Patent Application
20080038005
An embodiment of the present invention is now described with reference to the drawings.
The image forming apparatus forms a multicolor (full color) image or a monochrome image on a prescribed sheet (recording paper) in accordance with image data transmitted from an external device (e.g., a terminal device such as personal computer). As shown in
Image data handled by the image forming apparatus corresponds to a color image using colors of black (K), cyan (C), magenta (M), and yellow (Y). The image forming apparatus, therefore, has respective four units of developing devices 2 (2a to 2d), of photosensitive drums 3 (3a to 3d), of electrifiers 5 (5a to 5d), and of cleaner units 4 (4a to 4d) to form four kinds of images corresponding to the four colors. In
The photosensitive drum 3 is disposed on the upper part of the image forming apparatus, where the photosensitive drum 3 is exposed to laser light emitted from the exposure unit 1 to form an electrostatic latent image corresponding to image data. The photosensitive drum 3 is made by coating the surface of a cylindrical aluminum alloy with a photosensitive material in a layer (not shown), and is so supported that a driving means (not shown), such as a pulse motor, can control the rotation of the photosensitive drum 3.
The electrifier 5 is an electrifying means that uniformly electrifies the surface (photosensitive material layer) of the photosensitive drum 3 with a given potential. The electrifier 5 is provided as a contact type roller-shaped or brush-shaped electrifier, as shown in
The exposure unit 1 is composed of a laser scanning unit (LSU) having a laser emitter 1A and a reflective mirror 1B. The laser emitter 1A emits laser light hued in each color based on received image data. The laser emitter 1A may be replaced with an array of light-emitting elements, such as a writing head composed of EL or LED. The exposure unit 1 has a function of exposing the electrified photosensitive drum 3 to laser light according to input image data to form an electrostatic latent image corresponding to the image data on the surface of the photosensitive drum 3.
The developing unit 2 develops an electrostatic latent image formed on each photosensitive drum 3 into an apparent image, using toner (developer) of each color (K, C, M, and Y) The developing unit 2 causes the electrostatic latent image formed on the surface of photosensitive drum 3 to absorb the toner.
The cleaner unit 4 removes and recovers toner remaining on the surface of the photosensitive drum 3 after image development and transfer, in preparation for the next image formation. Usually, the photosensitive material is electrically neutralized following toner image transfer to facilitate the removal of toner remaining on the surface of the photosensitive drum 3, and then the residual toner is removed physically by scraping it off, using a brush, etc.
The intermediate transfer belt unit 8, which is disposed above the photosensitive drums 3, includes an intermediate transfer belt 7, an intermediate transfer belt driving roller 7-1, an intermediate transfer belt tension mechanism 7-3, an intermediate transfer belt driven roller 7-2, intermediate transfer rollers 6 (6a to 6d) serving as primary transfer rollers, and an intermediate transfer belt cleaning unit 9. The intermediate transfer belt driving roller 7-1, the intermediate transfer belt tension mechanism 7-3, the intermediate transfer rollers 6, and the intermediate transfer belt driven roller 7-2 cause the intermediate transfer belt 7 to run in an arrowed direction with rotating drive of the intermediate transfer belt driving roller 7-1 after the intermediate transfer belt 7 is set.
The intermediate transfer rollers 6 are supported rotatably on a roller mounting portion of the intermediate transfer belt tension mechanism 7-3. As a result, these intermediate transfer rollers 6 (6a to 6d) are disposed rotatably on the inside of the intermediate transfer belt 7, which faces to each of the photosensitive drums 3 (3a to 3d), respectively. The intermediate transfer rollers 6 are supplied with a transfer bias for transferring toner images on the photosensitive drums 3 to the intermediate transfer belt 7.
The intermediate transfer belt 7 is so arranged as to be able to come in contact with respective photosensitive drums 3. Toner images of respective colors formed on the photosensitive drums 3 are sequentially superimposed and transferred to the intermediate transfer belt 7 to form a color toner image (multicolor toner synthetic image) on the intermediate transfer belt 7. The intermediate transfer belt 7 is formed into an endless belt using a film of about 100 μm to 150 μm in thickness.
