JP2009122480A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of reducing the distortion and misalignment of a toner image from each photoreceptor drum, which is to be transferred to a transfer member. <P>SOLUTION: After a reference position (mark M) of a photoreceptor gear 21M is matched with a driving gear 22, a photoreceptor gear 21Y is so disposed that a reference position (mark M) is an angle θ (θ=360°×(L/πD+α)) off a position of engagement between an idler gear 23 and the photoreceptor gear 21Y to a downstream side in a rotation direction. Thus the distortion and color shift of toner images transferred from photoreceptor drums 11Y and 11M to an intermediate transfer belt 3 can be effectively reduced. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus capable of transferring, for example, a toner image free from distortion or color misregistration to a transfer member by rotating a rotating member such as a photosensitive drum with high accuracy.

  Conventionally, various types of image forming apparatuses such as printers and copiers for forming color and monochrome images have been proposed and commercialized. In particular, in recent years, with the spread of personal computers, the Internet, digital cameras, etc., development of color printers is remarkable. In the image forming apparatus such as the color printer, there is a strong demand for an apparatus capable of forming a color image for an office satisfying high speed, compactness, and low price similar to black and white.

  In order to form a high-quality color image in an image forming apparatus such as the above-described color printer, images of each color such as cyan, magenta, yellow, and black are formed on an image carrier, and these images of each color are formed. It is necessary to improve the accuracy of color registration to be superimposed.

  This image forming apparatus includes four image forming units each having a photosensitive drum as an image carrier, corresponding to, for example, cyan, magenta, yellow, black, etc., depending on the color of the toner image to be formed. The toner images of each color such as cyan, magenta, yellow, and black are continuously formed on the photosensitive drum of each image forming unit, and the toner images of these colors are recorded on a recording sheet or an intermediate transfer member (transfer member). There is a so-called tandem method in which a color image is formed by multiple transfer onto the image.

The tandem type image forming apparatus includes a plurality of (for example, four) image forming units that form toner images of the respective colors. Therefore, the position of the toner image formed by each image forming unit is determined by the transfer body. It is necessary to accurately match the predetermined position.
Therefore, there is a technique described in Patent Document 1.
JP 2005-308799 A

  However, in Patent Document 1, when the photoconductor gear also functions as an idler gear, it depends on the difference in accuracy between the driving tooth surface and the driven tooth surface of the corresponding photoconductor gear, and the difference in the circumferential phase between the driving unit and the driven unit. Since the influence is not considered, the influence is a color shift of the color image.

  An object of the present invention is to provide an image forming apparatus capable of reducing distortion and misalignment of toner images from respective photosensitive drums transferred to a transfer body.

  In order to achieve the above object, the configuration of the image forming apparatus adopted by the present invention is an image forming apparatus in which a plurality of photosensitive drums are arranged in parallel, and a driving gear to which driving force is transmitted by a driving motor, Each of the photosensitive drums is connected to each of the photosensitive drums to rotate integrally with the photosensitive drum, and an idler gear disposed between adjacent photosensitive drum gears. One photosensitive drum among the photosensitive drums which are formed in the same shape with a predetermined position in the circumferential direction as a reference position, and whose rotation axis is arranged in a straight line and driven by the photosensitive gear engaged with the idler gear. The distance between the transfer position where the toner image on the photoconductive drum is transferred to the transfer body and the transfer position where the toner image on the other photoconductive drum is transferred to the transfer medium is L, and the diameter of the photoconductive drum is D. , Drive gear and idleragi In the photoconductor gear for driving the photoconductor, the photoconductor gear that meshes with the drive gear is the center of the drive gear, where α is an angle for canceling the error at the time of drive transmission in the photoconductor gear meshing with the photoconductor gear. The straight line connecting the center of the corresponding photoconductor gear is used as a phase reference when the corresponding photoconductor gear is arranged, and the photoconductor gear that only meshes with the idler gear is the straight line connecting the center of the idler gear and the center of the corresponding photoconductor gear. When the reference position of the photoconductor drum of the photoconductor drum that forms an image first is set to coincide with the phase reference of the photoconductor gear as the phase reference when the body gear is arranged, the photoconductor drum that forms the next image The photoconductor gears are arranged so as to be shifted upstream of the rotation direction by an angle θ (angle θ = 360 ° × (L / πD) + α) with respect to the phase reference of the photoconductor gear. .

