JP2015068977A - Image forming apparatus - Google Patents

Abstract

A reference patch pattern for calculating an image forming condition used for image quality adjustment operation has a configuration that does not cause a detection error by a potential sensor, an increase in toner consumption, or an increase in a mechanical load on a cleaning unit. An image forming apparatus is provided. A control unit that calibrates image forming conditions detects latent image potentials for a plurality of patch patterns with different widths and gradations in the main scanning direction under fixed image forming conditions. Based on the latent image potential from one of the patch patterns and the other patch pattern, the image forming conditions used for the image forming condition calibration when calibrating the image forming conditions to be the target image forming conditions A correction coefficient for setting the image forming condition is calculated, and a potential correction process for correcting at least the latent image potential of the patch pattern to be calibrated for the image forming condition, based on the correction coefficient, can be executed. Features. [Selection] Figure 7

Description

  The present invention relates to an image forming apparatus, and more particularly to a control mechanism for acquiring information necessary for image formation using a patch pattern.

In an image forming apparatus such as a copying machine, a facsimile machine, a printer, or a printing machine, a visible image carried on a photosensitive member, which is a latent image carrier, is transferred to a transfer body to obtain a copied output.
The images obtained by the image forming apparatus include not only single-color monochrome images but also multicolor images including full colors.
When obtaining a multicolor image, as an example, an image formed by the image forming unit of each color is sequentially transferred to an intermediate transfer member such as a belt by primary transfer to form a superimposed image, and the superimposed image is formed on a recording paper or the like. There is a case where batch transfer is performed on the recording medium by secondary transfer.

By the way, in each color image forming unit, it is required to achieve stabilization of image quality such as color reproducibility. For this reason, it is known to use a patch pattern formed by setting conditions for charging characteristics, writing characteristics, and development characteristics, which are image forming conditions for a photosensitive drum used as a latent image carrier.
One purpose of using the patch pattern is to guarantee the image density of the output image by adjusting the image density.

In this case, the latent image potential of the patch pattern on the photosensitive member used for the latent image carrier, the detection of the amount of attached toner using an optical sensor, and the development using the latent image potential and the amount of attached toner are performed. A linear approximate expression relating to the relationship between the potential and the toner adhesion amount is obtained.
Then, a desired toner adhesion amount can be obtained from the linear approximation equation using a relational expression between development γ (slope in the linear approximation equation) and development start voltage (development potential when the adhesion amount is 0 in the linear approximation equation). The image forming conditions are controlled.

Specifically, the following procedure is used.
(1) A plurality of reference patch patterns are formed on the photosensitive member by changing the charging bias or the writing density of a laser diode (LD).
(2) The latent image potential of the formed patch pattern is detected by a potential sensor, and the latent image potential is obtained based on the detection result.
(3) The development potential of each toner patch is calculated based on the latent image potential and the development bias.
(4) The electrostatic latent image is subjected to visible image processing using toner in the developing unit, and transferred from the photosensitive member to a belt as an intermediate transfer member.
(5) The transferred patch pattern is irradiated with LED light, and reflected light (plate making light or diffuse reflected light) is detected by an optical sensor. The optical sensor used for this double is a photodiode or a phototransistor.
(6) The detection result from the optical sensor is converted into the toner adhesion amount, and the toner adhesion amount in each patch pattern is determined.
(7) The toner adhesion amount in each patch pattern is output as data related to the development potential actually obtained with respect to the development potential to be density guaranteed, and development γ that is the slope of the approximate line and development that is the x intercept A start voltage (Vk) is calculated.
(8) Based on the result calculated in (7), the development bias and the charging bias to be corrected are determined and fed back to the image forming conditions.

On the other hand, with regard to feedback control of image forming conditions, a halftone potential at which a target halftone density is obtained is calculated based on the result of (7), and a plurality of dithers are changed by changing the writing density by the laser diode (LD). A pattern may be used.
In this case, the latent image potentials in a plurality of dither patterns are detected, and the writing density in the laser diode (LD) is fed back so as to obtain a halftone potential based on the detection result.
By the above procedure, the development bias, the charging bias, and the writing density at the present time are feedback-controlled, so that the solid density in the image area and the density in the halftone image area can be optimized to a desired density.

  For example, Patent Document 1 proposes a configuration using a potential sensor and a toner density sensor for the above procedure, that is, density correction in a solid image portion and a halftone image portion.

There is the following problem when trying to use a patch pattern when optimizing density correction in a solid image and a halftone image portion by the above-described procedure using the configuration disclosed in Patent Document 1.
In other words, if the correspondence relationship between the sensor and the patch pattern is not matched, there is a possibility that erroneous detection will occur when the latent image potential is detected. As a result, the image forming conditions may not be optimized. Hereinafter, this reason will be described.
FIG. 17 is a diagram for explaining the relationship between the patch pattern and the detection range by the sensor.
In the same figure, (A) shows the case where the detection area of the potential sensor is included in the main scanning direction width of the patch pattern, and (B) shows the main scanning of the patch pattern with respect to the detection area of the potential sensor. The case where the direction width is small is shown.
As shown in (B), when the detection area of the potential sensor protrudes from the width of the patch pattern in the main scanning direction, it is actually affected by the background potential on the surface of the photoreceptor as compared with the case shown in (A). A result different from the detection result in the pattern portion is obtained.
FIG. 18 is a diagram showing the correlation between the size of the patch pattern and the detected potential obtained from this size.
As shown in the figure, when the main scanning width of the patch pattern is smaller than the detection area of the potential sensor, the influence of the background potential of the photoreceptor is affected as the detection area becomes larger than the width of the patch pattern in the main scanning direction. As a result, an error increases with the detected potential in the actual patch pattern.
FIG. 19 is a diagram showing development γ obtained from the relationship between the development potential and the toner adhesion amount. As shown in FIG. 19, when the width of the patch pattern in the main scanning direction is small, the width is large. As compared with the above, the development γ (inclination) tends to be large. For this reason, when the target toner adhesion amount is reached, the development potential is smaller than that at the appropriate time.

