JP2003316238A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a wasteful power consumption to a drum heater. <P>SOLUTION: The wasteful power consumption to the drum heater 20 can be reduced by controlling the energization of the heater 20 in a photosensitive drum 2 to turning off, if the absolute moisture quantity calculated by a controller 32 based on environmental sensing information from an environment sensor 33 is less than a set value when the power source of an image forming apparatus is on, and controlling the energization of the heater 20 by the controller 32 so as to hold the surface of the drum 2 at a predetermined temperature based on temperature sensing information from a temperature sensor 30 if the absolute moisture quantity is the set value or more. <P>COPYRIGHT: (C)2004,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 copying machine, a printer or a facsimile which forms an image by an electrophotographic method or the like.

[0002]

2. Description of the Related Art In an image forming apparatus (copier, printer, facsimile, etc.) using an electrophotographic image forming process,
Drum type electrophotographic photosensitive member (hereinafter referred to as photosensitive drum)
As a charging means for uniformly charging to a predetermined polarity and potential,
Conventionally, a corona charger (primary charger) is generally used. In this method, a corona charger is arranged in a non-contact manner on the photosensitive drum so that the surface of the photosensitive drum is uniformly charged to a predetermined polarity and potential by corona ions generated by corona discharge of the corona charger. .

In addition, in an image forming apparatus (copier, printer, facsimile, etc.) using an electrophotographic image forming process, in addition to the above corona charger (primary charger) for charging the photosensitive drum, a plurality of chargers are provided. Corona charger is used.

For example, a corona charger (pre-transfer charger) for enhancing the charge polarity of a charged toner image (toner) on the photosensitive drum, and a toner image on the photosensitive drum for transferring to a transfer material (paper). Corona charger (transfer charger),
For example, a corona charger (separation charger) for removing the charge from the transfer material (paper) on which the toner image is transferred to separate it from the surface of the photosensitive drum.

During operation of these corona chargers, corona products such as ozone O ₃ and nitrogen oxide NOX are produced. These corona products are oxidized by the discharge energy and atmospheric gas, moisture, etc. on the photosensitive drum to change them to hydrophilic compounds such as nitrogen compounds, aldehyde groups, carboxyl groups, etc. The so-called "image deletion" phenomenon occurs because the adhered compound absorbs moisture in the atmosphere and the surface resistance of the photosensitive drum decreases.

This image flow means that the corona product adhered to the corona charger (primary charger, etc.) by the image forming operation is accumulated on the photosensitive drum when the main power source of the image forming apparatus is OFF, and the image is formed in a band shape. In this case, the ambient humidity occurs from about 50 to 60%.

In particular, after the image forming operation (copying operation or printing operation) is finished, moisture absorption of the discharge product is accelerated during long-term storage (overnight storage, etc.) in an environment having the above humidity, and In the first image forming operation (copy operation or print operation), the occurrence rate becomes highest. In addition, the influence of the image deletion becomes large when more corona products are generated when an AC or negative DC voltage is applied to the corona charger.

These image deletion phenomena occur on most of the photosensitive drums. However, when the surface hardness of the photosensitive drums is particularly large, hydrophilic oxides such as ozone and NOX are easily deposited on the surface of the photosensitive drums. Bad image deletion occurs. It is estimated that this is because the surface hardness of the photosensitive drum is large and the formed low resistance layer is hard to be polished.

Therefore, the surface hardness of the amorphous silicon type photosensitive drum (a-Si photosensitive drum, etc.) is 1500 to 2
It is as high as 000 kg / mm ² , and the image deletion phenomenon easily occurs.

Further, since a photosensitive drum having a high surface hardness is naturally excellent in durability, it tends to be used in an image forming apparatus such as a high speed copying machine which is required to have high durability.
Further, the charging method is often a corona charger, which also contributes to the occurrence of a further image deletion phenomenon.

