JPH09197780A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably control the potential and to obtain excellent image quality without spoiling the image forming speed by correcting developing bias in accordance with difference between the potential of the non-image part of a latent image carrier and a specified value. SOLUTION: An electrifying roller 1 is set to abut on a photoreceptor 2 being the latent image carrier, and the photoreceptor 2 is uniformly electrified by a voltage impressing device functioning as an electrifying and impressing means by controlling the voltage impressing device in a state where the voltage impressing device is controlled by a control means controlling impressed voltage so that a fixed voltage may be impressed. An original optical image 3 is exposed on the photoreceptor 2 by an exposure device being an exposing means, so that an electrostatic latent image is formed. In such a case, potential is measured by a potential sensor 11 being a potential detecting means provided on the downstream side from the roller 1 at the non-image part at the leading edge of the image every time the image is formed, thereby detecting a difference from a potential target value. Then, the control means controlling the impressed voltage controls so that the fixed voltage may be impressed by shifting (correcting) the developing bias by an amount equivalent to the difference value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine, a printer,
The present invention relates to an electrophotographic image forming apparatus such as a facsimile, and more particularly to an image forming apparatus having a charging device and a developing device.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus, a corona charger is generally used as a uniform charging device for a photoconductor. However, since the corona charger has a property of generating ozone, NOx and the like secondarily generated by ozone adhere to the charger together with an environmental problem, which causes uneven charging. I have a problem.

Therefore, as an alternative to corona charging,
A contact charging device has been proposed in which a charging roller for applying a voltage is brought into contact with the surface of a photoconductor to perform charging. In this apparatus, since the photoconductor is charged by discharging between the charging roller and the surface of the photoconductor, the applied voltage is lower and the amount of ozone generated is smaller than that in corona discharge.

However, in the apparatus using the charging roller, there arises a problem that the electric potential of the photosensitive member changes due to the change in the electric characteristics of the charging roller depending on the use environment. To solve this problem, Japanese Patent Laid-Open No. 18163/1992
No. 81 discloses a technique for detecting the temperature of the charging member and varying the peak-to-peak voltage of the AC applied voltage. However, when an AC voltage is applied, a problem that vibration noise is generated from the charging member occurs. FIG. 2 is a charging characteristic diagram showing the relationship between the applied voltage due to temperature change and the potential of the photoconductor. When a DC voltage is applied, no vibration noise is generated, but as shown in FIG. 2, the change in charging characteristic with temperature is not only the applied voltage value (value of A to A ″) at the start of charging but also its inclination. Therefore, if the correction amount of the applied voltage with respect to the temperature is uniform, the potential controllability is deteriorated.

Further, FIG. 3 is a charging characteristic diagram showing the relationship of the potential of the photosensitive member with respect to the applied voltage due to a change in humidity. As shown in FIG. 3, since the charge amount changes not only with temperature but also with humidity (water content), there is a problem that sufficient potential controllability cannot be achieved only by correction for temperature.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and impairs the image forming speed regardless of fluctuations in the potential of the photoconductor due to changes in environmental conditions other than temperature. The purpose is to control the potential stably and obtain a good image quality.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention comprises a charging means for contacting a latent image carrier,
A charging application unit that applies a voltage to the charging unit, a control unit that controls the applied voltage of the charging application unit, and a temperature detection unit that detects the temperature of the charging unit are provided. In the image forming apparatus for correcting the applied voltage based on the above, a potential detection unit for detecting the potential of the latent image carrier is provided, and the development bias of the development bias is determined according to the difference between the potential of the non-image portion of the latent image carrier and the predetermined value. It is a correction. An electric potential detection unit that detects the electric potential of the latent image carrier is provided between the charging unit and the exposure unit, and image formation is performed according to the difference between the electric potential of the non-image portion at the image tip of the latent image carrier and a predetermined value. The developing bias may be corrected each time, and it is more preferable to correct the voltage applied to the charging unit according to the difference between the detected potential and the predetermined value. Further, when the temperature of the fixing unit is equal to or lower than a predetermined temperature, and when the image forming apparatus is powered on or at any time, the potential of the latent image carrier is detected, and the charging unit detects the potential according to the difference between the detected potential and the predetermined value. A correction mode for correcting the applied voltage may be executed.

[0008]

According to the image forming apparatus of the present invention, in the electrostatic printing apparatus using the contact charging device for detecting the temperature and correcting the applied voltage, the potential of the photoconductor is measured to detect the difference from the target potential value. However, by correcting the developing bias according to the difference value, the developing potential can be controlled to be constant and the image quality can be stably controlled even if the potential changes due to changes in humidity and the like.

