JP2019074375A - Distance measuring device, moving body, distance measuring method, and program - Google Patents

Abstract

To provide a distance measuring device, a moving body, a distance measuring method and a program with which it is possible to accurately discriminate between the signal of reflected light from an object and a noise signal and improve the accuracy of measuring the distance to the object.SOLUTION: Provided is a distance measuring device for emitting light from a light projection unit, receiving reflected light by a light detection unit and acquiring a detection signal, and measuring the distance to an object on the basis of a time until the detection signal is acquired. The distance measuring device comprises: a first acquisition unit for acquiring information relating to the detection signal; a determination unit for determining the number of times detected by the light detection unit; a measuring unit for performing operation to find a time until reflected light is detected by the light detection unit or a value based on the time, as many times as the detection times; a count unit for counting the number of detection signals for each rank, corresponding to the time or the value based on the time, where the time or the value based on the time is a rank; a specification unit for specifying a rank that corresponds to the largest of total value of count values; thus, finding the distance to the object on the basis of a time that corresponds to the rank or a value based on the time.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a distance measuring device, a moving body, a distance measuring method, and a program.

  It consists of a light emitting element, a light receiving element, and each drive circuit, and emits a light emission beam from the light emitting element toward the object of distance measurement, and emits light emission timing of the light emission beam and receives reflected light from the distance object A distance measuring device using a TOF (Time Of Flight) method is known which measures the distance between the object and the object by detecting the time difference from the reception timing detected by an element. Such distance measuring devices are widely used in various fields such as sensing of vehicles and the like, motion capture technology, and range finders.

  As an example of such a distance measurement device, there is a laser radar widely used in aircraft, railways, vehicles and the like. As such a laser radar, a laser beam emitted from a light source is scanned by a rotating mirror, and light reflected or scattered by an object is detected again by a photodetector through the rotating mirror, to obtain a desired range of There is a scanning laser radar that can detect the presence or absence of an object and the distance to the object (see Patent Document 1).

  What is important in ranging by such a laser radar is the separation of noise and a signal from an object (object). Among noises, shot noise is white noise associated with light quantity measurement, and its magnitude is proportional to the square root of the time average of light quantity. Therefore, when the sensitivity of the measuring instrument is high or disturbance light is strong, the size may be several tens of [mV] or more, which is more likely to be a problem than circuit noise, and erroneous detection in detection by a photodetector Are more likely to occur.

  As a technique for suppressing such false detection based on shot noise, the reflected light from the object is detected on the basis of the threshold voltage, and the threshold voltage is made sufficiently higher than the shot noise, so that the shot noise is caused. A technology for suppressing false detection has been proposed (see Patent Document 2).

  However, in the technique described in Patent Document 2, since it is necessary to set the threshold to such an extent that the shot noise is not erroneously detected as the reflected light from the object, the weak detection signal buried in the shot noise is There is room for improvement in that it is difficult to distinguish from shot noise.

  The present invention has been made in view of the above-mentioned problems, and accurately distinguishes a signal of light reflected from an object and a noise signal to improve the accuracy of measurement of the distance to the object. It is an object of the present invention to provide a distance measuring device, a moving body, a distance measuring method and a program capable of

  In order to solve the problems described above and to achieve the object, the present invention emits light from a light projecting unit to a scanning area, and the light reflects the light reflected by an object present in the scanning area. A distance measuring apparatus for receiving a light by a detection unit and acquiring a detection signal, and measuring a distance to the object based on time from emission of the light to acquisition of the detection signal, the information related to the detection signal The light is emitted from the light projecting unit to the object based on the first acquisition unit to be acquired and the information on the detection pulse acquired by the first acquisition unit, and the reflected light reflected by the object A determination unit that determines the number of times of detection by the light detection unit, the light emission unit emits the light to the object from the light projection unit, and the light detection unit detects the reflected light reflected by the object Time to or The operation for obtaining a value based on the time is a measurement unit that performs the number of times of detection, and the time or a value based on the time is a class, and the class determined by the measurement unit for the class divided at arbitrary intervals The maximum value among the total value in each measurement of the count unit for counting the number of detection signals corresponding to time or the value based on the time for each class, and the count value for each class counted by the count unit The distance to the object is determined based on a specific part that specifies the class corresponding to the sum of the values and the time corresponding to the class specified by the specific part or a value based on the time I assume.

  According to the present invention, it is possible to accurately distinguish the signal of the reflected light from the object and the noise signal, and to improve the accuracy of the measurement of the distance to the object.

FIG. 1 is a view showing an example of the entire configuration of the distance measuring device according to the first embodiment. FIG. 2 is a view for explaining schematic configurations and operations of the light projecting optical system and the synchronization system according to the first embodiment. FIG. 3 is a diagram for explaining a schematic configuration and an operation of the light receiving optical system according to the first embodiment. FIG. 4 is a view of the light projecting optical system and the light receiving optical system according to the first embodiment as viewed from the Y direction. FIG. 5 is a diagram for explaining a synchronization signal and an LD drive signal in the distance measuring device according to the first embodiment. FIG. 6 is a diagram for explaining an emitted light pulse and a reflected light pulse. FIG. 7 is a diagram for explaining an example of shot noise when light is received. FIG. 8 is a diagram showing an example of a functional block configuration of the distance measuring device according to the first embodiment. FIG. 9 is a diagram for explaining the contrast between the reflected light pulse and the shot noise when the distance to the object is short. FIG. 10 is a diagram for explaining the contrast between the reflected light pulse and the shot noise when the distance to the object is long. FIG. 11 is a diagram showing an example of the relationship between the actual distance to the object, the peak value of the reflected light pulse, and the shot noise. FIG. 12 is a diagram for explaining the comparison between a detection pulse due to rain and a reflected light pulse from an object. FIG. 13 is a diagram for explaining counting of signals exceeding the threshold for each classified histogram class. FIG. 14 is a view for explaining that the reflected light from the object is specified by counting the signal exceeding the threshold for each classified histogram class. FIG. 15 is a diagram showing a point to be improved in identifying reflected light from an object by counting signals exceeding a threshold for each classified histogram class. FIG. 16 is a diagram showing an example of the relationship between the peak value of the reflected light pulse and the number of measurements when a high ranging success rate is secured. FIG. 17 is a diagram for explaining that the measurement interval is different depending on the number of times of measurement. FIG. 18 is a flowchart showing an example of the process of setting the number of times between frames of the distance measuring device according to the first embodiment. FIG. 19 is a diagram for explaining the signal waveform width correlated with the peak value in the modification 1 of the first embodiment. FIG. 20 is a diagram showing the relationship between the signal waveform width and the peak value in Modification 1 of the first embodiment. FIG. 21 is a diagram for explaining which of a plurality of threshold values the detection signal has exceeded in the second modification of the first embodiment. FIG. 22 is a diagram for explaining inclinations of two time points which respectively exceed two threshold values correlated with the peak value in the modification 3 of the first embodiment. FIG. 23 is a diagram showing a relationship between slopes at two points in time when the two threshold values are exceeded in the third modification of the first embodiment, and a peak value. FIG. 24 is a diagram for explaining the difference in the signal waveform width at two threshold values that are correlated with the peak value in Modification 4 of the first embodiment. FIG. 25 is a diagram showing a relationship between a difference between signal waveform widths at two threshold values and a peak value in Modification 4 of the first embodiment. FIG. 26 is a view for explaining setting of the number of measurements for each scanning angle of view in the fifth modification of the first embodiment. FIG. 27 is a view showing an example of a functional block configuration of the distance measuring device according to the second embodiment. FIG. 28 shows an example of the relationship between the actual distance to the object, the peak value of the reflected light pulse and the shot noise, and is a diagram for explaining the difference in distance measurement performance depending on the size of the threshold. FIG. 29 is a diagram for describing identification of the reflected light from the object by counting the signals exceeding the threshold for each classified histogram class and further obtaining the standard deviation of the pulse width. FIG. 30 is a flowchart showing an example of pulse width censorship inter-frame processing of the distance measuring device according to the second embodiment. FIG. 31 is a diagram for explaining the variation in the distance measurement success rate due to the difference in the threshold when performing the pulse width censorship inter-frame process according to the second embodiment. FIG. 32 is a diagram for explaining the variation in the distance measurement success rate due to the difference in the threshold when inter-frame processing is performed. FIG. 33 is a diagram for explaining the variation in the ranging success rate due to the difference in the threshold when single frame processing is performed.

  Hereinafter, with reference to FIGS. 1 to 33, an embodiment of a distance measuring device, a moving body, a distance measuring method, and a program according to the present invention will be described in detail. In addition, the present invention is not limited by the following embodiments, and components in the following embodiments can be easily conceived of by those skilled in the art, substantially the same, and so-called equivalent ranges. Is included. Furthermore, various omissions, substitutions, changes and combinations of the components can be made without departing from the scope of the following embodiments.

First Embodiment
(Overall configuration of distance measuring device)
FIG. 1 is a view showing an example of the entire configuration of the distance measuring device according to the first embodiment. The entire configuration of the distance measuring device 100 according to the present embodiment will be described with reference to FIG.

