JP2002029094A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging apparatus in which the magnification error of a latent image caused by temperature variation or aging is corrected in the scanning direction of a deflection mirror, or the magnification of a latent image is corrected when an image is formed on the rear surface of a recording paper thermally shrunk once. SOLUTION: Magnification error is calculated in the main scanning direction of a deflection mirror and a latent image is formed on an image carrier by controlling a light beam based on the calculated magnification error or a latent image is formed on the rear surface of a recording paper while lowering the magnification with respect to the latent image on the surface.

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 for forming a latent image on an image carrier using a laser light source.

[0002]

2. Description of the Related Art A latent image is formed by controlling a light beam of a laser light source to irradiate an image carrier based on a document read by a scanner or an input image received from an external device. 2. Description of the Related Art An image forming apparatus that forms an image by using a configuration in which a toner image is transferred to a recording sheet and then thermally fixed after the toner image is developed is known. In such a configuration of the image forming apparatus, the toner image transferred to the recording paper, that is, the latent image on the image carrier needs to be accurately formed at a magnification set for the input image. In particular, when the set magnification is the same magnification (1.0 times), it is easy to compare the input image with the image formed on the recording paper, and it is a necessary condition for a user whose image size such as a design image is important. It is.

However, fluctuations in the driving system for driving the scanner of the image forming apparatus, fluctuations in the conveyance speed of the recording paper during latent image formation, aberrations in the optical system of the light beam, shrinkage of the recording paper on which the toner image has been thermally fixed, etc. As a result, a magnification error occurs with respect to the set magnification of the formed image.

At the time of manufacture, a conventional image forming apparatus is shipped after correcting a magnification error of a latent image caused by the above-described factors. For example, in a high-speed type image forming apparatus which forms an image at a speed of 50 sheets or more per minute, the magnification error is reduced to 0.1% or less by changing the pulse interval of a dot clock which is a drive signal of a light beam of a laser light source. Thus, a latent image is formed on the image carrier. Alternatively, in a low-speed type image forming apparatus that forms an image at a speed of 30 sheets per minute or less, the rotation speed of a deflecting mirror that scans by rotating a light beam is used instead of changing the pulse interval of a dot clock that adds a complicated signal circuit. The latent image is formed on the image carrier so that the magnification error becomes about 0.1% by the change of the magnification.

[0005]

However, in the shipped image forming apparatus, the plastic lens which is the optical system of the light beam is deformed or the light of the laser light source is changed due to the temperature change or the aging in the apparatus depending on the use environment of the user. There is a problem that a magnification error of a latent image in a direction in which the deflecting mirror scans varies due to a change in beam characteristics. Further, in an image forming apparatus that forms a color image by superimposing a plurality of colors by a plurality of image carriers, the magnification error varies with time in each of the plurality of image carriers, and the superimposed image positions match. However, there is a problem that image quality is deteriorated due to moire or the like.

Further, the recording paper on which the toner image has been transferred shrinks due to evaporation of water when heated in the fixing process. However, even if the recording paper shrinks due to the fixing process, it absorbs moisture from the outside air and restores to its original size over a period of about one hour, so it does not pose a major problem. However, after forming an image on the surface of the recording paper and fixing by heating,
When forming an image on the back surface, since the image is formed on the recording paper that has been heated and contracted once, the magnification of the image formed on the front surface is different from that of the image formed on the back surface.

Therefore, the objects of the present invention are as follows. (1) It is necessary to correct the magnification error of the latent image in the scanning direction of the deflecting mirror caused by temperature change or aging.

(2) In a low-priced low-speed image forming apparatus, if a change in the pulse interval of the dot clock is adopted as a method of correcting the magnification error of the above-mentioned problem (1), the cost increases, which is not preferable. .

(3) It is necessary to correct the fluctuation of the magnification error of the latent image in the scanning direction of the deflecting mirror of each of the plurality of image carriers of the color image forming apparatus.

(4) When forming an image on the front surface and forming an image on the back surface of the recording paper once heat-shrinked, it is necessary to form an image at a magnification different from that of the front surface.

An object of the present invention is to provide an image forming apparatus which solves the above-mentioned problem and accurately forms an image on a recording sheet at a set magnification.

