JP4494141B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus.

  In general, for example, a full color LED printer is well known as an electrophotographic image forming apparatus called a tandem type that forms a full color image. This full-color LED printer includes an image forming unit (image drum unit) that forms images of each color of cyan (C), magenta (M), yellow (Y), and black (B), and is modulated by image data of each color. The latent image is formed by irradiating the photoconductor of the image forming unit with the LED light, and the toner image is developed by supplying toner of each color to the photoconductor on which the latent image is formed. Further, the image forming unit transfers the toner image on the photosensitive member to the recording paper conveyed on the conveying belt, thereby superimposing the toner images of the respective colors on the recording paper to form a color image.

By the way, in the case of an image forming apparatus including a plurality of image forming units corresponding to respective colors, different toner images are sequentially superimposed on the same surface of the same recording sheet in each of the image forming units to form a color image. When a large amount of printing is repeated and the toner is consumed, if the toner density is different from the ideal value, the color quality of the printed image appears and the image quality deteriorates. The user recognizes such deterioration of the image quality only after looking at the image printed on the recording paper, and the reality is that it cannot be predicted. In order to maintain the image quality, it is necessary to correct and adjust the toner density to approach the ideal density. As a conventional technique disclosed regarding the toner density correction, for example, there is a publication of Japanese Patent Application Laid-Open No. 2004-151867. In this case, a detection image is formed on the conveyance belt that conveys the print medium in the initialization process after the main power is turned on, and the toner density of the detected image is detected by the reflection type optical sensor that is the density detection unit. The actual density value is calculated by converting the analog voltage signal thus obtained into a digital signal. It is disclosed that the toner voltage is controlled so that the toner density approaches the ideal value from the actual density value. Such toner density correction is generally performed at a stage where the number of printed sheets exceeds the set number in consideration of the density effect due to changes over time. Was temporarily stopped and corrected.
JP 2001-290327 A

  However, in such a conventional image forming apparatus and the color image forming apparatus disclosed in the above publication, the printing operation is stopped when the number of printed sheets exceeds the set number, and the toner density correction is performed. The interrupted printing operation is resumed. For this reason, there is a problem that the interval between the recording sheets printed before and after the toner density correction is widened, and the average printing speed (throughput) is lowered.

  SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to automatically correct a toner density when an image forming apparatus such as a color printer exceeds the set number and interrupt printing. It is an object of the present invention to provide an image forming apparatus capable of increasing the throughput by continuing a print job without doing so.

In order to achieve the above object, an image forming apparatus according to the present invention employs the following configuration.
<Configuration>
Based on the input image information, an image forming unit that forms a developer image, a transport unit that transports the formed developer image, and the density of a detection image formed on a part of the transport unit are detected. a concentration detection unit, and a transfer unit for transferring the printing medium the developer image, in the image forming apparatus that corrects the density of the developer image formed on the basis of the detected density by the density detection unit, wherein A print number counting unit that detects the number of sheets printed on a print medium, a determination unit that determines whether the number of prints detected by the print number count unit exceeds a predetermined amount, and a plurality of detection images A detection image generation unit that generates the detection image, and a remaining print number counting unit that detects a remaining number of prints being printed, wherein the detection image generation unit has a predetermined number of prints. The determination unit determines that the The number of divisions of the detection image used for density correction is determined according to the remaining number of prints detected by the remaining print number counting unit, and the detection image divided between the print media is formed by the image forming unit. It is a feature.

  For example, when the amount of an image to be printed exceeds a predetermined amount, a detection image is formed in an area between the preceding print medium and the subsequent print medium, thereby detecting the developer concentration of the detection image. If it is determined that the correction should be made by comparing with the ideal density value based on the value, the developer density can be corrected without interrupting printing even in the current print job, for example.

  Embodiments of an image forming apparatus according to the present invention will be described below in detail with reference to the drawings.

<Configuration of Example 1>
FIG. 1 is a diagram illustrating a configuration of a first embodiment of an image forming apparatus according to the present invention. The apparatus 1 includes a sheet feeding unit 2, a conveyance belt mechanism unit (conveyance unit) 3, an image forming unit 4 to 7, a fixing device 8, an image density detection unit 9, and each of these units. A drive mechanism unit (not shown) including a motor to be driven and a control unit 10 for controlling the drive are mainly configured. The following will be described in order.

