JP5046360B2 - Radio wave type displacement measuring device - Google Patents

Description

  The present invention relates to a displacement measuring method and a radio wave type displacement measuring apparatus using radio waves, and more specifically, radio wave amplitude measurement information and radio wave type displacement measuring apparatus which do not require radio wave amplitude information and are highly accurate. About.

As a measurement method of a conventional displacement measuring apparatus using radio waves such as microwaves and millimeter waves, a pulse method, an FMCW method, a phase change detection method, and the like are known.
In the pulse method, a transmission pulse is radiated toward an object, and a distance and a displacement are measured by measuring a time difference between a reception pulse and a transmission pulse reflected and returned.
In the FMCW method, the frequency of the transmission wave is changed continuously and linearly, and the difference between the frequency of the transmission wave and the frequency of the reflected wave from the object is measured. Since this frequency difference is proportional to the time delay due to the distance to the object, the distance and displacement can be measured.

The phase change detection method combines a transmission wave radiated toward an object and a reflected wave from the object, and detects a phase change due to the displacement of the object as a voltage level change (for example, Patent Document 1). ).
In addition, as a measuring device using a standing wave, a device for obtaining a distance to an object from a fluctuation period of an amplitude of a standing wave generated by interference between a transmission wave emitted from the measuring apparatus and a reflected wave from the object Is known (for example, Patent Documents 2 and 3).

JP 11-316140 A JP 2002-357656 A JP 2004-325085 A

A pulse-type measuring device requires a high-speed and high-resolution pulse generation circuit and a time difference measurement circuit to measure minute displacements, which increases the cost of manufacturing the device and complicates the device configuration. There's a problem.
Also, FMCW measurement equipment requires a high-precision high-frequency oscillator and frequency modulation circuit to achieve millimeter-resolution measurement (detection of 1 mm displacement), resulting in high equipment manufacturing costs. In addition, there is a problem that the device configuration becomes complicated.

Further, in the apparatus of Patent Document 1, it is necessary to measure radio wave amplitude information in order to detect a phase change, which is easily affected by noise, is expensive to ensure accuracy, and has a circuit configuration. There is a problem of complexity.
Further, the devices of Patent Documents 2 and 3 need to measure standing wave amplitude information, and have a problem that they are easily affected by noise as in the phase change detection method.
As described above, with a conventional measuring device, it has been difficult to realize a device that measures the displacement of an object at a distance of several hundreds of meters with an accuracy of millimeter resolution with a simple circuit configuration and at a low cost. .

  In order to solve the above problems, the present invention provides a method and apparatus for measuring the displacement of an object at a distance of several meters to several hundred meters with accuracy of millimeter resolution without using amplitude information of radio waves. With the goal.

The gist of the present invention is the following radio wave type displacement measuring method (1) to (3).
(1) A radio wave generated by a high-frequency oscillator is radiated to a reflecting means that continuously displaces, the reflected wave is received by a receiving means, and the received reflected wave is transmitted to a high-frequency oscillator to generate a pull-in phenomenon. A radio wave type displacement measuring method for calculating the distance displacement between the high frequency oscillator and the reflecting means based on the change in the frequency of the high frequency oscillator when the measurement frequency changes by a certain amount due to the displacement of the reflecting means. The first step of storing the frequency of the oscillator in the computer, the second step of stopping the transmission of the reflected wave to the high-frequency oscillator and returning the frequency of the high-frequency oscillator before the occurrence of the phenomenon, the oscillation frequency of the high-frequency oscillator by the computer The third step of controlling and shifting to the frequency stored in the first step, sending the reflected wave received by the receiving means to the high frequency oscillator and pulling it in The fourth step of generating the phenomenon and calculating the distance displacement between the high-frequency oscillator and the reflecting means based on the change in the frequency of the high-frequency oscillator, and the computer repeating the first to fourth steps, thereby continuously changing the distance displacement of the reflecting means. 5. A radio wave type displacement measuring method, characterized in that the fifth step of measuring is performed.
(2) the high frequency oscillator, the apparatus for stabilizing not added oscillator or wave type displacement measuring method, characterized in that an oscillator without using a crystal oscillator (1),.
(3) The radio waves radiated to the reflecting means are circularly polarized waves, reflected by the reflecting means without changing the rotational direction of the circularly polarized waves, and having the same rotational direction as the radio waves radiated by the receiving means. The radio wave type displacement measuring method according to (1) or (2), wherein only the reflected wave is received.
(4) The radio wave displacement measuring method according to any one of (1) to (3), wherein the reflecting means is a corner reflector.

