JPS6254283A - Picture forming device - Google Patents

Abstract

PURPOSE:To select plural developing tanks and to execute the development with a simple constitution by approaching or separating the auxiliary polarity provided at the back surface of the photosensitive body opposite to the roller having the main magnetic pole and controlling the map of the magnetic brush by means of the mutual action of the main magnetic pole and the auxiliary magnetic pole. CONSTITUTION:When an auxiliary magnetic pole 20 is located at an A position, the map due to a main magnetic pole ma is attracted by the S pole of the auxiliary magnetic pole 20, the map height comes to be higher, and contacts with the surface of a photosensitive body drum 10. Consequently, the toner of a developing tank 1a is stuck to the static latent image formed at the surface of the photosensitive drum 10. When the auxiliary magnetic pole is rotated and shifted to a B position, for the nap due to an auxiliary magnetic pole ma, the action by the auxiliary magnetic pole 20 is eliminated, the height comes to be lower and separation is executed from the surface of the photosensitive drum 10. On the other hand, the nap due to a main magnetic pole mb of a developing tank 1b is attracted by the auxiliary electrode, the height is comes to be higher and contacts with the surface of the sensitive body drum 10. Consequently, when the auxiliary electrode is located at the B position, development is executed by the toner of the developing tank 1b.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, or a printer, which is equipped with a plurality of developer tanks for depositing toner on a photoreceptor.

<Prior Art and Its Disadvantages> When developing an electrostatic latent image formed on the surface of a photoreceptor, an image can be formed in a desired color by selecting the color of toner. Conventional copying:
When selecting a color for one copy image, a method has been implemented in which developer tanks are separated for each color in advance and replaced as needed using a cartridge system. Such conventional copying machines have the disadvantage that the cartridge of the developing tank must be replaced every time the color is changed, resulting in extremely poor workability. In order to eliminate such drawbacks, it has been proposed that a plurality of developing tanks (1!J) are arranged close to the photoreceptor, and one of the developing tanks selectively performs development as necessary. FIG. 4 shows an example of this, where numeral 10 is a photosensitive drum, and la and b are developer tanks. Each developer tank is provided with a magnet roller, and a main magnetic pole maJmb is provided inside the roller.

The developer around the roller forms magnetic brush heads (hal and hbl) at the main pole. When the main magnetic poles are arranged at the positions indicated by solid lines in the figure, that is, mal and mbl, the developer in the developer tank 1b comes into contact with the surface of the photoreceptor drum 10, as is clear from the figure. Therefore, the toner contained in the developer in the developer tank 1b adheres to the electrostatic latent image already formed on the surface of the photoreceptor drum and is developed. When the main magnetic pole of developer tank 1a rotates to position ma2, and the main magnetic pole of developer tank] b rotates to position mb2,
The main magnetic pole ma2 contacts the surface of the photosensitive drum 10, and the development Jl'7 l b (7) m b
] The position of the bristles moves to the position ml)2 and leaves the surface of the photoreceptor l-ram 10. Therefore, developer tank 1
The image is developed using the toner contained in the developer a.

In such a conventional developing method, the main magnetic pole of the magnet roller (+:f position is moved, so it is difficult to adjust its position) 111. In other words, 3 shown in Figure 4
The angles θa and θb of the main magnetic pole toward the center of the photoreceptor drum with respect to the magneto I roller are different. Moreover, the angle of the main magnetic pole relative to the magnet roller also changes, so its position must be adjusted. is a trouble V. In addition, a high degree of part processing viscosity is required to maintain the clearance required for rotational movement.

It takes a lot of effort to manage it. In addition, the main magnetic pole has the greatest impact on image quality such as development density and fog.
It is also difficult to accurately adjust the developer density and degree of fog1.
It was 1.

<Objective of the Invention> An object of the invention is to provide an image forming apparatus that has a simple configuration that does not require high processing accuracy or assembly accuracy, and is capable of performing development by selecting a plurality of developing tanks. be.

<Structure and Effects of the Invention> To summarize, the present invention stores magnetic powder and toner in each of a plurality of developer tanks, and includes a roller having a main magnetic pole that causes the magnetic brush to stand up. An auxiliary magnetic pole is arranged on the back side of the facing photoconductor, and an auxiliary magnetic pole moving means is provided to arrange the auxiliary magnetic pole close to each other or apart, and the standing of the magnetic brush is controlled by the interaction between the main magnetic pole and the auxiliary magnetic pole. Features. For example, by making the auxiliary magnetic pole the same as the main magnetic pole and placing the auxiliary magnetic pole close to the main magnetic pole, the height of the magnetic brush caused by the main magnetic pole is lowered and the developer is separated from the surface of the photoreceptor, and the developing tank is Select.

