JP2016061721A - Magnetic permeability sensor and magnetic permeability detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic permeability sensor capable of accurately detecting fluctuation in magnetic permeability of a detection object even with a small and simple configuration, and provide a magnetic permeability detection method using the magnetic permeability sensor.SOLUTION: The magnetic permeability sensor includes: a first coil 1 and second coil 2; a first oscillation circuit 6 that includes the first coil 1 and performs oscillation; a second oscillation circuit 7 that includes the second coil 2 and performs oscillation; a measurement unit 41 for measuring the oscillation cycle of each of the first oscillation circuit 6 and second oscillation circuit 7; a calculation unit 42 for calculating the difference between the oscillation cycles measured by the measurement unit 41; and a conversion unit 43 for converting the difference calculated by the calculation unit 42 into magnetic permeability.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a magnetic permeability sensor for detecting the magnetic permeability of an object to be detected, and a magnetic permeability detection method using the magnetic permeability sensor.

  An electrophotographic copying machine or printer includes a toner sensor that magnetically detects a toner concentration or remaining amount in a developing unit used to develop an electrostatic image formed on a photoreceptor. . An example of such a toner sensor is disclosed in Patent Document 1. The sensor disclosed in Patent Document 1 uses four coils and detects toner density by a differential transformer method.

  Patent Document 2 discloses a first oscillation circuit that generates a phase shift in an oscillation wave corresponding to an inductance change in the first detection coil, and a phase shift in an oscillation wave that corresponds to an inductance change in the second detection coil. There is disclosed a technique that includes a second oscillation circuit, obtains a difference between the phase shifts of the two, and detects a metal state.

JP 2001-165910 A JP 2009-31257 A

  The toner sensor of Patent Document 1 adopts a differential transformer system, and when the drive coil and the differential coil are located in the vicinity, the influence of the toner affects both. It is difficult to completely eliminate the influence on the coil. Further, when an oscillation circuit is configured including a flat coil, there is little change in the degree of coupling of inductance when a magnetic body approaches, and it is difficult to operate such a flat coil with an analog circuit.

Since Patent Document 2 has two independent oscillation circuits, there is a possibility that the measurement result of the magnetic permeability varies if there is a difference in the characteristics of the respective oscillation circuits.
Patent Document 2 is a technique for magnetically detecting the torque of the rotating shaft, and its application to a sensor for detecting the toner concentration is neither disclosed nor suggested.

  In a sensor that detects magnetic permeability using two coils, the two coils are spaced apart in the horizontal direction in order to prevent the other coil from being affected by the magnetic flux generated in one coil. The configuration is common. Specifically, one coil is placed near the object to be detected (magnetic material) to be easily affected by the change in permeability, and the other coil is arranged away from the object to be detected (magnetic material). Make it less susceptible to changes in permeability. According to the arrangement of the plurality of coils extending in the horizontal direction, there is a problem that the sensor cannot be reduced in size.

  Further, the magnetic permeability is detected according to the change in the inductance of the plurality of coils, but many circuit components are used for this detection. There is a problem in that circuit components have variations in characteristics and the circuit components are easily affected by the detection environment, so that high-precision detection cannot be achieved.

  The present invention has been made in view of such circumstances, and uses a magnetic permeability sensor and a magnetic permeability sensor that can detect a change in the magnetic permeability of an object to be detected with high accuracy even with a small and simple configuration. An object of the present invention is to provide a magnetic permeability detection method.

  A magnetic permeability sensor according to the present invention includes a first oscillation circuit that oscillates including a first coil that receives magnetism from the object to be detected, and a magnetic field sensor that detects the magnetic permeability of the object to be detected; A second oscillation circuit that oscillates including a second coil that receives magnetism, a measurement unit that measures an oscillation period in each of the first oscillation circuit and the second oscillation circuit, and a difference between the oscillation periods measured by the measurement unit A calculating means for calculating, and a converting means for converting the difference calculated by the calculating means into a magnetic permeability, and the constituent members of the first oscillating circuit and the second oscillating circuit include the first coil and the second coil. It is common except except. Here, “being magnetized” means being magnetically coupled to an object to be detected.

