JP2015194356A - Distance measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a distance measurement device which, even if a desired wave and a clutter are synthesized, can be decomposed into two waves and can measure range of an object hidden behind fog or the like.SOLUTION: The distance measurement device includes: a light projection part 200 for outputting a transmission wave around an own vehicle; a light reception part 300 for receiving a refection wave of the transmission wave outputted by the light projection part 200; a time measurement part 500 for measuring the time in which the amplitude of the reflection wave received by the light reception part 300 exceeds a first predetermined threshold value and the time exceeding a second threshold value larger than the first threshold value; and a signal processing part 100 for estimating a distance up to a reflection object on the basis of a measurement result of the time measurement part 500. The second threshold value is set higher than a clatter amplitude value under adverse environment. The signal processing part 100 estimates the distance up to the measurement object on the basis of the first threshold value and the second threshold value.

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] = light speed [m / s] × time difference between light projection timing and light reception timing (round trip time) [s] / 2 + (circuit delay etc.) offset value [m] (Equation 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. 13, 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. 13, when the measurement target object is sufficiently away from the host vehicle, as shown in FIG. 14A, the 1st echo and the 2nd echo are detected as respective waveforms. On the other hand, when the measurement target object exists at a short distance from the host vehicle, a plurality of light reception pulses may be combined and detected as one light reception 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 of 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. Based on the measurement result of the measurement means, the measurement means for measuring the time when the amplitude of the signal exceeds the predetermined first threshold, and the time when the amplitude exceeds the second threshold greater than the first threshold. An estimation means for estimating the distance, wherein the second threshold is set to be higher than the clutter amplitude value in a bad environment, and the estimation means determines the distance to the measurement target object based on the first threshold and the second threshold. Is estimated.

  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 1st method which decomposes | disassembles a desired wave from the received light pulse by which 2 waves were combined by the distance measuring device which concerns on the 1st Embodiment of this invention 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 flowchart figure of the 3rd method which decomposes | disassembles a desired wave from the light reception pulse by which 2 distance synthesis | combination by the distance measuring device which concerns on the 3rd Embodiment of this invention was carried out. The figure explaining the 3rd method which decomposes | disassembles a desired wave from the light reception pulse by which 2 distance synthesis | combination by the distance measuring device which concerns on the 3rd Embodiment of this invention was carried out with an image. 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 4th method which decomposes | disassembles a desired wave from the light reception pulse by which 2 distance synthesis | combination was carried out by the distance measuring device which concerns on the 4th Embodiment of this invention. The figure explaining the worst case of the two-wave synthetic | combination light reception pulse assumed with the distance measuring device which concerns on the 4th Embodiment of this invention with an image The figure explaining the gain of the sensitivity time adjustment circuit of 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 light reception pulse by which the 2 wave synthesis | combination assumed with the distance measuring device which concerns on the 5th Embodiment of this invention was combined 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 determines whether the amplitude of the input waveform exceeds a predetermined low threshold (first threshold) and whether the amplitude exceeds a predetermined high threshold (second threshold) that is greater than the low threshold. Detect whether or not. Here, the Low threshold value is a threshold value used for normal distance measurement (corresponding to the conventional threshold value shown in FIG. 14), can detect the measurement target object up to the distance to be a distance measurement target, and is affected by noise. The predetermined threshold is set so as not to be received. The time measuring unit 500 measures the time when the amplitude of the reflected wave received by the light receiving unit 300 exceeds a predetermined Low threshold and the time when the reflected wave received by the light receiving unit 300 exceeds the High 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, the Low threshold value, and the High threshold value 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 or the High threshold may be greater than the Low threshold or the High threshold, or may be greater than or equal to the Low threshold or the High 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 comparator 402, and a second comparator 403. The amplifier 401 amplifies the voltage pulse input from the current / voltage converter 302 and outputs the amplified signal to the first comparator 402 and the second comparator 403. The first comparator 402 compares this amplified signal with a predetermined high threshold value, and detects a pulse (high echo) equal to or higher than the high threshold value. On the other hand, the second comparator 403 compares the amplified signal with a predetermined low threshold value, and detects a pulse (Low echo) that is equal to or higher than the low threshold value.

