JP4232324B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a so-called tandem type color image forming apparatus.
[0002]
[Prior art]
Conventionally, for example, Japanese Patent Application Laid-Open No. 7-28294 discloses a so-called tandem type color image forming apparatus in which a plurality of image forming units containing different color toners are arranged side by side along an intermediate transfer belt. .
[0003]
In this type of image forming apparatus, each image forming unit forms an image of a different color on the intermediate transfer belt, and the overlapped image is transferred onto a sheet. When the paper passes through the fixing unit, the image is heated and fixed on the paper and then discharged onto a paper discharge tray.
[0004]
[Problems to be solved by the invention]
In the conventional image forming apparatus described above, the supply of paper on which the image is to be transferred is delayed due to slip or the like with respect to the image formed on the intermediate transfer belt by each image forming unit. It may happen that the paper is not in time for transfer. In such a case, the apparatus is forcibly stopped so that the user removes the paper being fed by hand, and the image already formed on the intermediate transfer belt is scraped off with a cleaner. It was.
[0005]
However, in this method, the productivity is greatly reduced due to the stoppage of the apparatus, and all the toner constituting the scraped image becomes waste toner, so that the waste of toner is increased, and the paper in the middle of feeding is also recycled. It will be useless if it is not used.
[0006]
Accordingly, an object of the present invention is to provide an image forming apparatus capable of continuing an image forming operation without stopping the apparatus even when paper feeding is delayed with respect to an image on an intermediate transfer belt.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, an image forming apparatus of the present invention includes:
A rotatable intermediate transfer member;
A first image forming unit and a second image forming unit which are arranged along the intermediate transfer body and respectively form images of different colors on the intermediate transfer body;
Transfer means for transferring an image formed on the intermediate transfer member to a sheet;
A paper feeding means for feeding the paper to an area where an image is transferred by the transfer means;
Paper detection means for detecting the paper in the vicinity of the paper supply means;
Control means for controlling to start the image forming operation of the second image forming means according to the detection result of the paper detecting means when a monochrome image is formed only by the second image forming means;
It is equipped with.
[0008]
In the image forming apparatus according to the aspect of the invention, the second image forming unit and the paper feeding unit with respect to the transfer unit start feeding the paper toward the transfer area by the paper feeding unit. Even when the monochrome image forming operation of the second image forming unit is started, it is preferable that the monochrome image and the paper arrive at the transfer area in such a positional relationship that the arrival times thereof match each other.
[0009]
The image forming apparatus of the present invention further includes an image position detecting unit that detects an image position on the intermediate transfer member, and the control unit uses the first and second image forming units to form a color image. when forming a can Gyoshi control the feeding means in accordance with the image position detected by the image position detecting device, the sheet feeding of the sheet is delayed at the time of color image formation with respect to the color image on the intermediate transfer body when the to the feeding means so that the sheet takes the color image and the synchronization is fed to the transfer area control after said intermediate transfer member is idled by at least about one revolution.
[0011]
【The invention's effect】
In the image forming apparatus of the present invention, when a monochrome image is formed only by the second image forming unit, the image forming operation of the second image forming unit is controlled to start according to the detection result of the sheet detecting unit. Therefore, even when the paper arrives at the paper feeding means due to slip or the like, the monochrome image forming operation by the second image forming means after the paper is detected by the paper detecting means arranged in the vicinity of the paper feeding means Is started, the sheet can be fed to the transfer area by the sheet feeding means in synchronization with the monochrome image conveyed to the transfer area by the intermediate transfer member. As a result, even when the supply of paper to the paper feeding means is delayed, the image forming operation can be continued without forcibly stopping the apparatus, so that it is possible to prevent a decrease in productivity and waste of image forming materials and paper. It can be omitted.