  In the magnetic permeability sensor of the present invention, the oscillation period of the first oscillation circuit including the first coil disposed in the vicinity of the detected object, and the first coil in the vicinity of the detected object is the distance to the detected object. The measurement means measures the oscillation period of the second oscillation circuit including the second coil arranged differently. The calculating means calculates the difference between the two oscillation periods measured by the measuring means, and the converting means converts the difference calculated by the calculating means into magnetic permeability. When the magnetic permeability of the object to be detected increases, the inductance of the coil increases, and the oscillation period of the oscillation circuit including the coil increases. Here, the coil closer to the object to be detected has a large amount of change in inductance in accordance with the change in magnetic permeability, so that the fluctuation of the oscillation period in the oscillation circuit also becomes large. Therefore, the magnetic permeability can be detected from the difference between the oscillation periods of the respective oscillation circuits by using two coils arranged at different distances from the object to be detected. At this time, a flat coil such as a coil formed by patterning printing on the substrate can be used as the two coils, and the configuration is downsized.

  In addition, a series of processing of oscillation cycle measurement, oscillation cycle difference calculation, and conversion from difference to magnetic permeability can be performed by software using a microcomputer, etc., and the number of components can be reduced and the characteristics of components vary. The detection accuracy is high.

  In the first oscillating circuit and the second oscillating circuit, the other components except the first coil and the second coil are common. Therefore, the oscillation period measured by each of the first oscillation circuit and the second oscillation circuit is not affected by characteristic variations caused by different components other than the coil, and an accurate value is measured. Therefore, the magnetic permeability detection accuracy is high.

  The magnetic permeability sensor according to the present invention is characterized in that the measuring means is configured to alternately measure an oscillation period in the first oscillation circuit and an oscillation period in the second oscillation circuit.

  In the magnetic permeability sensor of the present invention, the measurement of the oscillation period in the first oscillation circuit and the measurement of the oscillation period in the second oscillation circuit are alternately performed while switching. Therefore, when the oscillation cycle of one oscillation circuit is measured, the other oscillation circuit is not oscillating, so the measurement value of the oscillation cycle of one oscillation circuit is not affected by the oscillation of the other oscillation circuit. Therefore, an accurate oscillation period in both oscillation circuits can be measured, and the permeability detection accuracy is high.

  The magnetic permeability sensor according to the present invention is characterized in that the first coil and the second coil are arranged coaxially.

  In the magnetic permeability sensor of the present invention, the first coil and the second coil are arranged coaxially. Therefore, the area required for arranging the coils is small, and the magnetic permeability sensor can be miniaturized.

  The magnetic permeability sensor according to the present invention comprises a substrate on which one surface of the first coil is disposed and the other surface of the second coil is disposed.

  In the magnetic permeability sensor of the present invention, the first coil is formed on one surface of the substrate, and the second coil is formed on the other surface of the substrate. Therefore, the coaxial arrangement of the first coil and the second coil can be realized with a simple configuration.

  The magnetic permeability detection method according to the present invention is the magnetic permeability detection method for detecting the magnetic permeability of an object to be detected, wherein the first coil and the second coil are arranged at different distances from the object to be detected. Measure the oscillation period of the oscillation circuit that oscillates including one coil and the oscillation period of the oscillation circuit that oscillates including the second coil, calculate the difference between the measured oscillation periods, and calculate the difference as the permeability. It is characterized by converting into.

  In the present invention, the magnetic permeability of an object to be detected can be detected with high accuracy even with a small and simple configuration.

