JP2001194843A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform highly accurate image density control by accurately performing the density detection of a patch on a transfer belt for each color even in the case that the transfer belt and an intermediate transfer body consist of a material incorporating a substance having the same absorption band as that of the toner of at least one color out of plural colors used. SOLUTION: When patch density is detected by using an optical sensor by which a normally reflected light quantity and an irregularly reflected light quantity by the patch on the transfer belt are simultaneously measured, though the density detection of the patch of black toner is not made possible at the sensor output value Vd of irregularly reflected light and the density detection of the patch of color toner is made difficult because of high density by the sensor output value Vm of normal reflected light, the difference Vm-Vd of sensor output are remarkably changed by the patch density for the black toner and the color toner, and the patch density is accurately detected, so that the patch density is detected by the difference value and image density control is performed based on it. The surface glossiness of the transfer belt is set to be >=50 and <=98 by the measuring angle of 20 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to image formation using an electrophotographic system such as a copying machine, a laser beam printer, and a facsimile, and more particularly, to a method for controlling image density.

[0002]

2. Description of the Related Art In an image forming apparatus using an electrophotographic process, as a means for obtaining an appropriate image density, a toner image (hereinafter, referred to as a patch) as a density reference is formed on an image carrier such as a photoconductor. After forming the patch, the density of the patch is detected by optical means, and based on the detected density, the image density such as charging potential, exposure intensity, developing bias potential, transfer voltage, toner replenishing amount (in the case of a two-component developer), etc. By applying feedback to parameters (image forming conditions) that affect the image density, the image density is appropriately controlled.

As an optical means for detecting patch density, light is emitted from a light emitting element such as an LED to a patch on an image carrier, and a reflected light amount depending on the patch density of the light is received by a photodiode or the like. An optical sensor that detects with an element is used.

[0004] As the optical sensor, an optical system of a light emitting element 11 and a light receiving element 12 as shown in FIG. Light emitting element 1 as shown in FIG.
Depending on the optical system of the light receiving element 1 and the light receiving element 12, there is a type of detecting the amount of irregularly reflected light from the toner itself, such as a decrease in the case of black toner and an increase in the case of color toner as the patch density increases. In addition, as shown in FIG.
ED) Two light receiving elements (photodiodes) for 11
There is also a type that has both light receiving elements 12 and 13 and can detect both the regular reflection light amount and the irregular reflection light amount by selectively using the light receiving elements 12 and 13 with the black toner and the color toner.

Recently, stations for forming images of a plurality of colors such as yellow, magenta, cyan, and black are arranged in a line for the purpose of high-speed output of a color image, and a recording medium such as paper is transferred to each station by a transfer belt. Tandem-type image forming apparatuses have been proposed and put to practical use, in which toner images of respective colors are successively superimposed and transferred onto a recording medium.

In such an image forming apparatus, as proposed in Japanese Patent Application Laid-Open No. 63-147177, a patch formed at each station is transferred onto a transfer belt, and one sensor is installed opposite to the transfer belt. A method of measuring the densities of patches of a plurality of colors transferred directly onto a transfer belt without overlapping them is known. This method has a cost advantage because only one sensor is required.

Further, a plurality of color toner images are superimposedly transferred onto an intermediate transfer member (intermediate transfer belt, intermediate transfer drum),
There is an image forming apparatus of a type in which the patches are collectively transferred onto a recording medium. In this image forming apparatus as well, patches of a plurality of colors are transferred onto an intermediate transfer body without overlapping, and the patch density is reduced by one. A method of detecting with the sensor of
It has also been implemented.

[0008]

However, when a system in which patches of a plurality of colors are formed on the transfer belt or the intermediate transfer member as described above and the density of the patches is detected by one sensor is adopted, the following method is used. Inconvenience may occur.

As a material of the transfer belt and the intermediate transfer member, polyimide, polycarbonate, PET and the like are used.
In some cases, a conductive material is added to this material for the purpose of ensuring good transferability, and the resistance is adjusted to an appropriate range before use. As the conductive material for adjusting the resistance value, for example, carbon or the like is used.

