JPH08674Y2 - Image density control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to an image density control device for an electrophotographic copying machine, and more particularly to an image density control device of the type that detects the transferred image density and controls the exposure amount or developing bias. Regarding

(Prior Art) In an image forming process of an electrophotographic copying machine which has been generally used, an insulating photoconductor is formed as a photoconductor on a dielectric substrate to have a thickness of 10 to 50 μm. An electrostatic charge is uniformly applied to the surface of the body by corona discharge at about 10 ^-3 C / m ² , and the surface charge of the exposed portion is released by image exposure to form an electrostatic latent image. Next, toner charged to the opposite polarity to the latent image is applied to the latent image to form a toner image, the toner image is transferred onto paper, and the toner image is fixed by heat and pressure. Further, the photosensitive drum after the transfer is charged and erased by an erasing lamp or the like in order to remove the residual potential.

When the copying process as described above is repeated, the residual potential increases due to potential fatigue of the photoconductor, and if an image is formed in that state, the background (background) image becomes dirty. In consideration of the above, the exposure amount or the bias amount of the developing electrode potential is set to a high value in the early stage of operation of the copying machine. That is, the image is slightly lightly exposed in the initial state, and the light-sensitive state becomes optimum as it is used, and when it is further used, the background (background) becomes dirty due to the potential fatigue of the photoconductor as described above.

However, the deterioration of the image formation due to the time-dependent change of the photoconductor due to the photoconductor potential fatigue and the adhesion of dust to the mirror and the reflection plate that form the optical path are various depending on the usage conditions. Although it is detected by a potential sensor or the like, there is a problem that a large error occurs and a stable output cannot be obtained.

(Purpose of the Invention) The present invention has been made in view of the above-mentioned problems, and the exposure fatigue of the photoconductor is determined by comparing the density detection output of the image transferred on the paper and the document density detection output. An object of the present invention is to provide a developing density control device for detecting a (residual potential) and controlling the exposure condition or the bias amount of the developing electrode potential based on the detected output to perform optimum image formation.

In order to achieve the above object, the present invention provides an original density detecting means for detecting the background density of an original with an optical sensor having spectral sensitivity in the peak spectral sensitivity region of the photoconductor, and Exposure control means for controlling the amount of exposure, image density detection means for detecting the density of the image transferred to the copy sheet, background density of the document before copying detected by the document density detection means, and the image density detection means Deterioration of image formation due to an increase in residual potential of the photoconductor is detected by comparing the background density of the image transferred to the copy sheet detected by the detection method, and the exposure amount in the next copying process is based on the detection result. Alternatively, a control means for controlling the bias amount of the developing electrode potential is provided.

Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings.

 FIG. 1 is a view showing an embodiment of the present invention.

In the figure, reference numeral 1 is a document placed on the contact glass 2, and the document 1 is fixed by a pressure plate sheet 4.

The scanner unit 5 includes a light source 6, a slit 7 and an optical mirror 8, and an optical path is formed by the optical mirrors 9 to 13 and the lens 14. On the side plate near the lens 14 and outside the exposure light path, a document density detection sensor 22 composed of a photodiode 21 is provided.

On the other hand, the transfer section is composed of a photoconductor drum 15, a toner developing section 16, and a toner fixing section 17, and further, between the photoconductor 15 and the fixing section 17 through which the copy sheet 20 passes, a light source 23 is provided on the upper part of the passage.
Also, an image density detection sensor 25, which is composed of a photodiode 24, is installed.

When power is turned on and copying is started in the copying apparatus configured as described above, the light source 6 is turned on to obtain the document density information in advance, and the scanner unit 5 performs preliminary scanning to emit light emitted from the light source. The original surface is illuminated, and the reflected light passes through the slit 7 and the optical mirrors 8, 9,
The light is reflected by 10 and enters the photodiode 21 through the front light receiving window of the document density detection sensor 22. The sensitivity characteristic of the sensor with respect to the wavelength has a spectral characteristic in the peak spectral sensitivity region of the photoconductor as shown in FIG. 2, which causes a deviation between the detection value obtained by the sensor and the sensitivity of the photoconductor. This is because it is not generated. The light incident on the photo diode is converted into a voltage by a voltage amplification conversion circuit composed of an amplifier 30, a resistor 31, and a capacitor 32 as shown in FIG. 3, and is input to a CPU provided on a control board (not shown). Then
The original exposure amount or the developing bias amount corresponding to the input signal is output from the CPU to control the original density. The relationship between the detected document density and the document exposure amount or the bias amount is as shown in FIG. 4, and the voltage or the bias amount is output in proportion to the document density.