Transfer of a toner image from the photosensitive drum 3 to the intermediate transfer belt 7 is carried out by the intermediate transfer roller 6 in contact with the back (inside) of the intermediate transfer belt 7. A high-voltage transfer bias for toner image transfer (positive high voltage that is reverse in polarity to negatively charged toner) is applied to the intermediate transfer roller 6. The intermediate transfer roller 6 is a roller that has a base material of a metal (e.g., stainless steel) shaft having a diameter of 8 mm to 10 mm, which metal shaft is coated with a conductive elastic material (e.g., ethylene-propylene rubber, urethane foam, etc.). This conductive elastic material allows uniform application of the high voltage to the intermediate transfer belt 7. While roller-shaped transfer electrodes are employed in the present embodiment, brushes may also be used as the transfer electrodes.
As described above, toner images developed on the photosensitive drums 3a to 3d according to respective hues are stacked on the intermediate transfer belt 7 to constitute image data (multicolor toner synthetic image) input into the image forming apparatus. The stacked image data is transferred onto a recording paper by a transfer roller 11, depending on the running of the intermediate transfer belt 7, the transfer roller 11 composing a transfer unit located at the point of contact between the recording paper conveyed on the paper conveyance path S1, which will be described later, and the intermediate transfer belt 7.
At this time, the intermediate transfer belt 7 and the recording paper are put under pressure to contact with each other by a given cramping force from the transfer roller 11 and a voltage for transferring toner to the recording paper is applied to the transfer roller 11. To constantly provide the transfer roller 11 with the above cramping force, either the transfer roller 11 or the intermediate transfer belt driving roller 7-1 is made of a hard material (metal, etc.) and the other is provided as an elastic roller, etc., made of a soft material (elastic rubber roller, expandable resin roller, etc.).
As described above, some toner sticks to the intermediate transfer belt 7 due to the contact with the photosensitive drum 3, or remains on the intermediate transfer belt 7 when the transfer roller 11 fails to transfer the toner to the recording paper. Such toner becomes the cause of a toner color mixture at the next process, and is, therefore, removed and recovered by the intermediate transfer belt cleaning unit 9. The intermediate transfer belt cleaning unit 9 has a cleaning blade 9-1 serving as a cleaning member in contact with the intermediate transfer belt 7, which cleaning blade 9-1 is supported by the intermediate transfer belt driven roller 7-2 from the back of intermediate transfer belt 7 with which cleaning blade 9-1 is in contact. Residual toner recovered by the cleaning blade 9-1 is dropped into a storage unit 9-2 placed below the cleaning blade 9-1 to be accumulated in the storage unit 9-2.
The paper feeding cassette 10 is the cassette that stores recording papers used for image formation. The paper feeding cassette 10 is disposed, for example, on the bottom of the image forming apparatus, that is, under the exposure unit 1. The paper ejecting tray 15, which is disposed on the top of the image forming apparatus, is the tray on which the printed recording papers are placed facedown.
The image forming apparatus has the paper conveyance path S1 through which a recording paper from the paper feeding cassette 10 is sent to the paper ejecting tray 15 via the transfer roller 11 and the fixing device 12. The paper conveyance path S1 extends substantially in the vertical direction from a paper feeding unit of the paper feeding cassette 10 toward the paper ejecting tray 15. The paper conveyance path S1 extending from the paper feeding cassette 10 to the paper ejecting tray 15 is provided with a pickup roller 16 (16-1), resist rollers 14, the transfer roller 11, the fixing device 12, conveyance rollers 17 (17-1, 17-2, and 17-3) conveying the recording paper, etc.
The conveyance roller 17 is a small roller that facilitates and assists with the conveyance of the recording paper, and a plurality of conveyance rollers 17 are arranged along the paper conveyance path S1. The pickup roller 16 is disposed on an end of the paper feeding cassette 10, working as a take-in roller that feeds recording papers one by one into the paper conveyance path S1.
The resist rollers 14 temporarily hold a recording paper conveyed on the paper conveyance path S1. The resist rollers 14 have a function of conveying the recording paper to the transfer unit (cramping unit between the transfer roller 11 and the intermediate transfer belt driving roller 7-1) in the timing so adjusted that the front end of a toner image on the intermediate transfer belt 7 is located at a given position from the front end of the recording paper.
