JPH0656292A - Image forming device - Google Patents

Abstract

PURPOSE:To secure the rigidity of a conveyor belt in the face direction and dispense with the scatter prevention of a toner by providing a mark corresponding to a junction section on the conveyor belt, and providing a detecting means detecting the mark near the conveyor belt. CONSTITUTION:Photosensitive drums 1a-1d holding an image with a developer and a conveyor belt 80 holding a transfer material 6 transferred with the image are arranged nearby, the conveyor belt 80 is formed into an endless shape with both ends jointed, and the transfer material 6 is circulatively moved and conveyed. An adhesive sheet 90 corresponding to a junction section 84 is stuck to the conveyor belt 80, and a reflection type sensor 91 detecting the difference of the light reflection factor between the adhesive sheet 90 and the conveyor belt 80 is provided near the conveyance belt 80. The rigidity of the conveyor belt 80 in the face direction can be secured, no stress concentration occurs when a tensile load is applied due to the circulative movement, and a stable conveyance function can be maintained. The configuration of the conveyor belt 80 is not changed, the detection precision can be maintained, and the picture quality can be kept satisfactory.

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 applied to, for example, an electrophotographic printer or a copying machine.

Further, the present invention relates to an image forming apparatus such as an electrophotographic or ink jet printer or a copying machine.

[0003]

[Prior art]

[First Conventional Example] An example of a color electrophotographic copying apparatus will be briefly described with reference to FIG. 9. First, second, third and fourth examples.
The image forming departments 500 to 503 are arranged in parallel. The image forming departments 500 to 503 are provided with electrophotographic photosensitive drums 504 to 507 as dedicated image carriers, respectively.

The photosensitive drums 504 to 507 are provided with latent image forming portions 508 to 511, developing portions 512 to 515, on the outer peripheral side thereof.
Cleaning units 516 to 519 are arranged, respectively.

Further, an endless conveyor belt 520 for conveying a recording material as a transfer material to each transfer position is arranged below each of the image forming sections 500 to 503, and the conveyor belt 520 is wound around a roller 521. There is. Further, transfer discharge units 522 to 525 are arranged inside the transport belt 520.

In the appropriate configuration, first the first image forming section 5
The latent image forming unit 508 forms a cyan component color latent image on the photosensitive drum 504 of No. 00 based on the image information. The latent image is formed into a visible image by the developer having the cyan toner in the developing unit 512. The recording material 526 is fed from the cassette 527, further sent to the conveying belt 520 through the registration roller 528, and the image is transferred to the recording material 526 by the transfer discharge unit 522.

On the other hand, while the cyan image is being transferred onto the recording material as described above, a latent image of a magenta component color is formed in the second image forming section 501, and subsequently, a magenta toner image is formed in the developing section 513. The image is transferred to a predetermined position of the recording material 526, which has been transferred by the first image forming section 500, in an overlapping manner.

Thereafter, the third and fourth methods are performed in the same manner as above.
The image forming departments 502 and 503 form images of yellow and black colors, and the yellow and black colors are transferred to the same recording material 526 so as to be further overlapped at a predetermined position.

When such an image forming process is completed, the image on the recording material 526 is fixed by the fixing unit 528,
Complete a multicolor image.

The conveyor belt 520 is a polyethylene terephthalate resin film sheet (PET sheet).
Also, a film made of a dielectric resin such as a polyvinylidene fluoride resin film sheet or a polyurethane resin film sheet, and both end portions of which are overlapped and bonded to each other to form an endless shape are used.

When the joint portion 529 is provided, the thickness of that portion is different from that of the other portions. Therefore, when transfer is performed while holding the recording material 526 at a position corresponding to the joint portion 529, a portion overlapping the joint portion 529 has a physical characteristic with the surroundings, that is, a contact pressure between the photosensitive drums 504 to 507. Since they are different, the transfer electric field is different from the surroundings. As a result, a line-shaped density unevenness appears and an image defect occurs.

Therefore, a method has been proposed in which the recording material 526 is not placed on the joining portion 529, and therefore the joining portion 529 is detected and the timing at which the recording material 526 is placed is adjusted. In order to detect the joint portion 529, a conveyor belt 520 having a hole 530 in the thickness direction is usually used as shown in FIG.

As a means for actually detecting the hole 530,
A light emitting unit 531 and a light receiving unit 532 are provided above and below the conveyor belt 520. Then, the joint 529 is obtained by back-calculating from the time when the light from the light emitting unit 531 has passed through the hole 530 and the light receiving unit 532 can detect the passing light. [Second Conventional Example] Conventionally, various types of color image forming apparatuses have been proposed. One of them is provided with a plurality of image stations for each color developer, and a photosensitive drum is provided in each image station. An electrophotographic color image in which a visible image for each color is formed by a well-known image forming process, these visible images are sequentially transferred to a transfer material, which is a recording material supplied from the outside, and then fixed collectively to obtain a color image. There is a forming device.

