JPH09193457A - Method for regulating interval of laser beams of image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to accurately regulate the interval of laser beams on a photosensitive member by detecting the specific position of each pattern in a sub-scanning direction, and regulating the interval of the beams so that the difference between the specific position as a reference and the specific position formed by each laser scanner coincides with a theoretical value. SOLUTION: At the time of alignment regulating a laser beam, the central position of the pattern as a specific position in a sub-scanning direction is detected based on the data from a CCD sensor 28, and the pattern of each laser scanner 18 nearest the sensor 28 is, for example, used as a reference pattern. Then, the difference between the difference between the central position of the reference pattern in the sub-scanning direction and the central position of each pattern in the sub-scanning direction and the theoretical value obtained from the interval as the reference is used as a correction value for each beam of the scanner 18. The interval of the beam on a photosensitive drum 20 is regulated by moving a laser light source or regulating the angle of a reflecting mirror based on the correction value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to a multicolor image forming apparatus equipped with a photoconductor, a plurality of laser scanning devices capable of simultaneously main scanning a plurality of laser beams, and a developing device. On how to adjust the spacing of.

[0002]

2. Description of the Related Art In order to speed up color image formation,
As shown in FIG. 1, the image forming unit 12 for each color (K: black, Y: yellow, M: magenta, C: cyan).
There has been proposed a color image forming apparatus 10 including one each.

In this color image forming apparatus 10, the image reading apparatus 14 scans an original, and the obtained optical signals are separated into R, G, and B color signals by a filter,
This is photoelectrically converted to form an image signal of each color. The image signals of the respective colors are input to the control unit 16, and the control unit 16 outputs these image signals at predetermined timings to the image forming units 12A to 12A.
Output to a 12D laser scanning device (ROS unit) 18. As shown in FIG. 13, each laser scanning device 18 has a laser light source 1 for emitting a laser beam,
A collimator lens 2 that shapes the laser beam emitted from the laser light source 1 into a parallel beam, a rotary polygon mirror 3 that deflects the parallel beam, and an fθ lens 4 for correcting the scanning speed.
And a start position detection sensor 5 for detecting an image signal writing start signal (SOS signal) in the main scanning direction on the photosensitive drum 20, and the photosensitive drum while timing with the image writing start signal. A latent image is formed on each of 20. Next, as shown in FIG. 1, the developing device 22 deposits color toner on the latent image, and the obtained toner image is sequentially conveyed by the transfer belt 24 onto the paper 26.
And is fixed by a fixing device (not shown) arranged downstream of the color image forming apparatus 10 in the conveying direction.

By the way, in the color image forming apparatus 10 as described above, in order to prevent the color deviation due to the position deviation from the reference transfer position in the image forming section 12, a color deviation detecting pattern as shown in FIG. As shown in FIG. 15, the transfer belt 24 is formed on the transfer belt 24 at a constant interval (X), and this is detected by a sensor 28 arranged downstream of the photosensitive drum 20 in the conveying direction. Detecting the central position in the sub-scanning direction, the correction value is obtained from the difference between the detected central position and the theoretical value obtained from the theoretical position between the central position in the sub-scanning direction of the reference pattern and the pattern, The color misregistration is corrected by changing the timing of the image signal output from the control unit 16 to the laser scanning device 18.

However, in order to achieve higher speed and higher image quality, as shown in FIG. 2, in each laser scanning device 18, a plurality of laser beams simultaneously main scan the photosensitive drum 20 to simultaneously scan a plurality of lines. It will be necessary to record. In this case, as shown in FIG. 3, there is a problem that color misregistration occurs due to misalignment (ΔL) of a plurality of laser beams in each laser scanning device 18, and a method for detecting this has been disclosed in JP-A-7-72399. It is shown in the official gazette.

As shown in FIG. 16, Japanese Patent Laid-Open No. 7-72.
The image forming apparatus according to Japanese Patent No. 399 has two right triangular prisms.
The sensors 6A and 6B of
In A and 6B, the end face including the hypotenuse is arranged on the upstream side in the main scanning direction.
Placed so that the extended faces of this end face intersect.
ing. Then, the image forming apparatus uses one of the laser light sources.
Only the light is turned on, and the sensors 6A and 6B emit the laser beam L1.
Time S to detect₁, S _TwoFrom these time differences T₁Seeking
In the same way, turn on only the other laser light source and
The time S during which the lasers 6A and 6B detect the laser beam L2_Three,
S_FourFrom these time differences T_TwoAsk for. And the time difference
T₁, T_TwoDeviation T_ThreeAnd the deviation reference value T
The alignment of the two laser beams L1 and L2
This has been calculated.

