JP2612685B2 - Image forming device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image forming apparatus, particularly to an electrophotographic image forming apparatus.

(Prior art)

As an example of an electrophotographic image forming apparatus that reads a document image with an optical sensor, develops an electrostatic latent image obtained on a photoconductor by image exposure corresponding to an electric signal corresponding to the document image density, and outputs a visible image FIG. 1 shows an example of a schematic configuration diagram of a conventional digital copying machine. 1 is a document reading unit, 2
Denotes a printer unit. This configuration is publicly known, but will be briefly described. The original 3 is exposed by a fluorescent lamp 4 and the reflected light thereof is transmitted through a mirror 5 and a lens 6 to an optical sensor 7 such as a CCD.
An image is formed thereon, and converted into an electric signal corresponding to the document density. The output of the optical sensor 7 is analog / digital (A /
D) After being converted to a digital signal by the converter,
The digital signal is subjected to binarization or dither processing by the digital signal processing device 9 and transmitted to the laser device 10 of the printer unit 2. The laser device 10 generates an optical signal according to the input signal, and is exposed on a photoconductor (drum) 13 via an optical system 11 such as a rotating polygon mirror and an f-θ lens and a mirror 12. The photosensitive drum 13 is uniformly charged by a charger 14 prior to exposure, and an electrostatic latent image corresponding to an image signal is formed on the surface of the photosensitive drum 13 by exposure. This latent image is visualized by a developing device 17 including a developer (toner) 15 and a developing sleeve (or cylinder) 16. At this time, a developing bias is applied to the developing sleeve 16 by a developing bias power supply 18. Subsequently, the visualized image is transferred onto a transfer material 20 such as paper by a transfer charger 19. The developer 15 remaining on the photoreceptor 13 without being transferred is removed by a cleaner 21.
Is configured to be cleaned.

In the digital copying machine as described above, the image characteristics depend on both the reading threshold value at the time of digitization in the document reading unit 1 and the image forming conditions in the printer unit 2.

The circumstances during this time will be described with reference to FIG. FIGS. 2 (A) to 2 (F) are signal characteristic diagrams in the case of digitizing an image into ternary values, in which a developer 15 is applied to a light portion on the photoconductor 13 and is not applied to a dark portion. The case of the reversal development type is shown.

FIG. 2A is a characteristic diagram of the original density Di versus the output i of the original reading unit 1, and a is an electric signal output proportional to the original density Di obtained by the original reading unit 1. This is defined as 3 using i ₁ and i ₂ as thresholds.
If digitized values, the output i ₁ of the document reading section 1, the as shown in FIG stepwise line a ', the original density Di is Di <i = 0 when the Di _1, Di ₁ ≦ Di <of Di ₂ When i = i ₁ , and Di> Di ₂
In the case of, i = i ₂ .

Laser light amount E corresponding to the document reading unit output i, as shown in FIG. 2 (B), i <when _{i 1 E = 0, i 1} ≦ i <i 1
It is set so that E = E ₂ when _{E = E 1, i ≧ i} 2 when. E ₁ and E ₂ may be varied current value forces the laser device 10, also by changing the pulse time of the input signal, may change the light emission time. 2A and 2B, the relationship between the document density Di and the laser light amount E has the characteristic shown in FIG.

2D shows the relationship between the laser light amount E and the surface potential V of the photoreceptor (hereinafter referred to as the EV characteristic). The dark portion surface potential is V ₀ , and the exposure amount is E. _If the surface potentials at ₁ and E ₂ are V ₁ and V ₂ , respectively, the relationship between the document density Di and the surface potential V is as shown in FIG.

Further, f in FIG. 2 (F) indicates the relationship between the surface potential V in the case of performing the reversal development and the image density Do after development (hereinafter referred to as V-Do characteristic). V
Assuming that the image densities at V ₁ and V ₂ are Do ₁ and Do ₂ , the relationship between the original density Di and the post-development image density Do (hereinafter referred to as Di-Do characteristic) is shown in FIG. (G) is obtained.

As described above, the Di-Do characteristics include the threshold values i ₁ and i ₂ , the laser light amount E, the EV characteristics, and the V-D
o Characteristics affect each. Among these factors, the image adjustment using the EV characteristic can be performed by changing the laser light amount E or the charge amount on the photoconductor 13, and the image adjustment using the V-Do characteristic is This can be performed by changing the photoconductor surface potential V or the developing bias potential.

Therefore, the image adjustment of this type of digital copying machine includes (1) a threshold value in the document reading unit 1, (2) a photosensitive drum.
It can be performed by adjusting any one of the exposure amount 13, (3) the charge amount of the photosensitive drum 13, and (4) the developing bias potential.

