JP2014219459A - Image forming apparatus and planarizing method of sheet surface - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve reading accuracy of a reference image during image quality adjustment.SOLUTION: An image forming apparatus includes an image forming unit that forms a reference image for image quality adjustment on a sheet, a reading unit that reads the reference image, a planation unit that planarizes the sheet surface of the sheet at a reading position by the reading unit, a measurement unit that measures a height position of the sheet surface at the reading position, and a control unit that determines conditions of the planarization according to the height position (step S9) and causes the planation unit to planarize the sheet surface with the conditions (step S10 and S1).

Description

  The present invention relates to an image forming apparatus and a sheet surface planarization method.

  An electrophotographic image forming apparatus forms a reference image for image quality adjustment on a sheet, changes image formation conditions according to a read value obtained by reading the reference image, and adjusts to a constant image quality. ing.

When the reference image is read, if the height position of the paper surface fluctuates due to paper curling, waving, fluttering, etc., the read value varies, and the image quality cannot be adjusted accurately.
Conventionally, the peripheral speed of the paper transport roller is adjusted (for example, refer to Patent Document 1), or an airflow flowing in the transport direction from the paper surface (for example, refer to Patent Document 2), and the height position of the paper surface The fluctuation of was suppressed.
Similarly, in order to suppress fluctuations in the height position, a guide plate is provided below the paper, and a gap through which the paper can pass at the reading position is narrowed by the guide plate (see, for example, Patent Document 3), or a line for reading a reference image In some cases, the sheet is brought into contact with the reading surface of the sensor.

JP 2009-37134 A JP 2010-14805 A JP 2010-145605 A

  However, depending on the conditions of the peripheral speed of the transport roller and the wind speed of the airflow, the transport of the paper may become unstable, and on the contrary, the reading value may vary greatly. Even if the conditions are optimized so that the sheet can be conveyed at a constant speed, the height position of the sheet surface may still fluctuate due to changes in environmental conditions such as temperature and humidity, and it is difficult to optimize the conditions.

Further, in the method of narrowing the gap through which the paper passes by the guide plate, the resistance of the paper during conveyance increases. As a result, the transportability at a constant speed is lowered, and the fluctuation of the reading value is also increased.
When the sheet is brought into contact with the reading surface of the line sensor, the reading surface tends to become dirty. In particular, when the paper is provided with a contamination-preventing coating layer, the coating layer may be peeled off due to friction with the reading surface, and may be read as streak noise, and the reading accuracy is significantly reduced.

  An object of the present invention is to improve the reading accuracy of a reference image during image quality adjustment.

According to the invention of claim 1,
An image forming unit that forms a reference image for image quality adjustment on paper;
A reading unit for reading the reference image;
A flattening unit for flattening the paper surface of the paper at a reading position by the reading unit;
A measurement unit for measuring the height position of the paper surface at the reading position;
A control unit that determines planarization conditions according to the height position, and planarizes the sheet surface under the conditions by the planarization unit;
An image forming apparatus is provided.

According to invention of Claim 2,
The control unit determines the planarization condition according to the height position and the type of paper used for forming the reference image.
An image forming apparatus according to claim 1 is provided.

According to invention of Claim 3,
The flattening unit includes two transport rollers positioned before and after the reading position in the paper transport direction, and planarizes the paper surface of the paper to be transported by adjusting the peripheral speed of each transport roller,
The control unit determines a condition of a peripheral speed of the transport roller as the planarization condition.
An image forming apparatus according to claim 1 or 2 is provided.

According to invention of Claim 4,
The flattening unit includes an air blowing unit, and air is blown against the reading position by the air blowing unit to flatten the paper surface.
The control unit determines the presence or absence of blowing by the air blowing unit and the condition of wind pressure at the time of blowing as the planarization condition,
An image forming apparatus according to claim 1 or 2 is provided.

According to the invention of claim 5,
The flattening unit includes a plurality of the air blowing units arranged in the main scanning direction of the paper,
The control unit divides the sheet surface in the main scanning direction according to the arrangement position of each air spray unit to set a plurality of areas, and for each area, the presence or absence of spraying by each air spray unit and the wind pressure at the time of spraying Determine the conditions of
An image forming apparatus according to claim 4 is provided.

According to the invention of claim 6,
The control unit further divides the area set by dividing in the main scanning direction and further sets the plurality of areas by dividing the area in the sub-scanning direction. Determine the wind pressure conditions of the
An image forming apparatus according to claim 5 is provided.

According to the invention of claim 7,
The flattening unit includes a conveyance belt that conveys the sheet at the reading position and a charging roller that charges the conveyance belt, and applies a voltage to the charging roller to charge the conveyance belt and convey the sheet to be conveyed. By electrostatically adsorbing to the conveyor belt, the paper surface is flattened,
The control unit determines a voltage condition to be applied to the charging roller as the planarization condition.
An image forming apparatus according to claim 1 or 2 is provided.

According to the invention described in claim 8,
The control unit determines the voltage condition for each position of the paper in the sub-scanning direction.
An image forming apparatus according to claim 7 is provided.

According to the invention of claim 9,
A step of measuring the height position of the paper surface at a reading position where a reference image for image quality adjustment is read;
Determining a peripheral speed condition of two transport rollers positioned before and after the reading position in the paper transport direction according to the height position;
Rotating the transport roller according to the determined condition to planarize a sheet surface of the sheet on which the reference image is formed;
Is provided.

According to the invention of claim 10,
A step of measuring the height position of the paper surface at a reading position where a reference image for image quality adjustment is read;
Determining the presence or absence of air blowing to the reading position and the condition of wind pressure at the time of blowing according to the height position;
Blowing air to the reading position in accordance with the determined condition, and planarizing a sheet surface of the sheet on which the reference image is formed;
Is provided.

According to the invention of claim 11,
A step of measuring the height position of the paper surface at a reading position where a reference image for image quality adjustment is read;
A step of determining a condition of a voltage to be applied to the charging roller when the conveying belt that conveys the sheet at the reading position is charged by the charging roller according to the height position;
Applying a voltage to the charging roller according to the determined condition to charge the transport belt, electrostatically adsorbing the paper on which the reference image is formed to the transport belt, and planarizing the paper surface; ,
Is provided.

