JP2009230003A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tandem type color image forming apparatus capable of adjusting an imaging condition between printed images during printing without lowering printing speed and without soiling the printed image by a residual toner of a reference toner pattern. <P>SOLUTION: The image forming apparatus includes: an image forming control part 31 for forming the printed images whose toner colors are different from each other on a plurality of photoreceptors 20c and also forming the reference toner pattern between the printed images; a reference density detection part 32 for detecting the density of the reference toner pattern; and an imaging condition adjusting part 33 for adjusting the imaging condition based on the detected density, and includes a transfer voltage control part 34 switching a control value of a transfer bias voltage applied to a transfer part 20e at least in a period in which each reference toner pattern formed on each photoreceptor 20c passes through the transfer part 20e to a second control value whose absolute value is smaller than that of a first control value applied to the transfer part 20e in order to transfer each printed image to a transfer belt 21. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention provides a plurality of photoconductor units that form images of different toner colors, and a transfer that forms a color image by transferring images formed on the photoconductor by each photoconductor unit at a predetermined transfer unit. The present invention relates to a tandem color image forming apparatus including a belt.

  In the tandem color image forming apparatus, a process is performed in which a print image is once transferred from a photosensitive member to a transfer belt and then transferred from the transfer belt to a recording sheet.

  In the tandem color image forming apparatus, a reference toner pattern is formed between print images, and image density is corrected by adjusting image forming conditions during printing.

For example, in Patent Document 1, a mark (reference toner pattern) for adjusting an image density or the like is formed in a range corresponding to a space between recording materials (between recording paper) of a transfer belt, that is, between printed images. An image forming apparatus that performs feedback control on the image density and the like by detecting the mark with a sensor arranged at a position opposite to the image is disclosed.
JP 2003-307902 A

  In the tandem color image forming apparatus as described above, since the reference toner pattern is formed between the print images being printed, not only the print image but also the reference toner pattern is transferred to the transfer belt.

  Since the print image transferred to the transfer belt is transferred from the transfer belt to the recording paper at the transfer portion, the residual toner on the transfer belt is reduced by the amount transferred. As a result, the residual toner is removed by a cleaning unit provided at the subsequent stage of the transfer unit.

  However, since the reference toner pattern transferred to the transfer belt is not transferred from the transfer belt to the recording paper at the transfer portion, the residual toner on the transfer belt is not reduced. As a result, the residual toner may not be sufficiently removed by the cleaning unit, and the residual toner may overlap with a print image formed thereafter, and the print image may be soiled.

  Therefore, when there is a reference toner pattern that could not be removed by the cleaning unit, it is necessary to make the reference toner pattern go around on the transfer belt and perform the residual toner removal process again in the cleaning unit. In the meantime, the print image cannot be transferred from the photoconductor to the transfer belt, resulting in a decrease in printing speed.

  In order to solve such a problem, among the tandem color image forming apparatuses, an apparatus configured to be able to measure the density of the reference toner pattern on the photoconductor does not transfer the measured reference toner pattern to the transfer belt. By controlling in this way, it is conceivable to prevent the transfer belt from being soiled and to prevent a decrease in printing speed. Such control is performed, for example, by not applying a transfer bias voltage when the reference toner pattern on the transfer belt reaches a position facing the transfer portion.

  However, since the reference toner pattern is formed between printed images, if the transfer bias is stopped only when the reference toner pattern reaches the position facing the transfer portion, the transfer bias is greatly changed during printing. As a result of fluctuations in the transfer bias, the driving torque of the stepping motor that operates the transfer belt fluctuates. As a result, the speed of the transfer belt becomes unstable, and color misregistration of the printed image may occur.

  In view of the above-mentioned conventional defects, the object of the present invention is to adjust image forming conditions between print images during printing without reducing the printing speed and without contaminating the print image with residual toner of the reference toner pattern. The object is to provide a tandem color image forming apparatus which can be performed.