When a patch of black toner containing carbon is also formed on a transfer belt or an intermediate transfer member made of a material to which carbon has been added in this manner, the transfer belt and the intermediate transfer member and the patch have the same light. To have an absorption band,
The LED light (near infrared light) of the sensor light emitting element is absorbed together.

For this reason, if a transfer belt or an intermediate transfer member having a low surface glossiness is used, a sensor as shown in FIG.
Even if a type that detects the amount of irregularly reflected light such as that shown in Fig. 2 or a type that detects the amount of specularly reflected light such as that shown in Fig. 2 is used, the sensor output will be reduced as a whole regardless of the patch density, making it difficult to accurately detect the patch density. Will be.

In order to accurately measure the patch density of a black toner formed on a transfer belt or an intermediate transfer member to which carbon has been added, those having high surface glossiness are used, and a sensor for detecting the amount of specular reflection is used. It is good to use the type which does. This is because even if the material of the transfer belt or the intermediate transfer body contains carbon, if the surface glossiness is high,
This is because the regular reflection of the irradiation light occurs on the surface, so that a sensor output corresponding to the patch density can be obtained. This makes it possible to accurately detect the patch density of the black toner.

On the other hand, it is more advantageous to use a diffuse reflection light amount detection type sensor for detecting the patch density of the color toner, and it is particularly advantageous for detecting the density on the high density side. As the patch density of the color toner increases, the amount of irregularly reflected light from the color toner itself increases.Therefore, if a regular reflection light amount detection type sensor is used, the irregular reflection component will be mixed with the regular reflection component and detected, and the high density side will be detected. May lead to erroneous detection of density. The diffuse reflection light amount detection type sensor does not have such a disadvantage.

In this case, it is sufficient to use a sensor in which the light receiving element is selectively used for the black toner and the color toner as shown in FIG. 4, but the following problem still remains.

When the use of the image forming apparatus advances to some extent, the detection window becomes dirty with the scattered toner inside the apparatus, and the output decreases. Therefore, the amount of reflected light from the image carrier is detected in a state where the toner is not adhered to the image carrier, and a window contamination coefficient is calculated by comparing this with an initial value. The patch density detected when the window is dirty is corrected.

However, when a transfer belt or an intermediate transfer member containing a material that absorbs light, such as carbon, is used, the sensor output of irregularly reflected light from these surfaces is always constant (about 0 V) regardless of the degree of window contamination. ), The output cannot be corrected by the window contamination coefficient.

An object of the present invention is to provide a transfer belt or an intermediate transfer member which is made of a material containing a substance having the same absorption band as at least one color toner among a plurality of color toners used for image formation. Performs accurate patch density detection for each color on the transfer belt and intermediate transfer body,
An object of the present invention is to provide an image forming apparatus capable of obtaining a high-quality image by high-precision image density control.

[0018]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
A reference image for density detection formed using toner on the image carrier is transferred to a belt-shaped recording medium conveying means, and the density of the reference image is detected by an optical detecting means on the conveying means, and the detection is performed. In the image forming apparatus that controls the image density based on the result, the optical detection unit can simultaneously measure the regular reflection light amount and the irregular reflection light amount based on the reference image on the conveyance unit, and the measured regular reflection light amount An image forming apparatus for detecting the density of the reference image and controlling the image density based on a difference between the reference image density and the amount of diffuse reflection light.

According to the present invention, the conveying means contains a substance having the same light absorption band as that of the toner, and has a glossiness of 50 to 98 at a measurement angle of 20 °. By the optical detection means, to measure the amount of regular reflection light in an area other than the formation area of the reference image on the transport means,
The density of the reference image may be corrected based on the measured regular reflection light amount in an area other than the formation area.

The image forming apparatus has a plurality of the image carriers, has one optical detecting means, and has a plurality of color images formed on the plurality of image carriers using a plurality of color toners. The reference image for density detection is transferred to the transport unit without overlapping, and the density of the reference image of a plurality of colors is detected on the transport unit by the one optical detection unit, and the one transport unit is It contains a substance having the same light absorption band as one of the toners of the plurality of colors, and has a glossiness of 50 to 98 at a measurement angle of 20 °.