Further, as another method of correcting the alignment deviation of a plurality of laser beams in each laser scanning device, as shown in FIG. 17, both beams of LD1 and LD2 are simultaneously turned on and both beams are simultaneously turned off. The density of the pattern 1 created on the photosensitive drum repeatedly, the density of the pattern 2 created on the photosensitive drum by alternately turning on only the LD2 and turning on only the LD1 are determined by the ESV (surface potential) arranged near the photosensitive drum. ) A method has been proposed in which the distance between the laser beams on the photosensitive drum is corrected based on the difference between the measured values by the sensor.

[0008]

However, Japanese Patent Laid-Open No. 7-7
The method disclosed in Japanese Patent No. 2399 requires a sensor dedicated to detecting the deviation of the alignment of the laser beam and requires high mounting accuracy, resulting in high cost.

On the other hand, the method of measuring the density has a problem that the accuracy of the measurement result is not good because the measured value is largely influenced by the sensitivity change of the photosensitive drum due to the surface temperature change and the like.

The present invention has been made to solve the above-mentioned problems, and is applied to an image forming apparatus equipped with a plurality of laser scanning devices capable of simultaneously performing a main scanning with a plurality of laser beams, and is low cost and highly accurate. It is an object of the present invention to provide a method for adjusting the distance between laser beams on a photoconductor.

[0011]

Therefore, the present invention is applied to a multicolor image forming apparatus provided with a photoconductor, a plurality of laser scanning devices capable of simultaneously performing main scanning with a plurality of laser beams, and a developing device. A method of adjusting the spacing between laser beams on the body, wherein each laser scanning device has a pattern of an integer multiple of the number of laser beams, in which a saturated region is formed in the composite light intensity profile, and all lasers of each laser scanning device are formed. The beams are formed at substantially equal intervals so as to form a writing start line of any pattern, and a specific position in the sub-scanning direction of each pattern is detected. The difference between the specific position and the specific position in the sub-scanning direction of each pattern formed by each laser scanning device is obtained from the theoretical distance between the specific positions in the sub-scanning direction. To match the logical value, adjusting the spacing of the laser beam on the photosensitive member.

In an image forming apparatus equipped with a laser scanning device capable of simultaneously performing main scanning with a plurality of laser beams, when all patterns are formed with only one laser beam, laser beam alignment deviations occur at all detected specific positions. Or a specific position in the sub-scanning direction of the reference pattern and all detected specific positions include misalignment of the laser beam alignment, and a specific position in the sub-scanning direction of the reference pattern Also, the misalignment of the laser beam cannot be detected because the misalignment of the laser beam alignment is canceled when the difference between the specific positions of the respective patterns in the sub-scanning direction is obtained. However, the laser beam interval adjusting method of the image forming apparatus according to the present invention has a pattern in which each laser scanning device has an integer multiple of the number of laser beams, and all the laser beams of each laser scanning device have a writing start line of any pattern. Since the laser beams are formed at substantially equal intervals so as to form, the misalignment of the alignment of each laser beam is included in any of the patterns. Therefore, by comparing the difference between the detected specific position and the specific position in the sub-scanning direction of the reference pattern with the theoretical value obtained from the theoretical interval in the sub-scanning direction between the specific positions, The misalignment of the laser beam alignment can be detected.

Further, as shown in FIG. 10, it is also conceivable to use a pattern composed only of the line formed by LD1 and a pattern composed only of the line formed by LD2 in combination, but FIG. As shown in 1
When a pattern is formed by lines, the light intensity profile has a single peak shape and a saturated region, that is, a region where the light intensity is constant, is not formed. Fluctuates greatly.
Further, as shown in FIG. 12, when a pattern is formed by two discontinuous lines formed by the same laser beam, the light intensity profile is not combined or the light intensity profiles are combined even if they are combined. Since the light intensity profile becomes bimodal and one pattern may be broken, it is difficult to accurately detect a specific position.

