JPH0448393B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a developing device, for example, an electronic copying machine, which uses a fine powder developer, and particularly relates to a developing device equipped with a means for detecting the concentration of the developer. This relates to improvements in equipment.

[Conventional technology]

In electrostatic recording and developing devices such as electronic copying machines, facsimile machines, and electrostatic printers, an electrostatic latent image recorded on the surface of an image bearing member such as a photosensitive drum is processed using a magnetic brush method using a magnetic developer. It is then developed and fixed by heat or pressure means to obtain the final visible image. In this case, in order to obtain a stable image, in a developing device that uses a two-component developer, it is necessary to monitor the mixing ratio of the ferromagnetic carrier and toner powder with high precision and maintain the appropriate density. A developing device equipped with a measuring means has been put into practical use.

FIG. 5 is a sectional view of essential parts of a developing device using a two-component developer. In the figure, reference numeral 1 denotes a developer tank which stores a developer 2 and is connected to an upper part via a supply roll 3 to a toner tank 5 which stores toner 4. As shown in FIG. The developer tank 1 includes a magnet roll 6 formed in a cylindrical shape and having a plurality of magnetic poles arranged on its surface.
A hollow cylindrical sleeve 7 made of a non-magnetic material is provided so as to be rotatable with respect to each other, and is opposed to the photosensitive drum 8. In the developer tank 1, rotating blades 9 are provided in parallel with the magnet roll 6 for stirring the developer 2 and triboelectrically charging the toner 4. Next, a doctor blade 10 is provided at the end of the developer tank 1 facing the photosensitive drum 8, and the gap between it and the sleeve 7 can be freely adjusted. Reference numeral 11 denotes a toner concentration sensor, and a detection portion is provided above the developer tank 1 so as to be in contact with the developer 2 .

With the above configuration, due to the relative rotation of the magnet roll 6 and the sleeve 7, the developer 2 on the sleeve 7 moves in the direction of the arrow, forms a magnetic brush on the sleeve 7, and rubs the surface of the photosensitive drum 8. Therefore, the electrostatic latent image formed on the photosensitive drum 8 can be developed. The developer 2 is further moved in the direction of the arrow by the sleeve 7 and returned to the developer tank 1, and is stirred by the rotary blade 9 together with the toner 4 supplied from the toner tank 5 via the supply roll 3.
The image is then subjected to development again. The toner concentration sensor 11 provided in contact with the developer 2 measures the toner concentration in the developer 2 and outputs an external signal in order to maintain the toner concentration in the developer 2 according to the measured concentration. ,
The replenishment roll 3 is driven via an appropriate driving means (not shown), and the toner 4 is controlled to be replenished from the toner tank 5.

[Problem that the invention seeks to solve]

In the conventional developing device as described above, the toner concentration sensor 11 is provided above the sleeve 7 as shown in FIG. If installed, it is limited to approximately three locations. In other words, the main reason for this is that the toner concentration sensor 11 is larger than the developer tank 1, as shown in FIG. It is difficult to do so, and the degree of freedom in the installation location is extremely small. Therefore, the optimum installation location for measuring the toner concentration of the developer 2 cannot be selected.
The measured results may not necessarily represent the true toner concentration of the developer 2. Depending on changes in environmental conditions and other factors, the height of the magnetic brush formed on the sleeve 7 may be adjusted by adjusting the doctor blade 10. In this case, the layer thickness of the developer 2 in contact with the toner concentration sensor 11 may be As a result, the measured value of toner density changes, and the true toner density may not be ascertained. When variations or errors occur in the measured values of toner concentration in this way, it becomes difficult to properly control and maintain the toner concentration of the developer, making it impossible to develop a high-quality image. The present invention solves the problems that exist in conventional developing devices as described above, and provides a developing device that can accurately detect and measure the toner concentration of the developer without variation, maintain it at an appropriate concentration, and develop high-quality images. The purpose is to provide a device.

[Means for solving problems]

In order to achieve the above object, the present invention provides a developing device having a developer density measuring means and an appropriate density maintaining means, in which the density measuring means is configured as follows. That is, (1) coils are provided concentrically on the front and back sides of the board to form a primary coil, (2) a detection coil is provided on one side of the board, and the primary coil and coupling degree adjustment means are provided on the other side of the board. (3) the detection coil and the reference coil are connected in opposite phases to each other to form a secondary coil; (4) the primary coil and the secondary coil form a differential transformer. (5) The substrate is mounted on a doctor blade with the detection coil side facing the developer.

〔Example〕

FIG. 1 is a sectional view of a developing device showing an embodiment of the present invention, and the same components are designated by the same reference numerals as in FIG. 5. In the figure, reference numeral 11a denotes a toner concentration sensor, which is provided on the side of the doctor blade 10 facing the developer 2. FIGS. 2 and 3 are an enlarged side view and a front view of the main part of the toner concentration sensor 11a. In the figure, reference numeral 12 denotes a substrate, which is made of a non-magnetic material and has a size of about 10 mm x 50 mm x 2 mm. Coils 13 and 14 are provided on the front and back sides of the substrate 12 at approximately the center thereof, respectively.
are arranged concentrically and connected to each other to form a primary coil. The coils 13 and 14 are formed flat and thin, for example, by sheet coils. Next, board 1
A detection coil 15 is provided on one surface of 2, and a reference coil 16 is provided on the other surface. An adjusting member 1 is provided between the coil 14 forming the primary coil and the reference coil 16 to adjust the degree of coupling between the two coils.
7 will be provided. The adjustment member 17 is made of, for example, a magnetic material such as soft ferrite, or a conductive material such as copper, and is provided on the substrate 12 so that its position can be adjusted.
Note that the detection coil 15 and the reference coil 16 are connected in opposite phases to form a secondary coil, and together with the primary coil, a differential transformer is formed. After constructing as described above, the detection coil 15 is fixed to the developer 2 side of the doctor blade 10 so as to face and contact the developer 2, as shown in FIG.

