JPH07120096B2 - Image density control device for recording device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image density control device for a recording device in which an image is formed according to an electrostatographic process, and in particular, desired recording is performed by optimal toner replenishment control and transfer current control. The present invention relates to improvement of image density control for obtaining image density.

(Prior Art) The electrostatic latent image on the photoconductor is visualized by the toner of the developing device, and this visualized image is transferred by the transfer belt to the copy paper conveyed from the paper feed unit by the transfer unit. In this type of image forming apparatus, it is necessary to supply toner according to the amount of consumption.

By the way, conventionally, in addition to the toner replenishment according to the change of the toner adhesion amount of the reference pattern on the photosensitive drum, a plurality of toner marks for each color toner are recorded on the recording medium, and the toner density of the toner mark is recorded. There is known a technique for optically detecting the toner and changing the toner concentration.

However, in these conventional techniques, since it is necessary to confirm the toner amount or the transfer condition (bias voltage etc.), it is not possible to perform comprehensive image density control.

Also, in the case of detecting the toner adhesion amount on the photosensitive drum, a photo sensor must be provided under the developing device due to the configuration of the device, but this is a place where toner scattering and agent spillage occur, As a result, toner adheres to the sensor and correct detection output cannot be obtained, which may cause runaway of toner concentration. Further, in the case of having a plurality of recording devices, a photo sensor must be attached to each of the plurality of photoconductors, which complicates the device.

(Purpose) The present invention has been made based on such a background.
Provided is an image density control device for a recording device, which can relatively easily obtain a desired recorded image density by controlling the toner replenishment and the transfer current comprehensively by examining the density of the recorded image, and which is less likely to deteriorate in use. The purpose is to

(Structure) In order to achieve this object, the present invention is directed to a density of a transfer image transferred by a transfer means after a reference latent image formed as a reference outside the original image forming area on the surface of the photoreceptor is developed by a developing device. An image density detecting means for detecting the toner density, and a toner replenishing control means for controlling the replenishment of toner to the developing device when the density of the transferred image detected by the image density detecting means is smaller than a preset first predetermined value. A ratio of respective densities of the first transfer image formed by the reference latent image which is detected by the image density detecting means and gives the intermediate density and the second transfer image formed by the reference latent image which gives the maximum density. And a transfer current control means for controlling the transfer current of the transfer means in accordance with the magnitude relationship between the density ratio and a preset second predetermined value.

Hereinafter, the configuration and operation of the present invention will be described in detail based on the embodiments shown in the drawings.

FIG. 1 shows a color copying machine as an example of the image forming apparatus. The copying machine includes a scanner unit 1 for reading an original, an image processing unit 2 for electrically processing an image signal output as a digital signal from the scanner unit 1, and image recording information of each color from the image processing unit 2. And a printer section 3 for forming an image on a copy sheet based on the above. The scanner unit 1 has a lamp 5 for scanning and illuminating the original document on the original document table 4, for example, a fluorescent lamp. The reflected light from the document when illuminated by the fluorescent lamp 5 is reflected by the mirrors 6, 7, 8 and enters the imaging lens 9. By the imaging lens 9,
The image light is imaged on the dichroic prism 10 and is split into, for example, light of three kinds of wavelengths of red R, green G, and blue B, and a light receiver 11, for example, CCD 11 for red, for each wavelength light.
It is incident on the R, green CCD 11G, and blue CCD 11B. Each CCD
11R, 11G, 11B convert incident light into a digital signal and output it, and the output is subjected to necessary processing in the image processing unit 2, and recorded color information of each color, for example, black (hereinafter abbreviated as Bk), The signals are converted into recording formation signals of yellow (abbreviated as Y), magenta (abbreviated as M), and cyan (abbreviated as C).

Although FIG. 1 shows an example of forming four colors of Bk, Y, M and C, it is also possible to form a color image with only three colors. In that case, the number of recording devices can be reduced by one from the example of FIG.

The signal from the image processing unit 2 is input to the printer unit 3,
It is sent to the laser light emitting devices 12Bk, 12Y, 12M and 12C of the respective colors.

In the example of the figure, the printer section has four sets of recording devices 13C, 13M, 13
Y and 13Bk are arranged side by side. Since each recording device 13 is composed of the same constituent member, the recording device for C will be described and the other colors will be omitted for simplification of description. For each color, the same parts are designated by the same reference numerals, and in order to distinguish the configurations of the respective colors, the reference numerals are added to indicate the respective colors.

The recording device 13C is a photoconductor 14C in addition to the laser beam emitting device 12C.
For example, it has a photosensitive drum.

The photoreceptor 14C has a charging charger 15C and a laser light emitting device.
Exposure position by 12C, developing device 16C, transfer charger 17C
Etc. are provided in the same manner as a known copying machine.

