JP2023072532A - Image forming apparatus - Google Patents

Abstract

To improve usability pertaining to correction of image quality using a test image.SOLUTION: An image forming apparatus includes: holding means holding a sheet; conveyance means conveying the sheet; and image forming means forming an image on the sheet. The image forming apparatus furthermore includes: reading means reading a test image formed on the sheet; and control means controlling the quality of an image formed on the sheet by the image forming means on the basis of a test image reading result. The control means determines whether or not a sheet proper for formation of the test image is held by the holding means. There is a case in which the sheet proper for formation of the test image is not held by the holding means. In this case, the control means outputs a message for urging an operator to set a sheet proper for formation of the test image in the holding means.SELECTED DRAWING: Figure 6

Description

The present invention relates to an image forming apparatus that forms a toner image on a sheet.

In recent years, electrophotographic image forming apparatuses have begun to spread in the printing industry, and the demand for high-speed output and high image quality is rapidly increasing. Among the requirements for high image quality, the uniformity of image density within a page (suppression of density unevenness) is of particular interest. Density unevenness can be, for example, a striped pattern parallel to the sheet conveying direction (Patent Documents 1 and 2) and a striped pattern perpendicular to the sheet conveying direction. There is (Patent Document 3). The former is called density unevenness in the main scanning direction, and the latter is called density unevenness in the sub-scanning direction. Density unevenness in the sub-scanning direction may occur periodically due to rotation unevenness of rotating bodies such as a developing sleeve, a photosensitive drum, and a charging roller. Japanese Patent Application Laid-Open No. 2002-200001 proposes to detect density unevenness in the sub-scanning direction by forming a belt-like pattern on a sheet, and to identify the cause of occurrence based on the detection result.

JP 2007-118194 A JP 2019-60984 A JP 2011-39418 A

By the way, if the density unevenness can be reduced by detecting density unevenness from a test image and correcting or adjusting the image forming conditions based on the detection result, it will be possible to meet the demand for higher image quality from the market. However, it is not easy to create correction information for image forming conditions from a test image. This is because there are various types and sizes of sheets on the market, and density unevenness in a test image cannot be accurately detected depending on the type and size of sheets, and appropriate correction information cannot be created. In particular, test images may be created not only by specialists such as maintenance workers (servicemen) but also by general users. It would be difficult for a general user to properly prepare a sheet on which density unevenness is easily detected. Accordingly, an object of the present invention is to improve usability regarding image quality correction using a test image.

The present invention, for example,
holding means for holding the sheet;
a conveying means for conveying the sheet;
an image forming means for forming an image on the sheet;
reading means for reading the test image formed on the sheet;
a control unit for controlling the image quality of the image formed on the sheet by the image forming unit based on the reading result of the test image;
The control means is
determining whether a sheet suitable for forming the test image is held by the holding means;
outputting a message prompting an operator to set a suitable sheet for forming the test image on the holding means in response to the fact that the holding means does not hold a suitable sheet for forming the test image; To provide an image forming apparatus characterized by:

According to the present invention, usability regarding image quality correction using a test image is improved.

Diagram for explaining an image forming apparatus Diagram explaining the phase sensor Diagram explaining the controller Diagram explaining the test image Flowchart for explaining density unevenness correction method Flowchart for explaining sheet preparation processing for test images Flowchart for explaining sheet preparation processing for test images Diagram for explaining an image forming apparatus

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. In addition, the following embodiments do not limit the invention according to the scope of claims. Although multiple features are described in the embodiments, not all of these multiple features are essential to the invention, and multiple features may be combined arbitrarily. Furthermore, in the accompanying drawings, the same or similar configurations are denoted by the same reference numerals, and redundant description is omitted.

<Example 1>
[Image forming apparatus]
The letters Y, M, C and K added to the end of the reference numerals in FIG. 1 indicate toner colors such as yellow, magenta, cyan and black. For example, components with a Y suffix are responsible for forming a yellow toner image. Reference numerals with suffixes omitted are used when there is no need to distinguish between colors in the description of components.

The image forming apparatus 100 is a copier or multifunction machine that forms an image on a recording material (hereinafter referred to as a sheet) using an electrophotographic process. The image forming apparatus 100 may use other image forming methods such as an inkjet recording method or a thermal transfer method. The image forming apparatus 100 has a printer 101 and an image reader 102 . The control circuit 40 is a controller that controls each part of the image forming apparatus 100 . For example, the control circuit 40 converts image data created by reading the document 99 with the image reader 102 to generate an image signal, and supplies the image signal to the exposure device 7 . The photoreceptor 1 is an image carrier that is driven by a drive source such as a motor to rotate clockwise and carries an electrostatic latent image and a toner image. The photoreceptor 1 is also called a photoreceptor drum because it is a cylindrical rotating body. The charging roller 2 is applied with a charging bias Vc by the control circuit 40 to charge the surface of the photoreceptor 1 to a uniform potential (dark potential Vd). The exposure device 7 forms an electrostatic latent image on the surface (peripheral surface) of the photoreceptor 1 by irradiating the photoreceptor 1 with laser light corresponding to an image signal. A developing sleeve 31 of the developing device 3 is supplied or applied with a developing bias Vdc, and adheres toner to the electrostatic latent image to form a toner image on the surface of the photoreceptor 1 . The developer housed in the developing device 3 is assumed to be a two-component developer having toner and carrier. A primary transfer bias is applied to the primary transfer roller 6 by a control circuit 40 to transfer the toner image from the photoreceptor 1 to the intermediate transfer belt 8 . The drum cleaner 4 is a member that removes and collects toner remaining on the photosensitive member 1 without being transferred onto the intermediate transfer belt 8 . The photoreceptor 1, developing sleeve 31, charging roller 2 and drum cleaner 4 may be housed in a cartridge and integrated. Such a cartridge is configured to be detachable from the body of the printer 101 .

