embodiment, the intermediate transfer belt 31 is used as the second image carrier. However, in the present embodiment, instead of this, the transfer material P is carried as the second image carrier. The transfer material transport belt 32 is used to transport the transfer material. In other respects, the present embodiment is configured similarly to the color image forming apparatus of the first embodiment. Therefore, members having the same functions and functions are denoted by the same reference numerals, and description thereof will be omitted.
[0063]
Also in the present embodiment, the main scan line length correction pattern and the registration pattern are formed on the transfer material transport belt 32, and the scan correction is performed after the scan line length of each laser is corrected. Therefore, also in the present embodiment, the same operation and effect as in the first embodiment can be achieved.
[0064]
(Third embodiment)
Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 13 is a diagram schematically illustrating one configuration of the stations provided in the image forming unit of the image forming apparatus according to the third embodiment of the present invention.
[0065]
This embodiment is different from the first and second embodiments in that two BD sensors 206 and 208 are arranged on the photosensitive drum 11 on the near side and the far side in the main scanning direction, respectively. Members having the same functions and functions as those of the first and second embodiments are denoted by the same reference numerals, and description thereof will be omitted.
[0066]
The BD sensor 206 is provided near the scanning start position of one line of laser light, and the BD sensor 208 is provided near the scanning end position. The laser light scans the photosensitive drum 11 and the scanning light passes through the BD sensors 206 and 208, whereby the scanning time between the BD sensors 206 and 208 can be detected. Outputs of the BD sensors 206 and 208 are input to a main scanning length difference detection circuit 209. The main scanning length difference detection circuit 209 compares the scanning time detected when only the laser chip 207a is turned on with the scanning time detected when only the laser chip 207b is turned on. This difference in scanning time is the difference in main scanning length. A correction amount is calculated from the difference in the main scanning length, and is input to the image writing timing control circuit 201 as a frequency setting value of the CLK generation circuit. As a result, the difference in the main scanning length of each laser can be corrected, and then the registration correction operation is performed in the same manner as in the first and second embodiments.
[0067]
As described above, the present embodiment is different from the first and second embodiments in that the two BD sensors 206 and 208 provided in the image forming unit detect the scanning length difference of each laser.
[0068]
【The invention's effect】
As described above, according to the present invention, a plurality of correction patterns for detecting the scanning length in the main scanning direction are provided on the image carrier through the multi-beam scanning optical system for each image forming process unit. Forming a plurality of correction patterns, correcting the frequency of the frequency variable clock generated for each light source from the frequency variable clock generation means based on the read result, and correcting the frequency of the frequency variable clock, Since registration correction is performed to correct the shift of each color image formed by the image forming process means, the difference in scanning position between a plurality of beams that scan the image carrier is reduced, or the image carrier during one scan is reduced. The difference in scanning line length (writing width) of each beam on the body is eliminated. As a result, a registration correction pattern can be formed correctly, and accurate registration correction can be performed.
[0069]
According to the invention, the scanning start position of the beam emitted from each of the plurality of light sources is detected for each image forming process unit, and the scanning end position of the beam emitted from each of the plurality of light sources is detected for each image forming process unit. Is detected, and the frequency of the variable frequency clock generated for each light source from the variable frequency clock generating means is corrected based on the detected scanning start position and the detected scanning end position. Thereafter, registration correction is performed to correct the shift of each color image formed by the plurality of image forming process units, so that the difference in the scanning position between the plurality of beams that scan the image carrier is reduced or one scan is performed. The difference in the length (writing width) of the scanning line of each beam on the middle image carrier is eliminated. As a result, a registration correction pattern can be formed correctly, and accurate registration correction can be performed.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a main part of an image forming apparatus according to a first embodiment of the present invention.
FIG. 2 is a diagram schematically illustrating one configuration of a station provided in an image forming unit of the image forming apparatus of FIG. 1;
3 is a schematic diagram of the vicinity of pattern image detecting means (including a CCD sensor) 60, 61 for detecting a pattern image for registration correction in the image forming apparatus of FIG.
