JPS62169182A - Picture density adjusting method for copying machine or the like - Google Patents

Abstract

PURPOSE:To prevent contamination of an original density detector and uncontrollable condition of an exposure lamp due to voltage fluctuation, by detecting the white color density of a standard white plate by means of a standard density detector at a home position and controlling the picture forming condition by correcting the detecting output of the original density detector by using the detected white color density as a reference. CONSTITUTION:At the initial state, an image formation corresponding section 26 by an exposure lamp 8 is positioned to a standard white plate 4 outside an original 1 and reflecting rays of light from the white plate 4 are photodetected by a standard density detector 27 provided between the 2nd and 3rd mirrors 12 and 13 in their optical axes. The standard white color density information detected by the detector 27 is fetched by a CPU 30 after AD-conversion. Following the exposing-scanning operations of an exposure optical system 6, an original density detector 24 detects the density of an original and the density information of the detector 24 is fetched by the CPU 30. The CPU 30 calculates (original density information)/(white color density information) and the original density information is corrected based on the detected density of the standard white plate 4.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an image density adjustment method in a copying machine or the like.

Conventional technology Generally, in image forming apparatuses such as copying machines.

In order to correct the exposure light amount, developing bias voltage, etc. according to the density (background density) of the original, the density of the original is detected. Such a function is called an AE function. Here, this method is disclosed in Japanese Unexamined Patent Publication No. 58-2
As shown in Japanese Patent No. 14144, there is a scanner in which a document density detector is mounted on a scanner, and the document density is detected by this detector prior to normal slit exposure.

According to this, automatic density adjustment can be performed without performing pre-scanning (scanning exclusively for detection performed before scanning a document to form a latent image for copying). In this method, when the scanner is located at the home position, the detector is also located at a position away from the original, so that the density of the original cannot be detected for a certain period after the scanner starts running up.

In other words, the density detection area of the document is small, making it difficult to accurately control the density.

However, among such devices without pre-scanning, a device with a larger document density detection area has been proposed by the present applicant in Japanese Patent Application No. 59-230775. This is done by placing the document density detector at a position that precedes the position of the image-forming part of the document by the scanner in the scanning direction, and also by placing the document density detector at a position that precedes the position of the image-forming part of the document by the scanner. The detector is set to face the original. According to this, the degree of improvisation can be detected from the time the scanner starts scanning.

However, in this method, if dirt occurs on the document density detector, the detection output decreases due to the dirt. In this case, it is not possible to correct this decrease in output, so the AE function cannot necessarily be said to be accurate. Furthermore, when changing the exposure lamp voltage, it is necessary to adjust the sensitivity for blank paper, but there is no standard for this. Furthermore, even though it is called AE, there are demands from users to make it brighter or darker depending on their preference, so some models are equipped with adjustment keys, but these cannot be adjusted by changing the lamp light intensity.

Usually, it is limited to control of the developing bias voltage.

Purpose The present invention was made in view of the above points, and it is possible to prevent poor control due to dirt on the document density detector or voltage fluctuations of the exposure lamp in a device that does not require pre-scanning, and to achieve more accurate density. An object of the present invention is to provide a method for adjusting image density in a copying machine, etc., which can be controlled.

Structure In order to achieve the above object, the present invention includes an exposure optical system that exposes and scans an original, detects the original density with an original density detector, and automatically adjusts the exposure light amount, developing bias voltage, etc. based on the detection signal. In the device for setting image forming conditions, the document density detector is mounted on the exposure optical system at a position preceding the image forming portion of the document by the exposure optical system in the scanning direction; The document density detector is set to face the document when the system is located at the home position and the image formation corresponding section does not face the document, and the exposure optical system is set at the home position and the image formation corresponding section is set so as to face the document. A standard white plate is provided at a position exposed by this image-forming corresponding section when the plate does not face a document, and is arranged so as to cross the optical axis of the exposure optical system when the exposure optical system is located at the home position. A standard density detector is provided to detect the amount of light reflected from the white plate, and the image forming conditions are controlled by correcting the density detected by the document density detector using the density detected by the standard density detector as a reference. That is.

Hereinafter, one embodiment of the present invention will be described based on the drawings. First, a reference scale 3 is provided at one end of the contact glass 2 on which the original 1 is set, and a standard white plate 4 is provided on the bottom surface of the reference scale 3. An exposure optical system 6 is provided that performs exposure scanning on the original 1 to form a latent image on the photoreceptor 5. This exposure optical system 6 is first provided with a first scanner 7 . This first scanner 7 is composed of an exposure lamp (for example, a halogen lamp) 8, a reflector 9, and a first mirror 10, and scans from a home position shown by a solid line in FIG. 2 to a return position shown by a chain line. Then, the original l is exposed. Further, a second scanner 11 that scans in the same direction at 1/2 the speed of the first scanner 7 is provided. This second scanner 11 has second and third mirrors 12 and 13.
are integrally supported by a bracket 14. A lens 15. which guides the light from the third mirror 13 onto the photoreceptor 5. A fourth mirror 16 and a filter 17 are provided.

Here, the photoreceptor 5 is uniformly charged by a charger 18, the charging width is regulated by an eraser 19, and an electrostatic latent image is formed by being imaged by an exposure optical system 6. Then, the image is developed by the developing sleeve 2o and visualized, and transferred onto the transfer paper by the action of the transfer charger 21. Thereafter, the photoreceptor 5 is cleaned by the cleaning device 22 and the charge is removed by the charge removal lamp 23.