For example, by setting the auxiliary magnetic pole to have a different polarity from the main magnetic pole and bringing the auxiliary magnetic pole close to the main magnetic pole, the magnetic brush by the main magnetic pole can be made to stand high and come into contact with the surface of the photoreceptor, thereby opening the developing tank. select.

According to this invention, there is no need to change the position of the main magnetic pole provided in the developer tank, so there are problems with the processing precision of parts necessary for position adjustment and movement by moving the main magnetic pole, and to ensure clearance. The problem of adjusting the degree of fogging can be solved.

<Embodiment> FIG. 3 is a diagram illustrating the internal structure of a copying machine to which the present invention is applied. 10 is a photoreceptor drum, around which are a charger 30, a developing tank 1a11 . bs transfer charger 33
and a cleaner 31 are provided. First, the surface of the photosensitive drum 10 is charged by the charger 30, and the document image is exposed at point P to obtain an electrostatic latent image. By further rotating the photosensitive drum 10 clockwise, the developing tank 1a or 1h is opened.
4=J of toner is deposited on this electrostatic latent image. In this way, a toner image is formed on the surface of the photoreceptor drum, the copy paper is generally fed by the conveyance roller 32, the toner image is transferred to the copy paper by the transfer charger 33, and the toner image is further transferred by the first general feed belt 34. The paper is generally fed once and fixed by the fixing roller 35. The 1 henna remaining on the surface of the photoreceptor tram 10 is removed by the cleaner 31.
Clean by. In this way, two developing tanks are installed (jf), and development is performed selectively using either of these developing tanks. FIG. 1 is a diagram showing a developing device installed in a copying machine to which this invention is applied. Ib is a developing device plJ, which is arranged in parallel along the surface of the photoreceptor drum 10. Each developing tank is provided with magnetic rollers 2a, 2b and sleeves 3a, 3b around them. Each of the developer tanks stores a developer in which magnetic powder and toner are mixed at a predetermined ratio. Due to the action of this magnetic powder, the sleeve 3
Magnetic brushes 4a and 4b are generated on the surfaces of the magnetic brushes a and 3b. As shown in the figure, this magnetic brush produces bristles at the position of the magnetic pole of the magneto 1 roller. Here, ``hodachi'' refers to the direction of the magnetic field generated by the magnet roller, in other words, the magnetic brush formed by arranging magnetic powder along the lines of magnetic force is concentrated in areas with high magnetic flux density, especially near the magnetic poles. Then, stand up high. In other words, the higher the magnetic flux density, the higher the height of \'di.

The magnetic roller is fixed and the sleeve rotates around it. Therefore, the magnetic brush on the sleeve surface has its spikes 1. -1 To rotate and move the developer without changing its position. Normally, as shown in the developer tank 1b, the spikes do not reach the surface of the photoreceptor drum 10 and the developer 6 does not come into contact with the surface. In addition, the pole closest to the center of the magnetic pole of the magnet I roller 2a, 21) is ma,
mb is the main magnetic pole, and as shown in the figure, both are N poles.

Reference numeral 20 denotes an auxiliary magnetic pole provided inside the photoreceptor drum 10, which is supported by a support 21 and configured to be rotatable between A and 8 as shown in the figure around a rotating shaft 22. The support body 21 is rotatably moved by a drive motor, and its movement range is defined by a stopper that regulates the rotation angle. The magnetic pole of the auxiliary magnetic pole 20 is located in the radial direction of the photoreceptor drum 10, and the south pole is magnetized in the centrifugal direction as shown in the figure. The base material of the photosensitive drum 10 is aluminum, and does not affect the lines of magnetic force of the auxiliary magnetic pole 20. As shown in the figure, when the auxiliary magnetic pole is at position A, the spikes caused by the main magnetic pole ma are attracted by the S pole of the auxiliary magnetic pole 20, the height of the spikes increases, and they come into contact with the surface of the photoreceptor drum 10. do. Therefore, the toner in the developer tank 1a adheres to the electrostatic latent image formed on the surface of the photoreceptor drum 10. When the auxiliary magnetic pole is rotated and shifted to position B, the effect of the auxiliary magnetic pole 20 on the spike caused by the auxiliary magnetic pole ma disappears, and its height becomes lower and moves away from the surface of the photoreceptor drum 1o. On the other hand, the spikes of the magnetic brush formed by the main magnetic pole mh on the side of the developer tank 1b are attracted by the auxiliary magnetic pole, and the height thereof increases to come into contact with the surface of the photoreceptor drum 10. Therefore, when the auxiliary magnetic pole is at position B, the toner in the developer tank 1b is used for development. By bringing the auxiliary magnetic pole close to the main magnetic pole of the magnetic roller in the developer tank to be selected in this way,
Development can be performed using the developer tank. In the case of the first embodiment, by setting the auxiliary magnetic pole to the opposite polarity to the main magnetic pole of the magnetic roller, there is an effect that magnetic powder falls from the developer tank less when the sleeve rotates. Furthermore, if the magnetic flux density of the auxiliary magnetic pole is lower than the magnetic flux density of the main magnetic pole (measured on the sleeve surface), the height of the spike can be significantly controlled and the selectivity is good.