In this case, the transfer material is placed on a conveyor belt, which is a thin belt member stretched between a driving roller as a conveyor roller and another driven roller located downstream in the conveying direction from the viewpoint of the conveying property. Then, by the circulation movement of the conveyor belt, the conveyor belt is sequentially conveyed to each image station, and the visible images formed on the respective photosensitive drums are sequentially transferred to the transfer material.
On the other hand, as a driving roller of the conveyor belt, since the conveyor belt is driven by a frictional force, it is said that a rubber roller is preferably used because it has a large friction coefficient and does not damage the conveyor belt.

In the image forming apparatus in which a plurality of image forming stations are juxtaposed in this way, images are sequentially transferred onto the same surface of the same transfer material. Therefore, when the transfer image position in each image station deviates from the ideal position, There is a problem that the difference in color, that is, the color shift causes a deterioration in image quality, and there has been a proposal to improve the color shift compared to the related art.
However, there are various factors for this color shift, and it has not been possible to solve all of them.

As one form of color misregistration, color misregistration as shown in FIG. 11 occurs. In the figure, the direction of the arrow A is the conveyance direction of the transfer material 400, and the image m ₂ is uniformly deviated over the entire surface in the direction of the arrow A from the front end (top) of the image m ₀ (hereinafter referred to as the top margin deviation). ). The causes are as follows.

From the exposure position of each image station,
The accuracy of the peripheral length of the photosensitive drum up to the transfer position does not match.

Inconsistency in accuracy of each station interval.

Mismatch in the rotational angular velocities of the respective photosensitive drums.

Variations in the moving speed of the conveyor belt.

As measures against this, it has been proposed to drive all the photosensitive drums by the same drive source for improving the accuracy and further, by using a digital type exposure means (for example, a laser beam). It is also practiced to make the exposure timing variable for each device and adjust the exposure timing to eliminate the top margin shift.

[0022]

[Problems to be Solved by the Invention]

[First Conventional Example] The transport belt 520 has a hole 530 whose rigidity in the surface direction is reduced. For this reason, if the tensile load is applied by cyclically moving the conveyor belt 520 for a long time, the holes 5
Stress concentration occurs around 30. As a result, the transport belt 520 is damaged due to fatigue, and the transport function is degraded. In addition, the stress concentration causes the hole 530 to expand and deform, which lowers the detection accuracy. As a result, image transfer failure occurs.

Further, the toner passes through the hole 530 and is scattered around, or penetrates inward of the conveyor belt 520. As a result, there are problems that the toner adheres to the transfer discharge parts 522 to 525 and the image quality is deteriorated, the toner enters between the roller and the belt, and the circulation movement of the conveyor belt 520 is obstructed. [Second Conventional Example] However, the conventional measures and proposals are insufficient. It's a matter of temperature,
In addition to the above-mentioned causes, the top margin shift occurs due to the temperature rise in the device and the change in the environmental temperature of the environment where the device is installed.

That is, since the linear expansion coefficient of the rubber forming the conveying roller is much larger than that of the metal material forming the apparatus, the diameter of the driving roller greatly changes due to the temperature change as compared with other elements, and therefore the recording The material conveying speed changes. As a result, the time required for the recording material to reach each image station varies depending on the temperature, resulting in color misregistration.

Specifically, the temperature rise of the temperature inside the machine is represented by ΔT [d
eg], the distance between the image stations is L (mm), the linear expansion coefficient of the driving roller is α ₁ , and the linear expansion coefficient of the support member of each image station is α ₂ , the top margin deviation Δl generated is Represented.

The △ l [mm] = △ T · L (α 1 -α 2) that is, when the linear expansion coefficient alpha ₂ of the linear expansion coefficient alpha ₁ and the support member of the driving roller is _{α 1 = α 2 △ l =} 0 Becomes However, since the supporting member is usually made of a metal material and the linear expansion coefficient of rubber is about 10 to 20 times the linear expansion coefficient of a metal material, the top margin deviation Δl becomes very large. The linear expansion coefficient α ₁ of the driving roller here means that the temperature is T [de
g] When raised, when the roller diameter D becomes D ′, α ₁ = D′−D / DT [/ deg]. An object of the first invention is to provide an image forming apparatus for solving the problem of the first conventional example, which secures rigidity in the surface direction of the conveyor belt, and which does not need to prevent toner scattering. Has an aim.

