JP2008203064A - Toner concentration detecting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a toner concentration detecting device capable of improving detection capacity, without preventing compaction of the device body. <P>SOLUTION: A wiring board constituting a toner concentration sensor 20 has six-layered structure, and each of spiral print coils 21-26 is formed on each layer. Each print coil 21-26 has the same winding number, winding direction and electrode arrangement and is constituted so that a position of the pattern center becomes substantially the same as a view from the thickness direction of the board. Printed coils on adjacent layers are electrically connected by through-holes 27a, 27b, 27c, 27d, respectively, and all the coils are connected in series, to form a single coil. The printed coils 21-26 are constituted so that the direction of a current is the same, when the current is made to flow, as viewed from the thickness direction of the board. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a toner concentration detection device that detects a toner concentration of a developer from an oscillation frequency of an LC oscillation circuit. More specifically, the present invention relates to a toner concentration detection device in which an inductance (coil) of an LC oscillation circuit is formed by a print pattern.

  As a developing method of a developing device used for an electrophotographic image forming apparatus, a one-component developing method and a two-component developing method are known. The latter two-component development method is a development in which magnetic carrier particles and non-magnetic toner particles are mixed at an appropriate mixing ratio, and the toner particles conveyed by the carrier particles are moved to the surface of the photosensitive member for development. It is a method.

  In the case of the two-component development method described above, only toner is consumed in the developing device, and the carrier circulates in the developing device. Such a two-component developing system developing device is provided with a toner concentration detecting device for detecting the toner concentration of the developer in the developing device. By detecting the toner density (that is, the remaining amount of toner), the toner is stably supplied from the toner replenishing device, and good image quality is ensured.

As the toner concentration detection device, a magnetic sensor using an LC oscillation circuit as a detection member is generally used. That is, the magnetic permeability of the two-component developer that is a mixture of the magnetic carrier and the nonmagnetic toner varies depending on the toner concentration. Therefore, when the coil is installed in the developer conveyance path, the inductance of the coil changes depending on the magnetic permeability of the atmosphere. Since the oscillation frequency of the LC oscillation circuit is given by the following equation (1), the toner density of the developer can be detected by measuring the oscillation frequency f.
f = 1 / 2π (LC) ^1/2 (1)

As a toner concentration detection apparatus using an LC oscillation circuit as described above, for example, in Patent Document 1, a coil (inductance) having a spiral print pattern is formed on one surface of a printed circuit board to constitute an LC oscillation circuit. A toner concentration detection device is disclosed. By forming the coil with a printed pattern, costs can be reduced and quality control can be facilitated. Further, for example, Patent Document 2 discloses a toner concentration detection device that defines a relationship between L, C, and coil resistance R, focusing on the problem of forming a coil with a print pattern and shifting the oscillation frequency with temperature. Yes.
Japanese Utility Model Publication No. 6-76961 JP-A-11-223620

  However, the above-described conventional toner concentration detection device has the following problems. That is, as in the toner concentration detection device disclosed in Patent Document 1 or Patent Document 2, the inductance of a coil based on a printed pattern (hereinafter referred to as “printed coil”) is determined by the occupied area in the substrate surface. Therefore, in order to improve the detection capability, it is necessary to increase the occupation area, which is disadvantageous for downsizing. On the other hand, if the occupied area is narrowed in order to prioritize compactness, the inductance component becomes small and sufficient detection capability cannot be obtained. If the LC oscillation circuit is configured using a printed coil that cannot obtain a large inductance value, the oscillation frequency becomes high and unnecessary radio wave radiation is generated.

  In addition, it is conceivable to increase the inductance value by forming a fine pattern. However, when the pattern width is narrowed, the resistance component increases. Therefore, the sensor characteristics, particularly the temperature characteristics, are deteriorated. In addition, if the pattern interval is narrowed, the insulation characteristics between patterns deteriorate. That is, the printed coil has the minimum necessary pattern width and pattern interval, and the maximum inductance is determined by the occupied area in the substrate surface.

  The present invention has been made to solve the problems of the above-described conventional toner concentration detection device. That is, an object of the present invention is to provide a toner concentration detection device in which the detection capability is improved without hindering the downsizing of the main body of the device.

