Distance measuring device

Abstract

To provide a distance measuring device capable of accurately detecting a distance to a movable object.SOLUTION: The distance measuring device includes a fixed-side device and a movable-side antenna including a movable-side parallel resonance circuit. The stationary side device includes a signal generator that generates an AC signal, and a bridge circuit having a variable reactance and a stationary side parallel resonance circuit that can be set to a resonance frequency different from a resonance frequency of the movable side parallel resonance circuit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a distance measuring device. [Background technology]

[0002] A known example of a conventional invention related to a distance measurement device is a short-range positioning system described in Patent Document 1. The short-range positioning system described in Patent Document 1 includes a fixed reference system and a movable object. The fixed reference system includes a voltage oscillator that generates a signal having a frequency, a bridge having a series resonant circuit, and a differential amplifier to which the output of the bridge is input. The movable object includes a resonant circuit. The series resonant circuit and the resonant circuit each generate a magnetic field. Furthermore, a current flows in the resonant circuit due to the magnetic field generated by the series resonant circuit. A current flows in the series resonant circuit due to the magnetic field generated by the resonant circuit. The frequency of the signal generated by the voltage oscillator is equal to the resonant frequency of the series resonant circuit and the resonant frequency of the resonant circuit. When the movable object moves, a current flows in the series resonant circuit of the bridge due to the magnetic field generated by the resonant circuit of the movable object, changing the impedance of the series resonant circuit. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2004-505262 Summary of the Invention [Problem to be solved by the invention]

[0004] In the short-distance positioning system described in Patent Document 1, the frequency of the signal generated by the voltage oscillator is equal to the resonant frequency of the series resonant circuit and the resonant frequency of the resonant circuit, so when the movable object approaches or moves away, the input voltage of the differential amplifier changes abruptly, which may result in the inability to accurately detect the distance to the movable object.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a distance measuring device that can accurately detect the distance to a movable object. [Means for solving the problem]

[0006] A distance measuring device according to one aspect of the present invention comprises: A fixed device; a movable-side antenna including a movable-side parallel resonant circuit; Equipped with The fixed device is a signal generator for generating an AC signal; a bridge circuit having a variable reactance and a fixed-side parallel resonant circuit whose resonant frequency can be set to a different frequency from the resonant frequency of the movable-side parallel resonant circuit; Includes.

[0007] In this embodiment, the resonant frequency of the fixed-side parallel resonant circuit can be set to a frequency different from the resonant frequency of the movable-side parallel resonant circuit. Furthermore, the frequency of the AC signal generated by the signal generator may be different from the resonant frequency of the fixed-side parallel resonant circuit and the resonant frequency of the movable-side parallel resonant circuit. Therefore, when the movable antenna moves, the change in impedance of the fixed-side parallel resonant circuit can be made to monotonically decrease. This allows a one-to-one correspondence between the distance to the movable antenna and the output voltage of the bridge circuit. As a result, this embodiment allows the distance to the movable antenna (movable object) to be detected with high accuracy. [Effects of the Invention]

[0008] According to the present invention, the distance to a movable object can be detected with high accuracy. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a circuit diagram of a distance measuring device 1. As shown in FIG. [Figure 2] FIG. 2 is a circuit diagram of the distance measurement device 1 showing the first wiring W1, second wiring W2, and third wiring W3 connected to the fixed-side antenna 100. [Figure 3]FIG. 3 is a perspective view of the fixed antenna 100 and the movable antenna 20. As shown in FIG. [Figure 4] FIG. 4 is a perspective view showing the internal structure of the fixed antenna 100. As shown in FIG. [Figure 5] FIG. 5 is a perspective view showing the internal structure of the movable antenna 20. As shown in FIG. [Figure 6] FIG. 6 is a diagram showing the frequency characteristics of the movable-side parallel resonant circuit and the coil when the frequency fd is higher than the resonant frequency f01. [Figure 7] FIG. 7 is a diagram showing the frequency characteristics of the movable-side parallel resonant circuit and the coil when the frequency fd is lower than the resonant frequency f01. [Figure 8] FIG. 8 is a diagram showing an example of the frequency fd. [Figure 9] FIG. 9 is a diagram showing the transition of the frequency characteristics of the fixed-side parallel resonant circuit when the variable inductor VL3 approaches the variable inductor VL2 in the case where the frequency fd is lower than the resonant frequency f02. [Figure 10] FIG. 10 is a diagram showing an example of the impedance Zd and voltage Vo of the fixed-side parallel resonant circuit when the bridge circuit 4 is balanced with the variable inductor VL3 being sufficiently separated from the variable inductor VL2. [Figure 11] FIG. 11 is a diagram showing an example of the impedance Zd and voltage Vo of the fixed-side parallel resonant circuit when the bridge circuit 4 is balanced in a state where the variable inductor VL3 is approaching the variable inductor VL2. [Figure 12] FIG. 12 is a diagram showing an example of the terminals T1, T2, T3, and T4. [Figure 13] FIG. 13 is a partially cutaway view of the fixed-side antenna 100. [Figure 14] FIG. 14 is a circuit diagram of the distance measurement device 1a. [Figure 15] FIG. 15 is a diagram showing an example of the frequency fd. [Figure 16]FIG. 16 is a diagram showing the transition of the frequency characteristics of the fixed-side parallel resonant circuit when the variable inductor VL3 approaches the variable inductor VL2 in the case where the frequency fd is higher than the resonant frequency f02. DETAILED DESCRIPTION OF THE INVENTION

[0010] [First embodiment] A distance measurement device 1 according to a first embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is a circuit diagram of the distance measurement device 1. Fig. 2 is a circuit diagram of the distance measurement device 1 showing the first wiring W1, second wiring W2, and third wiring W3 with the fixed-side antenna 100.

[0011] As shown in Fig. 1, the distance measurement device 1 includes a fixed device 10 and a movable antenna 20. The fixed device 10 is fixed at a predetermined position. The movable antenna 20 is not fixed at a predetermined position but is movable. The distance measurement device 1 detects the distance between the fixed device 10 and the movable antenna 20 in a short distance.

[0012] The movable-side antenna 20 has a capacitor C2, a resistor R4, and a variable inductor VL3. The resistor R4 and the variable inductor VL3 are connected in series. One end of the capacitor C2 is connected to the resistor R4. The other end of the capacitor C2 is connected to the variable inductor VL3. In addition, one end of the capacitor C1 is connected to the resistor R2. Therefore, the movable-side antenna 20 has a parallel resonant circuit (movable-side parallel resonant circuit).

[0013] The fixed device 10 includes a signal generator 2, an amplifier circuit 3, a bridge circuit 4, a differential amplifier circuit 5, a voltage detection circuit 6, and a distance calculation circuit 7.

[0014] The signal generator 2 generates an AC signal with a frequency fd. The signal generator 2 is connected to an amplifier circuit 3.

[0015] The amplifier circuit 3 amplifies the AC signal generated by the signal generator 2. The amplifier circuit 3 is connected to a bridge circuit 4. Note that the signal generator 2 may be connected to the bridge circuit 4 directly.

[0016] As shown in Fig. 2, the bridge circuit 4 includes resistors R1 and R2, variable resistors VR1, VR2, and VR3, a variable inductor VL1, a fixed-side antenna 100, a first wiring W1, a second wiring W2, and a third wiring W3. The bridge circuit 4 is an example of a bridge circuit according to the present invention. The variable inductor VL1 is an example of a variable reactance according to the present invention. The resistor R2 is an example of a first circuit element according to the present invention. The variable resistor VR2 is an example of a second circuit element according to the present invention.

