JPS623264A - Copying device - Google Patents

Abstract

PURPOSE:To adjust development density to a proper value automatically by providing a selecting circuit which selects and outputs only a signal corresponding to an original image with the lowest density among signals outputted by respective detecting elements at the same time and a control means which controls development density by using the signal that the selecting circuit outputs. CONSTITUTION:When an original 1 is replaced with an original having a gray background part, detecting elements s1-s4 detect it and their outputs e1-e4 decrease in maximum value. The density variation of the background part is detected as a signal voltage e0, which is compared by a comparator 23 in a control circuit with a reference voltage es to increase the quantity of exposure of a light source 3 immediately, thereby performing compensation so that the background part has specific development density. Consequently, even if an original has extremely deviating density variation, the density of its background part is detected securely and the quantity of exposure is adjusted automatically so as to obtain proper background density.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application This invention relates to a copying apparatus, and more particularly to a copying apparatus in which development density is automatically adjusted in accordance with the density of a document.

(B) Conventional technology In order to detect the density of the original image, a conventional copying apparatus of this type is equipped with a detection element in the optical path narrowed by a lens, and the average width of the exposed original image is There are devices that detect the density and use the detection signal to control the developed density (for example, Japanese Patent Laid-Open No. 59-1576).
No. 69).

(C) Problems to be Solved by the Invention In general, in order to improve the contrast in a copying machine, even if the background part is not white (colored), when copying the original, , it is preferable that the background be developed so that it becomes a white background.

By the way, in the above-mentioned conventional technology, the average density in the width direction of the original image is detected, so if there is a locally uneven black image on the original, the background density is not uniform. However, there was a problem in that the detected average density changed and uneven development occurred on the copies.

This invention was made in view of these circumstances,
An object of the present invention is to provide a copying apparatus that can reliably detect the density of a background portion of a document and automatically adjust the development density appropriately.

(d) Means for Solving the Problems The copying apparatus of the present invention guides an original image exposed by an exposure light source to a photoreceptor to form an electrostatic latent image, and converts the electrostatic latent image into a toner image by a developing device. A copying apparatus configured to visualize an original m-image, including a plurality of detection elements that output signals corresponding to the shading of an original m-image, and further comprising: an original having the lowest density among the signals simultaneously output by each of the detection elements; The present invention is characterized by comprising a selection circuit that selects and outputs only a signal corresponding to an image, and a control means that controls development density using the signal output from the selection circuit.

The detection element corresponds to the width direction and the longitudinal direction of the document,
It is preferable that a plurality of cylinders are arranged at predetermined intervals.

Further, the control means controls the developed density by changing the exposure amount of the exposure light source or the developing bias voltage of the developing device.

(E) Function The above-mentioned detection element simultaneously detects the shading of the image of the original from multiple locations, selects the lowest density part, detects that density as the density of the background part, and selects the part with the lowest density. The development density is determined based on. Therefore, even if the white or black portions of the original image are extremely biased, the background portion is always detected reliably, and uneven development due to erroneous density detection does not occur.

(f) Examples Hereinafter, the present invention will be described in detail based on examples shown in the drawings. Note that this invention is not limited to this.

FIG. 1 is an explanatory diagram showing a copying apparatus according to an embodiment of the present invention. Transparent document table (2) with document (1) placed on it
moves horizontally for slit exposure.

The light from the light source (3) is irradiated onto the original (1) via the reflecting mirror (3a) and the mounting table ('2J), and the original image follows the optical path (4) and passes through the reflecting mirrors +51, +6), +7
The light passes through a lens (8), is further reflected by a reflecting mirror (9), and is imaged onto a cylindrical photoreceptor. Photoreceptor 0
0) is rotationally driven in the direction of the arrow (1υ).The photoreceptor (
) is charged by the charging corona discharger Cl21, and an electrostatic latent image corresponding to the original image is formed in the exposure area 03. This electrostatic latent image is visualized into a toner image by the magnetic brush developing device.

This developing device (14) includes a developing sleeve (g) that rotates in the direction shown by arrow 05) and a stationary permanent magnet G? to visualize the electrostatic latent image formed on the photoreceptor ω). ′)
The toner is conveyed in the direction of arrow (15) by a magnetic brush formed by the color of the developing sleeve and the G force of a permanent magnet, and the electrostatic latent image formed on the photoreceptor 001 is visualized by the toner. do.

The toner image on the photoreceptor ω) is transferred using a corona discharger (incorporated) for transfer.
The image is transferred from the photoreceptor (K) to the copy paper opening.

A charge-eliminating corona discharger (2) is arranged downstream of the transfer corona discharger (2) in the copy paper conveyance direction, and the copy paper B is peeled off from the photoconductor 00) by the movement of the charge-eliminating corona discharger (2). , and transported to a fixing device (not shown).

FIGS. 2 and 3 are explanatory diagrams showing the installation positions of the detection elements (Sl) to (S4), each of which is installed at a position to receive reflected light from the original (1), and
``The detection element (S2) is located approximately in the center of the document placement position, the detection element (sl) (s3) is located on both sides of the detection element (S2), and the detection element (S4) is located behind the detection element (S2). Note that in this embodiment, a phototransistor is used as the detection element.