In the above-described configuration, there is provided a casing in which a gear arrangement portion in which the respective gears are arranged is formed, a mark is formed at a position at a predetermined angle in the circumferential direction from the reference position of the photoconductor gear, and the two photosensitive elements described above It is desirable that a positioning mark corresponding to the mark on the photoconductor gear is formed at a position where the phase relationship between the body gears is established.
For example, a positioning mark is formed at a position corresponding to the mark of the one photoconductor gear on one photoconductor gear arrangement portion of the casing, and an angle on the upstream side in the rotation direction of the positioning mark and the phase reference is A. The other photoconductor gear arrangement portion of the casing has a position corresponding to the mark of the other photoconductor gear at a position shifted from the phase reference of the other photoconductor gear by an angle A + angle θ to the upstream side in the rotation direction. In addition, a positioning mark is formed.

  In the above configuration, when the photoconductor gears are formed one by one from one mold, one positioning mark is formed on each photoconductor gear arrangement portion. Is desirable.

  In the above configuration, when the photoconductor gear is formed from a plurality of molds, it is preferable that the positioning marks formed on the photoconductor gear placement portions are respectively formed at positions corresponding to the molds. .

  In the above configuration, when the photoconductor gear is formed as a first gear and a second gear from a single mold, the positioning marks formed on the photoconductor gear placement portions are on the first gear. It is desirable to form in two positions, a corresponding position and a position corresponding to the second gear.

  In the above configuration, when the photoconductor gear is formed as a first gear and a second gear from a single mold, the positioning marks formed on the photoconductor gear placement portions are on the first gear. One is preferably formed between the corresponding position and the position corresponding to the second gear.

  In the image forming apparatus according to the present invention, the difference in accuracy between the driving tooth surface and the driven tooth surface of the photoconductor gear and the influence of the difference in the phase in the circumferential direction between the driving unit and the driven unit are offset by the phase difference α. Further, it is possible to reduce distortion and positional deviation of the toner image from each photosensitive drum transferred to the transfer body, and it is possible to form a high-quality image.

<Embodiment>
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating a configuration of an image forming apparatus 100 according to an embodiment of the present invention. The image forming apparatus 100 includes four image forming units 1Y, 1M, 1C, and 1K that form toner images of yellow (Y), magenta (M), cyan (C), and black (K) colors. An intermediate transfer belt 3 that is looped over a plurality of rolls 2 and moved in the direction of arrow A, and a toner image that is primarily transferred from the image forming units 1Y, 1M, 1C, and 1K to the intermediate transfer belt 3 A secondary transfer roll 5 for secondarily transferring to the recording paper P conveyed by 4, a fixing device 6 for fixing the toner image secondarily transferred to the recording paper P to the recording paper P by heating and pressing, A belt cleaner 7 for cleaning the intermediate transfer belt 3. A control device 8 for controlling the operation of each of the image forming units 1Y, 1M, 1C, 1K is provided.

Next, the configuration of the image forming units 1Y, 1M, 1C, and 1K will be described.
FIG. 2 is a diagram showing the configuration of the image forming unit 1K. As shown in FIG. 2, the image forming unit 1K irradiates the photosensitive drum 11K with light, the contact-type charging roll 12K that charges the photosensitive drum 11K to a predetermined charging potential, and the charged photosensitive drum 11K. An exposure device 13K for forming an electrostatic latent image, a developing device 14K for supplying black toner to the electrostatic latent image to form a black toner image on the surface of the photosensitive drum 11K, and a toner image on the intermediate transfer belt 3. A primary transfer roll 15K for primary transfer and a cleaning device 16K for removing toner remaining on the surface of the photosensitive drum 11K are provided.
In the image forming unit 1K, a corotron charging device may be used instead of the contact charging roll 12K.

