JPH08271481A - Toner density sensor - Google Patents

Abstract

PURPOSE: To ensure an installation place in a small-sized imaging system while preventing the detection accuracy from lowering by forming a resonance circuit and a shaping circuit on a flexible substrate. CONSTITUTION: The toner density sensor TS1 comprises a spiral planar coil LP, capacitors C1 , C2 , a resistor R and an integrated circuit IC having shaping function mounted, while being interconnected through a copper foil, on a flexible board. The flexible board has a structure where the copper foil is pasted to a polyimide film through an extremely thin adhesive. The planar coil LP is formed by etching the copper foil on the surface of the flexible printed board at the time of etching a wiring pattern for oscillation circuit in the rear surface of the flexible printed board. The capacitors C1 , C2 are provided after etching the coil LP. Frequency of the oscillation output from the toner density sensor TS1 is set higher, by one figure or more, than that of AC component being applied to a developing sleeve thus suppressing the effect of high frequency field.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-component developer toner in which carrier particles made of a magnetic material (hereinafter, simply referred to as magnetic carrier) and toner particles made of resin (hereinafter, simply referred to as toner particle) are mixed. The present invention relates to a density sensor, and more particularly, to improvement of a toner density sensor that detects a change in magnetic permeability of a so-called two-component developer with an oscillation output from an LC resonance circuit.

[0002]

2. Description of the Related Art An image forming apparatus which employs an electrostatic photography method or an electrophotography method visualizes an electrostatic latent image formed on an image bearing member as a toner image by a developing device loaded with a two-component developer. (See JP-A-57-38482, JP-A-62-157070, etc.). A developing device using such a two-component developer conveys the developer to a developing area by a developer conveying carrier in a state where magnetic carrier particles and non-magnetic synthetic resin toner particles are mixed at an appropriate mixing ratio. Then, the electrostatic latent image on the image carrier is visualized as a toner image to maintain the density of the toner image at a predetermined level. Therefore, in order to stabilize the density of the toner image, it is necessary to maintain the density of the toner loaded in the developing device at a predetermined level. Therefore, it is necessary to detect the toner density of the developer and replenish the toner appropriately.

As a sensor for detecting the toner concentration of a two-component developer, the fact that the apparent magnetic permeability of the developer, which is a mixture of magnetic carriers and toner particles, changes depending on the toner concentration is utilized, and it is close to the developer. Alternatively, the inductance of the coil embedded in the developer is measured. It is also well known to use an LC oscillation circuit to measure such an inductance (Japanese Patent Laid-Open No. 56-67872, etc.).

Since the oscillation frequency of the LC oscillation circuit is given by f = 1 / {2π (LC) ^1/2 }, the toner density is detected from the frequency f.

As the coil, a winding coil in which a thin wire is wound around a core having a strong magnetic permeability such as iron or ferrite, and a coil in which the developer flow is used as the core of the coil have been put into practical use. There is a problem that it is difficult to make contact with the developer and sensitivity is low, and it may be possible to use the inside of the coil as a passage for the developer in order to improve the contact between the developer and the coil. There is a problem of increasing the size.

With the recent downsizing of image forming apparatuses, downsizing of toner concentration sensors is also inevitable, and for this reason, a flat coil has been proposed (Japanese Patent Laid-Open No. 5-539).
4-7938).

The present applicant has also proposed in Japanese Patent Application No. 5-16176 and Japanese Patent Application No. 5-59580. In such a planar coil, a coil is spirally arranged between two coil electrodes inserted in a through hole formed in a printed circuit board, and the coil is covered with an insulating resin layer, or for the oscillation circuit wiring on the back surface of the printed circuit board. When the pattern is etched, the copper foil on the surface of the printed circuit board is also etched so that the width is 50 to 100 μm and the pitch is 100 to 20.
It is made of copper foil with a thickness of about 0 μm. However, if the detection range, which is the range through which the magnetic flux passes, becomes too wide, this plane coil will not only change the toner concentration in the developer but also the operation of mechanical parts such as stirring members. There is a drawback that it will be affected.

