JP2015200555A - Distance metrology device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a distance metrology device that can decompose even a wave having a desired wave and a clutter synthesized into two waves, and can meter distances of objects obscured by mists.SOLUTION: A distance metrology device according to the present invention comprises: a projection unit 200 that outputs a transmission wave to a surrounding of an own vehicle; a reception unit 300 that receives a reflection wave of the transmission wave output by the projection unit 200; a detection unit 400 that detects a desired wave corresponding to an object of measurement from the reflection wave received by the reception unit 300; a time counting unit 500 that counts a time when the desired wave is detected on the basis of the detection result of the detection unit 400; and a signal processing unit 100 that estimates a distance to the object of measurement on the basis of the counting result of the time counting unit 500. The detection unit 400 is configured to detect the desired wave corresponding to the object of measurement from the reflection wave on the basis of the reflection wave and an attenuation delay wave having the reflection wave attenuated and delayed by an attenuator 403 and a delay device 402.

Description

The present invention relates to a distance measuring device, and in particular, TOF (Time Of) realized by a time measuring device such as TDC (Time to Digital Converter).
The present invention relates to a multi-echo ranging type radar among the (Flight) type laser radars.

  Conventionally, a TOF (Time Of Flight) method is known as an active laser method for measuring a distance by measuring a round-trip time until light irradiated from a light source is reflected by an object to be measured and returns. In this TOF method, a time-to-digital converter (TDC), which is a device that quantizes analog information of time and digitally outputs it, is used as a means for measuring a short time from when light is irradiated until it is received. There is. The TDC is superior to the ADC (Analog to Digital Converter) in that it has excellent time resolution instead of obtaining the amplitude of the received light waveform, and can output in the order of several tens of ps, for example. In general, in the laser radar TOF method, the distance is calculated by the following equation based on the measurement result of the time difference between the light projection timing and the light reception timing.

(Equation 1)
Distance [m] = speed of light [m / s] × time difference between light projection timing and light reception timing (round trip time) [s] / 2 + (circuit delay, etc.) offset value [m] (Expression 1)
Here, in the laser radar, if there is an influence of weather such as rain, fog, snow, or a light transmitting substance, the reflection of one projection pulse and the reflection by the object to be measured ahead of it are reflected. A situation occurs in which a range of a plurality of received light pulses (echoes) is measured. For example, as shown in FIG. 17, a reflected wave (hereinafter referred to as clutter) due to fog or the like is first detected as a 1st echo, and a reflected wave (hereinafter referred to as desired wave) from a measurement target object (preceding vehicle) hidden behind this fog. May be detected as a 2nd echo. Here, as shown in FIG. 17, when the measurement target object is sufficiently away from the host vehicle, the 1st echo and the 2nd echo are detected as respective waveforms as shown in FIG. On the other hand, when the measurement target object exists at a short distance from the host vehicle, a plurality of received light pulses may be combined and detected as one received light pulse as shown in FIG. At this time, the 1st echo is detected, but the 2nd echo is not detected.

  The TOF method using TDC tends to be superior in distance resolution due to the characteristics of the device as compared with the TOF method using ADC, but the amplitude information of the received light pulse cannot be obtained. For this reason, when the object to be measured exists at a short distance from the host vehicle and two desired waves and clutter are synthesized at the threshold (TDC detection point) as shown in FIG. There are cases where waves cannot be detected.

  Therefore, in the conventional distance measuring apparatus, the time difference between the light projection timing and the light reception timing and the pulse width of the light reception pulse are measured using two upper and lower threshold values, and the received signal of the reflected wave is less than the upper threshold value. If the light receiving pulse width at the lower threshold is equal to or greater than the reference time width, it is determined that the desired wave and the clutter are combined signals of two waves, and distance measurement is not performed (see, for example, Patent Document 1).

JP 2004-184333 A

  However, in the conventional distance measuring device, it can be determined that the two reflected waves are combined, but the two reflected waves cannot be decomposed, and only the signal in which the two reflected waves are combined is excluded from the object to be measured. Therefore, there is still a problem that the object to be measured hidden in fog or the like cannot be measured.

  The present invention solves the conventional problem, and even if the signal is a signal in which the desired wave and the clutter are combined, the desired wave and the clutter can be decomposed and the measurement target object hidden in fog or the like An object of the present invention is to provide a distance measuring device capable of measuring a distance.

  In order to achieve the above object, the present invention provides a light projecting means for outputting a transmission wave around the host vehicle, a light receiving means for receiving a reflected wave of the transmission wave output from the light projecting means, and a reflected wave received by the light receiving means. Detection means for detecting a desired wave corresponding to the measurement target object from, a measurement means for measuring the time when the desired wave is detected based on the detection result of the detection means, and a measurement target object based on the measurement result of the measurement means And detecting means for detecting a desired wave corresponding to the object to be measured from the reflected wave based on the reflected wave and the attenuated delayed wave obtained by attenuating and delaying the reflected wave. It is characterized by.

  According to the present invention, even if the desired wave and the clutter are combined signals, the desired wave and the clutter can be decomposed, and the measurement target object hidden in the fog or the like can be measured. Play.

The block diagram which shows the structure of the distance measuring device which concerns on the 1st Embodiment of this invention. The figure explaining the operation | movement of the time measurement part of FIG. 1 with an image The figure explaining the process in the detection part of FIG. 1 with an image The figure explaining the process by the modification of the detection part of FIG. 1 with an image The figure explaining the measurement conditions by the distance measuring device which concerns on the 1st Embodiment of this invention with an image The block diagram which shows the structure of the distance measuring device which concerns on the 2nd Embodiment of this invention. The figure explaining the process in the detection part of FIG. 6 with an image The flowchart figure of the process which selects a desired wave from the two-wave synthetic | combination light reception pulse by the distance measuring device which concerns on the 2nd Embodiment of this invention. The block diagram which shows the structure of the distance measuring device which concerns on the 3rd Embodiment of this invention. The figure explaining the process in the detection part of FIG. 9 with an image The flowchart figure of the process which selects a desired wave from the two-wave synthetic | combination light reception pulse by the distance measuring device which concerns on the 3rd Embodiment of this invention. The block diagram which shows the modification of the detection part of FIG. The block diagram which shows the structure of the distance measuring device which concerns on the 4th Embodiment of this invention. The flowchart figure of the process which selects a desired wave from the two-wave synthetic | combination light reception pulse by the distance measuring device which concerns on the 4th Embodiment of this invention. The block diagram which shows the structure of the distance measuring device which concerns on the 5th Embodiment of this invention. The figure explaining the process in the detection part of FIG. 15 with an image Diagram explaining multi-echo ranging with an image The figure which explains the light reception pulse which is synthesized 2 waves with the image

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram showing the configuration of the distance measuring apparatus according to the first embodiment of the present invention. In FIG. 1, the distance measuring device includes a signal processing unit 100, a light projecting unit 200, a light receiving unit 300, a detecting unit 400, and a time measuring unit 500.

