JP2018155973A - Image formation apparatus and correction method of toner density detection means - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation apparatus which can form the excellent low-density patch even when the fluctuation in the development characteristic is large, and can properly perform correction of toner density detection means.SOLUTION: A printer 1 includes process cartridges 102a, b, c, d which form a toner image on an intermediate transfer belt 120. The printer also includes: a density sensor 126 which detects the density of the gradation pattern or the like on the intermediate transfer belt 120; and a control unit 200 which corrects one or more imaging conditions on the basis of the detected density information. The density sensor 126 includes: an infrared ray LED 127; a regular reflection type light reception element 128 which detects the regular reflection light; and a diffuse reflection type light reception element 129 which detects the diffuse reflection light. The toner pattern for color toner density adjustment is constituted by the toner patch made of a plurality of single colors formed of the different development biases. There are two levels in the supply offset amount being the difference between the development bias and the supply bias at the formation of the toner patch.SELECTED DRAWING: Figure 11

Description

  The present invention relates to an image forming apparatus and a calibration method for toner density detection means.

Conventionally, a toner density detecting means for detecting the density of an unfixed density adjusting toner pattern formed on an image carrier is provided with a light emitting element, a specular reflection light receiving element for detecting specular reflection light, and diffuse reflection light. An image forming apparatus having a diffuse reflection light receiving element to detect is known.
Further, in such an image forming apparatus, the sensitivity of any type of optical sensor used for the toner density detecting means is corrected in order to correct variations in the optical axis of light emitting elements, individual differences in light receiving elements, sensor mounting errors, and the like. Is calibrating. By performing such calibration, it is possible to perform accurate density detection (toner adhesion amount detection) as compared with a configuration in which the toner adhesion amount is uniquely obtained without performing calibration.

  For example, Patent Document 1 discloses that when a toner density detection unit is calibrated, a plurality of toner patches are formed with a plurality of colors in addition to a gradation pattern for correcting an image forming condition, and the gradation pattern and the formation are formed. A configuration is described in which all of the toner patches are used as calibration patches for the optical sensor.

  However, in the conventional image forming apparatus, the development characteristics fluctuate greatly, a good low density patch cannot be formed, and the accuracy of detecting the toner adhesion amount is lowered, so that proper calibration of the toner density detecting means cannot be performed. there were.

  In order to solve the above-described problems, the invention described in claim 1 is directed to a toner density detecting means for detecting the density of an unfixed density adjusting toner pattern formed on an image carrier, and a regular reflection. In an image forming apparatus having a regular reflection light-receiving element that detects light and a diffuse reflection light-receiving element that detects diffuse reflection light, a toner pattern for color toner density adjustment includes a plurality of single colors formed at different development biases. The difference between the development bias applied to the developer carrier and the supply bias applied to the developer supply member that supplies the developer to the surface of the developer carrier when the toner patch is formed. Is characterized by two or more levels.

  According to the present invention, it is possible to provide an image forming apparatus capable of forming a good low density patch and calibrating an appropriate toner density detecting means even when the development characteristics vary greatly.

1 is a schematic configuration diagram of a printer according to an embodiment. FIG. Explanatory explanatory drawing of the density sensor which concerns on one Embodiment. Explanatory drawing about the spectral characteristic of the light emitting element of a density sensor, and a light receiving element. Explanatory drawing about the spectral characteristic of the diffuse reflected light of cyan, magenta, and yellow. FIG. 5 is an explanatory diagram regarding a relationship between an adhesion amount of a toner patch and regular reflection light output / diffuse reflection output. Explanatory drawing about the relationship between the normalization value of the regular reflection output of only pure regular reflection light, the diffuse reflection output, and the sensitivity correction method of diffuse light output. Explanatory drawing about the relationship between the normalization value of the regular reflection output of only pure regular reflection light, and a toner adhesion amount. FIG. 6 is an explanatory diagram of a relationship between a normalized value of regular reflection output and a diffuse reflection output when a low adhesion amount patch cannot be formed. FIG. 3 is an explanatory diagram illustrating an example of a layout of gradation patterns formed on an intermediate transfer belt. FIG. 6 is an explanatory diagram of another example of a layout of gradation patterns formed on an intermediate transfer belt. 6 is an example of a graph showing the relationship between the toner adhesion amount and the development potential. The example of the graph which shows the relationship of the toner adhesion amount with respect to development potential, and the conditions selected as a pattern used for a calibration. The figure which showed the example of the pattern used as a halftone patch.

Hereinafter, as an image forming apparatus to which the present invention is applied, an embodiment of an electrophotographic color printer (hereinafter referred to as printer 1) will be described.
In this embodiment, a so-called intermediate transfer type tandem image forming apparatus will be described as an example, but the transfer system of the image forming apparatus is not particularly limited. Therefore, the present invention can also be applied to a direct transfer tandem image forming apparatus and a four-cycle color image forming apparatus.

FIG. 1 is a schematic configuration diagram of a printer 1 according to the present embodiment.
The printer 1 is a general tandem color image forming apparatus. For example, a process cartridge is a process unit corresponding to each of three colors such as yellow, magenta, and cyan and monochrome black. 102a, b, c, d. Each process cartridge 102a, b, c, d is detachably attached to the apparatus main body 100. Further, in the apparatus main body 100, an exposure device 103 as a latent image forming unit, primary transfer rollers 101a, 101b, 101c, 101d, a paper feed tray 104, a fixing device 106, a control unit 200, and the like are disposed.

The process cartridges 102a, b, c, d are set at predetermined positions of the apparatus main body 100, and are provided with photoconductors 108a, b, c, d which are image carriers (latent image carriers). Each of the photoconductors 108a, b, c, and d has a drum shape, and is rotated at a linear speed of 150 [mm / s] in the present embodiment. Roller-shaped chargers 110a, 110b, 110c, and 110d that rotate following the rotation of the photoreceptors 108a, 108b, 108c, and 108d are in contact with each other. Each charger 110a, b, c, d is applied with a DC voltage by a high-voltage power supply or a charging bias obtained by superimposing an AC voltage on the DC voltage, whereby each of the photoconductors 108a, b, c, d is uniformly distributed. Charged to a nearly uniform surface potential.
On the surfaces of the photoreceptors 108a, b, c, and d charged by the chargers 110a, b, c, and d, exposure processing corresponding to the image information of each color is performed by the exposure devices 103a, b, c, and d, respectively. The electrostatic latent image of each color is formed.