On the other hand, according to the present invention, each pattern is formed so that a saturation region is formed in the composite light intensity profile obtained by combining the light intensity profiles of the respective laser beams, and the saturated light intensity becomes constant. Since the width of the pattern does not largely change between the region and the skirt region of the light intensity profile, the specific position can be easily detected.

In the above invention, the write start line and the write end line having the same pattern can be formed by the same laser beam.

With this configuration, the width of each pattern can be made to correspond to the scanning pitch, and thus the width of each pattern can be made constant. Therefore, at the time of detecting a specific position of the pattern in the sub-scanning direction. The area for capturing the image data of the pattern can be fixed, and the detection time of the position detecting means can be shortened.

Further, in the pattern formed by each laser scanning device, the writing end line and the writing start line of the next pattern can be formed by the same laser beam.

In this way, in the pattern formed by each laser scanning device, the interval between the edge on the writing end side of the pattern and the edge on the writing start side of the next pattern can be made to correspond to the scanning pitch, As a result, the interval between the edges can be made constant, so that it is possible to fix the capture prohibited area of the image data of the pattern at the time of detecting the specific position of the pattern in the sub-scanning direction, and to reduce the detection time of the position detecting means. It can be shortened.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIGS.

FIG. 1 shows a color image forming apparatus 10 to which a laser beam interval adjusting method according to an embodiment of the present invention is applied. The color image forming apparatus 10 is
Control including a CPU, a ROM that stores a program for controlling the entire color image forming apparatus 10 and pattern creation data for adjusting a laser beam interval, which will be described later, an input / output buffer, a RAM as a work area, and an operation panel A scanning unit 16; an image reading device 14 which scans an original to obtain an optical signal of each color by a filter and photoelectrically converts the signals into an image signal of each color; and two pairs of conveying rollers 30 and 32. An endless transfer belt 24 that is wrapped around the transport rollers 30 and 32 and can transmit light.

Above the transfer belt 24, an image forming portion 12A for forming a black (K) image and a yellow (Y) image are formed.
An image forming unit 12B for forming an image, an image forming unit 12C for forming a magenta (M) image, and an image forming unit 12D for forming a cyan (C) image are arranged at substantially equal intervals in the transport direction (arrow A direction). ing.

The image forming sections 12A to 12D have the same structure, and each of the image forming sections 12A to 12D has
The photosensitive drum 20 is arranged such that its axial direction is orthogonal to the transport direction (direction of arrow A).
A charger 34 for charging the photosensitive drum 20 and a dual beam type laser scanning device (ROS) 1 for forming a latent image on the charged photosensitive drum 20 are provided around the photosensitive drum 20.
8. Developing device 2 for attaching toner of each color to the latent image
2 and a cleaning device 36 for removing the toner left on the photosensitive drum 20.

A CC for reading a pattern formed on the transfer belt 24 is provided on the downstream side of the image forming unit 12 in the conveying direction and on the upper side of both sides in the width direction of the transfer belt 24.
The D sensor 28 is arranged, and the CCD sensor 28 is the control unit 1.
6 is connected to the A / D (analog / digital) conversion circuit 38 connected to the circuit 6. Further, a light source 40 is arranged below the transfer belt 24 facing the CCD sensor 28, and a pattern formed on the transfer belt 24 is provided at a position facing the transport rollers 30 and 32 on the downstream side in the transport direction. A cleaner 42 for removing is arranged.

As shown in FIG. 2, the laser scanning device 1
Reference numeral 8 denotes a laser light source unit 44 having two laser light sources arranged along the sub-scanning direction, a collimator lens 46 for making a laser beam emitted from the laser light source unit 44 a parallel beam, and rotating at a substantially constant angular velocity. A rotating polygon mirror 48 for deflecting the parallel beam, an fθ lens 50 for correcting the scanning speed, a start position detection sensor 52 for detecting an image signal writing start signal on the photosensitive drum 20 in the main scanning direction, Is equipped with.

Further, as shown in FIG. 3, the reference interval L between the laser beams (between LD1 and LD2 in FIG. 3) in each laser scanning device 18 is set to an interval such that laser beam spots of adjacent lines overlap. The scanning pitch (Q) is twice the reference interval L between the laser beams. Further, the deviation of the alignment of the LD 2 in each laser scanning device 18 from the reference interval L is ΔL.

