JPH08146319A - Image forming device - Google Patents

Abstract

(57) [Abstract] [Purpose] The structure of the correction means for correcting the image shift is simplified to reduce the cost, the vibration of the mirror pair that causes the unevenness of the image density is suppressed, and the amount is very small. An image forming apparatus provided with a correction unit capable of effectively correcting a magnification shift. A misalignment correcting means for performing misalignment in the image scanning direction and misalignment in a direction perpendicular to the image scanning direction at an on / off timing of a laser beam to be scanned, and an incident scanning line for correcting an inclination misalignment. A pair of mirrors 6M and 7M that are rotatable in a predetermined vertical plane are arranged substantially at right angles to each other, and a pair of mirrors 5 (tilt deviation correcting means), a length of a reference image in a scanning direction for correcting a magnification deviation, and a length of each image. An image forming apparatus comprising: a magnification deviation correcting unit that compares lengths in a scanning direction and shifts a writing position in the scanning direction between a reference image and each image by about ½ of an absolute amount of the comparison value.

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 provided with a plurality of scanning optical systems and provided with a correction means for correcting an image shift caused by the scanning optical systems when forming images on a recording medium in a multiplex manner. .

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus of this type has a structure as shown in FIG. 6, and FIG.

In FIG. 6, a laser beam emitted from a laser light source (not shown) is bidirectionally scanned by a rotary polygon mirror 103 rotating in the direction of arrow B in the figure, and cyan (C), magenta (M), and yellow ( Fθ lens (not shown) corresponding to Y) and black (BK) respectively
Scanning line 102C passing through the fθ lens,
102M, 102Y, 102BK indicate arrow A'in the figure
Photoconductor drums 101C, 101M, 10 rotating in the direction
An image is formed on 1Y and 101BK by a known electrophotographic process, and is transferred in the arrow X'direction in the drawing.
By performing multiple transfer on No. 05, multiple images are formed. Incidentally, 113 is a transfer belt, and 114 is a transfer belt drive roller. 106C, 107C, 108C, 1
06M, ... Are reflection mirrors.

In such an apparatus having a plurality of image forming stations, since images of different colors are sequentially transferred onto the same surface of the same transfer material 105, the transfer image position in each image forming station is changed from the ideal reference position. For example, in the case of a multi-color image, image gaps or overlaps of different colors may occur, and in the case of a color image, a difference in color tint may occur, and when the degree is severe, a color shift may appear. The quality was significantly deteriorated.

By the way, as the type of positional deviation of the transferred image, as shown in FIGS. 7A, 7B, 7C and 7D, the scanning line writing direction (X1 'direction in the drawing) is used. Positional deviation (top margin) (FIG. 7A), positional deviation in the scanning direction (B'direction orthogonal to X1 'direction in the figure) (left margin) (FIG. 7B), tilt deviation in diagonal direction ( Figure 7
(C)), magnification shift (FIG. 7 (d)), etc., and in reality, the above four types of shifts are superimposed.

The main cause of the image shift is shown in FIG.
In the case of the top margin shown in (a), it is a deviation of the image writing timing of each image forming station (hereinafter, simply referred to as a station), and in the case of the left margin of FIG. In the case of the writing timing, that is, the deviation of the scanning start timing in one scanning line, and in the case of the inclination deviation in the oblique direction of FIG. 7C, the attachment angle deviation of the scanning optical system or the angular deviation of the rotation axis of the photoconductor drum In the case of the magnification shift of FIG. 7D, the scanning line length shift is caused by the error ΔL in the optical path length from the optical scanning optical system of each station to the photosensitive drum.

Therefore, regarding the top margin and the left margin, the scanning lines 102C, 102M, 102Y, 10
The amount of deviation is corrected by electrically adjusting the scanning timing of 2BK.

As for the magnification deviation and the inclination deviation, as shown in FIG. 8, of the folding mirrors in the optical path of each station, for example, a pair of mirrors 206 and 207 are arranged at a right angle to form a substantially inverted V shape. The mirror pair 200 is independently adjusted with respect to the apparatus main body in the arrow E'direction and the arrow F'direction, respectively, so that the respective shift amounts can be corrected.