The intermediate transfer belt 8 is an endless belt and is sometimes called an intermediate transfer body. The intermediate transfer belt 8 is driven by a driving source such as a motor to rotate counterclockwise. A full-color toner image is formed on the intermediate transfer belt 8 by transferring the toner images from the four photoreceptors 1 to the intermediate transfer belt 8 in an overlapping manner. The toner image transferred onto the intermediate transfer belt 8 is conveyed to the secondary transfer portion. A secondary transfer portion is a nip portion formed by the intermediate transfer belt 8 and the secondary transfer roller 11 .

The printer 101 has a sheet cassette 13, which is a feeding tray for feeding sheets. The sheet cassette 13 is a container that accommodates a large number of sheets P. As shown in FIG. The feeding roller 14 feeds the sheet P from the sheet cassette 13 to the conveying path 15 according to instructions from the control circuit 40 . The sheet P is conveyed to the secondary transfer portion by conveying rollers 16 and 18 provided along the conveying path 15 . The transport rollers 18 are sometimes called registration rollers. A sheet sensor 23 may be provided downstream of the conveying roller 18 in the sheet P conveying direction.

A secondary transfer bias is applied to the secondary transfer roller 11 by the control circuit 40 to transfer the toner image from the intermediate transfer belt 8 to the sheet P. FIG. The belt cleaner 9 removes and collects toner remaining on the intermediate transfer belt 8 without being transferred onto the sheet P. The secondary transfer roller 11 conveys the sheet P to the fixing device 17 . The fixing device 17 has two rotating bodies (a fixing roller 22 and a pressure roller 21), and applies heat and pressure to the sheet P and the toner image to fix the toner image on the sheet P. FIG. The sheet P is conveyed to the discharge roller 20 by rotating the fixing roller 22 and the pressure roller 21 . The discharge roller 20 discharges the sheet P to the outside of the image forming apparatus 100 . Photoreceptor 1, charging roller 2, exposure device 7, developing sleeve 31, primary transfer roller 6, intermediate transfer belt 8, secondary transfer roller 11, and fixing device 17 function as an image forming section that forms an image on sheet P. .

The image reader 102 is a so-called image reading device or document reading device. Image sensor 104 reads document 99 placed on platen glass 103 , creates image data (image signal), and transmits the image data to control circuit 40 . The platen glass 103 is sometimes called a platen. The operation panel 105 has a display device that displays information and an input device that receives information input by a user.

Incidentally, the sheet cassette 13 includes a regulating plate 42a for regulating the position of the sheet P in the conveying direction (longitudinal direction) and a regulating plate 42b for regulating the position of the sheet P in the direction perpendicular to the conveying direction (width direction). ,have. The size sensor 43a is a sensor that detects the length of the sheet P (the length in the conveying direction) based on the position of the regulation plate 42a. The size sensor 43b is a sensor that detects the width (the length in the width direction) of the sheet P based on the position of the regulation plate 42b. The sheet sensor 41 is a sensor that detects whether or not the sheet P exists in the sheet cassette 13 . The media sensor 45 is a sensor that detects the type of sheet P (eg, basis weight). A cassette sensor 44 is a sensor that detects that the sheet cassette 13 has been pulled out. The user pulls out the sheet cassette 13 to replenish the sheets P, exchange a certain type of sheet P for another type of sheet P, or exchange a certain size sheet P for another size sheet P. do. Therefore, the control circuit 40 detects insertion/removal of the sheet cassette 13 based on the detection result of the cassette sensor 44 . The density sensor 70 is a sensor that detects the density of the test image formed on the sheet P. FIG. These sensors are optional. A backup member 71 may be arranged at a position facing the density sensor 70 . The backup member 71 is a stabilizing member that stabilizes the posture of the sheet P passing through the detection position of the density sensor 70 .

[Phase detection]
As shown in FIG. 2, the photoreceptors 1Y to 1K and the developing sleeves 31Y to 31K may be provided with phase sensors 50 for detecting rotational phases. An output shaft 55 of the motor 54 is connected via a coupling mechanism or the like to a shaft 53 forming a rotation center of a rotating body such as the photosensitive member 1 . The phase sensor 50 has a photointerrupter 51 and a light blocking member 52 . The light shielding member 52 is provided integrally with the shaft 53 and rotates as the shaft 53 rotates. When the shaft 53 rotates and the light blocking member 52 reaches a predetermined rotational position, the light blocking member 52 is detected by the photointerrupter 51 . The phase sensor 50 detects the rotational phase of the rotating body based on the output of the photointerrupter 51 .

Although the example shown in FIG. 2 employs a direct drive system in which the shaft 53 of the photosensitive member 1 and the output shaft 55 of the motor 54 are directly connected, this is merely an example. A reduction mechanism may be inserted between the shaft 53 of the photoreceptor 1 and the output shaft 55 of the motor 54 . A similar driving method can be employed for the charging roller 2 and the developing sleeve 31 as well. However, the charging roller 2 may rotate following the photoreceptor 1, in which case the motor 54 for the charging roller 2 becomes unnecessary. Even if a charging member having another shape is employed in place of the charging roller 2, the motor 54 and the phase sensor 50 for the charging roller 2 are not required.

[controller]
FIG. 3 shows an example of the control circuit 40. As shown in FIG. A CPU 301 is a processing circuit that controls the image forming apparatus 100 according to a control program stored in a ROM (Read Only Memory) of a memory 302 . ROM is a general term for non-volatile storage devices. The memory 302 may include RAM (random access memory) and the like. RAM is a general term for volatile storage devices. An image processing unit 303 converts image data output from an external computer or image reader 102 to generate an image signal for the exposure device 7 . Furthermore, the image processing unit 303 may be configured to generate an image signal of a test image for measuring density unevenness.