When the development potential is obtained with a small value as described above, a small value is also selected for the development bias, which is another element of the image forming conditions, and a small value is also selected for the charging bias for making the background potential constant based on the development bias. Will be.
In addition, when the development potential is selected to be small, it is determined that the halftone density is small when the desired halftone density is obtained, and the output of the laser diode (LD) is also set small. become. For this reason, the output of the laser diode (LD) for setting the intensity of the writing light is set to a value lower than the output corresponding to the desired density.
As described above, the developing bias, the charging bias, and the output value of the writing laser diode used for the image forming conditions are selected and set to values that tend to decrease the density. For this reason, the image density obtained after the image quality adjustment operation by feedback control is thin, unlike the image density in the initial condition.

Therefore, it is important that the width of the patch pattern in the main scanning direction is formed so as to sufficiently include the detection region by the potential sensor so as not to cause the above-described problems.
However, when a patch pattern having a width in the main scanning direction that is larger than the detection area by the potential sensor is formed, toner consumption increases and excessive toner toner inflow tends to occur in the toner cleaning unit. New problems such as an increase in load on the member arise.
In order to avoid the fact that the image density of the solid image or halftone image described above cannot be accurately determined due to the difference in the size of the patch pattern in the main scanning direction and the detection area of the potential sensor, the potential sensor is Although it can be considered to be close to the photoconductor, in this case, it may be influenced by mechanical errors of the photoconductor. That is, when the photosensitive member is a drum, the photosensitive member is easily affected by the eccentricity due to the mechanical error of the photosensitive member. For example, problems such as a change in the patch pattern detection area due to a change in the distance from the potential sensor due to eccentricity and contamination due to toner scattering to the potential sensor occur.

  The present invention has a configuration in which a reference patch pattern for image formation condition calculation used for image quality adjustment operation does not cause a detection error by a potential sensor, an increase in toner consumption, or an increase in a mechanical load on a cleaning unit. An object of the present invention is to obtain an image forming apparatus.

  In order to achieve this object, the present invention is directed to detecting a latent image potential of each patch pattern and a toner adhesion amount for a plurality of patch patterns formed on the latent image carrier for correcting image forming conditions. And an image forming apparatus including a control unit that performs calibration for image quality adjustment with respect to charging potential, writing intensity, and developing bias used as target image forming conditions according to a detection result from the detecting unit. A pattern having at least two or more main scanning direction widths is formed as the patch pattern, and one of the patch patterns has a main scanning direction width similar to the patch pattern formed at the time of calibration of the image forming conditions. And the other patch patterns have a width in the main scanning direction according to at least two image forming conditions, and the control unit is fixed. When detecting the latent image potential for each patch pattern under the image forming conditions and calibrating the image forming conditions to be the target image forming conditions based on the detection results, Based on the latent image potential from the patch pattern, a correction coefficient for setting an image forming condition used for image forming condition calibration is calculated, and at least the image forming condition used at the time of image forming condition calibration based on the correction coefficient An image forming apparatus is characterized in that a potential correction process for correcting a latent image potential of a patch pattern to be calibrated can be executed.

According to the present invention, the influence of background potential is reduced by using a patch pattern having a main scanning direction width used at the time of image forming condition calibration and a patch pattern having a main scanning direction width according to at least two image forming conditions. False detection by the potential sensor can be reduced.
As a result, it is possible to maintain the proper density while optimizing the density adjustment based on the data obtained from the formed patch pattern and preventing an increase in the amount of toner consumed for patch pattern formation and an increase in the load on the cleaning unit. It becomes.

