JPH1026887A - Color image recorder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color image recorder capable of eliminating, with a simple structure, various troubles which are caused by heat acting on a transfer means, and capable of steadily obtaining a color image of high quality while preventing color slippage and unsatisfactory transfer. SOLUTION: In the color image recorder, the drive roller 11 of a transfer device 10 is disposed on the upstream side in the direction where recording paper (recording medium) P is carried, the rotation torque of the drive roller 11 is transmitted to a follower roller 12 via a torque limiter which causes a slip with a specific rotation torque, and also the speed at which the follower roller 12 carries a belt is set higher than that of the drive roller 11. Thus, because proper tension is applied to the side of the transfer belt 14 on which the recording paper P is carried and transferred (downstream from the drive roller 11), and it is restrained from slacking, the occurrence of unsatisfactory transfer due to slack in the transfer belt 14 is securely prevented. Further, because the drive roller 11 can be disposed apart from a fixing unit 17 being a heating source, color slippage of an image due to the heat expansion of the drive roller 11 can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image recording apparatus provided with a plurality of image forming units and for sequentially recording images in different colors on a recording medium.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional color image recording apparatus. The color image recording apparatus has four image forming units I, II, and
III, IV are arranged in parallel. Each of the image forming units I to IV includes a photosensitive drum 1Y, 1M, 1C, 1BK as an image carrier, and primary charging rollers 2Y, 2M, 2C, 2 as a primary charger.
BK, exposure units 3Y, 3M, 3C, 3BK, developing units 4Y,
4M, 4C, 4BK and cleaners 5Y, 5M, 5C, 5
BK is included. The developing units 4Y, 4M,
4C and 4BK contain yellow (Y), magenta (M), cyan (C), and black (BK) toners, respectively.

A transfer device 10 is provided below the image forming units I to IV. The transfer device 10 is an endless tension member stretched between a driving roller 11, a driven roller 12, and a tension roller 13. And a transfer charger 15 disposed opposite to the photosensitive drums 1Y, 1M, 1C, and 1BK of the image forming units I to IV.

On the other hand, a cassette 6 comprising a plurality of recording papers P stacked and stored as recording media is installed at the bottom of the apparatus main body 20. The recording papers P in the cassette 6 are fed by paper feed rollers 7. , And are conveyed to registration rollers 9 via a conveyance guide 8.

A separating charger 16 and a fixing device 17 are disposed on the downstream side (the left end side in FIG. 3) of the recording paper P in the apparatus main body 20 in the conveying direction. A paper output tray 18 is attached.

In each of the image forming units I to IV,
The photosensitive drums 1Y, 1M, 1C, and 1BK are rotationally driven at a predetermined speed in the direction of the arrow shown in the figure.
Each of Y, 2M, 2C, and 2BK is uniformly charged. Each photosensitive drum 1 thus charged is processed.
When exposure corresponding to image information is performed on Y, 1M, 1C, and 1BK by the exposure units 3Y, 3M, 3C, and 3BK, an electrostatic latent image is formed on each of the photosensitive drums 1Y, 1M, 1C, and 1BK. , Each electrostatic latent image is stored in each of the developing devices 4Y, 4M, 4
The toner image is developed by C, 4BK and visualized as a yellow toner image, a magenta toner image, a cyan toner image, and a black toner image, respectively.

On the other hand, as described above, the recording paper P conveyed from the cassette 6 through the conveyance guide 8 to the registration rollers 9
Is sent to the transfer device 10 at a timing adjusted by the registration roller 9, is attracted to the transfer belt 14 of the transfer device 10, and moves with the transfer belt 14 to move each image forming unit I.
To IV, the transfer paper P is transferred to the recording paper P in the process.
By the operation of 5, the yellow toner image, the magenta toner image, the cyan toner image, and the black toner image are transferred in an overlapping manner.

The recording paper P, to which the respective color toner images have been transferred as described above, is neutralized by the separation charger 16 and separated from the transfer belt 14, and then conveyed to the fixing device 17 to be transferred to the color fixing device 17. After the toner image is heated and fixed, the toner image is finally discharged from the apparatus main body 20 and stacked on the discharge tray 18.

[0009]

In recent years, there has been a demand for such a color image recording apparatus to be miniaturized. If the conventional color image recording apparatus shown in FIG. The distance between the fixing device 17 and the fixing device 17 is reduced, and the transfer device 10 approaches the fixing device 17 which is a heat source.
Then, the heat from the fixing device 17 causes the temperature of the drive roller 11 of the transfer device 10 to rise and thermally expand, and the diameter of the drive roller 11 increases, so that the moving speed of the transfer belt 14 increases as the temperature rises.
As a result, color shift occurs in the image.