Therefore, conventionally, as a measure to prevent the image deletion phenomenon, a heater (hereinafter referred to as a drum heater) is arranged on the inner surface of the photosensitive drum, and the surface of the photosensitive drum is heated by the heat generated by the drum heater, whereby ozone or NOX is discharged. Such a hydrophilic discharge product is prevented from absorbing moisture, and a decrease in surface resistance of the photosensitive drum is suppressed.

Conventionally, in the conventional drum heater disposed on the inner surface of the photosensitive drum, the main power source of the image forming apparatus is turned ON / O.
Regardless of FF (when image forming operation is possible or when left unattended),
The surface of the photosensitive drum is always heated while being energized (ON), so that hydrophilic discharge products such as ozone and NOX absorb moisture even during the first image forming operation (copying operation or printing operation) after leaving. To prevent the decrease in the surface resistance of the photosensitive drum.

[0013]

By the way, as in the conventional image forming apparatus having the drum heater in the photosensitive drum described above, the control in which the drum heater is always turned ON is performed in a low humidity environment or in the image forming operation. At times, the heat from the fixing unit is wasting power if the photosensitive drum is kept at a sufficient temperature and there is no image deletion even without the drum heater. It is uneconomical.

Therefore, an object of the present invention is to provide an image forming apparatus capable of preventing the image flow due to the heating of the photosensitive drum by controlling the energization of the drum heater and eliminating the waste of power consumption.

[0015]

In order to achieve the above object, the present invention is an image for forming an image by transferring a developer image formed on a photoconductor to a transfer material directly or through an intermediate transfer body. In the forming apparatus, a heating unit that heats the photosensitive member, a temperature detecting unit that detects the temperature of the photosensitive member, an environment detecting unit that detects an environment inside or outside the image forming apparatus, and an electric current to the heating unit. And a control unit that controls the temperature of the photosensitive member based on temperature detection information from the temperature detection unit when the image forming apparatus is powered off. When the power supply to the image forming apparatus is turned on, the absolute moisture content calculated based on the environment detection information from the environment detection means is less than a preset set value. Is the above When the absolute amount of water is controlled to be turned off and the absolute water content is equal to or greater than a preset value, the photosensitive member surface is preset based on the temperature detection information from the temperature detection unit. It is characterized in that energization to the heating means is controlled so as to maintain the temperature.

Further, a charging potential detecting means for detecting the charging potential of the surface of the photosensitive member is provided, and the surface of the photosensitive member is charged to a preset charging potential based on the charging potential information detected by the charging potential detecting means. As described above, when the potential is controlled with respect to the charging unit that charges the surface of the photoconductor at regular intervals, the heating is performed more than the execution interval of the potential control with respect to the charging unit when the energization of the heating unit is ON. It is characterized in that the execution interval of the potential control for the charging means is shortened when the power supply to the means is off.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will now be described based on the illustrated embodiments.

<First Embodiment> FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to a first embodiment of the present invention (in the present embodiment, an image forming apparatus such as an electrophotographic laser printer). is there.

In this image forming apparatus, the arrow direction (clockwise direction)
The photosensitive drum 2 is provided as an image bearing member that is driven to rotate. Around the photosensitive drum 2, a primary charger 10 along the rotation direction of the photosensitive drum 2, a potential sensor 21 for measuring the surface potential of the photosensitive drum 2, a developing device 3, a pre-transfer charger 4, a pre-transfer exposure lamp. 5, a transfer charger 6, a separation charger 7, a cleaning device 8 and a charge eliminating exposure lamp 9 are provided, and an exposure device 1 is provided above the primary charger 10 and the developing device 3. . Further, a fixing device 11 is arranged on the downstream side of the separation charging device 7 with respect to the conveying direction (arrow direction) of the transfer material (paper) 14.

In this embodiment, the primary charger 10, the pre-transfer charger 4, the transfer charger 6 and the separation charger 7 are all corona chargers.

