JPH0943932A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which forms a color image by superposing plural toner images of different colors and which can provide a favorable image without color shift caused by dislocation. SOLUTION: A circumferential length of a photoreceptor 414 is Ld, a circumferential length of a middle transfer body 415 is Ld, and a circumferential length of a middle transfer body drive roller 415D, where relations of Ld=m.Ld, Ld=n.Lr (n, m are integers desired) are almost satisifed. A rotation cycle of a drive gear to be engaged with a shaft gear of the photorecephor 414 to drive the photoreceptor 414 is set to almost coincide with a rotation cycle from an optical writing position of the photoreceptor 414 to a transfer position to the middle transfer body 415.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus having a photoconductor and an intermediate transfer member, in which color toner images formed on the photoconductor are successively transferred onto the intermediate transfer member. The present invention relates to an image forming apparatus of a type that forms an image and collectively transfers the superimposed transfer image onto a transfer paper.

[0002]

2. Description of the Related Art A photoconductor consisting of a rotary body which is rotationally driven, and an intermediate endless belt which is arranged facing the photoconductor and is rotated at the same peripheral speed as the photoconductor while being in contact with the photoconductor. A transfer member and an intermediate transfer member driving roller for driving the intermediate transfer member are provided, and a toner image of an arbitrary color is formed by optical writing and development during one rotation of the photosensitive member, and then the toner of the arbitrary color is formed. The process of transferring the image to the intermediate transfer member is repeated for each different color to obtain a color superimposed toner image on the intermediate transfer member, and the superimposed toner images are collectively transferred onto a transfer paper to obtain a color image. Image forming apparatuses are known.

[0003]

In such an image forming apparatus, the photoconductor is caused by an eccentricity error of gears, pulleys and the like which constitute a drive system for rotationally driving the photoconductor and a drive system for driving the intermediate transfer member. In reality, the periodical speed fluctuation occurs in the intermediate transfer member.

If such a speed variation occurs, it causes a positional shift between the superposed images and appears as a color shift in a color image, impairing the image quality.

The present invention provides an image forming apparatus for forming a color image by superimposing a plurality of toner images of different colors on each other and capable of obtaining a good image without color deviation due to positional deviation. With the goal.

[0006]

[Means for Solving the Problems]

[0007]

The present invention has the following configuration to achieve the above object. (1). A photosensitive member formed of a rotating body that is rotationally driven; an endless belt-shaped intermediate transfer member that is disposed facing the photosensitive member and is rotated at the same peripheral speed as the photosensitive member while being in contact with the photosensitive member; An intermediate transfer member driving roller for driving the intermediate transfer member is provided, and a toner image of an arbitrary color is formed by optical writing and development during one rotation of the photosensitive member, and then the toner image of the arbitrary color is transferred to the intermediate transfer member. In the image forming apparatus, the step of transferring to the body is repeated for each different color to obtain a color superposed toner image on the intermediate transfer body, and the superposed toner image is collectively transferred onto a transfer paper to obtain a color image, Perimeter of photoconductor is Ld, Perimeter of intermediate transfer body is L
b, when the peripheral length of the intermediate transfer member driving roller is Lr, the following relationships are substantially satisfied: Lb = m · Ld, Lb = n · Lr (where n and m are arbitrary integers) 1).

(2). A photosensitive member formed of a rotating body that is rotationally driven; an endless belt-shaped intermediate transfer member that is disposed facing the photosensitive member and is rotated at the same peripheral speed as the photosensitive member while being in contact with the photosensitive member; An intermediate transfer member driving roller for driving the intermediate transfer member is provided, and a toner image of an arbitrary color is formed by optical writing and development at the first rotation of the photosensitive member, and then the toner image of the arbitrary color is transferred to the intermediate transfer member. In the image forming apparatus, the step of transferring to the body is repeated for each different color to obtain a color superposed toner image on the intermediate transfer body, and the superposed toner image is collectively transferred onto a transfer paper to obtain a color image, The rotation cycle of the drive gear that meshes with the photoconductor shaft gear and drives the photoconductor is made substantially coincident with the rotation cycle of the photoconductor from the optical writing position to the transfer position to the intermediate transfer body. ).

(3). A photosensitive member formed of a rotating body that is rotationally driven; an endless belt-shaped intermediate transfer member that is disposed facing the photosensitive member and is rotated at the same peripheral speed as the photosensitive member while being in contact with the photosensitive member; An intermediate transfer member driving roller for driving the intermediate transfer member is provided, and a toner image of an arbitrary color is formed by optical writing and development at the first rotation of the photosensitive member, and then the toner image of the arbitrary color is transferred to the intermediate transfer member. In the image forming apparatus, the step of transferring to the body is repeated for each different color to obtain a color superposed toner image on the intermediate transfer body, and the superposed toner image is collectively transferred onto a transfer paper to obtain a color image, A rotation cycle of a drive gear that meshes with the intermediate transfer member shaft gear and drives the intermediate transfer member is a rotation cycle of the intermediate transfer member from a toner image transfer position from the photoconductor to a transfer position on the transfer paper. To They were substantially matched (claim 3).

(4). A photosensitive member formed of a rotating body that is rotationally driven; an endless belt-shaped intermediate transfer member that is disposed facing the photosensitive member and is rotated at the same peripheral speed as the photosensitive member while being in contact with the photosensitive member; An intermediate transfer member driving roller for driving the intermediate transfer member is provided, and a toner image of an arbitrary color is formed by optical writing and development at the first rotation of the photosensitive member, and then the toner image of the arbitrary color is transferred to the intermediate transfer member. In the image forming apparatus, the step of transferring to the body is repeated for each different color to obtain a color superposed toner image on the intermediate transfer body, and the superposed toner image is collectively transferred onto a transfer paper to obtain a color image, When the photoconductor peripheral length is Ld, the intermediate transfer member peripheral length is Lb, and the intermediate transfer member driving roller peripheral length Lr, Lb = m · Ld, Lb = n · Lr (where n and m are arbitrary integers) To satisfy the relationship of In addition, the rotation cycle of the drive gear that meshes with the photoconductor shaft gear and drives the photoconductor is made substantially coincident with the rotation cycle of the photoconductor from the optical writing position to the transfer position to the intermediate transfer body. 4).