Further, in the non-image portion at the front end of the image, which is a so-called paper interval, the potential difference value of the photoconductor is detected every time image formation
By correcting the development bias for each image formation, the development potential can be controlled to be constant even if there is a continuous potential change due to a continuous change in humidity or the like, and the image quality can be stably controlled without reducing the copy speed.

Further, by correcting the voltage applied to the charging member in the next image formation according to the detected potential difference value of the photoconductor, even if there is a continuous potential fluctuation due to a continuous change in humidity or the like. By controlling the potential to be almost constant and the developing potential to be constant by the developing bias, the image quality can be stably controlled without any side effect.

The potential difference value is detected independently of the image forming operation, the voltage applied to the charging member is corrected according to the detected value, and the potential is controlled to be substantially constant. Can be controlled stably.

Finally, by providing a mode (switch) for forcibly executing the correction mode independent of the image forming operation, the potential can be controlled to be substantially constant even if there is a sudden change in humidity, and the image quality is improved. Can be controlled stably.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 is an overall view of an image forming apparatus that is an embodiment of the present invention. The charging roller (1), which is a charging unit and a charging member, is installed in contact with the photoconductor (2), which is a latent image carrier, and a constant voltage is applied by a voltage applying device as a charging applying unit. The control means for controlling the applied voltage controls the voltage application device to uniformly charge the photoconductor (2). The photoconductor (2) has
The document light image (3) is exposed by an exposure device (not shown) that is an exposure unit to form an electrostatic latent image. The charges outside the image area are removed by the eraser (4) and then developed by the developing device (5) which is a developing means. The developed visible image is transferred by the transfer belt device (6) to the transferred body (7) carried by a paper feeding device (not shown). The photoconductor (2) on which the visible image is transferred is cleaned by the cleaning device (8).
After the transfer residual toner is removed by, the residual charge is removed by the quenching lamp (9), and a series of image forming cycles are repeated again.

The charging roller (1) is composed of an epichlorohydrin rubber roller or a roller having a coat layer having hydrin rubber and silica dispersed in a fluororesin on the surface layer thereof. The charging characteristics are as shown in FIG.
It changes greatly depending on the roller temperature. FIG. 4 is a diagram showing the applied voltage correction amount with respect to the detected temperature. The voltage applied to the charging roller (1) depends on the temperature of the charging roller (1) detected by the charging roller temperature detection device (10), and when the detected temperature is low as shown in FIG. 4, the correction amount is an absolute value. When the detected temperature is high, the correction amount is set to a high voltage, and the correction amount is corrected to a low voltage as an absolute value.

Furthermore, the charging characteristics of the charging roller (1) also change depending on the humidity (water content), as shown in FIG. FIG. 5 is a diagram showing the potential of the photoconductor at the original portion with respect to the original reflectance. FIG. 6 is a diagram showing a processing procedure of the present invention. After the main switch is turned on, it is determined whether or not the copy job has started, and if not started, it is determined again whether or not the copy job has started. If it has started, the image forming operation is started, the charging applied voltage is corrected, and the charging is applied.

The potential sensor (11), which is a potential detecting means provided on the downstream side of the charging roller (1), measures the potential at the non-image portion of the leading edge of the image for each image formation to obtain the potential target value. The control means controls the applied voltage so that a constant voltage is applied by detecting (developing) the developing bias by the difference value and detecting (developing) the developing bias by the difference value. As shown in FIG. 5, since the potential attenuation amount of the photoconductor at the original portion having the reflectance C is constant, the potential variation amount a is equal to the potential variation amount of the C portion. Therefore, if the developing bias is shifted by the same amount as the potential variation amount a, the developing potential based on the relative ratio of the potential and the developing bias can be kept constant. By doing so, the image density can be stably controlled regardless of changes in temperature and humidity.

Further, since the moisture content of the charging roller gradually changes with respect to the fluctuation of the atmospheric humidity, the speeds of the respective changes are different. Since it can be detected in consideration of the humidity fluctuation on the photoconductor, it can be accurately controlled. Furthermore, since a potential sensor is installed between the charging roller and the exposure unit, there is no effect of flare light after the exposure lamp is turned off when the scanner returns, and since the potential change can be measured during image formation,
Correction is performed more accurately without reducing the copy speed. Further, the applied voltage to the charging member at the time of the next image formation is shifted by the detected potential difference value.
After that, it is determined whether or not there is a repeat, and if there is a repeat, the image forming operation is restarted. If there is no repeat, it is checked whether the job is finished and the process is finished.

