JP2008116655A - Developer adhesive amount measuring device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developer adhesive amount measuring device having constitution capable of stabilizing image quality by exactly deducing toner adhesive amount also for a highlight image. <P>SOLUTION: Image density control 302 is performed by discriminating the adhesive amount by using a result of measurement of the adhesive amount for the highlight image, which is performed by forming the patch image by the highlight image by deviating a pattern where one writing dot and three non-writing dots adjacent thereto are continued in a main scanning direction by one dot in a subscanning direction, and measuring the adhesive amount for the formed oblique line patch image, differently from a result of measurement of the adhesive amount for a patch image by a solid image. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a developer adhesion amount measuring apparatus and an image forming apparatus, and more particularly to a configuration used for detecting the adhesion amount of powder in an image forming apparatus which is one of apparatuses using powder such as toner. .

  2. Description of the Related Art Conventionally, in an image forming apparatus such as an electrophotographic copying machine or a laser beam printer, in order to always obtain a stable image density, a density detection toner patch ( Hereinafter, a density pattern or density detection pattern is created, the patch density is detected by an optical detection means, and the development potential is changed based on the detection result (specifically, LD power, charging bias, The development bias is changed).

  In the case of the two-component development method, image density control is performed such that the maximum target adhesion amount (adhesion amount for obtaining a target ID) becomes a target value by changing the toner density control target value in the developing device. It is carried out.

  As such a density detection patch detection means, a reflection type optical sensor in which an LED is used as a light emitting element (light emitting means) and a PD (photodiode) or PTr (phototransistor) is used as a light receiving element (light receiving means) is generally used. Known to.

  Conventionally, as a configuration of a reflection type optical sensor, a configuration in which only specular reflection light from a toner patch is a detection target (for example, Patent Document 1), and a configuration in which only diffuse reflection light from a toner patch is a detection target (for example, Patent Document 2) and a configuration (for example, Patent Document 3) in which both reflected lights are detected are known.

  The specularly reflected light output (Vreg) obtained by detecting the specularly reflected light is light that is specularly reflected by the detection target surface (incident angle and reflection angle are equal), and the detection target surface is smooth (= mirror surface). In the case of high glossiness), the irradiated light is only slightly diffused on the detection target surface, and most of it is specularly reflected as specular reflection light.

  On the other hand, unlike the state of the detection target surface where the specularly reflected light output is obtained (the state where the specular gloss is high), when powder such as toner adheres, the incident light is diffused in the toner. Therefore, the amount of specular reflection light decreases, and conversely, the amount of diffuse reflection light, in other words, the amount of reflection light that does not become specular reflection increases. Such diffuse reflected light is conspicuous when color toner is used as a detection target, and in the case of black toner, the irradiated light is hardly absorbed and thus does not increase so much.

  Conventionally, when a color image is obtained using not only black but also a plurality of colors of toner, a latent image carrier is formed by combining regular reflection light and diffuse reflection light for toners of colors other than black and black. The amount of toner adhering on a certain photoconductor or transfer belt is detected (for example, Patent Document 4).

On the other hand, as a method for detecting the adhesion amount of toner of each color for a color image using toners of colors other than black and black by combining the regular reflection light output (Vreg) and the diffuse reflection light output (Vdif) For example, in the output of the light receiving sensor from which the specular reflection light output and the diffuse reflection light output are obtained, respectively, the pure specular reflection among the outputs obtained as the specular reflection light output by subtracting the diffuse reflection light output from the regular reflection light output A method for determining an output corresponding to a light component has been proposed (for example, Patent Document 4).
In the method of subtracting the diffuse reflection light output (Vdif) from the regular reflection light output (Vreg) described above, the toner adhesion amount measurement range is up to the point where one toner layer is completely covered. In some cases, it is impossible to reliably measure the amount of toner attached to the target. Therefore, by taking into consideration the development characteristics such as the particle size, density, or circularity of the toner used, the high adhesion amount that cannot be measured is estimated by correcting the sensitivity of the diffuse reflected light output from the low adhesion amount that can be measured. The method of doing is proposed (patent document 5).