Further, the gist of the present invention is the radio wave type displacement measuring device of the following (5) to (8).
(5) Radiation means for radiating radio waves generated by the high-frequency oscillator to the reflection means, frequency measurement means for measuring the frequency of the radio waves radiated from the radiation means, and reflection means for reflecting the radio waves radiated from the radiation means; Receiving means for receiving the reflected wave reflected by the reflecting means, transmitting means for transmitting the reflected wave received by the receiving means to the high-frequency oscillator, and control means for controlling the operation of each means and the oscillation frequency of the high-frequency oscillator. The radio wave generated by the high-frequency oscillator is radiated to the reflecting means that continuously displaces, the reflected wave is received by the receiving means, and the received reflected wave is transmitted to the high-frequency oscillator to generate a pull-in phenomenon. A radio wave type displacement measuring device for calculating a distance displacement between the high frequency oscillator and the reflecting means based on a change in frequency of the high frequency oscillator, wherein the control means is a displacement of the reflecting means. When the measurement frequency changes by a certain amount, the first step of storing the frequency of the high-frequency oscillator after the occurrence of the pull-in phenomenon is stopped, the transmission of the reflected wave to the high-frequency oscillator is stopped, and the frequency of the high-frequency oscillator is The second step of returning, the third step of controlling the oscillation frequency of the high-frequency oscillator to shift to the frequency memorized in the first step, the reflected wave received by the receiving means is transmitted to the high-frequency oscillator and the pulling phenomenon is generated The fourth step of calculating the distance displacement between the high-frequency oscillator and the reflecting means based on the change in the frequency of the high-frequency oscillator and the first to fourth steps are repeated, so that the distance displacement of the reflecting means is continuously measured. A radio wave type displacement measuring apparatus characterized by carrying out the process.
(6) The radio frequency displacement measuring device according to (5), wherein the high-frequency oscillator is an oscillator to which a stabilizing device is not added or an oscillator that does not use a crystal resonator.
(7) The radio wave radiated from the radiating means is circularly polarized, the reflecting means is reflected without changing the rotation direction of the circularly polarized wave, and the control means is circular with the receiving means. The radio wave displacement measuring device according to (5) or (6), wherein polarized waves are selectively received.
(8) The radio wave displacement measuring device according to any one of (5) to (7), wherein the reflecting means is a corner reflector.

According to the present invention, since amplitude information of radio waves is unnecessary, it is possible to realize measurement with higher accuracy than a device that requires amplitude information even under conditions that are susceptible to noise at a long distance. . That is, unlike the method using the phase change detection method or the standing wave method, since the amplitude information of the radio wave is not used, it is not easily affected by noise, and stable displacement measurement is possible even for a long-distance object.
Moreover, it is not necessary to measure the pulse time interval with high resolution as in the conventional pulse method, and displacement measurement with millimeter resolution can be easily realized only by measuring the frequency.

  In addition, no components for measuring the amplitude information of radio waves are required, and high-precision oscillators and modulation circuits are not required as in the FMCW system, so the device can be manufactured with a simple circuit configuration. The cost can also be reduced to a fraction of 1 to several tenths.

  Furthermore, even if the oscillator parameters such as temperature and power supply voltage fluctuate somewhat, the frequency is stabilized within a certain range, so stabilization or accuracy assurance can be achieved with a simple electronic circuit or control software. A highly reliable measuring device can be easily realized.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
The present invention performs high-accuracy position change detection by actively utilizing the “pull-in phenomenon” of a high-frequency oscillator such as a Gunn diode, and in principle, uses an inexpensive oscillator with low frequency stability. If possible.
Here, the “pull-in phenomenon” is an effect that occurs when the frequency of the oscillator and the independent frequency are combined, and means that the frequency of the oscillator changes so as to approach the independent frequency and becomes a different frequency. More specifically, this means that the reflected wave of the radio wave radiated from the oscillator returns to the oscillator again to automatically shift the oscillator to a state in which it can easily oscillate. That is, the oscillator itself automatically adjusts (locks) the oscillation frequency without external control so that the phase of the radio wave generated by the oscillator and the phase of the reflected wave are the same in the oscillator (to maintain a stable oscillation state). To do. The phase of the returned reflected wave depends on the distance to the reflecting object, and the frequency of the oscillator is stably locked within a range that is correlated with the distance to the object. Thus, a change in distance from the object can be detected with high accuracy. The relationship between the distance change ΔD with respect to the object and the change Δf in the frequency of the locked oscillator can be expressed by Equation 1 below. In Equation 1, D is the distance between the oscillator and the reflecting object, and f is the frequency of the oscillator. If D >> ΔD and f >> Δf, ΔD and Δf are proportional.