(5). A photosensitive member formed of a rotating body that is rotationally driven; an endless belt-shaped intermediate transfer member that is disposed facing the photosensitive member and is rotated at the same peripheral speed as the photosensitive member while being in contact with the photosensitive member; An intermediate transfer member driving roller for driving the intermediate transfer member is provided, and a toner image of an arbitrary color is formed by optical writing and development at the first rotation of the photosensitive member, and then the toner image of the arbitrary color is transferred to the intermediate transfer member. In the image forming apparatus, the step of transferring to the body is repeated for each different color to obtain a color superposed toner image on the intermediate transfer body, and the superposed toner image is collectively transferred onto a transfer paper to obtain a color image, When the photoconductor peripheral length is Ld, the intermediate transfer member peripheral length is Lb, and the intermediate transfer member driving roller peripheral length Lr, Lb = m · Ld, Lb = n · Lr (where n and m are arbitrary integers) To satisfy the relationship of In addition, one rotation cycle of the drive gear that meshes with the photoconductor shaft gear and drives the photoconductor is made substantially equal to the rotation cycle of the photoconductor from the optical writing position to the transfer position to the intermediate transfer body, and One rotation cycle of the intermediate transfer member drive roller shaft gear and a drive gear that meshes with the intermediate transfer member drive roller and drives the intermediate transfer member is set from the toner image transfer position of the intermediate transfer member from the photosensitive member to the transfer position to the transfer sheet. The rotation period is made to substantially match (Claim 5).

(6). (2) or (4) or (5)
In the image forming apparatus described above, the angle from the optical writing position of the photosensitive member on the peripheral surface of the photosensitive member to the transfer position to the intermediate transfer member on the peripheral surface of the photosensitive member is approximately 180 ° (claim 6). ).

(7). (1) or (2) or (3)
Alternatively, in the image forming apparatus according to (4), (5), or (6), a mark is provided on the intermediate transfer member, a sensor for detecting the mark is provided on the immovable member, and the mark of the rotating intermediate transfer member is set to the mark. The image forming process is started after a lapse of a certain time from the detection by the sensor (Claim 7).

[0014]

[Embodiment]

(1) Multicolor image forming apparatus to which the present invention is applied As an example of a multicolor image forming apparatus suitable for carrying out the present invention,
The color image forming apparatus will be described with reference to FIG.

A color image reading device (hereinafter referred to as a color scanner) 200 includes a contact glass 202.
The image of the upper original 180 is displayed on the illumination lamp 205 and the mirror group 2
04A, 204B, 204C, etc., and lens 206
An image is formed on the color sensor 207 via the, and the color image information of the document is, for example, blue (hereinafter, referred to as B),
Green (hereinafter referred to as G) red (hereinafter referred to as R) color-separated light is read for each color and converted into an electrical image signal.

The color sensor 207 is, in this example,
It is composed of B, G, and R color separation means and a photoelectric conversion element such as a CCD (solid-state image sensor), and simultaneously reads three colors.

B, G, R obtained by the color scanner 200
A color conversion process is performed by an image processing unit (not shown) based on the color-separated image signal intensity level of, and black (hereinafter, BK), cyan (hereinafter, C), and magenta (hereinafter, hereafter). Color image data including color information of yellow (hereinafter referred to as Y) is obtained.

The operation method of the color scanner 200 for obtaining the image data of BK, C, M and Y by using the color image recording device (hereinafter referred to as a color printer) 400 using the color image data is as follows. In response to the operation of the color printer 400 and the scanner start signal in timing, in FIG. 10, the illumination / mirror optical system including the illumination lamp 205 and the mirror groups 204A, 204B, and 204C scans the document in the direction of the left arrow, and Image data of one color is obtained every scanning. Then, each time, the images are sequentially visualized by the color printer 400, and these are superposed to form a full-color image of four colors.

Next, an outline of the color printer 400 will be described. Writing optical unit 40 as exposure means
1 converts the color image data from the color scanner 200 into an optical signal, performs optical writing corresponding to the original image, and places the image on a photosensitive drum 414 which is a latent image carrier corresponding to a photosensitive member according to the present invention. An electrostatic latent image is formed.

The optical writing optical unit 401 includes a laser emitting unit 441, an emission drive control unit (not shown) for driving the unit, a polygon mirror 443, a rotation motor 444 for driving the unit, a fθ lens 442, and a reflecting mirror 446.
It is composed of

The photoconductor drum 414 rotates counterclockwise as shown by the arrow, and around it, the photoconductor cleaning unit 421, the discharging lamp 414M, the charger 419 as a charging means, and the photoconductor drum Sensor 414D for detecting the latent image potential of the developing device, the selected developing device of the revolver developing device 420, and the developing density pattern detector 4
14P, an intermediate transfer belt 415 as an intermediate transfer member according to the present invention, and the like are arranged.

The revolver developing device 420 is a BK developing device 420K, a C developing device 420C, an M developing device 420M, a Y developing device 420Y, and a revolver rotation drive for rotating each developing device in a counterclockwise direction as shown by an arrow. (Not shown) and the like. These developing devices rotate the developing sleeves 420KS, 420 by bringing the brush of the developer into contact with the surface of the photosensitive drum 414 to develop the electrostatic latent image.
Assemble the developer with CS, 420MS, 420YS.
It is composed of a developing paddle that rotates to stir.

In the standby state, the revolver developing device 420 is set at the position where the BK developing device 420 develops, and when the copying operation is started, the color scanner 200 reads the BK image data from a predetermined timing. Based on this image data, optical writing and latent image formation by laser light starts (hereinafter, the electrostatic latent image based on the BK image data is referred to as BK latent image. C, M, Y
The same for each image data of. ).

In order to enable development from the front end of the BK latent image, the developing sleeve 420KS is started to rotate before the front end of the latent image reaches the developing position of the BK developing device 420K.
The K latent image is developed with BK toner.

Thereafter, the developing operation of the BK latent image area is continued, but when the trailing edge of the latent image passes the BK latent image position, the next color is immediately developed from the developing position by the BK developing device 420K. The revolver developing device 420 is driven and rotated to the developing position by the container. This rotation operation is completed at least before the leading end of the latent image based on the next image data arrives.

