JPH05249787A - Image forming device - Google Patents

Abstract

PURPOSE:To accurately detect the concentration of the toner of a different characteristic by providing two kinds of sensors properly used according to the characteristic of the toner. CONSTITUTION:A sensor part 10 as a concentration detecting means is arranged opposite to the surface of a photosensitive drum 1, on the downstream of the developing unit for black color, of a developing means. The sensor part 10 is provided with two concentration sensors 101 and 102, the concentration sensor 101 detects the concentrations of cyan color, etc., and the concentration sensor 102 detects the concentration of the black. The concentration sensor is composed of a light emitting element such as an LED, and a light receiving element such as a CdS. Moreover, when two concentration detecting sensors 101 and 102 are lined up in the axial direction of the photosensitive drum 1, and two color toner images A1 and A2 for detecting the concentration of the toner, are parallelly formed, the concentrations of two colors can be simultaneously, detected, and time for detecting the concentration, can be shortened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, such as a color copying machine, which uses toners (developers) of a plurality of colors as developers, and more specifically, density detection for detecting the density of a toner image. Regarding the configuration of the means.

[0002]

2. Description of the Related Art FIG. 12 schematically shows a conventional four-color full-color image forming apparatus using an electrophotographic multiple transfer system.

This device is provided with an electrophotographic photosensitive drum (hereinafter simply referred to as "photosensitive drum") 1 having a photoconductive layer provided on a conductive substrate as an image bearing member. The photosensitive drum 1 is supported by an apparatus body (not shown) so as to be rotatable in the direction of arrow R1, and its surface is uniformly charged by the primary charger 2. Next, image exposure 3 is performed based on the first-color cyan image information, and the photosensitive drum 1
An electrostatic latent image is formed on the surface. Next, a toner image is adhered to the electrostatic latent image by the cyan developing device 4c of the developing means 4, and a cyan toner image is formed.

On the other hand, a transfer material (generally transfer paper) P is supplied to the transfer drum 5, and the transfer drum 5 rotates in the direction of arrow R2 while carrying the transfer paper P on its surface. The cyan toner image on the photosensitive drum 1 is transferred onto the transfer paper P by the transfer charger 7.

After the transfer of the toner image is completed, the transfer residual toner on the photosensitive drum 1 is cleaned by the cleaner 6.

After the cleaning, the photosensitive drum 1 is again uniformly charged by the primary charger 2, and the image exposure 3 is performed based on the image information of the magenta of the second color to form an electrostatic latent image. This electrostatic latent image is made into a toner image by the magenta developing device 4b. The magenta toner image is transferred onto the transfer drum 5.
It is transferred so as to overlap the cyan toner image already transferred onto the transfer paper P held by. Photosensitive drum 1
The transfer residual toner on the top of the cleaner 6 is the same as that for cyan.
Will be removed.

Similarly, the third color yellow electrostatic latent image is transferred to the transfer paper P as a toner image by the yellow developing device 4a, and the fourth color black electrostatic latent image is transferred to black. A developing device 4d converts the toner image into a toner image and transfers the toner image onto the transfer paper P.

The transfer paper P on which the four color toner images of cyan, magenta, yellow and black have been transferred is separated from the transfer drum 5 by the separating means 8 and then the toner image is fixed by the fixing device 9.

On the other hand, FIG. 13 shows a full-color image forming apparatus using another conventional electrophotographic system. In this example, the photosensitive drum 1 is rotated in the direction of arrow R1 and is uniformly charged by the primary charger 2. Then 1
Image exposure 3 is performed based on the image information of cyan of the color, and an electrostatic latent image is formed. Next, this latent image is made into a toner image by the cyan developing device 4c of the developing device 4. When the photosensitive drum 1 makes one rotation, the photosensitive drum 1 is again uniformly charged by the primary charger 2 and the image exposure 3 based on the image information of the second color magenta is performed to form an electrostatic latent image. Next, this electrostatic latent image is made into a toner image by the magenta developing device 4b. When the photosensitive drum 1 makes one more rotation,
The photosensitive drum 1 on which the cyan toner image and the magenta toner image are formed is charged again by the primary charger 2 and 3
Image exposure 3 is performed based on the image information of the color yellow to form an electrostatic latent image. Then, this electrostatic latent image is made into a toner image by the yellow developing device 4a.

