JPH07140732A - Image forming device - Google Patents

Abstract

PURPOSE:To eliminate the position deviation and color irregularities of a transfer image in an image forming device having plural image carriers. CONSTITUTION:The driving force of a single drive motor 16 is transmitted to input pulleys 13a and 13c via gears 19, 20a and 20c. Further the force is transmitted to drum-driving pulleys 12a, 12b, 12c, and 12d fixed to corresponding photosensitive drums respectively via timing belts 15a, 15b, 15c, and 15d. The time required for moving the prescribed part of each photoreceptor drum from a latent from a latent image formation position P1 to a transfer position P2 is set to the integral multiples of the time required for rotating the input pulleys 13a and 13c one time. Thus, rotational irregularities of the photoreceptor drums at the time of passing the prescribed part of each photoreceptor drum through the latent image formation position P1 and the transfer position P2 become the same. Therefore, since the extension and contraction of a latent image at the time of latent image formation is cancelled by the extension and contraction of the toner image at the time of transfer to form a satisfactory image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for transferring a plurality of toner images on a transfer material in a superposed manner by rotating and driving a plurality of image bearing members by a single drive source.

[0002]

[Prior art]

<Prior Art 1> Conventionally, in an image forming apparatus employing an electrophotographic system, an electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) as an image bearing member is charged by a charging device, and this photosensitive drum is charged. A series of image forming processes in which a latent image is formed by irradiating light according to image information and the developed image (toner image) obtained by developing the latent image with a developing device is transferred to a transfer material such as paper. Is done.

On the other hand, a plurality of photosensitive drums for each of these image forming processes are prepared in accordance with the colorization of images, and yellow, magenta, cyan and black images are formed on the respective photosensitive drums. There is also proposed an image forming apparatus that forms a full-color image by forming an image on the transfer material and forming a full-color image on the transfer material at the transfer position of each photosensitive drum.

Since such a full-color image forming apparatus has an image forming section (image forming station) for each color, it is advantageous for speeding up, and since the transfer material conveying path can be configured in a straight line, the cardboard Although it has the advantage that it is adaptable to transfer materials such as paper and trapene, one of the biggest drawbacks is that it is difficult to properly register each color image formed in different image forming sections. There is a point. The deviation of the image forming positions of the four colors on the transfer material appears as an image defect such as a color deviation or a change in color tone in the final image.

To solve the above problem, it has been proposed to drive a plurality of photosensitive drums with a single drive source (for example, Japanese Patent Laid-Open No. 63-11967). In this proposal, the distance between the photosensitive drums is set so that the time interval during which the transfer material passes between the photosensitive drums becomes equal to an integral multiple of the drive unevenness cycle of the drive source (driving motor), and Color misregistration is prevented by matching the phase of misregistration in the image forming unit.

Further, in order to eliminate the expansion and contraction of the image formed in each image forming section, the time required for a predetermined portion of each photosensitive drum to rotate from the latent image forming position to the transfer position is set to drive each photosensitive drum. There has been a proposal that the drive unevenness of the source is made equal to an integral multiple of the cycle to cancel the exposure deviation and the transfer deviation caused by the uneven rotation of the photosensitive drum.

As shown in FIG. 4, in this device, a single drive motor 16 drives a first pulley 25 via a transmission means (not shown), and each photosensitive drum is driven by the first pulley 25. Second pulleys 12a, 12b, 1 for
2c, 12d independent timing belt 15
It is driven via a, 15b, 15c and 15d. Here, the moving time required for each photosensitive drum to move from the latent image forming position to the transfer position is configured to be equal to the time required for one rotation of the first pulley 25. <Prior Art 2> In a color image forming apparatus, a plurality of image carriers are juxtaposed and an electrophotographic process is performed on each image carrier to obtain a visible image (toner image) of each color. It is known that a desired color image is obtained by transferring onto a transfer material conveyed by.

FIG. 14 shows the construction of a laser beam printer which is one of the color image forming apparatuses of this type. The laser beam printer has three image forming stations P.
a, Pb, and Pc are arranged side by side, and each of the image forming stations Pa, Pb, and Pc has a dedicated photosensitive drum 1a, 1b,
It has 1c. Then, the photosensitive drums 1a, 1b,
Laser beam exposure means 3a, 3b, 3 are provided around 1c.
c, a dedicated image forming process unit including a charging unit, an exposing unit, a developing unit, a transferring unit, a cleaning unit, and the like, which are not illustrated, are arranged.

On the other hand, below the photosensitive drums 1a, 1b, 1c, there is arranged a conveying means 7 having an endless conveying belt 7a, and the transfer material S supplied from a paper feeding device (not shown) is Each image forming station P is conveyed by the conveying means 7.
It is conveyed in the direction of arrow K1 in the drawing through the transfer positions 31a, 31b, 31c of a, Pb, and Pc.

In the laser beam printer having the above structure, a visible image of yellow toner (yellow image) is formed at the first image forming station Pa, and the visible image is transferred by the transfer means 7. The image is transferred onto S at the transfer position 31a.

On the other hand, while the visible image (yellow image) is being transferred to the transfer material S, a visible image of magenta toner (magenta image) is formed at the second image forming station Pb, and the first image is formed. Image forming station Pa
When the transfer material S, which has been transferred in step S1, is carried into the transfer position 31b of the second image forming station Pb, the transfer material S is transferred to the transfer position 31b.
The magenta image is transferred to the predetermined position above.