[0012]

The above object is achieved by the following means.

(1) An image forming apparatus for forming a latent image on an image carrier by scanning a light beam based on an input image having a set magnification, comprising: a laser light source for emitting the light beam; The light beam from the laser light source, a deflection mirror that deflects by rotation and performs main scanning on the image carrier, and has a magnification error in the main scanning direction of the deflection mirror with respect to the set magnification, An image forming apparatus, comprising: a control unit that controls the light beam based on the calculated magnification error to form a latent image on the image carrier.

(2) A signal generator for generating a dot clock based on an input image having a set magnification, a laser light source for emitting a light beam in synchronization with the dot clock, and the light beam of the laser light source A deflecting mirror that deflects by rotation to scan the image carrier, a developing device that develops a latent image formed on the image carrier by scanning of the deflecting mirror into a toner image, A transfer unit for transferring the toner image to recording paper, wherein the transfer unit transfers the first toner image on the image carrier to the surface of the recording paper, and then transfers the second toner image on the image carrier. An image forming apparatus that transfers a latent image of the second toner image to the latent image of the first toner image at a reduced magnification with respect to the latent image of the first toner image. Image forming apparatus.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing the configuration of the image forming apparatus 1. 1, an image forming apparatus 1 includes an automatic document feeder (ADF) A and a document image reading unit B for reading an image of a document fed by the automatic document feeder.
An image processing unit C that encodes the read document image and performs data processing, an image carrier 10 including a photosensitive drum,
An image forming section E for exposing to form an electrostatic latent image on the image carrier 10; a developing device 20 for developing the electrostatic latent image on the image carrier 10 to form a toner image; A fixing unit H for fixing the toner image, paper feed units 22 and 24 for accommodating recording paper P for image formation, and a reversing path 25 for reversing the front and back of the recording paper P. The paper feed units 22 and 24 are provided with a recording paper sensor 23 for detecting the type of the recording paper P stored therein.

The automatic document feeder A includes a document table 37
And a document transport processing unit 36 including a roller group including the roller R1 and a switching unit (without reference symbols) for appropriately switching a document moving path.

The original image reading section B is located below the top glass G and can move back and forth while maintaining the optical path length, a fixed imaging lens 33, and an image sensor 35.
The image of the document conveyed by the automatic document feeder A is subjected to photoelectric conversion and output as an image signal.

When viewed from the direction of conveyance of the recording paper P, a pair of rollers shown on the front side of the transfer device 18 are registration rollers R.
10, a pair of rollers downstream of the separation electrode 19 is a fixing roller R15 having a heat source.

First, a process for forming an image on a recording sheet will be described below. One of the originals (not shown) placed on the original placing table 37 is transported in the original transport processing unit 36, passes under the roller R1, passes through the mirror units 30, 31 and the lens at the fixed position. An image is formed on the image sensor 35 via 33 and read. The scanned image of the original is
The image is encoded by sampling by the image processing unit C and stored in the memory as image data of the input image. Alternatively, image data received from an external device such as a personal computer is processed by an image processing unit C such as conversion of a language for image formation and stored in a memory. The laser light of the laser light source 38 of the writing unit D is emitted based on the image data of the input image stored in the memory. The laser light of the laser light source 38 is
The scanning is performed by the rotation of the deflecting mirror 39, and the image carrier 10 is exposed to form a latent image. Prior to the exposure, the image carrier 10 rotating in the direction of the arrow (counterclockwise) is cleaned of the adhered toner by the cleaning device 21 and is optically neutralized by a neutralizer (not shown) provided with a light source. Thereafter, the charged image carrier 10 is charged to a charger 17 by corona discharge.
By applying a grid voltage, a charging potential is applied and charged, and the exposure of the laser beam from the laser light source 38 changes the potential of the exposed portion in accordance with the amount of exposure. As a result, an electrostatic latent image is formed based on image data. It is formed on the image carrier 10. The developing sleeve 9 of the developing device 20 forms a magnetic brush by holding the developer by magnetic force. Thereafter, the developing sleeve 9 to which the developing bias has been applied rotates to supply the magnetic brush regulated to a certain height to the image carrier 10. By the applied developing bias, the toner of the developer of the developing sleeve 9 adheres according to the potential of the electrostatic latent image on the image carrier 10 to form a toner image, and development is performed.