FIG. 4 shows an example of a pattern for adjusting the laser beam interval. Here, two types of patterns formed by three continuous lines formed in each laser scanning device 18 are used, and a saturated region is formed in the composite light intensity profile of each pattern. Then, the pattern 1 (P1) is formed by LD1, LD2, and LD1, and the lines formed by LD1 are the write start line and the write end line.
Pattern 2 (P2) is LD2, LD1 and LD2.
The lines formed by LD2 and LD2 are the write start line and the write end line.

At the time of pattern formation, the control unit 16 equidistantly (4X) the respective laser scanning devices 18 at positions where they pass below the CCD sensor 28 due to the movement of the transfer belt 24.
Pattern 1 and pattern 2 are formed by the same method, and the same type of pattern is formed in each laser scanning device 18, for example, pattern 1
Are formed at equal intervals (X). This allows pattern 1
Is a group A (GA) arranged in parallel in the sub-scanning direction in the order of K, Y, M, and C, and pattern 2 is K, Y, M,
Group B arranged in parallel in the sub-scanning direction in the order of C
And (GB) are arranged on both sides of the transfer belt 24. As shown in FIG. 4B, the group A and the group B may be repeatedly formed, and each laser scanning device 1
The number of patterns formed on one side of the transfer belt 24 by 8 is an integral multiple of the number of laser beams of each laser scanning device 18, and as a whole, the product of the number of laser scanning devices and the number of laser beams of each laser scanning device 18 is obtained. An integral multiple pattern is formed.

The alignment adjustment of laser beams when the same number of patterns as the laser beams of each laser scanning device 18 are formed will be described below.

When adjusting the alignment of the laser beam,
Based on the data from the CCD sensor 28, the center position in the sub-scanning direction of the pattern as a specific position is detected, and, for example, each laser scanning device 1 closest to the CCD sensor 28.
8 patterns {upper pattern 1 in FIG. 4B} are used as reference patterns for each laser scanning device 18. When the patterns formed by each laser scanning device 18 are sequentially numbered from the reference pattern as n = 1, 2, the difference between the center position of the reference pattern in the sub-scanning direction and the center position of each pattern in the sub-scanning direction, Theoretical value obtained from the standard interval, that is, 4
The difference from X × (n−1) is set as a correction value for each laser beam of each laser scanning device 18.

Here, assuming that the central position in the sub-scanning direction of the write start line of the reference pattern {Pattern 1 of FIG. 4A} is X ₀ , in pattern 1, LD1 constitutes the write start line and the write end line. Because
The central position is (X ₀ + L) [= {X ₀ + (X ₀ +2
L)} / 2] and the LD2 alignment deviation (Δ
L) is not included. On the other hand, in the pattern 2, since the LD 2 constitutes the write start line and the write end line, the center position thereof is (X ₀ + 4X + L + ΔL) [=
{(X ₀ + 4X + ΔL) + (X ₀ + 4X + 2L + Δ
L)} / 2] and the LD2 alignment deviation (Δ
L). Therefore, the difference between the center position of the pattern 1 which is the reference pattern in the sub-scanning direction and the center position of the pattern 2 in the sub-scanning direction, that is, (4X + ΔL), and the theoretical value obtained from the reference interval, that is, 4X Is equal to the deviation ΔL of the LD2 alignment. Then this ΔL
Is set as a correction value, and the laser beam interval on the photosensitive drum 20 is adjusted based on the correction value. Photosensitive drum 2
The laser beam interval on the laser light source unit 44
When the laser light source is movable in the sub-scanning direction, the laser light source is moved or the rotary polygon mirror 48
If a reflection mirror (not shown) whose angle is adjustable is disposed between the photosensitive drum 20 and the photosensitive drum 20, the angle can be adjusted by adjusting the angle of the reflection mirror.

The calculation of the correction value and the adjustment of the laser beam interval are performed for each laser scanning device 18.

As described above, in the laser beam interval adjusting method in the color image forming apparatus 10 according to this embodiment, as shown in FIG.
Since the saturated region is formed in the composite light intensity profile of the pattern formed in 8, it is possible to reduce the change in the width of the pattern with respect to the change in the sensitivity of the photosensitive drum 20,
It is possible to easily detect the center position of each pattern in the sub-scanning direction.