The time measurement unit 500 includes a high threshold time measurement unit 501 and a low threshold time measurement unit 502. The high threshold time measurement unit 501 and the low threshold time measurement unit 502 are input from the rising edge (light reception timing) of each pulse input from the first comparator 402 and the second comparator 403 and from the signal processing unit 100, respectively. The time difference from the rise of the light projection pulse (light projection timing) is digitally output to the signal processing unit 100. As shown in FIG. 2, this time difference is the light from when the laser beam (projection pulse) is irradiated from the LD 202 and reflected by the object 600 until the reflected light (received pulse) is received by the light receiving element 301. Indicates the round trip time of the pulse. 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 in image form a first method for decomposing a desired wave from a received pulse in which the desired wave and clutter are combined by the distance measuring apparatus according to the first embodiment of the present invention. Moreover, FIG. 4 is a figure explaining the measurement conditions by the distance measuring device based on the 1st Embodiment of this invention with an image. 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 received light pulse is input to the first comparator 402 and the second comparator 403 in a state in which clutter such as fog and two desired waves of the measurement target object are combined. Here, the High threshold value set by the first comparator 402 is higher than the intensity of the assumed influence (hereinafter referred to as a bad environment) due to rain, fog, snow, or the like, in other words, the clutter amplitude value in the bad environment. Is set. 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. Thus, by setting the High threshold value higher than the clutter amplitude value in a bad environment, the pulse amplitude of the clutter does not exceed the High threshold value, and only the pulse amplitude of the measurement target object exceeds the High threshold value. For this reason, when the first comparator 402 detects that the received light pulse has exceeded the high threshold, the signal processing unit 100 uses the time measured by the high threshold time measuring unit 501 as the round trip time from the measurement target object. Estimate the distance of the object to be measured.

  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, Since the pulse amplitude value is sufficiently larger than the pulse amplitude value of the clutter, the high threshold value can be easily set. However, the pulse amplitude value of the clutter becomes larger as the environment is worse. For example, in the case of fog, as shown in FIG. 4, the visibility of clutter increases exponentially as visibility decreases in dense fog. For this reason, it becomes difficult to set a high threshold value that can be gradually distinguished 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) may be 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 shown in FIG. 4, 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 value, and the clutter amplitude value lower than the bad environment threshold value. 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 above-mentioned High threshold. 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, it is possible to determine whether the clutter and the desired wave are combined even in a bad environment such as fog, and the desired wave and the clutter are combined. Even if it is a signal, the desired wave and the clutter can be decomposed, and the object to be measured hidden in the fog can be measured.
(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.

In the distance measuring apparatus according to the second embodiment, in addition to the first embodiment described above, the High threshold value is 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. May be set. 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. With this set High threshold, the first comparator 402 can detect a pulse exceeding the High threshold as a desired wave when there is a desired wave at a shorter distance than the clutter. 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.
(Third embodiment)
In addition to the above-described embodiment, the distance measurement apparatus of the third embodiment estimates the peak amplitude value of a desired signal having a low amplitude that does not exceed the High threshold. At this time, as a peak amplitude value of a desired wave having a low amplitude that does not reach the High threshold value, a fixed value that can be taken in a range where the desired wave and one pulse of the clutter are not more than the High threshold value and not less than the Low threshold value may be used. This fixed value is set to an intermediate value between the High threshold and the Low threshold, for example.

  The signal processing unit 100 calculates a pulse width of at least one desired wave or clutter from a pulse in which the desired wave and the clutter are synthesized based on the peak amplitude value of the desired wave having a low amplitude that does not reach the high threshold and the low threshold. presume. The signal processing unit 100 estimates the pulse width with reference to the received light pulse shape determined by the circuit characteristics of the light projecting unit 200 and the light receiving unit 300. For example, the signal processing unit 100 stores in advance an approximate expression in which the pulse width of the received light pulse shape is a function of the amplitude, and uses this approximate expression and the ratio of the low threshold value to the peak amplitude value to thereby calculate the pulse width at the low threshold value. Is estimated. When the pulse width of the desired wave of the measurement target object is set as the first estimated pulse width W1, and the pulse width of the clutter is set as the second estimated pulse width W2, this approximate expression is exemplified by the following expression.