After that, a visible image (cyan image, black image) of cyan toner and, if desired, black toner is formed in the same manner, and when the visible image is transferred onto the transfer material S, 3 is transferred onto the transfer material S. The transfer material S on which the visible images of four colors or four colors are superimposed and transferred is subjected to image fixing by a fixing unit (not shown), and a desired color image is formed on the transfer material S. The photosensitive drums 1a, 1b, and 1c that have completed the transfer are cleaned of residual toner by a cleaning unit (not shown) to prepare for the subsequent latent image formation.

By the way, the color image forming apparatus such as the above-mentioned laser beam printer has the image forming stations Pa, Pb, and Pc for each color, which is advantageous for speeding up, and the transfer path may be linear. Therefore, it has the advantage that it is adaptable to transfer materials such as thick paper and transparent film, but on the other hand, there is the problem that it is difficult to perform good registration of each color formed at different image forming stations.

As a solution to the above-mentioned problem, the time interval for the transfer material S to pass between the photosensitive drums 1a, 1b, 1c is set to be equal to an integral multiple of the drive unevenness cycle of the drive source of the conveying means 7. Proposal to prevent color misregistration by setting the distance between the photosensitive drums 1a, 1b, and 1c and matching the phase of the misregistration at the image forming stations Pa to Pb caused by the driving unevenness of the driving source (for example, Japanese Patent Laid-Open No. Sho 63-63). -11967).

As a method of driving each of the photosensitive drums 1a to 1c, the time required for a portion of each of the photosensitive drums 1a to 1c to rotate from the latent image forming position to the transfer position is to drive each of the photosensitive drums 1a to 1c. Proposal to prevent the positional deviation due to the rotational unevenness of the photosensitive drum driving source by canceling the exposure deviation and the transfer deviation caused by the rotational unevenness of the photosensitive drums 1a to 1c so as to be equal to an integral multiple of the uneven driving cycle of the source. Has been done.

[0016]

[Problems to be Solved by the Invention]

<Problem of the First Invention> However, according to the conventional technique 1, the first pulley 25 and the second pulley 1 of each image forming unit are provided.
The lengths of the timing belts 15a to 15d that independently connect the 2a to 12d become long, and in particular, the timing belts 15a and 15d to the first image forming station Pa and the fourth image forming station Pd become long. . Timing belts generally have a spring constant, which generally decreases in inverse proportion to the length of the belt. Therefore, when the load is constant, the smaller the spring constant, that is, the longer the length of the original belt, the greater the length of expansion and contraction of the belt.

Therefore, as shown in FIG. 4, as the timing belts 15a and 15d become longer, the amount of expansion and contraction of the timing belts 15a and 15d becomes larger. As a result, the rotation unevenness of the photosensitive drums 21a and 12d becomes larger, resulting in pitch unevenness, color misregistration, etc. The problem occurs.

Therefore, in the first invention, in a system in which a plurality of image carriers are driven via a belt by a single drive source, the belt length is made short, and pitch unevenness due to substantial belt expansion and contraction, An object of the present invention is to provide an image forming apparatus that prevents color misregistration and improves image quality. <Problem of the Second Invention> Further, according to the above-mentioned conventional technique 2, it is impossible to suppress the periodical rotation unevenness of each of the photosensitive drums 1a to 1c.
A positional shift of a period of 1c occurs, and a color shift occurs.

Therefore, a second aspect of the present invention provides an image forming apparatus in which the phase shift of the image carrier period (photosensitive drum period) is surely aligned by a simple operation to minimize the color shift. That is the purpose.

[0020]

The present invention (first invention and second invention) has been made in view of the above circumstances, and has the following configurations. <Means of the First Invention> In the first invention, a plurality of image carriers to be rotationally driven by a driving unit are arranged along the conveyance direction of the transfer material, and the latent images are formed on the respective image carriers. In the image forming apparatus, in which the formed latent image is formed into a visible image by a developing device, and the visible image is sequentially transferred onto a transfer material that is sequentially conveyed to each of the transfer positions, the drive means includes A single drive source for driving the image carrier, a plurality of drive pulleys for receiving a driving force from the drive source, and a driven pulley coaxially fixed to each of the image carriers rotatably supported. And a belt member stretched between the drive pulley and the driven pulley, and the moving time of each image carrier moving from the latent image forming position to the transfer position Do not set it to an integral multiple of the time it takes for the pulley to make one revolution. , Characterized in that.

Further, a gear train is interposed between the drive source and the drive pulley, and the gear train sets the time required for the drive pulley to make one revolution to be an integral multiple of the time required for the drive source to make one revolution. You may. <Means of Second Invention> Further, according to the second invention, visible images of different colors are formed on a plurality of image carriers, and these visible images are sequentially transferred to the same transfer material to form a color image on the transfer material. In an image forming apparatus for forming an image, a plurality of rotating shafts respectively rotating the plurality of image bearing members, a plurality of helical gears or worm wheels respectively rotating the plurality of rotational shafts, and a plurality of these helical gears or worm wheels. It has a worm gear to be engaged, and the helical gear or the worm wheel and the rotary shaft are integrated with each other and are attachable to and detachable from the apparatus main body.

Further, in the image forming apparatus for forming visible images of different colors on a plurality of image carriers and sequentially transferring the visible images to the same transfer material to form a color image on the transfer material. A plurality of rotating shafts for rotating the image carrier, and a plurality of drive pulleys for rotating the plurality of rotating shafts, respectively. It is characterized by being removable.

In these cases, the helical gear or the worm wheel and the rotary shaft may be fastened by shrink fit, or the drive pulley and the rotary shaft may be fast fit by shrink fit.