Further, in the pattern shown in FIG. 4,
The writing start line and the writing end line of each pattern are formed by the same laser beam, and the width (d ₁ ) of the pattern can be made to correspond to the scanning pitch, thereby making the width of each pattern constant. Because you can
As shown in FIG. 6, it is possible to fix the image data fetching area at the time of detecting the central position of each pattern in the sub-scanning direction, and it is possible to shorten the detection time of the central position.

Further, the CCD sensor 28 can be used for detecting the positional deviation detection pattern from the reference transfer position of each laser scanning device 18 and for detecting the laser beam interval adjustment pattern on the photosensitive drum 20. Since a sensor dedicated to detecting the laser beam interval adjustment pattern on the drum 20 is not required, the cost of the color image forming apparatus 10 can be reduced.

When the laser scanning device 18 is a triple beam type laser scanning device, the laser beam L
Misalignment of D2 and LD3 (ΔL2,
To detect ΔL3), for example, the pattern shown in FIG. 5 can be used. Here, FIG. 5 (A)
As shown in FIG. 3, three types of patterns composed of three continuous lines formed in each laser scanning device 18 are used, and the composite light intensity profile of each pattern is similar to the pattern of FIG. A saturated region is formed. The pattern 1 (P1) is formed by LD1, LD2 and LD3. Also, pattern 2 (P2) is L
It is formed by D3, LD1 and LD2. Further, the pattern 3 (P3) is formed by LD2, LD3 and LD1. Then, in the pattern formed by each laser scanning device 18, the writing end line and the writing start line of the next pattern are formed by the same laser beam.
That is, for example, the laser scanning device 18 of the image forming unit 12A
The writing end line of the pattern 1 formed by the above and the writing start line of the pattern 2 which is the next pattern formed by the laser scanning device 18 of the image forming unit 12A are formed by the same laser beam LD3.

The operation of the control unit 16 at the time of pattern formation is similar to that of the pattern shown in FIG. 4, whereby the pattern 1 is arranged in the order of K, Y, M, and C in the sub-scanning direction. Group A (GA) arranged in the same direction, group B (GB) in which pattern 2 is arranged in parallel in the sub-scanning direction in the order of K, Y, M, V, and pattern 3 in K, Y,
A group C (GC) arranged in parallel in the sub-scanning direction in the order of M and C is arranged.

When adjusting the alignment of the laser beam,
Based on the data from the CCD sensor 28, the center position in the sub-scanning direction of the pattern as a specific position is detected, and C
The pattern (pattern 1 in FIG. 5B) of each laser scanning device 18 closest to the CD sensor 28 is set to each laser scanning device 1.
8 reference patterns. Next, the difference between the center position of the reference pattern in the sub-scanning direction and the center position of the next pattern in the sub-scanning direction and the theoretical value obtained from the reference interval, that is, 4X, is used as the correction value.

Here, assuming that the central position in the sub-scanning direction of the write start line of the reference pattern {Pattern 1 of FIG. 5A} is X ₀ , in pattern 1, LD1 forms the write start line and LD3 forms Since the write end line is configured, the center position thereof is {X ₀ + L + (ΔL3)
/ 2} [= {X ₀ + (X ₀ + 2L + ΔL3)} / 2], which is one half of the misalignment of the LD3 {(ΔL
3) / 2} is included. On the other hand, in pattern 2, since LD3 forms the write start line and LD2 forms the write end line, the central position thereof is {X ₀ + 4X + L.
+ (ΔL3 + ΔL2) / 2} [= {(X ₀ + 4X + ΔL
3) + (X ₀ + 4X + 2L + ΔL2)} / 2],
Half the displacement of the LD2 alignment {(ΔL2) /
2} and one half of the misalignment of LD3 {(ΔL
3) / 2}. Therefore, the difference between the center position in the sub-scanning direction of pattern 1 and the center position in the sub-scanning direction of pattern 2, which is the reference pattern, that is, {4X + (ΔL2) / 2}
And the theoretical value obtained from the reference interval, that is, 4X
Is half the deviation of the LD2 alignment
It matches {(ΔL2) / 2}.

Next, using pattern 2 as a reference pattern, a theoretical value obtained from the difference between the center position of the reference pattern in the sub-scanning direction and the center position of the next pattern in the sub-scanning direction and the reference interval, that is, 4X. The difference between and is the correction value.