The driving roller 11 is connected to the transfer belt 14.
In general, a rubber layer of a high friction member is coated on a metal roller so that the sheet can be transported without slippage. The linear expansion coefficient of iron is 1.2 × 10 ⁻⁵ / ° C., whereas the linear expansion coefficient of rubber is usually 2.0 × 10 ^-5 / ° C.
^-4 / ° C., and when the drive roller 11 has a rubber layer, the amount of thermal expansion thereof is large, and therefore the amount of color misregistration of the image is also large.

To solve such a problem, a method of using the drive roller after cooling it or heating it to a predetermined temperature is used. The temperature around the drive roller or the speed of the transfer belt is monitored, and the rotation speed is variably controlled. A method has been proposed.

However, the above method increases noise, increases the complexity and size of the device, and increases power consumption. Further, in the above method, since a minute speed is controlled, an expensive detector and a driving system are required.

Furthermore, in both methods, if there is a non-uniform temperature in the axial direction of the drive roller, it is extremely difficult to detect and control this. When the temperature of the drive roller is non-uniform, the outer diameter of the drive roller is non-uniform in the axial direction, which causes the transfer belt to drop off in the axial direction, to cause wrinkles and twists, and to cause image defects. Not only color misregistration but also transfer failure (transfer unevenness) occurs.

On the other hand, it has been proposed to dispose the driving roller on the sheet feeding section remote from the fixing device as a heat source.

However, in the above proposal, the transfer surface is on the loose side of the transfer belt, so that the recording paper transport surface becomes unstable. Further, when a contact type transfer charger that does not generate high-pressure discharge products (O ₃ , NO _x ) or the like is used, for example, a conductive brush, a blade, or a roller-type charger that is in contact with a roller, these chargers are transferred. As a brake against the movement of the belt, the transfer belt is slackened between the image forming units, which causes transfer failure or the recording paper transport path length fluctuates between the image forming units. Color shift occurs.

If a large tension is applied to the transfer belt in order to solve the above problem, the slack of the transfer belt can be reduced, but the life of the transfer belt is extremely shortened.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to solve various problems caused by heat acting on a transfer means with a simple structure and to reduce color misregistration and transfer defects. It is an object of the present invention to provide a color image recording apparatus which can stably obtain a high-quality color image while preventing the color image.

[0018]

According to a first aspect of the present invention, there is provided an image forming apparatus comprising: a plurality of image forming units for recording different colors; A transfer unit including a transfer belt and a transfer charger, and a color image recording apparatus that forms a color image by sequentially superimposing colors on a recording medium introduced into the transfer unit. Arranged on the upstream side in the transport direction of the medium, the rotational torque of the drive roller is transmitted to the driven roller via a torque limiter that generates a slip at a predetermined rotational torque, and the belt transport speed of the driven roller is set to that of the drive roller. It is characterized in that it is set to be larger than.

According to a second aspect of the present invention, in the first aspect of the invention, the predetermined rotational torque is a value at which a slip occurs in the torque limiter before a slip occurs between the transfer belt and the driven roller. The transfer belt is set to a value greater than the resistance of the transfer belt to the moving load of the transfer belt.

According to a third aspect of the present invention, in the first or second aspect of the present invention, a pitch circular linear velocity of the driven roller is set to be higher than that of the driven roller.

According to a fourth aspect of the present invention, in the first, second or third aspect, the driven roller is made of a metal having a high thermal conductivity.

According to a fifth aspect of the present invention, in the first to third or fourth aspects of the present invention, the transfer charger is a contact type.

According to a sixth aspect of the present invention, in the first to fourth or fifth aspects of the present invention, the primary charger included in each of the image forming sections is of a contact type.

According to a seventh aspect of the present invention, in each of the first to sixth or seventh aspects, each of the image forming sections includes a digital optical system.

Therefore, according to the first, second or third aspect of the present invention, a speed higher than the belt conveying speed of the driving roller is transmitted to the driven roller via the torque limiter.
Appropriate tension is applied to the side of the transfer belt on which the recording medium is conveyed and transferred (downstream side of the drive roller) to suppress the slack, and the occurrence of transfer failure due to the slack of the transfer belt is reliably prevented. . Further, since the drive roller that controls the moving speed of the transfer belt can be disposed on the side that is not affected by heat away from the heat source, it is possible to prevent color shift of an image due to thermal expansion of the drive roller. As a result, a high-quality color image can be stably obtained.

