JP2929671B2 - Image forming position adjusting method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an image forming / outputting apparatus having a sheet conveying / transferring medium, in which an image forming apparatus capable of correcting a positional shift caused by a fluctuation in the rotational angular velocity of a photosensitive member. The present invention relates to a position adjustment method and device.

[Prior Art] An image forming apparatus having a transfer drum for sheet conveyance and transfer,
For example, in a full-color copying machine or the like, images of three colors of yellow, cyan, magenta or four colors including black sequentially formed on a photoreceptor are electrostatically attracted and conveyed onto a transfer drum covered with a mesh. It is transferred to paper to obtain a full-color copy. At this time, a positional deviation (deviation from an ideal position on a print) occurs due to a change in the rotational angular velocity of the photoconductor, and finally appears as a color deviation.
In particular, in a tandem-type full-color printer in which a plurality of photoconductors are arranged around a transfer drum to obtain a full-color print in one pass, the rotational angular velocity of each photoconductor often differs from each other. It appears as a color shift, which significantly degrades the image quality. It is not a problem if the rotational accuracy of each photoconductor is improved as much as possible and the rotational accuracy is raised to a level at which color misregistration does not become a problem. However, doing so is costly and impractical.

[Problems to be Solved by the Present Invention] The present invention has been made in view of the above-described circumstances, and provides an image forming position adjusting method and apparatus capable of correcting a position shift with a simple configuration and low cost. With the goal. Another object of the present invention is to obtain a high-quality image by correcting misregistration.

[Means for Solving the Problems] In the method of correcting a position shift according to the present invention, a position shift due to a variation in the rotational angular velocity of a photoconductor is performed by focusing on the vibration component frequency from the image formation on the photoconductor to the transfer. The relationship between the angle and the fundamental frequency that depends on the average angular velocity of the photoconductor is an integer ratio.

[Operation] The ratio of the position shift of the photosensitive member to the position shift of the image on the print sample due to the rotational fluctuation is a periodic function of the ratio of the fundamental frequency dependent on the average angular velocity of the photosensitive member to the rotational fluctuation frequency component of the photosensitive member. By making the ratio of the fundamental frequency dependent on the average angular velocity of the photoconductor to the rotation fluctuation frequency component of the photoconductor an integer, the displacement of the image on the print sample can be substantially eliminated.

[Examples] Hereinafter, the present invention will be described in detail based on examples.

FIG. 3 shows a basic configuration of a color copying machine as an example using the displacement correction method of the present invention. Around the photoreceptor 1, a charger 2, an optical system unit 3, and developing units 4C, 4M, 4Y corresponding to respective colors of cyan, magenta, yellow, and black,
4K, a transfer drum 5, a pre-cleaning processing unit 6, and a cleaning unit 7 are arranged. Transfer drum 5
, A transfer unit 8, a peeling static eliminator 9, a peeling claw 10, and the like are arranged. The transfer paper on the cassette tray 11 is held on a transfer drum through a paper feed roll 12, a registration roll 13, and the like, and after the images developed on the photoconductor 1 are sequentially transferred to the transfer paper, the transfer drum The sheet is peeled from the sheet 5 and discharged to a sheet discharge tray 16 through a fixing device 14, a sheet discharge roll 15, and the like.

FIG. 4 shows the details of the transfer section. In the transfer drum 5, a dielectric or semi-dielectric paper transport medium 17 such as a metal mesh or mylar is adhered to a support drum made of Al or the like provided with an opening corresponding to the paper size. After the leading end of the sheet 18 is held by the gripper 19, the sheet 18 is adsorbed and conveyed to the surface of the sheet conveying medium 17 by electrostatic force or the like. The photoconductor 1 and the transfer drum 5 rotate in the directions of the arrows, and the image developed on the photoconductor 1 is transferred to the paper 18 by the transfer unit 8. The angle AOB between the imaging point 21 (A) on the photoconductor 1 and the transfer point 22 (B) with respect to the center 20 (O) of the photoconductor 1 is defined as the imaging point 21.
The angle measured along the rotation direction of the photoconductor 1 from (A) is θ
_Let it be ₁ .

