JPH09146388A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the quality of an image by maintaining the temperature of paper transfer roller so as to fall within a predetermined fixed range at all times. SOLUTION: A temperature maintaining means 7 maintains the temperature of the paper transfer roller 232 so as to fall within the predetermined fixed range, thereby keeping the resistance value of transfer paper and that of the paper transfer roller 232 equal. When the transfer paper is passed between the intermediate transfer belt 221 and the paper transfer roller 232 while pinched between them, a fixed voltage is applied to the paper transfer roller 232 to transfer a toner image, formed on the intermediate transfer belt 221, to the transfer paper.

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, and more particularly to improving the quality of an image formed.

[0002]

2. Description of the Related Art When a transfer paper passes between an intermediate transfer belt and a paper transfer roller, an image forming apparatus for charging the paper transfer roller to transfer the toner image formed on the intermediate transfer belt onto the transfer paper is used. There may be a problem of defective transfer at the end portion in which the density of a portion is lower than the density of a central portion. This is because the resistance value of the paper transfer roller 232 is extremely lower than the resistance value of the transfer paper 8 as shown in FIG. 4, so that at the end of the transfer paper 8, the transfer current I spills out of the transfer paper. It is generated because it does not flow to the end. On the other hand, by making the resistance values of the transfer paper 8 and the paper transfer roller 232 equal to each other, a uniform transfer current I flows between the end portion and the central portion of the transfer paper 8 as shown in FIG. Has been developed.

Since the resistance value of the paper transfer roller is easily affected by environmental changes such as temperature and humidity, in order to make the resistance values of the transfer paper and the paper transfer roller equal, for example, JP-A-2-22397.
In the contact charging device disclosed in Japanese Patent Publication No. 2, the heat source heats the water in the water tank to generate water vapor, thereby keeping the humidity environment of the paper transfer roller constant. In addition, JP-A-4-190
In the transfer corona discharge control device disclosed in Japanese Patent No. 381, the output set value of the transfer corona discharge is changed according to the humidity, so that the resistance of the transfer paper is changed by the humidity.

[0004]

However, as shown in FIG. 6, the transfer roller 232 tends to have a high resistance value at a low temperature, and the higher the resistance value, the more remarkable this tendency is. Therefore, the optimum transfer bias at a low temperature becomes extremely high as shown in FIG. 7, and the optimum transfer area F of the transfer bias may exceed the control range only by keeping the humidity environment constant.

The present invention has been made to solve the above disadvantages, and an object of the present invention is to improve the quality of a formed image by always keeping the temperature of the paper transfer roller within a predetermined temperature range. To do.

[0006]

An image forming apparatus according to the present invention comprises a temperature holding means, an intermediate transfer belt and a paper transfer roller, and the temperature holding means keeps the temperature of the paper transfer roller within a predetermined temperature range. Holds the resistance value of the transfer paper and the resistance value of the paper transfer roller to be equal, and when the transfer paper passes while being sandwiched between the intermediate transfer belt and the paper transfer roller between the intermediate transfer belt and the paper transfer roller, the paper transfer roller A toner image formed on the intermediate transfer belt is transferred to the transfer paper by applying a constant voltage to the transfer paper to prevent the density of the edge of the transfer paper from becoming lower than the density of the central part.

Further, the temperature holding means has a heater for heating the paper transfer roller, a temperature detecting means and a heater control means,
The temperature detection means detects the temperature of the paper transfer roller or the vicinity thereof, and the heater control means controls the current flowing through the heater for heating the paper transfer roller based on the temperature detected by the temperature detection means to control the temperature of the paper transfer roller. By keeping the temperature within a predetermined temperature range, the resistance value of the paper transfer roller changes within the predetermined temperature range.

Further, the temperature holding means holds the temperature of the paper transfer roller within a predetermined temperature range when a power outlet is inserted and turns on the main switch to turn on the power. In addition, the temperature of the paper transfer roller is set within a predetermined range to prevent uneven temperature distribution on the paper transfer roller.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The image forming apparatus of the present invention is used in, for example, a color copying apparatus, and an optical writing unit, a photoconductor drum, an intermediate transfer belt and a paper transfer roller are provided in a printer portion for writing an image. Prepare
The optical writing unit converts image data input from a scanner or the like into an optical signal and performs an optical writing process corresponding to the original image to form an electrostatic latent image on the photosensitive drum. The photosensitive drum transfers the toner image onto the intermediate transfer belt. The paper transfer roller is usually separated from the intermediate transfer belt,
The intermediate transfer belt is pressed at the timing when the image formed on the surface of the intermediate transfer belt is transferred to the transfer sheet. In this state, by applying a predetermined bias voltage to the paper transfer roller, the toner image on the intermediate transfer belt is transferred to the transfer paper.
Here, if the resistance value of the paper transfer roller is extremely lower than the resistance value of the transfer paper, the transfer current spills out of the transfer paper and does not flow to the end portion of the transfer paper. Since the phenomenon that the density becomes lower than the density may occur, by making the resistance values of the transfer paper and the paper transfer roller equal, a uniform transfer current is made to flow to the end part and the center part of the transfer paper, resulting in defective transfer at the end part. To prevent the occurrence of.

