JP2020106432A - Distance measuring device - Google Patents

Abstract

To enable a mode suitable for measuring the distance to a target to be appropriately discriminated, and further enable a satisfactory distance measurement result to be obtained for any target that is at a near or far distance by optimization of the mode.SOLUTION: A distance measuring device comprises a near distance measurement mode and a far distance measurement mode in which the frequency deviation width and transmission strength of a continuously modulated microwave transmission wave are different from each other, sequentially measuring the distance to a target in these near distance and far distance measurement modes. The beat waveform signal obtained in each mode is converted into a frequency spectrum, and a near distance measurement mode strength peak and a far distance measurement mode strength peak respectively are acquired from the frequency spectrum. At least one of a peak frequency position and a received strength level is compared between the near distance and far distance measurement mode strength peaks, and determination is made on the basis of the comparison result as to which of the near distance and far distance measurement modes is an appropriate mode.SELECTED DRAWING: Figure 1

Description

The present invention relates to a distance measuring device for measuring a distance to a target object based on the principle of a frequency modulated continuous wave (FMCW) radar.

The frequency-modulated continuous wave radar transmits a frequency-modulated continuous wave to a target object and obtains the distance from a beat waveform signal derived from the frequency difference between the transmitted wave and the reflected wave. Since the frequency-modulated continuous wave radar uses a continuous wave as a transmission wave, there is an advantage that a desired signal-to-noise ratio (SN ratio) can be easily obtained without a high transmission output.

It is known that the frequency modulation continuous wave radar has a frequency deviation width Δf of the transmitted wave and a speed of light as c, and the resolution of the distance measurement is proportional to c/(2·Δf). High resolution can be realized. However, when Δf is increased to obtain a high resolution, reception noise increases and the detection distance decreases due to a wider band, which makes it difficult to detect a distant target. Therefore, instead of setting a large Δf, the transmission output is reduced to improve the resolution with respect to a short-range target, and in contrast to this, Δf is reduced to increase the transmission output and reduce receiver noise. A distance measuring device has been proposed in which a long-distance measuring mode in which the detection distance is increased while being incorporated into one measuring system and the mode can be used while switching the mode according to the distance to the target object (Patent Document 1). ..

JP 2001-183449 A

However, in the distance measuring device disclosed in the above-mentioned related art, which of the long distance measuring mode and the short distance measuring mode is adopted is left to the user to select depending on which target object is to be measured. .. Therefore, there is a problem that it is difficult for a user who is not familiar with distance measurement to know whether or not the mode to be adopted is suitable for distance measurement of the target. For example, when it is not clear whether the distance to the target is short range or long range, or when it is difficult to know where the target exists in a wide space, the user can select two modes. There is a possibility that the measurement may be performed by selecting. At this time, there arises a problem that an appropriate judgment cannot be made as to whether or not the obtained distance measurement result reflects the correct distance to the target object.

An object of the present invention is, in a distance measuring device that can be used in both a long distance measuring mode and a short distance measuring mode, it is possible to appropriately determine which mode is suitable for measuring a distance to a target object. As a result, it is possible to obtain satisfactory distance measurement results for both short-distance and long-distance targets by automatically optimizing the modes.

In order to solve the above problems, the distance measuring device of the present invention is based on the input of the transmission waveform signal and a signal generation unit that generates a transmission waveform signal whose frequency is continuously modulated in a predetermined linear modulation pattern. And a transmission output unit for transmitting a microwave transmission wave whose frequency is continuously modulated toward a target object, wherein the frequency deviation width of continuous modulation is set to the first bandwidth and the transmission intensity of the transmission wave is the first. The short-range measurement mode is set to the transmission intensity, and the frequency deviation width is set to the second bandwidth which is narrower than the first bandwidth, and the transmission intensity of the transmitted wave is higher than the first transmission intensity. The transmission unit is set to be switchable between the long distance measurement mode set to the transmission intensity, the reception unit that receives the reflected wave of the microwave transmission wave, and the transmission waveform signal and the reception waveform signal of the reception unit are mixed. , A mixing unit that 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, and specify the distance of the target on the frequency spectrum A signal processing unit having an intensity peak acquisition unit for acquiring an intensity peak for the purpose of setting a short-distance measurement mode for the transmission unit and transmitting the microwave transmission wave toward the target object, Short-distance measurement mode Short-distance measurement mode measurement processing that acquires the intensity peak and long-distance measurement in the signal processing unit by setting the long-distance measurement mode for the transmission unit and transmitting microwave transmission waves to the target A measurement control unit that sequentially executes a long-distance measurement mode measurement process for acquiring a mode intensity peak, and at least one of a peak frequency position and a reception intensity level between the short-distance measurement mode intensity peak and the long-distance measurement mode intensity peak. And an appropriate mode determination unit that determines which of the short-distance measurement mode and the long-distance measurement mode is the appropriate mode based on the comparison result, and an intensity peak on the frequency spectrum generated in the appropriate mode. And a distance information output unit that outputs the generated distance information, the distance information generation unit that generates distance information to the target object based on the frequency position.