  On the other hand, with respect to the measurement of the amount of color toner adhered, diffuse reflection is performed by correcting fluctuations for the reference density according to the fluctuation rate of each output detected for the specular reflection light output and the diffuse reflection light output in the default state. There has also been proposed a method in which the density detection accuracy of color toner using light output is improved (for example, Patent Document 6).

JP 2001-324840 A (paragraph "0035" column) JP-A-5-249787 (paragraph "0019" column) JP 2001-194443 A (paragraph "0004" column) JP-A-10-319669 (paragraph “0018” column) Japanese Patent Laying-Open No. 2005-76885 (paragraph “0045” column) JP 2002-236402 A (paragraph 0057 column)

The technique relating to the adhesion amount measurement for the color toner is premised on stabilization of the adhesion amount in the solid portion in the image portion in accordance with environmental fluctuations.
However, the image portion obtained as a copy output includes not only a solid portion but also an image with a low printing rate of, for example, several percent, which is called a highlight image.

  The image quality variation factor for gradation expression in highlight images is not only due to the amount of toner adhering to solid images, but also because density increases due to absorption of diffused light by toner dots. Also included are fluctuations in the area ratio of dots (referred to as dot gain). For this reason, when the toner adhesion amount in the highlight image based on the solid image adhesion amount is determined, the toner adhesion amount for the actual highlight image may be different, and an error is likely to occur. There is.

  An object of the present invention is to provide a configuration capable of stabilizing image quality by accurately determining the toner adhesion amount even for a highlight image in view of the problems in the conventional developer adhesion amount measuring apparatus. Another object is to provide a developer adhesion amount measuring apparatus and an image forming apparatus.

In order to achieve the above object, the present invention comprises the following arrangement.
(1) A developer adhesion amount measuring device for measuring an adhesion amount of a developer for detecting an image density formed on an image carrier,
Means for forming a plurality of patch images composed of solid images on which the toner in the developer uniformly adheres on the image carrier by various development bias settings;
A detection output means for detecting the amount of toner adhesion in the plurality of patch images formed by applying predetermined light and detecting the amount of light in the regular reflection direction and the amount of diffuse reflection;
Control means for setting the developing bias and a writing output used for forming the patch image so that the toner adhesion amount in the patch image becomes a target adhesion amount based on information from the detection output means,
The control means sets the development bias and the writing output so that the toner adhesion amount in the patch image based on the solid image becomes a target adhesion amount, and then changes the writing output without changing the development bias. A developer adhesion amount measuring apparatus, comprising: forming a plurality of patch images based on a highlight image having a printing rate lower than that of the image; and detecting a toner adhesion amount of the patch image based on the plurality of highlight images.

  (2) The control unit includes a target adhesion amount table for the patch image based on the highlight image, in addition to the target adhesion amount table for the patch image based on the solid image. The developer adhesion amount measuring apparatus according to (1), wherein the writing output is adjusted so that a toner adhesion amount for an image becomes a target adhesion amount.

  (3) The control unit described in (1) or (2), wherein an output for sequentially changing the thickness of a writing dot is set as a writing output when the patch image is formed by the highlight image. Developer adhesion amount measuring device.

  (4) The control unit, as a patch image based on the highlight image, continues a plurality of non-write dots adjacent to one write dot on one line in the main scanning direction, and the write dots and non-write dots The developer adhering amount measuring apparatus according to (1) or (2), wherein the continuous portion is used while being shifted by one dot in the sub-scanning direction.

  (5) The writing output can be sequentially changed when a patch image is formed using a highlight image, and is set to be four times or more the half exposure amount of the image carrier (1) to (4) ) The developer adhesion amount measuring device according to any one of the above.

(6) The control unit sets the target adhesion amount in the patch image based on the highlight image to 1.5 to 3.5 g / m ^2. Any one of (1) to (5) The developer adhesion amount measuring apparatus according to claim 1.

  (7) The control unit constitutes a 1 on 3 off oblique line image in which three non-write dots adjacent to one write dot are continuous as a continuous portion of the write dot and the non-write dot ( The developer adhesion amount measuring apparatus according to 4).

