JP4143386B2 - Permeability detecting device, image forming device, digital copying machine, and toner concentration detecting device - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to an image forming apparatus using a dry electrophotographic method, and more particularly to a magnetic permeability detecting apparatus that detects the magnetic permeability of a magnetic material such as toner in a non-contact manner.
[0002]
[Prior art]
In an electrophotographic copying apparatus, generally, the surface of a photosensitive drum is uniformly charged by a charger, and an electrostatic latent image is formed by exposing the photosensitive member based on image information. The toner is selectively attached and developed, and the obtained toner image is transferred to plain paper and fixed to obtain a final image.
[0003]
A general configuration example of the developing device is shown in FIG. The developing device shown in FIG. 2 is a small-diameter two-stage developing roller system, and an upper developing sleeve and a lower developing sleeve are disposed adjacent to the photosensitive drum, and is composed of a non-magnetic toner mainly composed of a colorant and a magnetic carrier. The developer is fed to the surface of the photosensitive drum by a paddle roller. As the development is performed, the magnetic carrier hardly decreases but the toner decreases. Therefore, a toner hopper is provided to replenish the reduced toner, and the replenishing toner is accommodated in the hopper.
[0004]
When the mixing ratio of the toner with respect to the magnetic carrier decreases, the density of the developed image decreases, and vice versa when the mixing ratio increases. To obtain an image of appropriate quality, it is necessary to always maintain the toner contained in the developing device within an appropriate constant level range. For this purpose, a toner concentration detecting device (T sensor) for detecting the toner concentration in the developer. Is installed. Further, the developing device is provided with a stirring roller in order to make the mixed state of the developer and the replenishing toner uniform.
[0005]
As a conventional example, a specific magnetic detection device for detecting toner density in a developing device is driven by an AC drive source by connecting a detection coil adjacent to the developer and a reference coil separated from the developer in series. A magnetic difference in the developer is detected by obtaining a phase difference between the differential output voltage at the coil connection point and the voltage of the AC drive source. That is, a so-called differential transformer type phase difference detection is used (see, for example, Patent Document 1).
[0006]
Further, as a conventional technique for stably detecting whether or not the toner amount in the toner hopper has decreased to the reference amount, a developing device is disposed in the vicinity of the coil L1 and the coil L2 that are magnetically coupled to each other. Capacitors C1 and C2 connected in parallel to each of L2, L1 and C1 form a first resonance circuit, and L2 and C2 form a second resonance circuit to form a tuning circuit as a whole. (For example, refer to Patent Document 2). The tuning circuit is connected to the upstream solid-state oscillation circuit, and the output of the tuning circuit is input to the detection circuit and then compared with the reference voltage and the level by the comparison circuit, so that the toner level is the reference level. It is detected whether the level has been reached. In this prior art, when the toner level of the developing device becomes substantially equal to the reference amount, the resonance frequency of the resonance circuit approximates the oscillation frequency of the solid state oscillator due to the magnetic influence of the magnetic carrier of the toner level. As a result, the impedance of the tuning circuit is minimized. In addition, a capacitor C1 is connected in parallel to the coil L1 to form a resonance circuit. Further, coupled with the resonance circuit of L2 and C2, the Q value of the tuning circuit is increased, so that the toner level is made highly sensitive. It can be detected.
[0007]
In addition, as a circuit configuration for detecting the magnetic material of the prior art, a resonance circuit is formed by a coil on the primary side of a transformer and a capacitor connected in parallel to this, and an oscillation circuit (resonance frequency) is connected to the input / output of the inverting circuit. There is what constitutes f1) (see, for example, Patent Document 3). According to this, the detection unit is composed of a resonance circuit composed of two secondary coils and a capacitor that are differentially coupled to the primary coil, and the primary transformer has a primary resonance frequency 0.7 to 1.4 times the primary of the differential transformer. A part of the secondary voltage is mixed and detected, the zero crossing is avoided, the operation is stabilized, and the switching characteristic is changed to the analog characteristic.
[0008]
[Patent Document 1]
JP-A-6-289717
[0009]
[Patent Document 2]
JP 2000-131120 A
[0010]
[Patent Document 3]
See Japanese Patent No. 2501429
[0011]
[Problems to be solved by the invention]
Patent Document 1 of the prior art is a phase difference detection by a differential transformer using a detection coil and a reference coil, and its feature is that a sensitivity adjusting resistor is connected in parallel to one of the two coils. Thus, the phase of the differential output voltage is gradually changed with respect to the sudden inductance change on the detection coil side, so that the toner density control is stably performed. In this technique, since an oscillation circuit is formed by both coils and an AC power supply, it is necessary to adjust the magnetic core in the differential transformer according to the magnetic material to be detected. Further, it is difficult to oscillate stably, the oscillation frequency is as low as several hundred hertz, and it is necessary to increase L and C. Therefore, there are problems in miniaturization and cost reduction.
[0012]
Patent Document 2 of the prior art describes that the toner density can be detected using the solid-state oscillation circuit, the first resonance circuit, and the second resonance circuit. It is taken out as the output level of the tuning circuit consisting of a resonance circuit. According to Patent Document 2, since the change in the output amplitude of the tuning circuit is taken out as an output signal depending on the presence or absence of a magnetic material (no phase difference signal is detected), both accuracy and sensitivity are insufficient, and magnetic Although it may be possible to detect the presence or absence of a body, there is a problem that it is difficult to detect analog amounts of continuous amounts such as toner density.
