JP2010072585A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a high-quality image while preventing hue fluctuation while maintaining density correction accuracy at a high level, even when a distance between a patch image formed in an image carrier and a density sensor is changed. <P>SOLUTION: An irradiation light amount calculating part 93 calculates an amount of light to be irradiated on a part where the patch image 75 is formed in consideration that the influence of a distance deviation between a range-finding value obtained by a range-finding sensor 71 and a predetermined reference distance is canceled, based on the range-finding value and the predetermined reference distance, and feedback-outputs the calculation result to the density sensor 73. On the basis of the calculation result, the density sensor 73 irradiates the part where the patch image 75 is formed with light with the amount of irradiation light calculated by the irradiation light amount calculating part 93. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using an electrophotographic process such as a copying machine, a printer, or a facsimile machine, and in particular, causes a variation in distance between a patch image forming portion on an image carrier and a density sensor. The present invention also relates to an image forming apparatus capable of obtaining a high quality image while maintaining density correction accuracy at a high level and suppressing color fluctuation.

  In a color-compatible image forming apparatus using an electrophotographic process such as a copying machine, a printer, or a facsimile machine, calibration (density correction) plays an extremely important role for matching colors. Therefore, there is a strong demand for improving the correction accuracy.

  As one approach to satisfying such a demand, the applicant of the present application forms on each photosensitive drum on the downstream side of each developing unit and on the upstream side of each transfer roller in the rotation direction of the photosensitive drum for each color. While irradiating each reference image with measurement light, a density sensor that detects the amount of reflected light from the reference image is arranged, and in the vicinity of the downstream side of the photosensitive drum arranged on the most downstream side in the traveling direction of the intermediate transfer belt, A color misregistration detection sensor that detects the position of the reference image for color misregistration correction that is formed in each image forming unit and transferred onto the intermediate transfer belt is arranged, and density and color misregistration correction is performed based on the detection results of both detection sensors. Has proposed an image forming apparatus provided with a control means for performing the above in parallel (Patent Document 1). According to the technique of Patent Document 1, it is possible to provide a tandem type color image forming apparatus capable of performing density correction at the time of calibration execution with high accuracy and reducing the calibration execution time.

By the way, for example, a patch image for density detection is formed on an image carrier such as an intermediate transfer belt, and light irradiation is performed on the formation area of the patch image. In the conventional density correction technology using the density sensor, which is read by the density sensor and correcting the toner amount to an appropriate value based on the read image density or the like, the thickness variation in the image carrier or the image carrier is removed. There may be a variation in the distance between the density sensor and the patch image forming portion on the image carrier due to the shaft runout of the supporting roller. In such a case, there is a possibility that the density correction value may include an error if the amount of light applied to the patch image forming portion is kept constant regardless of whether or not the distance varies.
Japanese Patent Laid-Open No. 2008-170669

  In the conventional density correction technology using a density sensor, if the distance between the patch image formation location on the image carrier and the density sensor fluctuates, the density correction value may contain an error. It is a point.

  The present invention pays attention to the above-mentioned problems of the prior art, and maintains the density correction accuracy at a high level even when the distance between the patch image forming portion on the image carrier and the density sensor varies. In order to obtain a high-quality image while suppressing color variation, a patch image forming unit that forms a patch image for toner amount detection on an image carrier, and a patch that acquires the density of the formed patch image An image density acquisition unit, an actual toner amount calculation unit that calculates an actual toner amount based on the acquired density of the patch image, an image density based on the determined actual toner amount, and a predetermined reference toner amount An image forming apparatus configured to include an image density correcting unit that corrects, and irradiates the patch image forming portion with light, and detects the density related to the patch image forming portion. Based on a reflection type density sensor, a patch image formation location, a distance measuring sensor that measures the distance between the density sensor, a distance value by the distance sensor, and a predetermined reference distance, In consideration of canceling the influence of the distance deviation between the two, an irradiation light amount calculation unit that calculates the irradiation light amount to the patch image forming portion and outputs the calculation result to the density sensor as feedback The density sensor is characterized in that light irradiation is performed on the patch image forming portion with the irradiation light amount calculated by the irradiation light amount calculation unit.

  In the image forming apparatus according to the present invention, the patch image forming unit forms a patch image for toner amount detection on the image carrier. Then, the patch image density acquisition unit acquires the density of the formed patch image. The actual toner amount calculating means obtains the actual toner amount based on the acquired density of the patch image. Next, the image density correction unit operates to correct the image density based on the obtained actual toner amount and a predetermined reference toner amount.

