Electrophotography – Having particular structure – Modular or displaceable
Reexamination Certificate
2002-03-15
2004-05-18
Royer, William J. (Department: 2852)
Electrophotography
Having particular structure
Modular or displaceable
C399S112000, C399S121000
Reexamination Certificate
active
06738590
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to an image forming apparatus such as a printer, a copying machine or a facsimile machine, for forming color and black/white images based on an image forming process, e.g., electrophotography, electrostatic recording system, ionography, magnetic recording system and the like. More particularly, the invention relates to an electrophotographic image forming apparatus of the tandem type which is provided with a plurality of photoreceptor drums and a plurality of image carrying bodies, and is free from color misregistration after it is commercially supplied and undergoes maintenance and is capable of forming images of high quality for a long period of time. Further, the invention relates to a small color electrophotographic image forming apparatus which is small in size and low in cost, and improved in the operability of an image forming unit.
2. Description of Related Art
Various types of xerographic based image forming apparatus for forming color and black/white pictures, such as printers and copying machines, have been proposed and marketed. In particular recently, much effort has been made to develop color printers with the spread of personal computers, internet, digital cameras, and the like. In the field of image forming apparatus, e.g., color printers, there is a strong demand for developing an apparatus which is capable of forming office-use color images, and is operable at a high speed, compact in size, and low in cost.
To form a color image of high quality by using image forming apparatus, such as a color printer, it is necessary to improve accuracy of color registration, i.e., a registration of color component images. That is, to form a color image, color component images of colors, e.g., cyan, magenta, yellow, and black, are formed on an image bearing member, and those color component images are accurately registered to one another and superimposed one upon another.
An image forming apparatus of the tandem type is known for the image forming apparatus, such as a printer. This type of image forming apparatus includes a plurality of image forming units with photoreceptor drums as image carrying bodies corresponding to colors of toner images to be formed, e.g., cyan, magenta, yellow and black. Those color component toner images are successively formed on the image carrying bodies (e.g., photoreceptor drums) of the image forming units. Those toner images are transferred on a recording sheet or an intermediate transfer member in a superimposing fashion.
The tandem type image forming apparatus includes a plurality (e.g., four) of image forming units for forming color component images. Therefore, to improve the accuracy of color registration of the color component images as formed by the image forming units, it is necessary to locate the color component images formed by the image forming units accurately in predetermined positions. To this end, the image forming units of the tandem type are arranged such that the accuracy of color registration, which is performed when the images formed by the image forming units are superimposed one on another, is improved by controlling the scan start timings of the main scan and the sub-scan by an image exposure unit, which forms an image on the image carrying body by a laser beam, the phase of the polygon mirror for scanning by the laser beam, or the position of the mirror for guiding the laser beam to the image carrying body.
In color electrophotography-based image forming apparatus of the type in which a plurality of image forming units including the image carrying bodies (photoreceptor drums) are provided for each color, it is a common practice that the image forming units may be replaced with new ones for each color, as disclosed in Japanese Utility Model laid-open No. 29148/1987. In some image forming apparatus, a replaceable system is employed in which the respective color image forming units are fixed to a single image forming unit positioning member, and the positioning member is then mounted on the main body, as disclosed in Japanese patent laid-open No. 36346/1996. Either system needs the replacement of several number of image forming units. Accordingly, this fact remarkably increases a mental strain of the user when he or she replaces the an image forming unit with another image forming unit. In a case where the image forming units are assembled into a unit and the support shafts of the image carrying bodies are positioned to the frame of the unit, the following problem arises: an accuracy of positioning the writing unit, the intermediate transfer unit for superimposing the color component images, and the image carrying bodies is deteriorated. In the image forming unit as disclosed in Japanese patent laid-open No. 78686/1998, the position accuracy of the laser-based writing unit and the image carrying bodies, and the position accuracy of the image carrying bodies and the image carrying body transfer drums which are in contact with the image carrying bodies greatly affect the accuracy of color misregistration. A problem of color misregistration arises in the image forming unit disclosed.
In most cases, the color registration of the apparatus main body is adjusted at a factory before it is delivered. When the image forming unit greatly affects the color misregistration, the adjustment equivalent to that at the initial state of the product at the factory is required in a maintenance work, e.g., the user replaces the image forming unit with a new one, after the apparatus is commercially supplied. In this case, to lessen the user's load, some means to automatically adjust the color misregistration may be used additionally. A color misregistration adjusting technique is present which detects the result of superimposing the color component images by some means, and feeds back the detection result for adjustment. The technique needs a high accuracy detecting mechanism and adjusting mechanism. This fact results in remarkable increase of the apparatus cost. The color misregistration may be adjusted in a manner that the image formed is output, and a quantity of a color misregistration of the image is detected by the eye, and a color misregistration correction quantity based on the detection is input to the apparatus main body. In this approach, the adjusting accuracy is poor, however.
A color misregistration arises from a position accuracy of the image carrying bodies support shafts and a laser beam position accuracy of a ROS. A high position accuracy of several tens &mgr;m is required for satisfying a tolerable level. It is actually difficult to satisfy the requirement of such a high position accuracy, and a common practice is to adjust the timings of the laser beams for the purpose of preventing color misregistration. Accordingly, in order to make the user free from those sequential adjusting steps when he replaces the image forming unit including the photoreceptor drum with a new one, it is necessary to exactly position and fix the image carrying bodies support shafts to the apparatus main body.
Before delivery from a factory, color misregistration is adjusted, in both the main scan and sub-scan directions of the ROS, on the basis of the image as finally printed out and according to the writing timings of the ROS and the readout timing clock frequency. The color misregistration depends greatly on the position accuracy of the photoreceptor drums. In spite of this fact, its adjustment is carried out by controlling electrical times, not by adjusting those positions. For this reason, it is necessary to accurately position the image carrying bodies support shafts to the main body.
The conventional image forming apparatus employs a C-path transport system in which a sheet transporting path is curved shaped like a C when viewed from the side of the apparatus. The C-path transport system has the following advantages, and is employed in particular by small desk-top printers.
1) The sheet transport path is short, a time taken from sheet feeding to sheet discharg
Koizumi Hiromitsu
Okimura Naomasa
Okoshi Takeshi
Fuji 'Xerox Co., Ltd.
Royer William J.
LandOfFree
Image forming apparatus with detachable image forming unit... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Image forming apparatus with detachable image forming unit..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image forming apparatus with detachable image forming unit... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3255110