JP2003262993A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of appropriately controlling a bias voltage applied to an electrifying roller even when environment is changed without complicating its configuration and control and without causing a cost rising. <P>SOLUTION: The image forming apparatus equipped with an electrifying means for electrifying the surface of an image carrier, and a transfer means for transferring a toner image formed by the image carrier to transfer material, is constituted to solve the problems by being equipped with a resistance value detection means for detecting the resistance value of the transfer means due to environmental change and a control means for controlling bias applied to the electrifying means in accordance with the result of detection by the resistance value detection means. <P>COPYRIGHT: (C)2003,JPO

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 digital copying machine or a printer adopting an electrophotographic system, and more particularly to an image forming apparatus provided with an environmental control means for charging means.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a digital copying machine or a printer adopting the electrophotographic method, the surface of a photosensitive drum is uniformly charged by a charging means, and then the surface of the photosensitive drum is charged. Image exposure is performed to form an electrostatic latent image according to image information, and the electrostatic latent image is developed by a developing device to form a toner image. In the image forming apparatus, the toner image formed on the photoconductor drum is transferred onto the recording paper fed from the paper feeding device, and then the recording paper on which the toner image is transferred is fixed to the fixing device. The image is formed by fixing with heat and pressure.

By the way, as a charging means for uniformly charging the surface of the photoconductor drum, there are many charging rollers which can replace ozone of the conventional scorotron with less generation of ozone and the like and which can reduce the size of the high voltage power source. Has been used. Further, this charging roller is used by applying a DC bias voltage on which an AC bias voltage is superposed in consideration of the uniformity of charging and the adhesion of toner to the surface of the charging roller.

However, in the above-mentioned photoconductor drum, the charge transport layer (C) on the surface of the photoconductor (OPC photoconductor) drum is discharged by the discharge by applying the AC bias voltage of the charging roller.
TL) is deteriorated by discharge, and the charge transport layer (CTL) on the surface of the photosensitive drum, which has been deteriorated by discharge, is scraped by rubbing of a cleaning blade, a transfer roller, or the like, and the surface of the photosensitive drum cannot be charged. Becomes

Further, the voltage applied to the charging roller is
In an image forming apparatus that applies a fixed (constant) bias voltage to a charging roller without controlling according to environmental changes such as temperature and humidity, in order to cope with the high temperature and high humidity environment where charging conditions are the worst, The highest AC bias voltage must be applied to the charging roller, which greatly shortens the life of the photosensitive drum.

Therefore, the discharge deterioration of the photosensitive drum is suppressed as much as possible and the life of the photosensitive drum is extended more than when the voltage applied to the charging roller is set so as to be adapted to the environment where the highest AC bias voltage is required. In order to achieve the above, various technologies have been already proposed in which the voltage applied to the charging roller is controlled according to environmental changes such as temperature and humidity to set the AC bias voltage required for each environment.

Techniques for controlling the bias voltage applied to these charging rollers according to environmental changes include, for example, JP-A-5-181350 and JP-A-6-19.
Those disclosed in Japanese Patent No. 4933 or Japanese Patent Laid-Open No. 6-202446 have already been proposed.

The charging device according to the above-mentioned Japanese Patent Laid-Open No. 5-181350 discloses a charging means for charging the surface of a photosensitive member, an AC power supply for supplying an alternating current to this charging means, and an alternating current for superimposing the alternating current on the charging means. A DC power supply for supplying a DC current, a voltage detection means for detecting a voltage, a current detection means for detecting a current, and a control for controlling the DC power supply based on detection signals from the voltage detection means and the current detection means. And an environment detecting means for detecting temperature and humidity and outputting the detection signal to the control means.

Further, in the charging device according to the above-mentioned Japanese Patent Laid-Open No. 6-194933, the charging member is placed in contact with the member to be charged or facing the member to be charged with a minute gap therebetween. In a charging device that applies a DC voltage to discharge an object to be charged to charge the object to be charged, a constant current of a minute current is applied to a charging member, and the voltage V applied thereby is measured to discharge. The starting voltage is determined, and the voltage applied to the charging member is determined based on the starting voltage.

