JP7277135B2 - distance measuring device - Google Patents

Description

The present invention relates to a distance measuring device for measuring the distance to a target based on the principle of Frequency Modulated Continuous Wave (FMCW) radar.

A frequency-modulated continuous wave radar transmits a frequency-modulated continuous wave to a target, and obtains the distance from the beat waveform signal derived from the frequency difference between the transmitted wave and the reflected wave. Since frequency-modulated continuous wave radar uses continuous waves as transmission waves, it has the advantage of easily obtaining a desired signal-to-noise ratio (SN ratio) without high transmission power.

Frequency-modulated continuous wave radar is known to have a distance measurement resolution proportional to c/(2 Δf), where Δf is the frequency deviation width of the transmitted wave and c is the speed of light. Higher resolution can be achieved. However, if Δf is increased in order to obtain high resolution, there is a problem that it becomes difficult to detect a distant target because reception noise increases due to the widening of the band and the detection distance decreases. Therefore, instead of setting a large Δf, the transmission output is lowered to improve the resolution for short-range targets. A distance measuring device has been proposed that incorporates a long-distance measurement mode that increases the detection distance while increasing the detection distance into one measurement system, and that can be used while switching the mode according to the distance to the target (Patent Document 1). .

Japanese Patent Application Laid-Open No. 2001-183449

However, in the distance measuring devices disclosed in the prior art described above, it is left to the user to select which of the long-distance measurement mode and the short-distance measurement mode is to be used, depending on which target is desired to be measured. . For this reason, it is difficult for a user who is not accustomed to distance measurement to grasp whether or not the mode to be adopted is suitable for distance measurement of the target. For example, when it is unclear whether the distance to the target is short or long, or when it is difficult to grasp where the target exists in a large space, the user can select two modes as appropriate. It is also possible to select and measure At this time, there is also a problem that it is impossible to make an appropriate judgment as to whether the obtained distance measurement result reflects the correct distance to the target.

SUMMARY OF THE INVENTION An object of the present invention is to make it possible to appropriately determine which mode is suitable for distance measurement to a target in a distance measurement device that can use both a long distance measurement mode and a short distance measurement mode. Furthermore, by automatically optimizing the mode, it is possible to obtain satisfactory distance measurement results for both short and long distance targets.

In order to solve the above problems, the first distance measuring device of the present invention comprises a signal generator for generating a transmission waveform signal whose frequency is continuously modulated with a predetermined modulation pattern, and an input of the transmission waveform signal. and a transmission output unit for transmitting toward a target a microwave transmission wave whose frequency is continuously modulated based on the transmission intensity of the microwave transmission wave in which the frequency deviation width of the continuous modulation is set to a first bandwidth. is set to a first transmission intensity, and a frequency deviation width is set to a second bandwidth narrower than the first bandwidth, and the transmission intensity of the microwave transmission wave is set to the first transmission intensity. a transmission unit configured to be switchable between a long-distance measurement mode set to a second transmission intensity higher than the transmission intensity; a reception unit configured to receive reflected waves of microwave transmission waves; a mixing unit that mixes the waveform signal received by the unit and outputs a beat waveform signal based on the frequency difference between the transmission waveform signal and the reception waveform signal; a frequency spectrum generation unit that generates the frequency spectrum of the beat waveform signal; A signal processing unit having an intensity peak acquisition unit for acquiring an intensity peak for specifying the distance of the target, and a short-range measurement mode for the transmission unit to direct the microwave transmission wave to the target. short-distance measurement mode measurement processing for causing the signal processing unit to acquire the short-distance measurement mode intensity peak by transmitting, and setting the long-distance measurement mode for the transmission unit to transmit the microwave transmission wave toward the target object. a measurement control unit that sequentially executes a long-distance measurement mode measurement process that causes the signal processing unit to acquire a long-distance measurement mode intensity peak, and a peak frequency between the short-distance measurement mode intensity peak and the long-distance measurement mode intensity peak. At least one of the position and the received intensity level is compared as a first comparison , and distance information to the target is obtained based on the frequency position of the intensity peak on the frequency spectrum in the long-distance measurement mode. On the other hand, by dividing the distance for one round trip to the target obtained by multiplying the sampling period _tN of the beat waveform signal in the short distance measurement mode by the speed of light c, by 2, R _A =c· _tN · As a second comparison, whether or not the long-distance measurement mode measurement distance is large with respect to the ambiguous distance _RA expressed as /2 , and the result of the comparison processing of the first comparison and the comparison processing of the second comparison Based on the results of , a proper mode determination unit that determines which of the short-range measurement mode and the long-range measurement mode is the appropriate mode for measuring the distance to the target, and the frequency spectrum generated in the proper mode. a distance information generating unit that generates distance information to a target based on the frequency position of the intensity peak; and a distance information output unit that outputs the generated distance information. If the part can acquire the intensity peaks in both the short-range measurement mode and the long-range measurement mode, based on the comparison of the frequency position of the short-range measurement mode intensity peak and the long-range measurement mode intensity peak, the long-range measurement mode Determines whether or not the intensity peak is a multiple reflection peak derived from multiple reflections with the target, and if the intensity peak is determined to be a multiple reflection peak in the long-distance measurement mode, selects the short-distance measurement mode. It is characterized in that it is determined to be in the proper mode.
The second distance measuring device of the present invention comprises a signal generating section for generating a transmission waveform signal whose frequency is continuously modulated according to a predetermined modulation pattern; a transmission output unit for transmitting a microwave transmission wave toward a target, wherein the frequency deviation width of continuous modulation is set to the first bandwidth and the transmission intensity of the microwave transmission wave is set to the first transmission intensity. a short-range measurement mode to be set; and a second transmission in which the frequency deviation width is set to a second bandwidth narrower than the first bandwidth and the transmission intensity of the microwave transmission wave is higher than the first transmission intensity. A transmitting unit that is set to be switchable between a long-distance measurement mode that is set to high intensity, a receiving unit that receives the reflected wave of the transmitted microwave wave, and a received waveform signal from the transmitted waveform signal and the reflected wave receiving unit. A mixing section for mixing and outputting a beat waveform signal based on a frequency difference between a transmission waveform signal and a reception waveform signal, a frequency spectrum generation section for generating a frequency spectrum of the beat waveform signal, and a target distance on the frequency spectrum A signal processing unit having an intensity peak acquisition unit that acquires an intensity peak for specifying a signal processing unit, and a short-range measurement mode is set for the transmission unit to transmit the microwave transmission wave toward the target object. A short-range measurement mode measurement process that causes the unit to acquire a short-range measurement mode intensity peak, and a long-range measurement mode that is set for the transmission unit to transmit a microwave transmission wave toward a target, thereby allowing the signal processing unit to perform long-range measurement. a measurement control unit for sequentially executing long-distance measurement mode measurement processing for obtaining a distance measurement mode intensity peak; Either one is compared as a first comparison , and distance information to the target is generated as the long-distance measurement mode measurement distance based on the frequency position of the intensity peak on the frequency spectrum in the long-distance measurement mode, while the near-distance The ambiguity expressed as R _A =c· _tN ·/2 by dividing the distance for one round trip to the target obtained by multiplying the sampling period _tN of the beat waveform signal in the measurement mode by the speed of light c. As a second comparison, whether or not the measured distance in the long-distance measurement mode is greater than the distance _RA is compared , and based on the result of the first comparison and the result of the second comparison, the near distance is determined. Appropriate mode determination unit that determines which of the distance measurement mode and the long distance measurement mode is the appropriate mode for distance measurement to the target, and the frequency position of the intensity peak on the frequency spectrum generated in the appropriate mode. and a distance information output unit for outputting the generated distance information. If the intensity peak can be obtained in both the long-range measurement mode and the long-range measurement mode, based on the comparison of the frequency position of the short-range measurement mode intensity peak and the long-range measurement mode intensity peak, in the short-range measurement mode, the near-range measurement mode intensity The short-range measurement mode distance generated by the distance information generator based on the frequency position of the peak is due to the fact that the target exists farther than the maximum measurable distance within the sampling period. It is characterized in that it is determined whether or not the measurement is erroneously measured to be smaller than the distance, and if it is determined that the measurement is erroneously measured, the long-distance measurement mode is determined to be the proper mode.

