JPS6343169A - Image density control device - Google Patents

Abstract

PURPOSE:To contrive to stabilize an image by preparing two kinds of image density controlling patterns, reading out the patterns on the downstream side of a transfer belt, and in accordance with the read result, changing a copying condition and feeding toner. CONSTITUTION:A reference pattern for toner feeding control is exposed to the outside of an original image area of a photosensitive body by laser beams independently of an image to form a reference latent image. An original image and a pattern image are respectively transferred to copying paper and a transfer belt. The reflected light quantit values of respective colors are measured by a photosensor 28 arranged adjacently to a metal roller 26, compared with a previously determined set point, and if the reflected light valve is larger than the set point, a toner feeding signal is sent. Independently of the 1st reference patterns BK1, Y1, M1, C1, completely solid printed 2nd patterns BK2, Y2, M2, C2 of respective colors are formed every several sheets and then transferred. A transfer current is controller on the basis of the measured result by means of the reflected light quantity sensor 28 to change the copying condition. Thus, stable picture recording can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an image forming apparatus having a photoreceptor drum and a transfer belt, and more particularly to an image density control device for a color copying apparatus having a plurality of photoreceptor drums and a transfer belt.

(Prior art) The electrostatic latent image on the photoreceptor is visualized using toner in a developing device, and the developed image is transferred by a transfer belt to copy paper that is conveyed from a paper feed unit in a transfer unit. In this type of image forming apparatus, it is necessary to replenish toner according to the amount consumed.

Conventionally, in addition to replenishing toner according to changes in the amount of toner adhering to the reference pattern on the photoreceptor drum, a plurality of toner marks for each color of toner are recorded on the recording medium, and the toner density of the toner marks is Techniques for changing toner density by optically detecting toner are well known.

However, in these conventional techniques, either the amount of toner or the transfer conditions (bias voltage, etc.) are checked, and therefore comprehensive image density control cannot be performed.

In addition, for devices that detect the amount of toner adhering to the photoreceptor drum, due to the structure of the device, a photo sensor must be installed under the current device (i), but this is a place where toner scattering and agent spillage occur. As a result, toner adheres to the sensor, making it impossible to obtain the correct image output and causing the toner concentration to run out of control.Also, in devices with multiple recording devices, there is a risk of toner adhering to the sensor, making it impossible to obtain the correct image output, and causing the toner concentration to run out of control. A photo sensor must be attached, making the device complicated.

(Purpose) The present invention has been made based on this background,
An object of the present invention is to provide an image density control device capable of stabilizing an image with a simple configuration.

(Configuration) For this purpose, the present invention prepares two types of patterns for image density control, reads these on the downstream side of the transfer belt, changes copying conditions according to the reading results, and replenishes toner. It is something.

More specifically, a standard pattern for toner replenishment control is transferred to a transfer belt in one row at regular intervals for each color, the density of the pattern image of each color is read by a set of light receiving and emitting elements, and toner is transferred according to the output. It is characterized by controlling image density by changing replenishment and transfer conditions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure and operation of the present invention will be explained in detail below based on embodiments shown in the drawings.

In FIG. 1, a color copying machine is shown as an example of an image forming apparatus.The copying machine includes a scanner part 1 for reading a document, and an image signal outputted as a digital signal from the scanner part L, which is electrically processed. It has an image processing section 2 and a printer section 3 that forms an image on copy paper based on image recording information of each color from the image processing section 2. The scanner part 1 includes a lamp 5 that scans and illuminates the document on the document table 4.
, with, for example, fluorescent lights. The reflected light from the document when illuminated by the fluorescent lamp 5 is reflected by the mirror 6.7.8 and enters the imaging lens 9.

The image light is focused on the dichroic prism 10 by the imaging lens 9, and is separated into light of three different wavelengths, for example, red R, green G, and blue B, and the light receiver 1) for each wavelength is sent to the light receiver 1), for example, for red. CCDIIR, CC for green
It is input to DIIG and CCDIIB for blue. Each CC
DIIR, 1) G, IIB converts the incident light into a digital signal and outputs it, and the output is subjected to necessary processing in the image processing section 2 to record color information of each color, such as black (hereinafter abbreviated as Bk). ), yellow (abbreviated as Y), magenta (abbreviated as M), and cyan (abbreviated as C).

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

The signal from the image processing section 2 is input to the printer section 3,
Laser light emitting devices for each color t12Bk, 12Y,
Sent to 12M and 12C.

In the example shown in the figure, the printer section includes four sets of recording devices: 1) 3G;
13M, 13Y, and 138k are installed side by side. Since each recording device 13 is made of the same constituent members, in order to simplify the explanation, the recording device for C will be explained, and the explanations for other colors will be omitted. Note that for each color, the same parts are given the same reference numerals, and in order to distinguish the configuration of each color, a subscript indicating each color is added to the reference number.