  (8) An image forming apparatus using the developer amount measuring device according to any one of (1) to (7).

  (9) The image forming apparatus according to (8), comprising a plurality of image forming stations capable of forming images of different colors.

  According to the present invention, it is possible to measure the toner adhesion amount for a highlight image. In particular, instead of taking into account the amount of toner attached to a solid patch image, a patch image is formed directly on the image carrier and the amount of toner attached to the image is measured. Image density control can be performed by measuring the toner adhesion amount for an image based on the adhesion amount.

The best mode for carrying out the present invention will be described below with reference to the embodiments shown in the drawings.
FIG. 1 shows an image forming apparatus in which a developer adhesion amount measuring apparatus according to the present invention is used. The image forming apparatus shown in FIG. 1 includes a plurality of image forming stations capable of forming images of different colors. This is a tandem type color printer in which images of the respective colors are juxtaposed along a transfer body to be superimposed and transferred.

  In FIG. 1, reference numeral 101 is an intermediate transfer member, 102 is a first image forming unit, 103 is a second image forming unit, 104 is a third image forming unit, 105 is a fourth image forming unit, 106 to 109 are transfer units, and 110. Indicates an optical adhesion amount sensor as image detecting means.

FIG. 2 shows the configuration of the image forming means 102 to 105 used in each image forming station shown in FIG. 1. In FIG. 2, the image forming means includes a charger 201 and a photoconductor used as an image carrier. 202, an exposure unit 203, a developing device 205, and a photoconductor cleaner 206 are provided. Each of these means is configured as a process cartridge that is housed in a single unit and detachable from the apparatus.
In the image forming unit 102, the photosensitive member 202 using negatively charged OPC is uniformly charged by the charger 201.
Next, an exposure unit 203 corresponding to a writing unit for forming an electrostatic latent image on the photosensitive member 202 irradiates a laser beam 204 for forming a latent image on the photosensitive member 202 according to the image data. The exposure means used in this embodiment can modulate the laser output, so-called laser power LP.

Thereafter, the latent image formed on the photoconductor 202 is developed with toner by the developing device 205 to form a toner image. At this time, the developing bias potential Vb applied to the developing roll can be modulated. Next, the toner image formed on the photosensitive member 202 is transferred onto the intermediate transfer member 101 by the transfer device 106.
Next, the residual toner remaining on the photosensitive member 202 without being transferred to the intermediate transfer member 101 is collected by the photosensitive member cleaner 206.

  Similarly, in the image forming units 103 to 105 having different color toners, toner images are formed on the respective photosensitive members 202, and the toner images of the respective colors are transferred onto the intermediate transfer member 101 by the transfer units 107 to 109. Then, the image is transferred to the paper 112 by the transfer device 111 and fixed by a fixing device (not shown), and a series of printing processes is completed. In the above embodiment, different color images formed at the respective image forming stations are sequentially transferred to the transfer member. However, the transfer member is used as a transfer unit, and the sheet is electrostatically transferred to the transfer unit. It is also possible to adopt a configuration in which an image for each color is superimposed and transferred in the process of moving each image forming station in the adsorbed state.

In the image forming apparatus shown in FIG. 1, control for image formation is performed by the control unit shown in FIG. 3, and the control unit stabilizes the image density based on a sequence program for image formation. FIG. 3 shows the details of the portion where the control for making the control is executed.
FIG. 3 is a schematic diagram for explaining the configuration of the control unit. In FIG. 3, the control unit 302 indicates the toner adhesion amount of the test patch 301 formed on the intermediate transfer member 101 or the photosensitive member 202. An optical adhesion amount sensor 110 to be detected is connected to the input side, and a charger 201, a laser light source used for the exposure means 203, and a developing device 205 are connected to the output side.

Based on the amount of reflected light from the test patch 301 detected by the optical adhesion amount sensor 110, the control unit 301 calculates the toner adhesion amount at the patch 301, and the calculated result is the target adhesion amount. As described above, the development potential described above is changed (specifically, the LD power, the charging bias, and the development bias are changed).
In this embodiment, the laser power LP 204 from the exposure unit 203 and the developing bias potential Vb from the developing bias power source 303 are controlled.