  In such an image density correction technique, when a variation in the distance between the patch image formation location on the image carrier and the density sensor occurs, the density correction value may include an error.

  Therefore, the distance measuring sensor measures the distance between the patch image forming portion and the density sensor. The light reflection type density sensor irradiates the patch image forming portion with light and detects the density related to the patch image forming portion. The irradiation light amount calculation unit considers to cancel the influence of the distance deviation between the two based on the distance measured by the distance sensor and a predetermined reference distance, The amount of irradiation light is calculated, and the calculation result is fed back to the concentration sensor. In response, the density sensor irradiates the patch image forming portion with the irradiation light amount calculated by the irradiation light amount calculation unit. Therefore, even if the distance between the patch image formation location on the image carrier and the density sensor fluctuates, for example, with the irradiation light amount calculated in consideration of canceling the influence of such a distance deviation, As a result of light irradiation to the patch image formation location in real time and error mixing into the density correction value due to distance fluctuations being eliminated, the patch image formation location on the image carrier and the density sensor Even when the distance between the two changes, the density correction accuracy can be maintained at a high level, and the color change can be suppressed to obtain a high-quality image.

  Even when the distance between the patch image formation location on the image carrier and the density sensor changes, the density correction accuracy is maintained at a high level, and the color fluctuation is suppressed to obtain a high-quality image. For this purpose, the distance between the patch image formation location and the density sensor is measured, and the patch image formation location is irradiated with light, while the density at the patch image formation location is detected. The patch image is formed in consideration of canceling the influence of the distance deviation between the light reflection type density sensor, the distance measured by the distance sensor, and a predetermined reference distance. This is realized by a configuration related to a combination with an irradiation light amount calculation unit that calculates an irradiation light amount to a location and feedback-outputs the calculation result to the density sensor.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings.

[Machine Configuration in Image Forming Apparatus]
FIG. 1 is a schematic explanatory diagram of a mechanical configuration in an image forming apparatus according to an embodiment of the present invention. FIG. 2 is an example of a patch image for detecting the amount of toner formed on an intermediate transfer belt, and the traveling direction of the intermediate transfer belt. It is explanatory drawing which shows the mutual positional relationship of the ranging sensor and density sensor with respect to.
An image forming apparatus according to an embodiment of the present invention is, for example, a tandem type color printer, and includes a paper feed cassette 10, a transfer transport unit 20 disposed above the paper feed cassette, and an upper part of the transfer transport unit 20. The image forming unit 30 disposed, the fixing unit 40 disposed on the left side of the sheet with respect to the transfer conveyance unit 20, and the first conveyance for guiding the paper P set in the paper feed cassette 10 to the transfer conveyance unit 20. A path 50 and a second transport path 60 for guiding the paper P after the fixing process by the fixing unit 40 to the discharge tray 80 are provided.

  The paper feed cassette 10 contains paper P therein, picks up the paper P contained therein one by one by a not-shown paper feed roller, and discharges it to the first transport path 50 side.

  The image forming unit 30 includes image forming units 30K, 30Y, 30M, and 30C that form toner images of black (K), yellow (Y), magenta (M), and cyan (C), respectively. Since the image forming units 30K to 30C have the same configuration, only the image forming unit 30K will be described below, and descriptions of the other image forming units 30Y, 30M, and 30C will be omitted.

  The image forming unit 30K includes a photosensitive drum 31, a charging unit 32, an exposure unit 33, a developing unit 34, and a cleaner unit 35. The photosensitive drum 31 is a cylindrical member, and rotates in a clockwise direction (A direction in the drawing) by receiving a driving force from a motor (not shown). The exposure unit 33 includes a light source such as a light emitting diode or a laser diode. The exposure unit 33 irradiates the photosensitive drum 31 charged by the charging unit 32 with an optical signal modulated according to image data, thereby An electrostatic latent image is formed. The developing unit 34 includes a toner box 341 that stores black (K) toner, and supplies K toner to the photosensitive drum 31 on which the electrostatic latent image is formed to form a K toner image. The K toner image formed on the photosensitive drum 31 is transferred to the paper P or the intermediate transfer belt 21 by the transfer roller 22. The cleaner unit 35 removes toner adhering to the surface of the photosensitive drum 31 to which the K toner image is transferred.