  The paper feeding unit 2 separates and feeds the recording paper 2b stored in the paper feeding cassette 2a one by one by a paper feeding roller and a separating member, and feeds the recording paper 2b between the registration rollers. It comes to send. In the conveyor belt mechanism unit 3, an endless conveyor belt 3a is stretched between a pair of driving rollers 3b and a driven roller 3c, and rotational power is transmitted from a driving mechanism such as a driving motor controlled by the control unit 10 to the driving roller 3b. Thus, the conveyor belt 3a is rotated. In this case, for example, cyan (C), magenta (M), yellow (Y), and black (B) colors (hereinafter collectively referred to as CMYB) from the upstream side to the downstream side along the rotation direction of the transport belt 3a. Image forming units 4, 5, 6, and 7 are arranged. That is, the recording belt 2b fed out from the paper feeding unit 2 is sequentially conveyed to the CMYB color image forming units 4 to 7, and a cyan toner image, a magenta toner image, and a yellow toner image are recorded on the recording paper 2b. A toner image and a black toner image are sequentially formed.

  In the color image forming units 4 to 7 corresponding to CMYB, the respective photoconductors 4a to 7a are arranged at equal intervals along the traveling direction of the conveying belt 3a, and the charging units 4b to 4a are centered on the photoconductors 4a to 7a, respectively. 7b, exposure units 4c to 7c, development units 4d to 7d, transfer rollers (transfer units) 4e to 7e, cleaning units 4f to 7f, a charge removal unit (not shown), and the like are arranged. That is, the photoconductors 4a to 4a are uniformly charged by the charging units 4b to 7b, and the photoconductors 4a to 7a are irradiated with LED light whose light emission or non-light emission is determined based on image data by the exposure units 4c to 7c. An electrostatic latent image is formed. Each color toner image is formed by attaching each color toner of CMYB to the photoconductor on which the electrostatic latent image is formed by the developing units 4d to 7d. In addition, when the recording paper 2b is conveyed between the conveyance belt 3a and the photoconductors 4a to 7a, the image forming units 4 to 7 are configured so that the transfer rollers 4e to 7e disposed on the back surface of the conveyance belt 3a are transferred with the transfer voltage. And the CMYB toner images on the photoconductors 4a to 7a are sequentially transferred onto the recording paper 2b. After the toner images have been transferred, the photoreceptors 4a to 7a are configured so that residual toner is removed by the cleaning units 4f to 7f, and the charge removing units 4b to 7b are charged again after being neutralized by the neutralizing unit.

  On the other hand, in the image density detection unit 9, a reflection type optical sensor 9a including a pair of opposed light emitting units and light receiving units is disposed on the opposite side of the image forming units 4 to 7 with the conveyance belt 3a interposed therebetween. For example, a light emitting diode is used for the light emitting part, and a photodiode is used for the light receiving part. The detection target by the image density detector 9 is a detection image as shown in FIG. That is, in the detection image generating unit 18 shown in FIG. 2, the CMYB color toners are sampled, and how much the actual actual density value is different from the ideal value when the toner density value is 30%, for example. A detection image 30 for detecting whether or not there is is formed on the surface of the conveyor belt 3a. In this case, 50% detection image 31 and 70% detection image 32 are further formed. % Is further subdivided to form a larger number of detection images, so that highly accurate detection and toner density correction can be performed. Light is emitted from the light emitting portion of the reflective optical sensor 9a toward the conveyance belt 3a, and the light reflected by the detection images 30, 31, and 32 is received by the light receiving portion, and the received light amount is detected as an analog signal. Then, it is sent to the A / D converter 14 (see FIG. 2) of the control unit 10.

  Therefore, the control unit 10 shown in FIG. 2 calculates the actual density values of the detection images 30 to 32 based on the respective percentages formed on the conveyance belt 3a based on the detection values, and stores them in the storage unit. The density correction value is calculated by calculating the difference from the ideal density value using the characteristic table of FIG.