Subsequently, cyan, magenta, and yellow toner images on the photosensitive drum 1 are collectively transferred onto the transfer paper P by the transfer charger 7, and then these toner images are fixed by the fixing device 9.
Is fixed by and becomes a permanent image.

The transfer residual toner on the photosensitive drum 1 is cleaned by the cleaner 6. Here, the cleaner 6
The blade 6a can be switched on and off. The blade 6a is in an OFF state apart from the photosensitive drum 1 during image formation on the photosensitive drum 1, and is in an ON state in which the blade 6a contacts the photosensitive drum 1 only when cleaning transfer residual toner.

In this image forming apparatus, there is a system using a black developing device in addition to the cyan, magenta and yellow developing devices 4c, 4b and 4a.

By the way, in the above-mentioned two image forming apparatuses, if the image density changes due to various conditions such as the environment in which it is used and the number of prints, correct density and color tone cannot be obtained. Therefore, conventionally, a toner image (patch) for density detection is formed on the photosensitive drum 1 or the transfer drum 5,
The density was detected and fed back to the exposure amount, the developing bias, etc. to obtain a stable image.

[0014]

However, among the toners used, cyan, magenta, and yellow (hereinafter appropriately referred to as "cyan, etc.") are conventionally known pigments and dyes for producing a desired tint. On the other hand, since black uses carbon, each toner such as cyan reflects illumination light for density detection, whereas black toner absorbs it. Therefore, when the density detection sensor for cyan or the like and the density detection sensor for black have the same structure in detecting the density, the output results are significantly different.

For example, in FIG. 9, the irradiation angle (the angle formed by the incident light and the normal at the irradiation point on the surface of the photosensitive drum 1) and the light receiving angle (also the angle formed by the reflected light and the normal) are both 45 °. FIG. 1 shows the relationship between the density of the toner image and the output of the density detection sensor when the specular reflection light reflected from the toner image at the same angle as the incident angle is detected using the density detection sensor.
Reference numeral 0 indicates the relationship between the toner image density and the output of the density detection sensor when the diffused reflection light from the toner image is detected by using the density detection sensor with an irradiation angle of 45 ° and a light reception angle of 0 °. In FIG. 9, the output values of both cyan and black decrease as the toner image becomes higher in density, but in FIG. 10, black decreases but the output value of cyan and the like increases. .. As a result, as shown in FIG. 9, when the density detection sensor having the same irradiation angle and the same light reception angle is used, the change width of the output value of the density detection sensor is small and the density cannot be accurately detected when the density is close to 1 for cyan and the like. ..

On the other hand, when a density detecting sensor having a different irradiation angle and light receiving angle is used, even if the density of cyan or the like exceeds 1, the density of FIG.
It has a larger change range of output value. However, for black, it is smaller than the change width of black in FIG.

Therefore, it is understood that it is difficult to accurately detect the density over a wide range for all toners by using a sensor having a single irradiation angle and a light receiving angle.

Therefore, the present invention provides an image forming apparatus in which at least two density detection sensors having different structures are used to accurately detect the density of toner having different characteristics (different colors). The purpose is to do.

[0019]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances and uses at least two types of toner having different characteristics for electrostatic latent images sequentially formed on an image carrier. An image forming apparatus comprising: a developing unit that forms a toner image; a density detecting unit that detects the densities of these toner images; and a control device that controls the image density by the output of the density detecting unit. Is provided with at least two density detection sensors having different structures, and these density detection sensors individually detect the densities of toner images having different characteristics. In this case, the one density detection sensor may have an irradiation angle and a light reception angle that are equal to each other, and the other density detection sensor may have an irradiation angle and a light reception angle that are different from each other.

[0020]

According to the above construction, the density detecting means has at least two kinds of density sensors having different structures. Therefore, by properly using each of them according to the characteristics of the toner, accurate density measurement suitable for the characteristics of each toner can be performed. You can

[0021]

Embodiments of the present invention will be described below with reference to the drawings. <First Embodiment> FIG. 1 shows a schematic configuration of a four-color full-color image forming apparatus. However, components having the same configurations and operations as those in FIG. 12 (conventional example) are designated by the same reference numerals, and description thereof will be omitted.