On the other hand, the symbol S in the paper feed units 22 and 24 is a movable plate whose free end is constantly urged upward by urging means such as a coil spring (not shown). It comes into contact with the delivery roller 60. The recording paper P that has come into contact with the feed roller 60 is sent from the paper feed unit 22 and sent to a pair of rotatable rollers, a drive roller 61 and a driven roller 62. The drive roller 61 rotates and separates the recording paper P one by one, and conveys it toward the registration roller R10. The leading edge of the recording paper is applied to the registration roller R10 before the rotation is started, and a loop is formed on the recording paper P, and the skew of the recording paper P due to conveyance is corrected by the loop formation. Thereafter, the registration roller R10 starts rotating in synchronization with the toner image formed on the image carrier 10, and conveys the recording paper P.
The toner image of the image carrier 10 overlaps the recording paper P conveyed in synchronization with the image carrier 10, and the toner image is transferred to the recording paper P by the urging of the transfer device 18. Recording paper P is separated electrode 1
9 after being separated from the image carrier 10 by the urging of the fixing unit H
The toner powder that forms a toner image by the pressurizing and heating action of the fixing roller R15 is melted and fixed on the recording paper P.
The recording paper P on which the toner has been fixed is discharged onto a discharge tray T via a discharge roller 63.

Recording paper P on which the first toner image has been transferred
When an image is formed on the back surface of the recording paper P,
The branch guide 28 is positioned at a broken line position in the drawing, and is controlled to take a solid line position in the drawing after the recording paper P is fed into the conveyance path 27. Transport path 27
Represents a gentle arc and guarantees smooth movement of the recording paper P. The recording paper P that has descended after passing through the conveyance path 27
Crosses the conveyance path of the recording paper from the manual paper supply unit 26 and reaches the switchback roller R20. The switchback roller R20 is composed of a pair of reversible rotatable rollers, and is provided between the bottom (the same as the bottom wall) of the sheet feeding unit 24 provided below the switchback roller R20 and the bottom wall of the apparatus body. The recording paper P is directed to the reversing path 25 having a predetermined space. The leading end of the recording paper P that has reached the switchback roller R20 is nipped by the roller, and the roller rotates and is guided to the reversing path 25. At this time, the image on the surface transferred onto the recording paper P faces downward. Eventually,
The rotation is stopped with the switchback roller R20 sandwiching the rear end of the recording paper P. Thereafter, when the recording paper P starts rotating in the reverse direction, the recording paper P is transported in a state where the recording paper P is turned upside down in the reversing path 25, that is, in a state where the back surface of the recording paper P on which the image is not transferred is directed to the image carrier 10 side. It is sent to the road 29. The recording paper P sent to the transport path 29 is
The sheet 5 is sent to a transport roller R25 provided corresponding to the sheet feeding unit 24 closest to the sheet feeding unit 5. The conveying roller R25 conveys the recording paper P, and the registration roller R before starting rotation.
A loop is formed by applying the leading end of the recording paper P to the recording paper 10, and the skew of the recording paper P due to conveyance is corrected by the loop formation. On the other hand, a second toner image is formed on the image carrier 10, and the registration roller R10 starts rotating in synchronization with the second toner image formed on the image carrier 10 to form a loop-formed recording. The paper P is transported. The second toner image of the image carrier 10 overlaps the back surface of the recording paper P transported in synchronization with the image carrier 10, and the toner image is transferred to the recording paper P by the urging of the transfer electrode 18. Thereafter, a fixing process is performed, and the sheet is discharged onto a sheet discharge tray T via a sheet discharge roller 63.

FIG. 2 is a schematic diagram of the writing section D. The writing unit D includes a laser light source 38, a collimator lens 4,
1, the first cylindrical lens 42, the deflection mirror 39,
lens 43, a second cylindrical lens 44, a reflection mirror 45, a mirror driving source 46, and the like.