  According to the present invention, it is possible to determine the planarization condition so as to suppress the variation in the height position of the paper surface at the reference image reading position. By flattening the paper surface on which the reference image is formed in accordance with the conditions, fluctuations in the height position of the paper surface can be suppressed, and variations in the reading value of the reference image are suppressed, thereby improving the reading accuracy of the reference image. be able to.

1 is a diagram illustrating an image forming apparatus according to a first embodiment. FIG. 2 is a functional block diagram of the image forming apparatus in FIG. 1. It is a perspective view which shows the reading part and measurement part of FIG. FIG. 4 is a front view showing the color line sensor of FIG. 3 from the main scanning direction of the paper. It is a front view which shows the structure of the planarization part which concerns on 1st Embodiment. 6 is a flowchart illustrating a processing procedure when the image forming apparatus adjusts image quality. It is a perspective view showing the plane area of a paper. It is an example of a single color patch used as a reference image when the LUT for gradation correction is updated. It is an example of a secondary color patch used as a reference image when the LUT for gradation correction is updated. It is an example of a single color patch used as a reference image when updating a color conversion LUT. It is an example of a secondary color patch used as a reference image when updating a color conversion LUT. It is a figure which shows an example of a condition table. It is a perspective view which shows the structure of the planarization part which concerns on 2nd Embodiment. FIG. 6 is a plan view illustrating an example of an area set by dividing a sheet surface in a main scanning direction. 4 is a plan view showing an example of an area set by dividing a paper surface in a main scanning direction and a sub-scanning direction. FIG. It is a figure which shows an example of a condition table. It is a front view which shows the structure of the planarization part which concerns on 3rd Embodiment. It is a figure which shows an example of a condition table.

  Embodiments of an image forming apparatus and a sheet flattening method according to the present invention will be described below with reference to the drawings.

[First Embodiment]
FIG. 1 shows a schematic configuration of an image forming apparatus G according to the first embodiment.
As shown in FIG. 1, the image forming apparatus G includes a print controller g1, a paper feed unit g2, a main body unit g3, and a post-processing device g4.

The print controller g1 receives PDL (Page Description Language) data from a computer terminal on the network, and rasterizes the PDL data to generate bitmap format image data.
The print controller g1 generates image data for each color of C (cyan), M (magenta), Y (yellow), and K (black), and outputs the image data to the main unit g3.

The sheet feeding unit g2 includes a plurality of large capacity sheet feeding trays.
The paper feeding unit g2 conveys paper from the paper feeding tray designated by the main body unit g3 to the main body unit g3.

The main unit g3 includes an operation unit 3, a display unit 4, a scanner 6, an image forming unit 8, a paper feed tray g31, a reading unit 9, a measuring unit 10, a planarizing unit 11, and the like.
The main body unit g3 forms an image on a sheet by the image forming unit 8 based on image data obtained by reading a document by the scanner 6 or image data generated by the print controller g1. The main unit g3 conveys the sheet on which the image has been formed to the post-processing device g4.

  The post-processing device g4 performs post-processing on the paper conveyed from the main body unit g3 and discharges it. Examples of post-processing include stapling, punching, folding, and bookbinding. Post-processing is not essential, and the post-processing device g4 executes only when instructed by the main unit g3. When there is no post-processing, the post-processing device g4 discharges the conveyed paper as it is.

FIG. 2 is a functional block diagram of the main unit g3.
As shown in FIG. 2, the main unit g3 includes a control unit 1, a storage unit 2, an operation unit 3, a display unit 4, a communication unit 5, a scanner 6, an image processing device 7, an image forming unit 8, a reading unit 9, and a measurement. The unit 10 and the planarizing unit 11 are provided.

The control unit 1 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), and the like. The control unit 1 reads a program stored in the storage unit 2 and controls each unit of the image forming apparatus G according to the program.
For example, the control unit 1 feeds paper by the paper feed unit g2 or the paper feed tray g31 in accordance with job settings. In addition, the control unit 1 corrects and processes image data using the image processing device 7 and causes the image forming unit 8 to form an image. If the job setting includes post-processing settings, the control unit 1 instructs the post-processing device g4 to perform post-processing.

The control unit 1 can adjust the image quality at regular intervals or at an arbitrary timing.
Specifically, the control unit 1 causes the image forming unit 8 to form a reference image for image quality adjustment, causes the reading unit 9 to read the reference image, and obtains a read value.
The control unit 1 can adjust the image quality by adjusting the image forming conditions such as the development potential, the charging potential, and the laser power in the image forming unit 8 according to the obtained reading value.
Further, the control unit 1 can adjust the image quality by updating a LUT (Look Up Table) used at the time of color conversion or gradation correction according to the read value. Note that when updating the LUT, the control unit 1 switches the color conversion or gradation correction by the image processing apparatus 7 to invalid.

The control unit 1 causes the planarizing unit 11 to planarize the sheet surface of the sheet on which the reference image is formed.
The control unit 1 determines the planarization condition by the planarization unit 11 according to the height position of the sheet surface measured by the measurement unit 10. The control unit 1 causes the planarizing unit 11 to planarize the sheet surface according to the determined condition.

The storage unit 2 stores programs, files, and the like that can be read by the control unit 1. As the storage unit 2, for example, a storage medium such as a hard disk or a ROM (Read Only Memory) can be used.
The storage unit 2 stores a plurality of types of reference images.
The storage unit 2 stores a condition table used by the control unit 1 when determining the planarization condition.

The operation unit 3 includes an operation key, a touch panel configured integrally with the display unit 4, and the like, and outputs operation signals corresponding to these operations to the control unit 1. The user can input an instruction to set a job, change processing contents, or the like through the operation unit 3.
The display unit 4 can be an LCD (Liquid crystal display) or the like, and displays an operation screen or the like according to an instruction from the control unit 1.
The communication unit 5 communicates with a computer on the network, for example, a server or another image forming apparatus, according to an instruction from the control unit 1.

  The scanner 6 reads an image of a document, generates image data for each color of R (red), G (green), and B (blue), and outputs the image data to the image processing device 7.