  The distance measuring device 100 according to the present embodiment is mounted, for example, on a vehicle as a moving object, emits (projects) laser light, and an object (for example, a target vehicle such as a leading vehicle, a stopped vehicle, an obstacle or a pedestrian) An object is a scanning laser radar that receives light (reflected light) reflected (scattered) by the object and outputs information about the object such as the presence or absence of the object and the distance to the object. The distance measuring device 100 receives supply of power from, for example, a battery (storage battery) of a mounted vehicle.

  As shown in FIG. 1, the distance measuring device 100 includes an LD (Laser Diode) 10, an LD driving unit 12, a light emitting optical system 20, a light receiving optical system 30, a detection system 40, and a time measuring unit 45. The control unit 46, the object recognition unit 47, the storage unit 48, the communication unit 49, and the synchronization system 50 are provided.

  The LD 10 is also called an edge emitting laser, and is a semiconductor laser driven by the LD driving unit 12 to emit laser light. The LD 10 is, besides the LD, another light emitting element such as a VCSEL (Vertical Cavity Surface Emitting Laser: vertical cavity surface emitting laser), an organic EL (Electro-Luminescence) element, an LED (Light Emitting Diode: light emitting diode) or the like. You may use.

  The LD driving unit 12 is a device that lights up (emits light) the LD 10 using the LD driving signal (rectangular pulse signal) output from the control unit 46. The LD driver 12 includes, for example, a capacitor connected so as to supply current to the LD 10, a transistor for switching conduction / non-conduction between the capacitor and the LD 10, and a charging means capable of charging the capacitor. Including. When the LD drive signal is input to the LD drive unit 12, a drive current is applied from the LD drive unit 12 to the LD 10, and the laser light is emitted from the LD 10.

  Since the duty ratio of light emission of the LD 10 is limited from the viewpoint of safety and durability of the LD 10, it is preferable that the pulse width of the laser light pulse is narrow, and the pulse width is generally several [ns] to several It is set to about 10 [ns]. Also, the pulse interval of the laser light is generally on the order of several tens of [μs].

  The light projecting optical system 20 is an optical system that emits the laser light emitted from the LD 10 to the outside of the distance measuring device 100 and deflects and scans the laser light. Details of the projection optical system 20 will be described later with reference to FIG.

  The light receiving optical system 30 is an optical system that takes in the reflected light of the laser light emitted from the light projecting optical system 20 reflected by the object into the distance measuring device 100 and forms an image. Details of the light receiving optical system 30 will be described later with reference to FIG.

  The detection system 40 is a component group that detects the reflected light received by the light receiving optical system 30 as a voltage. The detection system 40 includes a reflection detection PD (Photo Diode) 42 and a detection circuit 44.

  The reflection detection PD 42 is a diode that detects the reflected light received by the light receiving optical system 30 and outputs a current (photocurrent) based on the intensity of the reflected light. The detection circuit 44 is a circuit that outputs a current based on the intensity of the reflected light detected by the reflection detection PD 42 as a voltage signal (detection signal).

  The time measurement unit 45 obtains the light reception timing of the reflected light in the reflection detection PD 42 based on the detection signal from the detection circuit 44, and based on the light reception timing and the rise timing of the LD drive signal from the control unit 46. , It is an apparatus which measures the reciprocation time to an object (object). The time measurement unit 45 outputs measurement data indicating the measurement result of time to the control unit 46.

  The control unit 46 is a control device that controls the entire operation of the distance measuring device 100. The control unit 46 calculates the distance to the target based on, for example, the measurement data received from the time measurement unit 45, and outputs the calculated distance to the object recognition unit 47 as distance data. Further, the control unit 46 outputs the object recognition data received from the object recognition unit 47 to an electronic control unit (ECU) 200 that performs operation control of the vehicle through the communication unit 49. The control unit 46 also outputs an LD drive signal for causing the LD 10 to emit light to the LD drive unit 12 and the time measurement unit 45 based on the synchronization signal output from the synchronization system 50. Here, the LD drive signal is a light emission control signal (periodic pulse signal) delayed with respect to the synchronization signal. The synchronization signal and the LD drive signal will be described later with reference to FIG. Further, control unit 46 starts and stops distance measurement in accordance with control signals (measurement start signal and measurement stop signal, etc.) received from ECU 200 via communication unit 49.

  The object recognition unit 47 receives a plurality of distance data acquired by scanning a plurality of laser beams from the control unit 46, and estimates the position of the object, the shape and size of the object, and the object based on the distance data. And the like, and outputs object recognition data indicating the processing result (recognition result) to the control unit 46. The object recognition data is output by the control unit 46 to the ECU 200 as described above, and is used for danger avoidance operation and the like. In the example shown in FIG. 1, the object recognition unit 47 is included in the distance measuring device 100, but is not limited to this and may be installed outside the distance measuring device 100. Alternatively, it may be included in the ECU 200 as a device responsible for the operation of the ECU 200.

  The storage unit 48 is a storage device that stores information necessary for the control unit 46 to control. The storage unit 48 stores, for example, distance data and the like calculated by the control unit 46. The storage unit 48 may be a volatile storage device or a non-volatile storage device according to the information to be stored.

  Communication unit 49 is a communication I / F for performing data communication with ECU 200. The communication unit 49 is, for example, an Ethernet (registered trademark) interface or a CAN (Controller Area Network) interface.

  The synchronization system 50 is a component group that detects the laser light emitted from the LD 10 at a specific timing by the projection optical system 20 and outputs a synchronization signal to the control unit 46. As shown in FIG. 1, the synchronization system 50 includes a synchronization lens 52, a synchronization detection PD 54, and a binarization circuit 56.

  The synchronous lens 52 is a lens for focusing the laser light reflected from the light projecting optical system 20 at a specific timing on the synchronous detection PD 54. The synchronization detection PD 54 is a diode that detects the laser beam collected by the synchronous lens 52 and outputs a current (photocurrent) based on the intensity of the laser beam. The binarization circuit 56 is a circuit that detects a current based on the intensity of laser light detected by the synchronization detection PD 54 as a voltage signal, and binarizes the voltage signal with reference to a threshold voltage. The binarization circuit 56 outputs the binarized signal (digital signal) to the control unit 46 as a synchronization signal.

  The synchronization system 50 does not necessarily have to include the synchronization lens 52, and may have another optical element (for example, a light collecting mirror or the like).

  In addition to the PDs, it is also possible to use APDs (Avalanche Photo Diodes) or SPADs (Single Photo Avalanche Diodes) that are Geiger mode APDs as the above-described PDs for reflection detection 42 and PDs for synchronization detection 54. APD and SPAD are advantageous in terms of detection accuracy because they are sensitive to PD.

  The ECU 200 is a control device that performs, for example, steering control (auto steering or the like) of an automobile, speed control (for example, auto braking), and the like based on object recognition data received from the distance measurement device 100. Specifically, when the ECU 200 determines that there is a danger based on the received object recognition data, it issues an alarm such as an alarm to alert the operator of a vehicle (mobile body) or turns the steering wheel. And outputs a command for avoiding danger to the steering control unit of the vehicle.

  The configuration of the distance measuring device 100 shown in FIG. 1 is merely an example, and it is not necessary to include all the components shown in FIG. 1, or other components may be included. For example, the object recognition unit 47 may be installed outside the distance measuring device 100 as described above. Further, in the configuration shown in FIG. 1, for example, the optical system portion, the LD of the optical system portion, the detection PD, and the like may be configured as separate devices from the distance measurement device 100.

(Configuration and operation of optical system etc.)
FIG. 2 is a view for explaining schematic configurations and operations of the light projecting optical system and the synchronization system according to the first embodiment. The schematic configuration and operation of the light projecting optical system 20 and the synchronization system 50 of the distance measuring device 100 according to the present embodiment will be described with reference to FIG. Hereinafter, description will be made using a three-dimensional orthogonal coordinate system of XYZ in which the Z-axis direction shown in FIG. 2 is the vertical direction as appropriate.

  As shown in FIG. 2, the light projecting optical system 20 includes a coupling lens 22, a reflecting mirror 24, and a rotating mirror 26.

  The coupling lens 22 is disposed on the optical path of the laser beam emitted from the LD 10 and is a lens that shapes the laser beam into a predetermined beam profile.

  The reflection mirror 24 is disposed on the optical path of the laser beam transmitted through the coupling lens 22 and is a mirror that reflects the laser beam toward the rotating mirror 26.

  The rotating mirror 26 is disposed on the optical path of the laser beam reflected by the reflecting mirror 24 and is a mirror that deflects the laser beam around the Z axis. The laser beam deflected into a predetermined deflection range around the Z axis by the rotating mirror 26 is the light emitted from the light projecting optical system 20, that is, the light (emission light) emitted from the distance measuring device 100. The rotating mirror 26 has a plurality of reflecting surfaces around the rotation axis (Z-axis), and reflects (deflects) the laser light from the reflection mirror 24 while rotating around the rotation axis, to the above-described deflection range. The corresponding effective scan area (the range from the left scan end to the right scan end shown in FIG. 2) is 1 in the horizontal 1-axis direction (Y axis direction in the example of FIG. 2) from the left scan end to the right scan end. Scan in two dimensions.