[0012]
In the case where a color image is formed by the first and second image forming means, the image forming apparatus of the present invention is configured to control the paper feeding means in accordance with the image position detected by the image position detecting means. In the case where the paper does not reach the paper feeding means due to slip or the like, and the paper cannot be fed in time for transferring the color image in the transfer area as it is, for example, the intermediate transfer in which the color image is formed. If the sheet feeding means is controlled so that the sheet is fed to the transfer area in synchronization with the color image after the body is idled for at least about one turn, the sheet is fed to transfer the color image in the transfer area. Can avoid the situation that is not in time. As a result, even when the supply of paper to the paper feeding means is delayed, the image forming operation can be continued without forcibly stopping the apparatus, so that it is possible to prevent a decrease in productivity and waste of image forming materials and paper. It can be omitted.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an overall configuration diagram of a tandem digital color printer (hereinafter simply referred to as “printer”) 10 according to an embodiment of the present invention.
[0014]
The printer 10 includes an intermediate transfer belt (intermediate transfer member) 12 at substantially the center of the inside thereof. The intermediate transfer belt 12 is supported on the outer peripheral portions of the three rollers 14, 16, and 18 and is driven to rotate in the direction of arrow A.
[0015]
Below the lower horizontal portion of the intermediate transfer belt 12, four image forming units 20Y, 20M, 20C, and 20K corresponding to yellow (Y), magenta (M), cyan (C), and black (K) colors, respectively. Are arranged side by side along the intermediate transfer belt 12. The image forming unit 20Y, 20M or 20C corresponds to the first image forming means, and the image forming unit 20K corresponds to the second image forming means.
[0016]
Each of the image forming units 20Y, 20M, 20C, and 20K has a photosensitive drum 22Y, 22M, 22C, and 22K, respectively. Around each of the photosensitive drums 22Y, 22M, 22C, and 22K, chargers 24Y, 24M, 24C, and 24K that uniformly charge the surfaces of the photosensitive drums 22Y, 22M, 22C, and 22K in order along the rotation direction; The print head portions 26Y, 26M, 26C, and 26K that form an electrostatic latent image by exposing the surface of the uniformly charged photosensitive drum according to each color image data, and the electrostatic latent image formed on the surface of the photosensitive drum Is developed on the surface of the photosensitive drum, facing the photosensitive drums 22Y, 22M, 22C, and 22K with the intermediate transfer belt 12 sandwiched between the developing devices 28Y, 28M, 28C, and 28K. Primary transfer rollers 30Y, 30M, 30C, and 30K for electrostatically attracting the toner image to the intermediate transfer belt 12 and performing primary transfer, and primary transfer Cleaner 32Y for cleaning and collecting toner remaining on the photosensitive drum surface, 32M, 32C, and a 32K are arranged respectively. The print head portions 26Y, 26M, 26C, and 26K are composed of a large number of LEDs arranged in the main scanning direction parallel to the axial direction of the photosensitive drum.
[0017]
A secondary transfer roller (transfer means) 34 is pressed against the portion of the intermediate transfer belt 12 supported by the roller 18. A nip portion between the secondary transfer roller 34 and the intermediate transfer belt is a transfer region 36. The secondary transfer roller 34 can be retracted to a position where it is not in contact with the intermediate transfer belt 12 by a retracting mechanism (not shown). A high transfer voltage is applied to the secondary transfer roller 34. The toner image formed on the intermediate transfer belt 12 by the transfer voltage is electrostatically attracted to the sheet conveyed to the transfer area 36 and is secondarily transferred as described later.
[0018]
A cleaner 38 is pressed against the portion of the intermediate transfer belt 12 supported by the roller 16. The cleaner 38 is for scraping and collecting the toner remaining on the intermediate transfer belt 12 after the secondary transfer into the waste toner box 40. Similarly to the secondary transfer roller 34, the cleaner 38 can also be retracted to a position where it is not in contact with the intermediate transfer belt 12 by a retracting mechanism (not shown).
[0019]
A paper feed cassette 42 is detachably disposed at the bottom of the printer 10. The sheets S stacked and accommodated in the sheet feeding cassette 42 are sent out one by one from the uppermost one to the conveying path 46 by the rotation of the sheet feeding roller 44.
