JPH0774924B2 - Image forming device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an image forming apparatus such as a copying machine or a printer.

(Prior Art) As a method for detecting the surface potential of a latent image carrier made of a photoreceptor or a dielectric in an image forming apparatus, there is a method of directly measuring the surface potential of the latent image carrier. Further, a method has been proposed in which the surface potential of the latent image carrier is estimated from the amount of toner adhering to the developing device without directly detecting the surface potential of the latent image carrier.

However, in the former method, the surface potential of the latent image carrier is measured as it is, so the measuring means becomes complicated. In the latter case, the surface potential is estimated from the amount of toner adhered on the latent image carrier,
This estimation is difficult due to the change in the toner adhesion amount due to the change in the toner charge amount and the like, and the accuracy is low.

(Object) It is an object of the present invention to provide an image forming apparatus capable of detecting electric potential simply and accurately with a simple device.

(Structure) The present invention includes a latent image carrier that is repeatedly used, a latent image forming unit that forms an electrostatic latent image on the latent image carrier, and a developing electrode to which a predetermined developing bias potential is applied. An image forming apparatus comprising: a developing device that visualizes an electrostatic latent image on the latent image carrier, and means for transferring the latent image on the latent image carrier to a transfer material. A charged area on the body is caused to develop by a plurality of different developing bias potentials, and the developing bias potential applied to the developing electrode is changed from a state in which no toner adheres to the latent image carrier to a state in which there is toner adhesion, or Bias switching control means for switching in a plurality of steps so as to change the state from the presence state to the absence state, the output means for outputting the value of the developing bias potential applied to the developing electrode, and the toner adhesion on the latent image carrier. Toner that detects the amount Based on the detection result of the adhesion amount detection means and the toner adhesion amount detection means, the state in which there is no toner adhesion on the latent image carrier has changed to a state in which there is toner adhesion, or the state in which there is no toner adhesion has changed A comparing unit for comparing the value of the developing bias potential output from the output unit and a reference voltage value at the time of the determination by the determining unit, and a comparing result of the comparing unit. , And a control means for controlling the image density parameter.

The figure shows an embodiment of an electrophotographic apparatus to which the present invention is applied.
In this embodiment, the exposure device 1 exposes a light image of a document on a document table and constitutes a copying machine. However, a printer is constituted by using an exposure device which exposes a light image by an input image signal. May be. This embodiment operates in a normal copy mode and a potential detection control mode. The potential detection operation mode is performed before the copying mode, after the copying mode, and immediately after the main switch is turned on.