Here, the center position of pattern 2 is {X ₀ + 4X + L + (ΔL3 + ΔL2) / 2} as described above, while in pattern 3, LD2 forms the write start line and LD1 forms the write end line. Therefore, the central position is {X ₀ + 8X + L + (ΔL2) /
2} [= {(X ₀ + 8X + ΔL2) + (X ₀ + 8X + 2
L)} / 2], and the deviation of the alignment of LD2 is 2
Includes a fraction {(ΔL2) / 2}. Therefore, the difference between the center position of the reference pattern in the sub-scanning direction of the pattern 2 and the center position of the pattern 3 in the sub-scanning direction, that is, {4X- (Δ
The difference between L3) / 2} and the theoretical value obtained from the reference interval, that is, 4X, is equal to one half of the deviation of the alignment of LD3 {(ΔL3) / 2}.

In this way, the reference patterns are sequentially shifted,
The difference between the center position of the reference pattern in the sub-scanning direction and the center position of the next pattern in the sub-scanning direction, and the theoretical value obtained from the reference interval are used as correction values, and on the photosensitive drum 20 based on this correction value. The spacing of the laser beams at can be adjusted.

In the pattern of FIG. 5, each laser scanning device 1
In the pattern formed in No. 8, the interval (d ₂ ) between the edge on the writing end side of the pattern and the edge on the writing start side of the next pattern can be made to correspond to the scanning pitch. Since it can be fixed, it is possible to fix the capture prohibited area of the image data of the pattern when detecting the center position of the pattern in the sub-scanning direction, and it is possible to shorten the calculation time of the position detecting means. In addition, it is possible to reduce the memory for storing the data and to reduce the cost.

In the above-mentioned embodiment, each pattern is composed of three continuous lines, but each laser scanning device 1 if a saturated region is formed in the composite light intensity profile.
It may be composed of four or more continuous lines formed in 8.

Further, in the above embodiment, the same kind of pattern, for example, pattern 1 is formed so as to be continuous in the order of K, Y, M, and C, but one laser scanning device 18 is used.
The patterns formed in 1 may be arranged continuously. That is, for example, a pattern for the image forming unit 12A (for example,
Patterns for the image forming unit 12B (for example, YP1 and YP in FIG. 4) are formed by continuously forming KP1 and KP2 in FIG.
2) may be formed continuously.

Further, in the above embodiment, the center position of each pattern in the sub-scanning direction is the specific position, but the position of the write start side edge or the write end side edge of each pattern may be the specific position.

Although the method of adjusting the laser beam interval has been described, the color misregistration may be minimized when the color image forming apparatus 10 does not have a correction unit for adjusting the laser beam interval. Specifically, the above-mentioned pattern is used to calculate the interval between the laser beams located at both ends, and the calculated average value of the intervals between the laser beams located at both ends and the interval between the laser beams located at both ends. The output timing and the like of the image signal output to each laser scanning device 18 is adjusted based on the difference from the theoretical average value of. For example, when each laser scanning device 18 is a dual-beam type laser scanning device, as described above, the deviation ΔL of the alignment from the reference interval L of LD2 from the pattern of FIG. 4, and thus the interval (L + ΔL) between LD1 and LD2. Is detected. Then, the average value (L + ΔL) / 2 of the intervals between the laser beams LD1 and LD2 located at both ends and the theoretical average value L of the intervals between the laser beams LD1 and LD2 located at both ends.
The output timing of the image signal to be output to each laser scanning device 18 is adjusted based on the difference from / 2, that is, ΔL / 2. That is, for example, the image forming unit 12A and the image forming unit 1
2B and LD of the laser scanning device 18 of the image forming unit 12C
The misalignment of 2 is 0, and the image forming unit 12
When the misalignment of the LD2 of the laser scanning device 18 of _D is ΔL _D , the LD of the image forming unit 12D is
1, LD2 line formed by, respectively from the line formed by 12A~C of LD1, LD2 of the image forming unit so as to [Delta] L _D / 2 shifted, the output timing of the image signal to be output to the laser scanning device 18 adjust. If the output timing is not adjusted in this way, the lines formed by the LD1 of each image forming unit 12 are the same, but the lines formed by the LD2 of the image forming unit 12D are the same as those of the image forming units 12A to 12C. Since ΔL _D shifts from the line formed by LD2, unacceptable color shift occurs when ΔL _D is large. But,
The deviation can be dispersed by adjusting the output timing as described above. When each laser scanning device 18 is a triple-beam type laser scanning device, the average value (2L + ΔL) of the intervals between the laser beams LD1 and LD3 located at both ends is used by using the pattern of FIG. 5 as described above.
3) / 2 and laser beams LD1 and LD located at both ends
The difference from the theoretical average value L of the intervals between 3, ie, (ΔL
3) / 2, the output timing of the image signal output to each laser scanning device 18 is adjusted.