  In addition, as shown in FIG. 2, although the rotating mirror 26 has two reflective surfaces (two opposing surfaces), it is not limited to this, Even if it is 1 surface, 3 surfaces It may be more than. It is also possible to provide at least two reflecting surfaces on the rotating mirror 26 and to arrange them at different angles with respect to the rotation axis so as to switch the effective scanning area in the Z-axis direction.

  Further, instead of the rotating mirror 26, another mirror such as a polygon mirror (rotating polygon mirror), a galvano mirror, or a micro electro mechanical systems (MEMS) mirror may be used as the laser light deflector.

  As described above, the projection optical system 20 contributes to the miniaturization of the distance measuring device 100 by providing the reflection mirror 24 on the optical path between the coupling lens 22 and the rotating mirror 26 and folding the optical path. doing.

  In the housing (the housing of the distance measuring device 100) in which the projection optical system 20 is stored, an opening is formed on the optical path of the light emitted from the projection optical system 20, and the opening is shown in FIG. It is closed by the light projection window 61 shown in FIG. The light projection window 61 is formed of, for example, a light transmitting member such as glass or resin.

  The reflection mirror 24 is disposed on the upstream side of the rotation direction of the rotating mirror 26 with respect to the above-described deflection range, and the laser light deflected to the upstream side of the deflection range by the rotation mirror 26 is incident. Then, the laser beam deflected by the rotating mirror 26 and reflected by the reflecting mirror 24 enters the synchronization system 50 and enters the synchronization detection PD 54 through the synchronization lens 52. Then, whenever the laser beam reflected by the reflecting surface of the rotating mirror 26 is detected by the synchronization detection PD 54, a photocurrent is output from the synchronization detection PD 54 to the binarization circuit 56. As a result, a synchronization signal is output from the binarization circuit 56 to the control unit 46 at predetermined intervals.

  The reflection mirror 24 may be disposed downstream of the rotation range of the rotation mirror 26 with respect to the above-described deflection range.

(Structure and operation of light receiving system)
FIG. 3 is a diagram for explaining a schematic configuration and an operation of the light receiving optical system according to the first embodiment. FIG. 4 is a view of the light projecting optical system and the light receiving optical system according to the first embodiment as viewed from the Y direction. The schematic configuration and operation of the light receiving optical system 30 of the distance measuring device 100 according to the present embodiment will be mainly described with reference to FIGS. 3 and 4. Hereinafter, description will be made using a three-dimensional orthogonal coordinate system of XYZ in which the Z-axis direction shown in FIGS. 3 and 4 is the vertical direction as appropriate.

  As shown in FIG. 3, the light receiving optical system 30 includes a rotating mirror 26, a reflecting mirror 24, and an imaging optical system 32.

  The rotating mirror 26 rotates and reflects the reflected light emitted from the light projecting optical system 20 and reflected by the object within the effective scanning area. The reflecting mirror 24 reflects the light reflected by the rotating mirror 26 toward the imaging optical system 32.

  The imaging optical system 32 is an optical system which is disposed on the optical path of the reflected light reflected by the reflection mirror 24 and focuses the reflected light on the reflection detection PD 42. Although the imaging optical system 32 is configured of two lenses in the example illustrated in FIG. 2, the present invention is not limited to this. The imaging optical system 32 may be configured of one lens, or 3 It may be composed of two or more lenses.

  As described above, the light receiving optical system 30 contributes to the miniaturization of the distance measuring device 100 by providing the reflecting mirror 24 on the optical path between the rotating mirror 26 and the imaging optical system 32 and folding the optical path. doing.

  In the housing (the housing of the distance measurement apparatus 100) in which the light receiving optical system 30 is stored, an opening is formed on the optical path of the reflected light received by the light receiving optical system 30, and the opening is shown in FIG. It is closed by a light receiving window 62 shown. The light receiving window 62 is formed of, for example, a light transmitting member such as glass or resin.

  In FIG. 4, an optical path from the LD 10 to the reflection mirror 24 and an optical path from the reflection mirror 24 to the reflection detection PD 42 are shown. As shown in FIG. 4, the light projecting optical system 20 and the light receiving optical system 30 are disposed so as to overlap in the Z-axis direction, and the reflecting mirror 24 and the rotating mirror 26 correspond to the light projecting optical system 20 and the light receiving optical system 30. It is common to and. As a result, the relative positional deviation between the irradiation range of the laser beam from the LD 10 on the object and the light reception possible range of the reflected light by the reflection detection PD 42 can be reduced, and stable object detection can be realized.

(Synchronization signal and LD drive signal)
FIG. 5 is a diagram for explaining a synchronization signal and an LD drive signal in the distance measuring device according to the first embodiment. The synchronization signal and the LD drive signal will be described with reference to FIG.

  As described above, every time the laser beam reflected by the reflection surface of the rotating mirror 26 is detected by the synchronization detection PD 54, the photocurrent based on the intensity of the laser beam is sent to the binarization circuit 56 from the synchronization detection PD 54. It is output. Then, the binarization circuit 56 detects the photocurrent output from the synchronization detection PD 54 as a voltage signal, and the voltage signal is binarized based on the threshold voltage as a synchronization signal as shown in FIG. As shown in FIG. 5, the control unit 46 outputs the data to the control unit 46 at predetermined intervals (synchronization detection intervals).

  As described above, when the synchronization signal is output from the binarization circuit 56 at a predetermined interval, the rotation timing of the rotating mirror 26 can be obtained from the output timing of the synchronization signal. Therefore, after the synchronization signal is output from the binarization circuit 56 (after the laser light for synchronization emitted from the LD 10 is detected by the synchronization detection PD 54), the control unit 46 performs the LD By outputting an LD drive signal (rectangular pulse signal) for outputting a pulse of laser light (hereinafter, may be referred to as “emission light pulse”) from the LD 10 to the drive unit 12 at a predetermined interval T, The effective scanning area can be optically scanned. That is, between the timings at which the synchronization signal is output from the binarization circuit 56, the emission light pulse is emitted from the LD 10, whereby the effective scanning area can be optically scanned.

(Emitting light pulse and reflected light pulse)
FIG. 6 is a diagram for explaining an emitted light pulse and a reflected light pulse. The emitted light pulse and the reflected light pulse will be described with reference to FIG.

  When the effective scanning region is scanned by the rotating mirror 26, the LD driving unit 12 drives the LD 10 to emit (emit) an emitted light pulse as shown in FIG. 6A. Then, the emission light pulse emitted from the LD 10 is reflected or scattered by the object (object), and the reflected or scattered pulse light (hereinafter sometimes referred to as “reflected light pulse”) is reflected by the detection PD 42. It is detected. At this time, the distance to an object (object) may be calculated by measuring a time t from when the LD 10 emits an emission light pulse to when the reflection detection PD 42 detects the reflection light pulse. it can.

  As for measurement of time, for example, as shown in FIG. 6 (b), the emitted light pulse is made a rectangular pulse binarized by a light receiving element such as PD, and the reflected light pulse is binarized by a detection circuit 44. A rectangular pulse may be used, and the time difference t between the rising timings of both rectangular pulses may be measured. Further, the waveforms of the emitted light pulse and the reflected light pulse are A / D converted and converted to digital data, and the time t is measured by correlating the output signal of the LD 10 and the output signal of the reflection detecting PD 42. It is also possible.

  As a detectable distance in the distance measurement method for calculating the distance to the object (object) as described above, an object on the order of 100 [m] is required, and in general, reflection from an object 100 [m] ahead The intensity (light quantity) of the reflected light that is received and returned is about several [nW] to several tens [nW]. That is, the detection system 40 is required to be able to detect several [nW] reflected light pulses without error. Since the signal intensity of the reflected light signal for weak light of several [nW] is small, it is susceptible to random noise, which affects the distance measurement accuracy and the reliability of object detection.

  The above-mentioned random noise is roughly classified into circuit noise and shot noise. Of these, shot noise is particularly problematic. Circuit noise is thermal noise generated from resistance and noise generated by the substrate picking up radiation noise, and is usually on the order of several [mV].

  On the other hand, shot noise is white noise associated with light quantity measurement, and its magnitude is proportional to the square root of the time average of light quantity. Therefore, when the sensitivity of the measuring instrument is high or disturbance light is strong, the magnitude may be several tens of [mV] or more, which is more likely to be a problem than circuit noise. Further, as is apparent from the fact that the magnitude of the shot noise is proportional to the square root of the time average of the light quantity, the shot noise also occurs as white noise when detecting light of constant intensity. The details of the shot noise problem will be described in FIG. 7 below.

(About shot noise)
FIG. 7 is a diagram for explaining an example of shot noise when light is received. Shot noise in the case of receiving sunlight will be described with reference to FIG. 7. In FIG. 7, the detection signal (voltage signal) waveform which the detection system 40 detected regarding the case where sunlight enters and does not enter is shown.

  As shown in FIGS. 7 (a) and 7 (b), compared to the case where sunlight does not enter, not only DC component increases but also shot noise increases when sunlight enters. The DC component can be removed by a high pass filter or the like, but as shown in FIG. 7C, the shot noise can not be removed by the high pass filter or the like.

