JP2007127529A - Distance measuring instrument, and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a distance measuring instrument and a distance measuring method capable of enhancing precision in distance measurement using a standing wave, and capable of measuring a distance even in a near distance of ≤2 m. <P>SOLUTION: This instrument/method comprises a transmission means 10 for outputting an electromagnetic wave, a detecting means 30 for detecting a signal intensity (standing wave S) in an associated wave of the electromagnetic wave output from the transmission means 10, and a reflected wave of the electromagnetic wave reflected on a measuring object T, and for outputting a detection signal having a signal level corresponding to the detected signal intensity, and a signal processing means 40 for calculating a distance d between the detecting means 30 and the measuring object, based on the detection signal, The transmission means 10 is constituted to make a frequency of the output electromagnetic wave variable, the signal processing means 40 forms a distance spectrum, based on a level difference between frequencies of the detection signals output from the detecting means 30, when changing the frequency of the electromagnetic wave output from the transmission means 10, and calculates the distance d between the detecting means 30 and the measuring object T, based on the distance spectrum. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a distance measuring device and a distance measuring method. When there is a measurement object in the traveling direction, electromagnetic waves (traveling waves) such as radio waves and light transmitted from an antenna or a light emitter become reflected waves that are reflected by the measurement object and travel in the opposite direction to the traveling wave. For this reason, when an electromagnetic wave having a constant frequency is output continuously from an antenna or the like, a standing wave generated by the synthesis of the traveling wave and the reflected wave is formed between the antenna and the measurement target.
The present invention relates to a distance measuring apparatus and a distance measuring method for measuring a distance to a measurement object using the standing wave as described above.

As a distance measuring device using radio waves, radio wave radars using microwaves or millimeter waves are generally well known, and pulse radars, FMCW radars, and the like are used.
The pulse radar obtains the distance to the measurement target by measuring the time from when the pulse signal is transmitted until it is reflected and returned by the measurement target.
The FMCW radar transmits a continuous wave that has been swept in frequency, and obtains the distance to the measurement object from the frequency difference between the transmitted signal and the reflected signal.

However, these radars are generally difficult to measure at short distances.
In the case of pulse radar, the minimum distance that can be measured (hereinafter referred to as the minimum detection distance) is determined by the pulse width of the pulse signal, and the shorter the pulse width of the pulse signal, the closer the distance can be measured. In order to generate a pulse signal having a very short pulse width, the signal transmitter must transmit a signal having a wide frequency bandwidth. However, the pulse radar can be used as a distance measuring device in a mobile object detection sensor for a specific low-power device defined by the Radio Law. The occupied frequency bandwidth is 76 MHz within a range of 24.05 GHz to 24.25 GHz. Therefore, the short distance measurement is difficult, and the minimum detection distance is only several tens of meters or more.
In the FMCW radar, the minimum distance that can be measured is determined by the frequency bandwidth that can sweep the transmitted signal. As in the case of the pulse radar, the mobile object detection sensor for a specific low-power device defined by the Radio Law. In this case, the FMCW radar can be used as a distance measuring device because the occupied frequency bandwidth is limited to 76 MHz within the range of 24.05 GHz to 24.25 GHz. It is only 10m or more.

In recent years, as a radio wave radar that can measure a shorter distance than pulse radar and FMCW radar, the distance to the measurement object is measured using a standing wave formed between a transmitter such as an antenna and the measurement object. The device which develops is developed (conventional example 1: patent document 1).
In the distance measuring device of Conventional Example 1, when an electromagnetic wave having a constant frequency is output continuously from the transmission unit, the output electromagnetic wave (traveling wave) and the traveling wave are transmitted between the transmission unit and the measurement target. The distance to the measurement object is measured using a standing wave generated by the combined wave of the reflected wave reflected by the measurement object. In the distance measuring device of Conventional Example 1, the distance to the measurement object is obtained based on the distance spectrum obtained from the periodic fluctuation of the signal intensity of the standing wave with respect to the traveling wave transmission frequency. Higher accuracy even at a short distance than conventional FMCW radar and pulse radar, without being affected by the time from output of electromagnetic waves to return to detection means for detecting signal strength of standing waves Can be measured. Specifically, even if the occupied frequency bandwidth is 76 MHz in the range of 24.05 GHz to 24.25 GHz, it is theoretically possible to measure up to about 2 m.

However, the distance measuring device of Conventional Example 1 also has the following problems.
(1) First, since the signal intensity of the electromagnetic wave that can be output from the moving body detection sensor of the specific low-power device specified by the Radio Law is weak, the signal intensity of the standing wave that can be observed becomes very weak. Then, in order to grasp the periodic fluctuation of the signal strength of the standing wave with respect to the transmission frequency of the traveling wave, it is necessary to amplify the observed signal.
The signal strength of the standing wave is detected in a state in which a periodic component that varies according to the traveling frequency of the traveling wave is added to a DC component that does not vary even if the traveling frequency of the traveling wave changes. Since the direct current component is very large compared to the amplitude of the signal, the dynamic range of the amplifier, AD converter, etc. must be matched to the direct current component. As a result, the accuracy of detection of fluctuations decreases and the accuracy of distance measurement also decreases. In the worst case, the distance may not be measured.

(2) Before being input to the amplifier and the AD converter, etc., the DC component included in the signal strength of the standing wave is removed by using an AC coupling circuit used for DC component removal in the signal in the time domain. For example, there is a possibility that the dynamic range can be adjusted to the amplitude of the periodic component. For this purpose, the waveform of the periodic signal must exist for one period or more.
In the case of a signal in the time domain, it is possible to make the signal waveform more than one period by increasing the observation time. However, in the case of the distance measuring device of Conventional Example 1, the occupied frequency bandwidth, that is, the width of the frequency that can be output as the transmission frequency is limited to 76 MHz in the range of 24.05 GHz to 24.25 GHz. In order to use the coupling circuit, a signal waveform that shows a fluctuation of one cycle or more in the measurement within the occupied frequency bandwidth is required. However, in the above measurement within the occupied frequency bandwidth, if the distance to the measurement object is 2 m or less, the waveform of the periodic signal will be less than one cycle, so the DC component of the signal will be reduced even if an AC coupling circuit is used. It is difficult to remove correctly.
If the DC component included in the signal strength of the standing wave is known in advance, the DC component may be correctly removed even if there is only a fluctuation of less than one cycle, but the DC component varies depending on the temperature. However, since it varies depending on the use conditions and environment, it is practically impossible to grasp the DC component in advance.