1 is a diagram for explaining a configuration of an image forming apparatus according to an embodiment of the present invention. It is a perspective view for demonstrating the structure of the sensor connected to the control part shown in FIG. FIG. 2 is a block diagram for explaining a configuration of a control unit used in the image forming apparatus shown in FIG. 1. FIG. 2 is a diagram illustrating an example of an image density adjustment patch pattern used in the image forming apparatus illustrated in FIG. 1. It is a figure which shows the modification of the patch pattern shown in FIG. It is a figure which shows the partial modification of the patch pattern shown in FIG. FIG. 4 is a flowchart for explaining a potential correction processing procedure executed in a control unit shown in FIG. 3. FIG. It is a diagram showing an approximate linear equation obtained from a result of plotting a main scanning direction width of a patch pattern and a latent image potential detected by a potential sensor. FIG. 4 is a flowchart for explaining an image density adjustment processing procedure executed by a control unit shown in FIG. 3. FIG. It is a figure which shows the optical attenuation curve of the writing laser used for a writing unit. It is a diagram showing an approximate linear equation for explaining the relationship between the development potential and the toner adhesion amount. FIG. 6 is a diagram illustrating an adjustment pattern for each gradation by changing a writing laser output in a plurality of steps with a charging bias and a developing bias fixed. It is an electrogram which shows the relationship between a writing laser output and a pattern part electric potential. 3 is a line showing a comparison result of the relationship between the development potential and the toner adhesion amount after the potential correction processing executed in the control unit shown in FIG. 3 and the relationship between the development potential and the toner adhesion amount when the potential correction processing is not performed. FIG. FIG. 4 is a flowchart showing a processing procedure for optimizing a main scanning direction width of an adjustment pattern, which is executed by a control unit shown in FIG. It is a figure which shows an example of the patch pattern used for the process sequence shown in FIG. It is a figure for demonstrating the relationship between a patch pattern and the detection range by a sensor. It is a diagram which shows the correlation of the magnitude | size of a patch pattern, and the detection electric potential obtained from this magnitude | size. FIG. 6 is a diagram showing development γ obtained from the relationship between development potential and toner adhesion amount.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating an image forming apparatus according to an embodiment of the present invention.
An image forming apparatus 100 shown in FIG. 1 is a full color printer of a quadruple tandem type intermediate transfer system. However, the present invention is not limited to this, and may be a full-color machine such as a 4-drum tandem direct transfer system or a 1-drum intermediate transfer system, or a monochrome machine such as a 1-drum direct transfer system.
In the intermediate transfer system, a plurality of image forming stations are juxtaposed along the direction in which a transfer belt used as an intermediate transfer member is stretched.
That is, in FIG. 1, the photosensitive drums 2Y, 2M, 2C, which are image bearing members and are latent image carriers used in the image forming station, along the extended surface of the intermediate transfer belt 1 that is an intermediate transfer member. 2K are installed side by side.
The symbol Y indicates yellow, M indicates magenta, C indicates cyan, and K indicates black.
The yellow (Y) image forming station in FIG. 1 will be described as a representative as follows.
Around the photosensitive drum 2Y, there are a charging charger 3, a writing unit 4Y, a developing unit 5Y as a charging means, a primary transfer roller 6Y as a primary transfer means, a photosensitive cleaning unit 7Y, and a quenching lamp 8Y in the order of rotation. Has been placed. The same applies to imaging stations of other colors.
Above the writing unit 4, a scanner unit 9, an ADF 10, and the like are provided.

The intermediate transfer belt 1 is rotatably supported by a plurality of rollers 11, 12, and 13, and an intermediate transfer belt cleaning unit 15 as a cleaning unit is provided at a portion facing the rollers 12.
A secondary transfer roller 16 as a transfer unit is provided at a portion facing the roller 13.
A plurality of paper feed trays 17 are provided at the lower part of the apparatus main body. A recording sheet 20 as a recording medium accommodated in these trays is fed by a pickup roller 21 and a sheet feeding roller 22, conveyed by a conveying roller pair 23, and a secondary transfer portion at a predetermined timing by a registration roller pair 24. Sent to.
A fixing unit 25 as a fixing unit is provided downstream of the secondary transfer portion in the sheet conveyance direction. In FIG. 1, reference numeral 26 denotes a paper discharge tray, and 27 denotes a switchback roller pair.

The image forming operation in the configuration shown in FIG. 1 will be described as follows.
When a print start command is input, the rollers around the photosensitive drum, the intermediate transfer belt, and the paper feed path start to rotate at a predetermined timing, and the recording paper feed starts from the lower paper feed tray. Is done.
On the other hand, the surface of each photosensitive drum 2 is charged to a uniform potential by the charging charger 3, and the surface is exposed according to the image data by the writing light emitted from the writing unit 4.
The potential pattern after the exposure is called an electrostatic latent image. The photosensitive drum 2 carrying the electrostatic latent image on the surface thereof is supplied with toner from the developing unit 5 to carry the electrostatic latent image. The electrostatic latent image is developed to a specific color.
In FIG. 1, since the photosensitive drums 2 have four colors, toner images of yellow, magenta, cyan, and black (color order varies depending on the system) are developed on the photosensitive drums.
The toner image developed on each photosensitive drum 2 is intermediated by a primary transfer bias and a pressing force applied to a primary transfer roller 6 disposed opposite to the photosensitive drum at a contact point with the intermediate transfer belt 1. Transferred onto the transfer belt 1.
A full color toner image is formed on the intermediate transfer belt 1 by repeating the four colors while matching the timing of the primary transfer operation.

The full-color toner image formed on the intermediate transfer belt 1 is transferred to the recording paper 20 conveyed at the timing by the registration roller pair 24 in the secondary transfer roller portion. At this time, the secondary transfer is performed by the secondary transfer bias applied to the secondary transfer roller 16 and the pressing force.
The recording paper 20 to which the full-color toner image has been transferred passes through the fixing unit 25, whereby the toner image carried on the surface is heated and fixed.
If it is single-sided printing, it is conveyed straight as it is to the paper discharge tray 26, and if it is double-sided printing, the conveyance direction is changed downward and conveyed to the paper reversing unit.
The recording paper 20 that has reached the paper reversing section is conveyed so that the conveying direction is reversed by the switchback roller pair 27 and exits the paper reversing section from the rear end of the paper. This is called a switchback operation, and the front and back of the recording paper can be reversed by this operation.
The recording paper that has been turned upside down does not return to the fixing unit, but passes through the refeed conveyance path and joins the original paper feed path.