In order to solve such a drawback, the present applicant has formed a planar board by connecting spiral planar coils in series on a circuit board so that the directions of magnetic flux produced by adjacent planar coils are opposite to each other. It has been proposed to concentrate the magnetic flux of a plane coil on the coil surface without reducing the coil inductance (see Japanese Patent Application No. 6-38626).

[0009]

However, since the toner concentration sensor lightened and thinned by using the above planar coil (see Japanese Patent Application No. 6-38626) is formed on the hard printed circuit board, there is a tendency of downsizing. Therefore, there is a drawback that the installation place is not restricted in the downsized apparatus, and the toner density sensor has a problem that the detection accuracy is lowered due to the influence of the high frequency electric field in the downsized image forming apparatus. The adverse effect of the high frequency electric field in the miniaturized image forming apparatus will be specifically described below.

In the recent color image forming apparatus, in order to downsize the entire apparatus, a plurality of downsized developing devices are arranged close to the periphery of the image bearing member having a reduced diameter. These developing devices employ a non-contact developing method in which an alternating current bias is superimposed on a high voltage direct current bias as a developing bias in order to prevent fogging. When these developing devices are driven, an AC electric field is formed around the developing devices, and a high frequency electric field having a frequency higher than the AC fundamental frequency is generated from the AC electric field. Therefore, the toner concentration sensor is arranged in the high frequency electric field. In such a situation, the electronic circuit that constitutes the toner concentration sensor will be modulated by the high frequency electric field, and the frequency cannot be measured reliably. The phenomenon will be further described.

FIG. 5 shows a general equivalent circuit of the toner concentration sensor, and FIG. 6 shows an output signal from the toner concentration sensor showing the influence of the high frequency electric field.

In FIG. 5, the coil L is for measuring the inductance of the developer, the capacitors C ₁ and C ₂ are connected in parallel with the coil L to form an oscillation circuit, and the gate IC ₂ is. It is an inverter having a function of amplifying an oscillation output to a predetermined level and has a gate I
C ₃ and the gate IC ₄ are inverters having an amplifying function for achieving the waveform shaping function.

FIG. 6A is a graph showing the waveform of the input signal of the gate IC ₂ , and FIGS. 6B and 6C are graphs showing the waveform of the output signal of the gate IC ₄ .

The sine wave shown by the dotted line in FIG. 6 (a) shows a state in which there is no distortion and is not affected by the high frequency electric field. Therefore, the pulse output from the gate IC ₄ forming the waveform shaping circuit has a rectangular wave shown by the alternate long and short dash line in FIG. By counting such pulses, the oscillation frequency of the LC oscillation circuit can be measured, so that the toner concentration can be detected accurately.

On the other hand, the output signal shown by the solid line in FIG. 6 (a) shows a distorted state under the influence of a high frequency electric field, and the output signal from the waveform shaping circuit obtained from such an input signal is as shown in FIG. 6 (b) outputs the pulse shown by the solid line.
If the waveform shaping circuit is also affected by the high frequency electric field,
The waveform output is as shown in (c). The pulse waveform shown in FIG. 6C is modulated and distorted due to the influence of the high frequency electric field. Such a pulse has an irregular duty ratio, the oscillation frequency obtained by counting such a pulse has low accuracy, and the toner concentration cannot be controlled stably.

SUMMARY OF THE INVENTION An object of the present invention is to provide a toner density sensor which has been made in view of the above problems and which secures an installation place in a miniaturized image forming apparatus and prevents deterioration of detection accuracy. .

[0017]

Means for achieving the above-mentioned object are as follows: an oscillation circuit comprising a plane coil and a capacitor; a waveform shaping circuit for shaping the oscillation output from the oscillation circuit; A toner concentration sensor for measuring output pulses to detect a mixing ratio of a two-component developer, characterized in that the resonance circuit and the waveform shaping circuit are formed on a flexible substrate. As a result, the toner concentration sensor can be made thinner, so that it is possible to easily provide an installation place in the downsized image forming apparatus.

