JP2001343808A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To completely prevent the distortion and the color slurring of an image in a subscanning direction even in the case of requiring high resolution in image forming. SOLUTION: This image forming device is provided with photoreceptor drums 6 in image forming parts 2, 3, 4 and 5 forming respective color images, respectively. A carrying belt 7 carries paper by moving in synchronization with the drum 6 while press-contacting with the drum 6, so that a toner image on the drum 6 is transferred to paper. The rotational angle of the drum 6 and the eccentric position of the center of circular cross section from the rotary shaft of the drum 6 are detected. Then, the eccentric amount and the eccentric rotational angle of the drum 6 and the radius of the drum 6 are obtained from the detected result, and the distortion and the color slurring of the toner image transferred to the paper are corrected based on the obtained values.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for image forming apparatuses capable of color printing, such as color printers and color copiers. In the case of models having a low output speed, an ink jet system has become mainstream. The electrophotographic method is going to spread in various models. There is a tandem-type color image forming apparatus as an electrophotographic method suitable for high speed.

JP-A-10-246995, JP-A-63-81373
In this tandem type color image forming apparatus, four photoconductor drums having an optical scanning unit are arranged in a paper (recording sheet) conveying direction on a conveying belt, and an optical scanning unit is disclosed. The exposure beam emitted from the scanner is used to perform exposure scanning on the rotating photosensitive drum. This is an operation called main scanning. As a result, an electrostatic latent image is formed on each photosensitive drum. Toners of different colors (cyan, magenta, yellow, and black) are supplied to the respective photosensitive drums from the respective developing devices, and the electrostatic latent images are developed with the toners. Then, the paper is conveyed to each photoconductor drum by the conveyance belt, and in the middle of the conveyance, the transfer charger sequentially transfers the toner images on each photoconductor drum onto the paper so that they overlap on the same scanning line. Thereafter, the toner image on the paper is fixed and discharged onto a paper discharge tray.

As described above, the tandem-type image forming apparatus draws four images in parallel on four photosensitive drums, and simply passes a sheet under each photosensitive drum once to form four colors. This method is suitable for creating a color image at high speed because an image can be formed.

In the tandem type color image forming apparatus, the transport speed of the transport belt and the peripheral speed of the peripheral surface of each photosensitive drum are made to coincide with each other, and each photosensitive drum is main-scanned at a constant timing to prevent color misregistration. For this purpose, a method is employed in which each photosensitive drum is pressed against the conveyor belt and the conveyor belt is driven so that each photosensitive drum follows the movement of the conveyor belt.

However, when the rotation axis of the photosensitive drum is eccentric, the peripheral speed at the optical writing position of the electrostatic latent image that is main-scanned at a constant timing changes with one rotation of the photosensitive drum as one cycle. Therefore, there is a problem that the density of the scanning lines is uneven in each cycle, and the image transferred to the paper is distorted in the sub-scanning direction.

In order to solve such a problem, Japanese Patent Application Laid-Open No. 10-2
Japanese Patent Publication No. 46995 proposes a technique of detecting a peripheral surface displacement based on the eccentricity of the photosensitive drum and correcting and controlling the interval between main scanning lines on the peripheral surface of the photosensitive drum based on the displacement.

[0008]

However, in image forming apparatuses such as printers and copiers, higher resolutions (1200 dpi or more) are required in the future.

On the other hand, the technique disclosed in Japanese Patent Application Laid-Open No. 10-246995 has a problem that it cannot cope with this. That is, in the technology disclosed in Japanese Patent Application Laid-Open No. 10-246995, correction of image distortion in the sub-scanning direction based on the eccentricity of the rotation axis of the photosensitive drum is performed, peripheral surface displacement is detected, and the displacement information is continuously obtained. It is done by using. However, when high resolution is required, the actual correction amount becomes worse as the correlation with the displacement information becomes higher.

An object of the present invention is to sufficiently prevent distortion and color misregistration of an image in the sub-scanning direction even when high resolution of image formation is required.

Another object of the present invention is to make subscanning pitch variations due to eccentricity of the photosensitive drum inconspicuous.

Another object of the present invention is to output main scan image data at the same timing as when there is no eccentricity of the photosensitive drum and no variation in the drum diameter.

Another object of the present invention is to reduce the manufacturing cost and to create correction data for correcting distortion and color misregistration of an image in the sub-scanning direction with high accuracy.

[0014]

According to a first aspect of the present invention, there is provided a photosensitive drum, and an optical writing device for performing at least one line of main scanning optical writing on a peripheral surface of the photosensitive drum.
A developing device that develops the optically written electrostatic latent image on the photosensitive drum with toner, and a sheet that is conveyed by moving in synchronization with the photosensitive drum while being pressed against the photosensitive drum; A conveying member for transferring the toner image on the photosensitive drum onto the sheet, or an intermediate transfer belt for transferring the toner image on the replacement drum, which moves in synchronization with the photosensitive drum while being pressed against the photosensitive drum; Rotation angle detection means for directly or indirectly detecting the rotation angle of the photoconductor drum, and eccentricity detection means for detecting the eccentric position of the center of the circular cross section of the photoconductor drum from the rotation axis of the photoconductor drum. The amount of eccentricity of the photosensitive drum, the eccentric rotation angle and the radius of the photosensitive drum are obtained from the detection results obtained by the rotation angle detecting means and the eccentricity detecting means. An image forming apparatus having a correction means for correcting the distortion and color misregistration of the toner image after the transfer to the sheet or the intermediate transfer belt based on.

Therefore, distortion and color misregistration of the transferred toner image are corrected based on the amount of eccentricity of the photosensitive drum, the eccentric rotation angle and the radius of the photosensitive drum. In the sub-scanning direction and color misregistration can be sufficiently prevented.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the correction unit is configured to perform the transfer between the photosensitive drum having an ideal shape and the actual transfer of the photosensitive drum. An error in the transfer position of the toner image later on the transport member is obtained, and distortion and color shift of the toner image are corrected based on the error.

Therefore, the error in the transfer position of the toner image between the photosensitive drum having the ideal shape and the actual photosensitive drum is accurately determined, and even if a high resolution of image formation is required, the image is scanned in the sub-scanning direction. Distortion and color misregistration can be sufficiently prevented.

According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the correction means includes: a shift amount of the exposure image from an ideal state; d, an eccentricity of ε; (The moving direction of the sheet or the intermediate transfer belt in the vicinity of the transfer position is θ = 0), the radius of the photosensitive drum is R, and the radius of the photosensitive drum is an ideal shape. Set the radius of the photosensitive drum to R
₀ , the exposure position on the photoconductor drum by the optical writing device, the exposure position on the ideal shape photoconductor drum, the rotation direction of the photoconductor drum from the transfer position of the ideal shape photoconductor drum , The shift amount d is calculated as follows: d = π (R ₀ −R) + R sin ⁻¹ {(ε / R) cos θ} + z
(R ₀ -R).

Therefore, the error in the transfer position of the toner image between the photosensitive drum having the ideal shape and the actual photosensitive drum is accurately determined, and even if a high resolution of image formation is required, the image is scanned in the sub-scanning direction. Distortion and color misregistration can be sufficiently prevented.

According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the correction means detects an error in a mounting position of the photosensitive drum or another member. Then, based on this error, distortion and color shift of the toner image are corrected.

Therefore, it is possible to absorb errors in the mounting position of the photosensitive drum and the like, and sufficiently prevent distortion and color misregistration of the image in the sub-scanning direction even when high resolution of image formation is required.

According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the correction means includes an image data for modulating an exposure beam output from the optical writing device. By selecting and controlling appropriate data among the above, the distortion and color shift of the toner image are corrected.

Therefore, it is possible to sufficiently prevent distortion and color misregistration of an image in the sub-scanning direction even when a high resolution of image formation is required, by using the optical writing device having the same hardware configuration as that of the prior art as it is. it can.

According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, the optical writing position in the sub-scanning direction on the photosensitive drum is fixed, and the correction unit is configured to correct an original image. Control is performed by selecting appropriate data from the interpolated image data using interpolated image data obtained by interpolating data in at least one of the sub-scanning direction and the main scanning direction.

Therefore, by using the optical writing device having the same hardware configuration as in the prior art as it is and correcting the image data, even if a higher resolution of image formation is required, distortion and color in the sub-scanning direction of the image are required. The displacement can be sufficiently prevented.