(Equation 1)
ΔD = − (D / f) · Δf

In the present invention, in order to cause the above-described pull-in phenomenon, a high-frequency oscillator that is easy to synchronize with the frequency and phase of an external signal, for example, an oscillator to which a structure such as a stabilizing plate for stabilizing the frequency or a control circuit is not added, In addition, it is necessary to use an oscillator that does not use a highly stable device such as a crystal resonator. This is because the pull-in phenomenon does not occur in an oscillator with high frequency stability.
The oscillator according to the present invention refers to an oscillator that oscillates in the UHF band (300 MHz to 3 GHz), the microwave band (3 to 30 GHz), and the millimeter wave band (30 to 300 GHz).

  In the present invention, although there is no upper limit in principle for the measurement distance, it is necessary to employ a highly accurate LNB or frequency counter because the frequency change with respect to the same displacement becomes smaller as the measurement distance becomes longer. In practice, it is necessary to consider atmospheric characteristic fluctuations such as humidity, and it can be said that a preferable range of distance is about several m to 500 m.

  As the distance increases, the frequency change Δf with respect to the displacement amount ΔD becomes smaller. Therefore, when the accuracy of the LNB and the resolution of the frequency counter are poor, it may be difficult to realize the millimeter resolution. In that case, the resolution may be increased by increasing the frequency change Δf by increasing the frequency f. However, in the case of outdoors, it is necessary to select a frequency (for example, 10 GHz band) that is not easily affected by rainfall, and it is necessary to select an optimal frequency according to the purpose.

Hereinafter, the details of the present invention will be described with reference to examples, but the present invention is not limited to the examples. Example 1 is a reference example.

"Constitution"
FIG. 1 is a basic configuration diagram of a radio wave type displacement measuring apparatus according to a first embodiment of the present invention.
As the high-frequency oscillator 1, an unstable Gunn diode module having a frequency of 10.2 GHz was used.
The circulator 2 is for a general microwave using a ferrite element, and the transmitting antenna 3 uses a satellite feed receiving center-feed parabolic antenna having a reflector diameter of 45 cm to guide the primary radiator of the antenna and the circulator 2. It is connected with a wave tube.
The reflecting plate 5 is a rectangular flat plate having a reflecting surface of 60 cm × 60 cm made of an aluminum plate, or a two-sided corner reflector. In the present embodiment, only aluminum is used as the material of the reflecting plate, but there is no limitation as long as it is a conductor, and for example, iron or copper may be used. Also, a grid-like or net-like one taking measures against wind and rain may be used.
The receiving antenna 7 uses a satellite feed receiving center-feed parabolic antenna having a reflector diameter of 45 cm, and the primary radiator of the antenna and the amplifier 8 are connected by a waveguide. It should be noted that the amplifier 8 is not necessarily required for measurement at a short distance (several meters).
Many of the parts used in the basic configuration described above can be used for consumer products used in satellite broadcasting equipment and the like, and the cost of the apparatus can be expected to be reduced.

<Operation>
A signal from the high frequency oscillator 1 is transmitted to the transmitting antenna 3 by the circulator 2 and radiated. The reflected wave 6 reflected by the reflecting plate 5 is received by the receiving antenna 7, amplified by the amplifier 8, and then returns to the high frequency oscillator 1 through the circulator 2. In the oscillator 1, the “pulling phenomenon” occurs due to the amplified reflected wave 6, and the frequency of the high-frequency oscillator 1 is locked.
The frequency of the radiated wave 4 is measured by a frequency counter 10 after being converted into an LNB output frequency which is an intermediate frequency by an LNB 9 (frequency converter) provided in the transmission antenna 3. When the reflector 5 is displaced, the frequency measured by the frequency counter 10 changes. That is, the phase is also locked at the frequency locked by the pulling phenomenon, and when the reflector is displaced after being locked, the distance between the oscillator and the reflector changes while the phase is locked, and the wavelength changes. Since the change in the wavelength becomes the change in the frequency, the distance change ΔD can be calculated from the frequency change Δf from the above equation 1.

