JP2015219120A - Distance measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a distance measuring device capable of discriminating between a desired wave and clutter irrespective of the presence or absence of the desired wave and the intensity of a bad environment. A distance measuring device according to the present invention includes a light projecting unit that outputs a transmitted wave to the surroundings of a vehicle, a light receiving unit that receives a reflected wave of the transmitted wave that the light projecting unit outputs, and a light receiving unit. The time measurement unit 500 that measures the time when the amplitude of the reflected wave received by the unit exceeds the predetermined first threshold value, the time measured by the time measurement unit 500, and the time of the reflected wave and the amplitude value are associated with each other. The signal processing unit 100 calculates the distance to the reflecting object and the amplitude value of the reflected wave based on the reference value, and estimates whether the reflecting object is the measurement target object or the clutter based on the calculation result. [Selection diagram] Figure 1

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. 9, 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. 9, when the measurement target object is sufficiently away from the host vehicle, the 1st echo and the 2nd echo are detected as respective waveforms. In such a distance measuring apparatus, a plurality of echoes can be detected as shown in FIG. 10, but it is difficult to distinguish between a desired wave and a clutter. On the other hand, conventionally, when the first reflection point having the second reflection point in the group of reflection points of the grouped clutter exists at a predetermined ratio or more, the segment is determined to be fog or the like. It was. (For example, see Patent Document 1).

JP 2009-42177 A

  However, in the conventional distance measuring device, if there is no second reflection point (desired wave), the clutter cannot be determined, and, as shown in FIG. However, the amplifier is saturated by the clutter, and the desired wave cannot be detected and cannot be determined.

  An object of the present invention is to solve the conventional problems and to provide a distance measuring device capable of discriminating clutter regardless of the presence / absence of a desired wave and the intensity of a bad environment.

  In order to achieve the above object, the present invention provides 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 light receiving unit that receives the light. Based on a measuring unit that measures a time when the amplitude of the reflected wave exceeds a predetermined first threshold, a time measured by the measuring unit, and a reference value that associates the time and amplitude value of the reflected wave with each other And an estimation means for calculating a distance to the reflecting object and an amplitude value of the reflected wave, and estimating whether the reflecting object is a measurement target object or a clutter based on the calculation result.

  According to the present invention, there is an effect that it is possible to discriminate clutter regardless of the presence / absence of a desired wave and the intensity of a bad environment.

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 Illustration explaining clutter measurement with an image The flowchart figure of the process by the distance measuring device which concerns on the 1st Embodiment of this invention. Flowchart diagram of reflectance estimation processing in FIG. The flowchart figure of the grouping process in FIG. The flowchart figure which shows the modification of the grouping process of FIG. The figure explaining the count of the echo in FIG. 7 with an image Illustration explaining multi-echo ranging with an image Diagram explaining distance measurement with clutter weak Diagram explaining distance measurement with strong clutter

(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 (first threshold), and whether or not it exceeds a predetermined high threshold greater than the low threshold. Here, the Low threshold value is a threshold value used for normal distance measurement (corresponding to the conventional threshold value shown in FIGS. 9 to 11), 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 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 signal processing unit 100 stores in advance a reference value in which the pulse width of the reflected light (light reception pulse) from the object 600 and the amplitude value are associated with each other. Specifically, the ratio of the peak amplitude value of the received light pulse to the time (pulse width) from the rising time when the received light pulse from the object 600 exceeds the Low threshold to the falling time lower than the Low threshold is stored. It is not limited to this. Any relational expression that can estimate the peak amplitude value of the received light pulse from the measured pulse width of the received light pulse may be used. Based on this, the distance to the object 600 and the peak amplitude value of the reflected wave are calculated. Then, the reflectance of the object 600 is estimated according to the calculated distance to the object 600 and the peak amplitude value, and based on this reflectance, it is determined whether the object 600 is a measurement target object or a clutter. Specifically, the signal processing unit 100 determines that the estimated reflectance exceeds a predetermined threshold value as a measurement target object, and determines that the estimated reflectance is less than the threshold value as clutter.