Actuators 227 and 228 such as a linear step actuator having a step motor, which is a drive source for linearly moving in stages, are provided as adjusting means for performing these adjustments.

The mirrors 206 and 207 are mirror holders 2.
The mirror holder 231 supported by the oscillating plate 231 moves the pressing portion 234 in the F ′ direction by the actuator 228 supported by the three fulcrums 232 a, 232 b, 232 c with respect to the oscillating plate 232 and supported by the oscillating plate 232. , 2
07 is rotated around the fulcrum 232a.

The oscillating plate 232 is supported by fulcrums 232d and 232e with respect to a fixed plate 233 which is fixed to the main body of the apparatus, and an actuator 227 supported by the fixed plate 233 moves a pressing portion 235 in the E'direction to cause a mirror. 206, 20
7 is rotated about fulcrums 232d and 232e.

Here, in order to correct the tilt deviation in FIG. 7C, it is possible to drive the actuator 228 as shown in FIG. 6C to shift the tilt positions of the front and back of the mirrors 206 and 207. Becomes

To correct the magnification deviation shown in FIG. 7D, the actuator 227 is driven to rotate the mirrors 206 and 207 including the oscillating plate 232 as shown in FIG. This is possible by changing the optical path length to the photosensitive drum of the scanning optical system. As described above, the mirrors 206 and 207 in which a pair of mirrors are installed at a substantially right angle are provided on the photosensitive drums 101C, 101M and 10 from the scanning optical device.
Scan lines 102C, 102M, 1 up to 1Y, 101BK
The pair of mirrors 2 are arranged in the optical path of 02Y, 102BK.
By adjusting the positions of 06 and 207 by the actuator 227 or the actuator 228, the optical path length or the scanning lines 102C, 102M, 102Y and 102B can be adjusted.
The inclination of K in the scanning direction can be adjusted independently.

That is, by moving the mirror pair 200 provided with a pair of mirror-shaped mirrors 206 and 207 in the E'direction, the photoconductor drums 101C and 101C are moved.
Scanning line 102 formed on M, 101Y, 101BK
Without changing the positions of C, 102M, 102Y, 102BK, the scanning lines 102C, 102M, 102Y, 102
Only the optical path length of BK, that is, the magnification shift can be corrected, and the scanning lines 102C, 102M, 102 can be moved by moving the pair of mirrors 206, 207 in the F'direction.
It is possible to correct the image forming position and angle on the photoconductor drums 101C, 101M, 101Y and 101BK without changing the optical path lengths of Y and 102BK.

Further, the above-mentioned means for reading various positional deviations is disclosed, for example, in Japanese Patent Application No. 4-196368 (image forming apparatus and scanning optical apparatus).

[0016]

However, since the structure of the mirror pair having the above-mentioned positional deviation correcting mechanism becomes very complicated, the following problems occur.

First, in order to drive the mirror pair, two actuators for tilt correction and magnification correction are required.
The actuator is an expensive component, and if the actuator drive circuit is included, the product cost will increase.
Further, accompanying this, the number of machine constituent parts also increases, so that the overall product cost greatly increases.

Next, the structure for supporting the mirror pair is a fixed plate,
Due to the triple structure of the oscillating plate and the mirror holder, the vibrations due to the natural vibration mode and the forced vibration mode are transmitted to the mirror by the excitation force from each drive source of the device main body.
Depending on the mode, the scanning line on the photosensitive drum causes a slight vibration in the transfer material feeding direction X ′ to cause a positional deviation. The frequency of the vibration that causes this misalignment is higher than the feed speed of the transfer material, and it occurs repeatedly in the transfer material.
It appeared as light and shade unevenness in the image, which was a cause of remarkably degrading the image quality.

It has been experimentally confirmed that the amount of magnification deviation in an actual apparatus is as small as 30 μm or less. However, in order to accurately correct a minute amount of 30 μm or less, a fixed plate is used. It is necessary to increase the mounting accuracy with the oscillating plate to make it a structure without backlash, which not only complicates the holding structure of the mirror pair, but also requires very high processing accuracy, which causes cost problems. There was a problem that became a constraint in handling the device.

