JP2019191386A - Image forming apparatus - Google Patents

Abstract

To correct a print condition according to the roughness of a surface of a sheet to prevent a deterioration in quality of a print image.SOLUTION: An image forming apparatus 10 comprises: image carriers 41; a transfer device 44; a fixing device 46; an image reading device 1; an arithmetic unit 8c; and a correction device 8d. The arithmetic unit 8c calculates a sheet surface roughness index value MT0 that is an index value of density unevenness in a non-image area in a document image read from a document 9. The correction device 8d corrects a print condition including one or both of a transfer power of the transfer device 44 and a heater power of the fixing device 46 according to the sheet surface roughness index value MT0.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electrophotographic image forming apparatus including an image reading apparatus.

  In general, an electrophotographic image forming apparatus includes a charging device, a developing device, a transfer device, and a fixing device. The image forming apparatus may include an image reading device that reads an image from a document.

  The charging device charges the image carrier. The developing device develops an electrostatic latent image formed on the image carrier into a toner image.

  The transfer device transfers the toner image from the image carrier to a sheet. The fixing device pressurizes the toner image transferred to the paper while heating it with a heater. As a result, the toner image is fixed on the sheet.

  Further, it is known that the image forming apparatus reads an image from a document on which a test pattern is printed, and sets the charging potential of the charging device and the developing bias of the developing device according to the density of the test pattern in the read image. (For example, refer to Patent Document 1).

JP 2008-15042 A

  By the way, the quality of the printed image is affected by the roughness of the surface of the paper. For example, when the surface of the paper is rough, the transfer device tends to fail to transfer the toner image from the image carrier to the paper.

  In addition, when the surface of the paper is rough, the fixing device is likely to fail to fix the toner image onto the paper.

  An object of the present invention is to provide an image forming apparatus that can prevent deterioration of the quality of a printed image by correcting printing conditions according to the roughness of the surface of the paper.

  An image forming apparatus according to one aspect of the present invention includes an image carrier, a transfer device, a fixing device, an image reading device, an arithmetic device, and a correction device. The image carrier carries a toner image. The transfer device transfers the toner image from the image carrier to a sheet by supplying transfer power. The fixing device includes a heater to which heater power is supplied, and fixes the toner image on the paper by pressing the toner image transferred onto the paper while being heated by the heater. The image reading device reads an image from a document. The arithmetic unit calculates a paper surface roughness index value that is an index value of density unevenness in a non-image area in a document image read from the document. The correction device corrects a printing condition including one or both of the transfer power and the heater power according to the paper surface roughness index value.

  According to the present invention, it is possible to provide an image forming apparatus capable of preventing the deterioration of the quality of a printed image by correcting the printing conditions according to the roughness of the surface of the paper.

FIG. 1 is a configuration diagram of an image forming apparatus according to an embodiment. FIG. 2 is a block diagram of a control device in the image forming apparatus according to the embodiment. FIG. 3 is a flowchart illustrating an example of the procedure of the calibration process in the image forming apparatus according to the embodiment. FIG. 4 is a flowchart illustrating an example of a procedure of print condition correction processing in the image forming apparatus according to the embodiment. FIG. 5 is a flowchart illustrating an example of the procedure of the print condition temporary correction process in the image forming apparatus according to the embodiment. FIG. 6 is a flowchart illustrating an example of the procedure of the print condition main correction process in the image forming apparatus according to the embodiment. FIG. 7 is a graph illustrating an example of a correspondence relationship between the paper surface roughness index value and the secondary transfer current correction value in the image forming apparatus according to the embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.

[Configuration of Image Forming Apparatus 10]
The image forming apparatus 10 according to the embodiment executes print processing by an electrophotographic method. The printing process is a process of generating a toner image, transferring the toner image onto a sheet, and fixing the toner image on the sheet.

  As shown in FIG. 1, the image forming apparatus 10 includes a print processing device 2, a control device 8, and an operation device 8x that execute the print processing. Further, the image forming apparatus 10 also includes an image reading apparatus 1 that executes a reading process for reading an image from the document 9. For example, the image forming apparatus 10 is a copying machine, a facsimile machine, or a multifunction machine.

  The image to be subjected to the printing process includes an image read from the document 9 by the image reading device 1 and an image represented by print data received from a host device (not shown).

  The control device 8 executes various data processing relating to the print processing job and the like, and further controls various electric devices. The operation device 8x is a device that receives a user operation. For example, the operation device 8x includes one or both of a push button and a touch panel.

  As shown in FIG. 1, the image reading device 1 includes a platen glass 13, an image sensor unit 110, a movable support device 11, a platen cover 12, and the like. The image reading apparatus 1 further includes an ADF (Auto Document Feeder) 14 incorporated in the platen cover 12.

  The platen glass 13 is a transparent document table on which the document 9 is placed. The platen cover 12 covers the platen glass 13 and the document 9 on the platen glass 13.