[0013]
Further, in Patent Document 3 of the prior art, it is necessary to adjust the position of the magnetic core in the differential transformer for each individual magnetic body to be detected, which is complicated. Further, it is difficult to oscillate stably, the oscillation frequency is as low as several hundred hertz, and it is necessary to increase L and C. Therefore, there are problems in miniaturization and cost reduction.
[0014]
SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic permeability detecting device that improves the detection sensitivity when detecting the magnetic permeability of a magnetic material such as toner concentration and can stably detect the magnetic permeability without being influenced by the ambient temperature.
[0015]
[Means for Solving the Problems]
In order to solve the above problems, the present invention mainly adopts the following configuration.
[0016]
In the magnetic permeability detection device that detects the magnetic permeability of the magnetic body using a coil that is disposed close to the magnetic body, the coil is magnetically coupled to the first coil of the first resonance circuit and the first coil. The capacitor of the first resonance circuit is a shared capacitor that also serves as the capacitor of the second resonance circuit, and the shared capacitor is controlled by the magnitude of the control voltage. A series connection circuit of a varicap and a DC cut-off capacitor that change the capacitance is connected in parallel, and the DC cut-off capacitor has a function of cutting off the control voltage, and the control voltage The capacitance value is set so that the change width of the combined capacitance of the series connection circuit with respect to the adjustment width is appropriate, and the varicap is a temperature A capacitor with a negative temperature coefficient is used for the shared capacitor so as to compensate for the change in capacitance of the varicap due to a change in the ambient temperature of the device. And a temperature compensation capacitor having the negative temperature coefficient The shared capacitor A trimmer capacitor capable of varying the capacitance is provided to compensate for variations in the capacitance allowed to widen the resonance frequency adjustment range of the first and second resonance circuits, and the trimmer capacitor is used as the temperature compensation capacitor. The shared capacitor Are connected in parallel.
[0020]
By adopting such a configuration, it is possible to adjust the total capacitor capacity appropriately while using the device by using a varicap as a capacitor, and control by connecting a DC cut-off capacitor in series with the varicap. Stable control responsiveness can also be ensured by setting the fluctuation range of the composite capacity due to voltage to an appropriate value.
[0021]
Further, by using a negative temperature compensation capacitor in the resonance circuit, it is possible to reduce the influence of variations in temperature coefficient in the varicap and the like.
[0022]
Further, by adopting the trimmer capacitor together with the temperature compensation capacitor, it is possible to absorb the capacitance variation of the temperature compensation capacitor.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Various magnetic permeability detection devices using the fact that inductance changes according to the magnetic permeability of a magnetic material according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an outline of an electrophotographic copying apparatus to which a magnetic permeability detecting device according to an embodiment of the present invention is applied. FIG. 2 shows a configuration of a developing device provided with a magnetic permeability detecting device such as a toner concentration sensor. FIG. 3 is a diagram showing a basic circuit configuration of the magnetic permeability detecting device according to the present embodiment, and FIG. 4 is a diagram for explaining basic functions related to the magnetic permeability detecting device according to the present embodiment. FIG.
[0024]
5 is a diagram illustrating a circuit configuration example 1 of the magnetic permeability detection device according to the present embodiment, and FIG. 6 is a diagram illustrating a circuit configuration example 2 of the magnetic permeability detection device according to the present embodiment. FIG. 8 is a diagram illustrating a circuit configuration example 3 of the magnetic permeability detection device according to the present embodiment, and FIG. 8 is a diagram illustrating a circuit configuration example 4 of the magnetic permeability detection device according to the present embodiment. FIG. 9 is a characteristic diagram showing the relationship between the control voltage of the varicap and the combined capacitance of the varicap and the cut-off capacitor in the resonance circuit of this embodiment, and FIG. 10 shows the temperature compensation capacitor in the resonance circuit of this embodiment. FIG. 11 is a diagram showing the detection voltage-temperature characteristic of the magnetic permeability detection device when using the above, and FIG. 11 is a diagram showing the adjustment width characteristic of the combined capacitance when a trimmer capacitor is used in the resonance circuit of the present embodiment. FIG. 12 is a diagram showing the time required for level adjustment when trimmer capacitors having different adjustment widths are used in the resonance circuit of the present embodiment.
[0025]
Here, 1 is a reading unit, 2 is a lamp, 3 is a CCD, 4 is an amplifier, 5 is an A / D conversion unit, 6 is an image processing unit, 8 is a shoe correction, 9 is a filter, 10 is a γ correction, 11 Is gradation processing, 12 is an image forming unit, 13 is a writing unit, 14 is exposure, 15 is a charging charger, 16 is a developing sleeve, 17 is a paper feed tray, 20 is a magnetic substance detection circuit, 1 is an oscillation circuit, and 22 is Resonance circuit (detection circuit), 23 is a phase comparison circuit, 24 is an integration circuit, 25 is an impedance conversion circuit, and 26 is a developer.
[0026]
The electrophotographic copying apparatus shown in FIG. 1 has an overall configuration. In the reading unit 1, the light emitted from the lamp 2 is reflected by the original surface and converted into an electrical signal by the CCD 3, and the amplitude is adjusted by the amplifier 4. After that, digital image data quantized by the A / D converter 5 is obtained. The generated digital image data is input to the image processing unit 6, subjected to shading correction processing 8, filter processing 9, γ correction processing 10, gradation processing 11, etc. in this order and sent to the image forming unit 12.
