JP2003084641A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the velocity fluctuation in an image carrier by suppressing an impact to be received from a recording medium when the recording medium collides with the image carrier or plunges into the nip part of the image carrier and a transfer body by decelerating a pair of carrying rollers. SOLUTION: This image forming apparatus having the image carrier 10 carrying a toner image, the transfer body 13 for transferring the toner image to the recording medium and the pair of carrying rollers 19 for carrying the recording medium is provided with a velocity-variable driving motor 32 for driving the pair of carrying rollers 19 and a control means 31 for switch- controlling the velocity of the velocity-variable driving motor 32. The velocity- variable driving motor 31 switch-controls the driving motor 32 so that the carrying velocity of the recording medium may be slower than the peripheral velocity of the image carrier 10 until the tip of the recording medium comes into contact with the image carrier 10 or the nip part formed by the image bearer 10 and the transfer body 13 or so that the carrying velocity of the recording medium may be nearly equal to the peripheral velocity of the image carrier 10 after the tip of the recording medium comes into contact with the image carrier 10 or the nip part.

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 such as a copying machine, a laser printer and a facsimile, and more particularly to a recording medium conveying speed control technique for the image forming apparatus.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus, a toner image is formed on an image bearing member (photoreceptor) by an electrophotographic process, while a recording medium (paper) is fed from a paper feeding unit.
Has been fed, and the pair of registration rollers is once waiting. Then, in synchronization with the front end of the toner image, the recording medium is sent to the transfer portion between the image carrier and the transfer means, where the toner image is transferred to the recording medium. After that, the recording medium is conveyed to the fixing means and the unfixed toner image is fixed.

With the progress of higher resolution and higher image quality in such an image forming apparatus, the demand for density uniformity in an intermediate density image has become stricter year by year.
The density fluctuation in the intermediate density image occurs due to various factors such as fluctuation of the charge amount on the image carrier, fluctuation of the developing density, position fluctuation of the laser beam, speed fluctuation of the image carrier, speed fluctuation of the recording medium. Among them, the speed fluctuation of the image carrier is one of the major factors.

The factors that cause the speed fluctuations of the image carrier are mainly speed fluctuations having a cycle caused by the eccentricity of the drive shaft of the image carrier and the meshing of the drive gears, and the recording medium colliding with the image carrier. There are two types of temporary speed fluctuations that occur at the time of entering or exiting the nip portion between the image carrier and the transfer body.

FIG. 6 is an explanatory view showing a defect of the conventional example, FIG.
FIG. 6 is a diagram showing a speed fluctuation waveform of an image carrier when a recording medium hits it. In FIG. 6, the recording medium 26 is conveyed by the registration roller pair 19 at a speed substantially equal to the speed of the image carrier 10 and does not come into contact with the transfer device (transfer belt) 13,
It directly collides with the image carrier 10 and enters the nip portion with the transfer device 13 to be conveyed, or directly enters the nip portion.

This is because when the recording medium 26 is conveyed in close contact with the transfer device 13, the toner image on the image carrier 10 is transferred to the recording medium 26 before entering the nip portion, so that the recording medium 26 is transferred. This is to prevent dust from occurring in the upper toner image. However, in that case, since the image carrier 10 is hit by the tip of the recording medium 26 as described above, the speed of the image carrier 10 often changes due to the impact force (see FIG. 7). In particular, the fluctuation becomes more remarkable as the thickness of the recording medium 26 increases.

[0007]

The former speed fluctuation having a cycle can be relatively easily dealt with by increasing the precision of meshing of the drive gear, but the latter temporary speed fluctuation cannot be controlled. It is generally said to be difficult. Therefore, conventionally, the rigidity of the image bearing member was increased, but the effect was not so great in a recording medium having a large thickness.

Therefore, when the recording medium collides with the image carrier or when it enters the nip portion between the image carrier and the transfer medium, the speed of the conveying roller pair is reduced and the impact received from the recording medium is applied. By making it smaller, it is intended to suppress the speed fluctuation of the image carrier.

It is an object of the present invention to detect the position of a recording medium with a sensor, accurately detect the position of various types of recording media, and perform speed control.

According to the third aspect of the present invention, the speed control is performed only for the recording medium having a large thickness and having a large impact on the image carrier, and the speed control is not performed for the other recording media to prevent the reduction of the processing capacity. Has an aim.

[0011]

In order to achieve the above object, an invention according to claim 1 is an image carrier for carrying a toner image, a transfer body for transferring the toner image to a recording medium, and a recording medium. An image forming apparatus having a pair of transport rollers for transporting a sheet is provided with a speed-variable drive motor for driving the pair of transport rollers, and control means for switching and controlling the speed of the drive motor. Until the nip portion formed by the transfer body and the transfer body is in contact, the conveyance speed of the recording medium is slower than the peripheral speed of the image carrier, and after the leading edge of the recording medium contacts the image carrier or the nip part. The most important feature of the image forming apparatus is that the control means switches and controls the drive motor so that the conveying speed of the recording medium becomes substantially the same as the peripheral speed of the image carrier.

