JPH01221775A - Image forming device - Google Patents

Abstract

PURPOSE:To reproduce an image faithful to an original, by accurately detecting a change in a developing characteristic, by constituting a latent image pattern for adjustment of image density formed on an image carrier in a spotted state or in a striped state. CONSTITUTION:The latent image pattern P is constituted in a spotted state. In this case, for example, a small fragment 2, which is in a spotted state, responding to the latent image pattern P is provided on an edge part X of an original platen glass 1. This latent image pattern P can also be a striped state pattern. Then at an optical sensor S the latent image pattern P is lit by a light emitting element 19, and by the reflected light being received by a light receiving element 20, the density of an image formed on a photosensitive drum 7 is detected. Therefore, the area of a developed pattern changes according to the change in the developer density, and the light volume of the reflected light changes noticeably. Thus when the optical density of the pattern P is detected by the optical sensor S, a difference in the output is easily derived, enabling an accurate density detection, and a faithful reproduction of the image.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention includes means for detecting the toner concentration of a developer consisting of toner and magnetic particles, and the amount of developer such as toner amount detection. The present invention relates to an image forming apparatus that performs development based on signals obtained from the image forming apparatus.

(Prior Art) Conventionally, a latent image such as an electrostatic latent image or a potential latent image is formed on an image carrier, and the latent image is developed to produce a copy directly or indirectly by a method such as transfer. Image forming apparatuses that obtain images are widely known.

In this type of apparatus, especially in an image forming apparatus equipped with a developing means that carries a two-component developer of toner and magnetic particles on a developer carrier and develops the surface of the image carrier, the image density is maintained constant. Therefore, devices equipped with means for detecting the developer concentration (toner weight ffi/magnetic particle weight or toner weight/(toner weight+magnetic particle weight)) are often used.

In this case, various methods have been proposed for detecting the developer concentration by utilizing changes in the physical properties of the developer due to changes in the mixing ratio of toner and magnetic particles, as shown below. . That is, they are.

(1) Optical detection...detects changes in the optical reflectance of the developer (2) Dielectric constant detection...detects changes in the dielectric constant of the developer (3)
) Volume detection: Detects changes in the body M (bulk density) of the developer (4) Magnetic permeability detection: Detects the concentration of the developer using methods such as detecting changes in the magnetic permeability of the developer. be.

(Problems to be Solved by the Invention) In such conventional examples, although the developer concentration can be maintained constant by the above-described method, due to so-called tripo changes due to deterioration of developer durability, etc. ,
Image deterioration such as decreased image density and background fog may occur.

To solve this problem, as shown in FIG. 8, a latent image pattern 101 such as an electrostatic latent image or a potential latent image is formed on the image carrier 100 separately from the original image.
After developing this latent image pattern 101, a light emitting element 102 illuminates the attached toner, and a light receiving element 103 receives the reflected light, thereby detecting the concentration of the developer. has been done. In other words, when using such means, even if the toner lipo changes due to environmental changes or long-term use, it is possible to detect the developer concentration that has a positive correlation with the density of one image, and perform development according to the change. Therefore, the image density can be maintained constant.

However, although developer concentration and image density generally have a positive correlation as shown in FIG.
If the gradient exceeds that value, the gradient decreases rapidly, and the image density becomes almost a constant value with respect to the developer concentration. Therefore, the developer concentration calculated from the pattern density detected by the detection means and the actual development In general, in a developing method using a two-component developer of toner and magnetic particles, an error with the developer concentration easily occurs, which tends to cause deterioration of one image. From the viewpoint of background fog and resolution, it is desirable to control the development to be performed in the A area of about 5 to lowt%).

For example, if there is a deviation in the detected developer concentration,
If the developer concentration is controlled in the area, over-development will occur as shown in Fig. 1θ, and when developed on the image carrier 100, the layer thickness of the toner T1 will be thicker than necessary, so the developed toner T1 layer will be transferred to the paper. When transferred to a transfer material 104 such as, the toner T1 layer tends to scatter and the resolution decreases.Furthermore, when the toner T1 is fixed with a fixing roller etc., the toner T1 is melted and compressed, so if the toner TI layer is thick The problem is that the image is distorted, resulting in a reduction in resolution.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems of the prior art, and its purpose is to provide an image forming apparatus that can accurately detect changes in developer concentration and reproduce faithful images. It is about providing.