The distance measurement device of the present invention has a short distance measurement mode and a long distance measurement mode in which the frequency deviation width and transmission intensity of continuously modulated microwave transmission waves are different from each other. are sequentially performed in the short-distance measurement mode and the long-distance measurement mode. Then, the beat waveform signal obtained in each mode is converted into a frequency spectrum, and a short-range measurement mode intensity peak and a long-range measurement mode intensity peak are obtained from the frequency spectrum. Then, at least one of the peak frequency position and the reception intensity level is compared between the short-range measurement mode intensity peak and the long-range measurement mode intensity peak, and based on the comparison result, the short-range measurement mode and the long-range measurement mode are selected. is the appropriate mode. As a result, it is possible to appropriately determine which of the short-distance measurement mode and the long-distance measurement mode is the mode suitable for measuring the distance to the target. Satisfactory range measurements will be obtained for any target in the range.

1 is a block diagram showing the electrical configuration of a distance measuring device that is an embodiment of the present invention; FIG. 4A and 4B are schematic diagrams showing a comparison of transmission wave modulation patterns in a long-distance measurement mode and a short-distance measurement mode; FIG. 4 is a diagram showing the concept of generating a frequency spectrum of a beat waveform signal by Fourier transform; 4 is a flowchart showing the overall processing flow of the measurement control program; 5 is a flowchart showing the flow of measurement processing in FIG. 4; FIG. 5 is a flow chart showing the flow of appropriate mode determination processing in FIG. 4 ; FIG. Schematic diagrams showing a comparison between normal reflection and multiple reflection. FIG. 4 is an explanatory diagram showing an example of changes in transmission wave frequency and beat waveform signals obtained in each mode when a short-range measurement mode and a long-range measurement mode are sequentially executed; FIG. 4 is an explanatory diagram showing a first example when the short-distance measurement mode is determined to be the proper mode; FIG. 9 is an explanatory diagram showing a second example when the short-distance measurement mode is determined to be the proper mode; In the short-range measurement mode, a situation in which the short-range measurement mode distance _RN is erroneously measured to be smaller than the actual distance RN _' to the target due to the fact that the target exists farther than the ambiguous distance _RA . A figure explaining. FIG. 4 is an explanatory diagram showing a first example when the long-distance measurement mode is determined to be the appropriate mode; FIG. 9 is an explanatory diagram showing a second example when the long-distance measurement mode is determined to be the proper mode; FIG. 5 is a diagram showing a modified example of a transmission wave modulation pattern; 6 is a flowchart showing the flow of a modification of measurement control;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a block diagram showing the electrical configuration of a distance measuring device 1 that is one embodiment of the present invention. A distance measuring device 1 is configured as a device for measuring the distance to a target based on the principle of a frequency modulated continuous wave (FMCW) radar, and comprises a microprocessor section 2 and a sensor section connected thereto. 3. The microprocessor section 2 functions as an operation control section and a signal processing section for the sensor section 3, and has a CPU 31, a RAM 32, a ROM 33, an input/output section 34, and a bus 30 connecting them. The sensor unit 3 has a transmission controller 35, a PLL control unit 41, an oscillation circuit 40, a directional coupler 39, a transmission amplifier 38t, and a transmission antenna 37t as transmission-side blocks. On the other hand, the receiving block has a receiving antenna 37r, a low noise amplifier 38r, a mixer 42, an input amplifier 44 and an A/D converter 45. FIG.

The transmission controller 35 receives the frequency instruction value of the transmission wave and the output intensity setting instruction of the transmission wave from the microprocessor section 2 via the input/output section 34, and controls the operations of the PLL control section 41 and the transmission amplifier 38t. Based on the frequency command value transferred from the transmission controller 35, the PLL control unit 41 feedback-controls the transmission output operation of the oscillation circuit 40 in a phase-synchronized form, and generates a transmission waveform signal (details will be described later with reference to FIG. 2) to the oscillation circuit 40 . That is, the microprocessor section 2, the transmission controller 35, the PLL control section 41, and the oscillation circuit 40 function as a signal generation section that generates a transmission waveform signal.