The fixing device 12 includes a heat roller 12-1 and a pressure roller 12-2, which rotate over a recording paper held between the rollers 12-1 and 12-2. The heat roller 12-1 is adapted to have a prescribed fixing temperature that is set by a controlling unit on the basis of a signal from a temperature detector, which is not shown. The heat roller 12-1 has a function to melt, mix and press a transferred multicolor toner image on the recording paper and thermally fix the multicolor toner image on the recording paper by thermally pressing the recording paper working with the pressure roller 12-2.
The recording paper on which the multicolor toner image is fixed is ejected on the paper ejecting tray 15 with the multicolor toner image directed downward by means of the conveyance rollers 17-2 and 17-3.
Next, the conveyance path for the recording paper is described. The image forming apparatus is provided with the paper feeding cassette 10 that stores recording papers in advance, and also with a manual insertion tray 18 that spares a user the trouble of opening/closing the paper feeding cassette 10 when the user makes a few prints. Recording papers from the paper feeding cassette 10 and from the manual insertion tray 18 are guided one by one to the paper conveyance path S1 via respective pickup rollers 16 (16-1 and 16-2).
A recording paper to be conveyed from the paper feeding cassette 10 is picked up by the pickup roller 16-1, and is conveyed by the conveyance rollers 17-1 to the resist rollers 14. At this time, the recording paper is conveyed by the transfer roller 11 in the timing so adjusted that the front end of image data on the intermediate transfer belt 7 is located at a given position from the front end of the recording paper and the image data is transferred to (written onto) the recording paper. Subsequently, the recording paper is sent through the fixing device 12, where unfixed toner on the recording paper is melted and fixed with heat, and the recording paper is ejected onto the paper ejecting tray 15 from the paper ejecting roller 17-3 via the conveyance roller 17-2 (in a case of a single-side printing request).
Meanwhile, a recording paper to be conveyed from the manual insertion tray 18 is picked up by the pickup roller 16-2, and is conveyed through a plurality of conveyance rollers (17-6, 17-5, and 17-4) to the resist rollers 14. Subsequently, the recording paper further travels through the same conveyance path as the recording paper from the paper feeding cassette 10 travels, and is ejected onto the paper ejecting tray 15.
When duplex printing is requested, the paper ejecting roller 17-3 chucks the rear end of the above recording paper that has traveled through the fixing device 12 following the completion of single-side printing. The paper ejecting roller 17-3 then rotates in reverse to send the recording paper to a switchback conveyance path S2 provided with conveyance rollers (17-7 and 17-8) and the printing is executed on the reverse side of the recording paper via the resist rollers 14 and the paper is finally ejected onto the paper ejecting tray 15.
In actual image formation operation, to reduce wearing, deterioration, etc., of the photosensitive drum 3 due to contact of the photosensitive drum 3 with the intermediate transfer belt 7, the intermediate transfer roller 6 is moved away from the intermediate transfer belt 7 according to a printing request to allow contact and separation of the photosensitive drum 3 with and from the intermediate transfer belt 7 along with the movement.
A printing request includes a color mode request and a monochrome mode request. When the color mode request is made, the intermediate transfer rollers 6 (6a to 6d) move to come in contact with the reverse side of the intermediate transfer belt 7, that brings the surface of the intermediate transfer belt 7 into contact with the photosensitive drums 3 (3a to 3d) to create a state of readiness for primary transfer of toner images of respective hues to the intermediate transfer belt 7. When the monochrome mode request is made, only the intermediate transfer roller 6a for black image formation moves to come in contact with the reverse side of the intermediate transfer belt 7, that brings the surface of the intermediate transfer belt 7 into contact with the photosensitive drum 3a for black image formation to create a state of readiness for primary transfer of a black toner image to the intermediate transfer belt 7.
The description made with reference to
As shown in
Detection of the position of the image at the given part is carried out for the photosensitive drums 3a to 3d (colors K, C, Y, and M), and times (ta, tb, tc, and td) to take to reach the measuring point D from the exposure point E are detected, respectively. A detected time is compared with a preset time to find the presence/absence of a difference between the detected time and the preset time to detect the extent of position shift of the toner image. If the position of the toner image is normal, thus shows no position shift, the rotation of the photosensitive drum 3 is normal, which leads to a conclusion that the synchronized rotation of the pulse motor 13 driving the photosensitive drum 3 is normal. If a detected position shift of the toner image is, for example, several hundreds μm, the photosensitive drum 3 has trouble in rotation, which brings a conclusion that the pulse motor 13 is in a state of abnormality (out-of-step).