  The transfer conveyance unit 20 includes an intermediate transfer belt (corresponding to an “image carrier” of the present invention) 21, a transfer roller 22, a right roller 23, and a left roller 24. The right roller 23 is disposed below the image forming unit 30K, and the left roller 24 is disposed below the image forming unit 30C. The intermediate transfer belt 21 is an endless belt member stretched between the right roller 23 and the left roller 24, and is rotated counterclockwise (B direction in the drawing) by the right and left rollers 23 and 24. It is rotated at a constant speed. The intermediate transfer belt 21 is made of a heat-resistant resin material such as polyimide resin. Four transfer rollers 22 are disposed on the inner peripheral side of the intermediate transfer belt 21 at positions facing the four photosensitive drums 31, respectively. The transfer roller 22 is made of a conductive rubber material or the like, and has a function of transferring each color toner image formed on the photosensitive drum 31 onto the paper P or the intermediate transfer belt 126.

  Below the outer peripheral side of the intermediate transfer belt 21, as shown in FIGS. 1 and 2, a distance measuring sensor 71 and a density sensor 73 are arranged at a substantially central position in the width direction (perpendicular to the paper surface) of the intermediate transfer belt 21. They are provided adjacent to each other at corresponding positions. The distance measuring sensor 71 is composed of, for example, a light reflection type photosensor, and has a function of measuring the distance between the location where the toner image detection patch image 75 is formed and the density sensor 73. On the other hand, the density sensor 73 is composed of, for example, a light-reflective photosensor, and irradiates light to the formation area of the patch image 75, while detecting the density related to the formation area of the patch image 75, thereby detecting the intermediate transfer belt 21. It has a function of acquiring the density of the patch image 75 formed above.

  The fixing unit 40 includes a heat shielding box 41, a fixing roller 42 with a built-in heater, and a pressure roller 43, and heats and conveys the paper P on which the toner image is formed, thereby fixing the toner image on the paper P.

[Functional Block Diagram showing Electrical Configuration in Image Forming Apparatus]
FIG. 3 is a functional block diagram centering on the control unit of the image forming apparatus.

  As shown in FIG. 3, a distance measuring sensor 71, a density sensor 73, an image forming unit 30, an image memory 81, and a scanner unit 83 are connected to the main control unit 85.

  The scanner unit 83 reads an image of a document with a photoelectric conversion element such as a CCD, and transfers the obtained image data of the document to the main control unit 85. The image memory 81 stores document image data read by the scanner unit 83. The image forming unit 30 reads the image data stored in the image memory 81 and prints it on the paper P.

  Even when a variation in the distance between the location where the patch image 75 is formed on the image carrier (intermediate transfer belt 21) and the density sensor 73 occurs, the density correction accuracy is maintained at a high level, and the color fluctuations. In order to achieve the object of obtaining a high-quality image while suppressing image quality, the main control unit 85 that controls the image forming apparatus is a patch image forming unit (corresponding to the “patch image forming unit” of the present invention) 87. A patch image density acquisition unit (corresponding to “patch image density acquisition unit” of the present invention) 89, an actual toner amount calculation unit (corresponding to “actual toner amount calculation unit” of the present invention) 91, and An irradiation light amount calculation unit 93 and an image density correction unit (corresponding to “image density correction unit” of the present invention) 95 are provided.

  The patch image forming unit 87 has a function of forming a toner image detection patch image on the intermediate transfer belt 21. In practice, upon receipt of a patch image formation command from the patch image forming unit 87, the image forming unit 30 forms a patch image 75 on the intermediate transfer belt 21.

The patch image density acquisition unit 89 has a function of receiving the density detection signal from the density sensor 73 and acquiring the density of the patch image 75 for detecting the toner amount.
The actual toner amount calculation unit 91 has a function of obtaining the actual toner amount based on the obtained density of the patch image 75 for detecting the toner amount.

The irradiation light amount calculation unit 93 takes into account the cancellation of the influence of the distance deviation between the two based on the distance measured by the distance sensor 71 and a predetermined reference distance. The irradiation light quantity is calculated, and the calculation result is fed back to the density sensor 73.
The image density correction unit 95 has a function of correcting the image density by setting a developing bias for realizing the reference toner amount based on the actual toner amount and the reference toner amount. The image density correction unit 95 stores and holds the relationship between the output value of the density sensor 73 and the toner adhesion amount as a toner adhesion amount table, while the toner concentration determined from the toner adhesion amount, the charge amount, A density correction table in which each parameter value used for density correction, such as a development bias characteristic value or exposure amount, is stored and held.
[Operation of Image Forming Apparatus]
Next, the operation of the image forming apparatus according to the embodiment of the present invention will be described with reference to FIG.