According to a seventh aspect of the present invention, in the image forming apparatus according to the fifth or sixth aspect, the optical writing device comprises:
A polygon mirror driven at a constant speed by a polygon motor deflects a light beam emitted from a light source to main-scan the photosensitive drum, and the position of the optical writing on the photosensitive drum is fixed. And the correction means outputs the image data so as to match the timing of starting the main scanning by the polygon mirror.

Therefore, the main scanning image scanned by the polygon mirror can be stably output without interruption, and a high quality image can be obtained.

According to an eighth aspect of the present invention, in the image forming apparatus according to the sixth or seventh aspect, the correction means changes the optical recording condition in accordance with a peripheral speed of the photosensitive drum to perform the optical writing. Do.

Therefore, the variation of the sub-scanning pitch due to the eccentricity of the photosensitive drum can be made inconspicuous.

According to a ninth aspect of the present invention, in the image forming apparatus according to any one of the fifth to eighth aspects, the correction means is configured to output image data for modulating an exposure beam output from the optical writing device. The position of the optical writing on the peripheral surface of the photosensitive drum is controlled so as not to select the appropriate data.

Therefore, the main scan image data can be output at the same timing as when there is no variation in the eccentricity of the photosensitive drum and the drum diameter.

[0032] The invention described in claim 10 is the invention according to claims 1 to 9.
In the image forming apparatus according to any one of the above, the contact portion between the conveyance member, the sheet or the intermediate transfer belt and the photoconductor drum may be in the conveyance member direction or the intermediate direction in a circular cross section of the photoconductor drum. It is the top in the transfer belt direction.

Therefore, even if the photosensitive drum is eccentric, if the conveying member moves at a constant speed, the rotation angle of the photosensitive drum becomes constant, so that the movement of the photosensitive drum and the conveying member is detected by one sensor. Therefore, the manufacturing cost can be reduced, and correction data for correcting distortion and color misregistration in the sub-scanning direction of an image can be created with high accuracy.

The eleventh aspect of the present invention relates to the first to first aspects.
0, the plurality of photoconductor drums are formed on the intermediate transfer belt or the transport member in a line in a moving direction of the intermediate transfer belt or the transport member. When the toner images formed on the respective photoconductor drums are transferred and superimposed, the coarse / dense phase relationship of the transferred images caused by the eccentricity matches each other for all the photoconductor drums. As described above, in the image forming apparatus, the phase relationship between the eccentricity of each of the photosensitive drums and the position of the electrostatic latent image formed on the photosensitive drums is substantially the same for all the photosensitive drums. is there.

Therefore, it is possible to reduce the image deterioration caused by the fluctuation of the sub-scanning pitch of the electrostatic latent image caused by the linear velocity fluctuation due to the eccentricity at the exposure position on each photosensitive drum.

The twelfth aspect of the present invention relates to the first to first aspects.
The image forming apparatus according to any one of the above, further comprising an image reading device that reads an image of a document, and capable of forming an image based on the read image data.

Accordingly, the same functions and effects as those of the image forming apparatus according to any one of the first to eleventh aspects are exhibited.

[0038]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment of the Invention] One embodiment of the present invention will be described as a first embodiment of the present invention.

FIG. 1 is a conceptual diagram showing a schematic configuration of an image forming apparatus according to Embodiment 1 of the present invention. The image forming apparatus 1 is a tandem-type image forming apparatus that forms a color image on a sheet such as paper by an electrophotographic method.
Image forming units 2, 3, 4, and 5 are arranged in one row. The image forming units 2, 3, 4, and 5 respectively include the photosensitive drums 6,
6, ... Although not shown in FIG. 1, an optical scanning device, which is a charging device for charging each photosensitive drum 6 and an optical writing device for optically writing an electrostatic latent image on each photosensitive drum 6, is provided around each photosensitive drum 6. A well-known device for forming an image by an electrophotographic process, such as a unit, a developing device that develops an electrostatic latent image with toner, and a cleaning device that removes residual toner on each photosensitive drum 6, is provided.
Each of the four image forming units 2, 3, 4, and 5 has a C
(Cyan), M (magenta), Y (yellow), Bk
An image of each color (black) is formed.

An endless conveying belt 7 as a conveying member is disposed below the image forming units 2, 3, 4, and 5. The transport belt 7 is wound around a driving roller 8, a driven roller 9, and a tension roller 10. The conveyor belt 7 is driven by a driving roller 8 to form an image forming unit 2.
The transport path sequentially transports the sheets to 3, 4, and 5.

As shown in FIG. 2, the tension roller 10
Is rotatably supported at one end by the other end of a shaft 11 rotatably attached to the frame of the image forming apparatus 1, and includes a spring 1
2 to prevent the transport belt 7 from being slackened and to make the transport belt 7 press against the tangent lines of the photosensitive drums 6, 6,. In order to assist the pressure contact between the endless transport belt 7 forming the paper transport path and the photosensitive drums 6, 6,.
3, 13, 13 are provided. Press roller 13,1
The members 3 and 13 are rotatably supported by a shaft and are urged by a spring so as to be pressed against the conveyor belt 7. For this reason, when the drive roller 8 is rotated at a constant speed by a drive motor (not shown), the transport belt 7 moves at a constant speed, and the paper on the transport belt 7 is transported at a constant speed. The drums 6, 6, ... rotate.

The conveyor belt 7 and the photosensitive drums 6, 6,...
When the paper on the conveyor belt 7 is located below each of the photosensitive drums 6, 6,... Under the conveyor belt 7 at the pressure contact portion, the toner image on the photoconductor 6 is transferred onto the paper. Are provided, respectively.

FIG. 3 is a block diagram showing the electrical connection of the control system of the image forming apparatus 1. As shown in FIG. 3, the control system performs various calculations and centrally controls each unit, a ROM 16 storing fixed data such as various control programs, and a RAM 17 serving as a work area of the CPU 15. Are connected by a bus 18. Various sensors 19 and various actuators 20 are connected to the bus 18. The various sensors 19 include various types of detectors described later, such as a linear encoder 22, an exposure start position detector 24, a sheet leading end position detector 25, and a reference position error detector 26, which will be described later. The various actuators 20 include various actuators to be described later, such as a motor for driving the photosensitive drum 6, the driving roller 8, and the pressing roller 13.

Hereinafter, the image forming apparatus 1 realized by the CPU 15 according to the control program stored in the ROM 16
The following 1． ~ 9. Each item will be described.

1. First, the relationship between the moving speed of the conveyor belt 7 and the rotational angular speed of the photosensitive drum 6 will be described. This implements a rotation angle detecting means.

The configuration shown in FIG. 1 can be modeled as shown in FIG. In FIG. 4, ε is the amount of eccentricity, θ
Is the angle of the eccentric position from the x-axis,
The moving speed of the contact point T between the photoconductor drum 6 (hereinafter, sometimes simply referred to as “drum”) and the photosensitive drum 6 (hereinafter, sometimes simply referred to as “drum”) may be expressed by coordinates as follows: ε sin θ · ω, ε cos θ · ω), ω = dθ / dt (1)

Therefore, the speed Vs in the direction S of rotation around the drum rotation center 0 is as follows: Vs = Vcosα−εsinθ · ω · cosα + εcosθ · ω · sinα (2) Here, V is the belt moving speed, and α is the angle between the belt and a line orthogonal to the line r connecting the contact point from the drum rotation center at the position of the contact point T.

Therefore, ω = Vs / r = (Vcosα−εsinθ · ω · cosα + εcosθ · ω · sinα) / r (3) Here, from the cosine formula, r ² = R ² + ε ² −2Rεcos (π / 2−θ) = R ² + ε ² −2Rε sin θ (4) where R is the drum radius.

Here, from the sine theorem, ε / sin α = r / sin (π / 2−θ) = r / cos θ (5) sin α = εcos θ / r, cos α = (R−ε sin θ) / r ( 6) From the above, by substituting (4) and (5) into equation (3), ω = {VR− (V + ωR) ε sin θ + ωε ² } / (R ² +
ε ² −2Rε sin θ) Accordingly, ω (R ² + ε ² −2Rε sin θ) = VR− (V + ωR) ε sin θ + ωε ² V = Rω (7) As is apparent from the above description, the rotational angular velocity of the drum is eccentric. Similarly, if there is no slip and the belt moving speed V is constant, it becomes constant similarly.