Further, according to the present invention, a reference image for density detection formed on an image carrier using toner is transferred to a belt-shaped or drum-shaped intermediate transfer member, and the density of the reference image on the intermediate transfer member is determined. Is an image forming apparatus that detects an image density by an optical detection unit and controls an image density based on a result of the detection.

[0022]

Embodiments of the present invention will be described below in detail with reference to the drawings.

Embodiment 1 FIG. 1 is a configuration diagram showing an embodiment of the image forming apparatus of the present invention. The image forming apparatus according to the present embodiment includes first, second, third, and fourth image forming units (stations) 4Y, 4M, 4C, and 4 along the upper trajectory of the transfer belt 60.
K are arranged in a line so that a full-color image can be formed at high speed. Image forming units 4Y, 4M, 4C, 4
K performs yellow, magenta, cyan, and black image formation, respectively.

The photosensitive drum 41 (41Y to 41K) of each image forming section 4 (4Y to 4K) is rotatably supported in the direction of the arrow in FIG. 1, and the photosensitive drum 41 is attached to the primary charger 46 (46Y). After the surface of the photosensitive drum 41 is uniformly charged by an exposure device 47 (47Y to 47K) using a laser beam exposure device or the like, the surface of the photosensitive drum 41 is irradiated with a light image of each color. An electrostatic latent image of each color is formed.

The latent images are stored in respective developing units 9 (9Y to 9Y).
9K) and visualized as yellow, magenta, cyan, and black toner images. In this embodiment, each developing unit 9 develops a latent image using a two-component developer obtained by mixing a non-magnetic toner and a magnetic carrier.

The toner images of each color formed on the photosensitive drum 41 of each image forming unit 4 in this manner are transferred to the transfer belt 6.
The transfer chargers 49 (49Y to 49K) successively transfer the images onto a recording medium such as a paper carried on the image forming unit 0 and conveyed to each image forming unit. In this embodiment, the transfer belt 60 is made of polycarbonate, and the volume resistivity is adjusted to about 10 ¹⁵ Ωcm by adding carbon to this material in order to obtain good transferability.

The recording medium to which the four color toner images have been transferred is
When the transfer belt 60 reaches the rear end in the transport direction of the transfer belt 60,
The toner image is then sent to the fixing device 51, where the toner image is pressurized and heated, so that the four-color toner image becomes a full-color fixed image. Transfer residual toner remaining on each photosensitive drum 41 without being completely transferred is removed and collected by the cleaning device 48 (48Y to 48K).

In the image formation using a multicolor toner as in the image forming apparatus of this embodiment, it is required that the image density of each color is appropriate and stable in order to obtain a high-quality full-color image. Therefore, in addition to the above-described normal image forming mode, a mode (hereinafter, referred to as a patch detection mode) for appropriately setting the image density of each color is provided.

In the patch detection mode, an electrostatic latent image of a patch (pattern having a certain area) is formed on the photosensitive drum 41, and is developed with a predetermined developing contrast voltage. Each color is transferred onto the transfer belt 60 by transfer on the transfer belt 60, and the patch of each color is transferred to the black image forming portion 4 of the fourth color of the final color.
The density of the patch (the amount of the adhered toner) is detected by a single optical sensor 70 provided at a position downstream of the transfer belt 60 immediately after 8K and opposed to the transfer belt 60.

As shown in FIG. 4, the optical sensor 70 has an LED 11 having a center wavelength of 970 nm as a light emitting element.
With two photodiodes 12 and 13 as light receiving elements
The LED 11 irradiates the patch 20 on the transfer belt 60 with light, and the photodiode 12 receives and detects the amount of regular reflection light corresponding to the density of the patch 20,
The optical system is configured to receive and detect the amount of irregularly reflected light by the photodiode 13.

The light incident on the photodiodes 12 and 13 generates a current depending on the amount of light, is converted into a voltage corresponding to the current, and is amplified to obtain an output value. The relationship between the output value Vm of the photodiode 12 and the output value Vd of the photodiode 13 with respect to the patch density is shown in FIG.
As shown in FIG.