A transmission waveform signal from the oscillation circuit 40 is amplified by the transmission amplifier 38t, and then output from the transmission antenna 37t as a transmission wave whose frequency is continuously modulated. The transmission output of the transmission amplifier 38t is adjusted based on the gain setting input value inputted from the transmission controller 35 in response to the output intensity setting instruction from the microprocessor. Then, the transmission output of the transmission amplifier 38t is transmitted from the transmission antenna 37t toward the target as a transmission wave. Therefore, the transmission amplifier 38t and the transmission antenna 37t function as a transmission output unit that transmits microwave transmission waves toward the target. In addition, the transmission output section forms a transmission section together with the aforementioned signal generation section.

On the other hand, the reflected wave of the transmitted wave is received by the receiving antenna 37r, the received waveform signal is amplified by the low noise amplifier 38r, and then mixed with the transmitted waveform signal distributed from the directional coupler 39 by the mixer 42. be. A beat waveform signal formed by the transmission waveform signal and the reception waveform signal is output from the mixer 42 . The beat waveform signal is amplified by the input amplifier 44, digitized by the A/D conversion section 45, and input to the microprocessor section 2 as input waveform data.

The distance measuring device 1 transmits a transmission wave whose frequency is continuously modulated and receives the reflected wave from a target. Then, the transmitted waveform signal and the received waveform signal are mixed, a beat waveform signal based on the frequency difference between them is extracted as a detection signal, and the distance to the target is measured based on the frequency analysis of the beat waveform signal. FIG. 2 shows an example of the waveform of the transmission wave, which follows a linear modulation pattern in which the frequency deviation width (occupied frequency band) and period are fixed.

The frequency of the transmitted wave also changes every moment during the period from when the transmitted wave is emitted to when the reflected wave returns, that is, during the period of radio wave flight. As a result, when a transmitted wave transmitted at a certain time returns as a reflected wave, if the received wave and the transmitted wave at the time of reception are mixed, a standing wave corresponding to the difference frequency between the two beats. (beat). Specifically, if the distance from the detection module to the reflector is R, the frequency of the beat waveform signal (=difference frequency between transmission frequency f1 and reception frequency f2) is δf, and the speed of light is c,
δf=2・R・Δf/(c・T)
becomes. Since c, T and .DELTA.f are constant, it can be seen that the frequency .delta.f of the beat waveform signal is simply proportional to the distance R to the reflector. Therefore, the distance R to the reflector can be obtained directly from the measurement of .delta.f.

In the distance measuring device 1, the transmission output section described above has a short distance measurement mode in which the frequency deviation width of continuous modulation is set to the first bandwidth and the transmission intensity of the transmission wave is set to the first transmission intensity. , a long-distance measurement mode in which the frequency deviation width is set to a second bandwidth narrower than the first bandwidth and the transmission power of the transmission wave is set to a second transmission power higher than the first transmission power; is set switchable. The lower part of FIG. 2 shows an example of the transmission wave MPN in the short distance measurement mode, and the upper part of FIG. 2 shows an example of the transmission wave MPF in the long distance measurement mode.

In this embodiment, in both the short-range measurement mode and the long-range measurement mode, the center frequency of the transmission wave is set to a predetermined frequency band, for example, a band of 75 GHz or more and 80 GHz or less. By using such a high frequency band, for example, when the target is a person, there is an advantage that the influence of the Doppler shift based on the relative movement of the target is reduced. The frequency deviation width Δf _N of the transmission wave MPN in the short-range measurement mode is set to a wide band of 1 GHz or more and 3 GHz or less (eg, 2 GHz), and the distance measurement resolution is ensured to be, for example, about 10 cm to 30 cm (eg, 15 cm). Also, the modulation cycle T _N in the short distance measurement mode is set to approximately 0.05 ms to 0.5 ms. On the other hand, the frequency deviation width _ΔfF of the transmission wave MPF in the long-distance measurement mode is set to a narrow band of 300 MHz or more and 1 GHz or less (for example, 900 MHz), and the distance measurement resolution is secured to, for example, about 30 cm to 1 m (for example, 33 cm). ing. Also, the modulation cycle T _F of the transmission wave MPN in the long distance measurement mode is set to approximately 0.5 ms to 1.0 ms.

FIG. 2 exemplifies a sawtooth linear modulation pattern, and the frequency change rate of each cycle T is always constant. On the other hand, it is also possible to adopt a triangular linear modulation pattern as shown in FIG. In this case, the absolute value of the frequency change rate is constant, but the sign is inverted every half cycle (T/2). However, since the frequency δf of the beat waveform signal appears as the difference between the transmission frequency f1 and the reception frequency f2, ignoring the sign of the frequency difference value is the same as using a sawtooth linear modulation pattern.

Returning to FIG. 1, the ROM 33 of the microprocessor unit 2 stores the following programs. All of them are executed by the CPU 31 using the RAM 32 as an execution area, and implement individual function implementation units.
Measurement control program 33a: Short-range measurement mode measurement processing for setting the short-range measurement mode for the transmission unit and causing the signal processing unit to acquire the short-range measurement mode intensity peak by transmitting microwave transmission waves toward the target. and long-distance measurement mode measurement processing in which the signal processing section acquires the long-distance measurement mode intensity peak by setting the transmission section to the long-distance measurement mode and transmitting the microwave transmission wave toward the target. Realize the function to perform.
Digital filter (for short distance) 33b: beat signal waveform data acquired in the short distance measurement mode is captured in filtering memory 32a of RAM 32, and digital filtering is performed to remove noise derived from harmonics and the like. Configured as a low-pass or band-pass filter.
Digital filter (for long distance) 33c: Performs the same digital filtering processing as digital filter (for short distance) 33b on the beat signal waveform data acquired in the long distance measurement mode. Configured as a low-pass or band-pass filter.