Another object of the present invention is to provide an image forming apparatus capable of detecting that the conveyor belt has moved in a direction orthogonal to the circulation direction. [Object of the second invention] An object of the present invention is to solve the problem of the second conventional example, and to provide an image forming apparatus capable of preventing the diameter of the conveying roller from expanding when the temperature rises.

[0028]

[Means for Solving the Problems]

[First invention] An image carrier for holding an image by a developer,
An image configured such that a transfer belt holding a transfer material on which an image is transferred is disposed in proximity to the transfer belt, and the transfer belt is joined to both ends to be formed into an endless shape, and the transfer material is circulated and moved to transfer the transfer material. In the forming apparatus, a mark corresponding to the joining portion is provided on the conveyor belt, and a detecting means for detecting the mark is provided near the conveyor belt.

Further, the mark has a structure having a reflectance different from that of the surface of the conveyor belt, and the detecting means has a structure for optically detecting the mark.

The mark is an adhesive sticker attached to the surface of the conveyor belt.

The mark has an adhesive layer and a light reflection layer, and the surface of the light reflection layer is covered with a transparent protective film, and the thickness of the mark is set to 50 μm or less.

Further, the detecting means is a reflection type sensor having a light emitting portion and a light receiving portion, and is configured to detect the mark by the amount of reflected light.

Further, the detection means has a structure capable of detecting the movement of the conveyor belt in the direction orthogonal to the circulating movement direction. [Second invention] A plurality of image stations arranged to form a plurality of images and an endless conveyor belt holding a recording material to which the plurality of images are transferred are arranged in proximity to each other, and a plurality of conveyor belts are provided. In an image forming apparatus provided with a plurality of conveyance rollers around which the conveyance belt is wound so as to circulate along the arrangement direction of the image stations, the conveyance roller has a metal layer and a cylinder fixed to the outer peripheral side of the metal layer. When the radius of the conveying roller is R and the radial thickness of the rubber layer is B, the relationship of B / R ≦ 0.1 is satisfied.

[0034]

[Action]

[First invention] The image on the image carrier is transferred onto a transfer material which is held and conveyed by a conveyor belt. Since it is the mark on the conveyor belt that is detected by the detection means, the surface rigidity of the conveyor belt is ensured. In addition, since there are no holes in the conveyor belt, the developer is neither scattered nor invaded.

The detection means detects the mark based on the difference in reflectance between the surface of the conveyor belt and the mark.

The detection means detects the adhesive seal.

Since the thickness of the mark is 50 μm or less,
The difference in contact pressure between the transfer material and the image carrier does not easily occur.

The light emitted from the light emitting portion of the detecting means is reflected by the mark, and the light is received by the light receiving portion to detect the mark.

The detecting means can detect that the conveyor belt has moved orthogonally to the circulating movement direction. [Second invention] Since the radius R of the conveying roller and the radial thickness B of the rubber layer have a relationship of B / R≤0.1, even if the rubber layer tries to expand when the temperature rises, the expansion is caused by the metal layer. Be detained.

[0040]

【Example】

[First Invention] (First Embodiment) Hereinafter, an embodiment of the image forming apparatus according to the present invention will be described in detail with reference to the drawings. The present invention is embodied in a color electrophotographic printer. That is, in the present embodiment, the image forming apparatus has the image forming department Pa,
Pb, Pc, and Pd are arranged, and the image forming department Pa to
A drive roller 12, a driven roller 11, and a tension roller 7b are provided below Pd. Rollers 7b, 11, 12
An endless conveyor belt 8 having a joint 80 as a joint portion is wound around the conveyor belt 8, and the conveyor belt 8 is circularly moved in the arrow direction. A registration roller 13 is arranged on the right side (paper feed side) of the conveyor belt 8.

The first, second, third, and fourth image forming stations Pa, Pb, Pc, and Pd, which are arranged side by side above the conveyor belt 8, have the photosensitive drums 1a, 1b, 1c, and 1d as image bearing members. Chargers 15a, 15b, 15c and 15d are provided on the upper left side of the respective photosensitive drums 1a, 1b, 1c and 1d.
Is provided.

Further, the photosensitive drums 1a, 1b, 1c, 1d have laser beam scanners 16a, 16b, 1 on their upper portions.
6c and 16d are provided, respectively. These laser beam scanners 16a, 16b, 16c, 16d are composed of semiconductor lasers, polygon mirrors, fθ lenses, etc., receive an input of an electric digital image signal, and charge the laser beams modulated according to the signal with the chargers 15a, 15b. , 1
5c and 15d and the developing devices 3a, 3b, 3c and 3d are formed so as to perform scanning exposure in the generatrix direction of the photosensitive drums 1a, 1b, 1c and 1d.