[0024]

[Action]

<Operation of the First Invention> Based on the above configuration, since the drive pulley rotates an integral number of times while the image carrier rotates from the latent image forming position to the transfer position, the drive pulley has uneven rotation. In this case, the rotational unevenness appears at the time of latent image formation and at the time of transfer. Therefore, for example, when the rotation speed of the image carrier at the time of latent image formation is faster than the normal state, the latent image is formed to extend in the rotation direction. After this latent image is developed,
Similarly, when a visible image is transferred to the transfer material, the rotation speed of the image carrier also increases. Therefore, this time, the visible image is transferred to the transfer material in a contracted state. In this way, the latent image extends during latent image formation, while the visible image shrinks during transfer, so that the two are offset and an image of almost normal length is formed. When the rotation unevenness of the image carrier appears late, the latent image is shortened and the visible image is extended, contrary to the above, and as a result, the images are offset to form a normal image. <Operation of Second Invention> Further, according to the second invention, since the helical gear or worm wheel and the rotary shaft are integrally formed, the relative positional relationship between the helical gear or worm wheel and the rotary shaft is accurate. Can be held. The same applies to the case where the drive pulley and the rotary shaft are integrally formed instead of the helical gear or the worm wheel.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. <Embodiment of First Invention> FIG. 3 schematically shows the configuration of an image forming apparatus to which the first invention is applied.

In this image forming apparatus, the first, second, and third portions are arranged from the upstream side (the right side in the drawing) to the downstream side (the same left side) in the conveying direction (arrow K1 direction) of the transfer material S to be image-formed. Third and fourth four image forming stations Pa, P
b, Pc, and Pd are arranged. Each of the image forming stations Pa, Pb, Pc, and Pd has a photosensitive drum 1a, 1b, 1c, and 1d as an image carrier, and around them, a dedicated charging means 2a, 2b, 2c,
2d, exposure means 3a, 3b, 3c such as a laser scanner,
3d, developing means 4a, 4b, 4c, 4d, cleaning means 6a, 6b, 6c, 6d, etc. are arranged respectively. Here, the image forming stations Pa, Pb, Pc,
Pd is for forming a yellow image, a magenta image, a cyan image, and a black image, respectively.

On the other hand, each image forming station Pa, P
Below the b, Pc, and Pd, the photosensitive drums 1a, 1b,
Conveying means 7 having an endless conveying belt 7a passing between the transfer means 5a, 5b, 5c and 5d and 1c and 1d.
The transfer material S fed by the paper feed roller 8 on the upstream side is transported by the transport belt 7a through the transfer units 5a to 5d of the image forming stations Pa to Pd.

In such a structure, first, the charging means 2a and the exposing means 3a of the first image forming station Pa are provided.
Photosensitive drum 1a by a known electrophotographic process means such as
After the latent image of the yellow component color of the image information is formed on the latent image, the latent image is visualized as a yellow toner image by the developer having the yellow toner by the developing means 4a, and the yellow toner image is conveyed by the conveying means 7. Transfer material S transported by
Is transferred to the sheet via the transfer means 5a.

On the other hand, while the yellow toner image is being transferred to the transfer material S, the second image forming apparatus station P
In b, a latent image of a magenta component color is formed, then a toner image with magenta toner is obtained by the developing means 4b, and a second image forming station is formed on the transfer material S which has been transferred at the first image forming station Pa. Pb transfer means 5b
At, the magenta toner image is transferred.

Thereafter, the cyan image and the black image are formed by the same method, and when the four color toner images are superposed on the transfer material S, the transfer material S is heated and fixed by the fixing means 10. A multicolor (full color) image is obtained on the transfer material S.

The photosensitive drums 1a, 1b, 1c and 1d, which have been transferred, have cleaning means 6a and 6a.
Residual toner is removed from the photosensitive drums 1a to 1d at b, 6c, and 6d, and the toner is subjected to the next image forming process, which is performed subsequently.

A method of driving the photosensitive drums 1a to 1d in such an image forming apparatus will be described with reference to FIGS. Note that FIG. 1 is a view of the driving device of the image forming apparatus shown in FIG. 3 as viewed from the back side of FIG. 1. Therefore, the upstream side, which is the right side in FIG. 3, is arranged on the left side in FIG.

In FIG. 1, 11a, 11b, 11c,
Reference numeral 11d denotes a drum shaft that supports the photosensitive drums 1a, 1b, 1c, and 1d, and is arranged at each of the four image forming stations Pa, Pb, Pc, and Pd described in FIG. Drum drive pulleys 12a, 12b, 12c, 12d are provided on the respective drum shafts 11a, 11b, 11c, 11d.
Is provided, and the driving force applied to the drum driving pulleys 12a to 12d is the drum driving pulley 1 of the first image forming station Pa and the second image forming station Pb.
2a and 12b, from the common input pulley 13a via different timing belts 15a and 15b, respectively, and on the other hand, the drum drive pulleys 12c and 12d of the third image forming station Pc and the fourth image forming station Pd.
Is transmitted from the common input pulley 13c via different timing belts 15c and 15d.

The power of the drum drive motor 16 which is the drive source is output from the output gear 17 to the gear 19 and the gears 20a, 2a.
0c through the input pulleys 13a, 13a at an appropriate reduction ratio.
It is transmitted to c.

As described above, the input pulleys 13a, 13c
Is divided into two parts by the drum drive motor 16, so that the driving force of the drum drive motor 16 is the gear 19 at the upstream input pulley 13a side (first and second image forming stations Pa, Pb). Side) gear 20a and a downstream side input pulley 13c side (third and fourth image forming stations Pc, Pd side) gear 20c.

21a, 21b, 21c and 21d in FIG.
Are idler pulleys for adjusting tensions of the timing belts 15a, 15b, 15c and 15d.

FIG. 2 is a development view of one of the four image forming stations Pa to Pd shown in FIG. 1, here, the photosensitive drum 1a of the first image forming station Pa and the driving device. Is shown.

