JP2002357934A - Image forming method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accomplish satisfactory image formation by preventing image abnormalities (density decrease, etc.), which are caused by a temperature rise of, e.g. a developing unit, when a high speed printer is used for a long time in a high temperature environment. SOLUTION: In a device provided with a heating element (drum heater) in order to maintain a photoreceptor drum at a fixed temperature or above, the temperature of a drum atmosphere is estimated from the amount of electricity supplied to the heating element. Thus, the peripheral velocity ratio of a developing sleeve to the drum is changed to a lower peripheral velocity when the temperature is high. This device can be applicable to a high speed monochrome printer and a high speed A-Si color printer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming method and apparatus for forming an image on a recording medium by electrophotography.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus for forming an image by an electrophotographic method has been used in devices such as a laser printer and a digital copy.

FIG. 2 is a configuration diagram showing a form of an image forming apparatus according to the conventional example. Here, the conventional configuration is described using a digital copier.

[0006] In FIG. 2, a reader section 18 is
The original 15 placed above is illuminated by an illumination lamp 16 and the reflected light is reflected by a one-line CCD 19 of a photoelectric conversion element.
The image is converted into an electric signal corresponding to the image information by forming an image thereon. Here, the reflected light from the original 15 illuminated by the illumination lamp 16 is reflected by mirrors 17a, 17b, 1
The photoelectric conversion element 19 is guided by the lens 17d and guided by the lens 17d.
Imaged on top. The electric signal output by the photoelectric conversion element 19 is A / D-converted by an A / D converter 21 to become 8-bit digital image data. Thereafter, the black signal generation circuit 22 converts the luminance information into density information. Is converted to image density data.

[0005] The 8-bit digital image data signal generated as described above is input to the laser drive circuit 24. The laser driving circuit 24 is a well-known PWM circuit, and controls the semiconductor laser 2 according to the magnitude of the input image density signal.
The light emission time of 0 is controlled.

In the image forming section, there is a photosensitive drum 1 as an image carrier, and the photosensitive drum 1 is mounted on or around a conductive support such as an aluminum drum installed on the inner peripheral side as is well known. Constituted by forming a photoconductive layer,
It rotates in the direction of the arrow in FIG.

Around the photosensitive drum 1, a charging device 2, a developing device 7, a pre-transfer charging device 5, a transfer charging device 8, an electrostatic separation charging device 9, a cleaning device 13, and the like are sequentially arranged.

In the illustrated example, the charging device 2 is a scorotron charger, which primarily charges the surface of the photosensitive drum 1 to uniform electrification. An electrostatic latent image is formed on the photosensitive drum 1 by exposure 3 from the exposure unit on the downstream side of the charging device 2 in the drum rotation direction.

The electrostatic latent image is developed by the developing device 7. The developing device 7 is provided with a developing roller having a magnetic field generating means inside. The developing roller frictionally charges the developer toner stored inside and develops an electrostatic latent image on the surface of the photosensitive drum 1. Toner is supplied to the electrostatic latent image, and the electrostatic latent image is developed to be visualized as a toner image.
The toner is a one-component magnetic toner (styrene-acrylic toner) and has a volume resistivity of 106 to 1012 Ω.
cm, the critical surface tension is about 35 dyn / cm. Incidentally, the critical surface tension of the surface of the photosensitive drum 1 is 40 to 45 dy.
n / cm.

A developed electrostatic image on the photosensitive drum 1 is charged to a pre-transfer charger 7 and a corona transfer charger (transfer charger).
By 8, the image is transferred onto a transfer sheet P which is a transfer material conveyed by a transfer guide or the like. The transfer paper P on which the toner image has been transferred is separated from the photosensitive drum 1 by an electrostatic separation charging device (separation charger) 9. The electrostatic separation charging device (separation charging device) 9 uses a corona discharge to transfer the toner image from the photosensitive drum 1 to the transfer paper P and to transfer the toner image from the photosensitive drum 1 to the transfer paper P after the transfer of the toner image. It helps with separation. Here, the polarity of the corona discharge used for the corona transfer charger (transfer charger) 8 is opposite to that of the toner, and the polarity of the corona discharge used for the electrostatic separation charger (separation charger) 9 is the same as the toner. It is.

The transfer paper P on which the toner image has been transferred is conveyed to a fixing device 12 after being separated from the photosensitive drum 1, where the toner image on the surface is fixed, and a desired print image is formed. It is discharged outside the body.