The distance measuring device of the present invention is provided with a short-distance measuring mode and a long-distance measuring mode in which the frequency deviation width and the transmission intensity of continuously modulated microwave transmission waves are different from each other, and the distance to the target is measured. 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 the short-distance measurement mode intensity peak and the long-distance measurement mode intensity peak are respectively acquired from the frequency spectrum. Then, at least one of the peak frequency position and the reception intensity level is compared between the short-distance measurement mode intensity peak and the long-distance measurement mode intensity peak, and the short-distance measurement mode and the long-distance measurement mode are based on the comparison result. Which of the two is in the proper mode is determined. Accordingly, it is possible to appropriately determine whether the mode suitable for measuring the distance to the target object is the short-distance measurement mode or the long-distance measurement mode. A satisfactory distance measurement result can be obtained for any target in the distance.

The block diagram which shows the electric constitution of the distance measuring device which is one Embodiment of this invention. The schematic diagram which compares and shows the transmitted wave modulation pattern of a long distance measurement mode and a short distance measurement mode. The figure which shows the concept which produces|generates the frequency spectrum of a beat waveform signal by Fourier transformation. The flowchart which shows the whole process flow of a measurement control program. The flowchart which shows the flow of the measurement process of FIG. The flowchart which shows the flow of the appropriate mode determination process of FIG. The schematic diagram which compares and shows a normal reflection and multiple reflection. Explanatory drawing which shows the transmission wave frequency change at the time of performing a short distance measurement mode and a long distance measurement mode one by one, and the example of the beat waveform signal obtained by each mode. Explanatory drawing which shows the 1st example when a short-distance measurement mode is determined to be an appropriate mode. Explanatory drawing which shows the 2nd example in case a short distance measurement mode is determined to be an appropriate mode. In the short distance measurement mode, the short distance measurement mode distance R _N is erroneously measured to be smaller than the actual distance R _N ′ to the target because the target exists farther than the ambiguous distance _RA. FIG. Explanatory drawing which shows the 1st example in case the long distance measurement mode is determined to be an appropriate mode. Explanatory drawing which shows the 2nd example in case the long distance measurement mode is determined to be an appropriate mode. The figure which shows the modification of a transmission wave modulation pattern. The flowchart which shows the flow of the modification of measurement control.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a block diagram showing an electrical configuration of a distance measuring device 1 according to an embodiment of the present invention. The distance measuring device 1 is configured as a device that measures a distance to a target object based on the principle of a frequency modulated continuous wave (FMCW) radar, and includes a microprocessor unit 2 and a sensor unit connected to the microprocessor unit 2. 3 and 3. The microprocessor unit 2 functions as an operation control unit and a signal processing unit of the sensor unit 3, and has a CPU 31, a RAM 32, a ROM 33, an input/output unit 34, and a bus 30 connecting them. The sensor unit 3 includes 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 a transmission side block. On the other hand, the reception block has a reception antenna 37r, a low noise amplifier 38r, a mixing unit 42, an input amplifier 44, and an A/D conversion unit 45.

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 unit 2 via the input/output unit 34, and controls the operation of the PLL control unit 41 and the transmission amplifier 38t. The PLL control unit 41 feedback-controls the oscillation output operation of the oscillation circuit 40 in a phase-locked manner based on the frequency instruction value transferred from the transmission controller 35, and a transmission waveform signal whose frequency is continuously modulated (details). (Which will be described later with reference to FIG. 2) is output to the oscillation circuit 40. That is, the microprocessor unit 2, the transmission controller 35, the PLL control unit 41, and the oscillation circuit 40 function as a signal generation unit that generates a transmission waveform signal.

The 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 input 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 the microwave transmission wave toward the target object. Further, the transmission output unit forms a transmission unit together with the signal generation unit described above.

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 in the mixing unit 42. It The beat waveform signal generated by the transmission waveform signal and the reception waveform signal is output from the mixing unit 42. The beat waveform signal is amplified by the input amplifier 44, further digitized by the A/D converter 45, and input to the microprocessor unit 2 as input waveform data.

The distance measuring device 1 transmits a transmission wave whose frequency is continuously modulated and receives the reflection wave of the target object. Then, the transmission waveform signal and the reception 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 object is measured based on the frequency analysis of the beat waveform signal. FIG. 2 shows an example of the waveform of the transmission wave, and a waveform that follows a linear modulation pattern in which the frequency deviation width (occupied frequency band) and the period are fixed is used.