[0017] The variable resistor VR1, resistor R1, variable inductor VL1, and variable resistor VR2 are connected in series. The variable resistor VR3, resistor R2, and fixed-side antenna 100 are connected in series. The series circuit of the variable resistor VR3, resistor R2, and fixed-side antenna 100 is an example of a second series circuit according to the present invention. The series circuit of the variable resistor VR1, resistor R1, variable inductor VL1, and variable resistor VR2 is connected in parallel to the series circuit of the variable resistor VR3, resistor R2, and fixed-side antenna 100.

[0018] The connection point between the variable resistors VR1 and VR3 is connected to one of the output terminals of the amplifier circuit 3. The connection point between the variable resistor VR2 and the fixed-side antenna 100 is connected to the other output terminal of the amplifier circuit 3 and to ground. The connection point between the resistor R1 and the variable inductor VL1 is connected to the inverting input terminal of the differential amplifier circuit 5. The connection point between the resistor R2 and the fixed-side antenna 100 is connected to the non-inverting input terminal of the differential amplifier circuit 5.

[0019] The fixed-side antenna 100 has a parallel resonant circuit (fixed-side parallel resonant circuit). More specifically, the fixed-side parallel resonant circuit has a capacitor C1, a resistor R3, and a variable inductor VL2. The variable inductor VL2 is an example of an inductor according to the present invention. The capacitance of the capacitor C1 is C1. The resistance value of the resistor R3 is R3. The inductance of the variable inductor VL2 is VL2. The resistor R3 is connected in series with the variable inductor VL2. The series circuit of the variable inductor VL2 and the resistor R3 is an example of a first series circuit according to the present invention. One end of the capacitor C1 is connected to the resistor R3. The other end of the capacitor C1 is connected to the variable inductor VL2. That is, the capacitor C1 is connected in parallel to the first series circuit. The variable inductor VL2 is magnetically coupled with the variable inductor VL3. By changing the inductance of the variable inductor VL2, the resonant frequency f01 of the fixed-side parallel resonant circuit can be set to a frequency different from the resonant frequency f02 of the movable-side parallel resonant circuit.

[0020] One end of the capacitor C1 is connected to the resistor R2 by a first wiring W1. The other end of the capacitor C1 is connected to the variable resistor VR2 by a second wiring W2. The other end of the capacitor C1 is also connected to the other output terminal of the amplifier circuit 3 and to ground by a third wiring W3.

[0021] The differential amplifier circuit 5 amplifies the voltage (output voltage of the bridge circuit 4) generated between the connection point between the resistor R1 and the variable inductor VL1 and the connection point between the resistor R2 and the fixed-side antenna 100, and outputs the voltage Vo. The differential amplifier circuit 5 is connected to a voltage detection circuit 6. The voltage detection circuit 6 detects the voltage Vo output by the differential amplifier circuit 5. The voltage detection circuit 6 is connected to a distance calculation circuit 7. The distance calculation circuit 7 calculates the distance between the fixed-side device 10 and the movable-side antenna 20 based on the voltage Vo detected by the voltage detection circuit 6.

[0022] The fixed-side antenna 100 and the movable-side antenna 20 will be described in more detail with reference to the drawings. Fig. 3 is a perspective view of the fixed-side antenna 100 and the movable-side antenna 20. Fig. 4 is a perspective view showing the internal structure of the fixed-side antenna 100. Fig. 5 is a perspective view showing the internal structure of the movable-side antenna 20.

[0023] 3, the fixed antenna 100 has a housing H1. The housing H1 is an example of a fixed housing according to the present invention. The housing H1 has a step S1.

[0024] The movable-side antenna 20 has a housing H2. The housing H2 is an example of a movable-side housing according to the present invention. The housing H2 has a step S2.

[0025] The surface of the housing H1 and the surface of the housing H2 are aligned. More specifically, the step S1 of the housing H1 and the step S2 of the housing H2 are tally-shaped, allowing the surface of the housing H1 to match the surface of the housing H2.

[0026] 4, the fixed-side antenna 100 has a core CO1, a bobbin B1, terminals T1, T2, T3, and T4, conductors CW1 and CW2, a capacitor C1, a first coil L1, and a second coil L2. The core CO1, bobbin B1, terminals T1, T2, T3, and T4, conductors CW1 and CW2, capacitor C1, the first coil L1, and the second coil L2 are waterproofed by a housing H1.

[0027] The core CO1 is a magnetic body inserted into the bobbin B1. In this embodiment, the core CO1 is a rod-shaped magnetic body having a rectangular cross section. The material of the core CO1 is, for example, ferrite, metal alloy, silicon steel plate, amorphous, or the like.

[0028] The bobbin B1 protects the core CO1. Specifically, the bobbin B1 is a resin component that prevents the core CO1 from being damaged by deformation or impact during manufacturing or product use. The bobbin B1 has multiple openings that expose the core CO1 to the outside at multiple locations.

[0029] The bobbin B1 has a first housing portion B11 that houses one end CO1A of the core CO1 and a second housing portion B12 that houses the other end CO1B of the core CO1. An adjustment mechanism B13 that is movable along the extension direction of the core CO1 is provided between the first housing portion B11 and the second housing portion B12.

[0030] The terminals T1 and T2 are provided on the surface of the first housing portion B11. The material of the terminals T1 and T2 is metal. The first wiring W1 is connected to and fixed to the terminal T1. The second wiring W2 and the third wiring W3 are each connected to and fixed to the terminal T2. The terminal T1 is connected to the terminal T3 by a conductor CW1. The conductor CW1 is wound around the terminals T1 and T3. The terminal T2 is connected to the terminal T4 by a conductor CW2. The conductor CW2 is wound around the terminals T2 and T4.

[0031] The terminals T3 and T4 are provided between the first housing portion B11 and the second housing portion B12. The terminals T3 and T4 are made of metal. The capacitor C1 is connected and fixed to the terminals T3 and T4 by soldering (not shown).

[0032] The first coil L1 is disposed between the capacitor C1 and the second housing B12. The winding of the first coil L1 is made of a metal wire such as a resistance wire or a copper wire. In this embodiment, the winding of the first coil L1 is made of a resistance wire. The resistivity of the winding of the first coil L1 is higher than the resistivity of the conductor connected to the first coil L1. The resistance wire is, for example, a copper-nickel resistance wire such as CN15 (CuNi10), which has a higher resistance value than copper wire. The winding of the first coil L1 is wound around a bobbin B1. This fixes the first coil L1 to the bobbin B1.

[0033] The second coil L2 is disposed between the first coil L1 and the second housing B12. The winding of the second coil L2 is made of a metal wire such as a resistance wire or a copper wire. In this embodiment, the winding of the second coil L2 is made of a copper wire. The resistivity of the winding of the second coil L2 is lower than the resistivity of the winding of the first coil L1. The winding of the second coil L2 is wound around the adjustment mechanism B13. This allows the second coil L2 to move along the extension direction of the core CO1. The number of turns of the second coil L2 is smaller than the number of turns of the first coil L1. In other words, the number of turns of the first coil L1 is greater than the number of turns of the second coil L2.

[0034] One end of the first coil L1 is connected to terminal T3. The other end of the first coil L1 is connected to one end of the second coil L2. The other end of the second coil L2 is connected to terminal T4. As described above, the capacitor C1 is connected to terminals T3 and T4. Therefore, the capacitor C1 is connected in parallel with the first coil L1 and the second coil L2. The sum of the inductance of the first coil L1 and the inductance of the second coil L2 is the inductance of the variable inductor VL2.

[0035] The equivalent resistance of the resistance components of terminals T1, T2, T3, T4, conductors CW1, CW2, capacitor C1, first coil L1, and second coil L2 is resistor R3. Therefore, the fixed-side parallel resonant circuit is housed in housing H1. Furthermore, by using a resistive wire for winding the first coil L1, the resistance value of resistor R3 can be set to a desired value.