When the image forming cycle is started, the photosensitive drum 414 rotates counterclockwise as indicated by an arrow, and the intermediate transfer belt 415 rotates clockwise by a drive motor (not shown). Move.

As the intermediate transfer belt 415 rotates, B
K toner image formation, C toner image formation, M toner image formation, Y
Toner image formation is sequentially performed, and finally BK, C, M,
A toner image is formed by superimposing it on the intermediate transfer belt 415 in the order of Y.

The BK image is formed as follows. The charger 419 uniformly charges the photosensitive drum 414 with a negative charge to about −700 V in the dark by corona discharge. Subsequently, the laser diode 441 performs raster exposure based on the BK signal. When the raster image is exposed in this way, in the exposed portion of the photosensitive drum 414 that is initially uniformly charged, the charge proportional to the amount of exposure light disappears and an electrostatic latent image is formed.

The toner in the revolver developing device 420 is
It is negatively charged by stirring with a ferrite carrier, and the BK developing sleeve 420KS of this developing device
Is biased by a power supply means (not shown) with respect to the metal base layer of the photosensitive drum 414 to a potential in which a negative DC potential and an alternating current are superposed.

As a result, the toner does not adhere to the portion of the photosensitive drum 414 where the electric charge remains, and the BK toner is adsorbed to the portion having no electric charge, that is, the exposed portion, which is similar to the latent image. A BK visible image is formed.

The intermediate transfer belt 415 is connected to the drive roller 41.
5D, a transfer counter roller 415T, a cleaning counter roller 415C, and a driven roller group, are stretched and controlled by a drive motor (not shown).

Now, the B formed on the photosensitive drum 414
The K toner image is transferred onto the surface of the intermediate transfer belt 415, which is driven at a constant speed in contact with the photoconductor, by a belt transfer corona discharger (hereinafter referred to as a belt transfer unit) 416. Hereinafter, from the photosensitive drum 414 to the intermediate transfer belt 4
The toner image transfer to 15 is called belt transfer.

A small amount of untransferred residual toner on the photoconductor drum 414 is cleaned by the photoconductor cleaning unit 421 in preparation for reuse of the photoconductor drum 414. The collected toner is stored in a waste toner tank (not shown) via a collection pipe.

On the intermediate transfer belt 415, the toner images of BK, C, M, and Y, which are sequentially formed on the photosensitive drum 414, are sequentially aligned on the same surface, and a belt transfer image of four-color overlapping is formed. Are formed, and thereafter, they are collectively transferred onto the transfer paper by a corona discharge transfer device.

On the side of the photosensitive drum 414, B
After the step of forming the K image, the process of forming the C image proceeds, but at a predetermined timing, the reading of the C image data by the color scanner 200 starts, and the formation of the C latent image is performed by writing the laser light with the image data. To do.

The C developing device 420C performs a rotating operation of the revolver developing device after the rear end of the previous BK latent image has passed and before the leading end of the C latent image has reached the developing position. , C latent image is developed with C toner.

After that, the development of the C latent image area is continued. At the time when the trailing edge of the latent image passes, the revolver developing device 420 is driven as in the case of the previous BK developing device to drive the C developing device 4.
20C is sent out and the next M developing device 420M is positioned at the developing position. This operation is also performed before the leading end of the next M latent image reaches the developing unit. The steps of forming the M and Y images are omitted because the operations of reading, forming the latent image, and developing the image data are similar to the steps of the BK image and the C image described above.

The belt cleaning device 415U comprises an inlet seal, a rubber blade, a discharge coil, and a contact / separation mechanism for these inlet seal and rubber blade. 1
After the BK image of the first color is transferred onto the belt, while the images of the second, third and fourth colors are transferred onto the belt, the entrance seal, the rubber blade, etc. are separated from the surface of the intermediate transfer belt by the blade contact / separation mechanism. .

A paper transfer corona discharger (hereinafter referred to as a paper transfer device) 417 is a corona discharge type AC to transfer the superimposed toner image on the intermediate transfer belt 415 to the transfer paper.
+ DC or DC component is applied to the transfer paper and the intermediate transfer belt.

Transfer paper cassettes 482 in the paper feed bank store transfer papers of various sizes, and a registration roller pair 418R is fed by a paper feed roller 483 from a storage cassette that stores papers of a specified size. Paper is fed and conveyed in the same direction. Reference numeral 412B2 indicates a paper feed tray for manually inserting OHP paper or thick paper.

At the time when the image formation is started, the transfer paper is fed from any one of the paper feed trays and stands by at the nip portion of the registration roller pair 418R. When the front end of the toner image on the intermediate transfer belt 415 reaches the paper transfer device 417, the registration roller pair 418R is driven so that the front end of the transfer paper coincides with the front end of this image,
Registration of the paper and the image is performed.

In this way, the transfer paper is superposed on the color superposed image on the intermediate transfer belt and passes over the paper transfer device 417 which is connected to the positive potential. At this time, the transfer paper is charged with a positive charge by the corona discharge current, and most of the toner image is transferred onto the transfer paper. Subsequently, when passing through a separation static eliminator by AC + DC corona (not shown) arranged on the left side of the paper transfer device 417, the transfer paper is discharged, and the intermediate transfer belt 4 is discharged.
It is peeled from the sheet 15, and is transferred to the paper transport belt 422.

The transfer paper on which the four-color superposed toner images have been collectively transferred from the surface of the intermediate transfer belt is conveyed to the fixing device 423 by the paper conveying belt 422, and the fixing roller 423A and the pressure roller 423B controlled to a predetermined temperature. The toner image is melted and fixed in the nip portion of, and sent out of the main body by the discharge roll pair 424, and is stacked face up on a copy tray (not shown) to obtain a full color copy.

The photosensitive drum 414 after the belt transfer
Is cleaned on its surface by a photoconductor cleaning unit 421 including a brush roller and a rubber blade,
In addition, the static elimination lamp 414M uniformly eliminates static electricity.