  The document 9 is placed on the platen glass 13 or conveyed by the ADF 14. The image sensor unit 110 can execute the reading process on the document 9 on the platen glass 13 and the reading process on the document 9 conveyed by the ADF 14. In the following description, an image read from the document 9 by the image reading device 1 is referred to as a document image.

  The print processing device 2 can execute the print processing based on the original image or the print processing based on an image represented by print data received from another device.

  As shown in FIG. 1, the print processing device 2 includes a paper transport device 3 and an image forming unit 4. The paper transport device 3 sends out the paper from the paper storage unit 20 to the paper transport path 30 and further transports the paper along the paper transport path 30.

  The paper transport device 3 includes a pickup roller 31, a delivery roller 32, and a retard roller 33.

  The pickup roller 31 picks up the sheets one by one from the sheet storage unit 20. The delivery roller 32 sends out the paper picked up by the pickup roller 31 to the paper conveyance path 30.

  The retard roller 33 is detachably supported with respect to the delivery roller 32 and is urged toward the delivery roller 32 by a spring 34. A torque limiter (not shown) is provided on the rotation shaft of the retard roller 33.

  Due to the action of the torque limiter, the rotation of the retard roller 33 stops when the paper passes between the delivery roller 32 and the retard roller 33, and at other times, the retard roller 33 moves to the delivery roller 32. Follow and rotate.

  The image forming unit 4 includes an image forming unit 4x, a laser scanning unit 40, a transfer device 44, and a fixing device 46.

  In the image forming unit 4x, the drum-shaped photoconductor 41 rotates, and the charging device 42 charges the surface of the photoconductor 41 uniformly. Further, an electrostatic latent image is written on the surface of the photoreceptor 41 charged by the laser scanning unit 40.

  Further, the developing device 43 of the image forming unit 4x develops the electrostatic latent image into a toner image. The transfer device 44 transfers the toner image on the surface of the photoreceptor 41 to the paper.

  Subsequently, the fixing device 46 fixes the toner image on the sheet. The fixing device 46 includes a fixing heater 46a, a fixing member 46b, a pressure roller 46c, and a temperature sensor 46d.

  The fixing heater 46a generates heat when the heater power is supplied to heat the fixing member 46b. The fixing member 46b heats the toner image on the paper. That is, the fixing heater 46a heats the toner image on the paper via the fixing member 46b when the heater power is supplied.

  The pressure roller 46c applies pressure to the toner image on the paper. The temperature sensor 46d detects the temperature of the fixing member 46b. For example, the temperature sensor 46d is a thermistor.

  The fixing device 46 fixes the toner image on the paper by heating the toner image on the paper with a fixing heater 46a and pressurizing the toner image on the paper with a pressure roller 46c.

  The control device 8 controls the power supplied to the fixing heater 46a so that the temperature detected by the temperature sensor 46d approaches a preset target fixing temperature. Therefore, when the target fixing temperature is high, the power supplied to the fixing heater 46a increases compared to when the target fixing temperature is low.

  A print processing apparatus 2 shown in FIG. 1 is a color printer having a tandem image forming unit 4. Therefore, the image forming unit 4 includes four image forming units 4x corresponding to different colors of toner. Further, the transfer device 44 includes four primary transfer devices 441, an intermediate transfer belt 440, a secondary transfer device 442, and a belt cleaning device 443.

  Each of the four image forming units 4x includes a photoreceptor 41, a charging device 42, and a developing device 43. The four image forming units 4x form the toner images of cyan, magenta, yellow and black on the surface of the photoreceptor 41, respectively.

  In each of the image forming units 4x, the primary transfer device 441 transfers the toner image from the photoreceptor 41 to the intermediate transfer belt 440. As a result, a color image composed of the four color toner images is formed on the intermediate transfer belt 440.

  The secondary transfer device 442 transfers the four color toner images on the intermediate transfer belt 440 to the paper when the secondary transfer power is supplied. In the image forming apparatus 10, the photoreceptor 41 and the intermediate transfer belt 440 of the transfer device 44 are examples of an image carrier that carries and rotates the toner image.

  The belt cleaning device 443 removes toner remaining on the intermediate transfer belt 440 without being transferred onto the sheet from the intermediate transfer belt 440.

  As described above, the print processing apparatus 2 forms the toner image representing the print image on the photoconductor 41 and the intermediate transfer belt 440 and transfers the toner image on the intermediate transfer belt 440 to the paper. .

  The print processing apparatus 2 further includes a charging bias applying device 42a, a developing bias applying device 43a, a transfer bias applying device 44a, an image density sensor 71, and a thickness sensor 72.

  The charging bias application device 42 a includes a charging voltage output circuit that applies a charging bias to the charging device 42. The developing bias applying device 43 a includes a developing voltage output circuit that applies a developing bias to the developing device 43. The transfer bias applying device 44 a includes a primary transfer current output circuit that supplies a constant primary transfer current to the primary transfer device 441 and a secondary transfer current output circuit that supplies a constant secondary transfer current to the secondary transfer device 442. Including.