The line connecting the plane coil and the capacitor in parallel is shorter than the connection line between the waveform shaping circuit and the capacitor. Therefore, even if the connection line is bent, the connection line is lengthened, or the connection line is shortened, the inductance on the oscillation circuit does not fluctuate. Alternatively, the detection accuracy of the toner concentration sensor can be maintained by reducing the influence of the inductance.

The oscillating frequency of the oscillating circuit is higher than the frequency of the AC voltage component applied to the developing sleeve by one digit or more. This makes it possible to reduce the influence of the high frequency electric field. Therefore, it is possible to accurately detect the toner density.

It is characterized in that the plane coil is separated by 1 mm or more from the high voltage application portion of the developing unit. Thereby, the influence of the high frequency electric field can be suppressed. Further, the toner density can be detected with high accuracy.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing a schematic structure of an image forming apparatus adopting the toner density sensor of the present invention.

The image forming apparatus includes a charger 12 that charges the image carrier 10 to a predetermined potential, and a laser writing unit 13 that exposes the image to form a color-separated electrostatic latent image on the image carrier 10. , A developing device 3, a developing device 4, a developing device 5, a developing device 6 by a magnetic brush developing method in which toners of a plurality of colors necessary for reproducing the electrostatic latent image in full color are individually loaded, and a transfer material as a roller. A resist roller 8 that conveys to the transfer device 9, a roller transfer device 9 that collectively transfers the toner images from the image carrier 10 onto the transfer material, a separation discharge device 10 that separates the transfer material from the image carrier 10, and a transfer material. A fixing device 20 for fusing and condensing a toner image, a paper feed cassette 15 for accommodating a large amount of general transfer material, and a non-standard-size transfer material or a small amount of transfer material such as thick paper or resin film. Paper tray 7 and exposure devices 11 and 14, A series of processes for forming the toner image on the image carrier 10 is repeated a plurality of times for each color, and a program for controlling the operation of each member described above is written so that the toner images of respective colors are superposed on the image carrier 10. ROM
(Not shown). The configuration and function of each member will be described below.

The image carrier 10 is formed by forming a photosensitive layer on the surface of a conductive substrate made of, for example, aluminum. The conductive base material is a drum-shaped photosensitive member having a diameter of 120.06 mm, which is composed of a (−) charged coating type OPC that is grounded and rotates in the direction of the arrow.

An encoder (not shown) is provided on the drive shaft of a DC motor M ₁ (not shown) that drives the rotation of the image carrier 10.
Is attached. A control unit (not shown) rotates the motor in synchronization with the index signal generated for each main scanning line of the laser. The control unit (not shown) detects the phase of the image carrier 10 by counting the drum pulses from the encoder (not shown) described above, and is also used for registration timing control and operation timing control of each member. ing. In other words, the control unit (not shown) can detect the leading edge position of the image from the timing of the index pulse that is first generated when forming an image on one screen. The phase is detected and each member is drive-controlled based on the phase.

The exposure device 11 is for exposing the toner image to remove the charge before transfer, and the exposure device 14 is for removing the charge remaining on the image carrier 10 before charging.
The cleaning device 17 removes the toner and dust remaining on the image carrier 10.

The laser writing unit 13 emits a semiconductor laser (not shown) based on a recording signal sent from a writing control section (not shown) to line scan the image carrier 10 to perform a latent image. Is formed. GaAlAs or the like is used for the semiconductor laser (not shown), and the maximum output is 5 mW. Since the color toners are sequentially superposed in this embodiment,
Exposure with wavelength light that is less absorbed by the colored toner is preferred, and is 780 nm.

Developing unit 3, developing unit 4, developing unit 5, developing unit 6
Contains, for example, yellow, magenta, cyan, and black developers, and is provided with a developing sleeve 31, a developing sleeve 41, a developing sleeve 51, and a developing sleeve 61 that keep a predetermined gap from the image carrier 10. The latent image on the body 10 is visualized by a non-contact reversal development method. The development sleeve 31, the development sleeve 41, and the development sleeve 5
1. The drive shaft of the developing sleeve 61 is connected to, for example, a drive shaft of a motor via a gear (not shown), and the sleeve drive shaft that is selectively driven changes the gear according to a drive signal to develop the developing sleeve 31. , Developing sleeve 4
1. The developing sleeve 51 and the developing sleeve 61 are controlled to either rotate or stop.