[0027]
The digital image data input to the image forming unit 12 is converted into laser light 14 in accordance with the data value in the writing unit 13 and irradiated to the photosensitive member charged by the charging charger 15, and an electrostatic latent image is formed on the surface of the photosensitive member. Form. The developing sleeve 16 adheres toner to the surface of the photoreceptor in accordance with the formed electrostatic latent image. The toner adhering to the photoreceptor surface is transferred onto the paper surface sent from the paper feed tray 17, passes through the fixing unit 18, and is output as a copy original.
[0028]
In the developing device shown in FIG. 2, it is necessary to detect the toner density in the developing device and maintain it at a predetermined value in order to obtain a high quality image by always maintaining the mixing ratio of the toner with respect to the magnetic carrier at an appropriate value. is there. If it is detected that the toner concentration is lowered, the toner is replenished from the toner hopper so as to obtain an appropriate toner concentration. Therefore, a toner concentration detection device (T sensor) that detects the toner concentration in the developer is installed.
[0029]
FIG. 3 shows a magnetic permeability detection circuit 20 using toner density detection as a specific example. The magnetic permeability detection circuit 20 represents the basic configuration of the embodiment of the present invention, and includes an oscillation circuit 21, a resonance circuit 22, a phase comparison circuit 23, an integration circuit 24, and an impedance conversion circuit 25. The oscillation circuit 21 oscillates using a solid oscillator such as crystal or ceramic, and the oscillation frequency is determined based on the inherent frequency of the solid oscillator such as crystal or ceramic. It is difficult to be affected by the use environment and power supply voltage, and enables stable and accurate detection as one component of magnetic permeability detection.
[0030]
Also, a resonance circuit (detection circuit: a magnetic permeability detection circuit that utilizes the fact that the inductance changes according to the magnetic permeability of the magnetic material) 22 oscillates. The output from the circuit 21 is input to the first coil L1 through the resistor R3. The resonant circuit 22 includes a first resonant circuit including a first capacitor L1 and a shared capacitor C3 sharing a capacitor, a second coil L2 coupled to the first coil L1 with a magnetic coupling constant k, and the shared capacitor C3. A second resonance circuit. In FIG. 2, a developer 26 in which a magnetic carrier and non-magnetic toner in the developing device are mixed in a non-contact manner is disposed in the vicinity of the first coil L1 and the second coil L2. Specifically, the substantial inductance of the coils L1 and L2 is influenced by the toner concentration or the like (the numerical value of magnetic permeability).
[0031]
In the basic configuration of the present embodiment, the capacitor of the first and second resonance circuits is made common or shared to be the capacitor C3, so that a capacitor having a large variation in the value among the components of the resonance circuit is obtained. By sharing, the difference between the primary and secondary resonance frequencies can be easily minimized.
[0032]
In addition, by sharing capacitors, it is possible to maintain the same resonance characteristics as those in which capacitors are provided in each resonance circuit, and it is possible to reduce costs by reducing the number of capacitors.
[0033]
Further, in order to obtain a large detection output of magnetic permeability such as toner concentration, it is desirable to match the oscillation frequency fosc of the oscillation circuit 21 and the resonance frequency fc of the resonance circuit 22 (for example, the toner concentration is an optimum value). In this state, fosc and fc are substantially coincided with each other.) At that time, in order to adjust the resonance frequency fc, it is only necessary to adjust the capacitance value of the capacitor C3, and the frequency can be adjusted easily. In this case, both the inductances of the first and second coils can be easily set to the same level by an appropriate coil forming method. Further, by making the oscillation frequency fosc and the resonance frequency fc substantially coincide with each other, it is possible to obtain a large output fluctuation value with respect to a change in toner density (details will be described later in the description of FIG. 4), and sufficient sensitivity for toner density detection. Can be secured.
[0034]
The output of the resonance circuit 22 is extracted as a phase difference. However, in the specific configuration shown in FIG. 3, the output V1 of the oscillation circuit and the output V2 at the shared capacitor side end of the second coil (that is, the resonance circuit ( The signal at the input terminal and the output terminal of the detection circuit) is applied to the input terminal of the exclusive OR of the phase comparison circuit 23 to obtain an output signal depending on the phase difference between V1 and V2. . The other input signal of the exclusive OR of the phase comparison circuit 23 shown in FIG. 3 may be derived from the first coil side end of the resistor R3 instead of the V2 of the illustrated second coil L2. That is, the phase difference can be obtained even if both ends of the resistor R3 are connected to both input ends of the exclusive OR. This is because the current flowing in the closed circuit composed of the output side of the oscillation circuit 21, the resistor R3, the first coil L1, and the shared capacitor C3 is a vector amount according to the impedance composed of the resistance component and the reactance component. There is a difference between the voltages at both ends. Although this phase difference extraction method is stable as a signal, the signal value is small. On the other hand, the phase difference extraction method shown in FIG. 3 has a large signal value, and a reliable and sufficient phase difference output can be obtained.
[0035]
Next, the function or action of phase comparison by the output from the resonance circuit side in the phase comparison circuit 23 will be described with reference to FIG. In the graph shown in FIG. 4, the horizontal axis represents the frequency in the resonance circuit 22, and the vertical axis represents the phase difference between V1 and V2 shown in FIG. The solid line indicates the phase difference characteristic with respect to the frequency when the toner density is appropriate, and the broken line indicates the phase difference characteristic with respect to the frequency when the toner density is lower than the appropriate value.
