JP2003266764A - Image forming equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately correct a lag in the time when the modulation of a plurality of beams is started, using a single detection means capable of detecting light beams passing through a prescribed position in a scanning range. <P>SOLUTION: After the measurement of an SOS period Tsx is carried out more than one time by lighting up a reference light beam s alone during an SOS period (cycle during which a light beam is made to arrive at an SOS sensor) of a certain horizontal scanning cycle, and lighting up the controlled light beam x alone during the SOS period of the next cycle, the measurement of the SOS cycle Txs is carried out more than one time by lighting up the controlled light beam x alone in the SOS period of a certain cycle and lighting up the reference light beam s alone during the SOS period of the next cycle, a timing lag Tx is computed on the basis of the average value Tsx (Ave) of the SOS cycle Tsx and the average value Txs (Ave) of the SOS cycle Txs, the timing of starting the modulation of the controlled light beam x based on the timing of starting the modulation of the reference light beam s in each horizontal scanning is corrected on the basis of the lag Tx. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly, to an image formed by a plurality of light beams emitted from a plurality of light sources, incident on the same reflecting surface of a rotary polygon mirror, and deflected and scanned. The present invention relates to an image forming apparatus to be formed.

[0002]

2. Description of the Related Art In order to realize a high speed formation of color images, a plurality of image forming sections are provided, and monochromatic images of different colors formed by the respective image forming sections are superimposed and transferred onto a sheet. A so-called tandem-type image forming apparatus that forms a color image by doing so has been proposed. Here, if there is a deviation (registration deviation) in the image forming position of each single color image, there is a problem that it is visually recognized as a color deviation on the color image, and a high quality color image without color deviation is formed. To this end, it is necessary to detect the registration shift amount of each single-color image and correct the image forming position of each single-color image according to the detected registration shift amount.

Regarding the correction of registration deviation, a toner image having a specific pattern is formed on an intermediate transfer member, the specific pattern is detected by a sensor including a light source and a light receiver, and the registration deviation amount is calculated. A technique for correcting the registration shift by relatively changing the image forming position of each monochromatic image has been conventionally known (for example, Japanese Patent Laid-Open No. 63-2712).
75, JP-A-3-142424, etc.).

As for the registration deviation (side registration deviation) along the main scanning direction of the light beam, the registration deviation amount frequently changes with the temperature change around and inside the image forming apparatus. For example, a laser diode (LD) as a light source that emits a light beam has an oscillation wavelength that varies with temperature,
Due to this fluctuation of the oscillation wavelength, the refractive index of the optical system in the optical scanning device with respect to the light beam changes, and the magnification in the main scanning direction also changes. When a difference in temperature rise between individual LDs that emit a light beam occurs due to a temperature gradient or the like in the image forming apparatus, the fluctuation amount of the oscillation wavelength of each LD also differs. The amount of change in magnification in the scanning direction is also different,
Along with this, the side registration shift amount changes.

Therefore, it is necessary to frequently stop the image forming process by frequently forming a specific pattern on the intermediate transfer member for the purpose of correcting the side registration deviation in which the registration deviation amount changes frequently. In order to avoid an increase in the amount of toner consumed for pattern formation, a specific one color is set as a reference color and the SO arranged at the main scanning start position is used.
When the light beam corresponding to the reference color is detected by the S (Start Of Scan) sensor, a signal (S
The difference between the timing at which the OS signal) is output and the timing at which the SOS signal corresponding to another light beam is output by the SOS sensor is detected, and according to the difference, an individual light beam corresponding to each single color image is used. A technique is known in which a write start timing (modulation start timing in each main scan of a light beam) is controlled to periodically correct a change in the side registration deviation amount due to a temperature change or the like.

By the way, in an optical scanning device having a structure in which the individual light beams are incident on the same surface of the rotary polygon mirror to perform deflection scanning, the individual light beams after the deflection scanning by the rotary polygon mirror are
By moving very close positions in the optical scanning device, individual light beams can be detected by a single SOS sensor. In addition, it is more cost effective to adopt a configuration in which a single SOS sensor detects individual light beams than to detect individual light beams using an SOS sensor provided for each individual light beam. It is also excellent in downsizing the optical scanning device. However, when the individual light beams are detected by the single SOS sensor as described above, the individual light beams are incident on the SOS sensor almost at the same time, and the SOS signals corresponding to the individual light beams are detected. It becomes difficult to detect the difference in the output timing of the.

Further, as shown in FIG. 7 as an example, by providing a mirror for changing the timing at which each light beam is incident on the SOS sensor in correspondence with each light beam, each light beam is transmitted to the SOS sensor. By generating a time difference between the incident timings and electrically separating the SOS signals corresponding to the individual light beams output from the SOS sensor in time series, the SOS signals corresponding to the individual light beams are generated. It is also possible. However, providing each of the mirrors corresponding to each light beam causes an increase in cost, and there is a problem that the effective scanning width of the light beam is narrowed by providing the mirror. Further, in an image forming apparatus designed to be capable of forming an image at high speed, the main scanning speed of the light beam is also high. Therefore, from the signal output from a single SOS sensor, the SOS signal corresponding to each light beam is obtained. Is very difficult to electrically isolate.

[0008] As a technique related to the above problem, Japanese Patent Laid-Open No.
In JP-A 1-208023, only a reference laser is made incident on an SOS sensor in two consecutive main scans to measure the time interval of the output timing of an SOS signal from the SOS sensor, and two consecutive main scans. In the first main scanning, the reference laser is made incident on the SOS sensor, and in the second main scanning, the comparison target lasers other than the reference laser are set to the SOS sensor.
A technique is disclosed in which the time interval of the output timing of the SOS signal is measured by making it enter the sensor and the modulation start timing in each main scan of the comparison target laser is corrected based on the measurement result of the time interval.

[0009]

However, it is difficult to keep the rotation speed of the rotary polygon mirror accurately and constant by the current technology, and the rotation speed of the rotary polygon mirror is always fluctuating though it is small. . On the other hand, JP-A-11-
In the technique described in Japanese Patent No. 208023, the measurement of the time interval when the SOS sensor is made to enter only the reference laser in the continuous two main scans, and the first of the two continuous main scans. In the main scanning, the reference laser is used, and in the second main scanning, the time interval when the comparison target laser is made incident on the SOS sensor is measured only once, so the influence of the fluctuation of the rotation speed of the rotary polygon mirror is affected. Therefore, there is a problem in that the correction accuracy of the modulation start timing is likely to decrease.