Developing unit 3, developing unit 4, developing unit 5, developing unit 6
Have the same configuration, the other detailed configuration will be described with respect to the developing device 3.
Will be described as a representative.

The developing unit 3 has a frequency of 8 KHz and a frequency of 200 to 4
An AC power supply (not shown) of 000 V _pp and a DC power supply (not shown) that outputs a DC component for preventing fog are connected to the developing sleeve 31 via a protective resistor (not shown) to generate an alternating current. A voltage with a direct current superimposed is applied to the magnet body, the stirring screw 34, and the regulating blade 3 as well.
2. A developing sleeve 3 including a cleaning blade 33 and a two-component developer in which magnetic carrier particles and toner particles are mixed and molded from a non-magnetic material rotatably supported.
A magnetic brush is formed from a two-component developer on the first surface, and the developing sleeve 31 is rotated in a state where the magnetic brush does not contact the image carrier 10 to convey the developer to the developing area and apply a predetermined developing bias. The latent image formed on the image carrier 10 is visualized with toner particles. A developing device adopting this developing method is abbreviated as a so-called two-component non-contact developing device.
The above is the detailed configuration of the developing device 3, the developing device 4, the developing device 5, and the developing device 6 of the present embodiment. Next, the arrangement state of the developing device 3, the developing device 4, the developing device 5, and the developing device 6 will be described.

The image forming apparatus of the present embodiment has an image carrier 10 formed in a cylindrical state having a small diameter in order to downsize the entire apparatus.
A miniaturized developing device 3, a developing device 4, a developing device 5, and a developing device 6 are arranged on the periphery of the toner concentration sensor TS in order to detect the toner concentration satisfactorily. The stirring screw 34, stirring screw 44, stirring screw 54 , Is installed below the stirring screw 64. According to this configuration,
Regulating blade 32, regulating blade 42, regulating blade 5
2. The regulation blade 62 tends to be arranged near the toner concentration sensor TS. When the developing device 3, the developing device 4, the developing device 5, and the developing device 6 are driven in such a configuration as described above, the AC electric field generated around the developing sleeve 31, the developing sleeve 41, the developing sleeve 51, and the developing sleeve 61 is changed. A high-frequency electric field higher than the fundamental frequency of the alternating current is also formed. Further, the developing blade 31, the developing sleeve 41, the developing sleeve 51, and the developing agent carried on the developing sleeve 61 are restricted by the developing blade 31, the regulating blade 32, the regulating blade 42,
By contacting the regulation blade 52 and the regulation blade 62, the developing device 3, the developing device 4, the developing device 5, and the developing device 6 form a housing with thin members in order to achieve downsizing. The influence of the high frequency electric field easily appears outside the developing device 3, the developing device 4, the developing device 5, and the developing device 6. As described above, the toner concentration sensor TS is installed in the vicinity of the stirring screw 34, the stirring screw 44, the stirring screw 54, and the stirring screw 64 on the bottom wall of the developing device 3, the developing device 4, the developing device 5, and the developing device 6. Therefore, the distance is directly affected by the above-mentioned high frequency electric field. In order to avoid the influence of such a high frequency electric field, the spiral planar coil L _p forming the toner concentration sensor TS is provided in the developing device 3, the developing device 4, the developing device 5, and the developing device 6, for example, the developing sleeve 31, the developing sleeve 41, The developing sleeve 51, the developing sleeve 61, and the regulating blade 32 and the regulating blade 4 which are connected to each other by the developer brush
2, 1 mm or more away from the high voltage application portion including the regulation blade 52 and the regulation blade 62. This makes it possible to reduce the influence of the high frequency electric field.
The installation location of the toner concentration sensor is not limited to the vicinity of the stirring screw 34, the stirring screw 44, the stirring screw 54, and the stirring screw 64 as described above. For example, the developing sleeve 31, the developing sleeve 41,
The influence of the high-frequency electric field can be similarly ignored at the developing sleeve 51, the developing sleeve 61, and the place 1 mm or more away from the high voltage application portion of the developer.

