JPWO2004095058A1 - Distance measuring method and apparatus - Google Patents

Abstract

The present invention relates to a distance measuring device such as a measurement of a human body shape, raises and lowers a horn antenna along a human body, radiates a microwave of about tens of GHz while changing the frequency, and reflects a reflected wave from the human body. A standing wave with a traveling wave is detected, a Fourier transform is performed on the signal from which the DC component is removed, and a distance to the human body is calculated. In order to perform distance measurement with high accuracy, feedback is performed to the transmission source so that the intensity of the detected standing wave is substantially constant.

Description

  The present invention relates to distance measurement such as measurement of a human body shape.

  JP 2002-357656 A (EP 1365256A1)

Patent Document 1 discloses distance measurement using a high frequency. The intensity of a standing wave composed of a reflected wave and a traveling wave is measured while radiating a directional high frequency from an antenna and changing the frequency of the high frequency. When the intensity of the obtained standing wave is Fourier transformed with respect to the frequency, the distance to the object is obtained.
The inventors examined application of this technique to measurement of a human body shape, particularly measurement of a human body shape suitable for apparel. In this process, the inventor found that in the measurement of the human body shape, the reflected wave is weak and the standing wave is also weak, and the human body has a position where the reflected wave is particularly weak. In the case of the human body, since the refractive index and the like change at the interface between the air inside the clothes and the human body, high-frequency reflection occurs. However, this reflection is weak and generally a slight reflected wave is present in the traveling wave. Next, the intensity of the reflected wave from the human body surface varies depending on the location. This is because the reflected wave is strong when the direction of high-frequency radiation is perpendicular to the human body surface, but most of the reflected wave does not return to the receiving antenna if it is not perpendicular.
Summary of the Invention

Problems to be solved by the invention

An object of the present invention is to make distance measurement with high accuracy by making the amplitude of a standing wave substantially constant.
Configuration distance measuring method of the present invention of the invention, sends waves of beam shape toward the measurement object from the oscillation source, the intensity of the standing wave based on the reflection of the wave, as measured while changing the frequency of the wave, In a method for obtaining a distance from a measurement object by performing Fourier transform, the intensity of the standing wave is detected and fed back to the oscillation source so that the intensity becomes substantially constant, thereby changing the energy of the wave. It is characterized by that.
The distance measuring device according to the present invention sends a beam-like wave from an oscillation source toward a measurement object, measures the intensity of the standing wave based on the reflection of the wave while changing the frequency of the wave, and performs a Fourier transform. In the apparatus for determining the distance to the object to be measured, means for detecting the intensity of the standing wave, and means for feeding back to the oscillation source so that the detected intensity is substantially constant, And is provided.
Preferably, the measurement object is a human body, and the wave is a microwave having a frequency of 5 GHz to 100 GHz. For example, the oscillation source is a microwave oscillation circuit having a frequency of 5 GHz to 100 GHz, particularly preferably 10 to 50 GHz, and the wave is scanned along the human body in the height direction or the circumferential direction to obtain the human body shape.
Preferably, the strength of the standing wave is determined by picking up the wave and detecting it, and then removing the DC component.
For example, a pickup means for picking up the wave, a detection means for detecting the picked-up wave, and a removal means for removing and outputting a DC component from the output of the detection means are provided. Is input to the feedback means.
In the present invention, feedback is applied to the oscillation source so that the amplitude of the standing wave is substantially constant. Therefore, when the reflection is weak, the output of the oscillation source increases and the distance can be measured with high accuracy. . “Substantially constant” means, for example, that the amplitude falls within a range of about 1/2 to 2 times the reference value.
When measuring the shape of the human body, the resolution is required to be in the order of cm. Therefore, the wave is preferably a microwave with a frequency of 5 to 100 GHz. The human body generally has a low reflectivity, and the surface has irregularities. Turn to the direction. For these reasons, the amplitude of the standing wave is small and the amplitude is likely to fluctuate. However, since the amplitude of the standing wave is made almost constant by adding feedback to the oscillation source, the human body shape can be measured with high accuracy. .
When picking up a standing wave, in general, a traveling wave is picked up in addition to the standing wave, and the amplitude of the traveling wave is often larger than that of the standing wave. If the DC component is removed from the detection signal here, the traveling wave can be removed, and the distance can be measured accurately.

FIG. 1 is a front view of the human body shape measuring apparatus according to the embodiment.
FIG. 2 is a side view of the horn antenna used in the example.
FIG. 3 is a block diagram of a signal processing system of the human body shape measuring apparatus according to the embodiment.
FIG. 4 is a flowchart showing a tracking algorithm in the human body shape measuring method of the embodiment.
FIG. 5 is a diagram schematically illustrating the removal of the background signal from the Fourier transform signal in the embodiment.
FIG. 6 is a diagram illustrating a Fourier transform signal and a human body shape signal along the height direction when tracking is not performed.
FIG. 7 is a diagram illustrating a Fourier transform signal and a human body shape signal along the height direction when tracking is performed.
FIG. 8 is a diagram illustrating a human body shape signal in the height direction when tracking is not performed.
FIG. 9 is a diagram illustrating a human body shape signal in the height direction when tracking is performed.