At the current level of processing technology, it is difficult to accurately align the sizes and directions of a plurality of reflecting surfaces of a rotary polygon mirror, which is often used as a means for deflecting and scanning a light beam. Strictly speaking, the size and orientation of the reflecting surface differ for each reflecting surface (hereinafter, referred to as surface division error). The above-mentioned JP-A-11-208023
In the technique described in the publication, in order to prevent the correction accuracy of the modulation start timing from being deteriorated due to the surface division error of the rotating polygon mirror, a specific reflecting surface among a plurality of reflecting surfaces of the rotating polygon mirror is set. It is used to measure the time interval of the output timing of the SOS signal.

However, as described above, it is necessary to periodically correct the modulation start timing in each main scanning of the light beam. In the technique disclosed in Japanese Patent Laid-Open No. 11-208023, the surface division of the rotary polygon mirror is performed. In order to prevent the correction accuracy in each correction from being varied due to the influence of an error, in each correction, a constant reflection surface among the plurality of reflection surfaces of the rotary polygon mirror is always used to change the output timing of the SOS signal. The time interval needs to be measured. Therefore,
In the technique described in Japanese Patent Laid-Open No. 11-208023, it is necessary to specify the reflecting surface that deflects and deflects the light beam in each main scanning of the light beam in each correction, which complicates the configuration. There was also a problem.

The present invention has been made in consideration of the above facts, and starts modulation of a plurality of light beams by using a single detecting means capable of detecting a light beam passing through a predetermined position within a scanning range. An object of the present invention is to obtain an image forming apparatus capable of correcting a timing shift with high accuracy.

[0013]

In order to achieve the above object, an image forming apparatus according to the invention of claim 1 is provided with a plurality of light sources for emitting a light beam, and a plurality of light sources respectively emitted from the plurality of light sources. Of the plurality of reflected surfaces, a rotary polygon mirror for deflecting and scanning each of a plurality of light beams incident on the same reflecting surface, and a deflective scan by the rotary polygon mirror to pass a predetermined position within a scanning range of the light beam. A single light source for a predetermined period during which the light beam passes through the predetermined position in the period in which the light beam is deflected and scanned by the detection means capable of detecting a plurality of light beams respectively and the arbitrary reflecting surface of the rotary polygon mirror. Only a single light source is turned on in the predetermined period of the next deflection scanning cycle, and at the same time, the time interval of the detection timing of the light beam by the detection means is measured a plurality of times, and the total is measured. It is configured to include a correction means for correcting the modulation start timing of each light beam, the at each time of the deflection scanning by the rotating polygon mirror with averaged data a plurality of time intervals and.

According to the first aspect of the present invention, a plurality of light beams emitted from a plurality of light sources are incident on the same reflecting surface among a plurality of reflecting surfaces formed on the rotary polygon mirror, and a plurality of light beams are emitted. The beams are deflected and scanned by the rotating polygon mirror. Further, the detecting means is capable of detecting a plurality of light beams each of which is deflected and scanned by the rotary polygon mirror and passes through a predetermined position within the scanning range of the light beam. Further, the correction means according to the invention described in claim 1 is, in the period in which the light beam is deflected and scanned by an arbitrary reflecting surface of the rotary polygon mirror,
Only a single light source is turned on for a predetermined period of time during which the light beam passes a predetermined position, and only a single light source is turned on for the predetermined period of the next deflection scanning cycle. The time interval is measured a plurality of times, and the data obtained by averaging the measured time intervals is used to correct the modulation start timing of each light beam in each deflection scan by the rotary polygon mirror.

As described above, according to the first aspect of the invention, since only a single light source is turned on during a predetermined period in which the light beam passes through a predetermined position, the detection timing of each light beam by the detection means is extracted. In addition, it is not necessary to provide a mirror for each light beam. In addition, the measurement of the time interval of the light beam detection timing is performed multiple times, and the modulation start timing of each light beam is corrected using the data obtained by averaging the measured time intervals. Even if the intervals include errors caused by fluctuations in the rotational speed of the rotary polygon mirror, the above errors are averaged by performing averaging, and as data obtained by averaging a plurality of measured time intervals, Accurate data corresponding to the actual time interval can be obtained. Therefore, according to the first aspect of the present invention, the deviation of the modulation start timing of a plurality of light beams can be accurately detected by using the single detection means capable of detecting the light beams passing through the predetermined position within the scanning range. Can be corrected to.

According to the first aspect of the invention, only a single light source is turned on during a predetermined period of a period in which a light beam is deflected and scanned by an arbitrary reflecting surface of the rotary polygon mirror, and a predetermined deflection scanning period is determined. At the same time as turning on only a single light source in a period, measuring the time interval of the detection timing of the light beam by the detecting means may be performed a plurality of times for the same reflecting surface of the rotating polygon mirror, for example. Considering the influence of the surface division error of the rotary polygon mirror, it is desirable to use a constant reflecting surface of the rotary polygon mirror in each correction when regularly performing the correction by the correction means. There is a problem that the configuration becomes complicated because it is necessary to specify the reflecting surface that reflects and deflects the light beam in each main scanning.

In view of the above, in the invention described in claim 1, as described in claim 2, the correction means is provided in a predetermined period of a period in which the light beam is deflected and scanned by an arbitrary reflecting surface of the rotary polygon mirror. Turning on only a single light source, turning on only a single light source in a predetermined period of the next deflection scanning cycle, and measuring the time interval of the detection timing of the light beam by the detecting means is a It is preferable to perform each of a plurality of reflecting surfaces different from each other.

Thus, at each measured time interval,
Even if each error due to the surface division error of the rotary polygon mirror is included, since the above error is leveled by performing averaging, even if the reflecting surface used in each correction is different, The correction can be performed accurately without being affected by the surface division error. As described above, according to the second aspect of the present invention, it is not necessary to specify the reflecting surface that reflects and deflects the light beam in each main scanning of the light beam. Therefore, the configuration of the image forming apparatus according to the present invention is achieved. It is possible to avoid complication.