(3) The signal level of the observed standing wave changes in accordance with the signal level of the reflected wave, and increases at a short distance and decreases at a long distance. If the amount of amplification is matched with the signal level, when measuring a measurement object at a short distance, the signal level of the reflected wave is large, and thus the amplified signal is saturated. Then, in order to prevent the saturation of the amplified signal, the amount of amplification must be suppressed, and it becomes impossible to detect the signal intensity of the standing wave formed between the amount of amplification and the object to be measured at a long distance. Therefore, the measurement distance is limited.

(4) In order to cope with this, if the level of the detection signal is varied according to the distance to the measurement object, saturation of the amplified signal can be prevented and the measurement distance is prevented from being limited. be able to. As a method for solving this, for example, a feature that a high-pass filter (HPF) has a low periodic signal signal level, but a high periodic signal does not attenuate the signal level is used. Can be mentioned.
However, when there is a transient response due to the time constant of the filter, the waveform of the observation signal is affected, and thus there arises a problem that unnecessary components are generated in the distance spectrum. Then, when the maximum value due to the unnecessary component is larger than the maximum value due to the measurement target, a correct measurement distance cannot be obtained. Specifically, even when there is no measurement target, there arises a problem that a distance spectrum in which the measurement target exists is formed.

Japanese Patent No. 3461498

  In view of such circumstances, the present invention provides a distance measuring device and a distance measuring method capable of improving the accuracy of distance measurement using a standing wave and capable of measuring a distance even at a short distance of 2 m or less. For the purpose.

A distance measuring device according to a first aspect of the present invention is a measuring device for measuring a distance to a measurement object, and the measurement device outputs electromagnetic waves to a propagation medium existing between the measurement object and the transmission means. The detection signal having a signal level corresponding to the detected signal intensity in the combined wave is detected by detecting the signal intensity in the combined wave of the electromagnetic wave output from the transmitting means and the reflected wave reflected by the measurement object. And a signal processing unit that calculates a distance between the detection unit and the measurement object based on a detection signal output from the detection unit, and the transmission unit outputs the electromagnetic wave to be output. The signal processing means changes the distance based on the level difference between adjacent frequencies of the detection signal when the frequency of the electromagnetic wave output from the transmitting means is changed. Forming a spectrum, and characterized in that to calculate the distance between the measuring object and the detection means based on the distance spectrum.
In the distance measuring apparatus according to a second aspect of the present invention, in the first aspect, the transmitting means supplies the frequency information of the output electromagnetic wave to the signal processing means, and the signal processing means is output from the transmitting means. When the frequency of the electromagnetic wave to be changed is changed, a detection value correction unit that calculates a level difference between adjacent frequencies of the detection signal in the previous period, a level difference of the signal calculated by the detection value correction unit, and a supply from the transmission unit A detection signal function forming unit that forms a detection signal function based on the frequency information of the electromagnetic wave, and a spectrum analysis by calculating a spectrum of the detection signal function formed by the detection signal function forming unit, and calculating the distance spectrum And a distance calculation unit for calculating a distance between the detection means and the measurement object.
In the distance measuring device according to a third aspect of the present invention, in the first aspect, the transmitting means supplies the frequency information of the output electromagnetic wave to the signal processing means, and the signal processing means is adjacent to the detection signal. A detection value correction unit that outputs a level difference between frequencies as a voltage corresponding to the level difference of the signal, frequency information of the electromagnetic wave supplied from the transmission unit, and a voltage supplied from the detection value correction unit. A detection signal function forming unit that forms a detection signal function based on the detection signal function, and a spectrum analysis is performed on the detection signal function formed by the detection signal function forming unit to calculate a distance spectrum, and the detection means and the detection unit based on the distance spectrum And a distance calculating unit that calculates a distance to the measurement object.
According to a distance measuring apparatus of a fourth invention, in the first invention, the signal processing means outputs a level difference between adjacent frequencies of the detection signal as a voltage corresponding to the level difference of the signal; , Supplying the voltage supplied from the detection value correction unit to a bandpass filter circuit, obtaining a distance spectrum based on the output of the bandpass filter circuit, and detecting the detection means and the measurement object based on the distance spectrum And a distance calculation unit that calculates the distance between the two.
In the distance measuring device according to the fifth aspect of the invention, the distance from the measurement object is disposed at a position different from the distance from the detection means to the measurement object, and the signal intensity of the synthesized wave at the position is detected and detected. A correction signal detecting means for outputting a correction signal having a signal level corresponding to the signal intensity of the combined wave, and the signal processing means changes the frequency of the electromagnetic wave output from the transmitting means. And forming an analytic signal function comprising a complex sine wave based on a level difference between adjacent frequencies of the detection signal and a level difference between adjacent frequencies of the correction signal. The distance spectrum is calculated by analysis.
A distance measuring method according to a sixth aspect of the invention is a measuring method for measuring a distance to a measurement object, wherein the electromagnetic wave is output to a propagation medium existing between the measurement object, the output electromagnetic wave, and the electromagnetic wave Detects the signal intensity in the combined wave with the reflected wave reflected by the measurement object, and calculates the distance from the detection position where the signal intensity in the combined wave is detected to the measurement object based on the detected signal intensity in the combined wave A method is used to form a distance spectrum based on a level difference between adjacent frequencies of a signal detected at a detection position when the frequency of an output electromagnetic wave is changed, and from the detection position based on the distance spectrum. It is characterized in that the distance to the measurement object is calculated.
The distance measurement method of the seventh invention is the electromagnetic wave that is output in the sixth invention by detecting the signal intensity of the synthesized wave at the correction signal detection position where the distance from the measurement object is different from the distance from the detection position to the measurement object. Based on the level difference between adjacent frequencies of the signal detected at the detection position and the level difference between adjacent frequencies of the correction signal detected at the correction signal detection position. Thus, an analysis signal function including a complex sine wave is formed, and the analysis signal function is subjected to spectrum analysis to calculate a distance spectrum.