Photoconductor 14C uniformly charged by charging charger 15C
Forms a latent image of a cyan light image by exposure with the laser beam emitting device 12C, and develops it with the developing device 16C to form a visible image. The copy paper supplied from the paper feed unit 19, for example, one of the two paper feed cassettes, by the paper feed roller 18 is fed to the transfer belt 21 with the leading ends aligned by the registration rollers 20 and at the same timing. The copy papers conveyed by the transfer belt 21 are the photoconductors 14Bk and 14B having the visible images, respectively.
The images are sequentially transferred to Y, 14M, and 14C, and a visible image is transferred under the action of the transfer charger 17. The transferred copy paper is fixed on the fixing roller 22.
The sheet is fixed by the sheet, and is discharged by the sheet discharge roller 23.

The copy paper is electrostatically attracted to the transfer belt 21,
It can be accurately conveyed at the speed of the transfer belt.

Among the transfer belts, 24 is a tension roller, 25 is a driving rubber roller, and 26 is a driven roller, which is made of metal.

An image density control mechanism using a pattern image for toner replenishment control will be described below with reference to FIGS. 2 and 3.

In FIG. 2, (a) is a front view of the main part of the present invention,
FIG. 3B is a perspective view of the belt.

First, a standard pattern for toner replenishment control is exposed to the outside of the original image area on the photoconductor by the laser beam in addition to the image, and a standard latent image is formed.

FIGS. 4, (a), (b), (c), and (d) show standard patterns for detection, and the digital copying machine shown in FIG. 1 has a basic matrix of 4 × 4 size. Area gradation is performed, and a standard pattern is created by repeating this 4 × 4 pattern. Of the 4 × 4 = 16 dots, which dot is black or white is related to the detection sensitivity, and in this embodiment, the dot type with an area ratio of 25% in (d) is used.

In addition, (a) is a 50% concentrated type, (b) is a 50% dust type,
(C) shows 25% concentrated type respectively.

This latent image is first developed with Bk by the same developing bias as the image signal portion. Then, the original image is transferred onto the copy paper and the pattern image is transferred onto the transfer belt under predetermined conditions. This process is similarly repeated for the next Y, M, and C, but at this time, the pattern image is
As shown in FIG. 2 (c), the transfer is controlled so as to be transferred to each predetermined position. After the development of C, when the pattern image passes, the photosensor 28 placed close to the metal roller 26 of FIG. 1 measures the amount of reflected light of each color and compares it with a preset value. If the amount of reflected light is larger than the set value, it is determined that the image density is low, that is, the toner supply level has been reached, and as shown in FIG. 3, the toner supply signal P _{M (BX)} Set P _{M (C)} , P _{M (M)} , P _{M (Y)} to O
N, and supply a fixed amount of toner to each developing device. In this case, the supply amount may be changed according to the output of the reflected light amount. If the transfer condition is changed due to dirt and fatigue of the charger and the transfer rate becomes low, the amount of reflected light does not decrease even if the supply is repeated, the toner concentration becomes high, and the toner scattering,
The dirt etc. will occur. On the other hand, if the transfer rate increases due to environmental changes, the number of replenishments decreases, which may cause an abnormality such as carrier adhesion. Also, as shown in Fig. 6, the transfer rate of the halftone dot area ratio changes, which affects the gradation, and even with the same halftone dot area ratio, the ID changes depending on the transfer conditions, and a stable image is obtained. I can't. In other words, in order to obtain a stable image, not only the toner concentration but also the transfer condition must be controlled. Therefore, in the present invention, in addition to the first standard pattern image every several sheets (preferably every 5 to 10 sheets), as shown in FIG.
A solid second pattern is created for each color, and the original image, standard pattern image, and 100% solid image are transferred to a transfer belt under certain predetermined conditions.

The first pattern is shown by Bk1, Y1, M1, C1 and the second pattern is shown by Bk2, Y2, M2, C2. Then, the above photo sensor 28 measures the reflected light amount of the pattern image (V ₂₅ ) and the reflected light amount of 100% solid (V ₁₀₀ ), and calculates the ratio (V ₂₅ / V ₁₀₀ ), and the ratio and the reference value The transfer current is changed according to.

The principle will be described below.

FIG. 6 shows the transfer rate when the transfer current is changed in the first and second pattern images.

This indicates that the transfer rate differs depending on the concentration even if the transfer current is the same, and the transfer rate varies depending on the transfer current even at the same concentration.

Then, FIG. 7 shows the case where the transfer current is changed (A,
The relationship between the dot area ratio of B, C, D, and E points) and the adhesion amount after transfer is shown.

Here, there is a relationship between the attached amount and the reflected light amount that the reflected light amount decreases as the attached amount increases, and the reflected light amount increases as the attached amount decreases.

Here, if the first transfer condition is point C, the transfer current becomes small due to dirt on the transfer charger, aging, etc. (A,
B point) and V ₂₅ / V _{100 become} smaller. Conversely, when the transfer current increases, V ₂₅ / V ₁₀₀ increases on the contrary. Then, by setting the ratio at the point C as a set value and changing the transfer current according to V ₂₅ / V ₁₀₀ , the transfer conditions can always be stabilized.

The transfer current signal is the port P _T of the CPU shown in FIG.
(Bk), P _T (C), P _T (M), and P _T (Y) are output to each transfer power pack.