The resistance value of the paper transfer roller is easily affected by environmental changes such as temperature and humidity. Especially, the transfer roller tends to have a high resistance value at a low temperature. The higher the resistance value, the more remarkable this tendency is. Become. Therefore, in the present invention, a temperature holding unit having a heater for heating the paper transfer roller is provided, and the temperature of the paper transfer roller is held within a predetermined temperature range by using the heater for heating the paper transfer roller. . It should be noted that the temperature within the predetermined constant temperature range is determined within the range set so that the optimum transfer bias does not exceed the control range, although it depends on the temperature of the recording paper or the like.

For example, the temperature holding means has a heater for heating the paper transfer roller, a temperature detection means, and a heater control means, the temperature detection means detects the temperature of the paper transfer roller or the vicinity thereof, and the heater control means has the temperature detection means. The temperature of the paper transfer roller is maintained within a predetermined temperature range by controlling the current flowing through the heater that heats the paper transfer roller based on the temperature detected by the Set within the range. The temperature detecting means may directly detect the temperature of the paper transfer roller, or may indirectly detect the temperature of the paper transfer roller by detecting the temperature around the paper transfer roller.

Further, since it may take a long time for the temperature of the paper transfer roller to reach a predetermined constant temperature after the power switch is turned on, the temperature holding means is used when the power outlet is inserted. Always keep the temperature of the paper transfer roller within a predetermined temperature range, and always keep the temperature of the paper transfer roller within the predetermined range when the main switch is turned on and the power is turned on. It is also possible to prevent unevenness in the temperature distribution above.

[0013]

FIG. 1 is a block diagram of an image forming apparatus according to an embodiment of the present invention. As shown in the figure, the image forming apparatus includes a scanner 1, a printer 2, a paper feed unit 3, and a transport unit 4. The scanner 1 irradiates a color image on the original 10 with an irradiation lamp 101.
From the original document 1 and the reflected light is imaged on the color sensor 104 via the mirror group 102 and the lens 103.
The color image on 0 is, for example, blue (hereinafter, referred to as “B”), green (hereinafter, referred to as “G”), and red (hereinafter, referred to as “G”).
It is called "R". ) Each color is read and converted into an electrical signal. The color sensor 104 is B in this example.
Equipped with G and R color separation means and a photoelectric conversion element such as CCD,
Three colors are read simultaneously. An image processing unit (not shown) performs color conversion processing based on the intensities of the B, G, and R color image signals obtained by the scanner 1, and black (hereinafter referred to as "Bk"), cyan (hereinafter referred to as "C"). .), Magenta (hereinafter referred to as “M”), and yellow (hereinafter referred to as “Y”) color image data.

Writing optical unit 201 of printer 2
Is provided with a laser 202, a light emission drive control unit (not shown) that controls light emission of the laser 202, a polygon mirror 203, a polygon mirror rotation motor 204, an fθ lens 205, and a reflection mirror 206, and outputs color image data from the scanner 1 It is converted into a signal, and an optical writing process corresponding to the original image is performed to form an electrostatic latent image on the photosensitive drum 211. The photoconductor drum 211 rotates counterclockwise. A photosensitive drum cleaning unit 21 is provided around the photosensitive drum 211.
2, static elimination lamp 213, charger 214, potential sensor 21
5, Bk developing device 216, C developing device 217, M developing device 21
8, Y developing device 219, developing density pattern detector 220, and intermediate transfer belt 221 are arranged.

When the copying operation is started, the scanner 1 starts reading Bk image data at a predetermined timing,
Based on this image data, optical writing with a laser beam and latent image formation are started. Hereinafter, an electrostatic latent image based on Bk image data is a Bk latent image, an electrostatic latent image based on C image data is a C latent image, an electrostatic latent image based on M image data is an M latent image, and an electrostatic latent image based on Y image data is a static latent image. It is called a Y latent image. In order to enable development from the front end of the Bk latent image, the developing sleeve 216a before the front end of the latent image reaches the developing position of the Bk developing device 216.
Is rotated to develop the Bk latent image with Bk toner. When the trailing edge of the latent image passes the Bk developing position, the Bk developing sleeve 216a is quickly cut off to put it into the development inoperative state.
This is completed at least before the leading edge of the C latent image by the next C image data reaches the developing position. In addition, the above-mentioned cutting is performed by switching the rotation direction of the developing sleeve 216a to the opposite direction to that during the developing operation.