Further, in the image forming apparatus according to Japanese Patent Laid-Open No. 6-202446, an image forming process including a charging step is applied to the image carrier to execute image formation, and the image carrier is repeatedly used. A charging device for charging the image carrier is a charging member that contacts the image carrier or faces the image carrier with a small gap, and a voltage applying means for applying a DC bias to the charging member. A detection means for detecting an effective current flowing through the charging member, and a DC voltage is repeatedly applied in a pulsed manner to the charging member by the voltage applying means during arbitrary non-image formation, and an effective current value at this time Is detected by the detection means, and the DC bias value applied to the charging member to charge the image carrier at the time of image formation is determined based on the detection result.

In addition to the above, a technique for controlling the applied bias of the charging roller based on the detection result of the surface potential of the photosensitive member or the film thickness of the photosensitive member, or a control for determining the applied current / applied voltage of the charging roller is used. Various techniques have been proposed.

On the other hand, in an image forming apparatus using a charging roller as a charging means for uniformly charging the surface of the photosensitive drum, a transfer for transferring a toner image formed on the photosensitive drum onto a recording sheet. A transfer roller is generally used as the means.

Usually, in an image forming apparatus using such a transfer roller, the toner image formed on the photosensitive drum is satisfactorily transferred onto a recording sheet even when the environment such as temperature and humidity changes. The bias voltage applied to the transfer roller is variable depending on the environmental conditions. At that time, in an image forming apparatus for the purpose of cost reduction, a constant current / constant voltage is applied to the transfer roller to control the environment from the resistance value of the transfer roller.

[0014]

However, the above-mentioned prior art has the following problems. That is, in the above-mentioned conventional charging device and image forming apparatus, the above-mentioned JP-A-5-181350 and JP-A-6-19 are mentioned.
In order to control the bias voltage applied to the charging roller according to the environment, as disclosed in Japanese Patent Publication No. 4933 or Japanese Patent Application Laid-Open No. 6-202446, environment detecting means for detecting temperature, humidity and the like. , A photoconductor surface potential sensor, a precise electric circuit for applying current / voltage to the charging roller and measuring the voltage / current applied at that time, and charging from the current / voltage detecting means of the charging roller When the environmental control of the roller is carried out, it overlaps with the environmental control of the transfer roller, and the control becomes complicated and the number of detection means increases, so that there is a problem that the cost of the apparatus increases. Further, when environmental control is performed based on the resistance value of the charging roller, it is necessary to reduce resistance variations in the manufacturing process of the charging roller, and there is a problem that the cost of the charging roller as a single unit increases. It was

Therefore, the present invention has been made in order to solve the above-mentioned problems of the prior art, and the object thereof is not to complicate the configuration and control, but also to increase the cost of the apparatus. It is an object of the present invention to provide an image forming apparatus capable of properly controlling the bias voltage applied to the charging roller even when the environment changes.

[0016]

In order to achieve the above-mentioned object, the invention described in claim 1 is a charging means for charging the surface of an image carrier, and a toner image formed by the image carrier is transferred. In an image forming apparatus provided with a transfer means for transferring onto a material, a resistance value detection means for detecting a resistance value of the transfer means due to an environmental change, and application to the charging means according to a detection result of the resistance value detection means. The image forming apparatus is characterized by further comprising: a control unit that controls the bias.

According to a second aspect of the invention, based on the resistance value of the transfer means, the bias applied to the charging means and the exposure light amount for exposing an image on the image carrier are controlled in combination. The image forming apparatus according to claim 1, further comprising means.

Further, in the invention described in claim 3, the bias applied to the charging means and the electrostatic latent image formed on the surface of the image carrier are developed based on the resistance value of the transfer means. The image forming apparatus according to claim 1, further comprising means for controlling by combining the developing biases.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 2 shows a digital printer as an image forming apparatus according to Embodiment 1 of the present invention.