In the invention according to claim 1 or 2, the correction by the correcting means is, as described in detail in claim 3, the light beam is deflected and scanned by an arbitrary reflecting surface of the rotary polygon mirror. The first light source is turned on during a predetermined period of the cycle, and the second light source is turned on during a predetermined period of the next deflection scanning cycle, and at the same time, the light beam emitted from the first light source is detected by the detection means. From the above, the first time interval until the light beam emitted from the second light source is detected is measured a plurality of times (as described above, the same reflection surface of the rotary polygon mirror is measured a plurality of times). However, as described in claim 2, it is preferable to measure each of a plurality of reflecting surfaces of the rotary polygon mirror different from each other.), And the light beam is deflected and scanned by any reflecting surface. Lap The second light source is turned on for the predetermined period of time, and the first light source is turned on for the predetermined period of the next deflection scanning cycle, and at the same time, the light beam emitted from the second light source is detected by the detection means. After that, the second time interval until the light beam emitted from the first light source is detected is measured a plurality of times (this is also performed on a plurality of different reflecting surfaces of the rotary polygon mirror). Preferably, the light beam emitted from the first light source based on data obtained by averaging the plurality of measured first time intervals and data obtained by averaging the measured plurality of second time intervals. And the timing of starting the modulation of the light beams emitted from the first and second light sources based on the difference in the passage timings of the light beams emitted from the second light source and the predetermined position. To It can be carried out by pairs corrected.

The correction by the correction means according to the third aspect of the present invention is, for example, as described in the fourth aspect, the first light source and the second light source in a predetermined period in each deflection scanning cycle.
By alternately turning on the light sources of, the plurality of reflecting surfaces of the rotating polygon mirror which are different from each other are present every other reflecting surface along the rotation direction of the rotating polygon mirror (separate along the rotation direction of the rotating polygon mirror. It is preferable to use each of the reflecting surfaces arranged with the reflecting surface of (1) interposed therebetween. Thereby, when the first time interval and the second time interval are measured for each of a plurality of mutually different reflecting surfaces of the rotary polygon mirror,
The time required for measurement can be shortened.

Further, in the invention described in claim 3, the correction means corrects the modulation start timing of each light beam, as described in detail in claim 5, for example.
A specific light source is used as the first light source, and a light source used as the second light source is selected from light sources other than the specific light source among a plurality of light sources, and a light beam emitted from the first light source and a second light source are selected. Correcting the modulation start timing of the light beam emitted from the second light source based on the difference in the passage timing of the light beam emitted from the second light source at a predetermined position,
This can be realized by switching and repeating the light source used as the second light source.

Further, in the invention described in claim 1, the correction means controls the turning on / off of a plurality of light sources, measures the time interval, and starts the modulation of each light beam, as described in claim 6, for example. The timing correction can be configured to be performed during a period in which image formation by a plurality of light beams is not performed. In this case, the image forming apparatus according to the first aspect of the present invention is configured such that the plurality of light beams are used. When an image is formed by, only a predetermined light source is turned on in a predetermined period in each deflection scanning cycle, and the modulation start timing corrected by the correction means is based on the detection timing of the light beam emitted from the predetermined light source by the detection means. It is possible to adopt a configuration in which the modulation is controlled so that the modulation of each light beam in each deflection scan is started.

According to the first aspect of the invention, for example, as described in the seventh aspect, a plurality of light beams are made to scan on different photoconductors to form an image on each photoconductor. An image forming apparatus having a configuration in which a plurality of images formed on individual photoconductors are superimposed and output as a single image is suitable, but the present invention is not limited to this, and for example, a plurality of light beams may be used. It is also possible to apply the present invention to an image forming apparatus having a configuration in which one photoconductor is scanned and a single image is formed on a single photoconductor by a plurality of light beams to output the image.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an image forming apparatus 10 as an image forming apparatus according to the present invention. The image forming apparatus 10 includes three conveyance rollers 12A to 1A.
2C, an endless transfer belt 14 wound around the transport rollers 12A to 12C, and a transfer roller 16 disposed opposite to the transport roller 12C with the transfer belt 14 interposed therebetween.

On the side of the transfer belt 14, the transfer belt 1 is provided.
An image forming portion 18K for forming a black (K) single color image and a cyan (C) single color image are formed along the moving direction of the transfer belt 14 (the direction of arrow A in FIG. 1) when the image forming apparatus 4 is rotationally driven. An image forming unit 18C for forming a color image, an image forming unit 18M for forming a magenta (M) single color image,
Image forming portions 18Y for forming a yellow (Y) single color image are sequentially arranged at substantially equal intervals.

Although not shown in detail in FIG. 1, each of the image forming portions 18 is provided with a photosensitive drum 19 which is arranged so as to be orthogonal to the moving direction of the transfer belt 14,
Around the photoconductor drums 19, an electrostatic latent image formed on the photoconductor drums 19 by a charger for charging the photoconductor drums 19 and an optical scanning device 20 (details will be described later) has a predetermined color (K or K). C or M or Y) developing device for developing with a toner to form a toner image, transfer device for transferring the toner image formed on the photoconductor drum 19 to the transfer belt 14,
A cleaning device for removing the toner remaining on the photoconductor drum 19 is arranged in order.

Photosensitive drum 19 of each image forming unit 18
The toner images of different colors formed on the transfer belt 14 are transferred to the transfer belt 14 so as to overlap each other on the belt surface of the transfer belt 14. As a result, a color toner image is formed on the transfer belt 14, and the formed color toner image is transferred to the transfer material 22 fed between the transport roller 12C and the transfer roller 16. Then, the transfer material 22 is sent to a fixing device (not shown), and the transferred toner image is fixed. As a result, a color image (full color image) is formed on the transfer material 22. As described above, the image forming apparatus 10 according to the exemplary embodiment is described in detail in Claim 7.
It corresponds to the image forming apparatus described in.

As shown in FIG. 2, the optical scanning device 20 includes a light source 24 composed of four laser diodes (LD) (each of the four LDs may be a separate structure, or may be integrated into a single package. The light source 24 emits four light beams for forming K, C, M, and Y monochromatic images, respectively. The four LDs of the light source 24 correspond to the plurality of light sources according to the present invention. The four light beams emitted from the light source 24 are made into parallel light fluxes by the collimator lenses 26 arranged on the beam emission side of the light source 24, and are then incident on the same reflecting surface of the single rotating polygon mirror 28. To be done. The rotary polygon mirror 28 has a regular polygonal columnar shape, and has a plurality of reflecting surfaces formed on its side surfaces by mirror finishing. Rotating polygon mirror 28
Is rotated at a high speed in the direction of arrow B in FIG. 2 by transmitting the driving force of the motor 46 (see FIG. 3), and the four light beams incident on the same reflecting surface are moved along the main scanning direction. Each is deflected and scanned.