Further, cleaning units 5a to 5d are provided around the photosensitive drums 1a to 1d. Furthermore, the conveyor belt 8
Transfer charging units 4a to 4d are provided inside 0 in correspondence with the photosensitive drums 1a to 1d.

With the appropriate configuration, first, the first image forming department P
The laser beam 16a of a forms a cyan component color latent image on the photosensitive drum 1a based on image information.
The latent image is made into a visible image by the developer having the cyan toner in the developing section 3a. On the other hand, the recording material 6 is fed from the cassette 60, further passes through the registration roller 13 and the conveyor belt 8
The image is sent to the recording material 6 by the transfer charging portion 4a.
Is transcribed to.

While the cyan image is being transferred onto the recording material 6 as described above, a latent image of a magenta component color is formed in the second image forming section Pb, and then a magenta toner image is formed in the developing section 3b. The recording material 6 that has been transferred in the first image forming section Pa is transferred to a predetermined position in an overlapping manner.

Thereafter, the third and fourth methods are performed in the same manner as described above.
The image forming departments Pc and Pd form images of yellow and black, respectively, and the yellow and black colors are transferred onto the same recording material at a predetermined position.

When the image forming process as described above is completed, the image on the recording material 6 is fixed on the recording material by the fixing unit 7.
When a multicolor image is completed, it is discharged from the paper discharge port 14 to the outside. On the other hand, the photosensitive drums 1a, 1 which have completed the transfer
b, 1c, 1d are cleaning units 5a, 5b, 5c, 5
The residual toner is removed by d, and the toner is prepared for the subsequent latent image formation.

The above is the main sequence for forming an image, but when obtaining a high image quality by a plurality of multiple transfer steps, it is important to balance each image quality due to image density, transfer efficiency and the like. Becomes Therefore, for example, a preparatory operation such as attaching and adjusting a potential sensor to each drum or preliminarily performing static elimination and / or cleaning by driving the transfer belt is often performed. Here, this is called a pre-rotation sequence.

On the other hand, as a cleaning means for the conveyor belt 80, generally a blade system and a brush system are main. The former does not have much vibration during cleaning, so it does not affect the image unevenness even if it is in constant contact, but
There is a problem in durability such as abrasion. Further, the latter has a great influence on the image quality due to the vibration and cannot be always contacted, but the durability is much longer than that of the blade.

When the latter is selected by the printer, a post-rotation sequence is performed in which the conveying belt 80 is driven separately from the image formation after image output so that the toner adhered on the conveying belt 80 will not be fused while being left. The conveyance belt 80 is cleaned.

Here, the conveyor belt 80 is made of polyethylene terephthalate resin film sheet (PET sheet),
It is a film made of a dielectric resin such as a polyvinylidene fluoride resin film sheet or a polyurethane resin film sheet, and has an endless shape in which both ends thereof are superposed and joined as shown in FIG.

In the figure, 90 is a marking for detecting a joint position, which is attached to the inner peripheral surface of the conveyor belt 80, and 91.
Is a light reflection type sensor as a detection means. The sensor has a structure in which the light emitting part and the light receiving part are integrated. A mark is attached at a predetermined distance from the joint 84 in order to prevent the recording material 6 from engaging with the joint (joint portion) 84 of the transport belt 80, and the reflective optical sensor 91 rotates the marking 90. It is placed on orbit.

When the marking 90 moves along with the circulating movement of the conveyor belt and reaches the position where the reflection type optical sensor 91 is installed, the reflectance between the marking 90 and the inner peripheral surface of the conveyor belt 80. The marking 90 is detected by the difference of At this time, since the distance between the position of the marking 90 and the position of the seam 84 is known in advance, the position of the seam 84 on the conveyor belt is calculated.

From this result, the timing of sending the recording material 6 to the conveyor belt 80 is determined, and the paper feed sequence is adjusted by the timing signal created thereby. Therefore, the recording material 6 is not held on the seam 84, the contact between the photosensitive drums 1a to 1d and the recording material 6 is maintained constant, and a high quality transferred image is obtained.

Since the marking 90 is attached to the conveyor belt 80, the rigidity of the conveyor belt 80 in the surface direction is secured. Therefore, stress concentration does not occur even if a tensile load is applied due to cyclic movement, and a stable transport function can be maintained. Further, since the form of the conveyor belt 80 does not change, the detection accuracy can be maintained and the image quality can be kept good.

Further, since the marking 90 is affixed to the marking 90, the developer does not pass through the marking 90 and scatter, or enter between the conveyor belt 80 and the rollers 11, 12, 7b. Therefore, the dirt on the periphery and the circulating movement performance of the conveyor belt 80 can be maintained.