The digital printer is configured to form an image on the basis of image information sent from a personal computer, an image reading device or the like (not shown). Inside the digital printer body 1, a process cartridge 2 in which an image forming member such as a photosensitive drum is integrally unitized is arranged. The process cartridge 2 is configured to be attachable / detachable to / from the printer body 1, and provided on the upper portion of the printer body 1 or the like when the photoconductor drum or the like provided in the process cartridge 2 reaches the end of its life. The cover can be opened and replaced with a new cartridge 2.

As shown in FIGS. 2 and 3, the process cartridge 2 has a photosensitive drum 3 as an image carrier.
A charging roller 4 as a charging means, a developing device 5 as a developing means, and a cleaning device 6.

As the photosensitive drum 3, for example, an organic material in which a charge generating layer (CGL), a charge transporting layer (CTL), etc. are sequentially laminated on a surface of a cylindrical metal core made of aluminum or the like. A photoconductor (OPC) is used, and the photoconductor drum 3 is driven at a predetermined rotational speed by a driving unit (not shown) along the arrow direction. The surface of the photosensitive drum 3 is
As shown in FIG. 3, after being uniformly charged to a predetermined potential by the charging roller 4, the ROS (Ras as the exposing means is used.
Image exposure is performed by a ter Output Scanner (see FIG. 2) to form an electrostatic latent image according to image information. As shown in FIG. 2, the ROS 7 modulates a semiconductor laser on the basis of image information that has been subjected to predetermined image processing by the image processing device 8, and outputs a laser beam LB emitted from the semiconductor laser to a collimator lens, An electrostatic latent image is formed on the surface of the photoconductor drum 3 by scanning and exposing the photoconductor drum 3 through an imaging optical system including a reflection mirror, a polygon mirror, an f-θ lens, and the like. Has been done. Then, the electrostatic latent image formed on the photoconductor drum 3 is developed by the developing device 5 containing the one-component developer (toner) to form a toner image. The developing device 5 may of course use a two-component developer.

As shown in FIG. 2, the toner image formed on the photosensitive drum 3 is transferred onto a recording sheet 10 as a recording medium by a transfer roll 9 as a transfer means. The recording paper 10 is fed from the paper feed cassette 12 by the feed roll 11, is separated by the separation roll 13 and the retard roll 14 one by one, is conveyed to the registration roll 15, and is temporarily stopped. Then, the recording paper 10 is conveyed to the surface of the photosensitive drum 3 by the registration roll 15 in synchronization with the toner image formed on the photosensitive drum 3, and the recording paper 1 is conveyed.
0, the toner image is transferred from the photosensitive drum 3 onto the transfer roll 9
Transcribed by

Recording paper 10 on which this toner image is transferred
After being separated from the photoconductor drum 3, the toner is conveyed to the fixing device 16, fixed by heat and pressure by the heating roll 17 and the pressure roll 18 of the fixing device 16, and then discharged by the discharge roll 19 to the printer body 1. The sheet is discharged onto the sheet discharge tray 20 provided on the upper part of the sheet, and a series of image forming steps is completed.

The cleaning device 6 removes residual toner from the surface of the photoconductor drum 3 after the toner image transfer process is completed, and prepares for the next image forming process.

FIG. 3 shows a process cartridge of the digital printer.

As shown in FIGS. 5 and 6, the process cartridge 2 comprises an upper cartridge 21 and a lower cartridge 22. The upper cartridge 21 and the lower cartridge 22 are connected so as to be tiltable about the engaging pin 25 by engaging portions 23 and 24 and an engaging pin 25 provided at both ends in the width direction thereof. In addition, as shown in FIG. 5, it is biased by a spring 26 provided on the upper surface of the lower cartridge 22, and as shown in FIGS. 7 and 8, the photosensitive drum 3 and the developing roller of the developing device 5 are urged. The tracking rolls 28 provided at both ends of 27 are configured to come into pressure contact with each other at a predetermined pressure (for example, 2 kg on one side).

Further, on the upper surface of the lower cartridge 22, as shown in FIG. 8, an irradiation space 29 for exposing the surface of the photosensitive drum 3 with the laser beam LB emitted from the ROS 7 is substantially fan-shaped. It is provided in.