[0036] The first coil L1 is disposed and fixed between the capacitor C1 and the second coil L2. Meanwhile, the second coil L2 is movable along the direction in which the core CO1 extends. By moving the second coil L2 along the direction in which the core CO1 extends, the position of the winding of the second coil L2 relative to the core CO1 can be changed, thereby adjusting the inductance of the second coil L2. Therefore, by moving the second coil L2, the inductance of the variable inductor VL2 can be adjusted. In other words, the adjustment mechanism B13 adjusts the distance between the first coil L1 and the second coil L2 to adjust the inductance of the fixed-side parallel resonant circuit. The fixed-side parallel resonant circuit also includes the second coil L2, the inductance of which can be adjusted.

[0037] The inductance of the variable inductor VL2 may be adjusted by moving the first coil L1 along the direction in which the core CO1 extends. Also, the inductance of the variable inductor VL2 may be adjusted by moving the core CO1.

[0038] As shown in Fig. 5, the movable-side antenna 20 has a core CO2, a bobbin B2, terminals T5 and T6, a capacitor C2, a third coil L3, and a fourth coil L4. Since the movable-side antenna 20 has a structure similar to that of the fixed-side antenna 100, only the differences from the fixed-side antenna 100 will be described, and the rest will be omitted. The core CO2 corresponds to the core CO1. The bobbin B2 corresponds to the bobbin B1. The terminals T5 and T6 correspond to the terminals T3 and T4. The capacitor C2 corresponds to the capacitor C1. The third coil L3 and the fourth coil L4 correspond to the first coil L1 and the second coil L2, respectively. The adjustment mechanism B23 corresponds to the adjustment mechanism B13.

[0039] Unlike the fixed antenna 100, the movable antenna 20 is not connected by wiring from outside the movable antenna 20. Therefore, the movable antenna 20 does not have members corresponding to the terminals T1, T2 and the conductors CW1, CW2.

[0040] The movable parallel resonant circuit is housed in a housing H2 and includes a fourth coil L4 whose inductance is adjustable.

[0041] As described above, the variable inductor VL3 is magnetically coupled to the variable inductor VL2. More specifically, the AC signal generated by the signal generator 2 causes a current to flow through the variable inductor VL2. This generates a magnetic field around the variable inductor VL2. When the variable inductor VL3 approaches the variable inductor VL2, mutual induction causes a current to flow through the variable inductor VL3. This also generates a magnetic field around the variable inductor VL3. The inductance of the variable inductor VL2 changes due to the magnetic field generated around the variable inductor VL3.

[0042] The present inventors conducted an experiment to confirm that the inductance of variable inductor VL2 changes due to magnetic field coupling between variable inductors VL2 and VL3. In the experiment, the present inventors measured the change in inductance of a single coil when variable inductor VL3 was brought close to the single coil. FIG. 6 shows the frequency characteristics of the moving-side parallel resonant circuit and the coil when frequency fd is higher than resonant frequency f01. FIG. 7 shows the frequency characteristics of the moving-side parallel resonant circuit and the coil when frequency fd is lower than resonant frequency f01. The horizontal axes of FIGS. 6 and 7 represent frequency. The vertical axes of FIGS. 6 and 7 represent the impedance of the moving-side parallel resonant circuit and the inductance of the coil, respectively. Note that in FIGS. 6 and 7, the frequency characteristics of the moving-side parallel resonant circuit are shown by dotted lines, and the frequency characteristics of the coil are shown by solid lines.

[0043] First, the inventors measured the inductance of the coil when the frequency fd was higher than the resonant frequency f01. In this experiment (hereinafter referred to as Experiment 1), the frequency fd was 125 kHz and the resonant frequency f01 was 118 kHz.

[0044] When the movable antenna 20 was moved away from the single coil, the inductance of the single coil was 471 μH. Next, the movable antenna 20 was moved closer to the single coil. The closer the movable antenna 20 was to the single coil, the smaller the inductance of the single coil became. When the distance between the movable antenna 20 and the single coil was approximately 20 mm, the inductance of the single coil was 459 μH.

[0045] When frequency fd is higher than resonant frequency f01, variable inductor VL3 becomes capacitive at frequency fd. As a result, the polarity of mutual induction from variable inductor VL3 to the single coil becomes capacitive. Therefore, the closer the movable antenna 20 is to the single coil, the smaller the inductance of the single coil becomes.

[0046] Next, the inventors measured the inductance of the coil when the frequency fd was lower than the resonant frequency f01. In this experiment (hereinafter referred to as Experiment 2), the frequency fd was 125 kHz and the resonant frequency f01 was 138 kHz.

[0047] When the movable antenna 20 was moved away from the single coil, the inductance of the single coil was 471 μH. Next, the movable antenna 20 was moved closer to the single coil. The closer the movable antenna 20 was to the single coil, the greater the inductance of the single coil. When the distance between the movable antenna 20 and the single coil was approximately 20 mm, the inductance of the single coil was 482 μH.

[0048] When frequency fd is lower than resonant frequency f01, variable inductor VL3 becomes inductive at frequency fd. As a result, the polarity of mutual induction from variable inductor VL3 to the single coil becomes inductive. Therefore, the closer the movable antenna 20 is to the single coil, the greater the inductance of the single coil.

[0049] The frequency fd will be described in more detail with reference to the drawings. FIG. 8 is a diagram showing an example of the frequency fd. In FIG. 8, the frequency characteristics of the fixed-side parallel resonant circuit are shown by a solid line, and the frequency characteristics of the movable-side parallel resonant circuit are shown by a dotted line. FIG. 9 is a diagram showing the transition of the frequency characteristics of the fixed-side parallel resonant circuit when the variable inductor VL3 approaches the variable inductor VL2 in a case where the frequency fd is lower than the resonant frequency f02. The horizontal axes in FIGS. 8 and 9 each represent frequency. The vertical axes in FIGS. 8 and 9 each represent impedance. In FIG. 9, the frequency characteristics of the fixed-side parallel resonant circuit when the variable inductor VL3 is sufficiently separated from the variable inductor VL2 are shown by a solid line, and the frequency characteristics of the fixed-side parallel resonant circuit when the variable inductor VL3 approaches the variable inductor VL2 are shown by a dashed dotted line.

[0050] 8, the resonant frequency f01 of the fixed-side parallel resonant circuit is different from the resonant frequency f02 of the movable-side parallel resonant circuit. In this embodiment, the resonant frequency f01 of the fixed-side parallel resonant circuit is higher than the resonant frequency f02 of the movable-side parallel resonant circuit.

[0051] The frequency fd of the AC signal is different from the resonant frequency f01 of the fixed-side parallel resonant circuit. In this embodiment, the frequency fd of the AC signal is higher than the resonant frequency f02 of the movable-side parallel resonant circuit and lower than the resonant frequency f01 of the fixed-side parallel resonant circuit. As a result, at frequency fd, the fixed-side parallel resonant circuit operates in the inductive region. Also, at frequency fd, the movable-side parallel resonant circuit operates in the capacitive region.

[0052] If the resonant frequency f01 is too low compared to the frequency fd, the impedance of the movable-side parallel resonant circuit becomes too low, and the effect of mutual induction itself becomes too small. On the other hand, if the resonant frequency f01 is only slightly lower than the frequency fd, the impedance Zd of the fixed-side parallel resonant circuit changes too rapidly due to movement of the movable-side antenna 20. Therefore, the output voltage of the bridge circuit 4 changes too rapidly, and the range of linear change relative to changes in the distance from the movable-side antenna 20 becomes narrow. Therefore, it is preferable to set the frequency fd appropriately lower than the resonant frequency f01.