(Means for Solving the Problem) In order to solve the above object, in the present invention, a latent image pattern for image density adjustment formed on an image carrier is visualized by a developing means, and the developed In the image forming apparatus that adjusts the image forming density based on a signal obtained by a detection means for detecting the optical density of the pattern, the latent image pattern is configured as a spot-like or striped pattern.

(Function) In the present invention having the above configuration, by configuring the WI image pattern in the form of spots or stripes, the area of the developed pattern changes according to changes in the developer concentration, and the reflected light Since the amount of light changes significantly, when the optical density of the pattern is detected by a detection means, a difference is likely to occur in the output, and accurate density detection can be performed.

(Example) The present invention will be explained below based on five embodiments shown in the drawings.

1 to 4 show a first embodiment of an image forming apparatus according to the present invention.

FIG. 3(a) shows a schematic configuration of the optical system of this embodiment. Reference numeral 2 denotes a document table glass for aE the document, and a small piece 2 for forming a latent image pattern P for image density adjustment is provided at the end X of the back surface of the document table glass.

L is a light source for illuminating the original; 3, 4.5, and 6 are reflecting mirrors that guide the image light reflected by the original to the photosensitive drum 7 as an image carrier; and 8 is a light source for illuminating the original on the photosensitive drum 7. This is an imaging lens for forming an image.

FIG. 3(b) shows a schematic configuration of the image forming section of the same embodiment. The photosensitive drum 7 is connected to a drive motor (not shown),
It rotates at a predetermined speed in the direction of the arrow in the figure. Around the photosensitive drum 7, there is a primary charger 7 that charges the drum 7, an exposure section 9 that forms a latent image on the surface of the charged drum 7, and a two-component developer that develops this latent image. a developing device 1O as a developing means, a transfer charger 12 that transfers the image on the surface of the photosensitive drum 7 shaped and shaped as a toner image onto a transfer paper 11;
Image forming means using a known electrophotographic process, such as a separation charger 13 for separating the transfer paper 11 from the surface of the photosensitive drum 7, is provided. Further, 14 is a cleaner for removing toner remaining on the photosensitive drum 7, and 15 is an illumination lamp for static elimination.

The developing device IO has the following configuration. That is, the developing container 16 is filled with a two-component developer consisting of magnetic particles C and toner T, and a latent image is formed on the photosensitive drum 9 in the exposure section 9 by the developing sleeve 17 rotating in the direction of the arrow. Visualize. This developing sleeve 17 faces the photosensitive drum 7.

It has a magnetic field generating means (not shown) such as a permanent magnet inside.

Reference numeral 18 denotes a pushing means for stirring the developer and uniformly mixing the toner T and magnetic particles C.

Further, S is a light sensor which is formed on the photosensitive drum 7 and serves as a detection means for detecting the density of the toner image of the latent image pattern P developed by the developing device 10.
9 and a light receiving element 20. This optical sensor S can detect the density of the image immediately after development as shown in Figure 3(b).
As shown.

It is provided outside the developer container 16 and on the downstream side in the rotational direction of the photosensitive drum 7 .

Reference numeral 21 denotes a toner supply means for supplying the toner T in the toner cartridge 22 to the developer container 16 based on a signal obtained by the optical sensor S.

FIG. 1 shows the optical sensor S and the latent image pattern P developed on the photosensitive drum 7 of this embodiment. It consists of a light receiving element 20.

On the other hand, the latent image pattern P is obtained by visualizing the optical image of the small piece 2 provided on the document platen glass 1 shown in FIG. 3(a) through a normal image forming process. Further, the latent image pattern P is formed in a non-image area on the photosensitive drum 7 by adjusting the position of the small piece 2 so as not to be transferred to the transfer paper 11.