  In the distance measuring device according to the first embodiment of the present invention, the light projecting unit 200 outputs a transmission wave (light projecting pulse) around the host vehicle in accordance with a command from the signal processing unit 100. The transmission wave output from the light projecting unit 200 is reflected by the surrounding object 600, and the light receiving unit 300 receives the reflected wave (light reception pulse) from the reflection object 600. The reflected wave received by the light receiving unit 300 is input to the detection unit 400. The detection unit 400 detects whether or not the amplitude of the input waveform exceeds a predetermined low threshold value (first threshold value). Here, the Low threshold value is a threshold value used for normal distance measurement (corresponding to the conventional threshold value shown in FIGS. 17 and 18), can detect a measurement target object up to a distance as a distance measurement target, and is noise. The predetermined threshold value is set so as not to be affected by. The time measurement unit 500 measures the time when the amplitude of the reflected wave received by the light receiving unit 300 exceeds a predetermined Low threshold from the detection result of the detection unit 400. The signal processing unit 100 estimates the distance to the reflective object 600 using the measurement result and the Low threshold as appropriate. The reflective object 600 includes a measurement target object or clutter such as rain, fog, and snow. Here, the meaning of exceeding the Low threshold may be greater than the Low threshold, or may be greater than or equal to the Low threshold. That is, the presence or absence of an equal sign is a design item that can be selected as appropriate, and does not affect the essence of the invention. The same applies to the following description.

  Next, the internal configuration of the distance measuring device will be described.

  The signal processing unit 100 includes, for example, a CPU and a memory, and performs various arithmetic processes. The signal processing unit 100 outputs a timing signal of the projection pulse to the projection unit 200 and the time measurement unit 500.

  The light projecting unit 200 is, for example, a laser radar capable of performing three-dimensional distance measurement by irradiating laser light at a wide angle, and includes an LD driving circuit 201 and an LD (Laser Diode) 202. The LD drive circuit 201 drives the LD 202 based on the timing signal of the light projection pulse input from the signal processing unit 100. The LD 202 reflects laser light (light projection pulse) to a mirror (not shown) that rotates according to the control of the LD drive circuit 201 and irradiates the reflected light around the host vehicle.

  The light receiving unit 300 includes a light receiving element 301 and a current / voltage conversion unit 302. The light receiving element 301 acquires the laser beam reflected from the object 600 around the host vehicle and converts it into a current pulse. The current / voltage conversion unit 302 is composed of, for example, a transimpedance amplifier, and converts the current pulse input from the light receiving element 301 into a voltage pulse.

  The detection unit 400 includes an amplification unit 401, a first delay unit 402, a first attenuator 403, a first adder 404, a first zero cross detector 405, and a second delay unit 406. , A first comparator 407 and a first AND circuit 408. The amplifier 401 amplifies the voltage pulse input from the current / voltage converter 302 and outputs the amplified signal from the branch 1 to the branch 3. Since the signals input from the branch 1 to the branch 3 are signals corresponding to the reflected wave of the object 600, the input signal may be expressed as a reflected wave below.

In branch 1, first, the first delay device 402 delays the reflected wave and outputs the delayed wave. Here, for example, a delay line is used as the delay device, but the present invention is not limited to this, and other configurations may be used. The first attenuator 403 attenuates the input delayed wave and outputs the attenuated delayed wave to the first adder 404. Here, for example, a resistor is used as the attenuator, but the present invention is not limited to this, and another configuration may be used.

  In branch 2, the reflected wave is input to the first adder 404. The first adder 404 inverts and adds the reflected wave to the input attenuated delayed wave. The addition result is output to the first zero cross detector 405. The first zero cross detector 405 detects a point at which the waveform input from the first adder 404 zero-crosses. In particular, the first zero cross detector 405 detects a point at which zero crossing occurs from negative to positive. The first zero cross detector 405 detects a section where the waveform is zero crossed and has a positive value. The first zero cross detector 405 outputs this detection result to the first AND circuit 408.

  In branch 3, the second delay device 406 delays the reflected wave and outputs a delayed wave. The first comparator 407 compares this delayed wave with a predetermined Low threshold value, and detects a pulse (Low echo) that is equal to or higher than the Low threshold value. The first comparator 407 outputs this detection result to the first AND circuit 408. The first AND circuit 408 compares the detection result input from the first zero-crossing detector 405 with the detection result input from the first comparator 407 and outputs a signal that is both positive to the time measuring unit 500. Output to.

The time measuring unit 500 includes a first zero cross time measuring unit 501. The first zero cross time measuring unit 501 calculates a time difference between the rising edge (light reception timing) of the pulse input from the first AND circuit 408 and the rising edge (light projection timing) of the light projection pulse input from the signal processing unit 100. Digitally output to the signal processing unit 100. As shown in FIG. 2, this time difference is reflected by the laser beam (light projection pulse) from the LD 202 and reflected by the object 600 as the measurement target object, and the reflected light (light reception pulse) is received by the light receiving element 301. The round trip time of the optical pulse until it is performed is shown. Based on this time difference, the signal processing unit 100 calculates the distance from the host vehicle to the object from the above equation (1). Further, the signal processing unit 100 calculates the rising and falling times of the received light pulse as the pulse width. Next, a method for decomposing a desired wave from a received light pulse in which the desired wave and clutter are combined will be described. FIG. 3 is a diagram for explaining the processing in the detection unit 400 of FIG. 1 with an image. FIG. 4 is a diagram for explaining the processing by the modification of the detection unit in FIG.
Hereinafter, the pulse after being amplified by the amplification unit 401 of the detection unit 400 is simply referred to as a light reception pulse.

  As shown in FIG. 3, the waveform (1) of the received light pulse output from the amplifying unit 401 is a waveform in which a desired wave is synthesized after clutter. In the waveform (2) output from the first adder 404, the delayed delayed wave delayed and attenuated by the first delay unit 402 and the first attenuator 403 in the branch 1 and the waveform of the branch 2 are inverted. A waveform obtained by adding the inverted wave. The waveform (3) output from the first zero-cross detector 405 is a pulse waveform in which a positive portion of zero or more is extracted from the added waveform shown in the waveform (2). Here, one pulse including the zero cross point shown in the figure is output originally, but particularly in a region where no pulse exists, a portion where the waveform fluctuates near zero due to the influence of noise is also output as a pulse. There is. In the waveform (4) output from the first comparator 407, a pulse in which a portion exceeding the Low threshold is extracted from the delayed wave delayed by the second delay device 406 in the branch 3 by the first comparator 407. It has a waveform. The waveform (5) output from the first AND circuit 408 is a pulse waveform obtained by the logical product of the pulse of the waveform (3) and the pulse of the waveform (4). Thereby, a noise component can be removed from the waveform (3).