The light beam emitted from the laser light source 38 is converted into parallel light by a collimator lens 41 and directed to a first cylindrical lens 42. The first cylindrical lens 42 forms the light beam on the image plane of the deflection mirror 39. The deflecting mirror 39 is rotated by the driving force of the mirror driving source 46 to deflect the light beam on the image plane. The deflected light beam passes through an imaging optical system including an fθ lens 43 and a second cylindrical lens 44, is reflected by a reflection mirror 45, is guided to the image carrier 10, and is rotated by a driving force of a driving source (not shown). Irradiation is performed on the image carrier 10. That is, the rotation of the deflection mirror 39 causes the light beam to perform main scanning in the illustrated direction, and the rotation of the image carrier 10 to perform sub-scanning in the illustrated direction, thereby forming an electrostatic latent image on the image carrier 10. A part of the light beam that the deflecting mirror 39 performs main scanning is detected by the beam detection sensor 47. The reflection mirror 45
An adjusting unit 48 is provided that moves in the X direction by a rotational force from a drive source (not shown), and the length of the optical path L of the light beam can be changed by the movement. Around the image carrier 10, a temperature sensor 50 for detecting a temperature and a registration sensor 49 for detecting a toner image on the image carrier 10 are provided.

Next, the latent image formed on the image carrier at the set magnification will be described below. FIG. 3 is a block diagram of a control unit of the image forming apparatus.

The control section 100 controls each section of the image forming apparatus 1 so as to input images of the original read by the image reading section B and I / O from an external device such as a personal computer device via a communication network such as the Internet. Based on the input image received by the F unit 120, the image processing unit C, the image writing unit D, and the image forming unit E are controlled to form an image on a recording sheet by the above-described exposure, development, transfer, and fixing processes. .

The memory 200 includes a hard disk, a CD,
A storage unit such as a RAM stores image data encoded by the image processing unit C, data of a magnification error with respect to temperature, data of a magnification correction value for each type of recording paper, and the like.

The input unit I includes a numeric keypad, and the magnification of an input image to be formed by the user is set using the numeric keypad of the input unit I. The control unit 100 controls the image processing unit C to perform image processing so that image data of the input image can be formed at a set magnification. In the image processing of the image processing unit C, for example, when the set magnification is twice (enlargement), image data of a twice enlarged image is created by uniform pixel interpolation of the image data. Alternatively, when the set magnification is 0.5 times (reduced), image data of a 1/2 reduced image is created by uniform pixel thinning of the image data. When the set magnification is the same magnification, no pixel interpolation or thinning is performed.

The image processing section C includes a signal generating section for generating a dot clock for driving a laser light source 38 for writing a latent image on the image carrier 10. An input image under the control of the control section 100 and an enlarged image generated from the input image. The dot clock is modulated by pulse width modulation (PWM) or the like based on image data such as an image or a reduced image, and output to the writing unit D.

In the writing section D, the laser light source 38 is driven in synchronization with a dot clock modulated based on image data, and emits a light beam. Therefore, the pixel interval of the latent image formed on the image carrier 10 is determined by the pulse interval of the dot clock.

The control unit 100 emits the light beam of the writing unit D in synchronization with the dot clock generated by the image processing unit C, and rotates the deflecting mirror 39 by the mirror driving source 46 via the deflecting mirror driver 110. The light beam is controlled by the speed (main scanning) and the rotation speed (sub-scanning) of the image carrier 10 by the driving source of the image carrier driver 112 to form a latent image on the image carrier 10.

Thereafter, an image of the recording paper is formed in accordance with the size of the formed latent image, and an image having a set magnification is obtained.

However, due to the temperature environment used by the user and aging, the formed latent image is displaced in the main scanning direction of the deflecting mirror 39 due to the deformation of the fθ lens 43 which is a plastic lens and the change in the light emission characteristics of the laser light source 38. Expansion and contraction occur, and the magnification error fluctuates.

Next, the image carrier 1 for the set magnification is set.
A method for calculating a magnification error in the main scanning direction of a latent image formed at 0 will be described.

FIG. 4 is an example of a reference pattern of a latent image formed on the image carrier 10 for calculating a magnification error.
The image forming apparatus 1 calculates the magnification error of forming the latent image of the reference pattern under predetermined forming conditions before forming an image or every predetermined operation time, and sets the latent image based on the calculated magnification error. Correct the magnification of the input image.