(Expression 2) W1 = A1 × f ₁ (Vlow / Vamplitude) (2)

(Expression 3) W2 = A2 × f ₂ (Vlow / Vamplitue) Equation (3)
However, Vlow is a low threshold value [V], Vamplit is a peak amplitude value [V], A1 is a constant determined by the pulse shape of the desired wave, and A2 is a constant determined by the pulse shape of the clutter. In the present embodiment, the approximate expression is used for the estimation of the pulse width. However, the pulse width may be estimated by mapping the received light pulse shape other than the approximate expression.

Here, a specific operation of the distance measuring apparatus according to the present embodiment will be described. FIG. 5 is a flowchart of a third method for decomposing a desired wave from a light-receiving pulse in which the desired wave and clutter are combined by the distance measuring apparatus according to the third embodiment of the present invention. FIG. 6 is a diagram for explaining in image form a third method for decomposing a desired wave from a light reception pulse in which the desired wave and clutter are combined by the distance measuring apparatus according to the third embodiment of the present invention. First, as shown in step S501, the signal processing unit 100 determines whether there is a high echo associated with the low echo from the measurement results of the high threshold time measurement unit 501 and the low threshold time measurement unit 502. Specifically, when there is a timing that exceeds the High threshold within a predetermined time from a timing that exceeds the Low threshold, it is determined that there is a High echo associated with the Low echo. If YES in step S501, it can be determined that the received light pulse is a combination of the desired wave and the clutter, and the signal processing unit 100 selects the high echo as the desired wave as shown in step S502, as shown in step S503. Ranging processing is performed with the measurement time of the high threshold. As a result, the desired wave hidden in the clutter can be identified. On the other hand, in the case of NO in step S501, as shown in step S504, the signal processing unit 100 determines whether or not the calculated received light pulse width is larger than the second estimated pulse width W2 represented by the above equation (3). judge. In the case of NO in step S504, the signal processing unit 100 can determine that only one desired wave is selected, selects the low echo as the desired wave as shown in step S505, and sets the low threshold value as shown in step S503. Ranging is performed at the measurement time. On the other hand, if YES in step S504, it can be determined that the desired pulse and clutter are combined in the received light pulse, and the signal processing unit 100 desires a value obtained by subtracting the first estimated pulse width W1 from the falling edge of the received light pulse. It is estimated as the wave measurement time, and the distance measurement process is performed with the estimated measurement time as shown in step S503. Thereby, the distance of the desired wave hidden behind the clutter can be estimated. 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 to specify the desired wave hidden in the clutter when the desired wave and the clutter are combined. Can do.
(Fourth embodiment)
In addition to the above-described embodiment, the distance measurement device of the fourth embodiment measures the peak amplitude value of a desired signal having a low amplitude that does not exceed the High threshold. Specifically, in the distance measuring apparatus according to the fourth embodiment, as shown in FIG. 7, a peak amplitude acquisition unit 700 that acquires a peak amplitude value of a low-amplitude desired wave that does not reach the high threshold, and a detection unit 400 And an STC (Sensitive Time Control) 404 that is a sensitivity time adjustment circuit that adjusts the gain of the amplified wave amplified by the amplification unit 401.

The peak amplitude acquisition unit 700 includes a peak hold circuit 701 and an ADC 702. The peak hold circuit 701 peaks and holds the adjustment wave adjusted by the STC 404. The ADC 702 acquires a peak value from the peak-held waveform and outputs the acquired peak value to the signal processing unit 100. The operating frequency of the peak amplitude acquisition unit 700 is set lower than the frequency of the received light pulse waveform. The STC 404 is provided before the first comparator 402 and the second comparator 403, and as the time difference between the timing signal of the projection pulse input from the signal processing unit 100 and the amplified wave input from the amplification unit 401 becomes larger ( Relatively increase the gain (as the distance to the object to be measured increases). As shown in FIG. 7, the gain displacement amount is a predetermined distance range (short distance) in the vicinity of the host vehicle where the presence of the clutter is assumed, or a predetermined distance far from the host vehicle where the presence of the desired wave is assumed. The bias may be given so as to be relatively lower than the gain in the distance range (medium distance). In this case, the ratio of the gain displacement amount is set to, for example, the ratio between the High threshold and the Low threshold. In addition, you may displace by another method, for example, you may displace linearly. Since the operating frequencies of the peak hold circuit 701 and the ADC 702 are lower than the frequency of the received light pulse waveform, when the amplitude of the clutter is higher than that of the desired wave, the peak amplitude acquisition unit 700 cannot obtain the peak amplitude value of the desired wave. There is a fear. However, according to the distance measuring apparatus of the present embodiment, the STC 404 increases the gain of the desired wave at medium distance relative to the clutter, so that the peak amplitude value of the desired wave is made larger than the peak amplitude value of the clutter. be able to. As a result, the peak amplitude acquisition unit 700 can acquire the peak amplitude value of the desired wave.