  The image density sensor 71 is a sensor that detects the density of the toner image carried by the intermediate transfer belt 440. The image density sensor 71 includes a light emitting element that irradiates light on the surface of the intermediate transfer belt 440 and a photoelectric conversion element that detects the amount of reflected light on the surface of the intermediate transfer belt 440. The output signal of the photoelectric conversion element represents the density of the toner image carried by the intermediate transfer belt 440.

  The thickness sensor 72 detects the thickness of the paper sent out from the paper storage unit 20 to the paper transport path 30. For example, the thickness sensor 72 is a displacement sensor that detects the amount of displacement of the rotation shaft of the retard roller 33 when the paper is fed by the feed roller 32.

  When the paper passes between the feeding roller 32 and the retard roller 33, the rotation shaft of the retard roller 33 is displaced against the elastic force of the spring 34. The displacement amount of the rotating shaft of the retard roller 33 corresponds to the thickness of the paper. For example, it is conceivable that the displacement sensor is an optical sensor or a magnetic sensor.

  As shown in FIG. 2, the control device 8 includes a CPU (Central Processing Unit) 80, a RAM (Random Access Memory) 81, a secondary storage device 82, and a communication device 83.

  The CPU 80 operates as a main control unit 8a, a job control unit 8b, an image data processing unit 8c, a calibration control unit 8d, and the like by executing a program.

  The main control unit 8a executes job selection processing, various data setting processing, and the like according to operations on the operation device 8x.

  The job control unit 8b executes various data processing and control related to various jobs such as the reading processing job, the printing processing job, and the copying processing job. The copying process includes the reading process and the printing process based on the document image obtained by the reading process.

  For example, the job control unit 8b causes the print processing apparatus 2 to execute the print processing for forming an image on the paper. As described above, the print processing apparatus 2 includes the photoreceptor 41, the transfer device 44 including the photoconductor 41, and the fixing device 46. The job control unit 8b of the CPU 80 in the control device 8 is an example of a print control device.

  The image data processing unit 8 c executes various image processing such as processing and data conversion processing on image data obtained through the image reading device 1 or the communication device 83.

  The calibration control unit 8d executes a calibration process. The calibration process is a process of causing the print processing apparatus 2 to execute the print process of a predetermined test image and correcting the condition of the print process according to the state of the test image. Details of the calibration process will be described later.

  Note that some or all of the job control unit 8b, the image data processing unit 8c, and the calibration control unit 8d may be realized by a processor such as an MPU (Micro Processing Unit) or a DSP (Digital Signal Processor). It is also conceivable that part or all of the job control unit 8b, the image data processing unit 8c, and the calibration control unit 8d are realized by a circuit such as an ASIC (Application Specific Integrated Circuit).

  The communication device 83 is a communication interface device that communicates with a host device (not shown) or other external device via a network (not shown). The host device is an information processing device such as a personal computer or a portable information terminal. The CPU 80 performs all transmission and reception of data with the external device through the communication device 83.

  The secondary storage device 82 is a computer-readable non-volatile storage device. The secondary storage device 82 stores programs executed by the CPU 80 and various data referred to by the CPU 80. For example, one or both of a flash memory and a hard disk drive are employed as the secondary storage device 82.

  The RAM 81 is a volatile storage device. The RAM 81 temporarily stores a program executed by the CPU 80 and data output and referred to in the course of the CPU 80 executing the program. The RAM 81 is a storage device that can access data at a higher speed than the secondary storage device 82.

  By the way, the quality of the printed image is affected by the roughness of the surface of the paper. For example, when the surface of the paper is rough, the transfer of the toner image from the intermediate transfer belt 440 to the paper by the secondary transfer device 442 tends to occur.

  Further, when the surface of the paper is rough, the fixing device 46 is liable to cause the fixing of the toner image onto the paper.

  In the image forming apparatus 10, the calibration control unit 8 d corrects the print condition according to the roughness of the surface of the paper by executing the calibration process. Thereby, it is possible to prevent the quality of the print image from deteriorating due to the roughness of the surface of the paper.

  The calibration control unit 8d executes the calibration process when a predetermined adjustment execution condition is satisfied. For example, the adjustment execution condition includes a first adjustment execution condition and a second adjustment execution condition described below.

  The first adjustment execution condition is a condition that the cumulative number of printed sheets has changed from a state below an integer multiple of a preset number of sheets to a state exceeding it. In this case, the calibration control unit 8d counts up the accumulated number of prints every time the print process for one page is performed, and performs the calibration process every time the accumulated number of prints exceeds an integral multiple of the set number of sheets. Execute.

  The second adjustment execution condition is a condition that a predetermined sheet changing operation is performed on the operation device 8x. The user performs the paper change operation on the operation device 8x when the type of the paper stored in the paper storage unit 20 is changed.