FIG. 2 represents another embodiment of the invention. The difference from the embodiment shown in FIG. 1 is that the auxiliary magnetic pole is of the same polarity as the main magnetic pole, and that the magnetic brush is exposed to light so that the spikes of the magnetic brush by the main magnetic pole are in contact with the surface of the photoreceptor drum in the active state. The distance between the body tram and the developing tank is determined. As shown in the figure, the developer comes into contact with the surface of the photoreceptor I ram 10 when the magnetic brush is in a normal state due to the main magnetic pole mb of the magnet roller 2b, that is, in a state where the auxiliary magnetic poles are spaced apart. On the other hand, due to the repulsion between the main magnetic pole ma of the magnet roller 2a and the N pole of the auxiliary magnetic pole 20, the height of the spikes is lowered and separated from the surface of the photoreceptor drum 10.

When the auxiliary magnetic pole is rotationally moved to position B, the relationship is reversed to the above, and the magnetic brush spikes due to the main magnetic pole +71a of the magnet row 2a are at the normal height and come into contact with the surface of the photoreceptor drum 10. do. On the other hand, magnet roller 2
The spikes of the magnetic brush caused by the main magnetic pole mb of b are repelled by the N pole of the auxiliary magnetic pole, their height is suppressed, and they are separated from the surface of the photoreceptor drum 10. By separating the auxiliary magnetic pole from the developer tank to be selected in this manner, the developer tank can be selected.

In the above example, there are two developer tanks, but if two or more developer tanks are arranged, a similar selection can be made by placing a plurality of auxiliary magnetic poles close to each unselected developer tank. Further, although all of the embodiments are copying machines, the present invention can also be applied to devices that perform magnetic brush development, such as facsimile machines and printers.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a developing device used in a copying machine to which the present invention is applied, and FIG. 2 is a diagram showing another embodiment to which the present invention is applied. Figure 3 is a diagram showing the internal structure of a copying machine to which the present invention is applied, and Figure 4 is a diagram showing a developing device of a conventional copying machine. )? Gunesoto l-+-u, 3a, 3b-sleeve, 4a, 4b-magnetic brush, 10-photosensitive drum, 20-auxiliary magnetic pole, ma, ml]
-El three magnetic poles.

Claims (4)

[Claims] (1) A device having a plurality of developer tanks in close proximity to the photoreceptor, and a selection means for selectively attaching toner to the photoreceptor, each of the plurality of developer tanks having magnetic powder and toner. Store the
The selection means includes an auxiliary magnetic pole disposed on the back surface of the photoreceptor facing the roller, and an auxiliary magnetic pole movement for arranging the auxiliary magnetic pole close to or apart from each other. An image forming apparatus comprising means for controlling the standing of the brush by interaction between the main magnetic pole and the auxiliary magnetic pole. (2) Two developer tanks are provided, the main magnetic poles of the two developer tanks have the same polarity, and the auxiliary magnetic pole is movable between the main magnetic poles of the two developer tanks.
The image forming apparatus described in . (3) The auxiliary magnetic pole is of the same polarity as the main magnetic pole, and the selection means is configured to arrange the auxiliary magnetic pole apart from the main magnetic pole in the developer tank to be selected. The image forming apparatus described in . (4) The auxiliary magnetic pole has a different polarity from the main magnetic pole, and the selection means arranges the auxiliary magnetic pole close to the main magnetic pole in the developer tank to be selected. The image forming apparatus according to item 2.