According to a second aspect of the present invention, a passage sensor for detecting passage of the recording medium is provided in the recording medium conveying path between the pair of conveying rollers and the image carrier, and the control means switches the drive motor according to the output of the passage sensor. The image forming apparatus according to claim 1 for controlling is a main feature.

The invention according to claim 3 is provided with a type sensor for detecting the type of the recording medium, and the control means determines whether or not to control the switching of the drive motor based on the output of the type sensor. The device is the main feature.

According to a fourth aspect of the invention, a type sensor for detecting the type of the recording medium and an operating means for turning on / off the function of the control means are provided, and the function of the control means is changed from the operating means by the output of the type sensor. The image forming apparatus according to claim 1, which is turned on and off, is a main feature.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention, FIG. 2 is a control block diagram of the image forming apparatus according to the embodiment of the present invention, and FIG.
FIG. 3 is an enlarged view of a main part of the image forming apparatus shown in FIG.

In FIG. 1, reference numeral 10 is a drum-shaped image carrier that rotates counterclockwise in the figure. Around the image carrier 10, the charging device 11 and the developing device 1 in the order of the electrophotographic process.
2, a transfer device 13, a cleaning device 14, etc. are provided. A writing device 15 is provided on the charging device 11.

Below the image carrier 10, there is formed a recording medium conveying path 16 which passes between the recording medium and the transfer device 13 and conveys the recording medium from left to right in the drawing. A paper feed tray 17 is provided at the upstream end of the recording medium conveyance path 16. Paper tray 17
A recording medium is loaded and stored in the. A paper feed roller 18 is provided at the feeding section. Recording medium transport path 1
6, a pair of registration roller pairs 19 is provided downstream of the paper feed roller 18 and upstream of the image carrier 10 and the transfer device 13.

A fixing device 22 including a heating roller 20 and a pressure roller 21 is provided downstream of the image carrier 10 and the transfer device 13 along the recording medium transport path 16. Further, a pair of discharge rollers 23 is arranged at the downstream position. A discharge tray 24 is provided downstream of the discharge roller 23.

As shown in FIG. 2, the control unit 31 of the present invention.
Is configured to control the drive motor 32 by inputting detection signals from a passage sensor 27 that detects passage of a recording medium and a type sensor 28 that detects the type of recording medium.

The drive motor 32 has a variable speed and drives the registration roller pair 19. The control unit 31 switches and controls the speed of the drive motor 32 according to the conveyance position (range) of the recording medium. As shown in FIG. 3, the passage sensor 27 is provided in front of the image carrier 10, and the type sensor 28 is provided in the paper feed tray 17 or in the vicinity thereof.

Now, returning to FIG. 1 again, first, a general image forming operation will be described. As the image carrier 10 rotates, the surface of the image carrier 10 is uniformly charged by the charging device 11, and then the writing device 15 exposes it to perform writing to form an electrostatic latent image on the image carrier 10. Then, toner is attached to the electrostatic latent image by the developing roller 25 provided in the developing device 12 to visualize the electrostatic latent image and form an image (toner image) on the image carrier 10.

On the other hand, with the rotation of the image carrier 10, the paper feed roller 18 is rotated to feed the recording medium from the paper feed tray 17, convey the recording medium in the recording medium conveyance path 16, and abut against the registration roller pair 19 to stop it. . Then, the registration roller pair 1 is synchronized with the image on the image carrier 10 in timing.
9 is rotated, the recording medium is conveyed in the recording medium conveying path 16, and is fed between the image carrier 10 and the transfer device 13.

Between the image carrier 10 and the transfer device 13, the transfer device 13 transfers the above-mentioned image formed on the image carrier 10 to the recording medium. The recording medium after the image transfer is conveyed in the recording medium conveying path 16 and reaches the fixing device 22. The heat roller 20 and the pressure roller 21 apply heat and pressure to fix the transferred image on the recording medium. The recording medium after fixing is discharged by the discharge roller 23 and discharged to the discharge tray 24.
Stack on top.

The image carrier 10 after the image transfer is rotated, and after the transfer residual toner on the surface thereof is removed by the cleaning device 14, the surface thereof is removed by a charge removing device (not shown) to prepare for image formation again. Here, the recording medium is between the image carrier 10 and the transfer device 13, and the transfer device 13 causes the image carrier 10 to move.
When the above-mentioned image formed on the recording medium is being transferred to the recording medium, if the speed of the image carrier 10 is stable, the image carrier 1
The toner image on 0 is transferred uniformly to the recording medium without being disturbed.

The present invention is characterized in controlling the conveyance speed of the recording medium. Normally, the recording medium is conveyed by the registration roller pair 19 at a speed substantially equal to the peripheral speed of the image carrier 10. However, in the present invention, as shown in FIG. Reduce collision energy.

Therefore, the impact on the image carrier 10 is also small, and the amount of speed fluctuation is also small. Further, as shown in FIG. 5, the same effect can be obtained even if the recording medium is conveyed at a constant low speed until it collides with the image carrier 10. Then, after the recording medium collides with the image carrier 10, the conveyance speed of the recording medium is made substantially equal to the peripheral speed of the image carrier 10.

