JPH08286494A - Image forming device - Google Patents

Abstract

PURPOSE: To restrain an toner image pattern from soiling a contact transfer member, to precisely control the toner concn., and to surely prevent a rear stain on a transfer paper. CONSTITUTION: When the toner image pattern for controlling the toner is prepared on a photoreceptor 2, the density sensor 20 mounted on an arm part 25a is held close to the photoreceptor 2. Moreover, the transfer paper is held apart from the photoreceptor 2, a detecting surface of the density sensor 20 is covered by the density sensor cover 21, the toner image pattern is restrained from soiling the contact transfer member 6, the toner concn. is precisely controlled, and dirt on the detecting surface of the density sensor 20 by the soil is prevented. Furthermore, when cleaning is performed on the surface of the transfer paper, bias impression is performed to the transfer paper from the surface of the transfer paper and the toner on the surface of the transfer paper is made to stick on the photoreceptor 2, and the toner quantity stuck from the transfer paper on the photoreceptor 2 surface is detected by the density sensor 20, the bias cleaning is performed again when the detected density exceeds the set value, and thus the dirt of the contact transfer member 6 is removed.

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 for forming an image by using a photoconductor such as a copying machine, a facsimile machine and a printer.

[0002]

2. Description of the Related Art Conventionally, in this type of image forming apparatus, the toner density is controlled in order to improve the image quality, and the toner density is controlled after the toner image pattern is developed on the photosensitive member for this control. Some are optically detected by a toner concentration sensor. In such a toner concentration sensor, scattered paper powder, contaminants such as toner adhere to the toner concentration sensor, and the amount of the toner cannot be accurately detected, so that reliable detection control may not be performed. Therefore, in order to reduce the adhesion of the toner to the toner concentration sensor, the toner is removed by blowing air or the like.

Although the toner adhering to the toner concentration sensor is removed by such blowing air, the state of the removal cannot be said to be sufficient, and the detection operation deteriorates with time. Further, since the toner concentration sensor is arranged in the vicinity of the photoconductor, the toner concentration sensor may come into contact with and damage the surface of the photoconductor when the cleaning unit for cleaning the photoconductor or the photoconductor is attached or detached. .

As a proposal for such improvement, JP-A-64-5
An image forming apparatus disclosed in Japanese Patent Laid-Open No. 0079 is known. In this publication example, the toner concentration sensor is provided so as to be freely movable between a detection position close to and opposite to the photoconductor and a retracted position away from the photoconductor, and when the cleaning unit or the photoconductor is attached to or detached from the apparatus main body. In addition, the concentration sensor can be moved to the retracted position. Further, when the cleaning blade is separated when the photosensitive drum is attached or detached, the toner concentration sensor is separated, and the incident surface of the toner concentration sensor is cleaned,
It prevents detection deterioration over time.

[0005]

However, in the image forming apparatus of the above-mentioned conventional example, it is considered that the toner image pattern contaminates the contact transfer member and the toner density cannot be controlled accurately. Further, it may be considered that the backside stain of the transfer paper cannot be reliably prevented.

The present invention solves the above-mentioned drawbacks in the prior art. The toner image pattern does not contaminate the contact transfer member, the toner density can be controlled accurately, and the toner image pattern is returned to the photosensitive member by applying a bias. It is an object of the present invention to provide an image forming apparatus capable of surely preventing backside smearing of transfer paper by performing bias cleaning again when the toner density thus obtained is equal to or higher than a predetermined density.

[0007]

In order to achieve the above object, the invention according to claim 1 is a toner image pattern for controlling toner density in an image forming apparatus using a two-component developing machine and a contact transfer member. When the density sensor is developed on the image carrier, the density sensor approaches the image carrier, the contact transfer member separates from the image carrier, and at least when the density sensor does not approach the image carrier, The detection surface is covered with the density sensor cover.

According to a second aspect of the present invention, there is provided a contact transfer member which comes into contact or non-contact with the image carrier, a bias is applied to the contact transfer member, and contaminants on the surface of the contact transfer member are transferred to the image carrier. In an image forming apparatus that adheres and cleans the surface of the contact transfer member, the density sensor detects the amount of toner that has adhered to the surface of the image carrier from the contact transfer member, and the bias application time is based on this detection level. Is controlled.

[0009]

With such a structure, in the image forming apparatus according to the first aspect, when the toner image pattern is developed on the image carrier, the contact transfer member is separated from the image carrier and the toner image pattern is formed. Contamination of the contact transfer member is prevented. Further, by bringing the density sensor close to the image carrier, the detection accuracy is improved, and the toner density is controlled with high accuracy. Further, since the detection surface is located under the density sensor cover when the density sensor is separated, the detection surface is prevented from being contaminated by contaminants and the detection operation does not deteriorate.