FIG. 5 shows the result obtained by picking up the rotation accuracy of the photoconductor 1 rotating in the direction of the arrow with a rotary encoder or the like. The upper graph is the data of the speed fluctuation, and the lower graph is the result of the fast Fourier transform (FFT) analysis. Photoconductor 1
Of the rotation fluctuation component of the primary vibration frequency components f ₁ or
It is understood that the f _2. These vibration frequency components f ₁ or f ₂ and the fundamental frequency f ₀ existing at θ ₁ shown in FIG.
And it is closely related, positional deviation appearing on the print, depending on the relationship of f ₁ or f ₂ and f ₀ (deviations from the ideal position) is increase or decrease. The present invention positively utilizes this effect.

 The rotational angular velocity ω (t) of the photoconductor 1 is represented by the following equation.

Result of FFT analysis shown in FIG. 5 has a main vibration frequency components of f ₁ and f ₂ in the case of k = 2.

Here, the relationship with the fundamental frequency f ₀ that depends on the angle θ ₁ from the imaging point 21 to the transfer point 22 on the photoconductor 1 is important. f ₀
Is represented by the following equation.

f ₀ = 1 / f ₀ = (θ ₁ / ω _m ) ⁻¹ = ω _m / θ ₁ (2) (t ₀ is the time between θ ₁ ) The displacement Δx _(p) on the print sample and the photoconductor The displacement Δx _(MQ) due to the rotation fluctuation ω (t) is expressed by the following equations.

When i = 1, Δx _(MQ) is expressed by the following equation.

Δx _(MQ) = Δω _(φ−P) / II f ₁ (5) From the equations (3) and (5), the position shift Δx _(p) on the print sample and the rotation fluctuation ω (t) of the photoconductor are caused. If the ratio of the displacement Δx _(MQ) is taken, it is expressed by the following equation.

Δx _(p) / Δx _(MQ) = F (f _i / f ₀ ) (6) Here, F (f _i / f ₀ ) is F when (f _i / f ₀ ) = n (integer).
(F _i / f ₀ ) = 0, and when (f _i / f ₀ ) = n + (1/2), F
(F _i / f ₀ ) = a.

Based on this formula, the displacement Δx on the print sample
_(p) Positional deviation Δ due to photoconductor rotation fluctuation Δω _(t)
x taking the ratio of _(MQ) on the vertical axis, the ratio f ₁ / f ₀ of the rotational fluctuation frequency components f ₁ and the fundamental frequency f ₀ taken on the horizontal axis the graph first
Shown in the figure. From FIG. 1, when f _i / f ₀ takes an integer n, the displacement amount on the print sample becomes almost zero. This also positional deviation amount of the photosensitive member 1 due to the rotation angular velocity fluctuation of the photosensitive member is no matter how large a finite amount, that f ₁ / f ₀ is not a positional shift on the print samples long integer Is shown. When f ₁ / f ₀ becomes n + (1/2), the amount of deviation becomes conversely maximum, and is repeated with periodicity. The same applies when i = 2. As described above, the present invention is characterized in that even if the rotation accuracy of the photoconductor is not particularly high, it is possible to correct the displacement on the print. That it is characterized where possible to correct the positional deviation on the print by changing relative rotational oscillation frequency f ₁ or f ₂ of the fundamental frequency f ₀ photoreceptor to near integral multiples or on it. To change the specific fundamental frequency f _0, may be successfully adjusting the angle theta ₁ between the transfer point 22 from the imaging point 21.