On the other hand, the residual toner after the transfer process is present on the photosensitive drum 1 after the transfer of the toner image, and the residual toner is removed by the cleaning device 13. The cleaning device 13 includes a cleaning assisting device that peels off the residual toner from the photosensitive drum 1 by a magnetic (magnet) roller and uniformly reapplies the residual toner to the photosensitive drum 1, and a cleaning auxiliary device that uniformly reapplies the residual toner to the photosensitive drum 1. And a main cleaning device for scraping off from the cleaning blade. However, this is not always the case depending on the image forming apparatus.

The photosensitive drum 1 from which the residual toner has been scraped off by the cleaning device has its residual charge removed by a pre-exposure (lamp) 30 and is ready for the next image formation.

In an image forming method using such an image forming apparatus, an image is generally formed by binary dots by turning on and off a laser beam in accordance with print data as described above. . As described above, even when the dots of the image are expressed in binary, the image can be expressed in gradation by using the error diffusion method or the dither method that expresses the density with a plurality of dots.

Further, an organic compound photoreceptor has conventionally been generally used for the photosensitive layer on the surface of the photosensitive drum of the above-described image forming apparatus. As in the conventional example, a photosensitive member mainly composed of amorphous silicon used in a high-speed analog copying machine is used.

The potential distribution of the electrostatic latent image formed by the exposure of the amorphous silicon photoreceptor is closer to the intensity distribution of the laser beam than the organic compound photoreceptor. For this reason,
When the amorphous silicon photoreceptor is used for the surface layer of the photosensitive drum, the electrostatic latent image is sharply formed, and fine lines in the main scanning direction can be reproduced well.

At present, the image exposure apparatus has two laser light sources and simultaneously exposes two main scanning lines to one photosensitive drum with two laser beams arranged in the sub-scanning direction. In some products, the forming speed is improved without lowering the resolution.

The photosensitive drum 1 in the conventional example has an amorphous silicon photosensitive layer having a thickness of 30 μm formed by glow discharge or the like on an aluminum cylinder having a diameter of 108 mm and a thickness of about 5 mm. The amorphous silicon photosensitive layer is worn by rubbing of the magnetic brush roller, contact of the cleaning blade, and the like, and the abrasion depends on the amount of toner in each rubbing / contact portion. In general, when toner is present in the contact portion, the amount of wear is small due to the lubricating action of the toner, and when the amount of toner is small, sufficient lubricating action cannot be obtained. ing. Amorphous silicon drums are characterized by extremely small wear and long life as compared to organic photoconductor drums that are often used in color and the like.

As shown in FIG. 1, a planar heating element heater 11 of about 80 W is disposed around the photosensitive drum 1 for one round, and the electric power is controlled so that the temperature of the aluminum shilling becomes 42 ° C. Note that the maximum image width of the electrophotographic copying machine of the conventional example is about 290 mm on the side of A4.

In recent years, higher productivity and higher image quality have been demanded from market requirements, and higher image forming speeds and higher image quality have been achieved. Increasing the image forming speed requires additional devices and requires more reliable behavior. In order to improve image quality, stable image quality is required regardless of environmental fluctuations. For this reason, most of the products called current high-speed machines are equipped with an environmental sensor that constantly monitors the temperature and humidity of the environment where the main body is placed, and a mechanism that operates with optimal image forming conditions for temperature and humidity. Has both.

[0021]

The above-described image forming apparatus having a higher speed requires an internal image forming apparatus due to mechanical stress in each apparatus, fixing heat, and temperature of a transfer material at both sides of a through-pass. However, there is a problem that the temperature rises. Due to the developing sleeve rotating at a high speed and the heat from the transfer material, the internal temperature of the developing device rises, thereby deteriorating the developer and reducing the image density on the transfer material.

To cope with this, various techniques have been tried to reduce the temperature and to prevent the image density from decreasing. Among them, a method is known in which the rotation speed of the developing sleeve is switched to a low speed in accordance with the environmental temperature conditions to maintain the image density. In this method, the temperature and humidity in the main body are predicted based on the environmental temperature and humidity obtained from the environment sensor installed in the main body and the image forming state, and the image forming conditions are changed.