FIG. 4 does not show the structure and measurement region of a general optical adhesion amount sensor 110.
In the figure, the light emitted from the infrared light source LED 401 is condensed on the measurement area 402 on the intermediate transfer member 101 or the toner patch 301 thereon by a slit or lens (not shown).
The measurement region 402 is usually installed facing the sensor 110, and the sensor central axis 403 is a normal line. Therefore, the incident angle from the LED 401 is θ1. On the other hand, the angle reflected at the same θ1 as shown in the figure is called a regular reflection angle, and the light reflected in this direction is called regular reflection light.
A PD (photodiode) 404 is condensed so that the regular reflection light is incident thereon, and a regular reflection output voltage Vn is obtained. Actually, diffuse reflection light around specular reflection light is also mixed.

  On the other hand, in FIG. 4, the light reflected in the direction of the angle θ2 that is greatly different from θ1 is condensed on the PD (photodiode) 404 to obtain the output voltage Vd. This light is only perfect diffuse reflected light. In the industry, specular reflection is sometimes called specular reflection, and diffuse reflection is sometimes called diffuse reflection, but they are synonymous.

  For example, the drive circuit of the LED 401 and the signal processing circuit of the PDs 404 and 405 are configured as disclosed in Patent Document 1 which is a prior application by the present applicant.

In the control unit 302 shown in FIG. 3, a control sequence according to the procedure shown in FIG. 10 is executed.
In FIG. 10, as shown in step 1001, the light emission intensity of the light emitting element LED is adjusted so that the regular reflection output becomes a constant value (4.0 V) with respect to the substrate on which the toner is not placed.
Next, as shown in step 1002, a developing bias Vbr is formed by shaking the developing bias Vb to form a solid patch image, and a target adhesion amount is obtained by measuring them.
Finally, as shown in step 1003, patch images having different densities are formed by sequentially changing the laser power LP using the developing bias Vbr set in step 10002, and the amount of toner attached to the patch image is measured to obtain a target. The laser power LPr is corrected and set so as to obtain cool adhesion. In this embodiment, the laser power is controlled, and the charging condition that affects the development potential, that is, the charger 201 is not controlled.

  The above-described patch image is created with different densities by sequentially changing the development bias Vb, which is conventionally performed when a solid image is a target. In this embodiment, separately from the solid image, A patch image is formed by a highlight image, and the toner adhesion amount by the highlight image is measured to optimize the image density.

Hereinafter, a method for forming a patch image using a highlight image will be described.
FIG. 8 is a diagram illustrating an example of a patch image based on a highlight image. In the drawing, the patch image is formed by continuing a plurality of non-writing dots adjacent to one writing dot on one line in the main scanning direction. The continuous portions of these writing dots and non-writing dots are formed in a state where they are shifted one dot at a time in the sub-scanning direction. In this embodiment, as shown in FIG. 8, a writing pattern called 1on3off is set, in which three non-writing dots D2 are continuous adjacent to one writing dot D1, and this writing pattern is Shift one dot at a time in the sub-scanning direction. A patch image with this writing pattern is formed in the sub-scanning direction while sequentially deflecting the laser power LP, thereby forming a hatched patch image (hereinafter referred to as a 1 on 3 off hatched patch).

FIG. 9 shows an image of a 1 on 3 off diagonal patch that is specifically recorded. In FIG. 9, 8 patches of each color (black, yellow, magenta, cyan) are formed from LP8 having a large laser output to LP1 having a small laser output.
At this time, the developing bias Vb is obtained in step 1002 described in FIG.
An enlarged view of the hatched patch is shown below the figure. When the laser power LP is increased, the average adhesion amount per patch increases due to the dot being thicker than the dot adhesion amount is increased.

Here, the 1on3off diagonal patch was selected because the adhesion amount range that can be accurately measured by the optical adhesion amount sensor is 1.5 to 3.5 g / m ² , so that the adhesion amount target value is within that range. In order to enter, 1on30ff on the signal, 25% printing rate. In the 1on3off diagonal patch, since adjacent dots continue in the diagonal direction, the amount of adhesion increases smoothly with the dot gain due to the increase in the laser power LP. On the other hand, with a halftone dot on a normal 45 degree screen, the amount of adhesion becomes unstable when dots are connected.