At this time, the delay time of the second delay unit 406 of the branch 3 is the delay time of the first delay unit 402 of the branch 1 so that the threshold judgment waveform of the branch 3 and the zero cross point of the branches 1 and 2 are likely to overlap. It is better to set it to about half of the time. On the other hand, when such a setting is performed, it may be assumed that the detection accuracy deteriorates due to variations in delay time. Therefore, the configuration shown in FIG. 4 may be modified. FIG. 4 is a diagram for explaining the processing according to the modification of the detection unit in FIG. 1 with an image. In FIG. 4, a third delay unit 410 is provided in the branch 1, and the third delay unit 410 is shared with the branch 3. The third delay unit 410 corresponds to the second delay unit 406 provided in the branch 2. Then, the degree of delay of the first delay unit 402 in the branch 1 is reduced by an amount corresponding to the second delay unit 406. As described above, by sharing the third delay unit 410 between the branch 1 and the branch 3, it is possible to improve resistance to variations in delay time.

  In the present embodiment, the first attenuator 403 is provided in the branch 1, but another configuration may be used. For example, the first attenuator 403 may not be provided in the branch 1 but an amplifying unit may be provided in the branch 2. It suffices that at least the input waveform of branch 1 is attenuated relative to the input waveform of branch 2. Subsequent embodiments may be similarly replaced.

  Here, the measurement conditions in this embodiment will be described. FIG. 5 is a diagram illustrating an image of measurement conditions by the distance measuring apparatus according to the first embodiment of the present invention.

  As shown in FIG. 3, the received light pulse is input from the branch 1 to the branch 3 in a state where the clutter such as fog and two desired waves of the measurement target object are combined.

  Here, in general, the reflectivity of the clutter is sufficiently lower than the reflectivity of the desired wave of the measurement target object. Therefore, when the distance between the measurement target object and the clutter is so close that the two waves are combined, The pulse amplitude value becomes sufficiently larger than the pulse amplitude value of the clutter. However, the pulse amplitude value of the clutter increases as it is under the influence (hereinafter referred to as a bad environment) due to assumed rain, fog, snow, or the like. For example, in the case of fog, the amplitude of clutter increases exponentially as visibility decreases in dense fog as shown in FIG. For this reason, it becomes difficult to distinguish from the desired wave, and the estimation accuracy of the distance of the measurement target object also deteriorates. Therefore, a bad environment detection means (not shown) is provided.

  The bad environment detection means may detect the bad environment by detecting at least one operation of, for example, a dense fog sensor, a rain sensor, a wiper, or a fog lamp, or may be bad by detecting a pattern from a camera image analysis or a laser radar scanning measurement result. The environment may be detected. When the bad environment detection means detects that the host vehicle is in a bad environment, the signal processing unit 100 does not estimate the distance to the measurement target object, and the bad environment detection means detects that the host vehicle has a bad environment. The distance to the measurement target object may be estimated only when it is detected that it is not below. For example, as illustrated in FIG. 5, the signal processing unit 100 does not estimate the distance to the measurement target object for the A region having a clutter amplitude value higher than the bad environment threshold, and the clutter amplitude value lower than the bad environment threshold The distance to the measurement target object may be estimated only for the B region. This bad environment threshold or a value obtained by adding a predetermined margin to this bad environment threshold is set as the High threshold.

Here, the High threshold value is larger than the Low threshold value, and is set higher than the strength of the adverse environment, in other words, the clutter amplitude value in the adverse environment. Note that the high threshold value may be set to the value of the saturation level of the device of the light receiving unit 300. The strength of the bad environment has at least a function of the environment. The environmental function is, for example, a function having visibility as a variable in the case of dense fog and a particle size or rainfall intensity as a variable in the case of rain, but is not limited thereto. The environment function may be switched according to the assumed environment. Further, the strength of the bad environment may have a function of the optical characteristics of the distance measuring device. For example, the function of optical characteristics is a function according to the optical characteristics and circuit characteristics of the light projecting unit 200 and the light receiving unit 300, but is not limited thereto.

  Further, it may further comprise notification means for notifying that the host vehicle is in a bad environment when the bad environment detection unit detects that the host vehicle is in a bad environment.

As described above, according to the first embodiment of the present invention, the received light pulse delayed and attenuated by delaying and attenuating the received light pulse of branch 1 and adding branch 2 to branch 1 is normally It is possible to detect a point that becomes higher with respect to the received light pulse. In other words, the waveform of the desired wave on the back side can be raised as a positive value out of the combined waveform of the desired wave and the fog clutter. Therefore, even when two waves of the desired wave and the fog clutter are combined, the desired wave hidden behind the fog can be reliably detected. Further, by adopting a configuration in which the same waveform is attenuated and compared as in the first embodiment of the present invention, the zero cross point serving as a reference for distance measurement is not affected by the amplitude of the received light pulse, and distance measurement is performed. Accuracy is improved.
(Second Embodiment)
Next, a second embodiment will be described. Note that detailed description of the same configuration and processing as those in the first embodiment is omitted, and only the reference numerals are given. The same applies to the following embodiments.

  FIG. 6 is a block diagram showing the configuration of the distance measuring apparatus according to the second embodiment of the present invention.

  As shown in FIG. 6, the distance measuring device according to the second embodiment is further provided with a branch 4 in addition to the first embodiment described above, and outputs the amplified signal amplified by the amplifying unit 401 to the branch 4. Further, a second comparator 411 is provided, and the second comparator 411 detects a pulse (High echo) equal to or higher than the High threshold by comparing the reflected wave input from the branch 4 with a predetermined High threshold.

  The second comparator 411 outputs this detection result to the time measurement unit 500. The time measuring unit 500 further includes a high threshold time measuring unit 502. The high threshold time measuring unit 502 calculates a time difference between the rising edge of the pulse input from the second comparator 411 (light reception timing) and the rising edge of the light projection pulse input from the signal processing unit 100 (light projection timing). Digital output to 100.