The attached marking 90 is
It is adhered with sufficient strength so as not to be scraped off even by rubbing by the conveyor belt cleaner, the driving roller 12, the driven roller 11 and the like.

The thickness of the marking 90 in the embodiment is 50 μm.
It is about m. When the marking 90 is engaged with the drive roller 12 and the driven roller 11, the state is similar to the case where a foreign matter is locally sandwiched between the conveyor belt 80 and the rollers 11 and 12, and when the conveyor belt 80 rotates, it becomes minute. Generate a shock. This shock may cause uneven rotation of the conveyor belt 80 and may appear as uneven transfer images on the image.
If the image unevenness due to this shock cannot be discerned by human eyes, there is no problem in practical use. If the thickness of the marking 90 is 50 μm or less, the above condition is satisfied regardless of the material and thickness of the conveyor belt. It will be.

FIG. 3 shows the sectional shape of the marking 90. In the figure, 100 is an adhesive layer, 101 is a light reflection layer,
102 is a transparent protective film layer. The light-reflecting layer 101 has a reflectance sufficient to be distinguished from the surface of the conveyor belt 80, and the transparent protective film layer 102 is specifically PE.
For example, T film. This transparent protective film layer 102
Is provided to prevent stains such as toner from stains and scratches on the light reflection layer 101. (Second Embodiment) As a marking method for detecting the seam position, a marking method as shown in FIG. 4 was devised.

In FIG. 4, 90 'is a marking,
The marking 90 'is formed in a band shape with a predetermined width along the circulation direction. Reference numeral 92 is a blank portion where the marking 90 'is missing, that is, a non-marking surface. Blank area 92
Needless to say, it is the material surface itself of the conveyor belt, and the seam detection sequence is the same as that of the first embodiment up to detection by the difference in reflectance between the marking 90 'and the non-marking surface 92.

In this embodiment, when the conveyor belt 80 rotates, the conveyor belt 80 is inclined in the direction orthogonal to the circulation, that is, in the roller thrust direction (arrow A) due to an accident such as the inclination of the driving roller. The belt position is detected by using the seam position detecting means.

When the deviation of the conveyor belt 80 occurs as described above, it is conceivable that the end of the conveyor belt 80 will eventually come into contact with the structural body of the apparatus main body 10 and be destroyed if the condition remains as it is. For this reason, in the embodiment, by forming a sequence in which an error code is generated and the apparatus is stopped when the sensor 91 cannot detect the marking 90 ′ for a certain period of time or longer,
Even in an emergency, the conveyor belt 80 and other parts can be prevented from being destroyed. Here, the blank portion 92 is usually for a certain period of time.
It is necessary to set the time longer than the detection time.

By adopting the above-mentioned structure, the position detection of the joint 84 of the conveyor belt 80 and the deviation detection of the conveyor belt 80 can be performed by the same detecting means in terms of hardware. [Second Invention] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 5 is a schematic sectional view of the present invention applied to an electrophotographic color printer. In this embodiment, first, second, third and fourth image stations Pa, Pb, Pc and Pd are provided in the printer body 110.
However, the present invention can be applied to an image forming apparatus including an arbitrary number of image stations larger than that.

A paper feed mechanism 113 is provided on one side of the main body 110, that is, on the right side in the figure, and a transfer material discharge port 114 is provided on the opposite side, that is, on the left side in the figure. A fixing device 107 is arranged inside the discharge port 114 adjacent to the discharge port 114.

In addition, the paper feeding mechanism 113 in the main body 110.
On the lower side of the path from the fixing device 107 to the fixing device 107, there is provided a driven roller means as a conveying roller, that is, an idler roller 12, in the vicinity of the paper feeding mechanism 113. Further, driving side roller means as a conveying roller, that is, a driving roller 111 is provided in the vicinity of the fixing device 107, and an endless conveying belt 108 is stretched around outer circumferences of the rollers 111 and 112.

Below the drive roller 111,
From the inner peripheral side of the conveyor belt 108, the conveyor belt 10
8, an adjusting roller 176 is provided which abuts on the belt 8 and freely adjusts the tensile force of the conveyor belt 108.

On the other hand, above the path from the idler roller 112 to the drive roller 111, the conveyor belt 1
08, the first, second, third, and fourth image forming units Pa, Pb, and Pc in order from the side of the paper feed mechanism 113.
And Pd are arranged in parallel.