FIG. 4A is a diagram illustrating a first line segment disposed at a predetermined angle with respect to a process direction, which is a moving direction of the intermediate transfer belt 31, and symmetrically disposed with respect to a virtual line perpendicular to the first line segment and the process direction. FIG. 4B shows a pattern formed by the second line segment, and FIG. 4B shows a first line segment arranged at a predetermined angle with respect to the process direction which is the moving direction of the intermediate transfer belt 31 and a direction orthogonal to the process direction (main scanning). FIG. 3 is a diagram showing a pattern formed by a second line segment parallel to a direction (direction).
FIG. 5 is a diagram schematically showing how the photo sensors 60 and 61 detect a registration correction pattern 301 on the intermediate transfer belt 31.
FIG. 6 is a diagram schematically illustrating a state in which a phototransistor 202 receives reflected light reflected by a pattern image 301 or an intermediate transfer belt 31 from light emitted by an LED 201;
FIG. 7 is a diagram showing a light receiving circuit in which a phototransistor 202 receives reflected light and converts the reflected light into an electric signal.
FIG. 8 is a diagram illustrating a principle of calculating a main scanning magnification using a pattern.
9A shows an image 901 in which a pattern image is written by the laser chip 207a and read by the photosensors 60 and 61, and FIG. 9B is a pattern image written by the laser chip 207b and the photosensors 60 and 61. FIG. 9 is a diagram showing a scanned image 902.
FIG. 10 is a diagram schematically illustrating a detailed configuration of an image writing timing control circuit 201 and a laser drive control circuit 202 in FIG. 2;
FIG. 11 is a flowchart illustrating a procedure of registration correction in the image forming apparatus of FIG. 1;
FIG. 12 is a longitudinal sectional view schematically illustrating a main configuration of an image forming apparatus according to a second embodiment of the invention.
FIG. 13 is a diagram schematically illustrating one configuration of stations provided in an image forming unit of an image forming apparatus according to a third embodiment of the present invention.
FIG. 14 is a diagram illustrating a state in which a multi-laser (two lasers) has a different scanning line length during image formation.
[Explanation of symbols]
10 Image forming unit
11a, 11b, 11c, 11d Photosensitive drum
31 Intermediate transfer belt
32 Transfer material transport belt
60,61 Photo sensor
201 Image writing timing control circuit
202 Laser drive control circuit
204 rotating polygon mirror
205 f-θ lens
206, 208 BD sensor
207 Semiconductor laser

Claims (13)

A plurality of image forming process units for performing image forming processes of different colors, the plurality of image forming process units exposing corresponding lines on the image carrier with beams respectively emitted from a plurality of light sources. An image forming apparatus comprising: a multi-beam scanning optical system for scanning; and a frequency variable clock generation unit that generates a frequency variable clock for performing modulation driving for each light source,
Via the multi-beam scanning optical system for each image forming process means, a correction pattern forming means for forming a plurality of correction patterns for detecting the scanning length in the main scanning direction on the image carrier,
Correction pattern reading means for reading the plurality of correction patterns,
Scanning length correction means for correcting the frequency of the frequency variable clock generated for each light source from the frequency variable clock generation means based on the result read by the correction pattern reading means,
Image forming, wherein after correcting the frequency of the frequency variable clock, performing registration correction for correcting a shift between images of respective colors formed by the plurality of image forming process units. apparatus. The plurality of image forming process units transfer, as the image carrier, a first image carrier on which the electrostatic latent image is formed and an electrostatic latent image formed on the first image carrier. The image forming apparatus according to claim 1, further comprising a second image carrier. The plurality of image forming process units transfer, as the image carrier, a first image carrier on which the electrostatic latent image is formed and an electrostatic latent image formed on the first image carrier. 2. The image forming apparatus according to claim 1, further comprising a second image carrier that carries and transports the transfer material. 3. The image forming apparatus according to claim 1, wherein when the number of beams emitted from each of the plurality of light sources is n, the driving speed of the first and second image carriers is set to 1 / n of that in normal image formation. 4. The image forming apparatus according to 2 or 3. The image forming apparatus according to claim 2, wherein the second carrier is formed of an endless belt. The image forming apparatus according to claim 1, wherein the correction pattern reading unit includes a light emitting element and a light receiving element for reading the correction pattern at a predetermined position. A plurality of image forming process units for performing image forming processes of different colors, the plurality of image forming process units exposing corresponding lines on the image carrier with beams respectively emitted from a plurality of light sources. An image forming apparatus comprising: a multi-beam scanning optical system for scanning; and a frequency variable clock generation unit that generates a frequency variable clock for performing modulation driving for each light source,