Figure 4 shows the detection element (phototransistor) (Sl) ~
An example of the selection circuit &I+ which selects and outputs the signal of the detection element with the largest number of reception times from among the signals outputted by (S4) is shown. (A1) to (A4) are operational amplifiers, (R1)
~ (R4) are resistors that are connected in series with the detection elements (sl) ~ (B4) and output signal voltages (el) ~ (B4), (
D1) to (B4) are diodes for selectively outputting only the maximum signal (eo) from each operational amplifier (A1) to (A4), and (Ro) is an output stabilizing resistor.

FIG. 5 is a block diagram showing the control circuit of this embodiment. When the light from the light Ill (31) is irradiated onto the original (1), the reflected light is detected by the detection elements (sl) to (B4) and input to the signal selection circuit 31), and its output (
eo) is compared with a reference voltage (es) by a comparator (c). The output of the comparator (c) is input to the voltage regulator (c), and the output of the voltage regulator (to) adjusts the light ω of the light source (3).
is adjusted to the set value.

The operation of this embodiment with such a configuration will be explained in the sixth section.
This will be explained in more detail with reference to the drawings and FIG. 7. The manuscript (1) in Figure 6 is a black image (B1) with a white background.
(B2). When this original m (1) is moved in the direction of the arrow and exposed and copied, the detection element (Sl)
~(B4) are arranged as shown in Figure 6, so
The signal voltage (el) of the selection circuit (21) shown in FIG.
(B4) changes corresponding to images (Sl) and (B2), respectively, and the changes with respect to time (1) are as shown in FIG. In other words, the signal voltage (el) (B3) is the image (
B2) decreases during the period in which it is detected, and the signal voltage (B2
) (B4) decreases during the period in which images (B1) and (B2) are detected. However, due to the relative relationship of the arrangement positions of the detection elements, the signal (eO) whose maximum value is selected is the seventh one.
As shown in the figure, the maximum value is always shown, and it is thus detected that the background of the document 11) is white. This signal (eO) is input to the comparator shown in FIG.
s) and input to the voltage regulator 24], the voltage regulator &41 changes the voltage supplied to the light source (3) so that the signal voltage (eO) almost matches the reference voltage (es), Since the exposure amount is adjusted, the background area is adjusted to the set development density.

Furthermore, if the original i (1) shown in Fig. 6 is replaced with one having a gray background, the detection element (Sl)
~(B4) detects it and outputs each output (el)
~(B4), the maximum value decreases as shown by the broken line in FIG. However, the density change in the background portion is detected as a signal voltage (eO) shown by a broken line, and is compared with a reference voltage (es) by a comparator (to) in the control circuit shown in FIG. Immediately, the exposure amount of the light source (3) is increased to compensate for the background portion to have a predetermined developed density.

In this way, even if the original has extremely uneven density changes, the density of the background area is reliably detected and the exposure amount is automatically adjusted to achieve the appropriate background density, thereby improving the contrast. Good copying becomes possible.

FIG. 8 is a block diagram of an error control circuit showing another embodiment of the present invention. (c) is the output (eo) of selection circuit 3 ()
(C) is a delay circuit that delays the exposed portion of the photoconductor (A) by the time it takes to move in the direction of the arrow (1υ) and reach the position where it is developed by the developing device (14). This is a bias voltage regulator that adjusts the voltage applied to the developing sleeve (G) of the developing device G41 in accordance with the input signal voltage (eO'). ) is small, that is, when the density of the background part of the document is high, the bias voltage is adjusted so that development is performed at a low density.In this embodiment, as in the previous embodiment, the density of the background part is adjusted appropriately. Controlled and high-quality copying results can be obtained.

(G) Effects of the Invention According to this invention, the density of the original is simultaneously detected using a plurality of detection elements, and the density of the background part of the original obtained from the maximum value of their outputs is used to control the development density. This makes it possible to obtain copies with good contrast and no uneven development even for originals with extremely uneven shading.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing one embodiment of the present invention, FIGS. 2 and 3 are explanatory diagrams showing the arrangement of detection elements in this embodiment, and FIG. 4 is an electric circuit showing a selection circuit of this embodiment. 5 is a block diagram showing the control circuit of this embodiment,
FIG. 6 is an explanatory diagram showing the manuscript of this embodiment as shown in FIG. 4, FIG. 7 is a time chart 1 showing the output waveform of FIG. 4, and FIG. 8 is a block diagram showing another embodiment of the present invention. (1)...Original, (3)...Light source, (Sl) to (S4)...Detection element, (21
)...Selection circuit, □□□...Reference voltage, (to)...Comparator, (to)...
...Voltage regulator. Figure 1 Ward 2 (v) Dimension report Figure 5 Figure 6 Figure 7 Figure 8

Claims (1)

[Scope of Claims] 1. A copying device that guides an original image exposed by an exposure light source to a photoreceptor to form an electrostatic latent image, and visualizes the electrostatic latent image into a toner image by a developing device, comprising: A selection circuit that includes a plurality of detection elements that output signals corresponding to the shading of the image, and further selects and outputs only the signal corresponding to the document image with the lowest density from among the signals simultaneously output by each of the detection elements. and a control means for controlling development density using a signal output from the selection circuit. 2. A copying apparatus according to claim 1, wherein a plurality of detection elements are arranged corresponding to the width direction and the longitudinal direction of the document and are spaced apart from each other at predetermined intervals. 3. The copying apparatus according to claim 1, wherein the control means controls the developed density by changing the exposure amount of the exposure light source. 4. The copying apparatus according to claim 1, wherein the control means controls the developed density by changing the developing bias voltage of the developing device.