At one end of the upper cartridge 21,
As shown in FIG. 4, a photosensitive drum 3 is rotatably mounted, a charging roll 4 is provided on a side of the photosensitive drum 3, and a cleaning device 6 is provided on an upper portion thereof. A cleaning blade 31 is provided. The cleaning device 6 also occupies most of the collected toner conveying member 32 that conveys the collected toner removed by the cleaning blade 31 and the upper cartridge 21 that stores the collected toner conveyed by the collected toner conveying member 21. And a toner storage chamber 33. Further, in the upper cartridge 21,
A cover 34 that covers the surface of the photosensitive drum 3 is provided to be openable and closable. As shown in FIG. 4, the cover 34 normally covers the surface of the photoconductor drum 3 to prevent the photoconductor drum 3 from being exposed and deteriorated. In the state of being mounted at a predetermined position, as shown in FIG. 3, it automatically opens with the mounting operation and comes into contact with the transfer roll 9.

On the other hand, the lower cartridge 22 constitutes the developing device 5 itself. A developing roll 27 is rotatably disposed at one end of the housing 35 of the developing device 5, and the surface of the developing roll 27 is triboelectrically charged with toner and regulates the layer thickness of the toner. The restricting member 36 is in contact with. A toner supply member 37 that supplies toner to the surface of the developing roll 27 is rotatably provided on the back side of the developing roll 27. On the back side of the toner supply member 37, a toner accommodating portion 39 that occupies most of the developing device 5 is integrally provided via a toner supply opening 38. A bottom surface 40 of the toner containing portion 39 is formed by connecting two portions 41 and 42 each having a substantially arcuate cross section.
Inside the toner container 40, the toner is agitated and conveyed, in which the contained toner is agitated and sequentially conveyed from the second toner container 42 on the back side to the first toner container 41 on the developing roller 27 side. The members 43 and 44 are rotatably arranged.

As shown in FIG. 3, a toner sensor 45 for detecting the presence / absence of toner is provided on the bottom surface of the first toner container 41.

By the way, in this embodiment, in the image forming apparatus provided with the charging means for charging the surface of the image carrier and the transfer means for transferring the toner image formed by the image carrier onto the transfer material. A resistance value detecting means for detecting a resistance value of the transfer means due to an environmental change, and a control means for controlling a bias applied to the charging means according to a detection result of the resistance value detecting means. Has been done.

FIG. 1 is a block diagram showing a control circuit of a digital printer as the image forming apparatus.

In FIG. 1, reference numeral 50 denotes a control device composed of a CPU, an MPU, etc. This control device 50 is based on a program stored in a ROM (not shown), a table or parameters stored in a RAM, etc. It controls an image forming operation of a digital printer as an image forming apparatus. Further, the control device 50 calculates the resistance of the transfer roller from the voltage value or the current value applied to the transfer roller 9 by the transfer roller bias measuring means described later, and changes the bias value applied to the charging roller based on the calculation. To do.

Further, 51 is a high voltage power supply device for the charging roller for applying a DC bias voltage in which an AC bias voltage is superimposed on the charging roller 4, and this high voltage power supply device 51 for the charging roller is instructed from the control device 50. The DC bias voltage and / or the AC bias voltage applied to the charging roller 4 are changed based on the above.

Further, 52 is a high voltage power supply device for the transfer roller which applies a DC bias voltage to the transfer roller 9. Reference numeral 53 is a transfer roller bias measuring unit that applies a constant current or voltage to the transfer roller 9 and measures the voltage value or current value applied to the transfer roller 9.

With the above arrangement, the digital printer as the image forming apparatus according to the embodiment of the present invention is
In the following manner, it is possible to properly control the bias voltage applied to the charging roller even when the environment changes without complicating the configuration and control and without increasing the cost of the device. ing.

That is, in the digital printer according to the present embodiment, when the power supply of the apparatus is turned on, before the printing operation is started, or when a certain number of prints is made, when a certain time elapses, and when no printing operation is performed for a certain time or more As shown in FIG. 9, the control device 50 applies a constant current or voltage to the transfer roller 9 by a high voltage power supply device 52 for the transfer roller at a predetermined timing such as before the start of the next printing. The voltage value or current value applied to the roller 9 is detected by the transfer roller bias measuring means 53 (steps 101 to 102).

