JPS6348063B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developing device for a recording device, and in particular to an automatic developing device that detects the surface potential of a charge carrier on which an electrostatic latent image is formed and automatically changes the bias potential of a developing electrode. This invention relates to a bias developing method. The auto-bias development method detects changes in the photoreceptor's sensitivity, dielectric's charge retention ability, etc., or changes in the surface potential of the photoreceptor and dielectric due to differences in the background of the original, and develops the process accordingly. This method determines the bias potential of the developing electrode using an electric circuit to prevent background stains on copy paper.

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, conventionally, as seen in JP-A-51-950 and JP-A-51-32642, the potential on the surface of the photoreceptor, especially the residual potential, is detected by a detection electrode, and this is used to detect the developing electrode. By automatically changing the bias potential of the
In addition, a developing device has been proposed that produces copies with 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. . However, in this developing device, the bias potential with respect to the residual potential is fixed in a one-to-one relationship, so it is possible to increase the image recording density by slightly increasing the background contamination, or to increase the image recording density.
It is not possible to make adjustments such as lowering the image recording density to further reduce background stains. For example, if the properties of the toner change, the recording density and background stain will vary with respect to the bias potential of the developing electrode, but this cannot be completely compensated for only by detecting the residual potential. In addition, it may be desirable to copy extremely low-density information on an original in a dark manner even if it causes background smudges, or to copy lightly so that the low-density information on the original disappears. Such adjustments cannot be made sufficiently by adjusting the exposure amount alone.

For example, when the developer becomes fatigued, the image density tends to increase and the background smudge tends to increase, and the background smudge cannot be completely prevented unless the bias potential is further increased to the initially applied bias potential.

An object of the present invention is to provide an auto-bias developing method that can automatically correct the bias potential of the developing electrode even in response to changes in developer properties (changes in developing ability). It's on offer.

A further object of the present invention is to provide an auto-bias developing method that can automatically determine the value of the additional potential of the developing electrode corresponding to the deterioration of the developer in accordance with the deterioration of the developer.

FIG. 1 is a schematic diagram of an electrophotographic copying apparatus showing essential parts of an embodiment of the present invention. First, the copying process will be explained.

The photosensitive drum 1, which is a charge carrier, has a photoconductive layer on its surface and rotates at a constant speed in the direction of the arrow. A charging corona discharger 2, a lens 3 of an exposure device, and a developing device 4 are arranged around the photosensitive drum 1 along the rotation direction thereof. Exposure device lens 3
In this method, a document placed on a transparent document table is irradiated with an exposure lamp, and an image of the document obtained is projected onto the surface of a photoreceptor. The developing device 4 is
A developer container 6 containing developer 5 and a magnet roller ₇ for holding and conveying the developer to a developing position.
It also includes a developing sleeve 7 ₂ , a separation plate 8 for scraping off the developer from the developing sleeve 7 ₂ , and an impeller 9 for stirring the developer in the developer container. Note that the developing sleeve ₇₂ serves as a developing electrode.

When the surface of the photosensitive drum 1 is uniformly charged to a predetermined polarity by the corona discharger 2, an original image is projected thereon by the exposure device 3. The charge on the photoreceptor is removed in bright areas of the optical image, and remains in dark areas, where an electrostatic latent image corresponding to the optical image is formed. This electrostatic latent image is visualized by the next developing device 4. Developer 5 in developer container 6
is stirred by an impeller 9, and the toner and carrier in the developer are frictionally charged and attracted to each other.

At this time, the materials of the toner and carrier are determined so that the toner is charged with a polarity opposite to that of the electrostatic latent image and with a predetermined amount of charge. The toner is attracted to the surface of the sleeve ₇₂ by the carrier, which is a magnetic material, and is conveyed upward as the roller rotates. It comes into contact with the electrostatic latent image and turns it into a visible image. After this, sleeve 7
The developer on ₂ is transferred to developer container 6 by separating plate 8.
Scraped inside.

The toner image on the photosensitive drum 1 is transferred to the paper feed cassette 1.
Transfer charger 11 onto recording paper fed out from 0
The image is transferred and fixed by the fixing device 12. The recording paper after the fixing is sent out to the paper discharge tray 13. The surface of the photoreceptor drum 1 is equipped with a static eliminating charger 11.
The static electricity is removed by the cleaning brush 15, and the residual toner is removed by the cleaning brush 15.