  The light projecting unit 200 is 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, an LD (Laser Diode) 202, a mirror driving circuit 230, a lens 250, and a scan. And a mirror 270. 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 irradiates the lens 250 with laser light. The lens 250 condenses this laser light. The condensed laser light is irradiated on the scan mirror 270. The scan mirror 270 rotates under the control of the mirror drive circuit 230 and adjusts the incident angle of the laser light collected by the lens 250. In other words, the mirror driving circuit 230 adjusts the irradiation angle to the outside vertically and horizontally by adjusting the scanning angle of the scan mirror 270. Specifically, the mirror drive circuit 230 sets the scan mirror 270 to a wide angle (for example, about 180 degrees) in the left-right direction (horizontal direction) and an acute angle (for example, about 40 degrees) in the vertical direction (vertical direction). adjust. In the present embodiment, the LD 202 and the scan mirror 270 are described as a single configuration for the sake of simplicity, but a plurality of them may be configured. In this case, since the scanning angle as a whole of the LD 202 and the scan mirror 270 is larger than that in the single configuration, the scanning angle for adjusting the single LD 202 and the scan mirror 270 in a plurality of configurations is a single angle. You may make smaller than the time of a structure. Thus, for the three-dimensional distance measurement, the light projecting unit 200 irradiates the periphery of the host vehicle with the laser light (light projection pulse).

  The light receiving unit 300 includes a light receiving element 301, a current / voltage conversion unit 302, and a lens 304. The light receiving element 301 acquires the laser beam reflected from the object 600 around the host vehicle through the lens 304 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 high threshold value is a threshold value set to separate the desired wave and the clutter when the reflected wave (desired wave) from the measurement target object and a plurality of received light pulses of the clutter are combined. It should be noted that the detection unit 400 of the present embodiment only needs to be able to detect whether or not at least the amplitude of the input waveform exceeds the Low threshold (first threshold), and detection of whether or not it exceeds the High threshold is always necessary. is not.

  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). The signal processing unit 100 performs various estimations described later based on the pulse width. Here, the time (pulse width) from the rise to the fall of each pulse is digitally output from the time measurement unit 500 to the signal processing unit 100, but the pulse width may be calculated by other methods. For example, the time measuring unit 500 digitally outputs the rising time and the falling time of each pulse to the signal processing unit 100, and calculates the time difference between the rising time and the falling time when the signal processing unit 100 is input. By doing so, the pulse width may be calculated.

  Here, the high threshold value set by the first comparator 402 is greater than the intensity of the assumed influence (hereinafter referred to as a bad environment) due to rain, fog, snow, etc., in other words, the clutter amplitude value in the bad environment. Set high. 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.

  In this embodiment, the high threshold is used as a method for separating the measurement target object and the clutter from the received light pulse. However, other methods may be used without using the high threshold. For example, the measurement target object and the clutter may be separated from the received light pulse by using a known method such as ADC.

  Next, processing by the distance measuring device according to the first embodiment of the present invention will be described.

  The signal processing unit 100 calculates the distance from the host vehicle to the measurement target object based on the above-described round-trip time of the light pulse. Further, the signal processing unit 100 calculates the received light pulse from the pulse width of the received light pulse calculated from the measurement result of the time measuring unit 500 based on the reference value (relational expression between the pulse width and the peak amplitude value) stored in advance. Estimate the peak amplitude value. Then, the signal processing unit 100 determines the true intensity (hereinafter, referred to as “intensity”) from which the influence of attenuation due to the distance is eliminated according to the peak amplitude value (hereinafter simply referred to as intensity) of the received light pulse and the distance from the own vehicle to the measurement target object. Estimated reflectance).