  It should be noted that various modes can be considered as the detection image generation unit 18 that is a means for forming the detection images 30, 31, 32 of each% on the surface of the conveyor belt 3a. The detection image generation unit 18 is not specified for the structure. Further, as a structure related to the image density detection unit 9, in this example, there is provided a shutter mechanism 9b having an opening / closing structure by a motor or an electromagnetic valve, which is opened only when density detection correction is performed, and is normally closed. The reflective optical sensor 9a is protected from scattered toner and the like.

  FIG. 2 is a functional block diagram showing the configuration of the control unit 10. The control unit 10 controls the overall operation of the printer, which is a specific example of the apparatus 1, and includes a CPU 11, ROM 12, RAM 13, A / D converter 14, a print number counter 15 that is an image amount integration unit according to the present invention, and a remaining number. A printing number counter 16 and a detection image generation unit 18 are provided. A control unit for data reception and image processing from a host computer (not shown) is also included. The ROM 12 stores various data necessary for executing the program 20 for the entire printer system, particularly data necessary for executing the density correction processing program incorporated in the system program, for example, “predetermined number of sheets” during continuous printing. Etc. are stored and stored. The RAM 13 is used as a work memory in the CPU 11 and stores various data. The CPU 11 uses the RAM 13 as a work memory based on the system program 20 in the ROM 12, controls each part of the printer, executes a sequence as the image forming apparatus 1, and performs density correction processing based on the set number of sheets during continuous printing. Do. The A / D converter 14 converts the analog detection signal from the reflection type optical sensor 9a constituting the image density detection unit 9 into a digital signal, and the CPU 11 reads it.

  FIG. 6 is a characteristic graph showing the correlation between the theoretical value and the actual value of the toner density. The characteristic graph is used as basic data for calculating the correction amount when the toner density correction process is performed, and is stored and stored in the RAM 13 in advance. ing. As shown in FIG. 5, the detection images 30, 31, and 32 that are targeted for theoretical density values of 30%, 50%, and 70%, for example, at predetermined positions on the surface of the conveyor belt 3a are toners of four colors of CMYB. Is formed. If the detected images 30 to 31 are detected and read by the image density detection unit 9 and the read value shows the characteristic indicated by the actual density curve in FIG. 5, the ideal density value indicated by the solid line 40 or the oblique line in the figure. The toner layer pressure and the like are controlled by the correction curve value so that the read value can be corrected close to the approximate area value 41 shown.

  In this example, when the preset number of prints reaches the preset number of times for forming the detection images 30 to 32 on the surface of the transport belt 3a, the remaining number of prints by the print job is counted. Based on this, detection images 30 to 32 are formed between the preceding and succeeding recording sheets 12 in the formation patterns as shown in FIGS. The operation and action will be described below with reference to the formation pattern diagrams of FIGS.

<Operation of Example 1>
Next, the operation and action of the first embodiment will be described with reference to the operation flowcharts of FIGS.

  The recording paper 2b fed out from the paper supply unit 2 is sequentially conveyed to the CMYB color image forming units 4 to 7 by the conveyance belt 3a, and the CMYB color toner images are sequentially formed on the recording paper 2b. In the image forming units 4 to 7, the photoconductors 4a to 4a are uniformly charged by the charging units 4b to 7b, and the photoconductors 4a to 7a are irradiated with LED light modulated by image data by the exposure units 4c to 7c. An electrostatic latent image is formed. The CMYB color toners are sequentially attached to the photosensitive member on which the electrostatic latent image is formed by the developing units 4d to 7d, thereby forming the color toner images.

  That is, when the recording paper 2b is conveyed between the conveyance belt 3a and the photoconductors 4a to 7a, the transfer rollers 4e to 7e on the back surface of the conveyance belt 3a apply a transfer voltage, and YMCB on the photoconductors 4a to 7a. Each color toner image is sequentially transferred onto the recording paper 2b. After the toner images have been transferred, the photoreceptors 4a to 7a have the residual toner removed by the cleaning units 4f to 7f, discharged from the discharging unit, and then charged again by the charging units 4b to 7b. The recording paper 2b on which each color image is formed by transferring the YMCB toner image in this manner is further conveyed in a state of being electrostatically adsorbed on the surface of the conveyance belt 3a, and is eventually peeled off from the conveyance belt 3a and fixed to the fixing device. 8 is sent.