  Here, a specific operation of the distance measuring apparatus according to the present embodiment will be described. FIG. 8 is a flowchart of a fourth method for decomposing a desired wave from a light receiving pulse in which the desired wave and clutter are combined by the distance measuring apparatus according to the fourth embodiment of the present invention. In the present embodiment, since the peak amplitude value acquired by the peak amplitude acquisition unit 700 is set to be the peak amplitude value of the desired wave, it is necessary to assume the pulse width of the clutter as in the third embodiment. Absent. First, as shown in step S801, the signal processing unit 100 determines whether there is a high echo associated with the low echo from the measurement results of the high threshold time measurement unit 501 and the low threshold time measurement unit 502. Specifically, when there is a timing exceeding the High threshold within a predetermined period from a timing exceeding the Low threshold, it is determined that there is a High echo associated with the Low echo. If YES in step S801, it can be determined that the received light pulse is a combination of the desired wave and the clutter, and the signal processing unit 100 selects the high echo as the desired wave as shown in step S802, as shown in step S803. Ranging processing is performed with the measurement time of the high threshold. As a result, the desired wave hidden in the clutter can be identified. On the other hand, in the case of NO in step S801, as shown in step S804, the signal processing unit 100 determines whether or not the calculated received light pulse width is larger than the first estimated pulse width W1 represented by the above equation (2). judge. In the case of NO in step S804, the signal processing unit 100 can determine that only one desired wave is selected, selects the low echo as the desired wave as shown in step S805, and sets the low threshold value as shown in step S803. Ranging is performed at the measurement time. On the other hand, if YES in step S804, it can be determined that the received light pulse is composed of the desired wave and the clutter, and the signal processing unit 100 desires a value obtained by subtracting the first estimated pulse width W1 from the falling edge of the received light pulse. It is estimated as the wave measurement time, and the distance measurement process is performed with the estimated measurement time as shown in step S803. As a result, the distance of the desired wave hidden behind the clutter can be estimated. 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 to specify the desired wave hidden in the clutter when the desired wave and the clutter are combined. Can do. In particular, it is not necessary to use a high-speed ADC having a high operating frequency in order to improve distance measurement accuracy, and the degree of freedom in design can be improved.

Thus, in this embodiment, the gain displacement is set so that the peak amplitude acquisition unit 700 whose operating frequency is slower than the frequency of the received light pulse waveform can reliably detect the desired wave. This is to make it possible to cope with the worst case as shown in FIG. In FIG. 9, the clutter peak amplitude value Pc is substantially the same as the high threshold value, the desired wave peak amplitude value Pd is substantially the same as the low threshold value, and two waves are combined. In this case, as shown in FIG. 10, the gain displacement of the STC 404 is set to High / Low or higher with respect to the gain G in the PWcf from the measurement time of the peak amplitude value Pc of the clutter to the measurement time of the peak amplitude value Pd of the desired wave. It only has to be set.
(Fifth embodiment)
In addition to the above-described embodiment, in the distance measuring device according to the fifth embodiment, as shown in FIG. 11, a third comparator that detects whether or not the received light pulse has exceeded a third threshold value lower than the Low threshold value. 405 and a third threshold time measuring unit 503. The third threshold time measurement unit 503 is a time difference between the rise of each pulse (light reception timing) input from the third comparator 405 and the rise of the light projection pulse (light projection timing) input from the signal processing unit 100. Is digitally output to the signal processing unit 100. The signal processing unit 100 includes the distance measurement result of the falling of the Low threshold acquired from the second comparator 403 and the Low threshold time measuring unit 502, and the first distance acquired from the third comparator 405 and the third threshold time measuring unit 503. Based on the distance measurement result of the falling of the threshold value of 3, as shown in FIG. 12, the slope of the fall of the received pulse in which the desired wave and the clutter are combined (the slope of the fall of the desired wave) is calculated. The peak amplitude value of the desired wave that does not reach the high threshold is estimated from the slope of the desired wave. Then, the signal processing unit 100 estimates a value obtained by subtracting the first estimated pulse width W1 from the fall of the received light pulse as the measurement time of the desired wave. The specific process is the same as the process described with reference to FIG. 8 of the fourth embodiment, and thus detailed description thereof is omitted.