[0020]
The conveyance path 46 extends from the paper feed cassette 42 to the paper discharge tray 11 through the nip portion of the timing roller pair (paper feed means) 48, the secondary transfer region 36, and the fixing unit 50. The timing roller pair 48 is for feeding the paper S sent from the paper feed cassette 42 to the transfer area 36 in synchronization with the image on the intermediate transfer belt 12.
[0021]
In the printer 10, the black image forming unit 20 </ b> K and the timing roller pair 48 with respect to the secondary transfer roller 34 start feeding the sheet S toward the transfer region 36 by the timing roller pair 48, and then the image forming unit 20 </ b> K. Even when the monochrome image forming operation is started, the positional relationship is such that the arrival time of the monochrome image and the paper S to the transfer area 36 matches. Specifically, as shown in FIG. 2, the distance e along the outer periphery of the photosensitive drum 22K and the intermediate transfer belt 12 from the exposure position 23 on the photosensitive drum 22K to the transfer region 36 by the print head unit 26K is as follows. The image forming unit 20K and the timing roller pair 48 are arranged in a positional relationship so as to be shorter than the distance b along the conveyance path 46 from the nip portion of the timing roller pair 48 to the transfer region 36.
[0022]
Although not shown, the outer periphery of the photosensitive drum 22Y from the exposure position on the photosensitive drum 22Y to the transfer region 36 by the print head unit 26Y of the image forming unit 20Y serving as the first color and along the intermediate transfer belt 12. The distance f is set longer than the distance b. If the distance f is also shorter than the distance b, the image forming operation in the image forming unit 20Y may be started after the feeding by the timing roller pair 48 is started. In order to achieve this, it is necessary to set the distance b to be considerably large, that is, the timing roller pair 48 needs to be arranged at a position far away from the secondary transfer roller 34. However, with this arrangement, the printer becomes large. Become. Therefore, by arranging the image forming unit 20Y and the timing roller pair 48 with respect to the secondary transfer roller 34 so that the relationship between the distance f and the distance b satisfies f> b as in the present embodiment, There is an effect that the size can be reduced.
[0023]
Referring again to FIG. 1, a timing sensor (paper detection means) 52 is disposed in the vicinity of the timing roller pair 48. The timing sensor 52 is for detecting that the leading edge of the paper S sent from the paper feed cassette 42 to the conveyance path 46 has reached the nip portion of the timing roller pair 48. When the leading edge of the paper S is detected by the paper feed sensor 52, the timing roller pair 48 temporarily stops its rotation, and then feeds the paper S to the transfer area 36 in synchronization with the toner image on the intermediate transfer belt 12. It comes to paper.
[0024]
In addition, a paper thickness sensor 54 is disposed to face one roller 48a of the timing roller pair 48. The paper thickness sensor 54 detects the amount of movement of the roller 48a when the leading edge of the paper is nipped by the timing roller pair 48, whereby the paper is plain paper, thick paper or OHP sheet. Can be determined.
[0025]
The fixing unit 50 is supported by a pair of rollers 56 and 58 and is driven to rotate in the direction of arrow B, and a fixing roller 62 that is pressed against the roller 56 via the fixing belt 60 and is driven to rotate in the direction of the arrow. The fixing region 64 is a nip portion between the fixing belt 60 and the fixing roller 62 through which the sheet on which the toner image is secondarily transferred passes. The fixing belt 60 is heated to a predetermined temperature by a heater (not shown).
[0026]
The printer also includes a control unit (control means) 70 as shown in FIG. The controller 70 includes an exposure / paper feed timer 72, a paper feed / exposure timer 74, and a paper feed slip watch timer 76 therein. The exposure / paper feed timer 72 is a timer that counts the time from the start of exposure in the image forming unit 20Y to the start of paper feed by the paper feed roller 44. The paper feed / exposure timer 74 is a timer that counts the time from when the timing roller pair 48 is turned on to when the image forming unit 20K starts exposure. The paper feed slip watch timer 76 sets the allowable slip time in the time from the start of driving of the paper feed roller 44 when the paper S is sent out from the paper feed cassette 42 without slipping until the timing sensor 52 detects the leading edge of the paper. It is a timer that counts the added time.