In the normal copying mode, the image carrier 2 composed of a photosensitive drum, which is repeatedly used, is rotationally driven in the direction of the arrow by the motor to be uniformly charged by the charging corona discharger 3, and then the optical image is generated by the exposure device 1. Is exposed to form an electrostatic latent image, and the electrostatic latent image is visualized by the developing device 4. Therefore, the charging corona discharger 3 and the exposure device 1 constitute a latent image forming means for forming an electrostatic latent image on the photosensitive drum 2. The high-voltage power supply 5 operates according to the timing signal from the timing generation circuit 6, and drives the charging corona discharger 3 via the charging current control circuit 7. The developing device 4 has a container 9 for accommodating a two-component developer 8 composed of toner and carrier. The developer 8 is a stirring and scooping roller by an impeller 10.
In the process of drawing up by 11, the toner is charged to the opposite polarity to the electrostatic latent image due to friction with the carrier. This developer is transferred from the scooping roller 11 to the developing roller 12 and supplied to the photosensitive drum 2, and the electrostatic latent image on the photosensitive drum 2 is visualized by the adhesion of toner. After passing the developing position, the developer on the developing roller 12 is scraped off from the developing roller 12 by the scraper 13, and the toner is replenished to the developer 8 by the toner replenishing device 14. On the other hand, a transfer material composed of transfer paper is sent from the paper feed cassette 15 by the paper feed roller 16 and the transport rollers 17 and 18, and the image of the original is transferred from the photosensitive drum 2 to the transfer paper by the transfer corona discharger 19. The toner on the transfer paper is fixed by the fixing device 20, and the transfer paper is discharged to the tray 21. Further, after the image transfer, the photoconductor drum 2 is subjected to the charge removal corona discharger 22 and the charge removal lamp 23 to remove the residual charges, and the cleaning device 24 to remove the residual toner. The exposure device 1 not only illuminates a document placed on the document table and projects the light image on the photoconductor drum 2, but is also provided outside the document image projection area of the document table at a different timing. The reference pattern having the reference density is illuminated and the reflected light is projected onto the photosensitive drum 2. Therefore, an electrostatic latent image of the reference pattern is also formed on the photosensitive drum 2, and this electrostatic latent image is visualized by the developing device 4. The density detector including the light emitting element 25 and the light receiving element 26 constitutes a toner adhesion amount detecting means for detecting the toner adhesion amount on the photoconductor drum 2, and detects the density (toner adhesion amount) on the photoconductor drum 2. Upon detection, the density detection circuit 27 operates according to the timing signal from the timing generation circuit 6 to convert the output signal of the density detector for the visible image of the reference pattern into a voltage. The toner replenishment control circuit 28 receives the output signal of the density detection circuit 27 through the switch 29 and compares it with the reference voltage. When the output signal of the density detection circuit 27 becomes larger than the reference voltage (the reference pattern (When the image density is lower than the reference value), the toner replenishing device 14 is operated to operate the developing device 4
Control the developing capacity of. The developing roller 12 also serves as a developing electrode, and a predetermined developing bias voltage from the bias power source 30 is applied.

In the potential detection control mode, the charging potential of the photosensitive drum 2 by the charging corona discharger 3 is detected and controlled to be constant. For example, after the copying operation is completed, the high voltage power source 5 drives the charging corona discharger 3 through the charging current control circuit 7 at a timing determined by the timing signal from the timing generation circuit 6 to uniformly charge the photosensitive drum 2. . At this time, the exposure device 1 and the erase lamp 31 do not operate, and the photosensitive drum 2 is rotationally driven by the motor. The bias switching control circuit 32 as the bias switching control means controls the developing bias potential of the bias power source 30 at the timing when the uniform charging portion of the photosensitive drum 2 passes the developing device 4 to the predicted charging potential of the uniform charging portion (here Then switch to a predetermined potential (+ 1000V) higher than 800V). Under this condition, the uniform charging portion on the photosensitive drum 2 has a potential lower than the developing bias potential, so that the developing device 4 does not adhere toner. This uniform charging unit is the light emitting element 25 and the light receiving element 26.
The density detection circuit 27 operates according to the timing signal from the timing generation circuit 6 at the timing of passing the density detection position of the density detector, and the output signal is output to the voltage detection circuit 33 via the switch 29. This concentration detection circuit
The output signal of 27 is a signal indicating that the toner adhesion amount on the photoconductor drum 2 is zero, and it can be seen that the potential of the uniform charging portion is lower than the developing bias potential of + 1000V.

The bias switching control circuit 32 switches the developing bias potential of the bias power source 30 to + 950V at the timing when the next uniform charging section on the photosensitive drum 2 passes the developing device 4, and this uniform charging section detects the density detectors 25, 26. The concentration detection circuit 27 operates at the timing of passing through the concentration detection device. Also at this time, the output signal of the density detecting circuit 27 becomes a signal indicating that the toner adhesion amount on the photosensitive drum 2 is zero.