  Here, each of the exposure apparatuses 103a, b, c, and d has an LED element having a desired number of pixels (image width × pixel density 1200 dpi), a driving circuit for the LED element, and a lens for condensing light emitted from the LED element, assembled in the housing. It is a device (LED head). Each LED element emits light according to an image signal to form a latent image on the photoreceptors 108a, b, c, and d. In addition, a lens that collects light emitted from the LED element has a large numerical aperture and a short focal length in order to efficiently secure the amount of emitted light. For this reason, the LED head is installed close to each photoconductor 108 (at a distance of several mm from each photoconductor 108). An array of a plurality of lenses is incorporated in a housing as a lens array, and a shape (hole, protrusion, plane, etc.) for mounting the LED head is formed on the housing. Further, a harness for supplying an image signal in accordance with the power source and image data is coupled to the LED head.

The electrostatic latent images formed on the respective photoreceptors 108a, b, c, and d are developed with the respective color toners by the developing devices 111a, 111b, 111b, and 111d as developing means corresponding to the respective colors.
The developing units 111a, b, c, and d of the present embodiment are one-component developing type developing units.
Each of the developing devices 111a, b, c, and d is supplied from the supply rollers 113a, b, c, and d to the developing rollers 112a, b, c, and d, which are developer carriers, by a predetermined supply bias supplied from a high voltage power source. Supply toner. The electrostatic latent images on the photoconductors 108a, b, c, and d are developed by a predetermined developing bias supplied from a high-voltage power source to the developing rollers 112a, b, c, and d carrying the respective color toners. The toner on the rollers 112a, b, c, and d is adhered. Thereby, the electrostatic latent images on the respective photoconductors 108a, b, c, and d are visualized as toner images.

  The four process cartridges 102a, 102b, 102c, and 102d are arranged side by side along the surface movement direction of the intermediate transfer belt 120 as an intermediate transfer member that is an image carrier (intermediate transfer member, transfer target). When a full color image is formed, each color toner image is primarily transferred onto the intermediate transfer belt 120 in the order of black (108d), cyan (108c), magenta (108b), and yellow (108a). Primary transfer rollers 101a, 101b, 101c, and 101d are opposed to the photoconductors 108a, b, c, and d with the intermediate transfer belt 120 interposed therebetween. A predetermined primary transfer bias (for example, +400 [V] to +1200 [V]) is applied to the primary transfer rollers 101a, 101b, 101c, and 101d from an independent high-voltage power source. By the action of the transfer electric field formed by this primary transfer bias, the toner images on the photoconductors 108a, b, c, and d are primarily transferred onto the intermediate transfer belt 120 so as to overlap each other.

  The intermediate transfer belt 120 is stretched and supported by a drive roller 122, primary transfer rollers 101a, 101b, 101c, and 101c, and a tension roller 121. The drive roller 122 is rotationally driven by a drive motor, and the surface is moved by this rotational drive. . Both ends of the roller shaft of the tension roller 121 are urged by springs as urging means, whereby a predetermined belt tension is applied to the intermediate transfer belt 120. Further, flanges are press-fitted into both ends of the tension roller 121, and this flange serves as a regulating member that regulates meandering of the intermediate transfer belt 120. The tension roller 121 also functions as a secondary transfer backup roller when the intermediate transfer belt 120 and the secondary transfer roller 125 form a secondary transfer nip portion.

  Further, each roller that stretches the intermediate transfer belt 120 is supported from both sides of the intermediate transfer belt 120 by a transfer belt unit side plate. Each photoreceptor 108 and the intermediate transfer belt 120 can be separated at an arbitrary timing by a contact / separation mechanism.

A sheet as a recording material in the sheet feeding tray 104 is a secondary sheet in which the leading end portion of the toner image superimposed on the intermediate transfer belt 120 is opposed to the secondary transfer roller 125 by the sheet feeding and conveying roller 105 and the registration roller pair 107. The paper is fed in accordance with the timing to reach the transfer position. A predetermined secondary transfer bias is applied to the secondary transfer roller 125 by a high voltage power source, whereby the toner image on the intermediate transfer belt 120 is secondarily transferred (transferred) to the sheet. In the present embodiment, the paper feed path has a vertical path as shown in FIG. The sheet is separated from the intermediate transfer belt 120 by the curvature of the secondary transfer roller 125, and the toner image transferred to the sheet is fixed by the fixing device 106 and then discharged outside the apparatus.
The control unit 200 disposed in the apparatus main body 100 includes a central processing unit (CPU), storage means such as a volatile memory (RAM) and a nonvolatile memory (ROM), and the like. The operation of each part is controlled.

Transfer residual toner remaining on the photoreceptors 108a, b, c, d after the primary transfer is collected by the cleaning means 117a, b, c, d and stored in the waste toner container 124. Here, there is also a cleanerless system in which a cleaning unit is not provided for the photoconductors 108a, b, c, and d, and a transfer residual toner is collected and reused by a developing device. The cleaning means can be employed.
Further, the transfer residual toner on the intermediate transfer belt 120 is scraped off by the cleaning blade 123 and discarded in the waste toner container 124.

Also, below the intermediate transfer belt 120, a density sensor 126 detects the toner amounts of a plurality of toner patches formed on each photoconductor 108 after being primary transferred onto the intermediate transfer belt 120 to form a toner pattern. (A, b, c, d) are arranged.
The density sensor 126 is a density sensor that detects the image density (toner adhesion amount) of an unfixed toner patch formed on the intermediate transfer belt 120 as described above, and is a regular reflection type sensor and a diffuse reflection type sensor. It is a forward expansion integrated optical sensor configured. The control unit 200 functioning as an image forming condition adjusting unit feeds back the image density of the toner patch detected by the density sensor 126, and at least sets one or more image forming conditions of exposure amount, charging bias, and developing bias. Determine (correct).

Here, as the optical sensor used to detect the density of the toner patch, a reflective sensor including a light emitting element such as an LED and a light receiving element such as a phototransistor is generally used. There are a regular reflection type sensor that detects regular reflection light of a light emitting element with a light receiving element, and a diffuse reflection sensor that detects diffuse reflection light of a light emitting element with a light receiving element.
In regular reflection, if the smoothness of the detection surface is high, the amount of reflected light is large, and if the detection surface is rough, the amount of reflected light is small. In general, the surface of a toner image is rough and has little specular reflection light. However, an image carrier such as a transfer belt such as the intermediate transfer belt 120 or a photoconductor has high smoothness and a lot of specular reflection light.