It is a perspective view which shows the structure of the magnetic permeability sensor of this invention. It is sectional drawing which shows the structure of the magnetic permeability sensor of this invention. It is sectional drawing which shows the example of attachment to the developing unit of the magnetic permeability sensor of this invention. It is a block diagram which shows the function structure of the magnetic permeability sensor of this invention. It is a circuit diagram which shows one structural example of the magnetic permeability sensor of this invention. It is a timing chart for demonstrating the operation | movement of the period measurement of the magnetic permeability sensor of this invention. It is sectional drawing which shows the example of attachment to the developing unit of the magnetic permeability sensor of a prior art example. It is a graph which shows the detection sensitivity characteristic of the toner density in this invention example and a prior art example. It is a graph which shows the control voltage characteristic for performing offset control in an example of the present invention and a conventional example. It is a perspective view which shows the structure of the coil in a 1st modification. It is sectional drawing which shows the structure of the magnetic permeability sensor in a 2nd modification. It is sectional drawing which shows the structure of the magnetic permeability sensor in a 3rd modification. It is sectional drawing which shows the structure of the magnetic permeability sensor in a 4th modification. It is sectional drawing which shows the structure of the magnetic permeability sensor in a 5th modification. It is a top view which shows the structure of the shield member suitable for the magnetic permeability sensor of this invention.

  Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof. 1 and 2 are a perspective view and a cross-sectional view showing the configuration of the magnetic permeability sensor of the present invention.

  1 and 2, reference numeral 10 denotes a flat rectangular substrate. A first coil 1 is formed on one surface (lower surface) of one end of the substrate 10 (see FIG. 2). A second coil 2 is formed on the other surface (upper surface) of one end of the substrate 10 so as to be coaxial with the first coil 1. The first coil 1 and the second coil 2 are formed, for example, by printing a copper foil pattern on the substrate 10.

  A connector 3 is mounted on the upper surface of the other end portion of the substrate 10 with a part protruding from the other end. On the upper surface of the central portion of the substrate 10, an electronic chip 4 composed of a microcomputer for performing various processes described later is mounted. Further, a circuit component 5 is mounted in the vicinity of the electronic chip 4. The circuit component 5 includes a capacitor for forming an oscillation circuit with the first coil 1 or the second coil 2. The magnetic permeability sensor 20 of the present invention is configured as described above.

  FIG. 3 is a cross-sectional view showing an example of attaching the magnetic permeability sensor 20 of the present invention to the developing unit. In FIG. 3, reference numeral 30 denotes a partition wall that partitions the inside and outside of the developing unit. A recess 31 is formed in the partition wall 30, and the magnetic permeability sensor 20 is attached to the developing unit while being housed in the case 21 so as to be fitted into the recess 31. The tip of the connector 3 protrudes from the case 21.

  At this time, the magnetic permeability sensor 20 is attached to the partition wall 30 of the developing unit so that the lower surface side of the substrate 10 shown in FIGS. Therefore, the first coil 1 is disposed closer to the developing unit than the second coil 2, in other words, closer to the developer in the developing unit. The recess 31 to which the magnetic permeability sensor 20 is attached is sealed with a seal 32.

  FIG. 4 is a block diagram showing a functional configuration of the magnetic permeability sensor 20 of the present invention. In FIG. 4, the same or similar parts as those in FIGS. 1 and 2 are denoted by the same reference numerals.

  The first coil 1 and a part of the circuit component 5 constitute a first oscillation circuit 6, and the second coil 2 and a part of the circuit component 5 constitute a second oscillation circuit 7. In the magnetic permeability sensor 20 of the present invention, in the first oscillation circuit 6 and the second oscillation circuit 7, the other constituent members except the first coil 1 and the second coil 2 are common. Therefore, the oscillation period measured by each of the first oscillation circuit 6 and the second oscillation circuit 7 is not affected by variations in characteristics due to different constituent members, and an accurate value is measured. Therefore, the magnetic permeability detection accuracy is high.

  In addition, the electronic chip 4 includes a measurement unit 41 that measures an oscillation period in each of the first oscillation circuit 6 and the second oscillation circuit 7, a calculation unit 42 that calculates a difference between the oscillation periods measured by the measurement unit 41, and a calculation unit. It has functionally the conversion part 43 which converts the difference calculated in 42 into magnetic permeability.

  FIG. 5 is a circuit diagram showing a configuration example of the magnetic permeability sensor 20 of the present invention. In FIG. 5, the coil L1 and the coil L2 correspond to the first coil 1 and the second coil 2 described above, respectively. The microcomputer U1 corresponds to the electronic chip 4 described above.

