JPS6339909B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic image forming apparatus that circulates and reuses developer.

2. Description of the Related Art In recent years, as the amount of information has increased and the speed of transmission has increased, the image forming speed of electrophotographic image forming apparatuses has been required to become even faster. However, in electrophotographic image forming apparatuses, the amount of developer consumed increases dramatically as the image forming speed increases. for example,
Conventional electrophotographic image forming equipment with medium speed or lower (A4
(20 sheets/min or less), residual developer on the image carrier that can be recovered by cleaning is
Since the amount was relatively small, there was little need to reuse it. However, in high-speed machines, the amount of developer consumed increases, and the amount of developer remaining on the image carrier also increases, and it is necessary to reuse the remaining developer from an economical point of view. In this case, there is a problem in that the developer to be reused contains paper powder, paper fibers, rubber scraps adhering to the conveyance system, shavings from the cleaning blade, and the like. In other words, if a developer containing these impurities is reused,
This will lead to a decrease in image quality.

Therefore, an object of the present invention is to remove the contaminants contained in the residual developer when it is reused, thereby making it possible to reuse the developer cyclically. Like this,
Enabling cyclical reuse of developer is particularly effective in high-speed image forming apparatuses.

To achieve the above object, the present invention provides an image forming apparatus that circulates and reuses developer, in which a filtering member for separating the developer and substances other than the developer is provided in the developer circulation path in the developer circulation direction. The present invention relates to an image forming apparatus characterized in that a number of meshes are provided in order of coarseness of the mesh.

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

FIG. 1 schematically shows the configuration of an image forming apparatus to which the present invention can be applied.

A laser beam emitted from a laser oscillator 1 enters an optical modulation system composed of a lens 2, an A/0 modulation element 3 using an acousto-optic effect, and a lens 4. Here, the lens 2 has the function of converging and projecting the laser beam onto the Bragg reflection surface generated in the A/0 modulation element, and the lens 4 has the effect of diffracting the laser beam from the Bragg reflection surface and converting it into a parallel beam of light. It has the effect of converting. Furthermore, when using an E/0 modulation element that utilizes the known electro-optic effect, lenses 2 and 4 are unnecessary, and when the laser oscillator is a gas laser or the like capable of current modulation, the above-mentioned optical modulation It goes without saying that the system can be omitted.

Now, the laser beam emitted from the lens 4 becomes a parallel beam of light and enters the beam expander 7, where the beam diameter is expanded while remaining a parallel beam of light. Furthermore, the laser beam whose beam diameter has been expanded is incident on a polyhedral rotating mirror 8 having one or more mirror surfaces. The polyhedral rotating mirror 8 is mounted on a shaft supported by a high-precision bearing (for example, an air bearing),
It is driven by a motor 9 that rotates at a constant speed (for example, a hysteresis synchronous motor or a DC servo motor). The laser beam swept horizontally by the polyhedral rotating mirror 8 is passed through the imaging lens 1 having f-θ characteristics.
3, an image is formed on the photosensitive drum 14 as a spot. In a general imaging lens, when the incident angle of a ray is θ, the image forming position r on the image plane has the following relationship: r=f・tanθ−(1) (f: focal length of the imaging lens) .
When the polyhedral rotating mirror is rotated at a constant speed as in this embodiment, the angle of incidence of the reflected laser beam on the imaging lens 13 changes linearly with time. Therefore, the moving speed of the imaged spot position on the photosensitive drum 14, which is the image surface, changes non-linearly and is not constant. That is, the moving speed increases at the point where the angle of incidence increases. Therefore, when a row of spots is drawn on the photosensitive drum 14 by turning on the laser beam at regular time intervals, the distance between the spots will be wider at both ends than at the center. In order to avoid this development, the imaging lens 13 is designed to have the following characteristic: r=f·θ −(2).

Such an imaging lens 13 is called an f-θ lens. Furthermore, when collimated light is imaged into a spot by an imaging lens, the minimum diameter of the spot dmin is dmin=fλ/A (3) where f; focal length λ of the imaging lens; wavelength A of the light used; If A is given by the entrance aperture of the image lens and f and λ are constant, a smaller spot diameter dmin can be obtained by increasing A. The beam expander 7 mentioned above is used to provide this effect. Therefore, the required dmin
is obtained by the beam diameter of the laser oscillator, the beam expander 7 is omitted.

