JPH07325442A - Image forming device - Google Patents

Abstract

PURPOSE:To eliminate the slacking and tension of a transfer material and to prevent the elongation of an image and the scattering of toner by eliminating the carrying speed difference between a transfer drum and a fixing unit with respect to the transfer material. CONSTITUTION:The carrying speed V0 of the transfer material by the transfer drum 6 is obtained by the length of the transfer material, the speed of revolutions of the transfer drum 6, etc., and the carrying speed V1 of the transfer material by the fixing unit 8 is obtained by the length of the transfer material and the time of the passage of the transfer material on a paper ejection sensor 34 on the downstream side of the fixing unit 8. When a difference dV(=V0-V1) is made between both carrying speeds by the wearing of a fixing roller 8a, etc., a transfer material is slacked or tensed when the transfer paper is simultaneously carried by both of the transfer drum 6 and the fixing unit 8. The rotation of a motor 6A or 8A is controlled by a CPU 50 to eliminate the speed difference dV.

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 or a laser beam printer, and more particularly, to an image forming apparatus in which the transfer material conveying speed is changed inside the main body of the image forming apparatus. Concerned.

[0002]

2. Description of the Related Art FIG. 7 shows a schematic structure of an electrophotographic color laser beam printer as an example of an image forming apparatus. The configuration and operation will be briefly described below.

A photosensitive drum (image bearing member) 1 is rotatably arranged in the substantial center of a laser beam printer body (hereinafter referred to as "apparatus body"). The photosensitive drum 1 is
It is rotationally driven at a predetermined speed in the direction of arrow R1 and its surface is uniformly charged by the charger 2 to a predetermined polarity and a predetermined potential.

Next, the transfer material P is fed one by one from the paper feed cassette 10 by the paper feed roller 9 at a predetermined timing. When the tip of the transfer material P is detected by the detector 3, laser light modulated by the image signal is emitted from the semiconductor laser 19 toward the polygon mirror 21, and the laser light is scanned by the polygon mirror 21. After passing through the lens and the mirror, it is guided onto the photosensitive drum 1, and the photosensitive drum 1 is exposed to form a first electrostatic latent image. Toner is attached to the first electrostatic latent image by the developing device 4a of the rotary developing device 5, and the first electrostatic latent image is developed to form a magenta first toner image on the photosensitive drum 1.

The transfer drum 6 holds the front end of the transfer material P fed at a predetermined timing by the gripper 14,
The whole of the transfer material P is carried by the adsorption high-voltage charger 22 in a state of being adsorbed so as to be wrapped around. A transfer bias voltage having a polarity opposite to that of the toner is applied to the transfer drum 6, whereby the first toner image on the photosensitive drum 1 is transferred onto the transfer material P.

The second, third, and fourth toner images are sequentially transferred onto the transfer material P on the transfer drum 6 onto which the first toner image has been transferred. After the transfer of the first toner image is completed, the photosensitive drum 1 is cleaned by a cleaner and then recharged by the charger 2 to be scanned by the laser beam to form a second electrostatic latent image on the surface. This second electrostatic latent image is developed by the developing device 4b that is switched to the developing position by the rotation of the developing device 5, and becomes a cyan toner image.
The cyan toner image is transferred to the transfer material P on the transfer drum 6. Similarly, a third electrostatic latent image is formed on the photosensitive drum 1, is developed as a yellow toner image by the developing device 4c, and is then transferred onto the transfer material P. Then the fourth
An electrostatic latent image is formed, developed as a black toner image by the developing device 4d, and transferred onto the transfer material P. Thus, the four color toner images are transferred onto the transfer material P in an overlapping manner.

When the front end of the transfer material P on which the toner image has been transferred approaches the position of the separating claw 16, the separating claw 16 contacts the surface of the transfer drum 6 to separate the transfer material P from the transfer drum 6. Let The separation claw 16 returns to the original position when the rear end of the transfer material P separates from the transfer drum 6. At that time, the charger 15
As a result, accumulated charges on the transfer material P are eliminated, facilitating separation of the transfer material P by the separation claw 16 and reducing air discharge during separation.