The recording device 13C has a photoreceptor 14C1, for example, a photoreceptor drum, outside the laser beam emitting device 12C.

A charger 15c, an exposure position by a laser beam emitting device 12G, a developing device 10C2, a transfer charger 17C, and the like are attached to the photoreceptor 14c in the same manner as in a known copying apparatus.

Photoreceptor 1 uniformly charged by charger 15C
4C forms a cyan latent image through exposure by the laser beam emitting device 12G, and develops it by the developing device 16C to form a developed image. Copy paper is fed by a paper feed roller 18 from a paper feed unit 19, for example, one of two paper feed cassettes, and the leading edge of the copy paper is aligned by a registration roller 20 and sent to a transfer belt 21 at the same timing. Transfer belt 2
The copy paper conveyed by 1 is sequentially sent to photoreceptors 148 14Y, 14M, and 14C on which a developed image is formed, and the developed image is transferred under the action of the transfer charger 17. The transferred copy paper is fixed by a fixing roller 22 and discharged by a paper discharge roller 23.

By being electrostatically attracted to the transfer belt 21, the copy paper can be conveyed with high precision at the speed of the transfer belt.

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

"The image density control AA structure using a pattern image for toner replenishment control will be described below with reference to FIGS. 2 and 3.

In FIG. 2, fa) is a front view of the main part of the present invention, and (b)
) is a perspective view of the belt.

First, apart from the image, a standard pattern for controlling toner replenishment is exposed outside the document image area on the photoreceptor by laser light, thereby forming a standard latent image.

Figure 4, (at, (bl, (C1, (dl) indicates a standard pattern for detection, and the digital copying machine shown in Figure 1 uses a basic matrix of 4 x 4 size to perform area gradation. The standard pattern is created by repeating this 4 x 4 pattern. Which dots are black or white among the 4 x 4 = 16 dots is related to the detection sensitivity, and in this example, (d ) is used.

In addition, (a) shows a 50% concentrated type, (bl shows a 50% chidori type, and (C1) shows a 25% concentrated type, respectively.

This latent image is first developed with the same developing bias as the image signal area.
is developed. Then, the original image is transferred onto copy paper, and the pattern image is transferred onto a transfer belt under predetermined conditions. This process is repeated in the same way for the next Y, M, and C, but at this time, the pattern images are each transferred to the predetermined positions as shown in FIG. After the development of C is completed,
When the pattern image passes, the photo sensor 28 placed close to the metal roller 26 in FIG. 1 measures the amount of reflected light of each color and compares it with a predetermined setting value. If the value is large, it is determined that the image density is low, that is, the toner supply level has been reached, and as shown in Figure 3,
As the first control means, l/ner replenishment signal P□□)+P□
C)+PM(M)+P□y, is ONL, and a certain amount of toner is supplied to each developing device. In this case, replenishment (2) may be changed depending on the output of the amount of reflected light. At this point, the transfer conditions change due to charger dirt or fatigue, resulting in a low transfer rate (if this happens, the amount of reflected light will not decrease no matter how many times you replenish the charger, the toner density will increase, and toner scattering, background smearing, etc.) will occur. On the other hand, if the transfer rate increases due to environmental changes, the number of replenishments will decrease, and abnormalities such as carrier adhesion may occur.Also, as shown in Figure 6, the dot area ratio will change due to changes in the transfer current. Since the ratio changes, the gradation is affected, and even if the halftone area ratio is the same, the ID changes depending on the transfer conditions, making it impossible to obtain a stable image.In other words, in order to obtain a stable image, not only the toner density but also the transfer conditions are required. Therefore, in the present invention, every few sheets (5 to 10
Separately from the first standard pattern image, a 100% solid second pattern is created for each color outside the document image area as shown in Figure 2 (bl), and the document image, standard pattern A 100% solid image is transferred to a transfer belt under certain conditions.

Note that the first pattern is indicated by Bkl, Yl, Ml, and C1, and the second pattern is indicated by Bk2. Y2. It is shown as M2°C2. Then, the photo sensor 28 detects the amount of reflected light of the pattern image (v*%) and the amount of reflected light of 100% solid (V lo
. ), find the ratio (■2°/V +...), and change the transfer current according to that ratio and the reference value.

The principle will be explained below.

Figure 6 is 1. The transfer rate when changing the transfer current in the second pattern image is shown.

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

Figure 7 shows when the transfer current is changed based on Figure 6 (A
, B, C, D, and E) and the relationship between the dot area ratio and the amount of adhesion after transfer.

