JPS6148876A - Image forming device - Google Patents

Abstract

PURPOSE:To form the best image all the time regardless of the kind of an original by detecting image density on the original surface at a position which precedes an image exposure position on the original surface in a scanning direction by length corresponding to the distance from an image formation position on a recording body to a development position on the original surface, and controlling a developing bias in real time. CONSTITUTION:A developing device 7 is supplied with an AC voltage from a high voltage unit 200 as the developing bias. A control circuit 100 controls the high-voltage unit 200 according to the output of a photosensor 8 which detects the image density on the original surface to vary the DC component of the AC voltage applied to the developing device 7. This photosensor 8 detects the image density on the original surface at the position D which precedes the exposure position C on the original surface in the scanning direction X by the length L corresponding to the distance L from the image formation position A on the photosensitive drum 1 to the development position B to control the developing bias on a real-time basis.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an image forming apparatus having an automatic density adjustment function.

Prior Art In a conventional image forming apparatus such as a copying machine, in order to adjust the transferred image density to an appropriate amount, adjust the volume 300 in the operation section as shown in Fig. i1 and change the variable resistor VRI shown in Fig. 2. It was common practice to obtain an appropriate image by changing the lighting voltage of the exposure lamp LAI.

However, in such a conventional method, there are many cases in which several sheets of transfer paper are wasted before obtaining a proper image, and there is a drawback that the amount of transfer paper used increases beyond the required number.

OBJECTS The present invention has been made in view of the above points, and an object of the present invention is to provide an image forming apparatus that eliminates the above drawbacks and is capable of always forming optimal images regardless of the type of document.

A further object of the present invention is to provide an image forming apparatus capable of performing density control that follows changes in image density on the same document surface.

Example The present invention will be described in detail below with reference to the drawings.

FIG. 3 is a diagram showing a schematic configuration of a copying apparatus which is an embodiment of an image forming apparatus to which the present invention is applied.

The photosensitive tram 1 is electrostatically uniformized in advance by a pre-static eliminator 2, and then smeared uniformly in a positive or negative direction by a static eliminator 3.The original placed on the original platen 4 is It moves and scans in the direction of the arrow X, and during this time it is irradiated by the exposure lamp 5, and the reflected light is imaged on the photosensitive drum l at the imaging position A by the short focus lens array 6, and the image is formed on the photosensitive drum l according to the original. An electrostatic latent image is formed.This electrostatic latent image is developed with toner by the developing device 7 at the developing position B, becomes visible, and is transferred to a sheet fed from a paper feeding means (not shown)1?
It is transferred by electric appliance 9. This transferred image is heated and fixed by the fixing device 10.

The developing device 7 is supplied with external pressure as a developing bias from a high pressure unit 200. Further, 8 is a photosensor for detecting an image ffai1 degree on the document surface, and has a photodiode 101 (FIG. 4). The output is input to a control circuit 100 described later. The control circuit 100 controls the high voltage unit 200 according to the output from the photosensor 8, and changes the DC component of the AC voltage applied to the developing device 7.

This photosensor 8 is placed on the document surface in front of the document surface from the exposure position C on the document surface in the scanning direction The structure is such that the image density at the position is detected and the developing bias is controlled in real time.

FIG. 4 is a block circuit diagram showing the control circuit of FIG. 3 and its surroundings.

The optical detection current of the photodiode 101 is transferred to the operational amplifier 10.
2 performs current-voltage conversion. The volume 104 is adjusted so that the output level becomes a predetermined level, for example 8V, when a white original is placed on the original glass. The Zener diode 105 limits the non-inverting input of the operational amplifier 103 through the diode 106 at the Zener level for dark documents where the amount of incident light is below a certain level. It means to apply a controlled up mitzah. operational amplifier 103
Then, the variable range of the output level is adjusted using the volume 107. As shown later, this is a high voltage (HVT)
) This is a means for adjusting the variable width of the developing bias DC component corresponding to the original density of 200, and by this means, it is possible to extract clear copied images from ordinary auxiliary character originals to newspapers without overlapping the background. The volume 108 is for adjusting the development bias for originals with auxiliary characters, and should be set to a level that does not cause the characters to be skipped. It is mitzah.

Next, FIG. 5 shows the input/output characteristics of the high voltage unit (HVT) 200 according to the present invention. Output D for control input voltage
The C component has linearity.

The larger the bias value, the thinner the copied image density becomes.

Therefore, in the circuit diagram shown in 41Δ, when the original density is high, the photocurrent of the photodiode 101 is small and the output level of the amplifier 102 is small, so the output of the amplifier 103 is also small, and the developing bias DC value from the high voltage unit 200 is It becomes larger and controls the direction in which the image is thrown. On the other hand, in the case of a thin original with text, the developing bias DC value becomes small, and control is performed so that the characters, etc. do not fly out.

The contents of the present invention can be summarized in an easy-to-understand manner as shown in FIG. In other words, for originals with various densities from auxiliary character originals to newspapers, the developing bias DC value is controlled linearly by j + JI with respect to 0 degrees of reflection, and this inclination and the developing bias DC level for auxiliary character originals are set to an appropriate amount. Then, an appropriate copy density can be obtained without being affected by variations in drum sensitivity or the like.

In the present invention, in order to control the developing bias in real time, the light incident on the photodiode, which is a light detection element, is focused by a distance of 21'L from the image exposure stop position, that is, by a short focus lens array on the drum. The reflected light is reflected forward in the scanning direction by a length corresponding to the distance from the image position 16 to the development position.

By doing this, the density information of the document currently being developed is inputted to the photo sensor in real time, so that density control that can handle shading within a single document can be realized.

However, it is necessary to scan the document by the document table by at least the above-mentioned distance ML after the document reaches the image exposure position. Alternatively, if the above method is difficult due to the mechanical structure, it is effective to control by fixing the developing bias 6 (i) of the developing area remaining at the developing bias value at the end of scanning.

In this embodiment, a copying apparatus with a movable document table is used as an example, but the present invention can also be applied to a copying apparatus with a movable optical system. It can also be applied to a device that copies a document while it is flowing.

According to the present invention, as described in "Effects" 2, optimal image reproduction corresponding to the density of the original is possible, and since the development bias control is real-time control within the same original, it is possible to reproduce images within the same original. This makes it possible to control the image quality by following changes in the density of the image, eliminates the waste of transfer paper due to copy mistakes, and realizes an efficient copying function.

[Brief explanation of the drawing]

Fig. 1 is a plan view showing the operation section of a conventional copying machine, f52.
The figure is a block circuit diagram showing the configuration of the lambreculator.
FIG. 3 is a diagram showing a schematic configuration of a copying machine to which the present invention is applied, FIG. 4 is a block circuit diagram showing the control circuit and its surroundings in FIG. 3, and FIG. 5 is a diagram showing input/output characteristics of the high voltage unit. , FIG. 6 is a characteristic diagram showing the relationship between the amount of light reflected from the original and the DC component of the developing bias. ■---Photosensitive drum, 5---one exposure lamp. 7---Developer, 8---Photo sensor, i o
o---- one control circuit, l O1----; y odd diode, 200---- one high voltage unit.

Claims (1)

[Claims] In an image forming apparatus that detects the image density on the document surface and controls the development bias according to the detected value, the image is exposed on the document surface for a length corresponding to the distance from the image formation position on the recording medium to the development position. An image forming apparatus characterized by detecting an image density on a document surface located in front of a position in a scanning direction, and controlling the developing bias in real time based on the detected value.