JPS61158353A - Developing device - Google Patents

Abstract

PURPOSE:To improve the controlling accuracy of toner concentration of a developing device provided with the toner concentration control of a developer fluidity detecting system and to maintain stable picture density by setting up the fluidity of toner to be used at the start of development differently from that of feeding toner. CONSTITUTION:Toner having fluidity higher than that of toner for charging to a developing hopper 8 together with a carrier is used as feeding toner 11 to be used at the initial stage. Even if the fluidity of toner is deteriorated due to friction between the toner and the carrier, the fluidity of the whole developer can be kept at a fixed level over a long period because the fluidity of the feeding toner 11 is high. Since a fine gap is formed on the lower part of a hopper 12 and a metallic roll 13 is rotated, toner 15 is dropped from the gap 14 between the roll 13 and the lower surface of the hopper 12 simultaneously with the rotation. Under said constitution, the hopper 12 is filled with a fixed quantity of toner, the metallic roll 13 is rotated for a fixed period and the quantity of toner 15 dropped on a pan 16 is measured to determine the relative fluidity. The relative fluidity is numerized so as to be used as a fluidity index.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a developing device used in an electrophotographic copying machine or a printer using electrophotographic technology.

[Prior art]

Conventionally, two types of methods have been proposed for developing an electrostatic latent image formed on an image carrier such as a photoreceptor or dielectric. For example, many types of development are known, such as a magnetic brush development method, a cascade development method, a powder cloud development method, a fur brush development method, and a liquid development method.

Among these developing methods, a two-component magnetic brush developing method using a developer mainly consisting of non-magnetic toner and carrier can provide relatively stable and good images.

However, in order to obtain stable image density, it is necessary to maintain the toner density within a certain range, and for this purpose, it is necessary to control the toner density with high precision.

For example, there has been a method of controlling toner concentration by detecting changes in the fluidity of developer in a developer.

In this system, a detection sensor is provided in a part of the developing hopper of the developing device, detects changes in the fluidity of the developer in the developing hopper, and replenishes toner from the toner hopper into the developing hopper.

A method of controlling toner density by detecting developer fluidity will be described below with reference to the drawings. Figure 2 is.

FIG. 2 is a sectional view of a developing section of an electrophotographic copying machine equipped with a conventional developing device.

The photosensitive drum 1 consists of a photosensitive layer 1a and a support drum 1b that supports the photosensitive layer 1a from inside.

After going through a charging and exposure process (not shown), an electrostatic latent image corresponding to the document is formed and held on the surface of the photosensitive layer 1a, and is transferred to a developing area facing the developing device 2a. reach.

On the other hand, on the developing device 2a side, the developer 5a is constantly conveyed to the developing area by the rotation of the non-magnetic developing sleeve 3, and comes into contact with the surface of the photosensitive layer 1a of the photosensitive drum 1 to form the electrostatic latent image. is developed.

That is, the developing sleeve 3 is made of a cylinder made of a non-magnetic material such as aluminum, and rotates in the direction of the arrow.

A magnet roll 4 magnetized with a large number of poles is fixed inside the developing sleeve 3. Further, the developer 5a
The carrier is made of a magnetic material and has a particle size of 20 to 200 μm, and a toner whose main component is resin and has a particle size of 10 to 15 μm is mixed. Incidentally, the carrier may be one in which the main component is a magnetic material coated with a resin, or one in which a resin is mixed.

The carrier and toner are stirred by a stirring roll 6, and as a result of the stirring, the toner is charged with a polarity opposite to that of the electrostatic latent image on the surface of the photosensitive layer 1a. The developer 5 is adsorbed onto the surface of the developing sleeve 3, rotated and conveyed in the direction of the arrow, and passes through a regulating member 7, thereby regulating the amount of adsorption.
Furthermore, it is sent to the developing area which is the closest part to the photosensitive drum 1. In the image area, the developer 5a is transferred to the magnetic roll 4.
The main pole N+ forms an ear and contacts the surface of the photosensitive layer 1a. Then, due to the Coulomb force from the electrostatic latent image, the developer 5
A part of the toner in a is transferred to the surface of the photosensitive layer 1a, and the electrostatic latent image is developed. As the developing device repeats the developing process in this way, the toner concentration in the developer 5a decreases, eventually causing a decrease in image density, so it is necessary to replenish toner.

Therefore, the developing device 2 adopts a method of controlling the toner concentration by detecting the fluidity of the developer 5a.

A detection sensor 10 (for example, an electrostrictive vibrator) is provided in the developing hopper 8, with its detection surface facing the developing sleeve 3 side and tilted at a predetermined angle.

Now, in the developing hopper 8, the developer 5a that has been conveyed on the developing sleeve 3 from the vicinity of the stirring roll 6 to the regulating member 7 is regulated by the regulating member 7 to a constant height. At this time, the excess developer 5a is prevented from passing through the regulating portion by the regulating member 7, and the blocked developer 5a bulges along the regulating member 7 due to the conveying force of the developing sleeve 3. The developer 5a, which has reached a position where it is not affected by the magnetic field of the magnetic nozzle 4, flows downward as if collapsing under its own weight. In this way, two flows occur: the developer 5a being conveyed to the regulating member 7 and the developer 5a collapsing. However, in the toner concentration control method by detecting the fluidity of the developer 5a, the toner flows downward in this collapsing manner. developer 5a
By detecting the fluidity of the toner, the rotation of the toner supply roll 9 is controlled, and the supply of the toner 11a' into the developer 5a is controlled.