Since the gradient of the potential with respect to the applied voltage is 70 to 90% as shown in FIGS. 2 and 3, this configuration can greatly reduce the fluctuation of the potential. Further, in the correction which is fed back to the developing bias, the background stain is generated when the potential is lowered, and there is a limit to the correction amount in order to prevent this. However, by correcting the charging voltage and bias voltage,
The correction range is expanded, and the image can be controlled more stably.

Next, the correction mode will be described. Figure 7
FIG. 8 is a view showing a correction mode processing procedure based on a fixing temperature, and FIG. 8 is a view showing a correction mode processing procedure. In the correction mode, first, the potential of the photoconductor is measured by the charging applied voltage that is determined by the temperature of the charging roller, which is the fixing unit, and the difference from the potential target value is obtained, which is less than or equal to the predetermined allowable difference value. Determine whether. If the difference value exceeds the allowable value, shift the applied voltage by the detected difference value, measure the potential again, repeat the shift measurement until the difference value is within the allowable value, and when the difference value is within the allowable value, enter the mode. To finish.

The correction mode of the present embodiment is executed when the temperature of the fixing roller of the fixing device is lower than a predetermined temperature, and when the power of the device is turned on. With the correction mode of this embodiment,
Even if it has not been used for a long period of time and the humidity changes during that period, the potential can be controlled stably from the first sheet after the power is turned on.
Further, by detecting the temperature of the fixing roller, the mode execution by turning the power on and off during the operation of the apparatus is prevented.
Further, since the correction mode is executed while the fixing roller temperature is raised to the specified value, the waiting time for executing the correction mode can be shortened.

Further, in the present embodiment, a correction mode compulsory switch is provided so that the correction mode can be executed at an arbitrary timing. With this configuration, the correction mode can be forcibly executed even when the charging roller that was stored in an environment different from the device operating environment is replaced, and the potential of the photoconductor is changed even when the charging roller is replaced. It is possible to control stably.

[0022]

The image forming apparatus according to the present invention stably controls the electric potential of the photoconductor without impairing the image forming speed regardless of the change of the electric potential due to the change of the environmental conditions other than the temperature and the like, and the excellent image quality is obtained. Can be controlled to obtain

[Brief description of drawings]

FIG. 1 is an overall view of an image forming apparatus that is an embodiment of the present invention.

FIG. 2 is a charging characteristic diagram showing a relationship between an applied voltage and a potential due to a temperature change.

FIG. 3 is a charging characteristic diagram showing a relationship between an applied voltage and a potential due to a change in humidity.

FIG. 4 is a diagram showing an applied voltage correction amount with respect to a detected temperature.

FIG. 5 is a diagram showing a charging potential of a photoconductor on a document portion with respect to document reflectance.

FIG. 6 is a diagram showing a processing procedure of the present invention.

FIG. 7 is a diagram showing a processing procedure of a correction mode based on a fixing temperature.

FIG. 8 is a diagram showing a processing procedure relating to a correction mode.

[Explanation of symbols]

 1 Charging Roller 2 Photoreceptor 5 Developing Device 10 Temperature Detection Device 11 Potential Sensor

Claims (5)

[Claims] 1. A charging unit that contacts the latent image carrier, a charging unit that applies a voltage to the charging unit, a control unit that controls the voltage applied to the charging unit, and a temperature of the charging unit. In the image forming apparatus that corrects the applied voltage based on the temperature detected by the temperature detecting unit, the image forming apparatus includes a potential detecting unit that detects the potential of the latent image carrier, An image forming apparatus which corrects a developing bias according to a difference between a potential of an image portion and a predetermined value. 2. The image forming apparatus according to claim 1, further comprising potential detecting means for detecting the potential of the latent image carrier between the charging means and the exposing means, and the non-image portion at the image front end of the latent image carrier. An image forming apparatus, wherein the developing bias is corrected for each image formation according to the difference between the potential of the image and a predetermined value. 3. The image forming apparatus according to claim 1, wherein the voltage applied to the charging unit is corrected according to the difference between the detected potential and a predetermined value. 4. The image forming apparatus according to claim 1, wherein the temperature of the fixing unit is equal to or lower than a predetermined temperature, and the potential of the latent image carrier is detected when the power of the image forming apparatus is turned on. An image forming apparatus, which executes a correction mode for correcting a voltage applied to a charging unit according to a difference from a predetermined value. 5. The image forming apparatus according to claim 1, wherein the potential of the latent image carrier is detected, and the applied voltage of the charging unit is corrected according to the difference between the detected potential and a predetermined value. An image forming apparatus characterized by forcibly executing.