As shown in FIG. 3, a drive control unit 30 is connected to the optical scanning device 20, and the drive control unit 30 is connected to the drive control unit 30.
Is provided with a reference clock generation unit 52 that generates a reference clock for rotating the motor 46 at a predetermined rotation speed. The reference clock generator 52 is connected to the motor 46 via the PLL controller 50 and the driver 48. PLL
The control unit 50 controls the rotation speed of the motor 46 via the driver 48 based on the reference clock supplied from the reference clock generation unit 52 and the rotation frequency signal output from a hall element or the like (not shown) that detects the position of the drive magnet. (PLL control). As a result, the motor 46 is rotated at a constant speed with high accuracy.

Fθ lenses 32 and 34 having power only in the main scanning direction are arranged on the light beam emission side of the rotary polygon mirror 28, and the light beam deflected / reflected by the rotary polygon mirror 28 is a photosensitive drum. The lens is refracted by the fθ lenses 32 and 34 so as to move at a substantially constant speed on the outer peripheral surface of the photosensitive drum, and the image forming position in the main scanning direction matches the outer peripheral surface of the photosensitive drum. Separation mirrors 36 (see also FIG. 1) are arranged on the light beam emission sides of the fθ lenses 32 and 34, and the four light beams incident on the separation mirror 36 are separated by the separation mirror 3
6, the light is reflected to the side where the corresponding image forming unit 18 is located.

As shown in FIG. 1, the image forming sections 18K, 1
Cylindrical mirrors 38K, 38C, 3 having power only in the sub-scanning direction are provided near 8C, 18M, 18Y.
8M and 38Y are arranged respectively. The four light beams emitted from the separation mirror 36 are respectively reflected by the cylindrical mirror 38 so that the image forming positions in the sub-scanning direction coincide with each other on the photosensitive drum 19, and the corresponding photosensitive drums of the image forming unit 18 are reflected. 19 are irradiated respectively. The cylindrical mirror 38 also has a plane tilt correction function that makes the outer peripheral surfaces of the rotary polygon mirror 28 and the photosensitive drum 19 conjugate in the sub-scanning direction.

As shown in FIG. 2, the fθ lens 32,
On the beam emission side of 34, a pickup mirror 40 is arranged at a position corresponding to the end portion (SOS) on the scanning start side in the scanning range of the light beam.
The SOS sensor 42 is arranged on the light beam emission side of 0. As for the light beam emitted from the light source 24, one of the reflecting surfaces of the rotary polygon mirror 28 that reflects the light beam is
When the incident beam is reflected in the direction corresponding to SOS, it is reflected by the pickup mirror 40 and the SO
It is incident on the S sensor 42, and a pulse signal (SOS signal) is output from the SOS sensor 42. The SOS sensor 42 corresponds to the detection means according to the present invention.

As shown in FIG. 2, in this embodiment, the number of reflecting surfaces of the rotary polygon mirror 28 is 6, and while the rotary polygon mirror 28 makes one rotation, the SOS sensor 42 outputs SO.
Six pulses are sequentially output as the S signal. Further, in the present embodiment, the light beam emitted from the light source 24 is emitted from the SOS sensor 4 in each main scanning by the rotary polygon mirror 28.
The drive of the light source 24 is controlled so that a single light beam is emitted from the light source 24 during a predetermined period of incidence on the light source 2 (details will be described later). Whichever of the light beams is emitted,
The size of the reflecting surface of the pickup mirror 40 and the size of the light receiving surface of the SOS sensor 42 are designed so that the light beam is incident on the SOS sensor 42.

As shown in FIG. 3, the drive control section 30 includes an image formation instructing section 54 and a light source drive control section 56.
The SOS signal output from the SOS sensor 42 is input to the image forming instruction unit 54, and Y, M, C, and K to be formed on the photoconductor drum 19 of each image forming unit 18 are input.
The image data representing the image is input. The image formation instructing unit 54 generates a synchronization signal serving as a reference for the modulation start timing in each main scanning of the light beam based on the input SOS signal, and drives the light source together with the Y, M, C, K image data. Output to the control unit 56.

Further, the drive control section 30 is constituted by including a microcomputer. In FIG. 3, the processing realized by the microcomputer is divided according to the function, and SO
S cycle measurement / calculation unit 58 and timing adjustment value calculation unit 6
It is shown as 0. Although the details will be described later, the SOS cycle measurement / arithmetic unit 58 outputs the SO output from the SOS sensor 42.
The cycle of the S signal (SOS cycle) is measured multiple times, and the average value is calculated. Further, the timing adjustment value calculation unit 60
SOS calculated by the SOS cycle measurement / calculation unit 58
Based on the average value of the cycles, the relative shift amount of the scanning timing of the four light beams emitted from the light source 24 is calculated, and the modulation start timing of the four light beams in each scanning is relatively adjusted. A timing adjustment value for performing the calculation is calculated and output to the light source drive control unit 56.

The light source drive control unit 56 modulates each light beam in each main scan based on the synchronization signal input from the image formation instruction unit 54 and the timing adjustment value input from the timing adjustment value calculation unit 60. An LD for determining the start timing and for turning on / off (PWM modulation) the light beams emitted from the four LDs of the light source 24 in each main scan in accordance with the corresponding image data from the determined modulation start timing. A drive signal is generated and supplied to each LD of the light source 24. As a result, an image (electrostatic latent image) is formed on each photosensitive drum 19 of the image forming unit 18.
Will be formed respectively.

Next, as an operation of this embodiment, a modulation timing correction process executed by the microcomputer of the drive control unit 30 will be described with reference to the flowchart of FIG. The modulation timing correction processing corresponds to the correction means (specifically, the correction means described in claims 2 to 4) according to the present invention (the SOS cycle measurement / calculation part 58 and the timing adjustment value calculation part). 60)), for example, each time a single image is formed, a single job is completed, or the temperature detected by a temperature sensor arranged inside the image forming apparatus 10 is equal to or higher than a predetermined value. Every time it changes, it is periodically executed at a timing such as.

