JPH0555868B2 - - 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.

In order to solve this problem, it has been proposed to pre-scan the original, measure the density of the original, and control the exposure amount and developing bias during actual image formation. However, the required pre-scan operation required extra time to obtain the copy.

Also, it is possible to perform optimal density control for each area of the document, but at the joints of each area,
It is conceivable that image forming conditions may change rapidly, causing density changes and deterioration of image quality.

The present invention aims to solve the above-mentioned problems,
In other words, the objective is to provide an image forming apparatus that allows detection of document density and image formation to be performed in parallel, enables control for each area, and makes the joints between areas inconspicuous. .

In detail, it includes a scanning means for exposing and scanning a document, a latent image forming means for forming an electrostatic latent image corresponding to the document image, and a developing means for developing the electrostatic latent image at a predetermined time delay with respect to the scanning timing of the scanning means. During scanning for image formation by the scanning means, the document is divided into several regions in the exposure scanning direction, and each divided region is sampled multiple times at a predetermined period. density detection means for detecting document densities within the divided areas; digital conversion means for converting each sample value of the density detection means into digital values; division of each of the divided areas in the exposure scanning direction including the divided area; calculation means for calculating the average value of document density in the expansion area by adding the outputs of the digital conversion means within the enlarged area including the divided areas adjacent to the area; It has a control means for controlling a developing bias value when a document image in a region corresponding to the region is developed by the developing means, and the calculating means and the controlling means respectively perform a calculation for calculating an average value and a developing bias value. The object of the present invention is to provide an image forming apparatus that repeats control in parallel.

According to such a configuration, it is possible to optimally control the image quality for each area of the document without requiring prescan time, and it is also possible to make the joints between areas inconspicuous, making it possible to obtain high-quality images. can.

These and other objectives will become clear from the examples below.

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 each 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 the potential due to the reflected light is measured with an electrometer 1b, and the measured value is the 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 to standard conditions. 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 this embodiment. In the figure, the outputs of the document density detection means 1, 1a, and 1b are digitized by the A/D converter 2, and the input/output ports are 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 the data table in which the light emission amounts are associated, 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 operational amplifier for amplification, 103 is an amplifier for level adjustment, 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 the blank original and the black paper with the same density, so in this embodiment, as shown in FIG. The amount of light emitted may be controlled so that copies with the same density can be obtained as shown by the broken line, and the remaining high densities will produce white eyes and the remaining low densities will produce black eyes.

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 shown in FIG. 3D, 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.

Furthermore, since it is 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 this embodiment, as shown in FIGS. 4C to 4F, the density of the original is non-linear with the amount of light emitted, and the amount of light emitted is increased for dark originals so that the copy density is almost the same near the intermediate density. Conversely, for thin documents, the amount of light emitted is controlled to be low.

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 in FIG. 5, the integrated value of the output of the document density detection means 1, such as the photodetection 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 this light emission data in step 3 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.
Here, the amount of light emitted from the light source 12 is controlled by, for example, controlling the voltage applied to the lamp 12 in accordance with the amount of light emitted data that has been returned to an analog value. 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.

Fig. 9 is a flow diagram showing the procedure for determining the developing bias by averaging and scaling processing after sampling, Figs. 10 and 11 are circuit diagrams for achieving this, and Fig. 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 RAM address space. 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).
Finally, since I have not sampled N times, register HD
Return one address data (Step 4-2)
Similar sampling and data storage are performed again with the next pulse 0.1 seconds later.

When the number of samples reaches N, that is, when samples from A to C are completed, N pieces of data in the RAM are added and set in register A (step 5).
Addition data is 1/N and loaded into register A (step 6). Since correction data corresponding to the copy magnification is stored in advance in ROM1, the 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). The data in register B is used as the developing bias output from port ₀₁ (step 10). Next, load N/2 into register C and sample the next area (C to D) again (however, N/2
2 times) and data storage is performed. N/2 pieces of data are newly stored in the RAM in steps 3 to 5, 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 in the rear non-image area of the zoom lens 106. This zoom lens performs a zooming operation using an input key for magnification selection. Then, the ROM1 is addressed by the latch data from this input key, and correction data is obtained. 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.

In addition, in this example, a document image is read by a reading means such as a CCD, converted into an electric signal, further converted into a binary video signal, and the video signal is used to modulate the brightness of a laser to form a latent image on the drum. It can also be applied to devices that transmit video signals. In this case, the density of the original is also detected by the original image reading means. Determine the original density from the original reading data. Further, one of the image forming conditions to be controlled may be the step of binarizing the read data. That is, this can be done by changing the threshold level for binarization according to the determination density.

[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. FIGS. 4A to 4F are diagrams showing the characteristics of the original density to luminescence amount of the present invention, FIG. 5 is a flowchart showing the processing procedure of the circuit in FIG. 2, and FIG. 1 is an integral circuit diagram having a detection means, FIG. 7 is a detailed flowchart of FIG. 5, FIG. 8 is a sectional view of a copying machine showing another example, FIG. 9 is a flowchart of another example, and FIG. 10 and 11 are circuit clock diagrams of other examples, FIG. 12 is a detailed flowchart of FIG. 9, and FIG. 13 is a control explanatory diagram of FIG. 12. In the figure, 1 is a concentration detection means, 4 is a control means, 1
2 is a lamp, and 15 is a developing means.

Claims (1)

[Scope of Claims] 1. A scanning device for exposing and scanning a document; a latent image forming device for forming an electrostatic latent image corresponding to the document image; and a latent image forming device for forming an electrostatic latent image for a predetermined time with respect to the scanning timing of the scanning device. an image forming means including a developing means that develops with a delay; during the scanning for image formation of the scanning means, the original is divided into several regions in the exposure scanning direction;
Density detection means for sampling each divided area a plurality of times at a predetermined period to detect the document density in each divided area, digital conversion means for converting each sample value of the density detection means into a digital value, Calculation for calculating the average value of document density in the enlarged area by adding the output of the digital conversion means within an enlarged area including the divided area and adding a divided area adjacent to the divided area in the exposure scanning direction for each of the divided areas. means, comprising a control means for controlling a developing bias value when a document image in an area corresponding to the divided area is developed by the developing means according to the calculation result of the calculation means, the calculation means and the An image forming apparatus characterized in that the control means repeats calculation for obtaining an average value and control of a developing bias value in parallel.