The drive motor 16 is driven by the drive circuit 22.
Driven at a constant speed. For example, drive motor 1
When using a DC motor with a built-in encoder as 6,
By performing the phase lock loop control by the drive circuit 22, the motor 16 is controlled to rotate at a constant speed. When a stepping motor is used as the drive motor 16, the stepping motor drive circuit 22 inputs a drive pulse corresponding to a constant clock to the stepping motor to rotate at a constant speed.

However, there is a limit to rotating the motor 16 at a constant speed, and uneven rotation occurs due to characteristics such as rotor balance, output shaft composition, output gear accuracy, and motor control responsiveness. . Further, the accuracy of the reduction gear train, here, the gear 19, the gears 20a, 20c and the eccentricity of the gears 20a, 20c with respect to the shafts 23a, 23c,
Uneven rotation occurs due to eccentricity of the input pulleys 13a and 13c with respect to the shafts 23a and 23c.

The rotation amount error caused by the rotation unevenness of these drive systems (the one-dot chain line portion in FIG. 2) appears as a positional deviation on the photosensitive drum 1a. Moreover, the latent image forming process and the transfer process are affected by the rotation unevenness at different times on the photosensitive drum 1a.

That is, due to the uneven rotation of the drive system A, an exposure deviation occurs during the latent image forming process, and a transfer deviation occurs during the transfer process. Therefore, depending on the rotation cycle of the drive system A, the exposure deviation and the transfer deviation may be synergistic or may be canceled.

Therefore, the first invention utilizes this property,
Both the exposure deviation and the transfer deviation cancel each other out so that the rotation irregularity of the motor does not become a positional deviation on the image.

That is, in the main body embodiment, the photosensitive drum 1
The time required for a to rotate from the latent image forming position P ₁ to the transfer position P ₂ is set to be equal to an integral multiple of the rotation unevenness cycle of the drive system A. The drive system A with the longest cycle has one rotation cycle of the input pulley 13a, the shaft 23a, and the gear 20a (hereinafter referred to as "input pulley one rotation cycle"), so that the photosensitive drum 1a is at the latent image forming position. The time required for the rotational movement from P ₁ to the transfer position P ₂ is set equal to one rotation cycle of the input pulley. In the main body embodiment, as shown in FIG. 3, the rotation angle from the latent image forming position P ₁ to the transfer position P ₂ is based on that the former is directly above the photosensitive drum 1a and the latter is directly below the photosensitive drum 1a. Since the rotation angle of the photosensitive drum 1a is 180 °, the diameter ratio of the drum driving pulley 12a and the input pulley 13a is set to 2: 1 and the rotation speed of the input pulley 13a is 40 rpm.
I am trying. Furthermore, the reduction ratio from the drum drive motor 16 to the input pulley 13a is 10: 1 (the rotation speed of the motor 16 is 400 rpm), and the integer ratio drive is performed.

Therefore, when the photosensitive drum 1a is exposed by the uneven rotation of the drive system A, for example, when the peripheral speed of the photosensitive drum 1a is higher than the standard, the image to be written is elongated. During transfer, n of the motor 16
The peripheral speed of the photosensitive drum 1a becomes high again after being shifted by the period, that is, the photosensitive drum 1a becomes faster relative to the transfer material S, so that the image is contracted and transferred. Therefore, the image formed on the transfer material is not affected by the rotational unevenness of the drive system A due to both the expansion during the exposure and the contraction during the transfer. <Second Embodiment of the Invention> FIG. 5 is a structural diagram of a photosensitive drum drive system of a laser beam printer (image forming apparatus) according to the present invention, FIG. 6 is a sectional view taken along the line II of FIG. 5, and FIG. 7 is a laser. It is a perspective view of the beam printer main part.

First, the basic configuration of the laser beam printer will be outlined with reference to FIG. 7. Three image forming stations Pa, Pb, and Pc are arranged in parallel in the laser beam printer, and each image forming station Pa, Pb, Pc
Is a dedicated photosensitive drum 1a, 1b, 1c which is an image carrier.
Is provided. Then, the photosensitive drums 1a, 1b,
A dedicated image forming process means is arranged around 1c, and these image forming process means are laser beam exposing means 3a, 3b, 3c, a charging unit (not shown), an exposing means,
The developing unit, the transfer unit, the cleaning unit, etc. are included.

On the other hand, below the photosensitive drums 1a, 1b, 1c, there is arranged a conveying means 7 having an endless conveying belt 7a, and the transfer material S fed from a sheet feeding device (not shown) is conveyed. Each image forming station P by means 7
It is conveyed in the direction of arrow K1 in the drawing through the transfer positions 31a, 31b, 31c of a, Pb, and Pc.

In this embodiment, each image forming station P
The photosensitive drums 1a, 1b, and 1c of a, Pb, and Pc are rotationally driven by a drive motor 32 that is a common drive source.
That is, as also shown in FIG. 5, the drive shaft 33 connected to the drive motor 32 has worm gears 33 a, 33 b, 3 and 3.
3c is engraved, and the worm gears 33a, 33
b and 33c are drum shafts 1 of the photosensitive drums 1a, 1b and 1c.
It meshes with worm wheels 35a, 35b, 35c which are bonded to the ends of 1a, 11b, 11c. The drive shaft 33 has the worm gears 33a, 33b, 33c.
The worm gear 3
Eccentricity is less likely to occur between the rotation centers of the drive shaft 33 and 3a, 33b, 33c.

Therefore, when the drive shaft 33 is rotationally driven by the drive motor 32, the rotation of the drive shaft 33 passes through the worm gears 33a, 33b and 33c and the worm wheels 35a, 35b and 35c, and the drum shafts 11a and 11a.
b, 11c, and the drum shafts 11a, 11b, 11
The photosensitive drums 1a, 1b, 1c supported by c are rotationally driven at a predetermined speed.