FIG. 2 is a laboratory experiment result of displacement detection by the radio wave type displacement measuring apparatus of the first embodiment of FIG. The distance D = 40 m, and the displacement of the reflector 5 is about 10 mm.
As can be seen from FIG. 2, the frequency of the frequency counter 10 changes approximately 2.5 MHz with respect to the displacement of the reflector 5 while being approximately proportional. It can be seen that the linearity of the frequency change with respect to the displacement is excellent, and a high resolution capable of detecting a displacement of about 0.2 mm is achieved. In this embodiment, the measurement distance is 40 m. However, even when the distance is several hundred meters or more, it is possible to measure displacement without problems from the antenna / radio wave propagation theory and the relational expression between displacement and frequency change. Needless to say.
In the actual oscillator, when the distance D and the oscillator parameters change greatly, a characteristic is observed in which the frequency that has been locked until then jumps to another frequency discontinuously and is locked. Need to be resolved. A device that solves this drawback will be described in a second embodiment.

FIG. 3 is a configuration diagram of the radio wave type displacement measuring apparatus of the second embodiment. As described above, there is a limit to the lock due to the naturally occurring pull-in phenomenon, and if the displacement of the reflector is too large, the lock is released and jumps to another frequency. Is provided with a control means to control the frequency of the oscillator.
In addition to the configuration of the first embodiment, the apparatus of the present embodiment includes a computer 11 connected to the high-frequency oscillator 1, the amplifier 8, and the frequency counter 10. The computer 11 can control the presence or absence of a pull-in phenomenon by controlling the amplifier 8 according to the frequency output from the frequency counter 10 to turn on and off the reflected wave signal returned to the high-frequency oscillator 1. The frequency can also be controlled. Control by the computer 11 is performed in the following procedure.

<Control procedure>
(1) When the measurement frequency of the frequency counter 10 changes by a certain amount due to the displacement of the reflector 5, the computer 11 stores the frequency after the change due to the pull-in phenomenon.
(2) When the computer 11 controls the amplifier 8 to turn off the reflected wave signal and eliminate the pulling phenomenon, the oscillation frequency of the high-frequency oscillator 1 naturally returns to the original frequency.
(3) The computer 11 controls the oscillation frequency of the high frequency oscillator 1 to shift to the frequency when the reflected wave signal is turned on, which is stored in (1).
(4) The computer 11 controls the amplifier 8 to turn on the reflected wave signal.
(5) By repeating (1) to (4), the subsequent displacement of the reflector 5 is continuously measured.
As described above, it is confirmed by an experiment using the apparatus of the second embodiment that the computer 11 controls the frequency of the high-frequency oscillator 1 to a frequency locked by the pull-in phenomenon, thereby preventing the occurrence of a frequency jump. I was able to.

  FIG. 4 is a configuration diagram of the displacement measuring apparatus of the third embodiment. The apparatus of this embodiment has a function of preventing a jump at a discontinuous frequency, and the apparatus is miniaturized by using a transmission / reception antenna 13 in which functions of a transmission antenna and a reception antenna are integrated. In this configuration, a phenomenon equivalent to the pull-in phenomenon is caused by the phase detection by the mixer 14 and the external control by the frequency control of the oscillator by the frequency control unit 15 to prevent the frequency jump.

The high-frequency oscillator 1, the circulator 2, the LNB 9, and the frequency counter 10 are the same as those in the first and second embodiments.
The directional coupler 12 and the mixer 14 are for general microwaves, the transmission / reception antenna 13 is a satellite feed receiving center-feed parabolic antenna having a reflector diameter of 45 cm, the frequency control unit 15 is an electronic circuit, Or a computer with control software.