In step 100, the rotary polygon mirror 28 is rotated at a constant speed by the motor 42, so that the light source 2
It is determined whether or not a period (corresponding to a predetermined period of the present invention: hereinafter referred to as SOS timing) in which the SOS sensor 42 detects the light beam has arrived while deflecting and scanning the light beam emitted from No. 4. Then, the determination of step 100 is repeated until the determination is affirmative. Step 100
If the determination is positive, the process proceeds to step 102 and the light source 2
Of the four LDs 4, the LD that emits the reference light beam s
Only the reference light beam s is made incident on the SOS sensor 42.

In the present embodiment, a single specific LD is used at the SOS timing in each main scan during image formation.
Only the four light beams emitted from the light source 24 are turned on, and the light beam emitted from the specific LD is detected by the SOS sensor 42 so that the SOS signal is output from the SOS sensor 42. The modulation start timing in each main scan is controlled. In the modulation timing correction process shown in FIG. 4, the light beam emitted from the specific LD (for example, the light beam for forming a Y image) is used as the reference light beam s.

The use of the light beam emitted from the specific LD as the reference light beam s corresponds to the invention of claim 6. The LD that emits the reference light beam s corresponds to the first light source described in claim 3.

In the next step 104, the SOS sensor 4
It is determined whether or not the SOS signal (pulse indicating that the light beam is incident on the SOS sensor 42) is input from 2
The determination of step 104 is repeated until the determination is affirmative.
If the determination in step 104 is affirmative, the process proceeds to step 106, the timer is started, and the LD that emits the reference light beam s is turned off. As a result, the measurement of the SOS cycle Tsx described later is started.

In step 108, it is determined whether or not the SOS timing in the main scanning cycle next to the main scanning cycle in which the LD of the reference light beam s is turned on at the SOS timing has come, and the determination is affirmative in step S108. Repeat 108. If the determination in step 108 is affirmative, step 11
0, and the controlled light beam x (any of the three light beams other than the reference light beam s: a light beam for forming an M image, for example) of the four LDs of the light source 24 Only the emitted LD is turned on, and only the controlled light beam x is made incident on the SOS sensor 42. The controlled light beam x
The LD that emits light corresponds to the second light source according to the third aspect.

In step 112, it is determined whether or not the SOS signal is input from the SOS sensor 42, and the determination in step 112 is repeated until the determination is affirmative. Step 11
When the determination of 2 is affirmed, the process proceeds to step 114, the timer value of the timer started in step 106 is taken in, and the measured value of the SOS cycle Tsx (corresponding to the first time interval described in claim 3). And the LD for emitting the controlled light beam x is turned off. In the next step 116, it is determined whether or not the SOS cycle Tsx has been measured a predetermined number of times. If the determination is negative, the process returns to step 100, and steps 100 to 116 are repeated until the determination of step 116 is positive.
As a result, as the "a plurality of reflecting surfaces of the rotating polygon mirror different from each other" according to claim 3, the reflecting surfaces that are present every other one along the rotation direction of the rotating polygon mirror 28 are used (claim 4). 5A) as an example, as shown in FIG. 5A, until the number of measurements reaches a predetermined number of times, the SOS
The cycle Tsx will be repeatedly measured.

The number of times the SOS cycle Tsx is measured may be a plurality of times. For example, the number of times that the total number of reflecting surfaces of the rotary polygon mirror 28 is divided by 2 is set to a number corresponding to an integer value or less (for example, the present embodiment). If the total number of reflecting surfaces of the rotary polygon mirror 28 is 6, like the embodiment, the number of times of measurement can be set to 3).
As a result, while the rotary polygon mirror 28 makes one revolution, the SO
The measurement of the S cycle Tsx is completed.

When the number of times the SOS cycle Tsx is measured reaches a predetermined number of times, the determination at step 116 is affirmed and the routine proceeds to step 118, at which it is determined whether or not the SOS timing has come, and steps are taken until the determination is affirmed. The determination of 118 is repeated. When the determination in step 118 is affirmative, the process proceeds to step 120, and among the four LDs of the light source 24, only the LD that emits the controlled light beam x is turned on, and only the controlled light beam x is incident on the SOS sensor 42. Let In the next step 122, it is determined whether or not the SOS signal is input from the SOS sensor 42, and the step 12 is performed until the determination is affirmative.
The judgment of 2 is repeated. If the determination at step 122 is affirmative, the routine proceeds to step 124, at which the timer is started and the LD for emitting the controlled light beam x is turned off. As a result, the measurement of the SOS cycle Txs described below is started.

In the next step 126, it is determined whether or not the SOS timing in the main scanning cycle following the main scanning cycle in which the LD of the controlled light beam x is turned on at the SOS timing has arrived, and the determination is affirmative. Until step 126, step 126 is repeated. When the determination in step 126 is affirmative, the process proceeds to step 128, and among the four LDs of the light source 24, only the LD that emits the reference light beam s is turned on, and only the reference light beam s is incident on the SOS sensor 42. . Step 1
At 30, it is determined whether the SOS signal is input from the SOS sensor 42, and the determination of step 130 is repeated until the determination is affirmative. If the determination at step 130 is affirmative, the routine proceeds to step 132, where the timer value of the timer started at the previous step 124 is fetched, and the SOS cycle Txs
The measured value (corresponding to the second time interval described in claim 3) is stored in a memory or the like, and the LD that emits the reference light beam s is turned off.

In the next step 134, the SOS cycle Txs
It is determined whether or not the measurement has been performed a predetermined number of times. If the determination is negative, the process returns to step 118 and step 13
Step 118 to Step 13 until the judgment of 4 is affirmed
Repeat 4. As a result, the SOS cycle T described above
Similar to the measurement of sx, as the "a plurality of reflecting surfaces of the rotating polygon mirror different from each other" according to claim 3, the reflecting surfaces existing every other one along the rotation direction of the rotating polygon mirror 28 are used ( (Corresponding to the invention of claim 4), for example, as shown in FIG. 5B, until the number of times of measurement reaches a predetermined number of times,
The SOS cycle Txs will be repeatedly measured.

