Minolta Company, Ltd.

Minolta Camera Kabushiki Kaisha

Hideaki Kodama

Yoshihiro Hattori

Suguru Hamamichi

Takeru Kinoshita

Kazuomi Sakatani

Kazuyuki Fukui

Naoyoshi Kinoshita

Yasuhiro Ohno

Yoshikazu Naito

Eiji Nakane

Makoto Takase

An image forming apparatus using an electrophotographic process is disclosed which measures the resistance of a page onto which an image is to be formed and optionally also measures the humidity of ambient environment. A controller controls image forming conditions, such as a development condition or a transfer condition, according to the measured resistance and/or the measured humidity.

Image forming apparatus having image transfer control

An image forming apparatus using an electrophotographic process including a photoconductor, a development device, and a transfer device, a measuring device measures an electrostatic capacitance between said photoconductor and said transfer device in predetermined conditions while a standard toner image is formed. Humidity of ambient environment is also measured. Then, a controller controls image forming conditions such as a development condition or a transfer condition according to the measured electrostatic capacitance and the humidity. Alternately, a resistance of the paper is measured, and a controller controls image forming conditions according to the measured resistance. In a still different way, an amount of toner charges of a standard toner image is measured, and a controller controls image forming conditions according to the measured amount of toner charges.

Image forming apparatus with controller for controlling image forming

In order to control development condition and/or transfer condition for stable image forming, toner patterns of the same density are formed on a photoconductor and are transferred onto a paper or the like while changing the transfer current. Then, the transfer efficiencies of the toner patterns are measured. Other characteristics such as the resistance of the paper and charge of toners may also be monitored. Then, the development condition and/or transfer condition is controlled according to the detected data.

Image forming apparatus with transfer efficiency control

In an electrophotographic copying machine, image quality is improved by suppressing phenomena such as narrowing and thickening of a linear image or discharge noises in a photograph image due to anomalies on transfer of a toner image. For example, a document type is discriminated and when a transfer brush is used for transfer, transfer current and pretransfer erasing are controlled according to the type of document image. The pretransfer erasing is controlled in various following situations: Bi-level exposure method or multi-level exposure method, edge emphasis, photoelectric efficiency, the surface potential of the photoconductor, and position of a developing device.

Image forming apparatus with enhanced pretransfer erasing

An image forming apparatus gets information on the thickness of the photosensitive layer by using the image transfer power source and transfer brush, and controls the contact position of the transfer brush on the paper carrying belt based on the thickness information, so that in case the photosensitive layer wears thin partially due to the long-term use, the apparatus increases in compensation the impedance of the carrying belt in its section from the image transfer zone to the contact position of the transfer brush. The apparatus may be designed to use selectively multiple transfer brushes having different impedances, instead of the position control of one transfer brush. Consequently, the apparatus can retain the difference of impedance between the toner image portion and non-toner image portion in the transfer zone of the photosensitive layer and thus can retain the unevenness of transfer electric field distribution across the transfer zone in the same degree as with a new photosensitive layer, whereby it performs high-quality image formation without the occurrence of dropout throughout the long-term use. For a multi-color image forming apparatus, the image forming unit for black color that is most sensitive to the print quality implements the impedance control.

Image forming apparatus with an impedance varying device and method of

A pressing force adjusting mechanism decreases a pressing force of a pressing member 16 when a leading edge or a rear edge of a transfer material P passes through a transfer point P1 based on the detection signals from a transfer material position sensor 57 and/or a transfer material type sensor 58.

Image forming apparatus

An image forming apparatus which sequentially transfers and superimposes sequentially formed electrostatic latent images onto a sheet wound around a sheet support. The image forming apparatus have either a photoconductor where the electrostatic latent images are sequentially formed on the surface or a plurality of photoconductors where the electrostatic latent images are formed respectively and sequentially. The quantity of print dot misregister is detected by forming reference patterns on a sheet and by reading the formed reference patterns. The rotational speed of conveying rollers for delivering a sheet to the sheet support is switched over in response to the quantity of the print dot misregister. The rotational speed of the conveying rollers can also be switched over in response to the thickness of a sheet. In the case that the image forming apparatus is a full-color copying machine, the electrostatic latent images are of four types for cyan, magenta, yellow and black.