The frequency of the transmitted wave changes momentarily during the period from the emission of the transmitted wave to the return of the reflected wave, that is, during the radio wave flight period. As a result, when the 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 will snarl. It occurs as a (beat). Specifically, if the distance from the detection module to the reflector is R, the frequency of the beat waveform signal (=the difference frequency between the transmission frequency f1 and the reception frequency f2) is δf, and the speed of light is c,
δf=2·R·Δf/(c·T)
Becomes Since c, T and Δf are constant, it can be seen that the frequency δf of the beat waveform signal is simply proportional to the distance R to the reflector. Therefore, the distance R to the reflector can be directly obtained from the measurement of δf.

In the distance measuring device 1, in the above-mentioned transmission output unit, 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 distance measurement mode in which the frequency deviation width is set to a second bandwidth narrower than the first bandwidth and the transmission intensity of the transmitted wave is set to a second transmission intensity higher than the first transmission intensity, and Is set to be 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, the center frequency of the transmitted wave is set to a predetermined frequency band, for example, 75 GHz or more and 80 GHz or less in both the short distance measurement mode and the long distance measurement mode. By using the high frequency band of this level, for example, when the target is a person, there is an advantage that it is less likely to be affected by the Doppler shift based on the relative movement of the target. The frequency deviation width Δf _N of the transmission wave MPN in the short distance measurement mode is set to a wide band of 1 GHz or more and 3 GHz or less (for example, 2 GHz), and the resolution of distance measurement is secured at, for example, about 10 cm to 30 cm (for example, 15 cm). The modulation cycle T _N in the short distance measurement mode is set to about 0.05 ms to 0.5 ms. On the other hand, the frequency deviation width Δf _F 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 Mz), and the resolution of distance measurement is ensured at, for example, about 30 cm to 1 m (for example, 33 cm). ing. Further, the modulation period T _F of the transmission wave MPN in the long distance measurement mode is set to about 0.5 ms to 1.0 ms.

Note that FIG. 2 exemplifies a sawtooth wave-like 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 wave-shaped 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 a difference between the transmission frequency f1 and the reception frequency f2, if the sign of the frequency difference value is ignored, it is the same as when using a sawtooth linear modulation pattern.

Returning to FIG. 1, the ROM 33 of the microprocessor unit 2 stores the following programs. Each of them is executed by the CPU 31 using the RAM 32 as an execution area, and embodies an individual function realizing unit.
-Measurement control program 33a: Short-distance measurement mode measurement processing for setting the short-distance measurement mode to the transmission unit and transmitting the microwave transmission wave toward the target object to cause the signal processing unit to acquire the short-distance measurement mode intensity peak And the long-distance measurement mode measurement process in which the signal processing unit acquires the 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 object. Realize the function to be executed.
Digital filter (for short distance) 33b: The beat signal waveform data acquired in the short distance measurement mode is taken into the filter processing memory 32a of the RAM 32, and digital filtering processing is performed to remove noise and the like derived from harmonics. It is configured as a low pass filter or a band pass filter.
Digital filter (for long distance) 33c: Performs the same digital filtering process as the digital filter (for short distance) 33b on the beat signal waveform data acquired in the long distance measurement mode. It is configured as a low pass filter or a band pass filter.

FFT module 33d: The beat signal waveform data after the filtering process is fetched 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: The frequency spectrum data is loaded into the peak analysis memory 32c of the RAM 32, and as shown in FIG. 3, a process of extracting and acquiring an intensity peak P equal to or higher than the threshold value LT appearing on the frequency spectrum Spm is performed.
Proper mode determination program 33f: Realizes the function of the proper mode determination unit. Specifically, between the short-distance measurement mode intensity peak and the long-distance measurement mode intensity peak, at least one of the peak frequency position and the reception intensity level is compared, and the short-distance measurement mode and the long-distance measurement mode are based on the comparison result. Which of the measurement modes is an appropriate mode suitable for measuring the distance to the target is determined.

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 set according to the sampling data length. For example, when taking explaining short-distance measurement mode as an example with reference to FIG. 2, the sampling period t _N of the beat waveform signal is set to be shorter than the modulation period T _N, the frequency shift width Delta] f _N of one modulation period T _N A plurality of sampling periods t _N having the same time length are set so as to be divided at equal intervals on the time axis. The frequency shift sections assigned to different sampling periods t _N have different frequency absolute values, but since the frequency modulation pattern MPN is linear, the frequency shift width and the slope of each section are all equal. As a result, if the position of the target object does not change, the beat waveform signals obtained in each sampling period t _N are also equivalent to each other. This circumstance is exactly the same in the long distance measurement mode, and here again, the frequency shift width Δf _F is time-divided within one modulation cycle T _F , and the sampling period t _F having the same sampling data length is Multiple are set.