FIG. 4 is an operation flowchart relating to density correction in the image forming apparatus according to the embodiment of the present invention.
As a premise, the density correction operation shown in FIG. 4 is executed at an appropriate timing determined in advance, for example, when the image forming apparatus is turned on, in the sleep mode, or every time 500 sheets are printed. With things.

In step S <b> 11, the patch image forming unit 87 forms a toner image detection patch image 75 for each color of MCYB on the intermediate transfer belt 21 as shown in FIG. 2.
In step S <b> 12, the distance measuring sensor 71 measures the distance between the location where the toner image detection patch image 75 is formed and the density sensor 73, and feeds back the distance measured value to the irradiation light amount calculation unit 93.

  In step S <b> 13, the irradiation light amount calculation unit 93 considers canceling the influence of the distance deviation between the two based on the distance measured by the distance sensor 71 and a predetermined reference distance. The amount of light irradiated to the formation location of is calculated. More specifically, when the distance measured by the distance measuring sensor 71 is smaller than the reference distance, the irradiation light amount calculation unit 93 reduces the amount of irradiation light on the patch image forming portion, while comparing with the reference distance. When it is large, the amount of light applied to the patch image forming portion is calculated so as to increase the amount of light applied to the patch image forming portion.

  In step S <b> 14, the density sensor 73 performs light irradiation on the formation location of the patch image 75 with the irradiation light amount obtained in step S <b> 13, while detecting and acquiring the density value related to the formation location of the patch image 75. It should be noted that when acquiring the density value relating to the formation location of the patch image 75, the density value (intermediate transfer belt 21) relating to the location where the patch image 75 is not formed is the same location as the formation location of the patch image 75. (Hereinafter, referred to as “background value”), or the patch image 75 is removed by performing a cleaning process after the patch image 75 is formed. A configuration in which the background value is acquired, and the density value relating to the formation location of the patch image 75 from which the influence of the background has been removed is obtained by subtracting the background value from the density value relating to the location where the patch image 75 is formed. It may be adopted. In this way, even if the surface deterioration of the intermediate transfer belt 21 with time or the like occurs, it is possible to eliminate the error mixing into the density correction value due to the change in the surface state. .

In step S15, the image density correction unit 95 executes density correction processing according to a predetermined procedure. That is, first,
The actual toner amount calculation unit 91 refers to the toner adhesion amount table in which the density value of the patch image 75 detected and acquired in step S14 and the relationship between the density of the patch image 75 and the toner adhesion amount are stored. The actual toner amount is obtained using a known method such as an up method. The actual toner amount calculation process is executed for each color of MCYB. Next, the image density correction unit 95, for example, based on the obtained actual toner amount and a predetermined reference toner amount, for example,
In consideration of matching the actual toner amount with the reference toner amount, density correction processing is executed by setting an appropriate development bias.
In step S16, the main control unit 85 monitors whether the calibration (density correction) in step S15 has been completed. As a result of this monitoring, when it is determined that the calibration is not yet finished, the main control unit 85 returns the process flow to step S11 and sequentially executes the following processes. On the other hand, when it is determined that the calibration is completed, the main control unit 85 ends a series of processes related to density correction.
As described above in detail, in the image forming apparatus according to the embodiment of the present invention, the irradiation light amount calculation unit 93 is based on the distance measurement value obtained by the distance measurement sensor 71 and a predetermined reference distance. In consideration of canceling the influence of the distance deviation, the amount of irradiation light to the formation location of the patch image 75 is calculated, the calculation result is fed back to the density sensor 73, and the density sensor 73 receives the calculation result. Light irradiation is performed on the formation location of the patch image 75 with the irradiation light amount calculated by the calculation unit 93. Therefore, even if the distance between the position where the patch image 75 is formed on the image carrier (intermediate transfer belt 21) and the density sensor 73 fluctuates, it is considered to cancel the influence of such a distance deviation. As a result of light irradiation to the formation portion of the patch image 75 in real time with the calculated irradiation light amount, and error mixing into the density correction value caused by the distance fluctuation is eliminated in advance, the image carrier (intermediate) Even when the distance between the location where the patch image 75 is formed on the transfer belt 21) and the density sensor 73 is varied, the density correction accuracy is maintained at a high level, and the color variation is suppressed to achieve high image quality. An image can be obtained.
[Others]
The present invention is not limited to the above-described embodiments, and can be appropriately changed without departing from the gist of the invention read from the claims and the entire specification or the technical idea, and image formation accompanied by such changes The apparatus is also included in the scope of the technical scope of the present invention.