As described above, the deflected and modulated laser beam is irradiated onto the photosensitive drum 14, visualized by an electrophotographic processing process, and then transferred and fixed onto plain paper and output as a hard copy.

As an example of the electrophotographic process applied to this embodiment, a photosensitive plate whose basic constituents are a conductive support, a photoconductive layer, and an insulating layer, as described in Japanese Patent Publication No. 42-23910 of the present applicant. The surface of the insulating layer 14 is uniformly charged positively or negatively in advance by the first corona charger 16, and a layer with a polarity opposite to the charged polarity is formed at the interface between the photoconductive layer and the insulating layer or inside the photoconductive layer. Capture charge. In addition, the surface of the insulating layer to be charged is irradiated with the laser beam, and at the same time, an AC corona discharge is applied by the AC corona discharger 17 to form a pattern due to the difference in surface potential that occurs according to the light and dark pattern of the laser beam. Formed on the surface of the insulating layer. Then, the entire surface of the insulating layer is uniformly exposed to light using a full-surface exposure lamp 18 to form a high-contrast electrostatic latent image on the surface of the insulating layer, and further, the electrostatic latent image is made mainly of charged colored particles. The image is visualized by developing it with a developer using a developing device 19. Thereafter, the visible image is transferred by the transfer charger 22 onto fan-hold paper (hereinafter referred to as paper) 30 which is fixed on the photosensitive drum 14 by means described later.

Next, the transferred image is fixed by a fixing means as described below to obtain an electrophotographic print image, and after the transfer, the surface of the insulating layer is cleaned by a cleaning device 2.
3 to remove the remaining charged particles, and the photosensitive plate 14 is used repeatedly. As yet another embodiment, an electrophotographic electrostatic image forming process as described in Japanese Patent Publication No. 19748/1974 by the applicant of the present invention is applied. That is,
Using a photosensitive plate whose basic components are a conductive support, a photoconductive layer, and an insulating layer, the surface of the insulating layer is uniformly positively or negatively charged in advance by a first corona discharge, and the photoconductive layer and A charge having a polarity opposite to the charged polarity is captured on the surface of the insulating layer or inside the photoconductive layer, and an alternating current corona discharge is applied to the charged surface to attenuate the charge on the surface of the insulating layer. Next, the laser beam as an information signal is irradiated to form an electrostatic latent image on the surface of the insulating layer according to the brightness of the laser beam, and the electrostatic image is developed.
The subsequent steps are the same as in the first embodiment. In addition,
15 is a charger for pre-static elimination, and 16 is a pre-exposure lamp. The pre-static charger 15 makes the surface potential of the photosensitive drum 14 constant and uniform, and the pre-exposure lamp 16 makes the surface potential of the photosensitive drum 14 constant and uniform.
To make the characteristics of the photosensitive layer constant and uniform. These functions work together to eliminate various predistortions, such as residual potential, remaining on the photosensitive drum 14 after passing through the cleaning device 23, and are useful for always obtaining stable images. The applicant has proposed an electrostatic latent image stabilization method as a means to always obtain stable and good images in the electrophotographic process applied to this embodiment. Reference numeral 21 designates an electrostatic electrometer for realizing such a means, which measures the electrostatic potential of each photosensitive drum 14 by providing a bright area, that is, an area scanned and exposed by a laser beam, and a dark area. 20
1 is a carrier removing device that prevents carriers mixed in the developer in the developing device 19 from adhering to the photosensitive drum 14, adhering to the paper, or being mixed into the cleaning device 23.