According to the fourth aspect of the present invention, the driven roller is made of a metal having a high thermal conductivity, thereby preventing the temperature of the driven roller from becoming non-uniform in the axial direction and reducing the displacement of the driven roller. Since the amount is the same in the entire area in the axial direction, it is possible to prevent the transfer belt from shifting, wrinkling or twisting.

According to the fifth or sixth aspect of the present invention, since the transfer type charger and the primary type charger are of the contact type which can be used at a low voltage, the capacity and size of the high voltage power supply can be reduced to reduce cost and consumption. The power can be reduced and the generation of discharge products can be prevented.

According to the invention of claim 7, according to claim 1,
In addition to the effect of the invention described in the item 2 or 3, an effect of preventing occurrence of image pitch unevenness is obtained.

[0029]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a sectional view showing a schematic configuration of a color image recording apparatus according to the present invention. The color image recording apparatus has four image forming units I and II, III, IV
Each of the image forming units I to IV includes a photosensitive drum 1Y, 1M, 1C, 1B as an image carrier that is driven to rotate in the direction of the arrow shown in the figure.
K, charging rollers 2Y and 2 which are primary chargers for uniformly charging each of the photosensitive drums 1Y, 1M, 1C and 1BK.
M, 2C, 2BK, each photosensitive drum 1Y, 1M, 1C, 1
Exposure sections 3Y, 3M, 3 for forming a latent image on BK
C, 3BK, developing units 4Y, 4M, 4C, 4BK for developing the latent image and visualizing the latent image, and collecting the transfer residual toner remaining on the photosensitive drums 1Y, 1M, 1C, 1BK after the transfer. And cleaners 5Y, 5M, 5C, and 5BK. Each of the developing units 4Y, 4M, 4
C and 4BK contain yellow (Y), magenta (M), cyan (C), and black (BK) toners, respectively.

A transfer device 10 is provided below the image forming units I to IV. The transfer device 10 includes a drive roller 11 disposed on the upstream side in the recording paper conveyance direction (the right side in FIG. 1). And a driven roller 12 disposed on the downstream side (left side in FIG. 1)
And an endless transfer belt 14 stretched between the tension rollers 13 and the photosensitive drum units 1Y, 1M, 1C, 1B of the image forming units I to IV inside the transfer belt 14.
Conductive rubber blades 1 abutting against K
5a, and includes a contact-type transfer charger 15. The transfer belt 14 includes a tension roller 13.
A predetermined tension is applied by the

On the other hand, a cassette 6 having a plurality of recording papers P stacked and housed as recording media is installed at the bottom of the apparatus main body 20. Are transported one by one, and are transported by a transport roller 7 to a registration roller 9 via a transport guide 8.

A separating charger 16 and a fixing device 17 are provided on the downstream side (the left end side in FIG. 1) of the apparatus body 20 in the recording paper conveying direction. A tray 18 is attached.

In each of the image forming units I to IV,
The photosensitive drums 1Y, 1M, 1C, and 1BK are rotationally driven at a predetermined speed in the direction of the arrow shown in the figure.
Each of Y, 1M, 1C, and 1BK is uniformly charged. Each photosensitive drum 1 thus charged is processed.
When exposure corresponding to image information is performed on Y, 1M, 1C, and 1BK by exposure units 3Y, 3M, 3C, and 3BK, an electrostatic latent image is formed on each of photosensitive drums 1Y, 1M, 1C, and 1BK. Each of the electrostatic latent images is supplied to each of the developing devices 4Y and 4Y.
The toner image is developed by M, 4C, and 4BK and visualized as a yellow toner image, a magenta toner image, a cyan toner image, and a black toner image, respectively.

On the other hand, as described above, the recording paper P conveyed from the cassette 6 through the conveyance guide 8 to the registration rollers 9
Is sent to the transfer device 10 at a timing adjusted by the registration roller 9, is attracted to the transfer belt 14, moves with the transfer belt 14, and passes through each of the image forming units I to IV. By the operation of the transfer charger 15, the yellow toner image, the magenta toner image, the cyan toner image, and the black toner image are transferred in an overlapping manner.

The recording paper P to which each color toner image has been transferred as described above is discharged by the separation charger 16 and separated from the transfer belt 14, and then conveyed to the fixing device 17 to heat the color toner image. After fixing, finally the main body 2
0 and is stacked on the paper discharge tray 18.

Next, the transfer belt 14 of the transfer device 10
Will be described with reference to FIG. FIG. 2 is a plan view showing a part of the transfer belt driving mechanism cut away.