  In the actual traveling environment of the vehicle, when the sunlight is reflected by a highly reflective object such as the window glass or bonnet of the vehicle and strong sunlight is received by the light receiving element (PD 42 for reflection detection in this embodiment), As shown in FIG. 7 (d), the shot noise increases and exceeds the threshold for discriminating the reflected light pulse. In this case, the reflected light pulse from the object can not be discriminated from the noise, resulting in erroneous detection. Furthermore, since the sunlight entering the light receiving element becomes stronger when the highly reflective object is at a short distance, the shot noise becomes larger, the phenomenon where the shot noise exceeds the threshold is more likely to occur, and the false detection also increases. Is concerned.

  In the conventional method of detecting the light reception signal based on the threshold to cope with such a problem, it is usually necessary to set the threshold (voltage) sufficiently higher than shot noise to prevent false detection due to shot noise. Basically, the threshold is determined on the assumption that the shot noise is maximum. Therefore, when the shot noise is relatively small, the threshold is set to be excessively large, and the detectable distance becomes smaller than necessary. In order to increase the detection distance, it is desirable to set the threshold to the minimum in the range where false detection does not occur. The detail of the distance measuring device 100 according to the present embodiment for solving such a problem will be described with reference to FIGS.

(Configuration of functional block of distance measuring device)
FIG. 8 is a diagram showing an example of a functional block configuration of the distance measuring device according to the first embodiment. The configuration of functional blocks of the distance measuring device 100 according to the present embodiment will be described with reference to FIG.

  As shown in FIG. 8, the distance measuring device 100 according to the present embodiment includes a light emitting unit 101, a light detecting unit 102, a determining unit 103, a measuring unit 104, a control unit 110, and a storage unit 121. And a communication unit 122.

  The light emitting unit 101 is a functional unit that emits (projects) a laser beam (emission light pulse) in accordance with the LD drive signal output from the control unit 110. The light projecting unit 101 is realized by the light projecting optical system 20, the LD 10, and the LD driving unit 12 shown in FIG.

  The light detection unit 102 detects a detection pulse (detection) by receiving the reflected light that is emitted from the light projection unit 101 and reflected by the object, and the other light (disturbance such as sunlight, noise). Function unit to detect as a signal). The light detection unit 102 is realized by the light receiving optical system 30 and the detection system 40 (PD for reflection detection 42 and detection circuit 44) shown in FIG.

  The determination unit 103 is a functional unit that determines whether or not the magnitude (for example, voltage) of the detection signal detected by the light detection unit 102 exceeds a predetermined threshold. Determination unit 103 is realized by time measurement unit 45 shown in FIG.

  The measurement unit 104 obtains the light reception timing of the detection signal that is determined to have exceeded the threshold by the determination unit 103 among the detection signals from the light detection unit 102, and the light reception timing and the rise of the LD drive signal from the control unit 110. It is a functional unit that measures the round trip time to an object (object) based on the timing. The measurement unit 104 outputs measurement data indicating the measurement result of time to the control unit 110. The measuring unit 104 is realized by the time measuring unit 45 shown in FIG.

  The control unit 110 is a functional unit that controls the overall operation of the distance measuring device 100. As shown in FIG. 8, the control unit 110 includes a distance calculation unit 111 (first calculation unit), a signal information acquisition unit 112 (first acquisition unit), a measurement count determination unit 113 (determination unit), and a count unit. And a final distance calculation unit 116 (second calculation unit). Control unit 110 is realized by control unit 46 shown in FIG.

  The distance calculation unit 111 is a functional unit that converts measurement data about the time received from the measurement unit 104 into a distance (an example of a value based on time) (calculates a distance). That is, the distance is a value based on the measured time. Here, the distance obtained by the distance calculation unit 111 is not used as the final distance to the object that is the target of distance measurement. As described later, the functions of the signal information acquisition unit 112, the measurement count determination unit 113, the count unit 114, the identification unit 115, and the final distance calculation unit 116 finally calculate the distance to the object. Although the distance calculation unit 111 converts measurement data of the time received from the measurement unit 104 into a distance, since the time has a one-to-one relationship with the distance, the time itself (a value based on the time) (Example) may be output as the calculation result.

  The signal information acquisition unit 112 extracts, from among the detection signals detected by the light detection unit 102, the peak value (an example of information related to a detection pulse) of the detection signal (detection pulse) determined by the determination unit 103 to have exceeded the threshold. Is a functional unit to be acquired. Here, the peak value is, for example, the voltage value of the peak portion of the detection pulse, or the height of the voltage level of the peak portion from the voltage level of the threshold of the detection pulse.

  The number-of-times-of-measurements determination unit 113 is performed on one or more detection pulses detected by the light detection unit 102 after the emission light pulse is emitted from the light emission unit 101 until the emission light pulse is next emitted. This is a functional unit that determines the number of measurements based on the peak value acquired by the signal information acquisition unit 112, with one series of processing as one measurement.

  The counting unit 114 performs each measurement for the number of times of measurement determined by the number-of-measurements determination unit 113 with respect to the class for the distance divided to create a histogram at an arbitrary distance interval as illustrated in FIG. The functional unit counts the number of detection pulses (detection signals) determined to have exceeded the threshold for each rank.

  The identifying unit 115 detects the reflected light signal (reflection from the object) of the detection signal (detection pulse) belonging to the class having the largest total value (total number) in each measurement of the count value for each class counted by the counting unit 114. It is a functional part specified as an optical pulse).

  The final distance calculation unit 116 sets the average value of the distances calculated by the distance calculation unit 111 as the distance from the object for each reflected light signal (reflected light pulse) from the object specified by the specification unit 115. It is a functional unit to calculate. As described above, since the average value of each distance corresponding to the reflected light signal specified by the specifying unit 115 is obtained, even if the class including the reflected light pulse includes noise, the influence can be reduced.

  The above-described distance calculation unit 111, signal information acquisition unit 112, measurement count determination unit 113, count unit 114, identification unit 115, and final distance calculation unit 116 are, for example, software whose control unit 110 is stored in storage unit 121. It is realized by reading and executing a program. A part or all of the distance calculation unit 111, the signal information acquisition unit 112, the measurement count determination unit 113, the count unit 114, the identification unit 115, and the final distance calculation unit 116 is not a program as software but an FPGA (Field- It may be realized by a hardware circuit such as a programmable gate array (ASIC) or an application specific integrated circuit (ASIC).

  The storage unit 121 is a functional unit that stores information necessary for the operation of the control unit 110. The storage unit 121 may, for example, detect the detection signal detected by the light detection unit 102, the measurement data measured by the measurement unit 104, the distance data calculated by the distance calculation unit 111, and the peak value acquired by the signal information acquisition unit 112. At least one of the measurement count determined by the measurement count determination unit 113, the count value for each class in each measurement counted by the count unit 114, and the distance from the object calculated by the final distance calculation unit 116 Remember. The storage unit 121 is realized by, for example, the storage unit 48 illustrated in FIG.

  Communication unit 122 is a functional unit for performing data communication with ECU 200. The communication unit 122 includes, for example, data of the distance from the object calculated by the control unit 110 (final distance calculation unit 116) in the object recognition data, and transmits the object recognition data to the ECU 200. The communication unit 122 is realized by the communication unit 49 shown in FIG.

  The light emitting unit 101, the light detecting unit 102, the determining unit 103, the measuring unit 104, and the control unit 110 (the distance calculating unit 111, the signal information acquiring unit 112, and the number of times of measurement determination unit 113) of the distance measuring device 100 illustrated in FIG. The counting unit 114, the identifying unit 115, and the final distance calculating unit 116), the storage unit 121, and the communication unit 122 conceptually show functions, and the present invention is not limited to such a configuration. For example, a plurality of functional units illustrated as independent functional units in the distance measurement device 100 illustrated in FIG. 8 may be configured as one functional unit. On the other hand, the function of one functional unit may be divided into a plurality of units in the distance measuring device 100 illustrated in FIG. 8 and configured as a plurality of functional units.

  Moreover, in FIG. 8, the main functional parts that the distance measuring device 100 has are shown, and the functions that the distance measuring device 100 has are not limited to these.

(Contrast of reflected light pulse and noise)
FIG. 9 is a diagram for explaining the contrast between the reflected light pulse and the shot noise when the distance to the object is short. FIG. 10 is a diagram for explaining the contrast between the reflected light pulse and the shot noise when the distance to the object is long. The comparison between the reflected light pulse and the shot noise will be described with reference to FIGS. 9 and 10.

  As shown in FIG. 9, for example, when the ambient illumination is very bright, the shot noise intensity (voltage) increases, but the distance to the object (object) is close (for example, 10 [m], 20 [m] ], 30 [m], 40 [m]) or when the reflectance of an object (object) is large, it is easy to distinguish from shot noise, and for detecting the peak of the reflected light pulse of the object The setting of the threshold (voltage) also becomes easy.

  On the other hand, as shown in FIG. 10, the distance to an object (object) is far (for example, 50 [m], 60 [m], 70 [m]) or the reflectance of the object (object) is large. In this case, the peak of the reflected light pulse of the object becomes very small, which makes it difficult to distinguish from the shot noise.