The image processing device 7 corrects the image data input from the scanner 6 or the print controller g 1, performs image processing, and outputs it to the image forming unit 8.
As illustrated in FIG. 2, the image processing apparatus 7 includes a color conversion unit 71, a gradation correction unit 72, and a halftone processing unit 73.

The color conversion unit 71 performs color conversion processing on the R, G, and B color image data output from the scanner 6 and outputs C, M, Y, and K color image data. At the time of color conversion processing, the color conversion unit 71 uses an LUT in which gradation values of C, M, Y, and K colors after color conversion are determined for gradation values of R, G, and B colors. .
The color conversion unit 71 performs color conversion processing on the C, M, Y, and K color image data output from the print controller g1 for color correction, and performs color correction on the C, M, Y, and K colors. Image data can also be output. In this case, the color conversion unit 71 uses an LUT in which C, M, Y, and K tone values after color correction are determined for the tone values of C, M, Y, and K colors.

The gradation correction unit 72 corrects the gradation of the image data output from the color conversion unit 71 or the print controller g1.
The gradation correction unit 72 uses an LUT in which correction values corresponding to the respective gradation values are determined so that the gradation characteristics of the image coincide with the target gradation characteristics at the time of gradation correction. The gradation correction unit 72 obtains a correction value corresponding to the gradation value of each pixel of the image data from the gradation correction LUT, and outputs image data including the correction value.

The halftone processing unit 73 performs halftone processing on the image data output from the gradation correction unit 72. The halftone processing is, for example, screen processing using a dither matrix, error diffusion processing, or the like.
The halftone processing unit 73 outputs the image data after the halftone processing to the image forming unit 8.

The image forming unit 8 forms an image on a sheet based on the image data output from the image processing device 7.
As shown in FIG. 1, the image forming unit 8 includes four sets of an exposure unit 81, a photosensitive member 82, and a developing unit 83 for each of C, M, Y, and K colors. The image forming unit 8 includes an intermediate transfer belt 84, a secondary transfer roller 85, a fixing device 86, and a reversing mechanism 87.

  The exposure unit 81 exposes the charged and rotating photoreceptor 82 by optical scanning based on the image data. The developing unit 83 develops the electrostatic latent image formed on the photoconductor 82 by exposure with toner. The images formed with the toners of the respective colors on the four photoconductors 82 in this way are sequentially transferred from the photoconductors 82 onto the intermediate transfer belt 84 in an overlapping manner. As a result, a color image is formed on the intermediate transfer belt 84. The secondary transfer roller 85 transfers the color image onto the paper fed from the paper feed unit g2 or the paper feed tray g31. The fixing device 86 heats and pressurizes the transferred paper and performs a fixing process.

  When forming images on both sides of the paper, the image forming unit 8 reverses the front and back of the paper with the reversing mechanism 87 and forms an image on the other side. The reversing mechanism 87 has a transport path for reversing the front and back of the passing paper and transporting the paper again to the transfer position by the secondary transfer roller 85.

The reading unit 9 reads the image formed on the paper by the image forming unit 8.
As shown in FIG. 3, the reading unit 9 includes a light source c and a color line sensor b1.
The light source c includes an LED (Light Emitting Diode) and emits light, and the color line sensor b1 photoelectrically converts light from the light source c reflected on the paper surface. The color line sensor b1 outputs the R, G, and B color signal values obtained by photoelectric conversion as read values of the image.

  The color line sensor b1 reads an image on the paper T in units of one line in the main scanning direction x. A dotted line in FIG. 3 represents a reading position L of one line image by the color line sensor b1. Since the paper T is conveyed in the sub-scanning direction y, the color line sensor b1 can read the entire surface of the paper T by repeating reading.

The measurement unit 10 measures the height position of the paper surface at the reading position L by the reading unit 9.
A method for measuring the height position of the paper surface is not particularly limited, and a stereo method using parallax, a time of flight (TOF) method using a phase difference between measurement light and reflected light, or the like is used. be able to. As the measurement light, laser light, infrared light, or the like can be used.
Hereinafter, an example in which the measurement unit 10 performs measurement by the stereo method will be described.

As shown in FIG. 3, the stereo measurement unit 10 includes a light source c, two color line sensors b1 and b2, and a calculation unit (not shown).
The two color line sensors b <b> 1 and b <b> 2 are respectively arranged before and after the sheet conveyance direction with the reading position L by the reading unit 9 interposed therebetween. The paper transport direction is the same as the sub-scanning direction y. The configuration of the color line sensor b2 is the same as that of the color line sensor b1.
In order to reduce costs, the measuring unit 10 can share the light source c and the color line sensor b1 with the reading unit 9 as shown in FIG. 3, or a light source and two color line sensors separately from the reading unit 9. Can also be provided.

  The measurement unit 10 reads images at the reading position L by the two color line sensors b1 and b2. The measurement unit 10 measures the height position of the paper surface in the height direction z based on the parallax that is the difference between the two read images. The height direction z is a direction perpendicular to the xy plane composed of the main scanning direction x and the sub-scanning direction y of the paper. The measurement unit 10 sets a virtual reference surface, and measures the height position of the paper surface with the height position of the reference surface as 0. When a guide plate is provided below the paper T, the height position of the paper surface may be measured using the surface of the guide plate as a reference surface having a height position of zero.

FIG. 4 is a front view showing the color line sensors b1 and b2 from the main scanning direction x of the paper.
As shown in FIG. 4, each of the color line sensors b1 and b2 includes an image sensor b3 and a lens b4 that forms an image of light from the reading position L on the image pickup surface of the image sensor b3. Each lens b4, the distance d _C from the reference plane z0 to the focus position f is on a plane the same, are arranged at a reference length d _B.
Since the reference plane z0, the imaging device b3 and the lens b4 position is fixed, the distance d _C, the focal length d _f from the reference length d _B and the focal position f to the imaging surface is a constant.

The measurement unit 10 calculates a parallax d _s that is a shift between the two images from the two images read by each imaging element b3. The measurement unit 10 calculates the distance d _A from the reading position L to the focal position f by the following equation (1) using the obtained parallax d _s .
(1) d _A = d _B · d _f / d _s · δ
Here, δ represents the size of one pixel of the image sensor.