FFT module 33d: The filtered beat signal waveform data is loaded into the FFT processing memory 32b of the RAM 32, and the beat waveform signal is subjected to Fast Fourier Transformation (FFT) as shown in FIG. Convert to
Peak analysis program 33e: Takes the frequency spectrum data into the peak analysis memory 32c of the RAM 32 and, as shown in FIG.
Appropriate mode determination program 33f: realizes the function of the appropriate mode determination unit. Specifically, at least one of the peak frequency position and the reception intensity level is compared between the short-range measurement mode intensity peak and the long-range measurement mode intensity peak, and based on the comparison result, the short-range measurement mode and the long-range measurement are performed. It is determined which of the measurement modes is the proper mode suitable for measuring the distance to the target.

Next, the sampling data length of the beat waveform signal for performing one fast Fourier transform is set to be the same in both the short-distance measurement mode and the long-distance measurement mode. The size of the FFT processing memory 32b is also determined according to the sampling data length. For _{example ,} taking the short _- distance measurement mode with reference to FIG _. A plurality of sampling periods _tN having the same length of time are set by dividing the time axis at equal intervals. The frequency deviation sections allocated to different sampling periods _tN have different frequency absolute values, but since the frequency modulation pattern MPN is linear, the frequency deviation width and slope of each section are all equal. As a result, if the position of the target does not change, the beat waveform signals obtained in each sampling period _tN are also equivalent to each other. This situation is exactly the same in the long-distance measurement mode, where the sampling period _tF having the same sampling data length is obtained by time-dividing the frequency deviation width _ΔfF within one modulation period _TF . Multiple settings.

Since a short-range target has a shorter radio wave flight time for distance measurement than a long-range target, as shown in _FIG . It is set smaller than _F. As described above, setting the same sampling data length in the short distance measurement mode and the _long distance measurement mode means that the beat waveform signal sampling points (S1, _S2 , . . . , Sn) are equal to each other. That is, the sampling points arranged within the sampling period are denser in the short-distance measurement mode than in the long-distance measurement mode. Since the modulation pattern of the transmitted wave is linear and the mathematical property of the Fourier transform as a linear mapping, the appearance interval on the frequency axis of the data points of the frequency spectrum obtained by Fourier transforming the beat waveform signal is also The short distance measurement mode is denser than the long distance measurement mode. This corresponds to the fact that the short distance measurement mode has a better distance measurement resolution than the long distance measurement mode, and also enables distance measurement of closer targets.

Also, the length of each sampling period _tN and _tF in the near-distance measurement mode and the far-distance measurement mode determines the maximum measurable distance in each mode. Specifically, the maximum measurable distance _RA in the short-range measurement mode is obtained by multiplying the sampling period _tN by the speed of light c and dividing the distance for one round trip to the target by 2.
R _A = c·t _N ·/2
(this distance _RA may be hereinafter referred to as the "ambiguous distance"). Similarly, the maximum measurable distance _RB in the long-distance measurement mode is
R _B =c·t _F ·/2
is represented as Furthermore, since the distance measurement resolution is lower in the long-distance measurement mode than in the short-distance measurement mode, the lower limit distance _RFC , which enables distance detection in the long-distance measurement mode, does not allow distance detection in the short-distance measurement mode. is greater than the lower limit distance _{R_NC} .

The flow of distance measurement control processing in the distance measurement device 1 will be described below.
FIG. 4 is a flow chart showing the overall processing flow of the measurement control program. In S1, the measurement mode is set to the short-distance measurement mode, and in S2, distance measurement is performed in the short-distance measurement mode. Subsequently, in S3, the measurement mode is set to the long-distance measurement mode, and in S4, distance measurement is performed in the long-distance measurement mode. Note that the order of the distance measurement in the short distance measurement mode and the distance measurement in the long distance measurement mode may be reversed.

FIG. 5 is a flowchart showing details of the measurement process. Although the details have already been described above, first, the beat waveform signal is sampled in S51, and the sampled beat waveform signal data is digitally filtered in S52. Subsequently, in S53, as shown in FIG. 3, the filtered beat waveform signal data is subjected to fast Fourier transform processing to obtain frequency spectrum Spm data. In S54, an intensity peak having a level equal to or higher than the threshold LT on the frequency spectrum Spm is extracted and acquired. Then, in S55, the distance R to the target is calculated from the acquired frequency value of the intensity peak. The peak intensity level (received intensity level) _LN of the short-range measurement mode intensity peak, the peak frequency position and the calculated measured distance _RN are stored in the short-range measurement mode result memory 32d in the RAM 32 in the long-range measurement mode. The obtained intensity peak value _LF , the peak frequency position and the calculated measured distance _RF are also stored in the long distance measurement mode result memory 32e. If the target does not exist or the distance cannot be measured for various reasons, the distance calculation result is not stored in the short distance measurement mode result memory 32d or the long distance measurement mode result memory 32e.

Returning to FIG. 4, in S5, the appropriate mode determination program 33f is activated to perform appropriate mode determination processing. FIG. 6 shows details of the appropriate mode determination process. First, in S101, it is determined whether or not an intensity peak (or measured distance) could be acquired only in one of the short distance measurement mode and the long distance measurement mode. In this case, if the intensity peak acquisition unit can acquire the intensity peak only in one of the short-range measurement mode and the long-range measurement mode, the appropriate mode determination unit determines the mode in which the intensity peak can be acquired as the appropriate mode. It is a process of determining as follows. As a result, the mode for which the measurement is successful is automatically set as the appropriate mode, which is convenient for the user.

Specifically, in S101, the stored contents of the short-distance measurement mode result memory 32d and the long-distance measurement mode result memory 32e are read, and the peak frequency position and calculated distance are stored for either the short-distance measurement mode or the long-distance measurement mode. (that is, whether the distance was detected). In S102, when only the short-distance measurement mode measurement distance _RN is detected, the process proceeds to S103, and the short-distance measurement mode is adopted. On the other hand, if the short-distance measurement mode measurement distance _RN is not detected in S102 and only the long-distance measurement mode measurement distance _RF is detected in 104, the process proceeds to S105 to adopt the long-distance measurement mode. If the measured distance has not been detected in either the short-distance measurement mode or the long-distance measurement mode, the process advances to S118 to output an error.