Thereafter, the toner image is transferred in the same manner as the front surface printing, and is discharged through the fixing unit 25. This is a double-sided printing operation.
The operation of each part will be explained to the last. The photosensitive drum 2 that has passed through the primary transfer part carries the primary transfer residual toner on its surface, and this is transferred to the photosensitive drum cleaning unit 7 constituted by a blade, a brush and the like. Removed.
Thereafter, the surface is uniformly discharged by the quenching lamp 8 to prepare for charging for the next image.
The intermediate transfer belt 1 that has passed through the secondary transfer portion also carries secondary transfer residual toner on its surface, which is also removed by an intermediate transfer belt cleaning unit 15 composed of blades and brushes. Removed and ready for transfer of next toner image.
By repeating such an operation, single-sided printing or double-sided printing is performed.

In FIG. 1, a toner image detection sensor 30 is provided in the vicinity of the intermediate transfer belt 1 as density detection means for detecting the density of the toner image formed on the belt 1. As the toner image detection sensor 30, a sensor capable of receiving and detecting reflected light from the toner image, such as an optical sensor, is used.
The toner image detection sensor 30 detects the density of the toner image of the image pattern formed on the surface of the intermediate transfer belt 1, and the detection result is used for image unevenness correction control.
In the configuration shown in FIG. 1, the toner image detection sensor 30 is disposed at a position P <b> 1 (position before secondary transfer) facing a portion of the intermediate transfer belt 1 that is wound around the roller 11.
The toner image detection sensor may be disposed on the downstream side of the secondary transfer unit. In this case, the toner image detection sensor is opposed to the backup roller 14 disposed inward of the intermediate transfer belt 1 for preventing the shaking. (In FIG. 1, for convenience, it is indicated by reference numeral 30 ').

  The toner image whose density is detected by the toner image detection sensor 30 is used as a control pattern image formed on the photosensitive member and then transferred to the intermediate transfer belt 1.

The potential sensor 31 (Y, C, M. K) used in the image forming apparatus according to the present embodiment is arranged on the downstream side of the exposure position in the moving direction of the photosensitive member, and the potential of the electrostatic latent image formed by exposure writing. It is used as a means for detecting
Although not shown, the potential sensor has the following configuration.
A potential measuring electrode disposed opposite to the surface of the photosensitive member, a tuning fork vibrator as a chopper disposed between the measuring electrode and the photosensitive member, an AC voltage measuring circuit, and a DC voltage measuring circuit are provided.
In this configuration, the tuning fork vibrator is vibrated by a piezoelectric element or the like to periodically change the effective facing area between the potential measuring electrode and the surface of the photosensitive member. This causes a capacitance change in the electric field between the electrostatic latent image on the photoconductor and the potential measurement electrode, which is generated when the distance between the electrostatic latent image and the potential measurement electrode changes periodically, and charges are induced in the potential measurement electrode. An AC signal is taken in as a measurement object using. Such a configuration is known, for example, from Japanese Patent Laid-Open No. 11-352167.

On the other hand, the toner image detection sensor 30 described above includes four sensor heads 30a to 30d arranged in parallel on a sensor substrate 32 having a longitudinal direction in a direction transverse to the moving direction of the intermediate transfer belt 1, as shown in FIG. It is prepared for. The toner image detection sensor 30 shown in FIG. 2 is arranged on the front side of the secondary transfer position (position indicated by reference numeral P1 in FIG. 1) located in the vicinity of the roller around which the intermediate transfer belt 1 is wound in FIG. It is a case.
Note that the configuration shown in FIG. 2 shows a case in which the number of sensor heads corresponding to each color is provided, and in this configuration, the toner adhesion amounts at four locations can be detected simultaneously. Of course, it is not limited to the number of heads. For example, the configuration may be a one-piece or two-piece toner image detection sensor 30 having one or two sensor heads, or four heads to seven having a sensor head dedicated to each color. The configuration of the individual toner image detection sensor 30 may be used.

On the other hand, the above-described potential sensor 31 is connected to the input side of the control unit 200 shown in FIG.
In FIG. 3, the control unit 200 includes, for example, a microcomputer, and includes a CPU (Central Processing Unit) 201 as an arithmetic processing unit, a RAM (Random Access Memory) 202 as a storage unit, and a ROM (Read Only Memory). 203 or the like.
The control unit 200 is electrically connected to the image forming stations 40Y, 40M, 40K, the writing unit 4, the optical sensor unit 30 using the toner image detection sensor 30, and the like. In FIG. 3, reference numeral 30 is attached to the optical sensor unit.
As will be described later, the control unit 200 performs the potential correction processing corresponding to the environmental variation, the number of printed sheets, and the change amount of the developing ability obtained at the time of the previous correction. Is connected.
In other words, a temperature detection unit is connected for environmental fluctuations, a print number detection unit such as a number counter is connected for the number of prints, and a predetermined threshold value is stored in advance for the amount of change in development capability.

Based on the control program stored in the RAM 202, the control unit 200 is based on the control of the apparatus related to the image formation, the patch pattern formation control which will be described later, and the patch pattern potential detection. Image quality adjustment control for image forming condition calibration is performed.
The RAM 202, which is a non-volatile memory, stores output conversion data (conversion table), which will be described later, and output conversion as output conversion information used when calculating the toner concentration (toner adhesion amount) from the detection value of each optical sensor in the optical sensor unit 30. Stores the formula (algorithm).