Therefore, a detector for detecting the movement or the absolute position of the belt (for example, as shown in FIG. 9), a fixed interval timing Mark 21 and a reference mark 23 indicating a reference position on the belt, and a linear encoder 22, a tip position detector 24, etc., which detects these marks 21 and 23 and recognizes the absolute position. If there is no rotary encoder for detecting the rotation angle that can detect the absolute position of each drum, the reference position of the rotation of the drum is detected (one pulse is output per rotation) and the rotation angle of the drum is detected. You will be able to know the location. Then, for example, rotate the drum,
If one cycle of the drum rotation of the reference position detector (a detector that outputs one pulse for one rotation of the photosensitive drum and detects the reference angular position) is measured by the linear encoder 22, one pulse of the output of the linear encoder 22 is obtained. The rotation angle of the rotating drum is known.

Conversely, one of the four tandem drums is provided with a detector such as a rotary encoder capable of measuring the absolute rotation angle, and the other drum is provided with the reference position capable of measuring the reference position of rotation. It can be seen that even if a detector is provided and only the reference position of the belt is detected to detect the position of the belt, the position on the belt or the rotation angle of each drum can be known. However, in this case, since the rotation angle positions of the four drums and the belt position are measured based on the radius of one selected drum, an error corresponding thereto is made. That is, in this method, there may be a slight magnification error in the transferred image on the sheet.

Further, if the rotational angular velocity of each drum is controlled to a constant rotational angular velocity according to the disk diameter, slip can be eliminated.

Even if the drum is eccentric, the contact portion between the belt and the drum does not become the maximum value (apex) in the belt side direction of the circular cross section of the drum (see FIG. 5).
It is obvious that the above cannot be said because the rotation speed of the drum is not constant even if the belt speed is constant. That is, in the configuration of the related art, the driving force is transmitted to the drum by pressing the drum against the belt by the spring force of the pressing roller. Since the contact portion between the belt and the drum is located below the rotation axis of the drum, that is, near the Y axis in FIG. 4, it is clear that the rotation angular velocity of the drum fluctuates due to eccentricity.

2. Next, detection of the eccentric position of the photosensitive drum 6 will be described. This realizes eccentricity detection means.

[0055] 6. Method for Detecting Change in Reflection Angle In FIG. 6, the deflection in the x-axis direction of the reflected light of the exposure light beam incident on the drum obliquely from the section perpendicular to the plane of the drawing including the y-axis is represented by “Y = R ₀ + b The position sensor 28 is installed at the position "" as shown in FIG. The eccentric position can be measured by rotating the drum. The rotation angle of the drum is detected by a rotary encoder (not shown) linked to the drum. This encoder may be of a known type capable of measuring an absolute angle, or may be of a type detecting using the above-described linear encoder 22 or the like.

Rotation angle θ of the eccentric position from the x-axis = π / 2
Alternatively, θ = 3π / 2 can be measured as follows.
In other words, when the optical scanning width on the position sensor 28 is W, the position where 1/2 W is detected is θ = π
/ 2. If this position is obtained, the position of θ = 0 or θ = π is obtained by each rotation of π / 2 detected by the rotation angle detection encoder according to the rotation of the drum. At this time, the beam position Xd irradiated on the position sensor 15 may be measured to obtain ε.

FIG. 7 shows a state where the eccentric position is at a positive position on the x-axis, that is, a state where θ = 0.

In FIG. 7, Xd = tan2β · (R ₀ + b−E) (8) where R ₀ is the radius of the ideal drum having an ideal shape (with no error in the drum shape), and β is the radius of FIG. Is the incident angle of light that is incident on and reflected from the exposure position E.

Then, ε / R = sin β (9) tan2β = ² sin β cos β / (cos ² β−sin ² β) = 2 (ε / R) ｛1− (ε / R) ² ｝ ^1/2 / ｛1 −2 (ε / R) ² ｝ (10) E = (R ² −ε ² ) ^1/2 … (11) Xd = 2 (ε / R) ｛1− (ε / R) ² ｝ ^1/2 / {1-2 (ε / R) ² } × [R ₀ + b−R · {1- (ε / R) ² } ^1/2 ] (12) ε / R = ρ (13) ^{, 4R 2 ρ 6 + 8RXdρ 5} + {4Xd 2 -8R 2 +4 (R 0 + b) 2} ρ 4 -12RXdρ 3 +4 {-Xd 2 + R 2 + (R 0 + b) 2} ρ 2 + 4RXdρ + Xd 2 = 0 ... (14) Since R is detected by another means described below, this X
If d can be detected, ε is determined. Actually, a solution of an equation using R and Xd as parameters may be prepared as a table in the ROM 16 or the like, and this table may be looked up.

As described above, the eccentric position (θ, ε) of the drum from the x-axis can be determined.

[0061] Displacement detection method of surface on photoconductor drum 6 This is a method of detecting peripheral surface displacement based on eccentricity of the drum, and a detector used is, for example, a light emitting element that emits a light beam to a displacement detection position on the peripheral surface of the drum. And a light receiving element (for example, 2) for receiving the light beam reflected by the drum.
An optical system (for example, a focus error detection method such as that implemented on an optical disc) in which the light detected on the light receiving element changes due to the eccentricity of the drum surface due to the split photodiode element and the drum peripheral surface. Optical system). With such a configuration, a photocurrent according to a change in the distance between the detector and the detection position flows through the light receiving element. By detecting this, the position of the eccentricity can be detected. Then, by detecting the zero-cross position and the peak position of the output signal change when the photosensitive drum rotates, the eccentric position (θ, ε) from the x-axis can be determined from the relationship with the detector installation position.

In this image forming apparatus 1, the eccentric position (θ,
It suffices if it is possible to detect where ε) is in the rotation angle of the drum. That is, in the image forming apparatus 1, since the rotation angle of the drum is detected by another means as described above, the eccentric position detected by one of the above two means is at any of the photoconductor rotation angles, and What is necessary is just to know how much the amplitude ε is.

3. Next, an angle from the exposure position on the drum to the transfer position of the toner image onto the sheet from the exposure position on the drum will be described. This implements a correction unit.

In FIG. 8 (in FIG. 8, for the sake of simplicity, the exposure position is set to a position E facing the belt with respect to the center axis of rotation of the photosensitive drum). The transfer position is determined by the determined dotted triangle OGE. That is, an image (on the drum indicated by a dotted line in FIG. 8) in which the drum center of gravity (the center of the cross section of the drum) G is exposed at the position of the rotation angle θ (angle GOx) (here, referred to as the eccentric position) has the rotation angle ΔT After the rotation, the image is transferred at a position (x = -s) outside the ideal transfer position (x = 0). Then, the rotation angle ΔT from exposure to transfer is ΔT = π−β (15), where β is the angle GEO.

Sinβ = (ε / R) cosθ (16) {T = π−sin ⁻¹ {(ε / R) cosθ} (17) The s indicating the transfer position is s = εcos (θ−β) = ε cos θ (ε / R) [{(R / ε) ² −cos ² θ} ^1/2 + sin θ] (18)

Based on this result, a means for outputting image data for modulating the exposure beam in order to correct image distortion and color shift will be described below.

For example, in a case where a toner image is transferred onto paper by applying a potential to a roller facing a known drum instead of the corona charger 14 for transfer,
The transfer position is determined by the rotation angle θ and the variation of the drum radius.
Although different from s here, it is corrected in a certain relationship,
ΘT and s may be obtained.

4. Means for Outputting Image Data This implements a correction means.

4-1. Constant exposure position method 1) Output timing of image data at exposure position The output timing of the main scanning image is adjusted so that the toner image is always transferred to the ideal position. That is, in the case of the ideal drum diameter R ₀ , transfer is performed after moving by πR ₀ . However, if the drum is eccentric and the diameter of the drum varies, the toner image is transferred onto the paper after the drum rotation angle ΔT, and the transfer position is shifted by −s from the ideal transfer position T. The transferred image on the belt moves at a speed V after the transfer. The exposure data is transferred from the ideal transfer position T by −s after ΔT / ω = τ time. That is, the transfer is performed after the belt has moved by a distance of Vτ. Assuming that the ideal drum radius is R ₀ and the respective drum rotation speeds at that time are ω ₀ , the following equation is established.

If V = R ₀ ω ₀ ideal drum, transfer should be performed after π / ω ₀ = τ ₀ hours. Therefore, on the belt, an image which should be at the moving distance x = Vτ ₀ after exposure can be set to x = Vτ. That is, if image data corresponding to x = Vτ is output on the exposure side, an ideal image can be obtained. That is, data before d = V (τ ₀ −τ) may be output.