The conveying belt 108 is driven by a driving roller 111 in a direction indicated by an arrow by frictional force to circulate, and carries the transfer material 106 as a recording material fed through the paper feeding mechanism 113. The image is sequentially conveyed below the image stations Pa, Pb, Pc, and Pd.

The paper feed mechanism 113 has a paper feed cassette 151 which is detachable from the main body 110, and a rotatable paper feed roller 152 which is provided at a mounting portion of the main body 110 where the paper feed cassette 151 is attached. The paper feed mechanism 113 includes a paper feed guide 153 for guiding the transfer material 106 fed into the main body 110 by the paper feed roller 152.
It has a registration roller pair 180 that receives the transfer material 106 guided by 53 and sends it to the idler roller 112 side at a predetermined timing.

Further, the paper feeding mechanism 113 is composed of a sensor (not shown) which outputs a predetermined signal when the leading end of the transfer material 106 moving in the paper feeding guide 153 is detected.

The paper feeding mechanism 113 carries out the function of placing the transfer material 106 on the conveyor belt 108 from the idler roller 112 side. The fixing device 107 receives the transfer material 106 fed from the drive roller 111 side, and collectively fixes the visible images transferred and superposed on the transfer material 106 at each of the image stations Pa, Pb, Pc, and Pd to form a permanent image. Is formed. The transfer material discharge port 114 has a main body 11 of the copying machine.
A paper discharge tray 117 that is detachable with respect to 0 is mounted.

The image stations Pa, Pb, Pc, and Pd have substantially the same structure, and the photoconductor drums 101a and 101 are driven to rotate in the direction of the arrow shown in the drawing as usual.
b, 101c and 101d. A charger 1 for uniformly charging the photoconductor drums is provided around each photoconductor drum.
15a, 115b, 115c and 115d, a developing device 103a for developing the electrostatic latent image formed on the photosensitive drum,
It has 103b, 103c and 103d.

Further, transfer material dischargers 104a, 104b, 104c for transferring the developed visible image to the transfer material 106.
And 104d, and cleaning means 105a, 105b, 105c and 105d for removing the toner remaining on the photosensitive drum are sequentially arranged in the drum rotating direction. Further, the imaging lenses 117a, 117b, 1 are provided above the respective photosensitive drums 101a, 101b, 101c and 101d.
17c and 117d and laser beam scanner 116
a, 116b, 116c and 116d are provided respectively.

The developing device 103a contains magenta toner, the developing device 103b contains cyan toner, the developing device 103c contains yellow toner, and the developing device 103d contains black toner. There is.

The laser beam scanners 116a, 11
Reference numerals 6b, 116c and 116d each include a semiconductor laser, a polygon mirror, an fθ lens, etc., and receive the input of an electric digital pixel signal to generate a laser beam modulated corresponding to the signal, respectively, and form the imaging lenses 117a, 117, respectively.
b, 117c and 117d through the charger 115
a, 115b, 115c and 115d and the developing device 103
The drum surface is exposed by scanning in the drum generatrix direction between a, 103b, 103c and 103d.

The laser beam scanner 116a corresponds to a pixel signal corresponding to a magenta component image of a color image, the laser beam scanner 116b corresponds to a pixel signal corresponding to a cyan component image, and the laser beam scanner 116c corresponds to a yellow component image. The pixel signal and the pixel signal corresponding to the black component image are input to the laser beam scanner 116d, respectively.

Further, a suction charger (not shown) is provided between the first image station Pa and the sheet feeding mechanism 113, and the suction charger is supplied from the sheet feeding mechanism 113. Corona discharge is performed in order to surely attract the transfer material 106 to the conveyor belt 108.

On the other hand, between the fourth image station Pd and the fixing device 107, a static eliminator (not shown) is provided almost directly above the drive roller 111, and this static eliminator is attached to the conveyor belt 108. An AC voltage is applied to separate the attracted transfer material 106.

In the color printer having the above structure, a cut sheet-like material is used as the transfer material 106 as shown in the drawing, and the transfer material 106 is sent out from the paper feed cassette 151 and is fed into the paper feed guide 153 of the paper feed mechanism 113. To move.

Then, the tip portion is detected by the sensor (not shown), and the detection signals output from the sensor detect the photosensitive drums 101a, 101b, 101c and 101 of the image stations Pa, Pb, Pc and Pd.
d starts rotating. The drive roller 111 is also driven at the same time, and the conveyor belt 108 is circularly moved in the direction of the arrow in FIG.

When the transfer material 106 is guided by the paper feed guide 153 and placed on the conveyor belt 108, it receives corona discharge from the adsorption charger (not shown) and is reliably adsorbed on the conveyor belt 108.