According to the first invention, the level difference between adjacent frequencies of the detection signal represents only the fluctuation amount of the signal level of the detection signal, in other words, the fluctuation amount of the signal intensity of the standing wave. Then, since the dynamic range of an amplifier, an AD converter, or the like can be matched with the fluctuation amount of the standing wave signal intensity, the fluctuation of the signal intensity of the AC component can be accurately detected. In addition, by obtaining the signal level difference, a small gain is applied when the distance to the measurement object is short, and a large gain is applied when the distance is long. That is, a gain according to the distance to the measurement object can be provided.
According to the second invention, since the spectrum analysis is performed after the detection signal function is formed, the distance spectrum can be easily calculated.
According to the third invention, since the spectrum analysis is performed after the detection signal function is formed, the distance spectrum can be easily calculated. In addition, since all the processes until the detection signal function is formed can be processed by hardware such as a circuit, the processing can be speeded up.
According to the fourth aspect of the present invention, since the signal processing means processes everything from the input of the detection signal to the formation of the distance spectrum by hardware such as a circuit, the processing speed can be increased.
According to the fifth aspect of the present invention, the analysis signal function including the complex sine wave is spectrally analyzed based on the level difference between adjacent frequencies of the detection signal and the level difference between adjacent frequencies of the correction signal. The distance spectrum to be obtained is only the distance spectrum in the period representing the distance between the actual detection means and the measurement object. Therefore, since it is possible to prevent the occurrence of measurement error due to the presence of the folded image, even if the effective frequency of the frequency band that can be used by the distance measuring device is limited to 76 MHz in 24.05 GHz to 24.25 GHz, A short distance of 2 m or less can be accurately measured. In addition, a gain corresponding to the distance to the measurement object can be provided.
According to the sixth invention, the level difference between adjacent frequencies of the detection signal represents only the fluctuation amount of the signal level of the detection signal, in other words, the fluctuation amount of the signal intensity of the standing wave. The dynamic range such as can be matched with the fluctuation amount of the signal strength of the standing wave, so that the fluctuation of the signal strength of the standing wave can be accurately detected. Moreover, by obtaining the signal level difference, a small gain is applied when the distance to the measurement object is short, and a large gain is applied when the distance is long. That is, a gain according to the distance to the measurement object can be provided. Thereby, a distance spectrum based on the level difference of the detected signal can be formed.
According to the seventh aspect of the present invention, a complex sine wave is formed based on a level difference between adjacent frequencies of the signal detected at the detection position and a level difference between adjacent frequencies of the signal detected at the correction signal detection position. Since the analysis signal function is subjected to spectrum analysis, the obtained distance spectrum is only the distance spectrum in the period representing the distance between the actual detection means and the measurement object. Therefore, since it is possible to prevent the occurrence of measurement error due to the presence of the folded image, even if the effective frequency of the frequency band that can be used by the distance measuring device is limited to 76 MHz in 24.05 GHz to 24.25 GHz, A short distance of 2 m or less can be accurately measured.

Next, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic block diagram of a distance measuring device 1 according to this embodiment.
As shown in the figure, the distance measuring apparatus 1 according to the present embodiment includes a transmitting unit 10, a transmitting unit 20, a detecting unit 30, and a signal processing unit 40, and is formed between the transmitting unit 10 and the measurement target T. The standing wave S is used to measure the distance from the detection means 30 to the measurement target T, and the signal processing means 40 is based on the signal intensity of the standing wave S detected by the detection means 30. The distance from the detection means 30 to the measurement target T is calculated. By removing the direct current component and the alternating current component included in the signal strength of the standing wave S without grasping the value of the direct current component, an amplifier, It has a function that allows the dynamic range of an AD converter or the like to be adjusted to the amount of fluctuation of the standing wave signal intensity.

First, the basic configuration of the distance measuring device 1 of the present embodiment will be briefly described.
In FIG. 1, the code | symbol T has shown the measuring object, and the several measuring object T1-Tn is described in FIG.

As shown in FIG. 1, the transmission means 10 includes a transmission unit 11 and a frequency control unit 12. The transmitter 11 can continuously output a signal having a constant frequency f, and can change the frequency f of the output signal. The transmitter 11 is connected to a frequency controller 12 that controls the frequency f of the output signal. That is, the transmitter 11 is controlled by the frequency controller 12 and outputs an output signal adjusted to a predetermined transmission frequency f 1.
Further, the frequency control unit 12 is configured to output a signal including information related to the output signal of the transmission unit 11.

For example, a transmitting unit 20 such as an antenna or an amplifier is connected to the transmitting unit 11 of the transmitting unit 10. This transmission means 20 has the same frequency f as the signal transmitted by the transmission section 11 of the transmission means 10 in a propagation medium such as air or water or in a vacuum existing between the transmission means 20 and the measurement target T. The electromagnetic wave which has is emitted.
Then, when an electromagnetic wave (hereinafter also referred to as traveling wave D) is output from the transmission means 20 into the propagation medium, the traveling wave D is reflected by the measurement objects T1 to Tn and reflected (hereinafter also referred to as reflected wave R). ) And the traveling wave D interfere, and a standing wave is formed between the transmission means 20 and the measurement objects T1 to Tn.
In addition, when the transmission means 20 can receive the signal intensity of electromagnetic waves, the reflected wave R is received by the transmission means 20 and then becomes an electrical signal between the transmission means 10 and the transmission means 20. Propagation also in the wiring and circuit to be connected. Then, the standing wave S is formed not only between the transmission means 20 and the measuring objects T1 to Tn, but also in wirings and circuits that electrically connect the transmission means 10 and the transmission means 20.