  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, it is not necessary to use a high-speed ADC having a high operating frequency in order to increase the distance measurement accuracy, and the degree of freedom in design can be improved.

  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.

  For example, in the third embodiment, in order to measure and estimate the peak amplitude value of a low-amplitude desired wave that does not exceed the High threshold, the peak amplitude value of the low-amplitude desired wave that does not reach the High threshold is used. Although a fixed value that can be taken in a range where the desired wave and one pulse of clutter are not more than the high threshold and not less than the low threshold is used, other methods may be used. For example, the desired wave may be specified by using the STC 404 of the fourth embodiment and amplifying the desired wave and correcting it so as to exceed the High threshold. According to this, it is not necessary to use the peak amplitude acquisition unit 700 used in the fourth embodiment, and the apparatus can be simplified and miniaturized.

  In the fourth embodiment, the STC 404 is used to adjust the gain of the desired wave according to the measurement time as shown in FIG. 10, but other methods may be used without using the STC 404. For example, the high threshold value may be lowered according to the measurement time. Specifically, the high threshold value may be maintained until the measurement time of the peak amplitude value Pc of the clutter of FIG. 10 and then gradually decreased until the measurement time of the peak amplitude value Pd of the desired wave. Specifically, the graph shape of the gradually increasing gain between Pc to Pd in FIG. 10 is inverted with the gain G as the center, and the curve shape becomes convex. It is desirable to suppress this. However, the method of gradual reduction is not necessarily limited to this method. For example, it may be gradually decreased after the measurement time of Pd, or the lower limit of the gradual decrease of the High threshold may be set as the Low threshold. In this case, the signal processing unit 100 controls the voltage value of the high threshold applied to the first comparator 402. According to such adjustment of the high threshold value, the STC 404 need not be used, and the apparatus can be simplified and downsized.

  The distance measuring device according to the present disclosure includes a light projecting unit that outputs a transmission wave around the 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. Based on the measurement result of the measurement means and the measurement result of the measurement means for measuring the time when the amplitude exceeds the predetermined first threshold and the time when the amplitude exceeds the second threshold greater than the first threshold, And the second threshold value is set to be higher than the clutter amplitude value in a bad environment, and the estimation means measures based on the first threshold value and the second threshold value. Estimate the distance to the target object.

  In the distance measuring apparatus, the detection unit further detects whether the amplitude of the reflected wave received by the light receiving unit exceeds the first threshold and whether the amplitude exceeds the second threshold. The measuring means includes the first threshold or the output from the light projecting means when the detecting means detects that the amplitude of the reflected wave exceeds the first threshold or the second threshold. You may measure the time until it exceeds the said 2nd threshold value.

In the distance measuring apparatus, the estimating unit may estimate a distance corresponding to a time exceeding the second threshold as a distance to the measurement target object.

  Further, in the distance measuring apparatus, the estimation unit detects that the amplitude of the reflected wave received by the light receiving unit exceeds the first threshold and does not exceed the second threshold. Then, based on a predetermined amplitude value that is an intermediate value between the first threshold value and the second threshold value, and the first threshold value, the pulse width of the reflected wave of the measurement target object or the pulse width of the clutter is calculated. Based on the estimated pulse width and the pulse width of the period exceeding the first threshold measured by the measuring means, whether or not the reflected wave and the clutter of the measurement target object are combined. You may judge.

  In the distance measurement device, when the estimation unit determines that the reflected wave and the clutter of the measurement target object are combined, the estimated pulse width and the first threshold value measured by the measurement unit are determined. The distance of the object to be measured may be estimated based on the pulse width in a period exceeding.