The Bk toner image formed on the photoconductor drum 211 is applied with a predetermined bias voltage to the transfer bias roller 222 while the photoconductor drum 211 and the intermediate transfer belt 221 are in contact with each other.
The image is transferred to the intermediate transfer belt 221 driven at the same speed as. The intermediate transfer belt 221 is stretched around a transfer bias roller 222, a counter roller 223 which is a driving roller, and a driven roller 224, and is rotated by a driving force from a driving motor (not shown). The intermediate transfer belt 22
There are three types of movements of 1 for example, "constant speed forward movement method", "skip forward movement method" and "reciprocating movement method", and the intermediate transfer belt 221 has 1 of these movements according to the copy size and the like.
The movement is based on a method or a combination of methods.

After the Bk toner image processing step, the printer 2 proceeds to the C image processing step. The C image data is read by the scanner 1 at a predetermined timing, and the writing optical unit 201 forms a C image latent image on the photosensitive drum 211 by laser writing based on the read image data. The C developing device 217 rotates the developing sleeve 217a after the trailing edge of the previous Bk latent image passes through the developing position and before the leading edge of the C latent image arrives, thereby making a spike. The image is developed with C toner. When the rear end portion of the latent image passes through the C developing device 217, the C developing sleeve 217a is cut off like the previous Bk developing device 216. Hereinafter, the M developing device 218 and the Y developing device 219 are referred to as the C developing device 21.
The same operation as 7 is performed.

The paper transfer unit 231 transfers the toner image formed on the intermediate transfer belt 221 to the transfer paper 8.
The paper transfer unit 231 includes a paper transfer roller 232, a roller cleaning blade 233, a contact / separation mechanism section 234, and the like. The paper transfer roller 232 is usually the intermediate transfer belt 2
It is separated from 21. The contact / separation mechanism section 234 causes the paper transfer roller 232 to move the intermediate transfer belt 221 at the timing of collectively transferring the four color images on the intermediate transfer belt 221 to the transfer paper 8.
Press While pressing the paper transfer roller 232 against the intermediate transfer belt 221, a predetermined bias voltage is applied to the paper transfer roller 232 to transfer the image on the intermediate transfer belt 221 to the transfer paper 8.

The paper feed roller 301 and the registration roller 302 of the paper feed unit 3 transfer the transfer paper 8 at the timing when the leading edge of the image on the intermediate transfer belt 221 reaches the paper transfer position.
Feed.

The conveying section 4 conveys the transfer paper 8 on which the four-color superimposed toner images are collectively transferred from the intermediate transfer belt 221 to the fixing device 5. The fixing device 5 has a fixing roller 501 and a pressure roller 502 which are controlled to reach a predetermined temperature. The fixing roller 501 and the pressure roller 502 melt and fix the toner image on the transfer paper 8. The transport unit 4 transports the transfer paper 8 on which the image is fixed by the fixing device 5 to the copy tray 6.

The photosensitive drum 2 after the transfer of the image
The surface of 11 is cleaned by the photoconductor cleaning unit 212, and the charge is uniformly discharged by the charge removing lamp 213.

In the image forming apparatus having the above structure, when the resistance value of the paper transfer roller 232 is extremely lower than the resistance value of the transfer paper 8,
Since the transfer current spills out of the transfer paper 8 and does not flow to the edge of the transfer paper 8, the edge transfer failure may occur in which the density of the edge of the transfer paper becomes lower than the density of the central portion.
And the paper transfer roller 232 have the same resistance value, a uniform transfer current is applied to the end portion and the central portion of the transfer paper 8, and the density of the end portion of the transfer paper becomes lower than the density of the central portion. To prevent the occurrence of.

