Electrophotography – Diagnostics – Consumable
Reexamination Certificate
2002-12-19
2003-11-25
Ngo, Hoang (Department: 2852)
Electrophotography
Diagnostics
Consumable
C399S024000, C399S025000, C399S396000
Reexamination Certificate
active
06654568
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an image forming apparatus for forming an electrostatic latent image on an electrophotographic photosensitive member by electrophotography and visualizing the electrophotographic latent image with a developer, an image bearing member life detecting method, and a process cartridge detachably attachable to the image forming apparatus.
The electrophotographic image forming apparatus includes, e.g., an electrophotographic copying machine, electrophotographic printer (e.g., LED printer or laser beam printer), and electrophotographic facsimile apparatus.
The cartridge detachably attachable to the main body of the electrophotographic image forming apparatus means a cartridge having at least one of an electrophotographic photosensitive member, an electrostatic charging means for electrostatically charging the electrophotographic photosensitive member, a developing means for supplying a developer to the electrophotographic photosensitive member, and a cleaning means for cleaning the electrophotographic photosensitive member. Among detachably attachable cartridges, a process cartridge is a cartridge which is an integral unit of an electrophotographic photosensitive member and at least one of an electrostatic charging means, developing means, and cleaning means, and is detachably attachable to the main body of an electrophotographic image forming apparatus, or which is an integral unit of at least a developing means and electrophotographic photosensitive member and is detachably attachable to the main body of an electrophotographic image forming apparatus.
2. Related Background Art
Conventionally, an electrophotographic image forming apparatus such as an electrophotographic copying machine or laser beam printer uniformly electrostatically charges an electrophotographic photosensitive member by using an electrostatic charging means, and irradiates the surface of the photosensitive member with light corresponding to image information to form a latent image. Then, the apparatus supplies a developer to the latent image by using a developing means to visualize the image, transfers the visualized image onto a recording medium, and fixes the image by a fixing apparatus to obtain the image. After transfer, the electrophotographic photosensitive member is cleaned by a cleaning means.
This image forming apparatus adopts a process cartridge method in order to facilitate replacement and maintenance of expendables such as an electrophotographic photosensitive member and developer. More specifically, an electrophotographic photosensitive member, a developing means, electrostatic charging means, and cleaning means as process means which act on the electrophotographic photosensitive member, a developer storage vessel, and a waste developer vessel are integrated into a cartridge. The cartridge is detachably attachable to the main body of the image forming apparatus.
According to the process cartridge method, the apparatus can be maintained not by the serviceman but by the user. For example, when the developer runs out or the life of the photosensitive drum has expired, the user can replace the cartridge with a new one and form an image again. This process cartridge method can significantly improve the operability of the apparatus, and is widely used in electrophotographic image forming apparatuses.
The process cartridge type image forming apparatus must warn the user that, e.g., the life of an expendable element such as an electrophotographic photosensitive member or developer has expired or will expire soon, and allows the user to replace the expendable element with a new one at arbitrary time.
The following conventional life detecting methods for a cylindrical electrophotographic photosensitive member, i.e., photosensitive drum, are available.
(1) The number of image forming sheets is integrated to detect the life of the photosensitive drum. According to the simplest method, each of image forming recording media of, e.g., different A4 and A3 sizes is counted as one sheet. In this case, however, the life of the photosensitive drum is detected with poor precision. Also when the number of image forming sheets is merely integrated, the life of the photosensitive drum is detected with poor precision because the rotation period of the photosensitive drum per recording medium changes depending on the number of image forming sheets per job, i.e., the successive number of recording media for forming an image after the start of image forming operation, and the life of the photosensitive drum (to be described later) changes depending on the rotation period.
(2) Japanese Patent Application Laid-Open No. 4-51259 discloses a conventional method of detecting the electrostatic charge amount of a photosensitive drum by a surface potential sensor. According to this method, a decrease in the electrostatic charge potential of the photosensitive drum or a decrease in latent image contrast can be actually detected directly by the surface potential sensor. Compared to method (1), the life can be detected with high precision while the output image state is reflected. Practicing this method, however, requires a surface potential sensor and an electrical circuit for processing an output from the sensor, resulting in high cost. As for the longitudinal direction of the photosensitive drum, determination is made based on only information on the photosensitive drum that corresponds to the sensor position. The detection ability is poor for a partial error, and the stability is low due to variations or changes over time in the surface potential sensor. The life of the photosensitive drum is not always accurately detected.
(3) As a method of solving the problems of method (1) and increasing the life detection precision for the photosensitive drum, Japanese Patent Application Laid-Open No. 5-188674 discloses a method of integrating not the number of image forming sheets but the number of turns of the photosensitive drum. Some methods integrate the rotation period of the photosensitive drum on the basis of the same principle. In any method, the number of turns (rotation period) is large for a large recording medium size in correspondence with the recording medium size in one image formation, and is small for a small recording medium size. A photosensitive drum life detection error by a difference in recording medium size is reduced in comparison with the case of integrating the number of image forming sheets. Since the number of turns (rotation period) of the photosensitive drum is directly integrated regardless of the number of image forming sheets per job, the life detection precision is relatively high.
As a method developed from method (3), Japanese Patent Application Laid-Open No. 4-98265 discloses that the number of turns of the photosensitive drum is integrated in actual image formation by integrating the number of turns of the photosensitive drum only when a transferring charger as a transferring means operates, and that the life of the photosensitive drum can be more accurately detected. Japanese Patent Application Laid-Open No. 6-180518 discloses that the number of turns of the photosensitive drum while the photosensitive drum undergoes electrostatic charging processing, and the number of turns of the photosensitive drum while a cleaning member for cleaning the photosensitive drum is in contact with the photosensitive drum are respectively integrated, and the life of the photosensitive drum is determined based on the comparison with their set values (lives).
The following method is known as a method of notifying the user of the replacement timing of a process cartridge. According to a method disclosed in Japanese Patent Application Laid-Open No. 5-333626, the user is notified of the replacement timing of a process cartridge constituted by a cleaner (cleaning means) and electrophotographic photosensitive member on the basis of the life of the electrophotographic photosensitive member. The number of image forming sheets is integrate
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