In the apparatus of the present embodiment, the signals from the circulator 2 and the directional coupler 12 are input to the mixer 14 for phase detection, and the frequency controller 15 causes the oscillator to adjust so that the phase of the oscillator and the phase of the reflected signal are in phase. To control the frequency. In other words, a phenomenon equivalent to the pull-in phenomenon is realized by external control without returning the reflected wave to the oscillator.
In the apparatus of the present embodiment, the signal from the high frequency oscillator 1 passes through the circulator 2 and the directional coupler 12 and is radiated from the transmission / reception antenna 13 and is also branched to the mixer 14 by the directional coupler 12. The reflected wave from the reflecting plate 5 is received by the transmission / reception antenna 13 and branched to the LNB 9 and the circulator 2 by the directional coupler 12. The reflected wave branched to the LNB 9 is converted to an intermediate frequency by the LNB 9, and then the frequency is measured by the frequency counter 10.
On the other hand, the reflected wave branched to the circulator 2 is supplied to the mixer 14 by the circulator 2. The mixer 14 detects the phase difference between the signal of the high frequency oscillator 1 supplied from the directional coupler 12 and the reflected wave signal supplied from the circulator 2, and outputs the phase difference signal to the frequency control unit 15. The frequency control unit 15 adjusts the frequency of the high-frequency oscillator 1 by changing the frequency so that the phase difference signal input from the mixer 14 has a phase difference of 0 (that is, the phase of the oscillator and the phase of the reflected signal are in phase). The adjustment is performed by the frequency control unit 15 each time the reflecting plate 5 is displaced. Thereby, the subsequent displacement of the reflecting plate 5 can be continuously measured.

FIG. 5 is an external view of a reflecting means using a corner reflector that can be used in the apparatuses of Examples 1 to 3, and shows a case of a two-sided corner reflector.
In the radio wave type displacement measuring apparatus of the first to third embodiments described above, it is assumed that the displacement is measured by a reflection means using a normal flat reflector. However, depending on the installation environment of the apparatus, various radio wave noises exist in the surroundings. However, it is assumed that the displacement measurement is adversely affected. In order to solve such a problem, it is conceivable to selectively receive only the reflected wave from the reflector using linearly polarized waves or circularly polarized waves. That is, the radiated radio wave is circularly polarized, and the radio wave radiated by right-handed circular polarization (or left-handed circular polarization) is reflected by the reflecting means without changing the direction of rotation of the circularly polarized wave, and is rotated clockwise. The reception means that receives only circularly polarized waves (or left-handed circularly polarized waves) receives only reflected waves in the same rotational direction as the radio waves radiated by eliminating circularly polarized waves and linearly polarized waves in different rotational directions. To do.
For example, when the right-handed circularly polarized wave is radiated from the transmitting antenna and reflected twice by the two-surface corner reflector of this embodiment, the reflected wave returns with the radiated right-handed circularly polarized wave remaining. By receiving this reflected wave with a receiving antenna adapted to right-handed circularly polarized waves, the selectivity of the reflected wave with respect to surrounding radio noise can be improved.
Further, by using the corner reflector, the reflected wave accurately returns in the direction of the radiated wave, so that there is an advantage that the direction of the reflecting plate can be easily adjusted as compared with a normal flat reflecting plate.

FIG. 6 is an external view of a reflecting means using a four-surface corner reflector. Since the double-sided corner reflector has a larger dimension in the depth direction, two double-sided corner reflectors are arranged side by side in an array to reduce the dimension in the depth direction while maintaining the same reflection area, and improve installation. ing.
Further, the use of the W-shaped configuration has an advantage that an installation pole or the like can be easily attached to the concave portion on the back surface.
Although this embodiment has four surfaces, the number of surfaces may be further increased by ensuring the width of each reflecting surface sufficiently larger than the wavelength of the radiated wave.

For example, in the field of disaster prevention, applications such as installing this device in countless landslide areas throughout the country and using it as a landslide sensor or monitoring deformation of civil engineering structures are conceivable.
In the security field, the present invention can also be applied to highly sensitive intrusion monitoring sensors in a wide monitoring area.
In these applications, it is possible to monitor outdoors that are not easily affected by rainfall by using radio waves in the microwave band, and the advantages of the radio wave system can be obtained over optical systems such as lasers.
Further, in the present invention, since the displacement measurement resolution improves as the distance becomes shorter, it can be applied to high-precision displacement measurement with micron resolution at a short distance (1 m or less) in the manufacturing / inspection field.

In addition, this invention is not limited to the case where a slow moving object like a landslide sensor is monitored over a long period of time, and can also measure a fast moving object.
For example, in applied experiments in the security field, human movements (breathing and hand movements) can also be detected as frequency changes.

It is a basic lineblock diagram of a radio wave type displacement measuring device of a first embodiment. It is a characteristic figure of displacement-frequency by the electric wave type displacement measuring device of a first embodiment. It is a basic lineblock diagram of a radio type displacement measuring device of a second embodiment. It is a basic lineblock diagram of a radio type displacement measuring device of a third embodiment. It is an external view of the reflection means using a two-surface corner reflector. It is an external view of the reflection means using a four-surface corner reflector.