  In order to achieve the above-mentioned object, a first characteristic configuration of a tandem color image forming apparatus according to the present invention is a plurality of images for forming images of different toner colors as described in claim 1 of the document of the claims. And a transfer belt for forming a color image by transferring an image formed on the photoconductor by each photoconductor unit at a predetermined transfer unit, and forming a print image on each photoconductor An image formation control unit that forms a reference toner pattern of a predetermined size between the print images, a reference density detection unit that detects the density of the reference toner pattern, and a density that is detected by the reference density detection unit. A tandem color image forming apparatus having an image forming condition adjusting unit for adjusting image conditions, wherein at least each reference toner pattern formed on each photoconductor The control value of the transfer bias voltage applied to the transfer unit during the period passing through the transfer unit is smaller in absolute value than the first control value applied to the transfer unit in order to transfer each print image to the transfer belt. The transfer voltage control unit for switching to the second control value is provided.

  According to the above configuration, the transfer bias control unit switches the control value of the transfer bias voltage to the second control value, so that the transfer force from the photoconductor to the transfer belt becomes weak, and the reference transferred to the transfer belt The amount of toner in the toner pattern decreases. As a result, it is possible to prevent the reference toner pattern from remaining on the transfer belt after cleaning for removing the residual toner.

  In the second characteristic configuration, as described in claim 2, in addition to the first characteristic configuration described above, the second control value is obtained when the transfer bias voltage is changed from the first control value. The speed fluctuation of the transfer belt occurring in the above is a control value that falls within a predetermined range.

  According to the above-described configuration, it is possible to prevent occurrence of color misregistration in a print image due to excessive speed fluctuation of the transfer belt caused by making the second control value too small.

  In the third feature configuration, as described in claim 3, in addition to the first or second feature configuration described above, the second control value is set to a different value for mono color printing and full color printing. There is in point.

  The tandem color image forming apparatus uses all the photoreceptors provided for each color (magenta (M), cyan (C), yellow (Y), and black (K)) in full-color printing.

  On the other hand, in monocolor printing, only the photoconductors for the colors to be used are used. Some tandem color image forming apparatuses have a configuration in which a transfer portion of a photosensitive member that is not used is retracted from the transfer belt and is not in contact with the transfer belt.

  That is, in the case of the tandem color image forming apparatus having such a configuration, the pressure from the transfer unit to the transfer belt is different between mono color printing and full color printing, and the second control value is different from mono color printing. Among full-color printing, there is a possibility that even if the value is appropriate for one printing, the value is inappropriate for the other printing.

  However, according to the above-described configuration, the second control value can be set to a value suitable for mono-color printing and full-color printing.

  According to the fourth feature configuration, in addition to any one of the first to third feature configurations described above, the image formation control unit assigns each reference toner pattern to each photoconductor. It is in the point which forms in a mutually different position along the axial center direction.

  When the reference toner patterns are formed at the same position, the reference toner patterns overlap when transferred to the transfer belt, that is, the toner density of the reference toner pattern on the transfer belt increases. As a result, it becomes more difficult to remove all the toner in the cleaning for removing the residual toner on the transfer belt compared to the case where the toner density is low.

  However, according to the above-described configuration, the respective reference toner patterns are formed at different positions. Therefore, the respective reference toner patterns do not overlap when transferred to the transfer belt. In other words, the toner density of the reference toner pattern on the transfer belt is reduced. Lower. As a result, it is easier to remove all the toner in the cleaning for removing the residual toner image as compared with the case where the toner density is high.

  As described above, according to the present invention, it is possible to adjust the image forming condition between print images during printing without reducing the printing speed and without contaminating the print image with residual toner of the reference toner pattern. It has become possible to provide a tandem color image forming apparatus capable of performing the above.

  Hereinafter, a tandem color image forming apparatus according to the present invention will be described.

  As shown in FIGS. 2 and 3, the tandem type color image forming apparatus is mounted on an operation unit 10 on which a display unit composed of a liquid crystal screen, a start key for starting a copying operation, and the like are arranged, and a document feeding table 11. An image reading unit 12 that sequentially feeds the placed originals, photoelectrically converts the original image to read as digital image data, and performs image processing such as gradation conversion, color adjustment, and magnification conversion on the digital image data; An image processing unit 13 that converts the output image data into magenta (M), cyan (C), yellow (Y), and black (K) components, and forms a print image as a toner image based on the output image data. An image output unit 2 that transfers the image to the recording paper, a fixing unit 15 that heats and fixes the print image output on the recording paper, a storage unit 14 that stores the recording paper fed to the image output unit 2, and a storage unit Part 14 A transport mechanism 16 that transports the fed recording paper, a paper discharge unit 17 that discharges the recording paper, a system control unit 3 that controls these functional blocks and executes processing as an image forming apparatus, and the like. It is prepared for.