Subsequently, in S101, when the intensity peak (or the measured distance) was obtained in both the short-distance measurement mode and the long-distance measurement mode, the process proceeds to S106. In this step, it is determined whether or not there is a large gap between the acquired short-distance measurement mode measured distance _RN and long-distance measurement mode measured distance _RF . _{Specifically ,} if the difference |R _F −R _N | It is determined that the mode measurement distance _RN and the long-distance measurement mode measurement distance _RF are substantially equal. If it is determined in S106 that |R _F −R _N |≧ε and there is a significant difference between the short distance measurement mode measurement distance R _N and the long distance measurement mode measurement distance R _F , the process proceeds to S110. Then, the process of comparing the long-distance measurement mode measurement distance _RF with the above-mentioned ambiguous distance _RA is performed. The processing in the case of R _F >R _A in this comparison result is the processing from S111 onwards, the details of which will be described later.

On the other hand, if R _F ≤ R _A in S110, the process proceeds to S113 and subsequent steps. In the processing, when intensity peaks can be acquired in both the short-range measurement mode and the long-range measurement mode, the far-range measurement is performed based on the comparison of the frequency positions of the short-range measurement mode intensity peak and the long-range measurement mode intensity peak. It is determined whether or not the distance measurement mode intensity peak is a multiple reflection peak derived from multiple reflection with the target. Then, when it is determined that the long-distance measurement mode intensity peak is the multiple reflection peak, the short-distance measurement mode is determined to be the appropriate mode. The frequency positions of the short-range measurement mode intensity peak and the long-range measurement mode intensity peak are compared and processed by comparing the short-range measurement mode measured distance _RN and the long-range measurement mode measured distance _RF indicated by each frequency position. The above are considered equivalent.

The left side of FIG. 7 shows the case where the microwave transmission wave from the measuring device 1 returns after normal reflection from the target, and the right side shows the case where it returns after multiple reflections. The radio wave flight distance for transmission/reception increases n times as much as in the case of normal reflection SR when n-order multiple reflection MR occurs. Therefore, the measured distance when the multiple reflection MR occurs is erroneously detected as a value larger than the measured distance normally measured by the normal reflection SR. Such multiple reflections tend to occur more easily when the target is present at a relatively short distance during measurement in the long-distance measurement mode with high radio wave transmission intensity. Therefore, by comparing the frequency positions of the intensity peaks in the short-range measurement mode and the intensity peaks in the long-range measurement mode, it is possible to discriminate erroneous detection due to multiple reflections in the long-range measurement mode. The measurement mode can be automatically set as an appropriate mode, enabling more reliable distance detection.

For _example , when |R _F −R _N |< _ε as shown in FIG. , it can be determined that the possibility of false detection due to multiple reflections in the long-distance measurement mode is low. In this case, it can be determined that the long distance measurement mode is suitable for distance measurement for distant targets, and the short distance measurement mode is suitable for distance measurement for comparatively close targets. to S107, the short distance measurement mode measurement distance R _N and the long distance measurement mode measurement distance R _F are replaced by a representative value (for example, the average value of both ( _RF + R _N )/2), and the short distance and the long distance The representative value is compared with a predetermined threshold value _R0 for discriminating between . If it is determined that the distance is short, the process proceeds to S108, and the short-distance measurement mode is adopted. If it is determined that the distance is long, the process proceeds to S109, and the long-distance measurement mode is adopted.

On the other hand, if |R _F −R _N |≧ε in S106 and R _F <R _A in S110, the multiple reflection determination for the long-distance measurement mode is performed as follows in the processing from S113 onward. First, the state where |R _F −R _N |≧ε is defined as “the short-range measurement mode distance RN indicated by the frequency position of the short-range measurement mode intensity peak and the long-range measurement distance _indicated by the frequency position of the long-range measurement mode intensity peak. It means a state in which there is a difference exceeding a predetermined range ε with respect to the mode distance R _F , that is, a state in which a considerable difference has occurred between R _N and R _F . At this time, in S113, the short distance measurement mode distance R _N is smaller than the lower limit distance R _FC at which distance detection is possible in the long distance measurement mode (R _N <R _F c), and the long distance measurement mode distance R _F is smaller than a predetermined short-range reference value R ₀ (R _F <R ₀ ), it is determined that the long-range measurement mode intensity peak is a multiple reflection peak, and the process proceeds to S114 to adopt the short-range measurement mode. do.

There are two reasons for considering the result in the telemetry mode measurement as multiple reflections when the above conditions hold:
Both conditions R _N < R _F c and R _F < R ₀ indicate that the target is fairly close to the measuring device and receive high intensity transmitted waves leading to multiple reflections in the long-range measurement mode. in a state of ease;
・The condition of _RN < _RFc is that the target detected in the short distance measurement mode is located closer than the lower limit distance _RFc of the long distance measurement mode, and is originally detected in the long distance measurement mode. means it shouldn't. Despite this, the fact that the distance was detected in the long-distance measurement mode is considered to be the result of the radio wave flying distance exceeding the lower limit distance _RFC due to the influence of multiple reflections.

Therefore, by adopting the above method, it is possible to accurately determine the occurrence of multiple reflections in the long-distance measurement mode. FIG. 9 shows such an example. The long-distance measurement mode distance _RF is approximately twice the short-distance measurement mode distance _RN , which corresponds to the case where second-order multiple reflection occurs in the long-distance measurement mode. That is, |R _F −R _N |>ε, and since the conditions of R ₀ >R _F and R _Fc >R _N are satisfied, the short-range measurement mode is determined to be the proper mode, and the measured value is the near-range measurement mode. A range measurement mode range _RN is employed.