[Calibration process]
Hereinafter, an example of the procedure of the calibration process will be described with reference to the flowchart shown in FIG. In the following description, S101, S102,... Represent identification codes of a plurality of steps in the calibration process.

<Step S101>
In the calibration process, the job control unit 8b causes each of the four image forming units 4x to form a first test image.

  Through the processing in step S <b> 101, the four color toner images of the first test image are developed on the surface of the photoreceptor 41 and then transferred to the intermediate transfer belt 440. In the process of step S101, the sheet is not transported and the secondary transfer current is not supplied to the secondary transfer device 442. Therefore, the toner image of the first test image is not transferred to the paper and is removed from the intermediate transfer belt 440 by the belt cleaning member 47b.

  For example, the first test image includes a patch image having a maximum density and a patch image having a predetermined intermediate density. The maximum density patch image is a so-called solid image.

<Step S102>
Next, the calibration control unit 8 d acquires the detected values of the density of the first test image of the four colors by the image density sensor 71.

<Step S103>
Subsequently, the calibration control unit 8d determines whether or not the detection result of the density of the first test image of four colors is within a predetermined target density range. If the calibration control unit 8d determines that all of the detected density values of the first test images of the four colors are within the target density range, the process proceeds to step S105, and if not, the process is performed. The process proceeds to step S104.

<Step S104>
In step S104, the calibration control unit 8d sets development conditions for each of the four image forming units 4x according to the difference between the detected values of the densities of the first test images of the four colors and the predetermined target densities. to correct. The developing conditions include the charging bias condition in the charging device 42 and the developing bias condition in the developing device 43.

  Specifically, the calibration control unit 8d determines the frequency of the AC component in the charging bias according to the difference between the density of the intermediate density patch image in the first test image and a predetermined first target density. Or correct the amplitude.

  The calibration control unit 8d corrects the frequency or amplitude of the AC component in the charging bias in the increasing direction when the density of the intermediate density patch image is lower than the first target density. Similarly, the calibration control unit 8d corrects the frequency or amplitude of the AC component in the charging bias in a decreasing direction when the density of the intermediate density patch image is higher than the first target density.

  The calibration control unit 8d determines the frequency or amplitude of the AC component in the developing bias according to the difference between the density of the maximum density patch image in the first test image and a predetermined second target density. to correct.

  The calibration control unit 8d corrects the frequency or amplitude of the AC component in the developing bias in the increasing direction when the density of the maximum density patch image is lower than the second target density. Similarly, the calibration control unit 8d corrects the frequency or amplitude of the AC component in the developing bias in the decreasing direction when the density of the maximum density patch image is higher than the second target density.

  The density of the intermediate density patch image and the density of the maximum density patch image are detection densities of the image density sensor 71.

  Then, the calibration control unit 8d shifts the process to step S101 after correcting the development conditions. Thereby, the calibration control unit 8d repeats the processes of steps S101 to S104 until it is determined that all the detected values of the density of the first test image of four colors are within the target density range.

<Step S105>
In step S105, the calibration control unit 8d initializes the printing conditions. The printing conditions include the secondary transfer current condition and the fixing temperature condition.

  Specifically, the calibration control unit 8d sets the target value of the secondary transfer current supplied to the secondary transfer device 442 to a predetermined reference current value, and sets the target fixing temperature in advance. Set to the reference temperature.

<Step S106>
Subsequently, the job control unit 8b causes the print processing apparatus 2 to execute the print processing of the second test image. As a result, the second test image is formed on the sheet. For example, the second test image is a patch image having the maximum density of each of four color toners.

  Further, in step S106, the calibration control unit 8d acquires a thickness detection value of the thickness sensor 72 when the paper is sent out from the paper storage unit 20 in the print processing of the second test image.

  In step S106, the job control unit 8b causes the four image forming units 4x to execute the process of forming the toner image of the second test image, and the process of transferring the toner image of the second test image onto the sheet. The transfer device 44 causes the fixing device 46 to execute processing for fixing the toner image of the second test image on the paper.

  By the process in step S106, the print process of the second test image is executed in a state where the development condition is appropriately corrected based on the first test image and the print condition is initialized. In the following description, the printed matter obtained by the printing process in step S106 is referred to as a primary test printed matter.

<Step S107>
Subsequently, the calibration control unit 8d executes a print condition correction process for correcting a predetermined print condition. In the present embodiment, the print condition includes a target value of the secondary transfer current and the target fixing temperature.

  The target value of the secondary transfer current is an example of a control value of the secondary transfer power that is power supplied to the secondary transfer device 442. The target fixing temperature is an example of a control value of the heater power supplied to the fixing heater 46a.

  The calibration control unit 8d ends the calibration process after the print condition correction process is completed.