The transfer material P separated from the transfer drum 6 is
Enter the fixing device 8. The fixing device 8 includes a fixing roller 8a,
It has a pressure roller 8b pressed against it from below, and the fixing roller 8a is internally heated by a halogen heater. When the transfer material P passes through the fixing roller 8a,
The unfixed toner image on the surface is fused and fixed and fixed. The transfer material P on which the toner image is fixed is then discharged onto a paper discharge tray 18 outside the apparatus main body. In the figure, 11 is a charge eliminating roller for removing unnecessary charges on the transfer drum 6, and 23 is a cleaning mechanism for cleaning the surface of the transfer drum 6.

In the laser beam printer having the above structure,
The transfer material, which is first supplied from the paper feed cassette 10 and is finally discharged onto the paper discharge tray 18, is usually set to a constant transport speed inside the apparatus main body.

Further, the fixing device 8 has the following means in order to improve the fixing property of the toner image. First, a high pressure is applied to the transfer material P passing there between by the two rollers, the fixing roller 8a and the pressure roller 8b arranged above and below, to improve the fixing property. Secondly, it is provided on the web 30 to eliminate the offset toner that tends to adhere to the surface of the fixing roller 8a. The web 30 is a belt-shaped sheet, which is wound around a web supply roller 31 and is gradually rolled up by a web winding roller 33 and pressed by the web roller 32 to clean the surface of the fixing roller 8a. Depending on the predetermined rotation amount of the fixing roller 8a, the take-up roller 33
The fixing roller 8a is satisfactorily cleaned by controlling the winding amount.

[0011]

However, according to the above-mentioned conventional example, the following problems are caused by taking the above-mentioned means for improving the fixing performance.

First, the fixing roller 8a and the pressure roller 8b
Due to the high pressure between them, deformation occurs in these rollers. Secondly, the surface of the fixing roller 8a is scraped by the cleaning of the surface of the fixing roller 8a, and the roller diameter changes. When the roller is deformed or the roller diameter is changed as described above, the peripheral speed of the fixing roller 8a changes even if the number of rotations (rotational speed) of the fixing roller 8a is constant. It will change.

A change in the conveying speed of the transfer material P by the fixing device 8 causes a speed difference with the peripheral speed of the transfer drum 6 arranged on the upstream side (in the conveying direction of the transfer material). Will end up. The transfer material P may be conveyed while being pinched by the fixing device 8 at the front end side and simultaneously carried by the transfer material at the rear end side. In this case, the transfer material P is loosened or pulled due to the above-described speed difference. When the transfer material P during transfer is pulled, the image is stretched or rubbed, or the rear end of the transfer material P jumps up when separating from the transfer drum 6, and the toner before fixing scatters. It was a factor of deterioration.

Therefore, in order to solve the above-mentioned problems, the present invention provides an image forming apparatus which eliminates the difference in the transfer speed of the transfer material and prevents the image deterioration such as the elongation and rubbing of the image and the scattering of the toner. That is the purpose.

[0015]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an image carrier on which a toner image is formed, and the toner image transferred onto a transfer material carried on the surface. An image forming apparatus including a transfer drum and a fixing device that fixes a toner image on the transfer material while nipping and transporting the transfer material separated from the transfer drum, a first drive for driving the transfer drum. Unit, a second driving unit that drives the fixing unit, and the first and second driving units are individually controlled to control the conveyance speed of the transfer material by the transfer drum and the transfer material by the fixing unit. And a speed detecting means for detecting a transfer speed of the transfer material by the fixing device, the control means based on the output of the speed detecting means. Second drive means And controlling at least one, and the conveying speed of the transfer material by the transfer drum, characterized in that to match the conveying speed of the transfer material by the fixing device.

In this case, a length detecting means for detecting the length of the transfer material in the conveying direction, a conveying time detecting means for detecting the conveying time of the transfer material by the transfer drum, and the transfer material by the fixing device. And a transfer time detection unit for detecting the transfer time of the transfer material, and the control unit controls the transfer material transfer speed by the transfer drum and the fixing unit based on the two transfer times and the transfer material length. You may make it calculate the conveyance speed of a transfer material.

