JP4731764B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND 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 conveyance speed control technique.
[0002]
[Prior art]
In an electrophotographic image forming apparatus, a toner image is formed on an image carrier (photoreceptor) by an electrophotographic process, while a recording medium (paper) is fed from a paper feeding unit and is temporarily set by a pair of registration rollers. Waiting. Then, in synchronization with the leading edge of the toner image, the recording medium is sent to a transfer portion between the image carrier and the transfer means, where the toner image is transferred to the recording medium. Thereafter, the recording medium is conveyed to a fixing unit, and an unfixed toner image is fixed.
[0003]
In such an image forming apparatus, the demand for density uniformity in an intermediate density image has become stricter year by year as the resolution and image quality are improved. The density fluctuation in the intermediate density image occurs due to various factors such as a change in charge amount in the image carrier, a fluctuation in development density, a position fluctuation of the laser beam, a speed fluctuation of the image carrier, and a speed fluctuation of the recording medium. Among them, the speed fluctuation of the image carrier is one of the major factors.
[0004]
The main causes of fluctuations in the speed of the image carrier are speed fluctuations that occur due to the change in the drive shaft of the image carrier and the engagement of the drive gear, the recording medium collides with the image carrier, and the image carrier. There are two types of temporary speed fluctuations that occur when entering or exiting the nip between the body and the transfer body.
[0005]
FIG. 6 is an explanatory diagram showing a problem of the conventional example, and FIG. 7 is a diagram showing a speed fluctuation waveform of the image carrier when the recording medium hits. In FIG. 6, the recording medium 26 is conveyed by the registration roller pair 19 at substantially the same speed as the image carrier 10, and does not contact the transfer device (transfer belt) 13 but directly collides with the image carrier 10 and is transferred to the transfer device. 13 enters the nip portion and is conveyed, or directly enters the nip portion.
[0006]
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. This is to prevent dust from appearing on the image. However, in that case, as described above, the image carrier 10 is hit with the tip of the recording medium 26, so that the impact force often causes a change in the speed of the image carrier 10 (see FIG. 7). In particular, the variation becomes more remarkable as the thickness of the recording medium 26 increases.
[0007]
[Problems to be solved by the invention]
It is said that speed fluctuation with the former period is relatively easy by increasing the meshing accuracy of the drive gear, but it is generally difficult to control the latter temporary speed fluctuation. ing. Conventionally, the rigidity of the image carrier has been increased, but the effect has not been found so much in a recording medium having a large thickness.
[0008]
Accordingly, the invention described in claim 1 reduces the impact received from the recording medium by reducing the speed of the conveying roller pair when the recording medium collides with the image carrier or enters the nip between the image carrier and the transfer body. Therefore, the object is to suppress the speed fluctuation of the image carrier.
[0009]
The second aspect of the invention is to detect the position of the recording medium with a sensor, accurately detect the position of various types of recording media, and perform speed control.
[0010]
According to the third aspect of the present invention, speed control is performed only on a recording medium having a large thickness that has a large impact on the image carrier, and speed control is not performed on other recording media, thereby preventing a reduction in processing capacity. .
[0011]
[Means for Solving the Problems]
The invention of claim 1, wherein in order to achieve the above object, an image bearing member for bearing a toner image, a transfer member for transferring the toner image carrying the image bearing member onto a recording medium, said recording medium in the image forming device having a pair of conveying rollers for conveying a variable speed drive motor for driving the conveying rollers, and control means for controlling switching of the speed of the drive motor, said control means, said recording medium until the tip of the contacts to a nip portion formed the the transfer member and the image bearing member or the image bearing member, the drive motor as the conveying speed of the recording medium is slower than the peripheral speed of said image bearing member controls switching the speed, and, after the leading edge of the recording medium is in contact with the image bearing member or the nip, the conveying speed of the recording medium becomes almost constant speed and the peripheral speed of said image bearing member And controlling switching of the sea urchin speed of the drive motor.
[0012]
According to a second aspect of the invention, a passage sensor for detecting passage of said recording medium during the recording medium conveying path between the image carrier and the conveying roller pair is provided, said control means output signals of the passage sensor the image forming apparatus according to claim 1, wherein the controller controls to switch the speed of the drive motor by.
[0013]
According to a third aspect of the invention, the type sensor for detecting a type of the recording medium is provided, said control means and characterized in that it is determined whether the speed switching control of the drive motor by the output signal of the type sensor the image forming apparatus according to claim 1, in which.