The CPU 301 implements various functions by executing control programs. The obtaining unit 311 causes the image reader 102 or the density sensor 70 to detect the test image formed on the sheet P, creates a density unevenness profile based on the detection result, and stores it in the memory 302 . A profile of density unevenness may be called a density profile. CPU 301 (acquisition unit 311 ) uses the output signal of phase sensor 50 and timer 305 to calculate the rotation phase of the rotating body. A collection unit 312 collects the detection result of the sheet sensor 41 , the detection result of the size sensors 43 a and 43 b , the detection result of the cassette sensor 44 , the detection result of the media sensor 45 , and stores them in the memory 302 . A determination unit 313 determines whether or not there is a sheet P in the sheet cassette 13 based on the detection result of the sheet sensor 41 . The determination unit 313 detects the size of the sheets P stacked in the sheet cassette 13 based on the detection results of the size sensors 43a and 43b. The determination unit 313 detects the long sides and short sides of the sheets P stacked in the sheet cassette 13 based on the detection results of the size sensors 43a and 43b. The determination unit 313 identifies the accommodation direction of the sheets P in the sheet cassette 13 based on the detection results of the size sensors 43a and 43b. A determination unit 313 detects that the sheet cassette 13 has been pulled out and that the sheet cassette 13 has been set at a predetermined position based on the detection result of the cassette sensor 44 . A determination unit 313 determines the type of the sheet P based on the detection result of the media sensor 45 .

A UI unit 314 displays information such as guidance on density unevenness correction on the display device 106 of the operation panel 105 and receives instructions input by the user through the input device 107 of the operation panel 105 . The input device 107 may be a touch panel sensor.

Actuator group 308 includes motor 54 and solenoid provided in image forming apparatus 100 . A high-voltage power supply 309 is a power supply circuit that generates various high voltages required in the image forming process, such as charging bias, developing bias, and transfer bias.

Further, the acquisition unit 311 associates the rotation phase (phase Φ) detected by the phase sensor 50 with the density (amplitude D) output from the density sensor 70 to create a density profile, and stores it in the memory 302 . may Phase Φ and amplitude D may be computed by applying a Fourier transform to the readout of test image 400 . A correction unit 315 determines a correction bias ΔVdc for correcting the development bias Vdc based on the profile. In this embodiment, the development bias Vdc refers to the DC component of the AC component and the DC component included in the development voltage. A correction unit 315 determines a correction bias ΔVc for correcting the charging bias Vc based on the profile. A bias setting unit 316 sets the high-voltage power supply 309 so that the developing bias Vdc and the charging bias Vc are output. The bias setting unit 316 adds the correction bias Δvdc to the initial value of the developing bias Vdc, or adds the correction bias Δvd to the initial value of the charging bias Vc. Thereby, the high voltage power supply 309 outputs the modulated developing bias Vdc and the modulated charging bias Vc. Since the developing bias Vd and the charging bias Vc are modulated in opposite phases with respect to the phase of density unevenness, density unevenness is reduced. It is not essential that both the developing bias Vdc and the charging bias Vc are modulated, either one of them may be modulated. If the density unevenness is very small, neither the developing bias Vdc nor the charging bias Vc need be modulated.

[Test image for detecting density unevenness]
FIG. 4 shows a test image 400 formed on a sheet P having a length W1 in the width direction and a length L1 in the length direction. The test image 400 has test patterns 401K-401C extending parallel to the transport direction. The test pattern 401K is a toner image formed with black toner at a constant density. The test pattern 401Y is a toner image formed with yellow toner at a constant density. The test pattern 401M is a toner image formed with a constant density using magenta toner. The test pattern 401C is a toner image formed with cyan toner at a constant density. The constant density is, for example, a density that is 50% of a predetermined maximum density of the toner image.

By the way, the test image 400 needs to be able to detect density unevenness that occurs periodically in the sub-scanning direction (conveying direction of the sheet P). Such density unevenness is often caused by rotating bodies such as the photoreceptor 1, the developing sleeve 31, and the charging roller 2. FIG. Therefore, the length L1 of the test patterns 401K-401C must be at least longer than the circumference of these rotating bodies. Of the circumferences of these rotating bodies, the circumference of the photoreceptor 1 is the longest. For example, if the diameter of the photoreceptor 1 is 30 mm, its circumference is approximately 95 mm. Therefore, the length L1 of the test patterns 401K to 401C can be set to 238 mm, which is about 2.5 times longer than the peripheral length of the photoreceptor 1. FIG. This is to reduce the effects of density streaks that occur suddenly, other noise, and the reflectance unevenness of the intermediate transfer belt 8 that is the base of the test pattern, in addition to the periodic density unevenness. As shown in FIG. 4, length L0 of sheet P must be longer than length L1 of test patterns 401K-401C. Therefore, the size of the sheet P is limited to a size that allows the entire test image 400 to be printed. Further, when a plurality of periodic density unevennesses occur simultaneously, a certain number of density measurement results (sample results) are required to accurately separate the plurality of periodic density unevennesses. Therefore, the length L1 of the test patterns 401K to 401C is selected to be twice or more (for example, 2.5 times) the maximum circumference of the plurality of rotating bodies.

Since the size of the sheet P on which the test image 400 can be formed is limited in this way, a maintenance worker or an operator such as a user must prepare a sheet P of an appropriate size. However, since expert knowledge is required to determine the size of the sheet P on which the test image 400 can be formed, it is not easy for the operator to prepare an appropriate sheet P.

[Method for Correcting Density Unevenness]
FIG. 5 is a flow chart showing a density unevenness correction method according to the first embodiment. Density unevenness correction is a process of correcting image forming conditions (process conditions) so as to reduce density unevenness based on the detection result of the test image 400 . Specifically, the density of the test image 400 formed with a constant charging bias Vc and a constant developing bias Vdc is detected. Next, unevenness components that depend on the rotation cycles of a plurality of rotating bodies such as the photoreceptor 1 and the developing sleeve 31 included in the density unevenness are extracted from the detection result. A method of modulating the charging bias Vc and the developing bias Vdc is determined so that density unevenness is canceled based on the extraction result. Here, the modulation is realized by adding the correction bias ΔVc to the initial value of the charging bias Vc and adding the correction bias ΔVc to the initial value of the development bias Vdc. The correction bias ΔVc is a correction value that changes according to the rotation phase of the photoreceptor 1 . The correction bias ΔVdc is a correction value that changes according to the rotational phase of the developing sleeve 31 .