By installing the toner concentration sensor TS as described above, the installation location is secured even in the image forming apparatus in which the developing unit 3, the developing unit 4, the developing unit 5, and the developing unit 6 are arranged close to each other to be miniaturized. At the same time, it is possible to prevent a decrease in detection accuracy.

The reason why the two-component non-contact developing method is adopted in the image forming method of this embodiment is that the toner particles can control triboelectric charging relatively easily and the toner particles do not easily aggregate. The magnetic brush has good ears, is excellent in friction with the surface of the image carrier, and has a feature that a sufficient cleaning effect is exhibited even when it is used for cleaning. This is because it is also suitable for non-contact development that develops by contact.

Next, the paper feed system of the image forming apparatus of this embodiment is
It comprises a paper feed cassette 15, a paper feed tray 7, a transfer roller 10, a fixing device 20, and the like. The transfer material stored in the paper feeding cassette 15 is separated into individual sheets by the rotation of the half-moon-shaped first paper feeding roller 16 and is fed to the registration rollers 8. The transfer material placed on the paper feed tray 7 is also fed to the registration rollers 8 after being separated one by one by the rotation of, for example, a half-moon shaped second paper feed roller 19. By providing passage detection sensors PA1 and PA2 (not shown) in the vicinity of the first feeding roller 16 and the second feeding roller 19 to detect passage of the transfer material regardless of the transparency of the transfer material, for example, by providing at least an actuator. A jam between the registration rollers 8 from the paper feed cassette 15 or the paper feed tray 7 is detected. Further, a transmission type passage detection sensor PA3 (not shown) is provided near the registration roller 8. The passage detection sensor PA3 includes a light emitting diode and a light receiving element. The passage detection sensor PA3
Shields the space between the light emitting diode and the light receiving element by passing a normal transfer material or thick paper. On the other hand, passage detection sensor PA3
Outputs a current corresponding to the transmittance of the transfer material from the light receiving element when passing through the transfer sheet having transparency. Although not shown, the output signals from the above-mentioned passage detection sensors PA1 to PA3 are sent to a control unit (not shown) via a signal line.

FIG. 2 is a schematic configuration diagram showing a first embodiment of the toner concentration sensor TS of the present invention, and FIG. 2A is a plan view showing the appearance of the toner concentration sensor TS1 of the present embodiment.

The toner concentration sensor TS1 comprises a spiral planar coil L _p and a capacitor C ₁ on a flexible substrate 101.
The capacitor C ₂ , the resistor R, and the integrated circuit IC are configured. Flexible substrate 101 is 1/2 oz (18 μm)
FPC (Freq) made by pasting the copper foil and the 1/2 mil (12.5 μm) polyimide film using an ultra-thin adhesive.
cilde Print Cirkitbord) structure. The spiral planar coil L _p has a width of 50 to 1 by etching the copper foil on the front surface of the flexible printed board when etching the oscillation circuit wiring pattern on the back surface of the flexible board.
The copper foil is formed to have a thickness of 00 μm and a pitch of 100 to 200 μm. The capacitors C ₁ and C ₂ are added after the planar coil L _p is etched. The toner concentration sensor TS1 is formed by connecting a spiral planar coil L _p , a capacitor C ₁ , a capacitor C ₂ , an integrated circuit IC having a waveform shaping function, and a resistance element R with a copper foil. Integrated circuit IC
Is mainly an integrated electronic circuit having a waveform shaping function.

As described above, in the toner concentration sensor TS1 of this embodiment, the spiral planar coil L _p is formed on the flexible substrate 101, and the chip component capacitors C ₁ , C ₂ and integrated circuit IC are mounted. By doing so, the overall thickness can be reduced. Therefore, it is easy to secure the installation space even in the downsized image forming apparatus.

FIG. 2B is a block diagram showing an equivalent circuit of the toner density sensor TS1 shown in FIG.