To change the angle theta ₁ between the transfer point 22 from the imaging point 21, there are two methods. One is a method of changing the imaging point 21. As a specific method, an example in which the optical system unit 3 itself is changed by using a swing device such as a cam is described in a sixth example.
Shown in the figure. The optical system unit 3 can swing about a fulcrum 23, and the angle of the entire optical system unit 3 with respect to the photoconductor 1 can be changed by the displacement of the swing cam 24. The optical system unit 3 is fixed in contact with the swing cam 24 by a fixing device 25 such as a spring, so that the entire optical system unit 3 is not shaken by vibration or the like. In this case, it should be noted that the position of the imaging point 21 of the light beam emitted from the optical system unit 3 is
Even if the above changes, the spot longitude of the imaging point should not substantially change. For this purpose, for example, a mechanism capable of changing the optical path length in the optical system unit 3 may be provided. As shown in FIG. 6, the transfer point 22
If the angle theta ₁ between'll shifted by [Delta] [theta] _g, since changes to θ ₁ -Δθ _g from angle theta ₁ related to the fundamental frequency of (3), the fundamental frequency f ₀ is Kakiarawasa by: F ₀ ′
Changes to

f ₀ ′ = 1 / t ₀ ′ = ((θ ₁ −Δθ _g ) / ωm) ⁻¹ = ω _m /
(Θ ₁ −Δθ _g) (7) By changing the angle between the imaging point 21 and the transfer point 22 on the photoconductor 1 in this manner, the fundamental frequency f ₀ is changed,
The relationship between the rotational vibration frequency f ₁ or f ₂ of the photosensitive member 1 can be close to an integer ratio.

The second method is to change the transfer point 22. As a specific method, the position of the transfer unit 8 may be changed with respect to the rotation direction of the transfer drum 5 in FIG.

The rotation speed of the photoconductor 1 shown in FIG. 5 can be easily measured by a device such as a rotary encoder.
Was treated with a microcomputer for FFT analysis, as the ratio of the rotational vibration frequency f ₁ or f ₂ and the fundamental frequency f ₀ of the photosensitive member 1 is always an integer, automatically swing cam 24 shown in FIG. 6 It is more effective if controlled. The method of changing the angle between the imaging point 21 and the transfer point 22 on the photoconductor 1 may be to change the position of the imaging point 21 or to change the position of the transfer point 22, Both may be changed.

FIG. 7 shows another example of a color image forming apparatus using the transfer position adjusting method of the present invention. 4 around the transfer drum 30
One image forming unit is arranged, and transfer corotrons (41, 42, 43, 44) are arranged inside the transfer drum 30 corresponding to each image forming unit. Each image forming unit has a charger (61, 62, 63, 64), an optical system (71, 72, 73, 74) around each photoconductor (51, 52, 52, 54), a developing machine (81, 82, 83, 84), cleaning means (91, 92, 9)
3, 94) are arranged one by one, and an image corresponding to each color is formed on each photoconductor by a known method. Each optical system unit includes a semiconductor laser 75, a polarizer 76, a lens system 77, and the like, and is provided with an angle adjusting mechanism (not shown) as shown in FIG. The paper 100 is conveyed by a feed roll 101 to a registration adjustment roll 102, and is held at a timing by a gripper provided on the transfer drum 30. The paper held by the gripper is electrostatically adsorbed and transported on a paper transport medium stretched over the transfer drum 30, for example, a dielectric such as a dielectric mesh or a mylar. Images formed on the photoconductors (51, 52, 53, 54) are sequentially transferred by transfer corotrons (41, 42, 43, 44). The paper on which the image transfer has been completed is peeled off by the peeling claw 104, and the fixing device 1
The paper is discharged to the paper discharge tray 106 through 05. In such an apparatus, a full-color print can be obtained by a single paper conveyance, so that the speed of the full-color printer can be increased. Further, since the transfer position is automatically adjusted in the apparatus according to the present embodiment, a very good color image can be obtained without a shift in the transfer position of each color. In such an apparatus that obtains a color image by superimposing four or three colors, images of each color formed by each image forming unit are simply superimposed without special measures as in the present invention. Then, the positional deviation due to the rotation fluctuation of each photoconductor appears as a color deviation of each color. That is, misregistration (color misregistration) occurs between yellow, magenta, cyan, and black, and the image quality level is significantly reduced.

