JP2502296B2 - Bias application method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a bias applying method in a developing device used in a copying machine or the like.

(Prior Art) In an image forming apparatus such as a copying machine, an electrostatic latent image is formed on a recording medium made of a photoconductor or a dielectric, and the latent image is developed to be visualized, and the visualized image is transferred to a transfer paper. Then, the image remaining on the recording medium is cleaned, and such a process is repeated. In this image forming apparatus, a voltage is applied to the developing electrode in the process of developing and visualizing the electrostatic latent image on the recording medium in the developing section to prevent toner from adhering to the non-image area on the recording medium during development. A method of preventing is adopted, and applying a voltage to this developing electrode is said to apply a bias. The biasing method includes a fixed bias method in which a constant voltage is always applied to the developing electrode, a float bias method in which a voltage is induced from the recording medium to the developing electrode, and this always changes, and characteristics of the float bias method and the fixed bias method. There are a combined semi-float bias system, an auto bias system in which a potential on a recording medium is detected and a bias corresponding to the potential is applied to a developing electrode.

In the auto-bias method, usually, after the electrostatic latent image is formed on the recording medium, immediately before the electrostatic latent image is developed, the surface potential of the recording medium is detected and a voltage corresponding to the detected potential is applied to the developing electrode. ing. Since the voltage applied to the developing electrode usually has the purpose of not applying a bias to develop the background portion of the image, a predetermined voltage is applied to the minimum value of the above detection voltage,
For example, it is assumed that a voltage of about + 40V to 100V is added.

Conventionally, as a developing electrode, a plate developing method has been generally adopted in which a planar electrode is brought close to a recording medium for developing. In this method, the developing effect is stable, but on the other hand, since the developing electrode is arranged close to the drum-shaped recording medium,
Part accuracy and assembly accuracy are required, and in connection with that, a certain time is required for development. Further, it is necessary to remove the toner adhering to the developing electrode side at the time of development by some method, and as a method for that, a reverse bias is applied to the developing electrode to attract the adhering toner on the developing electrode to the recording medium side for cleaning. The method is adopted. In addition to the plate developing system, a roller developing system has recently been adopted. This roller developing system is a conventionally known system. However, since the developing roller as a developing electrode is very close to the electrostatic latent image on the recording medium at the time of development, good developing cannot be performed. Therefore, when adopting this roller development method, multi-stage development was required.
On the other hand, the roller developing method has an advantage that no special cleaning process is required because the developing electrode can be mechanically cleaned with respect to the cleaning of the developing electrode performed by the plate developing method. Further, due to recent improvements in toner, it is not always necessary to provide the developing roller in multiple stages as described above, and sufficient development can be performed even with one to four developing rollers, which has recently been reviewed again. Further, the roller developing method has an advantage that the position of the developing portion with respect to the recording medium can be freely selected to some extent (the dish developing method has a condition of being under the recording medium due to the nature of development), and from this point, attention has been paid again recently Came to be.

However, in the roller developing method, how to detect the potential of the recording medium becomes a problem. In the conventional dish developing method, a part of the tip of the dish can be used as a detection electrode, but in the roller developing method, this cannot be done. A method has been proposed in which the roller also serves as a detection electrode and a development electrode. This method detects the voltage induced on the first developing roller when the leading edge of the electrostatic latent image on the recording medium passes a certain distance after passing the first developing roller and detects the bias voltage corresponding to this detected voltage. Is applied to the first developing roller and the subsequent developing rollers.

However, in this method, when the leading edge of the electrostatic latent image passes the first developing roller, the voltage induced on this developing roller is detected and a bias is applied to the first developing roller and the other developing rollers. At the leading end of the latent electrostatic image, the bias application at the first developing roller is insufficient, and the background is exposed as compared with other portions.

(Object) It is an object of the present invention to provide a bias applying method capable of eliminating the above-mentioned drawbacks and eliminating the background stain on the image front end portion.

(Structure) The present invention provides a bias applying method in a developing device for developing an electrostatic latent image by a plurality of developing rollers, wherein the detection electrode is detected by an image passing through a developing roller used as a detection electrode among the plurality of developing rollers. The voltage induced on the developing roller is detected, a bias voltage is applied to the plurality of developing rollers according to the detected voltage, and the image area used for the detection is the detection electrode of the plurality of developing rollers. The bias voltage applied to the other developing roller is corrected while passing the other developing roller after the developing roller for use.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 shows a developing device in an example of a copying machine. In this copying machine, the photosensitive drum 1 is rotationally driven in the direction of the arrow by the motor and uniformly charged by the corona discharger, and then the original image is exposed by the exposure device to form an electrostatic latent image. The latent image is developed by the developing device 2 and transferred to the transfer paper from the paper feeding device. The developing device 2 is a developing roller
3, 4 and the squeeze roller 5 are arranged around the photosensitive drum 1 with a minute interval along the rotation direction thereof, and the developing rollers 3, 4 are rotated in the opposite direction to the photosensitive drum 1 by the driving device. The squeeze roller 5 rotates in the same direction as the photosensitive drum 1. The developer is pumped up from the tank by a pump and supplied from the nozzle 6 between the photosensitive drum 1 and the developing rollers 3 and 4, so that the electrostatic latent image on the photosensitive drum 1 is developed. The squeeze roller 5 removes the excess developer on the photosensitive drum 1, and the developer on the developing rollers 3, 4 and the squeeze roller 5 is removed by scrapers 7 to 9 to remove the developer.
It is collected in the tank via. The developing roller 3 through which the electrostatic latent image on the photosensitive drum 1 first passes is used as a detection electrode, and the developing rollers 3 and 4 are used as developing electrodes.