When a predetermined start condition is satisfied, the CPU 301 executes the following processes. The predetermined start condition is that an explicit start instruction is input from the operation panel 105, that a consumable part or the like is replaced, or that the cumulative number of images formed reaches a predetermined number. There may be.

In S<b>501 , the CPU 301 executes preparation processing for the sheet P on which the test image 400 is to be formed. The preparation process for the sheet P will be described later with reference to FIG.

In S502, the CPU 301 (acquisition unit 311) detects the home position of the rotational phase. For example, the acquisition unit 311 detects the home position of the rotation phase of the photoreceptor 1 based on the detection result of the phase sensor 50 provided for the photoreceptor 1 . Similarly, the obtaining unit 311 detects the home position of the rotational phase of the developing sleeve 31 based on the detection result of the phase sensor 50 provided for the developing sleeve 31 . The acquisition unit 311 may cause the memory 302 to store the relationship between the timing of the home position and the position of the test image. This relationship may be used to identify factors of density unevenness and to determine the rotation phases of correction biases ΔVc and ΔVdc in density correction.

In S503, the CPU 301 (acquisition unit 311, bias setting unit 316) forms a test image on the intermediate transfer belt 8 without modulating the charging bias Vc and the development bias Vdc. As a result, the test image 400 shown in FIG. 4 is formed on the sheet P. As shown in FIG.

In S<b>504 , the CPU 301 (UI unit 314 ) outputs reading guidance for the test image 400 . For example, the UI unit 314 outputs reading guidance to the display device 106 of the operation panel 105 . The reading guidance includes a message prompting the user to place the sheet P on which the test image 400 is formed on the platen glass 103 of the image reader 102 . Here, it is assumed that the test image 400 is read by the image reader 102, but if the test image 400 is read by the density sensor 70, S504 is omitted.

In S<b>505 , the CPU 301 (UI unit 314 ) displays a read start button on the display device 106 of the operation panel 105 . It is assumed that the read start button is a software button, but it could also be a hardware button. In this case, S505 is omitted.

In S506, the CPU 301 (determining unit 313) determines whether or not the user has instructed to start reading. For example, when the reading start button displayed on the operation panel 105 is operated, the determination unit 313 determines that the user has instructed to start reading, and advances the process to step S507. If the test image 400 is read by the density sensor 70, S506 is omitted.

In S507, the CPU 301 (acquisition unit 311) reads the test image 400 with the image reader 102 (or density sensor 70). Here, four test patterns 401K-401C are read respectively. Different image forming units are responsible for black, yellow, magenta and cyan. Therefore, the correction biases ΔVc and ΔVdc may differ for each image forming unit.

In S508, the CPU 301 (acquisition unit 311) creates a density profile for each of the test patterns 401K to 401C based on the reading result of the test image 400. FIG. A density profile is a collection of density data sampled at a predetermined sampling rate. The density profile is stored in memory 302 .

In S509, the CPU 301 (acquisition unit 311) detects periodic density unevenness regarding the photoreceptor 1 and the developing sleeve 31 from the density profiles of the test patterns 401K to 401C. For example, the acquisition unit 311 extracts the relationship between the amplitude and phase of density (unevenness). Specifically, the acquisition unit 311 performs Fourier transform on the density profile to obtain the amplitude and phase of each frequency component, and extracts the density unevenness component caused by the rotation cycle of the photoreceptor 1 and the developing sleeve 31 based on the amplitude and phase. do. For example, assume that the process speed S is 240 mm/s, the diameter of the developing sleeve 31 is 20 mm, and the developing sleeve 31 is rotationally driven at a peripheral speed of 180% with respect to the photosensitive member 1 . In this case, the rotation period of the developing sleeve 31 is 145 ms. The photoreceptor 1 has a diameter of 30 mm and is rotationally driven at 240 mm/s, so the period of the photoreceptor 1 is 392 ms. The acquiring unit 311 associates the amplitude D and the phase Φ of the density unevenness component caused by the developing sleeve 31 and stores them in the memory 302 . Similarly, the CPU 301 causes the memory 302 to store the amplitude Dd and the phase Φd of the density unevenness component caused by the photoreceptor 1 in association with each other.

In S510, the CPU 301 (correction unit 315) determines correction biases ΔVdc and ΔVc. A correction unit 315 determines a correction bias ΔVdc for correcting the development bias Vdc based on the amplitude D and the phase Φ. Here, correcting the developing bias Vdc means determining a correction amount (correction bias ΔVdc) for the developing bias Vdc for each rotational phase of the developing sleeve 31 . A correction amount may be referred to as a correction component.

ΔVdc=Va×cos(ωt+θ) (1)
Here, Va is a potential difference (amplitude) corresponding to the amplitude D, which is called a development contrast difference. The memory 302 stores an equation or a conversion table for converting the amplitude D into the amplitude Va and is used by the CPU 301 . ω is the angular velocity of the developing sleeve 31 . t is time. The phase constant θ is pre-stored in the memory 302 . When the concentration sensor 70 is used, the phase constant θ is defined by the following equation.
θ=Φ−ω×Δt+π (2)
Here, Δt is a coefficient relating to the time difference, which is pre-stored in the memory 302 . Δt is the time difference from when the image is formed until it is detected by the density sensor 70 . From the process speed S and the distance ds from the developing device 3 to the density sensor 70, it is obtained by the following equation.
Δt=ds/S (3)
The development bias Vdc is modulated in a phase opposite to that of the density unevenness so that a development contrast Vcont corresponding to the amplitude D of the density unevenness is generated. As a result, the density unevenness component dependent on the developing sleeve 31 is canceled out. The CPU 301 calculates a development contrast difference (amplitude Va) corresponding to the amplitude D. FIG. Correction unit 315 stores amplitude Va, angular velocity ω, and phase constant θ in memory 302 .