[0017]

According to the above construction, for example, even when the transfer material is simultaneously conveyed by the transfer drum and the fixing device, that is, the leading end side of one transfer material is conveyed by the fixing device,
Even when the rear end side is conveyed by the transfer drum, the conveyance speed of the fixing device and the conveyance speed of the transfer drum with respect to the transfer material are the same, so that the transfer material is not loosened or pulled.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. The general structure of the image forming apparatus according to the present invention is substantially the same as that of the conventional image forming apparatus described with reference to FIG. <Embodiment 1> FIG. 1 shows a block diagram for controlling the conveying speed of the transfer material P. As described above, 1 is a photosensitive drum (image carrier), 6 is a transfer drum, and 8 is a fixing device having a fixing roller 8a and a pressure roller 8b. Transfer drum 6
Is rotationally driven by a motor (first drive means) 6A whose rotation is controlled via a driver 6B by a CPU (sequence controller) 50 as a control device. Similarly, the fixing roller 8a is also rotated by the CPU 50 via the driver 8B by the CPU 50 (second
It is rotationally driven by the driving means 8A). And C
The PU (control device) 50 controls the rotation of the motor 6a and the rotation of the motor 8a so that the conveyance speed of the transfer material P by the transfer drum 6 and the conveyance speed of the transfer material P by the fixing device 8 become the same. There is.

As described above, the transfer material P on which the four color toner images have been transferred is transferred to the transfer drum 6 by the separating claw 16.
And the fixing roller 8a separates the discharge tray 18
Discharged on top. At this time, the transfer material P is the transfer drum 6
It may be conveyed by the fixing device 8. That is, even when the front end of the transfer material P reaches the fixing device 8 and the conveyance of the transfer material P by the fixing device 8 is started, the rear end side of the transfer material P is still carried and conveyed by the transfer drum 6. There is. Further, when the length L1 of the transfer material P in the conveyance direction (hereinafter simply referred to as “length”) is long, the toner image is still transferred even after the conveyance of the transfer material P by the fixing device 8 is started. Sometimes. The transfer drum 6 and the fixing device 8
And the transfer of the transfer material P is continued until the rear end of the transfer material P is separated from the transfer drum 6.

Conveying speed V of the transfer material P by the transfer drum 6
When the speed difference dV between 0 and the conveyance speed V1 of the transfer material P by the fixing device 8 occurs, as described above, the transfer material P is slackened or pulled, and the image is deteriorated due to image elongation or toner scattering. Can be seen.