Of these, (1) is the document reading unit 1, and (2),
(3) and (4) are adjustments made by the printer unit 2,
Image adjustment in a conventional digital copying machine is performed only in one of the above two units. However, such an image adjustment has the following problems: That is, when only the threshold value for digitization in the document reading unit 1 is adjusted, up to what density image on the document Can be adjusted, but the output image density Do of the part recognized as halftone and the part recognized as black is
Since it is determined only by the conditions of the printer unit 2, the adjustment cannot be performed only by the document reading unit 1. In addition, it was impossible to adjust so-called fog development in which toner adhered to the image background portion.

When image adjustment is performed based on the conditions of the printer unit 2, that is, the amount of exposure to the photosensitive member 13, the amount of charge on the photosensitive member, the developing bias, etc., the image density Do and fog can be adjusted. It was impossible to reproduce a thin character whose white background was recognized by the reading unit 1.

In general, when a copier user adjusts an image, if the image is adjusted in a direction to increase the density of the image, it is expected that the image density will increase and the reproducibility of thin characters will improve. It is common to expect that if the image is adjusted in the direction in which the image is read, the image density will be reduced and the fog will be improved. However, as in the conventional case, the condition of only one of the original reading unit and the printer unit is adjusted. However, there is a disadvantage that image adjustment cannot be performed as desired by the user.

〔Purpose〕

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the conventional example, and has as its object to provide an adjusting device capable of adjusting both the output image density and fog of an image forming apparatus.

〔Example〕

Hereinafter, the present invention will be described based on examples. A feature of the present invention is that image adjustment is performed by simultaneously changing a threshold value for converting an electric signal corresponding to a document image density into a binary or more digital electric signal and a developing bias. It is in. FIG. 3 (A) to (D)
FIG. 4 shows signal characteristic diagrams of one embodiment, and FIG. 4 shows a schematic configuration circuit diagram of one embodiment of an image adjusting apparatus.

FIG. 3A shows the original image density in the original reading unit 1.
9 is a Di-Do characteristic (corresponding to FIG. 2 (G)) showing a relationship between output image densities when a digital digitization threshold of Di is changed. By adjusting the threshold value, the Di-Do characteristic becomes h
To j or k, but only the density of the original image, which is recognized as white, halftone, and black, is adjusted. The halftone density and maximum density of the output image do not change, and the fog also changes. do not do.

On the other hand, V _B -Do characteristic showing the relationship between the developing bias potential V _B and the output image density Do shown in FIG. (B), the change in the output image density Do when you want to adjust the development bias potential V _B of the printer unit 2 Is shown. The higher the development bias potential V _B, the image density
Do is high, fog becomes conspicuous, the lower the potential V _B image density Do is low, the head becomes less.

Next, the principle of changing the developing bias simultaneously with the threshold value of the document reading unit according to the present embodiment will be described. Fig. 3 (A)
Among the threshold values of the document density Di in (1), the standard threshold value for the white portion and the halftone portion is Di + h. Adjust this to make the new threshold Di
+ H ', then {Di + h = Di + h'-Di + h> 0
Then, the range that is recognized as a white part is expanded, and the output image is
The image has many white areas. In general, the user of the copying machine expects a decrease in the image density Do or a decrease in fog when performing such adjustment. Conversely, △ Dh ₊₁
If <0, the black area of the output image increases. In such a case, the user usually expects an increase in the halftone density and the maximum density.

Here, the present embodiment, at the same time as the threshold value Di + h, is intended to change the development bias potential V _B as shown in FIG. 3 (C). That is, when changing the threshold value of the document reading section 1 so as to extend recognized part and white part, as halftone density and the maximum density is increased, also changes the developing bias potential V _B. As a result, the change in the Di-Do characteristic due to the image adjustment changes as shown by h, j ', k' in FIG. 3D, as compared with FIG. The image density Do and fog can be adjusted together with the recognition level, and the image adjustment desired by the user can be performed.

FIG. 4 shows an example of the configuration of an image adjustment device for achieving the above object. A voltage corresponding to the variable resistor 22 is input as a reference voltage of the comparator 23, and a voltage obtained by superimposing a constant voltage Vo24 thereon is input as a reference voltage of the comparator 25.
Voltages proportional to the document density Di are input to the comparators 23 and 25, respectively, and are compared with the respective reference voltages. If the input voltage is greater than the reference voltage of the comparator 25 is output Recognized signal 26 and is Kurobe, (second diagram photoreceptor 13 by laser light amount E ₂ is exposed for Kurobe reproduction (B) ~
(D)). The input voltage is equal to the reference voltage of comparator 23 and the comparator
When the reference voltage is in the middle of 25 reference voltages, it is recognized as a halftone part and a signal 27 is output.
Photoreceptor 13 is exposed by _{E 1 (E 1 <E 2} ). If the input voltage does not reach either of the reference voltages, the signal is recognized as a white portion and the signal 28 is output, but the laser 10 does not emit light and the photoconductor 13 is not exposed.

