JP2002154715A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of reducing the effects of the vibration caused by the driving and stoppage of a resist roller and a transfer roller positioned on the upstream side of the resist roller on the dislocation of a color image. SOLUTION: When the speed of the resist roller 20 is controlled so that, after abutted on the resist roller 20, the sheet S is transferred at a high speed higher than an image forming speed with a specified sheet transfer timing after the sheet is detected by a resist pre-sensor 2k and then transferred at a speed approximately equal to the image forming speed with a specified sheet deceleration timing, the sheet deceleration timing is increased more than a latent image forming timing at the image forming part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a copying machine,
The present invention relates to an image forming apparatus such as a printer or a multifunction peripheral having these functions, and more particularly, to sheet conveyance control using a registration roller or the like disposed upstream of an image forming unit.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus employing an electrophotographic method, an electrophotographic photosensitive member serving as an image carrier is charged by a charger, and the photosensitive member is irradiated with light according to image information to form a latent image. It has an image forming unit that forms an image and transfers the image obtained by developing the latent image with a developing device to a sheet or the like.

On the other hand, a plurality of image carriers for each of these image forming processes are provided in accordance with the colorization of the image, and each of the color images of a cyan image, a magenta image, a yellow image, and preferably a black image is carried on each image carrier. There has also been proposed an image forming apparatus which forms a full-color image by forming the image on a body and superimposing and transferring each color image on a sheet at a transfer position of each image carrier.

[0004] Such a full-color image forming apparatus has an image forming section for each color, which is advantageous for speeding up. In addition, since the sheet transport path can be made linear, there is an advantage that the sheet is adaptable to a sheet such as a cardboard or a trappen.

In such an apparatus, sheets fed from a sheet stacking section by a sheet feeding section one by one are
The sheet once collides with a nip of a stopped registration roller adjacent to the sheet conveyance upstream of the image forming section.

At this time, the sheet detecting sensor disposed near the upstream of the registration roller detects the leading edge of the sheet. After the leading edge of the sheet abuts on the register roller, the sheet is generally fed upstream by about 5 to 15 mm at a predetermined timing. Stop the transport rollers. Therefore, the skew correction is performed by the leading edge of the sheet parallel to the nip line of the registration roller due to the waist of the sheet.

[0007] As a sheet detection sensor, a rotatable lever spring-biased so as to come into contact with the leading end of a sheet, and a transmissive photo-interrupter in which a light-emitting element and a light-receiving element are arranged to face each other are used. The presence or absence of a sheet is detected by blocking the light of the lever transmission type photo interrupter when the light is emitted, or a reflection that directs the light from the light emitting element to the sheet and detects the reflected light or diffused light with the light receiving element directly Type photo interrupters have become mainstream.

[0008] The position of the sheet detection sensor in the direction perpendicular to the sheet conveyance is located near the center in a device that divides and conveys the sheet to both sides based on the center of the sheet when conveying a sheet having a different width in the direction perpendicular to the sheet conveyance. In a device that conveys a sheet based on one end of the largest sheet, the sheet is arranged closer to the reference side.

After that, the registration roller and the conveyance roller are driven in synchronization with the sequential formation of each color image such as a cyan image, a magenta image, a yellow image, and a black image, and the position of the sheet image is adjusted. At this time, the peripheral speed of the registration roller is set substantially equal to the image forming speed.

[0010]

However, the above-mentioned conventional image forming process has a problem in how well each image formed by the image forming section can be registered.

The reason is that the registration roller is located very close to the image forming section, so that if the vibration at the time of driving or stopping the registration roller gets on the image carrier during the formation of the latent image, the registration roller will eventually be formed. This is because it appears as a color shift or a change in color tone.

In particular, when there are a plurality of transport rollers upstream of the registration rollers, and the plurality of transport rollers sandwich the sheet at the same time, the registration rollers and the plurality of transport rollers are generally driven and stopped simultaneously. Therefore, the vibrations accompanying the start and stop of a plurality of motors for moving the rollers occur simultaneously, and the problem of color misregistration or color tone change becomes more remarkable.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has as its object the effect of vibration of a registration roller and a conveyance roller located upstream thereof caused by driving or stopping on color misregistration of an image. It is an object of the present invention to provide an image forming apparatus capable of reducing image quality.

