JPS6336505B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a copy control device that obtains a copy image without background stains regardless of the background tone of the original to be copied. The present invention relates to a copy control device that obtains a copy image free from background stains by changing the developing bias voltage.

Conventionally, copying machines have three types of print switches: dark, normal, and light, which set the color tone of the copy according to the color tone of the original. For documents with a dark background, select the Dark switch.For general documents or originals with a light background, select the Normal switch.For documents with a dark background, select the Normal switch. By selecting a light switch, a preset development bias voltage is changed for each to obtain a copied image with less background smear.

By the way, some manuscripts to be copied have a large image area, while others have a small image area.
Even within the same image area, there are many different characteristics of manuscripts, such as some having a high density, some having a low density, and some having a colored background. Furthermore, regarding the optical system for exposure, there are problems such as deterioration of the exposure lamp and dirt on the exposure mirror, making it impossible to obtain a satisfactory copy image within the above three types of ranges.

The present invention has been made in view of the above-mentioned circumstances, and is particularly intended to prevent background stains caused by the optical system from the original to the exposure of the image to be copied onto a photoreceptor during copying, and to produce high-quality copied images. The purpose is to obtain. Therefore, in the present invention, the color tone of the background of the document is detected, and the amount of light reflected from the document from the exposure lamp is detected, and the amount of light to which the photoreceptor is exposed is determined depending on the background and contrast of the document. Therefore, the developing bias voltage is changed to prevent background stains caused by the optical system and to obtain high-quality copied images.

Note that there is an auto-bias development method for preventing background stains during development processing. If this autobias development method is used in combination with the present invention, even better quality copies without background stains can be obtained.

The auto bias development method is based on the sensitivity of the photoreceptor,
Changes in the surface potential of the photoreceptor and dielectric due to changes in the charge retention ability of the dielectric or differences in the background of the original are detected, and an electrical circuit determines the bias potential of the developing electrode accordingly. This is a method to prevent skin stains.

In general, in wet development methods and dry development methods, background staining can be prevented by applying a bias potential to the developing electrode, which is a potential (additional potential) of several tens of volts to a hundred and several tens of volts added to the background potential. However, excessive bias potential is undesirable because it results in a decrease in image contrast. However, the residual potential of a member that forms an electrostatic latent image, that is, a charge carrier such as a photoreceptor or dielectric material, during continuous use, that is, the surface potential of the photoreceptor, which corresponds to the background of a document, decreases over time of continuous use. It also changes due to fatigue of the charge carrier due to exposure and charging, wear, deterioration of the exposure light source, dirt on the exposure mirror, etc. This change in residual potential causes changes in the recording density and background stain of copy paper. In addition to this, changes in the charge voltage due to the temperature of the electric circuit and changes over time, etc., also affect the recording density and background stain of copy paper.

For this reason, the potential on the photoreceptor surface is
In particular, an auto-bias developing device is a developing device that detects the residual potential and automatically changes the bias potential of the developing electrode based on the detected residual potential to always produce copies with less background stain and high recording density. According to this developing device, the electric circuit uniquely determines the bias potential of the developing electrode in response to the residual potential, so copies with less background staining can be stably obtained despite fluctuations in the residual potential. .

A developing device to which a controlled bias voltage is applied according to the present invention is also such a developing device.

The present invention will be described in detail below based on embodiments shown in the drawings.