Based on this, in the method using the specular reflection type optical sensor, a toner patch is formed on an image carrier having a high degree of smoothness, and as the output detected by the light receiving element when the toner patch is irradiated with light, the toner adhesion amount increases. And the smaller the output of the light receiving element, the larger the toner adhesion amount. That is, the regular reflection light detects the amount of toner adhesion based on the amount of reflection light from the image carrier.
On the other hand, in the diffuse reflection type optical sensor, it is assumed that the light is evenly diffused on the surface of the toner image. The smaller the diffused light detected by the light receiving element, the smaller the amount of adhered toner, and the greater the diffused light, the greater the amount of adhered toner. to decide. That is, the toner adhesion amount is detected based on the amount of reflected light from the toner image.

  For both regular reflection type and diffuse reflection type optical sensors, sensitivity calibration is performed in order to correct variations in the optical axis of light emitting elements, individual differences among light receiving elements, sensor mounting errors, and the like. An error can be corrected by providing a reflector suitable for each of regular reflection and diffuse reflection as a calibration plate and correcting the output according to the output of the calibration plate.

The following is known as an example of using only a diffuse reflection type sensor.
A patch having the maximum density of color toner is formed on the surface of the intermediate transfer member, and further, a patch of density measuring black toner is formed thereon using this patch as a base, and the density of the black toner is detected. Further, a patch having the maximum density of black toner is formed on the surface of the intermediate transfer member, and further, a patch of density measuring color toner is formed thereon using this patch as a base, and the color toner density is detected. A technique for ensuring a wide dynamic range of an optical sensor by adopting such a configuration has already been known (for example, Patent Document 2).
On the other hand, as a method of calibrating an optical sensor with reduced cost and space, a method of using a belt background or a toner patch instead of a calibration plate without providing a calibration plate for the optical sensor is already known (for example, Patent Documents). 3, Patent Document 4, Patent Document 5).

The image forming apparatuses described in Patent Document 3, Patent Document 4, and Patent Document 5 use a forward expansion integrated optical sensor including one light emitting element, one specular reflection light receiving element, and one diffuse reflection light receiving element. ing.
The regular reflection type sensor cannot detect accurately in the region of high density (the amount of toner adhering is large and the toner particles are superposed on multiple layers). There is a problem that the sensitivity is lost because there is no difference in the specularly reflected light when they overlap and adhere. The aim is to accurately detect the toner adhesion amount in such a high density region by using a diffusion type sensor together.

  The amount of specularly reflected light from the image carrier is expected to vary due to factors such as scratches on the surface of the image carrier and a decrease in smoothness, or polishing of the image carrier by cleaning or the like to increase the glossiness. Therefore, the light quantity of the light emitting element is adjusted (sensitivity calibration is performed) so that the regular reflection output of the reference image carrier is constant.

  When the toner patch is detected, the regular reflection light receiving element receives regular reflection light (reflection light from the image carrier) and diffuse reflection light (diffuse light from the toner patch). Therefore, it is necessary to extract only pure regular reflection light from the output of the regular reflection light receiving element. When the ratio of the output of the regular reflection light receiving element (specular reflection output) and the output of the diffuse reflection light receiving element (diffuse reflection output) when the uniform diffused surface is detected by the optical sensor is α, the diffuse reflected light in the regular reflection output The component can be calculated by α times the diffuse reflection output. That is, an output obtained by subtracting α times the diffuse reflection output from the regular reflection output is obtained as an output by purely regular reflection light reception.

  Then, after adjusting the light amount of the light emitting element, the regular reflection output and the diffuse reflection output are detected for each of the plurality of toner patches, and the pure regular reflection output of each toner patch is obtained by the above procedure. Based on the relationship between the pure specular reflection output and the diffuse reflection output of each toner patch, a coefficient (hereinafter referred to as a normalized value) β for correcting the sensitivity of the diffuse reflection output is calculated. The diffuse reflection output is calibrated by multiplying the diffuse reflection output by β.

  However, in the method described in Patent Document 2, for example, in which only the conventional diffuse reflection type sensor is used, the order in which colors are superimposed on the intermediate transfer member can be restricted. For this reason, there is no problem in a 4-cycle machine in which the order of color superposition is variable, but in a tandem machine in which the order of color superposition cannot be changed, there is a problem that the degree of freedom in color order design is reduced.

In addition, in the methods described in Patent Document 3, Patent Document 4, and Patent Document 5, for example, a belt background or a toner patch is used instead of the calibration plate without providing a calibration plate for an optical sensor so far. In order to calculate β, a toner patch is formed in an analog manner as follows.
By using different development potentials, solid toner patches that satisfy a predetermined dynamic range from low density to high density are formed.
In the image forming apparatus of the two-component development system, the development characteristics (toner charge amount) can be controlled by adjusting the toner density, so that a low-density to high-density toner image can be formed relatively easily.
On the other hand, an image forming apparatus of a one-component development system does not have a function corresponding to toner density adjustment, and development characteristics vary greatly. For this reason, there is a case where the development characteristic cannot form a low density patch, and the calculated value of the normalized value β is inaccurate, that is, there is a problem that the detection accuracy of the toner adhesion amount is lowered.

As described above, these problems can also occur in the calibration of the toner density detection means described in Patent Document 1.
In the conventional image forming apparatus, the development characteristics fluctuate greatly, a good low-density patch cannot be formed, and the accuracy of detecting the toner adhesion amount is lowered, so that proper calibration of the toner density detection means cannot be performed. there were.
Accordingly, the inventors have examined whether an image forming apparatus that can form a good low density patch and can calibrate an appropriate toner density detection means even when development characteristics fluctuate greatly, and will be described below. A calibration method for the density sensor 126 was found.

Hereinafter, the calibration method of the density sensor 126 performed by the printer 1 of the present embodiment will be specifically described with reference to the drawings.
First, the density sensor 126 which is a toner density detection unit provided in the printer 1 of the present embodiment will be described.
FIG. 2 is an enlarged explanatory diagram of the density sensor 126 according to the present embodiment.
As shown in FIG. 2, the density sensor 126 includes an infrared LED 127 as a light emitting element, a regular reflection type light receiving element 128, a diffuse reflection type light receiving element 129, a casing 130, and the like.
Here, as the light emitting element, a laser light emitting element or the like may be used instead of the infrared LED. In addition, as the regular reflection type light receiving element 128 and the diffuse reflection type light receiving element 129, phototransistors are used, but it is also possible to use a photodiode or an amplifier circuit.