Measurement unit 10 uses the distance d _A obtained by the following equation (2) to calculate the distance D in the height direction z to the paper surface zn at position L read from the reference plane z0. The measurement unit 10 outputs the obtained distance D as the height position of the paper surface measured at the reading position L.
(2) D = d _C −d _A

The flattening unit 11 flattens the paper surface at the reading position L by the reading unit 9.
As shown in FIG. 5, the flattening unit 11 includes two transport rollers 11 a and 11 b provided respectively before and after the reading position L in the paper transport direction. Each of the transport rollers 11a and 11b is a pair of rollers that nip and transport the paper T.
As shown in FIG. 5, the flattening unit 11 can include a guide plate a below the paper T. The guide plate a is preferable because fluctuations in the height position of the paper surface at the reading position L can be suppressed.

The flattening unit 11 applies a pulling force to the paper transported by the transport rollers 11a and 11b by making the peripheral speeds of the transport rollers 11a and 11b constant or by providing a difference, thereby planarizing the paper surface.
The flattening unit 11 can adjust the peripheral speeds of both the transport rollers 11a and 11b, but can also adjust only the other peripheral speed by fixing one of the peripheral speeds. Since the adjustment is easy, it is preferable to fix the peripheral speed of the transport roller 11b while fixing the peripheral speed of the transport roller 11a.
Since the optimal circumferential speed condition is determined by the control unit 1 in accordance with the height position of the sheet surface, the planarizing unit 11 determines that each of the transport rollers 11a and the transport rollers 11a and 11b is rotationally driven.

FIG. 6 is a flowchart showing a processing procedure when the image forming apparatus G adjusts the image quality.
First, the control unit 1 feeds the same type of paper as the paper on which the reference image is formed from the paper feed tray g31 or the paper feed unit g2. Thereafter, the control unit 1 instructs the image forming unit 8 to perform a fixing process, and the image forming unit 8 preferably performs the fixing process on the fed paper. The planarization condition can be determined in consideration of the deformation characteristics of the paper generated by the fixing process.

  Next, the control unit 1 instructs the planarization unit 11 to perform planarization, and instructs the measurement unit 10 to perform measurement. The flattening unit 11 drives the transport rollers 11a and 11b according to the initially set peripheral speed condition to flatten the paper surface (step S1). Further, the measuring unit 10 measures the height position of the planarized paper surface (step S2).

The control unit 1 compares the measured height position of the paper surface with a threshold value, and determines an area where the height position of the paper surface is equal to or less than the threshold value as a plane area of the paper (step S3).
For example, when the threshold is 0.5 mm, the control unit 1 determines a region where the measured height position is 0.5 mm or less as a plane region.
As shown in FIG. 7, in the case of a sheet with curled edges, a region TF in which the height position of the sheet surface is within the range from the reference surface to the threshold value zth is determined as a planar region. The dotted line in FIG. 7 represents the paper surface when the height position is zth.
A region TN represented by diagonal lines is excluded from the planar region TF because the height position of the sheet surface is higher than the threshold value zth.

The control unit 1 determines whether or not sufficient flatness of the sheet has been secured based on the determined plane area (step S4).
For example, if the area of the plane area is 80% or more of the entire sheet, and the reference image can be sufficiently formed in the plane area, the control unit 1 sets the threshold to 80% and the area of the plane area is the entire sheet. If it is 80% or more of the area, it is judged that sufficient flatness can be secured.
The planar area is not limited to a single area, and may be divided into a plurality of planar areas. In this case, the control unit 1 has an area of the entire planar area that is the sum of the areas of the plurality of planar areas equal to or greater than a threshold value. Determine whether or not.

A sufficient area for forming the reference image varies depending on the type of the reference image.
For example, when the maximum density is adjusted as the image quality by changing the image forming conditions, the solid patch having the gradation value set to the maximum as the reference image has different image forming conditions, for example, the developing potential of the developing unit 83, A plurality of photoconductors 82 are formed with different charging potentials, laser power of the exposure unit 81, and the like.
When the color or gradation reproducibility is adjusted as the image quality by updating the LUT used for color conversion or gradation correction, a single color patch and a secondary color patch are used as the reference image.

FIG. 8a shows an example of a single color patch for gradation correction, and FIG. 8b shows an example of a secondary color patch for gradation correction. The single color patch includes a plurality of patches in which the gradation values of the single colors of Y, M, C, and K are different in stages. The secondary color patch includes a plurality of patches in which the gradation values of the secondary colors of K, Y, M, C, B, G, R, and Pb differ in stages.
FIG. 9a shows an example of a single color patch for color conversion, and FIG. 9b shows an example of a secondary color patch for color conversion. The single color patch includes Y, M, C, and K single color patches, and the secondary color patch includes Y, M, C, K, R, G, B, and Pb secondary color patches. Yes. In any case, a plurality of patches of the same color are arranged in a line.

  Thus, since the number of patches differs depending on the type of the reference image, the area sufficient for forming all the patches also differs. The storage unit 2 stores, as a threshold, a sufficient area that can be used to form the reference image, which is obtained in advance for each type of the reference image, and reads the threshold corresponding to the reference image formed by the control unit 1 from the storage unit 2 for comparison. Can be used.

If the control unit 1 determines that sufficient flatness of the paper has been secured (step S4; Y), the new paper of the same type is fed from the paper feed tray g31 or the paper feed unit g2 to form a reference image. To the image forming unit 8. The image forming unit 8 forms a reference image on the fed paper and performs a fixing process (step S5).
The control unit 1 instructs the reading unit 9 to read, and the reading unit 9 reads the reference image formed on the paper (step S6).

The control unit 1 acquires a reading value from the reading unit 9, adjusts the image quality according to the reading value (step S7), and ends the process.
For example, when the reference image is a solid patch for adjusting the maximum density and image quality is adjusted by changing the image forming condition, the control unit 1 identifies a solid patch whose read value matches the target value. The control unit 1 changes the image forming conditions such as the developing potential, laser power, and charging potential in the image forming unit 8 to the image forming conditions when the specified solid patch is formed.
When the reference image is a single color patch or a secondary color patch, the control unit 1 newly creates an LUT used for color conversion or gradation correction according to the difference between the read value of each patch and the target value.

