JPS6163864A - Automatic picture density adjusting device - Google Patents

Abstract

PURPOSE:To reduce the production cost of the titled device by deciding the density of an original on the basis of the detection of a proper ground density and using an electric lamp also as a density detecting lamp. CONSTITUTION:The 1st mirror unit 6 provided with an exposing lamp 4 and the 1st mirror 5 is arranged on the inside of a copying machine body 1 and the lower part of an original placing plate 2 so as to be moved straight in parallel with the original placing plate 2 (in the right and left direction of the drawing) to scan the whole surface of an original D optically. The 2nd mirror unit 9 obtained by uniting the 2nd and 3rd mirrors, 7, 8 is straight moved in the right and left direction at a half speed of the unit 6 and the reflected light from the original D is reflected by the 1st-3rd mirrors 5, 7, 8 and made incident upon the surface of the photosensitive drum 20 through a main lens 20 and the 4th mirror 11 and a slit S. The lamp 4 is also used as a projector. A sensor A is arranged on the side part of the main lens 10 so as to be separated from the main lens 10 by l and inclined by theta angle and the optical axis of the sensor A coincides with the picture center on the original setting board.

Description

[Detailed Description of the Invention] [Industrial Applications] The present invention relates to an automatic image density adjustment device used in a copying machine, which detects the density of a document to be copied, and adjusts the density according to the situation of the density distribution. The present invention relates to an improvement of an automatic image density adjustment device that automatically adjusts image density.

[Prior Art] In a copying machine such as an electrophotographic copying machine, an operator can adjust the amount of exposure to a photoconductor and the amount of development by selecting a dial or a button suitable for the image quality, depending on the nature of the document to be copied. A good copy image is obtained by adjusting the bias voltage value of the device. However, with this type of copying apparatus, in addition to simply pressing the copy start button, the user must also adjust a dial or select a plurality of buttons depending on the density of the original, which is extremely troublesome. Furthermore, since this adjustment and selection relies on human intuition, there is also the drawback that copying is likely to fail.

Because of this, recently automatic image density adjustment devices have appeared that detect the density state of the original to be copied by some method and automatically control the exposure amount or developing bias voltage value, etc. accordingly. became.

The following two systems are available for systems that optically detect document density and control image density.

The first method uses a light source different from the image-forming exposure lamp to illuminate the original, detects the density of the original using the reflected light, and then batch-processes the density information to determine the density. be.

In the second method, an exposure lamp for image formation is also used as a light source for document density detection, and density control is performed by real-time processing.

In the first method, the resolution of the sensor that detects the document density is high, or if a light source other than the U-light lamp is used as a light source for detecting the document density, the cost will increase, and mechanical precision is required to maintain high resolution. requirements and often result in reduced reliability.

In addition, when comparing real-time processing and batch processing when processing density information, there is no difference in performance for documents with a uniform screen such as text documents, but there is no difference in reproducibility for documents with gradation images. It is known that batch processing is better.

Conventionally, there has been no commercially available device that doubles as an exposure lamp for image formation to detect 6 degrees of a document and automatically adjusts the density by batch processing the data obtained by the sensor.

[Problems to be solved by the invention] A dedicated light source is not used to detect the original density, and an exposure lamp is also used for density detection to reduce costs, and batch processing is required to process density information. It is an object of the present invention to provide an automatic image density adjustment device that can perform appropriate density control for both character originals and originals with gradation characteristics.

[Means for solving the problem] An automatic image density adjustment device that achieves the above purpose is capable of determining the density of an original by detecting an appropriate background density; A U-light lamp for image formation is also used as a light source for exposure, and a sensor is provided to receive the light reflected from the exposure lamp on the document surface, and the detection range of the sensor is set to be greater than the range necessary to obtain the background density of the document. This is achieved by an automatic image density adjustment apparatus characterized in that it has a processing system that captures document density information as the sensor output through optical system preliminary scanning, and performs density control in batch processing.

[Embodiment] FIG. 1 is a sectional view of a main part of a copying apparatus showing an embodiment of the present invention. At the top of the copying machine main body 1, there are arranged an original platen 2 made of transparent glass on which an original plate is placed, and a platen cover 3 which covers the original plate after cutting the original plate on the original platen 2.