In order to ensure a constant dynamic range of the regular reflection output regardless of the individual difference of the intermediate transfer belt 120, the degree of gloss due to changes over time, and the individual difference of the density sensor 126 itself, the printer 1 of the present embodiment has the following: The light quantity of the infrared LED 127 is adjusted.
The light quantity of the infrared LED 127 is adjusted so that the regular reflection output Vsg_reg, which is the output of the regular reflection sensor when detecting the background of the intermediate transfer belt 120 without toner adhesion, becomes a constant value.

  Next, spectral characteristics of the infrared LED 127, which is the light emitting element of the density sensor 126, and the regular reflection type light receiving element 128 and the diffuse reflection type light receiving element 129, which are light receiving elements, will be described with reference to FIG. FIG. 3 is an explanatory diagram of the spectral characteristics of the light emitting element and the light receiving element of the density sensor 126.

The peak emission wavelength of the LED that is the light emitting element of the concentration sensor 126 and the peak sensitivity wavelength of the phototransistor that is the light receiving element are both 940 [nm], and the sensitivity wavelength range of the concentration sensor 126 is approximately 870 [nm] to 1000 [nm]. It is. According to the definition of JIS Z8120, the lower bound of the wavelength of the electromagnetic wave corresponding to visible light is approximately 360 [nm] to 400 [nm], and the upper bound is approximately 760 [nm] to 830 [nm]. In the sensitivity wavelength range of the density sensor 126, there is no difference in the reflectance of the three colors of cyan, magenta, and yellow.
Therefore, the concentration sensor 126 of the present embodiment has near-infrared light with a wavelength in the range of about 760 [nm] to 2500 [nm] and infrared with a wavelength in the range of about 760 [nm] to 1.0 [mm]. At least one of the light can be detected.

Here, the spectral characteristics of diffuse reflected light of cyan, magenta, and yellow will be described with reference to FIG.
FIG. 4 is an explanatory diagram of spectral characteristics of diffuse reflected light of cyan, magenta, and yellow.
Each time two or three colors of cyan, magenta, and yellow are mixed, the reflected light decreases in the visible light region and becomes darker, but there is no change outside the visible light region. Even the color toner used in the printer 1 of the present embodiment has substantially the same spectral reflection characteristic outside the visible light region. Therefore, if the adhesion amount is the same, the light reception output of the density sensor 126 is the same for the single color toner patch and the mixed color toner patch.
For this reason, the toner adhesion amount-output characteristics of the density sensor 126 are almost the same for cyan, magenta, and yellow toners.

In the sensitivity wavelength range of the density sensor 126 described above, there is no significant difference in the reflectance of the three colors of cyan, magenta, and yellow.
Therefore, at least one of near infrared light having a wavelength in the range of approximately 760 [nm] to 2500 [nm] and infrared light having a wavelength in the range of approximately 760 [nm] to 1.0 [mm] is detected. The density sensor 126 capable of producing the following effects can be obtained.
Since the spectral reflection characteristics of the color toners of the respective colors are the same in the detection range of the density sensor 126, they can be handled as the same color toner, and no color difference occurs when the color toner is detected.
For this reason, it is possible to provide a density expansion sensor 126 that is a positive expansion integrated type in a sensitivity wavelength range in which no significant difference occurs in the reflectance of each color of the color toner.

Next, the relationship between the adhesion amount of the toner patch and the regular reflection light output / diffuse reflection output will be described with reference to FIG.
FIG. 5 is an explanatory diagram of the relationship between the toner patch adhesion amount and the specular reflection light output / diffuse reflection output.
As the adhesion amount of the toner patch increases and the coverage increases, the detection surface by the density sensor 126 approaches the completely uniform diffusion surface. For this reason, when the toner patch completely covers the background of the intermediate transfer belt 120 and the regular reflection type light receiving element 128 does not receive the regular reflection light, as shown in FIG. The ratio between the regular reflection light output and the diffuse reflection output converges to a predetermined value α.

Here, the number of patches P [1] to P [N] is varied by varying the level of toner adhesion from a low coverage with which the belt background of the intermediate transfer belt 120 can be seen to a high coverage that can be regarded as a completely uniform diffusion surface. [N] shall be formed.
When the regular reflection output formed (transferred) on the intermediate transfer belt 120 when detecting the Nth patch P [n] is Vsp_reg [n] and the diffuse reflection output is Vsp_dif [n], α is Vsp_reg [n]. n] / Vsp_dif [n].
Further, the increase in the regular reflection output due to the reception of the diffuse reflection light can be calculated by α * Vsp_dif [n], and the output by the pure regular reflection light can be calculated by Vsp_reg [n] −α * Vsp_dif [n].

When the regular reflection output Vsg_reg of the belt background portion of the intermediate transfer belt 120 to which no toner is attached is used, the normalized value β of the pure regular reflection output of the Nth patch P [n] is [n] = (Vsp_reg [ n] −α * Vsp_dif [n]) / Vsg_reg.
The normalized value β is maximum when the toner is not attached (β = 1), decreases as the coverage increases, and decreases when the coverage is high enough to be regarded as a completely uniform diffusion surface (β = 0). . That is, the normalization value β can be regarded as a reverse of the toner coverage, that is, an exposure rate of the belt background of the intermediate transfer belt 120.

When a patch with a low coverage is detected, the diffuse reflection output of the density sensor includes a regular reflection light component from the belt background.
The regular reflection light from the belt background of the Nth patch P [n] can be calculated as β * Vsg_reg from the regular reflection output Vsg_reg of the belt background and the belt exposure rate (≈β).
Thus, the pure diffuse reflection output ΔVsp_dif [n] of the Nth patch P [n] excluding the influence of the regular reflection light on the belt background is ΔVsp_dif [n] = Vsp_dif [n] −β * Vsg_reg.