On the other hand, when the control unit 1 determines that sufficient flatness of the paper has not been secured (step S4; N), the flattening condition, that is, the peripheral speed condition of the transport rollers 11a and 11b is changed a certain number of times or more. Whether or not (step S8).
If the change has not been made more than a certain number of times (step S8; N), the control unit 1 determines the peripheral speed condition according to the height position of the paper surface measured by the measurement unit 10 (step S9). .

  As the difference between the peripheral speeds of the two transport rollers 11a and 11b increases, the tensile force applied to the paper also increases. Therefore, the strength of planarization can be adjusted by adjusting the difference in peripheral speed. If the pulling force is insufficient, the paper surface will not be flattened sufficiently, and if the pulling force is excessive, the paper will be wrinkled or the paper transportability will be reduced, making it difficult to transport the paper at a constant speed. Become.

When flattening by the transport rollers 11a and 11b, the peripheral speed conditions when the paper surface can be sufficiently flattened without impairing the paper transportability are the types of paper, especially the basis weight of the paper and the paper surface. It depends on the slipperiness.
However, even under the condition of the peripheral speed according to the type of paper, the paper surface may not be sufficiently flattened due to environmental changes or changes with time, and the height position of the paper surface may fluctuate. For example, the deformation of the paper may increase due to an increase in humidity. Further, the transport rollers 11a and 11b may be worn with time, and the frictional force with the paper and the outer diameter of the roller may change, and the intended pulling force may not be obtained.
Therefore, before forming the reference image, the control unit 1 determines the planarization condition when the sheet surface can be sufficiently planarized without damaging the sheet transportability, based on the height position of the sheet surface.

Specifically, the control unit 1 reads a condition table from the storage unit 2 and determines a planarization condition based on the condition table.
When the peripheral speed of the transport roller 11a is fixed and the peripheral speed of the transport roller 11b is changed, the control unit 1 can determine the conditions using, for example, the condition tables 21 and 22 shown in FIG.
In the condition table 21, the speed change rate (%) of the peripheral speed of the transport roller 11b is determined by the basis weight (g / m ² ) of the paper and the classification of plain paper, high-quality paper, or coated paper.
In the condition table 22, a change rate (%) of the peripheral speed of the transport roller 11b is determined for each height position (mm) of the sheet surface.

  The control unit 1 acquires from the condition table 21 conditions for the speed change rate corresponding to the basis weight and classification of the paper used for forming the reference image. Further, the control unit 1 acquires the condition of the speed change rate corresponding to the measured height position of the sheet surface from the condition table 22. The control unit 1 adds the gear ratios acquired from the condition tables 21 and 22, and determines the peripheral speed obtained by multiplying the obtained gear ratio by the currently set peripheral speed of the transport roller 11b.

For example, when the paper type is plain paper with a basis weight of 70 g / m ² and the height position of the paper surface is 1.7 mm, a speed change rate of −0.05% is obtained from the condition table 21. A speed change rate of + 0.15% is obtained from the table 22. The speed change rate of the peripheral speed obtained by adding each speed change rate is + 0.10% (+ 0.10 = −0.05 + 0.15). The controller 1 multiplies the initial peripheral speed by + 0.10%, and determines the obtained peripheral speed as the peripheral speed of the transport roller 11b.

  When the peripheral speed is changed, the conveyance speed of the paper by the conveyance rollers 11a and 11b changes, and the magnification of the image transferred onto the paper may change. When it is necessary to match the image magnification to the reference magnification, the peripheral speed may be determined within a range in which the image magnification does not change from the reference magnification.

  The control unit 1 changes the planarization condition set in the planarization unit 11 to the determined condition (step S10), and returns to the process of step S1. In step S1, the flattening unit 11 flattens the paper surface according to the changed condition.

  On the other hand, if the planarization condition has been changed more than a certain number of times (step S8; Y), it may be difficult to ensure flatness only by changing the planarization condition. Therefore, the control unit 1 causes the display unit 4 to display an operation screen that can change the type of paper used for forming the reference image. A sheet with less unevenness on the sheet surface or a sheet on which deformation such as curling or undulation hardly occurs has little variation in the height position of the sheet surface. When the user selects such a sheet, the area of the planar area is easily increased without greatly changing the planarization condition, and the image quality can be adjusted with high accuracy.

When an instruction to change the paper type is input by the user via the operation unit 3 (step S11; Y), the control unit 1 changes the paper used for forming the reference image to the type of paper instructed by the user. Change (step S12).
When an instruction not to change the paper type is input by the user via the operation unit 3 (step S11; N), the control unit 1 displays an error display screen on the display unit 4 so that the image quality cannot be adjusted. The user is notified (step S13) and the process is terminated.

As described above, according to the first embodiment, the image forming apparatus G includes the image forming unit 8 that forms a reference image for image quality adjustment on a sheet, the reading unit 9 that reads the reference image, and the reading At the reading position L by the unit 9, the flattening unit 11 for flattening the paper surface of the paper, the measuring unit 10 for measuring the height position of the paper surface at the reading position, and the flattening conditions according to the height position And a control unit 1 that determines and planarizes the sheet surface under the condition by the planarization unit 11.
The flattening unit 11 includes two transport rollers 11a and 11b positioned before and after the reading position in the sheet transport direction, and adjusts the peripheral speed of each of the transport rollers 11a and 11b to transport the sheet surface of the sheet. The control unit 1 determines the condition of the peripheral speed of the transport rollers 11a and 11b as the condition for planarization.

Thereby, the condition of the peripheral speeds of the transport rollers 11a and 11b can be determined so as to suppress the variation in the height position of the sheet surface at the reference image reading position. By flattening the paper surface of the paper on which the reference image is formed in accordance with the conditions, fluctuations in the height position of the paper surface can be suppressed, and variations in the reading value of the reference image can be suppressed, thereby improving the reading accuracy of the reference image. Can be improved.
By improving the reading accuracy of the reference image, the image quality can be adjusted with high accuracy.

[Second Embodiment]
According to the second embodiment, the planarization unit of the image forming apparatus planarizes the paper surface by blowing air onto the paper surface.
The image forming apparatus according to the second embodiment has the same configuration as the image forming apparatus G except that the planarizing unit 11 of the image forming apparatus G according to the first embodiment is changed to the planarizing unit 12 described below. can do. Therefore, the same reference numerals are assigned to the same components, and illustration and detailed description thereof are omitted. For the image forming apparatus according to the second embodiment, only the planarization unit 12 having a different configuration will be described.

