JPS63103267A - Control method for picture density of copying machine - Google Patents

Abstract

PURPOSE:To always obtain copies free from photographic fog and of high picture quality even in case of an original small in size by comparing the original density, which is read on the average in the slit lengthwise direction, with a reference value of each original size to control a copy parameter. CONSTITUTION:The reflected light from an original 1 is led onto a photosensitive body 10 from a slit 7 by an optical system, and an original image is formed to form an electrostatic latent image on the surface. Plural original size detectors S1 and S2 are provided apart from an original density detector 15, which receives the reflected light from the original 1 on the average in the lengthwise direction of the slit 7 to detect the density, in the lengthwise direction of the slit 7. The reference value preliminarily set for each original size is selected in accordance with the detected original size and is compared with the original density value, and the copy parameter is controlled by this control signal. Thus, copy pictures free from photographic fog and of high quality are obtained even if the original cannot cover all of the slit in the lengthwise direction.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to an image density control method for a copying machine in which copying parameters are controlled based on reference values set for each document size and the amount of light reflected from the document.

2. Description of the Related Art In a conventional electrophotographic copying machine, a light-receiving element is provided near a lens that focuses reflected light from an original onto a photoreceptor, and reads a portion of one reflected light approximately evenly in the longitudinal direction of an exposure slit. A copying machine that can always obtain fog-free copied images by comparing the value detected by this light-receiving element with nine preset reference values and controlling copying parameters according to the deviation. The following image density control method is known. For example, Japanese Patent Application Laid-Open No. 59-7354.

Problems to be Solved by the Invention In the conventional image density control method described above, the reflected light from one document is read almost evenly in the longitudinal direction of the exposure slit.
If the document is placed over the entire length of the exposure slit, highly accurate reading can be performed, but if the size of the document is small and the document is not placed over the entire length of the exposure slit, the document must be placed on the platen. The light reflected from the bottom surface of the platen cover that is pressed upwards and the white part of the bottom surface of the conveyor belt provided on the automatic document feeder also enters the light receiving element, so highly accurate reading is affected by these factors. As a result, in the case of small-sized originals, there were problems such as fogging and poor image quality.

This invention was made for the purpose of improving the above-mentioned problems.

Means and Effects for Solving the Problems In an apparatus in which reflected light from an original to be copied is directed onto a photoreceptor through a slit and an optical system to form an electrostatic latent image on the photoreceptor, the original is An original density detection means for detecting the density of the original by receiving reflected light from the slit almost evenly in the longitudinal direction of the slit, and an original size detection means for detecting the size of the original are provided. A reference value set in advance for each original size is selected from the selected original size, and a control signal is obtained by comparing this reference value with the original density value detected by the original density detection means, and the copying parameters are controlled by this control signal. An image density control method for a copying machine that makes it possible to obtain a high-quality copy image without fogging even if the original is small in size and cannot cover the entire longitudinal direction of the slit.

Example An embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a schematic configuration of an electrophotographic copying machine, in which a conveyor belt 3 of an automatic document feeder is provided on a platen 2 on which a document 1 to be copied is placed.

A document tray 4 is installed on the document input side of the conveyor belt 3, and 91 documents 1 loaded on the document tray 4 are transferred to the document feed roll 5, and 91 sheets are placed on the conveyor belt 3 and the upper surface of the platen 2. After being fed out during the interval, the conveyor belt 3 feeds the sheet to a predetermined position along the upper surface of the shear ten 2.

Further, a light source 6 is provided below the platen 2 for exposing and scanning the original 1 on the platen 2 while moving along the platen 2, and the light reflected from the original 1 is transmitted through a slit 7.
The document is guided onto the photoreceptor 10 by a plurality of reflective lenses ε and an optical system such as a lens 9, and an image of the document is formed on the photoreceptor 10, so that an electrostatic latent image is formed on the surface of the photoreceptor 10. It has become. After this electrostatic latent image Vi is developed into a toner image by a developing device 11, it is transferred onto a sheet of paper 13 by a transfer device 2. Toner e on top! is becoming established.

On the other hand, the exit side of the lens 9 that forms the original image onto the photoreceptor 10 receives the reflected light from the original 1 almost evenly in the longitudinal direction of the slit 7, and detects the density of the original 1. A plurality of document size detectors S, . . . St, for example, two document size detectors S, . The document size detector S1°S is set as follows so that it can detect all document sizes.