In this embodiment, an image density adjustment pattern having a configuration described later is used for image quality adjustment. Hereinafter, an image density adjustment pattern and a configuration for detecting this will be described.
In this embodiment, as shown in FIG. 4, the detection configuration is such that image density adjustment patterns are formed in series and the detection sensor is one head. In FIG. 4, sensors disposed on both sides in the width direction of the intermediate transfer belt 1 indicate position shift detection sensors that detect a position shift correction pattern formed on the intermediate transfer belt 1.
In FIG. 4, the image density adjustment pattern is arranged at the center of the image in the image region width. This is because the central portion is least affected by the density deviation within the image forming width in the main scanning direction.
These image density adjustment patterns have 5 gradations, and the power of a laser diode (hereinafter referred to as Ld for convenience) is fixed, and the charging potential and the developing bias are sequentially changed to change the developing potential to create an image. This is an analog pattern.
Although the image density adjustment pattern has been described with 5 gradations, it is desirable to select an appropriate gradation number from the stability of the image forming system. For example, FIG. 5 is a diagram showing another example of the image density adjustment pattern, and the pattern shown in FIG. 5 switches the density like the LD-DUTY format or the dot matrix format without switching the image forming bias. It is also possible to create patterns with different gradations.

In forming the above-described pattern, the control unit 200 forms patch patterns A and B having different widths in the main scanning direction as shown in FIG.
The A patch has the same main scanning direction width as the patch pattern used for calibration of the image forming conditions, and the B patch has a main scanning direction width different from the A patch.
In particular, for the B patch, in the potential sensor having the detection characteristics as shown in FIG. 19, the detection error due to the main scanning width of the patch pattern is ± 2% based on the patch pattern having a main scanning width of 20 mm or more. , A pattern having a main scanning width of 20 mm or more. In the patches shown in FIG. 6, the sub-scanning direction widths of the two types of patterns are the same, but for the B patch, the sub-scanning direction width can be increased instead of the main scanning direction.

Using the patch pattern image described above, the control unit 200 executes image quality adjustment control in a state where the influence of the background potential is reduced based on the latent image potentials obtained from the two types of patterns by the procedure shown in FIG.
FIG. 7 is a flowchart for explaining the creation of the A patch and the B patch, the acquisition of the latent image potential for each patch, and the determination of the correction coefficient based on the acquired latent image potential.
In FIG. 7, patch patterns having different widths in the main scanning direction are created while changing the writing width while fixing the charging bias, developing bias, and writing LD output used for the image forming conditions (step S1).
In this case, the conditions for creating each patch are as described above.
Each patch formed on the photoreceptor is transferred to the intermediate transfer belt 1, and the latent image potential is detected by the potential sensor 31 (step S2).

A correction coefficient is determined by plotting the interlayer relationship between the latent image potential of each patch acquired in step S1 and the main scanning direction width of each patch (step S3).
FIG. 8 shows a result obtained by linearly approximating the result obtained by plotting the width in the main scanning direction and the latent image potential detected by the potential sensor 31 by the least square method. From this result, the inclination α and the intercept β are determined as correction coefficients.
The correction coefficients α and β are used to obtain the latent image potential in the actual patch pattern by including the background potential in the latent image potential obtained from the patch pattern. In other words, only the patch pattern that is not affected by the background potential is compared by comparing the latent image potential obtained from the patch pattern including the background potential with the latent image potential obtained for the patch pattern formed for image quality adjustment. The latent image potential can be obtained.

The correction coefficient obtained in step S3 is stored (step S4).
By storing the correction coefficient, using the latent image potential based on the correction coefficient during image quality adjustment increases the accuracy with respect to the charge bias, development bias, and write output feedback control, which are the target image formation conditions during image quality adjustment. Will be.

  As described above, a plurality of patch patterns having different main scanning direction widths are created with the image forming conditions fixed. Then, by correcting the detected latent image potential, the latent image potential for only the actual patch pattern is determined, and image forming conditions for obtaining a target image density, that is, image formation Condition calibration is performed in the control unit 200.

The procedure for image quality adjustment processing executed in the control unit 200 is as follows.
FIG. 9 is a flowchart for explaining the image quality adjustment processing procedure.
In the procedure shown in FIG. 9, after the image density adjustment pattern is created for the image quality adjustment patch pattern, the latent image potential is detected before the development of the pattern, and the development potential is obtained. In FIG. 9, the patch pattern is described as a gradation pattern in advance.
In FIG. 9, first, calibration of the toner image detection sensor 30 is executed (step ST10).
In this case, the LED current is adjusted so that the regular reflection light from the background portion of the intermediate transfer belt is within the range of 4.0 ± 0.5 [V].

After step S10, an image density adjustment pattern latent image is formed (step S11).
In this case, a reference patch pattern having the image density adjustment pattern shown in FIG. 4 is formed. This patch pattern is used to determine the current image density with respect to the target image density. The reference patch pattern has the same size in the main scanning direction and sub-scanning direction as the A patch (see FIG. 4), and changes the developing bias and the charging bias sequentially while fixing the exposure potential. The gradation is made to be.
The image density adjustment pattern latent image uses the charging bias set in the previous image quality adjustment process, and the LD output also uses the value set in the previous image quality adjustment process.
However, when the image quality adjustment process is the first time, a portion where the writing LD output is stable with reference to the light attenuation curve shown in FIG. 10 is used.

  When the image density adjustment pattern is formed, the latent image potential is detected by the potential sensor 31 (step S12).