  As shown in FIG. 4, the image output unit 2 has a plurality of photoreceptor units 20 that form images of toner colors different from each other, and an image formed on the photoreceptor 20c by each photoreceptor unit 20 with a predetermined transfer. A transfer belt 21 is provided that forms a color image by being transferred by the portion 20e.

  In addition, the image output unit 2 supports the transfer belt 21 and rotates at a predetermined rotation speed, and after the leading edge is corrected by the registration roller 26 that is fed from the storage unit 14, the transfer timing is set. A secondary transfer unit 22 that secondary-transfers the print image on the transfer belt 21 to the adjusted and fed recording paper, and a residual toner image on the transfer belt 21 after the print image is secondarily transferred to the recording paper A fur brush 24 or the like is provided as a cleaning unit for removing water.

  Four photoconductor units 20 are provided along the circumferential direction of the transfer belt 21, and each photoconductor unit 20 includes magenta (M), cyan (C), yellow (Y), and black (K) from the upstream side. It corresponds to each color.

  Each photoconductor unit 20 is configured identically for each color, and is driven based on the photoconductor 20c, a charging charger 20a for uniformly charging the surface of the photoconductor 20c, and output image data corresponding to the toner color of the unit. An exposure head 20b, a developing device 20d that develops an electrostatic latent image that is exposed by the exposure head 20b and formed on the photoconductor 20c, and forms a printed image; after the primary transfer to the transfer belt 21, the photoconductor A cleaning blade 20f that removes the toner remaining on 20c and a static elimination lamp 20g that neutralizes the surface of the photoreceptor 20c are provided.

  A transfer bias voltage is applied to the transfer unit 20e by a bias power source (not shown), and the transfer bias voltage is a voltage having a polarity opposite to the charging polarity of the toner. The transfer unit 20e transfers the print image as a toner image attached to the surface of the photoconductor 20c to the transfer belt 21 by an electric field generated by the transfer bias voltage. Note that the secondary transfer unit 22 has the same configuration as the transfer unit 20e.

  Further, the tandem color image forming apparatus is provided with a toner density sensor 25 facing the surface of the photoconductor 20c of each photoconductor unit 20.

  The toner density sensor 25 is composed of an infrared reflection type photosensor or the like, and serves as a reference toner pattern for image forming condition adjustment formed on the surface of the photoconductor 20c when an image forming condition adjusting operation described later is executed. The light is projected and a signal having a level based on the reflected light is output. The reference toner pattern will be described later.

  The system control unit 3 includes a CPU, a ROM that stores a control program executed by the CPU, a RAM that stores control data, an input port that receives signals from various sensors, and various driving devices such as a motor. And so forth, and an output port for outputting a control signal to the like.

  The system control unit 3 includes a plurality of control units for causing each unit of the tandem type color image forming apparatus to execute predetermined processing as the tandem type color image forming apparatus, and the function of each control unit is controlled by the CPU. This is accomplished by executing and driving the associated hardware.

  As shown in FIG. 1, the system control unit 3 according to the present invention forms a print image on each photoconductor 20c, and forms an image formation control unit 31 that forms a reference toner pattern of a predetermined size between the print images, and a reference toner. A reference density detection unit 32 that detects the density of the pattern, and an image creation condition adjustment unit 33 that adjusts the image creation condition based on the density detected by the reference density detection unit 32 are one of the above-described plurality of control units. As a part.

  The image formation control unit 31 controls the photosensitive unit 20 for each color described above to form a print image and a reference toner pattern for each color.

  Here, the reference toner pattern is obtained by the exposure head 20b and the developing device 20d on the basis of the test patch data expressed by a predetermined gradation pattern output from the image processing unit 13. It is composed of a plurality of toner images having a solid density or a predetermined halftone density formed on the surface 20c.

  The image formation control unit 31 forms the reference toner patterns at different positions along the axial center direction of the photoconductors.

