Patent Document

CROSS REFERENCE TO RELATED APPLICATION 
   This document claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2002-175279 filed on Jun. 17, 2002, the entire contents of which are hereby incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to an image forming apparatus such as a copier, a printer, etc., and in particular to an image forming apparatus employing an intermediate transfer belt having a seam, which is capable of suppressing any adverse influence of the seam to obtain a high quality image. 
   2. Discussion of the Background 
   In an image forming apparatus such as an optical beam printer a drum type photoconductive member (PC member) is provided to rotate while receiving a scan of a beam having a color component in a main scanning direction in accordance with image data transmitted from either an image reading section or a host computer. Then, latent images are formed with color toner on the PC member and developed to be toner images in accordance with the color component. Subsequently, respective color toner images are transferred and superposed on an intermediate transfer belt one after another, and thereby a full-color image is formed in accordance with the image data. 
   It has been proposed to utilize a sensor to detect a full-color matching pattern formed on an intermediate transfer belt so that an image formation condition, such as an amount of toner to be supplied or pumped toward a latent image, can be controlled in accordance with data obtained by the sensor, to form a high quality color image in accordance with the image data. 
   In such a system, an intermediate transfer belt having a ring shape track requires a highly precise peripheral length in a conveyance direction to form a high quality image. Such an intermediate transfer belt is generally formed by connecting leading and trailing ends of a strip-shaped belt in a prescribed peripheral length. Thus, the intermediate transfer belt necessarily includes a seam. As a result, when a usage life exceeds a prescribed level, and accordingly a prescribed time period has elapsed, the intermediate transfer belt needs be replaced with a new one. That is, over time a fixation condition of the seam physically changes, and thereby the peripheral length sometimes deviates beyond an allowable range. 
   Further, in such a case, when in the background image forming apparatus a color-matching pattern is detected with a sensor, the sensor may erroneously detect a seam mark formed on a seam by regarding the seam mark as the color-matching pattern. Erroneously detecting such a seam mark pattern causes a difficulty in improving a precision of image formation control performed based upon a signal obtained by detecting the color-matching pattern with the sensor. 
   When an intermediate transfer belt is formed seamless and integral, erroneous detection of the seam mark as a color-matching pattern can be avoided. However, in order to form an intermediate transfer belt to be seamless and integral, complex manufacturing steps are generally needed, and thereby a manufacturing cost increases as a drawback. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in view of such problems and to address and resolve such noted problems. 
   Accordingly, it is an object of the present invention to provide a novel full-color image forming apparatus capable of forming a full-color image using a color-matching pattern of color components formed on an intermediate transfer belt. The image forming apparatus includes at least one pattern detection sensor that detects the color-matching pattern and generates pattern detection signals. A seam mark detecting sensor is provided to detect a seam mark formed on the intermediate transfer belt and to generate seam mark detection signals. The seam mark detecting sensor is aligned with the pattern detection sensor on the same axis extending vertically relative to a traveling direction of the intermediate transfer belt. A memory is provided to store digital signals converted from the pattern detection and seam mark detection signals. A seam mark detection signal deleting device is provided to delete a prescribed seam mark detection signal from the pattern detection signals when the pattern detection signal and the prescribed seam mark detection signal occur substantially simultaneously. A controlling device is provided to control the image forming apparatus in accordance with the pattern detection and seam mark detection signals excluding the prescribed seam mark detection signal. 
   In another embodiment, an advance notice mode setting device is provided to set an advance notice mode indicating a necessity to replace a used transfer belt with a new one. 
   In yet another embodiment, an advance notice time setting device is provided to set an advance notice time when an advance notice indicating a necessity to replace a used transfer belt with a new one is displayed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the present invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
       FIG. 1  is a block chart illustrating one example of an image forming apparatus according to the present invention; 
       FIG. 2  is a perspective view illustrating a transfer belt having color matching patterns and a plurality of detection sensors illustrated in  FIG. 1 ; 
       FIG. 3  is an explanatory chart illustrating an arrangement of the color-matching patterns and a seam mark transferred and formed on the transfer belt of  FIG. 1 ; 
       FIG. 4  is a flowchart illustrating an advance notifying operation for indicating a necessity to replace a currently used transfer belt with a new transfer belt; 
       FIG. 5  is a chart illustrating a signal level obtained by detecting the color patterns with the detection sensor in relation to a sampling number; and 
       FIG. 6  is a table illustrating sampling numbers counted when the signal level reaches reference levels. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, and in particular to  FIG. 1 , one example is provided of an image-forming unit  20  to form a full-color image, according to the present invention. 