Therefore, in order to eliminate the speed difference dV, the following is performed. First, the transfer speed V0 by the transfer drum 6
Is equal to the peripheral speed of the transfer drum 6 in this embodiment, and is therefore calculated from the radius of the transfer drum 6 and the rotational speed of the transfer drum 6 (rotational speed of the motor 6A). On the other hand, the transport speed V1 by the fixing device 8 is obtained from the length L1 of the transfer material P and the output of the discharge sensor (speed detecting means) 34. As shown in FIG.
The size piece 4 is placed at a position corresponding to the size of the transfer material P to be stored.
2 is attached, and the paper feed cassette 10 is attached to the main body 40 of the apparatus.
When is mounted, the position of the size frame 42 can be detected by the detection switch 41 on the apparatus body 40 side. The CPU 50, which is the control means, includes a detection switch 41
A table of the length L1 of the transfer material P or the transport time corresponding to the information of is stored. That is, the paper feed cassette 10
By loading the paper cassette 1 into the apparatus main body 40,
The length L1 of the transfer material within 0 is automatically detected. Length L
If 1 is determined, then the transport speed V1 can be obtained if the transport time T1 of the transfer material P by the fixing device 8 is known.
The discharge sensor 34 detects the transport time T1. The discharge sensor 34 is disposed at the exit of the fixing device 8, and as shown in FIG. The time T1 until the passage is completed is measured. In addition, T in the figure
0 is the regular transport time of the transfer material P, which is equal to the transport time of the transfer material P by the transfer drum 6 in this embodiment.
The transport speed V1 of the transfer material P by the above-mentioned fixing device 8 is calculated by V1 = L1 / T1. Therefore, the speed difference dV between the transfer speed V0 of the transfer drum 6 and the transfer speed V1 of the fixing device 8 is dV.
Becomes dV = V0-V1 = V0-L1 / T1. For example, when V0> V1 (when the transfer material P is loosened), the rotation speed of the motor 6A on the transfer drum 6 side is slowed or the fixing device 8 is set so as to cancel the speed difference dV.
The rotation speed of the side motor 8A is increased. On the contrary, V0 <
In the case of V1 (when the transfer material P is pulled), the rotation speed of the motor 6A on the transfer drum 6 side is increased or the motor 8A on the fixing device 8 side is set so as to cancel the speed difference dV.
Slow down the rotation speed of. When V0 = V1, the motor 6
a and 8a are designed to maintain their respective rotation speeds.
Regarding the change of the rotation of the transfer drum 6 or the rotation of the fixing device 8, if the former is changed, the rotation speed of the photosensitive drum 1 in contact with the transfer drum 6 or the transfer drum 6 is changed.
It is necessary to change the paper feed timing of the transfer material P with respect to the above. On the other hand, when the rotation of the fixing device 8 is changed in the latter case, the influence on other members is not as great as in the former case.
In this embodiment, the rotation of the latter fixing device is changed.

When a stepping motor is used as the above-mentioned motor 8a, the rotation frequency of the stepping motor is controlled by changing the cycle of the drive pulse, and the predetermined rotation of the fixing device 8 is thereby realized. <Second Embodiment> FIGS. 5 and 6 are speed charts showing a second embodiment of the present invention. In this embodiment, a method of changing the speed of the transfer drum 6 will be described. In addition, in FIG.
It is a figure for demonstrating the distance between each member. When the front end of the transfer material P enters the fixing roller 8a, the rear end of the transfer material P is still sandwiched between the photosensitive drum 1 and the transfer drum 6. Further, a latent image is formed on the photosensitive drum 1 by the laser light. While the image is being printed on the photosensitive drum 1 by the laser, when the speed of the transfer drum 6 is changed, the density of the image in the sub-scanning direction is changed, so the speed variable operation is not performed. When the latent image formation is completed, the speed of the motor 6a that drives the transfer drum 6 is quickly changed to V1.

At this time, if the distance from the transfer position to the entrance of the fixing roller 8a is Ls, the distance conveyed by the fixing roller 8a by the end of transfer is (L1-Ls), and the time is (L1-Ls). / V1. The distance conveyed by the transfer drum 6 within this time is (L1−Ls) × V0 / V
It is 1. The amount of tension or slack that occurs during this period is M
Then, M is the distance conveyed by the fixing roller 8a,
Since the difference is the distance conveyed by the transfer drum 6, M = (L1-Ls)-(L1-Ls) * V0 / V1 =
It is represented by (L1-Ls) (1-V0 / V1). When this is represented by a graph, the shaded area in FIGS. 5 and 6 is obtained.

On the other hand, if the distance from the transfer position to the separation position is Lu, it is necessary to pull or loosen during the transportation of Lu from the time when the trailing edge of the transfer material P leaves the transfer position until it is separated. According to the speed of the fixing device 8, the time between these is L
u / L1. Therefore, the transfer material P can be separated from the transfer drum 6 in a state where the tension and the slack are eliminated by controlling the speeds so that the areas of the two hatched portions shown in FIGS. 5 and 6 become equal. FIG. 5 shows the correction of the speed of the transfer drum 6 when the speed of the fixing roller 6 is higher than the normal speed.
Is a correction of the speed of the transfer drum 6 when the speed of the fixing roller 6 is lower than the normal speed. <Embodiment 3> The length L1 of the transfer material P is basically only a fixed number of steps, but the same applies to the case where the transfer material P out of the regulation is used or when the paper is fed from the manual feed port. Take control.
In FIG. 7, 3 is a transfer material detection sensor. This sensor is provided for jam detection and various timing triggers. Transfer material P in the print sequence
The actual length of the transfer material P can be measured by monitoring the sensor 3 during conveyance. By setting this measured value to L1 and comparing it with the passage time of the paper discharge sensor 34, it is possible to accurately detect the change in the conveyance speed of the fixing roller 8a. The correction means may be either the first embodiment or the second embodiment described above.