Furthermore, a correction bias ΔVc for the charging bias Vc is calculated from the following equation. The amplitude obtained from the density unevenness component for photoreceptor 1 is Vb, and the phase for photoreceptor 1 is Φd. These are determined from the concentration profile.

ΔVc=Vb×cos(ω2t+θ2) (4)
Here, Vb is called a development contrast difference and is a potential difference (amplitude) corresponding to the amplitude Dd. ω2 is the angular velocity of the photosensitive member 1; When concentration sensor 70 is used, phase constant θ2 is defined by the following equation.
θ2=Φd−ω2×Δt+π (5)
In S<b>510 , the CPU 301 (correction unit 315 ) stores the correction biases ΔVdc and ΔVc in the memory 302 . That is, the CPU 301 may store the formula (1), which is the correction formula for the developing bias Vdc, in the memory 302 . Similarly, the CPU 301 may store the equation (4), which is the correction equation for the charging bias Vc, in the memory 302 . Alternatively, the correction bias ΔVdc for each rotation phase based on the home position of the developing sleeve 31 may be obtained in advance and stored in the memory 302 . A set of pairs of rotation phases and correction biases ΔVdc may be referred to as a correction bias waveform. Similarly, the correction bias ΔVc for each rotation phase based on the home position of the photoreceptor 1 may be obtained in advance and stored in the memory 302 . Alternatively, the correction bias ΔVc for each rotation phase based on the home position of the developing sleeve 31 may be obtained in advance and stored in the memory 302 .

In step S<b>511 , the CPU 301 (UI unit 314 ) displays on the display device 106 of the operation panel 105 a completion message indicating that the density unevenness correction has been completed. This will allow the user to recognize that the density unevenness correction has been completed.

[Sheet preparation process]
FIG. 6 shows the sheet P preparation process. This corresponds to step S501 shown in FIG.

In S<b>601 , the CPU 301 (determination unit 313 ) determines whether or not there is a sheet P in the sheet cassette 13 based on the detection result of the sheet sensor 41 collected by the collection unit 312 . A plurality of sheet cassettes 13 may exist. The configuration of the sensor and feeding mechanism provided for each of the plurality of sheet cassettes 13 is common. In this case, the determination unit 313 detects the presence or absence of the sheet P for each sheet cassette 13 based on the detection result of the sheet sensor 41 provided for each of the plurality of sheet cassettes 13 . If the sheet P exists in the sheet cassette 13, the CPU 301 skips S602 and advances the process to S603. If the sheet P does not exist in the sheet cassette 13, the CPU 301 advances the process to S602.

In S602, the CPU 301 (UI unit 314) prompts the operator to replenish sheets. For example, UI unit 314 may display a message on display device 106 of operation panel 105 . This message may be, for example, a message such as "please put a sheet in the cassette". After that, the CPU 301 advances the process to S601.

In S<b>603 , the CPU 301 (determining unit 313 ) determines whether the size of the sheets P contained in the sheet cassette 13 is appropriate based on the detection result of the size sensor 43 a collected by the collecting unit 312 . As mentioned above, the length L0 of the sheet P must be longer than the length L1 of the test image 400. Therefore, if L0>L1, the determination unit 313 determines that the size of the sheets P accommodated in the sheet cassette 13 is appropriate, and advances the process to S605. On the other hand, if the size of the sheets P contained in the sheet cassette 13 is not appropriate, the determination unit 313 advances the process to S604.

In step S<b>604 , the CPU 301 (UI unit 314 ) prompts the operator to store sheets P of an appropriate size in the sheet cassette 13 via the operation panel 105 . For example, the UI unit 314 may display a message including a specific sheet P size on the display device 106 of the operation panel 105 . The message may be, for example, "Please put a sheet with a long side of 250 mm or more in the cassette". After that, the CPU 301 advances the process to S601.

In S<b>605 , the CPU 301 (determination unit 313 ) determines whether the type of sheets P contained in the sheet cassette 13 is appropriate. In general, the UI unit 314 and the collection unit 312 allow the operator to select or designate the type of sheet P via the operation panel 105 . Therefore, the determination unit 313 may determine whether the type of sheet P is appropriate based on the operator's input. Alternatively, the determination unit 313 may determine whether the type of sheet P is appropriate based on the type of sheet P detected by the media sensor 45 immediately before printing the test image. For example, if the cassette sensor 44 does not detect that the sheet cassette 13 is opened after the media sensor 45 detects the type, the type of the sheet P is not changed. Therefore, it can be presumed that the type of sheet P contained in the sheet cassette 13 matches the type detected by the media sensor 45 immediately before. If the type of sheet P is appropriate, the CPU 301 advances the process to step S607. If the type of sheet P is not appropriate, the CPU 301 advances the process to step S606.

In step S<b>606 , the CPU 301 (UI unit 314 ) prompts the operator to store the appropriate type of sheet P in the sheet cassette 13 via the operation panel 105 . For example, the UI unit 314 may display a message including a specific type of sheet P on the display device 106 of the operation panel 105 . The message may be, for example, "Please put plain paper in the cassette." After that, the CPU 301 advances the process to S601. In general, the process speed S of the sheet P differs depending on the type of the sheet P (basis weight, etc.). In the image forming apparatus 100, the most frequently used process speed S is set as a basic speed. Therefore, the process speed S used to form test image 400 is set to the base speed. However, the correction bias can also be determined using a process speed S other than the basic speed.