FIGS. 1 to 9 show examples and characteristics of the measurement of the human body shape as an example. However, the distance measurement target is arbitrary, and may be used, for example, for detecting the distance between the vehicle ahead and the distance to the obstacle. FIG. 1 shows the outer shape of the human body shape measuring device 2. Reference numeral 4 denotes a stand on which a person stands, and reference numeral 6 denotes a frame surrounding the periphery of the human body shape measuring apparatus 2. The lifting / lowering base 9 is moved up and down along the column 8 and is provided with one to a plurality of horn antennas 10. The horn antenna 10 is a high-frequency antenna with little diffraction loss, and the type of antenna itself is arbitrary.
A high frequency circuit 12 supplies a high frequency to the horn antenna 10, picks up and detects a standing wave of a traveling wave in the horn antenna 10 and a reflected wave from the human body, and removes a DC component, for example, Output to the signal processing unit 14. When a plurality of horn antennas 10 are provided, it is preferable to vary the frequency of the high frequency for each antenna. The signal processing unit 14 is configured by a digital signal processor or a signal processing circuit of a personal computer level, and outputs the obtained human body shape to the monitor 16 or the like and accepts an operation from the keyboard 18.
The structure of the horn antenna 10 is shown in FIG. 2. Reference numeral 21 denotes a waveguide which receives a high frequency from a high frequency oscillation circuit and radiates a high frequency from a horn 22 whose tip is expanded. A pickup 23 is inserted into the waveguide 21 and detected by a detection circuit 24 such as a GaAs Schottky diode, and a DC component is removed by a DC eliminator 25 using a capacitor or the like and output. The DC eliminator 25 may not be provided. The standing wave detection pickup 23 may be provided in an antenna different from the horn antenna 10, but a high frequency waveguide or antenna is expensive, and the pickup 23 is provided in the transmission horn antenna 10. It is preferable.
FIG. 3 shows the signal processing system used. A high-frequency output from the high-frequency oscillation circuit 29 is radiated toward the human body 20 via the horn antenna 10. The high frequency used is, for example, about 10 to 15 GHz, and a relatively inexpensive high-frequency element for satellite communication or the like can be used. The beam diameter in a plane perpendicular to the traveling direction is, for example, about 2 cm. A high-frequency traveling wave and a reflected wave exist in the horn antenna 10, and a standing wave is formed by these, and the ratio of the traveling wave is overwhelmingly large as energy. Then, the high frequency in the horn antenna is picked up by the pickup 23, detected by a detection circuit 24 using a GaAs Schottky diode or the like, for example, corresponding to a half wave, and the DC component is removed by the DC eliminator 25. Most of the DC components are caused by traveling waves, and instead of removing the DC components with a capacitor, the DC components may be removed by subtracting or differentiating the signals after AD conversion.
The signal from the DC eliminator 25 is fed back to the amplitude detector 26 and input to an ALC (automatic level control device) 27, and the difference from the reference value with respect to the amplitude is output. The output control unit 28 drives the high-frequency oscillation circuit 29 with a gain corresponding to the difference. The output of the high-frequency oscillation circuit 29 changes, for example, in the range of about 1 to 3 times the reference output. As a result, feedback is applied to the output of the high-frequency oscillation circuit 29 so that the amplitude of the output signal from the DC eliminator 25 is substantially constant, whereby the standing wave power (output from the DC eliminator 25) is small. In this case, the power (energy) of the traveling wave is increased so that the standing wave can be detected without being buried in noise by the detection circuit 24. That is, it is difficult to detect a standing wave having a small amplitude in the presence of a traveling wave having a large amplitude, but the detection becomes easier if the amplitude of the standing wave is increased. When the output from the DC eliminator 25 is large, the traveling wave power is reduced to keep the signal intensity from the DC eliminator substantially constant, thereby preventing the detector 24 and the like from being saturated.
The high-frequency circuit 12 changes the frequency to a plurality of, for example, 256 ways for one measurement point, for example, changes the frequency to 10-14 GHz or 11-13 GHz with respect to the center frequency 12 GHz, and so on. Enable Fourier transform. Next, the ALC 27 is operated at the first frequency for one measurement point, and the output of the ALC 27 is kept constant at the same measurement point. Alternatively, the ALC 27 is operated independently for each frequency, and the used gain (output of the ALC 27 output control unit 28) is input to the FFT 38 described later, and the ratio of the AD conversion signal to the gain is Fourier-transformed. good.
The AD converter 36 AD-converts the output signal of the DC eliminator 25, and the DC component in the AD-converted signal is meaningless because it appears at a position of zero distance, and this is digitally processed by the DC eliminator 37. For example, after AD-converted signal is leveled down by a predetermined value corresponding to the DC component, Fourier transform is performed to obtain distance information.
The FFT 38 performs Fourier transform on the signal from which the DC component has been removed by AD conversion by fast Fourier transform or the like. This Fourier transform is a Fourier transform related to frequency, and as described in Patent Document 1, the peak of the Fourier transform signal corresponds to the distance from the antenna 10 to the human body. Note that the AD-converted signal may be processed by a differential filter or the like to remove the DC component and input to the amplitude detector 26. Further, after the signal AD-converted by the AD converter 36 is Fourier-transformed by the FFT 38, the DC component may be removed by the DC eliminator 37.
The Fourier transform signal includes signals for reflection in the antenna and reflection in the background other than the human body. Therefore, the Fourier transform signal when there is no human body is stored in the background signal storage unit 39, and the difference from the Fourier transform signal when there is a human body is obtained by the difference unit 40. In this way, the effective part of the signal is extracted by removing the signal caused by the background from the Fourier transform.
Background signal removal is schematically illustrated in FIG. A solid line is a Fourier transform signal input from the FFT 38, and is a result of Fourier transform after level shift corresponding to the DC component. From this Fourier transform signal, the signal of the broken line stored as the background signal is subtracted to take out the peak of the Fourier transform signal caused by the human body. Instead of subtracting the background, since the approximate distance from the human body is known, a window function that picks up only signals in this range may be used. However, the use of such a window function is a process similar to tracking described later, and there is a limit to improving accuracy.