  In the present embodiment, the dots are thickened with the laser power LP, but the same result can be obtained by increasing the laser irradiation time to thicken the dots. In the case of laser power LP, it is desirable that the exposure characteristics of the photoconductor are sufficiently saturated. Usually, shaking with a half-exposure amount of the photoconductor is approximately four times or more, thereby causing interference with the solid image adhesion amount. It is possible to suppress. Therefore, even if the sequence 1003 is executed after the sequence 1002, the solid image adhesion amount does not change.

FIG. 5 shows the output characteristics of the black solid and black 1 on 3 off diagonal image patch 301 (see FIG. 3) when measuring the amount of adhesion. In FIG. 5, the horizontal axis represents the toner adhesion per unit area of the patch 301. It is an amount (g / m ² ), and is a value obtained by accurately measuring the amount of adhesion of a patch on the transfer belt by a suction method. The vertical axis represents the regular reflection output voltage Vn (V) of the sensor 110, and the output when the adhesion amount is 0 is normalized to 4.0V.

The black solid output cannot be measured because there is no inclination when the adhesion amount is 4.0 g / m ² or more. On the other hand, even when the output is a low adhesion amount of 3 V or more, the error becomes large due to uneven surface reflection of the transfer belt (not shown). Accordingly, 1 to 4 g / m ² is a measurable range.

On the other hand, the measurable range from the black 1 on 3 off diagonal output is also 1 to 4 g / m ² . As described above, when the target adhesion amount of the patch is 1.5 to 3.5 g / m ² , measurement can be performed with high accuracy.

  Further, comparing the characteristics of both, in the region where the amount of adhesion is small, the sensor output is lower in the 1on3off diagonal image than in the solid image, and conversely, in the region where the amount of adhesion is large, the sensor output is high, and the slope of the characteristic is It will be different.

  In the present embodiment, as shown in FIG. 5, in addition to the sensor output-attachment amount table for a commonly used solid image, the measurement output of a 1 on 3 off diagonal patch image is used for the measurement of the attachment amount. It is characterized by use. In other words, if an attempt is made to determine the amount of adhesion in a highlight image by using a table for a solid image as in the past, there is a large error between the measurement results for the solid image. Even in the image density control based on the measurement result of the adhesion amount, a result with a large error is obtained. Therefore, in this embodiment, an error is prevented from occurring by using a table for both solid images and 1 on 3 off diagonal lines.

FIG. 6 shows a solid image adhesion amount with respect to the developing bias Vb in an image forming apparatus using a general electrophotographic system.
The horizontal axis represents the development potential Vb (V), and the development bias potential becomes higher toward the right, and the toner adhesion amount in the patch image of the solid image tends to increase.
The vertical axis represents the toner adhesion amount (g / m ² ) in the patch image of the solid image.

Since a black solid image can only be measured up to an adhesion amount of 4.0 g / m ² , the development bias potential Vb to be set with respect to the target adhesion amount Tmr (approximately 6 g / m ² ) is a measurable low adhesion amount. Estimated from
In the figure, a method by linear approximation is specifically shown, but polynomial approximation can also be used depending on development characteristics.

FIG. 7 shows the amount of 1on3off oblique line adhesion with respect to laser power LP (on the photoreceptor image surface) in an image forming apparatus using a general electrophotographic system.
The horizontal axis is the laser power LP (mW), and the range in which it normally swings is limited. The vertical axis represents the toner adhesion amount (g / m ² ) in the 1on3off oblique patch image, and the toner adhesion amount tends to increase as the laser power LP increases.

Although the measurement range can not be similarly measured only up to deposition amount 4.0 g / ^{m 2} in the case of the black solid image, since the target coating weight Tmr is generally 2 to 3 g / ^{m 2,} the laser power LPr to be set (mW) is It is in the measurement range and can be obtained accurately. In the figure, a method by linear approximation is specifically shown, but polynomial approximation can also be used depending on characteristics.