  In the fixing device 8, the recording paper 2b conveyed by the conveying belt 3a is sandwiched between the fixing roller 8a and the pressure roller 8b, heated, and pressed to fix the toner of each color on the recording paper 2b. Thereafter, the paper is discharged into a paper discharge tray by a paper discharge roller.

  Next, in the processing operation flowchart (No. 1) during printing shown in FIG. 3, the CPU 11 of the control unit 10 determines whether or not the number of prints counted by the print number counter 15 has reached the set number stored in the RAM 13. Judgment is made (step: S1). If printing exceeds the set number (Yes), it is determined in the next step S2 whether or not the remaining number of prints counted by the remaining print number count 16 has reached the set number. The printed sheet counter 15 and the remaining printed sheet counter 16 function as an image amount integration unit in the present invention, and actually mean the amount printed on recording paper, for example, 5000 pages. At this time, it is determined whether the remaining number of prints is 4 or less, for example, and if it is 4 or less (Yes), the process proceeds to step S3, and as shown in FIG. A detection image A having a non-divided integrated pattern in which a detection image 30 having a theoretical density value of 30%, a detection image 31 having a theoretical density of 30%, and a detection image 32 having a theoretical density of 30% are continuously integrated is provided on the conveyance belt 3a. To form. That is, the detection image generation unit 18 generates a detection image including a plurality of images as a set. If the number of remaining prints is 4 or more in step S2 (No), the process proceeds to step S4 to determine whether the remaining print number counted by the remaining print number counter 16 is 4 or more. If (Yes), the process proceeds to step S5, and as shown in FIG. 8, a detection image B of a three-division pattern in which the detection images 30, 31, 32 are respectively formed between the recording paper of the preceding paper and the subsequent paper. Form. If it is 4 or less in step S4 (No), it proceeds to the next step S6, and it is determined whether or not the remaining number of prints of the count number checked by the remaining print number counter 16 is 13 or more. If the remaining number of prints is 13 or more (Yes), as shown in FIG. 9, the detection image C of the 12-division pattern is selected in the next step S7. In this detection image C, a density of 30%, 50%, and 70% is independently formed between the papers for every four colors of CMYB, so that it becomes a 12-division pattern. On the other hand, if the remaining number of prints is 13 or less (No), the process proceeds to step S8. In step S8, the shutter mechanism 9b (see FIG. 1) is opened and the print sheet count value is initialized. In addition, when the interval between successive sheets is narrow and it is difficult to form a detection image, the sheet feeding timing is controlled from the interval between the sheets and the detection image formation size.

  Next, in step S9 of the operation flowchart (part 2) in FIG. 4, processing for forming detection images A, B, and C according to the division pattern is performed. That is, in step S10, for example, when the detection image A formed by the integrated pattern of FIG. 7 is detected by the reflection type optical sensor 9a, the analog signal is converted into a digital signal by the A / D converter 14 of the control unit 10. The CPU 11 reads the value. In step S11, the CPU 11 calculates the difference between the read actual density value of each color toner and the theoretical density value based on the characteristics shown in FIG. 6, and calculates the density correction value to be corrected from the difference. 6 so as to approach the ideal density value or approximate region 41 represented by the solid line 40 in FIG. In step S12, it is determined whether or not the read actual density value is within the range of such ideal density value 40 or approximate region 41. If correction is necessary, density correction is executed in step S13 (step: S13). As described above, a series of toner density correction is performed during continuous printing, and there is no need to interrupt printing. At that time, the density correction may be applied from the next print job without performing the correction in the current print job. If the actual density value is within the ideal density value 40 or the approximate area 41, the process proceeds to step S14. In step S14, it is determined whether or not the density correction is completed. If it is not completed, the process returns to step S9 and the process is repeated.