  A toner concentration detecting device for solving this problem includes an LC oscillation circuit in which a coil constituting an inductance is formed by a spiral printed pattern, and the toner concentration of the developer is determined from the oscillation frequency of the LC oscillation circuit. A toner concentration detection device for detecting, having at least two layers in which coils are formed, and coils adjacent to each other are connected in series via a through hole, and oscillate as viewed from the thickness direction of the substrate. It is characterized in that it is patterned so that the directions of currents during operation are the same.

  In the toner concentration detection device of the present invention, at least two layers of coils (print coils) having a spiral print pattern are provided in the substrate thickness direction, and adjacent coils between the layers are connected in series. That is, adjacent coils between layers constitute one coil. Therefore, in the toner concentration detection device of the present invention, even if the printed coil of each layer is compact and the number of turns is small, a desired inductance can be obtained by connecting a plurality of them in series. In addition, since the printed coils of each layer are patterned so that the current direction during oscillation operation is the same when viewed from the thickness direction of the substrate, the influence of adjacent printed coils can be avoided. That is, a desired inductance can be obtained in the in-plane area without increasing the area occupied by the printed coil and without further reducing the pattern width and pattern interval. Since the inductance is large, highly accurate concentration detection is possible.

  In addition, the toner concentration detection apparatus of the present invention can adjust the inductance by increasing or decreasing the number of layers, and the printed coil can secure a pattern width considering the resistance component and a pattern interval considering the insulation characteristics. The pattern width of the printed coil is preferably in the range of 50 μm to 150 μm. Further, it is desirable that the pattern interval of the printed coil is in the range of 50 μm to 150 μm.

  The linear expansion coefficient of the base material forming the printed coil is preferably 14.4E-6 [/ ° C.] or less. In other words, in a toner concentration inspection apparatus in which an LC oscillation circuit is configured by a print coil, the resistance component of the coil has a great influence on the oscillation frequency, and in particular, the oscillation frequency fluctuates greatly with respect to temperature changes. Therefore, when the linear expansion coefficient of the base material satisfies the above-mentioned definition, the variation in inductance value due to temperature variation can be made sufficiently smaller than the inductance variation due to change in toner concentration. As a result, a decrease in detection accuracy due to a change in use environment can be suppressed within an allowable range, and the toner concentration detection accuracy is compensated.

  According to the present invention, a toner concentration detection device is realized in which the detection capability is improved without hindering the compactness of the device main body.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of an image forming apparatus according to the present invention will be described below in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to a magnetic sensor of a two-component developing type developing device.

  The developing device 100 of the present embodiment is a two-component developing type developing device that uses a mixture of toner and carrier as a developer, and is configured as shown in FIGS. 1 is a perspective plan view of the developing device 100, FIG. 2 is a cross-sectional view taken along line AA in FIG. 1, and FIG. 3 is a cross-sectional view taken along line BB in FIG.

  The developing device 100 contains a two-component developer and forms a developer transport path, a housing 10 that forms a transport path for the developer, a lid 11 that closes an upper opening of the housing 10, and a developing sleeve that transports the developer to the developing region E. 12, a magnet roller 13 that includes a plurality of magnets and forms a magnetic field on the developing sleeve 12, a paddle wheel 14 that supplies developer to the developing sleeve 12, and a developer layer formed on the developing sleeve 12 A regulating member 15 that regulates the layer thickness, and a first stirring screw 16 and a second stirring screw 17 that stir and convey the developer are provided. The developing device 100 is disposed on the downstream side of the exposure portion in the moving direction of the photosensitive drum 1, and the developing sleeve 12 faces the photosensitive drum 1 in a non-contact manner.

  The first stirring screw 16 is disposed in the vicinity of the toner supply port 18, and the second stirring screw 17 is disposed in the vicinity of the paddle wheel 14. The first stirring screw 16 and the second stirring screw 17 are arranged in parallel in a first stirring chamber 10B and a second stirring chamber 10C provided on both sides of a partition wall 10A arranged upright from the bottom of the housing 10, respectively. , And are driven to rotate in opposite directions as indicated by arrows in FIG. As a result, the developers in the first stirring chamber 10B and the second stirring chamber 10C move in opposite directions as indicated by arrows in FIG.