The detection means 30 is connected to the wiring or circuit that electrically connects the transmission means 10 and the transmission means 20 at positions separated from the measurement objects T1 to Tn by the distances d1 to dn. The detection means 30 is for detecting the signal intensity p (f, xs) of the standing wave S at the position, and is, for example, an amplitude detector or a square detector. The detection means 30 is a detection signal having a signal level corresponding to the signal strength p (f, xs) of the standing wave S, for example, the signal strength p (f, xs) or the signal strength p (f) of the standing wave S. , Xs) can output a current, voltage or the like proportional to the square.
Needless to say, the detection means 30 may be provided between the transmission means 20 or the transmission means 10 and the measurement objects T1 to Tn, but the transmission means 10 and the transmission means 20 are electrically connected. Providing wiring or a circuit is preferable because the distance measuring device 1 can be made compact.

A signal processing means 40 is connected to the detection means 30. The signal processing means 40 forms a distance spectrum based on the detection signal transmitted from the detection means 30, and calculates the distances d1 to dn between the detection means 30 and the measurement objects T1 to Tn from the distance spectrum. To do.
In the distance measuring apparatus 1 of the present embodiment, the signal processing unit 40 has a function of removing a direct current component of the signal intensity p (f, xs) of the standing wave S included in the detection signal. Details will be described later. The signal processing means 40 also has a function of giving a gain according to the distance from the measurement objects T1 to Tn, details of which will be described later.

Next, the basic principle of distance measurement by the distance measuring device 1 of this embodiment will be described.
As shown in FIG. 1, when the traveling wave D having the frequency f interferes with the reflected wave R that reflects the traveling wave D at the measurement target Tk (k = 1, 2,... N), the transmitting means 10 And a standing wave S is generated between the measurement target Tk. Then, the signal intensity p (f, xs) at the position of the detection unit 30 can be detected by the detection unit 30.

When the traveling wave D is reflected only by one measuring object, if the distance from the detecting means 30 to the measuring object is constant and the frequency of the traveling wave D is constant, the signal intensity p (f at the position of the detecting means 30 , Xs) is constant.
On the other hand, if the frequency f of the traveling wave D is changed while the distance from the detection unit 30 to the measurement target remains constant, the signal intensity p (f, xs) at the position of the detection unit 30 becomes the frequency f of the traveling wave D. Is a sine wave function (cos function).
For example, assuming that the frequency range transmitted by the transmitting means 10 is fw, the center frequency of the frequency transmitted by the transmitting means 10 is f0, and the distance from the detecting means 30 to the measuring object is d, the waveform of the signal intensity p (f, xs). Is as shown in FIG. Where c is the speed of light.
As shown in FIG. 2, the signal strength p (f, xs) is a sine wave function that periodically changes with respect to the frequency f 1, and the period c / 2 (d−xs) of this function is the position of the detection means 30. The relationship is inversely proportional to the distance d from xs to the measurement target. Therefore, if this sine wave function is subjected to spectrum analysis using Fourier transform, MUSIC method, or the like, a spectrum (distance spectrum) with respect to the distance from the detection means 30 can be calculated. Since the absolute value of the distance spectrum has a peak at the position of the distance from the detection means 30 to the measurement object, the distance d from the detection means 30 to the measurement object can be calculated based on the distance spectrum.

Here, when there are reflections from a plurality of measurement objects Tk, the signal intensity p (f, xs) at the position of the detection means 30 is determined by a plurality of constants formed between the transmission means 10 and each measurement object Tk. The signal intensity is obtained by adding the signal intensity at the position of the detection means 30 in the standing wave.
Then, when the frequency f of the traveling wave D is changed while the distances from the detecting unit 30 to the plurality of measurement objects Tk are constant, the signal intensity p (f, xs) at the position of the detecting unit 30 is the traveling wave. A sine wave having a plurality of periods corresponding to the distances d1 to dn to each measurement object Tk is compositely synthesized with the frequency f of D.

That is, since the traveling wave D emitted from the transmission unit 20 is expressed by the following Equation 1, if the distance to each measurement target Tk is dk, the reflected wave in which each measurement target Tk reflects the traveling wave D. R can be expressed as Equation 2.
In Equation 1, c is the speed of light, f is the transmission frequency, A is the amplitude level of the traveling wave D, and x is the transmission axis of the transmission signal. In Equation 2, γk is a magnitude of the reflection coefficient of the measurement target Tk and includes a propagation loss. Φk is a phase shift amount due to reflection.

  Then, since the standing wave S is the signal intensity of the synthesized wave generated by the additive synthesis of the traveling wave D and the reflected wave R, p (f, xs) at the position x = xs of the detection means 30 is And is expressed by Equation 3 using Equation 2.

  In general, since the level of the reflected wave R is very small, it is considered that γk << 1, so that the second and higher order terms of γk can be regarded as almost zero. Therefore, p (f, xs) at the position x = xs of the detection means 30 can be expressed as in Expression 4.

If the signal intensity p (f, xs) is subjected to spectrum analysis, a distance spectrum with respect to the distance x can be obtained, and the absolute value of the obtained distance spectrum corresponds to the distance from the detection means 30 to each measurement target Tk. Since each of the positions has a peak, the distance d from the detection means 30 to each measurement target Tk can be calculated based on the distance spectrum.
For example, if the distance spectrum is obtained by Fourier transform, the distance spectrum P as shown in Equation 6 can be obtained by applying the Fourier transform formula for obtaining the period information shown in Equation 5 below to the signal intensity p (f, xs). (X) can be calculated.

Next, the signal processing means 40 will be described in detail.
As shown in FIG. 1, the signal processing means 40 includes a detection value correction unit 41, a detection signal function formation unit 42, and a distance calculation unit 43.

The detection value correction unit 41 calculates a signal level difference (level difference) between adjacent frequencies of the detection signal. The detection value correction unit 41 receives a signal including information on the output signal of the transmission unit 11 from the frequency control unit 12 of the transmission unit 10, and the frequency f of the traveling wave D and each frequency of the traveling wave D The signal level of the detection signal at f is associated, and then the difference between the signal level of the detection signal at frequency f and the signal level of the detection signal at adjacent frequency f + Δf (hereinafter simply referred to as the signal level of the corrected detection signal). It calculates and outputs a correction detection signal. Δf is a step frequency when the frequency f of the traveling wave D is changed.
The detected value correcting unit 41 removes the DC component included in the detection signal, that is, the corrected detection signal is calculated. Further, the correction detection signal calculated by the detection value correction unit 41 is applied with a different gain depending on the distance from the detection means 30 to the measurement target, and details will be described later.