The intermediate transfer belt 415 after the toner image is transferred onto the transfer paper is again cleaned by the cleaning unit 4.
The surface is cleaned by pressing the blade with a 15U blade contact / separation mechanism.

In the case of repeat copying, the operation of the color scanner and the image formation on the photosensitive member continue to the first color image process of the first sheet, and then proceed to the first color image process of the second sheet at a predetermined timing.

Further, the intermediate transfer belt 415 continues to the batch transfer process of the first four-color superimposed image onto the transfer paper, and the surface of the intermediate transfer belt 415 is cleaned by the belt cleaning device. Allow the image to be belt transferred. Thereafter, the operation is the same as that of the first sheet.

The above is the description of the copy mode for obtaining the four-color full-color copy. In the case of the three-color copy mode and the two-color copy mode, the same operation as described above is performed for the designated color and the number of times. Will be done.

In the single-color copy mode, only the developing device of the predetermined color of the revolver developing device 420 is placed in the developing position of the predetermined color and is in the developing operation state until the predetermined number of sheets is completed, and the belt is moved. The copying operation is continuously performed while the blade of the cleaning device 415U is being pressed against the belt.

In such an image forming apparatus, a mark for position detection is provided on the outer peripheral surface or the inner peripheral surface of the belt 415. However, on the outer peripheral surface side, it is necessary to devise to avoid the passage area of the belt cleaning device 415U, which may cause difficulty in arrangement. In that case, the outer peripheral surface side is provided on the inner peripheral surface side. Although the optical sensor is not shown in FIG. 10, the drive roller 415 supporting the belt 415 is provided.
It is provided at a position between D and the support roller 415F.

The drive system for the photosensitive drum 414 and the intermediate transfer belt 415 is as shown in FIG.
That is, using the motor 500M as a drive source, the gear 9Z
→ Gear 72Z → Gear 31Z → Gear 62Z → Gear 20Z are common, and this gear 20Z is divided into two systems,
As the drive system of the photoconductor drum 414, the gear 40Z → 8
The photosensitive drum 414 is driven through 0Z. The drive system of the intermediate transfer belt 415 includes a gear 20Z ′ →
The drive roller 415D of the intermediate transfer belt is driven through the gear 40Z ′ → gear 30Z → gear 30Z ′.

(2) Example Corresponding to Claim 1 Fluctuations of the peripheral speed periodically appearing on the photosensitive drum 414 are generally shown in FIG. Further, FIG. 2B shows a change in the amount of deviation at an arbitrary position on the peripheral surface of the photosensitive drum due to this speed change. The amount of deviation periodically fluctuates as shown in FIG.

Here, the symbols are defined below. a: velocity variation rate v: linear velocity of the photosensitive drum (mm / sec) T: velocity variation cycle (sec) f: velocity variation frequency (Hz) When defined in this way, the sine curve of FIG. ,
It can be expressed as Vt = a · v · sin2π / T · t, and the following expression (1) is established.

[0054]

[Equation 1]

Further, optionally, the ideal position at time t,
That is, assuming that the amount of deviation from the position due to the actual speed fluctuation when there is no speed fluctuation is Xt, this Xt is expressed by the following equation (2).

[0056]

[Equation 2]

From this (2), it is understood that the speed fluctuation having a long cycle has a great influence on the positional deviation. This means that when a large number of gears are used in the gear series, the gear shift having a large number of teeth has a great influence on the positional deviation.

In this example, in FIG. 10, a mark is attached to a part of the peripheral surface of the intermediate transfer belt 415, and a sensor for reading the mark is placed at a position where the mark can be read.
It is provided by being provided on the immovable member.

As shown in FIGS. 10 and 11, the photosensitive drum 414 and the intermediate transfer belt 415 pass through the power transmission means by gears from the motor 500M, and are affected by the eccentricity of these gears. The speed is fluctuating.

Here, the speed fluctuation of the photosensitive drum can be represented as a sine wave having a constant period as shown in FIG. In FIG. 1A, the vertical axis represents the fluctuation of the speed Vd of the photosensitive drum 414, and the horizontal axis represents the time.

Similarly, the speed fluctuation of the intermediate transfer belt 415 can be expressed as a sine wave having a constant period as shown in FIG. 1 (b). In FIG. 1B, the vertical axis represents the fluctuation of the speed Vb of the intermediate transfer belt 415. Here, the speed fluctuation of the driving roller 415D has a relationship that repeatedly appears as the speed fluctuation of the intermediate transfer belt 415.

As can be seen from the equation (2), assuming that the gears of the drive transmission system as shown in FIG. 11 are made with the same accuracy, the larger the cycle T is, the more the influence on the positional deviation is affected. Is large, the photosensitive drum 41 is typically used.
4 is a gear 8 that rotates integrally with the photosensitive drum 414.
The speed fluctuation due to 0Z, the intermediate transfer belt 415 rotates integrally with the driving roller 415D, and the speed fluctuation due to the gear 30Z 'and the eccentricity of the driving roller 415D cause the respective 1
The speed fluctuation will appear in the rotation cycle.

Regarding the intermediate transfer belt 415, the color scanner 200 starts reading an original document after a lapse of a certain time t ₁ after the detection of a mark (generation of a pulse) by the sensor S as a reference. And process the image to initiate the imaging process for each color. As a result, the image forming positions of the respective colors are formed at the same position in the process. The intermediate transfer belt 415 makes one rotation between the start of image formation for the first color and the start of image formation for the second color.
14 has a relationship of rotating twice.

At this time, if the peripheral length of the photosensitive member 414 and the peripheral length of the drive roller 415D are in an integer ratio with respect to the peripheral length of the intermediate transfer belt 415, the photosensitive drums are exposed at the start of image formation for each color. It is possible to match the phase of the speed fluctuation of the body 414 and the phase of the speed fluctuation of the intermediate transfer belt.

For example, the ratio of the circumference of the intermediate transfer belt 415 to the circumference of the photosensitive drum 414 is 2: 1 and the ratio of the circumference of the intermediate transfer belt 415 to the circumference of the drive roller 415D is 4: 1. I am trying.