  Here, the detection image can be largely generated by the following two methods. One is generated by storing detection image data in a nonvolatile memory (a storage means such as a ROM or a hard disk device, the contents of which do not disappear even when the power is turned off), and reading the data. As a variation at this time, the detection image data is stored as it is, and the encoded (compressed) stored image is expanded at the time of generation. In addition, when a parameter such as a density value (%) is input instead of the image pattern itself, it is generated by calculating a corresponding detection image pattern. The calculation can be performed by calculating a numerical value or using a table.

<Effect of Example 1>
As is clear from the above, in the first embodiment, when printing reaches the set number of sheets, the space between the preceding medium and the succeeding medium during continuous printing is divided into a plurality of formation regions corresponding to the remaining number of printed sheets. Then, by forming, for example, detection images 30 to 32 that target different toner theoretical density values in the respective divided areas, the respective color toner densities of these detection images 30 to 32 are detected as actual density values. Thus, it is determined whether or not the actual density value should be corrected, and in the case of correction, control is performed without interrupting printing so that it is executed during printing.

<Configuration of Example 2>
FIG. 10 is a diagram illustrating a configuration of the control unit 10 as the second embodiment of the image forming apparatus according to the present invention. The control unit 10 of this example is different from the control unit 10 of the first embodiment in that an environmental sensor 17 that detects temperature and humidity under the environment is provided. Since the other units are the same as those in the first embodiment, the corresponding reference numerals are assigned and redundant descriptions are omitted.

<Operation of Example 2>
11 and 12 showing the processing during printing (Part 1 and Part 2), the CPU 11 of the control unit 10 reaches the set number of sheets stored in the RAM 13 by the number of printed sheets counted by the number of printed sheet counter 15. It is determined whether or not it has been done (step: S21). If printing exceeds the set number (Yes), the environmental sensor 17 detects the temperature and humidity under the environment in the next step S22, and compares it with the previous measurement value or initial state value stored in advance in the RAM 13 (step S22). : S23) If the temperature and humidity fluctuations detected this time are within the predetermined value range (Yes), the process is terminated without executing the process. If it exceeds the predetermined value range (No), the process proceeds to the next step S24, and steps S24 to S36 similar to the steps from step S2 to step S14 shown in FIG. 3 and FIG. Execute the process.

<Effect of Example 2>
In the second embodiment, considering that the toner component and the like are affected by the temperature and humidity in an environment such as an office where the image forming apparatus such as a printer operates, the same as in the first embodiment when the temperature and humidity vary greatly. Therefore, unnecessary toner density correction in an environment with little change in temperature and humidity can be deleted.

<Configuration of Example 3>
FIG. 13 is a diagram showing the configuration of the control unit 10 as the third embodiment of the image forming apparatus according to the present invention. The control unit 10 of this example is different from the first and second embodiments in that the remaining print number counter 16 and the environment sensor 17 are not provided, but only the print number counter 15 is provided. Since the other units are the same as those in the first and second embodiments, the corresponding reference numerals are assigned and redundant descriptions are omitted.

<Operation of Example 3>
In the operation flowchart of FIG. 14 showing processing during printing, the CPU 11 of the control unit 10 first checks whether or not a control flag indicating invalidity of toner density correction is set in step S40. If the invalid flag is set (Yes), the subsequent processing is terminated without executing. If the invalid flag is not set (No), the process proceeds to the next step S41, where it is determined whether or not the number of prints counted by the print number counter 15 has reached the set number stored in the RAM 13. If the number of prints exceeds the set number (Yes), a detection image pattern is selected in the next step S42, and in this case, a 70% density CMYB four-color detection image D is formed. Subsequently, the processes of steps S43 to S49 common to the steps from step S8 to step 14 (see FIGS. 3 and 4) of the first embodiment are executed. In step S50, it is determined whether or not density correction has been performed in step S48. If density correction has been performed (Yes), the process ends. If it is not necessary to perform density correction (No), an invalid flag is set in step S51, and subsequent density processing is not executed by this invalid flag set. In this example, the detection image D having a 70% density is described. However, a detection image at all densities can be formed or detected.