  The control device 8 sets a charging potential having a value considered appropriate, and charges the surface of the photosensitive drum 11K to the above-described charging potential by applying a voltage between the photosensitive drum 11K and the contact-type charging roll 12K. . Further, the control device 8 sets an exposure potential value that is considered appropriate for the charging potential, and controls the exposure device 13K based on the image data corresponding to black among the image data of each color of YMCK. An electrostatic latent image is formed by irradiating the photosensitive drum 11K with light and lowering the irradiated portion from the charged potential to the exposure potential.

  Thereafter, the electrostatic latent image formed on the surface of the photosensitive drum 11K moves to the developing device 14K as the photosensitive drum 11K rotates, and black toner is supplied by the developing device 14K to become a black toner image. This toner image is primarily transferred to the intermediate transfer belt 3 at the position of the primary transfer roll 15K.

Next, the rotation transmission mechanism 20 that rotates the photosensitive drums 11Y, 11M, and 11C will be described. FIG. 3 is a diagram schematically showing the rotation transmission mechanism 20 of the photosensitive drum. Note that the meshing portions of the gears are shown in a simplified manner. Since the photosensitive drum 11K is driven by a driving source different from the rotation transmission mechanism 20, illustration and description thereof are omitted.
The rotation transmission mechanism includes photoconductor gears 21Y, 21M, and 21C provided coaxially with the photoconductor drums 11Y, 11M, and 11C, and a drive gear 22 that is meshed between the photoconductor gear 21M and the photoconductor gear 21C. And an idler gear 23 meshed between the photoconductor gear 21M and the photoconductor gear 21Y.
The photoconductor gears 21Y, 21M, and 21C (referred to as “photoconductor gear 21” if not particularly required to be identified) are formed in the same shape, and as shown in FIG. A mark M is formed. The position of the idler gear 23 is determined by the relationship such as the number of teeth and the space of the casing.

The distance between the transfer position at which the toner image is transferred to the intermediate transfer belt 3 on the photoreceptor drum 11Y and the transfer position at which the toner image is transferred to the intermediate transfer belt 3 on the photoreceptor drum 11M is L, and the photoreceptor. The diameter of the drums 11Y, 11M, and 11C is D.
In the rotation transmission mechanism 20, when rotation is transmitted from a motor (not shown) to the drive gear 22, the drive gear 22 rotates in the direction of arrow a, and this rotation is transmitted to the meshed photoconductor gears 21 </ b> C and 21 </ b> M. And rotated in the direction of arrow b. Further, the idler gear 23 meshed with the photoconductor gear 21M receives the rotation of the photoconductor gear 21M and rotates in the direction of the arrow c, and further rotates the meshed photoconductor gear 21Y in the direction of the arrow b. As a result, the photosensitive drums 11Y, 11M, and 11C rotate in the same direction as the circumferential movement direction (arrow A direction) of the intermediate transfer belt 3.

Here, the characteristics of the photoconductor gear 21 will be described. The characteristic diagrams shown in FIG. 5 and FIG. 6 show the image position error due to the rotational speed error at a certain reference point in the circumferential direction of the gear, the horizontal axis is the angle (°), and the vertical axis is the amount of change (μm). It has become. The photosensitive gear 21 shown in the characteristic diagram uses a helical gear having a diameter of 78 mm and a number of teeth of 161.
Further, it is generally known that an image position error due to a rotational speed error as shown in FIG. 5A appears in the gear during rotation due to a manufacturing error that occurs during manufacturing. This error is due to eccentricity generated when the gear is manufactured from a mold by resin molding.
The characteristic diagram shown in FIG. 5A shows the image position error due to the rotational speed error of the photoconductor gear 21M.

  In the rotation transmission mechanism 20 of the present embodiment, the rotation of the photosensitive member 21M that is rotationally driven by the drive gear 22 is transmitted to the photosensitive member gear 21Y via the idler gear 23. As for the error, it is necessary to assemble the photoconductor gear 21 in consideration of not only one photoconductor gear 21 but also an image position error due to a rotation speed error of the two photoconductor gears 21 engaged with each other.