The present invention has been made in order to solve the above-mentioned problems of the prior art, and its object is to simplify the structure of the correction means for correcting the image shift to reduce the cost, and An object of the present invention is to provide an image forming apparatus that includes a correction unit that suppresses vibration of a mirror pair that causes unevenness in image density and that can effectively correct a minute magnification shift.

[0021]

In order to solve the above problems, the present invention provides at least one photoconductor drum and a plurality of scans for scanning the photoconductor drum to form a charged latent image. In an image forming apparatus that includes an optical system and a correction unit that corrects the deviation of each image formed in each scanning optical system by comparing it with a reference image The correction means corrects only the positional deviation and inclination deviation of each image from the reference image, and performs correction control to minimize the absolute amount of the comparison value of the deviation from the reference image.

Further, the correction means compares the length of the reference image in the scanning direction with the length of each image in the scanning direction as a magnification deviation correction, and the reference image and each image are halved by an absolute amount of the comparison value. It is characterized in that the writing start position in the scanning direction is shifted.

Further, the correcting means includes a mirror pair in which a pair of mirrors are arranged on the scanning optical path at a substantially right angle, and the mirror pair is rotatable on a predetermined plane substantially perpendicular to an incident scanning line. Characterize.

[0024]

In the image forming apparatus constructed as described above, the image formed by the plurality of scanning optical systems is corrected by the correcting means for the positional deviation and the inclination deviation with respect to the reference image, and the magnification is further increased. As the correction, the image to be corrected is moved to a position where the absolute amount of the comparison value of the deviation from the reference image is minimized.

Further, as a magnification correction, the length of the reference image in the scanning direction is compared with the length of each image in the scanning direction, and the writing position of each image is written to the reference image by about 1/2 of the absolute amount of the comparison value. Move from position.

Further, by providing a mirror pair in which a pair of mirrors are arranged at a substantially right angle on the scanning optical path, tilt deviation is corrected by rotating the mirror pair in a predetermined plane substantially perpendicular to the incident scanning line. To do.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to illustrated embodiments.

FIG. 1 shows a mirror pair 5 as a tilt deviation correcting means for an image deviation provided in a scanning optical system for correcting an image deviation according to the present invention. The mirror pair 200 is shown in FIG. Corresponding.

FIG. 2 is provided with an image shift correcting means according to the present invention, and each image formed by a plurality of scanning optical systems 9C, 9M, 9Y, 9BK can be formed on a sheet material S which is a recording medium in a multiple manner. FIG. 3 is an explanatory diagram of a main part of the image forming apparatus.

The structure of the image forming apparatus to which the present invention is applied will be described with reference to FIG. Reference numerals 9C, 9M, 9Y and 9BK are scanning optical systems. For example, the scanning optical system 9M scans a laser light source (not shown) and a laser beam emitted from the laser light source as a scanning line 2M in the direction of arrow B in the figure. It is composed of a rotating polygonal mirror 3 that rotates, an fθ lens (not shown) corresponding to magenta (M), and a plurality of mirrors 6M, 7M, and 8M arranged on the optical path of the scanning line 2M. The scanning line 2M scanned by the scanning optical system 9M scans on the photosensitive drum 1M rotating in the direction of arrow A in the figure to form a charged latent image, and then an image is formed by a known electrophotographic process. It is transferred onto the transfer material 5 that is conveyed in the direction of the arrow X.

The above process is carried out in the same manner as for magenta (M) corresponding to cyan (C), yellow (Y), and black (BK), and multiplex is carried out by successively carrying out multiple transfer on the transfer material 5 being conveyed. It forms an image. In addition, 4B is a transfer belt, and 4 is a transfer belt driving roller. 6C,
Reference numerals 7C, 8C, 6M, ... Are reflection mirrors.

In the image forming apparatus having this structure, there are four types of misregistration, that is, the top margin and the left margin, the misalignment, and the magnification deviation, which are positional deviations, as described with reference to FIG. 7 in the description of the prior art. Since they occur, a correction unit for correcting these deviations by comparing with the reference image is provided.