  Here, the high threshold value is the same value as in the first embodiment, but is set to a value close to the saturation level of the light receiving unit 300, for example, and higher than the assumed clutter amplitude value in a bad environment. The Alternatively, it may be set to a value lower than the minimum amplitude value of the desired wave of the measurement target object located at a position closer than the closest distance of the clutter. The closest distance of the clutter is a distance stored in advance as a measurement result closest to the host vehicle among the occurrence positions of the clutter measured for each clutter intensity. The second comparator 411 can detect a pulse that exceeds the high threshold as a desired wave when the desired wave is present at a shorter distance than the clutter by the set high threshold. The desired wave of the measurement target object at a shorter distance than the clutter is detected when the high threshold value is exceeded. On the other hand, all the desired waves with low amplitude that do not exceed the High threshold are located at a distance farther than the clutter. Here, since the reflectance of the clutter is sufficiently smaller than the reflectance of the desired wave of the measurement target object, the desired wave at a shorter distance than the clutter generally has an amplitude sufficiently higher than that of the clutter. For this reason, the High threshold value is set to a value higher than the clutter amplitude value in a bad environment and lower than the minimum amplitude value of the desired wave at the closest distance of the clutter. The minimum amplitude value of the desired wave is determined by setting the object to be measured at the closest distance of the above-mentioned clutter for each reflectance and the range and incident angle where the spot light of the laser beam hits the object to be measured. The lowest of the measurement results of the desired wave when placed is stored in advance.

Next, processing for detecting a desired wave from a waveform synthesized by two waves by the distance measuring apparatus according to the second embodiment will be described. FIG. 7 is a diagram for explaining the processing in the detection unit of FIG. 6 with an image. In the following description, a route through which the received light pulse is input to each branch after output from the amplification unit 401 is a route A, and a route through which the light is output from the first AND circuit 408 and input to the first zero cross time measurement unit 501 is a route. B, a path output from the second comparator 411 and input to the high threshold time measuring unit 502 will be described as a path C.

  In FIG. 7, (1) when the desired wave is generated near the clutter and the desired wave is saturated due to high reflectivity, (2) the desired wave is generated farther than the clutter and the desired wave is highly reflected. When the frequency is saturated due to the rate, (3) when the desired wave is generated farther than the clutter and the desired wave is not saturated with low reflectance, the processing in the paths A to C will be described.

  First, the case of (1) will be described. In the path A, a desired wave extends to cover the entire clutter. In this case, in the path B, a pulse erroneously detected is output in a state where the zero cross point deviates backward from the original position of the desired wave due to the influence of the extended desired wave. Even in this case, in the path C, a pulse equal to or higher than the High threshold is output, and a desired wave is detected. Therefore, in this case, the signal processing unit 100 can accurately estimate the distance to the measurement target object by performing distance measurement using the second measurement time measured by the High threshold time measurement unit 502. it can.

  The case (2) will be described. In the path A, the desired wave extends so as to partially cover the rear side of the clutter. Also in the path B in this case, as in (1), a pulse erroneously detected is output under the influence of the extended desired wave and the zero cross point deviates backward from the original position of the desired wave. Even in this case, in the path C, as in (1), a pulse equal to or higher than the High threshold is output, and a desired wave is detected. Therefore, in this case as well, the signal processing unit 100 can accurately estimate the distance to the measurement target object by performing distance measurement using the second measurement time measured by the high threshold time measurement unit 502. it can.

  The case (3) will be described. In the path A, the desired wave and the clutter have a combined waveform. In this case, in the path B, the desired wave is detected by the zero cross point as in the first embodiment. In this case, the path C does not output a pulse higher than the High threshold. Therefore, in this case, the signal processing unit 100 performs distance measurement using the first zero cross time measurement time measured by the first zero cross time measurement unit 501, thereby accurately estimating the distance to the measurement target object. can do.

  From such a relationship, the signal processing unit 100 performs the following processing. FIG. 8 is a flowchart of a process for detecting a desired wave from a received light pulse obtained by synthesizing two waves of the desired wave and the clutter by the distance measuring apparatus according to the second embodiment of the present invention.

  As shown in FIG. 8, in step S801, the signal processing unit 100 determines whether or not the difference between the first zero-cross measurement time and the second measurement time is within a certain time. In other words, it is determined whether there is a high echo associated with the echo from which the zero cross point is detected. Specifically, the signal processing unit 100 compares the first zero-cross measurement time measured by the first zero-cross time measurement unit 501 with the second measurement time measured by the high threshold time measurement unit 502. Then, it is determined whether or not the difference in measurement time is within a certain time.

When YES is determined in the step S801, it is highly likely that the received light pulse is in a state as shown in (1) or (2) in FIG. 7, and therefore, the signal processing unit 100 selects the high echo as shown in the step S802. . Specifically, the signal processing unit 100 estimates the measurement time measured by the high threshold time measurement unit 502 as the measurement time of the desired wave. On the other hand, if NO in step S801, the light reception pulse is likely to be in the state as shown in (3) of FIG. 7, and therefore, as shown in step S803, the signal processing unit 100 performs an echo in which the zero cross point is detected. Select. Specifically, the signal processing unit 100 estimates the measurement time measured by the first zero cross time measurement unit 501 as the measurement time of the desired wave.

  Then, as shown in step S804, the signal processing unit 100 performs distance measurement using the measurement time estimated in step S802 or step S803, and estimates the distance to the measurement target object.

According to the present embodiment, even when the desired wave and the clutter are synthesized by the high threshold value, the desired wave having a high amplitude can be detected separately from the clutter. In addition, since the threshold and the dynamic range are set so that the desired wave at a shorter distance than the clutter has an amplitude higher than the High threshold, detection of the desired wave at a shorter distance than the clutter by providing the branch 4 Accuracy can be improved. Further, even if the received light pulse is saturated and the waveform may be extended, the provision of the branch 4 can reduce erroneous detection of the desired wave.
(Third embodiment)
In addition to the above-described embodiment, a distance measuring device according to a third embodiment will be described. FIG. 9 is a block diagram showing a configuration of a distance measuring apparatus according to the third embodiment of the present invention.

  As shown in FIG. 9, the distance measuring device according to the third embodiment is further provided with branches 5 and 6 in addition to the above-described embodiment. In the branch 5, the amplified signal amplified by the amplification unit 401 is input to the fourth delay device 412. The delayed wave delayed by the fourth delay unit 412 is input to the second adder 414. In branch 6, the amplified signal amplified by amplification section 401 is input to second attenuator 413. The attenuation wave attenuated by the second attenuator 413 is input to the second adder 414.