  In the distance measuring apparatus, the second threshold value may be set to a value lower than a minimum amplitude value of a reflected wave of a measurement target object located at a position closer than a closest distance of the clutter.

  The distance measurement apparatus further includes a peak amplitude acquisition unit that acquires a peak amplitude value of a reflected wave received by the light receiving unit, and the estimation unit includes the peak value acquired by the peak amplitude acquisition unit, Based on the threshold value of 1, it may be determined whether the reflected wave of the measurement target object and the clutter are combined.

  In the distance measuring apparatus, the detection unit includes an amplification unit that amplifies the reflected wave received by the light receiving unit, a sensitivity time adjustment circuit that adjusts the gain of the amplified wave amplified by the amplification unit, and the sensitivity time. The first and second comparators for comparing the adjustment wave adjusted by the adjustment circuit and the first and second thresholds, respectively, and the peak amplitude acquisition unit is adjusted by the sensitivity time adjustment circuit You may have a peak hold circuit which carries out peak hold of the adjustment wave, and ADC which acquires a peak value from this peak hold waveform.

  In the distance measuring apparatus, the sensitivity time adjustment circuit increases the gain according to the time from the timing at which the light projecting means transmits the transmission wave to the timing at which the light receiving means receives the reflected wave, and the peak amplitude is increased. The operating frequency of the acquisition unit may be lower than the frequency of the reflected wave received by the light receiving means.

  Further, in the distance measuring apparatus, the estimation unit estimates the pulse width of the reflected wave of the measurement target object based on the peak value acquired by the peak amplitude acquisition unit and the first threshold, and the estimation is performed. Based on the pulse width and the pulse width of the period exceeding the first threshold measured by the measuring means, it may be determined whether or not the reflected wave of the measurement target object and the clutter are combined.

  In the distance measurement device, when the estimation unit determines that the reflected wave and the clutter of the measurement target object are combined, the estimated pulse width and the first threshold value measured by the measurement unit are determined. The distance of the object to be measured may be estimated based on the pulse width in a period exceeding.

  Further, in the distance measuring apparatus, the measuring means includes a first time when the amplitude of the reflected wave received by the light receiving means is equal to or lower than the first threshold, and a third threshold smaller than the first threshold. The following second time may be measured, and the estimation means may estimate the distance of the measurement target object based on the first time and the second time.

  In the distance measuring apparatus, the estimation unit estimates a pulse width of the measurement target object based on the first time and the second time, and the estimated pulse width and the measurement unit measure the pulse width. It may be determined whether or not the reflected wave and the clutter of the measurement target object are combined based on the pulse width of the period exceeding the first threshold.

  In the distance measurement device, when the estimation unit determines that the reflected wave and the clutter of the measurement target object are combined, the estimated pulse width and the first threshold value measured by the measurement unit are determined. The distance of the object to be measured may be estimated based on the pulse width in a period exceeding.

  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. Is detected, and when the bad environment detection means detects that the host vehicle is in a bad environment, the distance to the reflective object is not estimated. Also good.

  The distance measurement apparatus 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 amplifying unit 402 first comparator 403 second comparator 404 STC
405 Third comparator 500 Time measurement unit 501 High threshold time measurement unit 502 Low threshold time measurement unit 503 Third threshold time measurement unit 700 Peak amplitude acquisition unit 701 Peak hold circuit 702 ADC

Claims (16)