As shown in FIG. 6, it can be seen that the patch density of the black toner cannot be detected by the sensor output value Vd. The patch density of the color toner can be detected with the sensor output value Vm or Vd when the density is low,
When the patch density becomes high, as shown in FIG.
The output of Vm increases due to the mixing of the irregular reflection components,
In this case, it is difficult to accurately detect the patch density of the color toner.

FIG. 7 shows the relationship between the patch density and the difference Vm-Vd between the regular reflection light quantity output Vm and the irregular reflection light quantity output Vd. As shown in FIG. 7, the difference value Vm-Vd of the sensor output greatly changes with respect to the patch density for both the black toner and the color toner, and the patch density is accurately measured based on the difference value. You can see that it can be done. Therefore, a major feature of the present invention is that the patch density is detected based on the difference value and the image density control is performed based on the detected patch density.

Hereinafter, the image density control in this embodiment will be specifically described with reference to the flowchart of FIG. When the patch detection mode is started, a patch of each color is formed on the transfer belt, the patch density is detected by the sensor 70, and a difference = Vm−Vd is calculated from the detected sensor output values Vm and Vd by an arithmetic unit (not shown). Is calculated and the difference value Vm−
Vd is compared with an initial set value (reference value) Vm0-Vd0 recorded in the memory in advance.

If Vm-Vd> Vm0-Vd0, it is determined that the image density is low, and feedback is applied to an arbitrary parameter in a direction to increase the image density. When feedback is applied to the toner supply amount, a necessary toner supply amount is calculated from these deviations = (Vm−Vd) − (Vm0−Vd0), and toner supply to the corresponding developing device 4 is performed. Conversely, if Vm-Vd <Vm0-Vd0, it is determined that the image density is high, and feedback is applied to an arbitrary parameter in the direction of decreasing the image density. When applying feedback to the toner supply amount, the toner supply of the developing device is stopped.

The patches after the density detection are removed from the transfer belt 60 by a transfer belt cleaner (not shown), and the patch detection mode is ended to return to the normal image forming mode.

The patch detection mode is executed as described above. In order to obtain a sufficient specular reflection light amount, the transfer belt 60 having a surface with a certain high glossiness is used. If a transfer belt with low surface glossiness is used, regular reflection does not occur sufficiently on that surface.
Since the output value Vm of the sensor decreases as a whole, Vm−Vd
Is also small, and especially in the case of black toner, the S
The N ratio (signal / noise) deteriorates.

In this embodiment, the transfer belt 60 having a sufficiently high glossiness on the surface is used. As a result of the study, the glossiness of the surface of the transfer belt had to be in the range of 50 or more and 98 or less in order to perform satisfactory patch density detection. The upper limit of the glossiness of the transfer belt surface is set because, in order to obtain a glossiness higher than this, a material that does not satisfy the performance of the transfer belt must be selected, which is not suitable for practical use. . The gloss was measured at a measurement angle of 20 ° using a gloss meter (Model TC-108DP / A) manufactured by Tokyo Denshoku.

An example of the study will be described below. FIG. 9 shows a change in the difference Vm-Vd of the sensor output with respect to the patch density of the black toner formed on the transfer belt having the glossiness of 91.7 and the transfer belt having the glossiness of 19.2.

As shown in FIG. 9, the glossiness was 91.7.
In the case of the transfer belt, it can be seen that the difference in the sensor output greatly changes with the change in the patch density of the black toner. On the other hand, in the case of a transfer belt having a glossiness of 19.2, regular reflection does not easily occur on the surface of the transfer belt, so that the output value Vm is small as a whole, and the difference Vm is obtained even when the patch density on the transfer belt changes. Since the value of -Vd hardly changes, it is difficult to accurately detect the patch density.

In addition to the above, a transfer belt having a gloss of 48.8 and a transfer belt having a gloss of 41.9 were examined. The belt with a gloss of 48.8 was able to detect the patch density satisfactorily, while the belt with a gloss of 41.9 deteriorated sharply in S / N ratio and was as accurate as the belt with a gloss of 19.2. It was difficult to detect the patch density.