[Print condition correction processing]
Hereinafter, an example of the procedure of the print condition correction process will be described with reference to the flowchart shown in FIG. In the following description, S201, S202,... Represent identification codes of a plurality of steps in the print condition correction process.

<Step S201>
In the print condition correction process, the job control unit 8b causes the image reading apparatus 1 to execute the reading process using the primary test print as the document 9.

  Before the process of step S201 is executed, the user sets the primary test printed material as the document 9 in the image reading apparatus 1, and then performs a reading start operation on the operation device 8x. The job control unit 8b causes the image reading device 1 to execute the reading process when detecting the reading start operation on the operation device 8x.

<Step S202>
Subsequently, the image data processing unit 8c is an index value of density unevenness in the region of the second test image for each of the four color second test images in the original image read from the primary test printed matter in step S201. A graininess index value MT1 is calculated.

  The image data processing unit 8c that executes the process of step S202 in the CPU 80 of the control device 8 is an example of an arithmetic device that calculates the granularity index value MT1 of the region of the second test image in the document image.

  In the present embodiment, the image data processing unit 8c divides the region of the second test image into a plurality of predetermined unit regions, and calculates the standard deviation of the average value of the pixel values of each of the plurality of unit regions. Calculated as the index value MT1. The unit area is referred to as a tile.

  For example, when the area of the second test image is an area of 300 pixels in the X-axis direction and 300 pixels in the Y-axis direction, the unit area is an area of 30 pixels in the X-axis direction and 30 pixels in the Y-axis direction. It is possible that there is.

  In the above case, the image data processing unit 8c first calculates the average value of the pixel values of the 100 unit regions, and further calculates the standard deviation of the 100 average values as the granularity index value MT1. .

  In the present embodiment, a large granularity index value MT1 indicates that the degree of density unevenness in the region of the second test image is large.

<Step S203>
Subsequently, the calibration control unit 8d determines whether or not all the granularity index values MT1 corresponding to the four color toners are within a predetermined first allowable range.

  In step S203, when the calibration control unit 8d determines that one or more of the granularity index values MT1 corresponding to the four color toners are out of the first allowable range, the process proceeds to step S204. Let

  On the other hand, if the calibration control unit 8d determines in step S203 that all the granularity index values MT1 corresponding to the four color toners are within the first allowable range, the print condition correction process is terminated.

<Step S204>
In step S204, the calibration control unit 8d corrects the print condition based on the thickness detection value acquired in step S106 of FIG. 3, and shifts the process to step S205.

  Specifically, when the thickness detection value represents a thickness larger than a predetermined reference thickness range, the calibration control unit 8d corrects the target value of the secondary transfer current to be increased. On the other hand, when the detected thickness value represents a thickness smaller than the reference thickness range, the calibration control unit 8d corrects the target value of the secondary transfer current to be decreased.

  If the thickness detection value falls within the reference thickness range, the calibration control unit 8d does not correct the target value of the secondary transfer current in step S205.

<Step S205>
In step S205, the calibration control unit 8d calculates a paper surface roughness index value MT0 that is an index value of density unevenness in the non-image area in the document image read from the document 9 in step S201. Thereafter, the calibration control unit 8d executes the processes of step S206 and step S207.

  The non-image area is an area where the secondary test image is not formed on the original image, that is, an area where the toner image is not transferred on the original 9.

  The image data processing unit 8c that executes the process of step S205 in the CPU 80 of the control device 8 is an example of an arithmetic device that calculates a paper surface roughness index value MT0 of the non-image area in the document image.

  In this embodiment, the image data processing unit 8c divides the non-image area into the plurality of unit areas, and calculates the standard deviation of the average value of the pixel values of the plurality of unit areas as the paper surface roughness index value MT0. To do.

  The calculation method of the paper surface roughness index value MT0 is the same as the calculation method of the graininess index value MT1 except that the area to be processed in the original image is the non-image area.

<Steps S206 and S207>
In step S206, the calibration control unit 8d executes a print condition temporary correction process to be described later, and subsequently executes a print condition main correction process to be described later in step S207. Thereafter, the calibration control unit 8d ends the print condition correction process.

[Print condition temporary correction processing]
Next, an example of the procedure of the print condition temporary correction process will be described with reference to the flowchart shown in FIG. In the following description, S301, S302,... Represent identification codes of a plurality of steps in the print condition temporary correction process.

<Step S301>
In the print condition temporary correction process, first, the calibration control unit 8d initializes identification numbers i of a plurality of correction candidates determined in advance for the print condition.

  The plurality of correction candidates for the print condition is one or a combination of one or both of the correction of the secondary transfer current and the correction of the target fixing temperature.

<Step S302>
Subsequently, the calibration control unit 8d provisionally corrects the print condition according to the i-th correction candidate. Thereafter, the calibration control unit 8d shifts the process to step S303.