[0014]
Invention of claim 4 wherein the type sensor for detecting a type of the recording medium, on the function of the control means, provided an operating means for turning off, the output of the type sensor, from said operation means of said control means on the function, an image forming apparatus according to claim 1, wherein the turn off.
[0015]
DETAILED DESCRIPTION OF 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. 3 is a schematic diagram of the image forming apparatus shown in FIG. FIG.
[0016]
In FIG. 1, reference numeral 10 denotes a drum-shaped image carrier that rotates counterclockwise in the drawing. Around the image carrier 10, a charging device 11, a developing device 12, a transfer device 13, a cleaning device 14 and the like are provided in the order of the electrophotographic process. A writing device 15 is provided on the charging device 11.
[0017]
Under the image carrier 10, a recording medium conveyance path 16 is formed which conveys the recording medium from the left to the right in the drawing while passing between the transfer device 13. A paper feed tray 17 is provided at the upstream end of the recording medium conveyance path 16. A recording medium is stacked and stored in the paper feed tray 17. A paper feed roller 18 is provided at the feeding portion. A pair of registration rollers 19 is provided at a position downstream of the paper feed roller 18 and upstream of the image carrier 10 and the transfer device 13 along the recording medium conveyance path 16.
[0018]
A fixing device 22 including a heating roller 20 and a pressure roller 21 is provided along the recording medium conveyance path 16 at a downstream position of the image carrier 10 and the transfer device 13. Further, a pair of discharge rollers 23 is disposed at the downstream position. A discharge tray 24 is provided downstream of the discharge roller 23.
[0019]
As shown in FIG. 2, the controller 31 of the present invention controls the drive motor 32 by inputting detection signals from a passage sensor 27 that detects the passage of the recording medium and a type sensor 28 that detects the type of the recording medium. It is like that.
[0020]
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 or near the paper feed tray 17.
[0021]
Here, returning to FIG. 1 again, a general image forming operation will be described first. As the image carrier 10 rotates, the surface thereof is first uniformly charged by the charging device 11, and then the writing device 15 exposes and performs writing to form an electrostatic latent image on the image carrier 10. Subsequently, the developing roller 25 provided in the developing device 12 attaches toner to the electrostatic latent image, thereby visualizing the electrostatic latent image and forming an image (toner image) on the image carrier 10.
[0022]
On the other hand, along with the rotation of the image carrier 10, the paper feed roller 18 is rotated to feed out the recording medium from the paper feed tray 17, conveyed in the recording medium conveyance path 16, and abutted against the registration roller pair 19 and stopped. Then, the registration roller pair 19 is rotated in synchronization with the image on the image carrier 10, and the recording medium is conveyed in the recording medium conveyance path 16 and sent toward the image carrier 10 and the transfer device 13.
[0023]
Between the image carrier 10 and the transfer device 13, the transfer device 13 transfers the 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. Then, heat and pressure are applied by the heating roller 20 and the pressure roller 21 to fix the transferred image on the recording medium. The recording medium after fixing is discharged by the discharge roller 23 and stacked on the discharge tray 24.
[0024]
After the image transfer, the image carrier 10 is rotated and the transfer residual toner on the surface is removed by the cleaning device 14, and then the surface is removed by a static eliminator (not shown) to prepare for image formation again. Here, when the recording medium is between the image carrier 10 and the transfer device 13 and the transfer device 13 is transferring the image formed on the image carrier 10 to the recording medium, the image carrier 10 When the speed is stable, the toner image on the image carrier 10 is uniformly transferred to the recording medium without being disturbed.
[0025]
The present invention is characterized by controlling the recording medium conveyance speed. Normally, the recording medium is conveyed by the registration roller pair 19 at substantially the same speed as the peripheral speed of the image carrier 10, but in the present invention, as shown in FIG. Reduce collision energy.
[0026]
For this reason, the impact received by the image carrier 10 is also reduced, so that the speed fluctuation amount is also reduced. 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. After the recording medium collides with the image carrier 10, the conveyance speed of the recording medium is set substantially equal to the peripheral speed of the image carrier 10.
[0027]
Specifically, the 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 reduce the rotational speed, and the predetermined time A command is sent to increase the rotational speed later.