FIG. 4 is a diagram showing the winding structure and circuit blocks of the toner concentration sensor shown in FIGS. 1 to 3, and the same parts are designated by the same reference numerals as in FIGS. 2 and 3. In FIG. 4, 18 is an oscillator, which together with coils 13 and 14 constitutes an oscillation circuit. Detection coil 15 which then forms the secondary coil
An amplifier 19 is connected to the secondary coil, and a phase detector 20 is further connected to the secondary coil to form a phase detection circuit. 21 is a comparator, which is connected to the phase detector 20 and the DC power supply 23, and whose output side is connected to the drive output circuit 22. With the above configuration, the oscillator 1
8 and the primary coils 13 and 14, the oscillation signal of the oscillation circuit is transmitted to the detection coil 1 constituting the secondary coil.
5 and the reference coil 16 in opposite phases. In this case, since the developer is in contact with the upper part of the substrate 12 in FIG. 2 (not shown), the coil 13 containing the developer and the detection coil 15, and the substrate
If the magnetic resistances in the magnetic circuits of the lower coil 14, adjustment member 17, and reference coil 16 are the same, the differential voltage between the induced voltages in the detection coil 15 and the reference coil 16 forming the secondary coil will be equal to that of the amplifier 19. After being amplified by the oscillation voltage and phase detector 20 on the primary coil side, the signal is detected and output as a predetermined voltage value. However, when the development with the developer 2 shown in FIG. 1 is repeated and the toner is consumed, the toner density becomes thinner.
As the effective magnetic permeability of the developer 2 increases, the induced voltage of the detection coil 15 increases, and the detection output also increases. Therefore, the output of the comparator 21 becomes high level,
The drive output circuit 22 is activated to drive the replenishment roll 3 shown in FIG. 1, and the toner 4 is replenished into the developer layer 1. On the other hand, when the toner continues to be replenished and reaches the appropriate toner concentration, the induced voltage of the detection coil 15 becomes small and the detection output also becomes small, so the output of the comparator 21 becomes a low level, and as a result, the drive output circuit 22 is activated. stop. In this way, supply roll 3 is ON-
By turning off, the supply of toner 4 is controlled and the toner concentration of developer 2 is maintained at an appropriate value.

In this embodiment, the toner concentration sensor 11
Although an example has been shown in which the doctor blade 10 is fixed to the developer 2 side, the doctor blade itself may be used as the substrate 12 shown in FIGS. 2 and 3, and the two may be integrated. In addition, the center part of the doctor blade 10 is hollowed out according to the dimensions of the substrate 12, and
2 can also be fitted.

〔Effect of the invention〕

Since the developing device of the present invention has the structure and operation as described above, it has the following effects.

(1) Since the toner concentration sensor is installed inside the doctor blade, the developer is in the most dense state, and detection accuracy is good and reliability is high.

(2) Since the toner concentration sensor is formed extremely thin, there is no interference with other members constituting the developing device, and there is a high degree of freedom in selecting the mounting position.

(3) Even if the layer thickness of the magnetic brush is changed by adjusting the doctor blade, the conditions of the developer at the density sensor remain unchanged, so there is no change in the measured value. .

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a main part showing an embodiment of the present invention, FIGS. 2 and 3 are an enlarged side view and front view of a main part of the toner concentration sensor shown in FIG. 1, and FIG. 4 is a toner density sensor. FIG. 5 is an explanatory diagram showing the winding structure and circuit block of FIG. 1... Developer tank, 3... Supply roll, 6... Magnet roll, 7... Sleeve, 10... Doctor blade, 11, 11a... Toner concentration sensor, 12... Substrate, 13, 14... coil, 1
5...Detection coil, 16...Reference coil.

Claims (1)

[Scope of Claims] 1. A density measuring means for measuring a change in the density of a developer by a change in magnetic permeability, a means for maintaining the developer at an appropriate density according to a measurement result by the density measuring means, and a means for maintaining the developer at an appropriate density. In a developing device equipped with a developing means for conveying a latent image on an image bearing member to an image bearing member, coils are provided concentrically on each of the front and back sides of a substrate to form a primary coil, and a primary coil is formed on one side of the substrate. A detection coil is provided on one surface, and a reference coil is provided on the other surface via a degree of coupling adjustment means with the primary coil, and the detection coil and reference coil are connected to have opposite phases to each other to form a secondary coil. A developing device characterized in that the primary coil and the secondary coil form a differential transformer, and the substrate is provided on a doctor blade with the detection coil side facing the developer to constitute a density measuring means. 2. The developing device according to claim 1, wherein the substrate is integrated with the doctor blade. 3. The developing device according to claim 1 or 2, wherein the coil is a sheet coil. 4. The developing device according to any one of claims 1 to 3, wherein the means for adjusting the degree of coupling between the primary coil and the reference coil is a magnetic material or a conductive material.