The signal processing unit 100 determines that the estimated reflectance is smaller than a predetermined threshold value as clutter. Such intensity estimation using the pulse width is performed based on the received light pulse shape determined by the circuit characteristics of the light projecting unit 200 and the light receiving unit 300. The light receiving pulse shape is constant regardless of the amplitude. Specifically, the pulse width at 0 [V] is constant, and the time difference between the rising and falling points of the pulse at 0 [V] and the peak amplitude point is constant. For this reason, if the pulse width of the received light pulse can be measured, the peak amplitude value of the same ratio with respect to the peak amplitude value of the reference value can be estimated as the peak amplitude value of the received light pulse from the ratio with the pulse width of the reference value. For this reason, the intensity of the received light pulse can be estimated from the pulse width of the received light pulse and the threshold (for example, the Low threshold) set by the time measuring unit 500. Further, for example, the signal processing unit 100 may store and estimate an approximate expression or mapping table in which the pulse width of the received light pulse shape is a function of the peak amplitude value.

  Here, as a method of calculating the estimated reflectance according to the peak amplitude value of the received light pulse and the distance from the own vehicle to the measurement target object, it is performed based on a well-known radar equation (for example, Shiina as well-known literature) Tatsuo, Junichi Ikeda, “Measurement of transfer function of laser transmission beam spread propagating in fog and beam propagation analysis using the transfer function”, Illumination Society Journal, Vol.82, No.2, pp.76-83, 1998 reference). The object 600 to be measured by the distance measuring apparatus according to the present embodiment may be smaller than the beam diameter of the LD 202, and the amplitude attenuates in inverse proportion to the square to the fourth power of the distance. Therefore, the signal processing unit 100 receives a predetermined multiplier set based on the actual measurement result and the environmental condition in the power of the distance to the object 600, specifically, in the range of n-th power (2 ≦ n ≦ 4). The estimated reflectance is calculated by multiplying the peak amplitude value of the pulse.

  Further, the signal processing unit 100 may change the estimation criterion for estimating whether the object 600 is a measurement target object or a clutter based on the estimated reflectance according to the area to which the distance to the object 600 belongs. For example, when the distance to the object 600 is a short distance (up to about L1 = 2, 3 m) and a long distance (a distance from L1) (a predetermined threshold, specifically, for example, You may make it vary the value of the power n of the above-mentioned distance. In this case, the predetermined first threshold value in the case of an area belonging to a short distance is set smaller than the predetermined second threshold value in the case of an area belonging to a long distance. Thus, it is possible to reduce the fact that the desired wave is erroneously estimated as clutter at a short distance where there is a possibility of a collision due to the approach of the vehicle as compared with a long distance. On the other hand, at a long distance, the estimation accuracy of a desired wave or a clutter can be improved as compared with a short distance.

  In the distance measurement device according to the present embodiment, the signal processing unit 100 changes the degree of the estimation reference according to the area to which the distance to the object 600 belongs in order to increase the estimation accuracy of the desired wave or the clutter. Further, the following additional estimation process may be performed.

  When the intensity of the clutter is high (for example, when it is equal to or greater than the threshold value Vth of the A region in FIG. 11B), the obstacle 802 is irradiated from the own vehicle 800 to the obstacle 802 in the irradiation range 801 as shown in FIG. It is generated uniformly at a position equidistant from the irradiation position of the laser beam. Therefore, the signal processing unit 100 determines that the received light pulse having a uniform distance in the entire irradiation range 801 is clutter. Specifically, the signal processing unit 100 stores the calculated distance information to the object 600 for each scanning angle of the scan mirror 270 controlled by the mirror driving circuit 230, and the same distance information within a certain range. Is stored, the received light pulse of that distance is determined as clutter. For example, when a predetermined number or more of distance information within a predetermined threshold range is stored, the received light pulse is determined as clutter.

  In addition, when the signal processing unit 100 determines that the additional estimation processing is a clutter, the signal processing unit 100 further stores a difference value of the distance information of the clutter stored for each scanning angle of the scan mirror 270 and a dispersion value of the distance information. You may make it determine with a clutter when (distance dispersion | distribution) is below a predetermined 2nd threshold value and a 3rd threshold value, respectively. This can reduce the possibility of erroneous detection as a desired wave due to noise or the like.