The shape of the image carrier 10 is cylindrical, but here, for the sake of explanation, a latent image formed by developing the image carrier 10 on a plane is shown. The magnification in the main scanning direction is referred to as a horizontal magnification, and the magnification in the sub-scanning direction orthogonal to the main scanning is referred to as a vertical magnification.

In the figure, the solid line I represents the actual image carrier 1
The “F” -shaped reference pattern of the latent image having a positive magnification error in the main scanning direction (the latent image is enlarged) formed at 0 and the wavy line J indicate the “L” of the latent image formed when there is no magnification error. This is a reference pattern in the shape of a square. In the figure, the magnification error of the reference pattern is shown in an enlarged scale for the sake of explanation.

The latent image formed by the development of the developing device 20 is developed into a toner image. Registration sensor 49
Detects a “F” -shaped toner image at a detection position shown in the drawing, and outputs the detected output to the control unit 100;
Using 0, the distance Y1 from the horizontal line to the oblique line is measured.

The distance of the toner image when there is no magnification error known in advance from the design value of the image forming apparatus is represented by Y, the angle θ of the oblique line in the “F” shape, and the oblique line of the solid line I of the formed toner image. Assuming that the angle of the line is θ1, the magnification error in the main scanning direction is
It is represented by the following equation.

Magnification error = (Y1 / tan θ1) / (Y /
tanθ), where θ1 ≒ θ, the magnification error becomes Y1 / Y, and the control unit 100 calculates the magnification error from the detection output of the reference pattern of the registration sensor 49.

Further, the magnification error may be calculated by measuring the interval between the “F” -shaped reference patterns at both ends of the image carrier 10 by the registration sensors provided at both ends of the image carrier 10.

Next, a method of calculating the lateral magnification error calculation by detecting the temperature will be described below.

FIG. 5 is an example of a graph showing the magnification error in the main scanning direction with respect to the temperature in the image forming apparatus in percentage.

In the figure, the magnification error in the main scanning direction of the image forming apparatus 1 is adjusted at the time of shipment so that it becomes zero when the temperature inside the apparatus is 30 degrees. As you can see from the figure,
The magnification error varies in proportion to the temperature inside the apparatus.

Therefore, data of the magnification error in the main scanning direction with respect to the temperature in the image forming apparatus 1 is stored in the memory 200 in advance. The control unit 100 reads a magnification error from the memory 200 in accordance with the temperature inside the image forming apparatus 1 detected by the temperature sensor 50, and calculates a magnification error of the latent image of the image carrier 10 in the main scanning direction.

Next, the formation of a latent image based on the calculated magnification error in the main scanning direction will be described below.

The control unit 100 controls the scanning speed of the light beam by changing the rotation speed of the deflecting mirror 39 based on the calculated magnification error in the main scanning direction, and enlarges and reduces the image processing unit C to convert the input image. By changing the vertical magnification and the horizontal magnification at the same ratio, the main scanning interval of the light beam is controlled to form a latent image on the image carrier 10.

For example, assuming that the magnification error in the main scanning direction calculated from the temperature in the apparatus is 0.3%, first, the rotational speed of the deflecting mirror 39 for performing the main scanning is reduced by the calculated magnification error of 0.3%. 0.15%, which is half the ratio. The scanning speed of the light beam decreases due to the decrease in the rotation speed of the deflecting mirror 39, and the horizontal magnification decreases by 0.15%. However, the vertical magnification increases by 0.15%. This means that both the horizontal magnification and the vertical magnification have increased by 0.15% as compared with the time.

At the same time, the image processing section C reduces the image data of the input image by 0.15%, which is half the calculated magnification error of 0.3% in the main scanning direction. Due to the reduction of the image processing unit C, both the horizontal magnification and the vertical magnification are reduced by 0.15%.

As a result, since the lateral magnification of the latent image formed on the image carrier 10 is reduced by 0.3%, the magnification error is corrected.

Also, the calculated magnification error in the main scanning direction is minus (less than the originally set magnification, for example, -0.5
%), The rotation speed of the deflecting mirror 39 is increased at a rate of half the error (0.25%), and the image processing unit C converts the image data at a rate of half the error (0.25%). Expanding.