Next, with reference to FIGS. 6 and 7, the relationship between the normalized value of the specular reflection output of pure specular reflection light and the diffuse reflection output, the sensitivity correction method, and the normality of the specular reflection output of pure specular reflection light only. The relationship between the conversion value and the toner adhesion amount will be described.
FIG. 6 is an explanatory diagram of the relationship between the normalized value of the specular reflection output of pure specular reflection light and the diffuse reflection output, and the sensitivity correction method for the diffuse light output. FIG. 7 is an explanatory view of the relationship between the normalized value of the specular reflection output of only pure specular reflection light and the toner adhesion amount.

FIG. 6 shows the relationship between the normalized value β of the specular reflection output of only pure specular reflection light and the pure diffuse reflection output: ΔVsp_dif [β] when a certain Nth patch P [n] is detected (diffuse light Sensitivity characteristics).
As shown in FIG. 6, the sensitivity characteristics of diffused light by cyan (C), magenta (M), and yellow (Y) toners are linear within a predetermined range as shown by the solid line in FIG. It can be approximated.
As described above, in the printer 1 of the present embodiment, the output of the regular reflection sensor of the belt background portion of the intermediate transfer belt 120 to which no toner is attached: the infrared light LED 127 that is a light emitting element so that Vsg_reg is constant. The light intensity is adjusted. For this reason, since the amount of light applied to the reflecting surface is proportional to the reflected light, the density sensor calibration method employed in the printer 1 changes the sensitivity of the diffuse reflection output with respect to the toner adhesion amount each time calibration is performed.

Here, it is assumed that the sensitivity characteristic of the diffused light of the reference density sensor is V0 = ΔVsp_dif_0 [β], and the sensitivity characteristic of the diffused light of the density sensor 126 being calibrated is V1 = ΔVsp_dif1 [β]. Then, in order to keep the relationship between the diffused light output of the density sensor 126 and the toner adhesion amount constant, the sensitivity of the diffuse reflected output is set to η (= V1 / V1) so that the sensitivity characteristic of the diffused light matches that of the reference density sensor. V0) may be multiplied.
Since the sensitivity of diffuse reflection light is sufficiently secured even in the high adhesion amount region where the sensitivity of specular reflection light disappears, the high density portion adhesion amount of the color toner image is obtained by using the sensitivity correction coefficient η of the diffuse reflection output, η * Vsp_dif. [N] can be calculated with high accuracy.

FIG. 7 shows the relationship between the normalized value β [n] of the regular reflection output of only regular reflection light and the toner adhesion amount M [n].
The normalized value β of the regular reflection output has high sensitivity until the toner adhesion amount is around 0 to 4 g / m ² . In the printer of this embodiment, the sensitivity correction coefficient η of the diffuse reflection output is calculated at β = 0.10 shown in FIG. In order to accurately calculate η, it is desirable that data in a wide range (a toner patch having a toner adhesion amount of ^{2 to 5} g / m ² ) is obtained with β = 0.1.
However, as described above, in the configuration in which the development characteristics vary greatly, particularly in the configuration using the one-component development system, the calculated value of β may be inaccurate in the case of development characteristics in which it is difficult to form a low adhesion amount patch. .

Next, the relationship between the normalized value of the regular reflection output and the diffuse reflection output when the low adhesion amount patch cannot be formed will be described with reference to FIG.
FIG. 8 is an explanatory diagram of the relationship between the normalized value of the regular reflection output and the diffuse reflection output when the low adhesion amount patch cannot be formed.
When the toner adhesion amount of the calibration patch used for calibrating the optical sensor can secure an ideal dynamic range, the relationship between the normalized reflection output β and the diffuse reflection output is shown by the solid line in FIG. The reference shown is an approximate expression (positive). At this time, the diffuse reflection output at β = 0.10 as a calibration point is Vdif0, and the sensitivity correction coefficient is η0.
On the other hand, when a calibration patch having a low adhesion amount (0 to 3 g / m ² ) cannot be formed, the relationship between the normalized reflection value β of the regular reflection output and the diffuse reflection output is shown in FIG. 8 as cyan (C) and magenta. (M) is calculated as an approximate expression (false) plotting yellow (Y) data. At this time, the diffuse reflection output at β = 0.10 as the calibration point is Vdif, and the sensitivity correction coefficient is η.
In this example, η >> η0, and the toner patch adhesion amount detection result calculated by η * diffusion output is larger than the toner patch adhesion amount calculated from the normal calculated value η0 * diffusion output. turn into.

Next, an example of the layout of a toner pattern as a gradation pattern formed on the intermediate transfer belt 120 in the printer 1 of the present embodiment will be described with reference to FIG.
FIG. 9 is an explanatory diagram showing an example of the layout of the gradation pattern formed on the intermediate transfer belt 120.
In this example, as shown in FIG. 9, density sensors 126a, b, c, and d are arranged for each color, and the total length of the gradation pattern is shortened to reduce downtime. Specifically, a density sensor 126a for yellow, a density sensor 126b for magenta, a density sensor 126c for cyan, and a density sensor 126d for black are arranged to shorten the overall length of each gradation pattern and reduce downtime. doing.
The gradation pattern of each color is formed of solid patches (solid images) having different development potentials (toner adhesion amounts).

Here, another example of the layout of the gradation pattern formed on the intermediate transfer belt 120 will be described with reference to FIG.
FIG. 9 is an explanatory diagram of another example of the layout of the gradation pattern formed on the intermediate transfer belt 120.
In this alternative example, as shown in FIG. 10, the arrangement is such that all the colors are detected by one density sensor 126, the number of density sensors is reduced, the cost is reduced, and the total pattern length of each color is set between the photoreceptors 108. By making it less than the pitch, the downtime is also shortened.
The gradation patches for each color are composed of a plurality of patches having different toner adhesion amounts.

Next, the relationship between the toner adhesion amount and the development potential will be described with reference to FIG.
FIG. 11 is an example of a graph showing the relationship between the toner adhesion amount and the development potential. FIG. 11A shows the relationship between the toner adhesion amount and the development potential when a solid toner pattern is formed at a certain timing (hereinafter referred to as “the development potential”). , Development characteristics). FIG. 11B is an explanatory diagram of a configuration in which the calibration-specific patch for sensitivity correction and the development characteristic calculation patch used for determining the development potential are separately formed under the conditions shown in FIG. is there.