FIG. 1 shows the configuration of one copying apparatus implementing the present invention. In the copying apparatus shown in FIG. 1, in the copy mode, the light reflected from the original IP by the irradiation light from the exposure lamp HLA is reflected from the first mirror FMI, the second mirror SMI, the in-mirror lens IMI and the third mirror.
It is guided to the surface of the photoreceptor on the drum 1 by the mirror TMI. On the other hand, the photoreceptor is uniformly charged by the main charger 2, and is exposed to the guided light to form an electrostatic latent image. This electrostatic latent image is made visible by depositing charged toner supplied by the developing device 4. On the other hand, the copy paper is taken out from the cassette CAS1 or CAS2 by the paper feed roller PSR1 or PSR2. The taken-out copy paper is sent to the transfer section by rotating the registration rollers 6 in synchronization with the position of the latent image (the edge of the document). In the transfer section, the toner adhering to the latent image area is transferred onto the copy paper by the transfer charger 7, and the copy paper is separated from the drum 1 by the separation roller 8 and transferred to the fixing heater.
The HEP fuses (fixes) the toner onto the copy paper, and the copy paper is sent to the output tray COT.
On the other hand, the toner remaining on the drum 1 is neutralized by a static eliminating charger 5 and collected by a cleaning roller 10. 11 is a cleaning blade. The document reading scanning system consists of an exposure lamp HLA, mirrors FMI, and SMI, and they are moved in the direction of the solid line arrow.
It consists of a carriage that moves so that the optical path length does not change.

The developing device 4 is of a wet type developing type, as shown in detail in FIG. 1b, and includes a developer supply pump 4a and detection electrodes 291 to 2 for detecting surface potential.
93 and a developing electrode 27. An example of the developing bias circuit of this developing device 4 is shown in FIG. 1c. In this developing bias circuit 40, detection electrodes 291-293 are connected to the anodes of diodes 32-34, and cathodes of these diodes 32-34 are connected to the positive phase input terminal of the operational amplifier 35.
Therefore, the largest one of the outputs of the detection electrodes 291 to 293 is selected by the diodes 32 to 34 and applied to the operational amplifier 35 as the residual potential detection output of the photoreceptor 1. The positive and negative power terminals of the operational amplifier 35 are connected to an NPN transistor 36 and
Connected to the emitter of PNP transistor 37,
The collector of transistor 36 is grounded, and the collector of transistor 37 is connected to negative DC power supply 38. Each collector of the transistors 36 and 37,
Resistors 39 and 40 and capacitor 4 are connected between the bases.
1 and 42 are connected in parallel, and the transistors 36,
Constant voltage diodes 43 and 44 are connected between the base of 37 and the output terminal of the operational amplifier 35, and the output terminal of the operational amplifier 35 and the negative phase input terminal are connected. Therefore, the output of the DC power supply is supplied to the operational amplifier 35 through transistors 36 and 37, and the supply voltage is kept constant by the voltage regulator diodes 43 and 44, and the supply voltage level varies depending on the input voltage and has a wide range. Operates over input voltage range. The detection electrodes 291 to 293 are connected to the input side of the operational amplifier 35 via a cable 45, and the shield wire of this cable 45 is connected to the input side of the operational amplifier 35.
It is connected to the output terminal of 5. This is to prevent toner from settling on the detection electrode due to the grounding capacitance of the detection electrode itself, the input capacitance of the operational amplifier 35, leakage current, and the grounding capacitance of the cable 45. A voltage close to the detection output is applied and AC grounded. A bias power supply +V is connected to the output terminal of the operational amplifier 35 via a resistor 46 to a bias voltage generating circuit 50a configured as a voltage divider with series resistors 12 ₁ to 12 ₆ and a changeover switch 15. Each of the developing bias voltages obtained from the bias voltage generating circuit 50a is switched by the changeover switch 15 and applied to the developing electrode 27. In other words, since the auto bias development method is used here,
The residual potential detection output of the photoreceptor is added to the switching developing bias voltage. If auto bias development method is not used, series resistor 12 _1
126 and the bias voltage generating circuit 50a of the changeover switch 15 may be sufficient. The changeover switch 15 for changing the developing bias voltage is connected to a control circuit 50 which will be described later.
b, an appropriate developing bias voltage is selected and applied to the developing electrode 27.