Next, the latent image potential of the image density adjustment pattern detected by the potential sensor 31 is corrected (step S13).
Regarding the correction in this case, the latent image potential of the image density adjustment patch pattern used as the reference patch pattern formed in step S11 is detected by the potential sensor 31, and the latent image potential Vp is acquired. Further, the latent image potential of the patch pattern created under the previous imaging conditions is stored as a solid portion potential VL.
These latent image potential Vp and solid portion potential VL are corrected by the following equations (1) and (2). In this case, the correction coefficients α and β described with reference to FIG. 7 are used.
Patch pattern latent image potential (after correction) Vp ′ = α × Patch pattern latent image potential (before correction) Vp + β (1)
Solid part potential (after correction) = α × solid part potential (before correction) + β (2)

When the patch pattern latent image potential Vp ′ and the solid portion potential VL ′ are corrected, a development potential for performing development in each portion of the reference patch pattern and the solid portion is obtained based on these correction values.
The development potential (−V) is obtained by the following equation (3).
Development potential (−V) = Development bias Vb (−V) −Patch pattern latent image potential (after correction) VP ′ (− V) (3)
During development, the development bias is sequentially changed to the reference patch pattern latent image formed in step S11 so as to be visualized from the low development potential side, and finally the visible image is created using the previous development bias (step S14). ).

Image density determination is performed on a reference patch pattern that has undergone visible image processing. In this case, reflected light from each gradation pattern of the visualized reference patch pattern is detected (step S15), and the detection result is converted into the toner adhesion amount (step S16).
For the detection of the reflected light from the gradation pattern executed in step S15, regular reflection light and diffuse reflection light are selected or used according to the color of the patch pattern. This is intended to prevent a difference in reflectance depending on the toner color of the patch pattern from leading to a detection error.
As a method of converting the detection result into the toner adhesion amount, as disclosed in Japanese Patent Application Laid-Open No. 2006-139180, which is a prior application of the present applicant, a specular reflection type optical sensor and a diffuse reflection type optical sensor are used. A map in which the relationship between the output signal and the adhesion amount is set is used.

Once the toner adhesion amount is determined, the developing ability is calculated (step S17).
The developing ability is obtained by calculating a linear approximation expression indicating the relationship between the developing potential and the toner adhesion amount.
FIG. 11 is a diagram showing the results of plotting the development potential and the toner adhesion amount. Specifically, the development ability is obtained by linearly approximating the result obtained by using the data relating to the development potential calculated from the latent image potential and the toner adhesion amount by the least square method (Y = α × X + β).
In FIG. 11, the slope in the approximate linear equation is development γ (γ = α), and the intersection of the linear approximate equation and the X axis is the development start voltage Vk (Vk = −β / α).

An image forming bias is calculated after calculating the developing ability (step S18).
In FIG. 11, the source potential Vp obtained in step 14 is obtained.
The procedure is as follows.
(1) Obtain approximate linear equation of development γ.
(2) Obtain the maximum target adhesion amount.
(3) Calculate the source potential for obtaining the target adhesion amount.
The above procedure is shown in FIG.
The development potential acquired in step S18 is converted into a development bias.
Here, when the toner adhesion amount is M, the development γ is γ, the development start voltage is Vk, the latent image potential is Vs, the development bias is Vb, and the development potential is Vp. Each parameter has the following relationship.
(I) M = γ × (Vp−Vk) (4)
(II) Vp = Vs−Vb (5)
(III) Vs = (M / γ + Vk) + VB (6)
Based on the above relationship, the developing bias Vb is calculated by the following equation (7) using the solid portion potential VL ′ detected in step S13.
Development bias Vb (−V) = Development potential Vp ′ (− V) + Solid section potential VL ′ (− V) (7)
On the other hand, a target charging potential (charging bias) is calculated by the following formula (8) based on the calculated developing bias Vb, latent image potential Vs, and developing potential Vp.
Charging bias (−V) = Development bias Yb (−V) +200 (−V) (8)
Incidentally, 200 (−V) is a potential difference set by offsetting the developing bias Vb in order to prevent background contamination.

As described above, when the development bias Vb and the charging bias are respectively calculated as values for obtaining the target image density, the output of the writing LD, which is one parameter remaining in the image adjustment condition, is calculated (step S19).
A halftone potential Vpl ′ which is a target for the halftone portion to have a target halftone density using the development potential is calculated by the following equation (10).
Vpl ′ = ε × development potential Vp + VL (10)
ε is a value designed for the image forming system, and is determined so that a predetermined constant is applied according to a target halftone density, a line width, or the like.
Based on the calculated halftone portion potential, an LD output adjustment pattern is created so as to be written in the same manner as the gradation pattern of the reference pattern described above. The pattern in this case is a halftone pattern created by the halftone dither or duty change shown in FIG.
Specifically, in FIG. 12, the write LD output is changed in a plurality of steps with the charging bias and the developing bias fixed, and an adjustment pattern for each gradation is created.
The latent image potential in each of these adjustment patterns is detected by the potential sensor 31, and the correlation between the latent image potential and the writing LD output is plotted on the XY plane as shown in FIG.
By approximating the plotted results to a straight line, the write LD output when the target adjustment pattern portion potential Vpl ′ is obtained is calculated.
The latent image potential Vp of the adjustment pattern detected by the potential sensor 31 is corrected by the following equation (11). As a result, the latent image potential of the adjustment pattern is calibrated in the same manner as the corrected value including the development potential described above.
Adjustment pattern latent image potential (after correction) Vp ′ = α × Vp + β (11)
When the latent image potential of the adjustment pattern is corrected, the output of the writing LD is determined so as to correspond to this.