In the graphs shown in FIGS. 11A and 11B, the horizontal axis represents the development potential and the vertical axis represents the toner adhesion amount. A parameter indicating the slope of these graphs is referred to as development γ, and is a parameter indicating the correspondence between the development potential and the toner adhesion amount.
The development characteristics are not always constant, and change depending on the usage environment and the degree of deterioration of the apparatus.
Here, the development potential indicates the potential difference between the exposed portion potential on the photoconductor 108 and the development bias. If the development potential is large, the amount of toner attached to the electrostatic latent image increases and the image density increases. It will be.
The two lines shown in the graph of FIG. 11A indicate that when the supply bias (Vsupply) applied to the supply roller that supplies toner to the developing roller is high (High), and when the supply bias (Vsupply) is low (Low). ).
In addition, the supply offset amount that is the difference between the development bias and the supply bias is controlled to be constant.
Therefore, the supply offset amount, which is the difference between the development bias and the supply bias at the time of forming the toner patch, is the first level when the supply bias is high Vsupply = High and the second level when the supply bias is low Vsupply = Low. There are two levels.

When the supply bias is set high, a patch with a toner adhesion amount smaller than 3 g / m ² cannot be formed even if the developing potential is reduced, and the calculation of the sensitivity correction coefficient η as shown in FIG. It reaches.
On the other hand, when the supply bias is set low, a toner patch with a low adhesion amount can be secured, and the sensitivity correction coefficient η can be calculated normally.
Under the conditions of this example, a condition with a high supply bias was suitable as a printing condition from the viewpoint of solid followability. For this reason, in the printer 1 of the present embodiment, as shown in FIG. 11B, a calibration-dedicated patch necessary for sensitivity correction has a low supply bias, and a development characteristic calculation patch (calibration) used for determining the development potential. For the patches other than the dedicated patch, the supply bias is set high to form the patch.

Next, an example in which a halftone patch is used when changing and setting the supply bias when forming a calibration patch patch will be described with reference to FIGS.
FIG. 12 is an example of a graph showing the relationship between the toner adhesion amount with respect to the development potential and the conditions selected as a pattern used for calibration. 13A and 13B are diagrams showing examples of patterns used as halftone patches. FIG. 13A shows an example of a pattern with a coverage of 94%, and FIG. 13B shows an example of a pattern with a coverage of 88%. is there.

  In the description shown in FIG. 12, as shown in the legend in FIG. 12, the thin solid line “Vupply = High” plotted with ● represents a solid patch formed with a high supply bias, and the thick solid line “Vsupply = Low” A solid patch formed with a low supply bias is shown. Further, the broken line of “Vsupply = Low_HT” shows the correlation between the development potential of the halftone patch formed with a low supply bias and the toner adhesion amount, and a plot of Δ is a condition selected as a pattern used for calibration. Here, the halftone patch of “Vsupply = Low_HT” indicated by a broken line uses a pattern with a coverage of 88% shown in FIG.

  As the halftone pattern, as shown in FIGS. 13A and 13B, a pattern in which the coverage is reduced as uniformly as possible is preferable. It is desirable that the pattern is repeated with a sufficiently small matrix size compared to the spot diameter of the density sensor 126. If the amount of toner adhesion cannot be made sufficiently small even if the supply bias is reduced, it is used as an auxiliary.

As described above, the printer 1 according to this embodiment includes the following in the density sensor 126 that detects the density of an unfixed gradation pattern formed on the intermediate transfer belt 120. An infrared LED 127, a regular reflection type light receiving element 128 for detecting specular reflection light, and a diffuse reflection type light receiving element 129 for detecting diffuse reflection light.
The toner pattern for color toner density adjustment is composed of a plurality of single color toner patches formed at different development biases. There are two levels of supply offset, which is the difference between the development bias applied to the developing roller 112 and the supply bias applied to the supply roller 113 that supplies developer to the surface of the development roller 112 when the toner patch is formed. Specifically, the supply offset amount, which is the difference between the development bias and the supply bias at the time of toner patch formation, has two levels: Vsupply = High when supply bias is high, and Vsupply = Low when supply bias is low.

By configuring in this way, the following effects can be achieved.
In a conventional image forming apparatus, when forming a toner patch for calibration of the toner density detecting means, development with a large variation in development characteristics, particularly in a configuration using a one-component development system, development in which it is difficult to form a low adhesion amount patch. In the case of characteristics, the calculated value of the normalized value β may be inaccurate. Thus, if the calculated value of the normalized value β becomes inaccurate, the detection accuracy of the toner adhesion amount is lowered, and it becomes impossible to calibrate the appropriate toner concentration detection means.

On the other hand, in the configuration of the printer 1 of the present embodiment, a plurality of single color toner patches are formed with different development biases, and the difference between the development bias and the supply bias at the time of toner patch formation is set to two or more levels. it can. Since it can be set in this way, when forming a toner patch for calibrating the toner density detection means, a supply bias is set lower than the supply bias during normal printing, and a toner patch with a low adhesion amount is formed well. can do.
Therefore, it is possible to provide an image forming apparatus that can form a good low density patch and can calibrate an appropriate toner density detecting means even when the development characteristics fluctuate greatly.

Further, in the printer 1 of the present embodiment, the level of the supply offset amount is the first level when Vsupply = High when the supply bias used during normal printing is high, and when Vsupply = Low when the supply bias is lower than this level. It consists of two levels, the second level. The absolute value of the development potential at the time of formation of the calibration dedicated patch with the supply offset amount formed at the second level is the absolute value of the development potential at the formation of the toner patch with the supply offset amount formed at the first level. Less than the value.
By configuring in this way, the following effects can be achieved.
By setting the supply offset amount when forming a toner patch having a low development potential, the amount of toner conveyed onto the development rollers 112a, b, c, and d can be reduced. As a result, the amount of toner patches to be developed on the photoconductors 108a, b, c, d can be reduced.

In the printer 1 of this embodiment, the polarity of the supply bias when the supply offset amount is set to the first level and the supply bias when the supply offset amount is set to the second level are reversed. You can also.
By configuring in this way, the following effects can be achieved.
When the supply offset amount is set to the second level at the time of forming the calibration-dedicated pattern, the toner on the developing rollers 112a, b, c, and d is collected to the supply rollers 113a, b, c, and d, thereby developing. The amount of toner conveyed on the rollers 112a, b, c, d can be reduced. As a result, the amount of toner patches to be developed on the photoconductors 108a, b, c, d can be reduced.

Further, the printer 1 of the present embodiment can also make all the toner patches a solid image.
By comprising in this way, a development characteristic can be detected favorably.