That is, in the present embodiment, as shown in FIG. 3, the photoconductor gears 21Y, 21M, and 21C are arranged so that the rotation axes thereof are in a straight line, and the photoconductor gear 21M and the drive gear 22 are engaged with each other. In addition, after the reference position (mark M) of the photoconductor gear 21M is made coincident, the photoconductor gear 21Y has an angle θ (angle θ = 360 ° × () than the position where the idler gear 23 and the photoconductor gear 21Y mesh. The reference position (mark M) is shifted from the downstream side in the rotation direction by L / πD) + α). However, the angle α is a phase that cancels out the influence of the difference in accuracy between the driving tooth surface and the driven tooth surface of the photoconductor gear 21M and the difference in the phase in the circumferential direction between the driving unit and the driven unit. The reference position (mark M) and angle shown in FIG. 3 are schematically described and are different from the actual reference position (mark M) and angle.
On the other hand, the photoconductor gear 21C is arranged by shifting the reference position (mark M) by an angle θ0 (angle θ0 = 360 ° × L / πD) upstream in the rotation direction.

Next, a method for setting the angle θ will be described in detail.
As described above, FIGS. 5 and 6 are characteristic diagrams showing the image position error due to the rotational speed error in the photoconductor gears 21M and 21Y. In the photoconductor gear 21M, the mark M is positioned at the position where it meshes with the drive gear 22. The characteristic line at the time of rotation for 2 rounds is shown from the point at which 到達 has reached.
5A shows the image position error due to the rotational speed error in the photoconductor gear 21M, and FIG. 5B shows the image position due to the rotational speed error in the photoconductor gear 21M considering only the tooth surface that drives the idler gear 21. Indicates an error. For example, when the errors of both tooth surfaces of the photoconductor gear 21M are the same, the characteristic diagram in FIG. 5A is shifted by an angle β. That is, FIG. 5B shows the image position error due to the rotational speed error on the tooth surface that drives the idler gear 23 of the photoconductor 21M. The image position error due to the rotational speed error transmitted to the idler gear 23 becomes a characteristic line obtained by superimposing the characteristic line in FIG. 5B on the characteristic line in FIG. 5A, as shown in FIG. 5C.

On the other hand, an image position error due to the same rotational speed error occurs in the photoconductor gear 21Y as in the photoconductor 21M, and the photoconductor gear 21Y is downstream of the position where the mark M meshes with the idler gear 23. As a result, the characteristic position of the image position error due to the rotational speed error is drawn (see FIG. 5D).
When rotation is transmitted to the photoreceptor gear 21Y via the idler gear 23, the characteristic line in FIG. 5D is superimposed on the characteristic line in FIG. 5C, as shown in FIG. The combined characteristic line. That is, the image position error due to the rotational speed error in this characteristic line becomes the image position error due to the rotational speed error generated during the rotation of the photoconductor gear 21Y.

Therefore, as shown in FIGS. 6 (F) and (F ′), the characteristic line in FIG. 5 (E) is shifted by an angle θ to match the phase of the photoconductor gear 21Y with the phase of the photoconductor gear 21M.
Then, by calculating the difference between the image position error due to the rotational speed error in the photoconductor gear 21M shown in FIG. 6A and the image position error due to the rotational speed error shown in FIG. 6F ′, FIG. As shown, an image position error due to a rotational speed error in the photoconductor gear 21Y is obtained.

  Here, the angles used in FIGS. 3 and 5 and 6 are θ and β. The angle β is an opening angle between a position where the photoconductor gear 21M and the drive gear 22 mesh with each other and a position where the photoconductor gear 21M and the idler gear 23 mesh with each other. For this reason, the angle which can be changed at the time of an assembly becomes only (theta). Therefore, by setting the angle θ so that the fluctuation of the characteristic line shown in FIG. 6G is small, the image position error due to the rotation speed error can be minimized.

Considering the ideal relationship among the photosensitive drum 11Y, the photosensitive drum 11M, and the intermediate transfer belt 3, there is a mark M at the transfer position of the photosensitive drum 11Y, and the position of the intermediate transfer belt 3 at this transfer position moves L. Then, when moving to the photoconductive drum 11M, it is only necessary that the gear be assembled so that the mark M is at the transfer position of the photoconductive drum 11M.
That is, the angle θ0 at this time is an angle θ0 = 360 ° × L / πD.