In other words, platen 2 of a copying machine capable of copying up to A3 originals.
There are five possible placements on the soil as shown in the #'i third tooth.

When an A5 document is placed vertically, 0-C-U-N,! : When a B5 original is placed vertically, it becomes 0-D-T-M.

In addition, if an A5 original is placed horizontally or an A4 original is placed vertically, the position will be 0-person-8-L or 0-E-1, and B
If you place 4 originals vertically or B5 originals horizontally,
0-F-P- or 0-B-Q-, 0- if A3 original is placed vertically or A4 original is placed horizontally 11
G-H-J or 0-C-I-J.

Therefore, one document size detector S, and the slit longitudinal direction M,! :N, and the other document size detector 8
．． It is especially advantageous to set the signal between N and 0, and each time a document 1 is fed onto the platen 2 by the conveyor belt 3, a signal as shown in FIG. 4 is sent to each document size detector S according to the document size. ,,S, to the central processing bag #20, the density signal of the original 1 detected by the primary original density detector 15 is A/D converted by the human/D converter +8, and then sent to the central processing bag #20.
It is a trap to be input to each.

The central processing bag WL20 performs image density control as follows.

Next, the control will be explained with reference to chart 70 shown as the fifth factor. When the copy start button is pressed in step (2), the process proceeds to step (2) where the automatic document feeder starts conveying the document 1.

In step 2' of another flow, the size of the original 1 carried onto the platen 2 is detected by two original size detectors S, , S, and sent to one central processing unit 20. Central processing bag! it 20 digits step ■' original size detector 16
．． The size of the document 1 is determined based on the cross signal inputted from 17, and nine reference values previously set for each document size are selected from memory 25.

On the other hand, when the loading of the original 1 onto the platen 2 is completed in step 2, exposure scanning of the original 1 is started in step Φ, and the reflected light from the original 1 is directed approximately in the longitudinal direction of the slit 7 in step Φ'. The document density detector 15 reads and detects the document density on average, and outputs it to the central processing bag f120.

The central processing unit 20 compares the original density signal inputted from the original density detector 17 with the reference value for each original size selected in step ■', calculates a deviation, and then performs step (■).
′ calculates the control value based on the above deviation. The obtained control value is D/A converted by a D/A converter 21 and then outputted to, for example, a power source 22 that supplies power to the light source 6, a developing bias power source 23 to a charger power source 24, etc., and is outputted to the N light amount. Copying parameters such as development bias and charge amount are controlled. After that, the process proceeds to step ■, where copying is performed.
Even if the original size changes, the copy parameter is controlled by a value corrected according to the original size, so that clear copied images without fogging can be obtained even with small originals.

In the above embodiment, the document size detectors S, 8. are installed on the document import side. The document size is detected by the method, but document size detectors S, S, are provided below the platen 2, or the reference value is selected based on the document size signal input from the operation panel. You can.

Effects of the Invention As described in detail above, the present invention can be applied to originals to be copied.
The document density read almost averagely in the longitudinal direction of the slit,
The original size detected by the original size detection means is compared with a reference value for each original size selected to obtain a control value, and the copying parameters are controlled according to this control value. Even if the original is small and will not be blurred, the density of the original can be detected accurately, making it possible to always obtain high-quality copies without fogging.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, in which Fig. 1 is a schematic diagram of a copying machine, Fig. 2 is a block diagram of a control system, and Fig. 3 shows originals of various sizes placed on a platen. FIG. 4 is a waveform diagram of a signal detected by the document size detector, and FIG. 5 is a flowchart showing the operation. 1 is a document, 7 is a slit, and 10 is a photoreceptor.

Claims (1)

[Claims] In a device that guides the reflected light from the original 1 to be copied onto the photoreceptor 10 through a slit 7 and an optical system to form an electrostatic latent image on the photoreceptor 10, the reflected light from the original 1 to be copied is , a document density detection means for detecting the density of the document 1 by substantially average reading in the longitudinal direction of the slit 7;
A document size detection means for detecting the size of the document 1 to be copied is provided, a reference value set in advance for each document size is selected from the document size detected by the document size detection means, and this reference value and the above-mentioned reference value are selected. An image density control method for a copying machine, comprising: comparing original density values detected by original density detection means to obtain a control value; and controlling copying parameters using the control value.