The contact glass plate CGP on which the original is placed is
A color tone detector 90 is provided that detects the background color of an original using a photometric element such as a photo sensor (for example, ON2152 manufactured by Matsushita Electronic Components), which is a combination of a light emitting diode and a photodiode. The electric signal is obtained as an electric signal, and this electric signal is supplied as a digital signal to the control circuit 50b by the analog-to-digital converter 70.

In addition, a CDS and a photodiode are installed on the optical path in which light reflected from the original by the exposure lamp HLA is guided to the drum 1 by the first mirror FMI, the second mirror SMI, the in-mirror lens IMI, and the third mirror TMI. A light amount detector 80 using a photometric element such as the above is provided to detect dirt on the optical system such as dirt on the mirror and lens, and deterioration of the exposure lamp. The output signal of this light amount detector 80 is also supplied to the control circuit 50 as a digital signal by the analog-to-digital converter 60, and the developing bias voltage is controlled by the control circuit 50b together with the color tone signal.

FIG. 3 shows an example of the color tone detector 90. The color tone detector 90 includes a plurality of photo sensor units 95.
97, and an operational amplifier 94 that adds electrical signals obtained therefrom. Basically, it is possible to use only one photo sensor unit, but in this example, three units are used to detect the background tones of three points on the document. As shown in the internal structure of each of the photo sensor units 95 to 97, the block of one photo sensor unit 95 includes a light emitting diode 91 that irradiates the original IP with light, and a light emitting diode 91 that receives reflected light from the original IP. A photodiode 92 and a transistor 93 that amplifies the output voltage of the photodiode 92
Consists of. Other photo sensor units 96 and 97 also have the same configuration as photo sensor unit 95. In the photo sensor unit 95, the light emitting diode 91 emits light to the document IP,
The reflected light from the original is received by a photodiode 92, and its output is converted into an electrical signal to obtain a color tone signal. An example of changes in the electrical signal level depending on the background tone of the original IP is shown in FIG. 2. As shown in Figure 2, color tones such as white, yellow, pink, and gray are distinguished depending on the output signal voltage, so the developing bias voltage can be switched accordingly to prevent background stains on the copy due to the difference in color tone. Try to eliminate it.

Although not particularly shown, the light amount detector 80 shown in FIG. 1a has substantially the same configuration as the color tone detector shown in FIG. 3. However, since the light amount detector 80 only needs to detect the amount of light reflected from the background portion of the document, it is configured with only a light receiving section. For example, in the circuit shown in FIG. 3, only the light emitting diode 91 is omitted.
It is used as a light amount detector 80. Alternatively, a known light amount detector using CDS or the like may be used. Since these configurations are well known to those skilled in the art, their explanation will be omitted. Further, the analog-to-digital converters 70 and 60 for converting the analog electrical signals of the color tone detector 90 and the light amount detector 80 into 4-bit digital signals are also known A/D converters, so their explanation will be omitted.

FIG. 4a shows an example of the control circuit 50b.
The output of the color tone detector 90 is sent to the control circuit 5 as a 4-bit digital quantity by the analog-to-digital converter 70.
0b decoder 52. Decoder 52
decodes a 4-bit digital quantity so that an output "1" appears at one of 16 output terminals. Also, the decoder 51 is also a decoder 52.
, which decodes the signal obtained by analog-to-digital conversion 60 of the output of the light amount detector 80. The developing bias voltage is controlled to be switched by a combination of the output signal of the color tone detector 90 and the output signal of the light amount detector 80. Referring also to FIG. 4b, the output from the tone detector 90 is input to the upper decoder 52, the output of which is input as the vertical axis input of the matrix logic circuit 500. Further, the output from the light amount detector 80 is input to the left decoder 51, and the output thereof is input to the horizontal axis of the matrix logic circuit 500.
At the intersection of this matrix logic circuit 500, AND logic of the inputs of the vertical axis signal and the horizontal axis signal is taken. A combination of signals that represents the state of all inputs. The optimum developing bias voltage may be selected depending on one of the input states expressed by this intersection signal. FIG. 4b symbolically represents which intersection signal selects which bias voltage. For example, one bias voltage is represented by three intersection signals marked with circles, and seven intersection signals marked with Δ select the next bias voltage. Here, the color tone signals and the light amount signals are grouped along a diagonal line from the upper right to the lower left so that the bias voltages are selected substantially proportionally. This is a valid idea. That is, the reduction in contrast due to the color tone of the background of the document caused by the color tone detection signal and the reduction in contrast due to deterioration of the exposure lamp and dirt on the lens are both of the same nature. In order to select a more optimal bias voltage, one based on experimentally determined grouping may be used. Referring to FIG. 4a, the portion of the intersection signal circled in FIG. 4b is shown in detail. The intersection of each combination is then ANDed to produce one input signal, each of which is ored
5 to drive a switch ₁₅₁ that selects one bias voltage. 56 is a driver for driving the switch ₁₅₁ .
Note that the switches 15 ₁ to 15 ₅ correspond to the changeover switch 15 in FIG. 1c.