Next, the correction means will be described. In this embodiment, a case where a cyan (C) image formed by the scanning line 2C is used as a reference image and a magenta (M) image is corrected by comparison with the reference image is shown in FIGS. This will be explained in Section 5. In addition, yellow (Y), black (B
The same applies to K).

In FIGS. 1 and 3, reference numeral 5 denotes a mirror pair as a tilt deviation correcting means, and the mirrors 6M and 7M are supported by a mirror holder 31 at a substantially right angle. The mirror holder 31 has three fulcrums 33a, 33b,
By moving the pressing portion 34 in the F direction by the linear step actuator 28 supported by the fixed plate 33 supported by 33c, the mirrors 6M and 7M are moved around the fulcrum 33a as the scanning line 2.
Rotate on a plane substantially perpendicular to M. At this time, since the fixing plate 33 is fixed to the apparatus main body, it does not move. Therefore, the mirror pair 5 is tilted by driving the actuator 28, and the tilt deviation in FIG. 4A is corrected.

Next, as for the top margin and the left margin, similarly to the conventional example, the scanning start timing is electrically adjusted to correct the deviation amount.

By the correction so far, the three deviations of the inclination of the scanning line 2M, the top margin, and the left margin are corrected from the state of FIG. 4A with respect to the reference scanning line 102C, and FIG. ) State. Next, a method of correcting the remaining magnification deviation will be described.

In FIG. 4B, the magnification is shifted by Δl. Therefore, correction control is performed to shift the left margin of the scanning line 2M upward in the figure by Δ1 / 2 that is half the amount,
The state of (c) is obtained. FIG. 5 is a schematic view showing the positional deviation of the scanning lines in this state in an easy-to-understand manner, and the intervals are enlarged to make the position of each dot easy to understand.
5A corresponds to FIG. 4B, and FIG. 5B corresponds to FIG.
This corresponds to (c).

The scanning lines 2M and 2C are actually a set of dots, and the maximum absolute value of the comparison value of the magnification deviation Δl is
In FIG. 5A, the positional deviation of each dot increases as it goes upward, and the deviation occurs at the uppermost dot in the figure. That is, the difference in color and the color shift caused by the positional shift of the scanning lines increase as they go upward in the figure.

However, in the case of FIG. 4 (c) to which the present invention is applied, there are two places where the positional deviation occurs, that is, the upper part and the lower part in the diagram schematically shown in FIG. 5 (a). 1/2
Since it is half of Δl, the deterioration of the image quality due to the difference in tint and the color shift is slight.

In the above description, it was explained that the left margin is shifted by 1 / 2Δl which is half the magnification shift Δl. However, in reality, since the dots are digitally processed, even if the shift amount Δl is halved, a fraction is generated without being divisible. Therefore, the shift amount of the left margin may not be exactly Δl / 2 in order to round off the fraction to an integer, but that is not a problem.

Further, it has been found that the main cause of the magnification deviation is a change in the optical path length due to a temperature rise inside the apparatus, for example, an average temperature rise inside the apparatus is 15 deg.
The optical path length is 300 mm, the optical path divergence angle is 15 °, the structural material of the device is iron, and its linear expansion coefficient is 2.1 × 1.
Calculated as 0 ^-5 / ° C, the absolute length of the scan line is about 50
μm changes. However, the absolute length of the reference scanning line changes by about the same amount, and if the spread angle of the scanning line is θ, the absolute length change of the magnification shift is the change amount of the absolute length of the scanning line tan θ times. The amount of magnification deviation from the reference scanning line is only much smaller than 50 μm. Therefore, when it is limited to the magnification deviation, the correction control for minimizing the absolute amount of the comparison value of the deviation with the reference image according to the present invention, or more specifically, about half the absolute value of the comparison value of the deviation, the reference image and each image. By shifting the writing positions in the scanning direction with respect to and, it is possible to obtain an image that is sufficiently satisfactory in terms of image quality.

Further, as a result of the experiment, the amount of positional deviation after correction in the actual device is about 30/2 = 15 μm even under the worst conditions of temperature and flatness of the installation place, and therefore the difference in color tone is caused. Almost no deterioration in image quality due to color misregistration occurs.