As described above, in order to detect the patch density due to the toner on the transfer belt containing the substance having the same light absorption band as the toner, the gloss of the surface is high, preferably 50 or more. It is necessary to use a transfer belt. From the above, in the present invention, the glossiness of the surface of the transfer belt 60 is specified to be 50 or more and 98 or less.

As described above, when the use of the image forming apparatus has progressed to some extent, the sensor 70 is scattered by the toner scattered inside the apparatus.
The detection window becomes dirty, thereby reducing the output. In that case, it is preferable to detect the amount of light reflected from the area of the transfer belt 60 where no patch is formed, and compare the sensor output Vmb with the initial set value Vmb0 to correct the patch density due to the window stain. .

More specifically, a portion surrounded by a dotted line is added to the flow chart of FIG. 8 so that the amount of light reflected from the transfer belt during the pre-rotation after the start of copying without the toner on the transfer belt is attached. From the measured sensor output value Vmb and the previously stored initial setting value Vmb0 read from the memory, Vmb0 / Vm
b is calculated, and this is set as a window dirt coefficient. Then, the coefficient Vmb0 / Vmb is multiplied by the difference value Vm−Vd of the sensor output, and the patch density is calculated as (Vm−Vd) × Vmb0 / Vm.
b, and the patch density to be compared with the difference initial setting value Vm0-Vd0 is replaced with the corrected patch density. Thereafter, toner supply control or the like may be performed in the same manner as described above.

By doing so, erroneous detection of patch density can be prevented even if the sensor window becomes dirty. Therefore, it is preferable to make this correction in order to stabilize image density during long-term use.

The present embodiment is configured as described above. Even when the transfer belt is made of a material containing a substance having the same absorption band as at least one color toner among a plurality of color toners used for image formation. The density of the patch can be accurately detected for each color on the transfer belt, so that the image density can be controlled with high accuracy, and a high-quality image can be obtained.

Embodiment 2 FIG. 10 is a block diagram showing another embodiment of the image forming apparatus of the present invention.

In this image forming apparatus, the photosensitive drum 41 is
And an intermediate transfer belt 62 as a second image carrier. 10, the same reference numerals as those shown in FIG. 1 denote the same members.

The configuration of each image forming unit 4 (4Y-4K)
Although basically the same as the image forming apparatus of the first embodiment shown in FIG. 1, the toner images of each color formed on the photosensitive drums 41 (41 Y to 41 K) are temporarily placed on the intermediate transfer belt 62. Overlaid and transferred (primary transfer), then
On a recording medium such as paper conveyed to the intermediate transfer belt 62,
The images are collectively transferred by the transfer roller 30 (secondary transfer).

When such an intermediate transfer belt 62 is used, the fixing device 51 can be disposed below, so that the width of the main body of the image forming apparatus can be reduced, and each image forming section is made of a recording medium such as paper. There is an advantage in that it is not affected by foreign matter such as paper powder because it does not come into contact with. Further, an optical sensor 70 installed immediately after the image forming unit 4K for the final color black of the intermediate transfer belt 62 prevents contamination due to scattered toner generated by processing a recording medium carrying an unfixed image at the time of paper jam. Therefore, there is also an advantage that a decrease in sensor output due to this can be suppressed.

In this embodiment, the intermediate transfer belt 62 is made of polyimide, and carbon is added to the polyimide material so that the volume resistivity is about 10 ¹² for the purpose of good transferability of the intermediate transfer belt. Adjusted to Ωcm. The glossiness of the surface of the intermediate transfer belt was 50 or more and 98 or less, similarly to the transfer belt of Example 1.

Also in this embodiment, by setting the glossiness of the surface of the intermediate transfer belt to 50 or more, a sufficient amount of regular reflection light can be obtained. In the patch detection mode, the sensor 70 is used.
The difference Vm− between the regular reflection light quantity output Vm and the irregular reflection light quantity output Vd−
With Vd, the patch density could be accurately detected.