Explanation of symbols

1 High Frequency Oscillator 2 Circulator 3 Transmitting Antenna 4 Radiated Wave 5 Reflecting Plate 6 Reflected Wave 7 Receiving Antenna 8 Amplifier 9 LNB (Low Noise Block Down Converter)
DESCRIPTION OF SYMBOLS 10 Frequency counter 11 Computer 12 Directional coupler 13 Transmission / reception antenna 14 Mixer 15 Frequency control part

Claims (8)

Radiated to the reflection means for continuously displacing the radio waves generated in the high-frequency oscillator, received by the receiving means the reflected reflected wave, to generate entrainment by sending the high-frequency oscillator and the received reflected wave, high-frequency oscillator A radio wave type displacement measuring method for calculating a distance displacement between a high frequency oscillator and a reflecting means based on a change in frequency of
A first step of storing in a computer the frequency of the high-frequency oscillator after the pull-in phenomenon occurs when the measurement frequency changes by a certain amount due to the displacement of the reflecting means ;
A second step of stopping transmission of the reflected wave to the high-frequency oscillator and returning the frequency of the high-frequency oscillator before the pull-in phenomenon occurs;
Third step of shifting the frequency which stores the oscillation frequency in the first step is controlled by a computer of high-frequency oscillator,
A fourth step of transmitting the reflected wave received by the receiving means to the high frequency oscillator to generate a pull-in phenomenon, and calculating a distance displacement between the high frequency oscillator and the reflecting means based on a change in the frequency of the high frequency oscillator ;
A radio wave type displacement measuring method, wherein the computer repeats the first to fourth steps to implement the fifth step of continuously measuring the distance displacement of the reflecting means . The high frequency oscillator, the apparatus for stabilizing not added oscillator or wave type displacement measuring method according to claim 1, characterized in that the oscillator without using a crystal oscillator. The radio waves radiated to the reflecting means are circularly polarized waves, and are reflected by the reflecting means without changing the rotational direction of the circularly polarized waves, and only reflected waves having the same rotational direction as the radio waves radiated by the receiving means are used. The radio wave type displacement measuring method according to claim 1 or 2 , characterized in that: It said reflecting means, one of the radio wave type displacement measuring method of claims 1 to 3 characterized in that it is a corner reflector. Radiation means for radiating radio waves generated by a high-frequency oscillator to the reflection means, frequency measurement means for measuring the frequency of the radio waves radiated from the radiation means, reflection means for reflecting the radio waves radiated from the radiation means, and reflection means comprising reception means for receiving a reflected wave reflected, and transmission means for transmitting a reflected wave received by the receiving means to the high-frequency oscillator, a control means for controlling the oscillation frequency of the operation and the high-frequency oscillator of each of the units by,
The radio wave generated by the high-frequency oscillator is radiated to the reflecting means that continuously displaces, the reflected wave is received by the receiving means, and the received reflected wave is transmitted to the high-frequency oscillator to generate a pull-in phenomenon. A radio wave type displacement measuring device for calculating a distance displacement between a high frequency oscillator and a reflecting means based on a change in frequency of
The control means is
A first step of storing the frequency of the high-frequency oscillator after the pulling phenomenon occurs when the measurement frequency changes by a certain amount due to the displacement of the reflecting means ;
Second step of the transmission to the high-frequency oscillator of the reflected wave is stopped, Ru is restored before symptoms occur pull the frequency of the high-frequency oscillator,
A third step of controlling the oscillation frequency of the high-frequency oscillator to shift to the frequency stored in the first step;
A fourth step of transmitting the reflected wave received by the receiving means to the high frequency oscillator to generate a pull-in phenomenon, and calculating a distance displacement between the high frequency oscillator and the reflecting means based on a change in the frequency of the high frequency oscillator;
A radio wave type displacement measuring apparatus that performs the fifth step of continuously measuring the distance displacement of the reflecting means by repeating the first to fourth steps . 6. The radio wave type displacement measuring apparatus according to claim 5, wherein the high-frequency oscillator is an oscillator to which a stabilizing device is not added or an oscillator that does not use a crystal resonator. The radio wave radiated from the radiating means is circularly polarized,
The reflecting means reflects without changing the rotation direction of the circularly polarized wave,
The radio wave type displacement measuring apparatus according to claim 5 or 6 , wherein the control means selectively receives circularly polarized waves by the receiving means. It said reflecting means, radio wave displacement measuring apparatus 5 to claim characterized in that it is a corner reflector 7.