Next, the conveyance of continuous paper with perforations (hereinafter referred to as paper) used in the image forming apparatus will be described. In the figure, numeral 30 is an unprinted sheet of paper normally used for output from a computer, etc., and has feed holes at both ends in the width direction. Reference numeral 32 denotes a holding rod provided to help smoothly transport the paper, 33 a light source such as a light emitting diode, 34 a light receiver such as a photodiode, and 33 and 34 working together to detect the end of the paper. It is what makes up the vessel.
35 is a known tractor in which pins that engage with the feed holes are arranged, and a tractor shaft (not shown).
As the pin rotates, the pin rotates and conveys the paper. Further, 37 is a guide roller for conveying the paper. 38, the transfer ends when the paper is brought into pressure contact with the photosensitive drum 14 by the operation of the transfer rollers 39 and 40, and is further brought into close contact with the photosensitive drum 14 by the operation of the transfer charger 22, as will be described later. After the transfer charger 22 stops operating and the transfer rollers 39 and 40 are separated from the photosensitive drum 14,
This is a separating claw for separating the photosensitive drum 14 that is in close contact with it. Note that transfer rollers 39 and 40 operate simultaneously in the same direction to press the paper against the photosensitive drum 14. Further, reference numeral 41 denotes a guide roller which also functions to absorb tension applied to the paper during paper conveyance when the tension changes more than a specified value. Reference numeral 42 designates a preheating roller having a hollow cylindrical shape and having a heat source such as a heater in the center of the cylinder, and constitutes a fixing device together with a fixing roller 43 and a back-up roller 44 for fixing the toner transferred to the paper. It is something to do. Here, the fixing roller 43 is a hollow cylinder and has a heat source such as a heater in the center of the cylinder. 44 presses the paper onto which the toner has been transferred between it and the fixing roller 43 to facilitate the transmission of heat from the fixing roller 43 to the toner and the paper;
This is a back-up roller that applies high pressure to toner to fix it. Reference numerals 45 and 46 are discharge rollers for discharging the paper on which fixing has been completed, and 47 is a paper on which printing has been completed. The paper 30 used is fan-hold paper with feed holes formed in advance. However, when the fan-hold paper is punched out, there may be some parts that are not completely punched out, or there may be punch residue between the folded sheets.

The portion where the feed hole is not completely removed is punched out by the pin when it engages with the pin of the tractor 35, and that portion remains attached to the paper and contacts the photosensitive drum 14. In addition, punch scum attached to the paper can also be removed from the photosensitive drum 1.
Contact 4. On the other hand, punch scum is photosensitive drum 1.
4 adheres to the photosensitive drum 14 due to its surface potential or mechanically, and is removed by the cleaning means 23. In this embodiment, untransferred toner is removed from the photosensitive drum 14 by the cleaning means, and the toner is circulated to the developing device 19 for reuse. At this time, the punch scum gets mixed into the toner and adheres to the surface of the photosensitive drum 14 during development, resulting in the adhering portion being undeveloped, resulting in data loss. Furthermore, because the toner is recycled and reused, paper dust, paper fibers, cleaning blade shavings, and the like may be mixed into the toner. These contaminants may also have an adverse effect on image formation.

Here, a case in which the present invention is applied to a developer circulation path of an upper image forming apparatus will be shown with reference to FIG. In the figure, 50 is a blade that contacts the surface of the rotating photosensitive drum 14 to remove toner, 51 is a screw for conveying the removed toner to the circulation path 53, and 52 is a blade guided to the circulation path 53 by the screw. It's toner. The circulation path 53 guides toner from the cleaning device 23 to the developing device 19. For example, this circulation path 53 is provided with a filtering member according to the invention. 54a-54b-54c are provided at predetermined positions in the circulation path 53, and the toner 52
This is a cleaning process that filters out contaminants such as punch scum and blade shavings that have entered the machine. Contaminants such as punch scum are removed by screens 54a, 54.
b and 54c, and can prevent it from entering the developing device.