  However, in actuality, an image position error due to the rotational speed error as described above occurs, so that the toner images transferred from the photoconductive drums 11Y and 11M to the intermediate transfer belt 3 are distorted and misaligned. For this reason, when the photoconductor gear 21Y is assembled, it is necessary to correct the angle α in consideration of the image position error due to the rotational speed error based on the accuracy and the meshing phase of both the tooth surfaces of the photoconductor gear 21M with respect to the θ0.

  As described above, in the present embodiment, the reference position (mark M) of the photoconductor gear 21M is made coincident with the drive gear 22, and the photoconductor gear 21Y is a position where the idler gear 23 and the photoconductor gear 21Y mesh. The reference position (mark M) is shifted to the downstream side in the rotation direction by an angle θ (angle θ = 360 ° × (L / πD) + α). As a result, it is possible to effectively reduce the distortion and color misalignment of the toner image transferred from the photosensitive drums 11Y and 11M to the intermediate transfer belt 3. The image forming apparatus 100 realizes the formation of a high quality image.

Next, the mark N formed on the casing in which the photoconductor gear 21 is incorporated will be described with reference to FIGS.
A gear housing (not shown) is formed in the casing, and a mark N is formed around it. This mark N is for aligning with the mark M of the gear 21 in order to incorporate the photoconductor gear 21. is there.

On the other hand, when one mold is used for molding a gear, the error of the manufactured gear is the same error, but when two are formed with one mold, Even with manufactured gears, the error is different.
For this reason, when the photoreceptor gear 21 manufactured by resin molding one gear from one mold is incorporated in the casing, as shown in FIG. 7, the gear housing portion to which the photoreceptor gear 21Y is assembled is installed. A mark N is provided around the periphery of the gear housing portion around which the photoreceptor gear 21C is assembled. Then, the operator positions the photoconductor gear 21 so that the mark M of the photoconductor gear 21 is aligned with the mark N, and then attaches the photoconductor gear 21 to the gear housing portion.

Next, the case where the photoconductor gear 21 manufactured by resin-molding two gears from one mold is incorporated in the casing will be described. There are two types of photoconductor gear 21, gear I and gear II.
As shown in FIG. 8, marks N1 and gear II corresponding to the gear I are provided around the gear housing portion where the photoreceptor gear 21Y is assembled and around the gear housing portion where the photoreceptor gear 21C is assembled. A mark N2 corresponding to is provided. A mark M1 is formed on the gear I, and a mark M2 is formed on the gear II.
Then, the operator determines whether the photoconductor gear 21 is the gear I or the gear II. When the photoconductor gear 21 is the gear I, when the gear is the gear I, the mark M1 of the photoconductor gear 21 is aligned with the mark N1. After the photoconductor gear 21 is positioned so that the mark M2 of the photoconductor gear 21 is aligned with the mark N2, the photoconductor gear 21 is assembled to the gear housing portion.

  Further, when the photoreceptor gear 21 manufactured by resin molding of two gears from one mold is incorporated in the casing, marks N1, N2 are provided around the gear housing portion of the casing as shown in FIG. A mark N3 may be formed between the two. Thereby, although the accuracy of the positional deviation when transferring the toner image is lowered, the work for the operator to determine the type of the gear at the time of assembly can be omitted.

  On the other hand, when the photoreceptor gear 21 manufactured by resin molding of gears from a plurality of molds is incorporated into the casing, a plurality of marks corresponding to the molds are formed around the gear accommodating portion of the casing. Also good.

  In the above embodiment, the case where the mark M formed on the photoconductor gear 21 is used as the reference position has been described, but the mark may be formed at an arbitrary position. In this case, after aligning the reference position of the photoconductor gear 21M with the position where the photoconductor gear 21M and the drive gear 22 are meshed, the photoconductor gear 21Y is a position where the idler gear 23 and the photoconductor gear 21Y are meshed. The photosensitive member gear 21Y may be arranged so as to satisfy the condition that the reference position (mark M) is shifted by an angle θ relative to the downstream side in the rotation direction.

  In the image forming apparatus according to the embodiment, the configuration in which the toner image formed on the photoconductive drums 11Y, 11M, 11C, and 11K is transferred to a sheet or the like via the intermediate transfer belt 3 has been described. The present invention is not limited to this, and can also be applied to an apparatus that directly transfers a toner image on a photosensitive drum onto a sheet without using an intermediate transfer member such as the intermediate transfer belt 3.

