JPH0532748B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image forming apparatus such as a copying machine or a fax machine.

In conventional copying machines, in addition to a control device that controls the amount of light emitted by a light source for document illumination (hereinafter referred to as a light source) according to the sensitivity of the photosensitive drum, an operator also controls the amount of light emitted from a light source for document illumination (hereinafter referred to as a light source) according to the density of the document. It is common to have means for inputting quantities. In such a semi-automatic (almost manual) mode, selecting the appropriate amount of light is a difficult task, and in order to obtain copies with the appropriate contrast, it is often necessary to test print several copies and use expensive copy paper. I had to waste it.

To solve this problem, we proposed a copying machine equipped with a function (AE) that detects the density of the original using a photodetector or a photosensitive drum surface electrometer, and automatically controls the amount of light emitted accordingly. However, there are few that show any evidence of serious consideration of how to make the luminescence amount respond to the detected original density (i.e., copy density) in order to meet user demands; It is sufficient to have a linear correspondence between the density of the original and the amount of light emitted. In such an automatic exposure copying machine, the amount of light emitted is increased for high-density originals, and decreased for low-density originals. Normally, control is performed so that copies are made with black eyes, but if the density-emission amount is linearly correlated as described above, it is not possible to meet the needs of users who require dark copies and white copies. Ta.

In addition, the luminescence amount was sometimes determined by submitting the density of a portion of the manuscript, which was inaccurate.

Also, it may be possible to detect the density of the entire area of the document, but in that case, it would take too much time to find the appropriate output and start image formation.

Furthermore, there are some devices that adjust the exposure aperture in order to keep the light on the photosensitive surface constant even when the copying magnification changes, but it is difficult to adjust the aperture in consideration of the original density and the magnification.

The present invention aims to eliminate the above-mentioned drawbacks of the conventional apparatus, and is capable of faithfully developing black originals, white originals, and medium-density originals, while at the same time developing originals that are slightly darker or whitish than the medium density. The present invention provides an image forming apparatus that forms images closer to intermediate density.

To achieve the above object, the present invention is an image forming apparatus that detects the density of an original to be exposed to an electrophotographic photoreceptor and automatically determines the optimum exposure amount, and in which a light source image illuminated by a light source for illuminating the original is used. an optical means for guiding the image to the photoreceptor, an original density detection means for detecting the density of the original image, and a means for determining the exposure amount in response to the detected original density, the exposure amount when the density of the original is intermediate. Using this as a reference, the exposure amount for the highest density area of the original and the lowest density area of the original is the same as for the above intermediate density, and the area between the highest density area and the intermediate density is set to have a higher exposure amount than for the above intermediate density. The relationship between the detected original density and the exposure amount is set so that the amount of light is increased in the area between the intermediate density and the lowest density area, and the amount of light is decreased in the area between the intermediate density and the lowest density area than at the intermediate density. and an exposure amount determining means for determining the voltage to be applied to the document illumination light source based on the detection result by the document density detecting means.

Hereinafter, the present invention will be explained in detail based on the drawings.

FIG. 1 shows a schematic diagram of a copying machine of the present invention. The structure of this copying machine is publicly known, and when copying, the original
Light emitted from a light source 12 moving along the document table 1 and reflected from the document 11 on the document table forms an image on the photosensitive drum 10 (rotating in the direction of the arrow) via the mirror 13. An electrostatic latent image is formed on the drum charged by the charger 14 through this exposure. The latent image is developed by a developing means 15, and the developed image is transferred to a sheet by a transfer charger 16. After the transfer, the drum is cleaned by a cleaner 17 for reuse, and is charged and exposed again.

In the figure, a light source 12 is used as a concentration detection means according to the present invention.
A photodetector 1a provided near the photosensitive drum 10 and a surface electrometer 1b provided near the photosensitive drum 10 are shown. In the present invention, either of the above two methods may be used to detect the density of the original;
It is okay to use both. However, the light detection means 1a detects the amount of light reflected from the original 11, and the surface electrometer 1b detects the density of the original by detecting the surface potential of the photosensitive drum 10 after exposure.