The screens 54a, 54b, and 54c are arranged in order of coarser mesh in the toner circulation direction (indicated by arrow a). Therefore, large-sized contaminants are dammed up by screen 54a, medium-sized contaminants are dammed up by 54b, and even smaller contaminants are dammed up by 54c. By adopting such a configuration, it is possible to significantly delay the clogging of the screen compared to the conventional case where only a fine-mesh screen is provided. That is, the coarse mesh screen 54a blocks only large-sized contaminants and allows other contaminants to pass through. and a medium mesh screen 54
b blocks only medium-sized contaminants among the contaminants that have passed through the screen 54a. Further, the fine mesh screen 54c blocks only water-type contaminants. Therefore, the contaminants mixed into the toner are filtered out in stages by the screens 54a, 54b, and 54c. Therefore, it is possible to delay the clogging of the screen, and the number of times the screen is cleaned can be significantly reduced. Note that this embodiment is particularly effective when there is a large variation in the size of contaminants. Furthermore, as the screen becomes finer, it becomes more difficult for toner to pass through the screen. Therefore, as shown in the figure, by increasing the distance between the screens as the figure becomes thinner, the falling speed of the toner increases and the effect of crushing the toner by the screen can be obtained, and the toner can easily pass through the screen. .

In this embodiment, the mesh size of the screen 54a is set to approximately 4 mm in order to remove punch scum from the feed hole (cylindrical paper with a diameter of approximately 4 mm), and in order to further remove smaller contaminants. By setting the mesh size of the screen 54b to about 2 mm and further setting the mesh size of the screen 54c to about 1 mm, it was possible to remove contaminants and obtain a good image.

It goes without saying that the size of the mesh of each screen should be adjusted as appropriate depending on the size of the contaminants.

Furthermore, another embodiment is shown in FIG. In this embodiment, a screen is provided in the developing device, and in FIG. 4, 60 is a developing sleeve that has a magnetic pole (not shown) inside, and 61 and 62 are screws that rotate in the direction of the arrow shown in the figure. . here 61
62 is a return screw that sends the developer forward from the paper surface, and 62 is a feed screw that sends the developer toward the paper surface. Further, 63 is a doctor blade, and 64 is a screen according to the present invention.

In the figure, the developer is uniformly distributed in the axial direction of the developing sleeve 60 by a return screw 61 and a feed screw 62. Also, return screw 6
The carrier such as iron powder mixed into the developer from the upper part of the developing sleeve 60 attaches toner to the developing sleeve 60.
They are attracted by the magnetic poles provided inside the developing sleeve 60 and aggregate on the surface of the developing sleeve 60 . Reference numeral 63 denotes a doctor blade which functions to uniformize the developer that has aggregated on the developing sleeve 60 and visualizes the latent image formed on the surface of the photosensitive drum 14 by the developer. In this developing device, a screen 64 is provided between the developing sleeve 60 and the return screw 61 as shown. These screens 64a and 64b remove foreign matter such as punched paper fibers when the developer moves from the return screw 61 to the developing sleeve 60. In this embodiment as well, the screens 64a and 64b are provided in the order of coarse mesh in the developer traveling direction. Thereby, in this embodiment as well, the same effects as in the embodiment shown in FIG. 2 can be obtained.

Although the embodiments of the present invention were particularly conducted with respect to punch scum, it goes without saying that by selecting the mesh size of the screen according to the particle size of the developer, it is also effective against even smaller contaminants. Further, good results can be obtained by using a stainless steel wire mesh as the screen, for example. Furthermore, it goes without saying that the present invention is applicable to removing contaminants from either liquid or powder.

As described in detail above, according to the present invention, contaminants are removed stepwise by a plurality of screens according to their size, so that clogging of the screens can be delayed. In addition, by providing a plurality of screens, the effect of contaminants can be increased more than ever before, and omissions in image formation can be prevented, and a highly reliable image forming apparatus can be provided.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an image forming apparatus to which the present invention can be applied, FIG. 2 is a perspective view showing an embodiment of the present invention, and FIG. 3 is a sectional view of a developing device to which the present invention is applied. It is. In the figure, 14...photosensitive drum, 54a, 54b, 54c
...Screen, 53...Circulation path, 64, 66...
...Screen, 65...Circulation path.

Claims (1)

[Scope of Claims] 1. In an image forming apparatus that circulates and reuses developer, a plurality of filtration members for separating the developer and substances other than the developer are provided in the developer circulation path in the developer circulation direction. An image forming apparatus characterized in that filtering is carried out in stages by the filtering member provided separately. 2. The image forming apparatus according to claim 1, wherein the filtering member is mesh-shaped.