FIG. 11 shows a configuration of the planarization unit 12 according to the second embodiment.
The flattening unit 12 includes a plurality of air blowing units 12a arranged side by side in the main scanning direction x of the paper T as shown in FIG.
As shown in FIG. 11, the planarizing unit 12 includes a guide plate a below the paper T.

The flattening unit 12 blows air to the reading position L on the paper surface by each air blowing unit 12a, and flattens the paper surface at the reading position L. The flattening unit 12 is preferable in that pressure can be applied to the paper surface without hindering reading, and deformation of the paper can be effectively corrected.
The flattening unit 12 can control the presence / absence of air blowing of each air blowing unit 12a and the wind pressure at the time of blowing.
Since the control unit 1 determines whether or not each air blowing unit 12a is blowing air and the condition of the wind pressure at the time of blowing, the planarizing unit 12 is controlled by each air blowing unit 12a according to the conditions determined by the control unit 1. Blow air.

As described above, since the planarization means are different, the contents of the planarization conditions determined by the control unit 1 are different, but the processing procedure when the image forming apparatus according to the second embodiment adjusts the image quality is as follows. This is the same as the processing procedure in the first embodiment shown in FIG.
Therefore, in step S9 shown in FIG. 6, only the process in which the control unit 1 determines the planarization condition by the planarization unit 12 will be described, and the description of the other processes will be omitted.

In step S <b> 9 shown in FIG. 6, the control unit 1 determines a planarization condition by the planarization unit 12 according to the height position of the sheet surface.
The greater the air wind pressure, the greater the pressure applied to the paper surface. Therefore, the planarization strength can be adjusted by adjusting the wind pressure conditions. If the wind pressure is insufficient, the sheet is not sufficiently flattened. If the wind pressure is excessive, the end of the sheet flutters or the resistance of the sheet increases, making it difficult to transport the sheet at a constant speed.

In the case of flattening with air, the condition of wind pressure when the paper surface can be sufficiently flattened without impairing the transportability of the paper varies depending on the type of paper, particularly the bending stiffness of the paper.
However, even under conditions according to the type of paper, the paper surface may not be sufficiently flattened due to environmental changes or changes over time, and the height position of the paper surface may fluctuate. For example, the deformation of the paper increases due to a change in humidity, and it may not be possible to sufficiently flatten the sheet. In addition, the air blowing performance deteriorates with time, and it may not be sufficiently planarized.
Therefore, before forming the reference image, the control unit 1 determines the planarization condition when the sheet surface can be sufficiently planarized without damaging the sheet transportability, based on the height position of the sheet surface.

Specifically, the control unit 1 divides the sheet surface in the main scanning direction x in accordance with the arrangement position of the air blowing unit 12a, and sets a plurality of areas. FIG. 12a shows an example of five areas set by dividing the paper surface of the paper T into five in the main scanning direction x in accordance with the arrangement positions of the five air blowing portions 12a.
The control unit 1 can also set a plurality of areas by further dividing the sheet surface in an arbitrary number in the sub-scanning direction y. FIG. 12b shows an example of 25 areas set by dividing the area of FIG. 12a into five in the sub-scanning direction y.

  The control unit 1 calculates an average value of the height position of the sheet surface for each area, and determines whether the average value exceeds a threshold value. The control unit 1 determines that there is air blowing from the air blowing unit 12a in which the position in the main scanning direction x corresponds to the area exceeding the threshold, and the air blowing in which the area below the threshold corresponds to the position in the main scanning direction x. The air is not blown to the part 12a.

Next, the control unit 1 determines the condition of the wind pressure for the area determined to have air blowing. As a result, the paper surface can be flattened corresponding to the height position of the paper surface that is different for each area, and high-precision flattening is possible.
Specifically, the control unit 1 determines a wind pressure condition based on a condition table stored in the storage unit 2.

For example, the control unit 1 can use the condition table 23 shown in FIG.
As shown in FIG. 13, in the condition table 23, a change amount (MPa) of wind pressure is defined for each height position (mm) of the sheet surface and bending stiffness (mN · m) of the sheet.
The bending stiffness represents the resistance of the sheet to deformation, and can be measured as follows.
The end of the paper placed on the test table is projected from the test table by a length L (m), and the amount of deflection d (m) due to the weight of the end is measured. Based on the measured deflection amount d (m) and the basis weight W (g / m ² ) of the paper, the bending stiffness is obtained by the following equation.
Flexural rigidity (mN · m) = (WL ⁴ /8d)×9.81

  When the stiffness of the paper used for forming the reference image is 800 mN · m and the average value of the height position of the paper surface in the area is 1.7 mm, a wind pressure of +0.20 (MPa) is obtained from the condition table 23. The amount of change is obtained. The control unit 1 adds +0.20 (MPa) to the wind pressure currently set for this area, and determines the obtained wind pressure as the wind pressure of the air blowing unit 12a in the area.

As described above, the image forming apparatus according to the second embodiment includes the image forming unit 8 that forms a reference image for image quality adjustment on a sheet, the reading unit 9 that reads the reference image, and the reading by the reading unit 9. At the position L, the flattening unit 11 for flattening the paper surface of the paper, the measuring unit 10 for measuring the height position of the paper surface at the reading position, and the flattening conditions are determined according to the height position. And a control unit 1 that causes the paper surface to be flattened by the conversion unit 11 under the above conditions.
Further, the flattening unit 12 includes an air blowing unit 12a, and the air blowing unit 12a blows air against the reading position to flatten the paper surface. The control unit 1 uses an air blowing unit as a planarization condition. The presence or absence of spraying by 12a and the condition of wind pressure at the time of spraying are determined.

  As a result, air blowing conditions can be determined so as to suppress fluctuations in the height position of the paper surface at the reference image reading position. By flattening the paper surface of the paper on which the reference image is formed in accordance with the conditions, fluctuations in the height position of the paper surface can be suppressed, and variations in the reading value of the reference image can be suppressed, thereby improving the reading accuracy of the reference image. Can be improved. By improving the reading accuracy of the reference image, the image quality can be adjusted with high accuracy.

