JPH0418306B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a developing device for visualizing an electrostatic image formed on the surface of an image carrier by a magnetic brush method.

Prior Art In image forming devices such as electrophotographic devices and electrostatic recording devices, an electrostatic latent image is formed on the surface of an image carrier (selenium photoreceptor, zinc oxide photoreceptor, organic photoconductor, dielectric material, etc.). The electrostatic latent image is developed by a magnetic brush method using a magnetic developer and then fixed, or
Alternatively, the developed image is transferred onto a transfer sheet such as plain paper and then fixed to obtain the final image.

As the magnetic developer used in the magnetic brush method, a two-component developer which is a mixture of a ferromagnetic carrier and toner particles is often used. This magnetic carrier is made of iron powder, ferrite powder, nickel powder, etc., or their surfaces are coated with an organic polymer, and the toner particles are made by dispersing additives such as blue pigments and dyes in resin. The materials of the carrier particles and toner particles are selected so that when they are mixed, they are frictionally charged with opposite magnetism.

When an electrostatic latent image is developed using the above-mentioned two-component developer, toner particles are consumed during development, so that when development is repeated, the toner concentration in the developer decreases. If development is performed while the toner density remains low, the image density will drop.

Therefore, when using a two-component developer, in order to maintain the toner concentration in the developer at a predetermined level (approximately 3 to 10%), a means for detecting the toner concentration is installed, and a signal from the detection member is installed. Generally, a developing device is configured to replenish toner according to the amount of toner. Toner concentration detection methods often utilize the fact that the toner concentration in the developer changes and the magnetic permeability of the developer changes. For example, a Hall element is provided in the magnetic field of a permanent magnet member, and the developer Detection of leakage magnetic flux from (JP-A-51-117047
Although the Hall element has high detection accuracy, it is susceptible to temperature changes and has reliability problems. Therefore, the developer usually forms part of the magnetic circuit of the detection coil, and the toner concentration is often detected as a change in the inductance of the detection coil.
No. 54-159233).

In addition, in a developing device using a two-component developer,
Since it is necessary to mix the developer after development with the newly replenished toner, in order to scrape off the developer after development from the non-magnetic sleeve, a same-polarity opposing part is attached to the permanent magnet member inside the non-magnetic sleeve. (For example, see Japanese Utility Model Publications No. 51-19884, Japanese Utility Model Publication No. 53-35479, and Japanese Patent Publication No. 56-47552.)

In a developing device having a permanent magnet member provided with the same-polarity opposing parts, in order to prevent the toner concentration detection member from being affected by the magnetic flux generated from the permanent magnet member, the toner density detection member is placed between the same-polarity opposing parts. (For example, Japanese Patent Application Laid-Open No. 52-124339,
52-127241, 53-126944, and 54-76165).

However, in the above-mentioned known example, since detection is attempted within a range where the influence of magnetic flux lines is as small as possible, it is extremely difficult to convey the developer while maintaining it at a constant level in the detection section.

OBJECTS OF THE INVENTION An object of the present invention is to solve the problems of the prior art described above and to provide a developing device capable of detecting toner concentration with high reliability.

Arrangements of the Invention Arrangements of the invention include: a non-magnetic rotating sleeve holding a developer including a magnetic carrier and toner particles;
a permanent magnet member having a plurality of magnetic poles including a developing magnetic pole provided in the non-magnetic rotating sleeve and a scraping magnetic pole having a polarity opposite to this magnetic pole; a developer tank containing the developer; A developing device including a scraper member provided close to a rotating sleeve and behind the scraping magnetic pole when viewed from the rotating direction of the sleeve, and a toner concentration detection member provided around the sleeve,
The toner concentration detection member includes a pair of magnetic circuits including a detection side magnetic circuit whose degree of coupling changes depending on the toner concentration and a reference side magnetic circuit whose degree of coupling can be set to a predetermined degree, and a primary circuit of the pair of magnetic circuits. an oscillator that supplies an input signal to the magnetic circuit; and a phase detector that detects the phase of a differential AC output signal of both magnetic circuits obtained by a secondary coil of the pair of magnetic circuits,
The above-mentioned scraped-off magnetic pole is replaced by two magnetic poles S1a and S1b that are arranged in close proximity to each other in the rotational direction of the non-magnetic rotating sleeve.
At the same time, the magnetic flux density peak value of the rear magnetic pole S1b is made higher than the magnetic flux density peak value of the magnetic pole S1a on the near side with respect to the rotational direction of the non-magnetic rotating sleeve, and the detection surface of the toner concentration detection member is scraped off with respect to the magnetic pole S1a. The developing device is located between S1b and in contact with the developer.