  As shown in FIG. 1, a paddle portion 16A is provided on the most downstream side of the first agitating screw 16 in the developer conveying direction, and a paddle portion 17A is provided on the most downstream side of the second agitating screw 17 in the developer conveying direction. , Are formed integrally. Further, openings 10D and 10E are provided at both ends in the longitudinal direction of the partition wall 10A, respectively. As a result, the developer conveyed to the most downstream side passes through the openings 10D and 10E, and recirculates in the first stirring chamber 10B and the second stirring chamber 10C.

  Further, as shown in FIG. 3, a toner concentration sensor 20 for detecting the toner concentration of the developer is provided on the upstream side of the toner supply port 18 in the developer transport direction. That is, the toner density sensor 20 is disposed at a position where the toner density can be detected before the toner is recirculated from the developing unit E and new toner is supplied. Specifically, the toner density sensor 20 includes an LC oscillation circuit, and obtains an oscillation frequency that varies depending on the magnetic permeability of the developer present in the magnetic field formed by the density sensor 20 to obtain the toner density in the developer. It is to be detected and is arranged below the first stirring screw 16. Details of the toner density sensor 20 will be described later.

  Further, at the location where the toner concentration sensor 20 is disposed, a spacer 30 is disposed to fill a gap between the inner wall surface of the housing 10 and the outer periphery of the screw blades of the first stirring screw 16. The spacer 30 prevents a gap in which the developer stays between the housing 10 and the screw blades of the first stirring screw 16. That is, noise due to staying developer is avoided and accurate density detection is possible.

  Next, the developing operation by the developing device 100 will be briefly described. In the developing device 100, toner stored in a toner cartridge (not shown) is supplied to the first stirring chamber 10 </ b> B through the supply port 18 provided in the lid 11. The toner introduced through the replenishing port 18 is conveyed in the direction of the arrow in FIG. 1 while being agitated and mixed with the developer by the first agitating screw 16 rotating in the first agitating chamber 10B. Further, the developer is fed into the second stirring chamber 10C through the opening 10D. The developer fed into the second stirring chamber 10 </ b> C is conveyed in the direction of the arrow in FIG. 1 while being further stirred by the second stirring screw 17. At this time, a part of the developer is supplied to the paddle wheel 14 and further supplied onto the developing sleeve 12 via the paddle wheel 14.

  The developer supplied onto the developing sleeve 12 forms a developer layer on the developing sleeve 12 and is conveyed to a position facing the photosensitive drum 1 (developing region E). Then, the electrostatic latent image on the photosensitive drum 1 is developed in the development area E. Thereafter, the developed toner image is transferred to a recording medium such as paper and an image is output.

  On the other hand, the developer whose toner has been consumed by the development is peeled off from the surface of the developing sleeve 12 by the repulsive magnetic field formed by the magnet roller 13 and returned to the second stirring screw 17 by the paddle wheel 14. Further, the developer is fed into the first stirring chamber 10B through the opening 10E and is refluxed in the direction of the arrow in FIG.

  Next, the toner density sensor 20 will be described. The toner concentration sensor 20 is a printed wiring board on which a printed pattern is formed, and includes an LC oscillation circuit. Further, the inductance L of the LC oscillation circuit is constituted by a printed coil.

  In the toner concentration sensor 20, as shown in FIG. 4, a spiral printed coil 21 is formed on the surface of the substrate 2 made of glass epoxy resin. The toner concentration sensor 20 is arranged such that the surface on which the printed coil 21 is formed is a detection surface, and the detection surface faces the first stirring chamber 10B side. Electrodes 21a, 21b, and 21c are formed at the center of the print coil 21, and electrodes 21A, 21B, 21C, and 21D are formed at the outer periphery of the print coil 21, respectively. Are connected. In the toner density sensor 20, a spiral printed coil is also formed on the back surface, and other components (capacitor, transistor, etc.) constituting the oscillation circuit are mounted.

  As the LC oscillation circuit of the toner density sensor 20, for example, as shown in FIG. 5, a Colpitts oscillation circuit including a coil L having a predetermined inductance, capacitors C1 and C2, a transistor Q, and a resistor R can be applied. This coil L is constituted by a printed coil. In addition, RL in FIG. 5 is the resistance of the coil portion. When voltage V is applied to this circuit, an oscillation signal is output from transistor Q. The LC oscillation circuit is not limited to the Colpitts oscillation circuit.