[0053] As in Experiment 1, the closer the variable inductor VL3 is to the variable inductor VL2, the smaller the inductance of the variable inductor VL2. The resonant frequency f02 is inversely proportional to the inductance of the variable inductor VL2. Therefore, as shown in FIG. 9, the closer the variable inductor VL3 is to the variable inductor VL2, the higher the resonant frequency f02. As described above, the frequency fd is constant. Therefore, as the resonant frequency f02 increases, the impedance Zd of the fixed-side parallel resonant circuit decreases.

[0054] According to the distance measurement device 1, the bridge circuit 4 may be balanced when the variable inductor VL3 is sufficiently far from the variable inductor VL2, or when the variable inductor VL3 is close to the variable inductor VL2. That is, according to the distance measurement device 1, the bridge circuit 4 may be balanced by placing the movable-side antenna 20 at any position. In this embodiment, the bridge circuit 4 being balanced means that the output voltage of the bridge circuit 4 is approximately zero.

[0055] First, a case where the bridge circuit 4 is balanced when the variable inductor VL3 is sufficiently separated from the variable inductor VL2 will be described with reference to the drawings. FIG. 10 is a diagram showing an example of the impedance Zd and voltage Vo of the fixed-side parallel resonant circuit when the bridge circuit 4 is balanced when the variable inductor VL3 is sufficiently separated from the variable inductor VL2. The horizontal axis of FIG. 10 represents distance. The vertical axis of FIG. 10 represents the impedance Zd and voltage Vo of the fixed-side parallel resonant circuit. In FIG. 10, the voltage Vo is indicated by a dotted line, and the impedance Zd of the fixed-side parallel resonant circuit is indicated by a solid line.

[0056] The impedance Zd of the fixed-side parallel resonant circuit is expressed by the following equation 1 using the capacitance of the capacitor C1, the resistance value of the resistor R3, the inductance of the variable inductor VL2, and the imaginary unit j.

[0057]

number

[0058] As described above, the fixed-side parallel resonant circuit operates in the inductive region at frequency fd. Therefore, the bridge circuit 4 can be balanced by setting the resistance of the variable resistor VR2 to the same value as the real part of the impedance Zd of the fixed-side parallel resonant circuit and the inductance of the variable inductor VL1 to the same value as the imaginary part of the impedance Zd of the fixed-side parallel resonant circuit.

[0059] Even if the resonant frequency f02 shifts due to an error in the capacitance of the capacitor C1, as long as the fixed-side parallel resonant circuit operates in the inductive region, by adjusting the resistance of the variable resistor VR2 and the inductance of the variable inductor VL1, the resistance of the variable resistor VR2 can be made equal to the real part of the impedance Zd of the fixed-side parallel resonant circuit, and the inductance of the variable inductor VL1 can be made equal to the imaginary part of the impedance Zd of the fixed-side parallel resonant circuit. Therefore, the bridge circuit 4 can be balanced without changing the configuration of the bridge circuit 4.

[0060] If the capacitance error of the capacitor C1 is large, the fixed-side parallel resonant circuit may operate in the capacitive region. In this case, even if the inductance of the variable inductor VL1 is adjusted, it cannot be made equal to the imaginary part of the impedance Zd of the fixed-side parallel resonant circuit, and the bridge circuit 4 cannot be balanced. Therefore, it is preferable to use a capacitor with a narrow tolerance that minimizes capacitance error for the capacitor C1.

[0061] Furthermore, when frequency fd is approximately equal to resonant frequency f02, deviation of resonant frequency f02 may cause the fixed-side parallel resonant circuit to operate in the capacitive region. In this case, even if the inductance of variable inductor VL1 is adjusted, it cannot be made equal to the imaginary part of the impedance Zd of the fixed-side parallel resonant circuit, and the bridge circuit 4 cannot be balanced. Therefore, as shown in FIG. 8, it is preferable to set frequency fd outside the frequency region Nd near resonant frequency f02.

[0062] Furthermore, if the frequency fd is set within the frequency region Nd near the resonance frequency f02, the change in the impedance Zd of the fixed-side parallel resonance circuit due to movement of the movable-side antenna 20 becomes rapid. Therefore, the change in the output voltage of the bridge circuit 4 becomes rapid, and the range in which it changes linearly with changes in the distance to the movable-side antenna 20 becomes narrow. Therefore, also from the viewpoint of the accuracy of detecting the distance between the fixed-side device 10 and the movable-side antenna 20, it is preferable to set the frequency fd outside the frequency region Nd near the resonance frequency f02.

[0063] 10, the closer the variable inductor VL3 is to the variable inductor VL2, the smaller the impedance Zd of the fixed-side parallel resonant circuit. The closer the variable inductor VL3 is to the variable inductor VL2, the more unbalanced the bridge circuit 4 becomes. As the bridge circuit 4 becomes unbalanced, the voltage Vo increases. Therefore, the closer the movable-side antenna 20 is to the fixed-side device 10, the larger the voltage Vo becomes. By associating the voltage Vo with the distance between the fixed-side device 10 and the movable-side antenna 20, the distance calculation circuit 7 can calculate the distance between the fixed-side device 10 and the movable-side antenna 20 based on the voltage Vo.

[0064] Next, a case where the bridge circuit 4 is balanced when the variable inductor VL3 is approaching the variable inductor VL2 will be described with reference to the drawings. FIG. 11 is a diagram showing an example of the impedance Zd and voltage Vo of the fixed-side parallel resonant circuit when the bridge circuit 4 is balanced when the variable inductor VL3 is approaching the variable inductor VL2. The horizontal axis of FIG. 11 represents distance. The vertical axis of FIG. 11 represents the impedance Zd and voltage Vo of the fixed-side parallel resonant circuit. In FIG. 11, the voltage Vo is indicated by a dotted line, and the impedance Zd of the fixed-side parallel resonant circuit is indicated by a solid line.

[0065] Even in this case, the impedance Zd of the fixed-side parallel resonant circuit is expressed by the above equation 1. As described above, at frequency fd, the fixed-side parallel resonant circuit operates in the inductive region. Therefore, the bridge circuit 4 can be balanced by setting the resistance value of the variable resistor VR2 to the same value as the real part of the impedance Zd of the fixed-side parallel resonant circuit and the inductance of the variable inductor VL1 to the same value as the imaginary part of the impedance Zd of the fixed-side parallel resonant circuit.

[0066] 11, the impedance Zd of the fixed-side parallel resonant circuit increases as the variable inductor VL3 moves farther away from the variable inductor VL2. The bridge circuit 4 becomes more unbalanced as the variable inductor VL3 moves farther away from the variable inductor VL2. As the bridge circuit 4 becomes more unbalanced, the voltage Vo increases. Therefore, the voltage Vo increases as the movable-side antenna 20 moves farther away from the fixed-side device 10. By associating the voltage Vo with the distance between the fixed-side device 10 and the movable-side antenna 20, the distance calculation circuit 7 can calculate the distance between the fixed-side device 10 and the movable-side antenna 20 based on the voltage Vo.

[0067] As described above, the distance measurement device 1 can calculate the distance between the fixed device 10 and the movable antenna 20 by balancing the bridge circuit 4 with the movable antenna 20 at any position.

[0068] The distance measurement device 1 can accurately detect the distance to the movable-side antenna 20. More specifically, the resonant frequency f01 of the fixed-side parallel resonant circuit can be set to a frequency different from the resonant frequency f02 of the movable-side parallel resonant circuit. Furthermore, the frequency fd of the AC signal generated by the signal generator 2 may be different from both the resonant frequency f01 of the fixed-side parallel resonant circuit and the resonant frequency f02 of the movable-side parallel resonant circuit. Therefore, when the movable-side antenna 20 moves, the change in the impedance Zd of the fixed-side parallel resonant circuit can be made to monotonically decrease. This allows a one-to-one correspondence between the distance to the movable-side antenna 20 and the output voltage of the bridge circuit 4. As a result, the distance measurement device 1 can accurately detect the distance to the movable-side antenna 20.