When the peripheral length ratio is set as described above, the speed fluctuations of the photosensitive drum 414 and the intermediate transfer belt 415 at the time of image formation for each color are in phase with each other, so that the intermediate transfer belt 41 has the same phase.
It is possible to superimpose the images of the respective colors on No. 5 at the same timing of speed fluctuation.

Here, the peripheral length ratios are not limited to those shown in the above example, the peripheral length of the photosensitive drum is Ld, the peripheral length of the intermediate transfer belt is Lb, and the drive roller peripheral length of the intermediate transfer belt is L.
r, where Lb = m · Ld and Lb = n · Lr (where m and n are arbitrary integers) are satisfied, it is possible to similarly overlap at the same speed fluctuation timing. it can.

If the rotational speed ratios (gear ratio, pulley circumference ratio, etc.) of the drive transmission systems of the photosensitive drum and the drive roller of the intermediate transfer belt are integer ratios, the power transmission system will The cycle of speed fluctuation due to uneven rotation is also an integer ratio of the cycle of the photosensitive drum and the drive roller of the intermediate transfer belt, and the phases at the time of image formation for each color can be matched.

(3) Example corresponding to claim 2 In the above "(2) Example corresponding to claim 1", the phase of the speed fluctuation of the photosensitive drum 414 and the intermediate transfer belt 415 is set for each color image formation. Together, these photosensitive drums 4
14, it has been described that the positional shift (color shift) due to the phase shift of the mutual speed fluctuation of the intermediate transfer belt 415 can be prevented.

However, as another factor that deteriorates the image quality due to the speed fluctuation, there is an image expansion / contraction phenomenon due to a difference in linear velocity between the image writing position and the transfer position.

For example, in FIG. 3, writing light 502
The irradiation position on the photoconductor 414 is set to the optical writing position P, and when the image of the “line segment AB” is formed along the rotation direction of the photoconductor drum 414 indicated by the arrow 500, If the linear velocity is faster than normal,
The image formed on the photoconductor drum 414 is “line segment A
"Line segment A'B" is longer than "B", resulting in an extended image. If the image of the "line segment A'B" is transferred onto the intermediate transfer belt 415 as it is, the image becomes longer than it actually is.

Therefore, a drive gear (which engages with the photoconductor shaft gear (gear 80Z in the example of FIGS. 6 and 11) integrally formed with the photoconductor drum 414 and drives the photoconductor shaft gear (gear 80Z) ( The rotation cycle of the gear 40Z) coincides with the rotation cycle (moving time) from the position P in FIG. 3 which is the writing position of the photosensitive drum 414 to the position P ′ where the belt corona discharger 416 is arranged which is the transfer position. The configuration is

In this way, the relationship between writing and transfer is as shown in FIG. 3 and FIG.
The toner image formed by extending what should become the “line segment AB” at the time of writing above to the “line segment A′B” forms a toner image on the photosensitive drum 414 against the intermediate transfer belt 415 during the transfer of the intermediate transfer belt. Moves faster, the intermediate transfer belt 41
On line 5, the line segment A ″ B is contracted and transferred, and the deviation of the length is offset to obtain the original length of the line segment AB. Therefore, the phase of the speed fluctuation due to the eccentricity of the gear 40Z, which is the drive gear, is the same during writing and during transfer,
The problem of image expansion and contraction due to the effect of eccentricity due to the gear 40Z is solved.

The above equation is expressed by the following equation (3). However, Z ₁ : the number of teeth of the gear (80Z) integrated with the photosensitive drum Z ₂ : the number of teeth of the drive gear (40Z) θ: the angle from the writing position P to the transfer position P ′ n: an arbitrary integer

[0075]

(Equation 3)

If the relation of the expression (3) is satisfied, the expansion / contraction of the image at the time of writing is offset by the expansion / contraction of the image at the time of transfer, and the image returns to the original length as a result.

Here, as described in the section "(2) Example corresponding to claim 1", in order to match the phases of speed fluctuations when forming images of respective colors, the gears of the drive transmission system are arranged. The ratio must be an integer ratio of one rotation of the photosensitive drum.

(4) Example Corresponding to Claim 3 As described in the section "(3) Example corresponding to claim 2", the fact that the speed change of the intermediate transfer belt causes the photosensitive drum The same can be applied to the case of solving the problem of image expansion and contraction in the transfer of the toner image and the batch transfer of the toner image onto the transfer paper.

That is, based on the same idea, in FIG. 11, the gear 3 which is a drive gear which meshes with the gear 30Z 'which is the intermediate transfer belt shaft gear and drives the intermediate transfer belt is shown.
A belt transfer corona discharger 41, which is a toner image transfer position of the intermediate transfer belt from the photosensitive member, is rotated at a rotation cycle of 0Z ′.
If the rotation cycle from the position 6 (see FIG. 10) to the position of the paper transfer corona discharger 417 (see FIG. 10), which is the transfer position to the transfer paper, is matched, the “(3) Claim 2 is satisfied”. According to the same principle as described in "Examples", it is possible to obtain the effect of offsetting by the expansion and contraction of the image at the time of transfer from the photoconductor and at the time of transfer to the transfer paper, and avoid the influence of the speed fluctuation of the intermediate transfer belt. It becomes possible.

That is, the transfer position from the photosensitive drum to the intermediate transfer belt (the position of the belt transfer corona discharger 416).
From the intermediate transfer belt to the transfer position (the position of the paper transfer corona discharger 417) from the intermediate transfer belt to the transfer paper is set to an integral multiple of the circumference of the belt drive roller 415D, and the tooth ratio of the drive transmission system is also an integer ratio. The configuration is as follows.

(5) Example Corresponding to Claim 4 In the above "(2) Example corresponding to claim 1," the toner image of each color resulting from the phase shift of each speed fluctuation of the photoconductor drum and the intermediate transfer belt. In the "(3) Example corresponding to claim 2", expansion and contraction of an image due to speed fluctuation of the photosensitive drum is eliminated.