Although the configuration of the control circuit 50 is shown in the hard logic circuit diagram as described above, these controls can be easily configured using a microcomputer. Nowadays, microcomputers are increasingly being used to control the drive systems of copying machines, so it will be understood that this level of selection processing can be easily accomplished by utilizing their free time.

Finally, to explain the specific operation, it is assumed here that the signal from the light amount detector is constant. For example, for a general document with a white background, the color tone detector 90
The output is a high voltage of about 3V, as shown in Figure 2.
is obtained. This output is converted into a 4-bit code of "1111" by the analog-to-digital converter 70, and the bias voltage is set to 400V by the control circuit 50.
By switching the changeover switch 15 to set the image and applying a bias voltage of 400 V to the developing electrode 27, a copy image free from background stains can be obtained. Next, for an original with a gray background, the output of the color tone detector 90 becomes 0.4V as shown in FIG.
The digital converter 70 outputs a code of "0000".
The control circuit 50b is now switched to set the bias voltage to 200V, and the developing electrode 27 is set to 200V.
Since only the background image is given, the background will not be emphasized and the quality of the image will not deteriorate.

As described above, according to the present invention, an image with less background smear can be obtained regardless of the background of the original, and
It is possible to easily obtain images free from background stains caused by contamination of optical systems such as exposure lamps and mirrors, and by reduction in brightness.

[Brief explanation of the drawing]

FIG. 1a is a side view showing the configuration of one type of copying apparatus embodying the present invention, FIG. 1b is a sectional view showing the configuration of a developing device 4, and FIG. 1c is a developing bias circuit 4.
0 is a circuit diagram showing 0. Figure 2 shows the color tone detector 90.
FIG. 3 is a circuit diagram showing the configuration of the color tone detector 90. FIGS. 4a and 4b are circuit diagrams showing the control circuit 50b. HLA: Exposure lamp, IP: Document glass, FMI, SMI,
TMI: mirror, IMI: in-mirror lens, 1: drum, 4: developing device, 40: developing bias circuit,
50b: control circuit, 60, 70: analog-digital converter, 80: light amount detector, 90: color tone detector.

Claims (1)

[Claims] 1. An electrostatic latent image is formed on the photoreceptor by irradiating the image to be copied with an exposure lamp and exposing the reflected light to the photoreceptor. A copying apparatus that performs copying by developing with a developing device is provided with a detector that detects the color tone of an image to be copied and a detector that detects the amount of light from an exposure lamp. A copying control device comprising a control circuit that can change a developing bias voltage accordingly. 2. The copying control apparatus according to claim 1, wherein the color tone detector has a plurality of photo sensor units and detects the color tone of each part. 3. The detector for detecting the color tone detects the color tone of the background of the document, and the detector for detecting the amount of light detects the amount of light reflected from the document from an exposure lamp. Control device as described in section. 4. The copying control device according to claim 1 or 2, wherein the developing device in the copying device is an autobias developing device.