V = Rω = R ₀ ω ₀ (19) {T = π−sin ⁻¹ {(ε / R) cos θ} (20) d = V (π / ω ₀ −ΘT / ω) = R [ πω / ω ₀ −π + sin ⁻¹ {(ε / R) cos θ}] (21) d = π (R ₀ −R) + Rsin ⁻¹ {(ε / R) cos θ} (22) When there is no eccentricity , D = π (R ₀ −R) to output image data. In this case, since the peripheral speed of the drum is constant V, the sub-scanning pitch is constant. Then, when there is eccentricity, data following d may be output according to the above equation (22) (image data is output forward depending on the angle θ).

2) Synchronization signal for image data output A sub-scanning synchronization signal SYs, which is P / N (N: integer) of the sub-scanning pitch P, is generated by a clock synchronized with the movement of the belt. This may be achieved, for example, by forming a timing mark 21 on the belt as shown in FIG. When the main scan image data is output and exposed in synchronization with the sub-scanning pitch P, when the drum has an ideal shape, the sub-scanning pitch of the image exposed on the drum and the image The sub-scanning pitch is equal, and the image is transferred to the ideal position on the belt. In FIG. 9, reference numeral 7a indicates an area through which the paper on the transport belt 7 passes.

When the drum shape has no eccentricity and is larger than the ideal shape, the sub-scanning pitch is equal, but the transfer position to the belt is d _R = π | (R ₀ -R) | On the other hand, it is forward in the belt advancing direction. Therefore, if the image data before the timing of outputting the d _{R component} at the time of exposure on the ideal drum is output, an image can be formed at the same position as on the ideal drum.

When eccentricity is included, d minutes (d = π (R ₀ −
R) + Rsin ⁻¹ {(ε / R) cos θ}), it is sufficient to output image data after the timing of outputting the ideal drum at the time of exposure. The rotation angle θ of the eccentric position is detected by, for example, a rotary encoder (not shown) directly connected to the drum shaft.

3) Detection of Eccentricity ε and Drum Radius R Self-measuring method The drum radius is determined by moving the belt by a length L = 2πR ₀ corresponding to the circumference of the ideal drum and detecting the rotation angle θi of a rotary encoder (not shown) directly connected to the drum at that time. Desired. That is, R = L / θi (23)

If there is no rotary encoder and only the reference position of rotation can be detected, the belt movement distance Lb when the drum makes one rotation may be obtained. That is, R = Lb / (2π) (24)

The eccentricity ε can be detected by the above two methods. In the method of detecting the change in the reflection angle, for example, an optical system is configured to use a part of the reflected light of the main scanning exposure beam to the drum, or a light beam is irradiated separately by a light emitting element for detecting eccentricity. This is achieved by: When the eccentricity is detected at a position opposed to the transfer position of the toner image, the eccentricity is obtained by the above-described means. (In the case of this method, there is not necessarily an exposure position or an eccentricity detection position at the position opposed to the transfer position of the toner image. However, it is needless to say that, although the relational expressions are different, the same concept can be used.)

Method of Measuring in Manufacturing Process In the manufacturing process of the image forming apparatus 1, R and ε, and furthermore, angle θ ₀ information from the home position of a rotary encoder (not shown) interlocked with the rotation of the drum of ε is measured. This information is recorded in a non-illustrated non-volatile memory (connected to the bus 18 in FIG. 3) provided in the image forming apparatus 1 using the tandem system, and is used for deriving the above d. Can also be achieved.

4) Correspondence to movement speed fluctuation of the conveyor belt 7 For example, as shown in FIG. 9, a timing mark 21 is formed on the belt, and a linear encoder 22 capable of detecting a timing signal in synchronization with the movement of the belt is provided. If the image data is output as described above in synchronization with the clock signal detected thereby, there is an error in data output timing and the like (a phase error of a PLL (Phase Locked Loop) circuit and the like), but almost the same. Image is obtained.

5) Image Data Output Method When the eccentricity and the variation in the drum diameter are present, the image generated in the main scanning direction is shifted by d. When d /
Nd = <d / P> where P is rounded, rounded down or rounded up to the nearest whole number (in this description, "<>" indicates an integer of the numerical value in "<>") ) Minutes,
Shift the address of the image data to be output in the main scanning direction (in this description, when Nd is positive, shift in the delay direction)
I do.

Here, in order to further improve the image quality, it is desirable to adopt the rounding method. However, in order to further improve the image quality, interpolation information in the sub-scanning direction is added to the image information scanned on the drum. To select main scan image data.

[0082] A method of multiplying the image data to be output onto the photosensitive drum 6 by N _M in the sub-scanning direction Here, a method of multiplying N _M = 2 by way of example will be described.

The interpolation data is determined by predicting from the image data before and after in the sub-scanning direction. The image data used for prediction is not limited to one line before and after, but if a plurality of lines are used, the image quality becomes higher. In addition, when generating interpolation data in the main scanning direction at a certain point, the image quality is further improved by interpolating by predicting not only the relationship in the sub scanning direction but also the image data of the main scanning. I do.

The address NC for accessing the image data on the image memory including such interpolation data is "NC" if the image data address in the sub-scanning direction when exposing the ideal drum is Ns for the original data. = 2Ns +
<2d / P> ”. Further, the same can be realized by increasing the interpolation data in the sub-scanning direction. In FIG. 10, the main scanning image data is represented as a set of data for one dot (pixel). The data for a dot is composed of a plurality of bits (words) in order to represent information (quantization level, etc.) for recording, that is, is stored in a memory in units of words, and the main scan image is stored. Data is also configured to be fetched word by word.

[0085] Method of Forming Interpolated Data Without Increasing the Used Storage Capacity of Image Memory The above method requires N times as many memories, but the same can be performed without increasing the number of memories. That is, the main scanning image data is output while performing the calculation. That is, the original image memory is divided so that the interpolation operation can be performed immediately, and necessary image data can be output for simultaneous prediction. When prediction is performed using image data of main scanning, a buffer register is provided on the output side of the image memory, and data necessary for complementation is taken in from the image memory. Hereinafter, a case will be described as an example in which prediction is performed using main scan image data of two lines before and two lines after.

First, as shown in FIG. 11, the original image is divided into five parts, and five sub-image memories a, b,
.., Divided into sub-image memories e. The main scanning lines of the image are in order as shown in FIG. 11, the 0th line is a sub-image memory a, the first line is a sub-image memory b, the second line is a sub-image memory c,. Are stored in order as memories a,. A sub-image selection circuit (not shown) sequentially selects the sub-image memories a to e.
Each time the main-scan image data is sent once from the sub-image memories a to e, the sub-scan address is incremented by one. In this way, as shown in FIG. 11, the main scan image data is stored in the sub image memories a to e.

Next, a description will be given of means for outputting main scan image data actually written on the drum by light. First,
Nd = <d from the designated sub-scanning address for the ideal drum
/ P> is obtained by shifting the sub-scanning address Ns. Then, Ns is divided by 5, and the quotient is divided into the sub-scanning address register 3
1 and the remainder is set in the sub-image selection register 32.

In order to generate the interpolation data, it is necessary to simultaneously send the main scanning image data specified by the sub-scanning address Ns and ± 2 sub-scanning addresses before and after the sub-scanning address to the interpolation arithmetic circuit 33. Therefore, based on the data set in the sub-image selection register 32 in FIG. 11, the address Ns,
Further, two +1 addition circuits 35, 35 and -1 subtraction circuits 36, 36 are provided for selecting main scanning image data on the sub-image memories a to e before and after the sub-image memories a to e. For example, when Ns = 5, that is, when the fifth data of the main scanning image data is selected, Ns / 5 =
1 (the remainder is zero). At this time, 0 is set in the sub-image selection register and 1 is set in the sub-scanning register. Therefore, the sub-image memories a, b and c select the sub-scanning address 1 of the same sub-image memory, and the sub-image memories d and e store the sub-scanning address 0 of the sub-image memory.
Is selected. That is, image data of two main scans before and after the address Ns are simultaneously specified.