[0014]

In order to achieve the above object, according to the present invention, an image forming section for forming an image on a sheet and a sheet loaded on the image forming section are fed one by one. A sheet conveying unit including a separating and feeding unit, a variable-speed registration roller disposed upstream of the image forming unit, and a registration roller front sheet detection unit disposed near the upstream of the registration roller. In the image forming apparatus, after the sheet is abutted against the registration roller, the sheet is conveyed at a predetermined sheet conveyance timing at a predetermined sheet conveyance timing at a speed higher than the image forming speed after the sheet is detected by the sheet detection unit before the registration roller. When the speed of the registration roller is controlled to be substantially equal to the image forming speed at the sheet deceleration timing, the sheet deceleration timing is transmitted to the image forming unit. A sheet transport control means for earlier than kicking latent image formation timing, characterized by comprising a.

The registration roller is constituted by, for example, a pair of a driving roller and a driven roller which are pressed against each other.

The sheet conveyance timing is a timing at which the registration roller is accelerated at a speed higher than the image forming speed, triggered by detection of the leading edge of the sheet by the sheet detection means before the registration roller.

The sheet deceleration timing is a timing at which the registration roller is decelerated so as to be substantially equal to the image forming speed, triggered by the sheet conveyance timing.

When the sheet is conveyed by the above-described sheet conveyance control means so as to become substantially equal to the image forming speed at a predetermined sheet acceleration / deceleration timing after the sheet abuts on the registration roller, the sheet deceleration timing is determined by the image forming unit. The sheet conveyance control performed at a timing earlier than the latent image formation timing in the above is performed.

Further, the sheet conveying means includes a plurality of conveying rollers, and the sheet conveying control means includes a sheet of a conveying roller positioned upstream of the conveying rollers for holding the sheet when the sheet abuts against the registration roller. The deceleration timing is set earlier.

That is, it is assumed that transport rollers 1, transport rollers 2,..., And transport rollers n are arranged upstream from the registration rollers, and the transport rollers hold the sheet when the sheet abuts against the registration rollers. If
The sheet deceleration timing of the conveying roller is as follows: conveying roller n>...> conveying roller 2> conveying roller 1>
The order of the registration rollers is such that the roller on the upstream side decelerates the sheet earlier.

The image forming section includes a photosensitive drum, and a creepage distance from the latent image point to the transfer point on the photosensitive drum is L, and a distance from the registration roller to the transfer point is L '. When L ≦ L ′
It is arranged so that it becomes.

Preferably, the registration roller is driven by a stepping motor.

[0023]

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the dimensions of the components described in this embodiment,
The materials, shapes, relative arrangements, and the like are not intended to limit the scope of the present invention only to them unless otherwise specified.

(First Embodiment) This embodiment will be described using an electrophotographic copier as an image forming apparatus.

FIG. 3 is a sectional view showing a schematic configuration of a copying machine according to the present embodiment.

That is, an image forming section 2 for forming an image on a sheet S, a plurality of rollers constituting sheet conveying means, a registration roller 20 having a variable rotation speed disposed upstream of the image forming section 2, and a sheet conveying section And a controller 100 as control means.

As the rollers constituting the sheet conveying means, not only the conveying roller 22 on the upstream side of the registration roller 20 but also the separating and feeding means of the feeding section 3 for feeding the stacked sheets S one by one. It also includes a pickup roller 3c, a transport roller 3e, and a retard roller 3f.

In the vicinity of the upstream of the registration roller 20, a pre-registration sensor 2 as sheet detection means before the registration roller is provided.
k is arranged.

The controller 100 includes a registration roller 2
0, the sheet S is abutted against the pre-registration sensor 2
When the sheet S is conveyed at a predetermined sheet conveyance timing higher than the image forming speed after the sheet detection by k, and then the speed of the registration roller 20 is controlled to be substantially equal to the image forming speed at the predetermined sheet deceleration timing Then, the sheet deceleration timing is controlled to be earlier than the latent image formation timing in the image forming unit 2.