[0027]
Signals are input to the control unit 70 from the timing sensor 52, the paper thickness sensor 54, and the like. The control unit 70 outputs signals to a paper feed roller driving motor, an LED drive circuit, a timing roller pair driving motor, a secondary transfer roller retracting mechanism, a cleaner retracting mechanism, and the like. Further, the control unit 70 sequentially determines the toner image position on the intermediate transfer belt 12 that moves at a constant system speed based on the signal output to the LED drive circuit, that is, the elapsed time from the light emission driving of the print head units 26Y-26K. It also has a function to detect.
[0028]
Next, the operation of the printer 10 having the above configuration will be described.
When an image signal is input from an external device (for example, a personal computer) to an image signal processing unit (not shown) of the printer 10, the image signal processing unit digitally converts the image signal into yellow, cyan, magenta, and black. A signal is generated and transmitted to the LED drive circuit for the print head. This drive circuit performs exposure by causing the print head portions 26Y, 26M, 26C, and 26K of the image forming units 20Y, 20M, 20C, and 20K to emit light based on the input digital signals. This exposure is performed with a time difference in the order of the print head units 26Y, 26M, 26C, and 26K. Thereby, electrostatic latent images for the respective colors are formed on the surfaces of the respective photosensitive drums 22Y, 22M, 22C, and 22K.
[0029]
The electrostatic latent images formed on the photosensitive drums 22Y, 22M, 22C, and 22K are developed by the developing devices 28Y, 28M, 28C, and 28K, respectively, and become toner images of the respective colors. Then, the toner images of the respective colors are primarily transferred in a superimposed manner on the intermediate transfer belt 12 that moves in the direction of arrow A by the action of the primary transfer rollers 30Y, 30M, 30C, and 30K.
[0030]
The superimposed toner image formed on the intermediate transfer belt 12 in this way reaches the transfer area 36 as the intermediate transfer belt 12 moves. In the transfer area 36, the superimposed toner images are collectively delivered to the sheet S fed from the sheet feeding cassette 42 to the conveyance path 46 and fed by the timing roller pair 48 by the action of the secondary transfer roller 34. Secondary transferred. Note that the toner remaining on the intermediate transfer belt 12 after the secondary transfer is collected by the cleaner 38.
[0031]
The sheet S on which the toner image is secondarily transferred is sent to the fixing unit 50 through the conveyance path 46, where the toner image is heated and fixed on the sheet S by passing through the fixing region 64. Then, the paper S is discharged to the paper discharge tray 11.
[0032]
The color image forming operation is performed as described above. In the case of a monochrome image, only the image forming unit 20K operates based on the input monochrome image data, and a black toner image is formed on the intermediate transfer belt 12. Thereafter, similarly, the black toner image is secondarily transferred to the paper S in the transfer region 36, heated and fixed by the fixing unit 50, and the paper S is discharged to the paper discharge tray 11.
[0033]
Next, processing in the control unit 70 will be described with reference to the flowchart of FIG. Based on the image data input to the printer 10, the control unit 70 determines whether the image instructed to be printed is a color image or a monochrome image (step S1). If the image is a color image, exposure in each of the image forming units 20Y-20K is sequentially started (step S2), and an exposure / paper feed timer 72 is set (step S3). Then, waiting for the exposure / paper feed timer 72 to increase (step S4), the paper feed roller 44 starts paper feed and sets the paper feed slip watch timer 76 (step S5).