As described above, the transfer belt 14 is composed of the driving roller 11, the driven roller 12, and the tension roller 13 (FIG. 1).
2) and transported in the direction of the arrow in FIG.
Here, the driving roller 11 and the driven roller 12 are rotatably supported by the transfer frame 21 via bearings 22 and 23, respectively.

The driving roller 11 is formed by coating a rubber layer of a high friction member on a metal roller.
The transfer belt 14 is moved by friction transmission. One end of the drive roller 11 is provided with a large-diameter drive pulley 2.
4 is coupled to a large-diameter gear 25 formed on the drive pulley 24, and a small-diameter gear 27 coupled to an output shaft end of a drive motor 26, which is a driving source, meshes with the large-diameter gear 25.

On the other hand, a small-diameter driven pulley 28 and a torque limiter 30 that slips at a predetermined rotational torque are provided at one end of the driven roller 12, and an endless shape is provided between the driven pulley 28 and the driving pulley 24. Timing belt 2
9 are wound. The number of teeth of the driving pulley 24 and the number of teeth of the driven pulley 28 are set so that the number of teeth of the driven roller 12 is larger than that of the driven roller 11.

When the drive motor 26 is driven, the rotation of the output shaft is transmitted to the drive roller 11 via the gears 27 and 25, and the drive pulley 24, the timing belt 29, the driven pulley 28, Torque limiter 3
Then, the transfer roller 14 is transmitted to the driven roller 12 through the drive roller 21, and the driving roller 21 and the driven roller 12 are rotated and the transfer belt 14 stretched over these is transported in the direction of the arrow in FIG. Therefore, the moving speed of the transfer belt 14 is controlled by the driving roller 11.

In the present embodiment, the driven pulley 28 is rotatably supported by the driven roller 12, and the torque limiter 30 is
31 and the input roller 31 and the driven roller 1
2 is constituted by a coil spring 32 contracted between them. The torque limiter 30 is connected to the driven pulley 2
The rotation torque less than a predetermined value input to the driven roller 1
2 is transmitted to the driven roller 12 by a frictional force generated on a contact surface between the input spring 31 and the coil spring 32, and when a rotation torque larger than a predetermined value is input to the driven pulley 28, the gap between the coil spring 32 and the input spring 31 is increased. , The transmission of the rotational torque to the driven roller 12 is interrupted. still,
The predetermined value of the rotation torque is a value that does not damage the transfer belt 14, and the transfer belt 14 and the transfer charger 1
5 is larger than the frictional force with the transfer blade 15a (the moving load resistance of the transfer belt 14).

Thus, as shown in FIG.
When the transfer belt 14 is disposed on the paper feed side, the transfer belt 14 generally has the slack side on the downstream side of the drive roller 11, but in the present embodiment, the pitch circle of the drive roller 11 is interposed via the torque limiter 30. Since the linear speed greater than the speed is transmitted to the driven roller 12, an appropriate tension is applied to the side of the transfer belt 14 that conveys and transfers the recording sheet P (downstream side of the drive roller 11), and the slack is suppressed. In addition, the occurrence of transfer failure due to the slack of the transfer belt 14 is reliably prevented.
The exposure units 3Y, 3M, 3C, and 3 of the image forming units I to IV
When the BK is constituted by a digital optical system, the occurrence of image pitch unevenness is prevented.

Further, since the driving roller 11 which controls the moving speed of the transfer belt 14 can be disposed on the sheet feeding side which is not affected by heat and is away from the fixing device 17 which is a heat source, the driving roller 11 Color shift of the image due to thermal expansion can also be prevented, and a high-quality color image can be stably obtained.

In the present embodiment, the driven roller 12 approaches the fixing device 7 which is a heat source. However, since the driven roller 12 is not a roller that controls the moving speed of the transfer belt 14, the driven roller 12 Even if the outer diameter of the driven roller 12 increases due to expansion, this does not adversely affect the image. Here, if the driven roller 12 is made of a metal having a high thermal conductivity, uneven heating in the axial direction of the driven roller 12 is prevented, and the displacement of the driven roller 12 is the same in the entire axial direction. Therefore, the occurrence of wrinkling, twisting, or the like of the transfer belt 14 can be prevented.

The peripheral length of the drive roller 11 (strictly speaking, the feed pitch of the transfer belt 14) is adjusted so that even if the speed of the drive roller 11 fluctuates in one rotation cycle, color shift does not occur in the image as a result. Circumferential length) is set to be equal to an adjacent pitch length of the photosensitive drums 1Y, 1M, 1C, 1BK of each of the image forming units I to IV, or set to be an integer ratio. In the present embodiment, the circumference of the drive roller 11 is set to each of the image forming units I to IV
Of the adjacent photosensitive drums 1Y, 1M, 1C, 1BK.