  The detection signal function forming unit 42 forms a detection signal function based on the correction detection signal calculated by the detection value correction unit 41 and the frequency information of the traveling wave D output from the transmission means 10. The detection signal function is a function indicating the signal level of the corrected detection signal with respect to the frequency f when the difference between the signal level of the detection signal at the frequency f and the signal level of the detection signal at the adjacent frequency f + Δf is a corrected detection signal. .

  The distance calculation unit 43 performs spectrum analysis on the detection signal function formed by the detection signal function forming unit 42 to calculate a distance spectrum, and calculates a distance from the detection means 30 to the measurement object based on the distance spectrum. . A method for spectrally analyzing the detection signal function is not particularly limited, and Fourier transform, MUSIC method, or the like can be employed.

  The detection value correction unit 41 is configured to output a level difference between adjacent frequencies of the detection signal as a correction detection signal by using a signal level holding circuit such as sample hold and a differential circuit, for example. It is good. In this case, since the processing until the detection signal function is formed can be processed by hardware, the processing can be speeded up.

  When the correction detection signal is a voltage, a filter circuit such as a bandpass is provided, and this voltage is supplied to the bandpass filter circuit. The bandpass filter circuit converts the correction detection signal to each frequency component. A distance spectrum is obtained by determining the level. Then, in the signal processing means 40, all processes up to the formation of the distance spectrum can be performed by hardware such as a circuit, so that the processing can be speeded up. Moreover, in the case of such a configuration, the detection signal function forming unit 42 need not be provided, so that the configuration of the apparatus can be simplified.

Next, the analysis principle in the signal processing means 40 will be described.
As described above, in the distance measuring apparatus shown in FIG. 1, the signal intensity p (f, xs) detected at the position xs of a certain detecting means 30 can be expressed by the following equation 7 (the above equation 4 and The same formula). The symbol f 1 in Equation 7 is the frequency of the output signal output by the transmission means 10 of the distance measuring device in FIG.

  The transmitting means 10 changes the frequency of the output signal to be output in a step-like manner as shown in the following formula 8.

  Then, from Equation 7 and Equation 8, the signal level pd (f, xs) of the correction detection signal described above can be expressed as Equation 9 below.

As can be seen from Equation 9, the DC component A ² included in the signal strength p (f, xs) is removed from the signal level pd (f, xs) of the corrected detection signal. That is, if the detection value correction unit 41 calculates a level difference between adjacent frequencies of the detection signal, the DC component A ² included in the signal strength p (f, xs) can be removed.
As described above, the signal level pd (f, xs) of the correction detection signal has a direct current component removed, and only the periodic signal necessary for distance measurement is present, so that only this periodic signal can be amplified. Therefore, it is possible to effectively use the dynamic range of the amplifier and the AD converter.

  Further, since the signal level pd (f, xs) of the corrected detection signal includes the distance dk from the position of the detection means 30 to the measurement target, the longer the distance dk, the larger the amplification ratio of the amplitude of the periodic signal. Since the amplification ratio of the amplitude of the periodic signal decreases as the distance dk decreases, the gain corresponding to the distance to the measurement target can be obtained by calculating the level difference between adjacent frequencies of the detection signal in the detection value correction unit 41. Can be given. In general, the level of the reflected signal by the measurement target is large at a short distance and small at a long distance, but by providing a gain according to the distance to the measurement target, the signal intensity p ( The effect of canceling out the level difference of f, xs) is obtained.

  The distance spectrum obtained by Fourier transforming the signal level pd (f, xs) of the corrected detection signal of Equation 9 is as shown in Equation 10.

Since the signal level pd (f, xs) of the corrected detection signal does not include the DC component A ^2, there is naturally no term representing the DC component in Expression 10. Therefore, it is possible to prevent the occurrence of distance measurement error due to the DC component.

Next, a distance measurement procedure in the distance measurement apparatus 1 of the present embodiment will be described.
FIG. 3 is a flowchart of distance measurement in the distance measuring apparatus of FIG. As shown in FIG. 3, before the measurement is started, first, the frequency condition is set in the frequency control unit 12 of the transmission means 10. Specifically, the center frequency f0, the transmission frequency range fw, and the frequency step Δf to be swept are set for the output signal output from the transmitting means 10 (P01).

  When the frequency sweep condition is set, the frequency control unit 12 sets f = f0−fw / 2 as the transmission frequency f 1 at the start of the sweep. The frequency control unit 12 outputs a control signal for controlling the transmission unit 11 to the transmission frequency f (P02).

  The transmission unit 11 adjusts its transmission frequency to the transmission frequency f in accordance with the control signal from the frequency control unit 12 and outputs a signal having the sweep frequency f. Then, the transmission means 10 emits an electromagnetic wave having the same frequency f as the output signal to the Tk to be measured via the transmission means 20 (P03).

  Next, the detection means 30 detects the signal intensity of the composite wave generated by the traveling wave D of the transmission frequency f and the reflected wave R reflected by the measurement object (P04).

  The detection operation shown in P03 and P04 is performed by increasing the transmission frequency f 1 by the frequency step Δf (P06). The series of operations described above is repeated until the transmission frequency f finally reaches the frequency f0 + fw / 2 at the end of the sweep (P05).

  When the detection of the signal strength of the composite wave at each frequency f is completed at the predetermined frequencies f0-fw / 2 to f0 + fw / 2, a function p (f, xs) indicating the signal strength with respect to the frequency f is obtained.

  In the detection value correction unit 41 of the signal processing means 40, the signal of the correction detection signal that is the difference between the signal strength p (f, xs) of the synthesized wave at the frequency f and the signal strength p (f + Δf, xs) at the adjacent frequency f + Δf. A level pd (f, xs) is obtained for each frequency f (P07).

  A spectrum of the signal level pd (f, xs) of the obtained corrected detection signal is subjected to spectrum analysis by Fourier transform or the like, thereby calculating a distance spectrum Pd (x) (P08).