FIG. 2 shows the shape of the latent image pattern P. First, FIGS. 2(a), 2(b), and 2(c) show a latent image pattern P formed into a spot shape. In this case, for example, the second
In Figure (a), a spot-like small piece 2 corresponding to the latent image pattern PI is provided on the end X of the document table glass l. Moreover, this latent image pattern P is a striped pattern P2 as shown in FIGS.

P3. In that case as well, the small piece 2 corresponding to the latent image pattern P is moved to the end X as in ff13 (a).
In this embodiment, the draft-like latent image pattern P
2. Although the lines are formed at an interval of 2 lines per 1-1 as P3, two or more lines may be formed on the light-receiving surface of the light-receiving element 20.

In this way, in any case of Fig. 2 (a), (b), and (c), the direction 1 of the spot or draft pattern is
The spacing, size, etc. are arbitrary, and the one that best suits the light-receiving element 20 used, that is, the one that provides the most sensitive sensor output in response to changes in developer concentration, is selected.

In the above configuration, the image forming apparatus according to this embodiment adjusts the image density as follows.

First, a small piece 2 for forming a latent image pattern provided on the end X of the document platen glass l is illuminated by a light source, and the reflected light is transmitted through the reflecting mirrors 3, 4, 5.6 and the imaging lens 8 to the photosensitive material. A latent image of a predetermined pattern is formed on the drum 7.

This latent image is processed by the developing device 10 into a latent image pattern P of the toner image.
is formed. Then, as shown in Fig. 1, the optical sensor S
In this embodiment, the density of the image formed on the photosensitive drum 7 is detected by illuminating the latent image pattern P with the light emitting element 19 and receiving the reflected light with the light receiving element 20. P is the line width of 2 lines/m layer and is lO
The area of the layer was 1×10 layers, and the light emitting time of the light emitting element 19 when reading the latent image pattern P after development was set until the latent image pattern P passed through the light receiving element section.

In addition, the sensor output based on the amount of reflected light was taken as the average value after calculation processing.

Here, the relationship between the developer concentration and the optical density of the image formed on the photosensitive drum 7, that is, the sensor output, will be explained using an example in which a striped latent image pattern P is used. Fourth
In the figure, Q is an area where a latent image pattern P is to be formed, and when the developer concentration is appropriate, a latent image pattern Pa is formed. Further, when the developer concentration decreases due to a shortage of toner T in the developer, the latent image pattern Pb is formed in an area narrower than the area Q. On the other hand, as the developer concentration increases, the area of the latent image pattern P increases, and when it becomes excessive, the latent image pattern Pc of the toner image is formed over a considerably wider area than the area Q.

In this case, as the developer concentration increases, the image area of the developed latent image pattern increases and the amount of reflected light from the latent image pattern P illuminated by the light emitting element 19 decreases, so the output of the sensor S remains the same. From the graph in the figure, it is clear that IJI has a significant negative correlation with the developer concentration.

Therefore, compared to the case where the developer concentration is detected only based on the shading of the latent image pattern formed on the photosensitive drum as in the conventional device, by configuring the latent image pattern P in the form of spots or stripes, Since optical density (sensor output) with respect to development performance appears in IIA with a certain correlation, the accuracy of developer concentration detection is extremely high.

Further, the toner supply means 21 is operated based on the developer concentration detection signal obtained by the sensor S to control the supply of toner T, and the developer is stirred by the pushing means 23 to maintain an appropriate developer concentration. Image formation can be performed.

FIG. 5(a) shows the main parts of the second embodiment of the image forming apparatus according to the present invention, and the same parts as in the first embodiment are given the same reference numerals. In the embodiment, the sub-layer image carrier 30 is provided facing the developing sleeve 17 at a distance substantially equal to the distance between the developing sleeve 17 and the photosensitive drum 7 . This sublayer image carrier 30 is made of a conductive roller, and as shown in FIG. 5(b), the dark potential Vo (-700V) and the bright potential VL (-200V) on the surface of the photosensitive drum 7 are equal to each other. is pulse power supply 3
1 is applied periodically. As a result, a latent image pattern P similar to that of the first embodiment can be formed on the sublayer image carrier 30, and the optical density can be detected by the optical sensor S provided near the sublayer image carrier 30. 0 In this embodiment, the potential pattern that is periodically applied and formed on the sublayer image carrier 30 is a striped pattern of 2 lines/layer as in the first embodiment, and the pattern width is 10 layers. Finish reading the density of the pattern during the pre-rotation. The other configurations and functions are the same as those of the first embodiment, so their explanation will be omitted.

