JP5198319B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms a toner image by attaching toner to an image carrier on which an electrostatic latent image is formed, and forms the image by transferring the toner image onto a recording sheet.

  Conventionally, in an image forming apparatus such as a copier, a printer, a facsimile, etc., an electrical or mechanical state applied to an image forming output is changed due to a change in an environment in which the apparatus is placed, deterioration or wear of parts, and the like. End up. When such a change occurs, the image quality such as the color and density of the image differs before and after the change, making it impossible to supply a stable image quality.

  Therefore, in order to maintain the image quality of the output image constant, calibration is performed to adjust the output density by correcting the developing bias voltage applied to the developing device or correcting the output value of the laser light source in the case of a laser printer. It takes place in the device. However, if calibration is performed during image formation, the image formation is interrupted, resulting in a user waiting. Therefore, when performing calibration during image formation, Patent Documents 1 and 2 disclose a method in which calibration is performed by forming a toner patch in a region between printing toner images transferred to a recording sheet without interrupting image formation. It is described in.

JP 2008-26701 A JP 2008-77016 A

  However, when forming a toner patch in the area between printing toner images, if the intermediate transfer belt or the photosensitive drum as the image carrier is poorly cleaned, the toner patch may contain residual toner that could not be removed. As a result, the density of the toner patch could not be accurately measured.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus that performs calibration with high accuracy during image formation.

  In order to solve the above problems, an image forming apparatus according to the first aspect of the present invention forms a toner image on an image carrier by applying a developing bias voltage to the developing device, and the toner image is conveyed. An image forming unit that forms an image by transferring to a recording paper, a measuring unit that measures the toner density on the image carrier, and whether or not to adjust the image quality of the toner image is determined according to a predetermined condition. And when the image forming unit determines that the image forming unit performs image quality adjustment of the toner image, the image forming is performed during the formation of the printing toner image to be transferred to the recording paper. Control means for forming a toner patch for image quality adjustment in a region between the printing toner images, and for measuring the density around the toner patch by the measuring means; and the measured toner A determination unit that determines whether or not to perform image quality adjustment using a density of a toner patch formed in a region between the printing toner images based on a density around the patch; and the determination unit performs the image quality adjustment. If it is determined to perform correction, the correction unit causes the measurement unit to measure the density of the toner patch formed in the region between the printing toner images, and uses the measurement result to correct the density of the toner image. And comprising.

  For example, if the image carrier is poorly cleaned, residual toner may remain on the image carrier. In this case, the toner patch contains residual toner, and the measuring means accurately acquires the toner patch density. Can not do it. If the measured density of the toner patch is inaccurate, image quality adjustment cannot be performed accurately.

  Therefore, when image quality adjustment is performed during image formation by the image forming unit, the control unit causes the measurement unit to measure the density around the toner patch formed in the region between the printing toner images transferred to the recording paper. If no toner remains on the image carrier, the density around the toner patch should be a measured value within a predetermined range. Therefore, the determining means determines whether the density between the printing toner images depends on the measurement result. It is determined whether or not to perform image quality adjustment using the density of the toner patch formed in the region. That is, the determination unit permits image adjustment during image formation by the image forming unit only when the image carrier is in a normal state. As a result, the image quality can be adjusted with high accuracy even during printing.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the determining unit performs image quality adjustment based on a density around a toner patch formed in a region between the printing toner images. If it is decided not to do so, the control means causes the image forming means to form a toner patch for adjusting image quality after the formation of the printing toner image, and the correction control means causes the measurement means to The density of the toner image is measured, and the density correction of the toner image is performed using the measurement result.

  According to this configuration, when the determination unit determines not to perform the image quality adjustment during image formation, the image quality adjustment can be performed with high accuracy by performing the image quality adjustment after the image formation on the recording paper is completed.

  A third aspect of the present invention is the image forming apparatus according to the first or second aspect, wherein the correction control means uses the density of a toner patch formed in a region between the printing toner images. When the density correction of the toner image is performed, the determination unit determines whether to perform the next image quality adjustment at a timing shorter than a predetermined image quality adjustment interval.

  For example, if the predetermined image quality adjustment interval is every 100 printed sheets, the correction control means performs correction using the density of the toner patch formed in the area between the printing toner images. The means determines that the image quality adjustment is performed every time the number of printed sheets exceeds 70, for example, as “a timing shorter than the predetermined image quality adjustment execution interval”. As another implementation condition, if the predetermined image quality adjustment execution interval is when the temperature inside the apparatus fluctuates by ± 10 ° C. from the set temperature, the determination means determines that “the image quality adjustment execution interval is greater than the predetermined image quality adjustment execution interval. As the “short timing”, for example, the image quality adjustment is determined when the apparatus temperature fluctuates ± 7 ° C. from the set temperature.