The voltage corresponding to the variable resistor 22 is inputted to the developing bias power supply 29 capable of output control in accordance with an external signal, it is output developing bias potential V _B in accordance with this, the user is herein Variable resistor to obtain the desired image
When the resistance of 22 is changed, comparators 23 and 25
And the threshold value Di + h of the document reading unit 1 changes. At the same time, the input voltage to the developing bias power source 29 is changed, as shown in FIG. 3 (C) Di + h-V B characteristics, also change the developing bias potential V _B. With the above configuration, each characteristic shown in FIG. 3 can be realized.

[Other embodiments]

In the above-described embodiment, the case where the original image is digitized into ternary values has been described. However, when digitizing the original image into binary values or multivalued values having four or more values, the same principle is applied to the change of the threshold value. The present invention can be carried out by changing the developing bias.

Further, in the above-described embodiment, an example of the reversal development system in which the developer 20 is adhered to the exposed portion on the photoconductor 13 has been described. The present invention can be applied to a developing system.

In the above embodiment, the case where the printer unit 2 is a laser printer has been described. However, the printer unit is not limited to this, and may perform image exposure using an LED array or a liquid crystal array. Further, a multi-stylus may be used to form a latent image on an insulating drum.
As long as the Do or head is dependent on the development bias potential V _B, it is possible to apply the present invention likewise.

Furthermore, the schematic circuit diagram shown in FIG. 4 is not limited to this, and any circuit structure can be used as long as the principle of the present invention can be realized as shown in FIG. Absent.

Regardless of the circuit configuration as described above, some thresholds and developing bias values are stored in a storage device in a 1: 1 correspondence, and one set is selected by a user's selection. The present invention can be similarly applied to a case using software such as changing the threshold value and the developing bias potential.

(Effect)

As described above, the image forming apparatus according to the present invention includes a conversion unit that obtains a digital image signal having two or more values in accordance with the level of an input image signal, A latent image forming unit that forms an electrostatic latent image; a developing unit that develops the electrostatic latent image; and an adjusting unit that adjusts an image density in accordance with a user's instruction. When instructed to increase the density, the developing bias of the developing means is changed in a direction to increase the developing density, and the conversion characteristic of the converting means is changed so that the digital signal amount of the high density level is increased. When the image density is instructed to be reduced, the developing bias of the developing means is changed in a direction of decreasing the density, and the conversion characteristic of the converting means is changed so that the digital signal amount of the low density level is increased. Since the image forming apparatus is a unique feature, the user simply controls the development density level of the image part and the width of the dark part area by simply giving a density instruction, and the density is faithful to the user's intention. Control becomes possible.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an example of a conventional digital copying machine, FIGS. 2 (A) to 2 (G) are signal characteristic diagrams thereof, and FIG.
4A to 4D are signal characteristic diagrams of one embodiment of the present invention, and FIG. 4 is a schematic configuration circuit diagram of one embodiment of an image adjusting apparatus of the present invention for realizing the same. 1 Document reading section 2 Printer section 13 Photoconductor drums 18, 29 Developing bias power supply Di + h Document density threshold V _B Developing bias potential

Continued on the front page (72) Inventor Atsushi Asai 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Yoshihiro Murasawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Masahiro Goto 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Yasushi Sato 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Nobuo Nakazawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Hiroshi Sasame 3-30-2 Shimomaruko 3-chome, Ota-ku, Tokyo Inside Canon Inc. (72) Tetsuo Saito 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (56) References JP-A-60-83054 (JP, A) JP-A-57-185768 (JP, A)

Claims (1)

(57) [Claims] 1. A conversion means for obtaining a digital image signal having two or more values in accordance with the level of an input image signal, and a latent image for forming an electrostatic latent image on a recording medium in accordance with the digital image signal obtained by the conversion means. Image forming means, developing means for developing the electrostatic latent image, and adjusting means for adjusting image density in accordance with a user's instruction, wherein the adjusting means is instructed to increase the image density. In this case, the developing bias of the developing means is changed in a direction of increasing the developing density, and the conversion characteristic of the converting means is changed so that the digital signal amount of the high density level is increased, and the image density is instructed to be reduced. In this case, the developing bias of the developing means is changed in a direction of decreasing the density, and the conversion characteristic of the converting means is changed so as to increase the amount of the low density digital signal.