The image density control is performed in the same manner as in the first embodiment. That is, the density of the patch formed on the intermediate transfer belt 52 is detected by the sensor 70, and the sensor output value V
The difference Vm-Vd between m and Vd is calculated and compared with an initial set value Vm0-Vd0, and fed back to a parameter affecting image density, for example, a toner replenishment amount,
Image density control may be performed.

When the sensor 70 is used for a long time, it is preferable to perform correction based on the stain on the window of the sensor 70, and the correction is performed in the same manner as in the first embodiment. That is, in a state where the toner on the transfer belt is not attached, the amount of reflected light from the transfer belt is measured and detected, and the sensor output value Vmb and the initial set value Vm are detected.
The window contamination coefficient Vmb0 / Vmb is calculated from b0 and the difference value Vm− of the sensor output is calculated as the coefficient Vmb0 / Vmb.
Vd is multiplied to obtain a patch density of (Vm−Vd) × Vmb0.
/ Vmb, and compares the corrected patch density with the initial set value Vm0-Vd0 of the difference, and feeds it back to, for example, the toner supply amount to perform image density control.

This embodiment is configured as described above, and the intermediate transfer belt is made of a material containing a substance having the same absorption band as at least one color toner among a plurality of color toners used for image formation. However, the density of the patch can be accurately detected for each color on the intermediate transfer belt, and a high-quality image can be obtained by performing high-precision image density control.

Embodiment 3 FIG. 11 is a configuration diagram showing still another embodiment of the image forming apparatus of the present invention.

This image forming apparatus has one photosensitive drum 41
Around the primary charger 48, exposure means 46 such as a laser beam exposure device, a fixed black developing device 9K using a two-component developer, and a rotary developing device 9Y, 9M for each of yellow, magenta, and cyan. 9C, and intermediate transfer drum 64
The toner image of each color is superimposed and transferred onto the intermediate transfer drum 48 by charging, exposure and development on the photosensitive drum 41, and primary transfer on the intermediate transfer drum 48, and then collectively on a recording medium such as paper. Secondary transfer is performed.

The photosensitive drum 41 is, as shown in FIG.
The photosensitive drum 41 is rotatably supported in a direction indicated by an arrow. After the surface of the photosensitive drum 41 is uniformly charged by a primary charger 46, the exposure unit 47 first corresponds to a yellow portion obtained by color separation of a color image. And an electrostatic latent image corresponding to a yellow portion is formed on the surface of the photosensitive drum. Correspondingly, the rotary yellow developing unit 9Y has been moved to a position facing the photosensitive drum 41, and the developing unit 4Y develops the latent image using a two-component yellow developer to form a yellow toner image. Visualize as The obtained yellow toner image is transferred from the photosensitive drum 41 to the intermediate transfer belt 64 by applying a transfer bias to the metal core of the intermediate transfer drum 64.
Is transferred to the upper side (primary transfer).

The photosensitive drum 41 is uniformly charged again by the primary charger 46, and then irradiates a light image corresponding to a magenta portion to form an electrostatic latent image corresponding to a yellow portion on the surface of the photosensitive drum. Correspondingly, the latent image is developed using a magenta two-component developer and visualized as a magenta toner image by the rotary developing device 4M moved to a position facing the photosensitive drum 41. The obtained magenta toner image is transferred onto the intermediate transfer belt 64 from above the yellow toner image.

Similarly, the photosensitive drum 41 is uniformly charged, the light image corresponding to the cyan portion is irradiated, the development is performed using the two-component cyan developer by the rotary developing device 4C, and the obtained cyan toner image is formed. Superimposition transfer onto the intermediate transfer belt 64, uniform charging of the photosensitive drum 41, irradiation of a light image corresponding to a black portion, and development using a two-component black developer by a fixed developing device 4K were obtained. Superimposition transfer of the black toner image onto the intermediate transfer belt 64 is performed.