  For example, as shown in FIG. 5A, the reference toner patterns TPM, TPC, TPY, TPK for each color are formed on the photoreceptor 20c for each color. 5A and 5B are views of the image output unit 2 as viewed from above.

  The reference toner patterns for the respective colors are formed at different positions in the vertical direction with respect to the moving direction of the transfer belt 21 indicated by the arrow in FIG. 5A so as not to overlap each other. Therefore, the toner density sensors 25 for the respective colors are also arranged at different positions in the direction perpendicular to the moving direction of the transfer belt 21.

  FIG. 5B shows a print image formed by the image formation control unit 31 and transferred to the transfer belt 21 and an image of a reference toner pattern. In this example, the reference toner pattern of each color is transferred at regular intervals in the direction perpendicular to the traveling direction of the transfer belt 21 between the print images.

  Note that the reference toner pattern may be one having a variable density between print images as shown in FIG. 6A in addition to the one shown in FIG. 5B. Further, the reference toner pattern is not limited to be provided between all print images, but once for several print images as shown in FIG. 6B (once every two times in FIG. 6C). ) May be formed.

  The reference density detection unit 32 obtains the density of the reference toner pattern of each color based on the level of the signal input from the toner density sensor 25 of each color to the image formation control unit 31.

  The image forming condition adjusting unit 33 is configured to adjust the image forming condition based on the density detected by the reference density detecting unit 32, that is, to adjust the image forming condition for each color of MCYK.

  The image forming condition adjusting process for one color of each of the MCYK colors will be described in detail. The image forming condition adjusting unit 33 sets the density (detected density) of the reference toner pattern detected by the reference density detecting unit 32 and a preset value. The detected density is maintained at the set density by comparing the set density corresponding to the reference toner pattern and adjusting the developing bias voltage of the developing device 20d based on the difference between the set density and the detected density. For example, the developing bias voltage is set high when the detected density is low, and is set low when the detected density is high.

  Such adjustment of the image forming conditions is executed each time the density of the reference toner pattern is detected by the reference density detection unit. That is, it is executed between print images every time. Then, the toner density is appropriately maintained by feedback control of the adjustment result of each image forming condition. Note that the adjustment of the image forming conditions may be performed between several printed images instead of every printed image.

  The tandem type color image forming apparatus transfers the control value of the transfer bias voltage applied to the transfer unit 20e during a period when at least each reference toner pattern formed on each photoconductor 20c passes through the transfer unit 20e, and transfers each print image to the transfer belt. A transfer voltage control unit 34 that switches to a second control value whose absolute value is smaller than the first control value applied to the transfer unit 20 e for transferring to the transfer unit 20 e is provided.

  The transfer voltage controller 34 will be described in detail with reference to FIG. The middle part of FIG. 7 shows the transfer output control of the print image and the reference toner pattern of the conventional tandem color image forming apparatus, and the lower part of FIG. 7 shows the printing of the tandem color image forming apparatus of the present invention. The transfer output control of an image and a reference toner pattern is shown.

  That is, FIG. 7 shows a case where the print voltage and the reference toner pattern formed on the surface of the photoconductor 20c are transferred by the transfer voltage control unit 34 when the print image and the reference toner pattern are at positions that pass through the transfer unit 20e, that is, at positions opposite to the transfer unit 20e. The control value of the transfer bias voltage applied to the portion 20e is shown.

  In the case of the conventional configuration (middle stage in FIG. 7), the transfer bias voltage is also applied to the reference toner pattern between the print images, that is, whether the print image is at the position opposite to the transfer portion 20e. Regardless, as a result of the transfer bias voltage corresponding to the first control value being applied to the transfer portion 20e, the reference toner pattern is transferred to the transfer belt 21.

  On the other hand, in the case of the configuration of the present invention (lower stage in FIG. 7), when the reference toner pattern is at the position facing the transfer portion 20e, the transfer voltage control unit 34 changes the transfer bias voltage control value from the first control value to the second control value. When the transfer bias voltage corresponding to the second control value is applied to the transfer portion 20e, the reference toner pattern is transferred to the transfer belt 21 at a lower density than in the conventional configuration.

  Here, the second control value is a control value in which the speed fluctuation of the transfer belt 21 that occurs when the transfer bias voltage is changed from the first control value falls within a predetermined range.