The number of times of measurement of the SOS cycle Txs may be the same as the number of times of measurement of the SOS cycle Tsx, and the number of times of measurement is equivalent to an integer value equal to or less than the number obtained by dividing the total number of reflecting surfaces of the rotary polygon mirror 28 by 2, for example. When the number of times is set, the measurement of the SOS cycle Tsx and the SOS cycle Txs is completed while the rotary polygon mirror 28 makes two rotations.

When the number of times the SOS cycle Txs is measured reaches a predetermined number of times, the determination at step 134 is affirmative and the routine proceeds to step 136, where the average value Tsx (Ave) of the SOS cycle Tsx is obtained.
Is calculated according to the following equation (1). Tsx (Ave) = [Tsx (1) + Tsx (2) + ... + Tsx (n)] / n (1) However, in the formula (1), n is the number of times the SOS period Tsx is measured. The average value Tsx (Ave) of the SOS cycle Tsx is
It corresponds to “data obtained by averaging a plurality of measured first time intervals” according to claim 3.

Further, in the next step 138, the average value Txs (Ave) of the SOS cycle Txs is calculated according to the following equation (2). Txs (Ave) = [Txs (1) + Txs (2) + ... + Txs (n)] / n (2) However, in the equation (2), n is the number of times the SOS cycle Txs is measured. The average value Txs (Ave) of the SOS cycle Txs is
This corresponds to "data obtained by averaging a plurality of measured second time intervals" according to claim 3.

The rotating speed of the rotary polygon mirror 28 is constantly fluctuating though it is slight, and each reflecting surface of the rotary polygon mirror 28 also has a surface division error. Therefore, the individual measurement values of the SOS cycle Tsx are affected by fluctuations in the rotation speed of the rotary polygon mirror 28 and surface division errors, and the individual measurement values of the SOS cycle Txs also vary. It fluctuates due to fluctuations in rotation speed and surface division errors.

On the other hand, in the modulation timing correction processing shown in FIG. 4, as described above, the SOS cycle Tsx and SO
The S period Txs is measured multiple times, and the average value Tsx of each is measured.
Since (Ave) and Txs (Ave) are calculated, the rotary polygon mirror 28
Of the individual measurement values of the SOS cycle Tsx due to the influence of the fluctuation of the rotation speed of the S and the surface division error of the rotary polygon mirror 28 and S
The dispersion of individual measured values of the OS cycle Txs is leveled, and SO
Average value Tsx (Ave) of S cycle and average value Txs of SOS cycle
As (Ave), a value accurately representing the actual cycle is obtained.

In the next step 140 and subsequent steps, the modulation start timing of the controlled light beam x in each main scan is calculated by using the average value Tsx (Ave) of the SOS cycle and the average value Txs (Ave) of the SOS cycle. Therefore, in each main scan, it is possible to perform correction so that the image writing position by the controlled light beam x exactly matches the image writing position by the reference light beam s. Note that steps 100 to 138 described above correspond to the SOS cycle measuring / calculating section 58, and the subsequent step 140 and subsequent steps correspond to the timing adjustment value calculating section 60.

In step 140, the timing deviation amount Tx is calculated according to the following equation (3) based on the average value Tsx (Ave) of the SOS cycle and the average value Txs (Ave) of the SOS cycle. Tx = [Tsx (Ave) −Txs (Ave)] / 2 (3) Then, in the next step 142, the timing deviation amount Tx obtained by the calculation in step 140 is compared with 0,
The process branches depending on the magnitude relationship between the timing deviation amount Tx and 0.

That is, when the timing shift amount Tx is 0, it can be determined that the reference light beam s and the controlled light beam x are incident on the SOS sensor 42 at the same timing, and therefore no processing is performed. The modulation timing correction process ends (without changing the modulation start timing of the controlled light beam x with respect to the modulation start timing of the reference light beam s in each main scan).

Further, the reference light beam s is the SOS sensor 42.
When the timing at which the controlled light beam x is incident (detected) on the SOS sensor 42 is delayed by a predetermined time with respect to the timing at which the reference light beam s is incident on (detected by), the reference light beam s is incident on the SOS sensor 42. After that, the SOS cycle Tsx when the controlled light beam x is incident on the SOS sensor 42 is increased by the predetermined time (this predetermined time corresponds to the absolute value | Tx | of the timing deviation amount). The value of the SOS cycle Txs when the reference light beam s is incident on the SOS sensor 42 after the controlled light beam x is incident on the SOS sensor 42 is reduced by the predetermined time.

Therefore, when the sign of the timing deviation amount Tx is positive (greater than 0), the reference light beam s is SOS.
Since it can be determined that the timing at which the controlled light beam x is incident (detected) on the SOS sensor 42 is delayed with respect to the timing at which it is incident (detected) on the sensor 42, the process proceeds to step 144, and main scanning of each time is performed. The modulation start timing of the controlled light beam x is the absolute value of the timing deviation amount | Tx
The timing adjustment value for the controlled light beam is set so as to be faster by |, and the modulation timing correction process is ended. As a result, the write start position of the image by the controlled light beam x in each main scan is moved in the “−” direction shown in FIG. 5C, and is exactly matched with the write start position of the image by the reference light beam s. It will be.

Further, the reference light beam s is the SOS sensor 42.
When the timing at which the controlled light beam x is incident (detected) on the SOS sensor 42 is earlier than the timing at which it is incident (detected) on the SOS sensor 42 by a predetermined time, after the reference light beam s is incident on the SOS sensor 42, Regarding the SOS cycle Tsx when the control light beam x is incident on the SOS sensor 42, the value becomes smaller by the predetermined time (this predetermined time also matches the absolute value | Tx | of the timing deviation amount), and the controlled S when the reference light beam s is incident on the SOS sensor 42 after the light beam x is incident on the SOS sensor 42
The value of the OS cycle Txs is increased by the predetermined time.

Therefore, when the sign of the timing deviation amount Tx is negative (smaller than 0), the reference light beam s is SOS.
Since it can be determined that the timing at which the controlled light beam x is incident (detected) on the SOS sensor 42 is earlier than the timing at which it is incident (detected) on the sensor 42, step 146
The control light beam is controlled so that the modulation start timing of the controlled light beam x is delayed by the absolute value | Tx | of the timing shift amount with respect to the modulation start timing of the reference light beam s in each main scan. The timing adjustment value for is set, and the modulation timing correction process ends. As a result, the write start position of the image by the controlled light beam x in each main scan is moved in the “+” direction shown in FIG. 5C, and is exactly matched with the write start position of the image by the reference light beam s. It will be.