In the present example, both are combined in order to eliminate the image shift due to these different causes. That is,
When the peripheral length of the photoconductor is Ld, the peripheral length of the intermediate transfer belt is Lb, and the peripheral length of the intermediate transfer belt driving roller is Lr, Lb = m · Ld, Lb = n · Lr (where n and m are arbitrary integers) And the rotation cycle of the drive gear that meshes with the photoconductor shaft gear and drives the photoconductor is matched with the rotation cycle of the photoconductor from the optical writing position to the transfer position to the intermediate transfer belt. That is, the condition of the expression (3) is satisfied. In this case, θ = 360 / m (provided that m is an arbitrary integer).

(6) Example Corresponding to Claim 5 In this example, the technique in "(5) Example corresponding to claim 5" is further added to "(4) Example corresponding to claim 3". Apply with technology added. As a result, the overlapping position shift of the toner images of the respective colors due to the phase shift of each speed fluctuation of the photoconductor drum and the intermediate transfer belt, the expansion and contraction of the image due to the speed fluctuation of the photoconductor drum, and the speed fluctuation of the intermediate transfer belt are caused. The expansion and contraction of the image due to it is eliminated.

Application to the intermediate transfer belt is performed from the transfer position from the photosensitive drum to the intermediate transfer belt (the position of the belt transfer corona discharger 416) to the transfer position from the intermediate transfer belt to the transfer paper (paper transfer corona discharger 417). The distance to the position) is set to an integral multiple of the circumference of the belt driving roller 415D, and the ratio of the number of teeth of the drive transmission system is also set to an integer ratio.

(7) Example corresponding to claim 6 The above-mentioned "(3) Example corresponding to claim 2" and "(5)
When the contents described in "Example corresponding to claim 4" and "(6) Example corresponding to claim 5" are carried out, θ = 180
° is good. Specifically, as shown in FIG. 5, the charger 419 and the belt transfer corona discharger 416 are arranged on a line passing through the center of the photosensitive drum 414.

In FIGS. 10 and 11, the photosensitive drum 4
14 has a diameter of 80 mm, and the driving roller 415D has a diameter of 4
0 mm, the peripheral length of the intermediate transfer belt 415 is 502.5 mm
As a result, the peripheral length ratios of the photosensitive drum, the intermediate transfer belt driving roller, and the intermediate transfer belt are set to 2: 1: 4, and the phases at the time of image formation of the respective colors are matched. Further, the angle from the writing position on the photosensitive drum to the transfer position is θ = 185.7 °, the condition of about 180 ° is satisfied, and the number of teeth of the gear 80Z: the number of teeth of the gear 40Z = 80: 40, The rotation cycle of the drive system gear train of the photoconductor drum is substantially matched with the rotation cycle from the optical writing position to the transfer position onto the intermediate transfer belt.

(8) Example Corresponding to Claim 7 In each of the examples described above, the image formation start timing of each color is as described with reference to FIG.
The mark provided at 15 is read by the sensor S (see FIG. 10), and the mark is detected after a certain time t ₁ has elapsed from the time when this mark was detected. (9) Concept of allowable tolerance for phase matching As described above, if the phases of the photoconductor drum and the intermediate transfer belt are matched, theoretically the positional deviation due to each speed fluctuation can be prevented. You can Therefore, if the conditions specified in each claim are completely satisfied, even if the gear is eccentric and the speed of the photosensitive drum or the intermediate transfer belt fluctuates, the problems of image shift and expansion / contraction can be solved. be able to.

By the way, each claim substantially satisfies the condition. This is to allow the degree of freedom in layout and to relax the required accuracy in manufacturing machines and machine parts by including a relaxation condition of "abbreviation".

As described above, when the condition of "substantially" is entered, the position of the image tends to be misaligned. To that extent, the eccentricity of the drive system gear and the eccentricity of the drive roller are reduced. Cover.

There are various factors related to the positional deviation of the image, and the extent of the approximate range of the conditions defined in each claim is determined by the required value of the positional deviation of the image, economically,
It is determined by the relationship with the machining eccentricity error that is technically possible. Below, we generalize and disclose the relationship between these three parties,
It is used as a guideline for implementing the present invention.

(I) Relational expression between image shift amount and speed variation In FIG. 7A, reference numeral 503 is a speed variation of the photosensitive drum during the image forming process of the first color, and reference numeral 504 is an image formation of the second color. The respective speed variation curves of the photosensitive drum during the process are shown. FIG. 7B shows a change in the amount of image shift on the photosensitive drum caused by the speed fluctuation shown in FIG. 7A.

In FIG. 7B, the speed fluctuation curve 503
Reference numeral 503 'denotes the deviation curve corresponding to
The shift curves corresponding to 4 are indicated by reference numeral 504 ', respectively.
Then, the deviation amount Xt from the ideal position at an arbitrary time point t is
The curve 503 ′ is expressed by the equation (4) that is a function, and the curve 5
04 ′ is represented by the equation (5), where the phase difference between the two waveforms of the curve 503 ′ and the curve 504 ′ is the angle α = 360 × k / T.

[0093]

(Equation 4)

Then, the amount of deviation in the actual image is expressed as the difference between these equations (4) and (5), and therefore is given by equation (6).

[0095]

(Equation 5)

Here, the fluctuation period T of the velocity v and the deviation amount is
It is a value that is determined by the operating conditions of the image forming apparatus and is a periodic function based on the variable t, so the maximum value of Xt Xt (ma
x) will be determined by the value of the speed variation rate a.

Generally, the deviation amount on the image is 0.1 mm.
It is said that the extent is the limit, and this 0.1 is required X
As t (max), it becomes possible to obtain an allowable value of the speed variation rate. From this equation, it is understood that the larger the period T, the smaller the speed variation rate a needs to be.

The cause of the speed fluctuation in one rotation cycle of the photoconductor drum is the photoconductor shaft gear (for example, gear 80 in the example of FIG. 11).
The cause of the eccentricity of Z) and the speed fluctuation of the intermediate transfer belt 415 is the drive roller gear (for example, the gear 30 in the example of FIG. 11).
The eccentricity of Z ′) and the eccentricity of the drive roller (for example, drive roller 415D in the example of FIG. 11) are included.

However, for the intermediate transfer belt, as described above, the distance from the transfer position from the photosensitive drum to the transfer position on the transfer paper is set to be an integral multiple of the circumference of the drive roller 415D. By doing so, it is possible to prevent positional displacement due to speed fluctuations, and in the case of a belt, it is possible to completely satisfy the above integer multiple conditions because the idle roller is arranged so that the length can be adjusted freely. Yes, no problem.