  The predetermined range is a range of fluctuation speed that is within an allowable range in terms of performance of the tandem color image forming apparatus even if color misregistration of the print image does not occur or color misregistration of the print image occurs. is there.

  The second control value for keeping the speed fluctuation within a predetermined range is preferably a value corresponding to 10% to 20% of the first control value, for example.

  However, the second control value may vary depending on the type of the tandem color image forming apparatus (for example, the type of the mounted photoconductor 20c or the transfer unit 20e) and the like. The value is not limited to 20%. In this case, the predetermined range is statistically derived by detecting the degree of color misregistration of the print image with respect to various values of the transfer bias voltage for each type of tandem color image forming apparatus.

  The tandem color image forming apparatus may have a configuration in which the second control value is set to a predetermined value, or a configuration in which the second control value is set by operating the operation unit 10 by the operator. It may be.

  In FIG. 7, the switching timing from the first control value to the second control value and the switching timing from the second control value to the first control value are the boundary between the print image area and the non-print image area, In other words, the timing is t1 and t2, but the switching timing is not limited to the boundary.

  For example, as indicated by a one-dot chain line in FIG. 7, t3 after a predetermined time has elapsed from the boundary where the print image area is switched to the non-print image area, and t4 before the predetermined time before the boundary where the non-print image area is switched to the print image area. May be configured with the switching timing.

  In FIG. 7, the transfer bias voltage has a positive value, but the transfer bias voltage may have a negative value. In this case, the second control value is a value larger than the first control value, that is, a value having a small absolute value.

  The tandem color image forming apparatus according to the present invention aims to weaken the transfer force at the second control value by making the transfer bias voltage of the second control value smaller than the first control value. The second control value is the same as the first control value in terms of positive and negative.

  Hereinafter, switching control of the control value of the transfer bias voltage by the tandem color image forming apparatus of the present invention will be described based on the flowchart shown in FIG.

  When the tandem color image forming apparatus starts the printing process, a print image and a reference toner pattern are formed on the photoconductor 20c by the pixel formation control unit 31 (S1).

  The transfer voltage control unit 34 determines whether the current position of the photoconductor 20c facing the transfer unit 20e, that is, the transfer target position, is a print image or between print images (S2).

  When the transfer target position is a print image, the transfer voltage control unit 34 sets the control value of the transfer bias voltage applied to the transfer unit 20e as the first control value (S3). As a result, the print image is transferred to the transfer belt 21 with a transfer force (hereinafter referred to as a normal transfer force) that provides an optimal print image (S4).

  On the other hand, when the transfer target region is between print images, the transfer voltage control unit 34 sets the control value of the transfer bias voltage applied to the transfer unit 20e as the second control value (S5). As a result, the reference toner pattern formed between the printed images is transferred to the transfer belt 21 with a transfer force weaker than the normal transfer force (S6).

  The tandem color image forming apparatus repeats the processing from step S2 to step S6 until there are no more images to be printed (S7).

  Hereinafter, another embodiment will be described. The second control value may be configured to have different values for mono color printing and full color printing.

  This will be described in detail below. For example, when the tandem-type color image forming apparatus is in a mono-color printing mode with only black (K), transfer corresponding to magenta (M), cyan (C), and yellow (Y) as shown in FIG. The portion 20e is retracted to a position where it does not contact the transfer belt 21.

  That is, in the case of monocolor printing, only the transfer portion 20e corresponding to a predetermined color (black (K)) is in contact with the transfer belt 21, whereas in the case of full color printing, the transfer portion 20e corresponding to four colors. Is in contact with the transfer belt 21.

  As a result, there is a possibility that the degree to which the transfer belt 21 is affected by the fluctuation of the control value of the transfer bias voltage is different. Specifically, when the second control value is the same for mono color printing and full color printing, the speed fluctuation of the transfer belt 21 is within a predetermined range in mono color printing, but the speed fluctuation is predetermined in full color printing. There is a possibility that the speed fluctuation of the transfer belt 21 falls within a predetermined range in full-color printing, but the speed fluctuation does not fall within the predetermined range in mono-color printing.