   In  FIG. 1 , a control unit  21  is provided to control the image-forming unit  20  to operate. A writing unit  1  is arranged in the image-forming unit  20  to receive an input of image data F 3  transmitted from either an image reading section or a host computer. A photo-sensitive drum (PC drum)  3 M is also arranged below the writing unit  1  to form a latent image of magenta in accordance with color separation data of magenta included in the image data F 3 . Similarly, photo-sensitive drums  3 C,  3 Y and  3 BK are arranged below the writing unit  1  to form latent images of cyan, yellow, and black in accordance with cyan, yellow, and black color separation data included in the image data F 3 , respectively. A plurality of developing devices  2 M,  2 C,  2 Y, and  2 BK are arranged in the vicinity of the respective PC drums  3 M,  3 C,  3 Y, and  3 BK to develop the latent images formed thereon to be visible images of M, C, Y, and BK. 
   Further, a transfer belt  7  is arranged in the image forming unit  20  in contact with the respective PC drums  3 M,  3 C,  3 Y, and  3 BK and is rotated by a pair of driven rollers  6   a  and  6   b  and a guiding roller  11 . On the opposite side to the respective PC drums  3 M,  3 C,  3 Y, and  3 BK of the transfer belt  7 , a plurality of transfer devices  5 M,  5 C,  5 Y, and  5 BK are arranged to transfer respective M, C, Y, and BK visible images on the PC drums  3 M,  3 C,  3 Y, and  3 BK to the transfer belt  7  one after another. A detection sensor unit  12  is arranged to detect a seam mark and full-color-matching patterns formed on the transfer belt  7 . 
   As illustrated in  FIG. 2 , the detection sensor unit  12  includes a pair of pattern detection sensors  15   a  and  15   b  separately arranged apart from each other in the vicinity of the transfer belt  7  on an arrangement line D extending perpendicular to a conveyance direction of the transfer belt  7 . Also included is a seam mark detection sensor  16  arranged on the arrangement line D opposing a region excluding the color-matching patterns on the transfer belt  7 . 
   Referring again to  FIG. 1 , a cleaning unit  10  is arranged in the vicinity of the transfer belt  7  between the guide roller  11  and driven roller  6   a  to clean the transfer belt  7  after completion of an image forming operation. Further, the control unit  21  is connected to an output terminal (not shown) of the detection sensor unit  12 . A control calculation unit  13  is also connected to the detection sensor unit  12  to calculate detection signals detected by the detection sensor unit  12  and to output an adjustment signal to control an image forming operation to be adjusted. A general control unit  14  is connected to the control calculation unit  13  to generally control the image forming operation. A display  22  is connected to the general control unit  14  to display various information. 
   An image formation control signal F 2  is input to the image-forming unit  20  from the general control unit  14 . Further, the control calculation unit  13  includes a replacement number setting device, which sets a number of seam mark detection signals output from the seam mark detection sensor  16  to determine a replacement time for a new transfer belt  7 . A replacement notification-selecting device is also provided to selectively determine if an advance notice of replacement is to be given when a prescribed number of the seam marks is detected, and accordingly, that of the detection signals is counted. 
   An exemplary operation of the above-mentioned system is now described. The image-forming unit  20  executes an image forming operation in accordance with an image formation control signal F 2  input from the general control unit  14  to the image-forming unit  20 . Specifically, the pair of driven rollers  6   a  and  6   b  rotates the transfer belt  7  at a prescribed surface speed in a direction shown by an arrow. When the PC drums  3 M,  3 C,  3 Y, and  3 BK are rotated clockwise at a same surface speed as that of the transfer belt  7 , the writing unit  1  initially extracts and obtains M image data from the image data F 3 . An optical unit serving as the writing unit  1  formed from a laser, a polygon mirror, f-theta lens, and a reflection mirror writes an image in accordance with the M image data, and thereby a magenta latent image (herein after referred to as an M-latent image) is formed on the PC drum  3 M. When the M-latent image passes through the developing unit  2 M while the PC drum  3 M is rotated, the M-latent image formed on the PC drum  3 M is developed by the developing unit  2 M with M toner, and thereby a M-visible image is formed thereon. Further, when the M visible image then passes through a transfer roller  2 M while the PC drum  3 M rotates, the M-visible image is transferred to the transfer belt  7  under influence of a bias voltage impressed onto the transfer roller  5 M. 