Then, of these designated main scan image data (main scan line data), the dot image data designated by the main scan address register 37 is output from each of the sub-image memories a to e. Interpolation arithmetic circuit 33
Is interpolated based on the input main scanning dot data, so that the input of the interpolation operation circuit 33 is rearranged so that the main scanning image data specified by the sub-scanning address Ns always comes to the center. This sorting is performed by the data sorting circuit 38.
Run by. When Ns = 5, as a result, the main scanning dot data corresponding to the sub-scanning address 5 becomes
And the main scanning dot data before and after in the sub-scanning direction are aligned and appear at 00, 01, 03, and 04. The data rearrangement circuit 38 converts the output S of the sub-image selection register 32.
, S4, the sub-image memory output D
.., D4 are obtained from the input / output table shown in FIG.
.., 04 are rearranged.

Here, corresponding to the amount of shift d in the sub-scanning direction, the main scanning image corresponding to the position obtained by further dividing the pitch P by n with respect to the sub-scanning address value <d / P> to be shifted. Na =
<Nd / P> −n <d / P> is calculated, and the interpolation operation circuit 33 is calculated.
To enter. In other words, the calculation is performed by the interpolation calculation circuit 33 so as to be as if there were image data of main scanning at a fine resolution of 1 / n. From the data 00, 01,..., 04 input to the interpolation arithmetic circuit 33, for example, an interpolation prediction curve is drawn, a value corresponding to the position of Na × P / n is obtained, and the main scanning dot data is output. I do.
In FIG. 11, the main scanning address decoder 39
Is a decoder for decoding main scanning address information.

As described above, the image quality can be improved in the image forming apparatus 1 of the type in which the exposure is performed at the fixed position as in the polygon motor type, and the exposure and scanning are performed continuously at fixed time intervals.

6) Polygon Motor Constant Rotation Method In the image forming apparatus 1, when the polygon motor rotates at a constant speed and the exposure scanning is performed at a constant speed in the main scanning direction, the polygon motor rotates at a constant speed and moves onto the drum. The exposure beam is scanned at a constant timing (time interval) in the main scanning direction (a direction orthogonal to the rotation direction of the drum). The scanning timing by the polygon mirror is determined on the premise of an ideal drum. That is, exposure scanning is performed at a constant speed by the exposure beam regardless of the eccentricity of the drum and the drum diameter.

The drum rotates at a constant rotational angular speed ω. Therefore, when there is eccentricity, when the distance from the rotation center O to the exposure position E is longer than the average value of the drum radius, the drum peripheral speed becomes faster than the average peripheral speed V, and when it is shorter, the drum peripheral speed becomes slower. Beams scanned by the polygon motor are at regular time intervals in the sub-scanning direction. Therefore, when the peripheral speed of the drum changes, the scanning pitch of the laser varies. For example, on the drum near the exposure position where the drum radius is long, scanning is performed with a long pitch interval.

[0094] Correction of Image Quality Degradation due to Drum Eccentricity Fluctuation due to Drum Eccentricity In order to prevent image deterioration caused by drum eccentricity, the size of dots (pixels) drawn on the drum is controlled and corrected. That is, where the pitch is coarse, the dot diameter is increased, and where the pitch is fine, the dot diameter is reduced. The image quality can be further improved by changing the dot diameter only in the sub-scanning direction. This can be realized by appropriately controlling the laser optical system and the irradiation laser intensity, pulse length, and pulse shape according to the photoconductor characteristics and the charged state.

Regarding the drum peripheral speed VL, the following equation is established in FIG.

VL = eωcosβ = eω [1-sin ² β] ^1/2 = eω [1- (ε / R) ² · cos ² θ] ^1/2 = eω [1-g] ^1/2 where e = [R ² + ε ² -2R ² ｛g- (ε / R) sin θ (1-g) ^1/2 ｝] ^1/2 g = {(ε cos θ) / R} ² (25) Determined that the instantaneous temporal changes of e and β were minimal. Therefore, the laser emission pulse is finally determined by the dot (pixel) data and the peripheral speed.

[0097] Relationship between Belt Movement and Beam Scanning on Drum by Polygon Belt speed fluctuation is zero, and there is a phase difference between the timings at which main scan image data is output at every sub-scanning pitch P in synchronization with polygonal beam scanning and belt movement. If not,
The main scan image data may be output by the above-described means according to the eccentricity of the drum and the diameter of the drum. However, for example, if there is a speed fluctuation of the belt, this relationship is broken. Since laser scanning by a polygon is performed at a constant rate, it is necessary to output main scanning image data in synchronization with the main scanning of a polygon.

The main scanning image data I _M is specified in synchronization with the sub-scanning pitch P by the clock C synchronized with the movement of the belt.
The main scan image data I _M at the time of the main scan image output timing Tb synchronized with the belt corresponding to mc may be selected. Timing Tb corresponding this time, if there is an output timing and phase deviation in the main scanning image data I _M synchronized with the belt, to correct the minute d. That is, when the timing Tb is delayed by the duty k of the clock synchronized with the sub-scanning pitch P, the output timing d by P × k
May be corrected to generate main scan image data. k
Sometimes exceeds 1. If it is delayed by one pulse or more, k ≧ 1.

That is, the output of the main scanning image data and the interpolation may be performed as d = kP + π (R ₀ −R) + R sin ^-1 {(ε / R) cos θ} (26)

2) Optical scanning unit system formed by arranging a plurality of light emitting elements (laser diodes or light emitting diodes) In this system, the main scanning image data can be selected at any time, so that d = π (R ₀ -R ) + Rsin ^-1 {(ε / R) cos θ} (27) The output and interpolation of the main scan image data described above may be performed.

4-2. Exposure Position Variable Method In FIG. 14, even when the eccentricity (ε, θ) and the drum diameter R vary at the exposure position E, if the main scan image data is output at the timing of the ideal drum, d is greater than the ideal transfer position.
The image is transferred at a position in the foreground, and this color shift occurs. Therefore, the exposure beam may be exposed to Cr on the drum such that main scan image data delayed by d at the intersection E between the drum circumference and the positive y-axis at this moment is output.

Therefore, since the exposure timing can always be output at the same timing as that of the ideal drum, the exposure position may be controlled such that the information delayed by d appears at the intersection E on the positive y-axis with the circumference of the drum. Therefore, it suffices to expose the Cr position on the drum corresponding to the rotation angle δ from the positive y axis in FIG. The exposure position Cr overlaps the positive y-axis after an angle δ rotation. Then, in the image exposed at the exposure position Cr, after Dt = δ / ω time, the image is shifted by d minutes when the angle of the eccentric position is θ + δ. By exposing the position Cr at an angle δ reaching the positive y-axis over a time corresponding to the moving time Dd = d / V of the transport belt 7 corresponding to the d, color shift does not occur. That is, when the following relationship is established, the color shift is eliminated.

Dt = δ / ω = Dd = d / V That is, δ = d / R (28) (where d = π (R ₀ −R) + Rsin ⁻¹ ｛(ε / R) co
s (θ + δ)｝) δ may be obtained from this relational expression.

That is, when the eccentric position is at the angle θ, the positive y
The exposure may be performed at the exposure position Cr corresponding to the angle δ determined by the equation (28) before the axis. In other words, when the main scan image data is output, by irradiating to the front angle δ of the positive y-axis, the electrostatic latent image corresponding to the delay distance d after the Dd time is automatically generated on the positive y-axis. You will come to the position.

The rotation center Mc of the oscillating mirror for correction is provided at the position of R ₀ + M on the y-axis. Laser incidence on the mirror is assumed to be parallel to the x-axis. The reflecting surface of the mirror is
In the case of an ideal drum, it forms an angle of π / 4 with the x axis. The mirror swing angle for exposing at the exposure position Cr is θm
And Further, if the distance between a line connecting the two points of the exposure position E and the exposure position Cr is w, and the angle between this line and the positive y-axis is η, the following equation is established.

W / sin (2θm) = (R ₀ + Me) / sin (π−2θm−η) (29) w / sinδ = e / sin (η−δ) (30) −w / sin {2 (β + η)} = R / sin (β + η) (31) −w / (2R) = cos (β + η) (32) sinβ = (ε / R) · cos θ (33) β = sin ⁻¹ {(Ε / R) · cos θ} (34) g = {(εcos θ) / R} ² (35), e ² = R ² + ε ² -2Rε sin (β−θ) (36) e = [R ² + ε ² -2R ² {g− (ε / R) sin θ (1-g) ^1/2 }] ^1/2 (37) Therefore, cot (2θm) = (R ₀ + Me) / (W · sin η) −cot η (38) In this equation, equations (28), (30), (32), (35),
The mirror swing angle θm is obtained using (37). The transfer position of the toner image is corrected by changing the exposure position on the drum by controlling the exposure beam incident angle θm on the mirror based on the drum radius R, the eccentricity ε, and the drum rotation angle (eccentric angle) θ. If R and the eccentric position (ε, θ) are known, θm is calculated in advance by the CPU 15 for θ = 0 to 2π, stored in the RAM 17, and set as θ as a reference signal of a control circuit of a swing mirror unit (not shown). Enter as appropriate.