When the scanner unit returns to the HP home position, it starts scanning for copying, the surface of the document is exposed on the photosensitive drum to form an electrostatic latent image, and the image is developed on the photosensitive member by the toner developing unit 16. It is formed. The image is a paper cassette
The copy paper is transferred to the copy paper fed one by one from 40 or 41 at the transfer timing, and the copy paper on which the image is transferred is fixed in the fixing unit.
Transported to 17.

The image density detection sensor 25 starts detection after the transfer power pack is turned on for 1 to 2 seconds (timer ON), and the light source 23
Lights up, illuminates the image surface, and the reflected light is received by the photodiode 24, converted into a voltage by the equivalent of the voltage amplification conversion circuit described above, and input to the CPU provided on the control board (not shown). . The input data is compared with the document density detection result at the leading edge, and this comparison result is used as the document density detection result in the next document copying process as the detection result of the image formation deterioration due to the residual potential of the photoconductor. It is stored in a memory (not shown) for correction control.

FIG. 5 is a flow chart for controlling the exposure amount of the document or the developing bias amount based on the document density information. When the copying apparatus is started, first, it is judged whether the document density is detected or not, and the mode is the mode for detecting the document density. For example, the threshold value of a sensor that detects the illuminance of the light source that illuminates the document and the reflected light is temporarily stored in a buffer, and then the background density of the document is measured. Next, the image density control unit is controlled by configuring a loop of the B register so that the image density when the document is transferred is optimized, and when the scanner unit finishes the preliminary scanning and returns to the home position, the document exposure is performed. , Latent image formation, paper feed, and transfer. Upon completion of a series of copying steps, image data information is detected and used for image density control in the next copying step. Further, when the same original is copied many times, the image density state of the copied transfer paper is detected, and the loop of the C register is controlled so as to always hold the optimum value.

Thus, in order to detect the deterioration of image formation due to an increase in the residual potential of the photoconductor, the state of the original document before copying and the state of the copied copy sheet after copying are compared, and the result of this comparison is used to Since a defect in image formation due to a change in the potential state due to the residual potential of the body or a temperature change and a decrease in the reflectance of the reflection plate and the mirror on the optical path is compensated, a high quality image copy can be obtained.

(Effects of the Invention) As described above, the present invention compares the background density of a document before copying detected by the document density detection means with the background density of the image transferred to the copy paper detected by the image density detection means. By doing so, deterioration of image formation due to an increase in residual potential of the photoconductor is detected, and the exposure amount or the bias amount of the developing electrode potential in the next copying process is controlled based on the detection result, so that high quality is always maintained. Image copies can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing the spectral sensitivity of an optical sensor used in the present invention, FIG. 3 is a diagram showing a voltage amplification conversion circuit, and FIG. FIG. 5 is a graph showing the relationship between document density and document exposure amount or bias amount;
The figure is a comparison flowchart of the image density and the image density detection sensor. 1 ... manuscript, 2 ... contact glass, 4 ... pressure plate, 5
...... Scanner unit, 6, 23 ...... Light source, 7 ...... Slit, 8 to 13 ...... Optical mirror, 14 ...... Lens, 15 ......
Photoreceptor, 16 ... Toner developing section, 17 ... Toner fixing section, 20
…… Copy paper, 21, 24 …… Photodiode, 22 …… Original density detection sensor, 25 …… Image density detection sensor, 30 ……
Amplifier, 31 ... Resistor, 32 ... Capacitor, 40, 41 ... Paper cassette

Claims (1)

[Scope of utility model registration request] 1. A document density detecting unit for detecting a background density of a document by an optical sensor having a spectral sensitivity in a peak spectral sensitivity region of a photoconductor, an exposure control unit for controlling an exposure amount to the photoconductor, and a copy sheet. Image density detecting means for detecting the density of the image transferred to the background, the background density of the original before copying detected by the original density detecting means and the background of the image transferred to the copy paper detected by the image density detecting means Control for detecting deterioration of image formation due to an increase in residual potential of the photoconductor and controlling the exposure amount or the bias amount of the developing electrode potential in the next copying step based on the detection result. And an image density control device.