Next, the controller 50 calculates and measures the resistance value of the transfer roller 9 based on the voltage value or the current value applied to the transfer roller 9 measured by the transfer roller bias measuring means 53 (step). 103).

The resistance value of the transfer roller 9 normally varies from 10 MΩ to 800 MΩ, as shown in FIG.
Approximately 10 MΩ to 50 MΩ in a high temperature and high humidity environment, 50 MΩ to 300 MΩ in a normal temperature and normal humidity environment, and 3 in a low temperature and low humidity environment.
It becomes 00 MΩ to 800 MΩ.

Therefore, the control device 50, based on the table stored in advance as shown in FIG. 10, changes the resistance value of the transfer roller due to the environmental change and the AC bias and DC applied to the charging roller 4. At least one of the biases is changed (step 103 in FIG. 9).

At this time, the charging performance of the charging roller 4 is as follows.
In the case of constant current control, since the charging performance is poor in a low temperature and low humidity environment, it is necessary to set the AC bias current about 0.1 mA higher than the high temperature and high humidity environment / normal temperature and normal humidity environment, as shown in FIG. On the contrary, in the charge removal performance of the charging roller 4, the charge removal performance of the transfer discharge history is required especially in a high temperature and high humidity environment. For example, if a current value of 1.7 mA is required in a normal temperature and normal humidity environment, set to 1.8 mA in order to secure charging performance in a low temperature and low humidity environment, and 2.0 mA in a high temperature and high humidity environment to secure static elimination performance. Set to.

Further, since the light quantity sensitivity of the photosensitive drum 3 may vary greatly depending on the environment, it is effective to control the exposure light quantity to be decreased in the high temperature and high humidity environment where the sensitivity is high and to increase the exposure light quantity in the low temperature and low humidity environment. Accordingly, by changing the charging potential of the photosensitive member by the DC bias of the charging roller 3 and the developing potential by the developing bias in accordance with the environment,
Optimal image quality can be set in response to insufficient exposure light amount in a low temperature and low humidity environment. As an example, FIG. 10 shows the settings of the AC bias current value, the DC bias voltage value, the exposure light amount, and the developing bias of the charging roller 4 for each environment based on the resistance variation of the transfer roller 9.

As described above, in the embodiment of the present invention, the output of the charging roller 4 is controlled by utilizing the fact that the resistance value of the transfer roller 9 changes depending on the environment. Costs do not increase because there are more means. Further, since the resistance value of the charging roller 4 is not controlled according to the environmental change, even if the resistance of the charging roller 4 varies in the manufacturing process, the environment of the charging roller 4 can be controlled. Can be cheaper.

Further, in the embodiment of the present invention, by changing the AC bias of the charging roller 4 to a value suitable for the environment, the charging roller 4 can be used in an environment where the highest AC bias is required.
The effect of discharge deterioration of the photoconductor can be made smaller than that of the case where the current values of are combined, and the life of the photoconductor is extended. In addition, by setting the DC bias of the charging roller 4, the exposure light amount, and the developing bias to parameters suitable for the environment by environmental control, the charging potential, the exposure potential, and the developing potential can be adjusted to perform control suitable for each environment. It is possible to obtain excellent image quality.

Second Embodiment FIG. 11 shows a second embodiment of the present invention. The same parts as those in the first embodiment will be designated by the same reference numerals in the following description. According to the resistance value of the transfer roller 9, the high temperature / high humidity environment, the normal temperature / normal humidity environment, and the low temperature / low humidity environment are classified and controlled. In the second embodiment, the resistance value of the transfer roller 9 is further finely controlled. It is configured to be divided and to perform smoother control.