However, in the method of controlling the image forming conditions and speed according to the environmental condition in which the main body is installed, there are cases where the temperature does not correspond to the actual temperature of the developing device and the photosensitive member, and the control does not function well. Is known. This is because the environmental sensor installed on the main unit is used to monitor the environment where the main unit is installed. Is installed.

It is also known that in a low-temperature environment, from the viewpoint of maintaining the image density, the density becomes too high if the sleeve speed is reduced to an appropriate value or less.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has as its object to provide an image forming apparatus in which image abnormality is reduced by more accurately grasping an image forming environment.

[0026]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention is directed to an image forming apparatus that forms an electrostatic latent image formed on the surface of an image carrier whose surface temperature is controlled, into a visible image using a developer carried and conveyed by the developer carrier. The image forming apparatus is characterized in that the operation of the surface temperature control means of the image carrier is recorded in the forming apparatus, and the image is formed by changing the image forming conditions, particularly the speed of the developing sleeve, based on the recording. .

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A first embodiment of the present invention will be described below with reference to FIGS.
FIG. 1 is a schematic vertical sectional side view showing the configuration of an image carrier having surface temperature management control of the image forming apparatus according to the present embodiment. FIG. 3 is a diagram showing the image carrier surface installed inside the image carrier. It is a schematic diagram which shows the temperature characteristic of the planar heating element heater (henceforth a drum heater) which carries out temperature management control. FIG. 3 plots the temperature of the drum heater over time when a constant voltage is applied, with time on the horizontal axis and temperature on the vertical axis.

The image forming apparatus of the present embodiment forms an image with the same behavior as the image forming apparatus described in the conventional example.

Here, when the temperature of the drum heater reaches a certain set surface temperature of the image carrier, the drum heater 11 in FIG.
The power is controlled by the heater control board 12 arranged at the center of the drum of the thermistor installed inside, and the power supply to the drum heater 11 is cut off. When the temperature drops to a certain degree from the set temperature, the power is supplied to the drum heater 11 and heat is generated so that the surface temperature becomes the set temperature. Here, the set temperature is set to 42 degrees in consideration of the image flow in a high-humidity and high-temperature environment and the temperature rise of each part.

As described above, the energization of the drum heater 11 is controlled by sensing the temperature of the surface of the photosensitive drum as an image carrier by the thermistor even during image formation. Here, when image formation is performed on both sides of the through-pass, the paper as the transfer material enters the photosensitive drum unit 1 again while retaining the heat of fixing, and causes a rise in the temperature around the photosensitive drum. In other words, when image formation is performed on both sides of the through-pass, heat generation by the drum heater 11 is hardly required, and the energization time from the heater control board 12 to the heater 11 becomes extremely short. Further, due to the influence of heat from the transfer paper and the mechanical friction caused by the peripheral speed of the developing sleeve, the temperature of the developing device is reduced to a temperature (50) at which the developer may aggregate.
℃ or more). Further, the use of the developer at a high temperature causes deterioration of the developer and also causes a reduction in image density.

The present embodiment focuses on the power supply time to the drum heater 11 to prevent the developer from deteriorating and the image density from lowering to an apparatus temperature of 50 ° C. or higher, thereby obtaining a high quality image. A mechanism for suppressing the image density reduction by switching the speed of the developing sleeve by predicting the surface temperature of the drum and the ambient temperature of the developing device by recording the energizing time B in a certain unit time A, and changing the speed of the developing sleeve is added. .

In this embodiment, the unit time A is 10 minutes,
When the energizing time B became 20% or less and 2 minutes or less, the normal sleeve speed was changed from 1 to 2. The sleeve speed is a peripheral speed ratio of 1 to the photosensitive drum 1 in a normal state.
From 94%, the peripheral speed ratio to the photosensitive drum 1 having the lowest sleeve speed that can be lowered from the viewpoint of image quality is set to 124%. In the configuration of the first embodiment, the peripheral speed of the developing sleeve is
If it is less than this, an image failure image such as white background fog occurs.

Here, the time setting of 20% is a result of experimentally obtaining the optimum value in this embodiment, and is not applicable to all forms. However, the image forming speed and the drum heater It goes without saying that the optimum value is obtained by experiments depending on the shape / temperature characteristics of the device and the position of each element device.

As described above, the energizing time to the drum heater according to the first embodiment is recorded, and the developing condition is changed thereby to increase the device temperature in the environment of the image carrier such as both sides of the through-pass under a high temperature environment. Under such an environment, it is possible to more faithfully recognize environmental changes, apply optimal image forming conditions, and perform image formation without a decrease in image density.