According to another aspect of the image forming apparatus of the present invention, when cleaning the surface of the contact transfer member, application of a bias causes contaminants such as paper powder and toner adhering to the surface of the contact transfer member to the image carrier. Will be returned. The toner density is measured by a density sensor, and when a density equal to or higher than a set value is detected, bias cleaning (control of bias application time) is performed again to remove dirt on the contact transfer member.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the image forming apparatus of the present invention will be described in detail with reference to the drawings. FIG. 1 is a side view showing the configuration of an image forming unit in an embodiment of the image forming apparatus of the present invention.
In FIG. 1, this image forming unit applies a charge to the charge eliminating lamp 1 that emits light for eliminating charge, a photoconductor (image carrier) 2 that is irradiated with the light from the charge eliminating lamp 1, and the photoconductor 2. The charging roller 3 is provided. Also, a developing unit 4 for applying a bias to the image portion of the photoconductor 2,
A developing roller 5 to which a bias is set by the developing unit 4 on the image portion of the photoconductor 2, a transfer roller (contact transfer member) 6 for conveying the transfer paper, and a cleaning blade for scraping off the residual toner remaining on the photoconductor 2. 7 are provided.

Further, a transfer section 8 consisting of the transfer roller 6 and a drive section shown in FIG. 2 and a density sensor section 9 shown in FIG. 3 are provided.

FIG. 2 is a side view showing the structure of the transfer section 8. FIG. 2A shows a state in which the solenoid is on, and FIG. 2B shows a state in which the solenoid is off. 2A and 2B, a transfer case 10 is attached to the transfer roller 6 by biasing the transfer roller 6 with a spring so as to contact the surface of the photoconductor 2, and the transfer case 10 is a fulcrum. An arm 11 for vertically moving (transfer roller 6 is in contact with / not in contact with the photosensitive member 2) around 11a is provided.

Further, the end of the arm 11 is connected so as to move up and down by turning on / off, and the transfer case 10 is connected.
The solenoid 12 for contacting / non-contacting the transfer roller 6 with the surface of the photoconductor 2, the spring 13 having elasticity in the direction to bring the transfer roller 6 of the transfer case 10 into contact with the photoconductor 2, and the transfer roller 6. A spring 14 that biases the photoconductor 2 so as to press it is provided.

FIG. 3 is a side view showing the structure of the density sensor unit 9. FIG. 3A shows a state in which the density sensor is arranged at the non-detection position, and FIG. 3B shows a state in which the density sensor is arranged at the detection position. In FIGS. 3A and 3B, the density sensor unit 9 includes a density sensor 20 for detecting the toner density, and to prevent the density sensor 20 from being contaminated by contaminants such as paper powder and toner. A density sensor cover 21 is provided on the upper part of the density sensor 20 in the figure so as to be openable and closable.

Further, when the density sensor 20 moves, a cleaner 22 for touching the detection surface of the density sensor 20 and for moving and cleaning the detection surface, and turning on when detecting the toner density, drives the arm to drive the density sensor. 20 for photoconductor 2
A solenoid 23 for displacing the density sensor 20 so as to face the same, a spring 24 for positioning the density sensor 20 under the density sensor cover 21, and an arm for moving the density sensor 20 to face the photoconductor 2 when the solenoid 23 is turned on. Two
And 5 are provided.

The arm 25 has an inverted L-shaped upper part to which the density sensor 20 is fixed, and the lower end is connected to the solenoid 23 and moves in the horizontal direction so that the density sensor 20 faces the photoconductor 2. An arm part 25a for arranging (tilting), an arm part 25b fixed to the drive part of the solenoid 23, and extending entirely in an L shape, and having the concentration sensor cover 21 attached to the tip thereof. It has an arm portion 25c for connecting the arm portions 25a and 25b to facilitate driving (movement).

Density sensor 20 and density sensor cover 21
When the solenoid 23 is turned on, the density sensor cover 21
Is drawn. Further, the cleaner 22 pushes up the open / close part of the density sensor cover 21 while cleaning the detection surface of the density sensor 20. As a result, the detection surface of the density sensor 20 is tilted at a position close to and opposite to the photoconductor 2. When the solenoid 23 is turned off, the elasticity of the spring 24 pulls the arm 25, and the concentration sensor 20 retracts below the concentration sensor cover 21. Since the transfer roller 6 and the density sensor 20 are separated from the photoconductor 2 when the main motor (not shown) is off, the solenoid 12 and the solenoid 23 are off. During a normal copying operation, the solenoid 12 is turned on and the transfer roller 6 is in contact with the photoconductor 2.