  The second adder 414 inverts and adds the attenuated wave input from the second attenuator 413 to the delayed wave input from the fourth delay unit 412. The addition result is output to the second zero cross detector 415.

  The second zero cross detector 415 detects a point at which the waveform input from the second adder 414 zero-crosses. In particular, the second zero cross detector 415 detects a point at which zero crossing occurs from negative to positive. The second zero cross detector 415 detects a section where the waveform is zero crossed and has a positive value. The second zero cross detector 415 outputs this detection result to the second AND circuit 416. The second AND circuit 416 compares the detection result input from the second zero-cross detector 415 with the detection result input from the first comparator 407 and outputs a signal that is both positive to the time measuring unit 500. Output to.

  The time measuring unit 500 further includes a second zero cross time measuring unit 503. The second zero cross time measuring unit 503 calculates a time difference between the rising edge (light receiving timing) of the pulse input from the second AND circuit 416 and the rising edge (light emitting timing) of the light projection pulse input from the signal processing unit 100. Digitally output to the signal processing unit 100.

  Next, processing for detecting a desired wave from a waveform synthesized by two waves by the distance measuring apparatus according to the third embodiment will be described. FIG. 10 is a diagram for explaining the processing in the detection unit of FIG. 9 with an image. In the following description, a route through which the received light pulse is input to each branch after output from the amplification unit 401 is a route A, and a route through which the light is output from the first AND circuit 408 and input to the first zero cross time measurement unit 501 is a route. B, a path output from the second AND circuit 416 and input to the second zero cross time measuring unit 503 will be described as a path C.

  In FIG. 10, (1) when the desired wave is generated near the clutter and the desired wave is saturated due to high reflectivity, (2) the desired wave is generated farther than the clutter and the desired wave is highly reflected. When the frequency is saturated due to the rate, (3) when the desired wave is generated farther than the clutter and the desired wave is not saturated with low reflectance, the processing in the paths A to C will be described.

  First, the case of (1) will be described. In the path A, a desired wave extends to cover the entire clutter. In this case, in the path B, a pulse erroneously detected is output in a state where the zero cross point deviates backward from the original position of the desired wave due to the influence of the extended desired wave. On the other hand, in the path C, the zero cross point of the waveform obtained by adding the inverted attenuation wave to the delay wave is detected, and the pulse detected at the original position of the desired wave is output. Therefore, in this case, the signal processing unit 100 accurately estimates the distance of the measurement target object by performing distance measurement using the second zero cross time measurement unit 503 measured by the second zero cross time measurement unit 503. be able to. In the case of (1), the measurement time measured for the zero-cross point of the waveform of the path B and the measurement time measured for the zero-cross point of the waveform of the path C have a large time difference of about the saturation period of the desired wave. .

  The case (2) will be described. In the path A, the desired wave extends so as to partially cover the rear side of the clutter. Also in the path B in this case, as in (1), a pulse erroneously detected is output under the influence of the extended desired wave and the zero cross point deviates backward from the original position of the desired wave. Even in this case, in the path C, as in (1), the zero cross point of the waveform obtained by adding the inverted attenuation wave to the delay wave is detected, and is detected at the original position of the desired wave. Pulse is output. Therefore, in this case, the signal processing unit 100 accurately estimates the distance of the measurement target object by performing distance measurement using the second zero cross time measurement unit 503 measured by the second zero cross time measurement unit 503. be able to. In the case of (2), as in the case of (1), the measurement time measured for the zero-cross point of the waveform of the path B and the measurement time measured for the zero-cross point of the waveform of the path C There is a large time difference of about the saturation period.

  Next, the case of (3) will be described. In the path A, the desired wave and the clutter have a combined waveform. In this case, in the path B, the desired wave is detected by the zero cross point as in the first embodiment. In this case, on the path C, clutter is detected by the zero cross point. Therefore, in this case, the signal processing unit 100 accurately estimates the distance of the measurement target object by performing distance measurement using the first zero cross measurement time measured by the first zero cross time measurement unit 501. be able to. In the case of (3), the measurement time measured for the zero-cross point of the waveform of the path B and the measurement time measured for the zero-cross point of the waveform of the path C are compared with the cases of (1) and (2). The time difference is small.

  From such a relationship, the signal processing unit 100 performs the following processing. FIG. 11 is a flowchart of processing for detecting a desired wave from a light reception pulse obtained by synthesizing two waves of the desired wave and the clutter by the distance measuring apparatus according to the third embodiment of the present invention.

  As shown in FIG. 11, as shown in step S <b> 1101, the signal processing unit 100 measures the first zero cross measurement time measured by the first zero cross time measurement unit 501 and the second zero cross time measurement unit 503. The time difference of the echo (rise) from the measured second zero cross measurement time is calculated.

  Next, as shown in step S1102, the signal processing unit 100 determines whether or not the time difference calculated in step S1101 is a predetermined value or more.

  When YES in step S1102, there is a high possibility that the received light pulse is in the state as shown in (1) or (2) of FIG. 10, and therefore, as shown in step S1103, the signal processing unit 100 performs the second zero crossing time. The second zero cross measurement time measured by the measurement unit 503 is estimated as the measurement time of the desired wave.

  On the other hand, when NO in step S1102, there is a high possibility that the received light pulse is in the state as shown in (3) of FIG. 10, and therefore, as shown in step S1104, the signal processing unit 100 includes the first zero-cross time measuring unit. The first zero cross measurement time measured by 501 is estimated as the measurement time of the desired wave.

  Then, as shown in step S1105, the signal processing unit 100 performs distance measurement using the measurement time estimated in step S1103 or step S1104, and estimates the distance to the measurement target object.

  According to the present embodiment, even when the desired wave and the clutter are combined, it is possible to detect the desired wave having a high amplitude separately from the clutter. Further, since the threshold value and the dynamic range are set so that the desired wave in front of the clutter has an amplitude higher than the High threshold value, by providing the branches 5 and 6, the desired wave located behind the clutter Detection accuracy can be improved. Even if the received light pulse is saturated and the waveform is extended, the erroneous detection of the desired wave can be reduced by providing the branches 5 and 6. In particular, as in the second embodiment, instead of using the measurement time measured by the high threshold time measurement unit 502 when the high threshold is exceeded, the first zero cross measurement time and the second zero cross measurement time are used. Since the zero cross point is always selected depending on the time difference, the distance measurement accuracy can be improved as compared with the second embodiment.

  In the distance measuring device according to the third embodiment of the present invention, the time difference between the first zero-cross measurement time and the second zero-cross measurement time is calculated, but the first zero-cross measurement time and the second zero-cross measurement time are calculated. In selecting the time, the selection is not necessarily limited to this time difference, and may be made by another method. FIG. 12 is a block diagram illustrating a modification of the detection unit of FIG.