A standard white plate 18 is provided outside the original exposure area, and before starting image formation, it is irradiated with a lamp 12 and its reflected light is measured with a detector 1a or an electrometer 1b to measure the potential using the reflected light, and the measured value is a standard value. If it is not at the standard value, the lamp 12 or charger 14 is controlled so that the standard value is reached.
This allows the device to be preset in a ready state. Thereby, proper control of reproduction density after the start of image formation can be achieved with high precision. This standardization process can be performed after turning on the power switch of the apparatus and before turning on the image forming start switch (copy key). This saves image formation start-up time.

FIG. 2 is a block diagram of the exposure amount control system of the copying machine of the present invention. In the figure, the output of the document density detection means 1 (1a, 1b) is digitized by the A/D converter 2 and the input/output port is digitized by the A/D converter 2. 3 to the CPU 4. The CPU 4 uses the integrated value of the sent concentration data to store the concentration in the ROM (read-only memory) 5, which will be described later.
The light emission amount data is determined by referring to a data table in which the light emission amounts are associated with each other, and this data is sent to the input/output port 3. FIG. 6 shows an example of a circuit for integrating detected values.
101 is a light or potential sensor, 102 is an amplifier-like operational amplifier, 103 is a level adjustment amplifier, and 104 is an integral reset switch. The integration time is A/
By D converter. Determined by conversion time.
This is effective when pre-scanning a document to detect and average the density of a region to obtain an appropriate output. This light emission amount data is converted into an analog signal by a D/A converter 6 and sent to the light source 12, so that the light emission amount of the light source 12 is controlled.

The data from concentration to luminescence amount is stored in the ROM 5 as a constant characteristic curve, for example, as 8-bit information. That is, data on the amount of light emitted is stored in each address of 8 bits, that is, 256 addresses, in 8 bits each. Each address corresponds to each data of detected concentration. That is, a memory address corresponding to the detected integrated concentration data is found and the light emission amount data stored at that address is output. ROM
5 may be RAM whose data can be changed.

An example of a characteristic curve of concentration versus luminescence amount is shown below.

Adjust the density of the original from pure black to pure white from No.1 to No.11.
Divided into 11 stages, (pure black: No. 1, pure white: No. 11) 3rd
Assume that the document density exists as shown by the solid line in FIG. (With a conventional copying machine, if copying is performed with a constant amount of light emitted, a copy with the same density as this solid line will be obtained.Hereinafter, the density of the copy is shown by a broken line, and the density of the original is shown by a solid line.In other words, Fig. 3A In this case, the dashed line and the solid line overlap.) The first idea is to automatically control the amount of light emitted so that when all originals with such a density distribution are copied, they all end up with the same density. It's a method. The finished density of the copy at this time is shown by a broken line in FIG. 3B. In other words, the No. 1 (pure black) manuscript is also No.
All 11 (pure white) originals will be finished with the same density.

However, it is practically meaningless to finish both blank paper and black paper with the same density, so in the present invention, as shown in FIG. The amount of light emitted may be controlled so that copies with the same density can be obtained as shown in FIG.

However, in the example shown in FIG. 3C, a completely black original cannot be copied completely black, and a completely white original cannot be copied completely white. Therefore, as is the object of the present invention, it is desirable to control the finished copy density so that it approaches the original density in the high density area and the low density area, as shown in FIG. 3D.

Furthermore, since it would be inconvenient if the copy density suddenly changes from a certain point, it would be ideal if the original density corresponds to the copy density by a curve as shown in FIG. 3E. Furthermore, photosensitive drum 1 that uses this
An example of correction according to the sensitivity of 0 is shown in FIG. 3F.

In order to obtain the copy densities shown in FIGS. 3A to 3F, the amount of light emitted is controlled as shown in FIGS. 4A to 4F, respectively. That is, in the present invention, the relationship between the original density and the amount of light emitted is determined according to the fourth
The settings are as shown in Figures D to F. That is, based on the exposure amount when the density of the original is medium density, the exposure amount of the highest density area of the original and the lowest density area of the original is the same as when the original density is the above-mentioned medium density, and the exposure amount of the highest density area and the middle density is In the area between, the amount of light is set to be greater than when the density is above the intermediate density, and conversely, in the area between the middle density and the lowest density area, the amount of light is set to be smaller than when the density is at the middle density. . This not only makes it possible to achieve almost the same copy density near the intermediate density, but also faithfully reproduces originals with dark black or white. An image with a density closer to a medium density can be formed from an original.