[0034]
Next, it is determined whether or not the timing sensor 52 has been turned on (that is, whether or not the leading edge of the sheet has been detected) (step S6). If not yet turned on, it is determined whether or not the paper feed slip watch timer 76 has been raised (step S9). . If the paper feed slip watch timer 76 is not up, it is determined again whether the timing sensor 52 is turned on (step S6). As described above, when the timing sensor 52 is turned on before the paper feed slip watch timer 76 is increased while the processes in steps S6 and S9 are repeated, it is determined that the paper S has reached the timing roller pair 48 within an allowable time without delay. Is done. As shown in FIG. 2, the distance c from the leading edge corresponding position 13 to the transfer area 36 that is separated from the leading edge of the toner image I by the distance d corresponding to the blank portion on the intermediate transfer belt 12 is the nip of the timing roller pair 48. After waiting for the distance b to be equal to the distance b between the transfer area 36 and the transfer area 36 (step S7), the driving of the timing roller pair 48 is started (step S8). Since the moving speed of the intermediate transfer belt 12 and the feeding speed of the timing roller pair 48 are the same system speed, the sheet S is fed to the transfer area 36 in synchronization with the toner image on the intermediate transfer belt 12 and the toner image is Secondary transfer is performed from the intermediate transfer belt 12 to the paper S.
[0035]
On the other hand, if the paper feed slip watch timer 76 is activated before the timing sensor 52 is turned on in the processes of steps S6 and S9, the timing roller due to slip or the like is caused with respect to the toner image position on the intermediate transfer belt 12. It is determined that the arrival of the sheet S to the pair 48 is delayed more than the allowable time. In this case, the secondary transfer roller 34 and the cleaner 38 are retracted from the intermediate transfer belt 12, and the intermediate transfer belt 12 is idled for at least about one rotation without performing the secondary transfer of the toner image (step S10). . Then, when the timing sensor 52 is turned on by the paper S that has arrived late with respect to the timing roller pair 48 (step S11), the timing roller pair 48 is driven in synchronization with the toner image on the intermediate transfer belt 12 (step S7). Start (step S8). At this time, the secondary transfer roller 34 and the cleaner 38 are returned to their original positions. As a result, the toner image on the intermediate transfer belt 12 is secondarily transferred to a predetermined position on the paper S in the transfer region 36.
[0036]
On the other hand, when it is determined in step S1 that the image is a monochrome image, the paper supply roller 44 is driven to start paper supply (step S12). Subsequently, waiting for the timing sensor 52 to be turned on (that is, the leading edge of the sheet reaches the nip portion of the timing roller pair 48) (step S13), the timing roller pair 48 is driven toward the transfer region 36 of the sheet S. Is started (step S14), and the paper feed / exposure timer 74 is set (step S15). Then, after the paper feed / exposure timer 74 is up (step S16), exposure in the image forming unit 20K, that is, an image forming operation is started (step S17). As a result, the black image formed on the intermediate transfer belt 12 by the image forming unit 20K is secondarily transferred to a predetermined position on the paper S in the transfer region 36.
[0037]
As described above, in the printer 10 according to the present embodiment, when a monochrome image is formed, the timing sensor 52 detects the sheet S and then the image forming unit 20K starts the image forming operation. Even if the paper S arrives late at the timing roller pair 48 due to the cause, the situation where the paper S is not in time for the secondary transfer of the monochrome image in the transfer region 36 does not occur. As a result, even when the supply of the paper S to the timing roller pair 48 is delayed, the image forming operation can be continued without forcibly stopping the printer, so that it is possible to prevent a decrease in productivity and waste of toner and paper. It can be omitted. This effect is very large in consideration of the fact that in color printers, monochrome images such as text are generally overwhelmingly larger than color image prints.
[0038]
Further, when forming a color image, the sheet S is delayed in reaching the timing roller pair 48 due to slipping or the like, so that the sheet S cannot be fed in time for transferring the color image in the transfer region 36 as it is. In this case, after the intermediate transfer belt 12 is idly rotated with the secondary transfer roller 34 and the cleaner 38 retracted, the color image is transferred to a predetermined position on the paper S, so that the image is not forcedly stopped. The forming operation can be continued. Accordingly, it is possible to prevent a significant reduction in printer productivity and to eliminate waste of toner and paper.
[0039]
In the present embodiment, the intermediate transfer member is a belt, but it may have another shape such as a drum.