The four-color toner images superimposed and transferred on the intermediate transfer belt 46 in this manner are then transferred onto a recording medium such as paper conveyed to an intermediate transfer drum 64 by a transfer bias 54 to a belt-type transfer means 54. Is applied, and this is brought into contact with the intermediate transfer drum 64 with the recording medium interposed therebetween, whereby the image is collectively transferred (secondary transfer). Then, the recording medium is fixed to the fixing device 5.
When the toner image is sent to 1 and pressed and heated, the four color toner images are melt-mixed and fixed, and a full-color permanent image is obtained.

The advantage of the image forming apparatus using the intermediate transfer member as in the present embodiment is that even if only one photosensitive drum is used, the conveyance path of the recording medium such as paper is provided in a straight line, and the recording medium is provided with four colors. A full-color image can be formed, and various recording media can be used.

The intermediate transfer drum 62 is made of polyimide, and carbon is added to the polyimide material to adjust the volume resistivity to about 10 ¹⁰ Ωcm for the purpose of good transferability of the intermediate transfer drum. ing. The glossiness of the surface of the intermediate transfer drum was 50 or more and 98 or less similarly to the transfer belt of Example 1.

Also in this embodiment, by setting the glossiness of the surface of the intermediate transfer drum to 50 or more, a sufficient amount of regular reflection light can be obtained. In the patch detection mode, the regular reflection light amount output Vm and irregular reflection Difference Vm-V of light output Vd
With d, the patch density could be accurately detected.

As in the first embodiment, the density of the patch formed on the intermediate transfer drum 64 is controlled by the sensor 70.
And the difference Vm− between the sensor output values Vm and Vd.
Vd is calculated, compared with the initial set value Vm0-Vd0, and fed back to a parameter affecting the image density, for example, a toner replenishment amount, to perform image density control.

During long-term use, it is preferable to perform correction based on the contamination of the window of the sensor 70. As in the first embodiment, the amount of reflected light from the intermediate transfer drum is measured and detected in a state where toner is not attached. From the sensor output value Vmb and the initial set value Vmb0, the window contamination coefficient Vmb0 / Vmb
Is calculated, and the coefficient is multiplied by the difference value of the sensor output to correct the patch density. This corrected patch density (Vm-Vd)
× Vmb0 / Vmb and the difference initial setting value Vm0−Vd0
In comparison with the above, for example, the image density control may be performed by feeding back to the toner supply amount.

The present embodiment is configured as described above, and the intermediate transfer drum is made of a material containing a substance having the same absorption band as at least one color toner among a plurality of color toners used for image formation. However, the density of the patch can be accurately detected for each color on the intermediate transfer drum, and a high-quality image can be obtained by performing highly accurate image density control.

In each of the first to third embodiments, the case of a full-color image forming apparatus has been described.
The present invention can also be applied to a monochrome image forming apparatus using only a black developer. Further, the developing device uses a two-component developer, but may use a magnetic one-component developer composed of only a magnetic toner or a non-magnetic one-component developer composed of only a non-magnetic toner.

[0069]

As described above, according to the present invention,
As an optical detection means for patch density, using a detection means that can simultaneously measure the amount of specular reflection and the amount of irregular reflection from a patch on a transfer belt or an intermediate transfer member, the amount of specular reflection and the amount of irregular reflection of a patch is measured and specular reflection is performed. Since the patch density is detected based on the difference between the light quantity and the diffuse reflection light quantity, the patch density can be accurately detected for each color, and a high-quality image can be obtained by highly accurate image density control.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of an image forming apparatus of the present invention.

FIG. 2 is an explanatory diagram showing an optical system of an optical sensor of a type for measuring the amount of specular reflection.

FIG. 3 is an explanatory diagram showing an optical system of an optical sensor of a type that measures the amount of diffusely reflected light.

FIG. 4 is an explanatory diagram showing an optical system of an optical sensor of a type for simultaneously measuring a regular reflection light amount and a diffuse reflection light amount.

5 is a graph showing a sensor output value Vm with respect to a patch density when a regular reflection light amount by a patch is measured by the sensor of FIG. 4;

FIG. 6 is a graph showing a sensor output value Vd with respect to a patch density when a diffused light amount by a patch is measured by the sensor of FIG. 4;

7 is a graph showing a difference Vm-Vd between the output values of the regular reflection light amount and the irregular reflection light amount of the sensor of FIG. 4 with respect to the patch density.