  FIG. 7 shows an example of a correspondence relationship between the paper surface roughness index value MT0 and the secondary transfer current correction values IT0 for the three correction candidates. The secondary transfer current correction value IT0 is a correction value for the secondary transfer current, which is one of the printing conditions.

  In FIG. 7, D01 represents data of the secondary transfer current correction value IT0 in the first correction candidate, D02 represents data of the secondary transfer current correction value IT0 in the second correction candidate, and D03 represents The data of the secondary transfer current correction value IT0 in the third correction candidate is shown.

  As illustrated in FIG. 7, the calibration control unit 8d performs temporary correction of the print condition according to the i-th correction candidate based on a plurality of predetermined correction candidate data D01, D02, and D03. I do.

  FIG. 7 shows a secondary transfer current correction value IT0 as an example of the correction candidate for the print condition. In step S302, the calibration control unit 8d may temporarily correct the target fixing temperature according to the paper surface roughness index value MT0 in the same manner as the secondary transfer current.

<Step S303>
In step S303, the job control unit 8b causes the print processing apparatus 2 to execute the print processing of the correction candidate image. Thereafter, the job control unit 8b shifts the process to step S304.

  The correction candidate image includes the second test image and an identification image for identifying the correction candidate corresponding to the second test image.

  For example, the identification image is an image of an identification number of the correction candidate or a QR code (registered trademark) representing a correction value of the correction candidate.

<Step S304>
In step S304, the calibration control unit 8d ends the print condition temporary correction process when the print process of the correction candidate images corresponding to all of the plurality of correction candidates is completed, and otherwise. The process proceeds to step S305.

<Step S305>
In step S305, the calibration control unit 8d counts up the identification number i, and then shifts the process to step S302. As a result, the processes in steps S302 to S305 are repeated until the print processing of the correction candidate images corresponding to all of the plurality of correction candidates is performed.

  By performing the print condition temporary correction process, the development condition is appropriately corrected based on the first test image, and the print condition is temporarily corrected according to the plurality of correction candidates. The printing process of the correction candidate image including two test images is executed. In the following description, a printed material obtained by the print condition temporary correction process is referred to as a secondary test printed material.

[Print Condition Main Correction]
Next, an example of the procedure of the print condition main correction process will be described with reference to the flowchart shown in FIG. In the following description, S401, S402,... Represent identification codes of a plurality of steps in the print condition main correction process.

<Step S401>
In the print condition main correction process, the job control unit 8b causes the image reading apparatus 1 to execute the reading process using the secondary test print as the document 9.

  Before the process of step S401 is executed, the user sets the secondary test printed matter as the document 9 in the image reading apparatus 1, and then performs the reading start operation on the operation device 8x. The job control unit 8b causes the image reading device 1 to execute the reading process when detecting the reading start operation on the operation device 8x.

<Step S402>
Next, the image data processing unit 8c extracts the identification image from the correction candidate image read from the secondary test print in step S201.

  The image data processing unit 8c that executes the process of step S402 is an example of an image extraction device that extracts the predetermined identification image from the document image including the secondary test image and the identification image.

<Step S403>
Further, the image data processing unit 8c specifies the correction candidate corresponding to the identification image extracted from the correction candidate image.

<Step S404>
Further, the image data processing unit 8c calculates a granularity index value MT1 for each of the four color second test images in the correction candidate image.

<Step S405>
Subsequently, the calibration control unit 8d determines whether or not all of the granularity index values MT1 corresponding to the four color toners are within the first allowable range.

  In step S405, when the calibration control unit 8d determines that one or more of the granularity index values MT1 corresponding to the four color toners are out of the first allowable range, the process proceeds to step S407. Let

  On the other hand, if the calibration control unit 8d determines in step S405 that all the granularity index values MT1 corresponding to the four color toners are within the first allowable range, the process proceeds to step S406.

<Step S406>
In step S406, the calibration control unit 8d sets the correction candidate specified in step S403 as a main correction candidate. Thereafter, the calibration control unit 8d shifts the process to step S407.

  As will be described later, the calibration control unit 8d finally corrects the print condition according to one of the main correction candidates.

<Step S407>
In step S407, the calibration control unit 8d shifts the process to step S407 when the reading process of the secondary test printed matter corresponding to all of the plurality of correction candidates is completed, and performs the processing otherwise. To step S401.

  Accordingly, the processes in steps S401 to S406 are repeated until the reading process of the correction candidate images corresponding to all of the plurality of correction candidates is performed.

<Step S408>
In step S408, the calibration control unit 8d determines whether or not the correction candidate set as the main correction candidate exists.

  If the calibration control unit 8d determines that the correction candidate set as the main correction candidate is present, the calibration control unit 8d shifts the process to step S409, and if not, shifts the process to step S410.

<Step S409>
In step S409, the calibration control unit 8d selects one of the correction candidates set as the main correction candidate, and performs the main correction of the print condition according to the selected correction candidate. Thereafter, the calibration control unit 8d ends the print condition main correction process.