In FIG. 3, the copying machine photoelectrically converts image information read by a reader unit 1 having a traveling optical system, transfers the image information to an image forming unit 2, and forms an image on a sheet S fed by a feeding unit 3. Image formation is performed in the unit 2. The sheet S after the image formation is conveyed to the fixing unit 4 where heat and pressure are applied to fix the transferred image. Hereinafter, the above-described process from when an image is formed to when the sheet is discharged will be described step by step.

First, in the reader unit 1, a document D placed on a document table glass 1a is irradiated with light by a scanning optical system 1b, and its reflected light is transmitted through a reduction lens 1c to a CCD.
An image is formed on 1d and photoelectrically converted. Next, the image information is transferred to a memory after A / D conversion.

Next, paper is fed from the feeding section 3. At the lower part of the copying machine, sheet cassettes 3a and 3b containing sheets S of different sizes are detachably mounted. Hereinafter, since the operation is the same, the sheet feeding operation from the upper sheet feeding cassette 3a will be described.

FIG. 1 is a diagram showing the conveying position of the leading end and the trailing end of the sheet with respect to time in the present embodiment. The horizontal axis represents time, and the vertical axis represents distance. Therefore, the inclination of the line indicates the transport speed.

The sheet is fed by turning on / off a solenoid connected to the pickup roller 3c at a constant interval, so that the pickup roller 3c is driven to rotate. Even if a plurality of sheets S are picked up, the conveyance roller 3 e and the retard roller 3
f, the uppermost sheet is fed only by the retard roller 3f driven in the direction opposite to the conveying direction via a torque limiter (not shown), so that the sheet is not double fed.

Next, the fed sheet S reaches the registration roller 20 after passing through the pre-registration sensor 2k. The registration roller 20 is configured such that a driven roller 20b (not shown) is paired with a driving roller 20a and is biased by a spring.

The drive roller 20a is formed by fixing rubber to the outer periphery of a metal core, and the driven roller 20b is formed of metal having a small outer surface roughness.

The drive roller 20a is driven by a stepping motor (not shown),
00 allows speed control. When the leading edge of the sheet S collides with the registration roller 20, the registration roller 20 is stopped, and after detecting the leading edge by the pre-registration sensor 2k, the registration roller 20 is rotated at a peripheral speed of 500 mm / s at a predetermined timing t1. Drive.

FIG. 2 is an enlarged view of a diagram showing the position of the sheet around the registration roller.
2, the distance R is the amount of pushing by the transport roller 22 when the registration roller stops. The sheet S is generated by the stiffness of the paper due to the pushing amount.
To the registration rollers to correct the skew of the sheet S.

The skew-corrected sheet is transferred to the registration roller 2
0, the conveyance speed of the registration roller 20 is the same as the image formation speed at a predetermined timing t2.
The speed is reduced to 0 mm / s. At this time, since the sheet is also bitten by the transport roller 22, the speed must be reduced to 250 mm / s or less. The conveyance roller 22 is driven by a stepping motor different from the registration roller 20, and the speed can be controlled by the controller 100.

By the above-described control, even before the registration roller 20 where the sheet interval becomes the shortest, the time before the registration sensor 2k can detect the leading and trailing edges of the sheet is secured.

The pre-registration sensor 2k, when there is a sheet on the sensor, the photo interrupter 2k1 is shielded by the lever 2k2 as shown in FIG. 4A, and when there is no sheet, it is shown in FIG. 4B. The lever 2k2 is configured to escape from the photointerrupter 2k1 by the urging force of a spring that does not. Therefore, the sheet interval is set to sensor OFF / O
It should be noted that sheet detection becomes impossible when the distance is shorter than the inter-N distance La.