The photosensitive drum 2 has a diameter of 8 in this embodiment.
It is 0 mm a-Si (amorphous silicon), and is rotationally driven in the arrow direction (clockwise direction) at a predetermined peripheral speed (process speed) by driving a driving device (not shown). As shown in FIG. 2, the photosensitive drum 2 includes a blocking layer 2 on a cylindrical substrate 2e made of a conductive material such as aluminum.
d, photoconductive layers (I, II) 2c and 2b, and a surface layer 2a are sequentially laminated.

The photoconductive layers (I, II) 2c, 2b are formed mainly of an amorphous silicon material in which silicon atoms contain hydrogen atoms and halogen atoms. The surface hardness of the photosensitive drum 2 is about 2000 kg / mm ² , and the primary charger 10, the pre-transfer charger 4, the transfer charger 6, and the separation charger 7 are all corona chargers. The photosensitive drum 2 has a durable life of 300,000 sheets or more.

A drum heater 20 is provided inside the photosensitive drum 2, and the surface of the photosensitive drum 2 is heated by turning on the electricity to the drum heater 20 (the drum heater 20 in the present embodiment). Energization (O
N / OFF) control will be described later).

Next, an image forming operation by the above image forming apparatus will be described.

At the time of image formation, the photosensitive drum 2 is rotationally driven at a predetermined peripheral speed (process speed) in the arrow direction (clockwise direction) by the drive of a driving device (not shown), and a primary charger to which a charging bias is applied. The surface of the photosensitive drum 2 is charged by 10 to a predetermined polarity and potential. Then, the image exposure L according to the image information is applied from the exposure device 1 to the charged surface of the photosensitive drum 2, so that the potential of the surface of the photosensitive drum 2 is lowered, An electrostatic latent image corresponding to the input image information is formed.

Then, the toner charged to the same polarity as the charging polarity of the photosensitive drum 2 is attached to the electrostatic latent image by the developing device 3 to visualize it as a toner image. Then, the toner image of the toner image is further strengthened by the pre-transfer charger 4 and the potential of the image area of the photosensitive drum 2 is lowered by the pre-transfer exposure lamp 5. The image is transferred onto the transfer material 14 by the transfer charger 6 to which a transfer bias (polarity opposite to the toner) is applied.

The transfer material 14 on which the toner image has been transferred is separated from the surface of the photosensitive drum 2 by the separation charging device 7 to which a separation charging bias is applied, and is guided to the fixing entrance guide 12 by the conveying device 13 to the fixing device 11. Be transported. The transfer material 14 conveyed to the fixing device 11 is heated and heated to fix the toner image on the transfer material 14, and then is discharged to the outside.

On the other hand, the transfer residual toner remaining on the surface of the photosensitive drum 2 after the transfer of the toner image is removed and collected by the cleaning device 8. The residual charges on the surface of the photosensitive drum 2 are removed by the static elimination exposure lamp 9 to prepare for the next image forming operation.

Next, control of energization (ON / OFF) to the drum heater 20 in the present embodiment will be described with reference to the block diagram shown in FIG.

As shown in FIG. 3, a drum heater 20 is built in the photosensitive drum 2 at the peripheral edge near the surface. As the drum heater 20, in the present embodiment, a planar heater whose temperature rises quickly is used. Drum heater 20
As the electric capacity of, a heater of about 30 to 100 watts may be generally used. The drum heater 20 is electrically connected to a power supply unit (not shown) via a power switch 31 of the drum heater 20. Power switch 31 O
N / OFF is controlled by the controller 32.

In order to heat the photosensitive drum 2 quickly and uniformly, a built-in heater system is used in this embodiment, but an external heater may be used although the thermal efficiency is lowered.

A temperature sensor 30 for detecting the surface temperature of the photosensitive drum 2 is arranged near the surface of the photosensitive drum 2, and the temperature and humidity inside the image forming apparatus are detected inside the image forming apparatus. The environment sensor 33 is arranged. The temperature information detected by the temperature sensor 30 and the temperature / humidity information detected by the environment sensor 33 are input to the control unit 32.