[0036]
When the phase difference output of V1 and V2 of the resonance circuit shown in FIG. 3 is plotted, the characteristics of the solid line and the broken line shown in FIG. 4 can be obtained (data obtained experimentally), and the frequency used in the resonance circuit is The phase difference output exhibits a characteristic that fluctuates greatly in a region that matches or is approximately equal to the frequency fosc of the oscillation circuit. This characteristic shows the same tendency regardless of the toner density. If the frequency is the same as the resonance frequency fosc, the phase difference is 47 degrees if the toner density is appropriate, and the phase difference is 88 degrees if the toner density is low. Then, the phase difference changes from 47 degrees to 88 degrees, and a sufficient output difference can be obtained.
[0037]
As shown in FIG. 4, Q1 of the first resonance circuit (L1, C3) and the second resonance circuit (L2, C3) are qualitative explanations for obtaining a large phase difference output at the resonance frequency that matches the oscillation frequency. In addition to obtaining an output based on the integrated Q obtained by multiplying Q2), it is considered to be due to a synergistic effect due to mutual feedback to the first and second resonance circuits by sharing the capacitor C3.
[0038]
On the other hand, when the resonance frequency fc lower than the oscillation frequency fosc is used in the resonance circuit 22, as is apparent from the phase difference characteristics of the solid line and the broken line shown in FIG. Thus, almost no phase difference output occurs.
[0039]
Returning to FIG. 3, the output of the phase comparison circuit 23 undergoes waveform conversion processing via the integration circuit 24 and the impedance conversion circuit 25, and becomes the output of the magnetic permeability detection circuit 20 as a whole.
[0040]
The magnetic permeability detection circuit as described above can be applied to an image forming apparatus having a developing device as shown in FIG. 2, and is also applied to a digital copying machine including a printer and a scanner as shown in FIG. Of course, it can be adopted. Furthermore, in the above description, it is utilized that the inductance changes according to the magnetic permeability by arranging the magnetic body near the first coil and the second coil in a non-contact manner. Not limited to this, a conductor may be disposed in a region close to both coils, and the fact that the coil inductance changes due to the influence of the magnetic field due to the eddy current in the conductor due to the magnetic flux from the coil may be used. That is, the present invention can also be applied to conductor detection using the fact that the inductance changes according to the electric conductivity.
[0041]
Further, in the circuit configuration of FIG. 3, an example in which the output of the resonance circuit (detection circuit) is extracted as a phase difference and the phase comparison is shown, but instead of extracting the output of the detection circuit as a phase difference, for example, the proximity of the coil A change in the amplitude of the current flowing in the first and second resonance circuits caused by a change in the inductance of the first coil and the second coil due to a change in the permeability of the magnetic material in the region may be taken out as an output through the detection circuit. In addition, it has been described that the developer 26 is provided in the vicinity of the first and second coils L1 and L2. However, the developer 26 may be provided in the vicinity of one of the coils.
[0042]
Next, a specific configuration example regarding the magnetic permeability detection device according to the embodiment of the present invention will be described below with reference to FIGS. The resonance circuit of FIG. 3 showing the basic configuration of the present embodiment has a sharp sensitivity characteristic. Therefore, the circuit constant may deviate from the resonance condition due to variations in individual components. That is, in designing a circuit, some means for adjusting a tolerance of several percent that a single component has as a standard is required to maintain a strict resonance condition.
[0043]
Therefore, in this embodiment, as shown in FIG. 5, a configuration in which a varicap (variable capacitor: VC) is connected in parallel to the shared capacitor C3 of the resonance circuit is adopted as the adjusting means. The varicap VC is a capacitor whose capacitance changes depending on the magnitude of the control voltage. That is, by adjusting the level of the control voltage Vcont, the combined capacity of the shared capacitor C3 and the varicap VC can be adjusted, and the capacitor capacity can be adjusted to the resonance condition. Here, C2 is a DC cut-off capacitor for the control voltage, and the total capacitor capacity of the resonance circuit can also be adjusted by this series-connected C2. Thus, in the resonant circuit shown in FIG. 5, instead of the single shared capacitor C3 shown in FIG. 3, the varicap VC and the DC cut-off capacitor C2 are connected in series in order to change the capacitor capacity. A variable capacitor is obtained by changing the control voltage using a configuration in which the control voltage is applied to the connection point. In the configuration example of FIG. 5, the variable capacitor is connected in parallel to the capacitor C3. However, a circuit configuration including a varicap VC and a DC cut-off capacitor C2 may be used without using the C3.
[0044]
FIG. 9 shows a change in the combined capacitance in which the varicap VC and the DC cut-off capacitor C2 are connected in series according to the control voltage, and a change in the combined capacitance due to the magnitude of the capacitance of C2. A simple method of changing the control voltage can be adjusted to an appropriate combined capacitance value, and a circuit that can set the resonance frequency to a predetermined value can be realized even if there is some variation in the components. According to FIG. 9, it can be seen that when the control voltage is changed within the range of 1 to 5 V, the combined capacitance can be changed greatly, and this change is larger as C2 is larger. C2 also naturally has a role of preventing the applied control voltage from passing through the coil and falling directly to the ground (DC cut-off). By inserting the DC cut-off capacitor C2, a specified voltage can always be supplied to the varicap VC.
[0045]
As described above, the capacitance of the varicap VC can be changed by the control voltage (externally applied voltage) Vcont, and the resonance frequency of the resonance circuit can be shifted by changing the capacitance of VC. In this way, the range of control by the control voltage can be given, and when used for a toner density sensor, the detection level can be adjusted by the control voltage using this characteristic. Since the characteristics of the developing device are different depending on the model and the characteristic variation of the developer is assumed to be relatively large, the toner concentration sensor according to the present embodiment used in combination with a variation of such characteristics is the control voltage. By adjusting the VC capacity according to the above, it is possible to absorb variations on the developing device side and maintain a predetermined output level.