A sensor portion 10 which is a density detecting means is arranged slightly downstream of the black developing device 4d of the developing means 4 so as to face the surface of the photosensitive drum 1. The sensor unit 10 includes two density detection sensors 101 and 102 as shown in FIG.

The density detection sensor 101 is for detecting the density of cyan or the like, and the density detection sensor 102
Is for detecting the density of black. These are arranged side by side in the rotation direction R1 of the photosensitive drum 1 so as to be aligned with each other. FIG. 5 shows a cross-sectional view of the density detection sensor 101 for toner such as cyan. The density sensor is LE
Light emitting element 103 such as D, photodiode, CdS
And a light receiving element 104 such as a light emitting element 103 for irradiating the toner image on the surface of the photosensitive drum 1 with the light emitted from the light emitting element 103, and the light reflected from the light receiving element 10
The density is measured by receiving light at 4. It should be noted that the attachment angle between the light emitting element 103 and the light receiving element 104 does not matter as long as accurate measurement can be performed at the angle at which irregularly reflected light is received. The angle between the light L ₁ and the normal H) α is 30
It is preferable that the angle of reception is 60 ° and the angle of light reception (the angle between the reflected light L ₂ and the normal line H) β is 0 ° to 15 °.

FIG. 6 is a sectional view of the density detection sensor 102 for black toner. The density detection sensor 102 is composed of a light emitting element 105 such as an LED and a light receiving element 106 such as a photodiode or CdS like the density detection sensor 101 for cyan and the like, and is sensitive to the light emitted from the light emitting element 105. Irradiate the toner image on the drum 1,
The density is measured by receiving the light reflected from the light receiving element 106. Note that the mounting angles of the light emitting element 105 and the light receiving element 106, that is, the irradiation angle α and the light receiving angle β
It does not matter as long as it is the same as the above, and it receives specularly reflected light. However, it is desirable to set the angle to 30 ° to 60 ° because there are restrictions in manufacturing the sensor.

It does not matter which of the density detecting sensors 101 and 102 is combined first.

For density detection, as shown in FIG. 4, first, a toner image (patch) A for density detection from high density to low density is formed on the photosensitive drum 1 with black toner, and the density is measured by the density detection sensor 102. I do. Next, a density detection patch is formed on the photosensitive drum 1 with yellow toner, and the sensor 101
Measure the concentration with. Similarly, the density is measured for other magenta and cyan toners. The measurement result is sent to the control device 11 connected to the sensor unit 10, and the control device 11 adjusts the exposure amount of the image exposure 3 and the developing bias of the developing device 4 to optimize the density of the toner image. Control to be. Of course, the order of the colors for density measurement may be arbitrary.

FIG. 11 shows the result of density detection performed with such a configuration. A wide dynamic range can be set for all toners of cyan, magenta, yellow, and black, and accurate density measurement can be performed for all colors.

Further, as shown in FIG. 7, the structure of the sensor unit 10 is such that the density detecting sensors 101, 1 are arranged in the axial direction of the photosensitive drum 1.
If two 02 are arranged side by side, it is possible to detect the densities of the cyan toner image and the black toner image at the same time.
The time required for density detection can be reduced by one color.
At this time, the combination of the density detection sensors 101 and 102 may have a positional relationship opposite to that shown in the drawing. <Second Embodiment> FIG. 8 shows a schematic structure of another embodiment of the sensor unit 10 of FIG. The light emitted from the light emitting element 107 is reflected by the toner image, and the light receiving element 108 generates regular reflection light for detecting the density of black toner, and the light receiving element 109 generates irregular reflection light for detecting the density of toner such as cyan. Receive light. By doing so, the light emitting element 107 can also be used as a single element, and the measurement can be performed by one concentration detection sensor as a whole. Therefore, the sensor unit 10 can be downsized, and the cost can be further reduced. You can <Third Embodiment> FIG. 2 shows a schematic structure of another color image forming apparatus of the present invention. The components having the same configurations and functions as those of the first embodiment shown in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

Reference numeral 10 denotes a sensor unit for detecting the toner density on the surface of the transfer drum, which is the sensor unit 1 of the first embodiment shown in FIG.
It has the same function as 0. Then, the density detection patch formed on the photosensitive drum 1 is transferred to the transfer drum 5, and the sensor unit 10 detects the density. <Fourth Embodiment> FIG. 3 shows a schematic structure of still another color image forming apparatus of the present invention. Components having the same configurations and functions as those in FIG. 13 (conventional example) are designated by the same reference numerals and description thereof is omitted.