  As described above, when the correction control unit performs correction using the density of the toner patch formed in the region between the printing toner images, the reason why the determination unit determines that the subsequent image quality adjustment execution interval is short is the image This is because image quality adjustment performed during formation may be slightly less accurate than image quality adjustment performed after image formation. Therefore, when image quality adjustment is performed during image formation, the execution interval is shortened and the frequency of image quality adjustment is increased, so that the accuracy of image quality adjustment can be prevented from decreasing.

  When image quality adjustment is performed during image formation by the image forming means, the measurement means measures the density of the periphery of the toner patch formed in the area between the toner images transferred to the recording paper, and the toner image according to the measurement result By determining whether the image quality adjustment is performed using the toner patch formed in the area between the two, the image quality adjustment can be performed with high accuracy even during printing.

FIG. 2 is a cross-sectional view illustrating a schematic configuration of a printer. FIG. 2 is a functional block diagram illustrating an electrical configuration of a printer. FIG. 4 is a diagram illustrating an example of a toner patch. FIG. 4 is a diagram illustrating an example of a toner patch. The figure which showed the density | concentration measurement position by a density sensor. The flowchart which showed the flow of the calibration process.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this embodiment, a color printer is described as an example of the image forming apparatus, but the present invention can also be applied to a copying machine, a facsimile machine, and a multifunction machine having various functions. Furthermore, in this embodiment, a tandem color printer is described as an example, but other printing methods may be used as long as the image forming apparatus is an electrophotographic method.

  FIG. 1 is a cross-sectional view showing a schematic configuration of a tandem type printer 1 which is an example of an image forming apparatus according to the present invention. The printer 1 shown in FIG. 1 includes a paper feed unit 12 having a paper feed cassette 120 that is detachable from the apparatus main body 11 to store recording paper P, and a paper feed cassette 120 driven by the paper feed unit 12. A secondary transfer roller 137 that transfers the toner image onto the recording paper P while conveying the recording paper P fed out from the recording paper P, and fixing the toner image to the recording paper P onto which the toner image has been transferred by the secondary transfer roller 137. And a paper discharge unit 15 for discharging the recording paper P that has been subjected to the fixing process by the fixing device 14.

  The paper feeding unit 12 is provided with a pickup roller 121 at the upper left position of the paper feeding cassette 120 shown in FIG. 1, and the recording paper P stored in the paper feeding cassette 120 by the drive of the pickup roller 121 is one sheet at a time. Picked up and sent toward the secondary transfer roller 137.

  The image forming unit 13 includes an image forming unit 131K that forms a black toner image, an image forming unit 131C that forms a cyan toner image, an image forming unit 131Y that forms a yellow toner image, and an image that forms a magenta toner image. The image forming unit 131M, the intermediate transfer belt 136 onto which the toner image is transferred by the image forming units 131K, 131C, 131Y, and 131M, and the toner image on the intermediate transfer belt 136 are fed from the paper feeding cassette 120. And a secondary transfer roller 137 for further transferring to the recording paper P. Hereinafter, the image forming units 131K, 131C, 131Y, and 131M are collectively referred to as “image forming unit 131”.

  The image forming units 131 are sequentially arranged in the order of the image forming units 131K, 131C, 131Y, and 131M from the upstream side (the right side of the sheet of FIG. 1) to the downstream side. Each image forming unit 131 is positioned and attached to each device in the device main body 11 with a predetermined relative positional relationship.

  Each image forming unit 131 is provided with a photosensitive drum 132, and a charger 134 is provided to face each photosensitive drum 132. An exposure device 135 is provided downstream of the charger 134 in the rotation direction of the photosensitive drum 132 (the arrow direction in FIG. 1). The exposure device 135 irradiates the circumferential surface of the photosensitive drum 132 uniformly charged by the charger 134 with a light beam based on the image data. An electrostatic latent image is formed. A developing device 133 is provided further downstream of the exposure device 135 in the rotation direction of the photosensitive drum 132. The developing device 133 is supplied with a developing bias voltage from a power supply device (not shown) to supply toner from the toner container to the electrostatic latent image, and forms a toner image on the peripheral surface of the photosensitive drum 132.

  Further, each of the photosensitive drums 132 is provided with a cleaning device 20 that removes residual toner on the circumferential surface of the photosensitive drum 132 and cleans it. The peripheral surface of the photosensitive drum 132 cleaned by the cleaning device 20 is directed to the charger 134 for a new charging process.