As the temperature sensor 30, a sensor using a thermistor, infrared rays or the like can be used. The temperature sensor 30 is the photosensitive drum 2 in this embodiment.
I tried to install it 1-5mm away from the surface,
The temperature sensor 30 may be brought into contact with the surface of the photosensitive drum 2,
Further, it may be provided inside the photosensitive drum 2.

The control unit 32 calculates the absolute water content based on the temperature / humidity information input from the environment sensor 33.

In the present embodiment, as a measure against image deletion, the surface of the photosensitive drum 2 is heated to a predetermined temperature T ₀ (40 by the heat generated by the drum heater 20 incorporated in the photosensitive drum 2).
In order to heat the drum heater 20, the power supply switch 31 is turned on / off by a switch control signal S ₁ from the control unit 32 to heat the drum heater 20. That is, the temperature sensor 30
The surface temperature of the photosensitive drum 2 is detected by the control unit 32 based on the switch control signal (surface temperature signal) S ₂ from the temperature sensor 30, the photosensitive drum 2 surface is the predetermined temperature T ₀
Turn on the power switch 31 so that it is maintained at (40 ° C)
/ OFF control.

The main power source of the image forming apparatus (not shown)
When the image forming operation or the standby state is turned on, the control unit 32 calculates the absolute water content in the usage environment of the image forming apparatus based on the temperature / humidity information from the environment sensor 33, and calculates the calculated absolute water content. When the value of is larger than the preset value, the power switch is switched by the switch control signal S ₁ so that the surface temperature of the photosensitive drum 2 detected by the temperature sensor 30 is maintained at the predetermined temperature T ₀ (40 ° C.). 31 is turned on / off to control energization of the drum heater 20.

By the way, when the main power source (not shown) of the image forming apparatus is ON, heat from the fixing device 11 and
Since the surface of the photosensitive drum 2 is heated to some extent by the heat generated during the image forming operation, the sliding operation of the cleaning device 8 with the photosensitive drum 2, and the like, an image is formed in a low humidity environment in such a situation. There is no flow.

Next, in order to evaluate the effect of the energization control for the drum heater 20 in the embodiment of the present invention, the drum is turned on with the main power source (not shown) of the image forming apparatus being turned on (remaining in the standby state). Turn off the power to the heater 20 and perform the image forming operation for 5,000 consecutive sheets,
After leaving for a while, the images of the character chart (characters are formed over the entire image area) and the halftone chart (HT chart: solid black and solid white halftone) are output to change the absolute water content. The flow level was evaluated. Figure 4
Is the evaluation result. In this evaluation, ○
Indicates a level at which image deletion did not occur, Δ indicates a level at which image deletion occurred a little, and × indicates a level at which image deletion occurred.

As is clear from the results of this evaluation, in an environment where the absolute water content is 11 gr / kg or less, the image flow on the character chart and the halftone chart is achieved even when the drum heater 20 is heated and the surface of the photosensitive drum 2 is not heated. Was not confirmed.

Therefore, in this embodiment, the energization control is performed on the drum heater 20 only when the absolute water content is 11 gr / kg or more. On the other hand, the absolute water content is 1
If it is less than 1 gr / kg, the power to the drum heater 20 is turned off regardless of the temperature detection result of the temperature sensor 30.
F, the energization control is not performed on the drum heater 20.

When the main power source (not shown) of the image forming apparatus is OFF, the heat from the fixing device 11 and the heat generated during the image forming operation, and further, the cleaning device 8 slides on the photosensitive drum 2. Since there is no temperature rise factor in the image forming apparatus due to a rubbing operation, the control unit 32 controls the environment sensor 3
3, the surface temperature of the photosensitive drum 2 detected by the temperature sensor 30 is the predetermined temperature T ₀ (40
Temperature), the power source switch 31 is turned on / off by the switch control signal S ₁ so that the drum heater 20
Control energization to.