On the other hand, if either one of R _N <R _F c and R _F <R ₀ is not established in S113, it is considered that the possibility of multiple reflection occurring in the long distance measurement mode is low, and the process proceeds to S115. In this case, of the short-range measurement mode intensity peak and the long-range measurement mode intensity peak, the mode that produces the higher received intensity level is determined as the appropriate level. That is, the intensity level (received intensity level) of the short-range measurement mode intensity peak is L _N , the intensity level of the long-range measurement mode intensity peak is L _F , and when L _N >L _F , the process proceeds to S116 and the short-range measurement mode is adopted, and if not, the process proceeds to S117 to adopt the long distance measurement mode.

FIG. 10 shows an example of this, where the long-range measurement mode distance R _F is different from the short-range measurement mode distance R _N , and |R _F −R _N |>ε is satisfied. (but R _F is not an integer multiple of R _N ). R ₀ >R _F is satisfied, but R _Fc >R _N is not satisfied. Therefore, the intensity levels L _N and L _F of the peaks in the short-distance measurement mode and the long-distance measurement mode are compared, and since L _N >L _F , the short-distance measurement mode is determined to be the appropriate mode, and the measurement is performed. A short-range measurement mode distance _RN is adopted as the value.

Returning to FIG. 6, next, the processing when the long distance measurement mode measured distance _RF exceeds the ambiguous distance _RA in S110 will be described. A situation in which a large difference occurs between the long-distance measurement mode measurement distance _RF and the short-distance measurement mode measurement distance _RN is not limited to the case where multiple reflections occur in the long-distance measurement mode measurement as described above. This can also occur when a target that is slightly distant beyond the ambiguous distance _RA of mode measurement is measured smaller than it should be due to data processing reasons in the short-distance measurement mode. The details will be described below.

As already described with reference to FIG. 2, one period _TN of the linear modulation pattern MPN is divided into a plurality of sampling periods _tN in which the sampling data length is constant in the short-range measurement mode. Data sampling of the beat waveform signal is executed each time a new sampling period _tN arrives within the modulation period _TN , and the frequency spectrum is updated based on the sampled waveform data. The frequency position corresponding to the origin of that sampling period _tN gives the zero point of the distance measurement. Also, the frequency position corresponding to the end point of the sampling period _tN corresponds to the maximum distance measurable within the sampling period _tN , ie, the ambiguous distance _RA . At this time, if the radio wave flight time until the transmitted wave is reflected by the target and returned is set to be infinitely long, the upper limit of the measurable distance is not limited as long as the detection sensitivity of the device is ensured. However, if the sampling data length for one distance measurement is limited as described above, the upper limit of the measurable distance is also restricted by the ambiguous distance _RA .

As shown in FIG. 11, for example, consider a situation where the target is at a distance R _F ' slightly beyond the maximum distance of the short-range measurement mode, ie, the fuzzy distance R _A . The frequency deviation width wf' corresponding to the distance R _F ' is within the frequency deviation width Δf _N (FIG. 2) of one cycle of the modulation pattern MPN, and at first glance it seems that accurate measurement is possible. However, in reality, the radio wave flight time τ _T required for measuring the distance R _F ' in this case exceeds the sampling period t _N , and the reflected wave of the transmitted wave output at the starting point S0 of a certain sampling period is , is received at a timing that falls into the next sampling period. Then, the distance measurement of the target will be made with the start point S0′ of the next sampling period as the starting point. As a result, the distance _RF to be measured is calculated based on the frequency shift width wf with reference to the starting point S0' of the next sampling period, using the corresponding radio wave flight time _τF . is erroneously measured as a value obtained by subtracting the ambiguous distance R _A from the distance R _F '. At this time, the corresponding intensity peak P _F appears on the distance axis in such a manner that the period protruding from the ambiguous distance _RA is folded back.

That is, in the short-distance measurement mode, when a target exists at the above position, the measured distance R _F is erroneously measured to be smaller than the actual distance R _F ′ due to the influence of the ambiguous distance R _A . sell. However, in principle, this problem does not occur in the long-distance measurement mode in which the upper limit of the measurable distance is large. Therefore, when there is a possibility that a distance smaller than the actual distance R _F ′ is erroneously measured due to the presence of the target at a distance greater than the ambiguous distance (maximum distance) R _A , short-range measurement When intensity peaks can be acquired in both the mode and the long-range measurement mode, the near-range measurement mode distance It is possible to determine whether or not _RN is an erroneous measurement due to the above factors. Then, when it is determined that the measurement is erroneous, determination is made so that the long-distance measurement mode becomes the proper mode.

Specifically, in FIG. 6, the short-range measurement mode distance RN calculated based on the frequency position of the near-range measurement mode intensity peak and the long-range measurement _RN calculated based on the frequency position of the long-range measurement mode intensity peak There is a difference ε exceeding a predetermined value with the mode distance R _F (|R _F −R _N |>ε: S106→S110), and the long-distance measurement mode distance R _F is an ambiguous distance R _A (the maximum distance measurable within the sampling period in the short-range measurement mode) (R _N >R _A : S110→S111), in S111, the short-range measurement mode distance _RN and the maximum distance R The difference between the total value _RN + _RA *n of _A times natural number (n: n≧1) and the long-distance measurement mode distance _RF is a predetermined value δ (for example, ( _RN + _RA *n ) and _RF , whichever is greater, such as 10%). As explained with reference to FIG. 11, the short-range measurement mode distance R _N approaches the real distance R _F ′ by adding the fuzzy distance R _A (or the value of R _A ×n) to compensate for the aliasing effect. should be. On the other hand, since the long-distance measurement mode distance R _F is not affected by the ambiguous distance R _A , if it is considered that this reflects the actual distance R _F ′, the degree of agreement between R _N +R _A ×n and R _F is By evaluating , it can be accurately determined whether or not the short-range measurement mode distance _RN is an erroneous measurement derived from the ambiguous distance _RA .