  In such a case, when the speed fluctuation falls within a predetermined range in mono-color printing but the speed fluctuation does not fall within the predetermined range in full-color printing, the second control value in full-color printing is set to the second control value in mono-color printing. Set to a value larger than the control value (that is, set to a value closer to the first control value). In full-color printing, the speed fluctuation falls within a predetermined range, but in mono-color printing, the speed fluctuation falls within the predetermined range. If it does not fit, set the second control value for mono-color printing to a value greater than the second control value for full-color printing. It can be within a predetermined range.

  In the above-described embodiment, the configuration in which the image forming condition adjustment unit 33 maintains the print density at the set density by adjusting the bias voltage is not limited to adjustment of the bias voltage. For example, it may be configured to adjust the transfer bias voltage.

  The image forming apparatus according to the present invention adjusts the image forming conditions by forming a reference toner pattern between printed images, and if the reference toner pattern is transferred to the transfer belt 21, the image forming apparatus will be described in the above embodiment. The tandem color image forming apparatus is not limited to the above.

  For example, in the above-described embodiment, the configuration in which the image forming apparatus according to the present invention is a tandem color image forming apparatus for single-sided printing as shown in FIG. 3 has been described, but for double-sided printing as shown in FIG. Or a tandem color image forming apparatus.

  In the above-described embodiment, the configuration in which the image forming apparatus according to the present invention is a color image forming apparatus has been described. However, the image forming apparatus is not limited to a color machine and may be a monochrome machine.

  Furthermore, in the above-described embodiment, the configuration in which the image forming apparatus according to the present invention is a tandem color image forming apparatus has been described. However, the image forming apparatus is not limited to a tandem color image forming apparatus, and may be a facsimile, for example.

  Each of the above-described embodiments is merely an example of the present invention, and the scope of the present invention is not limited by the description. The specific configuration of each part is appropriately selected within the scope of the effects of the present invention. It goes without saying that changes can be designed.

Block diagram of tandem color image forming apparatus External view of tandem color image forming device Internal illustration of a tandem color image forming apparatus Illustration of the image output unit (A) shows reference toner patterns arranged in a direction perpendicular to the moving direction of the transfer belt, and (b) is an explanatory view showing a state in which the reference toner patterns of FIG. 5 (a) are transferred to the transfer belt. (A) shows a state where a reference toner pattern having a variable density between print images is transferred to a transfer belt, and (b) shows a reference density pattern formed only once for several printed images. Explanatory drawing showing the state transferred to the transfer belt Explanatory drawing about transfer output control by transfer voltage controller Flowchart for explaining switching control of transfer bias voltage control value by tandem color image forming apparatus Explanatory drawing of the image output unit when the transfer unit is retracted Internal illustration of a tandem color image forming device that supports duplex printing

Explanation of symbols

20: Photoconductor unit 20e: Transfer unit 21: Transfer belt 31: Image formation control unit 32: Reference density detection unit 33: Image forming condition adjustment unit 34: Transfer voltage control unit

Claims (4)

A plurality of photoconductor units that form images of different toner colors, and a transfer belt that forms a color image by transferring the images formed on the photoconductor by each photoconductor unit at a predetermined transfer section,
An image formation controller that forms a print image on each photoconductor and forms a reference toner pattern of a predetermined size between the print images, a reference density detector that detects the density of the reference toner pattern, and the reference density detection A tandem color image forming apparatus including an image forming condition adjusting unit that adjusts an image forming condition based on the density detected by the unit,
At least a control value of a transfer bias voltage applied to the transfer unit during a period when each reference toner pattern formed on each photoconductor passes through the transfer unit, and a transfer value for transferring each print image to the transfer belt. A tandem color image forming apparatus including a transfer voltage control unit that switches to a second control value having an absolute value smaller than a first control value to be applied.   2. The tandem color according to claim 1, wherein the second control value is a control value in which a speed fluctuation of the transfer belt that occurs when a transfer bias voltage is changed from the first control value falls within a predetermined range. Image forming apparatus.   3. The tandem color image forming apparatus according to claim 1, wherein the second control value is set to a different value for mono color printing and full color printing. 4.   4. The tandem color image forming apparatus according to claim 1, wherein the image formation control unit forms each reference toner pattern at a position different from each other along the axial direction of each photoconductor.

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