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;
Measuring means for measuring the time when the amplitude of the reflected wave received by the light receiving means exceeds a predetermined first threshold and the time when the amplitude exceeds a second threshold greater than the first threshold;
An estimation unit that estimates a distance to a reflecting object based on a measurement result of the measurement unit;
The second threshold is set to be higher than the clutter amplitude value in a bad environment,
The estimation means estimates a distance to a measurement target object based on the first threshold value and the second threshold value. Detecting means for detecting whether the amplitude of the reflected wave received by the light receiving means exceeds the first threshold and whether the amplitude exceeds the second threshold;
The measuring means detects the first threshold value or the first threshold value from the time when the light projecting means outputs when the detecting means detects that the amplitude of the reflected wave exceeds the first threshold value or the second threshold value. The distance measuring device according to claim 1, wherein a time until a threshold value of 2 is exceeded is measured.   The distance measuring apparatus according to claim 1, wherein the estimating unit estimates a distance corresponding to a time exceeding the second threshold as a distance to a measurement target object.   The estimating means detects the first threshold when the detecting means detects that the amplitude of the reflected wave received by the light receiving means exceeds the first threshold and does not exceed the second threshold. The pulse width of the reflected wave of the measurement target object or the pulse width of the clutter is estimated based on a predetermined amplitude value that is an intermediate value between the second threshold and the first threshold, and the estimated pulse width And determining whether or not the reflected wave and the clutter of the measurement target object are combined based on the pulse width of the period exceeding the first threshold measured by the measuring unit. Item 3. The distance measuring device according to item 1 or 2.   When the estimation unit determines that the reflected wave and the clutter of the measurement target object are combined, the estimated pulse width and a pulse width in a period exceeding the first threshold measured by the measurement unit The distance measuring device according to claim 4, wherein the distance of the measurement target object is estimated based on the distance.   The said 2nd threshold value is set to the value lower than the minimum amplitude value of the reflected wave of the measurement target object in a position nearer than the closest distance of the said clutter. Distance measuring device.   Further comprising a peak amplitude acquisition unit for acquiring a peak amplitude value of the reflected wave received by the light receiving means, the estimation means based on the peak value acquired by the peak amplitude acquisition unit and the first threshold value The distance measuring device according to claim 6, wherein it is determined whether or not the reflected wave of the measurement target object and the clutter are combined. The detection unit includes an amplification unit that amplifies the reflected wave received by the light receiving unit, a sensitivity time adjustment circuit that adjusts the gain of the amplified wave amplified by the amplification unit, and an adjustment wave that is adjusted by the sensitivity time adjustment circuit. And first and second comparators respectively comparing the first and second threshold values,
The peak amplitude acquisition unit includes a peak hold circuit for peak-holding the adjustment wave adjusted by the sensitivity time adjustment circuit, and an AD for acquiring a peak value from the peak-held waveform.
The distance measuring device according to claim 7, further comprising:   The sensitivity time adjustment circuit increases the gain according to the time from the timing at which the light projecting means transmits the transmission wave to the timing at which the light receiving means receives the reflected wave, and the operating frequency of the peak amplitude acquisition unit is 9. The distance measuring device according to claim 8, wherein the distance is lower than the frequency of the reflected wave received by the light receiving means.   The estimation unit estimates a pulse width of a reflected wave of the measurement target object based on the peak value acquired by the peak amplitude acquisition unit and the first threshold value, and the estimated pulse width and the measurement unit measure The distance according to any one of claims 7 to 9, wherein it is determined whether or not the reflected wave and the clutter of the measurement target object are synthesized based on the pulse width of the period exceeding the first threshold. measuring device.   When the estimation unit determines that the reflected wave and the clutter of the measurement target object are combined, the estimated pulse width and a pulse width in a period exceeding the first threshold measured by the measurement unit The distance measurement apparatus according to claim 10, wherein the distance of the measurement target object is estimated based on the distance. The measuring means includes a first time when the amplitude of the reflected wave received by the light receiving means is less than or equal to the first threshold value, and a second time when the amplitude is less than or equal to a third threshold value that is less than the first threshold value. And measure
The distance measuring apparatus according to claim 6, wherein the estimating unit estimates a distance of the measurement target object based on the first time and the second time.   The estimation means estimates a pulse width of the measurement target object based on the first time and the second time, and exceeds the estimated pulse width and the first threshold measured by the measurement means. The distance measuring device according to claim 12, wherein it is determined whether or not a reflected wave and a clutter of the measurement target object are combined based on a pulse width of a period.   When the estimation unit determines that the reflected wave and the clutter of the measurement target object are combined, the estimated pulse width and a pulse width in a period exceeding the first threshold measured by the measurement unit The distance measuring device according to claim 13, wherein the distance of the measurement target object is estimated based on the distance. 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 reflecting object when the bad environment detection means detects that the host vehicle is not in a bad environment, and the bad environment detection means has the host vehicle in a bad environment. The distance measuring device according to any one of claims 1 to 14, wherein the distance to the reflecting object is not estimated when this is detected.   16. The distance according to claim 15, 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.