Since the short-distance target has a shorter radio flight time for distance measurement than the long-distance target, as shown in FIG. 2, the short-distance measurement mode sampling period t _N is the long-distance measurement mode sampling period t. It is set smaller than _F. As described above, the setting of the same sampling data length in the short distance measurement mode and the long distance measurement mode means that the sampling points (S1, S2) of the beat waveform signal included in the respective sampling periods t _N and t _F are included. ,..., Sn) are equal in number n to each other. That is, the time intervals of the sampling points arranged in the sampling period are closer in the short distance measurement mode than in the long distance measurement mode. The modulation pattern of the transmitted wave is linear, and from the mathematical property as a linear mapping of the Fourier transform, 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 the distance measurement of a closer target.

The length of each sampling period t _N and t _{F in} the short distance measurement mode and the long distance measurement mode determines the maximum measurable distance in each mode. Specifically, the maximum measurable distance _RA in the short distance measurement mode is obtained by dividing the distance for one round trip to the target object obtained by multiplying the sampling period t _N by the speed of light c by 2.
R _A =c·t _N ·/2
(This distance _RA may be referred to as an "ambiguous distance" hereinafter). Similarly, the maximum value R _B of the measurable distance in the long distance measurement mode is
R _B =c·t _F ·/2
Expressed as Further, since the long distance measurement mode has a lower distance measurement resolution than the short distance measurement mode, the lower limit distance R _FC that enables distance detection in the long distance measurement mode enables distance detection in the short distance measurement mode. Is larger than the lower limit distance R _NC .

The process flow of the distance measurement control in the distance measuring device 1 will be described below.
FIG. 4 is a flowchart showing the flow of the entire processing of the measurement control program. In S1, the measurement mode is set to the short distance measurement mode, and in S2, the 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, the distance measurement in the long distance measurement mode is performed. The distance measurement in the short distance measurement mode and the distance measurement in the long distance measurement mode may be performed in reverse order.

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 beat waveform signal data sampled in S52 is digitally filtered. Subsequently, in S53, as shown in FIG. 3, the beat waveform signal data after the filtering process is subjected to the fast Fourier transform process to obtain the data of the frequency spectrum Spm. In S54, the intensity peak having a level equal to or higher than the threshold value LT on the frequency spectrum Spm is extracted and acquired. Then, in S55, the distance R from the acquired frequency value of the intensity peak to the target object is calculated. Short-distance measurement mode The peak intensity level (reception intensity level) L _{N of the} intensity peak and the peak frequency position and the calculated measurement distance R _N are obtained in the short-distance measurement mode result memory 32d in the RAM 32 in the long-distance measurement mode. The intensity peak value L _F , the peak frequency position, and the calculated measurement distance R _F are similarly 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 proper mode determination program 33f is started, and proper mode determination processing is performed. FIG. 6 shows details of the appropriate mode determination process. First, in S101, it is determined whether or not the intensity peak (or measurement distance) was acquired in only one of the short distance measurement mode and the long distance measurement mode. In this case, when the intensity peak acquisition unit can acquire the intensity peak in only one of the short distance measurement mode and the long distance measurement mode, the appropriate mode determination unit sets the mode in which the intensity peak can be acquired as the appropriate mode. The determination process is as follows. As a result, the mode that succeeds in the measurement is automatically set as the proper 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 the calculated distance are stored for both the short distance measurement mode and the long distance measurement mode. Check (that is, whether the distance can be detected). In S102, when only the short distance measurement mode measurement distance R _N is detected, the process proceeds to S103, and the short distance measurement mode is adopted. On the other hand, when the short distance measurement mode measurement distance R _N is not detected in S102 and only the long distance measurement mode measurement distance R _F is detected in 104, the process proceeds to S105, and the long distance measurement mode is adopted. If the measured distance is not detected in either the short distance measurement mode or the long distance measurement mode, the process proceeds to S118 and an error is output.

Subsequently, if the intensity peak (or measurement distance) can be acquired in S101 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 measurement distance R _N and long distance measurement mode measurement distance R _F. Specifically, when the difference |R _F −R _N | between these distances is smaller than a predetermined value ε (for example, 10% of the larger value of R _F and R _N ), the near distance measurement is performed. It is determined that the mode measurement distance R _N and the long distance measurement mode measurement distance R _F are substantially equal. If |R _F −R _N |≧ε in S106 and it is determined that there is a significant difference between the short distance measurement mode measurement distance _RN and the long distance measurement mode measurement distance R _F , the process proceeds to S110. Going forward, the process of comparing the long distance measurement mode measurement distance R _F with the aforementioned ambiguous distance R _A is performed. In the comparison result, the process in the case of R _F >R _A is the process from S111 onward, and the details will be described later.