In addition to this, for example, a human body is measured using a pair of cameras 30 and 31, a stereoscopic image of the human body is created, and the outline extraction unit 32 extracts the outline shape of the human body. Since the cameras 30 and 31 photograph the human body shape of the clothes, the actual human body surface should be present inside the human body shape extracted by the outline extraction unit 32. Alternatively, before measurement, a person's weight, height, body fat percentage, and the like may be measured, and age may be taken into account to estimate a rough body shape, which may be used instead of the signal of the outline extraction unit 32. Furthermore, the cameras 30, 31 and the outline extraction unit 32 may not be provided.
On the other hand, the lifting platform 9 is moved up and down by the lifting drive unit 34 and scans the surface shape of the human body within a predetermined height range. Further, the left-right motion drive unit 35 swings the horn antenna 10 to the left and right, for example, or shifts the position to the left and right, so that scanning is started from the point where a large signal is obtained from the human body. In addition, the structure of the raising / lowering drive part 34 or the left-right drive part 35 is arbitrary, and the left-right drive part 35 may not be provided.
At the start of scanning, the comparison unit 41 checks whether or not a signal greater than a predetermined threshold value is obtained, and operates the left-right motion drive unit 35 so as to obtain a signal greater than or equal to the predetermined threshold value. The direction of the antenna 10 is changed. The tracking unit 42 measures the distance between the horn antenna and the human body at each height in the process of moving up and down the horn antenna 10 and scanning the human body shape, and the previous measurement point or a plurality of previous measurement points. A reasonable range of the distance to the next human body surface that is expected from the above is obtained, and tracking is performed so as to extract a signal within this range. The reasonable range means that the continuity of the human body surface is maintained or the range of unevenness on the human body surface. Details of the processing of the comparison unit 41 and the tracking unit 42 are shown in FIG.
At the time of starting measurement in FIG. 4, the horn antenna is at the upper end or the lower end of the scan range, and the maximum value of the Fourier transform signal input to the comparison unit 41 is detected to check whether the maximum value is greater than or equal to the threshold value. If the maximum value is small and is less than or equal to the threshold value, processing such as searching for a position where a stronger signal can be obtained by changing the direction of the horn antenna by the left and right motion drive unit 35 is performed.
When a maximum value equal to or greater than the threshold value is obtained at the upper or lower end of the scan range, tracking is started. When tracking is started, the distance from the human body is updated and held as a variable “tracking position”, and the position of the horn antenna is changed by 5 mm, for example, and the measurement point is moved up and down to obtain the next maximum value. This maximum value is the maximum value in the output of the difference unit 40 and corresponds to the distance from the human body. The range in which the maximum value is detected is limited as a search range, and is limited to, for example, within ± 1 cm or within ± 5 mm with respect to the distance from the human body at the previous measurement point. When using not only the previous measurement point but also a plurality of previous measurement points, the search range is limited to about ± 5 mm with respect to the points obtained by extrapolating these measurement points. Then, the maximum value of the Fourier transform signal within the search range is detected.
It is assumed that the threshold value is determined with respect to the obtained maximum value, and if the maximum value equal to or greater than the threshold value is obtained, the measurement is effective and the distance to the human body at the new measurement point is obtained. If the maximum value equal to or greater than the threshold value is not obtained, the threshold value in the next threshold value determination is reduced by, for example, about 5 to 10%, or the range in which the maximum value is searched is assumed to be ± Increase from 5 mm to ± 7 mm. The maximum value measured this time is arbitrary, but the detected maximum value is invalidated, for example, assuming that an effective maximum value was not obtained. When the above processing is repeated up to the final measurement point, the shape of the human body along one scan line is obtained.
Returning to FIG. 1, a plurality of horn antennas 10 are provided, and scanning along a plurality of lines is performed at the same time by changing the frequency of the high frequency in order to prevent interference between the antennas. If the number of antennas is small, the frame 6 is rotated to repeat scanning. By repeating such scanning, a three-dimensional shape of the human body surface can be obtained.
FIG. 6 shows an example in which tracking is not performed and the maximum value of the Fourier transform signal in the scanning process is simply used as a distance signal to the human body. The solid line indicates a Fourier transform signal. There are two peaks near 700 mm and 900 mm, and the peak near 900 mm is large, and this is a distance signal. The human body shape signal obtained along the height direction by simply using the peak of the Fourier transform signal as a distance signal is indicated by dots. Note that the positions of the horizontal axis of the Fourier transform signal and the human body shape signal are changed. If tracking is not performed as shown in FIG. 6, the human body shape signal jumps discontinuously.
On the other hand, FIG. 7 shows the result when only the maximum value within a predetermined range is extracted from the distance signal at the previous measurement point for the same Fourier transform signal. Although the peak of the Fourier transform signal is split into two, the human body shape signal is obtained as a continuous line.
FIG. 8 shows a human body shape signal when the measurement of FIG. 6 is performed for one scan line. FIG. 9 shows a human body shape signal when the measurement of FIG. 7 is performed for one scan line. When tracking is not performed, the human body shape signal fluctuates unnaturally around a height of 800 to 900 mm. On the other hand, when tracking is performed, such noise can be removed.
When the tracking is not performed, unnatural results such as those shown in FIGS. 6 and 8 are affected by, for example, reflection from the human body other than the measurement point at the position straight ahead from the horn antenna. It seems to be. Such reflection can be reduced by increasing the frequency of the high frequency and reducing the beam diameter. For example, if the frequency is doubled, the beam diameter will be about ½, and the signal near the distance of 900 mm in FIG. 6 should decrease in intensity. However, when the frequency is increased, the high-frequency element for consumer use cannot be used, and the circuit cost increases rapidly. Thus, by tracking, it is possible to measure the human body shape using a consumer high-frequency element used for satellite communications or the like.
In the embodiment, the high-frequency power (energy) radiated is increased at the measurement point where the amplitude of the standing wave is small, so that the standing wave is not buried in noise and cannot be detected. Further, at the measurement point where the amplitude of the standing wave is large, the high frequency power is reduced, so that saturation of the detection circuit and the like can be prevented. Therefore, it is possible to generate a standing wave having a substantially constant amplitude regardless of the standing wave amplitude and to measure the distance with high accuracy. In the embodiment, a high frequency such as a microwave is used, but an ultrasonic wave of about 10 kHz to 100 kHz may be used.