The drive control section 30 repeats the above-mentioned modulation timing correction processing while switching the controlled light beam x (using all the light beams other than the reference light beam s as the controlled light beam x) (above-mentioned). Thus, repeating the modulation timing correction process while switching the controlled light beam x corresponds to the correction means according to claim 5), and as described above, the modulation timing correction process is periodically performed. Image forming apparatus 1
Even if the side registration shift amount changes due to a change in the internal temperature of 0 or the internal temperature of the optical scanning device 20, it is possible to suppress the occurrence of color shift in the main scanning direction (side registration shift).

In the above description, the case where the SOS cycle Txs is measured a plurality of times and then the SOS cycle Txs is measured a plurality of times has been described. However, the present invention is not limited to this, and the SOS cycle Txs is measured a plurality of times. The SOS cycle Tsx may be measured a plurality of times, or the SOS cycle Tsx and the SOS cycle Txs are alternately measured a plurality of times (for example, in FIG. 5A, the SOS cycle Tsx (1) is measured. Between the period during which the SOS cycle Tsx (2) is being measured and the period during which the SOS cycle Tsx (2) is being measured).

The modulation timing correction processing corresponding to the correction means according to the present invention is not limited to the processing shown in FIG. 4, and for example, the modulation timing correction processing shown in FIG. 6 may be performed. . In the modulation timing correction process shown in FIG. 6, in order to eliminate the influence of the surface division error of the rotary polygon mirror 28, in measuring the SOS cycle Tsx, in step 98, among the plurality of reflecting surfaces of the rotary polygon mirror 28, Then, it is determined whether or not a predetermined constant reflecting surface has reached a period for deflecting and scanning the light beam, and then step 9
After the determination of step 8 is affirmed, step 10 described above is performed.
The processing after 0 is performed. Further, in measuring the SOS cycle Txs, in step 117, it is determined whether or not a predetermined fixed reflection surface of the plurality of reflection surfaces of the rotary polygon mirror 28 has reached a cycle for deflecting and scanning the light beam. However, after the affirmative determination is made in step 117, the processing of step 118 and subsequent steps described above is performed.

In the modulation timing correction process shown in FIG. 6,
In order to carry out the determinations in step 98 and step 117,
Since it is necessary to provide a mechanism for determining which of the plurality of reflecting surfaces of the rotary polygon mirror 28 is the reflecting surface for deflecting and scanning the light beam in each main scanning, the optical scanning device 20 is required. SOS becomes complicated and
If the number of times of measurement of the period Tsx and the SOS period Txs is n times, respectively, there is a disadvantage that the measurement time corresponding to rotating the rotary polygon mirror 28 2n times is required, but similar to the modulation timing correction processing shown in FIG. , SOS cycle Tsx and S
The OS cycle Txs is measured several times, and the average value Tsx (Av
Since the modulation start timing of the controlled light beam x is corrected using e) and Txs (Ave), the modulation start timing of the controlled light beam x can be adjusted without being affected by the fluctuation of the rotation speed of the rotary polygon mirror 28. It can be corrected accurately. The invention according to claim 1 includes the above-mentioned aspect.

Further, in the above description, as the "time interval of the light beam detection timing" described in claim 1, the LD for emitting the reference light beam s at the SOS timing of a certain main scanning cycle.
Only the LD that emits the controlled light beam x at the SOS timing of the next main scanning cycle is turned on and the SO is turned on.
An LD that measures the S period Tsx multiple times, turns on only the LD that emits the controlled light beam x at the SOS timing of a certain main scanning period, and emits the reference light beam s at the SOS timing of the next main scanning period. Although the mode in which only the SOS period Txs is measured by lighting only the light source has been described, the present invention is not limited to this, and the "time interval of light beam detection timing" may be, for example, two consecutive main times. L that emits the reference light beam s at the SOS timing of the scanning cycle
Only D is turned on to measure the SOS cycle Tss a plurality of times, and only the LD that emits the controlled light beam x at the SOS timings of two consecutive main scanning cycles is turned on to turn the SOS cycle Txx a plurality of times. You may make it measure. In this case, based on the average value Tss (Ave) of the SOS cycle Tss measured a plurality of times and the average value Txx (Ave) of the SOS cycle Txx measured a plurality of times, the controlled light beam x in each deflection scan by the rotary polygon mirror The modulation start timing of can be corrected.

Further, in the above, according to the present invention, a plurality of light beams emitted from the light source 24 are made to scan on the photoconductor drums 19 different from each other, and monochromatic images of different colors are formed on the respective photoconductor drums 19. An image forming apparatus 10 configured to superimpose a plurality of single-color images formed on the respective photoconductor drums 19 and output as a single color image.
However, the present invention is not limited to this, and is also applied to an image forming apparatus configured to form a plurality of lines of a single image by one scanning with a plurality of light beams. It goes without saying that it is possible.

[0066]

As described above, according to the first aspect of the present invention, only a single light source is turned on during a predetermined period of a period in which a light beam is deflected and scanned by an arbitrary reflecting surface of a rotary polygon mirror. At the same time as turning on only a single light source in a predetermined period of the deflection scanning cycle, the time interval of the detection timing of the light beam by the detection means is measured a plurality of times, and the data obtained by averaging the measured time intervals is obtained. Since the modulation start timing of each light beam in each deflection scan by the rotating polygon mirror is corrected by using a single detecting means capable of detecting a light beam passing a predetermined position within the scanning range, a plurality of light beams are detected. It has an excellent effect that the deviation of the modulation start timing of the light beam can be corrected with high accuracy.

According to a second aspect of the present invention, in the first aspect of the present invention, only a single light source is turned on during a predetermined period of a period in which a light beam is deflected and scanned by an arbitrary reflecting surface of a rotary polygon mirror. Since only a single light source is turned on in a predetermined period of the deflection scanning cycle of 1, the time interval of the detection timing of the light beam by the detecting means is measured for each of a plurality of different reflecting surfaces of the rotary polygon mirror. In addition to the above effects, there is an effect that it is possible to prevent the configuration of the image forming apparatus from becoming complicated.