When the transfer position is adjusted using the image forming position adjusting method of the present invention, the frequencies f _i and f ₀ may be adjusted in advance based on a value specific to the apparatus, or the frequency may be adjusted to the image forming apparatus itself. And an exposure position or transfer position adjusting means may be provided to measure and analyze the data, and the automatic adjustment may be performed at the time of image formation. FIG. 2 is a block diagram showing an example of a configuration for performing automatic adjustment.

[Advantage of the Invention] According to the image forming position adjusting method of the present invention, when a plurality of images are superimposed to form an image, even if there is a slight fluctuation in the rotation of the photoconductor, the images are superimposed without shifting their positions. be able to. Further, in the image forming position adjusting apparatus in which the image forming point or the transfer point is made variable as in the present invention, the image forming position can be adjusted without using a highly accurate motor. Further, in a color image forming apparatus in which an image forming point or a transfer point can be automatically adjusted, a high-quality color print without color shift can be easily obtained, so that a high-speed color image forming apparatus can be provided at low cost.

[Brief description of the drawings]

FIG. 1 is a diagram showing the principle of the image forming position adjusting method of the present invention. FIG. 2 is a block diagram when performing automatic adjustment. FIG. 3 is a diagram showing an overview of an image forming apparatus using the image forming position adjusting method of the present invention. FIG. 4 is a diagram showing details of a transfer portion. FIG. 5 is an example showing how the speed of the photoconductor varies. FIG. 6 is a diagram showing an example for changing the imaging point. FIG. 7 shows another example of an image forming apparatus using the image forming position adjusting method of the present invention. DESCRIPTION OF SYMBOLS 1 ... Photoreceptor drum, 2 ... Charger, 3 ... Optical system unit, 4 (C, M, Y, K) ... Developing machine, 5 ... Transfer device, 6 ...
... Cleaning pre-processing unit, 7 ... Cleaning unit, 8 ... Transfer drum, 9 ... Peak eliminator, 10 ...
Peeling claw, 11 Cassette tray, 12 Paper feed roll, 13
… Registration roll, 14… Fixer, 15… Discharge roll, 16… Discharge tray, 17… Paper transport medium, 18… Paper, 19… Gripper, 20… Center of photosensitive drum ,twenty one
…… imaging point, 22 …… transfer point, 30 …… transfer drum, 41,42,
43,44… Transfer corotron, 51,52,53,54 …… Photoconductor, 6
1,62,63,64 …… Charging device, 71,72,73,74 …… Optical system, 81,8
2,83,84 developing machine, 91,92,93,94 cleaning means, 100 paper, 101 feed roller, 102 resist roller, 103 guide plate, 104 peeling claw , 105
…… Fixer, 106 …… Output tray

Claims (2)

(57) [Claims] An image forming and outputting apparatus for transferring and outputting an image on a photosensitive member to a transfer medium carried by a transport medium, wherein a vibration frequency included in a variation in angular velocity of the photosensitive member is fi, and an image on the photosensitive member is formed. A is the point, B is the transfer point, and O is the center of the photoreceptor.
And an angle θ1 measured from A to A along the rotation direction of the photoconductor with respect to O.
And the fundamental frequency depending on the average angular velocity of the photoconductor
An image forming position adjusting method, wherein fi / fo is an integer when fo is set. 2. An image forming and outputting apparatus for transferring and outputting an image on a photoconductor onto a transfer medium carried by a transport medium, wherein at least one of an image forming point and a transfer point on the photoconductor is variable. The vibration frequency included in the angular velocity fluctuation of the photoconductor
fi, the imaging point on the photoconductor is A, the transfer point is B, the center of the photoconductor is O, and the A
The angle AOB formed by the B and the angle A1 measured along the rotation direction of the photoconductor from the A and the fundamental frequency depending on the average angular velocity of the photoconductor is fo, so that fi / fo is an integer. An image forming position adjusting device comprising an angle adjusting means for changing the angle θ1.