  By extracting the maximum value of the absolute value | Pd (x) | of the distance spectrum Pd (x), the distance dk of the measurement target Tk can be obtained (P09).

[Embodiment using analysis signal function]
Further, when the signal processing means 40 of the distance measuring device 1 forms an analytic signal function consisting of a complex sine wave from the corrected detection signal and Fourier transforms the analytic signal function to calculate a distance spectrum, In addition, accurate distance measurement can be performed even at a distance where the fluctuation of the AC component of the standing wave signal intensity p (f, xs) with respect to the frequency sweep range fw becomes less than one cycle.
The configuration will be described below.
The embodiment described above except that the signal processing means 40 is provided with the correction signal detection means for forming the analysis signal function and detecting the correction signal for forming the analysis signal function. Are substantially equivalent, so the explanation is omitted.
Furthermore, the correction signal detected by the correction signal detection means is also formed in the same way as the correction detection signal is formed from the detection signal in the detection value correction unit 41 of the signal processing means 40. Is done.

FIG. 4 is a schematic block diagram of a distance measuring device 1 according to another embodiment. In FIG. 4, reference numeral 50 indicates a correction signal detecting means. The correction signal detection means 50 is disposed at a position different from that of the detection means 30.
The correction signal detection means 50 has a configuration substantially similar to that of the detection means 30. That is, the correction signal detection means 50 can detect the signal intensity p (f, x1) at the position and can output a detection signal having a signal level corresponding to the detected signal intensity. Specifically, the signal strength p (f, xs) of the standing wave to be detected is provided at a position where the distance from the measurement object is different, that is, even at the same frequency.

As shown in FIG. 4, in the signal processing means 40, an analysis signal generation unit 45 is provided between the detection value correction unit 41 and the distance calculation unit 43 instead of the detection signal function formation unit 42.
The analysis signal generation unit 45 is supplied with the correction detection signal and the correction correction detection signal from the detection value correction unit 41, and forms an analysis signal function based on the correction detection signal and the correction correction detection signal.
The distance spectrum obtained by Fourier transforming the analytic signal function does not generate a folded image that occurs when the detection signal function is Fourier transformed. Therefore, the signal intensity p (f, xs of the standing wave, specifically, the short distance. ) Measurement error at a distance where the fluctuation of the AC component is less than one cycle can be reduced. That is, even if the effective frequency of the frequency band that can be used by the distance measuring device is limited to 76 MHz in 24.05 GHz to 24.25 GHz, a short distance of 2 m or less can be accurately measured.

Next, the measurement principle of the distance measuring device using the analytic signal function will be described.
The signal intensity p (f, xs) of the composite wave detected at the position x = xs of the detection means 30 is the same as the above-described equation 4, as in the following equation 11.

  The frequency f in the equation 11 is the frequency f of the output signal output from the transmitting means 10 in the distance measuring device of FIG. The frequency f is changed stepwise as in the following equation (12).

  Then, the signal level pd (f, xs) of the correction detection signal in the equation 11 obtained from the frequency f in the equation 12 is expressed by the following equation 13.

  The signal level pd (f, xs) of the correction detection signal of Expression 13 is expressed as Expression 14.

  Here, assuming that the reference observation point is xs = 0, the signal level pd (f, 0) of the correction detection signal at xs = 0 is expressed by the following Expression 15.

  In the corrected detection signal pd (f, 0), the analytic signal function (complex sine wave) pa (f, 0) obtained by calculating the amplitude component m (f) and the phase component θ (f) is Become.

  A distance spectrum obtained by Fourier transforming the analytic signal function pa (f, 0) of Equation 16 is expressed by Equation 17.

  The magnitude | Pa (x) | of the distance spectrum obtained by Fourier transforming the analytic signal function has a single maximum value from Equation 17. As a result, it is possible to avoid the position of the maximum value of | P (x) | caused by the interference of the components of each term of Equation 6 and to reduce the measurement error at a short distance.

  Note that the Hilbert transform is generally known as a method for deriving the complex sine wave function exp (jθ (f)) from the cos function. According to this, a complex sine wave function exp (jθ (f)) is obtained by obtaining an orthogonal sin function from the cos function. However, in order to generate a complex sine wave function by the Hilbert transform, a periodicity sufficient for the basic cos function, that is, a signal of one period or more is required. Therefore, it can be said that the Hilbert transform is difficult to apply when the distance dk is short and sufficient cosine function is not recognized as in the present embodiment.

  As shown in FIG. 4, when the correction signal detection means 50 is provided in addition to the detection means 30, the signal level of the correction detection signal and the signal level of the correction correction detection signal are generated from the signal intensity detected by each means. And the amplitude components m (f) and θ (f) can be obtained to generate an analysis signal. Then, by performing a Fourier transform on the obtained analysis signal, the measurement error can be reduced even at a distance where the waveform of the observation signal corresponds to less than one period.

  The correction signal detection means 50 is provided at the position of xs = x1. Then, the signal level pd (f, x1) of the correction signal for correction correction can be expressed by the following equation (18).

  From Equation 18 and Equation 15, the phase component θ (f) and the amplitude component m (f) are calculated from Equation 19 and Equation 20.

  When the amplitude component m (f) and the phase component θ (f) are obtained by the equations 19 and 20, the analytic signal function shown in the equation 16 is generated. A distance spectrum Pa (x) shown in Formula 17 is obtained by performing Fourier transform on the analytic signal function pa (f, 0).

Next, a distance measurement procedure in the distance measuring apparatus 1 using the analytic signal function will be described.
FIG. 5 is a flowchart of distance measurement in the distance measuring device using the analytic signal function. As shown in FIG. 5, before starting the measurement, first, the frequency condition is set in the frequency control unit 12 of the transmission means 10. Specifically, the center frequency f0, the transmission frequency range fw, and the frequency step Δf to be swept are set for the output signal output from the transmission means 10 (P10).

  When the frequency sweep condition is set, the frequency control unit 12 sets f = f0−fw / 2 as the transmission frequency f at the start of the sweep. The frequency control unit 12 outputs a control signal for controlling the transmission unit 11 to the transmission frequency f (P11).