  Further, the signal processing unit 100 further receives light when the dispersion value (distance dispersion) of the distance information is smaller than a predetermined fourth threshold value that is smaller than the third threshold value or as shown in FIG. When the pulse width (Wlow) exceeding the pulse low threshold is larger than the predetermined fifth threshold (Wth5) in a scanning angle range of a certain value or more, the distance measurement of the measurement target object as shown in FIG. Judged as a difficult adverse environment. As a result, the area where the measurement target object cannot be measured as shown in the area A of FIG. 12B can be excluded from the process of estimating the distance to the measurement target object. In the present embodiment, the signal processing unit 100 determines the bad environment when determining the clutter. However, the signal processing unit 100 is not limited to this, and may determine the bad environment in the case of other estimation processes. . For example, the signal processing unit 100 may determine a bad environment when separating the desired wave from the pulse in which the clutter and the desired wave are combined. As described above, the signal processing unit 100 may function as a bad environment detection unit, and may exclude various estimation processes when a bad environment is determined.

  Next, the overall processing by the distance measuring apparatus according to the first embodiment of the present invention as described above will be described. FIG. 4 is a flowchart of processing performed by the distance measuring apparatus according to the first embodiment of the present invention. Each of these processes is performed by the signal processing unit 100 or each component according to the command.

  First, as shown in step S401, the light projecting unit 200 starts horizontal scanning. Specifically, an initial value (scan start angle = 0 °) is set as the laser beam irradiation angle, and a horizontal scan of 0 to 180 ° is started. Then, the horizontal scan is repeatedly performed by the rotation of the scan mirror 270. Although the horizontal scan has been described here, the vertical scan may be performed, or both the horizontal scan and the vertical scan may be performed. In addition, the same scanning operation may be performed repeatedly. Such a scan improves the accuracy of clutter determination.

  Then, as shown in step S402, the signal processing unit 100 determines whether or not there is a low echo (light reception pulse). If YES in step S402, as shown in step S403, if there is an echo that exceeds the Low threshold (first threshold), the signal processing unit 100 performs distance measurement processing. The distance measurement processing result is stored in a memory (not shown) in the signal processing unit 100 for grouping processing to be described later. For example, an irradiation angle, an echo generation distance, and an echo pulse width are stored. Thereafter, as shown in step S404, the signal processing unit 100 performs a reflectance estimation process (a process for determining weak clutter), which will be described later.

  After the reflectivity estimation process in step S404 or in the case of NO in step S402, as shown in step S405, the laser beam irradiation angle is updated by the angular resolution. For example, the laser beam irradiation direction is updated by adding an angular resolution of 1 ° to the previous irradiation angle.

  Next, as shown in step S406, the signal processing unit 100 determines whether or not the horizontal scan is finished. Specifically, it is determined whether the horizontal scan angle (0 to 180 °) has been completed. In the case of NO at step S406, the processes after step S402 are repeated again. For example, when the angular resolution is 1 °, the above-described flow is repeated 180 times. If YES in step S406, as shown in step S407, the signal processing unit 100 performs grouping processing (strong clutter discrimination) described later.

  Next, detailed processing of the reflectance estimation processing (processing for determining weak clutter) in step S404 will be described with reference to FIG. Here, the following process is repeated for the number of times that the amplitude value of the received light pulse (echo) exceeds the Low threshold.

As shown in step S501, the signal processing unit 100 determines whether or not the calculated distance of the received light pulse is smaller than a predetermined value L [m] (for example, L = 3).

  If NO in step S501, the process ends. This is because the reflectance estimation process is performed only for a short distance (for example, within 3 m) where there is a high possibility of occurrence of clutter for discrimination of clutter. Since clutter generally has an estimated reflectance smaller than that of the measurement target object, it is set that a low echo does not occur at a long distance (for example, 3 m or more). By such processing, the processing load of the signal processing unit 100 can be reduced. Although the processing load increases, the processing in step S501 can be omitted.

  On the other hand, if YES in step S501, as shown in step S502, the signal processing unit 100 determines that the pulse width at which the amplitude value of the received light pulse exceeds the low threshold is greater than a predetermined value W [m] (for example, W = 5). It is determined whether or not it is small. This is to determine whether the pulse width is extended or saturated. If the pulse width is extended or saturated, the peak amplitude value of the received light pulse cannot be accurately estimated. Therefore, if NO in step S502, the process ends.