According to a fourth aspect of the present invention, in the third aspect of the invention, the first light source and the second light source are alternately turned on in a predetermined period in each deflection scanning cycle, so that a plurality of reflections different from each other are obtained. As the surfaces, every other reflecting surface existing along the rotation direction of the rotary polygon mirror is used,
In addition to the above effects, there is an effect that the time required to measure the first time interval and the second time interval can be shortened.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an exemplary embodiment.

FIG. 2 is a schematic configuration diagram of an optical scanning device.

FIG. 3 is a block diagram showing a schematic configuration of a drive control unit connected to the optical scanning device.

FIG. 4 is a flowchart showing an example of modulation timing correction processing.

5A is a measurement of SOS cycle Tsx, FIG. 5B is S
A timing chart of measurement of the OS cycle Txs, (C) is a conceptual diagram for explaining calculation of the timing deviation amount Tx and correction of the modulation start timing.

FIG. 6 is a flowchart showing another example of the modulation timing correction process.

FIG. 7 is an explanatory diagram for explaining a problem in a case where a mirror is provided to separate SOS signals corresponding to individual light beams in a configuration in which light beams are respectively incident on a single SOS sensor.

[Explanation of symbols]

10 image forming apparatus 18K, 18C, 18M, 18Y image forming unit 19 photoconductor drum 20 Optical scanning device 24 light sources 28 rotating polygon mirror 30 Drive control unit 42 SOS sensor 56 Light source drive controller 58 SOS cycle measurement / arithmetic unit 60 Timing adjustment value calculator

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 1/036 B41J 3/00 D 5C072 1/113 H04N 1/04 104A F term (reference) 2C362 AA07 BA04 BA54 BA69 BA70 BA89 BB31 BB32 BB38 BB39 CA22 CA39 2H045 BA22 BA34 CA82 CA88 CA98 2H076 AB05 AB06 AB12 AB22 AB31 AB67 EA01 2H300 EB04 EB07 EB12 EC02 EC05 EF08 EH16 EDB34 C02 DB02 A02 DB22 A02C02 DB02 A04C22 2 DC05 DC07 DE29 EA01 5C072 AA03 BA02 BA04 HA02 HA06 HA09 HA13 HB08 HB11 QA14 XA05

Claims (7)

[Claims] 1. A plurality of light sources that emit light beams, and a plurality of light beams that are respectively emitted from the plurality of light sources and are incident on the same reflecting surface of a plurality of reflecting surfaces that are deflected and scanned. A rotating polygon mirror for detecting, a detecting means capable of detecting a plurality of light beams each of which is deflected and scanned by the rotating polygon mirror and passes a predetermined position within a scanning range of the light beam, and an arbitrary reflecting surface of the rotating polygon mirror. In the cycle in which the light beam is deflected and scanned, only a single light source is turned on in a predetermined period in which the light beam passes through the predetermined position, and only a single light source is turned on in the predetermined period in the next deflection scanning cycle. At the same time, the time interval of the detection timing of the light beam by the detecting means is measured a plurality of times, and the data obtained by averaging the plurality of measured time intervals is used for each deflection scanning by the rotary polygon mirror. An image forming apparatus including: a correction unit that corrects a modulation start timing of an individual light beam in the image forming apparatus. 2. The correcting means turns on only a single light source during the predetermined period of the deflection scanning of the light beam by an arbitrary reflecting surface of the rotary polygon mirror, and the predetermined period of the next deflection scanning period. To turn on only a single light source,
The image forming apparatus according to claim 1, wherein the measuring of the time interval of the detection timing of the light beam by the detecting means is performed for each of a plurality of different reflecting surfaces of the rotary polygon mirror. 3. The correcting means turns on the first light source in the predetermined period of the period in which the light beam is deflected and scanned by an arbitrary reflection surface of the rotary polygon mirror, and the predetermined period of the next deflection scanning period. The second light source is turned on at the same time, and at the same time from the detection of the light beam emitted from the first light source by the detection means to the detection of the light beam emitted from the second light source. The time interval of 1 is measured a plurality of times, and the second light source is turned on during the predetermined period of the deflection scanning of the light beam by an arbitrary reflecting surface, and during the predetermined period of the next deflection scanning period. At the same time as turning on the first light source, the second time from the detection of the light beam emitted from the second light source by the detection means to the detection of the light beam emitted from the first light source. Multiple measuring intervals The light beam emitted from the first light source based on the data obtained by averaging the measured first time intervals and the data obtained by averaging the measured second time intervals. The difference of the passage timing of the light beam emitted from the two light sources at the predetermined position is obtained,
3. The correction start timing of the light beams emitted from the first light source and the second light source is relatively corrected based on the difference in the passage timing.
The image forming apparatus described. 4. The correcting means alternately turns on the first light source and the second light source during the predetermined period in each deflection scanning cycle, whereby a plurality of reflecting surfaces of the rotary polygon mirror different from each other are provided. 4. The image forming apparatus according to claim 3, wherein each of the reflecting surfaces is present as every other reflecting surface along the rotation direction of the rotary polygon mirror. 5. The correction means sets a specific light source to the first light source.
Of the plurality of light sources, the light source used as the second light source is selected from the light sources other than the specific light source, and the light beam emitted from the first light source and the light beam emitted from the second light source are selected. Correcting the modulation start timing of the light beam emitted from the second light source based on the difference in the passage timing of the light beam at the predetermined position,
The image forming apparatus according to claim 3, wherein the light source used as the second light source is repeated while being switched. 6. The correction means controls the turning on / off of the plurality of light sources, measures the time intervals, and corrects the modulation start timing of each light beam by performing image formation by the plurality of light beams. When the image is formed by the plurality of light beams, the predetermined light source is turned on only during the predetermined period in each deflection scanning cycle, and the light emitted from the predetermined light source by the detection means is performed. 2. The image according to claim 1, wherein the control is performed so that the modulation of each light beam in each deflection scan is started at the modulation start timing corrected by the correction unit with reference to the beam detection timing. Forming equipment. 7. The image forming apparatus scans the plurality of light beams on photoconductors different from each other to form an image on each photoconductor, and forms a plurality of images on each photoconductor. The image forming apparatus according to claim 1, wherein the images are superimposed and output as a single image.