  One end of the coil L1 is connected to the sixth terminal of the microcomputer U1, and one end of the coil L2 is connected to the third terminal of the microcomputer U1. The other end of the coil L1 and the other end of the coil L2 are connected to the base of the transistor Q1 via the capacitor C1. A resistor R2 is provided between the base and collector of the transistor Q1, and a capacitor C2 is provided between the base and emitter of the transistor Q1. The collector of the transistor Q1 is connected to the second terminal of the microcomputer U1 and is grounded through the resistor R3.

  The first terminal of the microcomputer U1 is connected to the input terminal for the power supply voltage Vdd. The input terminal of the power supply voltage Vdd is connected to the emitter of the transistor Q1 through the resistor R1. One end of a capacitor C3 is connected between the resistor R1 and the emitter of the transistor Q1, and the other end of the capacitor C3 is grounded. One end of a capacitor C6 is connected between the input terminal of the power supply voltage Vdd and the first terminal, and the other end of the capacitor C6 is grounded. A grounding terminal is connected to the eighth terminal of the microcomputer U1.

  An output terminal that outputs a detection voltage Vout corresponding to the magnetic permeability is connected to the seventh terminal of the microcomputer U1 via a resistor R4. One end of a capacitor C7 is connected between the output terminal and the resistor R4, and the other end of the capacitor C7 is grounded. An input terminal for inputting a control voltage Vcont for performing offset control is connected to the fifth terminal of the microcomputer U1 via a resistor R6. One end of a capacitor C4 is connected between the fifth terminal of the microcomputer U1 and the resistor R6, and the other end of the capacitor C4 is grounded.

  The coil L1, the two capacitors C2 and C3, and the transistor Q1 constitute the first oscillation circuit 6 (Colpitts oscillation circuit). The coil L2, the two capacitors C2 and C3, and the transistor Q1 described above. A second oscillation circuit 7 (Colpitts oscillation circuit) is configured. Then, by the switching operation of the microcomputer U1 (the switching operation is performed at the third terminal and the sixth terminal of the microcomputer U1), the first oscillation circuit 6 and the second oscillation circuit 7 oscillate alternately at predetermined time intervals. It is like that.

  Next, the operation of the magnetic permeability sensor 20 of the present invention will be described. FIG. 6 is a timing chart for explaining the period measurement operation of the magnetic permeability sensor 20 of the present invention.

  The first oscillation circuit 6 and the second oscillation circuit 7 are alternately oscillated by a predetermined number of pulses, and the oscillation period in each oscillation is measured by the measurement unit 41. The predetermined number of pulses is, for example, 256. At this time, as shown in FIG. 6, in the period in which the first oscillation circuit 6 is oscillated and the oscillation cycle is measured, the second oscillation circuit 7 is not oscillated, and the second oscillation circuit 7 is oscillated and the oscillation is performed. The first oscillation circuit 6 is not oscillated during the period for which the period is measured. Therefore, since the oscillation period is measured without being influenced by the oscillations, the measured value is highly accurate.

  When the measurement of the oscillation cycle by a predetermined number of pulses (for example, 256) is completed, the measured oscillation cycle (derived from the first coil 1) in the first oscillation circuit 6 and the (second coil 2) in the second oscillation circuit 7 The calculation unit 42 calculates a difference from the measured oscillation period (derived from the above). And the conversion part 43 converts the calculated difference into a magnetic permeability, and calculates | requires the variation | change_quantity of a magnetic permeability. A magnetic permeability sensor (toner sensor) 20 attached to the developing unit detects the toner concentration.

  Further, in the period in which the first oscillation circuit 6 is oscillated and the oscillation period is measured, the difference between the previous measurement values (for example, A ′ and B ′) of the first oscillation circuit 6 and the second oscillation circuit 7 is calculated as follows: Since the calculation unit 42 calculates the difference, and the conversion unit 43 converts the calculated difference into the magnetic permeability to obtain the change amount of the magnetic permeability, the change amount of the magnetic permeability is measured at the timing of starting the measurement of the oscillation period of each oscillation circuit. Updates are made sequentially.