  Based on the above equations, the development bias Vb, the charging bias, and the writing LD output that are subject to image formation condition calibration are updated from the values for the previous reference pattern and adjustment pattern, respectively (step S20).

The results using the corrected parameters described above are as shown in FIG.
In FIG. 14, when the patch pattern potential correction process is not performed, the development γ is calculated to be higher, but an accurate latent image potential can be calculated for the patch pattern by the potential correction process. . Thereby, it is possible to easily match the condition of each parameter necessary for image density adjustment with the target condition.

The control unit 200 described above is not only intended for potential correction processing for image quality adjustment by adjusting image density, but is also executed in response to environmental changes. The reason is as follows.
That is, in the image forming apparatus, when the environment in the apparatus, particularly temperature, changes, the facing relationship of the devices incorporated may change according to the thermal expansion coefficient of the housing frame. In particular, the detection distance between the potential sensor and the photoconductor may change, and the charging characteristics on the photoconductor drum may change.
As a result, an error may occur in the latent image potential detection result used for the patch portion potential correction process. In the present invention, detection errors that occur during such environmental changes are eliminated.
When the environmental change is a predetermined condition, for example, when the temperature change amount exceeds the temperature change amount in the previous potential correction process, the above-described patch pattern potential correction process is performed. Thereby, it is possible to suppress the occurrence of a potential detection error when an environmental change occurs.

On the other hand, as a case where the charging characteristics of the photoconductor change in addition to the environmental change, it may be caused by repeated image forming processing including charging.
In the present invention, the above-described patch pattern potential correction processing is executed in such a case, that is, in a case where a change in charging characteristics occurs.
Further, in addition to the above-described case, the patch pattern potential correction processing can also be performed when the development γ calculated during the image density adjustment processing changes greatly.
That is, when development γ changes greatly, each parameter used for image forming conditions may change greatly, or the charging characteristics of the photoreceptor may change.
Accordingly, in the present invention, the potential correction error of the latent image potential is prevented by performing the above-described patch pattern potential correction processing when the environment fluctuates so that the development γ easily changes so as to exceed the allowable range. Yes.
In addition, potential detection errors may occur due to mechanical errors in the equipment installed in the apparatus. For example, when a rotating body is used as a roller for a photosensitive member or charging member. These eccentricities change the detection distance of the potential sensor, resulting in detection errors.
Therefore, in the present invention, the patch pattern is formed so as to correspond to the rotation cycle in consideration of the rotation cycle of a rotating member such as a charging roller used for setting the charging potential. As a result, the patch pattern formed on the rotating member is formed under a uniform rotation cycle condition, and the influence of eccentricity, that is, the change in the detection distance due to rotation unevenness can be reduced. The photoreceptor is not limited to the drum but may be a belt. In this case, unevenness similar to the rotation period occurs due to slack of the belt. Therefore, when a belt is used, a patch pattern can be formed corresponding to the moving period of the photoreceptor.

  In addition, the potential correction processing is performed when the change amount of the developing ability based on the patch pattern latent image potential detection result and the toner adhesion amount detection result of the patch pattern exceeds a threshold value with respect to the change amount at the previous potential correction processing. Is supposed to run.

In the control unit 200, the detection accuracy of the latent image potential in the reference patch pattern is increased by using the patch patterns having different main scanning direction widths used for the image density adjustment processing. Hereinafter, processing for determining an appropriate width for patches having different widths in the main scanning direction will be described.
When such patch patterns having different widths in the main scanning direction are formed, processing for preventing an increase in toner consumption and an increase in load on the cleaning unit due to an increase in toner amount is executed. Regarding the size of the patch pattern in this case, the B patch of the A patch and the B patch shown in FIG.

Hereinafter, patch width optimization processing executed by the control unit 200 will be described with reference to the flowchart shown in FIG.
(1) A patch pattern latent image having a plurality of different main scanning direction widths is formed (step S21).
In this case, a plurality of patterns having different widths in the main scanning direction are created by changing the exposure width as shown in FIG. . The sub-scanning length is the same as the sub-scanning width of the patch pattern created during the image quality adjustment operation. FIG. 16 shows a pattern image on the intermediate transfer belt.

(2) The latent image potential of the patch pattern latent image is detected (step S22).
Using the potential sensor 31, the potential of the patch pattern latent image created in step S21 is detected.

(3) The optimum width related to the width of the patch pattern in the main scanning direction is calculated (step S23).
In this case, the correlation between the main scanning direction width of the patch pattern created in step S21 and the latent image potential of the patch pattern detected in step S22 is plotted.
As a result, the main scanning width of the patch pattern when the error from the latent image potential of the patch pattern having the largest main scanning width falls within a predetermined error range is used for the image quality adjustment operation.
In the present embodiment, when the potential sensor is attached with a detection distance of 3.0 mm, the following conditions are used. When the patch pattern when the error from the latent image potential of the pattern having the largest width in the main scanning direction is within a range of ± 2% is used for the B patch, the width of the B patch in the main scanning direction is 20 mm.

(4) The optimum value of the width in the main scanning direction of the B patch obtained in step S23 is stored (step S24).
By storing the optimum value in the main scanning direction width of the B patch, it can be referred to in the patch formation in the image adjustment process described above.
The control unit 200 calculates the main scanning direction width of the patch pattern so that the difference in latent image potential between the patch patterns having the maximum main scanning direction width among the plurality of formed patch patterns falls within a predetermined range. Based on the result, a process of detecting a latent image potential is performed for a patch pattern created under two or more imaging conditions.