[0069] On the other hand, in the short-distance positioning system described in Patent Document 1, the frequency of the signal generated by the voltage oscillator needs to be equal to the resonant frequency of the series resonant circuit of the fixed reference system and the resonant frequency of the resonant circuit. However, the resonant frequency of the series resonant circuit and the resonant frequency of the resonant circuit of the movable object vary due to errors in the inductance of the coil and the capacitance of the capacitor, respectively. Therefore, it is difficult to equalize the frequency of the signal generated by the voltage oscillator with the resonant frequency of the series resonant circuit and the resonant frequency of the resonant circuit, respectively. As a result, it is difficult to balance the bridge while making the frequency of the signal generated by the voltage oscillator, the resonant frequency of the series resonant circuit, and the resonant frequency of the resonant circuit equal.

[0070] Furthermore, in the short-distance positioning system described in Patent Document 1 (JP 2004-505262 A), the bridge must be balanced when the movable object is sufficiently far from the fixed reference system, and therefore the bridge cannot be balanced with the movable object at an arbitrary position.

[0071] Furthermore, in the short-distance positioning system described in Patent Document 1 (JP 2004-505262 A), the bridge has a series resonant circuit. When the resistor of the series resonant circuit is formed by copper wire, the resistance value of the resistor becomes extremely low. Even when the resistor of the series resonant circuit is formed by resistive wire, the resistance value of the resistor becomes low. Therefore, the power supplied to the bridge by the voltage oscillator must be increased.

[0072] Furthermore, in the short-distance positioning system described in Patent Document 1 (JP 2004-505262 A), when the movable object is sufficiently far from the fixed reference system, the bridge is balanced at the resonant frequency of the series resonant circuit. Therefore, when the movable object is brought closer to the fixed reference system, the impedance of the series resonant circuit decreases rapidly, and the input voltage of the differential amplifier may exceed the maximum voltage that can be applied to the differential amplifier.

[0073] In the distance measurement device 1, the resonant frequency f01 of the fixed-side parallel resonant circuit can be set to a frequency different from the resonant frequency f02 of the movable-side parallel resonant circuit. Furthermore, the frequency fd of the AC signal generated by the signal generator 2 may be different from both the resonant frequency f01 of the fixed-side parallel resonant circuit and the resonant frequency f02 of the movable-side parallel resonant circuit. Therefore, the frequency fd at which the bridge circuit 4 is balanced does not need to be equal to both the resonant frequency f01 of the fixed-side parallel resonant circuit and the resonant frequency f02 of the movable-side parallel resonant circuit. As a result, the distance measurement device 1 allows the bridge circuit 4 to be easily balanced.

[0074] Furthermore, in the distance measurement device 1, the fixed-side resonant circuit and the movable-side resonant circuit are each a parallel resonant circuit. As a result, compared to when the fixed-side resonant circuit and the movable-side resonant circuit are each a series resonant circuit, the impedance Zd of the fixed-side parallel resonant circuit does not suddenly decrease even when the movable-side antenna 20 is brought closer to the fixed-side device 10. Therefore, in the distance measurement device 1, there is no risk that the input voltage of the differential amplifier circuit 5 will exceed the maximum voltage that can be applied to the differential amplifier circuit 5.

[0075] Furthermore, in the distance measurement device 1, the bridge circuit 4 has a parallel resonant circuit. At a resonant frequency f01, the impedance Zd of the fixed-side parallel resonant circuit is expressed by the following equation 2 using the resistance value of the resistor R3 and the inductance of the variable inductor VL2.

[0076]

number

[0077] On the other hand, at the resonant frequency, the impedance of the series resonant circuit is equal to the resistance value of the series resonant circuit. Therefore, at the resonant frequency, the impedance Zd of the fixed-side parallel resonant circuit is higher than the impedance of the series resonant circuit. Therefore, compared to when the bridge has a series resonant circuit, the power supplied from the signal generator 2 to the bridge circuit 4 can be smaller. As a result, the distance measurement device 1 can reduce the output capacitance of the signal generator 2 and the power consumption of the distance measurement device 1.

[0078] Furthermore, in the distance measurement device 1, the resistivity of the coil winding of the fixed-side parallel resonant circuit is higher than the resistivity of the conductor connected to the coil. The change in resistance value of the coil winding of the fixed-side parallel resonant circuit due to temperature change is smaller than the change in resistance value of the conductor (e.g., copper wire) connected to the coil due to temperature change. Therefore, according to the distance measurement device 1, the resistance value of resistor R3 is less likely to change even if the ambient temperature changes, and is less susceptible to the influence of ambient temperature changes.

[0079] Note that the smaller the resistance value of resistor R3, the larger the Q value of the fixed-side parallel resonant circuit. Therefore, the smaller the resistance value of resistor R3, the more abrupt the change in impedance Zd of the fixed-side parallel resonant circuit due to movement of the movable-side antenna 20, and the narrower the range over which it changes linearly with changes in the distance from the movable-side antenna 20. Therefore, by using resistance wire for the coil winding of the fixed-side parallel resonant circuit, the resistance value of resistor R3 can be made larger than when copper wire is used, and the distance from the movable-side antenna 20 that can be detected with high accuracy can be made longer.

[0080] Furthermore, in the distance measurement device 1, the fixed-side parallel resonant circuit and the movable-side parallel resonant circuit each have a coil with adjustable inductance. Therefore, by adjusting the inductance of the coil, the resonant frequency f01 of the fixed-side parallel resonant circuit and the resonant frequency f02 of the movable-side parallel resonant circuit can be adjusted. Therefore, the distance measurement device 1 can accurately detect the distance to the movable-side antenna 20 according to the desired measurement distance range without changing the circuit configuration.

[0081] Even if the movable-side antenna 20 is placed in a high-temperature environment and the resonant frequency f02 of the movable-side parallel resonant circuit changes, the fixed-side parallel resonant circuit has a coil with adjustable inductance, so the resonant frequency f01 of the fixed-side parallel resonant circuit can be adjusted. Therefore, the distance measurement device 1 can accurately detect the distance to the movable-side antenna 20 according to the desired measurement distance range without changing the circuit configuration.

[0082] Furthermore, in the distance measurement device 1, the surface of the housing H1 and the surface of the housing H2 are aligned. More specifically, the step S1 of the housing H1 and the step S2 of the housing H2 are tally-shaped, allowing the surface of the housing H1 to be aligned with the surface of the housing H2. Therefore, the state in which the housings H1 and H2 are aligned can be set as zero (the origin) for the distance to the movable-side antenna 20. Therefore, the distance measurement device 1 can achieve reproducibility in the measurement of the distance to the movable-side antenna 20. As a result, the reliability of the measurement results of the distance to the movable-side antenna 20 can be improved.

[0083] In the distance measurement device 1, one end of the capacitor C1 is connected to the resistor R2 via a first wiring W1. The other end of the capacitor C1 is connected to the variable resistor VR2 via a second wiring W2. The other end of the capacitor C1 is connected to the other output terminal of the amplifier circuit 3 and to ground via a third wiring W3. This makes it possible to suppress the influence of the wiring resistances of the first wiring W1, the second wiring W2, and the third wiring W3.

[0084] Furthermore, in the distance measurement device 1, the resonant frequency f01 of the fixed-side parallel resonant circuit is different from the resonant frequency f02 of the movable-side parallel resonant circuit. Therefore, the distance measurement device 1 can suppress the influence of variations due to errors in the inductance of the coil and the capacitance of the capacitor.