FIG. 12 shows an example of such measurement. In the short-range measurement mode, the long-range measurement mode distance _RF indicated by the solid line becomes the short-range measurement mode distance _RN that has been folded once by the ambiguous distance _RA. ing. In this case, it is determined in S111 whether or not |R _F −(R _N +R _A ×1)|<ε, and |R _F −(R _N +R _A ×1)|<δ. In this case, it is assumed that an ambiguous distance has been affected, and the process proceeds to S112, where it is determined that the long-distance measurement mode is the appropriate mode, and the long-distance measurement mode distance _RF is adopted as the measured value. Also, depending on the distance to the target, the effect of folding may occur multiple times (n times: n>2). For example, if the fuzzy range R _A is 20 m and the target range is 50 m, the short range measurement mode range _RN is measured to be 10 m as a result of two folds (ie n=2). That is, considering the case where folding occurs more than once, the value of |R _F −(R _N +R _A ×n)| If |R _F −(R _N +R _A ×n)| Make judgments. For example, in FIG. 12, the long-distance measurement mode distance R _F ' indicated by the dashed line is the short-distance measurement mode distance R _N that has been folded three times by the ambiguous distance _RA in the short-distance measurement mode.

On the other hand, in S111, |R _F −(R _N +R _A ×n)|≧δ, and if there is a non-negligible difference between R _F and (R _N +R _A ), the ambiguous distance R _A It is determined that the malfunction is not caused by The following processing is the same as when it is determined that the possibility of occurrence of multiple reflections is low in the long distance measurement mode. FIG. 13 shows such an example. That is, |R _F −(R _N +R _A ×n) |<δ is not satisfied, and as a result of comparing the intensity levels L _N and L _F of each peak in the short-range measurement mode and the long-range measurement mode, Since L _N <L _F , the long-distance measurement mode is determined to be the proper mode, and the long-distance measurement mode distance _RF is adopted as the measured value.

The appropriate mode determination process is executed as described above, and the appropriate mode for distance measurement is determined. After that, returning to the process of FIG. 4, in S6, the measured distance determined to be the appropriate mode among the contents stored in the result memories 32d and 32e of each mode of FIG. 1 is read out and output. As shown in FIG. 1, the measured distance is output together with information on the type of measurement mode adopted as the proper mode. If the process is not completed in S7, the process returns to S1, and the following processes are repeated.

Although the embodiment of the present invention has been described above, the present invention is not limited to this. For example, in the processing flow of the measurement control program shown in FIG. I was trying to judge it over and over again. However, if the existence status of the target for distance measurement does not change frequently, the appropriate mode is determined by executing the flow of S1 to S5 in FIG. It is also possible to configure such that the measurement is repeated while maintaining the appropriate mode determined by the method. FIG. 15 shows an example of processing in that case. The processing from S1 to S7 is the same as in FIG. Then, if the process is not completed in S7, the process advances to S8 to perform the process of determining whether or not to re-determine the proper mode. For example, when the distance measurement result for the target object changes in the approaching direction or in the separating direction as the measurement is repeated, the measured distance changes over a predetermined threshold that defines the boundary between the short distance and the long distance. Then, in S8, it is determined that the proper mode needs to be re-determined. In this case, returning to the flow of S1 to S5, the appropriate mode is reset. On the other hand, if the measured distance does not change beyond the threshold value, it is determined in S8 that re-determination of the appropriate mode is unnecessary, and the current appropriate mode is maintained while proceeding to S9 to perform the measurement process of FIG. do. When the measurement process is completed, the process returns to S6 to output the result.

1 distance measuring device 2 microprocessor unit 3 sensor unit 30 bus 31 CPU
32 RAMs
33 ROMs
33a measurement control program 33b digital filter (for short distance)
33c Digital filter (for long distance)
33dFFT module 33e Peak analysis program 33f Appropriate mode determination program 34 Input/output unit 35 Transmission controller 38t Transmission amplifier 37t Transmission antenna 37r Reception antenna 38r Low noise amplifier 39 Directional coupler 40 Oscillation circuit 41 PLL control unit 42 Mixing unit 44 Input amplifier 45 A/D converter

Claims (5)