Next, the developing method of the present invention will be explained. A detection electrode device A is arranged to detect the potential on the surface of the photoreceptor drum 1 on which an electrostatic latent image has been formed.The detection electrode device A detects the surface potential and sends an electric signal representing the detected surface potential to the surface. A potential detection circuit 16 generates a bias voltage corresponding to the electric signal, and a developing electrode bias circuit 17 generates a bias voltage corresponding to the electric signal. On the other hand, a sensor B ₁ for detecting image density is arranged at a position for detecting the developed image on the photoreceptor drum 1, and an electrical signal representing the detected density is emitted from the density detection circuit 18, and correction corresponding to the detected density is made. A signal is generated by the bias voltage correction circuit and applied to the bias circuit 17, and correction is applied to the bias voltage based on this correction signal. The configuration of each part from surface potential detection to bias potential generation is explained in the second section.
As shown in the figure. In FIG. 2, the detection electrode device A is
It is composed of three detection electrodes 291 to 293 distributed in the axial direction of the drum 1. These detection electrodes 291 to 293 are connected to the anodes of diodes 32 to 34 of the surface potential detection circuit 16, and the cathodes of the diodes 32 to 34 are connected to the positive phase input terminal of the operational amplifier 35. Therefore, the smallest output of the detection electrodes 291 to 293 is selected by the diodes 32 to 34 and sent to the operational amplifier 3.
5 as a residual potential detection output of the photoreceptor 21. The positive and negative power supply terminals of the operational amplifier 35 of the bias circuit 17 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.
connected to the output terminal of This is to prevent toner from being adsorbed to the detection electrode due to the ground capacitance of the detection electrode itself, the input capacitance of the operational amplifier 35, the lease current, and the ground capacitance of the cable 45. A voltage close to the detection output of is applied, and it is AC grounded.

The output terminal of the operational amplifier 35 is connected via a resistor 46 to the intermediate potential point of the series-connected Zener diodes 49 ₁ to 49 ₆ (the connection point between the anode of 49 ₃ and the cathode of 49 ₄ ) and the relay switch. Connected to normally open contacts. The cathode of the Zener diode ₄₉₁ is connected via the resistor 47,
Further, the anode of the Zener diode 49 ₆ is connected via a resistor 48 to a positive output terminal and a negative output terminal of a DC constant voltage circuit (not shown), respectively. Each connection point of the Zener diodes 49 ₁ to 49 ₆ is connected to a relay switch S1 to S7 as shown in the figure.
, and each of these normally open contacts is connected to each connection point of another set of series-connected Zener diodes 52 ₁ to 52 ₇ .
Movable contact pieces of relay switches S1 to S6 are connected to a developing electrode 7. The Zener diodes 49 ₁ to 49 ₆ connected in series constitute a superimposed voltage adjustment circuit, and the cathode voltage of the Zener diode 49 ₄ is the output voltage of the operational amplifier 35.
The cathode voltages of the Zener diodes 49 ₅ and 49 ₆ are lower than the output voltage of the operational amplifier 35 by the sum of the breakdown voltage of the Zener diode 49 ₅ and the breakdown voltage of the Zener diodes 49 ₅ and 49 ₆ , _respectively . The cathode voltages of 49 ₂ and 49 ₁ are the breakdown voltage of Zener diode 49 ₃ and the breakdown voltage of Zener diode 4, respectively.
The output voltage of the operational amplifier 35 is higher by the sum of the breakdown voltages of the zener diodes 9 ₃ , 49 ₂ and the Zener diodes 49 ₃ , 49 ₂ , 49 ₁ . Therefore, when the output voltage of operational amplifier 35 (that is, the residual potential of photoreceptor 21) changes, the potential of each normally open contact of relay switches S1 to S7 changes as shown in FIG. In FIG. 3, the solid line indicates the potential of the normally open contact connected to the output terminal of the operational amplifier 35 via the resistor 46, and the dotted line indicates the potential of the other normally open contacts. The reason why the potential of each normally open contact becomes a constant value when the detection voltage exceeds a certain value is due to the breakdown of each of the Zener diodes 52 ₁ to 52 ₇ connected in series. The reason why the upper limit of the potential is determined in this manner by the Zener diodes 52 ₁ to 52 ₇ is to perform development without losing information whether the background of the document is black or white.

The detection electrodes 291 to 293 generate an induced potential based on the surface potential of the photoreceptor 1. Toner adheres to the photoreceptor drum 1 only in areas where the surface potential is higher than that of the developing electrode 7 and is visualized, but toner is attracted to the electrode side in areas where the surface potential is lower than the potential of the electrode 7. It does not stick to the skin and prevents skin stains.

Each movable contact piece of relay switches S1 to S7 is driven to close by relay coils L1 to L7, respectively, and these relay coils L1 to L7 are driven by a relay driver.
It is powered by the output of the decoder DEC via RD.
The output code of the analog-to-digital converter (hereinafter referred to as A/D converter) CON of the concentration detection circuit 18 is given to the decoder DEC via the latch LUT, and the amplifier is connected to the A/D converter CON.
A concentration detection signal from the concentration sensor _B1 is provided via the AMP. The combination from the amplifier AMP to the decoder DEC is such that the sensor _B1 detects the developed density of the electrostatic latent image formed under the standard conditions described later, and when the density is at the standard value, the relay coil L4 is energized. Close the standard relay switch S4, and when the developer density is low, relay coil L is turned on depending on the degree.
3. Activate L2 or L1 and switch relay switch S
3. Close S2 or S1, and when the developer density is high or the background dirt is large, the relay coil L5, L6 or L7 is energized depending on the degree, and the relay switch S5, S6 or S7 is closed. There is.