On the other hand, since the driven roller 12 is not a roller that governs the moving speed of the transfer belt 14 as described above, its outer diameter can be arbitrarily selected. For example, when the diameter of the driven roller 12 is reduced, the curvature separation using the stiffness (rigidity) of the recording paper P can be performed without depending on the separation charger using the normal corona discharge. The corona charger used for separating the recording paper P requires a power supply in which an AC high voltage of about 10 kV is superimposed on a DC voltage, but this power supply can be eliminated.

Further, as shown in FIG.
IV, each photosensitive drum 1Y, 1M, 1C, 1BK
Rollers 2Y, 2M, 2C,
Since a contact charging type that can be used at a low voltage is used as the 2BK2 and the transfer charger 15, the capacity and size of the high-voltage power supply can be reduced to reduce cost and power consumption, and to generate discharge. The generation of things can be prevented.

[0049]

As is apparent from the above description, according to the first, second or third aspect of the present invention, a speed higher than the belt conveying speed of the driving roller is transmitted to the driven roller via the torque limiter. In addition, appropriate tension is applied to the side of the transfer belt on which the recording medium is conveyed and transferred (downstream of the drive roller), and the slack is suppressed, and the occurrence of transfer failure due to the slack of the transfer belt is reliably prevented. It is. Further, since the drive roller that controls the moving speed of the transfer belt can be disposed on the side that is not affected by heat away from the heat source, it is possible to prevent color shift of an image due to thermal expansion of the drive roller. As a result, it is possible to stably obtain a high-quality color image.

According to the fourth aspect of the present invention, the driven roller is made of a metal having a high thermal conductivity, thereby preventing the temperature of the driven roller from increasing non-uniformly in the axial direction and reducing the displacement of the driven roller. Since the amount is the same in the entire area in the axial direction, the transfer belt can be prevented from wrinkling or twisting.

According to the fifth or sixth aspect of the present invention, since the transfer type charger and the primary type charger are of the contact type which can be used at a low voltage, the capacity and size of the high voltage power supply can be reduced to reduce cost and consumption. It is possible to obtain an effect that power can be reduced and generation of a discharge product can be prevented.

According to the invention of claim 7, according to claim 1,
In addition to the effect of the invention described in the item 2 or 3, an effect of preventing occurrence of image pitch unevenness is obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a schematic configuration of a color image recording apparatus according to the present invention.

FIG. 2 is a partially cutaway plan view showing a transfer belt driving mechanism of the color image recording apparatus according to the present invention.

FIG. 3 is a cross-sectional view illustrating a schematic configuration of a conventional color image recording apparatus.

[Explanation of symbols]

 I, II, III, IV Image forming unit 2Y, 2M, 2C, 2BK Primary charger 10 Transfer device (transfer unit) 11 Drive roller 12 Follower roller 14 Transfer belt 15 Transfer charger 30 Torque limiter P Recording medium (recording paper)

Claims (7)

[Claims] A transfer unit including a transfer belt and a transfer charger stretched between a driving roller and a driven roller, wherein a plurality of image forming units for performing recording of different colors are arranged in parallel.
In a color image recording apparatus for forming a color image by successively superimposing colors on a recording medium introduced into the transfer means, a driving roller of the transfer means is arranged on an upstream side in a conveying direction of the recording medium, and rotation of the driving roller 2. The method according to claim 1, wherein the torque is transmitted to the driven roller via a torque limiter that generates a slip with a predetermined rotation torque, and a belt conveyance speed of the driven roller is set to be higher than that of the driving roller. Color image recording device. 2. The method according to claim 1, wherein the predetermined rotation torque is a value at which a slip occurs in the torque limiter before a slip occurs between the transfer belt and the driven roller, and the predetermined rotational torque is a resistance to a transfer load of the transfer belt by the transfer charger. 2. The color image recording apparatus according to claim 1, wherein the value is set to a value larger than the force. 3. The color image recording apparatus according to claim 1, wherein a pitch linear velocity of the driven roller is set to be higher than that of the driven roller. 4. The color image recording apparatus according to claim 1, wherein said driven roller is made of a metal having a high thermal conductivity. 5. A color image recording apparatus according to claim 1, wherein said transfer charger is of a contact type. 6. The color image recording apparatus according to claim 1, wherein a primary charger included in each of the image forming units is of a contact type. 7. The color image recording apparatus according to claim 1, wherein each of the image forming units includes a digital optical system.