FIG. 1 shows an example of an embodiment circuit of the present invention, and FIG. 2 is a timing chart thereof. In Fig. 1, RA1 and RA2 are relays, CV is a DC-DC converter, D1 to D4 are diodes, and Z1.
~ Z4 is a Zener diode, FET is a field effect transistor, Q1 to Q4 are transistors, C1 to C3 are capacitors, RA11
Is a normally closed contact of relay RA1, RA12 and RA13 are normally open contacts of relay RA1, RA21 is a normally open contact of relay RA2, resistances of R1 to R9, A
˜C are terminals to which a timing signal is applied from the control section of the copying machine, and D and E are terminals connected to the developing rollers 3 and 4, respectively. In addition, field effect transistor FET, transistor Q1,
Q2, diodes D3, D4, capacitors C1, C2, contacts RA12, RA1
3, the resistors R3 to R6 constitute the detection circuit VD, the capacitor C3 and the resistors R8 and R9 constitute the memory circuit M, and the transistors Q3 and Q
4, Zener diode Z3, Z4, contact RA11, RA21, resistor R7
Constitutes the output circuit OC.

The relays RA1 and RA2 and the DC-DC converter CV are controlled by the control section via terminals A to C as shown in FIG. 2, that is, the DC-DC converter CV develops the electrostatic latent image on the photosensitive drum 1. When passing through the section, it is turned on at T ₁ to output a high voltage, and the relay RA1 detects the surface potential of the photosensitive drum 1, that is, the tip of the electrostatic latent image on the photosensitive drum 1 is the developing roller. At time T ₂ when passing through 3, the normally closed contact RA11 is opened and the normally open contacts RA12, RA13 are closed. The relay RA2 and the surface potential detection time T _2, the normally open contact is turned on to the time T ₄ consisting of time T ₃ Metropolitan the trailing edge of the leading end portion of the electrostatic latent image passes between the developing roller 3, 4 Close RA21.

First surface potential detection time T ₂ the relay RA1 is the voltage induced in the developing roller 3 in a state of ON is input to the gate of the field effect transistor FET in the detection circuit VD. The field effect transistor FET is used because the voltage induced in the developing roller 3 is very small and the input impedance of the detection circuit VD is made high to eliminate the influence on the induced voltage. The input of the transistor FET is current-amplified and output to the memory circuit M. The storage circuit M stores the voltage of the capacitor C3 charged by the output of the detection circuit VD and stores the voltage at least during development T ₁ , and the output circuit OC determines the bias voltage according to the voltage of the capacitor C3. In the output circuit OC, the collector output of the transistor Q4 is 1 with respect to the input.
It comes out in the form of 1 and adds a voltage of + α to it. This +
α is usually around + 40V to + 80V. High voltage (+ 100V to +)
(200 V) is applied to the developing roller 4 by adding the time T ₄ with the Zener diodes Z3 and Z4. Therefore, the bias voltage applied to the developing roller 4 is highly corrected until the leading edge of the electrostatic latent image passes the developing roller 4, and the electrostatic voltage is detected in order to detect the induced voltage of the developing roller by the leading edge of the electrostatic latent image. There is no shortage of bias in the development of the leading edge of the latent image, and the background stain on the leading edge of the image is eliminated. When the leading edge of the electrostatic latent image passes the developing roller 4 after the time T ₄ has passed, the relay RA2 is turned on, the Zener diode Z3 is short-circuited by the normally open contact RA21, and + α is the normal value by the Zener diode Z4. A normal bias voltage is applied to the developing roller 4 as a voltage. During the surface potential detection time T2, the developing roller 3 is used as a detection electrode as described above when the relay RA1 is turned on. After that, when the relay RA1 is turned off, a normal bias voltage is applied as a developing electrode from the output circuit OC.

(Effects) As described above, according to the present invention, in the bias applying method in the developing device for developing the electrostatic latent image by the plurality of developing rollers, the developing roller that is used as the detection electrode among the plurality of developing rollers is passed. The voltage induced on the detection electrode developing roller is detected by the image, the bias voltage is applied to the plurality of developing rollers according to the detected voltage, and the image area used for the detection has the plurality of developing rollers. Since the bias voltage applied to the other developing roller is corrected while passing through the other developing roller after the detecting electrode developing roller, the bias does not become insufficient even at the development of the tip portion of the electrostatic latent image. It is applied sufficiently to eliminate background stains on the leading edge of the image.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment circuit example of the present invention, FIG. 2 is a timing chart of the embodiment circuit example, and FIG. 3 is a sectional view showing a developing device in an example of a copying machine. Z3: Zener diode, RA2: Relay.

Claims (1)

(57) [Claims] 1. A bias applying method in a developing device for developing an electrostatic latent image by a plurality of developing rollers, wherein the detection electrode developing is performed by an image passing through a developing roller used as a detecting electrode among the plurality of developing rollers. The voltage induced in the roller is detected, a bias voltage is applied to the plurality of developing rollers according to the detected voltage, and the image area used for the detection is the detection electrode developing of the plurality of developing rollers. A bias applying method characterized in that the bias voltage applied to the other developing roller is corrected while passing through the other developing roller after the roller.