More specifically, this conveyance speed switching control is performed by the control unit 31 shown in FIG. That is, in the example of FIG. 4, when the passage sensor 27 detects the passage of the recording medium (detects the arrival of the leading edge), the control unit 31 sends a command to the drive motor 32 to decrease the rotation speed, and the predetermined time is passed. Later, send a command to increase the rotation speed again.

Further, in the example of FIG. 5, the control unit 31 raises the rotation speed, which was low, to the peripheral speed of the image carrier 10 after a predetermined time has passed since the passage sensor 27 detected the passage of the recording medium. Sends a command to the drive motor 32.

Further, the image forming apparatus of the present invention is provided with a type sensor 28 for detecting the type (mainly thickness) of the recording medium, and the control unit 31 switches the speed of the drive motor 32 according to the detection result of the type sensor 28. Determine whether to control.

That is, if a high level image forming processing capability is required and it is not desired to reduce the conveying speed of the recording medium, thin paper is conveyed as before. Further, the detection result of the type sensor 28 may be confirmed on the operation unit, and the user may operate it to turn on / off the function of the control unit 31.

[0031]

According to the first aspect of the invention, an image having an image carrier for carrying a toner image, a transfer body for transferring the toner image to a recording medium, and a pair of carrying rollers for carrying the recording medium. The forming apparatus includes a speed-variable drive motor for driving the pair of conveyance rollers, and control means for switching and controlling the speed of the drive motor, and the nip portion where the leading end of the recording medium is formed by the image carrier or the image carrier and the transfer body. Until the contact point of the recording medium is lower than the peripheral speed of the image carrier, and after the leading edge of the recording medium contacts the image carrier or the nip portion, the transfer speed of the recording medium is Since the control means controls the switching of the drive motor so that the speed becomes substantially the same as the peripheral speed of the carrier, the speed fluctuation of the image carrier due to the collision of the recording medium is reduced. Therefore, since the toner image is stably formed on the image carrier, the density uniformity in the intermediate density image can be improved.

According to the second aspect of the present invention, a passage sensor for detecting passage of the recording medium is provided in the recording medium conveying path between the pair of conveying rollers and the image carrier, and the control means uses the output of the passage sensor to drive the drive motor. By switching control,
The position of the recording medium can be accurately detected, and more accurate speed control can be performed.

According to the third aspect of the present invention, a type sensor for detecting the type of the recording medium is provided, and the control means determines whether or not to control the switching of the drive motor based on the output of the type sensor, thereby carrying out image carrying. With respect to the recording medium which is relatively small in impact on the body, it is not necessary to reduce the processing capacity of the image forming apparatus.

According to the invention described in claim 4, the type sensor for detecting the type of the recording medium and the function of the control means are turned on.
By providing an operating means for turning off and turning on and off the function of the controlling means from the operating means by the output of the type sensor,
An effect similar to the above is produced.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a control block diagram of the image forming apparatus according to the embodiment of the present invention.

FIG. 3 is an enlarged view of a main part of the image forming apparatus shown in FIG.

FIG. 4 is a characteristic diagram showing a first example of recording medium conveyance speed control of the present invention.

FIG. 5 is a characteristic diagram showing a second example of recording medium conveyance speed control of the present invention.

FIG. 6 is an explanatory diagram showing a defect of a conventional example.

FIG. 7 is a diagram showing a velocity fluctuation waveform of the image carrier when the recording medium hits it.

[Explanation of symbols]

10 Image carrier 13 Transfer device (transfer body) 19 Registration roller pair (conveying roller pair) 27 Passage sensor 28 types of sensors 31 control unit (control means) 32 drive motor 33 Operation part

Claims (4)

[Claims] 1. An image forming apparatus having an image bearing member carrying a toner image, a transfer member for transferring a toner image onto a recording medium, and a carrying roller pair for carrying the recording medium. Variable speed drive motor,
It is equipped with control means for switching control of the speed of the drive motor,
The conveying speed of the recording medium is slower than the peripheral speed of the image carrier until the leading edge of the recording medium contacts the nip portion formed by the image carrier or the image carrier and the transfer body, and the leading edge of the recording medium. After contact with the image carrier or the nip,
An image forming apparatus characterized in that the control means controls the switching of the drive motor so that the conveying speed of the recording medium becomes substantially equal to the peripheral speed of the image carrier. 2. A passage sensor for detecting passage of a recording medium is provided on a recording medium conveying path between a pair of conveying rollers and an image carrier, and a control means switches and controls a drive motor according to an output of the passage sensor. The image forming apparatus according to claim 1. 3. The image forming apparatus according to claim 1, wherein a type sensor for detecting the type of the recording medium is provided, and the control means determines whether or not to control the switching of the drive motor based on the output of the type sensor. . 4. A type sensor for detecting the type of recording medium and an operating means for turning on / off the function of the control means are provided.
The image forming apparatus according to claim 1, wherein the function of the control unit is turned on and off from the operation unit according to the output of the type sensor.