Similarly, the bias switching control circuit 32 sequentially lowers the developing bias potential of the bias power source 30 at each timing when each uniform charging section on the photosensitive drum 2 passes the developing section 4, and the uniform charging sections detect the density. The concentration detection circuit 27 operates at the timing of passing the concentration detection positions of the containers 25 and 26. Toner uniformly begins to adhere to the uniformly charged portion on the photosensitive drum 2 by the developing device 4 when the potential thereof and the developing bias potential become substantially the same. The potential detection circuit 33 has means 34 for reading the developing bias potential of the bias power supply 30, and the density detection circuit
The voltage comparison circuit detects the potential of the uniform charging portion by detecting the time when toner starts to adhere to the uniform charging portion on the photosensitive drum 2 from the output signal of 27 and detecting the developing bias potential at this time. Output to 35. Therefore, the potential detection circuit 33 includes a judgment means for judging, based on the output signal of the density detection circuit 27, that there is a change from the state where no toner adheres to the photosensitive drum 2 to the present state. The voltage comparison circuit 35 as a comparison means compares the detection potential of the potential detection circuit 33 with a reference voltage of + 800V, and the charging current control circuit 7 as a control means for controlling the image parameter based on the difference.
Adjusts the charging current of the charging corona discharger 3 to control the charging potential of the photosensitive drum 2 to the reference voltage of + 800V. Therefore, the voltage detection circuit 33, the voltage comparison circuit 35, and the charging current control circuit 7 constitute control means for controlling the charging potential of the photoconductor drum 2.

In this embodiment, the developing bias potential is varied from a high value to a low value by utilizing the principle that toner hardly adheres to the photosensitive drum when the developing bias potential is higher than the surface potential of the photosensitive drum. However, the developing bias potential may be changed from a low value to a high value. However, when the developing bias potential is changed from a value lower than the expected surface potential of the photoconductor drum to a higher value, the amount of toner adhered to the photoconductor drum increases and the toner consumption increases. To avoid this, the development bias potential is changed from a value higher than the expected surface potential of the photoconductor drum to a value lower than that, and when the toner starts to adhere to the photoconductor drum or after a predetermined timing. At this point, the change of the developing bias potential may be stopped. The method of varying the developing bias potential may be a method of sequentially selecting a plurality of different developing bias potentials, or a method of continuously varying the developing bias potential.

In the above embodiment, the charging current was controlled by detecting the charging potential by the charging corona discharger of the photoconductor drum, but instead of controlling the charging current, the control of the exposure light amount or the image bias potential during the copy mode is performed by the charging. The image density may be made constant depending on the potential. Further, in the above embodiment, the charging potential by the charging corona discharger of the photosensitive drum is detected, but what is the charging potential by the transferring corona discharger 19 of the photosensitive drum 2 in the developing device under the condition of the appropriate transfer current? If it is known whether the potential is reached, the charging current may be detected in the same manner as in the above embodiment to control the charging current of the transfer corona discharger 19. In this case, the discharging corona discharger 2, the discharging lamp 23, the cleaning device 24, the charging corona discharger 3, the exposure device 1, and the erase lamp 31 are turned off or separated from the photoconductor drum 2. Further, the target of the detection control is not limited to the charging corona discharger 3 and the transfer corona discharger 19, but may be the exposure lamp, the charge eliminating lamp 23, etc., which in effect affects the latent image formation on the latent image carrier, That is, any image density parameter may be used.

There is a developing device in which toner is not attached to the latent image carrier even if the surface potential of the latent image carrier is higher than the potential of the developing electrode. This method is, for example, a dry development method using magnetic toner, and since a magnet is provided on the developing electrode, it is both the electrolytic and magnetic fields that determine the moving direction of the developer, and the electric field is sufficient to overcome the force due to the magnetic field. Need to be strong. The present invention can be implemented even in such a system. This is because the relationship between the magnetic field, the electric field, and the movement of the toner can be obtained in advance by experiments, and the detection control target can be controlled based on this relationship. Further, even if the surface potential of the latent image carrier is lower than the potential of the developing electrode, the present invention can be similarly implemented by a method of attaching toner to the latent image carrier.