On the other hand, if R _F ≦R _A in S110, the process proceeds to S113 and thereafter. In the processing, when the intensity peaks can be acquired in both the short distance measurement mode and the long distance measurement mode, the long distance is calculated based on the comparison of the frequency positions of the short distance measurement mode intensity peak and the long distance 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. 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 proper mode. The comparison of the frequency positions of the short-distance measurement mode intensity peak and the long-distance measurement mode intensity peak is performed by comparing and processing the short-distance measurement mode measurement distance R _N and the long-distance measurement mode measurement distance R _F indicated by each frequency position. The above is considered equivalent.

The left side of FIG. 7 shows a case where the microwave transmission wave from the measuring apparatus 1 is normally reflected back by the target object, and the right side thereof is a case where multiple reflection is returned by the target object. When the nth-order multiple reflection MR occurs, the radio flight distance for transmission and reception increases to n times that in the case of the normal reflection SR. Therefore, the measurement distance when the multiple reflection MR occurs is erroneously detected as a value larger than the measurement distance normally measured by the reflection SR. Such multiple reflection tends to occur easily when the target object is present at a relatively short distance in the long distance measurement mode measurement in which the radio wave transmission intensity is large. Therefore, based on the comparison of the frequency positions of the short-distance measurement mode intensity peak and the long-distance measurement mode intensity peak, erroneous detection due to multiple reflection in the long-distance measurement mode is determined, and thus the short-distance measurement is less likely to be affected by multiple reflection. The measurement mode can be automatically set as an appropriate mode, and more reliable distance detection becomes possible.

For example, when |R _F −R _N |<ε as shown in FIG. 8, that is, when it is determined that the short distance measurement mode measurement distance R _N and the long distance measurement mode measurement distance R _F are substantially equal to each other. It can be judged that the possibility of erroneous detection due to multiple reflection 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 a distant target object, and the short-distance measurement mode is suitable for distance measurement for a relatively close target object. Therefore, in FIG. 6, S106. To S107, the short-distance measurement mode measurement distance R _N and the long-distance measurement mode measurement distance R _F are replaced with a representative value (for example, the average value of both (R _F +R _N )/2) to obtain the short-distance and long-distance. A predetermined threshold value R ₀ for distinguishing between and the representative value is compared. If it is determined that the distance is short, the process proceeds to S108 to adopt the short distance measurement mode, and if it is determined to be the long distance, the process proceeds to S109 to adopt the long distance measurement mode.

On the other hand, in S106, |R _F −R _N |≧ε, and in the case of R _F < _{RA in} S110, the multiple reflection determination for the long-distance measurement mode is performed in the following processes in S113. First, _| R F _-R N | a ≧ epsilon state, long distance measurement shown the frequency position of the short distance measurement mode distance R _N and the long distance measurement mode intensity peak indicating the frequency location of the "near measurement mode intensity peaks It means that the difference between the mode distance R _F and the mode distance R _F exceeds a predetermined range ε”, that is, “the condition that a considerable difference occurs 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 the distance can be detected in the long distance measurement mode ( _RN <R _F c ), and the long distance measurement mode distance R _F Is smaller than a predetermined short-distance reference value R ₀ (R _F <R ₀ ), it is determined that the long-distance measurement mode intensity peak is a multiple reflection peak, and the process proceeds to S114 to adopt the short-distance measurement mode. To do.

When the above conditions are met, there are two reasons to consider the result in long-distance measurement mode as multiple reflection:
・ Both of the conditions of R _N <R _F c and R _F <R ₀ indicate that the target object is considerably close to the measuring device, and in the long-distance measurement mode, the high-intensity transmitted wave that leads to multiple reflection is received. In an easy state;
The condition of R _N <R _F c is that the target object detected in the short-distance measurement mode is located closer than the lower limit distance R _F c in the long-distance measurement mode. It means that it should not be done. Nevertheless, the fact that the distance is detected in the long distance measurement mode is considered to be the result of the radio wave flight distance extending beyond the lower limit distance R _FC due to the influence of multiple reflection.

Therefore, by adopting the above method, it is possible to accurately determine the occurrence of multiple reflection in the long distance measurement mode. FIG. 9 shows an example thereof. The long-distance measurement mode distance R _F is almost twice the short-distance measurement mode distance R _N , which corresponds to the case where secondary multiple reflection occurs in the long-distance measurement mode. _That, | R F _-R N |> is epsilon, and because they meet the condition of _R 0> _{R F} and _R Fc> _{R N,} short distance measurement mode is determined that proper mode, near a measure The distance measurement mode distance R _N is adopted.