  The present invention has the following advantages. Depending on the type of toner used, the toner density control range may change. In this case, for example, by using an unused terminal of the microcomputer U1 and controlling the voltage level of the unused terminal from the outside, the toner density control range is adjusted to an appropriate range for the toner to be used. Offset function can be given.

  In recent years, depending on the electrophotographic method, the particle size of the toner itself tends to be small in order to obtain high image quality. Further, the amount of unnecessary toner is reduced as much as possible to reduce the cost and weight, and as a result, the change in magnetic permeability that can be detected tends to be small. In order to accurately detect the change in the reduced permeability, it is necessary to increase the measurement sensitivity by a method such as amplification in order to increase the change in the small permeability. In this case, the change in the magnetic permeability is not linear, and the magnetic permeability cannot be measured accurately. According to the present invention, by using a method using software such as linear correction, it becomes possible to improve the deteriorated linearity, and it is possible to accurately grasp the change in magnetic permeability.

  Note that although FIG. 5 shows a microcomputer having eight terminals as an example, it is not limited to this configuration. If necessary, it is possible to use a microcomputer with a different number of terminals and transmit information such as permeability change to the upper control side by means of serial communication etc. and receive control signals from the upper side. is there.

  Hereinafter, the principle that the magnetic permeability can be detected (the toner density can be detected) by the above-described procedure will be described.

  When the magnetic permeability of the object to be detected increases, the inductance of the coil arranged in the vicinity of the object to be detected increases according to the fluctuation of the magnetic permeability. As a result, the oscillation frequency of the oscillation circuit including the coil decreases, that is, the oscillation period increases. Here, when two coils are arranged at different distances from the object to be detected, the inductance of each coil increases, and the oscillation period of any oscillation circuit increases. However, the coil closer to the object to be detected is more affected by the change in the magnetic permeability than the coil farther away. Therefore, in the above case, the amount of increase in inductance increases and the amount of increase in oscillation period also increases. Become. Therefore, a difference corresponding to the degree of change in the magnetic permeability occurs in the oscillation period in the two oscillation circuits including the two coils. Thus, since there is a correlation between the difference between the two oscillation cycles and the magnetic permeability, in the present invention, the magnetic permeability of the object to be detected can be detected based on the difference between the oscillation cycles of the two oscillation circuits. Is possible.

  In the magnetic permeability sensor 20 in the above-described embodiment, the first coil 1 corresponds to a coil closer to the detected object, and the second coil 2 corresponds to a coil farther from the detected object.

  The developer in the developing unit is a mixture of toner and magnetic material (iron powder). At the time of copying, the toner adheres to the paper and the magnetic material hardly adheres. Therefore, as the copying process proceeds, the amount of toner decreases but the amount of magnetic material hardly changes, so the magnetic permeability of the developer increases. Therefore, there is an inversely proportional correlation between the magnetic permeability in the developing unit and the toner density. In the present invention, since the magnetic permeability of the detection target (developer) can be detected as described above, the toner concentration can be detected based on the detected magnetic permeability of the developer in the developing unit.

  In the above-described embodiment, changes in inductance of two coils (first coil 1 and second coil 2) coaxially arranged on the substrate 10 are two oscillation circuits (first oscillation) controlled by a microcomputer. The difference between the oscillation periods in the circuit 6 and the second oscillation circuit 7) is detected, and the difference (amount of change in the oscillation period) is calculated by a microcomputer and detected as a change in magnetic permeability. Here, the two coils are alternately connected to the oscillation circuit, the oscillation cycle is alternately measured over a predetermined time by a microcomputer, and the difference is calculated to detect the change in the magnetic permeability.

  In the present embodiment, since the first coil 1 and the second coil 2 are coaxially arranged on the upper and lower surfaces of the substrate 10, the area necessary for the arrangement of the coils can be reduced, and the narrowing in the horizontal direction can be achieved. . Further, since the coil is formed by printing the conductor pattern on the substrate 10, the height in the height direction can be reduced. Furthermore, since various processes are performed using a microcomputer, the number of components can be reduced and the area for mounting circuit components can be reduced. From the above, the magnetic sensor can be greatly downsized.