As described above, in the present embodiment, the main power source (not shown) of the image forming apparatus is turned on, and the absolute water content in the use environment of the image forming apparatus is preset during the image forming operation or the standby. When it is smaller than the predetermined value, it is possible to prevent the image flow from occurring without turning on the power to the drum heater 20 and controlling the power to the drum heater 20.

Therefore, when the absolute water content in the environment of use of the image forming apparatus is larger than the preset value,
When the photosensitive drum 2 is heated by controlling the energization of the drum heater 20, the occurrence of image deletion is prevented, and when the absolute moisture content in the usage environment of the image forming apparatus is smaller than a preset value, the drum heater 20 is heated. Power off
Thus, it is possible to eliminate waste of power consumption for the drum heater 20. In the case of the present embodiment described above, energy saving of about 15 W · h / h was realized.

Further, in the present embodiment, when the absolute water content is less than 11 gr / kg based on the evaluation result shown in FIG. 4, it does not depend on the temperature detection result by the temperature sensor 30,
Turn off the power supply to the drum heater 20,
Although the configuration is such that the energization control is not performed for 0, the set value of the absolute water content in this case can be set to an arbitrary value according to the configuration of the image forming apparatus, the type of transfer material, and the like.

<Embodiment 2> Also in this embodiment, the image forming apparatus according to Embodiment 1 shown in FIG. 1 and the energization control system for the drum heater according to Embodiment 1 shown in FIG. 3 are provided. Therefore, the energization control to the drum heater 20 similar to that of the first embodiment is performed.

In the first embodiment, the absolute water content is calculated based on the temperature / humidity information from the environment sensor 33, and the energization control of the drum heater 20 is performed based on the calculated result, whereby the drum heater 20 is controlled. Power consumption has been reduced.

By the way, when the power supply to the drum heater 20 is completely turned off regardless of whether the main power source (not shown) of the image forming apparatus is turned on or off, the surface temperature of the photosensitive drum 2 rises in the image forming apparatus. It does not become constant due to changes in temperature and temperature / humidity environment of the installation location. Therefore, the photosensitive drum 2
Since the chargeability changes depending on the temperature characteristics of, the problem that the target image density cannot be satisfied occurs.

Therefore, in the present embodiment, when the power supply to the drum heater 20 described in the first embodiment is controlled, the main power source (not shown) of the image forming apparatus is ON, and the drum heater 20 is supplied. Potential control that was normally executed at 1-hour intervals when the energization was turned off (control for adjusting the output of the primary charger 10 based on the detection information from the potential sensor 21 in order to obtain the target charging potential). A short interval, eg 20
I tried to run it every minute.

As described above, in the present embodiment, in addition to the effects obtained in the first embodiment, the exposure is performed when the main power source (not shown) of the image forming apparatus is ON and the power supply to the drum heater 20 is OFF. It is possible to prevent the occurrence of image defects due to variations in the charging ability of the drum 2.

<Third Embodiment> This embodiment also has an image forming apparatus according to the first embodiment shown in FIG. 1 and an energization control system for the drum heater according to the first embodiment shown in FIG. Therefore, the energization control to the drum heater 20 similar to that of the first embodiment is performed.

In the second embodiment, when the energization control to the drum heater 20 described in the first embodiment is performed, the main power source (not shown) of the image forming apparatus is ON, and the drum heater 2
When the power supply to 0 is turned off, the potential control that was normally performed at 1-hour intervals is performed every 20 minutes, so that the drum heater 20 is turned on when the main power source (not shown) of the image forming apparatus is turned on. In this way, it is possible to prevent the occurrence of image defects due to the variation in the charging ability of the photosensitive drum 2 when the power is turned off.

In this embodiment, a transfer material (paper) is further used.
The potential control execution interval is set based on the fact that the temperature of the photosensitive drum 2 also changes depending on the sheet passing state (paper temperature) to the transfer nip portion between the photosensitive drum 2 of 14 and the transfer charger 6. did. For example, during double-sided image formation in which images are formed on both sides of the transfer material (paper) 14, the transfer material (paper) 14 that has been heated by passing through the fixing device 11 is conveyed again to the transfer nip portion and is transferred to the photosensitive drum 2. Since they come into contact with each other, the temperature of the surface of the photosensitive drum 2 increases greatly.