[0028]
In the example of FIG. 5, the control unit 31 drives the drive motor so that the low rotational speed is increased to the peripheral speed of the image carrier 10 a predetermined time after the passage sensor 27 detects the passage of the recording medium. A command is sent to 32.
[0029]
The image forming apparatus of the present invention also includes a type sensor 28 that detects the type (mainly thickness) of the recording medium, and the control unit 31 performs speed switching control of the drive motor 32 based on the detection result of the type sensor 28. Determine whether or not.
[0030]
That is, when a high level of image forming processing capability is required and it is not desired to reduce the conveyance speed of the recording medium, the conventional conveyance is performed for thin paper. Further, the detection result of the type sensor 28 may be confirmed by the operation unit, and the user may operate to turn on / off the function of the control unit 31.
[0031]
【The invention's effect】
According to the first aspect of the invention, an image bearing member for bearing a toner image, a transfer member for transferring the toner image carrying the image bearing member onto a recording medium, a pair of conveying rollers for conveying the recording medium in the image forming apparatus having the bets, and variable speed drive motor for driving the conveying rollers, and control means for controlling switching of the speed of the drive motor, the control means, the leading end of the recording medium is the image until it contacts the nip portion formed between carrier or said image bearing member and said transfer member control switching speed of the drive motor as the transport speed is slower than the peripheral speed of the image bearing member of said recording medium and, and, after said leading end of the recording medium is in contact with the image bearing member or the nip, the drive motor to be substantially constant velocity transport speed and the peripheral speed of the image bearing member of said recording medium And it controls the switching of the speed, the speed variation 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.
[0032]
According to the second aspect of the present invention, a passage sensor for detecting passage of said recording medium during the recording medium conveying path between the image carrier and the conveying roller pair is provided, the control means of the passage sensor by controlling the switching speed of the drive motor by the output signal, the position of the recording medium accurately detects, it is possible to perform a more accurate speed control.
[0033]
According to the invention of claim 3, wherein the type sensor for detecting the type of the recording medium is provided, the control means by determining whether the speed switching control of the drive motor by the output signal of the type sensor For a recording medium that has a relatively small impact on the image carrier, it is not necessary to reduce the processing capability of the image forming apparatus.
[0034]
According to the fourth aspect of the present invention, the type sensor for detecting a type of the recording medium, on the function of the control means, the operating means is turned off provided by the output of said type sensor, the control from the operation means By turning on / off the function of the means, the same effects as described above can be obtained.
[Brief description of the 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.
3 is an enlarged view of a main part of the image forming apparatus shown in FIG.
FIG. 4 is a characteristic diagram illustrating a first example of recording medium conveyance speed control according to the present invention.
FIG. 5 is a characteristic diagram illustrating a second example of recording medium conveyance speed control according to 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 it hits a recording medium.
[Explanation of symbols]
10 Image carrier 13 Transfer device (transfer body)
19 Registration roller pair (conveying roller pair)
27 Passing sensor 28 Type sensor 31 Control unit (control means)
32 Drive motor 33 Operation part

Claims (4)

An image bearing member for bearing a toner image, a transfer member for transferring the toner image carrying the image bearing member onto a recording medium, an image forming device having a pair of conveying rollers for conveying the recording medium, the transport and variable speed drive motor for driving the roller pairs, and control means for controlling switching of the speed of the drive motor, said control means, said transfer tip of the recording medium and the image bearing member or the image bearing member until it contacts the nip portion formed between the body, the conveying speed of the recording medium is controlled to switch the speed of the drive motor to be lower than the peripheral speed of the image bearing member, and the leading end of the recording medium after contact with the image bearing member or the nip, controls child switched nearly speed of the drive motor so that constant velocity transport speed and the peripheral speed of the image bearing member of said recording medium An image forming apparatus comprising. The passage sensor for detecting passage of said recording medium during the recording medium conveying path between the image carrier and the conveying roller pair is provided, the control means switches the speed of the drive motor by the output signal of the passage sensor The image forming apparatus according to claim 1, wherein the image forming apparatus is controlled. Type sensor for detecting the type of the recording medium is provided, the control unit image formation according to claim 1, wherein the determining whether the speed switching control of the drive motor by the output signal of the type sensor apparatus. And type sensor for detecting a type of the recording medium, on the function of the control means, the operating means is turned off provided by the output of said type sensor, turns on the function of said control means from said operating means, a turning off The image forming apparatus according to claim 1, wherein:

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