A non-linear characteristic curve relating the document density to the amount of light emitted as described in detail above is stored in the ROM 5, and the CPU 4 refers to this to control the amount of light emitted. A flowchart of this processing procedure is shown in FIG. 5. That is,
In step 1 of FIG. 5, the integrated value of the output of the light source concentration detection means 1, such as the light detection means 1a or the surface electrometer 1b, is loaded into the CPU 4 from the input/output port 3 via the A/D converter 2. Next, in step 2, the CPU determines the light emission amount data by comparing the sent concentration data with the address of the density-light emission characteristic curve digitized and stored in the ROM 5. That is, the memory is addressed using the density data as address data to output light emission data, and then in step 3 this light emission data is loaded into the CPU. Then, in step 4, this light emission amount data is sent to the D/A converter 6 via the input/output port 3, where the light emission amount of the light source 12 is controlled, for example, according to the light emission amount data converted back to an analog amount. lamp 1
This is done by controlling the applied voltage in step 2. Note that it is also possible to control the developing bias voltage of the developing device 15.

FIG. 7 further details the flow shown in FIG. 5. At S10, the microprocessor CPU senses a predetermined port of I/O port 3, and senses data a.
(detected integrated concentration) is loaded into one of the registers in the CPU, and the start address b of the ROM is loaded into the CPU in S11.
Load it into the address register of , add the previous data a and the first address data b in S12, and
The data c in the address resulting from the addition is sent to the CPU
data C in S14.
is set to the I/O port and outputs control data.

Next, consider another example, in which a light-receiving element is installed in the optical path of an optical system in which the reflected light from the original forms an image on the photoreceptor via a lens, and the illuminance on the photoreceptor drum changes by changing the copying magnification. An example will be described in which the deviation from the output of the light receiving element is corrected according to the copy magnification, and the developing bias is further controlled according to the corrected data to make the copy density appropriate.

FIG. 8 is similar to FIG. 1.

When the copy start button is pressed, the first mirror 10
4 and the second and third mirrors 105 start scanning the original 101 at a speed ratio of 2:1. The light amount detection means 107 measures the amount of light at regular intervals during scanning and samples data. A, B, C, D and a,
b, c, and d indicate the correspondence between the position of the original and the position where the original image is formed on the drum.

Figure 2 is a flow diagram showing the procedure for determining the developing bias by averaging and scaling processing after sampling, Figures 10 and 11 are circuit diagrams for achieving this, and Figure 12 is the same as the one shown in Figure 10. Program of ROMO
This is a flowchart of the above procedure program stored in . The CPU 40 in FIG. 11 is a CPU with a built-in A/D converter.

FIG. 10 is an electrical configuration diagram. The sampled data is digitized via an A/D converter and sequentially allocated and stored in the address space of the RAM. Data is averaged while the latent image formed on the photoreceptor drum by exposure reaches the position of the developing device, and the developing bias is controlled according to the data. In FIG. 8, the developing device 110 is performing development at point b, and the value of the developing bias at this time is averaged using data sampled N times every 0.1 sec between A and C of the original. It is determined according to that value. Next, when development at point C is started, the data (N pieces) sampled by the light receiver 107 between originals B to D are averaged (see Figure 13), and the DC component of the development bias is calculated according to that value. control. In this way, the DC component of the developing bias is sequentially controlled.

Output correction when the magnification is different is performed by multiplying the averaged value by the correction value from the correction ROM. The sampling method shown in FIG. 4 is performed by periodically inputting an interrupt signal (for example, at 0.1 sec) and storing the sampling data in the address space of the RAM.

115 and 116 in FIG. 11 are similar to the integrating circuit in FIG. 6, and 118 and 120 are D/
These are an integrating circuit and a buffer amplifier that constitute the A converter 6. A transformer 119 applies a bias voltage to the developing roller 110.