Embodiments Hereinafter, embodiments of the present invention will be described based on the drawings.

Here, FIG. 1 is a sectional view of a developing device according to an embodiment, FIG. 2 is a diagram showing a circuit configuration of the toner concentration detection member of FIG. 1, and FIG. 3 is a circuit output of the toner concentration detection member of FIG. FIG. 3 is a diagram showing waveforms.

First, in FIG. 1, a two-component developer 2 consisting of a magnetic carrier and toner is contained in a developer tank 3, and inside the developer tank 3 is a photosensitive drum 1 rotating in the direction of arrow Z in the figure. A cylindrical non-magnetic sleeve 4 is rotatably arranged opposite to each other. There are a plurality of non-magnetic sleeves (4 in the figure) on the surface of the non-magnetic sleeve 4.
A permanent magnet member 7 is disposed in which a permanent magnet 5 having 5 magnetic poles is fixed to a shaft 6. Among the magnetic poles, the N ₁ pole is a developing magnetic pole located opposite the developing gap D, and the S ₁ a pole and S ₁ b pole are scraping magnetic poles.

A scraper member 15 is installed behind the S ₁ b pole when viewed from the direction of rotation of the non-magnetic sleeve 4 .
A pair of screws 9, 9' are rotatably installed on the opposite side of the non-magnetic sleeve 4 from the photosensitive drum 1, and above the screws 9, 9',
A toner tank 10 containing toner 2a is formed. A toner supply roll 13 having a porous elastic layer 12 fixed around a shaft 11 is rotatably provided at the lower opening of the toner tank 10 . Further, a doctor member 14 is installed in the developer tank 3 to regulate the thickness of the developer on the non-magnetic sleeve 4.

The operation of the developing device configured as described above is as follows: First, when the non-magnetic sleeve 4 is rotated in the direction of the arrow X shown in the figure, the developer 2 adsorbed onto the sleeve 4 is conveyed from the doctor gap d toward the developing gap D. Ru. Near the development gap D, a magnetic brush formed by the developer 2 rubs the surface of the photosensitive drum 1, and an electrostatic latent image (not shown) formed on the drum 1 is developed. After passing through the developing gap D, the developer 2 is scraped off from the non-magnetic sleeve 4 by a scraper member 15 and collected into the developer tank 3.

Next, the collected developer 2 is stirred and mixed together with the toner 2a discharged from the toner tank 10 by the screws 9 and 9' due to the rotation of the toner supply roll 13, and then transferred onto the non-magnetic sleeve 4 again. It is absorbed and subjected to development.

Further, after the developer 2 passes through the development gap D, the toner concentration in the developer 2 is detected by a toner concentration detection member 8 that contacts the developer layer, and an external signal is output according to the detected toner concentration. The rotation of the toner replenishing roll 13 is controlled by a driving means (not shown).

Next, various structures are known as the toner concentration detection member 8 that utilizes changes in the inductance of a detection coil, and for example, one having the structure shown in FIG. 2 has been proposed.