In the above embodiment, it is important to detect the critical point of whether or not toner adheres to the photosensitive drum. Thus, for example, when a two-component developer or a wet type developer is used, the potential difference between the surface potential of the latent image carrier and the potential of the developing electrode is constant depending on the state, for example, toner concentration, of the latent image carrier. Even when the toner adhesion amount changes, the surface potential of the photosensitive drum can be accurately detected with almost no change in the critical point regardless of the change in the state of the developer. For example, if the surface potential of the photosensitive drum is detected by detecting the point where the toner adhesion amount corresponds to the image density of 1.0, when the toner density of the developer fluctuates by 1 to 6%, the surface potential detection error becomes about 200V. Also becomes. However, in the above embodiment, when the toner concentration of the developer fluctuates by 1 to 6%, the surface potential detection error is about 30 V, which is within the allowable range in the design of the image forming apparatus.

Further, in the above embodiment, the detection potential of the potential detection circuit 33 and / or the predicted value of the charging potential obtained by controlling the charging current by the charging current control circuit 7 may be displayed on the display device.

As described above, according to the present invention, a latent image carrier that is repeatedly used, a latent image forming unit that forms an electrostatic latent image on the latent image carrier, and a predetermined developing bias. Image having a developing device having a developing electrode to which an electric potential is applied to visualize an electrostatic latent image on the latent image carrier, and means for transferring the visualized image on the latent image carrier to a transfer material. In the forming apparatus, the charged area on the latent image carrier is developed with a plurality of different developing bias potentials, and the developing bias potential applied to the developing electrode is from a state where no toner adheres on the latent image carrier. A bias switching control unit that switches in a plurality of steps so as to change from a state in which toner is attached to a state in which toner is not attached, an output unit that outputs the value of the developing bias potential applied to the developing electrode, Toner on latent image carrier -Toner adhesion amount detecting means for detecting the adhesion amount, and a state in which there is no toner adhesion on the latent image carrier, or there is toner adhesion, based on the detection result of the toner adhesion amount detection means Determination means for determining that the state has changed to a non-use state, comparison means for comparing the value of the developing bias potential output from the output means at the time of the determination by the determination means, and a reference voltage value, and the comparison The image density parameter can be controlled by simply and accurately detecting the potential with a simple device because the image density parameter is controlled according to the comparison result of the means.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an embodiment of an electrophotographic apparatus to which the present invention is applied. 1 ... exposure device, 2 ... photosensitive drum, 3 ... charging corona discharger, 4 ... developing device, 7 ... charging current control circuit, 19 ... transfer corona discharger, 25,26. Concentration detector, 30 ... bias power supply, 32 ... bias switching control circuit, 33 ... voltage detection circuit, 35 ... voltage comparison circuit.

Claims (1)

[Claims] 1. A latent image carrier that is repeatedly used, a latent image forming unit that forms an electrostatic latent image on the latent image carrier, and a developing electrode to which a predetermined developing bias potential is applied. An image forming apparatus comprising: a developing device that visualizes an electrostatic latent image on the latent image carrier; and means for transferring the latent image on the latent image carrier to a transfer material. Of the developing region is changed by a plurality of different developing bias potentials, and the developing bias potential applied to the developing electrode is changed from a state in which no toner adheres to the latent image carrier to a state in which there is toner adherence. Bias switching control means for switching in multiple steps so as to change from the state to the non-state, output means for outputting the value of the developing bias potential applied to the developing electrode, and toner adhesion amount on the latent image carrier. Toner adhesion amount to detect Based on the detection result of the knowing means and the toner adhesion amount detecting means, it is determined whether the state in which the toner is not adhered on the latent image carrier is changed to the state in which the toner is adhered or the state in which the toner is not adhered is changed to the state in which the toner is not adhered. Determining means, comparing means for comparing the value of the developing bias potential output from the output means with a reference voltage value at the time of the determination by the determining means, and an image according to the comparison result of the comparing means. An image forming apparatus comprising: a control unit that controls a density parameter.