[0085] In the distance measurement device 1, the frequency fd of the AC signal is different from the resonant frequency f01 of the fixed-side parallel resonant circuit. Therefore, it is not necessary to make the frequency fd for balancing the bridge circuit 4 equal to the resonant frequency f01 of the fixed-side parallel resonant circuit. As a result, the distance measurement device 1 makes it easy to balance the bridge circuit 4.

[0086] Furthermore, in the distance measurement device 1, the frequency fd is higher than the resonant frequency f02 of the movable-side parallel resonant circuit and lower than the resonant frequency f01 of the fixed-side parallel resonant circuit. As a result, at frequency fd, the fixed-side parallel resonant circuit operates in the inductive region. At frequency fd, the movable-side parallel resonant circuit operates in the capacitive region. Therefore, according to the distance measurement device 1, the bridge circuit 4 can be balanced by positioning the movable-side antenna 20 at any position without changing the configuration of the bridge circuit 4, and the distance between the fixed-side device 10 and the movable-side antenna 20 can be calculated.

[0087] Furthermore, in the distance measurement device 1, the number of turns of the first coil L1 is greater than the number of turns of the second coil L2, which is made of copper wire. The resistivity of the winding of the first coil L1 is higher than the resistivity of the conductor connected to the first coil L1. Because the number of turns of the first coil L1 is large, even if a current flows and the winding of the first coil L1 generates heat, the ambient temperature does not rise suddenly. Therefore, according to the distance measurement device 1, even if the ambient temperature changes, the impedance Zd of the fixed-side parallel resonant circuit is less likely to change and is less susceptible to changes in ambient temperature.

[0088] Furthermore, in the distance measurement device 1, the first coil L1 is disposed between the capacitor C1 and the second coil L2. The resistivity of the winding of the first coil L1 is higher than the resistivity of the conductor connected to the first coil L1. When a current flows, the winding of the first coil L1 generates heat. The heat generated by the first coil L1 is transferred almost uniformly to the capacitor C1 and the second coil L2. Therefore, the temperature around only one of the capacitor C1 and the second coil L2 does not rise suddenly. Therefore, according to the distance measurement device 1, even if the ambient temperature changes, the impedance Zd of the fixed-side parallel resonant circuit is less likely to change and is less susceptible to the influence of changes in the ambient temperature.

[0089] The movable antenna 20 may move along the direction in which the fixed antenna 100 and the movable antenna 20 face each other. The movable antenna 20 may also move along a direction perpendicular to the direction in which the fixed antenna 100 and the movable antenna 20 face each other. In this case, the distance measurement device 1 may detect the distance to the movable antenna 20 when the movable antenna 20 passes by the fixed antenna 100 and is closest to the fixed antenna 100.

[0090] In this embodiment, the adjustment mechanism B13 is provided at the end of the core CO1. Therefore, by moving the adjustment mechanism B13, the inductance of the second coil L2 can be easily adjusted. As a result, the resonant frequency f01 of the fixed-side parallel resonant circuit can be easily adjusted. Similarly, the adjustment mechanism B23 is provided at the end of the core CO2. Therefore, by moving the adjustment mechanism B23, the inductance of the third coil L3 can be easily adjusted. As a result, the resonant frequency f02 of the movable-side parallel resonant circuit can be easily adjusted.

[0091] The adjustment mechanism B13 may be provided in the center of the core CO1. In this case, the inductance of the second coil L2 is less likely to change with the amount of movement of the adjustment mechanism B13. Therefore, the resonant frequency f01 of the fixed-side parallel resonant circuit can be adjusted more precisely. Similarly, the adjustment mechanism B23 may be provided in the center of the core CO2. In this case, the inductance of the fourth coil L4 is less likely to change with the amount of movement of the adjustment mechanism B23. Therefore, the resonant frequency f02 of the movable-side parallel resonant circuit can be adjusted more precisely.

[0092] In this embodiment, the terminals T1 and T2 to which the first wiring W1, the second wiring W2, and the third wiring W3 are connected are separate members from the terminals T3 and T4. This prevents stress from the first wiring W1, the second wiring W2, and the third wiring W3 from concentrating on the terminals T3 and T4. Furthermore, a conductor CW1 is wound around the terminals T1 and T3, and a conductor CW2 is wound around the terminals T2 and T4. The conductors CW1 and CW2 are easily deformed. Therefore, stress from the first wiring W1, the second wiring W2, and the third wiring W3 is also less likely to concentrate on the terminals T1 and T2.

[0093] Fig. 12 shows an example of terminals T1, T2, T3, and T4. When entangling the conductors CW1 and CW2, as shown in Fig. 12, overlapping portions and aerial wiring of the conductor CW1 (conductor CW2) can be eliminated. This makes it possible to stabilize the quality of soldering performed after entangling the conductors CW1 and CW2.

[0094] It is also possible to provide a relay antenna having a parallel resonant circuit between the fixed-side antenna 100 and the movable-side antenna 20. This makes it possible to increase the detectable distance between the fixed-side device 10 and the movable-side antenna 20.

[0095] The inside of the housing H1 and the housing H2 may be filled with foam SP. The foam SP has shape recovery properties, which can protect the internal components of the housing H1 and the housing H2 from shocks such as dropping.

[0096] Fig. 13 is a partially cutaway view of the fixed-side antenna 100. When the interior of the housings H1 and H2 is filled with foam SP, a rib R may be provided inside the housing H1, as shown in Fig. 13. This allows the foam SP of the same shape to be used regardless of whether or not there is a step S1.

[0097] The inside of the housing H1 and the housing H2 may be filled with epoxy resin, silicone resin, or urethane resin to provide a gap between the housing H1 and the housing H2, thereby protecting the internal components of the housing H1 and the housing H2 from shocks such as being dropped.

[0098] For example, metal terminals T3, T4 (T5, T6) may be fixed to a resin bobbin B1 (B2) by passing posts on the bobbin B1 (B2) through holes formed in the terminals T3, T4 (T5, T6). The thermal stress coefficient of resin is different from that of metal. Therefore, if the posts on the bobbin B1 (B2) expand due to heat applied during manufacturing, the expansion of the posts may deform the terminals T3, T4 (T5, T6), potentially causing cracks in the capacitor C1 (C2). Increasing the clearance between the posts on the bobbin B1 (B2) and the holes formed in the terminals T3, T4 (T5, T6) can prevent cracks from occurring in the capacitor C1 (C2).

[0099] The terminals T3, T4 (T5, T6) may be provided with recesses, which can prevent the solder connecting the capacitor C1 (C2) from flowing during manufacturing, melting the resin bobbin B1 (B2) due to the heat of the solder, and preventing the first coil L1 and the second coil L2 (the third coil L3 and the fourth coil L4) from being deformed.

[0100] [First Modification] A distance measurement device 1a according to a first modified example of the present invention will be described below with reference to the drawings. FIG. 14 is a circuit diagram of the distance measurement device 1a. FIG. 15 is a diagram showing an example of frequency fd. In FIG. 15, the frequency characteristics of the fixed-side parallel resonant circuit are shown by a solid line, and the frequency characteristics of the movable-side parallel resonant circuit are shown by a dotted line. FIG. 16 is a diagram showing the transition of the frequency characteristics of the fixed-side parallel resonant circuit when the variable inductor VL3 approaches the variable inductor VL2 in a case where frequency fd is higher than the resonant frequency f02. The horizontal axes in FIGS. 15 and 16 represent frequency. The vertical axes in FIGS. 15 and 16 represent impedance. In FIG. 16, the solid line represents the frequency characteristics of the fixed-side parallel resonant circuit when the variable inductor VL3 is sufficiently separated from the variable inductor VL2, and the dashed-dotted line represents the frequency characteristics of the fixed-side parallel resonant circuit when the variable inductor VL3 approaches the variable inductor VL2. Regarding the distance measurement device 1a, only the differences from the distance measurement device 1 will be explained, and the rest will be omitted.