Since the resistance value of the paper transfer roller 232 is susceptible to environmental changes such as temperature and humidity, the temperature holding means 7 is provided as shown in FIG. The temperature holding unit 7 includes a heater 701 that heats the paper transfer roller 232 and a thermo switch 702. The heater 701 is the paper transfer unit 23.
1, which is provided in the lower part of 1, heats the paper transfer unit 231. The thermo switch 702 is connected to the heater 701 and the power source unit 703 as shown in FIG.
When 31 exceeds the set temperature range, heating by the heater 701 is stopped and the temperature of the paper transfer roller 232 is maintained within a predetermined constant temperature range. Here, the set temperature range refers to a temperature range set so that the optimum transfer bias does not exceed the control range, and is set to, for example, a range of 25 ° C to 28 ° C. In the figure, since the thermo switch 702 is provided on the registration roller cover 241, the actual paper transfer roller 232.
Although there is an error with the temperature of, it is handled by changing the setting of the temperature range.

In the above embodiment, the thermoswitch 70 is used.
Although the heater 701 is controlled by using 2, the thermistor is used as a temperature detecting means for detecting the temperature of the paper transfer roller 232, and the paper transfer roller 232 detected by the thermistor is used.
The heater 701 is controlled based on the temperature of the paper transfer roller 2
A heater control means for maintaining the temperature of 32 within a predetermined temperature range may be provided. By directly measuring the temperature of the paper transfer roller 232 using a thermistor, more accurate control can be performed.

Further, since it may take a long time for the temperature of the paper transfer roller 232 to reach a predetermined constant temperature after the power switch is turned on, the temperature holding means 7 is plugged into a power outlet. At this time, the temperature of the paper transfer roller 232 is always kept within a predetermined temperature range, and when the main switch is turned on and the power is turned on, the temperature of the paper transfer roller 232 is always within the predetermined range. You may do it.

Further, in the above-described embodiment, the temperature of the paper transfer roller 232 is kept constant by passing or shutting off the current to the heater 701, but the current flowing to the heater 701 is changed to change the temperature of the paper transfer roller 232. The temperature may be kept constant.

[0027]

As described above, according to the present invention, since the temperature of the paper transfer roller is kept within a predetermined temperature range, the toner image formed on the intermediate transfer belt is transferred to the intermediate transfer belt and charged on the paper. When transferring to the transfer paper passing between the rollers, it is possible to keep the resistance value of the transfer paper and the resistance value of the paper transfer roller equal, and it is possible to prevent unevenness in image density.

Further, the temperature of the paper transfer roller or in the vicinity thereof is detected, and the temperature of the paper transfer roller is controlled within a predetermined temperature range by controlling the current flowing through the heater for heating the paper transfer roller based on the detected temperature. Since it is held at, the change in the resistance value of the paper transfer roller can be kept within a certain temperature range.

Further, the temperature of the paper transfer roller is always kept within a predetermined temperature range when the power outlet is inserted, and the paper transfer is performed when the main switch is turned on and the power is turned on. Since the temperature of the roller is set within a predetermined range, it is possible to prevent uneven temperature distribution on the paper transfer roller.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a basic configuration of an embodiment of the present invention.

FIG. 2 is a configuration diagram of a paper transfer unit.

FIG. 3 is a connection diagram of a thermoswitch.

FIG. 4 is a configuration diagram showing a configuration when an edge transfer defect occurs.

FIG. 5 is a configuration diagram showing a schematic configuration for preventing edge transfer failure.

FIG. 6 is a waveform diagram showing the relationship between the temperature of the paper transfer roller and the resistance value of the paper transfer roller.

FIG. 7 is a waveform diagram showing the relationship between the temperature of the paper transfer roller and the optimum transfer bias.

[Explanation of symbols]

 1 Scanner 2 Printer 211 Photosensitive Drum 221 Intermediate Transfer Belt 231 Paper Transfer Unit 232 Paper Transfer Roller 7 Temperature Holding Means 701 Heater 702 Thermo Switch 703 Power Supply 704 Thermistor 705 Heater Control Means 8 Transfer Paper

Claims (3)

[Claims] 1. A toner formed on an intermediate transfer belt by applying a constant voltage to the paper transfer roller when the transfer paper passes while being sandwiched between the intermediate transfer belt and the paper transfer roller by the intermediate transfer belt and the paper transfer roller. An image forming apparatus for transferring an image onto a transfer sheet, comprising: a temperature holding unit for holding a temperature of a paper transfer roller within a constant temperature range. 2. The temperature holding means is a heater for heating the paper transfer roller, a temperature detecting means for detecting the temperature of the paper transfer roller or its vicinity, and a heater for heating the paper transfer roller based on the temperature detected by the temperature detecting means. The image forming apparatus according to claim 1, further comprising a heater control unit that controls a current to flow to maintain the temperature of the paper transfer roller within a predetermined constant temperature range. 3. The image forming apparatus according to claim 1, wherein the temperature holding unit holds the temperature of the paper transfer roller within a predetermined temperature range when a power outlet is inserted.