The first scanner 7 is equipped with a document density detector 24 for detecting the density of the document 1. The original density detector 24 doubles as the exposure lamp 8 as a light source, and detects the reflected light from the original l illuminated through the slit 9a formed in the reflective plate 9 as a detection light 2.
5 for light reception and detection. Here, assuming that the image forming corresponding section by the first scanner 7 is 26, the document density detector 24 is arranged at a position preceding the image forming corresponding section 26 in the scanning direction. Furthermore, at the home position of the first scanner 7 as shown in FIG.
Although it is possible to face the detection light 25 and receive the detection light 25, in this state, the imaging corresponding section 26 is set in a positional relationship that illuminates the outside of the document 1, specifically, the standard white plate 4. A hole is formed in a part of the bracket 14 of the second scanner 11, and when the second scanner 11 is located at the home position, the second and third mirrors 12.
A standard density detector 27 is provided which projects between the second and third mirrors 12 and 13 and receives reflected light from the standard white plate 4 that crosses the optical axis between the second and third mirrors 12 and 13. More specifically, the standard density detector 27 is supported upward by a support member 28 fixed to the bottom plate or side plate of the exposure optical system 6. In other words, this standard density detector 27 has the same configuration as the original density detector 24 and is supported in the same upward position. Standard concentration detector 2
7 is a fixed position.

The detection signals from these detectors 24 and 27 are A
The signal is input to the CPtJ 30 via the /D converter 29. A VB power source 31 is connected to the CPU 30 in order to control the developing bias power source V of the developing sleeve 20 as an image forming condition.

In such a configuration, the density of the original l is detected by the original density detector 24. Here, the first Sukiyana 7
When the camera is located at the home position, the imaging corresponding section 26 does not face the original 1, but the detection light 25 has already been irradiated onto the original 1 and entered the original density detector 24, so pre-scanning is not performed. In parallel with scanning for normal copying, the document density can be detected from the home position in a wide detection area without having to carry out scanning. Based on the detection signal from the original density detector 24, the CPU 30 controls the VB power supply 31 to set the developing bias voltage to an appropriate value. In this embodiment, prior to detecting the original density, the white density of the standard white plate 4 is detected by the standard density detector 27 while the exposure optical system 6 is located at the home position. That is, in the initial state as shown in FIG. The light is received and detected by a standard density detector 27 located between the mirrors 12 and 13 in the front axis thereof. Then, the reference white density information detected by the standard density detector 27 is A/D converted and then taken into the CPU 30. Then, as the exposure optical system 6 performs the exposure scanning operation, the original density detector 24 detects the original density as described above, and the density information is taken into the CPU 30. Then, the CPU 30 performs the calculation (original density information)/(white density information), and the original density information is corrected based on the detected density of the standard white plate 4. Then, V and the power supply 31 are controlled based on this correction value.

Considering the states of the original density detector 24 and the standard density detector 27, both are facing upward, and it is considered that the degree of contamination is approximately the same, and the decrease in sensitivity is also approximately the same. Under such conditions, in this embodiment, the detection output from the original density detector 24 is corrected based on the output from the standard density detector 27, which always detects the white density of the standard white plate 4. Therefore, even if the original density detector 24 is contaminated, the original density can be properly detected. As a result, accurate AE control can be performed over a long period of time, and stable copies can be obtained. Further, this can be handled in the same way even when the light amount (voltage) of the exposure lamp 8 changes, and the detection output of the document density detector 24 is appropriately corrected based on the output of the standard density detector 27.

As a result, even if the voltage of the exposure lamp 8 is adjusted, the A
E Sensitivity adjustment becomes less troublesome. That is, A.E.
In terms of functions, brighter or darker generally refers to the appearance of low contrast, and the method of adjusting the low contrast by largely changing the light amount of the exposure lamp 8 is better than the method of changing the developing bias voltage Va. is also preferable. This is because, when the developing bias voltage V is increased, the density of the solid area decreases, and the trailing edge image of the halftone solid area is likely to be lost. Therefore, it is possible to easily cope with the case where the user manually changes the brightness or darkness setting of the AE function to vary the amount of lamp light.

Effects As described above, the present invention detects the white density of the a whitening plate using the standard density detector at the home position position, corrects the detection output of the original density detector based on this density, and adjusts the image forming conditions. Even if the original density detector is dirty or the voltage of the exposure lamp changes, the detection output from the original density detector will be corrected to the appropriate value, so it will remain stable over a long period of time. Do A
In this case, the effect of enlarging the detection area without pre-scanning due to the arrangement of the document density detector etc. can be maintained as it is.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention, and FIG. 1 is a side view showing an enlarged main part at the home position, and FIG. 2 is a schematic side view showing the overall configuration. DESCRIPTION OF SYMBOLS 1... Original, 4... Standard white plate, 6... Exposure optical system, 24... Original density detector, 26... Imaging corresponding part, 27... Standard density detector

Claims (1)

[Claims] In an apparatus that includes an exposure optical system that performs exposure scanning of an original, detects the original density with an original density detector, and automatically sets image forming conditions such as exposure light amount and developing bias voltage based on the detection signal, the original density is A detector is mounted on the exposure optical system at a position that precedes in the scanning direction a position corresponding to the image formation of the document by the exposure optical system, and the exposure optical system is located at the home position and corresponds to the image formation. The document density detector is set to face the document when the image forming section does not face the document, and when the exposure optical system is located at the home position and the image forming corresponding section does not face the document, the image forming corresponding section is set to face the document. A standard white plate is provided at a position to be exposed, and when the exposure optical system is located at a home position, the standard density detection is arranged to cross the optical axis of the exposure optical system and detects the amount of reflected light from the standard white plate. A method for adjusting an image density in a copying machine or the like, characterized in that the density detected by the document density detector is corrected based on the density detected by the standard density detector, and image forming conditions are controlled.