[0101] 14, the distance measurement device 1a differs from the distance measurement device 1 in that the bridge circuit 4 has a variable capacitor VC1 instead of the variable inductor VL1. The variable capacitor VC1 is an example of a variable reactance according to the present invention.

[0102] In this modification, as shown in Fig. 15, the resonant frequency f01 of the fixed-side parallel resonant circuit is lower than the resonant frequency f02 of the movable-side parallel resonant circuit. The frequency fd is higher than the resonant frequency f01 of the fixed-side parallel resonant circuit and lower than the resonant frequency f02 of the movable-side parallel resonant circuit. As a result, at frequency fd, the fixed-side parallel resonant circuit operates in the capacitive region. At frequency fd, the movable-side parallel resonant circuit operates in the inductive region.

[0103] If the resonant frequency f01 is too high compared to the frequency fd, the impedance of the movable-side parallel resonant circuit becomes too small, and the effect of mutual induction itself becomes too small. On the other hand, if the resonant frequency f01 is only slightly higher than the frequency fd, the impedance Zd of the fixed-side parallel resonant circuit changes too rapidly due to movement of the movable-side antenna 20. Therefore, the voltage (output voltage of the bridge circuit 4) generated between the connection point between the resistor R1 and the variable capacitor VC1 and the connection point between the resistor R2 and the fixed-side antenna 100 changes too rapidly, narrowing the range of linear change relative to changes in the distance from the movable-side antenna 20. Therefore, it is preferable to set the frequency fd appropriately higher than the resonant frequency f01.

[0104] As in Experiment 2, the closer the variable inductor VL3 is to the variable inductor VL2, the greater the inductance of the variable inductor VL2. The resonant frequency f02 is inversely proportional to the inductance of the variable inductor VL2. Therefore, as shown in FIG. 16, the closer the variable inductor VL3 is to the variable inductor VL2, the lower the resonant frequency f02. As described above, the frequency fd is constant. Therefore, as the resonant frequency f02 decreases, the impedance Zd of the fixed-side parallel resonant circuit decreases.

[0105] In the distance measurement device 1a as well, the bridge circuit 4 may be balanced with the variable inductor VL3 sufficiently separated from the variable inductor VL2, or with the variable inductor VL3 approaching the variable inductor VL2. That is, in the distance measurement device 1a as well, the bridge circuit 4 may be balanced with the movable-side antenna 20 positioned at any desired position. In this modification, the bridge circuit 4 being balanced means that the output voltage of the bridge circuit 4 is approximately zero.

[0106] First, a case where the bridge circuit 4 is balanced in a state where the variable inductor VL3 is sufficiently separated from the variable inductor VL2 will be described.

[0107] The impedance Zd of the fixed-side parallel resonant circuit is expressed by the above equation 1. As described above, at frequency fd, the fixed-side parallel resonant circuit operates in the capacitive region. Therefore, the bridge circuit 4 can be balanced by setting the resistance value of the variable resistor VR2 to the same value as the real part of the impedance Zd of the fixed-side parallel resonant circuit and the capacitance of the variable capacitor VC1 to the same value as the imaginary part of the impedance Zd of the fixed-side parallel resonant circuit.

[0108] Even if the resonant frequency f02 shifts due to an error in the capacitance of capacitor C1, as long as the fixed-side parallel resonant circuit operates in the capacitive region, by adjusting the resistance of variable resistor VR2 and the capacitance of variable capacitor VC1, the resistance of variable resistor VR2 can be made equal to the real part of the impedance Zd of the fixed-side parallel resonant circuit, and the capacitance of variable capacitor VC1 can be made equal to the imaginary part of the impedance Zd of the fixed-side parallel resonant circuit. Therefore, the bridge circuit 4 can be balanced without changing the configuration of the bridge circuit 4.

[0109] If the capacitance error of the capacitor C1 is large, the fixed-side parallel resonant circuit may operate in the inductive region. In this case, even if the capacitance of the variable capacitor VC1 is adjusted, it cannot be made equal to the imaginary part of the impedance Zd of the fixed-side parallel resonant circuit, and the bridge circuit 4 cannot be balanced. Therefore, in this modification, it is preferable to use a capacitor with a narrow tolerance that has a small capacitance error as the capacitor C1.

[0110] Furthermore, when frequency fd is approximately equal to resonance frequency f02, deviation of resonance frequency f02 may cause the fixed-side parallel resonant circuit to operate in the inductive region. In this case, even if the capacitance of variable capacitor VC1 is adjusted, it is not possible to make it equal to the imaginary part of the impedance Zd of the fixed-side parallel resonant circuit, and the bridge circuit 4 cannot be balanced. Therefore, in this modification as well, it is preferable to set frequency fd outside the frequency region Nd near resonance frequency f02, as shown in FIG.

[0111] Furthermore, if the frequency fd is set within the frequency region Nd near the resonance frequency f02, the change in the impedance Zd of the fixed-side parallel resonance circuit due to movement of the movable-side antenna 20 becomes rapid. Therefore, the change in the output voltage of the bridge circuit 4 becomes rapid, and the range in which it changes linearly with changes in the distance from the movable-side antenna 20 becomes narrow. Therefore, also in this modified example, from the viewpoint of the accuracy of detecting the distance between the fixed-side device 10 and the movable-side antenna 20, it is preferable to set the frequency fd outside the frequency region Nd near the resonance frequency f02.

[0112] The closer the variable inductor VL3 is to the variable inductor VL2, the smaller the impedance Zd of the fixed-side parallel resonant circuit. The closer the variable inductor VL3 is to the variable inductor VL2, the more unbalanced the bridge circuit 4 becomes. As the bridge circuit 4 becomes more unbalanced, the voltage Vo increases. Therefore, the closer the movable-side antenna 20 is to the fixed-side device 10, the larger the voltage Vo becomes. By associating the voltage Vo with the distance between the fixed-side device 10 and the movable-side antenna 20, the distance calculation circuit 7 can calculate the distance between the fixed-side device 10 and the movable-side antenna 20 based on the voltage Vo.

[0113] Next, a case where the bridge circuit 4 is balanced in a state where the variable inductor VL3 is approaching the variable inductor VL2 will be described.

[0114] Even in this case, the impedance Zd of the fixed-side parallel resonant circuit is expressed by the above equation 1. As described above, at frequency fd, the fixed-side parallel resonant circuit operates in the capacitive region. Therefore, the bridge circuit 4 can be balanced by setting the resistance value of the variable resistor VR2 to the same value as the real part of the impedance Zd of the fixed-side parallel resonant circuit and the inductance of the variable inductor VL1 to the same value as the imaginary part of the impedance Zd of the fixed-side parallel resonant circuit.

[0115] The impedance Zd of the fixed-side parallel resonant circuit increases as the variable inductor VL3 moves farther away from the variable inductor VL2. The bridge circuit 4 becomes more unbalanced as the variable inductor VL3 moves farther away from the variable inductor VL2. As the bridge circuit 4 becomes more unbalanced, the voltage Vo increases. Therefore, the voltage Vo increases as the movable-side antenna 20 moves farther away from the fixed-side device 10. By associating the voltage Vo with the distance between the fixed-side device 10 and the movable-side antenna 20, the distance calculation circuit 7 can calculate the distance between the fixed-side device 10 and the movable-side antenna 20 based on the voltage Vo.

[0116] As described above, in the distance measurement device 1a as well, the movable-side antenna 20 can be placed at any position to balance the bridge circuit 4, and the distance between the fixed-side device 10 and the movable-side antenna 20 can be calculated.

[0117] The distance measurement device 1a also has the same effects as the distance measurement device 1.