In this case, the main scan image data may be output in synchronization with a timing signal synchronized with the movement of the belt. In the method of scanning light by driving a polygon motor, an exposure beam scans a drum in a main scanning direction at a constant speed. A signal similar to that when an ideal drum is present may be placed on the exposure beam in the main scanning direction. That is, the image data may be output regardless of the eccentricity and the variation of the drum diameter. At this time, color shift and image distortion of the image formed on the sheet do not occur.

Here, the images in the sub-scanning direction on the drum are not at the same pitch. That is, the transfer position is εcosθ
Therefore, the exposure position is shifted so as to compensate for that.

The image data output means described above is
The invention can be applied not only to the tandem type image forming apparatus 1 but also to a well-known one-drum type color copying machine or color printer. In other words, in the one-drum system,
Although there is little problem of color misregistration, the above-described image data output means is effective for improving image quality against image quality deterioration such as image distortion due to eccentricity and variation in diameter of the photosensitive drum.

5. Correction of the error _ε bET0 x from the drum distance D _bET x ideal drum distance _D bET0 x of now be described the correction of the error relationship of the photosensitive drum between the mounting position in the tandem type image forming apparatus. This implements the correction means.

D_bETx = D_bET0x + ε_bET0x (x: 0, 1, 2) (39) (where D_bET0 is a photoconductor corresponding to C in FIG.
Distance between the drum and the photosensitive drum corresponding to M, D_bET
1 is a photoconductor drum corresponding to C and a photoconductor corresponding to Y
Distance between drums and D_bET2 is photosensitive corresponding to C
Indicates the distance between the body drum and the photosensitive drum corresponding to BK
The main scan image data for the drum corresponding to M is
From the corresponding drum, D _bET0 / P number of sub-scans, corresponding to Y
The main scan image data on the drum
D from the ram_bETFor 1 / P sub-scanning number and BK
The main scan image data on the drum
D from the ram_bET2 / P Delayed by the number of sub-scans and
Output main scan image data in synchronization with the default
No. Where D_bETIf x / P is not an integer, correct accordingly
Must.

Therefore, the ideal drum position D _bET0 x
Is set to be an integral multiple of the sub-scanning pitch P. The error amount _ε bET0 x, when the amount d is corrected in accordance with the eccentricity and the drum diameter of the drum and dx, error of the _dx ε bET0
x (positive in the direction longer than the ideal position)
In order to correct the above, a process of outputting main scan image data may be performed.

Driving of the entire tandem mechanism is performed, for example,
Perform on either the drum or the belt. That is, there is one drive source.

6. Regarding the start position and timing of transfer of the toner image to the paper The correction means is thereby realized.

If the transfer is started when the paper arrives at the ideal position x = 0 of the drum corresponding to C, the exposure must be started before the transfer. That is, the ideal position x = 0 to πR
When the paper comes to a position at a distance of ₀ before, exposure of the drum corresponding to C is started. Here, the eccentricity and the diameter of the drum, and further, the correction of d according to the deviation from the ideal position of the drum corresponding to C are performed.

By performing the above, a high-quality image with little color shift can be formed.

7. Measurement of the deviation of the drum position from the ideal position (measurement of the deviation of the drum corresponding to ε _bET0 x and C) The correction means is thereby realized.

[0118] Measurement in Manufacturing Process This is a method of measuring in the manufacturing process, recording this information in the flash memory (not shown) of the image forming apparatus 1 using the tandem system, and using the information for deriving the d.

[0119] Self-measurement method In the polygon method, the rotation phase of the polygon motor is corrected so that the main scan image data on the drum is exposed by the laser in synchronization with the main scan output timing synchronized with the belt movement. . This can be realized using a PLL circuit, as in the prior art. As shown in FIG. 9, a reference mark 23 is provided at a position on the belt deviating from the area 7a through which the sheet passes.

That is, in FIG. 9, a reference mark 23 corresponding to the leading end position of the sheet is provided at a position on the belt deviating from the place where the sheet passes, and is disposed πD ₀ before the ideal position of the drum corresponding to C. The position at which the reference mark 23 passes through the detected tip position detector (exposure start position detector) 24 indicates the exposure start position. When a toner image is actually transferred to a sheet, a sheet leading end position passage detector 25 is provided at a position where the sheet in the main scanning direction passes, and thereby the exposure start position can be determined. The main scanning image data (in this case, d is not corrected) that is transferred to the position of the reference mark 23 assuming that the drum is at the ideal position is output, and as shown in FIG. The test mark 27 is transferred onto a belt, and a difference from the reference mark 23 is measured to measure a deviation from an ideal position. That is, the test mark 2 passing through the reference position error detector 26
Timing 7 is measured by the linear encoder 22 that detects the movement of the belt, and the deviation from the ideal position is measured. At this time, the transfer mark position shift d occurs due to the eccentricity of the drum and the variation in the drum diameter. However, the position shift is calculated by correcting the position shift d (delay by d by the definition of the sign of d). Test mark 2 at the timing corrected first for d minutes
The reason why the image data of No. 7 is not output is that an appropriate timing has already passed due to the eccentric position, and there is a case where recording cannot be performed.

A method may be used in which four reference marks 23 are shifted in the sub-scanning direction and measured. This method requires fewer measuring elements. However, it is necessary to shift the output timing of the main scanning image data in the sub-scanning direction by the shifted amount.

8. Example of Operation Sequence This implements a correction unit.

In FIG. 9, although not shown, the drum corresponding to C, the drum corresponding to M, the drum corresponding to Y, and the drum corresponding to BK are not shown in the drawings. And a detector for detecting the eccentric position by detecting the displacement of the drum surface. Although not shown, a motor for driving the belt is also provided.

As a first example, a method in which a polygon mirror is driven to rotate at a constant speed and a beam emitted from a laser diode is main-scanned to a drum by a polygon mirror that deflects the beam, and an exposure (light writing) position is fixed. Think first.

First, when the power of the image forming apparatus 1 is turned on, the belt is driven without feeding paper. The belt and drum move together without slipping, so the drum also moves. Then, one rotation of the drum is detected by a detector that detects a reference position of the rotation angle, and the number of output pulses of the linear encoder 22 at this time (in some cases,
The phase of the pulse interval is also measured to improve the accuracy) and the diameter of the drum is measured. Further, the eccentric position is measured by the output of the detector for detecting the reference position of the rotation angle of one rotation of the drum and the output of the linear encoder 22. Since the number of output pulses of the linear encoder 22 corresponding to one rotation of the drum is known, the rotation angle can be calculated. The eccentric amplitude can be detected by detecting the AC amplitude in the output waveform of the detector at the eccentric position. The above detection is performed for each drum. Based on the above detection data, the correction value d
(D = π (R ₀ −R) + R sin ⁻¹ {(ε / R) cos θ})
Is calculated for one round for each drum (θ = 0 to 2π), and
It may be stored in the RAM 17 as a table in advance and used.

Next, the reference mark 23 is detected by the tip position detector 24 at the end on the belt, and a test is performed on the reference mark 23 assuming that each drum is at an ideal position and has an ideal shape. Image data of main scanning for transferring the mark 27 is optically written on each drum.

In the above example, the timing phase of the main scanning of the polygon mirror is assumed to be coincident with the timing phase of the sub-scanning outputted by the movement of the belt. Here, an example in which the timing phase does not coincide will be described. The start timing of the main scanning is performed based on the pulse signal detected by the linear encoder 22 at the timing mark 21 on the belt, but does not always coincide with the main scanning timing of the polygon mirror.
Therefore, when the main scanning timing of the polygon mirror is not reached at the output timing of the test mark 27, kP
The test mark 27 is recorded at the delayed main scanning timing of the polygon motor. Then, after detecting an error with respect to the reference mark 23, d is generated due to the eccentricity and the variation of the diameter.
And the kP here, the drum mounting error can be corrected. In this manner, the correction data d based on the mounting position of the drum and the like, and the eccentricity and the variation of the diameter of the drum are obtained. If an image is output using this data, an image without color shift and without distortion can be output. .