As shown in FIG. 12, in the distance measuring apparatus according to the third embodiment, a branch 7 may be further provided. In the branch 7, the amplified signal amplified by the amplification unit 401 is input to the state determination comparator 417. The state determination comparator 417 determines whether or not the received light pulse exceeds the high threshold. When a signal exceeding the High threshold is input from the state determination comparator 417, the signal processing unit 100 estimates that the desired wave is saturated, selects the second zero-cross measurement time, and selects the High threshold. When a signal exceeding the threshold value is not input, the second zero cross measurement time may be selected by estimating that the desired wave is not saturated.
(Fourth embodiment)
In addition to the above-described embodiment, a distance measuring device according to a fourth embodiment will be described.

  FIG. 13 is a block diagram showing a configuration of a distance measuring apparatus according to the fourth embodiment of the present invention.

As shown in FIG. 13, in the distance measuring device according to the fourth embodiment, in addition to the above-described embodiment, a branch 8 is further provided, and the amplified signal amplified by the amplification unit 401 is output to another amplification unit 418. . An amplified signal amplified by the amplifying unit 418 so as to have a higher gain than the other branches is output to the second comparator 411. The second comparator 411 compares the reflected wave input from the branch 8 with a predetermined high threshold value and detects a pulse (High echo) that is equal to or higher than the high threshold value. The high threshold time measuring unit 502 measures the time exceeding the high threshold based on the pulse detected by the second comparator 411, and outputs the second measurement time to the signal processing unit 100. Note that although the amplification unit 418 is provided here, the High threshold value of the second comparator 411 may be set to a lower threshold value.

  Next, processing for detecting a desired wave from a waveform obtained by synthesizing two waves of the desired wave and the clutter by the distance measuring apparatus according to the fourth embodiment will be described. FIG. 14 is a flowchart of a process of selecting a desired wave from the two-wave synthesized light reception pulse by the distance measuring apparatus according to the fourth embodiment of the present invention.

  As shown in step S1401, the signal processing unit 100 first estimates the distance of the measurement target object based on the first zero cross measurement time input from the first zero cross time measurement unit 501.

  Next, as shown in step S1402, the signal processing unit 100 determines whether the first zero-cross measurement time is longer than a predetermined time. In other words, the signal processing unit 100 determines whether or not the measurement target object is within a predetermined short distance.

  If YES in step S1402, that is, if it is assumed that the measurement target object is at a long distance, as shown in step S1403, the signal processing unit 100 selects the second measurement time. Then, the signal processing unit 100 estimates the distance of the measurement target object based on the second measurement time.

  On the other hand, if NO in step S1402, that is, if it is assumed that the measurement target object is at a short distance, the signal processing unit 100 selects the first zero-cross measurement time as shown in step S1404. Then, the signal processing unit 100 estimates the distance to the measurement target object based on the first zero cross measurement time.

  As described above, according to the distance of the measurement target object, by using either the first zero cross measurement time or the second measurement time to estimate the distance of the measurement target object, the adder is used. It is possible to suppress the deterioration of the S / N ratio caused by combining the waveforms into positive and negative.

Since the first adder 404 relatively attenuates the positive-side amplitude used for detecting the desired wave, the S / N ratio may be deteriorated. This can also reduce the detectable distance. On the other hand, clutter with low reflectivity is likely to occur at a short distance. For these reasons, with regard to the short distance where the two-wave synthesis of the desired wave and the clutter is likely to occur, the long distance where the two-wave synthesis of the desired wave and the clutter is unlikely to occur using the first zero cross measurement time. With respect to, by measuring each distance using the second measurement time, it is possible to maintain a detectable distance by suppressing the deterioration of the S / N ratio.
(Fifth embodiment)
In addition to the above-described embodiment, a distance measuring device according to a fifth embodiment will be described. FIG. 15 is a block diagram showing a configuration of a distance measuring apparatus according to the fifth embodiment of the present invention. On the other hand, FIG. 16 is a diagram for explaining the processing in the detection unit of FIG. As shown in FIG. 15, in the distance measuring device of the fifth embodiment, branches 9 and 10 are further provided in addition to the above-described embodiment.

The third adder 420 is provided in an arrangement in which the positive and negative are reversed with respect to the first adder 404. Specifically, the third adder 420 inverts the attenuated delayed wave input from the branch 1 via the first delay unit 402 and the second attenuator 403 to the reflected wave input from the branch 2. And add. This addition result is input to the third zero cross detector 421 to detect a zero crossing point. That is, in the above-described embodiment, branch 2 is subtracted (inverted addition) from branch 1, whereas in this embodiment, branch 1 is subtracted (inverted addition) from branch 2. The zero cross point is detected.

  In the branch 9, a delayed wave delayed by the first delay unit 402 is output from between the first delay unit 402 and the second attenuator 403 in the branch 1. This delayed wave is input to the fourth adder 423.

  In the branch 10, the amplified signal amplified by the amplification unit 401 is input to the fourth attenuator 422. The attenuation wave attenuated by the third attenuator 422 is input to the fourth adder 423. The fourth adder 423 inverts and adds the attenuated wave input from the third attenuator 422 to the delayed wave input from the first delay unit 402. Then, the fourth zero cross detector 424 detects a zero crossing point from the addition result.

  Then, the AND circuit 408 compares the detection result of the third zero cross detector 421 and the detection result of the fourth zero cross detector 424, and outputs a signal that is both positive to the time measurement unit 500. The first zero cross time measuring unit 501 is a signal processing unit that calculates a time difference between the rising edge of the pulse input from the AND circuit 408 (light reception timing) and the rising edge of the light projection pulse input from the signal processing unit 100 (light projection timing). Digital output to 100.

  Next, processing for detecting a desired wave from a waveform obtained by synthesizing two waves of the desired wave and the clutter by the distance measuring device according to the fifth embodiment will be described. FIG. 16 is a diagram for explaining the processing in the detection unit of FIG. 15 with an image. In the following description, a path where a received light pulse is input to each branch after output from the amplification unit 401 is a path A, and a path output from the third zero cross detector 421 and input to the first AND circuit is a path B. , A path C output from the fourth zero cross detector 424 and input to the first AND circuit, and a path output from the first AND circuit 408 and input to the first zero cross time measuring unit 501. This will be described as route D.