  On the other hand, if YES in step S502, as shown in step S503, the signal processing unit 100 estimates the peak amplitude value (intensity) of the received light pulse based on a predetermined approximate expression. Since the shape of the received light pulse is constant regardless of the amplitude, the signal processing unit 100 stores a reference value (for example, a ratio between amplitude and pulse width or a relational expression) in advance in a memory (not shown), and calculates the calculated pulse width and Low The ratio with the reference value is calculated from the relationship of the threshold value, and the peak amplitude value of the received light pulse is estimated.

  Next, as shown in step S504, the signal processing unit 100 calculates an estimated reflectance by eliminating the influence of attenuation due to distance based on a predetermined approximate expression. As a method for calculating the estimated reflectance, for example, the laser radar equation shown in the above-described well-known document may be used, or another well-known method may be used. Further, the laser radar equation may be made different depending on whether or not all irradiated laser light hits an object. In addition, various variables such as optical characteristics and circuit characteristics may be used in order to perform accurate distance measurement, normalization may be performed for simplification of mathematical formulas, and variables that have little influence may be omitted.

  Then, as shown in step S505, the signal processing unit 100 determines whether or not the estimated reflectance calculated in step S504 is smaller than a predetermined threshold RR [%] (for example, RR = 1). This is to make it lower than the reflectance of the desired wave as a distance measurement target. In order to prevent the desired wave from being erroneously determined as clutter, it is desirable to set the predetermined threshold value to be small. Therefore, for example, RR <1% may be set. Here, even when the signal processing unit 100 cannot discriminate the clutter, the clutter can be discriminated again by performing a grouping process (strong clutter discrimination) described later.

  If NO in step S505, the process ends. On the other hand, if YES in step S505, as shown in step S506, the signal processing unit 100 determines that the received light pulse (echo) that is the object at this time is clutter.

  Next, detailed processing of the grouping processing (processing for discriminating strong clutter) in step S407 will be described with reference to FIG. Here, the distance measurement processing result stored in step S403 is used as data.

First, in step S601, the signal processing unit 100 counts light reception pulses (echoes) that are within a measurement distance L [m] (for example, L = 3) in all sections of the horizontal scan. Next, in step S602, the signal processing unit 100 determines whether the count number is equal to or greater than K times. For example, the signal processing unit 100 determines whether there are K = 162 times or more of the count number of about 90% during the total number of scans of 180 times when the angular resolution is 1 °. As a result, when an echo within the measurement distance L [m] is equal to or greater than a certain value (count number) within the horizontal scan range, the echo is marked as clutter and the subsequent processing is performed.

  If NO in step S602, it is determined that the environment is not in an adverse environment, and the process is terminated.

  On the other hand, if YES in step S602, as shown in step S603, the signal processing unit 100 calculates the difference between the measured distance information at the center and the end of the horizontal scan. For example, the difference between the average value of several points stored for the central portion of the horizontal scan and the average value of several points stored for the end portions may be calculated. If the distance between the center and the edge is large, there is a high possibility of an object (desired wave) that is not uniformly distributed in the surrounding area, and if it is small, the possibility of clutter distributed uniformly in the surrounding area is high. It is.

  Next, as shown in step S604, the signal processing unit 100 determines whether or not the difference calculated in step S603 is smaller than a predetermined value M [m] (for example, M = 1) that is a second threshold value.

  If NO in step S604, it is determined that the environment is not in an adverse environment, and the process is terminated. On the other hand, if YES in step S604, as shown in step S605, the signal processing unit 100 calculates the standard deviation value of the distance information of the first received light pulse (for example, the 1st echo shown in FIG. 5) for each horizontal scan angle. Is calculated.

  Next, as shown in step S606, the signal processing unit 100 determines whether or not the standard deviation value calculated in step S605 is smaller than a predetermined value O [m] (for example, O = 0.1) that is a fourth threshold value. Determine whether.