That is, in the second embodiment, as shown in FIG.
, The transfer roller 9 has a resistance value of 10 MΩ to 50 MΩ.
In a high temperature and high humidity environment in the range of MΩ, control is performed in the same manner as in the first embodiment, but the resistance value of the transfer roller 9 is 50 MΩ to 1
In the normal temperature and normal humidity environment of 00 MΩ, the AC current value to the charging roller 4 is controlled so as to linearly change from 2.0 mA to 1.7 mA, and the resistance value of the transfer roller 9 is 100 MΩ.
In the range of normal temperature and normal humidity environment of up to 250 MΩ, the first embodiment
Control as with. In addition, the resistance value of the transfer roller 9 is 25
The AC current value to the charging roller 4 is 1.7 mA in the range from the room temperature and normal humidity environment of 0 MΩ to the low temperature and low humidity environment of 550 MΩ.
In the range of the low temperature and low humidity environment in which the resistance value of the transfer roller 9 is 550 MΩ or more, the AC current value to the charging roller 4 is set to 1. Control to 8 mA.

By doing so, it becomes possible to perform more suitable control in a normal temperature and normal humidity environment or a low temperature and low humidity environment in which the resistance value of the transfer roller 9 largely changes.

The other structure and operation are the same as those in the first embodiment, and the description thereof will be omitted.

[0051]

As described above, according to the present invention, even if the environment changes without complicating the configuration and control, and without increasing the cost of the device,
It is possible to provide an image forming apparatus capable of appropriately controlling the bias voltage applied to the charging roller.

[Brief description of drawings]

FIG. 1 is a block diagram showing a control circuit of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing a digital printer as an image forming apparatus according to the first embodiment of the present invention.

FIG. 3 is a cross-sectional configuration diagram showing an image forming unit.

FIG. 4 is an exploded perspective view showing an image forming unit.

FIG. 5 is an external perspective view showing an image forming unit.

FIG. 6 is an exploded plan view showing an image forming unit.

FIG. 7 is an exploded perspective view showing an image forming unit.

FIG. 8 is an exploded side view showing the image forming unit.

FIG. 9 is a flowchart showing an operation of the digital printer as the image forming apparatus according to the first embodiment of the present invention.

FIG. 10 is a chart showing a table used for controlling a digital printer as an image forming apparatus according to the first embodiment of the present invention.

FIG. 11 is a graph used for controlling a digital printer as an image forming apparatus according to a second embodiment of the present invention.

[Explanation of symbols]

3: photoconductor drum, 4: charging roller, 9: transfer roller,
50: control device, 51: high-voltage power supply device for charging roller,
52: High voltage power supply device for transfer roller, 53: Transfer roller bias measuring means.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroshi Hashino             Fuji Zero, 2274 Hongo, Ebina City, Kanagawa Prefecture             X Co., Ltd. (72) Inventor Hideaki Ozawa             Fuji Zero, 2274 Hongo, Ebina City, Kanagawa Prefecture             X Co., Ltd. F term (reference) 2H027 DA01 DE04 DE07 EA01 EA02                       EA05 EA20 EB01 EC06 EC19                 2H073 AA01 BA02 BA22                 2H076 AB05 AB12 DA11                 2H200 FA01 GA16 GA23 GA34 GA44                       GA56 GB11 GB22 GB25 HA02                       HA28 HB12 HB22 HB46 JA02                       JA26 JA30 MB06 PB02 PB05                       PB08

Claims (3)

[Claims] 1. A charging means for charging the surface of an image carrier,
In an image forming apparatus including a transfer unit that transfers a toner image formed by the image carrier onto a transfer material, a resistance value detection unit that detects a resistance value of the transfer unit due to an environmental change, and the resistance value detection unit. An image forming apparatus comprising: a control unit that controls a bias applied to the charging unit according to a detection result of the unit. 2. An image forming apparatus according to claim 1, further comprising a unit for controlling a bias applied to the charging unit and an exposure light amount for exposing an image on the image carrier, based on a resistance value of the transfer unit. apparatus. 3. A means for controlling a bias applied to the charging means and a developing bias for developing the electrostatic latent image formed on the surface of the image carrier, in combination, on the basis of the resistance value of the transfer means. The image forming apparatus according to claim 1, further comprising.