Degradation of image quality is caused by misalignment between laser beams on the photosensitive drum 20, as well as oblique lines and stair-like defects (jagged edges) at the time of curve formation. In the scanning method, there is known a method of preventing this by changing the LD light amount and adjusting the position of one dot or less at the edge of the image. In this method, the following correction is performed in order to reduce variations due to changes in the LD light amount and changes in the sensitivity of the photosensitive drum 20, and to perform stable control.

First, while measuring the light quantity (LD light quantity) of the laser beam by a light quantity measuring device (not shown) arranged in the vicinity of the laser light source, a pattern in which the LD light quantity is changed in k steps is formed on the photosensitive drum 20. As shown in FIG. 7, the potential of the photosensitive drum 20 where the latent image is formed is measured by an ESV sensor arranged near the photosensitive drum 20 between the laser scanning device 18 and the developing device 22, Figure 8
The electric potential characteristic of the photosensitive drum 20 with respect to the LD light amount shown in is obtained. Next, an LD light amount satisfying the target potential VL is obtained from the potential characteristic of the photosensitive drum 20 with respect to the obtained LD light amount, and this is set as the reference LD light amount. Next, when the width in the sub-scanning direction of the pattern formed by three continuous lines formed by the laser beam of the reference LD light quantity is 3 dots, the width of the pattern in the sub-scanning direction is 1 / each. 4,
1/2, 3/4 dot change [(edge change) = {Δ
L * 2 (SOS side) + [Delta] L * 2 (EOS side) / 2]] is calculated based on a predetermined calculation formula.

Next, as shown in FIG. 9, in addition to the above-mentioned pattern for adjusting the interval, a pattern composed of three lines formed by a laser beam of a reference LD light amount is provided for each laser scanning device. 1 (P1), and one line formed by the laser beam of the reference LD light amount and the theoretical value of the LD light amount that changes the width in the sub-scanning direction of the two lines and the pattern by 1/2 dot. The pattern 2 (P2) composed of the lines is alternately formed. Next, the center position of each pattern in the sub-scanning direction is detected, and the pattern 2
The width of the pattern in the sub-scanning direction can be changed by 1/2 dot based on the difference between the actual center position of the pattern in the sub-scanning direction and the theoretical value of the center position of the pattern 2 in the sub-scanning direction. A correction value for the LD light amount of the line is obtained.

Then, the temperature of the photosensitive drum 20 is measured by a temperature sensor arranged in the vicinity of the photosensitive drum 20 in advance, and L
The set value of the LD light amount with respect to the temperature of the photosensitive drum 20 measured from the potential characteristic of the photosensitive drum 20 and the correction value with respect to the D light amount is predicted. As described above, it is possible to effectively prevent the color misregistration due to the sensitivity change of the photosensitive drum 20 after the laser beam interval adjustment on the photosensitive drum 20.

[0051]

According to the laser beam interval adjusting method for an image forming apparatus of the present invention, in each laser scanning device, a pattern of an integer multiple of the number of laser beams is formed in the composite light intensity profile and a saturated region is formed, and each laser scanning is performed. Since all the laser beams of the apparatus are formed at substantially equal intervals so as to form the write start line of any pattern, the misalignment of each laser beam is included in any pattern and the detected By comparing the difference between the specific position and the specific position in the sub-scanning direction of the reference pattern with the theoretical value obtained from the theoretical distance between the specific positions in the sub-scanning direction, the alignment deviation of the laser beam on the photoconductor can be determined. Can be detected.

Further, in the method for adjusting the laser beam interval of the image forming apparatus according to the present invention, the saturated area is formed in the composite light intensity profile of each pattern, so that the change of the pattern width due to the sensitivity change of the photoconductor is reduced. Therefore, it is possible to easily detect the specific position.