In the printer 1 of the present embodiment, the toner patch can be a halftone image of a solid image and an image with an image area ratio of less than 100%.
With this configuration, in the calibration-specific pattern, the toner adhesion amount can be thinned out digitally by reducing the image area ratio of the halftone image.

In the printer 1 of the present embodiment, the level of the supply offset amount is set such that the first supply level when the supply bias used during normal printing is high Vsupply = High, and the supply bias different from the first level is low Vsupply = Low. It can be set to 2 levels, the second level of time. The toner patch formed with the first level supply offset amount can be formed as a solid image, and the toner patch formed with the second level supply offset amount can be formed as a halftone image.
With this configuration, when the supply offset amount is set to the second level at the time of forming the calibration-dedicated pattern, the image area ratio of the halftone image is reduced, and the toner adhesion amount by both analog and digital means Can be thinned out.

Further, the calibration method of the toner density detecting means of this embodiment is a calibration method of the density sensor 126 employed in the configuration of the printer 1 described above.
That is, the color toner density adjustment toner pattern is composed of a plurality of single color toner patches formed with different development biases, and the supply offset amount, which is the difference between the development bias and the supply bias at the time of toner patch formation, is set. There are two levels. Specifically, there are two levels of difference between the development bias at the time of toner patch formation and the supply offset of the supply bias, such as when Vsupply = High when the supply bias is high, and when Vsupply = Low when the supply bias is low.

By configuring in this way, the following effects can be achieved.
In the conventional calibration method, when forming a toner patch for calibration of the toner density detection means, the development characteristics in which the variation in development characteristics is large, particularly in the configuration using the one-component development system, it is difficult to form a low adhesion amount patch. In this case, the calculated value of the normalized value β may be inaccurate. Thus, if the calculated value of the normalized value β becomes inaccurate, the detection accuracy of the toner adhesion amount is lowered, and it becomes impossible to calibrate the appropriate toner concentration detection means.

On the other hand, in the calibration method of the density sensor 126 of the present embodiment, a plurality of single color toner patches are formed with different development biases, and there are two levels of difference between the development bias and the supply bias when forming the toner patches. Thereby, when forming a toner patch for calibrating the density sensor 126, it is possible to satisfactorily form a toner patch with a low adhesion amount by setting the supply bias low.
Therefore, it is possible to provide a calibration method for the density sensor 126 that can form a good low-density patch and can perform appropriate calibration even when the development characteristics vary greatly.

  As described above, the present embodiment has been described with reference to the drawings. However, the specific configuration is not limited to the configuration of the printer 1 of the present embodiment described above, and the design can be changed without departing from the gist. May be performed.

What was demonstrated above is an example, and there exists an effect peculiar for every following aspect.
(Aspect A)
A light emitting element such as an infrared LED 127 is used as a toner density detecting means such as a density sensor 126 for detecting the density of a density adjusting toner pattern such as an unfixed gradation pattern formed on an image carrier such as the intermediate transfer belt 120. Forming a regular reflection light receiving element such as a regular reflection light receiving element 128 that detects specular reflection light, and a diffuse reflection light receiving element such as a diffuse reflection light receiving element 129 that detects diffuse reflection light. In the apparatus, the toner pattern for adjusting the density of color toners such as yellow, magenta, and cyan is composed of a plurality of single-color toner patches formed at different development biases, and the developing roller 112 at the time of forming the toner patch. Development bias applied to the developer carrier, and a supply roller 113 for supplying the developer to the surface of the developer carrier. Wherein the difference between such supply the offset amount of the supply bias applied to the image agent supplying member there are two or more than such as when the supply bias is higher Vsupply = High or when supply bias is low Vsupply = Low.

According to this, as described in the present embodiment, the following effects can be achieved.
In a conventional image forming apparatus, when forming a toner patch for calibration of the toner density detecting means, development with a large variation in development characteristics, particularly in a configuration using a one-component development system, development in which it is difficult to form a low adhesion amount patch. In the case of characteristics, the calculated value of the normalized value β may be inaccurate. Thus, if the calculated value of the normalized value β becomes inaccurate, the detection accuracy of the toner adhesion amount is lowered, and it becomes impossible to calibrate the appropriate toner concentration detection means.

On the other hand, in the configuration of this embodiment (Aspect A), a plurality of single color toner patches can be formed with different development biases, and the difference between the development bias and the supply bias at the time of toner patch formation can be set at two or more levels. . Since it can be set in this way, when forming a toner patch for calibrating the toner density detection means, a supply bias is set lower than the supply bias during normal printing, and a toner patch with a low adhesion amount is formed well. can do.
Therefore, it is possible to provide an image forming apparatus that can form a good low density patch and can calibrate an appropriate toner density detecting means even when the development characteristics fluctuate greatly.

(Aspect B)
In (Aspect A), the level of the difference is a first level such as Vsupply = High when the supply bias used during normal printing is high and a low supply bias lower than the first level such as Vsupply = Low. The absolute value of the developing potential at the time of forming a toner patch such as a calibration-dedicated patch, which is composed of two levels of the second level and the difference is formed at the second level, is formed at the first level. It is characterized by being smaller than the absolute value of the developing potential when forming a toner patch.
According to this, as described in the present embodiment, the following effects can be achieved.
By setting the difference when forming a toner patch with a low development potential small, the amount of toner conveyed onto the developer carrying member such as the developing rollers 112a, b, c, d can be reduced. As a result, the amount of toner patches to be developed on the latent image carrier such as the photoconductors 108a, b, c, and d can be reduced.

(Aspect C)
In (Aspect A), the level of the difference is a first level such as Vsupply = High when the supply bias used during normal printing is high and a Vsupply = Low when the supply bias different from the first level is low. It consists of two levels of the second level, and the polarity of the supply bias when the difference is set to the first level and the supply bias when the difference is set to the second level are opposite .
According to this, as described in the present embodiment, the following effects can be achieved.
When the difference is set to the second level such as when a calibration-only pattern is formed, the toner on the developer carrier such as the developing rollers 112a, b, c, d is supplied to the supply rollers such as the supply rollers 113a, b, c, d. By collecting on the side, the amount of toner conveyed onto the developer carrying member can be reduced. As a result, the amount of toner patches to be developed on the latent image carrier such as the photoconductors 108a, b, c, and d can be reduced.