By the way, the photosensitive drums 11a, 1b, 1c
Are arranged at a predetermined distance from each other, but the distance between them is such that the conveying means 7 and the transfer material S are adjacent to the photosensitive drum 1.
a, 1b and the transfer positions 31a of the photosensitive drums 1b, 1c,
Time T for passing between 31b and transfer positions 31b and 31c
₁ and T ₂ are set to be equal to an integral multiple of the drive unevenness cycle of the drive motor (not shown) of the conveying means 7 and the drive roller. Therefore, each photosensitive drum 1a, 1b, 1c
At the transfer positions 31a, 31b, and 31c, the phases of the drive unevenness of the transporting unit 7 match each other.

The details of the drive system for the photosensitive drums 1a, 1b, 1c will be described with reference to FIGS. In the present embodiment, in order to prevent the drive shaft 33 from bending and deforming due to the force received by the worm gears 33a, 33b, 33c when the worm gears 33a, 33b, 33c are meshed with the worm wheels 35a, 35b, 35c, the drive shaft 33 is configured to prevent the drive shaft 33 from being deformed. , 33b, 33c are connected to bearings 36a, 3
It is supported by 6b, 36c and 36d. The bearings 36a to 36d are the bearing support members 37a, 37b, 37.
c, 37d, and the bearing support member 37
a to 37d are fixed to the driving side plate 39 (see FIG. 6). The bearing support members 37a to 37d may be configured to be positionally adjustable with respect to the main body so that the positions of the bearings 36a to 36d can be adjusted.

Each drum shaft 11 (hereinafter, drum shaft 11a,
When it is not necessary to distinguish 11b and 11c, they are simply referred to as "drum shaft 11". The same applies to other members such as the photosensitive drum 1. ) Is a bearing 42 fixed to the drive speed plate 39 and a bearing 43 fixed to the main body side plate 40.
And a bearing 44 fixed to the centering plate 41 so as to be rotatably supported.

The rotational driving force of the drum shaft 11 is equal to that of the drum shaft 1.
The drive pin 114 on No. 1 is transmitted to the photosensitive drum 1 by engaging with the pin groove 113 of the drum front flange 112. A thrust stop member 46a is fixed on the drum shaft 11 between the bearing 42 and the bearing 43, a spring receiving member 46b is provided on the bearing 42 side, and a thrust stop member 46a and a spring receiving member 46b are provided between the thrust stop member 46a and the spring receiving member 46b. , The compression coil spring 45 is provided, and the drum shaft 11
It eliminates the thrust rattling.

Further, in this embodiment, the worm wheel 3 is used.
In order to avoid thrust adjustment in the direction of the drum shaft 11 of No. 5, a helical gear is used for the worm wheel 35. The engagement between the helical gear 35 and the drum shaft 11 is performed by shrink fit, and eccentricity caused by looseness at the time of coupling the two is prevented. Therefore, in the present embodiment, the helical gear 35 and the drum shaft 11 are handled as one body. That is, the helical gear 35 is shrink-fitted and coupled to the drum shaft 11 in advance, and the thrust stopper 46a, the compression coil spring 45, the spring receiving member 46b, and the bearing 42 are connected.
Is attached to the drum shaft 11 and assembled as a drum shaft unit. After pushing the tip of the drum shaft 11 (the left side in FIG. 6) into the bearing 43 fixed on the main body side plate 40, the drum shaft unit abuts on the thrust stopper 46a of the drum shaft 11. While the compression coil spring 45 is being compressed, the bearing 42 is fixed to the driving side plate 39 with a screw. The holes 351 and 352 provided in the helical gear 35 are tool holes for fixing the bearing 42 to the driving side plate 39 with screws.

Next, the drive pin 114 is placed on the drum shaft 11.
And a method of engaging with the drum front flange 112 will be described with reference to FIGS. The same figure (a)
Shows a tip portion of the drum shaft 11, FIG. 11B is a view taken along the line A in FIG. 11A, and FIG.
Shows the engagement state between the drum front flange 112 and the drive pin 114 when viewed from the A direction.

Pin groove 113 of drum front flange 112
Is formed in a V shape as shown in FIG. 7C, and by urging the drum front flange 112 in the B direction,
The drive pin 114 fits into the tapered portion of the pin groove 113, and the rotational drive force of the drum shaft 11 is transmitted to the photosensitive drum 1.

In FIG. 6, reference numeral 120 denotes a drum fixing means for urging the above-mentioned drum front flange 112 in the B direction, which is constituted by a knob 121 and a knob 122. FIG. 16 is a state diagram in which the drum fixing means 120 is released. The knob 122 has a U provided on the drum shaft 11.
There is a convex portion 124 that engages with the V-shaped groove 115 (see FIGS. 15B and 15C). On the other hand, on the drum front flange 112, the convex portion 1 that engages with the U-shaped groove 115 of the drum shaft 11 is formed.
16 and the convex portion 124 of the knob 122 described above is provided with the groove 115.
The screw part 123 of the knob 121 into the drum shaft 1
As it is tightened into the threaded portion 117 of the No. 1, the end surface of the convex portion 124 of the knob 122 becomes the convex portion 11 of the drum front flange 112.
The drum front flange 112 is biased in the direction B of FIG. 15C by abutting against the end portion of 6 and further screwed, and the V-shaped groove 113 of the drum front flange 112 is joined to the drive pin 114 without backlash. It Note that FIG. 6 shows the combined state.