On the other hand, if one of R _N <R _F c and R _F <R ₀ is not satisfied in S113, it is considered that multiple reflection is unlikely to occur in the long distance measurement mode, and the process proceeds to S115. In this case, of the short-distance measurement mode intensity peak and the long-distance measurement mode intensity peak, the mode in which the reception intensity level is high is determined as the appropriate level. That is, the intensity level (reception intensity level) of the short-distance measurement mode intensity peak is L _N , and the intensity level of the long-distance measurement mode intensity peak is L _{F. When} L _N >L _F , the process proceeds to S116, and the short-distance measurement mode is performed. If not, the process proceeds to S117 to adopt the long-distance measurement mode.

FIG. 10 shows an example thereof, and there is a difference between the long-distance measurement mode distance R _{F and} the short-distance measurement mode distance R _N, and |R _F −R _N |>ε is satisfied. (However, R _F is not an integral multiple of R _N far). _And, although _R 0> R _F is _{satisfied, 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 with each other, and L _N >L _F is satisfied. Therefore, the short-distance measurement mode is determined to be the proper mode, and the measurement is performed. The short range measurement mode distance R _N is adopted as the value.

Returning to FIG. 6, next, in S110, the processing when the long distance measurement mode measurement distance R _F exceeds the ambiguous distance R _A will be described. Situation where a large difference is generated in the long-distance measurement mode measurement distance R _F and near measurement mode measurement distance R _N is not only when the multiple reflection occurs in the long distance measurement mode measurement as described above, near field measurements This may also occur in the case where a target existing slightly farther than the ambiguous distance _RA of the mode measurement is measured smaller than it should be in the short distance measurement mode due to data processing. The details will be described below.

As already described with reference to FIG. 2, one cycle T _N of the linear modulation pattern MPN in the short distance measurement mode is divided into a plurality of sampling periods t _{N in} which the sampling data length is constant. Then, each time a new sampling period t _N arrives within the modulation cycle T _N , data sampling of the beat waveform signal is executed, and the frequency spectrum is updated based on the sampled waveform data. The frequency position corresponding to the starting point of the sampling period t _N gives the zero point of the distance measurement. The frequency position corresponding to the end point of the sampling period t _N corresponds to the maximum measurable distance within the sampling period t _N , that is, the fuzzy distance _RA . At this time, if the radio wave flight time until the transmitted wave is reflected by the target object and returned can be set to be unlimited, the upper limit of the measurable distance is not limited as long as the detection sensitivity of the device is secured. However, if the sampling data length for one distance measurement is limited to a certain value as described above, the upper limit of the measurable distance is also limited by the fuzzy distance _RA .

As shown in FIG. 11, for example, consider a situation in which the target object is present at the maximum distance in the short-distance measurement mode, that is, at a distance R _F ′ that slightly exceeds the fuzzy distance _RA . The frequency shift width wf′ corresponding to the distance R _F ′ is within the frequency shift width Δf _N (FIG. 2) of one period of the modulation pattern MPN, and 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 start point S0 of a certain sampling period is , It will be received at the timing of cutting into the next sampling period. Then, the distance measurement of the target object becomes a form starting from the starting point S0′ of the next sampling period. As a result, the measured distance R _F is calculated based on the frequency shift width wf based on the start point S0′ of the next sampling period and the corresponding radio wave flight time τ _F. and thus are erroneously as the distance R _{F 'value} obtained by subtracting the ambiguity distance R _a from the measurement. At this time, the corresponding intensity peak P _F appears on the distance axis in a form in which the period protruding from the ambiguous distance _RA is folded.

That is, in the short-distance measurement mode, when the target object is present at the position as described above, the measurement distance R _F becomes smaller than the actual distance R _F ′ due to the influence of the ambiguous distance R _A , which causes a malfunction. sell. However, this problem does not occur in principle 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 existence of the target object at a distance farther than the ambiguous distance (maximum distance) R _A , the short distance measurement is performed. When the intensity peak can be acquired in both the long range measurement mode and the long range measurement mode, the short range measurement mode distance is calculated based on the comparison of the frequency position (or measurement distance) between the short range measurement mode intensity peak and the long range measurement mode intensity peak. for R _N it can be determined whether or not the measurement error due to the factors. When it is determined that the measurement is erroneous, the determination is made so that the long distance measurement mode becomes the proper mode.