[0046]
Here, considering the responsiveness of the magnetic permeability detection device taking the toner concentration sensor as an example with respect to the control voltage, if the above-described large adjustment (control) capability exceeding the various variations to be absorbed, that is, the variable region of VC is too large. The response to the control voltage becomes too agile, and even if the control voltage is moved a little, the output will change greatly, resulting in unstable control. Therefore, it is desirable that the variable capacity range of VC is appropriately small while having an adjustment range capable of absorbing variations on the developing device side. Therefore, in this embodiment, a DC cut-off capacitor C2 is connected in series with the varicap VC, and the combined capacitance with VC is changed by the capacitance of C2. FIG. 9 shows the combined capacitance with respect to the control voltage. The state of change is shown.
[0047]
In FIG. 9, since VC and C2 are connected in series, the combined capacity increases when C2 increases, but when C2 is short-circuited (characteristic curve of black diamond) is the largest combined capacity, and It can be seen that it has the largest variable region. In this way, more stable control can be performed by selecting the optimum C2 capacity in consideration of both the control voltage response and the necessary adjustment range. In other words, C2 not only has a control voltage cut-off function, but also has a stable control response function in the combined capacity with VC.
[0048]
Next, a configuration using a temperature compensation capacitor having a negative temperature coefficient as a shared capacitor of the resonance circuit according to the present embodiment will be described. Generally, an electronic component has an element whose characteristic value changes due to a temperature change. In particular, an electronic component having a particularly large positive temperature coefficient is a varicap VC. A change in the capacitance of the varicap accompanying a change in the ambient temperature of the device causes a situation in which the output value of the magnetic permeability detecting device fluctuates, and it is necessary to compensate for the change in the ambient temperature. Therefore, in the present embodiment, as a temperature compensation method, a temperature compensation capacitor having a negative temperature coefficient is employed as the shared capacitor C3 of the resonance circuit shown in FIG. That is, a temperature compensation capacitor having a negative temperature coefficient is connected in parallel or in series with a varicap VC having a positive temperature coefficient to correct ambient temperature changes.
[0049]
FIG. 10 shows the detected voltage-temperature characteristics of the magnetic permeability detector. In general, it is not desirable for the detection device that the output fluctuates due to a factor other than the detection target (for example, magnetic permeability). According to the experimental results shown in FIG. 10, in the detection device that does not perform any temperature compensation, it is confirmed that the output of the detection device fluctuates due to a change in ambient temperature of 25 ° C. to 60 ° C. (temperature range in the specification). did. Therefore, if the temperature compensation capacitor C3 having a negative temperature coefficient in the present embodiment is connected in parallel or in series with the varicap, the temperature change is suppressed, and the detection voltage does not fluctuate depending on the temperature. (The characteristics from 25 ° C. are shown in FIG. 10, but it was confirmed that the characteristic tendency shown in FIG. 10 was exhibited even when the ambient temperature of the apparatus was 10 ° C.). In addition to the VC, the same effect can be obtained for an electronic component having a positive temperature coefficient. In the above description, the effectiveness of the temperature compensation capacitor C3 with respect to the varicap VC has been described. However, the present invention is not limited to this, and even when a plurality of capacitors connected in series with VC and C2 are used as shown in FIG. Have the same effect.
[0050]
In addition, when a temperature compensation capacitor C3 is connected in parallel to a capacitor having a large temperature coefficient (a plurality of capacitors), for example, a varicap VC, the temperature compensation capacitor C3 also has a plurality of capacitors having different temperature coefficients. Specifically, for example, capacitors having different temperature coefficients such as temperature coefficients of −120 ppm / ° C., −330 ppm / ° C., and −400 ppm / ° C. are commercially available for temperature compensation capacitors having capacitances of 10 pF and 30 pF, respectively. The coefficient represents the change in capacitance with respect to temperature, but is also related to the capacitance of the temperature compensation capacitor itself, so if the capacitance of the temperature compensation capacitor itself is large, the same temperature Even if the coefficient is −120 ppm / ° C., the capacity variation with respect to the temperature change is large.) The one with the larger coefficient tends to have a larger variation in the temperature coefficient, and in order to reduce the influence of the variation in the temperature coefficient (and hence the variation in the capacitance), it is better to select the one with the smallest temperature coefficient as much as possible. desirable.
[0051]
Therefore, if the capacitance of the varicap is large compared to the capacitance of the temperature compensation capacitor, the variation increase of the varicap capacitance due to the temperature rise is large, so in order to compensate for this variation increase, temperature compensation with a large temperature coefficient However, if the capacitance of the temperature compensation capacitor is larger than the maximum capacitance of the varicaps connected in parallel, the temperature compensation capacitor with the larger capacitance has the smaller temperature coefficient. However, the capacity fluctuation due to the temperature rise of the low-capacity varicap can be sufficiently compensated (by using a large-capacity temperature-compensating capacitor, it is not necessary to employ a varicap having a large temperature coefficient. The capacity fluctuation due to the temperature rise of the Thus, when a temperature compensation capacitor having a larger capacity than the varicap capacity is connected in parallel to a capacitor having a large temperature fluctuation, for example, a varicap, the temperature coefficient is small to compensate for the temperature fluctuation of the varicap. One of the temperature compensation capacitors can be employed, and there is an effect that the influence of the variation in temperature coefficient, and hence the variation in capacitance can be reduced.