  Since the measurement of the oscillation period in the two oscillation circuits is performed alternately, the measurement of the oscillation circuit including one coil is not affected by the magnetic flux generated in the other coil (inductance change in the other coil). Therefore, an accurate oscillation cycle can be measured, and as a result, the magnetic permeability can be detected with high accuracy.

  In this embodiment, since the transistors and capacitors constituting the two oscillation circuits are shared, and the coils are arranged in the oscillation circuits, the number of parts can be reduced and the cost can be reduced. In addition, since the number of parts is small, variations in part characteristics can be reduced, and further accurate measurement is possible without being affected by disturbances such as temperature changes and noise.

  Since various processes are performed by software using a microcomputer, the number of circuit parts as hardware can be reduced and the influence of variations in characteristics of circuit parts is reduced. In addition, since it is processed by software, it is less affected by the environment (temperature, humidity, etc.). Therefore, the accuracy of the detected magnetic permeability can be increased.

  Further, even when the set toner density is different, it can be easily dealt with only by changing the contents of the software. Therefore, since management for each set value with different toner density is not required, mass production is facilitated, and cost can be reduced.

  Next, a comparison of characteristics (toner density detection) between the example of the present invention and the conventional example will be described. The magnetic permeability sensor (toner sensor) of the present invention example has the configuration shown in FIGS. 1 and 2 described above, and is attached to the developing unit as shown in FIG. 3 described above.

  FIG. 7 is a cross-sectional view showing an example of attaching a conventional magnetic permeability sensor to a developing unit. In FIG. 7, the same or similar parts as those in FIG.

  A differential transformer 51 is provided on the upper surface side of one end of the substrate 10. The differential transformer 51 includes a drive coil to which an alternating oscillation signal is applied, and a differential coil (reference coil and detection coil) coupled to the drive coil. A hole 33 is formed in the partition wall 30 at a position facing the differential transformer 51, and a part (detection coil side) of the differential transformer 51 protrudes from the hole 33, and the detection coil serves as a developer in the developing unit. It comes to touch directly. A connector 3 is formed on the lower surface of the other end portion of the substrate 10 with a part protruding from the other end, and various circuit components 5 are mounted on the lower surface of the central portion of the substrate 10. The magnetic permeability sensor having such a configuration is attached to the recess 31 of the partition wall 30 while being accommodated in the case 21.

  In the conventional magnetic permeability sensor, since the differential transformer 51 protrudes, there is a disadvantage that the shape of the case 21 is complicated, and the configuration is larger than that of the present invention example. Moreover, since the hole 33 is formed in the partition wall 30, the developer may leak.

  FIG. 8 is a graph showing detection sensitivity characteristics of toner density in the present invention example and the conventional example. In FIG. 8, the horizontal axis represents the toner concentration, and the vertical axis represents the output voltage as a result of magnetic permeability detection. Further, (a) and (b) in FIG. 8 show the characteristics of the present invention example and the conventional example, respectively.

  When the present invention example and the conventional example are compared, in the present invention example, the portion where the output voltage fluctuates linearly with respect to the change in the toner density is wider than the conventional example. Therefore, it can be seen that the detection accuracy of the example of the present invention is superior to the detection accuracy of the conventional example.

  FIG. 9 is a graph showing control voltage characteristics for performing offset control in the present invention example and the conventional example. In FIG. 9, the horizontal axis represents the control voltage to be applied, and the vertical axis represents the output voltage. Also, (a) and (b) in FIG. 9 show the characteristics of the inventive example and the conventional example, respectively.

  When the present invention example is compared with the conventional example, the output voltage varies only linearly with respect to the change in the control voltage in the conventional example, whereas in the present invention example, the change in the control voltage occurs. On the other hand, the output voltage varies linearly throughout. Therefore, it can be seen that the accuracy of the offset control in the example of the present invention is superior to the accuracy of the conventional example.