Next, returning to FIG. 3, the image forming section 2 will be described. Based on the image information read by the already explained reader unit 1 and stored in the memory, the laser light emitting unit 2a emits a laser beam, and is scanned in the generatrix direction of the photosensitive drum 2c by the rotation of the polygon mirror 2b. A latent image is formed on the surface of the photosensitive drum 2c charged by the charger 2d. This latent image is developed by a developing device 2e provided around the photosensitive drum 2c, and the pre-transfer roller pair 2
A toner image is formed on the sheet S conveyed by f by the transfer charger 2g. The toner remaining on the drum surface after the image transfer is removed by the cleaning device 2h.

Here, as shown in FIG. 3, the distance L 'from the registration roller 20 to the transfer point is arranged such that L≤L' with respect to the distance L from the latent image point to the transfer point. Therefore, the latent image is formed after a predetermined time has elapsed from when the registration roller 20 is turned on.

Generally, the maximum vibration of the motor is not at the time of steady rotation, but at the time of start-up and fall of the motor. Therefore, the moment when the vibration of the motor that drives the registration roller 20 becomes maximum precedes the latent image formation by a predetermined time, and the vibration does not affect the latent image formation, and the color of the image is not affected. Displacement and change in color tone can be reduced.

As described above, when the registration roller 20 is driven at 500 mm / s and thereafter is reduced to 250 mm / s, which is the same as the image forming speed, the timing of driving at 500 mm / s is as follows.
/ S, the timing of registration roller 2
What is necessary is just to control so that the distance from 0 falls within the range of L'-L. By controlling in this way, the rise and fall of the motor for driving the registration roller does not affect the latent image formation.

Further, the controller 100 as the sheet conveyance control means is configured to advance the sheet deceleration timing of the upstream conveyance roller among the conveyance rollers that hold the sheet when the sheet abuts against the registration roller 20. ing.

That is, when the registration roller 20 is stopped, the rear end of the sheet S is also held by the conveyance roller 22. Therefore, there is a timing at which the sheet S is held by the two rollers of the registration roller 20 and the conveyance roller 22. I do.

Generally, in such a case, in accordance with the deceleration timing of the registration roller 20, the transport roller 22 must also be decelerated at or before the same timing.
If the deceleration timing of the conveyance roller 22 is brought after the deceleration timing of the registration roller 20, there will be a period in which the conveyance speed of the conveyance roller 22 is faster than the registration roller 20, and as a result, This is because the amount of press-in increases, and wrinkles and image shifts at the image transfer point are affected.

Since the deceleration timing of the registration roller 20 precedes the latent image formation timing, even if the deceleration timing of the conveyance roller 22 is set equal to that of the registration roller 20, the vibration of the motor driving the conveyance roller 22 causes the latent image formation. , And the effect on both is reduced. However, in order to further reduce the influence of the vibration, in the present embodiment, the deceleration timing of the transport roller 22 is set earlier than the deceleration timing of the registration roller 20. As a result, the moment when the vibration of the motor driving the registration roller 20 becomes maximum is shifted from the moment when the vibration of the motor driving the conveyance roller 22 becomes maximum, so that the influence of the vibration on the latent image formation can be further reduced. Will be.

The shift of the deceleration timing from the registration roller 20 is not limited to the conveyance roller 22 alone. A3
In large-size paper such as paper and sized paper, a roller may be held between the rollers further upstream than the transport roller 22 in some cases. Also in this case, the timing at which the vibration of all the motors driving the rollers for holding the sheet is maximized is gradually shifted by gradually decelerating the deceleration timing of the roller further upstream, and the image is shifted by the vibration. Etc. can be effectively reduced.

Thereafter, the sheet S on which the toner image has been transferred in the image forming section 2 is guided to the fixing section 4 by the conveyor belt 8, and heat and pressure are applied when the sheet S passes through the fixing roller pairs 4a and 4b. The image is fused to the sheet S. The sheet S on which the image has been fixed is discharged out of the apparatus via a pair of discharge rollers 5a and 5b.

According to the embodiment described in detail above, when the latent image is formed in the image forming unit 2, the registration roller 20
It can be seen that the effect of reducing the influence of driving or stopping the conveyance roller 22 located upstream thereof on the latent image and affecting the color misregistration of the image can be obtained.