  The transmission unit 11 adjusts its transmission frequency to the transmission frequency f in accordance with the control signal from the frequency control unit 12 and outputs a signal having the sweep frequency f. Then, the transmission means 10 emits an electromagnetic wave having the same frequency f as the output signal to the measurement target Tk via the transmission means 20 (P12).

  Next, the detection means 30 and the correction signal detection means 50 are provided with the signal intensity of the combined wave generated by the traveling wave D of the transmission frequency f and the reflected wave R reflected by the measurement target Tk, respectively. (P13).

  The detection operation shown in P13 and P14 is performed by increasing the transmission frequency f by the frequency step Δf (P14). The series of operations described above is repeated until the transmission frequency f finally reaches the frequency f0 + fw / 2 at the end of the sweep.

  When the detection of the signal strength of the combined wave at each frequency f is completed at the predetermined frequencies f0-fw / 2 to f0 + fw / 2, the signal strength p with respect to the frequency f at the respective positions of the detection means 30 and the correction signal detection means 50. A function indicating (f, 0) and signal intensity p (f, x1) is obtained.

  In the detection value correction unit 41 of the signal processing means 40, the signal of the correction detection signal that is the difference between the signal strength p (f, 0) of the synthesized wave at the frequency f and the signal strength p (f + Δf, 0) at the adjacent frequency f + Δf. Of the correction correction signal, which is the difference between the level pd (f, 0) and the signal intensity p (f, x1) of the combined wave at the frequency f and the signal intensity p (f + Δf, x1) at the adjacent frequency f + Δf. A signal level pd (f, x1) is obtained for each frequency f (P16).

  The analysis signal function pa (f, 0) is generated from the signal level pd (f, 0) of the generated correction detection signal and the signal level pd (f, x1) of the correction correction signal (P17).

  A spectrum of the generated analysis signal function pa (f, 0) is analyzed by Fourier transform or the like to calculate a distance spectrum Pa (x) (P18).

  By extracting the maximum value of the absolute value | Pa (x) | of the distance spectrum Pa (x), the distance dk of the measurement target Tk can be obtained (P19).

A distance measured by the distance measuring device of the present application (this example) and a conventional distance measuring device using a standing wave (conventional example) was obtained by numerical calculation.
Numerical calculation is center frequency f0 = 24.088 GHz, sweep frequency range fw = 76 MHz, transmission signal amplitude A = 1, reflection coefficient γ1 = 0.1, phase shift amount φ1 = 0, observation position xs = 0, measurement target The distance d1 was 0.01 m to 10 m.
FIG. 7 shows the absolute value | P (x) | of the distance spectrum in the conventional example, FIG. 6 shows the measurement distance obtained from the absolute value, and FIG. 8 shows the distance to the measurement object in FIG. The absolute value | P (x) | of the distance spectrum when the distance is 0.5 m is shown. The distance spectrum P (x) of the conventional example obtains an average value of p (f, 0), removes the average value from p (f, 0), and a Hamming window to p (f, 0) from which the average value is removed. Is obtained from the Fourier transform of
FIG. 10 shows the absolute value | Pd (x) | of the distance spectrum in this example, FIG. 9 shows the measurement distance obtained from the maximum value, and FIG. 11 shows the measurement object in FIG. The absolute value | Pd (x) | of the distance spectrum when the distance is 0.5 m is shown. Note that Fourier transformation is performed by multiplying pd (f, 0) by a Hamming window.

6 and 9, when the distance to the measurement target is 2 to 3 m, it can be seen that in the conventional example, the difference between the distance to the measurement target and the measurement distance varies.
Further, in this example, it can be seen that the variation in the difference between the distance to the measurement object and the measurement distance is smaller than that in the conventional example. This is because in the conventional example, the average value of p (f, 0) and the direct current do not completely coincide with each other, and therefore the direct current component cannot be completely removed. On the other hand, in this embodiment, since the DC component of p (f, 0) can be removed, the difference between the distance to the measurement object and the measurement distance is conventionally between 2 to 3 m. It is smaller than the example.

Further, in this embodiment, as shown in FIG. 10, as the distance to the measurement object becomes longer, the absolute value | Pd (x) | of the calculated distance spectrum becomes larger. It is possible to have a gain effect corresponding to the gain.
In this numerical calculation, the reflection coefficient γ1 is constant regardless of the distance to the measurement object, but in general, the reflected wave level is large in a nearby measurement object, and the reflected wave level is small in a distant measurement object. . That is, according to the present embodiment, an effect that the level difference is canceled according to the distance to the measurement object can be obtained.

  In Example 2, the measurement distance calculated by the distance measurement device of the present invention that forms a distance spectrum from the analytic signal function was obtained by numerical calculation. The numerical calculation conditions of Example 2 are the same as those of Example 1 except that x1 = −2 mm. Note that the Fourier transform is performed by multiplying pa (f, 0) by a Hamming window.

As shown in FIG. 7, the absolute value | P (x) | of the distance spectrum calculated in the conventional example is due to each term of Equation 6. However, the magnitude of the first term of Equation 6 is to the DC A ² to remove the average value of p (f, 0). In the conventional example, the distance spectrum when the distance to the measurement object is 0.5 m is as shown in FIG. 8, and when the distance to the measurement object is less than 2 m as shown in FIG. It will be longer than the distance to the measurement object.
Also, as shown in FIG. 10, the absolute value | Pd (x) | of the distance spectrum calculated in the first embodiment is due to each term of Equation 10. In Example 1, the distance spectrum when the distance to the measurement target is 0.5 m is as shown in FIG. 11, and as shown in FIG. 9, when the distance to the measurement target is less than 2 m, The difference from the distance to the actual measurement object increases.