That is, when the toner concentration in the developer 5a in the developer hopper 8 is relatively high, the fluidity of the developer 5a flowing down is poor;
Since the contact resistance with the detection surface of the detection sensor 10 increases during flowing down, the detection signal of the detection sensor 10 is turned ON.
The situation is as follows.

The rotation of the toner supply roll 9 is stopped.

Therefore, the toner 11a is not replenished. As the developing process is repeated from this state, the toner concentration in the developer 5a gradually decreases. Then, the fluidity of the developer 5a becomes good, the contact resistance on the detection surface of the detection sensor 1° decreases, and the detection signal of the detection sensor 10 becomes OFF. Utilizing the ON/OFF of such detection signals,
By controlling the rotation of the toner replenishing roll 9, the toner concentration in the developer 5a is maintained constant by controlling the replenishment of the toner 11a.

[Problems with conventional technology]

In the above-mentioned developing device, the developer conventionally used has a drawback in that fluidity decreases when the developer is stirred for a long time with a stirring roll in the developing hopper. This is mainly due to the carrier being agitated with the toner for a long time.

This is thought to be due to so-called filming development in which the resin in the toner adheres to the carrier surface. In this way, even though the fluidity of the paste is reduced due to factors other than fluctuations in toner concentration, the detection signal of the detection sensor remains in the ON state, and toner replenishment is not performed. Therefore, when two or more types of developers are used, as shown in FIG.
There was a drawback that the toner concentration gradually decreased.

[Purpose of the invention]

SUMMARY OF THE INVENTION In view of the above-mentioned conventional drawbacks, it is an object of the present invention to maintain stable image density by improving the accuracy of toner density control in a developing device equipped with toner density control using a developer fluidity detection method.

[Key points of the invention]

According to the present invention, the above object is achieved by providing a developing device in which the fluidity of the toner used at the start of development is different from the fluidity of the replenishing toner.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to nine drawings. FIG. 1 is a sectional view of a developing section of an electrophotographic copying machine equipped with two developing devices of the present invention. The developing device 2 is a developing device that controls toner concentration using a developer fluidity detection method, and its basic structure is the same as that of the developing device 2 shown in FIG. Numbers are given and explanations of basic structures and operations are omitted.

Now, what is the replenishment toner 11 used in the present invention?

A toner having higher fluidity than the toner initially filled into the development hopper 8 together with the carrier is used. Therefore.

Even if the fluidity deteriorates due to friction between the toner and the carrier, the fluidity of the developer as a whole can be kept constant over a long period of time because the replenishment toner 11 has high fluidity.

In other words, as shown in Figure 3, even if the number of copies increases,
The toner concentration can be kept approximately constant.

Next, regarding the fluidity index of the toner, as shown in FIG. Fill a certain amount of toner into the impeller 12, rotate the metal roll 13 for a certain period of time, and measure the amount of toner 15 that has fallen into the tray 16. , shi, determine the relative flow rate. This is quantified into a liquidity index. For example, if 10 g of toner is filled into the hopper 12 and the metal roll 9 is rotated for 1 minute, and the amount of toner that falls into the tray 16 is 5 g, the fluidity index is 5.
I have decided that. In such a method, when the fluidity index is unstable, the toner in the developer is around 5 and the replenishment toner is around 7 to 8, and a stable density is controlled at around 10%. I was able to do it. As described above, in a developing device equipped with fluidity detection type toner density control, by using replenishment 1 toner with higher toner fluidity than the developer toner at the start, it is possible to produce toner with high precision. Concentration control can be performed.

〔Effect of the invention〕

According to the developing device of the present invention configured as described above, it is possible to perform toner density control using a fluidity detection method with high precision, and to maintain stable image density.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a developing section of an electrophotographic copying machine equipped with a developing device according to the present invention. FIG. 2 shows an electrophotographic copying machine equipped with a conventional developing device. FIG. 3 is a diagram showing the relationship between the number of copies and toner density when the developing device of the present invention is used. FIG. 4 is a block diagram of an apparatus for determining a fluidity index. FIG. 5 is a diagram showing the relationship between the number of copies and toner density when a conventional developing device is used. 1... Photosensitive drum. 1a...Photosensitive layer. lb...Support drum. 2...Developing device. 3...Developing sleeve. 4... Magnet roll. 5...Developer. 6... Stirring roll. 7...Regulating member. 8...Developing hopper. 9... Toner supply roll. 10...Detection sensor. 11 ・ ・ ・ Toner. 12... Toner hopper. 13...Metal roll. 14...Gap. 15 ・ ・ ・ Toner. 16...Saucer patent Applicant: Casio Computer Co., Ltd. Same as above
Casio Electronic Industries Co., Ltd. Patent Attorney Dai
Yoshi Suga 2 Figure 1 Figure 2 Figure 3 Goby cane tξ (XIOI clothes) Figure 4

Claims (2)

[Claims] (1) A developing device characterized in that the fluidity of the toner used at the start of development is different from the fluidity of the toner. (2) The developing device according to claim 1, wherein the fluidity of the replenishment toner is higher than the fluidity of the toner used at the start of development.