Specifically, in FIG. 6, the short-distance measurement mode distance R _N calculated based on the frequency position of the short-distance measurement mode intensity peak and the long-distance measurement calculated based on the frequency position of the long-distance measurement mode intensity peak. A difference ε exceeding a predetermined value is generated 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. If it is larger than _A (maximum distance measurable within the sampling period in the short distance measurement mode) ( _RN > _RA :S110→S111), in S111, the short distance measurement mode distance R _N and the maximum distance R _A difference δ between a total value R _N + _RA ×n that is a natural number (n:n≧1) times _A and a long distance measurement mode distance R _F is a predetermined value δ (for example, ( _RN + _RA ×n ) And R _F , such as 10% of the larger value). As described with reference to FIG. 11, the short-distance measurement mode distance R _N approaches the actual distance R _F ′ by adding the ambiguous distance R _A (or the value of R _A ×n) to compensate for the influence of aliasing. Should be. On the other hand, since the long distance measurement mode distance R _F is not affected by the fuzzy distance R _A , if it is considered that this reflects the actual distance R _F ′, the degree of coincidence between R _N +R _A ×n and R _F can be considered. It is possible to accurately determine whether or not the short-distance measurement mode distance R _N is an erroneous measurement derived from the ambiguous distance R _A.

FIG. 12 shows an example of the measurement. In the short-distance measurement mode, the long-distance measurement mode distance R _F shown by the solid line is the short-distance measurement mode distance R _N that has been folded once by the fuzzy 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 considered that the influence of the ambiguous distance is reached, and the process proceeds to S112 to determine that the long distance measurement mode is the proper mode, and the long distance measurement mode distance R _F is adopted as the measurement value. Further, depending on the distance to the target object, the influence of folding may occur a plurality of times (n times: n>2). For example, if the fuzzy distance R _A is 20 m and the target distance is 50 m, the short range measurement mode distance R _N is measured as 10 m, which results in two turns (ie n=2). That is, considering the case where aliasing occurs more than once, while increasing one by one the value of the natural number n at _{S111 | R F - (R N} + R A × n) | values and calculations, n is when a two or more of the values _{| R F - (R n +} R a × n) | < if δ is satisfied, it is considered that the impact of ambiguity distance, the long-distance measurement mode proper mode Make a decision. 12 For example, the long-distance measurement mode distance R _{F 'indicated} by a broken line, the short distance measurement mode, and has a vague distance R _A short distance measurement mode Distance received three times the folded by R _N.

On the other hand, in S111, |R _F −(R _N +R _A ×n)|≧δ, and when there is a non-negligible difference between R _F and (R _N +R _A ), the ambiguous distance R _A It is determined that the defect is not affected by the above, and the process proceeds to S115. The following process is the same as the process performed when it is determined that multiple reflection is unlikely to occur 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 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, Since L _N <L _F , the long distance measurement mode is determined to be the proper mode, and the long distance measurement mode distance R _F is used as the measurement 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, of the stored contents of the result memories 32d and 32e of each mode of FIG. 1, the measured distance determined to be the proper mode is read and output. As shown in FIG. 1, the measurement 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 of FIG. 4, the measurement in the short distance measurement mode and the measurement in the long distance measurement mode are repeated for each distance measurement, and which is the proper mode each time. I was trying to judge repeatedly. However, when the existence condition of the target object for distance measurement does not change frequently, the flow of S1 to S5 in FIG. The measurement may be repeated while maintaining the proper mode determined by the above. 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 proceeds to S8, and a process of determining whether or not to re-determine the proper mode is performed. For example, when the distance measurement result for the target object changes in the approaching direction or the separating direction as the measurement is repeated, the measured distance changes beyond a predetermined threshold value that defines the boundary between the short distance and the long distance. If so, it is determined that it is necessary to re-determine the proper mode in S8. In this case, the process returns to S1 to S5 to perform the proper mode resetting process. On the other hand, if the measured distance does not change beyond the threshold value, it is determined in S8 that the proper mode does not need to be re-determined, the current proper mode is maintained, and the process proceeds to S9 to perform the measurement process of FIG. To do. When the measurement process ends, the process returns to S6 and the result is output.