In other words, the latent image on the image carrier 10 changes the rotation speed of the deflecting mirror 39 based on the magnification error in the main scanning direction, and changes the horizontal magnification and the vertical magnification of the input image at the same ratio. Thus, the laser beam is formed by controlling the interval of the main scanning of the light beam.

The latent image is formed based on the calculated magnification error in the main scanning direction by changing the scanning interval of the light beam by changing the pulse interval of the dot clock generated by the image processing unit C. The pixel interval of the latent image formed on the body 10 may be controlled. Correction of magnification error in the sub-scanning direction
The rotation speed of the image carrier 10 and the total transport K of the recording paper P
It can be done by changing D control.

However, in a low-priced low-speed image forming apparatus, mounting a circuit for changing the pulse interval of the dot clock increases the cost. For this reason, if the configuration is such that the latent image is formed by correcting the lateral magnification under the control of the above-described deflection mirror driver 110 and the image processing unit C, a circuit for changing the pulse interval of the dot clock is not added.
Image formation can be performed at the set accurate magnification.

Further, in this embodiment, the magnification of the latent image in the main scanning direction in the formation of a single color image by the image carrier 10 is corrected. However, a multicolor image forming apparatus such as Y
In a color image forming apparatus provided with a plurality of image carriers using toners of four colors (yellow), M (magenta), C (cyan), and K (black), main scanning of each of the plurality of image carriers is performed. The correction of the magnification in the direction may be performed by the above-described configuration. By correcting the magnification of the color image forming apparatus, the degree of overlapping of the toner images of the respective colors transferred to the recording paper is improved, and image quality deterioration such as moire is reduced.

Next, the change of the pulse interval of the dot clock when an image is formed on the front surface and an image is formed on the back surface of the recording paper which has been thermally contracted once will be described below.

Among the low-priced low-speed types described above, few models have a function of forming an image on both sides of recording paper, and the multifunctional high-speed type has many functions. Therefore, an image forming apparatus that forms an image on both sides of a recording sheet is often equipped with a circuit that changes the pulse interval of the dot clock. Therefore, in the following image forming apparatus of the present embodiment, an image processing unit C having a dot clock pulse width changing circuit is mounted.

FIG. 6 is a block diagram of a signal generating unit of the image processing unit C which can change the pulse interval of the dot clock mounted on the image forming apparatus.

The signal generating section 400 has a reference clock generating section 401, a delay chain section 410, a synchronous clock detecting section 420, a delayed clock switching control section 440, a delayed clock selecting section 450, a PWM section 460, and the like.

The delay chain unit 410 is composed of a plurality of delay elements for delaying the time of at least two cycles of the main scanning of the light beam, and delays the reference clock signal of a constant cycle output from the reference clock generation unit 401. To generate a plurality of delayed clock signals having different phases. The synchronous clock detection unit 420 detects a delayed clock signal synchronized with the detection signal a of the beam detection sensor 47 via the control unit 100 from among the plurality of delayed clock signals from the delay chain unit 410. The delay clock switching control unit 440 includes:
Based on the delayed clock signal synchronized with the light beam output from the synchronous clock detection unit 420 and the magnification correction value b from the control unit 100, the pulse interval of the dot clock whose magnification is corrected is calculated. A select signal for selecting a delayed clock signal having an appropriate delay time from the delayed clock signals to output the pulse interval is output.

Here, the magnification correction value is a correction value of the magnification of the latent image of the second toner image transferred to the back surface with respect to the latent image of the first toner image transferred to the front surface, and is set in advance according to the type of recording paper. It is stored in the memory 200 of the forming apparatus 1. The magnification correction value is calculated by a contraction rate at which the recording paper contracts due to the heating and fixing of the fixing unit H of the image forming apparatus 1 or, under a predetermined environment, the recording paper on which the image is formed is restored after a predetermined time has elapsed. The magnification of the image at that time is measured and determined.

The delay clock selection section 450 selects an appropriate delay clock based on the magnification correction value b from a plurality of delay clock signals from the delay chain section 410 by using the select signal output from the delay clock switching control section 440. A signal is selected, and the selected delayed clock signal is synthesized to generate a dot clock pulse train.
That is, the pulse interval of the dot clock is controlled based on the magnification correction value b, and the magnification of the latent image is corrected. The generated dot clock is supplied to the PWM unit 46.
At 0, the image data is PWM-modulated by the image data of the input image subjected to the image processing and output to the writing unit D.