The function of the integrated circuit IC shown in FIG. 2A can be equivalently expressed by _three gate IC ₂ , gate IC ₃ and gate IC ₄ . The gate IC ₂ functions as an inverter, and in addition to the inverter function, the oscillation output is amplified to a predetermined level and output to the subsequent gate IC ₃ (not shown) and gate IC ₄ (not shown). Is. The gate IC ₃ and the gate IC ₄ achieve the waveform shaping function. As described with reference to FIG. 2A, by arranging the spiral planar coil L _p and the capacitor C ₁ and the capacitor C ₂ apart from each other, the spiral planar coil L _p , the capacitor C ₁ and the capacitor C ₁ are separated. Since the line connecting C ₂ in parallel is made long, the fluctuation L _{pf of the} reactance component caused by bending the connection line, lengthening the connection line, or shortening the connection line is taken into consideration. Need to be installed.

FIG. 3 is a schematic configuration diagram showing a second embodiment of the toner concentration sensor of the present invention, and FIG. 3A is a plan view showing the appearance of the toner concentration sensor TS2 of the present embodiment.

The toner concentration sensor TS2 is composed of a spiral flat coil L _p and a capacitor C ₁ on a flexible substrate 101.
The capacitor C ₂ , the resistor R, and the integrated circuit IC are configured. Flexible substrate 101 is 1/2 oz (18μ
This is an FPC structure in which a copper foil of (m) and a polyimide film of 1/2 mil (12.5 μm) are bonded together using an ultrathin adhesive. The spiral planar coil L _p has a width of 50 to 100 μm and a pitch of 100 to 100 μm by etching the copper foil on the front surface of the flexible printed board when etching the oscillation circuit wiring pattern on the back surface of the flexible board.
It is formed of copper foil with a thickness of about 200 μm. The capacitors C ₁ and C ₂ are added after the planar coil L _p is etched. Toner concentration sensor TS2
Arranging the spiral plane coil L _p , the capacitor C ₁ , and the capacitor C ₂ in close proximity to each other to connect a line connecting the spiral plane coil L _p , the capacitor C ₁ , and the capacitor C ₂ in parallel. It is shorter than the connection line between the integrated circuit IC having a waveform shaping function and the capacitors C ₁ and C ₂ . The integrated circuit IC is mainly an integrated electronic circuit having a waveform shaping function.

As described above, in the toner concentration sensor TS2 of the present embodiment, the spiral planar coil L _p is formed on the flexible substrate 101, and the chip parts capacitors C ₁ , C ₂ and integrated circuit IC are mounted. By doing so, the overall thickness can be reduced. Therefore, it is easy to secure the installation space even in the miniaturized image forming apparatus, and the oscillation frequency is not affected by the outside due to the variation of the connection line length, the bending, and the like.

FIG. 3B is a block diagram showing an equivalent circuit of the toner density sensor TS2 shown in FIG.

In the integrated circuit IC shown in FIG. 3A, the function can be equivalently expressed by _three gate IC ₂ , gate IC ₃ and gate IC ₄ . The gate IC ₂ functions as an inverter, and in addition to the inverter function, the oscillation output is amplified to a predetermined level and output to the subsequent gates IC ₃ and IC ₄ . Gate IC ₃ , Gate IC
₄ achieves the waveform shaping function. As described with reference to FIG. 3A, the spiral planar coil L _p and the capacitor C ₁ ,
By arranging the capacitor C ₂ close to each other, the line connecting the spiral planar coil L _p and the capacitors C ₁ and C ₂ in parallel is shortened, so that the reactance due to bending of the connection line or the like is caused. There is no need to consider the ingredients. Therefore, it is easy to secure the installation place in the downsized image forming apparatus and is not affected by the fluctuation of the reactance component of the connection line, so that the detection accuracy can be prevented from lowering.

Next, a structure for removing the influence of the high frequency electric field will be described.