1 is a diagram illustrating an image forming apparatus according to an embodiment of the present invention. It is a figure which shows the image forming unit which concerns on this embodiment. FIG. 3 is a diagram schematically illustrating a rotation transmission mechanism of a photosensitive drum. It is a top view which shows a photoconductor gear. It is a characteristic diagram which shows the characteristic of a photoconductor gear. FIG. 6 is a characteristic diagram following FIG. 5. It is a figure which shows the assembly | attachment position of a gear. It is a figure which shows another assembly position of a gear. It is a figure which shows the other assembly position of a gear.

Explanation of symbols

3 ... Intermediate transfer belt, 11Y, 11M, 11C, 11K ... Photoconductor drum, 20 ... Rotation transmission mechanism, 21Y, 21M, 21C ... Photoconductor gear, 22 ... Drive gear, 23 ... Idler gear, M, M1, M2, N , N1, N2 ... mark.

Claims (6)

An image forming apparatus having a plurality of photosensitive drums arranged side by side,
A driving gear to which driving force is transmitted by the driving motor;
A photoreceptor gear coupled to each of the photoreceptor drums and rotating integrally with the photoreceptor drum;
An idler gear disposed between adjacent photoconductor gears,
Each photoconductor gear is formed in the same shape with a predetermined position in the circumferential direction as a reference position, and is arranged so that its rotation axis is in a straight line,
Of the photoconductor drums driven by the photoconductor gear engaged with the idler gear, the transfer position at which the toner image on one photoconductor drum is transferred to the transfer body and the toner image on the other photoconductor drum are transferred. When the distance from the transfer position transferred to the body is L, the diameter of the photosensitive drum is D, and the angle for canceling the error in driving transmission in the photosensitive gear in which the driving gear and the idler gear mesh with each other is α. ,
In the photoconductor gear for driving the photoconductor,
The photoconductor gear that meshes with the drive gear uses the straight line connecting the center of the drive gear and the center of the photoconductor gear as a phase reference when the photoconductor gear is arranged, and the photoconductor gear that meshes only with the idler gear is The straight line connecting the center and the center of the corresponding photoconductor gear is used as the phase reference when the photoconductor gear is arranged, and the reference position of the photoconductor gear of one photoconductor drum that forms an image first is set as the phase of the corresponding photoconductor gear. When placed according to the standard,
Next, the other photoconductor gear of the photoconductor drum for image formation is upstream of the rotation direction by an angle θ (angle θ = 360 ° × (L / πD) + α) with respect to the phase reference of the photoconductor gear. An image forming apparatus, wherein the image forming apparatus is arranged so as to be shifted. The image forming apparatus according to claim 1.
Having a casing formed with a gear arrangement portion in which the gears are arranged;
A mark is formed at a position at a predetermined angle in the circumferential direction from the reference position of the photoconductor gear,
An image forming apparatus, wherein a positioning mark corresponding to the mark on the photoconductor gear is formed at a position where the phase relationship between the two photoconductor gears is established. The image forming apparatus according to claim 2.
When the photoconductor gears are formed one by one from one mold,
The image forming apparatus according to claim 1, wherein one positioning mark is formed on each of the photoconductor gear arrangement portions with respect to the photoconductor gear. The image forming apparatus according to claim 2.
When the photoconductor gear is formed from a plurality of molds,
The image forming apparatus, wherein the positioning mark formed on each photoconductor gear arrangement portion is formed at a position corresponding to each mold. The image forming apparatus according to claim 2.
When the photoconductor gear is formed as one first gear and two second gears from one mold,
The image forming apparatus, wherein the positioning marks formed on each of the photoconductor gear placement portions are formed at two positions, a position corresponding to the first gear and a position corresponding to the second gear. The image forming apparatus according to claim 2.
When the photoconductor gear is formed as one first gear and two second gears from one mold,
An image forming apparatus, wherein one positioning mark formed on each photoconductor gear arrangement portion is formed between a position corresponding to the first gear and a position corresponding to the second gear.

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