Next, formation of a latent image when an image is formed on the front surface and an image is formed on the back surface of the recording paper once heat-shrinked will be described below.

The image forming apparatus 1 stores a magnification correction value according to the type of recording paper in the memory 200 in advance. Control unit 100
Reads a magnification correction value from the memory 200 in accordance with the type of recording paper detected by the recording paper sensor 23 of the paper supply unit 22 when forming a latent image of the second toner image. After transferring the first toner image formed on the image carrier 10 to the surface of the recording paper, the control unit 100 replaces the latent image of the second toner image with the latent image of the first toner image based on the read magnification correction value. Is formed at a reduced magnification.

Table 1 shows an example of a magnification correction value depending on the type of recording paper when a latent image of the second toner image is formed.

[0066]

[Table 1]

In Table 1, magnification correction values are the same in the horizontal direction and the vertical direction, so they are not distinguished. However, different magnification correction values may be used in the horizontal and vertical directions depending on the type of recording paper.

For example, the magnification correction value for glossy paper is 0.5%. That is, when an image is formed on glossy paper at the set magnification of 1 ×, the control unit 100 sets the latent image of the second toner image to 0.995 times the latent image of the first toner image. To reduce the magnification of the input image.

A specific method of forming a latent image of the second toner image on the first toner image will be described below.

When the set magnification is the same magnification and the magnification correction value read from the memory 200 is 0.5%, first, the pulse interval of the dot clock output from the image processing section C is set to the above-mentioned signal generation. The magnification correction value 0.5 by the unit 400
In this case, a dot clock narrowed by 1.0%, which is twice the ratio of the dot clock, is generated. Thereby, the latent image of the second toner image formed is
The image is reduced by 1.0% in the horizontal direction, and does not change in the vertical direction. At the same time, the rotation speed of the deflecting mirror 39 is reduced to a magnification correction value of 0.5%.
0.5% of the same ratio as above. As the rotation speed of the deflecting mirror 39 increases, the scanning speed of the light beam increases,
The pixel interval of the latent image of the formed second toner image is enlarged, and the latent image is enlarged by 0.5% in the horizontal direction and reduced by 0.5% in the vertical direction.

That is, the latent image of the second toner image is twice as large as the latent image of the first toner image with respect to the magnification correction value (0.5%) by twice the pulse interval of the dot clock (1). .0
%) And by increasing the rotation speed of the deflecting mirror 39 at the same rate (0.5%),
In the vertical direction, the image is formed at a magnification reduced by the magnification correction value (0.5%). The latent image of the formed second toner image is
The toner image is developed and becomes a second toner image, which is transferred to the back surface of the recording paper.

The recording paper on which the image has been formed absorbs water with the passage of time, and is enlarged and restored by a magnification correction value of 0.5%. Therefore, the second toner image transferred to the back surface is formed at the set magnification without being affected by the contraction of the recording paper.

In order to enlarge the pixel interval of the latent image of the second toner image formed on the image carrier 10, a rotational driving force is applied to the adjusting unit 48 so that the light path L of the light beam is shortened by the reflecting mirror 45. May be moved in such a manner.

That is, in the latent image of the second toner image, the pulse interval of the dot clock is narrowed and the optical path of the light beam is shortened so that the magnification correction value (0.
5%) at a reduced magnification. The formed latent image is developed, becomes a second toner image, and is transferred to the back surface of the recording paper.

[0075]

According to the present invention, an image forming apparatus for accurately forming an image on a recording sheet at a set magnification is provided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus.

FIG. 2 is a schematic diagram of a writing unit.

FIG. 3 is a block diagram of a control unit of the image forming apparatus.

FIG. 4 is an example of a reference pattern of a latent image formed on an image carrier for calculating a magnification error.

FIG. 5 is an example of a graph in which a magnification error in the main scanning direction with respect to a temperature in the image forming apparatus is expressed as a percentage.

FIG. 6 is a block diagram of a signal generation unit of an image processing unit that can change a pulse interval of a dot clock mounted on the image forming apparatus.