As described above, according to the present embodiment, a 1 on 3 off oblique patch is used to measure the state of the highlight image, and a high-accuracy measurement of the highlight portion attachment amount is possible by having an original attachment amount conversion table. It becomes.
As a result, not only the conventional solid image but also the highlight image is controlled with high accuracy, so that high image quality can be stably maintained.

1 is a schematic diagram illustrating a configuration of an image forming apparatus using a developer adhesion amount measuring apparatus according to the present invention. FIG. 2 is a schematic diagram for explaining a configuration of an image forming unit used in an image forming station of the image forming apparatus illustrated in FIG. 1. It is a typical block diagram for demonstrating the control mechanism using the developer adhesion amount measuring apparatus by this invention. It is a schematic diagram for demonstrating the structure of the optical adhesion amount sensor used for the control mechanism shown in FIG. It is a diagram for demonstrating the measurement result of the sensor output and adhesion amount which made the solid image and the highlight image object. It is a diagram for explaining the relationship between the development bias and the adhesion amount. It is a diagram for demonstrating the relationship between a laser power and the adhesion amount. It is a figure for demonstrating the formation pattern of the patch image by the highlight image by the Example of this invention. It is a figure for demonstrating the detail of the patch image by the highlight image shown in FIG. It is a flowchart for demonstrating the effect | action of the control mechanism shown in the figure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Intermediate transfer body 110 Adhesion amount sensor 202 Photoconductor 203 Exposure means 204 Laser beam 205 Developing apparatus 301 Patch image 302 Control part 303 Developing bias power supply

Claims (9)

A developer adhesion amount measuring device for measuring an adhesion amount of a developer in order to detect an image density formed on an image carrier,
Means for forming a plurality of patch images composed of solid images on which the toner in the developer uniformly adheres on the image carrier by various development bias settings;
A detection output means for detecting the amount of toner adhesion in the plurality of patch images formed by applying predetermined light and detecting the amount of light in the regular reflection direction and the amount of diffuse reflection;
Control means for setting the developing bias and a writing output used for forming the patch image so that the toner adhesion amount in the patch image becomes a target adhesion amount based on information from the detection output means,
The control means sets the development bias and the writing output so that the toner adhesion amount in the patch image based on the solid image becomes a target adhesion amount, and then changes the writing output without changing the development bias. A developer adhesion amount measuring apparatus, comprising: forming a plurality of patch images based on a highlight image having a printing rate lower than that of the image; and detecting a toner adhesion amount of the patch image based on the plurality of highlight images.   The control unit includes a target adhesion amount table for the patch image based on the highlight image separately from the target adhesion amount table for the patch image based on the solid image, and targets the patch image of the highlight image. 2. The developer adhesion amount measuring apparatus according to claim 1, wherein the writing output is adjusted so that the toner adhesion amount is a target adhesion amount.   3. The developer adhesion amount according to claim 1, wherein the control unit sets an output for sequentially changing a thickness of a writing dot as a writing output when the patch image is formed by the highlight image. measuring device.   The control unit continues a plurality of non-writing dots adjacent to one writing dot on one line in the main scanning direction as a patch image based on the highlight image, and a continuous portion of these writing dots and non-writing dots. 3. The developer adhesion amount measuring apparatus according to claim 1, wherein the developer is used while being shifted by one dot in the sub-scanning direction.   5. The writing output according to claim 1, wherein the writing output can be sequentially changed when a patch image is formed by a highlight image, and is set to be four times or more of a half exposure amount of the image carrier. The developer adhesion amount measuring apparatus as described. 6. The development according to claim 1, wherein the control unit sets the target adhesion amount in the patch image based on the highlight image to 1.5 to 3.5 g / m ^2. Agent adhesion amount measuring device.   5. The control unit forms a 1 on 3 off oblique line image in which three non-writing dots adjacent to one writing dot are continuous as a continuous part of the writing dot and the non-writing dot. The developer adhesion amount measuring apparatus as described.   An image forming apparatus using the developer amount measuring apparatus according to claim 1.   The image forming apparatus according to claim 8, further comprising a plurality of image forming stations capable of forming images of different colors.

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