[0052]
Further, the function of the temperature compensation capacitor C3 in this embodiment will be described. There are other circuit components whose characteristics change due to changes in the capacitance of the capacitor due to changes in environmental temperature. These changes shift the resonance conditions of the resonance circuit and lead to a change in output. Therefore, it is necessary to correct the temperature change. The components that change greatly (the temperature coefficient is large) include a varicap VC and an oscillator. As will be described later, the temperature coefficient of the varicap VC used in the circuit configuration examples A and B is 4 to 350 ppm / ° C. The temperature coefficient of the oscillator is 42.5 ppm / ° C. (actual measurement). In this embodiment, the temperature compensation of the resonance circuit including these is performed by selecting an appropriate capacitance of C3 and a temperature coefficient (negative).
[0053]
Here, the capacitance of the temperature compensation capacitor C3 is a parameter that contributes to both C and the temperature coefficient of the resonance condition. However, since the specification standard value of the commercially available temperature compensation capacitor is limited, There are cases where proper temperature compensation cannot be performed with a capacitor alone. Therefore, as in the circuit shown in FIG. 5, other capacitors (VC, C2, etc.) are added to adjust the capacitance, and the capacitance and temperature coefficient of the temperature compensation capacitor suitable for the circuit are optimized (to C2). A temperature compensation capacitor may be used, and in that case, VC capacity adjustment is also added). Further, in the circuit of FIG. 5, it is also possible to adjust using another capacitor in series with the temperature compensation capacitor C3. However, since the calculation is somewhat complicated when connected in series and the constant can be determined by simple addition when connected in parallel, FIG. 5 illustrates parallel connection.
[0054]
Next, FIG. 6 shows a configuration example in which a trimmer capacitor C4 is connected in parallel to a temperature compensation capacitor C3 as a capacitor of the resonance circuit according to the present embodiment. The temperature compensation capacitor C3 has a relatively wide tolerance for capacitance due to the characteristics of the temperature coefficient, and generally has a large variation in capacitance. Therefore, when a temperature compensation capacitor is used in the resonance circuit, a trimmer capacitor C4 (capacitance variable capacitor) is connected in parallel to the temperature compensation capacitor C3 in FIG. 6 in order to further widen the adjustment range of the resonance frequency of the resonance circuit. . In the above description, the use of the trimmer capacitor is based on the reason that the variation in the capacitance of the temperature compensation capacitor C3 is large. However, the present invention is not limited to this, and the capacitance of the shared capacitor connected to the resonance circuit is to be changed. In addition, the overall capacitor capacity may be adjusted to a desired value by appropriately adjusting the capacity by connecting a trimmer capacitor. In short, the connection arrangement of the trimmer capacitors makes it possible to easily match or approximate the resonance frequency fc of the resonance circuit shown in FIG. 4 to the oscillation frequency fosc of the oscillation circuit.
[0055]
FIG. 11 is a diagram illustrating the combined capacity of the trimmer capacitor C4 having an adjustable width of 5 to 30% of the temperature compensation capacitor capacity, the temperature compensation capacitor C3, and the like for 10 samples. According to FIG. 11, due to variations in the capacitance values of the temperature compensation capacitor C3 and the like and the trimmer capacitor C4, the combined capacitance also varies. However, by adjusting the trimmer capacitor, if the capacitance variation of the temperature compensation capacitor C3 and the like generated for each sample of each magnetic permeability detection device is within the adjustment range of the trimmer capacitor C4, the combined capacitance is made uniform. Is easily possible. That is, in FIG. 11, when it is desired to set the combined capacitance to 40 pF, even if the temperature compensation capacitor has a capacitance variation of 32 to 37 pF (combination with the capacitor VC or C2 in addition to the temperature compensation capacitor), the adjustment range If a trimmer capacitor of about 12 pF is connected, the combined capacitance can be adjusted to the desired 40 pF for all 10 samples.
[0056]
Further, a specific circuit configuration using the trimmer capacitor C4 will be described. As described above, the temperature compensation capacitor C3 has a large variation of ± 5% (general specification tolerance), and this capacitance variation cannot be ignored in the resonance circuit. Therefore, the capacitance width of the trimmer capacitor c4 absorbs variations in the temperature compensation capacitor C3 and other components constituting the resonance circuit. On the other hand, if the variable capacitance range of the trimmer capacitor is too large, the adjustment range is wide. Therefore, it becomes difficult to find the optimum capacitance value of the trimmer capacitor.
[0057]
FIG. 12 shows the time required for level adjustment in a toner density sensor using trimmer capacitors having different adjustment ranges. The adjustment time in the production process is targeted at 30 seconds (s). However, if the trimmer capacitor has a large capacitance, it takes time to adjust (some samples cannot be adjusted because the optimum value cannot be found). It was found that it causes work difficulties. The standard value of the trimmer capacitor has only a discrete value. In order to adjust in an appropriate time, as shown in FIG. 12, a capacitance adjustment width of 15.5 pF is suitable, and a maximum of about 20 pF is the limit. From this, it can be said that the capacity of the trimmer capacitor needs to have a width that can absorb the variation of components and can be adjusted in an appropriate time.