FIG. 6 shows the main parts of a third embodiment of the image forming apparatus according to the present invention, and the same parts as in the first embodiment are given the same reference numerals. In,
As shown in FIG. 3(b), the optical sensor S was arranged near the developing device 10 to detect the optical density of the image immediately after development. is different from the above embodiment. That is, in this example,
As shown in FIG. 6, a belt or drum-shaped transfer body 40 that comes into contact with the photosensitive drum 7 is provided, and the latent image pattern P is transferred to a portion of the transfer body 40 other than the portion where the transfer paper 11 is attached. The optical density of the image is detected by an optical sensor S provided near the image sensor. Although the optical sensor S is arranged on the front side of the transfer body 40 in FIG.
0 may be made of a transparent film and placed on the back side.The other configurations and functions are the same as those of the first embodiment, so their explanation will be omitted.

In each of the embodiments, the latent image pattern P is placed on the original platen glass l! Although the structure is formed by the small piece 2 provided on the A side, the present invention is not limited to this, and as shown by Z in the timing chart of FIG. or laser, LED
A latent image pattern similar to that of the first embodiment can also be formed by using a light emitting source such as the above light source and lighting it intermittently.

Further, in the first embodiment, the detection output of the optical sensor S is fed back to the toner supply means 21 to control the developer concentration, but the present invention is not limited to this. Instead, it may be fed back to the image control means described below.

1. Development bias (DC component, AC component) 2. Rotation speed of the developer carrying member 3. Amount of developer coated on the developer carrying member 4. Exposure amount of the light source 5. Charging ability Furthermore, the spot according to this example It is also possible to use a pattern or a striped latent image pattern together with a conventional solid pattern.

(Effects of the Invention) In the present invention having the above configuration and operation, the latent image pattern for adjusting the image density formed on the image carrier is configured in a spot shape or a striped shape, thereby reducing detection errors. Therefore, changes in development characteristics can be accurately detected, and an image that is faithful to the original can be reproduced.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a latent image pattern and its forming operation in an image forming apparatus according to the present invention, and FIGS.
c) is a plan view showing an example of a latent image pattern in the same example; FIG. 3(a) is a schematic configuration diagram showing the optical system of the same example;
The same figure (b) is a schematic block diagram showing the image forming part of the same example,
FIG. 4 is an explanatory diagram showing the relationship between the developing performance and the optical density of the image in the same embodiment, and FIG. 5(a) is a schematic configuration diagram showing the main parts of the second embodiment of the image forming apparatus according to the present invention. , FIG. 5(b) is a graph showing the applied voltage in the same example.
FIG. 7 is a timing chart showing another example of latent image pattern formation, and FIG. 8 is a latent image pattern in a conventional image forming apparatus. 9 is a graph showing the relationship between developer concentration and image density in the conventional example, and FIG. 10 is an explanation showing the state of toner adhesion in the image forming process of the conventional example. It is a diagram. Explanation of symbols 2...Small piece 7...Photosensitive drum (image carrier) 10...Developer @ (developing means) 19...Light emitting element 20...Light receiving element 21.
... Toner supply means C ... Magnetic particles P ... Latent image pattern S ... Optical sensor (detection means) T ... Toner js -' , ", ゛Figure 1'♂ (78") No. Figure 2 (0) (b) (c) ・・・ ノ
ノ rs,”j PH ・!? □ ■−■ Figure 3 (C) @ Figure 3 (b) Figure 5 (0) f

Claims (1)

[Claims] A latent image pattern for adjusting image density formed on an image carrier is visualized by a developing means, and a signal obtained by a detecting means for detecting the optical density of the developed pattern is An image forming apparatus that adjusts image forming density based on the image forming apparatus, wherein the latent image pattern is configured as a spot-like or striped pattern.