Further, the wiring substrate constituting the toner density sensor 20 has a six-layer structure as shown in FIG. 6, and spiral printed coils 21 to 26 are formed in each layer. The printed coils 21 to 26 are configured such that the number of turns, the arrangement of electrodes, the pattern width, and the pattern interval are equal, and the positions of the pattern centers are substantially the same when viewed from the thickness direction of the substrate. However, the winding direction of the printed coil differs between adjacent layers. Further, the connection between the printed coil and the electrode differs depending on each layer. The coil connections are as shown in Table 1 below.

  Further, the printed coils between adjacent layers are electrically connected by through holes 27a, 27B, 27b, 27C, and 27c. Specifically, as shown in FIG. 7, the print coils 21 to 26 of the toner density sensor 20 of the present embodiment are alternately provided with through holes that connect the coil centers and through holes that connect the outer circumferences of the coils. , All coils are connected in series to form one coil.

  Further, as shown by the arrows in FIG. 7, the printed coils 21 to 26 are configured such that the direction of the current when the current flows is the same when viewed from the thickness direction of the substrate. That is, the toner density sensor 20 is configured such that a current flows clockwise in all the print coils. If the lines of magnetic force excited by the current flowing in each printed coil are arranged to cancel each other, desired inductance characteristics cannot be obtained. Therefore, by aligning the current direction, the influence of adjacent printed coils is avoided and desired inductance characteristics are ensured.

  Furthermore, in order to use the coil as a sensor, it is necessary that the fluctuation of the inductance value due to the fluctuation of the usage environment is sufficiently smaller than the fluctuation of the inductance due to the change of the toner concentration as the sensing object. However, when a printed coil is used as in the present embodiment, the resistance component of the coil has a great influence on the oscillation frequency, and the oscillation frequency varies greatly with changes in temperature.

  Usually, in order to compensate for such a frequency variation due to temperature, a method of selecting a temperature compensation capacitor having an appropriate temperature characteristic and suppressing it to a desired temperature characteristic is adopted. In order for this temperature compensation capacitor to operate correctly, there must be no temperature difference between the printed coil to be compensated and the capacitor to be compensated. On the other hand, the toner temperature sensor 20 of this embodiment is a printed board having two or more layers, and a printed coil is formed on each layer. That is, the printed coil and the temperature compensating capacitor are not necessarily mounted on the same plane. That is, with the toner temperature sensor 20 of this embodiment, it is difficult to perform temperature compensation using only the temperature compensation capacitor.

  Therefore, in the toner temperature sensor 20 of this embodiment, the linear expansion coefficient of the base material of the printed coils 21 to 26 is defined, and frequency fluctuation due to temperature is compensated. FIG. 8 shows the result of simulating the relationship between the temperature coefficient of the printed coil (the amount of change in inductance with respect to temperature) and the linear expansion coefficient of the printed circuit board.

  For the toner concentration sensor 20 of this embodiment, the lower limit of the operating temperature is 10 ° C., the upper limit is 50 ° C., the fluctuation amount (control target) of the oscillation frequency corresponding to the change in the toner concentration of 1% is 5 kHz, and the fundamental frequency is 3 MHz. And The frequency variation allowed in the operating temperature range is set to ½ of the control target. In this case, the temperature coefficient of the target frequency fluctuation is 42 [ppm / ° C.] ≈5 [kHz] / 30 [MHz] / (50-10) or less.

  It can be seen from the graph shown in FIG. 8 that the linear expansion coefficient of the substrate corresponding to a temperature coefficient of frequency of 42 [ppm / ° C.] is 14.4E-6 [/ ° C.]. Therefore, in the toner concentration sensor 20 of the present embodiment, the linear expansion coefficient of the base material forming the coils 21 to 26 is set to 14.4E-6 [/ ° C.] or less. As a result, the fluctuation of the inductance value due to the use environment fluctuation is suppressed within a desired range, and the detection of the toner density with high accuracy is compensated. As the base material satisfying the above linear expansion coefficient, for example, a glass epoxy base material or ceramic can be applied.

  Further, each printed coil of this embodiment has a pattern width of 100 μm. This pattern width should just be in the range of 50 micrometers-150 micrometers. When the pattern width becomes narrower than 50 μm, the resistance component of the coil increases and the temperature coefficient of frequency fluctuation becomes unacceptable. On the other hand, when the pattern width is wider than 150 μm, the number of turns of the coil is reduced and a large inductance cannot be obtained.