A first mirror unit 6 including an exposure lamp 4 and a first mirror 5 is provided below the document table 2 and inside the copying machine body 1, and is arranged parallel to the document table 2 and in the left-right direction in the drawing. 07 and 8 are second and third mirrors, respectively, which are mounted so as to be linearly movable and optically scan the entire surface of the document tray, and a second mirror unit 9 in which these are integrated maintains a predetermined optical path length. The first mirror unit moves linearly in the left and right direction at a speed of V2. Of course, the movement of the second mirror unit 9 is the same as that of the first mirror unit. e4@Parallel to the mounting stand 2. The reflected light from the original on the original placing table 2 is reflected by the first mirror 5,
It is reflected by the second mirror 7 and the third mirror 8, further passes through the main lens 10 and the fourth mirror 11, and then enters the photosensitive drum zO as an image support via a slit s provided near the document surface. It has become.

In a copying machine with such an optical system, an exposure lamp 4 is used as a projector.
1, and a sensor A is provided on the side of the main lens 1o. Figure 3 shows the optical path from the top of the copying machine main body.
The sensor A is placed at a position 7 degrees apart from the main lens 1 degree of the main body, and is tilted by θ so that the original axis of the sensor A coincides with the image center on the document table surface.

The detection range by the sensor at this time is as shown in the optical path diagram of FIG. That is, the distance between the sensor A and the document table slit is L, the focal length of the condensing lens provided in front of the photodiode FD, which is the light receiving element, is f1, and the effective diameter is a,
If the sensor chip size of the photodiode PD is b, then the following relationship holds: f detection range = (a - 1-2L tan θ x slit width L = (a + □) x slit width).

The reflected light from the document surface in the detection range received by the photodiode FD is electrically processed to perform density control, and Figure 2 shows an example of a specific circuit configuration. The part surrounded by a dotted line in FIG. 2 is the sensor A in FIG. A photodiode PD receives reflected light from the document surface, and a photocurrent beam obtained by a photodiode FD is converted into a knee voltage by an amplifier A1. Here, the output of the amplifier A1 is 1 horse, which indicates a value proportional to the original density. Then, the voltage is amplified by the amplifier A2, and the output becomes R, R3. This is a value proportional to the original density.

The original density information voltage from sensor A is A/D converted at a certain sampling time and sent to the OPU, where it is stored in the OPU's RAM.
form a histogram within. This is repeated within the range that falls within the minimum original while the optical system shown in FIG. 1 is preliminarily scanning the original.

After the preliminary scan is completed, the optimum density is selected from the formed histogram, and copying is performed at the selected constant density during image formation.

As shown in FIG. 2, the inventor conducted various studies on A/D converting the electrical output proportional to the document density received by the photodiode PD and performing batch processing to select the optimum density. It has been discovered that when the present invention employs a method of detecting the original density using an exposure lamp, it is optimal to detect the background density of the original and select the optimum density based on this.

The present inventor conducted experiments by variously changing the detection range for various manuscripts. Copying machines that perform slit exposure, such as the one shown in Figure 1, generally have a slit width of around 10u, and some copying machines use variable slit width to adjust the amount of exposure onto the photoreceptor, so the optical system Experiments were conducted by varying the light receiving range (detection length) of the photodiode FD in a direction perpendicular to the scanning direction. When the detection length is narrowed,
Perhaps due to the influence of IrL characters and gradation drawings, sampling values tend to appear, and there is a high chance that data different from the background density will be included in the histogram, which often leads to errors in selecting the optimum density. The inventor selected 50 by sampling.
As a result of a test of 0 originals with various detection lengths set at intervals of 10 blades, several judges judged the copy density when the detection length was set to 70 mm or more. The results showed that an appropriate concentration could be selected with a probability of 90% or more.

[Effects of the Invention] As explained above, according to the present invention, the configuration is simple by means of average photometry batch processing, and text originals and F.
An automatic image density R plate device that can obtain proper copies for III formats will be provided.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the main parts of a copying machine showing one embodiment of the present invention. FIG. 2 is an embodiment of a circuit diagram of the present invention, and FIGS. 3 and 4 are optical path diagrams showing the relationship between the sensor of the present invention and a document. 1...Copy machine body 2...Document table 4...Exposure lamp 10...Main lens A...07 Sensor FD...Photodiode Al , AJ! ···Amplifier

Claims (2)

[Claims] (1) An exposure lamp for image formation is also used as a light source for detecting the density of the original, and a sensor is provided to receive light reflected from the exposure lamp on the surface of the original, and the detection range of the sensor is to obtain the background density of the original. An automatic image density adjustment device characterized by having a processing system that takes in document density information as the sensor output through a preliminary scan of an optical system, and performing density control by batch processing. . (2) The range necessary to obtain the above original background density is (70
2. The automatic image density adjustment device according to claim 1, wherein the image density is greater than or equal to (mm x slit width).