Image forming apparatus for controlling a sheet conveying speed

In an electrophotographic image forming apparatus including a photoconductive drum, the photoconductive drum is electrically charged by a corona charger, and light corresponding to an image is projected onto the photoconductive drum by an exposure optical system, thereby forming an electrostatic latent image thereon. Thereafter, the formed electrostatic latent image is developed with toner by a developing unit to form a toner image thereon, and then the toner image is transferred onto a sheet of paper. There is further provided a voltage sensor for detecting a surface voltage at at least one position of the photoconductive drum. An operation value of at least one of the corona charger, the exposure optical system and the developing unit is adjusted by an adjustment controller based on the surface voltage detected by the voltage sensor at a timing between respective image forming processes when an image forming process is continuously repeated a plurality of times. Further, the operation value of at least one of the corona charger, the exposure optical system and the developing unit is further adjusted with a preciseness higher than that of the adjusting controller, based on the surface voltage detected by the voltage sensor, prior to a process of continuously repeating an image forming process a plurality of times.

Electrophotographic image forming apparatus adjusting image forming

A digital half-tone image is reproduced by exposing a photoconductor by modulating the intensity of laser beam. In order to correct the effect of the size of laser beam on the gradation characteristic, the surface potential of the photoconductor is detected under various conditions. The sensitizing potential and the sensitivity of the photoconductor are corrected according to the measured values for stabilizing the gradation potential. Then, the beam size is corrected according to the surface potential or the amount of adhered toners detected under prescribed conditions, without detecting the beam size.

Apparatus for forming digital images

In forming a digital image on the photoconductor wherein the intensity of the laser beam is modulated according to multi-level image data, a standard toner image is formed at an intermediate intensity at which the reproduced image density is not affected by the beam size, and the toner density is detected. On the other hand, the size of the beam for exposing the photoconductor is measured. Then, the gradation characteristic is controlled according to the toner density and the beam size. Thus, the effect of the beam size on the gradation characteristic is corrected.

Apparatus and method for forming digital image

In an electrophotographic image forming apparatus, a charger sensitizes the photoconductor at a desired initial potential and the photoconductor is exposed to form an electrostatic latent image, which is developed by a developer to form a toner image. A gradation correction table on the relation of the input image signal to the exposure amount is provided in a memory, and it is amended by adding a common amendment value to the image density signal in the gradation correction table. The common amendment value is determined according to the density of a standard toner image. If a plurality of gradation correction tables are stored in a memory, one of them is selected according to the output voltage of the charger or the bias potential of the developer. The selected gradation correction table is amended according to the surface potential of the photoconductor, the temperature of the photoconductor or the humidity of the photoconductor. Alternately, the detection value of the surface potential, the temperature or the humidity may be used to select the gradation correction table. The gradation table may be amended according to the state of the photoconductor. The amplification factor of the exposure amount for the photoconductor can be changed according to the state of the photoconductor, the temperature or the humidity of the photoconductor. The bias voltage of the developer or the output voltage of the charger may also be changed according to the state of the photoconductor.

Image forming apparatus having correction means for modifying image

In an image forming apparatus with use of electrophotographic process, a plurality of toner images are formed on a photoconductor by changing stepwise a predetermined operating parameter such as light intensity of laser beam or the grid potential of sensitizing charger, and the densities of the toner images are measured. Thus, the value of the operating parameter is determined which corresponds with the smallest non-zero toner density among the measured densities. When an image is formed on the photoconductor, for example the gamma table is corrected according to the determined minimum light intensity.

Image forming apparatus controlled according to smallest non-zero toner

In an image forming apparatus for forming an image on a sheet of paper, including an image forming device for forming a reference toner image having a predetermined density on an image retaining member. A first detector detects a density of the reference toner image formed on the image retaining member and outputs first density data for representing the detected density thereof, and then, the reference toner image formed on the image retaining member is transferred onto a sheet of paper. On the other hand, a second detector detects a density of the reference toner image transferred on the sheet of paper and outputs second density data for representing the detected density thereof. Further, a controller automatically adjusts an image density of an image formed on a sheet of paper so as to obtain a predetermined image density by controlling operation conditions of the image forming device based on the first and second density data respectively outputted from the first and second detectors.

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Okazaki, Japan

Hideaki Kodama