Reference numeral 10 denotes a sensor section for detecting the toner density on the surface of the photosensitive drum, which has the same function as in the first embodiment.

To detect the density, first, a density detecting patch with a high density to a low density is formed on the photosensitive drum 1 with black toner, and the density detecting sensor 102 measures the density. The measured patch is cleaned by turning on the blade 6a of the cleaner 6, then a density detection patch is formed on the photosensitive drum 1 with yellow toner, and the density detection sensor 101 measures the density. Similarly, the density detection sensor 101 measures the density of other toners and controls the image. The order of the colors for density control may be arbitrary.

Further, if the structure of the sensor unit 10 is as shown in FIG. 7 of the first embodiment, the densities of black and cyan can be detected simultaneously, so that the time required for the density detection can be shortened by one color. At this time, the density detection sensors 101, 1
The combination of 02 does not matter even if they are opposite.

If the sensor section 10 is constructed as shown in FIG. 8 of the second embodiment, it goes without saying that downsizing and cost reduction can be realized.

[0034]

As described above, according to the present invention, density detection is performed by at least two density detection sensors that detect the density of a toner image, and even if the characteristics of the toner image are different, Since the density of the toner can be detected by a suitable density sensor, the density of the toner can be accurately detected.

Furthermore, since the image density can be controlled by such accurate density detection data, the image quality of the density is improved.

By using two or more density detecting sensors, even if one of the light receiving elements fails, the density of the remaining light receiving elements is not accurate until the replacement. There is also an effect that detection can be performed.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an outline of an image forming apparatus according to the present invention.

FIG. 2 is a vertical cross-sectional view showing the outline of another image forming apparatus.

FIG. 3 is a sectional view showing the outline of still another image forming apparatus.

FIG. 4 is an explanatory perspective view showing the arrangement of a sensor unit.

FIG. 5 is a vertical cross-sectional view showing the configuration of a sensor unit.

FIG. 6 is a vertical cross-sectional view showing the configuration of another sensor unit.

FIG. 7 is a perspective explanatory view showing another example of the arrangement of the sensor unit.

FIG. 8 is a vertical cross-sectional view showing the configuration of still another sensor unit.

FIG. 9 is a diagram showing a relationship between a toner image density measured by a density detection sensor having an irradiation angle of 45 ° and a light reception angle of 45 ° and a sensor output voltage.

FIG. 10 is a diagram showing a relationship between a toner image density measured by a density detection sensor having an irradiation angle of 45 ° and a light reception angle of 0 ° and a sensor output voltage.

FIG. 11 is a diagram showing a relationship between a toner image density and a sensor output voltage by two different density detection sensors.

FIG. 12 is a vertical sectional view showing an outline of a conventional image forming apparatus.

FIG. 13 is a sectional view showing an outline of another conventional image forming apparatus.

[Explanation of reference numerals] 1 image carrier (photosensitive drum) 4 developing means 10 density detecting means (sensor section) 11 control device 101 density detecting sensor 102 density detecting sensor α irradiation angle β light receiving angle

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Toshiaki Miyashiro 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Naoki Enomoto 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Incorporated (72) Inventor Mashiro Saito 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Tetsuya Kobayashi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Haruo Fujii 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (2)

[Claims] 1. A developing unit for forming a toner image with at least two types of toner having different characteristics with respect to an electrostatic latent image sequentially formed on an image carrier, and a density detecting unit for detecting the density of these toner images. In the image forming apparatus, the image forming apparatus includes a unit and a controller for controlling the image density by the output of the density detecting unit, wherein the density detecting unit includes at least two density detecting sensors having different structures. The image forming apparatus is characterized by individually detecting the densities of toner images having different characteristics. 2. The one density detecting sensor has an irradiation angle and a light receiving angle which are equal to each other, and the other density detecting sensor has an irradiation angle and a light receiving angle which are different from each other. The image forming apparatus according to claim 1.