Therefore, the eccentricity of the drive roller 415D and the eccentricity of the gears (here, for example, the gear 80Z, which may have a great influence on the positional deviation with a large period, may be considered). A formula for calculating speed fluctuations is derived.

The following equation of speed fluctuation can be used to obtain the required accuracy of gears, drive rollers, etc. for the allowable speed fluctuation rate a.

(Ii) Estimation of misregistration due to speed fluctuation of the intermediate transfer belt In the example of FIG. 11, the cause of the speed fluctuation of the intermediate transfer belt is the deviation of the gear 30Z 'that drives the driving roller 415D of the intermediate transfer belt. Variations in the effective rotation radius due to unevenness of rotation of the drive roller due to the core and eccentricity of the drive roller itself can be mentioned. So, for these two, consider the model formula,
The amount of misalignment due to speed fluctuations of the intermediate transfer belt is estimated.

(A) Speed fluctuation due to gear eccentricity FIGS. 8A and 8B show gear eccentricity models. In FIG. 8A, the eccentric amount of the rotation center O ′ with respect to the center O of the gear is e ₁ . Further, the number of gear teeth is Z. If there is no eccentricity, the rotation angle for one gear tooth is 2θo
Then, the expression (7) is established.

[0104]

(Equation 6)

Further, in FIG. 8A, when the rotation angle with respect to one gear tooth when the eccentricity amount e ₁ is 2θ ₁ ,
As shown in FIG. 8B, when the rotation center O ′ deviates below the center O, the rotation angle 2θ ₁ becomes the minimum. Here, when the pitch circle diameter of the gear is Dp, the equation (8) is established.

[0106]

(Equation 7)

On the contrary, when the rotation center O'is displaced above the center O, the rotation angle becomes maximum, and the equation (9) is established.

[0108]

(Equation 8)

Here, assuming that each speed fluctuation is a ₁ , (1
Equation (0) holds.

[0110]

[Equation 9]

Here, in the case of θ ₁ = θmax, the equation (11) is established from the equations (7), (9), and (10).

[0112]

(Equation 10)

When θ ₁ = θ min, the equation (12) is established from the equations (7), (8) and (10).

[0114]

[Equation 11]

(B) Speed fluctuation due to eccentricity of drive roller FIG. 9 shows an eccentricity model of the drive roller 415. In FIG. 9, assuming that the eccentricity of the drive roller 415 is e ₂ , the effective radius of the drive roller with respect to the intermediate transfer belt 415 is “(D _R / 2) −e ₂ ” to “(D _R / 2) + e ₂ In this range, the driving roller changes in one rotation cycle. If the speed fluctuation is a ₂ , then equation (13) holds.

[0116]

(Equation 12)

(C) Belt Speed Fluctuation Due to Two Speed Fluctuations Since speed fluctuation due to gear eccentricity and speed fluctuation due to roller eccentricity form a series system, the speed of the intermediate transfer belt affected by both is V. _Assuming that _{B is B} and the set speed is V _BO , the formula (1
4) is established.

[0118]

(Equation 13)

Further, letting the speed fluctuation rate be a, (1
Equation 5) holds.

[0120]

[Equation 14]

The speed variation rate a becomes maximum when the phases of both are in agreement, that is, the advance angle θ ₁ by one gear tooth.
Is the case where the effective radius of the drive roller becomes the maximum when is the maximum. Since the positional deviation becomes the largest in the case of this combination, this case will be considered below.

If the speed variation rate in this case is a _O ,
Equation (17) is obtained from equations (11), (14), and (16).

[0123]

(Equation 15)

In this way, the combined speed fluctuation rate of the drive gear and the drive roller applied to the intermediate transfer belt is obtained by the equation (17), and the gear 80Z which is the drive gear of the photosensitive drum is obtained by the equation (11). The velocity fluctuation rate of the above is calculated, the shift amounts are respectively calculated by the equation (2) using the obtained speed variation rates, and the sum of the two is the shift amount on the image. Therefore, appropriate e ₁ , e ₂ If you repeat the trial calculation using
The amount of eccentricity e ₁ of the gears 30Z ′ and 80Z that is allowed for the positional deviation Xt given as a condition, the driving roller 4
The combination of the eccentricity amounts e ₂ for 15D can be obtained.

[0125]

According to the present invention, it is possible to provide an image forming apparatus for forming a color image by superimposing a plurality of toner images of different colors on each other and capable of obtaining a good image without color deviation due to positional deviation. .

[Brief description of drawings]

FIG. 1 is a diagram illustrating a relationship between phases of a photosensitive member and an intermediate transfer member due to speed fluctuations.

FIG. 2 is a diagram illustrating a relationship between a speed fluctuation of a rotating body and a positional deviation due to the speed fluctuation.

FIG. 3 is a diagram for explaining an image canceling action due to image expansion and contraction at a writing position on a photoconductor and a transfer position.

FIG. 4 is a diagram illustrating the relationship between the timing of writing and transfer during one rotation of the photosensitive drum and the phase of speed fluctuation.

FIG. 5 is a diagram illustrating a positional relationship between writing and transfer on a photoconductor and a drive gear system.

FIG. 6 is a diagram illustrating a drive gear system of a photosensitive drum.

FIG. 7A is a speed fluctuation diagram showing a speed fluctuation during image formation of 1 and a speed fluctuation during image formation of 2 on the photoconductor, and FIG.
FIG. 4A is a diagram of the shift amount showing the relationship between the shift amount at the time of image formation 1 and the shift amount at the time of image formation 2 in relation to (a).

FIG. 8A is a diagram for explaining how speed fluctuations appear due to gear eccentricity, and FIG. 8B is a diagram for schematically explaining how speed fluctuations appear due to gear eccentricity.

FIG. 9 is a diagram illustrating eccentricity of a driving roller of an intermediate transfer belt.

FIG. 10 is a diagram illustrating a configuration of an image forming apparatus to which the present invention is applied.

FIG. 11 is a diagram exemplifying drive gear series of a photosensitive drum and an intermediate transfer member.