Then, for example, a toner image pattern is formed in a valley between the image portions at a timing of once or twice every five copying operations, and a solenoid is provided while the toner image pattern passes through the transfer roller 6 portion. 12 is turned off, and the transfer roller 6 is separated from the photoconductor 2. At the same time, the solenoid 23 is turned on, the density sensor 20 approaches the photoconductor 2, detects the density of the toner image pattern, and controls the toner density by the detection.

Next, the operation of this embodiment will be described. In FIG. 1, the image forming unit includes a charge eliminating lamp 1 to a photoconductor 2
Exposure is performed by irradiating light to the. The surface potential of the photoconductor 2 is set to a reference potential of 0 to -150 volts (V), for example. Next, the charging roller 3 charges the photoconductor 2 to set the surface potential of the photoconductor 2 to, for example, about -1100V. Then, the digitally recorded image information is received and amplified by a line driver (not shown). This digitally recorded image information has 1 bit per pixel (recorded / non-recorded)
Corresponding to the binarized signal, the laser driver drives a laser diode (not shown) to emit light.

The laser light from the laser diode forms an image on the photoconductor 2. Here, the surface potential of the photoconductor 2 in a portion (image portion) irradiated with light is, for example, 0 to −290 V.
In this image portion, the toner in the developing unit 4 adheres to the developing roller 5 in the next developing unit 4 because the developing roller 5 has a bias of, for example, about -800V.
The non-image area (background area) remains around -1100V,
No toner adheres.

When the development of the toner image is completed, the photosensitive member 2 is rotationally moved, and the transfer sheet (not shown) is conveyed from the sheet feeding section (not shown) at such a timing that the leading edge of the sheet and the leading edge of the image are aligned by the transfer roller 6. To be done. Transfer roller 6 to photoreceptor 2
The toner image having the surface potential of is transferred to the transfer paper, and the transfer paper is separated by a separation unit (not shown).

This transfer paper is conveyed to a fixing unit (not shown), and the toner is fused to the transfer paper by heat and pressure and sent out as copy paper. On the other hand, the residual toner remaining on the photoconductor 2 is scraped off by a cleaning blade 7 of a cleaning unit (not shown), and the toner is not attached to the photoconductor 2. Simultaneously with the end of the copy operation, the drive source on the main body side operates in reverse and stops. After that, the process proceeds to the next image forming process again.

In FIG. 2, the transfer roller 6 is attached to the transfer case 10 so as to be pressed by the spring 13 against the photoconductor 2, and the transfer case 10 is connected to the solenoid 12 via the arm 11. Has been done. Figure 2
When the solenoid 12 is turned on as shown in (a), the transfer roller 6 comes into contact with the photoconductor 2, and when the solenoid 12 is turned off as shown in FIG. Separate.

In FIG. 3, the density sensor unit 9 is located under the density sensor cover 21 when the density sensor 20 is separated from the density sensor unit 20, and is contaminated by contaminants such as paper dust and toner. I try not to occur. Further, when the detection surface of the density sensor 20 becomes dirty, a cleaner 22 is provided on the lower surface of the density sensor cover 21 to remove the dirt. Then, when the density sensor 20 moves as shown in FIG. 3B, the detection surface thereof is cleaned.

Density sensor 20 and density sensor cover 21
When the solenoid 23 is turned on, the density sensor cover 21 is pulled from the position shown in FIG. 3A and the cleaner 22 cleans the detection surface with the cleaner 22, while the density sensor 20 opens and closes the density sensor cover 21. It is pushed up and displaced to the position shown in FIG. 3B, which is close to the photoconductor 2 and the detection surface faces the photoconductor 2.

When the solenoid 23 is turned off, the elasticity of the spring 24 pulls the arm 25 and the concentration sensor 20
Is retracted under the density sensor cover 21. Transfer roller 6
Since the density sensor 20 is separated from the photoconductor 2 when the main motor (not shown) is off, the solenoid 1
2 and the solenoid 23 are off. During a normal copying operation, the solenoid 12 is turned on and the transfer roller 6
Is in contact with the photoconductor 2.

FIG. 4 is a timing chart showing an operation state at the time of forming a toner image pattern, and FIG. 5 is a timing chart showing an operation state at the time of bias cleaning.