  By the way, in the above-described embodiment, the magnetic permeability sensor 20 is attached to the developing unit in a state of being accommodated in the case 21. However, in the present invention, since there is no possibility that the developer leaks, the case 21 is not necessarily provided. good. In such a case, notches are formed in a plurality of locations on the substrate 10, and the magnetic permeability sensor 20 is attached to the developing unit by hooking the claw of the developing unit to the notches, or the substrate 10 and the double-sided adhesive tape are used. What is necessary is just to attach the partition 30 and attach the magnetic permeability sensor 20 to the developing unit.

  In the above-described embodiment, the first coil 1 and the second coil 2 are formed coaxially by printing conductor patterns on the upper surface and the lower surface of the substrate 10, respectively. The forming method 2 is not limited to this, and may be another method. Hereinafter, these other methods will be described as modified examples.

(First modification)
FIG. 10 is a perspective view showing the configuration of the coil in the first modification. 10, the same or similar members as those in FIGS. 1 and 2 are denoted by the same reference numerals. In FIG. 10, the upper and lower surfaces of the substrate 10 are illustrated opposite to FIG. 1. In the first modification, the first coil 1 and the second coil 2 are formed concentrically on the lower surface of the substrate 10 by, for example, pattern printing of copper foil. A coil is not formed on the upper surface of the substrate 10, and the electronic chip 4, the circuit component 5, and the connector 3 similar to those in the above-described embodiment are mounted.

(Second modification)
FIG. 11 is a cross-sectional view showing the configuration of the magnetic permeability sensor in the second modification. In FIG. 11, the same or similar members as those in FIGS. 1 and 2 are denoted by the same reference numerals. In the second modification, the first coil 1 and the second coil 2 are formed on the lower surface of the substrate 10 in a coaxial manner with an insulating layer interposed therebetween, for example, by pattern printing of copper foil. Further, no coil is formed on the upper surface of the substrate 10, and the electronic chip 4, the circuit component 5, and the connector 3 similar to those of the above-described embodiment are mounted. The first coil 1 and the second coil 2 are formed immediately below the mounting position of the electronic chip 4 and the circuit component 5. Therefore, further downsizing of the configuration of the magnetic permeability sensor can be achieved. Unlike the configuration shown in FIG. 11, the concentric first coil 1 and second coil 2 as described in the first modification are formed immediately below the mounting positions of the electronic chip 4 and the circuit component 5. You may do it.

(Third Modification)
FIG. 12 is a cross-sectional view showing the configuration of the magnetic permeability sensor in the third modification. 12, the same or similar members as those in FIGS. 1 and 2 are denoted by the same reference numerals. In the third modification, a first coil 1 is formed by mounting a separate air core coil on the lower surface of one end portion of the substrate 10, and is coaxial with the first coil 1 on the upper surface of one end portion of the substrate 10. The second coil 2 is formed by mounting a separate air core coil. In the remaining area on the upper surface of the substrate 10, the electronic chip 4, the circuit component 5, and the connector 3 similar to those in the above-described embodiment are mounted.

(Fourth modification)
FIG. 13 is a cross-sectional view showing the configuration of the magnetic permeability sensor in the fourth modification. 13, the same or similar members as those in FIGS. 1 and 2 are denoted by the same reference numerals. In the fourth modification, the first coil 1 and the second coil 2 are formed by stacking and mounting two air core coils of different parts on the upper surface of one end of the substrate 10. In the remaining area on the upper surface of the substrate 10, the electronic chip 4, the circuit component 5, and the connector 3 similar to those in the above-described embodiment are mounted. Note that, unlike the configuration shown in FIG. 13, the first coil 1 and the second coil 2 that form the stacked configuration of the two air-core coils as described above may be formed on the lower surface of the substrate 10.

(5th modification)
FIG. 14 is a cross-sectional view showing the configuration of the magnetic permeability sensor in the fifth modification. 14, the same or similar members as those in FIGS. 1 and 2 are denoted by the same reference numerals. In the fifth modification, a plurality of chip coils are mounted on the lower surface of one end portion of the substrate 10 to form the first coil 1, and the upper surface of one end portion of the substrate 10 is coaxial with the first coil 1, A plurality of chip coils are mounted to form the second coil 2. In the remaining area on the upper surface of the substrate 10, the electronic chip 4, the circuit component 5, and the connector 3 similar to those in the above-described embodiment are mounted.