(Relationship between the actual distance to the object and the peak value and shot noise)
FIG. 11 is a diagram showing an example of the relationship between the actual distance to the object, the peak value of the reflected light pulse, and the shot noise. The relationship between the actual distance to the object (target object), the peak value (voltage) of the reflected light pulse, and the shot noise will be described with reference to FIG. In addition, in FIG. 11, the shot noise assumes the largest shot noise when light is received at a strong west day, and the shot noise is indicated by an error bar 300 from 0 [mV].

  As shown in FIG. 11, the peak value (voltage) of the reflected light pulse of the object (object) is saturated at the near distance principle (10 to 25 [m]). In addition, when setting a threshold for avoiding false detection due to shot noise, as shown in FIG. 11, for example, when a threshold is set at 400 [mV], measurement of a long distance of 50 [m] or more is performed. In the case of distance measurement, the target value can not be measured because the peak value is below the threshold. That is, in order to perform distance measurement of an object to a further distance, a technique for separating the shot noise and the reflected light pulse while setting the threshold small is required.

(Other factors that misdetect the reflected light pulse from the object)
FIG. 12 is a diagram for explaining the comparison between a detection pulse due to rain and a reflected light pulse from an object. With reference to FIG. 12, a detection pulse by rain will be described as an example of a factor that erroneously detects a reflected light pulse from an object.

  Other factors that erroneously detect the reflected light pulse from the object (object) include rain and fog. Also in this case, as with shot noise, the possibility of exceeding the threshold for detection of the reflected light pulse (reflected light signal) from the object is increased, and also in this case, which signal is the reflected light pulse from the object It becomes difficult to determine the

  In FIG. 12, assuming that it is the timing (emission timing) at which the emission light pulse is emitted at time 0, detection pulses by reflection from three rains (1) to (3), and one object (object Shows a reflected light pulse due to the reflection from. Assuming that the threshold for detecting the reflected light pulse is set to the broken line level shown in FIG. 12, the detection pulses of rain (1) to rain (3) and the reflected light pulse of the object exceed the threshold. It is detected as a detection pulse. We want to recognize that it is dangerous for objects without recognizing it as dangerous for rain, but if we look at the 4 detection pulses, it is usually determined which is the rain and which is the object Have difficulty. Therefore, it can not be determined where the position of the object to be recognized as danger is.

(Operation to count detection pulses exceeding the threshold for each distance class)
FIG. 13 is a diagram for explaining counting of signals exceeding the threshold for each classified histogram class. FIG. 14 is a view for explaining that the reflected light from the object is specified by counting the signal exceeding the threshold for each classified histogram class. FIG. 15 is a diagram showing points to be improved in identifying the reflected light from the object by counting the signals exceeding the threshold for each classified histogram class. The operation of counting detection pulses exceeding the threshold for each distance class will be described with reference to FIGS. 13 to 15.

  The distance measuring apparatus 100 according to the present embodiment counts the number of detection pulses exceeding the threshold, including noise such as rain or shot noise (hereinafter, described as “shot noise” to make the explanation relevant). And the storage unit 121 stores a distance or the like corresponding to the detected pulse.

  As shown in FIG. 13, for example, measurement is performed to record a detection pulse of shot noise and reflected light exceeding a threshold (set to 100 [mV] in the example of FIG. 13) to an object (object). Should be done several times. Next, the counting unit 114 divides the histogram class (hereinafter, simply referred to as “class”) by a predetermined distance, and determines the number of detection pulses determined to have exceeded the threshold value in each measurement of a plurality of measurements. , Count by divided classes. By taking such a method, even if the measurement is performed multiple times, the detection pulse (reflected light pulse) from the object is stably detected in the same class, but the shot noise exceeding the threshold It is possible to identify the class in which the reflected light pulse from the object is included, using that the class in which the detection pulse based on is detected is random for each measurement.

  Here, FIG. 14 shows an example in which the class is divided every 2 [m], and the number of times of measurement is five, and the detection pulses are counted in each class. First, in the first measurement, detection pulses are counted in a rank of 20 to 22 [m], and detection pulses are similarly counted in a rank of 30 to 32 [m]. Next, in the second measurement, detection pulses are counted in the 24 to 26 [m] class, and detection pulses are similarly counted in the 30 to 32 [m] class. As a result of performing such counting operation in each of five measurements, the class in which the shot pulse of the shot noise is counted is random, so only a small number can be entered in each class even if the measurement is repeated. Since the reflected light pulse from the object is a detection pulse corresponding to the distance at which the object is located, it is basically counted in the class corresponding to the distance. That is, the class of 30 to 32 [m] is counted every five measurements, and it can be estimated that the detection pulse counted in this class is the reflected light pulse from the object. If the average value (31.1 [m] in the example of FIG. 14) of only the detected pulse distance corresponding to this class is calculated based on this estimation, the distance to the object can be obtained. The process of deriving the distance to the object by the plurality of measurements described in FIG. 13 and FIG. 14 described above is referred to as “inter-frame process” for convenience.

  However, there are points to be improved in the above-described inter-frame processing when the class interval is narrowed and when the number of frames (the number of measurements) is reduced. When the interval between classes is narrowed, when the calculated distance is dispersed near the division of classes, there is a possibility that it may be counted in the next class. In addition, when the number of measurements is reduced, the count number of the shot noise detection pulse may be equal to the count number of the reflected light pulse by chance in other classes. In this case, the shot noise and the reflected light It can not be distinguished from the pulse.

  For example, FIG. 15 shows an example in which the classes are classified by 1 [m], the number of times of measurement is three, and the detection pulses are counted in each class. In the first measurement, the shot noise detection pulse is counted in the 27 to 28 [m] class, and the reflected light detection pulse (reflected light pulse) is counted in the 31 to 32 [m] class. However, in the second measurement, as in the first measurement, the detection pulse of shot noise is counted in the 27 to 28 [m] class, and furthermore, the class width is narrow. (Pulse) is counted in the class of 30 to 31 [m], not the class of 31 to 32 [m]. As a result, the detection pulses are counted twice in total in the classes of 27 to 28 [m], and the detection pulses are also counted twice in total in the classes of 31 to 32 [m]. Therefore, it is not possible to determine which of the average values 27.5 [m] and 31.1 [m] of the distances of the detection pulses corresponding to these two classes is the distance of the true object.

  In view of these, the distance measuring device 100 according to the present embodiment performs the process of setting the number of frames as described with reference to FIGS.

(Processing for setting the number of frames of distance measuring device)
FIG. 16 is a diagram showing an example of the relationship between the peak value of the reflected light pulse and the number of measurements when a high ranging success rate is secured. FIG. 17 is a diagram for explaining that the measurement interval is different depending on the number of times of measurement. The relationship between the peak value of the reflected light pulse and the number of measurements will be described with reference to FIGS. 16 and 17.

  The graph shown in FIG. 16 shows the peak of the reflected light pulse at which the distance measurement success rate is 90% or more when the shot noise is 120 mV and the threshold is 170 mV in the above-described interframe processing. It is a graph which shows the relationship between a value and the number of times of measurement. Here, with the distance measurement success rate, for example, an object is placed at 40 [m], and if the value calculated as the distance of the object is about 40 [m], it is regarded as distance measurement success and exceeds the threshold. When the shot noise is incorrectly detected as a reflected light pulse from the target object, or when the distance measurement can not be performed because the peak value is smaller than the threshold, etc., the distance measurement succeeds with respect to the entire number of distance measurements. The ratio of the number of times is calculated.

  In the graph of FIG. 16, for example, when the peak value of the reflected light pulse from the object is 600 [mV], measurement is performed to distinguish from shot noise while securing a ranging success rate of 90 [%] or more. It shows that the number of times is 5 times.

  In the conventional processing (inter-frame processing) described above with reference to FIGS. 14 and 15, the number of measurements is uniquely determined (five times in FIG. 14 and three times in FIG. 15). It is the same as that of the projection optical system 20 shown to, and the rotation speed of a rotating mirror is 500 [rpm]. In this case, the time for one measurement is 60 [ms], and if the number of measurements is five, the measurement at 300 [ms] will be repeated under any circumstances. Such inter-frame processing has the points to be improved as described above, but also needs to be improved even when the object viewed from the distance measuring device 100 is relatively moved. The points to be improved will be described below with reference to FIG.

  For example, as shown in FIG. 17, the first distance measurement processing (inter-frame processing) is performed at a distance of 10 m to the moving object (target object) approaching the distance measuring device 100 at 60 [km / h]. Suppose it was done. FIG. 17A shows an example where the number of measurements is five for one distance measurement process. In this case, the time taken for one measurement is 60 [ms], and the object moves by 1 [m] per one measurement (relatively closer to the distance measuring device 100), so at intervals of 5 [m] It can only output the distance to the object. On the other hand, FIG. 17B shows an example in which the number of measurements is two for one distance measurement process. In this case, the distance to the object can be output at 2 [m] intervals.

  As apparent from the above, when the object is a moving object or the like existing at a short distance (10 [m] in FIG. 17) as assumed in FIG. In order to detect quickly, it is required to repeat distance output with a small number of measurements and to update distance information.

  Therefore, in the present embodiment, the correlation between the peak value of the reflected light pulse and the number of measurements shown in FIG. 16 described above is used. From the graph shown in FIG. 16, it is indicated that the peak values at which a distance measurement success rate of a certain amount or more can be secured have differences in the number of measurements, and there are optimum or preferred numbers of measurements. The number of times of measurement is determined (set) from the peak value of the detected pulse based on the correlation between the peak value of the reflected light pulse and the number of times of measurement. Do.