  As shown in FIG. 16, the path A has a waveform obtained by combining two desired waves and clutter. In this case, in the path B, a falling point that switches from positive to negative is detected as the third zero-crossing point from the addition result of the third adder 420. In the path C, a rising point that switches from negative to positive is detected from the addition results of the fourth adder 423 as the fourth zero cross point. In the path D, a pulse obtained from the logical product of the pulse input from the path B and the pulse input from the path C is detected. The rising point of the detection pulse of the path D indicates the position of the clutter, and the falling point indicates the position of the desired wave.

  Therefore, according to the embodiment of the present invention, the signal processing unit 100 performs distance measurement using the first zero-cross measurement time measured by the first zero-cross time measurement unit 501, so that the clutter and the desired wave are detected. It is possible to accurately estimate the distance to the measurement target object. It is also possible to estimate the distance to the clutter.

  Further, the signal processing unit 100 can determine whether or not the desired wave is extended by the length W of the pulse width of the pulse input from the path D. For example, when the pulse width is equal to or greater than a predetermined threshold, the signal processing unit 100 determines that the desired wave is extended. As a result, the functions of the second comparator 411 and the state determination comparator 417 for detecting whether or not the high threshold value is exceeded can be substituted, so that the size and the apparatus can be simplified.

  As described above, according to the present embodiment, it is possible to determine whether or not the desired wave and the clutter are combined by a simple system, and when the desired wave and the clutter are combined, the desired wave hidden in the clutter can be specified. it can.

  In addition, this invention is not limited to the above-mentioned structure, A various deformation | transformation is possible in the range which does not deviate from the summary of invention. Moreover, the said embodiment is shown as an example and is not intending limiting the range of invention.

  The distance measuring device according to the present disclosure includes a light projecting unit that outputs a transmission wave around the host vehicle, a light receiving unit that receives a reflected wave of the transmission wave output from the light projecting unit, and a reflected wave received by the light receiving unit. A detection unit that detects a desired wave corresponding to a measurement target object; a measurement unit that measures a time when the desired wave is detected based on a detection result of the detection unit; and a measurement result of the measurement unit, Estimating means for estimating the distance to the measurement target object, and the detection means is based on the reflected wave and the attenuated delayed wave obtained by attenuating and delaying the reflected wave from the reflected wave to the measurement target object. A corresponding desired wave is detected.

  Further, in the distance measuring apparatus, the detecting means may invert and add the reflected wave to the attenuated delayed wave and detect a point at which the addition result crosses zero.

  In the distance measuring apparatus, the detecting unit may detect a point where the addition result zero-crosses from negative to positive.

  In the distance measuring apparatus, the detection means includes a first delay unit that delays the reflected wave, a first attenuator that attenuates a delayed wave delayed by the delay unit, and the first delay. A first adder that inverts and adds the reflected wave to the attenuated delayed wave that is attenuated and delayed by the first attenuator and a first point that detects a zero-crossing point of the addition result by the first adder. You may make it have a zero cross detection part.

  In the distance measuring device, the detection means includes a first comparator that detects whether or not a predetermined first threshold is exceeded, and a second delay that delays a reflected wave input to the first comparator. A delay unit, and a first filter unit that outputs an overlapping portion of the range exceeding the first threshold detected by the first comparator and the detection result of the first zero-cross detection unit. Also good.

  In the distance measuring apparatus, at least a part of the first delay device and the second delay device may be shared.

  In the distance measuring apparatus, the detection unit includes a second comparator that detects whether or not a predetermined second threshold value that is larger than the first threshold value is exceeded, and the second threshold value is It is set higher than the clutter amplitude value in a bad environment, the measurement means measures the time when the reflected wave exceeds the second threshold value, and the estimation means determines the measurement target object based on the measurement result. May be estimated.

  In the distance measuring apparatus, the detection means inverts and adds the reflected wave to the attenuated delayed wave, and a first zero cross point where the addition result is zero-crossed and a delayed wave obtained by delaying the reflected wave The attenuation wave obtained by attenuating the reflected wave is inverted and added, and a second zero cross point at which the addition result zero-crosses is detected, and the measuring means detects the time at which the first zero cross point is detected. The time when the second zero cross point is detected may be measured, and the estimation unit may estimate the distance to the measurement target object based on the measurement result.

In the distance measuring apparatus, the detection means includes a third delay device that delays the reflected wave, a second attenuator that attenuates the reflected wave, and an attenuation attenuated by the second attenuator. A second adder that inverts the wave and adds it to the delayed wave delayed by the third delay unit; and a second zero-cross detection unit that detects a point at which the addition result by the second adder zero-crosses A range exceeding the first threshold detected by the first comparator and a second filter unit that outputs an overlapping portion of the detection result of the second zero-cross detection unit may be provided.

  Further, in the distance measuring device, the detection unit includes a state determination comparator that detects whether or not a predetermined second threshold value that is larger than the first threshold value is exceeded, and the second threshold value is It is set higher than the clutter amplitude value in a bad environment, and the estimation means detects the time when the first zero cross point is detected and the second zero cross point based on the detection result of the state determination comparator. Alternatively, the distance to the measurement target object may be estimated by selecting any of the determined times.

  The distance measuring apparatus may further include an amplifying unit that amplifies the reflected wave input to the second comparator, and the estimation unit is a measurement result of a time when the reflected wave exceeds the second threshold value. If the distance estimated based on is a predetermined distance or more, this distance is estimated as the distance to the measurement target object, and is estimated based on the measurement result of the time when the reflected wave exceeds the second threshold When the measured distance is a short distance less than a predetermined distance, the distance estimated based on the reflected wave and the attenuated delayed wave obtained by attenuating and delaying the reflected wave may be estimated as the distance to the measurement target object. .

  In the distance measuring apparatus, the detection means includes a first delay unit that delays the reflected wave, a first attenuator that attenuates a delayed wave delayed by the delay unit, and the first delay. A third adder for inverting the attenuated delayed wave attenuated and delayed by the first attenuator and adding it to the reflected wave, and a third for detecting a point where the addition result by the third adder crosses zero. A zero cross detector, a third attenuator for attenuating the reflected wave, a first attenuator attenuated by the third attenuator and added to the delayed wave delayed by the first delayer. 4, a fourth zero-cross detection unit that detects a point where the addition result by the fourth adder zero-crosses, a detection result of the third zero-cross detection unit, and detection of the fourth zero-cross detection unit Get duplicate result A third filter portion that, may have a.

  The distance measuring apparatus further includes a bad environment detection means for detecting whether or not the host vehicle is in a bad environment, and the estimation means is such that the bad environment detection means is not in a bad environment. The distance to the object to be measured is detected, and when the bad environment detecting means detects that the host vehicle is in a bad environment, the distance to the reflecting object is not estimated. It may be a feature.