8 is a flowchart illustrating image density control in the embodiment of FIG.

FIG. 9 is a graph showing a change in sensor output difference Vm-Vd with respect to patch density of black toner formed on transfer belts having gloss levels of 91.7 and 19.2, respectively.

FIG. 10 is a configuration diagram showing another embodiment of the image forming apparatus of the present invention.

FIG. 11 is a configuration diagram showing still another embodiment of the image forming apparatus of the present invention.

[Explanation of symbols]

 9Y to 9K Developing device 11 LED 12, 13 Photodiode 20 Patch 41Y to 41K Photosensitive drum 60 Transfer belt 62 Intermediate transfer belt 64 Intermediate transfer drum 70 Optical sensor

Claims (8)

[Claims] 1. A reference image for density detection formed on an image carrier using toner is transferred to a belt-shaped recording medium conveying means, and the density of the reference image is detected by an optical detecting means on the conveying means. In the image forming apparatus for detecting and controlling the image density based on the detected result, the optical detection means can simultaneously measure the regular reflection light amount and the irregular reflection light amount by the reference image on the transporting means, An image forming apparatus comprising: detecting a density of the reference image based on a difference between the measured regular reflection light amount and the irregular reflection light amount to control the image density. 2. The image forming apparatus according to claim 1, wherein said conveying means contains a substance having the same light absorption band as that of the toner, and has a glossiness of 50 to 98 at a measurement angle of 20 °. . 3. The method according to claim 1, wherein the optical detection unit measures a regular reflection light amount in an area other than the reference image forming area on the transporting unit, and based on the measured regular reflection light quantity in an area other than the formation area. 3. The image forming apparatus according to claim 1, wherein the density of the reference image is corrected. 4. An apparatus for detecting a density of a plurality of colors formed by using a plurality of color toners on the plurality of image carriers, comprising a plurality of the image carriers and one optical detection means. The reference image is transferred to the transporting unit without being superimposed, and the density of the reference image of a plurality of colors is detected on the transporting unit by the one optical detection unit. Contains a substance having the same light absorption band as that of one of the toners, and the glossiness of the surface thereof is measured at a measurement angle of 2
The image forming apparatus according to claim 1, wherein the angle is 50 to 98 at 0 °. 5. A reference image for density detection formed on an image carrier using toner is transferred to a belt-shaped or drum-shaped intermediate transfer member, and the density of the reference image is optically transferred on the intermediate transfer member. In an image forming apparatus that detects by a detecting unit and controls an image density based on the detected result, the optical detecting unit can simultaneously measure a regular reflection light amount and a diffuse reflection light amount by a reference image on the intermediate transfer body. And
Based on the difference between the measured regular reflection light amount and the irregular reflection light amount,
An image forming apparatus, wherein the density of the reference image is detected to control the image density. 6. The image forming apparatus according to claim 5, wherein the intermediate transfer member contains a substance having the same light absorption band as that of the toner, and has a glossiness of 50 to 98 at a measurement angle of 20 °. apparatus. 7. The optical detection means measures the amount of specular reflection in an area other than the formation area of the reference image on the intermediate transfer member, and based on the measured amount of specular reflection in an area other than the formation area, 6. The density of the reference image is corrected.
Or the image forming apparatus of 6. 8. A plurality of image carriers, one of said optical detecting means, and a plurality of color toners for detecting a density of a plurality of colors formed on said plurality of image carriers using a plurality of color toners. Is transferred without being superimposed on the intermediate transfer body, and
Detecting the density of a reference image of a plurality of colors on the intermediate transfer member by using one optical detection unit, wherein the intermediate transfer member detects a substance having the same light absorption band as one of the toners of the plurality of colors; Contained, and the glossiness of the surface is measured at a measurement angle of 2
6. The image forming apparatus according to claim 5, wherein the angle is 50 to 98 at 0 [deg.].