  If YES in step S606, that is, if the distance variance value is further smaller than the difference in distance, as shown in step S607, the signal processing unit 100 is in a bad environment indicated by area A in FIG. It is determined that it is below, and a bad environment alarm is output via notifying means (not shown). On the other hand, if NO in step S606, the process ends.

  In the grouping process shown in FIG. 6, the bad environment alarm is performed using the distance dispersion value. As a modification, as shown in the grouping process shown in FIG. 7, the distance difference is small and the distance dispersion is small. You may make it determine whether it is a clutter. Hereinafter, the grouping process of FIG. 7 will be described. In addition, about the process (step S703-S705) common to FIG. 6, only the number of a step process is changed and detailed description is abbreviate | omitted.

In FIG. 7, as shown in step S <b> 701, the signal processing unit 100 counts received light pulses (echoes) that are within the measurement distance L [m] (for example, L = 3) in each section of the horizontal scan. Specifically, the signal processing unit 100 divides the horizontal scan into fixed intervals, and confirms whether there are a plurality of echoes having the same distance within the range. As this fixed section, for example, as shown in the fixed sections 801 to 805 in FIG. 8, it may be a section set as a section of a predetermined range in advance, or as shown in the moving sections 811 to 815 in FIG. It is good also as a section which moves dynamically within a predetermined range. In addition, as a dynamic section, a sequential section may be set so that one section is obtained each time a certain number of scans are performed. For example, when the scan angle is 180 ° and the angular resolution is 1 ° and the number of scans in one section is set to 36, when the 36 scans are performed, the count of step S701 is performed in that section and the next scan (37th scan). In the case where is performed, the count in step S701 may be performed with the section represented by this scan (the 37th time) and the previous scan of the previous section (the second to 36th times) as a new section. In this case, the process of step S407 is performed immediately after the process of step S404. According to this, since the distance measurement information in step S403 is stored in only a part of the section, the storage capacity in the signal processing unit 100 can be reduced.

  In step S702, the signal processing unit 100 determines whether or not the count number is equal to or greater than K times. For example, when the scan angle is 180 ° and the signal processing unit 100 is set to be equal to five intervals as shown in FIG. 8, the count number is 36 during the total number of scans in each interval when the angle resolution is 1 °. It is determined whether K = 32 times or more of about 90%. As a result, when an echo within the measurement distance L [m] is equal to or greater than a certain number (count number) within the horizontal scan range of each section, the echo is marked as clutter and the subsequent processing is performed. In this way, by performing the clutter determination processing for each section, it is possible to accurately determine clutter even when there is variation in the distribution range, such as when the clutter is shaded and partly has clutter.

  Then, as shown in step S706, the signal processing unit 100 determines whether or not the standard deviation value calculated in step S705 is smaller than a predetermined value N [m] (for example, N = 0.5) that is a third threshold value. judge. This is to determine whether or not the clutter is based on the small distance difference and the small distance variance. The predetermined value N [m] in step S706 is set larger than the predetermined value O [m] in step S606. This is because the clutter is weak when there is clutter only in some sections, and the distribution is more likely to vary than when there is clutter in all sections. This makes it possible to determine weak clutter.

  In the case of YES in step S706, as shown in step S707, the signal processing unit 100 measures the measurement distance L [m] among the received light pulse groups (1st echo group) received first that uniformly exist in the horizontal scan angle range. ] Are determined as clutter. On the other hand, if NO in step S706, the process ends.

  In addition, in these grouping processes, marking was performed for groups that are close to each other with an absolute distance relationship, but marking is performed for groups that are close to each other with a relative distance relationship (those that are close to each other). Also good. For example, in steps S602 and S702, the echo may be marked as clutter when the number of echoes of X [m] ± 0.5m is K times or more.

  As described above, according to the embodiment of the present invention, there is an effect that clutter can be determined even in a bad environment such as fog, regardless of the presence of a desired wave and the strength of the bad environment. 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 present embodiment, both reflectance estimation processing (processing for estimating weak clutter) and grouping processing (processing for estimating strong clutter including determination of a bad environment) are described as processing by the distance measurement device. It is sufficient that at least the reflectance estimation process is performed.