  The intermediate transfer belt 136 is stretched between the driving roller 136 a and the driven roller 136 b so that the surface thereof is in contact with the peripheral surface of the photosensitive drum 132 at a position immediately above each image forming unit 131. A primary transfer roller 136 c is provided immediately above each photosensitive drum 132 via an intermediate transfer belt 136. Then, according to the traveling speed of the intermediate transfer belt 136 driven by the driving roller 136a, the respective toner images formed on the photosensitive drum 132 of each image forming unit 131 are superimposed on each other by the primary transfer roller 136c. Then, the image is transferred to the intermediate transfer belt 136, and a color toner image is formed on the surface of the intermediate transfer belt 136.

  A registration roller 145 for transporting the recording paper P to the nip portion is provided in the recording paper transport path from the paper feeding cassette 120 toward the nip portion of the secondary transfer roller 137 and the driving roller 136a. The registration roller 145 adjusts the recording paper conveyance timing to the nip portion of the secondary transfer roller 137 and the driving roller 136a, and then conveys the recording paper P to the nip portion. In this nip portion, the color toner image on the intermediate transfer belt 136 is transferred to the recording paper P by the secondary transfer roller 137, and a color toner image is formed on the recording paper P.

  Incidentally, an intermediate transfer belt cleaning device 160 is provided on the right side of the driven roller 136b in FIG. 1, and the toner remaining on the surface of the intermediate transfer belt 136 after the transfer of the toner image onto the recording paper P is removed. The intermediate transfer belt 136 that has been removed by the intermediate transfer belt cleaning device 160 and cleaned thereby is supplied to the photosensitive drum 132.

  The fixing device 14 performs a fixing process on the color toner image transferred to the recording paper P by the image forming unit 13. The fixing device 14 includes a heat roller 141 that is heated by an energized heating element, and a pressure roller 142 that is disposed so as to face the heat roller 141 and whose peripheral surface is pressed against the peripheral surface of the heat roller 141. . The color toner image transferred to the recording paper P by the secondary transfer roller 137 in the image forming unit 13 is fixed by heating when the recording paper P passes between the heat roller 141 and the pressure roller 142. Then, the paper is discharged to the paper discharge unit 15.

  Further, a density sensor 17 is disposed on the most downstream side of the intermediate transfer belt 136. The density sensor 17 detects the optical density of the toner image transferred onto the intermediate transfer belt 136. The density sensor 17 is, for example, a specular reflection type sensor that detects reflected light, an LED light source disposed at a predetermined angle with respect to a detection position on the surface of the intermediate transfer belt 136, a phototransistor as a light receiving element, and the like. Consists of. The toner image on the intermediate transfer belt 136 is irradiated with light from the LED light source, and the phototransistor detects the amount of reflected light, thereby measuring the optical density (hereinafter simply referred to as “density”) of the toner image. . The concentration sensor 17 converts the measurement result into an electric signal and outputs it to a control unit described later.

  FIG. 2 is a functional block diagram showing an electrical configuration of the printer 1 shown in FIG. The printer 1 includes a control unit 30, a storage unit 31, an image memory 32, an image processing unit 33, an image forming unit 13, a density sensor 17, an input operation unit 34, and a network I / F unit 35. In addition, the same code | symbol is attached | subjected to the same component as demonstrated in FIG. 1, and detailed description is abbreviate | omitted.

  The storage unit 31 stores programs and data for realizing various functions of the printer 1. The image memory 32 temporarily stores image data transmitted from an external device (not shown) via the network I / F unit 35. The image processing unit 33 performs image processing such as image correction and enlargement / reduction on the image data input via the network I / F unit 35.

  The input operation unit 34 is a power key, a start button, a setting key for setting various functions, and the like, and outputs an operation signal to the control unit 30. The network I / F unit 35 includes a communication module such as a LAN board, and transmits / receives various data to / from an external device via a network (not shown) connected to the network I / F unit 35.

  The control unit 30 is configured by a CPU (Central Processing Unit) or the like, and executes processing based on a predetermined program in accordance with an input instruction signal or the like, and outputs an instruction signal to each functional unit, data transfer, or the like. And controlling the printer 1 in an integrated manner. The control unit 30 includes a calibration execution determination unit 301, a toner patch formation control unit 302, a calibration execution control unit 303, and a calibration execution unit 304. The calibration execution determination unit 301 determines whether to perform calibration according to a predetermined condition. The predetermined conditions are, for example, when the ambient temperature or humidity of the printer 1 changes by a predetermined value or more, when the number of printed sheets exceeds a predetermined number, and the calibration execution determining unit 301 appropriately determines according to such conditions. Image quality can be maintained by determining execution of calibration.