(Embodiment 2) In the first embodiment, the energizing time to the drum heater is recorded and the developing condition is changed thereby to increase the device temperature in the environment of the image carrier such as both sides of the through-pass under a high temperature environment. In the lower part, it is possible to more accurately recognize the environmental change, apply the optimal image forming conditions, and perform image formation without a decrease in image density.

In the second embodiment, a case where the above configuration is applied to a 4-drum color image forming apparatus will be described.

FIG. 4 shows an image forming apparatus according to the second embodiment. As a method of forming a color image at high speed, using a photosensitive drum, a developing device, a cleaner and a transfer mechanism for each color,
The method of transferring and fixing to one transfer material is well known. Hereinafter, an image forming process using four drum colors will be described.

An example of the image forming apparatus will be briefly described with reference to FIG. 4. First, second, third, and fourth image forming units Pa, Pb, Pc, and Pd are provided in the apparatus. Toner images of different colors are formed through a latent image and development transfer process.

Each of the image forming units Pa, Pb, Pc, and Pd is a dedicated image carrier, in this example, the electrophotographic photosensitive drum 3
a, 3b, 3c, 3d.
A toner image of each color is formed on b, 3c and 3d. A transfer belt 200 is installed adjacent to each of the photosensitive drums 3a, 3b, 3c, 3d, and the photosensitive drums 3a, 3b, 3c, 3d
The toner images of the respective colors formed thereon are sequentially transferred onto the recording material P carried and conveyed on the transfer belt 200 in a superimposed manner.
At the same time, the recording material P is electrostatically attracted to the transfer belt 200.
Further, the recording material P on which the toner images of the respective colors have been transferred is separated from the transfer belt 200 by the separation unit, and the fixing unit 9 fixes the toner image by heating and pressurizing, and then is discharged outside the apparatus as a recording image.

Here, in order to achieve a higher speed and a longer life, amorphous silicon is used for the photosensitive member, and an image forming station for each color is called a station.

As shown in FIG. 4, the stations are arranged as C, M, Y and BK from the upstream side. This configuration is an example, but does not specify the arrangement of stations. However, due to the nature of color reproduction, BK is often the configuration of the most downstream station.

Here, due to the structure of the image forming apparatus, since the fixing device is close to the fourth station at the most downstream, there is a problem that the fourth station itself easily receives the heat of the fixing and the temperature rises. This is the higher the speed machine, the more
Needless to say, the amount of heat required per unit time for fixing increases, and the influence of heat is greater.

On the other hand, similarly to the first embodiment, the temperature of the upstream first station is likely to rise due to the thermal influence of the paper as the transfer material during both sides of the through-pass.

In the image forming apparatus of this embodiment, since the diameter of the drum is not large as in the first embodiment, the drum heater 5 for adjusting the surface temperature on the surface of the photosensitive drum is used.
1, a heating element is installed in the drum shaft 52 as shown in FIG. This heating element is voltage-controlled by a thermoswitch (not shown), similarly to the planar heating element of the first embodiment.
Here, the thermoswitch may have any configuration regardless of whether it is arranged inside the photosensitive drum 1 or on the surface of the photosensitive drum 1 as long as it achieves its purpose.

Each of the heaters 51 has a thermistor, and controls the heater independently. That is,
By adapting the change of the developing condition by the control voltage of the drum heater, the developing condition can be set according to the drum surface temperature of each station.

When images are continuously formed on one surface of the transfer material, the ambient temperature of the fourth station, which is most susceptible to the heat of fixing, rises, and the developing conditions of the fourth station are changed. Becomes

In addition, in the case of a two-sided pass in which the transfer material is reversely conveyed in the apparatus and an image is continuously formed on both surfaces of the transfer material, the first upstream station is fixed from the transfer material in addition to the fourth station. Is transferred, the ambient temperature of the first station rises, the developer deteriorates, and there is a problem that the concentration of only the first station decreases. However, this problem can be solved by changing the developing conditions in conjunction with the heater voltage control as in the first embodiment.

In the case where the respective heaters are controlled in the respective stations as described above, by applying the present invention described in the first embodiment, it is possible to construct the optimum developing conditions in the respective stations, and It has become possible to provide a good image forming apparatus without deterioration in density.