Further, the photosensitive drum 10 is driven at a predetermined timing with the driving timing of the registration roller pair 180 as a base point.
The image forming process for 1a, 101b, 101c and 101d is sequentially started.

That is, a magenta image is formed on the photosensitive drum 101a of the first image station Pa, a cyan image is formed on the photosensitive drum 101b of the second image station Pb, and a photosensitive drum 101 of the third image station Pc is formed.
A yellow image is formed on c and a black image is formed on the photosensitive drum 101d of the fourth image station Pd.

These image stations Pa, Pb, Pc
Since the principle of image formation in Pd and Pd is already well known as the Carlson process, its explanation is omitted.

The transfer material 1 is moved by the movement of the conveyor belt 108.
06 sequentially passes under the photosensitive drums 101a to 101d of the first to fourth image stations Pa to Pd and is conveyed toward the fixing device 107, and the transfer discharge devices 104a and 104b of the image stations are transferred. 104c and 104
By d, the visible images of the respective colors formed in the respective image forming portions are sequentially superposed and transferred on the transfer material 106 to synthesize the color image.

After the transfer material 106 passes through the fourth image station Pd, the transfer material 106 is discharged by the static eliminator (not shown) to which an AC voltage is applied, and is separated from the conveyor belt 108. The transfer material 106 separated from the transport belt 108 is sent to the fixing device 107, and after the visible image transferred in the fixing device 107 is fixed, the transfer material 106 is discharged from the transfer material discharge port 114 to the paper discharge tray 117, thus. One image forming cycle is completed.

FIG. 6 is a detailed view of the drive unit of the conveyor belt 108. The drive roller 111 is fixed to the rotary shaft 200, and both ends of the rotary shaft 200 are connected to the frame 2 of the main body 110.
It is held by the bearing 202 provided in No. 01. A belt pulley 203 is fixed to one end of the rotary shaft 200.

On the other hand, a belt pulley 206 is fixed to the drive shaft 205 of the stepping motor 204, and a timing belt 207 is wound around the belt pulleys 203 and 206. The stepping motor 204 is connected to the pulse oscillation source 210 via the stepping motor drive circuit 208 and the stepping motor control circuit 209.

The driving force of the stepping motor 204 is transmitted to the belt pulley 203 via the belt pulley 206 and the timing belt 207, and the driving roller 111 rotates at a constant speed.

FIG. 7 shows the structure of the driving roller 111 according to the present invention. The hollow metal rotary shaft 200 was press-fitted into both ends of the cylindrical metal layer 211, and the thin rubber layer 212 was fixed to the outer periphery of the metal layer 211 with a uniform thickness. Between the roller radius R and the thickness B of the rubber layer 212, B / R ≦ 0.1
The relationship is established. Further, the rubber layer 212 and the metal layer 21
1 is adhered and joined by vulcanization molding or the like via the boundary surface a.

FIG. 8A is a schematic diagram of the drive roller 111, and FIG. 8B is a ratio B / R of the rubber thickness B and the roller radius R.
And the linear expansion coefficient α ₁ of the driving roller 111. The applicant has experimentally found that it is possible to realize α ₁ ≈α ₂ (where α _G is the linear expansion coefficient of the rubber material).

That is, as shown in FIG. 9B, when the rubber thickness B exceeds a certain thickness (point Y), the linear expansion coefficient α ₁ of the driving roller 111 is controlled by that of the rubber material, and α ₁ ≈α _G. . However, when the thickness (X point) or less is reached to some extent, the rubber layer thickness B tries to expand when the temperature rises, but the boundary a is fixed to the metal layer 211 and is constrained, and the expansion decreases. Therefore, the linear expansion coefficient α ₁ of the drive roller 111 approaches the linear expansion coefficient α ₂ of the metal layer 211, and α ₁ ≈α ₂ . Then, it was discovered that this inflection point is B / R≈0.1, which is similar to the condition of the boundary between a thin cylinder and a thick cylinder in material mechanics.

Here, the temperature rise of the in-machine temperature is expressed as ΔT [de
g], the interval between the image stations Pa to Pd is L [m
m], the linear expansion coefficient of the drive roller 111 is α ₁ , and the linear expansion coefficient of the support member of each image station is α ₂ , the image shift occurring in the moving direction of the transport belt 108, that is, the top margin shift Δl is It is expressed by the following equation.

Δl [mm] = ΔT · L (α ₁ −α ₂ ) In the present embodiment, α ₁ ≉α by configuring as described above.
_{Since the value of 2} is realized, the linear expansion coefficient of the drive roller 111 can be approximated to that of a single metal material as a whole, and the expansion of the drive roller 111 due to temperature rise can be suppressed.