  The toner patch formation control unit 302 controls the image forming unit 13 to form a toner patch when the calibration execution determination unit 301 determines to execute calibration. When the calibration execution determination unit 301 determines to execute calibration while the image forming unit 13 is printing on the recording paper, the toner patch formation control unit 302 transfers the image forming unit 13 to the recording paper. A toner patch is formed in a region between toner images to be printed.

  FIG. 3 illustrates a toner patch that the image forming unit 13 forms on the intermediate transfer belt 136 when the calibration execution determining unit 301 determines to execute calibration while the image forming unit 13 is printing on a recording sheet. It is the figure which showed the example of. Reference numeral 41 denotes a toner image (print page) transferred to the recording paper, and reference numeral 42 denotes a toner patch. At least one toner patch 42 is formed in the area between the print pages 41.

  FIG. 4 is a diagram illustrating an example of a patch pattern that the image forming unit 13 forms on the intermediate transfer belt 136 when the calibration execution determining unit 301 determines to execute calibration after printing of the image forming unit 13 is completed. This is an example of a patch pattern by calibration conventionally performed. When calibration is executed during printing on recording paper, conventionally, the image forming unit 13 temporarily suspends printing and forms a toner patch as shown in FIG. Since the printing end time is delayed by that amount, the user is kept waiting, causing inconvenience.

  However, when the calibration execution determination unit 301 determines execution of calibration during printing, the image forming unit 13 interrupts printing by forming a toner patch using an area between the print pages 41. Calibration can be performed without any problem.

  The calibration execution control unit 303 causes the density sensor 17 to measure the density around the toner patch 42 when the toner patch 42 is formed in the area between the print pages 41 as shown in FIG. It is determined whether or not to perform calibration using the toner patch 42 formed between 41. The reason for determining whether or not to perform calibration using the toner patches 42 formed between the print pages 41 is that residual toner may remain on the belt if the cleaning state of the intermediate transfer belt 136 is poor. This is because it may happen that the toner patch 42 contains residual toner and the density sensor 17 cannot accurately obtain the density of the toner patch 42. If the density of the toner patch 42 is not accurately measured, calibration cannot be performed with high accuracy, leading to a reduction in image quality.

  Further, when the density sensor 17 measures the density of the toner patch 42, a process for comparing the density of the toner patch 42 with the density of the surface of the intermediate transfer belt 136 around the toner patch 42 is performed. For this reason, if there is residual toner around the toner patch 42 or if the intermediate transfer belt 136 has scratches due to the passage of time, the measurement accuracy deteriorates.

  Therefore, in order to obtain a reliable measurement result from the density sensor 17, the calibration execution control unit 303 causes the toner patch to the density sensor 17 when the toner patch 42 is formed in an area between the print pages 41. The density around 42 is measured, and if the density around the toner patch 42 is within a specified range, it is determined that calibration is to be performed. That is, calibration during printing is performed only when the surface state of the intermediate transfer belt 136 on which the toner patch 42 is formed is normal.

  FIG. 5 is a diagram showing a position where the density sensor 17 measures the density. When the toner patch 42 is formed in the area between the print pages 41, the calibration execution control unit 303 causes the density sensor 17 to measure the density around the toner patch 42 (for example, the area 43). In addition, the calibration execution control unit 303 stores in advance an internal memory or the like (not shown) including a specified range including the measurement value of the density sensor 17 when there is no residual toner or scratches on the surface of the intermediate transfer belt 136. If the density of the area 43 is within the specified range, it is determined that the calibration is performed using the density of the toner patch 42 formed in the area between the print pages 41. On the other hand, if the density of the area 43 is outside the specified range, it is determined that calibration using the density of the toner patch 42 formed in the area between the print pages 41 is not performed.

  The calibration execution unit 304 causes the density sensor 17 to measure the density of the toner patch formed by the image forming unit 13 and corrects the developing bias voltage using the measurement result, or a laser light source when the printer 1 is a laser printer. Calibration is performed by correcting the output value.

  FIG. 6 is a flowchart showing the flow of calibration processing in the present embodiment. First, the calibration execution determination unit 301 determines whether it is time to perform calibration (step S11). If it is determined that it is time to perform calibration (step S11; YES) and the image forming unit 13 is printing on a recording sheet (step S12; YES), the toner patch formation control unit 302 is as shown in FIG. Then, the toner patch 42 is formed in the area between the print pages 41 by the image forming unit 13 (step S13).