Further, in the laser beam interval adjusting method of the image forming apparatus according to the present invention, the write start line and the write end line of the same pattern are formed by the same laser beam, whereby the width of each pattern is reduced. Since it can be fixed, it is possible to fix the capture area of the image data of the pattern when detecting the specific position of the pattern in the sub-scanning direction, and it is possible to shorten the detection time of the position detection means.

Further, in the laser beam interval adjusting method of the image forming apparatus according to the present invention, in the pattern formed by each laser scanning device, the writing end line and the writing start line of the next pattern are formed by the same laser beam. Therefore, the interval between the edge on the writing end side of the pattern and the edge on the writing start side of the next pattern formed by the same laser scanning device can be made to correspond to the scanning pitch. Since it is possible to keep constant, it is possible to fix the capture prohibited area of the image data of the pattern at the time of detecting the specific position of the pattern in the sub-scanning direction, and it is possible to shorten the detection time of the position detecting means.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a color image forming apparatus to which the present invention is applied.

FIG. 2 is a schematic configuration diagram of a laser scanning device included in the color image forming apparatus of FIG.

FIG. 3 is an explanatory diagram showing a positional relationship between beam spots of two laser beams and a scanning pitch in one laser scanning device.

FIG. 4 is an example of a pattern for adjusting a laser beam interval, which is formed in the embodiment of the present invention and is applied to a dual beam type laser scanning device.

FIG. 5 is an example of a laser beam interval adjustment pattern formed in the embodiment of the present invention and applied to a triple beam type laser scanning device.

FIG. 6 is an explanatory diagram showing a positional relationship between an image data capture area and an image data capture prohibited area.

FIG. 7 is an explanatory diagram illustrating a step for correcting the LD light amount.

FIG. 8 is a graph showing a potential characteristic of a photosensitive drum with respect to an LD light amount.

FIG. 9 is an example of a pattern for adjusting the LD light amount.

FIG. 10 is an example of a pattern for adjusting a laser beam interval.

FIG. 11 is a diagram showing a relationship between the number of lines forming a pattern and a light intensity profile, and is a diagram showing a case where the pattern is formed by one line.

FIG. 12 is a diagram showing a relationship between the number of lines forming a pattern and a light intensity profile, in which the pattern is non-continuous 2
It is a figure which shows the case where it is comprised by the line.

FIG. 13 is a schematic configuration diagram of a single-beam type laser scanning device.

FIG. 14 is an example of a pattern for detecting a positional deviation from a reference transfer position of a laser scanning device applied to a color image forming apparatus including a plurality of single beam type laser scanning devices.

FIG. 15 is a schematic perspective view of a color image forming apparatus including a plurality of laser scanning devices.

FIG. 16 is an explanatory diagram illustrating an example of a conventional beam interval adjustment method for correcting misalignment between beams in a multi-beam type laser scanning device.

FIG. 17 is an explanatory diagram illustrating an example of a conventional beam interval adjustment method for correcting misalignment between beams in a multi-beam type laser scanning device.

[Explanation of symbols]

 10 Color Image Forming Device 16 Control Unit 18 Laser Scanning Device 20 Photosensitive Drum 22 Developing Device 28 CCD Sensor

Claims (3)

[Claims] 1. A multicolor image forming apparatus comprising a photoconductor, a plurality of laser scanning devices capable of simultaneously performing main scanning with a plurality of laser beams, and a developing device, and adjusting the interval of the laser beams on the photoconductor. In the method, in each laser scanning device, a pattern of an integral multiple of the number of laser beams is formed in a composite light intensity profile, and a saturated region is formed, and all the laser beams of each laser scanning device have a writing start line of any pattern. Are formed at substantially equal intervals so that a specific position in the sub-scanning direction of each pattern is detected, and a specific position in the sub-scanning direction of the reference pattern in each laser scanning device and each laser scanning device are formed. In order to make the difference between the specific positions in the sub-scanning direction of each pattern coincide with the theoretical value obtained from the theoretical distance between the specific positions in the sub-scanning direction, A laser beam interval adjusting method for an image forming apparatus, which adjusts an interval between laser beams on a body. 2. A laser beam interval adjusting method for an image forming apparatus according to claim 1, wherein the write start line and the write end line of the same pattern are formed by the same laser beam. 3. The image forming apparatus according to claim 1, wherein in a pattern formed by each laser scanning device, a writing end line and a writing start line of the next pattern are formed by the same laser beam. Laser beam spacing adjustment method.