Further, in this embodiment, the photosensitive drums 1a to 1 are
Latent image forming position on c (laser writing position, see FIG. 7)
34a, 34b, 34c to transfer positions 31a, 31b,
The rotation angle of the photosensitive drums 1a to 1c up to 31c is 180.
It has become °.

Therefore, the reduction ratio between the worm gears 33a to 33c and the helical gears 35a to 35c is set to 1 / 2n (n is an integer). For example, when n = 1, the reduction ratio is 1/2
In this case, the rotation unevenness of the photosensitive drums 1a to 1c is 1/2 of the photosensitive drum period.

FIG. 8 is a conceptual diagram thereof. When such rotation unevenness is present on the photosensitive drums 1a to 1c, for example, when a latent image is formed at timing A on the time axis t, the image is misaligned in the extending direction (exposure misalignment). However, at this time, in the written latent image, at timing B, the photosensitive drums 1a to 1c rotate 180 °,
Transfer is performed. At this time, since the speeds of the photosensitive drums 1a to 1c deviate in the fast direction, a positional deviation (transfer deviation) occurs in the image contracting direction during the transfer process. The exposure deviation and the transfer deviation cancel each other out, and the image transferred onto the transfer material S becomes an image without positional deviation. That is,
Latent image forming positions 34a to 34 on the photosensitive drums 1a to 1c
from the photosensitive drum 1a to the transfer positions 31a to 31c
When the rotation angle of 1c is 180 °, the worm gear 33
a to 33c and the helical gears 35a to 35c have a reduction ratio of 1
/ 2n (n is an integer), the worm gears 33a to 3a
The rotation unevenness of the rotation cycle of 3c does not appear as a positional deviation on the transferred image.

Furthermore, if the speed reduction ratio between the worm gears 33a to 33c and the drive motor 32 is set to 1 / n (n is an integer), uneven rotation of the drive motor 32 will not appear as a positional deviation on the transferred image. What remains is to suppress uneven rotation of the photosensitive drum cycle. The factors causing the uneven rotation of the photosensitive drum cycle include cumulative pitch error of the helical gears 33a to 33c (worm wheel), the drum shafts 11a to 11c and the helical gears 33a to 33.
Eccentricity (when the worm wheel) is coupled (the eccentricity is prevented by shrink fitting in the present embodiment), runout of the drum shafts 11a to 11c, etc. As a result, uneven rotation of the photosensitive drum cycle appears. The above-mentioned items 1 to 5 improve the accuracy of each part and improve the level by adjusting and assembling, but it is difficult to completely suppress the uneven rotation of the drum cycle.

As a result, each image forming station Pa ...
The image formed by Pc has a positional deviation (image expansion / contraction) of the photosensitive drum period unique to each of the image forming stations Pa to Pc. The present invention reads the image formed by each of the image forming stations Pa to Pc, detects the angle of the phase of the image expansion and contraction of the photosensitive drum cycle at each of the image forming stations Pa to Pc, and detects the angle.
Image of the drum driving unit so that the phase angle of Pc coincides. The parts that control the expansion / contraction drum cycle phase angle, that is, the parts that control the phase angle of the uneven rotation of the drum cycle are reconstructed comprehensively. There is. Specifically, the drum shaft 11a of the photosensitive drum and the helical gear (or worm wheel) 35
The image expansion / contraction drum cycle phase angle difference rotation may be integrally performed in the state where a is combined. For example, based on the image expansion / contraction of the first image forming station Pa, the drum cycle image expansion / contraction phase of each of the second and third image forming stations Pb and Pc is made to match that of the first image forming station. Then, the meshing position of the worm gear 33a of the first image forming station Pa and the helical gear (or worm wheel) 35a is fixed, and the worm gears 33b of the second and third image forming stations Pb and Pc are fixed.
33c, the helical gears (or worm wheels) 35b, 35c of the second and third image forming stations.
It suffices to shift the respective phase difference meshing positions.

Next, how to obtain the drum cycle phase angle of image expansion and contraction will be described.

FIG. 9 shows an example of a test pattern image for reading the expansion and contraction of the image. For example, a straight line extending in the main scanning direction on the A3 size transfer material S is 1 mm in the sub scanning direction.
The pattern is arranged at pitch intervals. Figure 10 for each line
As shown in, the names (line number k) from 1 to 20 are given. Such a test pattern image is output and the amount of positional deviation ΔL with respect to the nominal position of each line is measured.
FIG. 10 is a graph showing an example of the measurement result of the positional deviation amount ΔL, in which the horizontal axis represents the line number k of the test pattern line image and the vertical axis represents the positional deviation amount ΔL.
(Μm) is shown. As shown in the figure, since the positional deviation amount ΔL is a periodic function in which one rotation of the photosensitive drums 1a to 1c is one cycle, it can be approximated by the following equation using a Fourier series.

ΔL (θ) = a ₀ + a ₁ cos θ + a ₂ cos 2θ + ... + a _n cos nθ + b ₀ + b ₁ sin θ + b ₂ sin 2θ + ... + b _n cos nθ (1) Then, the above equation is expressed by the following equation. Is converted into ΔL (θ) = a ₀ c ₁ cos (θ + δ ₁ ) + c ₂ cos (2θ + δ ₂ ) + ... + c ₂ cos (nθ + δ _n ) ... (2), and the position shift of the Kth line pattern The quantity ΔL _k
The constants a ₀ by the least square method _{as, a m, b m, c} m
Is calculated,

[0065]

[Formula 1] Here, comparing equations (1) and (2),

[0066]

[Formula 2] Is obtained.

Here, the governing term of the photosensitive drum period is c ₁ co
Since s (θ + δ ₁ ), tan δ ₁ = −a ₁ / b ₁ and the drum cycle phase angle δ ₁ of image expansion / contraction can be calculated.