Therefore, when the energization control of the drum heater 20 described in the first embodiment is performed, the main power source (not shown) of the image forming apparatus is ON, and the energization of the drum heater 20 is OFF. In some cases, when the double-sided image formation is executed, the potential control is executed at an interval shorter than that in the second embodiment, for example, every 5 minutes. Therefore, the potential control is executed even during the image forming operation.

As described above, in this embodiment, in addition to the effects obtained in the first and second embodiments, when the main power source (not shown) of the image forming apparatus is ON, the electricity to the drum heater 20 is turned off.
Even when double-sided image formation is performed during FF, it is possible to prevent the occurrence of image defects due to variations in the charging ability of the photosensitive drum 2.

[0055]

As described above, according to the present invention, when the power of the image forming apparatus is turned on, the absolute water content calculated based on the environment detection information from the environment detection means is less than the preset value. Is controlled so as to turn off the power supply to the heating means, and when the absolute water content is equal to or more than a preset value, the photosensitive member surface is preset based on the temperature detection information from the temperature detection means. By controlling the energization of the heating means so as to maintain the temperature, it is possible to prevent the image flow due to the heating of the photosensitive member by the energization control of the heating means, and to eliminate the waste of power consumption.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to first, second and third embodiments of the present invention.

FIG. 2 is a diagram showing a layer structure of a photosensitive drum of the image forming apparatus according to Embodiments 1, 2, and 3 of the present invention.

FIG. 3 is a block diagram showing an energization control system for a drum heater according to Embodiments 1, 2, and 3 of the present invention.

FIG. 4 is a diagram showing the relationship between the absolute water content and the level of image flow when a character chart and an HT chart (halftone chart) are output.

[Explanation of symbols]

1 Exposure device 2 Photosensitive drum (photoconductor) 3 developing device 4 Charger before transfer 5 Pre-transfer exposure lamp 6 Transfer charger 7 Separation charger 8 cleaning device 9 Static elimination exposure lamp 10 Primary charger 11 Fixing device 20 Drum heater (heating means) 21 Potential sensor (charge potential detection means) 30 Temperature sensor (temperature detection means) 31 Power switch 32 control unit (control means) 33 Environmental sensor (environmental detection means)

Claims (2)

[Claims] 1. An image forming apparatus for forming an image by transferring a developer image formed on a photoconductor onto a transfer material directly or via an intermediate transfer body, comprising: a heating unit for heating the photoconductor; A temperature detecting unit that detects the temperature of the photoconductor, an environment detecting unit that detects the environment in or near the outside of the image forming apparatus, and a control unit that controls the energization of the heating unit. When the power source of the image forming apparatus is turned off, the energization to the heating unit is controlled so as to keep the surface of the photoconductor at a predetermined temperature set based on the temperature detection information from the temperature detection unit, and When the power of the forming apparatus is turned on, when the absolute water content calculated based on the environment detection information from the environment detection means is less than a preset set value, the power supply to the heating means is controlled to be turned off. , Said When the water content is equal to or more than a preset value, the energization of the heating means is controlled so as to keep the surface of the photoconductor at a preset temperature based on the temperature detection information from the temperature detection means. An image forming apparatus characterized by the above. 2. A charging potential detecting means for detecting a charging potential of the surface of the photoconductor, and charging the surface of the photoconductor to a preset charging potential based on charging potential information detected by the charging potential detection means. As described above, when the potential is controlled with respect to the charging unit that charges the surface of the photoconductor at regular intervals, the heating is performed more than the execution interval of the potential control for the charging unit when the energization of the heating unit is ON. The image forming apparatus according to claim 1, wherein an execution interval of potential control for the charging unit is shortened when energization to the unit is off.