As a second example, there is described an exposure position variable system using the oscillating mirror. Also in this example, a case where the main scanning is performed by the polygon mirror will be described. The generation of the eccentricity and the drum radius data is the same as in the above example. Here, there are two methods for recording the test mark 27. In the first case, the angular position of the oscillating mirror is fixed so that the exposure position is at the origin (x = 0), and is the same as the method described above. Second, a test mark is recorded while performing only the correction (control of θm) corresponding to the eccentricity and the variation in the diameter. The problem of the phase difference of the main scanning timing by other polygon mirrors may be handled in the same manner as in the first example.

Now, the structure of the oscillating mirror will be described. The oscillating mirror has an angle detector for detecting the rotation of the mirror, and the angle is detected and fed back to control the target angle θm to be obtained. As the structure of the drive unit of the oscillating mirror, a structure in which a well-known voice coil motor is used as a drive source and the mirror is supported by a cross spring structure can be used.

9. Conclusion In the technology disclosed in Japanese Patent Application Laid-Open No. H10-246995, peripheral displacement based on the eccentricity of the rotation axis of the photosensitive drum is detected, and control based on the detected displacement is performed to solve the problem due to the eccentricity of the photosensitive drum. are doing.

On the other hand, the image forming apparatus 1 detects the eccentric position and the rotation angle of the drum with respect to the center point of the cross section circle of the drum, and, based on the detected data, the absolute value of the eccentric amount, the eccentric rotation angle, and The control is to detect the drum radius and correct the transferred image on the belt or paper.

From equation (22), the correction amount d is d = π (R ₀ −R) + R sin ^-1 {(ε / R) cos θ}, and the second term on the right side includes the radius R. And the relationship with the rotation angle θ is not a simple sinusoidal relationship. Therefore, as higher resolution is required, the influence of radius variation must be considered. In the prior art,
This has not been achieved.

In the tandem type image forming apparatus,
A variation in the drum diameter and the drum position occurs, and in the polygon method, there has conventionally been a problem that a large color shift occurs when there is a fluctuation in the belt speed. Since the data correction amount d also depends on the radius R of the disk, it is obvious that a variation in the radius R cannot be detected by the conventional method of detecting the circumferential displacement, and therefore, high-precision color matching cannot be realized.

The detection amount of the eccentric displacement of the prior art is (3
A value proportional to e in equation (7) is detected, which is different from the correction scheme in equation (22). The formulas are listed below. It can be seen that in the peripheral displacement detection method of the related art, an error occurs in the correction.

D = π (R ₀ −R) + R sin ⁻¹ {(ε / R) cos θ} (22) e = [R ² + ε ² −2R ² ｛g− (ε / R) sin θ (1-g) ^1/2 )] ^1/2 (37) where g = {(εcos θ) / R} ² (35) In the image forming apparatus 1, the phase of the eccentric position of the drum in the manufacturing process is further increased. If the phase of the main scanning line transferred from the drum onto the paper in the sub-scanning direction is matched or almost matched to all the drums, the laser scanning method using a polygon mirror is used. When the exposure position is fixed, the fluctuation of the sub-scanning pitch formed on the paper becomes almost equal, so that the image quality is further improved. However, if the drum diameter varies, the phase gradually shifts when printing or copying is repeated. This deviation may be repaired on a regular basis. Further, in a case where the four drums are driven by a single motor connected by gears, for example, so as to rotate in the same manner, there is no phase relationship between the motors. However,
In this case, it is necessary to make all drum diameters equal. If the diameter varies, rubbing occurs between the belt and drum,
Image blur occurs.

In the above description of the first embodiment, the image forming apparatus 1 including the photosensitive drums 6, 6,... That is, the toner image formed on the photosensitive drum 6 is directly transferred from the photosensitive drum 6 to a sheet. As another method to which the present invention can be applied, a color image is formed by transferring a toner image formed on each photosensitive drum 6 onto a belt (intermediate transfer belt), and forming a color image on the intermediate transfer belt. An image forming apparatus of a type in which an image is transferred onto a sheet by a known means can be used. That is, the transfer of the toner image directly from the photosensitive drum 6 to the paper
What is necessary is just to replace it with transfer to an intermediate transfer belt.

In the description of the first embodiment of the present invention, the exposure position on the photosensitive drum 6 has been described as the point E in FIGS. 4 and 8 and the like. The explanation holds. In this case, the amount of movement of the sheet or the intermediate transfer belt corresponding to the shift of the exposure position from the point E may be corrected. That is, in FIG. 8, when the exposure position is located at the angle z in the rotation reversal direction of the photosensitive drum 6 from the point E, the correction term z (R ₀ -R) may be added to the equation (22). That is, the movement of the paper or the intermediate transfer belt by the angle z may be corrected. At this time, the equation (22) becomes the following equation (40).

D = π (R ₀ −R) + R sin ⁻¹ {(ε / R) cos θ} + z (R ₀ −R) = (π + z) (R ₀ −R) + R sin ⁻¹ ｛(ε / R) cos θ … (40) Needless to say, the above description does not limit the content of the present invention. For example, the present invention can be applied to a system in which an electrostatic latent image of each color is simultaneously formed with a plurality of exposure beams to speed up image forming processing.

[Second Embodiment of the Invention] Another embodiment of the present invention will be described as a second embodiment of the present invention.

FIG. 16 is a block diagram showing a schematic configuration of a copying machine 41 according to the second embodiment of the present invention. The copying machine 41 implements the image forming apparatus of the present invention, and includes an image reading apparatus 42 having a well-known configuration for reading a color image of a document, and the image forming apparatus 1. It is possible to form an image based on the image data obtained by the image forming apparatus 1.

Therefore, according to the copying machine 41, the same functions and effects as those of the image forming apparatus 1 according to the first embodiment of the present invention can be obtained.

[0142]

According to the first aspect of the present invention, the distortion and color misregistration of the transferred toner image are corrected based on the amount of eccentricity of the photosensitive drum, the eccentric rotation angle, and the radius of the photosensitive drum. Even if high resolution is required, distortion and color misregistration of the image in the sub-scanning direction can be sufficiently prevented.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, an error in the transfer position of the toner image between the photosensitive drum having the ideal shape and the actual photosensitive drum is precisely determined. Therefore, distortion and color misregistration of the image in the sub-scanning direction can be sufficiently prevented even if high resolution of image formation is required.

According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the error in the transfer position of the toner image between the photosensitive drum having the ideal shape and the actual photosensitive drum is precisely corrected. Therefore, distortion and color misregistration of the image in the sub-scanning direction can be sufficiently prevented even if high resolution of image formation is required.

According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, an error in a mounting position of a photosensitive drum or the like is absorbed, and high resolution of image formation is required. Even if this is done, distortion and color misregistration of the image in the sub-scanning direction can be sufficiently prevented.

According to a fifth aspect of the present invention, there is provided the image forming apparatus according to any one of the first to fourth aspects, wherein the optical writing device having the same hardware configuration as in the prior art is used as it is to form an image. Even if high resolution is required, distortion and color misregistration of the image in the sub-scanning direction can be sufficiently prevented.

According to a sixth aspect of the present invention, there is provided the image forming apparatus according to the fifth aspect, wherein the image data is corrected by directly using the optical writing device having the same hardware configuration as in the prior art. Even if a higher resolution is required, distortion and color misregistration of the image in the sub-scanning direction can be sufficiently prevented.

According to a seventh aspect of the present invention, in the image forming apparatus according to the fifth or sixth aspect, a main scanning image scanned by a polygon mirror can be output stably without interruption, so that a high quality image can be obtained. Can be obtained.

According to an eighth aspect of the present invention, in the image forming apparatus according to the sixth or seventh aspect, variation in the sub-scanning pitch due to the eccentricity of the photosensitive drum can be made inconspicuous.

According to a ninth aspect of the present invention, in the image forming apparatus according to any one of the fifth to eighth aspects, the main scanning is performed at the same timing as when there is no eccentricity of the photosensitive drum and no variation in the drum diameter. Can be output.

According to the tenth aspect of the present invention, even if the photosensitive drum is eccentric, if the conveying member moves at a constant speed, the rotation angle of the photosensitive drum becomes constant. Can be detected by a single sensor, so that manufacturing costs can be reduced, and correction data for correcting distortion and color misregistration of an image in the sub-scanning direction can be created with high accuracy.