Switches S1 to S7 as described above are activated in response to the density of each part of the developed image obtained by developing the electrostatic latent image of each part of the original image.
When selective closing control is performed, the developing voltage is changed for the electrostatic latent image to be developed based on the image density of each part that has already been developed, so the developing bias changes randomly. Therefore, a latch LUT is inserted between the A/D converter CON and the decoder _DEC , and the A/D converter CON The output is latched. For example, after the power is turned on and the recording device is ready for recording, the memory of this latch LUT stores a standard image (full black or white,
If it is set to black, the density will be controlled by bias control for the black image of the original, and if it is set to white, the white density or background density will be controlled by bias control for the white image or background of the original. Close relay switch S8 and develop the latent image with the standard bias voltage (timing signal) until the latent image is developed, and while the developed image is directly under sensor _B1 , send a Load command (timing signal) to the latch LUT. The code for setting the bias voltage, which corresponds to the density of the image exposed and developed under standard conditions, is held in the latch LUT, and then the print ready display is displayed, and the code loaded in the latch LUT is used until the power is turned off. Bias voltage characteristics (Figure 3) 1
This is a form in which one is in a specified state. Furthermore, the memory of the latch LUT may be updated by such an operation every time the print button is pressed.
In this case, the standard image may be projected onto the photosensitive drum 1 immediately before projecting the original image.

In this case, the illumination light 3c that illuminates the document 3b on the document table 3a and the optical system leading to the lens 3 are arranged to project the standard image 20 onto the drum 1 at their standby positions, and the standard image 20 is projected at the same time as printing starts. is projected onto drum 1 21 and then original 3
Set to scan b. In this case, since the projection 21 of the standard image 20 is not transferred to the recording paper, the sensor _B1 may be placed downstream of the transfer charger 11, as shown in FIG.

When recording a standard image on the edge of the recording paper or detecting the background density of the recording paper and correcting the bias potential, the sensor B ₁ is installed immediately before the tray 13 as shown by the two-dot chain line in FIG. In particular, when controlling background stains, sensor _B2 may be placed after the cleaning brush 15 as shown by the two-dot chain line in _FIG . The detection accuracy can be increased by determining the amount of dirt.

The invention can also be practiced by omitting the standard image 20. In this case, the photosensitive drum 1
An electrode is placed at a position outside the document image projection area or at a position corresponding to the edge of the document, and the electrode is developed with a constant potential applied to it, and the developed density is measured by sensor _B1 . Detect with. In this case, the bias voltage is corrected only in accordance with the properties of the developer.

In addition, in the above embodiment, a mode was shown in which the bias voltage is corrected by superimposed voltage control, but the bias voltage may be corrected by applying the output of sensor B ₁ to the amplifier 35 or an amplifier inserted in either the front or rear stage thereof. You may also do so.

As described above, according to the present invention, developer deterioration,
The bias voltage of the developing electrode can always be kept at an appropriate value in response to changes in the properties of the charge carrier, etc.
You can always get high quality copies.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of an electrophotographic copying apparatus showing the main parts of an embodiment of the present invention, FIG. 2 is a circuit diagram showing the configuration of the developing bias control section, and FIG. 3 is a potential on the surface of the drum 1. 3 is a graph showing the relationship between the bias voltage and the bias voltage. FIG. 4 is a schematic configuration diagram showing another embodiment of the present invention. 1: Photosensitive drum, 2: Charging corona discharger,
3: Exposure device lens, 3a: Original stage, 3
b: original, 3c: exposure lamp, 4: developing device,
5: Developer, 6: Developer container, 7 ₁ : Magnetic roller, 7 ₂ : Sleeve, 8: Separation plate, 9: Impeller, 10: Paper feed cassette, 11: Transfer charger, 12: Fixing device, 13 : Paper output tray, 14:
Static neutralization charger, 15: Cleaning brush, 2
0: Standard image.

Claims (1)

[Claims] 1. Detecting the surface potential of a charge carrier on which an electrostatic latent image has been formed, and applying a bias potential determined by a certain calculation using the surface potential to a developing electrode to reduce the electrostatic potential of the charge carrier. In a developing method for developing a latent image, a surface potential is set on at least a part of the developing surface under predetermined conditions, that part is developed, and the image density of the image transferred to the developed surface or recording paper is detected. and applying to the developing electrode a potential higher than the bias potential determined by the calculation when the image density is high, and a potential lower than the bias potential calculated by the calculation when the image density is low. Method. 2. The developing method according to claim 1, wherein the developing surface on which the surface potential is set under predetermined conditions is the surface of the charge carrier. 3. The developing method according to claim 1, wherein the developing surface whose surface potential is set under predetermined conditions is an electrode.