  In step S409, when there are a plurality of the correction candidates set as the main correction candidates, the calibration control unit 8d gives priority to the correction candidates that do not include the correction of the target fixing temperature, and sets the print conditions. Perform this correction. The correction of the target fixing temperature corresponds to the correction of the heater power.

  There may be a plurality of correction candidates that are set as the main correction candidates and do not include the correction of the target fixing temperature. In this case, the calibration control unit 8d performs the main correction of the print condition according to the correction candidate when the granularity index value MT1 closest to a predetermined target value is obtained. The target value of the granularity index value MT1 is a representative value within the first allowable range.

<Step S410>
On the other hand, in step S410, the calibration control unit 8d performs temporary correction of the print condition according to the correction candidate when the graininess index value MT1 closest to the first allowable range is obtained. Thereafter, the calibration control unit 8d repeats the process from step S206 in the print condition correction process based on the temporarily corrected print condition (see FIG. 4).

  Therefore, the calibration control unit 8d changes the reference value of the print condition while changing the reference value of the print condition until all the granularity index values MT1 of the second test image of the four color toners are within the first allowable range. The condition temporary correction process and the print condition main correction process are repeated.

  As described above, in step S302 of FIG. 5 and step S409 of FIG. 6, the calibration control unit 8d corrects the print condition according to the paper surface roughness index value MT0. The print conditions include one or both of a secondary transfer power supplied to the secondary transfer device 442 and the heater power supplied to the fixing heater 46a.

  As described above, since the printing conditions are corrected according to the surface roughness of the paper, it is possible to prevent the quality of the print image from deteriorating due to the surface roughness of the paper.

  Note that the calibration control unit 8d of the CPU 80 that executes the processes of step S302 in FIG. 5 and step S409 in FIG. 6 is an example of a correction device.

  More specifically, the calibration control unit 8d determines the paper surface roughness index value when the granularity index value MT1 of the area of the first test image in the document image is outside the predetermined first allowable range. The print conditions are corrected according to MT0 (see steps S202, S206, and S207 in FIG. 4, step S302 in FIG. 5, and step S409 in FIG. 6).

  Therefore, it is possible to prevent the image quality from being disturbed by the correction of the print condition based on the paper surface roughness index value MT0.

  In addition, when the granularity index value MT1 is out of the predetermined first allowable range, the calibration control unit 8d sequentially executes temporary correction of the print conditions according to the predetermined correction candidates ( (See steps S301, S302, S304, and S305 in FIG. 5).

  Further, the job control unit 8b causes the print processing apparatus 2 to execute the print processing of the correction candidate image every time the print condition is temporarily corrected according to the correction candidate (see step S303 in FIG. 5). ).

  Furthermore, after the print processing of the correction candidate image is performed, the image data processing unit 8c calculates the granularity index value MT1 for the document image including the correction candidate image, and the calculated granularity index When the value MT1 falls within the first allowable range, the calibration control unit 8d performs the main correction of the print conditions (Steps S303 in FIG. 5, Steps S404, S405, S406, S408, and S409 in FIG. 6). reference).

  Further, the calibration control unit 8d performs the main correction of the print condition according to the correction candidate corresponding to the identification image extracted from the correction candidate image by the image data processing unit 8c (step S403 in FIG. 6). (See S406, S408, and S409).

  By performing the above processing, an appropriate one of the plurality of possible correction candidates in the print condition is adopted.

  In addition, after the print processing of the correction candidate image is performed, the image data processing unit 8c calculates the graininess index value MT1 for each of the plurality of document images each including the correction candidate image, and the first There may be a case where there are a plurality of correction candidates corresponding to the granularity index value MT1 falling within the allowable range. In this case, the calibration control unit 8d executes the main correction of the print condition by giving priority to the correction candidate that does not include the correction of the heater power (step S303 in FIG. 5, steps S404, S405, and S406 in FIG. 6). , S408 and S409).

  By performing the above-described processing, the correction candidate is employed that consumes less power and is less likely to damage the paper due to heat.

  Further, the calibration control unit 8d corrects the print condition according to the detection value of the thickness sensor 72 when the print process of the second test image is performed (Steps S106 and S107 in FIG. 3 and Steps in FIG. 4). (See steps S204 and S205).

  By performing the above processing, the correction of the print condition corresponding to the thickness of the paper and the correction of the print condition corresponding to the surface roughness of the paper are appropriately performed independently.

  Further, the calibration control unit 8d corrects the development condition according to the density of the toner image of the first test image transferred to the intermediate transfer belt 440 (S101 to S104 in FIG. 3).

  The calibration control unit 8d corrects the development condition, and then corrects the print condition based on the thickness detection value of the thickness sensor 72 and corrects the print condition based on the paper surface roughness index value MT0. (See steps S106 and S107 in FIG. 3 and steps S204, S206, and S207 in FIG. 4).