[0058]
In addition, the function or operation of the trimmer capacitor will be described with specific circuit configuration values. First, as a circuit configuration example A, a circuit of FIG. 7 described later in which a varicap VC and a DC cut-off capacitor C2 are connected in parallel to the circuit of FIG. 6 is illustrated. That is, VC = 10 pF, C2 = 10 pF, C3 = 33 pF (temperature coefficient −330 ppm / ° C. (= −0.01089 pF / ° C.)), trimmer capacitor = 3 to 10 pF (change width 7 pF). When these four capacitors are configured as shown in FIG. 7, the total capacitance C is about 45 pF, and this total capacitance value is determined by the relationship with the inductance values (L values) of the coils L1 and L2. A combination of the L value and the C value that satisfies the resonance condition can be arbitrarily selected. It has been experimentally confirmed that the combination of the circuit configurations A satisfies the resonance condition, satisfies the conditions such as the control voltage response, the control voltage adjustment range, and the absorption of component variations, and is established as a toner density sensor. Furthermore, it was experimentally confirmed that there was no temperature fluctuation in a temperature change of 10 ° C. to 50 ° C.
[0059]
Therefore, FIG. 11 shows the total capacity by the combination of the circuit configuration example A. The black bar graph is VC + C2 + C3 + trimmer capacitor minimum value, and the upper limit of the white bar graph is actually measured data of VC + C2 + C3 + trimmer capacitor maximum value (sample N = 10). Thus, the width that can be adjusted by the trimmer capacitor C4 is the width of the white bar graph, and can be adjusted to a resonance point in the vicinity of the total capacity of about 40 pF within the adjustment range of the trimmer capacitor. The change width 7 pF of the trimmer capacitor selected in the circuit configuration example A is 17.5% of the total capacitance C and 21% of C3. Further, the trimmer capacitor of the circuit configuration example A can be expanded by using a trimmer capacitor having a change width of 15.5 pF (4.5 to 20 pF), and 38.75% of the total capacitance C and 45 of C3. It was found to be 9%. However, if a trimmer capacitor having a large capacitance change of 33 pF is used, it is difficult to adjust the trimmer capacitor, which is not appropriate in the production process.
[0060]
Next, the circuit configuration example B (without VC, C2 = 5 pF, C3 = 150 pF (temperature coefficient −150 ppm / ° C. (:)) is obtained by eliminating the varicap VC and reducing the L value of the coil and setting the total capacitance C to 175 pF. -0.0225 pF / ° C.), trimmer capacitor = 3 to 10 pF (variation width 7 pF)) as an example, it is confirmed that the circuit configuration example B is also formed as a toner density sensor as in the circuit configuration example A. did. At this time, the change width 7 pF of the trimmer capacitor is 4% of the total capacitance C and 4.67% of C3. Further, the trimmer capacitor having the change width of 15.5 pF (4.5 to 20 pF) can be established by expanding the capacitance variable range of the trimmer capacitor of the circuit configuration example B (the change width of the trimmer capacitor at this time is the total capacitance C). Of 8.85% of C3 and 10.3% of C3).
[0061]
From the above specific experimental results, it was found that the proper adjustment range of the trimmer capacitor is appropriate to be 40% or less of the total capacity and 50% or less of the temperature compensation capacitor C3. In other words, the trimmer capacitor is mainly used to absorb variations in the temperature compensation capacitor C3. Temperature compensation capacitors with a tolerance of ± 5% are the mainstream, but if they are selected, ± 1% products are available, so if you can adjust more than 2% of the temperature compensation capacitor capacity with a trimmer capacitor, variations in temperature compensation capacitors will be absorbed it can. Furthermore, since the temperature compensation capacitor is used to compensate for VC with a large temperature coefficient, it is assumed that capacitors with almost the same capacitance are connected in parallel, and each tolerance is ± 1%. It is sufficient that 1% or more of the capacity can be absorbed by the trimmer capacitor.
[0062]
FIG. 7 shows a configuration example of this embodiment in which a temperature compensation capacitor C3, a series connection circuit of a varicap VC and a DC cut-off capacitor C2, and a trimmer capacitor C4 are connected in parallel. Here, since the capacitance of ordinary capacitors including the varicap VC tends to increase as the ambient temperature rises, the temperature compensation capacitor C3 has a negative temperature coefficient in order to reduce the influence of the ambient temperature. use.
[0063]
Here, the varicap VC varies the capacitance of the varicap by changing the control voltage during use of the magnetic permeability detecting device when the resonance conditions change due to the toner conditions or the values of the components of the resonance circuit. This is for setting the overall capacitance of the capacitor to a desired value (so that fc shown in FIG. 4 is matched with fosc). The trimmer capacitor C4 is for adjusting the capacitance of the temperature compensation capacitor C3 having a large capacitance variation, and for adjusting the capacitance of the capacitor for optimizing the resonance condition, and is usually adjusted at the time of shipment from the factory. It is. The functions and roles of the varicap VC and the trimmer capacitor C4 are not limited to the circuit configuration shown in FIG. 7, and the same applies to all circuit configurations using these capacitors.
[0064]
In another configuration example of the resonance circuit according to the present embodiment shown in FIG. 8, the parallel connection capacitor of the temperature compensation capacitor C3, the trimmer capacitor C4, and the varicap VC functions as a shared capacitor, and the control voltage is DC. The cutoff capacitors are connected to the points A and B of the coils L1 and L2 in FIG. 8 like C2-1 and C2-2, and have the same effect as the circuit in FIG.
[0065]
【The invention's effect】
According to the present invention, by using a shared capacitor for the first resonance circuit and the second resonance circuit, the resonance frequency of the resonance circuit (detection circuit) can be easily adjusted, and the first and second resonance circuits can be adjusted. The resonance frequencies can be easily aligned. Furthermore, the magnetic permeability detection output can be greatly extracted by making the resonance frequency of the magnetic permeability detection device including the first resonance circuit and the second resonance circuit substantially coincide with the oscillation frequency of the oscillation circuit. Furthermore, the magnetic substance detection sensitivity can be improved by detecting the phase difference output at the input / output end of the resonance circuit having the shared capacitor.