[Third Embodiment]
According to the third embodiment, the planarization unit of the image forming apparatus planarizes the sheet surface by charging the sheet conveyance belt and electrostatically adsorbing the sheet to the conveyance belt.
The image forming apparatus according to the third embodiment has the same configuration as the image forming apparatus G except that the planarizing unit 11 of the image forming apparatus G according to the first embodiment is changed to the planarizing unit 13 described below. can do. Therefore, the same reference numerals are assigned to the same components, and illustration and detailed description thereof are omitted. For the image forming apparatus according to the third embodiment, only the planarizing unit 13 having a different configuration will be described.

FIG. 14 shows a configuration of the planarization unit 13 according to the third embodiment.
As shown in FIG. 14, the planarization unit 13 includes a transport belt 13a, two rollers 13b and 13c, and a power source 13d.

The conveyor belt 13a is wound around two rollers 13b and 13c, and is rotated by the rotation of the rollers 13b and 13c. By the rotation, the transport belt 13a transports the paper T in the transport direction at the reading position L.
The conveyor belt 13a can be made of a belt member for electrostatic attraction, such as polyimide having high conductivity.

The rollers 13b and 13c are charging rollers that are charged with a voltage by a power source 13d to charge the transport belt 13a. As the rollers 13b and 13c, conductive metal rollers can be used.
Only one of the rollers 13b and 13c may be a charging roller.
In addition, as long as the conveyor belt 13a can be charged, a charging roller that contacts the outer peripheral surface of the conveyor belt 13a can be provided separately from the rollers 13b and 13c around which the conveyor belt 13a is wound.

  The power source 13d applies a voltage having a polarity opposite to the charging polarity of the toner to the rollers 13b and 13c. When the charging polarity of the toner is negative, a positive voltage is applied to each of the rollers 13b and 13c, so that the conveyance belt 13a contacting the rollers 13b and 13c is also charged to a positive polarity.

  The flattening unit 13 applies a voltage to the rollers 13b and 13c by the power supply 13d and charges the transport belt 13a via the rollers 13b and 13c, thereby electrostatically adsorbing the paper T to the transport belt 13a. Flatten the paper surface. The flattening unit 13 is preferable in that it can apply pressure due to suction to the paper surface without hindering reading, and can effectively correct deformation of the paper.

The planarizing unit 13 can control the voltage applied to the rollers 13b and 13c by the power source 13d.
Since the controller 1 determines the condition of the voltage to be applied to each of the rollers 13b and 13c, the planarizing unit 13 applies the voltage to each of the rollers 13b and 13c by the power supply 13d according to the condition determined by the controller 1. .

As described above, since the flattening means are different, the contents of the flattening conditions determined by the control unit 1 are different, but the processing procedure when the image forming apparatus according to the third embodiment adjusts the image quality is as follows. This is the same as the processing procedure in the first embodiment shown in FIG.
Therefore, in step S9 shown in FIG. 6, only the process in which the control unit 1 determines the planarization condition by the planarization unit 13 will be described, and the description of the other processes will be omitted.

In step S <b> 9 shown in FIG. 6, the control unit 1 determines the planarization condition by the planarization unit 13 according to the height position of the paper surface.
The greater the absolute value of the voltage applied to each of the rollers 13b and 13c, the greater the adsorption force of the paper. Therefore, the intensity of planarization can be adjusted by adjusting the absolute value of the voltage. If the suction force of the paper is insufficient, the paper surface cannot be sufficiently flattened, and if the suction force is excessive, the paper may be wrinkled or the paper may be difficult to peel off from the transport belt 13a and may be jammed. .

In the case of flattening by electrostatic attraction, the voltage condition when the paper surface can be sufficiently flattened without impairing the transportability of the paper varies depending on the type of paper, particularly the bending stiffness of the paper.
However, even under conditions according to the type of paper, the paper surface may not be sufficiently flattened due to environmental changes or changes over time, and the height position of the paper surface may fluctuate. For example, the deformation of the paper increases due to a change in humidity, and planarization may be insufficient. In addition, the charging property of the transport belt 13a may decrease with time, and the intended suction force may not be obtained, and planarization may be insufficient.
Therefore, before forming the reference image, the control unit 1 determines a planarization condition that can sufficiently planarize the sheet surface without impairing the sheet transportability, based on the height position of the sheet surface.

Specifically, the control unit 1 determines a voltage condition based on a condition table stored in the storage unit 2.
For example, the control unit 1 can use the condition table 24 shown in FIG.
As shown in FIG. 15, in the condition table 24, the change amount (kV) of the voltage applied to each of the rollers 13b and 13c is different for each height position (mm) of the sheet surface and bending rigidity (mN · m) of the sheet. It has been established.
When the bending stiffness of the sheet used for forming the reference image is 250 mN · m and the height position of the sheet surface is 1.3 mm, +1.00 kV is obtained from the condition table 24 as the change amount of the applied voltage. The control unit 1 determines a voltage obtained by adding +1.00 kV to the application voltage currently set in the planarization unit 13 as a voltage condition to be applied to the rollers 13b and 13c.

The control unit 1 can also determine the voltage condition for each position in the sub-scanning direction y of the paper. As a result, the paper surface can be flattened in accordance with the height position of the paper surface, which differs depending on the position in the sub-scanning direction, and high-precision flattening is possible.
For example, the control unit 1 divides the paper surface into an arbitrary number in the sub-scanning direction y, sets a plurality of areas, and calculates the average value of the height positions of the paper surfaces in each area. The control unit 1 obtains the voltage change amount corresponding to the average value of the height position of each area from the condition table 24, and determines the voltage condition of each area.

As described above, the image forming apparatus according to the third embodiment includes the image forming unit 8 that forms a reference image for image quality adjustment on a sheet, the reading unit 9 that reads the reference image, and the reading by the reading unit 9. At the position, the flattening unit 11 for flattening the paper surface of the paper, the measuring unit 10 for measuring the height position of the paper surface at the reading position, and the flattening conditions are determined according to the height position, and the flattening is performed. And a control unit 1 that causes the sheet surface to be planarized by the unit 11 under the conditions.
The flattening unit 13 includes a conveyance belt 13a that conveys the sheet at the reading position, and rollers 13b and 13c that charge the conveyance belt 13a. A voltage is applied to the rollers 13b and 13c to apply the conveyance belt 13a. And the sheet to be conveyed is electrostatically attracted to the conveyance belt 13a to planarize the sheet surface, and the control unit 1 determines the condition of the voltage applied to the rollers 13b and 13c as the planarization condition. .