  By performing the above processing, the development conditions are corrected to a state where a toner image having an appropriate density is formed on the intermediate transfer belt 440, and then the printing conditions are corrected. As a result, the development condition and the print condition are corrected with an appropriate balance.

[First application example]
Hereinafter, a first application example of the image forming apparatus 10 will be described.

  In this application example, instead of the image forming apparatus 10 including the thickness sensor 72, the main control unit 8a of the CPU 80 executes a thickness setting process for setting the thickness information indicating the thickness of the paper according to the operation on the operation device 8x.

  The main controller 8a of the CPU 80 when executing the thickness setting process is an example of a thickness setting device.

  In this application example, the calibration control unit 8d corrects the print condition according to the thickness information when the print process is performed. When this application example is adopted, the same effect as that obtained when the first embodiment described above is adopted can be obtained.

[Second application example]
Hereinafter, a second application example of the image forming apparatus 10 will be described.

  In this application example, the transfer bias applying device 44 a includes a secondary transfer voltage output circuit that supplies a constant secondary transfer voltage to the secondary transfer device 442. In this application example, the power supplied to the secondary transfer device 442 under the printing conditions is performed by correcting the secondary transfer voltage.

1: Image reading device 2: Print processing device 3: Paper transport device 4: Image forming unit 4x: Image forming unit 8: Control device 8a: Main control unit 8b: Job control unit 8c: Image data processing unit 8d: Calibration control Unit 8x: Operating device 9: Document 10: Image forming device 11: Movable support device 12: Platen cover 13: Platen glass 20: Paper storage unit 30: Paper transport path 31: Pickup roller 32: Delivery roller 33: Retard roller 34: Spring 40: Laser scanning unit 41: Photoconductor 42: Charging device 42a: Charging bias applying device 43: Developing device 43a: Developing bias applying device 44: Transfer device 44a: Transfer bias applying device 46: Fixing device 46a: Fixing heater 46b: Fixing member 46c: pressure roller 46d: temperature sensor Sir 47b: belt cleaning member 71: the image density sensor 72: Thickness sensor 80: CPU
81: RAM
82: Secondary storage device 83: Communication device 110: Image sensor unit 440: Intermediate transfer belt 441: Primary transfer device 442: Secondary transfer device 443: Belt cleaning device IT0: Secondary transfer current correction value MT0: Paper surface roughness index Value MT1: Granularity index value

Claims (6)

An image carrier for carrying a toner image;
A transfer device that transfers the toner image from the image carrier to a sheet by supplying transfer power; and
A fixing device including a heater to which heater power is supplied, and fixing the toner image to the paper by pressurizing the toner image transferred to the paper while being heated by the heater;
An image reading device for reading an image from a document;
An arithmetic unit that calculates a paper surface roughness index value that is an index value of density unevenness of a non-image area in an original image read from the original;
An image forming apparatus comprising: a correction device that corrects a printing condition including one or both of the transfer power and the heater power according to the paper surface roughness index value. The arithmetic device further calculates a graininess index value that is an index value of density unevenness in a predetermined test image area in the document image read from the document,
The image forming apparatus according to claim 1, wherein the correction device corrects the print condition according to the paper surface roughness index value when the graininess index value is out of a predetermined allowable range. A print control device that causes a print processing device including the image carrier, the transfer device, and the fixing device to execute print processing for forming an image on the paper;
An image extracting device for extracting a predetermined identification image from the document image including the test image,
The correction device sequentially executes temporary correction of the print conditions according to a plurality of predetermined correction candidates when the granularity index value is out of a predetermined allowable range;
The print control apparatus includes a correction candidate image including the test image and the identification image that identifies the correction candidate corresponding to the test image every time the print condition is temporarily corrected according to the correction candidate. Causing the print processing apparatus to execute the print processing;
After the print processing of the correction candidate image, the arithmetic device calculates the graininess index value for the document image including the correction candidate image, and the calculated graininess index value is the The said correction apparatus performs this correction | amendment of the said printing conditions according to the said correction candidate corresponding to the said identification image extracted from the said correction candidate image by the said image extraction apparatus, when it is settled in an allowable range. Image forming apparatus.   After the print processing of the correction candidate image, the calculation device calculates the granularity index value for each of the plurality of document images each including the correction candidate image, and the granularity falls within the allowable range. 4. When the plurality of correction candidates corresponding to the sex index value exist, the correction device preferentially executes the main correction of the print condition with priority on the correction candidates not including the correction of the heater power. The image forming apparatus described in 1. A thickness sensor for detecting the thickness of the paper;
The image forming apparatus according to claim 3, wherein the correction device corrects the print condition according to a detection value of the thickness sensor when the print processing is performed. A thickness setting device that sets thickness information indicating the thickness of the paper;
The image forming apparatus according to claim 3, wherein the correction device corrects the print condition according to the thickness information when the print process is performed.

Images