[0025]

As described above, according to the present invention,
The speed difference between the transfer speed of the transfer material by the transfer drum and the transfer speed of the transfer material by the fixing device is calculated, and at least one of the first drive means and the second drive means is controlled by the control device, Since the speed difference is eliminated, for example, even when the front end side and the rear end side of one transfer material are simultaneously conveyed by the fixing device and the rear end side, the transfer material is not loosened or pulled. As a result, it is possible to effectively prevent image defects such as image expansion and toner scattering.

[Brief description of drawings]

FIG. 1 is a control block diagram of a transfer material conveying speed in an image forming apparatus according to a first exemplary embodiment.

FIG. 2 is a timing chart of the paper discharge sensor according to the first embodiment.

FIG. 3 is a diagram illustrating a mechanism for detecting a length of a transfer material in a conveyance direction according to the first embodiment.

FIG. 4 is an enlarged view of the vicinity of the separation claw of the second embodiment.

FIG. 5 is a speed chart showing the transfer speed of the transfer material according to the second embodiment.

FIG. 6 is a speed chart showing the transfer speed of the transfer material according to the second embodiment.

FIG. 7 is a vertical cross-sectional view showing a schematic configuration of a laser beam printer (image forming apparatus).

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Image carrier (photosensitive drum) 2 Charging device 3 Transfer material detection sensor 4a-4d Developing device 5 Developing device 6 Transfer drum 8 Fixing device 8a Fixing roller 8b Pressure roller 10 Paper feed cassette 16 Separation claw 18 Paper ejection tray 19 Semiconductor Laser 21 Polygon mirror 34 Paper ejection sensor 40 Device body 41 Length detection means (detection switch) 42 Length detection means (size frame) L1 Transfer material conveyance direction length Ls Distance from transfer position to fixing roller entrance Lu Transfer position To the separation position T0 Transfer material transfer time by transfer drum (regular transfer time) T1 Transfer material transfer time by fixing device dT Transfer material transfer time by transfer drum and transfer material transfer time by fixing device Difference (= T0-T1) V0 Transfer material transfer speed by transfer drum V1 Transfer material transfer speed by fixing device dV Speed difference between transfer material transfer speed by transfer drum and transfer material transfer speed by fixing device (V0-V1)

Claims (2)

[Claims] 1. An image carrier on which a toner image is formed, a transfer drum on which the toner image is transferred to a transfer material carried on the surface, and a transfer material separated from the transfer drum while being nipped and conveyed. In an image forming apparatus including a fixing device that fixes a toner image on the transfer material, a first driving unit that drives the transfer drum, a second driving unit that drives the fixing device, and A control unit that individually controls the second driving unit to individually change the transfer speed of the transfer material by the transfer drum and the transfer speed of the transfer material by the fixing unit; A speed detection unit that detects a conveyance speed, and the control unit controls at least one of the first and second driving units based on an output of the speed detection unit to transfer the transfer material by the transfer drum. Transport of And degree, to match the conveying speed of the transfer material by the fixing device, an image forming apparatus characterized by. 2. A length detecting means for detecting a length of the transfer material in a conveying direction, a conveying time detecting means for detecting a conveying time of the transfer material by the transfer drum, and a transfer time of the transfer material by the fixing device. And a transfer time detection unit that detects a transfer time. The control unit is configured to transfer the transfer material by the transfer drum and transfer the transfer material by the fixing device based on the two transfer times and the length of the transfer material. The image forming apparatus according to claim 1, wherein the transport speed of the material is calculated.