In detection of a position shift of a toner image, a color shift is detected to provide a proper color image. When a position shift is detected, timing for image reading, etc., is adjusted (resist adjustment). In this case, a shift of pixels of about 42 μm each is detected to find a position shift of the toner image, and this means detection of a color shift of several score μm. Based on a detection result, timing for image formation is corrected. The detection is carried out using a test patch image, etc., at the time of starting the image forming apparatus, restarting the image forming apparatus after a long period of service suspension, and inspecting equipment, etc.
In contrast, the method of abnormality detection according to the present invention allows detection of a position shift of an image that is actually under a printing process. The position shift detection, for example, is carried out regularly on a given print time basis or print page basis.
The image data controlling unit 21 controls a printer controlling unit 26 to print the read image data on a recording paper. The printer controlling unit 26 takes a recording paper out of a paper tray 29a or 29b (or a manual insertion tray), and detects the edge of the paper with a sensor to select timing of transfer of the image data to the paper. A recording paper conveyance process unit 28 determines a conveyance path, conveyance timing, etc., for the recording paper taken out of the paper tray 29a or 29b. An image formation process unit 27 sets and selects the concentration, position, size, etc., of an image.
The image forming apparatus has a toner concentration sensor 30a that measures the concentration of transferred toner or a resist sensor 30b that detects a color irregularity or a color shift of a color image. Usually, a detection patch image is formed when the image forming apparatus is started or restarted after a long period of service suspension, and the sensors 30a and 30b detect a shift of the toner concentration or color of the patch image. A shift of toner concentration or color is corrected into a proper value to obtain a proper image. This detection by the sensors, however, is not carried out on a regular basis, but the sensors 30a and 30b are usually not used during operation of the image forming apparatus.
A rotation failure of the photosensitive drum during operation of the image forming apparatus may lead to the formation of a defective image or even to the formation of no image at all. In such a case, a user usually does not realize the occurrence of fault until looking at a printed out image. When image data under a printing process is the data transmitted through such a communication line such as fax line, reprinting the image data may be difficult. In such a case, the image forming apparatus must be stopped immediately to store the image data in the memory.
According to the present invention, a rotation failure of the photosensitive drum can be detected on a regular basis by using the toner concentration sensor 30a or the resist sensor 30b, which are not used regularly, according to the method described with reference to
Then, at step S3, it is detected whether the position of the detected toner image is normal or shifted. When the position of the toner image is normal (Yes), the rotation of the photosensitive drum is determined to be normal (synchronized operation of the pulse motor is normal). Subsequently, image formation is continued at step S9 to complete printing work. When the position of the toner image is shifted at step S3, image formation is continued at step S4 (image forming apparatus is not stopped immediately). Meanwhile, image data that follow the image data under a printing process is stored in the memory at step S5 and not deleted even after the end of printing.
At step S6, a pulse motor out of normal rotation is specified, and a printer is brought to a stop at step S7, then a state of rotation failure is displayed on the display unit at step S8. Preferably, the display unit displays a message of specifying the motor in fault, of indicating the cause of the fault, of a countermeasure to the fault, etc.
According to the above image processing method, even in the case of the image data such as fax data received through an external communication line, the image reproduction is possibly carried out by immediately detecting an image failure due to an abnormal rotation of the photosensitive drum and saving image data that follow the occurrence of the image failure. When image data not obtained through a communication line is printed, the image processing method can clarify the cause of a defective printed image when an image failure occurs due to an abnormal rotation of the photosensitive drum and stop continuing useless printing.
The present invention offers the following effect.
According to the present invention, a rotation failure of a photosensitive drum due to out-of-step operation, etc., of a pulse motor can be detected using an existing optical sensor, etc., so that an increase in space and costs due to the installation of a dedicated sensor means can be suppressed. When a rotation failure is detected, image data stored temporarily in a nonvolatile memory means, etc., is protected from deletion to prevent the loss of the image data.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-219294 | Aug 2006 | JP | national |