In S<b>607 , the CPU 301 (determination unit 313 ) determines whether the orientation of the sheets P accommodated in the sheet cassette 13 is appropriate. For example, the determination unit 313 can detect the size of the sheet P and the accommodation direction of the sheet P based on the detection results of the size sensors 43 a and 43 b collected by the collection unit 312 . For example, even if the long side of the sheet P is longer than the test image 400, the sheet P may be accommodated in the sheet cassette 13 so that the long side of the sheet P is orthogonal to the conveying direction. In this case, the short sides of the sheet P are parallel to the conveying direction. If the short side is shorter than the test image 400, it becomes impossible to form the entire test image 400 on the sheet P. If the accommodation direction of the sheets P with respect to the sheet cassette 13 is appropriate, the CPU 301 advances the process to S502 in FIG. If the accommodation direction of the sheet P is not appropriate, the CPU 301 advances the process to step S608.

In S<b>608 , the CPU 301 (UI unit 314 ) prompts the operator to change the accommodation direction of the sheets P through the operation panel 105 . For example, the UI unit 314 may output to the display device 106 a message such as "Please rotate the accommodation direction of the sheets in the cassette by 90 degrees."

As described above, according to the first embodiment, the usability of density unevenness correction is improved. For example, image forming apparatus 100 can guide the user when performing density unevenness correction, so the user can perform necessary operations without hesitation. It should be noted that although the description here is intended for general users, it will also be possible to reduce the work burden on maintenance workers.

[Operation after density unevenness correction]
When the operator instructs image formation, the CPU 301 detects the home position of the developing sleeve 31, reads out the correction bias ΔVdc for each rotation phase based on the home position from the memory 302, and corrects the development bias Vdc. For example, the development bias Vdc is modulated by adding the correction bias ΔVdc to the initial value of the development bias Vdc. Note that the correction bias ΔVdc for each rotation phase may be calculated from a formula or coefficients stored in the memory 302 . Similarly, the CPU 301 detects the home position of the photoreceptor 1, reads out the correction bias ΔVc for each rotation phase based on the home position from the memory 302, and corrects the charging bias Vc. For example, the charging bias Vc is modulated by adding the correction bias ΔVc to the initial value of the charging bias Vc. Note that the correction bias ΔVc for each rotation phase may be calculated from a formula or coefficients stored in the memory 302 .

<Example 2>
In Example 1, the presence/absence of the sheet P, appropriateness of size, appropriateness of type, and appropriateness of storage direction are checked one by one in order. However, the confirmation process and the guidance display process may be made more efficient.

FIG. 7 shows the sheet P preparation process. This corresponds to step S501 shown in FIG.

In S<b>701 , the CPU 301 (determination unit 313 ) determines whether or not there is an appropriate sheet P in the sheet cassette 13 . That is, S701 is a determination condition that combines the determination conditions of S601, S603, S605 and S607. For example, if the sheet sensor 41 cannot detect the sheet P, the determination unit 313 advances the process to S702. Alternatively, if the size detected by the size sensor 43a is inappropriate, the determination unit 313 advances the process to S702. Alternatively, if the type input by the operator is inappropriate, the CPU 301 advances the process to S702. Alternatively, if the accommodation direction of the sheet P based on the comparison of the detection results of the size sensors 43a and 43b is not appropriate, the determination unit 313 advances the process to S702. If the sheets P accommodated in the sheet cassette 13 are appropriate, the determination unit 313 advances the process to S502 in FIG.

In S702, the CPU 301 (UI unit 314) prompts the user to store an appropriate sheet. For example, UI unit 314 may display a message on display device 106 of operation panel 105 . This message may be, for example, "Please set plain paper with a long side of 250 mm or more in the cassette so that the long side is parallel to the transport direction." After that, the CPU 301 advances the process to S701.

As described above, according to the second embodiment, as in the first embodiment, the usability of density unevenness correction is improved. In the second embodiment, since the guidance is streamlined, usability is further improved.

<Example 3>
According to Example 1, a specific type of sheet P (eg, plain paper) is used, and the test image 400 is formed at a specific process speed S. FIG. Therefore, the correction biases ΔVdc and ΔVc are correction values suitable for a specific type of sheet P (eg, plain paper). However, there are a wide variety of types of sheets P on which an arbitrary image actually prepared by the operator is printed. For example, a process speed S slower than the process speed S for plain paper may be applied to thick paper, coated paper, embossed paper, etc., in order to ensure transferability and fixability.

The memory 302 may hold the relationship between the type of sheet P and the process speed S. FIG. The CPU 301 reads the process speed S corresponding to the type of sheet P specified by the operator from the memory 302 and acquires it. The CPU 301 can obtain the correction biases ΔVdc and ΔVc for each type of the sheet P by calculating the formula (3) from the read process speed S.

Alternatively, the memory 302 may store a conversion formula or a conversion table for converting the correction biases ΔVdc and ΔVc obtained at the basic speed based on the process speed S corresponding to the type of sheet P designated by the operator. good. In this case, the CPU 301 applies the process speed S corresponding to the type of sheet P designated by the operator to the conversion formula or conversion table, thereby obtaining correction biases ΔVdc and ΔVc corresponding to the type of sheet P designated by the operator. you may ask.

Thus, from the correction biases ΔVdc and ΔVc constructed using a specific type of sheet P, correction biases ΔVdc and ΔVc for other types of sheets P may be calculated.

According to the third embodiment, as in the first and second embodiments, the usability of density unevenness correction is improved. In the third embodiment, since the correction biases ΔVdc and ΔVc are obtained for each type of sheet P, it is considered that the density unevenness correction accuracy is improved. Furthermore, if the plain paper prepared by the operator is too small for the test image 400, another type of sheet P of a sufficient size can be used to calculate the correction biases ΔVdc and ΔVc for plain paper. Usability is thus further improved.

<Example 4>
In the first embodiment, the test image 400 is read by the image reader 102 in S507. However, as also mentioned in Example 1, the test image 400 may be read by the density sensor 70 . In this case, among the steps shown in FIG. 5, S504, S505 and S506 are omitted. In other words, the user's workload is further reduced.