[Explanation of symbols]

 23 Recording paper sensor 47 Beam detection sensor 49 Registration sensor 50 Temperature sensor 100 Control unit 110 Deflection mirror driver 120 I / F unit 200 Memory A Automatic document feeder B Image reading unit C Image processing unit D Writing unit E Image forming unit I Input Department

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Claims (13)

[Claims] 1. Based on an input image of a set magnification,
An image forming apparatus for forming a latent image on an image carrier by scanning a light beam, comprising: a laser light source that emits the light beam; and the light beam from the laser light source is deflected by rotation to form the image carrier. A deflection mirror that performs main scanning on the body, and calculates a magnification error in the main scanning direction of the deflection mirror with respect to the set magnification, and controls the light beam based on the calculated magnification error. An image forming apparatus comprising a control unit for forming a latent image on an image carrier. 2. The method according to claim 1, wherein the control of the light beam includes changing a rotation speed of the deflecting mirror to control a main scanning speed of the light beam, and a lateral magnification of the input image in a main scanning direction of the deflecting mirror. 2. The image forming apparatus according to claim 1, wherein an interval between main scans of the light beam is controlled by changing a vertical magnification of the deflecting mirror in a direction orthogonal to main scan at the same ratio. 3. The image forming apparatus according to claim 2, wherein the rotation speed of the deflecting mirror is changed at a ratio of half of the calculated magnification error. 4. The image forming apparatus according to claim 2, wherein the change of the horizontal magnification and the vertical magnification of the input image is performed by enlarging or reducing the input image by image processing. apparatus. 5. The image forming apparatus according to claim 4, wherein the enlargement and reduction of the input image are performed at a ratio of half of the calculated magnification error. 6. A developing device for developing the latent image on the image carrier to form a toner image, and a registration sensor for optically detecting the toner image, wherein the magnification error is calculated by The image forming apparatus according to claim 1, wherein the calculation is performed based on detection of the toner image by a registration sensor. 7. A memory for storing a change in the magnification error with respect to a temperature, and a temperature sensor for detecting a temperature inside the image forming apparatus, wherein the magnification error is calculated based on the temperature detected by the temperature sensor. 6. The method according to claim 1, wherein the magnification error is read from the memory.
Item 10. The image forming apparatus according to item 1. 8. Based on an input image of a set magnification,
A signal generation unit that generates a dot clock, a laser light source that emits a light beam in synchronization with the dot clock, a deflection mirror that scans the image carrier by deflecting the light beam of the laser light source by rotation. A developing unit that develops a latent image formed on the image carrier by the scanning of the deflecting mirror to form a toner image, and a transfer unit that transfers the toner image of the image carrier to recording paper, An image forming apparatus, wherein the transfer device transfers a first toner image of the image carrier to a front surface of the recording paper and then transfers a second toner image of the image carrier to a back surface of the recording paper. An image forming apparatus comprising: a control unit configured to form a latent image of a toner image at a reduced magnification with respect to the latent image of the first toner image. 9. The image forming apparatus according to claim 8, wherein a reduction ratio of the magnification of the latent image of the second toner image is changed according to a type of the recording paper. 10. A reduction in the magnification of the latent image of the second toner image is achieved by narrowing a pulse interval of the dot clock and narrowing a scanning interval of the light beam with respect to formation of the latent image of the first toner image. 10. The image forming apparatus according to claim 8, wherein the rotation speed of the deflecting mirror is increased to increase the scanning speed of the light beam. 11. The reduction of the magnification of the latent image of the second toner image may be achieved by narrowing the pulse interval of the dot clock and narrowing the scanning interval of the light beam with respect to the formation of the latent image of the first toner image. The image forming apparatus according to claim 8, wherein a length of an optical path of the light beam is extended. 12. A light-reflecting mirror for reflecting the light beam from the deflecting mirror to guide the light beam to the image carrier, and extending the optical path of the light beam by moving the reflecting mirror. The image forming apparatus according to claim 11, wherein: 13. The signal generating unit includes a digital delay element that delays a reference signal having a constant period to generate a plurality of delayed signals having different phases. The image forming apparatus according to any one of claims 10 to 12, wherein the image forming apparatus generates by synthesizing a delay signal selected from the plurality of delay signals.