Electrophotography – Image formation – Development
Reexamination Certificate
2001-12-21
2003-12-30
Grainger, Quana M. (Department: 2852)
Electrophotography
Image formation
Development
C399S043000, C399S053000
Reexamination Certificate
active
06671485
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophotographic-type image forming apparatus, which is applicable to a copier, printer, facsimile machine or any composite apparatus thereof and, more specifically, to an image forming apparatus of the type which uses mono-component nonmagnetic toner as a developer for image formation. Still more specifically, the invention relates to an image forming apparatus which is capable of producing images with consistent quality without being influenced by variations in toner carry quantity and chargeability by the application of a predetermined bias voltage to a toner layer forming blade.
2. Description of the Related Art
Electrophotography has been used extensively in a copier, a laser beam printer, etc. as a technology for printing images on a sheet of plain paper as image recording medium. Electrophotographic development can be roughly grouped into wet developing and dry developing, and generally the latter dry method is more popularly used. The dry development can be further grouped into two processes according to the type of developer or development agent to be used. One developer is two-component developer and the other is mono-component or mono-component developer, and the development using the latter mono-component developer is prevailing predominantly as the developing method mainly for small-size printers or copiers. Mono-component developer contains no carrier such as iron or ferrite powder and the developing apparatus using mono-component developer can be constructed simpler than that using two-component developer, thus offering advantages in terms of compactness and cost over the two-component counterpart.
Thus, mono-component development uses mono-component nonmagnetic developer for image formation. As a method of mono-component developing, impression development is known to those skilled in the art, in which the electrostatic latent image on a photosensitive drum and toner particles or toner carrier are brought into contact with each other such that the relative peripheral speeds therebetween are substantially zero. Such mono-component developing method is disclosed in U.S. Pat. No. 3,152,012, U.S. Pat. No. 3,731,148, Japanese Patent Application KOKAI Publication No. 47-13088 and Japanese Patent Application KOKAI Publication No. 47-13089. This mono-component developing method has many advantages; for example, it can dispense with carrier or magnetic material and, therefore, the developing apparatus and hence the image forming apparatus operable according to this method can be constructed simpler in structure and smaller in size and also it makes easier to use color toners.
As compared with the two-component development, however, the mono-component development is disadvantageous in terms of toner chargeability and toner carriability (or toner carry quantity) during operation immediately after a start-up of the image forming apparatus because the mono-component toner as the developer has no carrier which serves to charge the toner and to carry the toner onto the developing roller. Improvement of toner chargeability has been provided, for example, by Japanese Patent Application KOKAI Publication No. 6-130790 or Japanese Patent Application KOKAI Publication No. 2000-221776, which each proposes changing the material for a toner charging blade from plastic to metal and also applying a bias voltage to that toner charging blade (referred to as “blade biasing method”).
According to the proposed blade biasing method, the effect of charge injection, as well as that of triboelectrification, are available, so that consistent toner charging can be accomplished. However, in this blade biasing method, a difference in toner chargeability is recognized between the leading end portion of an image and the remaining portion thereof, when the developing apparatus is used constantly and when the apparatus is used after a start-up following an idle or unused state thereof for a while. To be more specific, fogging toner appears increasingly in the background area in the above former case, while irregular image density in the solid area occurs in the latter case.
The above-cited KOKAI Publication No. 2000-221776 also discloses a technology of controllably changing the bias voltage for application to the toner layer forming blade in dependence on a change in cohesion of the mono-component toner which occurs due to toner deterioration with age or by a change of ambient humidity. According to this technology, an optimum toner layer can be formed on the developing roller by changing the bias voltage across the toner layer forming blade according to a change in the toner cohesion, with the result that good image formation can be maintained successfully. However, a problem of inconsistent image quality remains unsolved because the toner chargeability varies with an increasing number of prints.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-described problems. It is an object of the present invention to provide an image forming apparatus for using mono-component nonmagnetic toner, the image forming apparatus being capable of forming images with consistent quality without being influenced by variations in toner carry quantity and chargeability. More specifically, bias voltages are applied to a toner feed roller, developing roller and blade through a toner feed bias supply, development bias supply and blade bias supply, respectively. In this regard, the blade bias voltage is increased by a predetermined magnitude after a release of sleep mode of the fixing device until a predetermined number of image recording media have been imaged. Additionally, the blade bias voltage is decreased for a period of time corresponding to the first turn of the developing roller and increased for a period of time corresponding to the second or more turns thereof. In this manner, the blade bias voltage and the toner feed bias voltage are controllably changeable with a life or an increasing number of image formations.
In order to achieve the above objects, according to one embodiment of the present invention, an image forming apparatus is provided with a photosensitive member for forming thereon an electrostatic latent image, a developing roller for supplying mono-component nonmagnetic toner to visualize the latent image on the photosensitive member, a toner feed roller for feeding the toner to the developing roller, a blade for forming a layer of toner on the developing roller, a fixing device for fixing the visualized image on an image recording medium, and a blade bias voltage controllable means for applying a bias voltage to the blade and controllably changing the blade bias voltage at a time when a predetermined number of image recording media have been imaged after a start of operation of the fixing device following an idle state thereof continued for a predetermined period of time or longer.
According to one aspect of the present invention, the blade bias voltage is higher during the period of time before the predetermined number image recording media imaged than that after this period of time.
According to another aspect of the present invention, the idle state of the fixing device is accomplished by sleep mode setting thereof and the start of operation of the fixing device is effected by terminating the sleep mode setting.
According to another aspect of the present invention, a life-dependent blade bias voltage controllable means is provided for controllably changing a bias voltage for application to the toner feed roller, as well as the bias voltage for application to the blade, in response to a life or an increase in the number of image recording media formed with images.
According to another aspect of the present invention, the bias voltage for application to the blade is increased with an increase in the bias voltage for application to the toner feed roller.
According to another aspect of the present invention, the absolute value of the bias voltage for application to the blade is low
Foley & Lardner
Grainger Quana M.
Kabushiki Kaisha Toshiba
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