That is, for example, in the embodiment of the present invention, the distance measuring sensor 71 and the density sensor 73 have been described by way of an example in which the distance measuring sensor 71 and the density sensor 73 are arranged at a position substantially corresponding to the center of the intermediate transfer belt 21 in the width direction. The distance measuring sensor 71 and the density are not limited to examples, and are arranged at appropriate positions in consideration of facing the patch image in correspondence with the toner image detection patch image formation location on the intermediate transfer belt 21. The sensor 73 may be disposed.
Further, in the embodiments of the present invention, the present invention has been described with reference to an example in which the present invention is applied to a tandem color printer. However, the present invention is not limited to such embodiments, and the present invention is applied to an image carrier. The present invention can be applied as it is to a color printer that forms a toner image of each color and directly transfers the formed toner image of each color onto a sheet. In this case, it goes without saying that the image carrier is an intermediate transfer roller, and patch image density acquisition may be performed on the patch image formed on the intermediate transfer roller.

1 is a schematic explanatory diagram of a mechanical configuration in an image forming apparatus according to an embodiment of the present invention. FIG. 4 is an explanatory diagram illustrating an example of a toner image detection patch image formed on an intermediate transfer belt and a mutual positional relationship between a distance measuring sensor and a density sensor with respect to a traveling direction of the intermediate transfer belt. 2 is a functional block diagram centering on a main control unit of the image forming apparatus. FIG. FIG. 7 is an operation flowchart relating to density correction in the image forming apparatus according to the embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 30 Image formation part 71 Distance sensor 73 Density sensor 75 Patch image for toner amount detection 85 Main control part 87 Patch image formation part (patch image formation means)
89 Patch image density acquisition unit (patch image density acquisition means)
91 Actual toner amount calculation unit (actual toner amount calculation means)
93 Irradiation light quantity calculation unit 95 Image density correction unit

Claims (6)

Patch image forming means for forming a patch image for detecting the toner amount on the image carrier, patch image density acquiring means for acquiring the density of the formed patch image, and actual toner based on the density of the acquired patch image An image forming apparatus comprising: an actual toner amount calculating unit that calculates an amount; and an image density correcting unit that corrects the image density based on the determined actual toner amount and a predetermined reference toner amount. There,
A light-reflective density sensor that detects the density of the patch image forming portion while irradiating the patch image forming portion with light;
A distance measuring sensor for measuring a distance between the patch image forming portion and the density sensor;
Based on the distance measured by the distance sensor and a predetermined reference distance, in consideration of canceling the influence of the distance deviation between the two, calculating the irradiation light amount to the formation location of the patch image, An irradiation light amount calculation unit that feedback outputs the calculation result to the density sensor;
Further comprising
In the density sensor, with the irradiation light amount calculated by the irradiation light amount calculation unit, light irradiation is performed on the patch image forming portion.
An image forming apparatus. The image forming apparatus according to claim 1,
The distance measuring sensor is provided on the upstream side of the density sensor with respect to the formation location of the patch image.
An image forming apparatus. The image forming apparatus according to claim 1, wherein:
The irradiation light amount calculation unit
When the distance measured by the distance measuring sensor is small compared to the reference distance, the amount of light applied to the patch image forming portion is reduced. On the other hand, when the distance measured is large compared to the reference distance, the patch image forming portion is moved to. To calculate the irradiation light amount to the formation position of the patch image so as to increase the irradiation light amount of
An image forming apparatus. The image forming apparatus according to any one of claims 1 to 3,
The patch image density acquisition means includes
In obtaining the density of the patch image, the patch image formation location in which the influence of the background is removed by subtracting the background value relating to the same location as the formation location from the density value relating to the patch image formation location. To obtain the density value according to
An image forming apparatus. An image forming apparatus according to any one of claims 1 to 4,
The image forming apparatus is a tandem color printer,
The image carrier is an intermediate transfer belt,
The density acquisition of the patch image is performed on the patch image formed on the intermediate transfer belt.
An image forming apparatus. An image forming apparatus according to any one of claims 1 to 4,
The image forming apparatus is a color printer that forms a toner image of each color on the image carrier and transfers the formed toner image of each color onto paper.
The image carrier is an intermediate transfer roller,
The density acquisition of the patch image is performed on the patch image formed on the intermediate transfer roller.
An image forming apparatus.