  As shown in FIG. 16, when the peak value is 1200 [mV], the ranging success rate is 90 [%] or more even if the number of measurements is two, and in this case, the number of measurements is two, that is, 2 [m] Distance output becomes possible for each. Based on the above values, for example, if the peak value is 1200 [mV] or more, the number of measurements is two, and if it is 1050 to 1200 [mV], the number of measurements is three, 850 to 1050 [mV] If so, the number of measurements is four, if it is 600 to 850 [mV], the number of measurements is five, and if less than 600 [mV], the number of measurements is set to five or more. The flow of the inter-frame processing for setting the number of times for performing the distance measurement process by appropriately setting the number of measurements according to the peak value of the reflected light pulse as described above in the present embodiment will be described with reference to FIG.

  FIG. 18 is a flowchart showing an example of the process of setting the number of times between frames of the distance measuring device according to the first embodiment. The flow of the process of setting the number of times between frames of the distance measuring device 100 according to the present embodiment will be described with reference to FIG.

<Step S11>
The light emitting unit 101 of the distance measuring device 100 emits (projects) laser light (emission light pulse) in accordance with the LD drive signal output from the control unit 110. The light detection unit 102 of the distance measurement device 100 detects a detection pulse (detection) by receiving reflected light that is emitted from the light emitting unit 101 and reflected light reflected by the object, and other light (such as noise). As a signal). The light detection unit 102 outputs the detected detection pulse (detection signal) to the control unit 110 and the determination unit 103. Then, the process proceeds to step S12.

<Step S12>
The determination unit 103 of the distance measurement device 100 determines whether or not the magnitude (for example, voltage) of the detection signal detected by the light detection unit 102 exceeds a predetermined threshold. When the threshold is exceeded (step S12: Yes), the process proceeds to step S13, and when the threshold is not exceeded (step S12: No), the process proceeds to step S21.

<Step S13>
When the number of times of measurement has already been determined (set) by the number-of-measurements determination unit 113 of the distance measurement apparatus 100 (step S13: Yes), the measurement unit 104 of the distance measurement apparatus 100 is determined by the determination unit 103 to exceed the threshold. The light reception timing of the detection signal is obtained, and based on the light reception timing and the rise timing of the LD drive signal from the control unit 110, the reciprocation time of the object (object) is measured. The measurement unit 104 outputs measurement data indicating the measurement result of time to the control unit 110. Then, the process proceeds to step S16.

  On the other hand, when the number of times of measurement has not been determined (set) by the number of times of measurement determination unit 113 of the distance measurement device 100 (step S13: No), the process proceeds to step S14.

<Step S14>
The signal information acquisition unit 112 of the distance measurement device 100 extracts and acquires the peak value of the detection signal (detection pulse) determined to have exceeded the threshold value by the determination unit 103. Note that the detection pulse that is the target of extraction of the peak value by the signal information acquisition unit 112 is, for example, the light detection unit after the emission light pulse is emitted from the light emission unit 101 until the emission light pulse is next emitted. Among the one or more detection pulses detected by 102, the detection pulse having the highest peak value exceeding the threshold may be used. Then, the process proceeds to step S15.

<Step S15>
The number of times of measurement determination unit 113 of the distance measurement device 100 determines one or more detection pulses detected by the light detection unit 102 after the emission light pulse is emitted from the light emission unit 101 until the emission light pulse is next emitted. The number of measurements is determined (set) on the basis of the peak value acquired by the signal information acquisition unit 112 in order to create a histogram by taking a series of processes to be performed for one measurement as one measurement. In this case, the number-of-measurements determination unit 113 determines the number of measurements from the peak value, for example, based on the correlation between the peak value and the number of measurements as shown in FIG. 16 described above. Then, the process proceeds to step S16.

<Step S16>
The distance calculation unit 111 of the distance measurement device 100 converts the distance into a distance (calculates the distance) based on the measurement data of the time received from the measurement unit 104. Then, the process proceeds to step S17.

<Step S17>
The count unit 114 of the distance measuring device 100 sets the number of detection pulses (detection signals) determined to have exceeded the threshold with respect to the class for the distance divided to create a histogram at an arbitrary distance interval. Count by rank of Then, the process proceeds to step S18.

<Step S18>
When the calculation of the distance by the distance calculation unit 111 and the process of the counting process by the counting unit 114 are performed by the number of times of measurement determined by the number of times of measurement determination unit 113 (step S18: Yes), the process proceeds to step S19. If not executed (step S18: No), the process returns to step S11.

<Step S19>
The identifying unit 115 of the distance measuring device 100 detects the detection signal (detection pulse) belonging to the class having the largest total value (total number) in each measurement of the count value for each class counted by the counting unit 114 from the object. It identifies as a reflected light signal (reflected light pulse). Also, the measurement number determination unit 113 resets the determined number of measurements. Then, the process proceeds to step S20.

<Step S20>
The final distance calculation unit 116 of the distance measurement device 100 targets the average value of the distances calculated by the distance calculation unit 111 for each reflected light signal (reflected light pulse) from the object specified by the specifying unit 115 Calculated as the distance from the object. The final distance calculation unit 116 transmits, to the ECU 200, the distance data on the calculated distance from the target, for example, included in the object recognition data via the communication unit 122. Then, the process of setting the number of times is completed.

<Step S21>
If the magnitude of the detection signal detected by the light detection unit 102 does not exceed the threshold value by the determination unit 103, the control unit 110 of the distance measurement device 100 does not have an object or a collision due to another object or the like It is determined that there is no risk of Then, the process proceeds to step S22.

<Step S22>
The control unit 110 discards the information of the detection pulse received from the light detection unit 102. Then, the process returns to step S11.

  By the above steps S11 to S22, the process of setting the number of frames is executed, and the distance to the object (object) is calculated.

  As described above, in the distance measuring device 100 according to the present embodiment, there is a difference in the number of times of measurement between the peak values at which the distance measurement success rate of a certain amount or more can be secured. The number of measurements is determined (set) from the peak value of the detected pulse based on the correlation between the peak value of the reflected light pulse and the number of measurements, and the number of times of distance measurement processing is set according to the number of measurements. Perform inter-frame processing. That is, in each measurement for the number of measurements determined (set) according to the peak value, detection pulses exceeding the threshold are counted for each class of distance, and the total value in each measurement belongs to the largest class The signal (detection pulse) is specified as a reflected light signal (reflected light pulse) from the object, and the distance calculation unit 111 calculates each reflected light signal (reflected light pulse) from the specified object. The average value of each distance is calculated as the distance from the object. Thereby, the detection signal of the reflected light from the object and the noise can be accurately distinguished by the optimum or suitable number of times of measurement according to the peak value, and the accuracy of the measurement of the distance to the object can be improved. .

  Also, the reflected light from the object such as distance measurement of the object under a long distance, distance measurement for an object with low reflectance, or distance measurement of an object under a strong ambient light such as a west sun In a situation where the magnitude of the noise is not negligible with respect to the magnitude of the pulse, the number of measurements is set according to the situation, so even if the threshold for detecting the reflected light pulse is set low, noise and reflection Optical pulses can be discriminated with high accuracy.

(Modification 1)
FIG. 19 is a diagram for explaining the signal waveform width correlated with the peak value in the modification 1 of the first embodiment. FIG. 20 is a diagram showing the relationship between the signal waveform width and the peak value in Modification 1 of the first embodiment. The process using the correlation between the signal waveform width and the peak value according to the modification 1 of the present embodiment will be described with reference to FIGS. 19 and 20.

  In FIG. 19, the magnitude of the signal waveform width Δt, which is the time width between the rise time (rise time tr) of the detection signal exceeding the threshold (first threshold) and the fall time (fall time tf) It shows. FIG. 20 is a graph showing an example of the relationship between the signal waveform width Δt and the peak value of the detection signal (detection pulse) when the threshold is 170 [mV]. From the graph shown in FIG. 20, it can be seen that the peak value also increases as the signal waveform width Δt increases.

  From the above, in this modification, the correlation between the signal waveform width Δt and the peak value as shown in FIG. 20 and the correlation between the peak value of the reflected light pulse and the number of measurements shown in FIG. Then, the number of times of measurement is determined (set) from the signal waveform width Δt, and a process of setting the number of times of distance measurement is performed according to the number of times of measurement. For example, if the signal waveform width Δt is 55 [ns] or more, the peak value becomes 1200 [mV] or more, and the number of measurements is determined (set) twice. Similarly, if the signal waveform width Δt is 45 to 55 [ns], the number of measurements is three times, and if the signal waveform width Δt is 40 to 45 [ns], the number of measurements is four times and the signal waveform width Δt is If it is less than 40 [ns], the number of measurements is appropriately determined (set) such as five times or more.

  Specifically, of the detection signals detected by the light detection unit 102, the signal information acquisition unit 112 determines the signal waveform width Δt of the detection signal (detection pulse) determined to have exceeded the threshold value by the determination unit 103 (second The waveform width and an example of information on the detection pulse are extracted and acquired. Then, the number-of-measurements determination unit 113 obtains a peak value from the signal waveform width Δt, and determines (sets) the number of measurements based on the peak value. The determination of the peak value from the signal waveform width Δt may be performed by the signal information acquisition unit 112 instead of the measurement number determination unit 113.