In the grouping process of this embodiment, the standard deviation value is used in steps S605 and S606 in FIG. 6 and steps S705 and S706 in FIG. 7, but a pulse width may be used instead. For example, in step S605, when the average pulse width is larger than a predetermined value Q [m] (for example, Q = 5), the signal processing unit 100 has a bad environment (A region) as shown in step S606 because the pulses are extended. ) May be determined to output a bad environment alarm. Further, for example, in step S705, when the average pulse width is larger than a predetermined value P [m] (for example, P = 3), the signal processing unit 100 is close to the saturation state, and as shown in step S706, the 1st echo group Of these, the measurement distance L [m] or less may be determined as clutter. Here, the predetermined value P [m] is set to a value smaller than the predetermined value Q [m].

  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 a measurement unit that measures a time when the amplitude exceeds a predetermined first threshold, a time measured by the measurement unit, and a reference value that associates the time of the reflected wave with the amplitude value, An estimation means for calculating a distance to the object and an amplitude value of the reflected wave and estimating whether the reflection object is a measurement target object or a clutter based on the calculation result is provided.

  In the distance measuring apparatus, the estimating means calculates an estimated reflectance that eliminates the influence of attenuation due to the calculated distance to the reflecting object, and based on the estimated reflectance, the reflecting object is a measurement target object or a clutter. It may be estimated.

  Further, in the distance measuring apparatus, the estimating means may calculate an estimated reflectance by multiplying an amplitude value of the reflected wave by a power of the calculated distance to the reflecting object.

  Further, in the distance measuring apparatus, the estimating means may calculate an estimation criterion for estimating whether the reflecting object is a measurement target object or a clutter based on the estimated reflectance according to an area to which the calculated distance to the reflecting object belongs. It may be different.

  Further, in the distance measuring apparatus, the estimating means sets the degree of the estimation reference to be smaller in the case of an area belonging to a short distance than in the case of an area where the calculated distance to the reflecting object belongs to a long distance. May be.

  Further, in the distance measuring apparatus, the estimation means sets the estimation threshold for the estimation criterion to be smaller in the case of an area belonging to a short distance than in the case of an area where the calculated distance to a reflective object belongs to a long distance. It may be set.

  The distance measuring apparatus may further include a detecting unit configured to detect whether an amplitude of a reflected wave received by the light receiving unit exceeds the first threshold, and the measuring unit includes the reflecting unit When it is detected that the amplitude of the wave exceeds the first threshold, the time output by the light projecting means may be measured.

  Further, in the distance measuring device, the measuring means detects the first threshold value from when the detecting means detects that the amplitude of the reflected wave exceeds the first threshold value, and exceeds the first threshold value. You may measure the time until it becomes smaller.

  Further, in the distance measuring apparatus, the detecting unit amplifies the reflected wave received by the light receiving unit, and compares the gain of the amplified wave amplified by the amplifying unit with the first threshold. A comparator.

  In the distance measuring apparatus, the light projecting unit outputs a transmission wave in a predetermined angle range, the light receiving unit receives the reflected wave in the predetermined angle range, and the measuring unit is configured to receive the light receiving unit. The time when the amplitude of the reflected wave received by the means exceeds a predetermined first threshold is measured within the predetermined angle range, and the estimating means is configured to detect a similar reflecting object within a predetermined range of the predetermined angles. When this distance is calculated, this reflective object may be determined as clutter.

Further, in the distance measuring apparatus, the estimation unit calculates a difference in distance to the reflecting object and a distance variance calculated for each predetermined angle, and the difference is smaller than a second threshold, and the distance variance is calculated. However, when the value is smaller than the third threshold value, the reflective object may be determined as clutter.

  Further, in the distance measuring apparatus, the estimating unit may be configured such that the distance variance is smaller than a fourth threshold value that is smaller than the third threshold value, or when the reflected wave exceeds the first threshold value. When the time from when the time is smaller than the first threshold to the time when the time is smaller than the fifth threshold is within a certain range, it may be determined that the environment is difficult to measure.