Claims (6)

A beam-like wave is sent from the oscillation source to the measurement object, and the intensity of the standing wave based on the reflection of the wave is measured while changing the frequency of the wave, and the Fourier transform is performed to measure the distance from the measurement object. In the method for obtaining
A distance measuring method, wherein the intensity of the standing wave is detected and fed back to the oscillation source so that the intensity becomes substantially constant, thereby changing the energy of the wave. The distance measuring method according to claim 1, wherein the object to be measured is a human body, and the wave is a microwave having a frequency of 5 GHz to 100 GHz. The distance measuring method according to claim 1, wherein the strength of the standing wave is obtained by picking up the wave and detecting it, and then removing the DC component. Sending a beam-like wave from the oscillation source toward the measurement object, measuring the intensity of the standing wave based on the reflection of the wave while changing the frequency of the wave, and performing a Fourier transform, the distance from the measurement object In a device that seeks
A distance measuring apparatus comprising: means for detecting the intensity of the standing wave; and means for feeding back to the oscillation source so that the detected intensity becomes substantially constant. The measurement object is a human body, the oscillation source is a microwave oscillation circuit having a frequency of 5 GHz to 100 GHz, and a human body shape is obtained by scanning a wave along the human body. 4. A distance measuring device according to item 4. Pickup means for picking up the wave, detection means for detecting the picked up wave, and removal means for removing and outputting a DC component from the output of the detection means are provided, and the output of the removal means The distance measuring device according to claim 4, wherein: is input to the feedback means.

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