In the same figure, the U-shaped magnetic core 16a has a primary coil L ₁ a and a secondary coil L ₂ a.
A primary coil L ₁ b and a secondary coil L ₂ b are wound around b to form two transformers. The primary coils L ₁ a and L ₁ b are connected to the output terminal (not shown) of the oscillator 17, and the secondary coils L ₂ a and L ₂ b are connected to the signal input terminal (not shown) of the phase comparator 18. ), and comparison signal detection coils LR ₁ and LR ₂ are wound around the secondary side of each transformer, and these are connected to the comparison signal input terminal of the phase comparator 18. The output terminal (not shown) of the phase comparator 18 is the input terminal (not shown) of the potential comparator 19.
There, it is compared with a reference voltage corresponding to a predetermined toner concentration, and a signal corresponding to the potential difference is output. The potential comparator 19 is connected to the drive circuit 20.
It is connected to a load (a drive source such as a motor) 21 via.

According to the above circuit configuration, when the transmission output from the transmitter 17 is applied to each of the primary coils L ₁ a and L ₁ b, an output signal corresponding to the degree of coupling of each magnetic circuit is transmitted to the secondary coils L ₂ a and L 1 b. induced by L ₂ b.

Here, if the degree of coupling of both magnetic circuits is equal, the outputs of the secondary coils L ₂ a and L ₂ b are in opposite phases, so they cancel each other out, and their differential output becomes 0.
becomes. Therefore, if the degrees of coupling between the two magnetic circuits are different, the output of one of the secondary coils L ₂ a and L ₂ b will be larger, resulting in a differential output corresponding to the difference in the degree of coupling. , the differential output is compared with a reference value by a phase comparator 18, and a phase detection output corresponding to the phase is output.

In other words, the reference voltage is adjusted so that when the toner concentration is equal to the set value, the phase detection output becomes 0 [see Figure 3 A], and as the toner concentration changes, the magnetic permeability of the developer changes. What is necessary is to output a phase detection output corresponding to the change in magnetic permeability when the change in magnetic permeability occurs [see FIG. 3B].

As the sensitivity adjustment mechanism of the toner concentration detection member 8, for example, a screw core made of a magnetic material such as soft ferrite may be used, and this may be provided on the reference magnetic circuit side.

As described above, since the toner concentration detection member detects the toner concentration by comparing the output signals of the two magnetic circuits, it is substantially unaffected by changes in environmental conditions such as temperature and humidity. This makes it possible to detect toner concentration with extremely high reliability.

As mentioned above, when detecting toner concentration using the inductance change of this detection coil,
If the fluctuation width (noise) of the output signal is large, toner concentration cannot be detected with high accuracy. Therefore, it is generally necessary to keep this variation range as small as possible. However, in the conventional developing device, the detection surface of the toner concentration detection member 8 is installed directly above the scraping magnetic poles S ₁ a and S ₁ b, that is, above the peak of the magnetic flux density of the magnetic poles. A similar problem occurs.

Therefore, as a result of studies conducted by the present inventor, it was found that detection accuracy can be greatly improved by providing the detection surface of the detection member in front of the peak of the scraped magnetic pole when viewed from the rotational direction of the non-magnetic sleeve. .

To be more specific, if the peak value of the magnetic flux density of the S ₁ b pole is made larger than the peak value of the magnetic flux density of the S ₁ a pole (see Figure 1) and a detection surface is provided between them, on the S ₁ a pole, A wide and relatively flat magnetic brush is formed so that the developer material is in steady contact with the sensing surface. That is, since detection is performed while the density of the developer is substantially constant, the fluctuation range of the output signal can be narrowed, and highly accurate detection can be achieved.
On the other hand, when the peak value of the S ₁ a pole is the same as the peak value of the S ₁ b pole, the magnetic force becomes approximately 0 between the two magnetic poles due to the action of the repulsive magnetic field, resulting in a coarse magnetic brush, which makes detection difficult. The contact between the surface and the developer becomes unstable, and the fluctuation range of the output signal increases.

For comparison, FIG. 4 shows a configuration with a single scraping magnetic pole S1, and the detection surface of the toner concentration detection member 8 is located in front of the magnetic flux density peak point of this magnetic pole S1. The other configurations are the same as those in the previous embodiment, so their explanation will be omitted.

Note that the broken lines in FIGS. 1 and 4 indicate the magnetic flux density distribution on the nonmagnetic sleeve 4 of the scraped-off magnetic pole.