   In accordance with the C-image data extracted and obtained from the image data F 3 , the optical unit  1  forms a cyan latent image (herein after referred to as a C-latent image) on the PC drum  3 C with a delay of a prescribed time period from the optical writing for the M-latent image on the PC drum  3 M. Subsequently, the C-latent image formed on the PC drum  3 C is developed by the developing unit  2 C with the C-toner; thereby a C-visible image is formed on the PC drum  3 C. In synchronism with the leading end of the C-visible image arriving at a position of the transfer roller  5 C, the leading end of the M-visible image on the transfer belt  7  arrives at the transfer position. Then, the C-visible image on the PC drum  3 C is sequentially transferred by the transfer roller  5 C to overly on the M-visible image on the transfer belt  7 , and thereby the M and C-visible images are sequentially formed on the transfer belt  7 . 
   Similarly, the optical unit  1  forms a yellow latent image (herein after referred to as a Y-latent image) on the PC drum  3 Y with a delay of a prescribed time. The Y-latent image is then developed by the developing device  2 Y with Y toner. The Y visual image is then transferred by the transfer roller  5 Y to overly the M and C, visual images conveyed to a transfer position of the transfer roller  5 Y. Thereby, the M, C, and Y visual images are sequentially formed and superposed on the transfer belt  7 . Then, the optical unit forms a black latent image as a BK-image (herein after referred to as a BK-latent image) on the PC drum  3 BK with a delay of a prescribed time period. The BK-latent image is then developed by the developing device  2 BK with BK toner. The BK visual image is then transferred by the transfer roller  5 BK to overly the M, C, and BK visual images conveyed to a position of the transfer roller  5 BK. Thereby, the M, C, Y, and BK visual images are sequentially formed and superposed on the transfer belt  7 . 
   Thus, a full-color image of the M, C, Y, and BK visual images is formed on the transfer belt  7  in accordance with the image data F 3 . The full-color image is then transferred at once to a transfer sheet (not shown) in the vicinity of the guiding roller  11  from the transfer belt  7 . The full-color image then receives a fixing process in accordance with the image data, and thereby the full-color image forming process is completed. 
   Beside the full-color image forming process, a plurality of full-color matching patterns  18   a  and  18   b  each having M, C, Y, and BK visual images for color offset adjustment use are periodically or optionally formed on the PC member in accordance with prescribed instructions. The full-color matching patterns  18   a  and  18   b  are then transferred to both end sides of the transfer belt  7 . A seam mark  17  is unavoidably formed at a seam of the transfer belt  7  to be detected by the seam detection sensor  16 . 
   As illustrated in  FIG. 2 , the pattern detection sensors  15   a  and  15   b  are separately arranged from each other in the vicinity of the transfer belt  7  on the arrangement line D drawn perpendicular to the conveyance direction of the transfer belt  7 . Specifically, the pattern detection sensors  15   a  and  15   b  are positioned downstream of the transfer positions for the full-color matching patterns  18   a  and  18   b  on the transfer belt  7 . These pattern detection sensors  15   a  and  15   b  detect the full-color matching patterns  18   a  and  18   b , respectively, as illustrated in FIG.  5 . The seam mark detection sensor  16  is also arranged on the arrangement line D opposing a region of the transfer belt  7  other than where the color-matching patterns  18   a ,  18   b  are formed. 
   Detection signals continuously output from the pattern detection sensors  15   a  and  15   b  are sampled at a prescribed frequency and input to the control calculation unit  13  and receive AID conversion into digital signals (i.e., voltage values) one after another. The digital signals are sequentially stored in a memory (not shown) provided in the control calculation unit  13 . 
   Specifically, the control calculation unit  13  may execute an A/D conversion process by converting the detection signal as an analog signal into a digital signal using, e.g., a conventional saw tooth state wave signal and reference clock, which reference clock determines a frequency of sampling. The control calculation unit  13  may then count a number of reference clocks (i.e., sampling clocks) until the detection signal arrives at the reference signal level as illustrated in  FIG. 5  as a first count value. The reference signal level is set in proportion to a normal density of a pattern, for example. A number of reference clocks is subsequently calculated by the control calculation unit  13  after the detection signal arrives and decreases from the reference signal level until the detection signal arrives again at the reference signal level as a second count value. The control calculation unit  13  may add half a difference between the first and second count values to the first count value to obtain a center of the first and second count values to determine a central position within a mark. The control calculation unit  13  may then store the thus counted values in the memory as a center positional information of the detected mark in the pattern one after another. 
   The seam mark detection signal output from the seam mark detection sensor  16  also receives similar A/D conversion, clock number counting, and positional information calculation, and storage as performed for the pattern detection signals from the control calculation unit  13 . 