The density sensor 70 may be installed not only in the image forming apparatus 100 provided with the image reader 102 as shown in FIG. 1, but also in the image forming apparatus 100 without the image reader 102 as shown in FIG. Either case can be used to sense the density of the test image 400 . However, the density sensor 70 is arranged downstream of the fixing device 17 and upstream of the discharge roller 20 in the sheet P conveying direction.

<Technical Concept Derived from Examples>
[Viewpoint 1]
The sheet cassette 13 is an example of holding means for holding the sheet P. As shown in FIG. The transport rollers 16 and 18 are an example of transport means for transporting the sheet P. As shown in FIG. The photoreceptor 1 and the like are an example of image forming means for forming an image on the sheet P. As shown in FIG. The image reader 102 and the density sensor 70 are an example of reading means for reading the test image formed on the sheet P. FIG. The CPU 301 functions as a control unit that controls the image quality (eg, density unevenness) of the image formed on the sheet P by the image forming unit based on the reading result of the test image. The CPU 301 determines whether the sheet P suitable for forming the test image is held by the holding means. Further, when the sheet P suitable for forming the test image is not held by the holding means, the CPU 301 instructs the operator to set the sheet P suitable for forming the test image on the holding means. output a message prompting An operator (eg, a user or a maintenance worker) can easily store the sheets P in the sheet cassette 13 according to the message. Therefore, the usability of correcting the image quality (eg, density unevenness) using the test image is improved.

[Viewpoints 2 to 4]
The collection unit 312, the operation panel 105, or the size sensors 43a and 43b are examples of size acquisition means for acquiring the size of the sheet P held by the holding means. The size information acquired by the operation panel 105 or the size sensors 43 a and 43 b may be stored in the memory 302 and referred to by the determination unit 313 . The determining unit 313 determines whether the sheet P suitable for forming the test image is held by the holding means based on whether the size acquired by the size acquiring means is a size that can accommodate the entire test image. You can determine whether there is The collecting unit 312 may acquire the size of the sheet P held by the holding means based on the operator's input or the detection results of the sensors (eg, size sensors 43a and 43b) that detect the size of the sheet P. The message to the operator may include size information indicating the size of the sheet that can contain the entire test image. This will allow the operator to easily understand what size sheet P should be prepared.

[Viewpoints 5 to 7]
The collection unit 312, the operation panel 105, or the size sensors 43a and 43b are an example of a direction acquisition unit that acquires the accommodation direction of the sheets P held by the holding unit. The collection unit 312 can identify the long side and the short side of the sheet P by comparing the lengths of the two sides acquired by the size sensors 43a and 43b. Furthermore, the collection unit 312 can determine whether the long side is parallel to the transport direction based on which of the size sensors 43a and 43b has detected the long side. The determination unit 313 determines whether or not the accommodation direction of the sheet P acquired by the direction acquisition unit is an accommodation direction in which the entire test image can be accommodated on the sheet P. FIG. The determination unit 313 determines whether or not the sheet P suitable for forming the test image is held by the holding means based on the determination result. In this manner, the collection unit 312 may acquire the accommodation direction of the sheets P held by the holding unit based on the operator's input to the operation panel 105 . The collection unit 312 may acquire the accommodation direction of the sheets P held by the holding unit based on the detection results of sensors (eg, size sensors 43a and 43b) that detect the accommodation direction of the sheets P. FIG. The message may include information prompting the holding means to rotate the accommodation direction of the sheet P by 90 degrees. This will allow the operator to appropriately set the direction in which the sheets P are to be accommodated.

[Viewpoints 8 to 10]
The collection unit 312, the operation panel 105, or the media sensor 45 is an example of a type acquiring unit that acquires the type of the sheet P held by the holding unit. The determination unit 313 determines whether the sheet P suitable for forming the test image is held by the holding means based on whether the acquired type of the sheet P matches the type specified in advance for forming the test image. It may be determined whether The collection unit 312 acquires the type of the sheet P held by the holding means based on the operator's input to the operation panel 105 . Alternatively, the collection unit 312 acquires the type of the sheet P held by the holding means based on the detection result of a sensor (eg, the media sensor 45) that detects the type of the sheet P. FIG. The media sensor 45 may be an ultrasonic sensor having a transmitter that transmits ultrasonic waves and a receiver that receives the ultrasonic waves that have passed through the sheet P. FIG. The message may include type information indicating the type of sheet P suitable for forming the test image. This allows the operator to easily understand what kind of sheet P should be prepared.

[Viewpoint 11]
The holding means may have first holding means and second holding means (a plurality of sheet cassettes 13). The determination unit 313 may determine whether the sheet P suitable for forming the test image is held in either the first storage means or the second storage means. There is a case where the sheet P suitable for forming the test image is not held in either the first storage means or the second storage means. In this case, the UI unit 314 may output a message prompting the operator to set the appropriate sheet P for forming the test image on the holding means.

[Viewpoint 12]
The obtaining unit 311 may extract density unevenness that occurs periodically in the conveying direction of the sheet P based on the reading result of the test image. A correction unit 315 corrects the image forming conditions applied to the image forming unit so as to reduce the density unevenness. This will appropriately reduce density unevenness.

[Viewpoints 13 and 14]
Photoreceptor 1 is an example of a photoreceptor that rotates in one direction. The charging roller 2 is an example of charging means for uniformly charging the photoreceptor using a charging bias. The exposure device 7 is an example of exposure means that exposes the photosensitive member to form an electrostatic latent image. The developing sleeve 31 is an example of developing means that forms a toner image by causing toner to adhere to the electrostatic latent image using a developing bias. A high-voltage power supply 309 is an example of a power supply that generates a charging bias and a developing bias. A bias setting unit 316 modulates the charging bias or developing bias in the power supply based on the result of reading the test image so as to reduce density unevenness. As described using equation (3), the correction unit 315 modulates the charging bias or developing bias (eg, correction bias ΔVdc, ΔVc) according to the process speed, which is the toner image forming speed on the sheet P. may be controlled.