  Then, the calibration execution control unit 303 causes the density sensor 17 to measure the density around the toner patch 42 and determines whether the density around the toner patch 42 is within the specified range (step S14). If it is within the specified range (step S14; YES), the calibration execution unit 304 causes the density sensor 17 to measure the density of the toner patch 42 formed in the area between the print pages 41 and executes calibration (step S14; YES). Step S15).

  On the other hand, the peripheral density of the toner patch 42 formed in the area between the print pages 41 when the image forming unit 13 is on standby (that is, printing on recording paper is not performed. Step S12; NO) is outside the specified range. In some cases (step S14; NO), the calibration execution unit 304 causes the image forming unit 13 to form a normal patch pattern as shown in FIG. 4 (after printing, if printing is in progress), and the density of each toner patch. Is measured by the density sensor 17, and calibration is executed (step S16).

  As described above, when the calibration is performed while the image forming unit 13 is printing, the density of the periphery of the toner patch formed in the area between the print pages is measured, and the print page is determined according to the measurement result. By determining whether or not to perform calibration using a toner patch formed in the area between the two, calibration can be performed with high accuracy even during printing.

  The present invention is not limited to the configuration of the present embodiment, and various modifications can be made. When the image forming unit 13 is printing and calibration is performed using the density of the toner patch formed in the area between the print pages, the interval for performing the next calibration is shortened. Also good. For example, if the predetermined calibration execution interval is every 100 printed sheets, and calibration is performed during printing, the calibration execution determination unit 301 may, for example, print the number of printed sheets as the next calibration timing. The execution of calibration is determined every time 70 sheets are exceeded. As another implementation condition, if the predetermined calibration interval is when the temperature inside the apparatus fluctuates ± 10 ° C. from the set temperature, the calibration execution determination unit 301 may, for example, When the temperature inside the apparatus fluctuates by ± 7 ° C. from the set temperature, the execution of calibration is determined. It is known that the calibration performed during printing is slightly less accurate than the calibration performed by forming the normal patch pattern shown in FIG. Therefore, when calibration is performed during printing, the execution interval is shortened and the execution frequency is increased to prevent the calibration accuracy from being lowered.

  Alternatively, the number of continuous calibrations performed during printing is limited, and if the number of continuous calibrations during printing exceeds a predetermined number, the next calibration is performed by forming a normal patch pattern after printing is completed. Calibration may be performed.

1 Printer (image forming device)
DESCRIPTION OF SYMBOLS 11 Apparatus main body 12 Paper feed part 13 Image formation part (image formation means)
136 Intermediate transfer belt (image carrier)
14 Fixing device 15 Paper discharge unit 17 Density sensor (measuring means)
30 Control unit 301 Calibration execution determination unit (determination means)
302 Toner patch formation control unit (control unit)
303 Calibration execution control unit (determination unit)
304 Calibration execution unit (correction control means)
31 Storage Unit 32 Image Memory 33 Image Processing Unit 34 Input Operation Unit 35 Network I / F Unit

Claims (3)

An image forming means for forming a toner image on an image carrier by applying a developing bias voltage to the developing device and transferring the toner image to a conveyed recording paper to form an image;
Measuring means for measuring the toner density on the image carrier;
Determination means for determining whether or not to perform image quality adjustment of the toner image according to a predetermined condition;
If the determination unit determines that the image quality adjustment of the toner image is to be performed during the image formation by the image forming unit, the image quality to the image formation unit during the formation of the printing toner image to be transferred to the recording paper Control means for forming an adjustment toner patch in a region between the printing toner images, and causing the measurement means to measure a density around the toner patch;
Determining means for determining whether or not to perform image quality adjustment using the density of the toner patch formed in a region between the printing toner images based on the measured density around the toner patch;
When the determination unit determines to perform the image quality adjustment, the measurement unit is caused to measure the density of a toner patch formed in a region between the printing toner images, and the measurement result is used to measure the toner image. Correction control means for correcting the density of
An image forming apparatus. When the determining unit determines not to perform image quality adjustment based on the density around the toner patch formed in the region between the printing toner images, the control unit performs the printing after the printing toner image is formed. The image forming unit forms an image quality adjustment toner patch, and the correction control unit causes the measurement unit to measure the density of the toner patch and uses the measurement result to correct the density of the toner image. The image forming apparatus according to claim 1, which is performed.   When the correction control unit performs density correction of the toner image using the density of the toner patch formed in the area between the printing toner images, the determination unit performs the predetermined image quality adjustment. The image forming apparatus according to claim 1, wherein execution of the next image quality adjustment is determined at a timing shorter than the interval.

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