   Then, the control calculation unit  13  may generate a series of count values Na1 to Nan in correspondence with the Bk, Y, C, and M pattern mark positions detected by the pattern detection sensor  15   a . The control calculation unit  13  may also generate a count value Nc in correspondence with the seam mark position detected by the seam mark detection sensor  16 . 
   Then, the below described calculation is performed wherein legend “A” represents a prescribed approximation judgment value:
 
−A&lt;Nax−Nc&lt;A ( x= 1·2  . . . n )  (1)
 
   Similarly, a series of count values Nb 1  to Nbn are generated in correspondence with the Bk, Y, C, and M pattern mark positions detected by the pattern detection sensor  15   b , and the below described calculation is similarly performed:
 
−A&lt;Nbx−Nc&lt;A ( x= 1·2  . . . n )  (2)
 
   Then, where Nax and Nbx simultaneously meet these formulas (1) and (2) are determined and deleted from the memory by regarding that the seam mark is improperly detected by the pattern detection sensors  15   a  and  15   b  as a part of the pattern mark as illustrated in FIG.  6 . Specifically, these approximate control values are highly provably obtained from the seam  17  making a right angle with the traveling direction of the transfer belt  7 . As a result, only count values corresponding to the actually formed patterns  18   a ,  18   b  can be stored in the memory while excluding the count value corresponding to the seam mark  17  detected by the pattern detection sensors  15   a  and  15   b.    
   Then, the control calculation unit  13  calculates an adjustment signal F 1  adjusting and controlling the image forming apparatus to operate in accordance with the count values corresponding to full-color matching patterns while excluding erroneous detection signals. The adjustment signal F 1  is then output from the control calculation unit  13  to the general control unit  14 . The general control unit  14  generates an image formation control signal F 2  controlling the image-forming unit  20  to form an image in accordance with the adjustment signal F 1 . The image formation control signal F 2  is input to the image forming unit  20 . The image-forming unit  20  performs an image-forming operation in accordance with the image formation control signal F 2 . 
   Thus, the image forming unit  20  precisely adjusts an amount of toner supplied to developing units  2 M,  2 C,  2 Y, and  2 BK, bias voltages impressed to the transfer rollers  5 M,  5 C,  5 Y, and  5 BK, color offset, or the like, in accordance with the detection signals of the full-color matching patterns. As a result, a high quality image is always formed in accordance with the image data F 3 . 
   An operation of an advance notice mode notifying the necessity of replacement of a currently used transfer belt is now described with reference to FIG.  4 . As shown in  FIG. 4 , the count value Nc corresponding to the seam mark detection signals generated by the seam mark detection sensor  16  is stored in the memory, as mentioned earlier, in step S 1 . If it is determined that the transfer belt  7  includes a seam  17 , the process goes to step S 2 . Then, it is determined if the count value Nc exceeds a prescribed setting value. If the prescribed setting value is determined as positive, YES in step S 2 , the process goes to step S 3 . It is then determined if the advance notice mode is set. If the determination is determined as YES in step S 3 , the process goes to step S 4 . Messages indicating the need to replace the current transfer belt  7  are then displayed on a display  22  by the general control unit  14  in response to an instruction from the control calculation unit  13 . 
   Thus, when a user selectively sets the advance notice mode to the control calculation unit  13 , a usage life of the transfer belt  7  is checked in accordance with a number of detections of the seam mark  17  and the replacement, i.e. the need to replace the current transfer belt  7 , status is displayed at a prescribed time as mentioned above. As a result, a high quality image is continuously formed while appropriately replacing a used transfer belt  7  with a new one in accordance with an operational condition of the image forming apparatus. 
   In contrast, if the user does not select the advance notice mode, the transfer belt  7  is periodically replaced at a prescribed interval. 
   Mechanisms and processes set forth in the present invention may be implemented using one or more conventional general-purpose microprocessors and/or signal processors programmed according to the teachings in the present specification as will be appreciated by those skilled in the relevant arts. Appropriate software coding can readily be prepared by skilled programmers based on the teachings of the present disclosure, as will also be apparent to those skilled in the relevant arts. However, as will be readily apparent to those skilled in the art, the present invention also may be implemented by the preparation of application-specific integrated circuits by interconnecting an appropriate network of conventional component circuits or by a combination thereof with one or more conventional general purpose microprocessors and/or signal processors programmed accordingly. The present invention thus also includes a computer-based product which may be hosted on a storage medium and include, but is not limited to, any type of disk including floppy disks, optical disks, CD-ROMs, magnet-optical disks, ROMs, RAMs, EPROMs, EEPROMs, flash memory, magnetic or optical cards, or any type of media suitable for storing electronic instructions. 
   Numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein.

Technology Category: g