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

If the initial transfer condition is set to 0, the transfer current will become smaller due to lη of the transfer charger, changes over time, etc.
A, B points) and V zs/V Io. becomes smaller. Conversely, when the transfer current increases, Vzs/V+. .

On the contrary, it becomes larger. Then, V is/V + with the ratio at 0 point as the set value. . By changing the transfer current according to the transfer current, the transfer conditions can be kept stable at all times.

Note that the transfer current signal is the CPU port (described later in FIG. 3).
PT (Bk), PT (C), PT (M).

It is output from PT (Y) to each transfer power pack.

Also, this Vzs/V+. . If the value deviates significantly from the set value, it can be displayed on the display device (omitted) as a transfer abnormality.For example, if the transfer current becomes smaller than A in Figure 6, or larger than E in Figure 6, (This is V
zs/V+. . This can be regarded as a transfer abnormality (which can be seen more easily) (causing white spots in solid areas or abnormal images).

FIG. 3 shows a circuit diagram of the photosensor. 5V is applied to the phototransistor for light detection of the photosensor 28, and the reference voltage can be adjusted by adjusting the variable volume at 4V.
~5■ is set. The reference voltage is an output voltage value due to light reflected by the metal roller 26. In addition, the detection output is displayed on the output PI according to the amount of light incident on the phototransistor.
Each color is output.

Further, FIGS. 5A and 5B show the output waveform of the output of the photosensor which is taken into the CPU 30. (a) is a waveform diagram when only the toner replenishment control pattern (first pattern = 25%) is read, (bl is the waveform diagram when reading the second pattern (100%).
%peta) is also read.

In the embodiment, the second control means is used as the transfer condition, but other methods such as bus ass control and laser power control are also possible.

FIG. 8(b) shows a flowchart of means for reading 25% of the pattern image each time and controlling toner replenishment, and means for reading 100% of the pattern image every five sheets and controlling the transfer conditions.

In the figure, V2SIK+ Vzsv r Vzsp+ *
Vt5c is Bk.

25 reflected light amount value (voltage) of Y, M, C, (V2S
/V. . )□−・・・− is 25% of BK−・−・−
The ratio of the and 100% pattern, the reference value Bk-... is Bk
Initial setting value of 25% reflected light amount of ・-・-, LIK・-・
--. is the initial setting value of the pattern ratio of 25% and 100% for Bk--.--.

(Effects) The present invention is as described above, and according to the image density control device according to the present invention, since the first and second patterns are transferred onto the transfer belt and the relationship between them is read, It becomes possible to control not only the toner concentration of the developing device but also the transfer conditions, resulting in stable images and preventing runaway toner concentration, reducing costs and making the device easier to install.

[Brief explanation of drawings]

Fig. 1 is a schematic F8 configuration diagram of an image forming apparatus to which the present invention is applied, Fig. 2 shows the configuration of main parts of the present invention, Ta+ is a front view when opened, (b), (C1 are different from each other) Fig. 3 is a control circuit diagram, Fig. 4 (al, (bl, fcl, +dl are density detection pattern diagrams, Fig. 5 Tag, (b) is a 25%, 1
00% pattern photosensor output waveform diagram, Figure 6 is a characteristic diagram of transfer rate, Figure 7 is a diagram showing the relationship between halftone area ratio and toner adhesion amount, Figure 8 (al, (bl is a flow chart) 14... Anger body, 21... Transfer belt. Fig. 2 (C) Fig. 4 (a) (b) (c) (d) Fig. 5 (b) Fig. 6 Fig. 7 Rod Kongmen prisoner

Claims (3)

[Claims] (1) A photoreceptor, a charger that uniformly charges the surface of the photoreceptor, an exposure unit that projects image light on the photoreceptor according to recorded information, and a developer that develops an electrostatic latent image on the photoreceptor; In an image forming apparatus that includes a transfer means for transferring a developed image of a photoreceptor onto a copy paper, the copy paper is brought into contact with the photoreceptor by a transfer belt, and the image is transferred. A first pattern image is formed at a predetermined location, the developed image is transferred to a transfer belt, the density of the image is detected by a photosensor, and the first control means is driven in accordance with the output. An image density control device that also forms a second pattern image in the same way for each sheet or a plurality of sheets, detects the density, and drives a second control means in accordance with the output thereof. (2) A plurality of the recording apparatuses are provided, and the copy paper is sequentially conveyed to each recording apparatus by a transfer belt so that the images are transferred in an overlapping manner. Image density control device. (3) The first control means is a toner supply control means,
The image density control device according to claim 1, wherein the second control means is a transfer control means.