[0043]

The present invention has the above-described structure and operation, and corrects only the positional deviation of each image from the reference image in the image scanning direction, the positional deviation in the direction perpendicular to the image scanning direction, and the inclination deviation. At that time, by performing correction control that minimizes the absolute amount of the comparison value of the deviation from the reference image, it becomes possible to correct the magnification deviation, and an image with good image quality can be obtained.

By shifting the writing start positions of the reference image and each image in the scanning direction by approximately ½ of the absolute value of the comparison value of the magnification shift, the magnification shift can be appropriately corrected.

The image shift correction means is a correction means for correcting only the positional shift in the image scanning direction with respect to the reference image, the positional shift in the direction perpendicular to the image scanning direction, and the tilt shift. By correcting the writing start position by shifting the writing position, the correction means for the scanning optical system dedicated to the magnification shift becomes unnecessary, and high precision mechanical parts for magnification correction and parts such as expensive linear stepping actuators are unnecessary compared to the conventional example. Therefore, a significant cost reduction is achieved.

Further, since the mechanical structure for supporting the mirror pair of the scanning optical system is simplified, the number of natural vibration modes and forced vibration modes is reduced, and the unevenness of image density is reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a mirror pair to which the present invention is applied.

FIG. 2 is an explanatory view of a main part of the image forming apparatus.

FIG. 3 is a diagram of a scanning optical system.

FIG. 4 is a step of image correction.

FIG. 5 is an enlarged explanatory diagram of magnification correction.

FIG. 6 is a perspective view illustrating a main part of a conventional image forming apparatus.

FIG. 7 is a conventional image correction step.

FIG. 8 is a configuration diagram of a conventional mirror pair.

[Explanation of symbols]

 2C, 2M, 2Y, 2BK Scan line 5,200 Mirror pair (tilt deviation correcting means) 6M, 7M, 8M Mirror 9C, 9M, 9Y, 9BK Scanning optical system 31 Mirror holder 32 Swing plate 33 Fixed plate 28 Linear step actuator

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G03B 5/00 Z G03G 15/01 115 15/043 15/04

Claims (4)

[Claims] 1. At least one photoconductor drum, a plurality of scanning optical systems that scan the photoconductor drum to form a charged latent image, and a deviation of each image formed in each scanning optical system is a reference. An image forming apparatus comprising: a correction unit that corrects the image by comparing it with each other so that each of the images can be multiply formed on a recording medium. In the image forming apparatus, the correction unit corrects only a positional deviation and an inclination deviation of each image from a reference image. However, the image forming apparatus is characterized in that correction control is performed to minimize the absolute amount of the comparison value of the deviation from the reference image. 2. The correction means compares the length of the reference image in the scanning direction with the length of each image in the scanning direction as a correction of the magnification shift, and each of the reference image and each of the reference images is equal to about ½ of the absolute amount of the comparison value. The image forming apparatus according to claim 1, wherein a writing start position with respect to the image is shifted in a scanning direction. 3. The correcting means comprises a mirror pair in which a pair of mirrors are arranged on the scanning optical path at a substantially right angle, and the mirror pair is rotatable on a predetermined plane substantially perpendicular to an incident scanning line. The image forming apparatus according to claim 1 or 2, which is characterized in that. 4. At least one photoconductor drum, a plurality of scanning optical systems that scan the photoconductor drum to form a charged latent image, and a deviation of each image formed in each scanning optical system is a reference. An image forming apparatus comprising: a correction unit that corrects by comparing with an image, wherein each image can be formed on a recording medium in a multiplex manner. Positional deviation correcting means for performing positional deviation in a direction perpendicular to the scanning direction at the on / off timing of the scanned laser light, and a predetermined plane substantially perpendicular to the incident scanning line for correcting the inclinational deviation between each image and the reference image. A tilt deviation correcting means composed of a pair of mirrors each of which is rotatable by means of a pair of mirrors arranged substantially at right angles, and a length of a reference image in a scanning direction and a scanning of each image for correcting a magnification deviation between each image and the reference image. And a magnification deviation correcting unit that compares the lengths in the directions and shifts the writing positions of the reference image and the respective images in the scanning direction by about ½ of the absolute amount of the comparison value. An image forming apparatus characterized in that a magnification shift is corrected after the correction.