In this way, each image forming station Pa
Drum cycle phase angle [delta] ₁ of the image stretch is determined in each image forming station Pa~Pc than the test pattern output image in to Pc.

The phase angle δ ₁ at the first image forming station (Y image forming station) Pa is δ _1Y , and similarly the second
The image forming station Pb and the third image forming station Pc have phase angles δ ₁ of δ _1M and δ _1C , respectively. FIG. 11 shows the displacement amount ΔL of the test pattern line output image.
Is a diagram showing an example in which is approximated by a Fourier series, and the vertical axis of the figure shows the amount of positional deviation ΔL. In FIG. 11, ΔL _Y
Is the displacement deviation of the Y image (yellow image) formed by the first image forming station Pa, and ΔL _M is the displacement deviation of the M image (magenta image) formed by the second image forming station Pb. Shows. As is clear from the figure, in order to eliminate the color shift between the two, the phase angle δ
_It suffices to match _1Y and δ _1M for image formation. FIG. 12 is a flowchart showing an example of a phase angle calculation procedure of each of the image forming stations Pa to Pc. In the figure, S1 to S4 indicate each step. In calculating the phase angle δ ₁ , first, a test pattern image is output by the pattern generator PG (not shown) (S1). The pattern generator PG may be provided in the ROM of the printer controller of the image forming apparatus or may be external to the image forming apparatus. Next, the output image is read by an image reader (not shown) (S2), and the positional deviation amount ΔL _k of each line of the test pattern image is calculated (S3). As the image reader, an image reader connected to the image forming apparatus may be used, or another image reader may be used. In this way, the phase angle δ ₁ at each of the image forming stations 1a to 1c is calculated (S4). For example, using the first image forming station Pa as a reference station, the second and third image forming stations Pb and Pc are used.
When the positional deviation phase angles δ _1M and δ _1C of δ _1M are matched with δ _1Y , (δ _1M −δ _1Y ) in the second image forming station Pb and (δ _1C −δ in the third image forming station Pc. _1Y ), the meshing position of each helical gear (or worm wheel) 35a and worm gear 33a may be shifted in the opposite direction to the rotation direction. As described above, how to shift the meshing position between the helical gear (or worm wheel) 35a and the worm gear 33a is as follows.
It is to rotate integrally without releasing the connection with the drum shaft 11a. That is, it means that the phase angle is rotated comprehensively while maintaining the relationship of each element that controls the phase angle of the photosensitive drum cycle.

The method will be described with reference to FIG. For example, when it is desired to shift the meshing position by (δ _1M −δ _1Y ) at the second image forming station Pb, the fixing screw of the bearing 42 fixed to the driving side plate 39 is removed from the tool holes 351 and 352 of the helical gear 35, and the drum is removed. The shaft 11 is pulled out in the C direction, and the engagement between the worm gear 33 and the helical gear 35 is released. Then, after rotating the drum shaft 11 by (δ _1M −δ _1Y ) in the direction opposite to the rotation direction,
The drum shaft 11 is pushed in the direction opposite to the C direction, the worm gear 33 and the helical gear 35 are meshed with each other, and the bearing 42 of the drive side plate 39 is fixed with a screw.

Through the worm gears 33a to 33c and the helical gears or the worm wheels 35a to 35c, the single drive motor 32 drives the plurality of photosensitive drums 1a to 1c.
Although the phase matching when driving c has been described, the photosensitive drum 1a is connected via the timing belt and the belt pulley.
When driving .about.1c, the phases can be similarly adjusted.

FIG. 13 shows an example of this, in which the drive pulley 51 is driven by a drive motor (not shown). Drum pulley 52a on the drum shaft of the first image forming station Pa, drum pulley 52b on the drum shaft of the second image forming station Pb, and drum pulley 52c of the drum shaft of the third image forming station Pc.
Timing belts (belt members) 53a, 53b, 53c are wound around the drive pulley 51 independently of each other, and the driving force of the drive motor is transmitted to each of the image forming stations Pa to Pc. In the figure, 55a,
55b and 55c are idler pulleys. Also in the above configuration, as described above, with the first image forming station Pa as a reference, in the second image forming station Pb, (δ _1M −δ _1Y ) and in the third image forming station Pc, (δ _1C − δ _1Y ) only, the drum pulleys 52b and 52c of the second image forming apparatus station Pb and the third image forming station Pc
And the drum shafts 11b and 11c may be shifted integrally.

FIG. 17 is a diagram showing the structure of the drum shaft 1.
1 has the same configuration as that of FIG. 6 except that the driving member coupled to 1 uses a timing pulley (driving pulley) 35A, and the description thereof will be omitted.

[0074]

【The invention's effect】

<Effect of the First Invention> As described above, according to the present invention, it is possible to transmit the drive of the image carrier in which the rotation unevenness of the drive source does not appear as the positional deviation of the image. Further, since the driving force from the driving source is branched into a plurality of (two in the above-mentioned embodiment) driven pulleys, the length of the driving pulley and the belt member suspended between the driven pulleys can be shortened. Therefore, the amount of expansion and contraction of the belt can be reduced, and uneven rotation due to expansion and contraction of the belt can be suppressed. For example, one driving pulley drives four driven pulleys via four belt members, whereas two driving pulleys each drive two driven pulleys, and four driven pulleys drive four belt members. Since the driven pulleys are driven, it is possible to reduce the tilting moment applied to the shafts supporting these pulleys. Therefore, it is possible to suppress uneven rotation of the driving pulley and the driven pulley.