The eleventh aspect of the present invention relates to the first to first aspects.
0, it is possible to reduce the image deterioration caused by the fluctuation of the sub-scanning pitch of the electrostatic latent image caused by the linear speed fluctuation due to the eccentricity at the exposure position on each photosensitive drum. .

The twelfth aspect of the present invention relates to the first to the first aspects.
1, the same operation as the image forming apparatus according to any one of the above,
It works.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram illustrating a schematic configuration of an image forming apparatus according to a first embodiment of the present invention;

FIG. 2 is a front view illustrating a configuration of a tension roller of the image forming apparatus.

FIG. 3 is a block diagram illustrating an electrical connection of a control system of the image forming apparatus.

FIG. 4 is an explanatory diagram illustrating a relationship between a moving speed of a transport belt of the image forming apparatus and a rotational angular speed of a photosensitive drum.

FIG. 5 is an explanatory diagram illustrating a relationship between a moving speed of a conveyor belt and a rotation angular speed of a photosensitive drum in a conventional image forming apparatus.

FIG. 6 is a diagram illustrating a unit for detecting an eccentric position of a photosensitive drum of the image forming apparatus.

FIG. 7 is a diagram illustrating a unit that detects an eccentric position of a photosensitive drum of the image forming apparatus.

FIG. 8 is a diagram illustrating a unit for calculating an angle from an exposure position to a transfer position of the image forming apparatus.

FIG. 9 is a plan view of each photosensitive drum and a transport belt of the image forming apparatus.

FIG. 10 is an explanatory diagram illustrating a unit that outputs image data of the image forming apparatus.

FIG. 11 is an explanatory diagram illustrating a unit for outputting image data of the image forming apparatus.

FIG. 12 is an explanatory diagram illustrating a unit that outputs image data of the image forming apparatus.

FIG. 13 is an explanatory diagram illustrating a unit that outputs image data of the image forming apparatus.

FIG. 14 is an explanatory diagram illustrating a unit that outputs image data of the image forming apparatus.

FIG. 15 is an explanatory diagram illustrating a relationship between a test mark formed on the belt by exposing each photosensitive drum of the image forming apparatus and a reference mark formed on the belt.

FIG. 16 is a block diagram illustrating a schematic configuration of an image forming apparatus according to a second embodiment of the present invention;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image forming apparatus 6 Photoreceptor drum 7 Conveying member 41 Image forming apparatus 42 Image reading apparatus

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) G03G 15/00 303 G03G 15/16 5C072 15/043 H04N 1/06 5C074 15/04 1/29 C 5C079 15/16 B41J 3/00 M 21/14 G03G 15/04 120 H04N 1/04 21/00 372 1/06 H04N 1/04 D 1/29 1/46 Z 1/46 F term (reference) 2C362 BA52 BA70 BA71 BA90 BB40 BB47 BB50 CA22 CA39 CB59 CB60 DA04 2H027 DA20 DA22 DA23 DC04 DE07 EA02 EA20 EB04 EC06 EC09 ED02 ED04 ED16 ED24 EE05 2H030 AA01 AB02 AD05 AD17 BB02 BB16 BB42 BB44 2H032 AA02 AAB15 AB01 AB12 AB15 AB01 AB12 AB15 AB01 AB09 AA03 BA04 JA07 JA08 QA14 XA01 5C074 AA10 BB02 BB26 CC26 DD24 EE04 EE05 FF15 GG02 GG09 GG12 GG14 GG15 HH02 5C079 HA07 KA03 KA09 KA17 KA18 LA01 LA24 LA28 LA31 MA11 NA01 NA25 NA29 PA02 PA03

Claims (12)

[Claims] 1. A photosensitive drum, an optical writing device for performing main scanning optical writing on at least one line at a time on a peripheral surface of the photosensitive drum, and an electrostatic latent image having the optical writing written on the photosensitive drum And a transport member that transports a sheet by moving in synchronization with the photosensitive drum while being pressed against the photosensitive drum, and transfers a toner image on the photosensitive drum onto the sheet. Or an intermediate transfer belt that transfers a toner image on the photosensitive drum that moves in synchronization with the photosensitive drum while being pressed against the photosensitive drum, and directly or indirectly detects a rotation angle of the photosensitive drum. An eccentricity detecting means for detecting an eccentric position of a center of a circular cross section of the photosensitive drum from a rotation axis of the photosensitive drum; The amount of eccentricity of the photosensitive drum, the eccentric rotation angle, and the radius of the photosensitive drum are obtained from the detection result of the center detecting means, and the toner after the transfer to the sheet or the intermediate transfer belt is determined based on the obtained values. An image forming apparatus comprising: a correction unit configured to correct image distortion and color misregistration. 2. The method according to claim 1, wherein the correcting unit calculates an error in a transfer position of the toner image after the transfer between the photosensitive drum and the photosensitive drum when the photosensitive drum has an ideal shape. 2. The image forming apparatus according to claim 1, wherein distortion and color shift of the toner image are corrected based on the error. 3. The method according to claim 1, wherein the correcting unit sets a shift amount of the exposed image from an ideal state as d, an eccentric amount as ε, and an eccentric rotation angle as θ (for the sheet or the intermediate transfer belt near the transfer position). The moving direction is θ = 0), the radius of the photoconductor drum is R, and the radius of the photoconductor drum when the photoconductor drum is an ideal shape is _R0. The exposure position on the body drum is assumed to be at an angle (π-z) in the rotational direction of the photosensitive drum from the transfer position of the ideal shape photosensitive drum from the transfer position of the ideal shape photosensitive drum. At this time, the shift amount d is calculated as follows: d = π (R ₀ −R) + R sin ⁻¹ {(ε / R) cos θ} + z
The image forming apparatus according to claim 2, wherein the value is obtained by (R ₀ −R). 4. The apparatus according to claim 1, wherein the correction unit detects an error in the mounting position of the photosensitive drum or another member, and corrects the distortion and color shift of the toner image based on the error. The image forming apparatus according to any one of the above. 5. The correction unit corrects distortion and color misregistration of the toner image by selecting and controlling appropriate data from image data that modulates an exposure beam output from the optical writing device. The image forming apparatus according to any one of claims 1 to 4, wherein the image forming apparatus performs the operation. 6. The optical writing position in the sub-scanning direction on the photosensitive drum is fixed, and the correction unit performs positional interpolation of the original image data in at least one of the sub-scanning direction and the main scanning direction. The image forming apparatus according to claim 5, wherein control is performed by selecting appropriate data from the interpolated image data using the interpolated image data obtained. 7. The optical writing device deflects a light beam emitted from a light source by a polygon mirror that is driven to rotate at a constant speed by a polygon motor, and performs main scanning on the photosensitive drum. 7. The image forming apparatus according to claim 5, wherein the position of the optical writing is fixed, and wherein the correction unit outputs the image data so as to match a timing of starting main scanning by the polygon mirror. 8. . 8. The image forming apparatus according to claim 6, wherein the correction unit changes the optical recording condition according to a peripheral speed of the photosensitive drum to perform the optical writing. 9. The image forming apparatus according to claim 1, wherein the correcting unit is configured to adjust the exposure data on the peripheral surface of the photosensitive drum so as not to select the appropriate data of the image data that modulates the exposure beam output from the optical writing device. 6. The optical writing position is controlled.
An image forming apparatus according to any one of claims 1 to 8. 10. A contact portion between the conveying member, the sheet or the intermediate transfer belt and the photosensitive drum is a vertex in a direction of the conveying member or the intermediate transfer belt in a circular cross section of the photosensitive drum. Item 10. The image forming apparatus according to any one of Items 1 to 9. 11. A plurality of the photosensitive drums are formed on the intermediate transfer belt or the transport member in a line in a moving direction of the intermediate transfer belt or the transport member. When the formed toner images are transferred and superimposed, the eccentricity of each of the photosensitive drums is adjusted so that the phase relationship of the density of the transferred images caused by the eccentricity matches each other for all of the photosensitive drums. The phase relationship between a position of an electrostatic latent image formed on the photosensitive drum and a position of the electrostatic latent image substantially coincides with each other for all the photosensitive drums. Image forming device. 12. The image forming apparatus according to claim 1, further comprising an image reading device that reads an image of a document, and capable of forming an image based on the read image data.