[Viewpoints 15 and 16]
The image reader 102 is configured to read a test image from the sheet P discharged from the image forming apparatus. The density sensor 70 is provided inside the image forming apparatus and is configured to read a test image from the sheet P conveyed inside the image forming apparatus.

[Viewpoint 17]
If there is no sheet P held by the holding means, the UI unit 314 prompts the operator to store the sheet P into the holding means. If the size of the sheet P held by the holding unit is not the predetermined size, the UI unit 314 prompts the operator to store the sheet P of the predetermined size in the holding unit. The UI unit 314 prompts the operator to store a predetermined type of sheet P in the holding unit if the type of the sheet P held by the holding unit is not the predetermined type. The UI unit 314 prompts the operator to rotate the sheet P held by the holding means by 90 degrees if the accommodation direction of the sheet P held by the holding means is not the predetermined accommodation direction.

The invention is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the claims are appended to make public the scope of the invention.

13: sheet cassette, 18: conveying roller, 102: image reader, 301: CPU

Claims (17)

holding means for holding the sheet;
a conveying means for conveying the sheet;
an image forming means for forming an image on the sheet;
reading means for reading the test image formed on the sheet;
a control unit for controlling the image quality of the image formed on the sheet by the image forming unit based on the reading result of the test image;
The control means is
determining whether a sheet suitable for forming the test image is held by the holding means;
outputting a message prompting an operator to set a suitable sheet for forming the test image on the holding means in response to the fact that the holding means does not hold a suitable sheet for forming the test image; An image forming apparatus characterized by: further comprising size acquisition means for acquiring the size of the sheet held by the holding means;
Based on whether the size acquired by the size acquisition means is a size capable of accommodating the entire test image, the control means determines whether the sheet suitable for forming the test image is held by the holding means. 2. The image forming apparatus according to claim 1, wherein it is determined whether or not the image forming apparatus is held in a state. 3. The image according to claim 2, wherein the size acquisition unit acquires the size of the sheet held by the holding unit based on the operator's input or a detection result of a sensor that detects the size of the sheet. forming device. 4. The image forming apparatus according to claim 2, wherein the message includes size information indicating a size that can accommodate the entire test image. further comprising direction acquisition means for acquiring an accommodation direction of the sheet held by the holding means;
The control means controls whether or not the sheet accommodation direction acquired by the direction acquisition means is an accommodation direction in which the entire test image can be accommodated on the sheet. 5. The image forming apparatus according to claim 1, wherein it is determined whether an appropriate sheet is held by said holding means. 6. The apparatus according to claim 5, wherein the direction acquisition unit acquires the storage direction of the sheet held by the holding unit based on an input by the operator or a detection result of a sensor that detects the storage direction of the sheet. image forming device. 7. The image forming apparatus according to claim 5, wherein the message includes information prompting rotation of the direction in which the sheet is accommodated in the holding means by 90 degrees. further comprising type acquisition means for acquiring the type of the sheet held by the holding means;
The control means determines whether or not the type of the sheet acquired by the type acquisition means matches the type specified in advance for forming the test image. 6. The image forming apparatus according to any one of claims 1 to 5, wherein it is determined whether or not is held by said holding means. 9. The image according to claim 8, wherein the type acquisition unit acquires the type of the sheet held by the holding unit based on an input by the operator or a detection result of a sensor that detects the type of the sheet. forming device. 10. The image forming apparatus according to claim 8, wherein the message includes type information indicating a type of sheet suitable for forming the test image. The holding means has a first containing means and a second containing means,
The control means is
determining whether a sheet suitable for forming the test image is held in either the first storage means or the second storage means;
Forming the test image on the holding means in response to the fact that the sheet suitable for forming the test image is not held in either the first containing means or the second containing means. 11. The image forming apparatus according to any one of claims 1 to 10, wherein a message prompting an operator to set an appropriate sheet is output. The control means extracts density unevenness that occurs periodically in the conveying direction of the sheet based on the reading result of the test image, and performs image forming applied to the image forming means so as to reduce the density unevenness. 12. The image forming apparatus according to claim 1, wherein conditions are corrected. The image forming means is
a photosensitive member that rotates in one direction;
charging means for uniformly charging the photoreceptor using a charging bias;
an exposure unit that exposes the photoreceptor to form an electrostatic latent image;
developing means for forming a toner image by applying toner to the electrostatic latent image using a developing bias;
a power supply that generates the charging bias and the developing bias;
13. The image forming apparatus according to claim 12, wherein the controller modulates the charging bias or the developing bias in the power supply based on the result of reading the test image so as to reduce the density unevenness. 14. The image forming apparatus according to claim 13, wherein said control means controls the amount of modulation of said charging bias or said developing bias in accordance with a process speed, which is a speed at which said toner image is formed on said sheet. 15. The image forming apparatus according to claim 1, wherein said reading means is configured to read said test image from a sheet discharged from said image forming apparatus. 15. The reading means is provided inside the image forming apparatus and configured to read the test image from a sheet conveyed inside the image forming apparatus. The image forming apparatus according to any one of . holding means for holding the sheet;
a conveying means for conveying the sheet;
an image forming means for forming an image on the sheet;
reading means for reading the test image formed on the sheet;
a control unit for controlling the image quality of the image formed on the sheet by the image forming unit based on the reading result of the test image;
The control means is
prompting an operator to store a sheet in the holding means if there is no sheet held by the holding means;
prompting the operator to store the sheet of the predetermined size in the holding means if the size of the sheet held by the holding means is not a predetermined size;
prompting the operator to store the predetermined type of sheet in the holding means if the type of the sheet held by the holding means is not a predetermined type;
An image characterized by prompting the operator to rotate the sheet held by the holding means by 90 degrees if the holding direction of the sheet held by the holding means is not the predetermined holding direction. forming device.

Images