[0040]
In the above description, the intermediate transfer type tandem printer has been described. Next, the direct transfer type tandem printer will be described.
The direct transfer tandem printer includes a paper transport belt having the same form as the intermediate transfer belt 12. The timing roller pair 48 is provided on the side of the yellow image forming unit 20Y that is the first color. The sheet S fed by the timing roller pair 48 is conveyed to the position facing each image forming unit 20Y-20K while being attracted to the sheet conveying belt, and is formed by each image forming unit 20Y-20K during the conveyance. Each color toner image is directly transferred to the paper S.
[0041]
In such a direct transfer type printer, when the distance between the exposure position of the yellow image forming unit 20Y on the photosensitive drum 22Y and the transfer position is larger than the distance from the timing roller pair 48 to the yellow image transfer position, When forming a color image, the feeding operation by the timing roller pair 48 is started after a predetermined time has elapsed after the start of the first color yellow image forming operation, that is, the exposure by the print head unit 26Y of the image forming unit 20Y. Control by the controller.
[0042]
On the other hand, when forming a monochrome image, when the sheet S conveyed by the sheet conveying belt reaches a predetermined position, the image forming operation by the black image forming unit 20K, that is, the exposure by the print head unit 26K is started. To control. As described above, when the monochrome image is formed, the image forming operation in the image forming unit 20K can be started with the position of the sheet S as a reference. Therefore, even if the arrival of the sheet S to the timing roller pair 48 is delayed due to a slip or the like, The image forming operation can be continued without stopping.
[0043]
In the above description, the printer is taken as an example. However, the present invention can also be applied to other image forming apparatuses such as a copying machine, a facsimile, and a combination machine of these and a printer.
[0044]
The present invention is not limited to the electrophotographic image forming apparatus as described above, but can be applied to other image forming apparatuses such as an ink jet system. In the ink jet type intermediate transfer image forming apparatus, the primary transfer position of the image by each of the image forming units 20Y-20K corresponds to the image writing position by each color ink jet head.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of a printer.
FIG. 2 is a diagram illustrating a positional relationship between a black image forming unit and a timing roller pair with respect to a transfer region.
FIG. 3 is a block diagram of a control unit.
FIG. 4 is a flowchart showing processing in a control unit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Printer, 12 ... Intermediate transfer belt (intermediate transfer body), 20Y, 20M, 20C ... Image forming unit (first image forming means), 20K ... Image forming unit (second image forming means), 34 ... Two Next transfer roller (transfer means), 48... Timing roller pair (paper feed means), 52... Timing sensor (paper detection means), 70... Control section (control means, image position detection means).

Claims (2)

A rotatable intermediate transfer member;
A first image forming unit and a second image forming unit which are arranged along the intermediate transfer body and respectively form images of different colors on the intermediate transfer body;
Transfer means for transferring an image formed on the intermediate transfer member to a sheet;
A paper feeding means for feeding the paper to an area where an image is transferred by the transfer means;
Paper detection means for detecting the paper in the vicinity of the paper supply means;
Image position detecting means for detecting an image position on the intermediate transfer member;
When said second forming a monochrome image only imaging means Gyoshi control so as to start an image forming operation of the second image forming means in accordance with a detection result of said sheet detecting means, the first When a color image is formed by the second image forming means, the paper feeding means is controlled according to the image position detected by the image position detecting means, and the color image on the intermediate transfer member is formed at the time of color image formation. When the sheet feeding is delayed with respect to the sheet, the intermediate transfer member is rotated at least about one turn and then fed to the transfer area in synchronization with the color image. An image forming apparatus comprising: a control unit that controls a paper unit .   The second image forming unit and the paper feeding unit with respect to the transfer unit start monochrome feeding in the second image forming unit after the paper feeding unit starts feeding paper toward the transfer area. The image forming apparatus according to claim 1, wherein even when an image forming operation is started, the image forming apparatus is disposed in such a positional relationship that the arrival times of the monochrome image and the paper to the transfer region are matched.

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