[Explanation of symbols]

 414 Photoconductor drum (as a photoconductor) 415 Intermediate transfer belt (as an intermediary transfer member) 415D (Intermediate transfer member) drive roller

Claims (7)

[Claims] 1. A photoreceptor comprising a rotating body that is rotationally driven,
An endless belt-shaped intermediate transfer member, which is arranged facing the photosensitive member and is rotated at the same peripheral speed as the photosensitive member while being in contact with the photosensitive member, and an intermediate transfer member driving roller for driving the intermediate transfer member. A step of forming a toner image of an arbitrary color by optical writing and development during one rotation of the photoconductor, and then transferring the toner image of the arbitrary color to the intermediate transfer body for each different color. In an image forming apparatus which repeatedly obtains a color superposed toner image on the intermediate transfer member and transfers the superposed toner image onto a transfer sheet at a time to obtain a color image, the photosensitive member peripheral length is Ld, and the intermediate transfer member peripheral length is Is Lb, and the peripheral length of the intermediate transfer member driving roller is Lr, it is characterized by substantially satisfying the following relationship: Lb = m · Ld, Lb = n · Lr (where n and m are arbitrary integers) Image forming apparatus. 2. A photoreceptor comprising a rotating body that is rotationally driven,
An endless belt-shaped intermediate transfer member, which is arranged facing the photosensitive member and is rotated at the same peripheral speed as the photosensitive member while being in contact with the photosensitive member, and an intermediate transfer member driving roller for driving the intermediate transfer member. The process of forming a toner image of an arbitrary color by optical writing and development at the first rotation of the photoconductor, and then transferring the toner image of the arbitrary color to the intermediate transfer member is performed for each different color. In an image forming apparatus that repeatedly obtains a color superposed toner image on the intermediate transfer body and transfers the superposed toner image onto a transfer sheet at a time to obtain a color image, the photoconductor shaft gear is meshed with the photoconductor to form a color image. An image forming apparatus characterized in that a rotation cycle of a driving gear to be driven is made substantially equal to a rotation cycle of the photoconductor from a light writing position to a transfer position onto an intermediate transfer body. 3. A photoreceptor comprising a rotating body that is rotationally driven,
An endless belt-shaped intermediate transfer member, which is arranged facing the photosensitive member and is rotated at the same peripheral speed as the photosensitive member while being in contact with the photosensitive member, and an intermediate transfer member driving roller for driving the intermediate transfer member. The process of forming a toner image of an arbitrary color by optical writing and development at the first rotation of the photoconductor and then transferring the toner image of the arbitrary color to the intermediate transfer member is performed for each different color. In an image forming apparatus that repeatedly obtains a color superposed toner image on the intermediate transfer body and transfers the superposed toner image onto a transfer sheet at a time to obtain a color image, the intermediate transfer body is engaged with the axial gear to form the intermediate transfer body. An image formation characterized in that the rotation cycle of a drive gear for driving the body is made substantially coincident with the rotation cycle of the intermediate transfer body from the toner image transfer position from the photoconductor to the transfer position on the transfer paper. Location. 4. A photosensitive member comprising a rotating member that is rotationally driven,
An endless belt-shaped intermediate transfer member, which is arranged facing the photosensitive member and is rotated at the same peripheral speed as the photosensitive member while being in contact with the photosensitive member, and an intermediate transfer member driving roller for driving the intermediate transfer member. The process of forming a toner image of an arbitrary color by optical writing and development at the first rotation of the photoconductor and then transferring the toner image of the arbitrary color to the intermediate transfer member is performed for each different color. In an image forming apparatus which repeatedly obtains a color superposed toner image on the intermediate transfer member and transfers the superposed toner image onto a transfer sheet at a time to obtain a color image, the photosensitive member peripheral length is Ld, and the intermediate transfer member peripheral length is Where Lb is the peripheral length Lr of the intermediate transfer member drive roller, Lb = m · Ld, Lb = n · Lr (where n and m are arbitrary integers) are substantially satisfied, and The feeling of meshing with the gear The rotation period of the drive gear for driving the body, the image forming apparatus is characterized in that is substantially coincident with the rotation period of the optical writing position of the photosensitive member to the transfer position to the intermediate transfer member. 5. A photoreceptor comprising a rotating body that is rotationally driven,
An endless belt-shaped intermediate transfer member, which is arranged facing the photosensitive member and is rotated at the same peripheral speed as the photosensitive member while being in contact with the photosensitive member, and an intermediate transfer member driving roller for driving the intermediate transfer member. The process of forming a toner image of an arbitrary color by optical writing and development at the first rotation of the photoconductor and then transferring the toner image of the arbitrary color to the intermediate transfer member is performed for each different color. In an image forming apparatus which repeatedly obtains a color superposed toner image on the intermediate transfer member and transfers the superposed toner image onto a transfer sheet at a time to obtain a color image, the photosensitive member peripheral length is Ld, and the intermediate transfer member peripheral length is Where Lb is the peripheral length Lr of the intermediate transfer member drive roller, Lb = m · Ld, Lb = n · Lr (where n and m are arbitrary integers) are substantially satisfied, and The feeling of meshing with the gear One rotation cycle of the drive gear for driving the body is made to substantially coincide with the rotation cycle of the photoconductor from the optical writing position to the transfer position on the intermediate transfer body, and meshes with the intermediate transfer body drive roller shaft gear. One rotation cycle of a drive gear for driving the intermediate transfer body is made substantially equal to a rotation cycle of the intermediate transfer body from a toner image transfer position from the photoconductor to a transfer position on the transfer paper. Image forming apparatus. 6. The image forming apparatus according to claim 2, 4, or 5, wherein an optical transfer position of the photoconductor on the peripheral surface of the photoconductor to an intermediate transfer member on the peripheral surface of the photoconductor. The image forming apparatus is characterized in that the angle to the transfer position is about 180 °. 7. The image forming apparatus according to claim 1, claim 2, claim 3, claim 4, claim 5, or claim 6, wherein the intermediate transfer member is provided with a mark. The image forming apparatus is characterized in that an image forming process is started after a lapse of a predetermined time after the sensor detects.