As a result, it is possible to obtain a high-quality color image free from uneven pitch color deviation. <Effect of Second Invention> Further, according to the second invention, a rotary shaft for supporting and rotating each image carrier and a driving means (worm wheel, belt pulley) fixed on the rotary shaft are integrated. By being configured to be attachable to and detachable from the main body of the apparatus, each of the factors that control the phase of image expansion and contraction of the drum cycle of the image formed at each image forming station can be maintained while maintaining the mutual relationship. The drum cycle phase of image expansion / contraction of the image forming station can be matched. Therefore, it is easy to match the image expansion / contraction phase of each image forming station, and it is possible to obtain a high-quality color image without color misregistration. Further, by handling the rotary shaft and the drive means as a unit, it is possible to check the parts in a state where the rotary shaft and the drive means are connected before the main mounting, so that the product can be stabilized. it can.

[Brief description of drawings]

FIG. 1 is a side view showing a configuration of a driving unit of an image carrier according to a first embodiment of the first invention.

FIG. 2 is a top development view showing a structure of a driving unit of the image carrier according to the first embodiment.

FIG. 3 is a vertical cross-sectional view schematically showing the configuration of the image forming apparatus according to the first embodiment.

FIG. 4 is a side view showing the structure of a conventional driving unit for an image carrier.

FIG. 5 is a vertical cross-sectional view showing a configuration of a drive system of a photosensitive drum of a laser beam printer (image forming apparatus) of the second invention.

FIG. 6 is a sectional view taken along line I-I of FIG.

FIG. 7 is a perspective view showing a main part of the same laser beam printer.

FIG. 8 is a diagram showing the relationship between the rotation period and rotation unevenness of the photosensitive drum.

FIG. 9 is a diagram showing a test pattern for reading image expansion and contraction.

FIG. 10 is a diagram showing a positional shift of a test pattern line output image in the same manner.

FIG. 11 is a diagram in which the positional shift amount of the test pattern line output image is approximated by a Fourier series.

FIG. 12 is a flowchart showing a phase calculation procedure of each image forming station.

FIG. 13 is a vertical cross-sectional view showing the configuration of a drive system of a photosensitive drum of another laser beam printer.

FIG. 14 is a perspective view showing a main part of a conventional laser beam printer.

FIG. 15A is a diagram showing a tip end portion of a drum shaft of the image forming apparatus of the second invention. (B) is a line A arrow line view of the tip part of the drum shaft of (a). FIG. 6C is an operation explanatory view showing a state of engagement between the drum front flange and the drive pin when the front end portion of the drum shaft in FIG.

FIG. 16 is a vertical cross-sectional view showing a state in which the drum fixing means of the second invention is released.

FIG. 17 is a vertical cross-sectional view showing another drive means (drive pulley) of the second invention.

[Explanation of symbols]

1a, 1b, 1c, 1d Image carrier (photosensitive drum) 11a, 11b, 11c, 11d Rotating shaft (drum shaft) 12a, 12b, 12c, 12d Driven pulley (drum driving pulley) 13a, 13c Driving pulley (input pulley) ) 15a, 15b, 15c, 15d belt member (timing belt) 16 drive source (drive motor) 19, 20a, 20b gear train (gear) K1 transport direction P ₁ latent image forming position P ₂ transfer position 31 drive member (drive shaft) ) 31a, 31b, 31c transfer position 32 drive source (drive motor) 33a, 33b, 33c drive gear (worm gear) 34a, 34b, 34c latent image forming position 35a, 35b, 35c driven gear (worm wheel, helical gear) 51 drive Pulleys 52a, 52b, 53c Driven pulleys 53a, 53b, 53c Belt members ( Lee timing belt) S transfer material

Claims (6)

[Claims] 1. A plurality of image carriers that are rotationally driven by a driving unit are arranged along a transfer material conveyance direction, and a latent image formed at a latent image forming position on each of the image carriers is developed by a developing device. In an image forming apparatus that forms a visible image and further transfers the visible image onto a transfer material that is sequentially conveyed to each of the transfer positions, the drive unit includes a single unit for driving the plurality of image carriers. One drive source, a plurality of drive pulleys that receive a drive force from the drive source, a driven pulley that is coaxially fixed to each of the image carriers that are rotatably supported, and the drive pulley and the driven target. A belt member stretched between the pulley and a pulley, and the moving time of each image carrier moving from the latent image forming position to the transfer position is an integral multiple of the time taken for the drive pulley to make one rotation. Is set to Image forming apparatus. 2. A gear train is interposed between the drive source and the drive pulley, and the gear train sets the time required for the drive pulley to make one revolution to be an integral multiple of the time required for the drive source to make one revolution. The image forming apparatus according to claim 1, wherein: 3. An image forming apparatus for forming visible images of different colors on a plurality of image carriers and sequentially transferring the visible images to the same transfer material to form a color image on the transfer material. A plurality of rotary shafts respectively rotating the image bearing member, a plurality of helical gears or worm wheels respectively rotating the plurality of rotary shafts, and a plurality of these helical gears or a worm gear engaged with the worm wheel, the helical gears Alternatively, the image forming apparatus is characterized in that the worm wheel and the rotary shaft are integrated and can be attached to and detached from the apparatus main body. 4. An image forming apparatus for forming visible images of different colors on a plurality of image carriers and sequentially transferring these visible images to the same transfer material to form a color image on the transfer material. A plurality of rotating shafts for rotating the image carrier, and a plurality of drive pulleys for rotating the plurality of rotating shafts, respectively. An image forming apparatus that is removable from the image forming apparatus. 5. The image forming apparatus according to claim 3, wherein the helical gear or the worm wheel and the rotary shaft are fastened by shrink fit. 6. The image forming apparatus according to claim 4, wherein the drive pulley and the rotary shaft are fastened together by shrink fit.