  In FIG. 19, the pulse width at the threshold is set as the signal waveform width Δt for the detection signal exceeding the threshold, but it is not limited to this. For example, at a position above or below the threshold by a predetermined value The pulse width may be the signal waveform width Δt.

  As described above, the number of times of measurement may be determined according to the pulse width (signal waveform width Δt) of the detection signal, and the process of setting the number of times between frames may be performed. As a result, the detection signal of the reflected light from the object and the noise can be accurately distinguished by the optimum or preferred number of measurements according to the pulse width of the detection signal (signal waveform width Δt), and the distance to the object The accuracy of the measurement can be improved.

(Modification 2)
FIG. 21 is a diagram for explaining which of a plurality of threshold values the detection signal has exceeded in the second modification of the first embodiment. The process of determining the number of times of measurement depending on which threshold the detection pulse of the modification 2 of the present embodiment exceeds will be described with reference to FIG.

  FIG. 21 illustrates an example in which, for example, four threshold values Vth1 to Vth4 are provided to determine the threshold value for the detection signal (detection pulse). As described above, the peak value can be estimated by providing a plurality of threshold values and determining which threshold value the detection signal exceeds, and the number of measurements can be determined (set) according to the determination result. Then, according to the determined number of times of measurement (number of times), the inter-frame process is performed for setting the number of times of distance measurement.

  For example, in FIG. 21, assuming that four threshold values Vth1 to Vth4 are respectively 170 [mV], 850 [mV], 1050 [mV] and 1200 [mV], as shown in (Table 1) below, detection signals The number of measurements can be determined depending on which threshold the

  As shown in FIG. 21 and (Table 1), when the exceeded threshold is the threshold Vth3, the peak value is constant because there is a peak between 1050 [mV] of the threshold Vth3 and 1200 [mV] of the threshold Vth4. It can be determined that the number of measurements for securing the above ranging success rate is three.

  Specifically, of the detection signals detected by the light detection unit 102, the signal information acquisition unit 112 detects a detection signal (detection pulse) determined by the determination unit 103 as exceeding the threshold (for example, the threshold Vth1). Information on which threshold is exceeded (an example of information on a detected pulse) is acquired. Then, the number of times of measurement determination unit 113 determines (sets) the number of times of measurement based on information on which threshold the detection signal has exceeded.

  As described above, the number of times of measurement may be determined according to which of the plurality of thresholds the detection signal has exceeded, and the process of setting the number of times between frames may be performed. As a result, the detection signal of the reflected light from the object and the noise can be accurately distinguished by the optimum or preferred number of times of measurement depending on which of the plurality of thresholds the detection signal has exceeded. The accuracy of distance measurement can be improved. Note that FIG. 21 and (Table 1) are an example in the modified example, the number of threshold values is not limited to four, and each threshold value is a value different from the above-mentioned value It is also good.

  Although the example shown in FIG. 21 has described the operation of estimating the peak value depending on which of the plurality of threshold values is exceeded, it is also possible to estimate the peak value according to the number of the threshold values. In this case, the number of measurements can be determined according to the number.

(Modification 3)
FIG. 22 is a diagram for explaining inclinations of two time points which respectively exceed two threshold values correlated with the peak value in the modification 3 of the first embodiment. FIG. 23 is a diagram showing a relationship between slopes at two points in time when the two threshold values are exceeded in the third modification of the first embodiment, and a peak value. A process using correlation between peak values and slopes at two points in time when the two threshold values are exceeded in the third modification of the embodiment will be described with reference to FIGS. 22 and 23.

  FIG. 22 shows the slopes at two points of rise time (rise time tr1, tr2) of each detection signal exceeding the thresholds 170 [mV] and 350 [mV]. And FIG. 23 showed an example of the relationship of the inclination of two time points which exceeded each two threshold when the two threshold of 170 [mV] and 350 [mV] were exceeded, and a peak value. It is a graph. It can be seen from the graph shown in FIG. 23 that as the slopes at two time points increase, the peak value also increases.

  From the above, in this modification, as shown in FIG. 23, the slopes of two time points respectively exceeding the two threshold values, the correlation with the peak value, and the peak of the reflected light pulse shown in FIG. Using the correlation between the value and the number of measurements, determine (set) the number of measurements from the slope of the two points that each exceeded two threshold values, and perform inter-frame processing for setting the number of times ranging processing is performed according to the number of measurements . For example, if the slope is 5.3 [mV / ns] or more, the peak value becomes 1200 [mV] or more, and the number of measurements is determined (set) twice. Similarly, if the slope is 5.0 to 5.3 [mV / ns], the number of measurements is four, if the slope is 3.5 to 5.0 [mV / ns], the number of measurements is five, the slope If is less than 3.5 [mV / ns], the number of measurements is appropriately determined (set) such as five times or more.

  Specifically, of the detection signals detected by the light detection unit 102, the signal information acquisition unit 112 exceeds two thresholds for the detection signal (detection pulse) determined to have exceeded the threshold by the determination unit 103. The slopes at two points in time (an example of the information on the detection pulse) are obtained and acquired. Then, the number-of-measurements determination unit 113 obtains peak values from the slopes of the two points when the two thresholds are respectively exceeded, and determines (sets) the number of measurements based on the peak values. The determination of the peak value from the slopes at two points in time when the two threshold values are exceeded may be performed by the signal information acquisition unit 112 instead of the measurement number determination unit 113.

  Note that the threshold used by the determination unit 103 may match either of the two thresholds used by the signal information acquisition unit 112, or may be a threshold different from the two thresholds.

  As described above, the number of times of measurement may be determined according to the inclination of two points in time when the two threshold values of the detection signal are respectively exceeded, and the process of setting the number of times between frames may be performed. By this, the detection signal of the reflected light from the object and the noise can be accurately distinguished by the optimum or preferred number of times of measurement depending on the inclination of two time points respectively exceeding the two threshold values of the detection signal. The accuracy of the distance measurement can be improved.

(Modification 4)
FIG. 24 is a diagram for explaining the difference in the signal waveform width at two threshold values that are correlated with the peak value in Modification 4 of the first embodiment. FIG. 25 is a diagram showing a relationship between a difference between signal waveform widths at two threshold values and a peak value in Modification 4 of the first embodiment. The process using the correlation between the difference between the signal waveform widths of the two threshold values and the peak value in the fourth modification of the present embodiment will be described with reference to FIGS. 24 and 25.

  FIG. 24 shows the signal waveform widths Δt1 and Δt2 at the two threshold values in the detection signal that exceeds the two threshold values 170 [mV] and 350 [mV]. FIG. 25 shows an example of the relationship between the peak value and the difference between the signal waveform widths Δt1 and Δt2 at each of the two thresholds in the detection signal exceeding the two thresholds of 170 [mV] and 350 [mV]. It is a graph. It can be seen from the graph shown in FIG. 25 that the peak value decreases as the difference between the signal waveform widths Δt1 and Δt2 at each of the two threshold values increases.

  From the above, in this modification, the correlation between the difference between the signal waveform widths Δt1 and Δt2 at each of the two threshold values as shown in FIG. 25 and the peak value, and the reflected light pulse shown in FIG. The number of frames for performing ranging processing according to the number of measurements by determining (setting) the number of measurements from the difference between the signal waveform widths Δt1 and Δt2 at each of the two thresholds using the correlation between the peak value of the Perform inter-process. For example, if the difference between the two signal waveform widths is less than 5.0 [ns], the peak value becomes 1200 [mV] or more, and the number of measurements is determined to be two. Similarly, if the difference between the two signal waveform widths is 5.0 to 6.9 [ns], the number of measurements is 3 times, and if the difference is 6.9 to 8.3 [ns], the number of measurements is 4 times, 8 If it is 3 [ns] or more, the number of measurements is appropriately determined (set) such as 5 or more.

  Specifically, of the detection signals detected by the light detection unit 102, the signal information acquisition unit 112 determines, with respect to each of the two threshold values, a detection signal (detection pulse) determined by the determination unit 103 to have exceeded the threshold. The difference between the signal waveform widths Δt1 and Δt2 (an example of the information related to the detection pulse) is obtained and acquired. Then, the number-of-measurements determination unit 113 obtains a peak value from the difference between the signal waveform widths Δt1 and Δt2 at each of the two threshold values, and determines (sets) the number of measurements based on the peak value. The determination of the peak value from the difference between the signal waveform widths Δt1 and Δt2 for each of the two threshold values may be performed by the signal information acquisition unit 112 instead of the measurement count determination unit 113.

  Note that the threshold used by the determination unit 103 may match either of the two thresholds used by the signal information acquisition unit 112, or may be a threshold different from the two thresholds.

  As described above, the number of times of measurement may be determined according to the difference between the signal waveform widths Δt1 and Δt2 at each of the two threshold values of the detection signal, and the process of setting the number of times between frames may be performed. By this, the detection signal of the reflected light from the object and the noise can be accurately distinguished by the optimum or preferred number of measurements according to the difference between the signal waveform widths Δt1 and Δt2 at each of the two threshold values of the detection signal. The accuracy of the measurement of the distance to the object can be improved.