  Further, each printed coil of this embodiment has a pattern interval of 100 μm. The pattern interval may be in the range of 50 μm to 150 μm. If the pattern interval is narrower than 50 μm, insulation between patterns cannot be obtained. On the other hand, when the pattern interval is wider than 150 μm, the number of turns of the coil is reduced and a large inductance cannot be obtained.

  Note that the number of printed coil layers to be stacked is not limited to six, and varies depending on the required inductance and the AC voltage applied to the coil. Therefore, at least two layers are sufficient. In order to obtain the designed inductance, it is necessary to ensure a certain insulation distance. Therefore, considering the cost and the size in the thickness direction of the substrate, the number of layers is preferably 6 layers or less.

  In addition, the insulation resistance of the substrate of the wiring board varies depending on the voltage applied to the coil during the oscillation operation, but is preferably approximately 1 MΩ or more. If the base material satisfies this condition, insulation failure between layers can be avoided.

  As described in detail above, the toner density sensor 20 of this embodiment is provided with six layers of print coils 21 to 26, and all the print coils are connected in series. That is, one coil (coil L in FIG. 5) is configured by the print coils 21 to 26. Therefore, even if the printed coil of each layer is compact and has a small number of turns, a desired inductance can be obtained by connecting a plurality of them in series. That is, a desired inductance can be obtained in the in-plane region of the substrate without increasing the area occupied by the printed coil and without further reducing the pattern width and pattern interval. Since the inductance is large, highly accurate concentration detection is possible. Also, the printed coils of each layer are patterned so that the current direction during oscillation operation is the same when viewed from the thickness direction of the substrate, so that the influence of adjacent printed coils is avoided and the desired inductance is avoided. Characteristics can be secured. Therefore, a toner concentration detection device is realized in which the detection capability is improved without hindering the downsizing of the device main body.

  Moreover, the linear expansion coefficient of the base material which forms the printed coils 21 to 26 is 14.4E-6 [/ ° C.] or less. When the linear expansion coefficient of the base material satisfies the above-mentioned regulations, the fluctuation of the inductance value due to the use environment fluctuation can be made sufficiently smaller than the inductance fluctuation due to the change of the toner concentration. As a result, a decrease in detection accuracy due to a change in use environment can be suppressed within an allowable range, and the toner concentration detection accuracy is compensated.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, the shape of the coil is not limited to a circle. That is, the shape may be a spirally wound shape, and the outer shape may be, for example, a rectangle.

1 is a plan perspective view showing a schematic configuration of a developing device according to an embodiment. It is a figure which shows the AA cross section in FIG. It is a figure which shows the BB cross section in FIG. It is a figure which shows the pattern of the outermost layer of the toner density | concentration sensor concerning Embodiment. FIG. 3 is a circuit diagram showing an LC oscillation circuit of the toner concentration sensor according to the embodiment. It is a figure which shows CC cross section in FIG. It is a figure which shows the connection image of the print pattern of each layer. It is a figure which shows the relationship between the temperature coefficient of printed coil inductance, and the linear expansion coefficient of a printed circuit board.

Explanation of symbols

20 Toner concentration sensor (toner concentration detector)
21 to 26 Print coil 27a Through hole 100 Developing device

Claims (4)

In a toner concentration detection device comprising an LC oscillation circuit in which a coil constituting an inductance is formed by a spiral printed pattern, and detecting the toner concentration of the developer from the oscillation frequency of the LC oscillation circuit,
Having at least two layers on which coils are formed;
Coil adjacent to each other between layers is connected in series through a through hole, and is patterned so that the current direction during oscillation operation is the same when viewed from the thickness direction of the substrate. Concentration detector. The toner concentration detection device according to claim 1,
A toner concentration detection device, wherein the base material forming the coil has a linear expansion coefficient of 14.4 × 10 ⁻⁶ [/ ° C.] or less. In the toner concentration detection device according to claim 1 or 2,
The toner density detecting device, wherein the pattern width of the coil is in a range of 50 μm to 150 μm. In the toner concentration detection apparatus according to any one of claims 1 to 3,
The toner density detecting device, wherein the coil pattern interval is in a range of 50 μm to 150 μm.

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