Specific Example In FIG. 1, a Se drum (outer diameter 120 mmφ, circumferential speed 150 mm/sec) was used as the photosensitive drum 1, and a Ba-ferrite magnet with an outer diameter of 32 mmφ was used as the nonmagnetic sleeve 4. Moreover, in the permanent magnet 5,
The N ₁ pole is 800G, the S ₁ and S ₂ poles are all 650G (all values on the sleeve), the angle θ ₁ is 10°, and the interpole angles θ ₂ and θ ₃ are 80° and 210°, respectively. It was ゜. As the developer 2', an iron powder carrier (EFV manufactured by Nippon Iron Powder Co., Ltd.) with a particle size of 100 to 200 μm and toner particles with a particle size of 5 to 20 μm were used.

Then, the doctor gap d and the developing gap D are both set to 4 mm, and the non-magnetic sleeve 4
was rotated at 200 rpm, the standard value of the toner concentration in the developer was set to 5%, and a continuous copy test of 10,000 sheets was conducted.

Here, as a detection member, the one shown in Figure 2 was used, and as a result of measuring the output signal with the median value of the output signal set to 2.5V and the target fluctuation width set to 1V or less, the fluctuation range of the output signal was was able to be kept within 1V. Further, for comparison, when the detection member 8 was set as shown in FIG. 4, the variation range of the output signal was 2V.

Effects of the Invention As described above, the present invention obtains a detection output directly from the difference in magnetic coupling force between a pair of magnetic circuits from a change in the inductance of a detection coil, and phase-detects the output, thereby detecting temperature and temperature. The toner concentration can be detected with extremely high reliability without being substantially affected by changes in environmental conditions such as humidity, and the scraping magnetic poles are two magnetic poles S1a and S1b,
Regarding the rotation direction of the non-magnetic rotating sleeve, the magnetic pole S1 behind the magnetic flux density peak value of the front magnetic pole S1a
Since the toner concentration is detected by increasing the magnetic flux density peak value of b and placing the detection surface of the toner concentration detection member at a position where it contacts the developer between both magnetic poles S1a and S1b, the developer does not touch the detection surface. This has the effect of making it possible to accurately detect the toner concentration in the developer by making contact in a stable state and reducing the fluctuation range of the output signal.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the developing device according to the present invention, FIG. 2 is a diagram showing the circuit configuration of the toner concentration detection member, and FIG. 3 is a diagram showing the waveform of the circuit output of FIG. The figure shown in FIG. 4 is a sectional view showing a developing device shown for comparison. 1... Photosensitive drum, 2... Developer, 3... Developer tank,
4...Nonmagnetic sleeve, 7...Permanent magnet member, 8...Toner concentration detection member, 15...Scraper member.

Claims (1)

[Claims] 1. A non-magnetic rotating sleeve that holds a developer containing a magnetic carrier and toner particles, and a plurality of magnetic poles including a developing magnetic pole provided in the non-magnetic rotating sleeve and a scraping magnetic pole having a polarity opposite to this magnetic pole. a developer tank containing the developer; a scraper member provided close to the non-magnetic rotating sleeve and behind the scraping magnetic pole when viewed from the rotational direction of the sleeve; In a developing device having a toner concentration detection member provided around the sleeve, the toner concentration detection member has a detection side magnetic circuit whose degree of coupling changes depending on the toner concentration and a reference side magnetic circuit which can be set to a predetermined degree of coupling. an oscillator that supplies an input signal to a primary circuit of the pair of magnetic circuits, and a differential AC output signal of both magnetic circuits obtained by a secondary coil of the pair of magnetic circuits; The scraped-off magnetic pole is made into two magnetic poles S1a and S1b that are adjacent to each other in the rotational direction of the non-magnetic rotating sleeve, and the magnetic pole on the near side with respect to the rotational direction of the non-magnetic rotating sleeve. Magnetic pole S1b behind the magnetic flux density peak value of S1a
The detection surface of the toner concentration detection member is scraped off by the magnetic poles S1a and S1.
A developing device characterized in that the developing device is provided at a position where it comes into contact with a developer between portions (a) and (b).