  The distance measuring device of the present invention is a measurement object regardless of the presence of a desired wave or the strength of a bad environment among TOF (Time Of Flight) laser radars realized by a time measuring device such as TDC (Time to Digital Converter). This is useful as a distance measuring device that can discriminate between an object and clutter.

DESCRIPTION OF SYMBOLS 100 Signal processing part 200 Light projection part 201 LD drive circuit 202 LD
230 mirror driving circuit 250 lens 270 scan mirror 300 light receiving unit 301 light receiving element 302 current / voltage converting unit 304 lens 400 detecting unit 401 amplifying unit 402 first comparator 403 second comparator 500 time measuring unit 501 high threshold time measuring unit 502 Low threshold time measurement unit

Claims (12)

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;
Based on the time measured by the measuring means and the reference value in which the time and amplitude value of the reflected wave are related to each other, the distance to the reflecting object and the amplitude value of the reflected wave are calculated. A distance measuring apparatus comprising: an estimation unit that estimates whether the reflecting object is a measurement target object or a clutter.   The estimating means calculates an estimated reflectance that excludes the influence of attenuation due to the calculated distance to the reflecting object, and estimates whether the reflecting object is a measurement target object or a clutter based on the estimated reflectance. The distance measuring device according to claim 1.   3. The distance measuring device according to claim 1, wherein the estimating unit calculates an estimated reflectance by multiplying an amplitude value of the reflected wave by a power of the calculated distance to the reflecting object. 4.   The estimation means varies an estimation criterion for estimating whether a reflection object is a measurement target object or a clutter based on the estimated reflectance according to an area to which the calculated distance to the reflection object belongs. Item 4. The distance measuring device according to any one of Items 1 to 3.   The estimation means sets the degree of the estimation criterion to be smaller in the case of an area belonging to a short distance than in the case of an area where the calculated distance to the reflecting object belongs to a long distance. 4. The distance measuring device according to 4.   The estimation means sets the determination threshold for the estimation criterion to be smaller in the case of an area belonging to a short distance than in the case of an area where the calculated distance to a reflective object belongs to a long distance. Item 6. The distance measuring device according to Item 5. Detecting means for detecting whether the amplitude of the reflected wave received by the light receiving means exceeds the first threshold;
7. The measurement unit according to claim 1, wherein when the detection unit detects that the amplitude of the reflected wave exceeds the first threshold, the measurement unit measures the time output by the light projecting unit. The distance measuring device according to claim.   When the detecting unit detects that the amplitude of the reflected wave exceeds the first threshold, the measuring unit calculates a time from when the first threshold is exceeded to when the amplitude is smaller than the first threshold. The distance measuring apparatus according to claim 1, wherein the distance measuring apparatus measures the distance.   The detection unit includes an amplification unit that amplifies the reflected wave received by the light receiving unit, and a first comparator that compares the gain of the amplified wave amplified by the amplification unit with the first threshold value. The distance measuring device according to claim 1. The light projecting means outputs a transmission wave in a predetermined angle range,
The light receiving means receives the reflected wave in the predetermined angle range;
The measuring means measures the time during which the amplitude of the reflected wave received by the light receiving means exceeds a predetermined first threshold in the predetermined angle range,
10. The estimation unit according to claim 1, wherein when the distance to a similar reflecting object is calculated within a predetermined range of the predetermined angle, the estimating object is determined as clutter. The distance measuring device described in 1.   The estimation means calculates a difference in distance to the reflecting object and a distance variance calculated for each predetermined angle, the difference is smaller than a second threshold value, and the distance variance is smaller than a third threshold value. The distance measuring device according to claim 10, wherein the reflection object is determined to be clutter when it is small.   The estimation means is smaller than the first threshold when the distance variance is smaller than a fourth threshold smaller than the third threshold or when the reflected wave exceeds the first threshold. 12. A bad environment in which ranging is difficult is determined when there is a certain period of time until a certain time is greater than a fifth threshold. Distance measuring device.