As a result, the circulating speed of the conveyor belt 108 can be maintained constant, the image formed by each of the image stations Pa to Pd is accurately transferred to the proper position on the transfer material 106, and the image quality is improved. To do.

The present invention is an inkjet printer,
It can also be applied to copiers.

[0097]

【The invention's effect】

[First Invention] Since the conveyor belt is marked, the rigidity of the conveyor belt in the surface direction is ensured. Therefore,
Even if a tensile load is applied by circulation movement, stress concentration does not occur and a stable transfer function can be maintained. Further, since the form of the conveyor belt does not change, the detection accuracy can be maintained and the image quality can be kept good.

Further, since the mark is a mark, the developer does not pass through and scatter from the mark or penetrate into the inside of the conveyor belt. Therefore, it is possible to maintain the surrounding dirt and the circulating movement performance of the conveyor belt.

Further, since it is possible to detect the movement of the conveyor belt in the direction perpendicular to the circulation direction, it is possible to prevent defective movement and deterioration of image quality. [Second Invention] Even if the rubber layer expands when the temperature rises, the expansion is restrained by the metal layer.

As a result, the circulating speed of the conveyor belt can be maintained constant, the image formed by the image station is transferred to a proper position on the recording material with high accuracy, and the image quality is improved.

[Brief description of drawings]

FIG. 1 is a front sectional view of a first embodiment in which the first invention is applied to an electrophotographic color printer.

FIG. 2 is a perspective view of the conveyor belt of FIG.

FIG. 3 is a cross-sectional view of markings attached to the conveyor belt of FIG.

FIG. 4 is a perspective view of a conveyor belt according to a second embodiment of the first invention.

FIG. 5 is a front sectional view of an electrophotographic printer to which the second invention is applied.

6 is a configuration diagram showing a drive system of a drive roller used in FIG.

FIG. 7A is a front view of the drive roller used in FIG.
FIG. 6B is a partial cross-sectional view of the drive roller.

FIG. 8A is a schematic front view of the drive roller of the second invention, and FIG. 8B is a graph showing the relationship between the rubber thickness / radius ratio of the drive roller and the linear expansion coefficient.

FIG. 9 is a sectional view of a color printer of a first conventional example.

10 is a perspective view of the conveyor belt of FIG.

FIG. 11 is a plan view showing an image shift on a transfer material in a conventional example.

[Explanation of symbols]

 1a to 1d Photosensitive drum (image bearing member) 6 Recording material (transfer material) 80 Conveying belt 90, 90 'Marking (mark) 91 Sensor (detecting means) 100 Adhesive layer 101 Light reflection layer 102 Transparent protective film Pa to Pd Image station 108 conveyor belt 111 driving roller (conveying roller) 211 metal layer 212 rubber layer R radius of driving roller B thickness of rubber layer

Claims (7)

[Claims] 1. An image carrier for holding an image formed by a developer and a conveyor belt for holding a transfer material on which an image is transferred are arranged in close proximity to each other, and the conveyor belt is endlessly formed by joining both ends. In the image forming apparatus configured to circulate and transfer the transfer material, the transfer belt is provided with a mark corresponding to the joining portion, and a detection means for detecting the mark is provided near the transfer belt. An image forming apparatus characterized by the above. 2. The image forming apparatus according to claim 1, wherein the mark has a structure having a reflectance different from that of the surface of the conveyor belt, and the detecting unit has a structure for optically detecting the mark. 3. The image forming apparatus according to claim 1, wherein the mark is an adhesive sticker attached to the surface of the conveyor belt. 4. The mark has an adhesive layer and a light reflection layer, the surface of the light reflection layer is covered with a transparent protective film, and the thickness of the mark is set to 50 μm or less. 3. The image forming apparatus according to item 3. 5. The image forming apparatus according to claim 2, wherein the detecting means is a reflective sensor having a light emitting portion and a light receiving portion, and is configured to detect the mark based on the amount of reflected light. 6. The image forming apparatus according to claim 1, wherein the detection unit has a configuration capable of detecting that the conveyor belt has moved in a direction orthogonal to the circulating movement direction. apparatus. 7. A plurality of image stations arranged to form a plurality of images and an endless conveyor belt holding a recording material to which the plurality of images are transferred are arranged in proximity to each other,
In an image forming apparatus provided with a plurality of transport rollers around which the transport belt is wound so as to circulate the transport belt along the arrangement direction of a plurality of image stations, the transport roller comprises a metal layer and an outer periphery of the metal layer. And a cylindrical rubber layer adhered to the side, where the radius of the conveying roller is R and the radial thickness of the rubber layer is B, the relationship of B / R ≦ 0.1 is satisfied. Image forming apparatus.