Scanning start position detecting means for detecting a scanning start position of a beam emitted from each of the plurality of light sources for each of the image forming process means,
Scanning end position detecting means for detecting a scanning end position of a beam emitted from each of the plurality of light sources for each of the image forming process means,
Scanning length correction means for correcting the frequency of the frequency variable clock generated for each light source from the frequency variable clock generation means based on the detection result of the scan start position detection means and the detection result of the scan end position detection means, ,
Image forming, wherein after correcting the frequency of the frequency variable clock, performing registration correction for correcting a shift between images of respective colors formed by the plurality of image forming process units. apparatus. The plurality of image forming process units transfer, as the image carrier, a first image carrier on which the electrostatic latent image is formed and an electrostatic latent image formed on the first image carrier. The image forming apparatus according to claim 7, further comprising a second image carrier. The plurality of image forming process units transfer, as the image carrier, a first image carrier on which the electrostatic latent image is formed and an electrostatic latent image formed on the first image carrier. 8. The image forming apparatus according to claim 7, further comprising a second image carrier that carries and conveys the transfer material. 3. The image forming apparatus according to claim 1, wherein when the number of beams emitted from each of the plurality of light sources is n, the driving speed of the first and second image carriers is set to 1 / n of that in normal image formation. 10. The image forming apparatus according to 8 or 9. The image forming apparatus according to any one of claims 7 to 10, wherein the second carrier is formed of an endless belt. A plurality of image forming process units for performing image forming processes of different colors, the plurality of image forming process units exposing corresponding lines on the image carrier with beams respectively emitted from a plurality of light sources. A registration correction method for an image forming apparatus, comprising: a multi-beam scanning optical system for scanning; and a frequency variable clock generating unit that generates a frequency variable clock for performing a modulation drive for each light source,
A correction pattern forming step of forming a plurality of correction patterns for detecting a scanning length in the main scanning direction on the image carrier through the multi-beam scanning optical system for each of the image forming process means;
A correction pattern reading step of reading the plurality of correction patterns,
A scanning length correction step of correcting a frequency of a frequency variable clock generated for each light source from the frequency variable clock generation means based on a result read by the correction pattern reading step;
A registration correction step of performing a registration correction for correcting a shift of each color image formed by the plurality of image forming process units after correcting the frequency of the frequency variable clock. Device registration correction method. A plurality of image forming process units for performing image forming processes of different colors, the plurality of image forming process units exposing corresponding lines on the image carrier with beams respectively emitted from a plurality of light sources. A registration correction method for an image forming apparatus, comprising: a multi-beam scanning optical system for scanning; and a frequency variable clock generating unit that generates a frequency variable clock for performing a modulation drive for each light source,
A scanning start position detecting step of detecting a scanning start position of a beam emitted from each of the plurality of light sources for each of the image forming process units;
A scan end position detecting step of detecting a scan end position of a beam emitted from each of the plurality of light sources for each of the image forming process units;
A scan length correction step of correcting a frequency of a frequency variable clock generated for each light source from the frequency variable clock generation means based on the detection result of the scan start position detection step and the detection result of the scan end position detection step. ,
A registration correction step of performing a registration correction for correcting a shift of each color image formed by the plurality of image forming process units after correcting the frequency of the frequency variable clock. Device registration correction method.

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