  By optimizing the width in the main scanning direction by the above processing, the following advantages can be obtained when forming a B patch that may be larger than the reference patch pattern. That is, by preventing the B patch from becoming excessively large, wasteful toner consumption can be suppressed, and an increase in load on the cleaning unit due to an increase in the toner amount can be suppressed.

Even when the main scanning direction width of the B patch is optimized, the main scanning direction width of the B patch can be obtained in an optimal state by performing the patch width optimizing process according to the environmental variation described above. In addition, the patch optimization process is not limited to environmental fluctuations, and should be performed as appropriate for mechanical errors of devices in the apparatus, changes in charging characteristics on the photoconductor, etc., as in the image density adjustment process described above. Can do. As a result, it is possible to determine the width in the main scanning direction without causing a detection error during the patch portion potential correction process.
It should be noted that as a condition for executing the patch width optimization process, it is desirable to maintain a state where the execution frequency is lower than the execution condition of the potential correction process described above. This is to prevent the execution opportunity of regular image density adjustment processing from being hindered.

In the above configuration, in addition to the reference patch pattern formed at the time of image density adjustment processing, a patch pattern in which the area occupied by the potential sensor is different from the reference patch pattern is used, thereby eliminating the influence of the potential of the background portion. The latent image potential in the actual patch pattern can be determined.
Accordingly, it is possible to improve the accuracy of the image forming conditions obtained by the image density adjustment process by reducing the erroneous detection when detecting the latent image potential of the patch pattern and using the patch potential correction process for the image density adjustment process. .
In addition, when forming patch patterns of different sizes, the width of the patch pattern in the main scanning direction can be optimized, so that excessive toner consumption can be suppressed, and the cleaning unit into which excessive toner enters can be used. Can be prevented from increasing.
Furthermore, the image forming conditions determined by the image density adjustment process can be adjusted in accordance with the influence of environmental fluctuations, mechanical errors, and the like, and can be updated to conditions that are always optimized and have high accuracy.

DESCRIPTION OF SYMBOLS 1 Intermediate transfer belt 2 Photoconductor 3 Charger charger 4 Writing unit 5 Developing unit 30 Toner image detection sensor 31 Potential sensor 200 Control unit

JP 2004-184583 A

Claims (9)

Detection means for detecting the latent image potential of the patch pattern and the toner adhesion amount for a plurality of patch patterns formed on the latent image carrier for calibration of image forming conditions, and detection results from the detection means An image forming apparatus including a control unit that performs calibration for image quality adjustment with respect to charging potential, writing output, and developing bias used as target image forming conditions in response,
As the patch pattern, a pattern having a width in the main scanning direction of at least two stages is formed,
One of the patch patterns has the same main scanning direction width as that of the patch pattern formed at the time of calibrating the image forming conditions, and the other patch pattern uses a main scanning direction width of at least two or more image forming conditions. And
The control unit detects a latent image potential for each patch pattern in a fixed image forming condition, and calibrates the image forming condition to be a target image forming condition based on a detection result. Based on the latent image potential from one of the patch patterns and the other patch pattern, a correction coefficient for setting the image forming condition used for the image forming condition calibration is calculated, and is used at the time of the image forming condition calibration based on the correction coefficient. An image forming apparatus capable of executing at least a potential correction process for correcting a latent image potential of a patch pattern to be calibrated for the image forming condition.   The control unit uses the latent image potential obtained from one of the patch patterns having a width in the main scanning direction similar to that formed at the time of calibration of the image forming conditions as the correction coefficient and the main image based on the two or more image forming conditions. 2. The image forming apparatus according to claim 1, wherein an inclination and an intercept obtained by linearly approximating a result of plotting a latent image potential obtained from another patch pattern having a scanning direction width are used.   A temperature detection unit is connected to the control unit, and the control unit executes the potential correction process when the temperature detection unit exceeds a temperature change amount in the previous potential correction process. The image forming apparatus according to claim 1.   The number of printed sheets detecting means is connected to the control section, and the control section executes the correction processing when a predetermined number of printed sheets has been exceeded since the previous potential correction processing. The image forming apparatus according to any one of the above.   In the control unit, the change amount of the developing ability based on the latent image potential detection result of the patch pattern and the toner adhesion amount detection result of the patch pattern exceeds the threshold with respect to the change amount in the previous potential correction process. 5. The image forming apparatus according to claim 1, wherein the potential correction process is executed in some cases.   The image forming apparatus according to claim 1, wherein the patch pattern is formed corresponding to a moving cycle of the latent image carrier.   7. The patch pattern according to claim 1, wherein when the member used for setting the charging potential is a rotating body, the patch pattern is formed corresponding to a rotation cycle of the rotating body. The image forming apparatus described in 1.   The control unit forms a plurality of patch patterns by changing the exposure writing area while fixing the image forming conditions in the charging unit, the developing unit, and the exposure writing unit used for image formation. 6. The image forming apparatus according to claim 1, wherein a main scanning direction width of the patch pattern is set based on an image potential detection result.   The control unit calculates a main scanning direction width of the patch pattern so that a difference in latent image potential between patch patterns having the maximum main scanning direction width among the plurality of formed patch patterns falls within a predetermined range. 9. The image according to claim 1, wherein a latent image potential is detected for a patch end created under two or more imaging conditions based on the result. Forming equipment.

Images