<Effect of Example 3>
In the third embodiment, only the density limited between the papers during continuous printing is detected, and the necessity of density correction is determined based on whether or not the detected density is within a predetermined range. Toner density correction can be deleted.

  In the first, second, and third embodiments, a direct transfer system that directly transfers a toner image developed on the surface of the photosensitive drum to a recording sheet, and a so-called tandem that includes a plurality of image forming units and performs image formation in parallel. The color printer of the system has been described as an example. However, a printer using an intermediate transfer system in which a toner image developed on the surface of a photosensitive drum is temporarily transferred to an intermediate transfer member such as a belt or a drum and then transferred to a recording sheet again by a transfer device. Alternatively, the present invention is also applicable to a single color printer that includes one or a plurality of image forming units, all of which use a single color toner. Further, the present invention can be applied not only to a printer but also to a facsimile machine or a copying machine that records an image on a cut sheet.

1 is a configuration diagram showing an image forming apparatus to which each embodiment according to the present invention is applied. FIG. 3 is a functional block diagram illustrating a control unit according to the first embodiment. FIG. 3 is an operation flowchart (No. 1) according to the first embodiment. FIG. 6 is an operation flowchart (No. 2) according to the first embodiment. FIG. 3 is a diagram schematically illustrating an aspect of a detection image formed on the conveyance belt according to the first exemplary embodiment. 6 is a characteristic graph showing a correlation between an actual density value and a theoretical density value of the toner of Example 1. FIG. 3 is a plan view illustrating a detection image A using a non-divided pattern according to the first embodiment. FIG. 3 is a plan view illustrating a detection image B using a divided pattern according to the first embodiment. FIG. 3 is a plan view illustrating a detection image C using a divided pattern according to the first embodiment. FIG. 6 is a functional block diagram illustrating a control unit according to the second embodiment. The operation | movement flowchart (the 1) of Example 2. FIG. Operation | movement flowchart (the 2) of Example 2. FIG. FIG. 10 is a functional block diagram illustrating a control unit according to a third embodiment. 9 is an operation flowchart of the third embodiment. FIG. 6 is a plan view showing a detection image D of Example 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Paper feed part 2a Recording paper (printing medium)
DESCRIPTION OF SYMBOLS 3 Conveyance belt mechanism part 3a Conveyance belt 4-7 CMYB image formation part of each color 8 Fixing device 9 Image density detection part 9a Reflection type optical sensor 9b Shutter mechanism part 10 Control part 11 CPU
12 ROM
13 RAM
14 A / D converter 15 Printed sheet counter (image amount integration unit)
16 Remaining print sheet counter (image amount integration unit)
17 Environmental Sensor 18 Detection Image Generation Unit 20 Program Unit 30 to 32 Detection Image

Claims (4)

Based on the input image information, an image forming unit that forms a developer image, a transport unit that transports the formed developer image, and the density of a detection image formed on a part of the transport unit are detected. In an image forming apparatus that includes a density detection unit and a transfer unit that transfers the developer image to a print medium, and corrects the density of the developer image formed based on the density detected by the density detection unit.
A print number counting unit for detecting the number of printed sheets on the print medium;
A determination unit that determines whether or not the number of printed sheets detected by the printed sheet count unit exceeds a predetermined amount;
A detection image generation unit that generates the detection image including a plurality of detection images as a set;
A remaining number-of-prints counting section for detecting the remaining number of printed sheets during the printing process;
With
When the determination unit determines that the number of printed sheets exceeds a predetermined amount, the detection image generation unit is configured to divide the number of detection images used for density correction according to the remaining number of printed sheets detected by the remaining printed sheet number counting unit. And an image for detection divided between print media by the image forming unit is formed. The image forming apparatus according to claim 1, wherein the detection image includes a plurality of types of images having different densities. The image forming apparatus according to claim 1 , wherein the transport unit transports a print medium onto which the formed developer image is directly transferred . 4. The transfer unit according to claim 1 , wherein the transfer unit is an intermediate transfer member that is transferred again to the print medium by the transfer unit after the developer image is transferred to the surface thereof . 5. The image forming apparatus described in 1.

Images