(Second Embodiment) In this embodiment,
A one-way clutch that locks in the sheet conveyance direction is provided on the drive shaft of the conveyance roller 22. Thereby, the stepping motor of the registration roller 20 and the conveyance roller 22 can be made common. Other configurations and operations are the same as those of the first embodiment, and therefore, description thereof is omitted.

After the sheet S is nipped by the registration roller 20, the driving of the conveyance roller 22 is turned off, and the sheet S is pulled in the idling direction of the one-way clutch by the registration roller 20, whereby the same sheet as in the first embodiment is obtained. The transfer can be performed with a simple configuration.

[0055]

As described above, according to the present invention, after the sheet is abutted against the registration roller, the sheet is detected at a predetermined sheet conveyance timing after the sheet is detected by the sheet detection means before the registration roller, at a speed higher than the image forming speed. When the speed of the registration roller is controlled so that it is substantially equal to the image forming speed at a predetermined sheet deceleration timing after the conveyance, the sheet deceleration timing is set earlier than the latent image formation timing in the image forming unit, so that the registration roller Thus, the effect of reducing the color misregistration and the change in color tone of the image can be obtained without the vibration generated when the motor for driving the image rises and falls affecting the latent image forming process.

Further, the vibration of all the motors that drive the rollers for holding the sheet is made earlier by the sheet deceleration timing of the roller located upstream in the conveying rollers that hold the sheet when the sheet abuts on the registration roller. By shifting the maximum timing little by little, it is possible to effectively reduce an image shift due to vibration and the like.

[Brief description of the drawings]

FIG. 1 is a sheet feeding diagram of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is an enlarged view of a diagram around a registration roller of FIG. 1;

FIG. 3 is an overall configuration diagram of the image forming apparatus controlled along the diagram of FIG. 1;

4 (a) and 4 (b) are detailed views of the pre-registration sensor of FIG. 1. FIG.

FIG. 5 is a sheet feeding diagram in a conventional image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Leader part 2 Image forming part 2k Pre-registration sensor 3 Feeding part 3c Pickup roller 3e Conveyance roller 3f Retard roller 4 Fixing part 20 Registration roller 22 Conveyance roller 100 Controller (sheet conveyance control means)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H027 DA17 DA20 DA22 DC03 DE02 DE07 DE09 ED02 ED17 ED24 EE04 EE05 2H072 AA13 AA24 AA32 AB07 BA03 BA12 CA01 CA02 CA05 3F102 AA07 AA11 AB01 BA02 BB02 CA04 CB01 FA08 EA03 EC03

Claims (4)

[Claims] An image forming section for forming an image on a sheet; a sheet conveying means including a separating and feeding means for feeding sheets stacked on the image forming section one by one; and an upstream of the image forming section. A registration roller having a variable rotational speed, a sheet detection unit in front of the registration roller disposed in the vicinity of the registration roller, and a sheet abutting against the registration roller, and after a sheet is detected by the sheet detection unit in front of the registration roller. When the sheet is conveyed at a higher speed than the image forming speed at a predetermined sheet conveying timing, and then the speed of the registration roller is controlled to be substantially equal to the image forming speed at a predetermined sheet deceleration timing, the sheet deceleration timing is A sheet conveyance control unit for making a timing earlier than a latent image forming timing in the image forming unit. Equipment. 2. The image forming apparatus according to claim 1, wherein the sheet conveying unit includes a plurality of conveying rollers, and wherein the sheet conveying control unit includes a sheet of a conveying roller positioned upstream of the conveying rollers that grips the sheet when the sheet abuts against the registration roller. 2. The image forming apparatus according to claim 1, wherein the timing is set earlier as the deceleration timing. 3. The image forming section includes a photosensitive drum, wherein a creepage distance from a latent image point on the photosensitive drum to a transfer point is L, and a distance from the registration roller to a transfer point is L '. 2. The method according to claim 1, wherein the arrangement is such that L ≦ L ′.
Or the image forming apparatus according to 2. 4. The image forming apparatus according to claim 1, wherein said registration roller is driven by a stepping motor.