Figures 12 and 13 will be explained in detail. When an interrupt occurs due to an input pulse, the data on input port AD1
Load CRO into register A in the CPU (step 1), increase register C indicating the number of samples by +1
(Step 2), senses the register HD indicating the RAM address, and stores the data in register A at the top address of the RAM (Step 3).
Since we have not sampled N times yet, register HD
Advance the address data by one (step 4-
2) Perform the same sampling and data storage again with the next pulse 0.1 seconds later.

When the number of samplings reaches N, that is, A~
When sampling between C is completed, the N pieces of data in the RAM are added and set in registers A and B (step 4-15). Addition data is 1/N and loaded into register A (step 6). Since correction data according to the copy magnification is stored in ROM1 in advance,
Data at the current magnification is loaded from ROM1 to register B (step 7). Multiply the data in registers A and B and load into A (step 8).
The ROM2 is addressed using the data in register A, and the bias data stored at the corresponding address is loaded into register B (step 9). Register B
The data is output from ports 0 _{and 1} and used as the developing bias (step 10). Next, register C is loaded with N/2, and the next area (C to D) is sampled (N/2 times) and data is stored again. RAM
In steps 3 to 5, N/2 pieces of data are newly stored, but in steps 5 to 6, the N pieces of data, that is, the data for B to D are calculated to obtain an average value. Therefore, since the data before and after the data from the light receiving element are averaged, accuracy is high. Note that the light receiving element 107 is provided at the rear non-surface portion of the zoom lens 106. A zooming operation is performed by the input key for selecting the zoom lens magnification. Then, ROM1 is set by the latch data by this input key.
Addressing is performed to obtain correction data. It should be noted that even if the electrometer is provided at a position immediately after the exposure station, the bias control as described above can be performed.

With these examples, automatic density control can be performed immediately during image exposure for image formation, and wasted time can be reduced.

According to the present invention, it is possible to form an image that is slightly darker or whitish than an intermediate density into an image closer to an intermediate density, and to faithfully develop a black original, a white original, or an original with an intermediate density. made possible.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a schematic configuration of a copying machine according to the present invention, FIG. 2 is a block diagram showing a control circuit of the copying machine, and FIGS. 3A to 3F are diagrams showing the correspondence between original density and copy density. FIGS. 4A to 4F are diagrams showing the characteristics of original density to light emission amount, and FIGS. 4D to F show the characteristics of the embodiment of the present invention. FIG. 5 is a flowchart showing the processing procedure of the circuit in FIG. 2, and FIG.
Fig. 7 is an integral circuit diagram with the detection means shown in Fig. 5.
8 is a sectional view of a copying machine showing another example, FIG. 9 is a flowchart of another example, FIGS. 10 and 11 are circuit clock diagrams of other examples,
Figure 12 is a detailed flowchart of Figure 9, and Figure 13 is a detailed flowchart of Figure 9.
The figure is a control explanatory diagram of FIG. 12. In the figure, 1 is a density detection means, 4 is a control means, 12 is a lamp, and 15 is a developing means.

Claims (1)

[Scope of Claims] 1. In an image forming apparatus that detects the density of an original to be exposed to an electrophotographic photoreceptor and automatically sets the optimum exposure amount, the original image illuminated by a light source for illuminating the original is guided to the photoreceptor. an optical means; an original density detection means for detecting the density of the original image; and a means for determining an exposure amount corresponding to the detected original density, the exposure amount being based on the exposure amount when the density of the original is intermediate; The exposure amount for the highest original density area and the lowest original density area is the same as for the above intermediate density, and the area between the highest density area and the intermediate density is exposed to a higher amount of light than for the above intermediate density. However, conversely, in the area between the intermediate density and the lowest density area, a storage means is set that sets the relationship between the detected original density and the exposure amount so that the amount of light is smaller than at the intermediate density. An image forming apparatus comprising: exposure amount determining means for determining a voltage to be applied to a light source for illuminating an original based on a detection result by the original density detecting means.