In addition, if this V ₂₅ / V ₁₀₀ deviates significantly from the set value, it is possible to post it as a transfer abnormality on a display device (omitted). For example, if the transfer current becomes smaller than A in Fig. 6 or the transfer current becomes larger than E (this is V ₂₅ / V
_{It is possible to} consider it as a transfer abnormality (because it is easier to understand than ₁₀₀ ) (white spots in the solid area or abnormal images are caused).

FIG. 3 shows a circuit diagram of the photo sensor. Photo sensor
5V is applied to the 28 photo-sensing phototransistors, and the adjustment of the reference voltage is 4-5V by the variable volume.
Is set to. The reference voltage is an output voltage value due to the reflected light from the metal roller 26. In addition, the detection output is output for each of the four colors on the output PI according to the amount of light incident on the phototransistor.

Further, FIGS. 5 (a) and 5 (b) show output waveforms of the output of the photo sensor which is taken in by the CPU 30. (A) is a waveform diagram when only the toner replenishment control pattern (first pattern: 25%) is read, and (b) is a waveform diagram when the second pattern (100% solid) is also read. is there.

Although the second control means is used as the transfer condition in the embodiment, other controls such as bass ass control and laser power control are also possible.

FIGS. 8 (a) and 8 (b) are flow charts showing a means for controlling the toner replenishment control by reading a 25% pattern image each time and a means for controlling the 100% solid read transfer condition for every 5 sheets.

In the figure, V _25BK , V _25Y , V _25M , and V _25C are the 25 reflected light intensity values (voltages) of Bk, Y, M, and C, (V ₂₅ / V ₁₀₀ ) _BK …… is 25% of BK …… and 1
00% pattern ratio, reference value Bk …… is the initial setting value of the 25% reflected light amount of Bk ……, and L _BK …… is the initial setting value of the pattern ratio of 25% and 100% of Bk …….

(Effects) As described above, according to the present invention, when the density of the transferred image is smaller than the preset first predetermined value, the developing device is replenished with toner, and at the same time, the reference latent image giving an intermediate density is used. The density ratio of each of the formed first transfer image and the second transfer image formed by the reference latent image giving the maximum density is calculated, and the density ratio is compared with the preset second predetermined value. Since the transfer current of the transfer means is controlled according to the magnitude relationship between them, the toner replenishment and the transfer current can be comprehensively controlled, so that the desired recorded image density can be relatively easily obtained. Therefore, it is possible to provide an image density control device for a recording device that is less likely to deteriorate during use.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus to which the present invention is applied, FIG. 2 shows a configuration of a main part of the present invention, (a) is a simplified front view, and (b) and (c) are respectively. FIG. 3 is an external perspective view showing a different pattern on the belt, FIG. 3 is a control circuit diagram,
4 (a), (b), (c), and (d) are density detection pattern diagrams, and FIGS. 5 (a) and (b) are 25% and 100% pattern photosensor output waveform diagrams, and FIG. Is a characteristic diagram of transfer rate, FIG. 7 is a diagram showing the relationship between dot area ratio and toner adhesion amount, FIG.
Figures (a) and (b) are flow charts. 14 …… photoreceptor, 21 …… transfer belt.

Continuation of the front page (56) Reference JP-A-60-23868 (JP, A) JP-A-55-15185 (JP, A) JP-A-59-13264 (JP, A) JP-A-55-12916 (JP , A) JP 60-57868 (JP, A) JP 57-60348 (JP, A) JP 58-80663 (JP, A) JP 59-22067 (JP, A) JP 61-213865 (JP, A) JP-A-60-73645 (JP, A) JP-A-59-136754 (JP, A) Actually developed 61-53757 (JP, U) JP-B-4-44271 (JP, A) B2) Japanese Patent Publication 4-73792 (JP, B2)

Claims (1)

[Claims] 1. A photoconductor, a charger for uniformly charging the photoconductor surface, an exposing means for projecting image light according to recording information onto the photoconductor surface, and a static image formed on the photoconductor surface. The image forming apparatus includes a developing device for developing an electrostatic latent image, a transfer unit for transferring the visible image of the photoconductor onto a copy sheet, and a transfer belt for bringing the copy sheet, which is in contact with the photoconductor and having the visible image transferred, to the downstream side. In the image density control device of the recording apparatus, the reference latent image formed as a reference outside the original image forming area on the surface of the photoconductor is developed by the developing device, and the density of the transfer image transferred by the transfer unit is changed. An image density detecting means for detecting, and a toner replenishing control means for controlling to replenish the developing device with toner when the density of the transferred image detected by the image density detecting means is smaller than a preset first predetermined value. And the image density Detected by the detection means,
The density ratio of each of the first transfer image formed by the reference latent image giving the intermediate density and the second transfer image formed by the reference latent image giving the maximum density is calculated, and the density ratio and the density ratio are calculated in advance. An image density control device for a recording apparatus, comprising: a transfer current control means for comparing the set second predetermined values and controlling the transfer current of the transfer means according to their magnitude relationship.