The modulation noise due to the high-frequency electric field described with reference to FIG. 6 is generated everywhere in the oscillation output, but the phase shift of the rectangular wave after the waveform shaping (see FIG. 6B) causes the detection accuracy. It has a great influence. Specifically, FIG.
It is observed that a phase difference is generated when modulated at the rising edge of the sine wave shown in (a). Therefore, in this embodiment, in order to prevent the rising waveform from being affected by the modulation, the oscillation frequency of the oscillation circuit is higher than the frequency of the AC voltage component of the developing bias of 500 Hz to 20 KHz by one digit or more and the high frequency of 5 kHz to 200 kHz. Is set to. The effect of such a relationship will be described with reference to FIG.

FIG. 4 is a graph showing the relationship between the oscillation frequency of the toner concentration sensor of this embodiment and the frequency of the AC component of the developing bias.

FIG. 4A shows the waveform of the AC component of the developing bias applied to the developing sleeve 31, the developing sleeve 41, the developing sleeve 51 and the developing sleeve 61. FIG. 4B shows the detection output output from the toner density sensor of this embodiment. Since the duty ratio of the developing bias is 125 μsec and the duty ratio of the output from the toner concentration sensor is 0.286 μsec, it is understood that the influence of the high frequency electric field is less likely to occur when the sensor output rises.

Therefore, the toner density sensor TS of this embodiment is
By setting the frequency of the oscillating output from the developing sleeve 31, the developing sleeve 41, the developing sleeve 51, and the frequency of the AC component applied to the developing sleeve 61 by one digit or more, the influence of the high frequency electric field can be reduced. it can.

[0049]

According to the first aspect of the present invention, since the toner density sensor can be made thin by providing the above-described structure, it is possible to easily provide the installation place in the downsized image forming apparatus. it can.

According to the second aspect of the present invention, by providing the above configuration, even if the length of the connection line is changed, the shape of the connection line is changed, or the connection line is bent, the coil of the oscillation circuit is not changed. The inductance can be prevented from fluctuating, and the detection accuracy of the toner concentration sensor can be maintained.

According to the third aspect of the present invention, by providing the above configuration, it is possible to reduce the influence of the high frequency electric field. Therefore, it is possible to accurately detect the toner density.

According to the fourth aspect of the present invention, by providing the above configuration, the influence of the high frequency electric field can be suppressed, and the toner concentration can be detected accurately.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a schematic configuration of an image forming apparatus adopting a toner density sensor of the present invention.

FIG. 2 is a schematic configuration diagram showing a first embodiment of the toner concentration sensor of the present invention.

FIG. 3 is a schematic configuration diagram showing a second embodiment of the toner density sensor of the present invention.

FIG. 4 is a graph showing the relationship between the oscillation frequency of the toner concentration sensor of this embodiment and the frequency of the AC component of the developing bias.

FIG. 5 shows a general equivalent circuit of a toner concentration sensor.

FIG. 6 shows an output signal from a toner concentration sensor showing an influence of a high frequency electric field.

[Explanation of symbols]

3, 4, 5, 6 developing device 31, 41, 51, 61 developing sleeve 101 flexible substrate TS toner concentration sensor C ₁ , C ₂ capacitor IC waveform shaping circuit L _p plane coil

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazunori Yamamoto 1st Sakura-cho, Hino City, Tokyo Konica Stock Company In-house

Claims (4)

[Claims] 1. An oscillating circuit including a plane coil and a capacitor, a waveform shaping circuit for shaping a waveform of an output signal from the oscillating circuit, and a pulse output from the waveform shaping circuit is measured to mix a two-component developer. A toner concentration sensor for detecting a ratio, wherein the resonance circuit and the waveform shaping circuit are formed on a flexible substrate. 2. The line connecting the planar coil and the capacitor in parallel is shorter than the connection line connecting the waveform shaping circuit and the capacitor.
The toner concentration sensor described in 1. 3. The toner concentration sensor according to claim 1, wherein the oscillation frequency of the oscillation circuit is higher than the frequency of the AC voltage component applied to the developing sleeve by one digit or more. 4. The toner concentration sensor according to claim 1, wherein the plane coil is separated from the high voltage application portion of the developing unit by 1 mm or more.