A signal generator that generates a transmission waveform signal whose frequency is continuously modulated according to a predetermined modulation pattern; and a microwave transmission wave whose frequency is continuously modulated based on the input of the transmission waveform signal. a short-range measurement mode in which the frequency deviation width of the continuous modulation is set to a first bandwidth and the transmission intensity of the microwave transmission wave is set to the first transmission intensity; A long distance in which the frequency deviation width is set to a second bandwidth narrower than the first bandwidth and the transmission intensity of the microwave transmission wave is set to a second transmission intensity higher than the first transmission intensity a transmission unit configured to be switchable between measurement modes;
a receiving unit that receives the reflected wave of the microwave transmission wave;
a mixer for mixing the transmission waveform signal and a waveform signal of the reflected wave received by the reception unit and outputting a beat waveform signal based on a frequency difference between the transmission waveform signal and the reception waveform signal; and the beat waveform signal. a signal processing unit having a frequency spectrum generation unit that generates a frequency spectrum of and an intensity peak acquisition unit that acquires an intensity peak for specifying the distance of the target on the frequency spectrum;
Short-range measurement mode measurement processing for causing the signal processing unit to acquire a short-range measurement mode intensity peak by setting the short-range measurement mode for the transmission unit and transmitting the microwave transmission wave toward the target. and a long-distance measurement mode for causing the signal processing unit to acquire a long-distance measurement mode intensity peak by setting the long-distance measurement mode for the transmission unit and transmitting the microwave transmission wave toward the target. a measurement control unit that sequentially executes a measurement process;
comparing at least one of a peak frequency position and a received intensity level between the short-range measurement mode intensity peak and the long-range measurement mode intensity peak as a first comparison ; and further, a frequency spectrum in the long-range measurement mode. Based on the frequency position of the intensity peak above, distance information to the target is generated as a long-distance measurement mode measurement distance, while the sampling period _tN of the beat waveform signal in the short-distance measurement mode is multiplied by the speed of light c. By dividing the obtained distance for one round trip to the target by 2, it is determined whether the long-distance measurement mode measured distance is larger than the ambiguous distance _RA expressed as _RA =c· _tN ·/2. is compared as a second comparison , and based on the result of the comparison processing of the first comparison and the result of the comparison processing of the second comparison, which of the short distance measurement mode and the long distance measurement mode is selected a proper mode determination unit that determines whether the mode is a proper mode suitable for measuring the distance to the target;
a distance information generator that generates distance information to the target based on the frequency position of the intensity peak on the frequency spectrum generated in the proper mode;
a distance information output unit that outputs the generated distance information,
The appropriate mode determination unit determines that, when the intensity peak acquisition unit is able to acquire the intensity peaks in both the short-range measurement mode and the long-range measurement mode, the short-range measurement mode intensity peak and the long-range measurement Based on the comparison of the frequency position with the mode intensity peak, it is determined whether the long-distance measurement mode intensity peak is a multiple reflection peak derived from multiple reflections with the target, and the long-distance measurement mode A distance measuring device, wherein when it is determined that an intensity peak is the multiple reflection peak, the short distance measurement mode is determined to be the appropriate mode. The appropriate mode determination unit determines the distance based on the short-range measurement mode distance RN generated by the distance information generation unit based on the frequency position of the short-range measurement mode intensity peak and the frequency position of the long-range measurement mode intensity peak. There is a difference exceeding a predetermined value from the long-distance measurement mode distance RF generated by the information generation unit, and the short-distance measurement mode distance RN is capable of distance detection in the long-distance measurement mode. and when the long-distance measurement mode distance RF is smaller than a predetermined short-distance reference value R0, the long-distance measurement mode intensity peak is determined to be the multiple reflection peak. 2. A distance measuring device according to claim 1. A signal generator that generates a transmission waveform signal whose frequency is continuously modulated according to a predetermined modulation pattern; and a microwave transmission wave whose frequency is continuously modulated based on the input of the transmission waveform signal. a short-range measurement mode in which the frequency deviation width of the continuous modulation is set to a first bandwidth and the transmission intensity of the microwave transmission wave is set to the first transmission intensity; A long distance where the frequency deviation width is set to a second bandwidth narrower than the first bandwidth and the transmission intensity of the microwave transmission wave is set to a second transmission intensity higher than the first transmission intensity a transmission unit configured to be switchable between measurement modes;
a receiving unit that receives the reflected wave of the microwave transmission wave;
a mixer for mixing the transmission waveform signal and a waveform signal of the reflected wave received by the reception unit and outputting a beat waveform signal based on a frequency difference between the transmission waveform signal and the reception waveform signal; and the beat waveform signal. a signal processing unit having a frequency spectrum generation unit that generates a frequency spectrum of and an intensity peak acquisition unit that acquires an intensity peak for specifying the distance of the target on the frequency spectrum;
Short-range measurement mode measurement processing for causing the signal processing unit to acquire a short-range measurement mode intensity peak by setting the short-range measurement mode for the transmission unit and transmitting the microwave transmission wave toward the target. and a long-distance measurement mode for causing the signal processing unit to acquire a long-distance measurement mode intensity peak by setting the long-distance measurement mode for the transmission unit and transmitting the microwave transmission wave toward the target. a measurement control unit that sequentially executes a measurement process;
comparing at least one of a peak frequency position and a received intensity level between the short-range measurement mode intensity peak and the long-range measurement mode intensity peak as a first comparison ; and further, a frequency spectrum in the long-range measurement mode. Based on the frequency position of the intensity peak above, distance information to the target is generated as a long-distance measurement mode measurement distance, while the sampling period _tN of the beat waveform signal in the short-distance measurement mode is multiplied by the speed of light c. By dividing the obtained distance for one round trip to the target by 2, it is determined whether the long-distance measurement mode measured distance is larger than the ambiguous distance _RA expressed as _RA =c· _tN ·/2. is compared as a second comparison , and based on the result of the comparison processing of the first comparison and the result of the comparison processing of the second comparison, which of the short distance measurement mode and the long distance measurement mode is selected a proper mode determination unit that determines whether the mode is a proper mode suitable for measuring the distance to the target;
a distance information generator that generates distance information to the target based on the frequency position of the intensity peak on the frequency spectrum generated in the proper mode;
a distance information output unit that outputs the generated distance information,
The frequency spectrum generator divides each period of the linear modulation pattern into a plurality of sampling periods with a constant sampling data length, and samples the beat waveform signal each time a new sampling period arrives within the period. and updating the frequency spectrum based on the sampled waveform data,
In both the short-distance measurement mode and the long-distance measurement mode, the distance information generation unit causes the frequency position corresponding to the starting point of the sampling period to correspond to the zero point of distance measurement, and the frequency position to correspond to the end point of the sampling period. generating distance information to the target in the form of setting the frequency position to the maximum distance measurable within the sampling period;
The appropriate mode determination unit determines that, when the intensity peak acquisition unit is able to acquire the intensity peaks in both the short-range measurement mode and the long-range measurement mode, the short-range measurement mode intensity peak and the long-range measurement Based on the frequency position comparison with the mode intensity peak, in the short distance measurement mode, the short distance measurement mode distance generated by the distance information generation unit based on the frequency position of the short distance measurement mode intensity peak is determined during the sampling period. determining whether or not the target is erroneously measured to be smaller than the actual distance to the target due to the fact that the target exists farther than the maximum measurable distance within the A distance measuring device characterized in that, when it is determined that the long distance measurement mode is set to the appropriate mode. The appropriate mode determination unit determines the distance information based on the short-range measurement mode distance generated by the distance information generation unit based on the frequency position of the short-range measurement mode intensity peak and the frequency position of the long-range measurement mode intensity peak. a difference exceeding a predetermined value from the long-distance measurement mode distance generated by the generator, the long-distance measurement mode distance being greater than the maximum distance, and the short-distance measurement mode distance If the difference between the total value of the maximum distance multiplied by a natural number and the long-distance measurement mode distance is within a predetermined range, the short-distance measurement mode distance is determined to be the erroneous measurement. 4. The distance measuring device according to claim 3. When the intensity peak acquisition unit is able to acquire the intensity peak in only one of the short-distance measurement mode and the long-distance measurement mode, the proper mode determination unit selects the mode in which the intensity peak can be acquired. 5. The distance measuring device according to any one of claims 1 to 4, wherein the appropriate mode is determined to be the appropriate mode.

Images