(Aspect D)
In any one of (Aspect A) to (Aspect C), the toner patches are all solid images.
According to this, as described in the present embodiment, the development characteristics can be well detected by forming all the toner patches solid.

(Aspect E)
In any one of (Aspect A) to (Aspect C), the toner patch is a halftone image such as a solid image and an image having an image area ratio of less than 100%.
According to this, as described in the present embodiment, in the calibration-dedicated pattern such as the calibration-dedicated pattern, the toner adhesion amount can be thinned out digitally by reducing the image area ratio of the halftone image.

(Aspect F)
In any one of (Aspect A) to (Aspect C), the level of the difference is different from the first level such as Vsupply = High when the supply bias used during normal printing is high, and the supply bias different from the first level. The toner patch formed by the difference of the first level is a solid image and is formed by the difference of the second level, such as when Vsupply = Low. The toner patch is a halftone image.
According to this, as described in the present embodiment, when the difference is set to the second level such as when a calibration-dedicated pattern is formed, the image area ratio of the halftone image is lowered, and both analog and digital means are used. Can thin out the toner adhesion amount.

(Aspect G)
Image forming means such as process cartridges 102a, 102b, 102c, and 102c for forming toner images of a plurality of colors such as yellow, magenta, cyan, and black on an image carrier such as an intermediate transfer belt 120; A toner density detection unit such as a density sensor 126 for detecting the density of a density adjustment toner pattern such as an unfixed gradation pattern formed on the toner, and an exposure amount based on density information detected by the toner density detection unit. An image forming condition adjusting unit such as a control unit 200 that corrects an image forming condition such as one or more of a charging bias and a developing bias, and the toner density detecting unit emits light such as an infrared LED 127. Diffusion elements such as a regular reflection light receiving element such as a regular reflection type light receiving element 128 for detecting specular reflection light, and a diffuse reflection type light receiving element 129 for detecting diffuse reflection light In the calibration method of the toner density detecting means used in the image forming apparatus such as the printer 1 having the radiation receiving element, the toner patterns for adjusting the density of the color toners such as yellow, magenta, and cyan are formed with different developing biases. The toner patch is composed of a plurality of single-color toner patches, and the difference between the developing bias and the supply bias supply offset amount at the time of forming the toner patch is two or more levels.

According to this, as described in the present embodiment, the following effects can be achieved.
In the conventional calibration method, when forming a toner patch for calibration of the toner density detection means, the development characteristics in which the variation in development characteristics is large, particularly in the configuration using the one-component development system, it is difficult to form a low adhesion amount patch. In this case, the calculated value of the normalized value β may be inaccurate. Thus, if the calculated value of the normalized value β becomes inaccurate, the detection accuracy of the toner adhesion amount is lowered, and it becomes impossible to calibrate the appropriate toner concentration detection means.

On the other hand, in the calibration method of the toner density detection means of the present (Aspect G), a plurality of single color toner patches are formed with different development biases, and the difference between the development bias and the supply bias at the time of toner patch formation is two levels. That is all. Thereby, when forming a toner patch for calibrating the toner density detecting means, it is possible to satisfactorily form a toner patch with a low adhesion amount by setting the supply bias low.
Therefore, it is possible to provide a calibration method for the toner density detecting means that can form a good low density patch and perform appropriate calibration even when the development characteristics fluctuate greatly.

DESCRIPTION OF SYMBOLS 1 Printer 100 Main body 101 Primary transfer roller 102 Process cartridge 103 Exposure device 106 Fixing device 108 Photoconductor 110 Charger 111 Developing device 112 Developing roller 113 Supply roller 120 Intermediate transfer belt 125 Secondary transfer roller 126 Density sensor 127 Infrared LED
128 regular reflection type light receiving element 129 diffuse reflection type light receiving element 130 casing 200 control unit

Japanese Patent No. 5262671 JP 09-034210 A JP 2006-139180 A JP 2004-279664 A JP 2004-354623 A

Claims (7)

A light emitting element as a toner density detecting means for detecting the density of an unfixed density adjusting toner pattern formed on the image carrier, a regular reflection light receiving element for detecting specular reflection light, and a diffuse reflection for detecting diffuse reflection light In an image forming apparatus having a light receiving element,
The toner pattern for color toner density adjustment is composed of a plurality of single color toner patches formed with different development biases.
The difference between the developing bias applied to the developer carrying member and the supply bias applied to the developer supplying member for supplying the developer to the surface of the developer carrying member when the toner patch is formed is at least two levels. An image forming apparatus. The image forming apparatus according to claim 1.
The level of the difference is composed of two levels, a first level used during normal printing and a second level smaller than the first level.
The absolute value of the development potential at the time of forming a toner patch in which the difference is formed at the second level is
The image forming apparatus according to claim 1, wherein the difference is smaller than an absolute value of a developing potential at the time of forming a toner patch formed at the first level. The image forming apparatus according to claim 1.
The level of the difference is composed of two levels, a first level used during normal printing and a second level different from the first level.
An image forming apparatus, wherein the polarity of the supply bias when the difference is set to a first level and the supply bias when the difference is set to a second level are opposite. The image forming apparatus according to any one of claims 1 to 3,
An image forming apparatus, wherein all of the toner patches are solid images. The image forming apparatus according to any one of claims 1 to 3,
The image forming apparatus, wherein the toner patch is a solid image and a halftone image. The image forming apparatus according to any one of claims 1 to 3,
The level of the difference is composed of two levels, a first level used during normal printing and a second level different from the first level.
The toner patch formed by the difference of the first level is a solid image;
The image forming apparatus, wherein the toner patch formed by the difference of the second level is a halftone image. An image forming means for forming toner images of a plurality of colors on the image carrier, a toner density detecting means for detecting the density of an unfixed density adjusting toner pattern formed on the image carrier, and the toner density detection; An image forming condition adjusting unit that corrects an image forming condition based on density information detected by the unit, the toner concentration detecting unit including a light emitting element, a specular reflection light receiving element that detects specular reflection light, and diffuse reflection light. In a method for calibrating toner concentration detecting means used in an image forming apparatus having a diffuse reflection light receiving element for detecting
The toner pattern for color toner density adjustment is composed of a plurality of single color toner patches formed with different development biases.
A method for calibrating a toner density detecting means, wherein a difference between a developing bias and a supply bias at the time of forming the toner patch is at least two levels.