As a result, the condition of the voltage applied to each of the rollers 13b and 13c can be determined so as to suppress the variation in the height position of the paper surface at the reference image reading position. By flattening the paper surface of the paper on which the reference image is formed in accordance with the conditions, fluctuations in the height position of the paper surface can be suppressed, and variations in the reading value of the reference image can be suppressed, thereby improving the reading accuracy of the reference image. Can be improved.
By improving the reading accuracy of the reference image, the image quality can be adjusted with high accuracy.

The above embodiment is a preferred example of the present invention, and the present invention is not limited to this. Modifications can be made as appropriate without departing from the spirit of the present invention.
For example, in the processing procedure shown in FIG. 6, planarization is performed according to the initial setting conditions (the conditions that are currently set after changing the conditions once) in step S <b> 1, and in step S <b> 9, However, the method for determining the planarization condition is not limited to this.
In step S1, planarization conditions are determined according to the type of paper, and after roughly adjusting the conditions, in step S9, planarization conditions are determined in accordance with the height position of the paper surface, and fine adjustment is performed. You can also.

Further, the planarization unit 11 according to the first embodiment and the planarization unit 12 according to the second embodiment are combined, and the planarization unit including the conveyance roller and the air blowing unit is used to planarize the conveyance roller. And planarization by air blowing can be performed in parallel.
By combining the planarizing unit 13 according to the third embodiment and the planarizing unit 12 according to the second embodiment, by the planarizing unit including the conveying belt and the air blowing unit, the planarization by the conveying belt, Planarization by blowing air may be performed in parallel.

Moreover, each planarization part 11-13 can planarize a paper surface partially. Therefore, the control unit 1 may select the formation position of the reference image instead of the entire sheet surface, and may planarize only at the formation position by the planarization units 11 to 13.
When the area of the reference image is small, the cost required for planarization can be reduced by partially planarizing.

  Further, as a computer-readable medium for the program executed by the control unit 1, a non-volatile memory such as a ROM or a flash memory, or a portable recording medium such as a CD-ROM can be applied. A carrier wave is also used as a medium for providing the program data via a communication line.

G Image forming apparatus g1 Print controller g3 Main unit 1 Control unit 2 Storage unit 3 Operation unit 71 Color conversion unit 72 Tone correction unit 8 Image forming unit 9 Reading unit 10 Measurement unit b1, b2 Color line sensor 11 Planarization unit 11a, 11b Conveying roller a Guide plate 12 Planarizing unit 12a Air blowing unit 13 Flattening unit 13a Conveying belts 13b, 13c Roller 13c Power supply

Claims (11)

An image forming unit that forms a reference image for image quality adjustment on paper;
A reading unit for reading the reference image;
A flattening unit for flattening the paper surface of the paper at a reading position by the reading unit;
A measurement unit for measuring the height position of the paper surface at the reading position;
A control unit that determines planarization conditions according to the height position, and planarizes the sheet surface under the conditions by the planarization unit;
An image forming apparatus comprising: The control unit determines the planarization condition according to the height position and the type of paper used for forming the reference image.
The image forming apparatus according to claim 1. The flattening unit includes two transport rollers positioned before and after the reading position in the paper transport direction, and planarizes the paper surface of the paper to be transported by adjusting the peripheral speed of each transport roller,
The control unit determines a condition of a peripheral speed of the transport roller as the planarization condition.
The image forming apparatus according to claim 1. The flattening unit includes an air blowing unit, and air is blown against the reading position by the air blowing unit to flatten the paper surface.
The control unit determines the presence or absence of blowing by the air blowing unit and the condition of wind pressure at the time of blowing as the planarization condition,
The image forming apparatus according to claim 1. The flattening unit includes a plurality of the air blowing units arranged in the main scanning direction of the paper,
The control unit divides the sheet surface in the main scanning direction according to the arrangement position of each air spray unit to set a plurality of areas, and for each area, the presence or absence of spraying by each air spray unit and the wind pressure at the time of spraying Determine the conditions of
The image forming apparatus according to claim 4. The control unit further divides the area set by dividing in the main scanning direction and further sets the plurality of areas by dividing the area in the sub-scanning direction. Determine the wind pressure conditions of the
The image forming apparatus according to claim 5. The flattening unit includes a conveyance belt that conveys the sheet at the reading position and a charging roller that charges the conveyance belt, and applies a voltage to the charging roller to charge the conveyance belt and convey the sheet to be conveyed. By electrostatically adsorbing to the conveyor belt, the paper surface is flattened,
The control unit determines a voltage condition to be applied to the charging roller as the planarization condition.
The image forming apparatus according to claim 1. The control unit determines the voltage condition for each position of the paper in the sub-scanning direction.
The image forming apparatus according to claim 7. A step of measuring the height position of the paper surface at a reading position where a reference image for image quality adjustment is read;
Determining a peripheral speed condition of two transport rollers positioned before and after the reading position in the paper transport direction according to the height position;
Rotating the transport roller according to the determined condition to planarize a sheet surface of the sheet on which the reference image is formed;
A method for flattening a paper surface including A step of measuring the height position of the paper surface at a reading position where a reference image for image quality adjustment is read;
Determining the presence or absence of air blowing to the reading position and the condition of wind pressure at the time of blowing according to the height position;
Blowing air to the reading position in accordance with the determined condition, and planarizing a sheet surface of the sheet on which the reference image is formed;
A method for flattening a paper surface including A step of measuring the height position of the paper surface at a reading position where a reference image for image quality adjustment is read;
A step of determining a condition of a voltage to be applied to the charging roller when the conveying belt that conveys the sheet at the reading position is charged by the charging roller according to the height position;
Applying a voltage to the charging roller according to the determined condition to charge the transport belt, electrostatically adsorbing the paper on which the reference image is formed to the transport belt, and planarizing the paper surface; ,
A method for flattening a paper surface including