On the other hand, in the case of the present Example 2 in which the distance spectrum is formed from the analytic signal function, Pa (x) is formed from only a single term as shown in Equation 17, so the absolute value | Pa (x) | There is only a single local maximum (FIG. 13). Then, since the absolute value | Pa (x) | of the distance spectrum at a distance of 0.5 m is also as shown in FIG. 14, the calculated distance is the difference from the distance measurement value even when the distance to the measurement object is less than 2 m. It can be seen that does not increase (FIG. 12).
As described above, in the second embodiment in which the distance spectrum is formed from the analysis signal function, the distance to the measurement object is less than 2 m, that is, the distance corresponding to the waveform of p (f, 0) being less than one cycle. Can also measure the distance.

It is a schematic block diagram of the distance measuring device 1 of this embodiment. It is the figure which showed the relationship between the signal strength p (f, xs) and the frequency f. It is a flowchart of the distance measurement in the distance measuring device of FIG. It is a schematic block diagram of the distance measuring device 1 of other embodiment. It is a flowchart of the distance measurement in the distance measuring device using an analytic signal function. It is the figure which compared the distance to the measurement object set with the distance measurement result by a prior art example, and the set measurement object. It is a distance spectrum calculated in a conventional example. It is a distance spectrum calculated when the measurement distance is 0.5 m in the conventional example. It is the figure which compared the distance to the set measurement object with the distance measurement result by a present Example. It is a distance spectrum calculated in a present Example. In this embodiment, the distance spectrum is calculated when the measurement distance is 0.5 m. It is the figure which compared the distance to the measurement object set with the distance measurement result by the present Example 2, and the set measurement object. It is a distance spectrum calculated in a conventional example. It is a distance spectrum calculated when the measurement distance is 0.5 m in the conventional example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Distance measuring device 10 Transmission means 30 Detection means 40 Signal processing means 41 Detection value correction part 42 Detection signal function formation part 43 Distance calculation part 45 Analytical signal generation part 50 Correction signal detection means T Measurement object S Standing wave
I Folded image

Claims (7)

A measuring device for measuring the distance to a measuring object,
The measuring device is
Transmitting means for outputting an electromagnetic wave to a propagation medium existing between the measurement object;
A detection signal having a signal level corresponding to the detected signal intensity in the combined wave is detected by detecting the signal intensity in the combined wave of the electromagnetic wave output from the transmitting means and the reflected wave reflected by the measurement object. Detection means for outputting;
Based on the detection signal output by the detection means, the signal processing means for calculating the distance between the detection means and the measurement object,
The transmitting means has a variable frequency of the output electromagnetic wave,
The signal processing means includes
When the frequency of the electromagnetic wave output from the transmitting means is changed, a distance spectrum is formed based on a level difference between adjacent frequencies of the detection signal, and the detecting means and the measurement object are formed based on the distance spectrum. A distance measuring device for calculating the distance between the two. The transmitting means supplies the frequency information of the outputted electromagnetic wave to the signal processing means;
The signal processing means includes
When changing the frequency of the electromagnetic wave output from the transmitting means, a detection value correction unit for calculating a level difference between adjacent frequencies of the previous detection signal;
A detection signal function forming unit that forms a detection signal function based on the level difference of the signal calculated by the detection value correction unit and the frequency information of the electromagnetic wave supplied from the transmission unit;
A distance calculation unit that calculates a distance spectrum by performing spectrum analysis on the detection signal function formed by the detection signal function forming unit, and calculates a distance between the detection unit and the measurement object based on the distance spectrum; The distance measuring device according to claim 1, further comprising: The transmitting means supplies the frequency information of the outputted electromagnetic wave to the signal processing means;
The signal processing means includes
A detection value correction unit that outputs a level difference between adjacent frequencies of the detection signal as a voltage corresponding to the level difference of the signal;
A detection signal function forming unit that forms a detection signal function based on the frequency information of the electromagnetic wave supplied from the transmitting unit and the voltage supplied from the detection value correction unit;
A distance calculation unit that calculates a distance spectrum by performing spectrum analysis on the detection signal function formed by the detection signal function forming unit, and calculates a distance between the detection unit and the measurement object based on the distance spectrum; The distance measuring device according to claim 1, further comprising: The signal processing means includes
A detection value correction unit that outputs a level difference between adjacent frequencies of the detection signal as a voltage corresponding to the level difference of the signal;
The voltage supplied from the detection value correction unit is supplied to a band pass filter circuit, a distance spectrum is obtained based on the output of the band pass filter circuit, and the detection means and the measurement object are obtained based on the distance spectrum. The distance measuring device according to claim 1, further comprising a distance calculating unit that calculates a distance between the two. The distance from the measurement object is disposed at a position different from the distance from the detection means to the measurement object, the signal intensity of the combined wave at the position is detected, and the detected signal intensity of the combined wave corresponds to the detected signal intensity A correction signal detecting means for outputting a correction signal having a signal level;
The signal processing means includes
A complex sine wave based on the level difference between adjacent frequencies of the detection signal and the level difference between adjacent frequencies of the correction signal when the frequency of the electromagnetic wave output from the transmitting means is changed. 2. The distance measuring device according to claim 1, wherein an analytic signal function is formed, and the analytic signal function is subjected to spectrum analysis to calculate a distance spectrum. A measurement method for measuring a distance to a measurement object,
Output electromagnetic waves to the propagation medium existing between the measurement object,
Detect the signal intensity in the combined wave of the output electromagnetic wave and the reflected wave reflected by the measurement object,
Based on the detected signal intensity in the combined wave, a measurement method for calculating the distance from the detection position where the signal intensity in the combined wave is detected to the measurement target,
When the frequency of the output electromagnetic wave is changed, a distance spectrum is formed based on the level difference between adjacent frequencies of the signal detected at the detection position, and the distance from the detection position to the measurement object is based on this distance spectrum. The distance measuring method characterized by calculating. The signal intensity of the synthesized wave is detected at the correction signal detection position where the distance from the measurement object is different from the distance from the detection position to the measurement object.
When the frequency of the output electromagnetic wave is changed, the level difference between the adjacent frequencies of the signal detected at the detection position and the adjacent frequency of the correction signal detected at the correction signal detection position 7. The distance measuring method according to claim 6, wherein an analytical signal function including a complex sine wave is formed based on the level difference, and a spectral spectrum is analyzed for the analytical signal function to calculate a distance spectrum.

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