  In the present invention, the first coil and the second coil may be covered with an electrostatic shield. The coil described in the present invention uses an air-core coil. If there is a coil having a dielectric constant close to the coil, the measured value may vary due to a change in capacitance. In such a case, the influence from the outside can be suppressed by covering the coil with a shield member made of copper or the like. However, in the case of the magnetic permeability sensor of the present invention, it is considered that an eddy current is generated in the shield member due to a change in magnetic permeability, that is, a change in magnetic field lines, and this eddy current may cause a measurement error in the magnetic permeability sensor. Therefore, it is necessary to provide a shield member that takes measures against eddy currents into consideration.

  15A to 15C are plan views showing the configuration of a shield member suitable for the magnetic permeability sensor of the present invention. In the example shown in FIG. 15A, a copper shield member 61 having a shape in which a plurality of comb teeth are extended in the same direction is provided above the coil 60 formed on the substrate 10. The shield member 61 is grounded. Further, in the example shown in FIG. 15B, a copper shield member 62 having a shape in which a plurality of comb teeth are alternately extended in the opposite direction is provided above the coil 60 formed on the substrate 10. The shield member 62 is grounded. By providing the shield member having such a configuration, eddy current can be reduced.

  FIG. 15C shows an annular shield member. A shield member 63 having a C-shape with a part of the copper ring missing is provided on the outer peripheral side of the coil 60 formed on the substrate 10. The shield member 63 is grounded. By providing the shield member 63, eddy current can be reduced. In the example of FIG. 15C, since the shield member 63 is provided in the same plane as the coil 60, the magnetic permeability sensor can be thinned, however, as compared with the form of covering the coil 60 as shown in FIGS. The shielding effect is small.

  The shield member as described above may be provided on both sides of the substrate 10 or may be provided only on the surface opposite to the development unit. Further, as described above, the shield member is preferably grounded. However, the effect can be obtained even if it is not grounded.

  The disclosed embodiments should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 1st coil 2 2nd coil 3 Connector 4 Electronic chip 5 Circuit component 6 1st oscillation circuit 7 2nd oscillation circuit 10 Board | substrate 20 Magnetic permeability sensor 41 Measurement part 42 Calculation part 43 Conversion part

Claims (5)

In a magnetic permeability sensor for detecting the magnetic permeability of an object to be detected,
A first oscillation circuit that oscillates including a first coil that receives magnetism from the object to be detected;
A second oscillation circuit that oscillates including a second coil that receives magnetism from the object to be detected;
Measuring means for measuring an oscillation period in each of the first oscillation circuit and the second oscillation circuit;
Calculating means for calculating a difference between oscillation cycles measured by the measuring means;
Conversion means for converting the difference calculated by the calculation means into magnetic permeability,
The magnetic permeability sensor according to claim 1, wherein components of the first oscillation circuit and the second oscillation circuit are common except for the first coil and the second coil.   2. The magnetic permeability sensor according to claim 1, wherein the measuring unit is configured to alternately measure an oscillation period in the first oscillation circuit and an oscillation period in the second oscillation circuit.   The magnetic permeability sensor according to claim 1 or 2, wherein the first coil and the second coil are arranged coaxially.   The magnetic permeability sensor according to any one of claims 1 to 3, further comprising a substrate on which the first coil is disposed and the second coil is disposed on the other surface. In the magnetic permeability detection method for detecting the magnetic permeability of the object to be detected,
Disposing the first coil and the second coil at different distances from the object to be detected;
Measure the oscillation period of the oscillation circuit that oscillates including the first coil and the oscillation period of the oscillation circuit that oscillates including the second coil,
Calculate the difference between the measured oscillation cycles,
A magnetic permeability detection method, wherein the calculated difference is converted into a magnetic permeability.

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