  The distance measurement device may further include a notification unit that notifies that the host vehicle is in a bad environment when the hostile environment detection unit detects that the host vehicle is in a hostile environment. .

  The distance measuring device of the present invention is useful as a distance measuring device that measures multi-echo among laser radars of TOF (Time Of Flight) system realized by a time measuring device such as TDC (Time to Digital Converter).

DESCRIPTION OF SYMBOLS 100 Signal processing part 200 Light projection part 201 LD drive circuit 202 LD
300 light receiving unit 301 light receiving element 302 current / voltage converting unit 400 detecting unit 401, 418 amplifying unit 402, 406, 410, 412 delay unit 403, 413, 422 attenuator 404, 414, 420, 423 adder 405 first zero cross Detector 407 First comparator 408, 416 AND circuit 411 Second comparator 415 Second zero cross detector 417 State determination comparator 421 Third zero cross detector 424 Fourth zero cross detector 500 Time measurement unit 501 First Zero cross time measurement unit 502 High threshold time measurement unit 503 Second zero cross time measurement unit

Claims (14)

A light projecting means for outputting a transmission wave around the vehicle;
A light receiving means for receiving a reflected wave of the transmission wave output by the light projecting means;
Detecting means for detecting a desired wave corresponding to the object to be measured from the reflected wave received by the light receiving means;
Measuring means for measuring the time when the desired wave is detected based on the detection result of the detecting means;
An estimation unit that estimates a distance to the measurement target object based on a measurement result of the measurement unit;
The detection means detects a desired wave corresponding to the object to be measured from the reflected wave based on the reflected wave and an attenuated delayed wave obtained by attenuating and delaying the reflected wave. .   2. The distance measuring apparatus according to claim 1, wherein the detecting means inverts and adds the reflected wave to the attenuated delayed wave, and detects a point where the addition result crosses zero.   The distance measuring apparatus according to claim 2, wherein the detection unit detects a point where the addition result zero-crosses from negative to positive. The detection means includes
A first delay device for delaying the reflected wave;
A first attenuator for attenuating the delayed wave delayed by the delay unit;
A first adder that inverts and adds the reflected wave to the attenuated delayed wave attenuated and delayed by the first delay unit and the first attenuator;
4. The distance measuring device according to claim 1, further comprising: a first zero-cross detection unit that detects a point at which the addition result obtained by the first adder zero-crosses. 5. The detection means includes
A first comparator for detecting whether a predetermined first threshold is exceeded;
A second delay device for delaying a reflected wave input to the first comparator;
The first filter unit that outputs an overlapping portion between a range exceeding the first threshold detected by the first comparator and a detection result of the first zero-cross detection unit. The distance measuring device according to any one of 1 to 4.   6. The distance measuring apparatus according to claim 5, wherein at least a part of the first delay device and the second delay device are shared. The detection means includes a second comparator that detects whether or not a predetermined second threshold value greater than the first threshold value is exceeded,
The second threshold is set to be higher than the clutter amplitude value in a bad environment,
The measuring means measures a time when the reflected wave exceeds the second threshold;
The distance measuring device according to claim 5 or 6, wherein the estimating means estimates a distance to the measurement target object based on the measurement result. The detecting means inverts and adds the reflected wave to the attenuated delayed wave, and attenuates the reflected wave to a first zero cross point where the addition result zero-crosses and a delayed wave obtained by delaying the reflected wave Inverting and adding the attenuation wave, and detecting the second zero-crossing point where the addition result zero-crosses,
The measuring means measures the time when the first zero-cross point is detected and the time when the second zero-cross point is detected;
The distance measuring apparatus according to claim 1, wherein the estimating unit estimates a distance to the measurement target object based on the measurement result. The detection means includes
A third delay device for delaying the reflected wave;
A second attenuator for attenuating the reflected wave;
A second adder for inverting the attenuated wave attenuated by the second attenuator and adding the inverted wave to the delayed wave delayed by the third delay device;
A second zero-cross detection unit that detects a point where the addition result by the second adder zero-crosses;
The second filter unit that outputs an overlapping portion between a range exceeding the first threshold detected by the first comparator and a detection result of the second zero-cross detection unit. 9. The distance measuring device according to 8. The detection means includes a state determination comparator that detects whether or not a predetermined second threshold value greater than the first threshold value is exceeded.
The second threshold is set to be higher than the clutter amplitude value in a bad environment,
The estimation means selects either the time when the first zero-cross point is detected or the time when the second zero-cross point is detected based on the detection result of the state determination comparator, and the measurement target The distance measuring apparatus according to claim 8, wherein a distance to the object is estimated. An amplifying unit for amplifying the reflected wave input to the second comparator;
When the distance estimated based on the measurement result of the time when the reflected wave exceeds the second threshold is a predetermined distance or more, the estimation means estimates the distance as the distance to the measurement target object. When the distance estimated based on the measurement result of the time when the reflected wave exceeds the second threshold is a short distance less than a predetermined distance, the reflected wave and the attenuated delayed wave obtained by attenuating and delaying the reflected wave The distance measuring apparatus according to claim 7, wherein the distance estimated based on the estimated distance is a distance to the measurement target object. The detection means includes
A first delay device for delaying the reflected wave;
A first attenuator for attenuating the delayed wave delayed by the delay unit;
A third adder that inverts the attenuated delayed wave attenuated and delayed by the first delay unit and the first attenuator and adds the inverted delayed wave to the reflected wave;
A third zero-cross detection unit for detecting a point where the addition result by the third adder zero-crosses;
A third attenuator for attenuating the reflected wave;
A fourth adder that inverts the attenuated wave attenuated by the third attenuator and adds the inverted wave to the delayed wave delayed by the first delay device;
A fourth zero-cross detection unit for detecting a point where the addition result by the fourth adder zero-crosses;
4. The apparatus according to claim 1, further comprising: a third filter unit that obtains an overlapping portion of the detection result of the third zero-cross detection unit and the detection result of the fourth zero-cross detection unit. The described distance measuring device. It further includes a bad environment detection means for detecting whether or not the host vehicle is in a bad environment,
The estimation means estimates the distance to the measurement target object when the adverse environment detection means detects that the own vehicle is not in an adverse environment, and the adverse environment detection means causes the own vehicle to be in an adverse environment. 13. The distance measuring device according to claim 1, wherein when the presence is detected, the distance to the reflecting object is not estimated.   14. The distance according to claim 13, further comprising notification means for notifying that the host vehicle is in a bad environment when the bad environment detection unit detects that the host vehicle is in a bad environment. measuring device.