1 distance measuring device 2 microprocessor unit 3 sensor unit 30 bus 31 CPU
32 RAM
33 ROM
33a Measurement control program 33b Digital filter (for short distance)
33c Digital filter (for long distance)
33d FFT 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 (6)

A signal generator that generates a transmission waveform signal whose frequency is continuously modulated according to a predetermined modulation pattern, and transmits a microwave transmission wave whose frequency is continuously modulated based on the input of the transmission waveform signal, toward a target object. And a transmission output unit for performing the continuous modulation frequency deviation width is set to a first bandwidth, the transmission intensity of the transmission wave is set to a first transmission intensity short-distance measurement mode, the frequency deviation The distance measurement mode in which the transfer width is set to a second bandwidth narrower than the first bandwidth and the transmission strength of the transmission wave is set to a second transmission strength higher than the first transmission strength is A transmitter that is set to be switchable,
A receiving unit for receiving a reflected wave of the microwave transmission wave,
A mixing unit that mixes the transmission waveform signal and a reception waveform signal of the reflected wave by the reception unit, and outputs 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 section having a frequency spectrum generating section for generating a frequency spectrum of, and an intensity peak acquiring section for acquiring an intensity peak for specifying the distance of the target on the frequency spectrum,
A short-distance measurement mode measurement process that causes the signal processing unit to acquire a short-distance measurement mode intensity peak by setting the short-distance measurement mode for the transmission unit and transmitting the microwave transmission wave toward the target object. And a long-distance measurement mode in which the signal processing unit acquires the long-distance measurement mode intensity peak by setting the long-distance measurement mode to the transmission unit and transmitting the microwave transmission wave toward the target object. A measurement control unit that sequentially executes measurement processing,
At least one of the peak frequency position and the reception intensity level is compared between the short-distance measurement mode intensity peak and the long-distance measurement mode intensity peak, and the short-distance measurement mode and the long-distance distance are based on the comparison result. An appropriate mode determination unit that determines which of the measurement modes is an appropriate mode suitable for measuring the distance to the target,
A distance information generation unit that generates distance information to the target object 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,
A distance measuring device comprising: The proper mode determining unit is a mode in which the intensity peak can be acquired when the intensity peak acquiring unit can acquire the intensity peak in only one of the short distance measurement mode and the long distance measurement mode. The distance measuring device according to claim 1, wherein the distance measurement device is determined to be in the proper mode. The proper mode determination unit, when the intensity peak acquisition unit can acquire the intensity peak in both the short distance measurement mode and the long distance measurement mode, the short distance measurement mode intensity peak and the long distance measurement. Based on the comparison of the frequency position with the mode intensity peak, it is determined whether or not 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. The distance measuring device according to claim 1, wherein when the intensity peak is determined to be the multiple reflection peak, the short distance measurement mode is determined to be the proper mode. The proper mode determination unit, on the basis of the frequency position of the short distance measurement mode distance R _N and the long-distance measurement mode intensity peaks the distance information generating unit is generated based on the frequency location of the near measurement mode intensity peaks There is a difference exceeding a predetermined value with the long distance measurement mode distance R _F generated by the distance information generation unit, and further, the short distance measurement mode distance R _N is the distance detection in the long distance measurement mode. When the distance measurement mode distance R _F is smaller than the lower limit distance R _FC and the distance measurement mode distance R _F is smaller than a predetermined short distance reference value R ₀ , the long distance measurement mode intensity peak is the multiple reflection. The distance measuring device according to claim 3, wherein the distance is determined to be a peak. The frequency spectrum generation unit divides each cycle of the linear modulation pattern into a plurality of sampling periods in which the sampling data length is constant, and data of the beat waveform signal each time a new sampling period arrives within the cycle. Sampling is performed, and the frequency spectrum is updated based on the sampled waveform data.
The distance information generation unit associates the frequency position corresponding to the starting point of the sampling period with the zero point of the distance measurement in both the short distance measurement mode and the long distance measurement mode, and corresponds to the end point of the sampling period. It is to generate the distance information to the target object in the form of the frequency position being the maximum distance that can be measured within the sampling period,
The proper mode determination unit, when the intensity peak acquisition unit can acquire the intensity peak in both the short distance measurement mode and the long distance measurement mode, the short distance measurement mode intensity peak and the long distance measurement. Based on the comparison of the frequency position 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 the sampling period. The erroneous measurement is performed while determining whether or not the target is erroneously measured smaller than the actual distance to the target due to the existence of the target farther than the maximum measurable distance. The distance measuring device according to any one of claims 1 to 4, wherein when it is determined that the distance measurement mode is set to the appropriate mode, the distance measurement mode is set to the proper mode. The appropriate mode determination unit, the distance information based on the frequency position of the short distance measurement mode intensity peak and the distance measurement mode intensity peak generated by the distance information generation unit based on the frequency position of the short distance measurement mode intensity peak. A difference exceeding a predetermined value is generated between the long distance measurement mode distance generated by the generation unit, the long distance measurement mode distance is larger than the maximum distance, and the short distance measurement mode distance and When the difference between the long distance measurement mode distance and the total value of the maximum distance multiplied by a natural number is within a predetermined range, the short distance measurement mode distance is determined to be the erroneous measurement. The distance measuring device according to claim 5.

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