[0066]
In addition, by using a varicap as a capacitor, the capacitance of the capacitor can be adjusted appropriately during use of the device, and by connecting a DC cut-off capacitor in series with the varicap, the fluctuation range of the combined capacitance due to the control voltage can be adjusted appropriately. A stable control response can be ensured as a small value.
[0067]
In addition, by using a negative temperature compensation capacitor in the resonance circuit, it is possible to reduce the influence of variations in temperature coefficient in the developing device components including the varicap and the like, and to eliminate temperature drift.
[0068]
Further, by adopting the trimmer capacitor together with the temperature compensation capacitor, it is possible to absorb the capacitance variation of the temperature compensation capacitor.
[Brief description of the drawings]
FIG. 1 is a diagram showing an outline of an electrophotographic copying apparatus to which a magnetic permeability detection apparatus according to an embodiment of the present invention is applied.
FIG. 2 is a diagram illustrating a configuration of a developing device provided with a magnetic permeability detection device such as a toner concentration sensor.
FIG. 3 is a diagram showing a basic circuit configuration of the magnetic permeability detection device according to the present embodiment.
FIG. 4 is a diagram for explaining basic functions related to a magnetic permeability detection device according to the present embodiment.
FIG. 5 is a diagram showing a circuit configuration example 1 of the magnetic permeability detection device according to the present embodiment.
FIG. 6 is a diagram illustrating a circuit configuration example 2 of the magnetic permeability detection device according to the present embodiment.
FIG. 7 is a diagram illustrating a circuit configuration example 3 of the magnetic permeability detection device according to the embodiment.
FIG. 8 is a diagram illustrating a circuit configuration example 4 of the magnetic permeability detection device according to the embodiment.
FIG. 9 is a characteristic diagram showing the relationship between the control voltage of the varicap and the combined capacitance of the varicap and the cut-off capacitor in the resonance circuit of the present embodiment.
FIG. 10 is a diagram showing a detection voltage-temperature characteristic of the magnetic permeability detection device when a temperature compensation capacitor is used in the resonance circuit of the present embodiment.
FIG. 11 is a diagram illustrating adjustment width characteristics of a combined capacitance when a trimmer capacitor is used in the resonance circuit of the present embodiment.
FIG. 12 is a diagram illustrating time required for level adjustment when a trimmer capacitor having a different adjustment width is used in the resonance circuit of the present embodiment.
[Explanation of symbols]
1 Reading unit
2 lamps
3 CCD
4 Amplifier
5 A / D converter
6 Image processing section
8 Pudging correction
9 Filter
10 γ correction
11 gradation processing
12 Image forming unit
13 Writing part
14 Exposure
15 Charger charger
16 Development sleeve
17 Paper tray
20 Magnetic body detection circuit
21 Oscillator circuit
22 Resonance circuit (detection circuit)
23 Phase comparison circuit
24 Integration circuit
25 Impedance conversion circuit
26 Developer
L1 primary coil
L2 secondary coil
C, C3 shared capacitor
C2 DC cut-off capacitor
C4 trimmer capacitor
VC Varicap (variable capacitor)
OSC oscillation circuit

Claims (8)

In the magnetic permeability detection device for detecting the magnetic permeability of the magnetic body using a coil disposed close to the magnetic body,
The coil includes a first coil of a first resonance circuit and a second coil of a second resonance circuit magnetically coupled to the first coil;
The capacitor of the first resonance circuit is a shared capacitor that also serves as the capacitor of the second resonance circuit,
For the shared capacitor, a series connection circuit of a varicap and a DC cut-off capacitor whose capacitance is variable depending on the magnitude of the control voltage is connected in parallel,
The DC cut-off capacitor has a function of cutting off the control voltage, and has an electrostatic capacitance so that a change width of the combined capacitance of the series connection circuit with respect to an adjustment width of the control voltage is appropriate. The capacity value is set,
The varicap has a positive temperature coefficient as a temperature characteristic,
A capacitor having a negative temperature coefficient is used as the shared capacitor so as to compensate for the capacitance change of the varicap accompanying the change in the ambient temperature of the device,
Capacitance variable for widening the adjustment range of the resonance frequency of the first and second resonance circuits by compensating for variations in capacitance allowed for the shared capacitor, which is a temperature compensation capacitor having the negative temperature coefficient. Provided is a trimmer capacitor, and the trimmer capacitor is connected in parallel to the shared capacitor as the temperature compensation capacitor. In claim 1,
The magnetic permeability detecting device, wherein the DC cut-off capacitor is connected to a connection point between the first coil and the second coil. In claim 1 or 2,
The magnetic permeability detecting device, wherein the capacitance of the shared capacitor which is the temperature compensation capacitor is larger than the maximum capacity of the varicap. In claim 3,
The magnetic permeability detecting device, wherein the capacitance of the shared capacitor which is the temperature compensation capacitor is larger than a maximum value of a combined capacitance of the varicap and the DC cut-off capacitor. In claim 1 or 2,
The variable width of the capacitance of the trimmer capacitor is in the range of 1% to 40% of the total capacitance and 2 to 50% of the shared capacitor as the temperature compensation capacitor. .   An image forming apparatus comprising the developing device and the magnetic permeability detection device according to claim 1.   A digital copying machine comprising the developing device and the magnetic permeability detection device according to any one of claims 1 to 5.   6. A toner concentration detection device that detects the toner concentration of a developing device using the magnetic permeability detection device according to any one of claims 1 to 5.

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