[0118] The distance measurement device according to the present invention is not limited to the distance measurement devices 1 and 1a, and can be modified within the scope of the gist thereof. Furthermore, the structures of the distance measurement devices 1 and 1a may be combined arbitrarily.

[0119] The present invention has the following configuration.

[0120] (1) A fixed device; a movable-side antenna including a movable-side parallel resonant circuit; Equipped with The fixed device is a signal generator for generating an AC signal; a bridge circuit having a variable reactance and a fixed-side parallel resonant circuit whose resonant frequency can be set to a different frequency from the resonant frequency of the movable-side parallel resonant circuit; Including, Distance measuring device.

[0121] (2) the fixed-side parallel resonant circuit has a coil, The resistivity of the winding of the coil is higher than the resistivity of the conductor connected to the coil. A distance measuring device according to (1).

[0122] (3) the fixed-side parallel resonant circuit and the movable-side parallel resonant circuit each have a coil whose inductance is adjustable; A distance measuring device according to (1) or (2).

[0123] (4) the fixed device includes a fixed housing, the movable-side antenna includes a movable-side housing, the fixed-side parallel resonant circuit and the movable-side parallel resonant circuit are housed in the fixed-side housing and the movable-side housing, respectively; The surface of the fixed housing and the surface of the movable housing are aligned. A distance measuring device according to any one of (1) to (3).

[0124] (5) The bridge circuit includes: A first wiring; The second wiring; The third wiring, and The fixed-side parallel resonant circuit is a first series circuit including an inductor and a resistor connected in series with the inductor; a capacitor connected in parallel to the first series circuit; and one end of the capacitor is connected by the first wiring to a first circuit element connected in series to the fixed-side parallel resonant circuit, the other end of the capacitor is connected by the second wiring to a second circuit element connected in parallel to a second series circuit including the fixed-side parallel resonant circuit and the first circuit element, and is connected to ground by the third wiring; A distance measuring device according to any one of (1) to (4).

[0125] (6) a resonant frequency of the fixed-side parallel resonant circuit is different from a resonant frequency of the movable-side parallel resonant circuit; A distance measuring device according to any one of (1) to (5).

[0126] (7) the frequency of the AC signal is different from the resonant frequency of the fixed-side parallel resonant circuit; A distance measuring device according to any one of (1) to (6).

[0127] (8) the frequency of the AC signal is higher than the resonant frequency of the movable-side parallel resonant circuit and lower than the resonant frequency of the fixed-side parallel resonant circuit, or higher than the resonant frequency of the fixed-side parallel resonant circuit and lower than the resonant frequency of the movable-side parallel resonant circuit; A distance measuring device according to (6).

[0128] (9) the fixed-side parallel resonant circuit includes a first coil and a second coil whose winding is made of copper wire; the resistivity of the winding of the first coil is higher than the resistivity of the conducting wire connected to the first coil; The number of turns of the first coil is greater than the number of turns of the second coil, the fixed-side device includes an adjustment mechanism that adjusts the distance between the first coil and the second coil to adjust the inductance of the fixed-side parallel resonant circuit. A distance measuring device according to (6) or (8).

[0129] (10) the fixed-side parallel resonant circuit includes a first coil, a second coil whose winding is made of copper wire, and a capacitor connected in parallel with the first coil and the second coil, the resistivity of the winding of the first coil is higher than the resistivity of the conducting wire connected to the first coil; the fixed-side device includes an adjustment mechanism that adjusts the distance between the first coil and the second coil to adjust the inductance of the fixed-side parallel resonant circuit, The first coil is disposed between the capacitor and the second coil. A distance measuring device according to (6), (8) or (9). [Explanation of symbols]

[0130] 1, 1a: distance measuring device 2: Signal generator 3: Amplification circuit 4: Bridge circuit 5: Differential amplifier circuit 6: Voltage detection circuit 7: Distance calculation circuit 10: Fixed side equipment 20: Movable antenna 100: Fixed antenna B1, B2: Bobbin B11: First storage section B12: Second storage section B13,B23:Adjustment mechanism C1, C2: Capacitors CO1, CO2: Core CO1A: One end CO1B:Other end CW1,CW2: Conductor H1, H2: Housing L1: First coil L2: Second coil L3: Third coil L4: 4th coil Nd: Frequency domain R: Rib R1~R4: Resistance S1, S2: Steps SP: Foam T1~T6:Terminal VC1: Variable capacitor VL1, VL2, VL3: variable inductors VR1~VR3: Variable resistors V: Voltage W1: First wiring W2: Second wiring W3: Third wiring Zd: Impedance f01,f02: Resonance frequency fd: frequency

Claims

1. A fixed device; a movable-side antenna including a movable-side parallel resonant circuit; Equipped with The fixed device is a signal generator for generating an AC signal; a bridge circuit having a variable reactance and a fixed-side parallel resonant circuit whose resonant frequency can be set to a different frequency from the resonant frequency of the movable-side parallel resonant circuit; Including, Distance measuring device.

2. the fixed-side parallel resonant circuit has a coil, The resistivity of the winding of the coil is higher than the resistivity of the conductor connected to the coil.

2. A distance measuring device according to claim 1.

3. the fixed-side parallel resonant circuit and the movable-side parallel resonant circuit each have a coil whose inductance is adjustable; 3. A distance measuring device according to claim 1 or 2.

4. the fixed device includes a fixed housing, the movable-side antenna includes a movable-side housing, the fixed-side parallel resonant circuit and the movable-side parallel resonant circuit are housed in the fixed-side housing and the movable-side housing, respectively; The surface of the fixed housing and the surface of the movable housing are aligned.

3. A distance measuring device according to claim 1 or 2.

5. The bridge circuit includes: A first wiring; A second wiring; A third wiring; and The fixed-side parallel resonant circuit is a first series circuit including an inductor and a resistor connected in series with the inductor; a capacitor connected in parallel to the first series circuit; and one end of the capacitor is connected by the first wiring to a first circuit element connected in series to the fixed-side parallel resonant circuit, the other end of the capacitor is connected by the second wiring to a second circuit element connected in parallel to a second series circuit including the fixed-side parallel resonant circuit and the first circuit element, and is connected to ground by the third wiring; 3. A distance measuring device according to claim 1 or 2.

6. a resonant frequency of the fixed-side parallel resonant circuit is different from a resonant frequency of the movable-side parallel resonant circuit; 3. A distance measuring device according to claim 1 or 2.

7. the frequency of the AC signal is different from the resonant frequency of the fixed-side parallel resonant circuit; 3. A distance measuring device according to claim 1 or 2.

8. the frequency of the AC signal is higher than the resonant frequency of the movable-side parallel resonant circuit and lower than the resonant frequency of the fixed-side parallel resonant circuit, or higher than the resonant frequency of the fixed-side parallel resonant circuit and lower than the resonant frequency of the movable-side parallel resonant circuit; 7. A distance measuring device according to claim 6.

9. the fixed-side parallel resonant circuit includes a first coil and a second coil whose winding is made of copper wire, a resistivity of a winding of the first coil is higher than a resistivity of a conducting wire connected to the first coil; The number of turns of the first coil is greater than the number of turns of the second coil, the fixed-side device includes an adjustment mechanism that adjusts the distance between the first coil and the second coil to adjust the inductance of the fixed-side parallel resonant circuit.

7. A distance measuring device according to claim 6.

10. the fixed-side parallel resonant circuit includes a first coil, a second coil whose winding is made of copper wire, and a capacitor connected in parallel with the first coil and the second coil, a resistivity of a winding of the first coil is higher than a resistivity of a conducting wire connected to the first coil; the fixed-side device includes an adjustment mechanism that adjusts the distance between the first coil and the second coil to adjust the inductance of the fixed-side parallel resonant circuit, The first coil is disposed between the capacitor and the second coil.

7. A distance measuring device according to claim 6.

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