As shown in FIG. 4A, a toner image pattern is formed in the valley between the image portions at the timing of once or twice every five times of the copy operation, and the toner image pattern is formed. While (paper interval) passes through the transfer roller 6 portion, the solenoid 12 is turned off and the transfer roller 6 is separated from the photoconductor 2 as shown in (b) of FIG. Figure 4 at the same time
As shown in (c), the solenoid 23 is turned on,
The density sensor 20 is close to the photoconductor 2, detects the density of the toner image pattern, and controls the toner density by the detection.

After the concentration is detected, the solenoid 12 is turned on again and the solenoid 23 is turned off. This returns to the normal copy operation. Alternatively, it is also possible to create a toner image pattern and perform density detection after copying a certain number of copy sheets (passing). This case is effective when there is no room to form a toner image pattern between sheets at high speed.

Further, in the bias cleaning mode shown in FIG. 5A of the transfer roller 6 performed every time a certain number of copy papers are processed (paper passing) and after the transfer paper is jammed, the bias cleaning mode shown in FIG. As shown in (b) and (c), the solenoid 12 and the solenoid 23 are turned on, the transfer roller 6 contacts the photoconductor 2, and the density sensor 20 approaches the photoconductor 2.

In this transfer roller cleaning mode,
The toner attached to the transfer roller 6 is first applied with a voltage having a polarity opposite to that of the toner, for example, for 4 seconds, and then a voltage having the same polarity as the toner is applied for 4 seconds. This operation is once,
The toner attached on the transfer roller 6 is returned to the photoconductor 2. At this time, the density of the toner returned to the photoconductor 2 is detected by the density sensor 20 at a predetermined timing, as shown in (d) of FIG. 5, and the density is larger than the set value (the detection voltage is low. In this case, execute the cleaning mode again.

When the density becomes lower than the set value, the cleaning mode is terminated and the solenoid 12
And the solenoid 23 is turned off. Therefore, the adhered toner on the transfer roller 6 is removed and the backside of the transfer paper is prevented from being soiled. In the cleaning mode, the transfer paper is not passed.

Although the digital copying machine has been described in this embodiment, an analog copying machine operates similarly.

[0035]

As is apparent from the above description, according to the image forming apparatus of claim 1, when the toner image pattern is developed on the image carrier, the contact transfer member is separated from the image carrier. In addition, since the density sensor is brought close to the image carrier and the detection surface is located under the density sensor cover when the density sensor is separated, it is possible to prevent the contact transfer member from being contaminated with the toner image pattern, and The detection accuracy is improved, the toner concentration is controlled with high accuracy, and the detection surface is prevented from being contaminated by contaminants, so that the detection operation does not deteriorate. According to the image forming apparatus of claim 2, when the surface of the contact transfer member is cleaned, the contaminants attached to the surface of the contact transfer member are returned to the image carrier by the bias application, and the toner density is reduced. Since the bias cleaning is performed again when the density is measured and the density above the set value is detected,
It has an effect that dirt on the contact transfer member can be removed.

[Brief description of drawings]

FIG. 1 is a side view showing a configuration of an image forming unit in an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a side view showing a configuration of a transfer roller and a driving unit in the embodiment. (A) is a side view showing a state in which a solenoid is turned on. (B) is a side view showing a state in which the solenoid is off.

FIG. 3 is a side view showing a configuration of a density sensor and a driving unit in the embodiment. (A) is a side view showing a state in which the density sensor is arranged at a non-detection position. (B) is a side view showing a state in which the density sensor is arranged at the detection position.

FIG. 4 is a timing chart showing an operation state at the time of forming a toner image pattern in the embodiment.

FIG. 5 is a timing chart showing an operation state during bias cleaning in the embodiment.

[Explanation of symbols]

 1 Static Elimination Lamp 2 Photosensitive Member 3 Charging Roller 4 Developing Unit 5 Developing Roller 6 Transfer Roller 7 Cleaning Blade 10 Transfer Case 11, 25 Arms 12, 13, 14, 23 Solenoid 20 Density Sensor 21 Density Sensor Cover 22 Cleaner

Claims (2)

[Claims] 1. In an image forming apparatus using a two-component developing machine and a contact transfer member, when a toner image pattern for controlling toner density is developed on an image carrier, a density sensor is brought close to the image carrier. Further, the image forming apparatus is characterized in that the contact transfer member is separated from the image carrier and at least the detection surface is covered with the density sensor cover when the density sensor is not close to the image carrier. 2. A contact transfer member which is in contact with or non-contact with the image carrier, and a bias is applied to the contact transfer member,
An image forming apparatus that cleans the surface of a contact transfer member by adhering contaminants on the surface of the contact transfer member to the image carrier. And the bias application time is controlled based on this detection level.