[0049]

As described above, according to the present invention,
By recording the energizing time of the drum heater, the ambient temperature of the photosensitive drum can be more accurately predicted, and even in an environment where the developer is degraded due to a rise in temperature, the speed of the developing sleeve is switched to a lower speed, thereby lowering the image density. This makes it possible to form a high-quality image without defects.

[Brief description of the drawings]

FIG. 1 is a vertical side view showing a drum and a drum heater of an image forming apparatus according to a first embodiment.

FIG. 2 is a vertical sectional side view showing a configuration of an image forming apparatus according to a conventional example and the first embodiment.

FIG. 3 is a temperature characteristic graph of the drum heater according to the first embodiment.

FIG. 4 is a vertical sectional side view showing a configuration of a 4 ° C. ram image forming value according to the second embodiment.

FIG. 5 is a vertical sectional side view showing a drum and a drum heater of the image forming apparatus according to the second embodiment.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 photosensitive drum as latent image holding means 2 charging device as surface charging means 3 optical path of electrostatic latent image exposure means 7 developing device as latent image developing means 8 transfer charger as toner transfer means 9 transfer medium separating means Certain separation charging device 12 Thermal fixing device for thermally fixing a toner image on a transfer medium 13 Cleaning means for cleaning the photosensitive drum 30 Pre-exposure lamp P for removing residual electrification on the photosensitive drum after toner cleaning P Recording medium Printing paper

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 21/00 350 G03G 21/00 350 21/20 534 F term (Reference) 2H027 DA13 DA32 DA38 DE07 EA04 EA13 EC06 ED08 EE03 JA08 JC01 2H030 AB02 AD17 BB02 BB33 BB63 2H035 CA07 CB01 CZ03 2H068 DA17 DA23 DA37 2H077 AD02 AD06 BA03 DB14 GA13

Claims (8)

[Claims] An image carrier on which an electrostatic latent image is formed; a charging device for uniformly charging the image carrier; and an electrostatic latent image on the image carrier charged by the charging device. A latent image exposing device for forming an image, a developing device for carrying the electrostatic latent image on a developer carrier and developing the image with a developer conveyed to form a toner image, and a transfer device for transferring the toner image onto a recording medium A fixing device for thermally fixing the transferred toner image on the recording medium to the recording medium; and a cleaning device for cleaning the developer remaining on the image carrier after the transfer. In an image forming apparatus having a heating element that maintains a surface temperature at a certain level or more, a power supply state to the heating element is recorded, and image formation is performed by changing at least one image forming condition. Image forming method. 2. The image forming apparatus according to claim 1, wherein a rotation speed of the developer carrier of the developing device is variable at least in two or more steps. 3. The image forming apparatus according to claim 1, wherein the image forming condition changed according to a power supply state to the heating element defines a rotation speed using the developing device according to claim 2. apparatus. 4. The latent image bearing member has a cylindrical aluminum tube and has a surface having a thickness of 2
2. The image forming apparatus according to claim 1, wherein a photosensitive layer of 0 to 40 ([mu] m) is formed. 5. A plurality of image carriers on which an electrostatic latent image is formed, a charging device for uniformly charging the plurality of image carriers, and a static device on the image carrier charged by the charging device. A latent image exposing device for forming an electrostatic latent image, a developing device for carrying an electrostatic latent image on a developer carrier and developing it into a toner image with a developer conveyed, and a toner image on a recording medium A transfer device for transferring, and a cleaning device for cleaning the developer remaining on the image carrier after the transfer are provided for each image carrier, and the transferred toner image on the recording medium is transferred to the recording medium by heat. In an image forming apparatus each having a fixing device for fixing, and a heating element that maintains a surface temperature of each of the plurality of image carriers at a certain level or more, a power supply state to the heating element is recorded, and an image forming condition is recorded. Image forming by changing at least one of Image forming method. 6. The latent image bearing member has a cylindrical aluminum tube with a thickness of 2
6. The image forming apparatus according to claim 5, wherein a photosensitive layer of 0 to 40 ([mu] m) is formed. 7. The image forming apparatus according to claim 5, wherein the developer carrier of the developing device can be rotated at at least two or more rotational speeds. 8. The image forming apparatus according to claim 5, wherein the image forming condition changed according to a power supply state to the heating element defines a rotation speed using the developing device according to claim 7. apparatus.