(Modification 5)
FIG. 26 is a view for explaining setting of the number of measurements for each scanning angle of view in the fifth modification of the first embodiment. A process of determining (setting) the number of measurements for each scanning angle of view in the fifth modification of the present embodiment will be described with reference to FIG.

  In FIG. 26, the detection range “the detection range within which the distance of the object can be detected within the range of scanning angle of view (0 to 140 degrees in the example of FIG. 26) defined in the effective scanning region described above in FIG. It shows as ". In the example of FIG. 26, it is assumed that two objects A and B having different distances from the distance measuring device 100 exist in this detection range. For the object A, the scanning angle of view is in the direction of 55 degrees, and for the object B, it is assumed that the direction of scanning angle of view different from the direction in which the object A is present is 80 degrees. And the peak value of the reflected light pulse (detection pulse) from the object A is 1100 [mV], and the peak value of the reflected light pulse (detection pulse) from the object B is 700 [mV] Do. In this case, for the object A present at a scanning angle of view of 55 degrees, the peak value is in the range of 850 to 1050 [mV], so the number of measurements is determined to be four from the relationship of FIG. For the object B present at a scanning angle of view of 80 degrees, the peak value is in the range of 600 to 850 [mV], so the number of measurements is determined (set) five times.

  Specifically, the signal information acquisition unit 112 further receives information on the scanning angle of view of the detection signal (detection pulse) from the light detection unit 102, and the determination unit 103 among the detection signals detected by the light detection unit 102. The peak value of the detection signal (detection pulse) determined to have exceeded the threshold value is extracted and acquired. In this case, the signal information acquisition unit 112 associates the peak value of the extracted detection signal with the scanning angle of view of the detection signal. Then, based on the peak value acquired by the signal information acquisition unit 112, the measurement number determination unit 113 determines (sets) the measurement number in association with the scanning angle of view corresponding to the peak value. That is, in this modification, the number of times of measurement is determined (set) for each scanning angle of view of the detection signal, and the number of times setting interframe processing is performed to perform the distance measurement process according to the number of times of measurement.

  As described above, the number of times of measurement may be determined for each scanning angle of view of the detection signal, and the process of setting the number of times between frames may be performed. Thereby, the detection signal of the reflected light from the object and the noise are accurately distinguished for each scanning angle of view by the optimum or preferred number of times of measurement determined for each scanning angle of view of the detection signal. The accuracy of the distance measurement can be improved.

  The process of determining the number of measurements for each scanning angle of view of the detection signal as in this modification can be applied to each of the above-described modifications 1 to 4.

Second Embodiment
The distance measurement device according to the second embodiment will be described focusing on differences from the distance measurement device 100 according to the first embodiment. In the first embodiment, the number of measurements is determined (set) from the peak value of the detected pulse based on the correlation between the peak value of the reflected light pulse and the number of measurements, and the number of times distance measurement processing is performed according to the number of measurements. The interframe processing has been described. In the present embodiment, a process of identifying a reflected light pulse from an object based on a standard deviation of pulse widths of detection pulses detected in each measurement of a predetermined number of times of measurement will be described. The overall configuration of the distance measuring device according to the present embodiment, and the schematic configurations of the light projecting optical system, the light receiving optical system, and the synchronization system are the same as the configurations described in the first embodiment.

(Configuration of functional block of distance measuring device)
FIG. 27 is a view showing an example of a functional block configuration of the distance measuring device according to the second embodiment. The configuration of functional blocks of the distance measuring device 100a according to the present embodiment will be described with reference to FIG.

  As shown in FIG. 27, the distance measuring device 100 a according to the present embodiment includes a light projecting unit 101, a light detecting unit 102, a determining unit 103, a measuring unit 104, a control unit 110 a, and a storage unit 121. And a communication unit 122. The functions of the light emitting unit 101, the light detecting unit 102, the determining unit 103, the measuring unit 104, the storage unit 121, and the communication unit 122 illustrated in FIG. 27 are the same as those described in the first embodiment.

  The control unit 110a is a functional unit that controls the entire operation of the distance measurement device 100a. As shown in FIG. 27, the control unit 110a includes a distance calculation unit 111 (first calculation unit), a signal information acquisition unit 112a (second acquisition unit), a count unit 114, and a standard deviation calculation unit 117 (third). A calculation unit), a specification unit 115a, and a final distance calculation unit 116 (second calculation unit). The control unit 110a is realized by the control unit 46 shown in FIG. The functions of the distance calculation unit 111, the count unit 114, and the final distance calculation unit 116 are the same as those described in the first embodiment.

  The signal information acquisition unit 112 a extracts the pulse width (first waveform width) of the detection signal (detection pulse) determined to have exceeded the threshold value by the determination unit 103 among the detection signals detected by the light detection unit 102. It is a functional unit to acquire. Here, the pulse width is, for example, as shown in FIG. 13 described above, a width at the threshold (in the example shown in FIG. 13, the pulse of the detection pulse related to shot noise) in the detection signal (detection pulse) exceeding the threshold. The width is shown as "shot noise width", and the pulse width of the reflected light pulse of the object is shown as "target peak width". In FIG. 13, regarding the detection signal exceeding the threshold, the width of the detection pulse at the threshold is taken as the pulse width, but it is not limited to this. For example, at a position above or below the threshold by a predetermined value The width of the detection pulse may be the pulse width.

  The standard deviation calculation unit 117 calculates the standard deviation of the pulse width (value indicating variation) corresponding to all the classes having the largest total value (total number) in each measurement of the count value of each class counted by the counting section 114. It is a functional part which calculates an example), respectively.

  The identifying unit 115a determines that the standard deviation is equal to or less than a predetermined value (for example, “1”) in the class having the largest total value (total number) in each measurement of the count value of each class counted by the counting unit 114. And it is a functional part which specifies a detection signal (detection pulse) belonging to the smallest class among each standard deviation as a reflected light signal (reflected light pulse) from an object.

  The above-described distance calculation unit 111, signal information acquisition unit 112a, count unit 114, standard deviation calculation unit 117, identification unit 115a, and final distance calculation unit 116 are, for example, software whose control unit 110a is stored in storage unit 121. It is realized by reading and executing a program. A part or all of the distance calculation unit 111, the signal information acquisition unit 112a, the count unit 114, the standard deviation calculation unit 117, the specification unit 115a, and the final distance calculation unit 116 is not a program as software but an FPGA or ASIC May be realized by the following hardware circuit.

  Note that the light emitting unit 101, the light detecting unit 102, the determining unit 103, the measuring unit 104, and the control unit 110a (the distance calculating unit 111, the signal information acquiring unit 112a, the counting unit 114, and the standard of the distance measuring device 100a illustrated in FIG. The deviation calculating unit 117, the specifying unit 115a, and the final distance calculating unit 116), the storage unit 121, and the communication unit 122 conceptually show functions, and the present invention is not limited to such a configuration. For example, a plurality of functional units illustrated as independent functional units in the distance measurement device 100a illustrated in FIG. 27 may be configured as one functional unit. On the other hand, the function of one functional unit in the distance measuring device 100a shown in FIG. 27 may be divided into a plurality of units and configured as a plurality of functional units.

  Further, FIG. 27 illustrates the main functional units of the distance measuring device 100a, and the functions of the distance measuring device 100a are not limited to these.

(Relationship between the actual distance to the object and the peak value and shot noise)
FIG. 28 shows an example of the relationship between the actual distance to the object, the peak value of the reflected light pulse and the shot noise, and is a diagram for explaining the difference in distance measurement performance depending on the size of the threshold. The relationship between the actual distance to an object (object), the peak value (voltage) of the reflected light pulse, and the shot noise will be described with reference to FIG.

  FIG. 28 shows the results of actual measurement of distances by changing the distances with a black screen with a reflectance of 10 [%] in a square of 1 [m]. At this time, shot noise at a location delayed by 15 [μs] from the emission pulse is measured with an oscilloscope, and the artificial sun lamp is installed in front of the distance measurement device assuming severe conditions of incidence from the front of the west day. The standard deviation of shot noise was adjusted to be 100 [mV]. When the standard deviation of shot noise was 100 [mV], the average of the maximum value of shot noise was 300 [mV]. The average of the maximum value of the shot noise is indicated by an error bar 300a from 0 [mV]. In addition, when the reflected light pulse is observed from the object with an oscilloscope, the peak value becomes smaller as the distance becomes longer as shown in FIG. 9 and FIG. 10 described above. FIG. 28 shows the relationship between those peak values and the average of the maximum values of shot noise, and the relationship between them for the thresholds 100 [mV], 200 [mV], 300 [mV] and 400 [mV]. ing.

  As shown in FIG. 28, the shot noise does not almost exceed the threshold at the threshold of 400 [mV], but since the peak value falls below the threshold at an actual distance to the object of 50 [m] or later, distance measurement It turns out that you can not do it. The threshold 300 [mV] is the position of the average of the maximum values of shot noise, and it is predicted that the shot noise will exceed the threshold at a certain rate. Furthermore, although it can be seen that the distance which can be measured is extended at the threshold of 100 [mV] and 200 [mV], the shot noise exceeding the threshold becomes a considerable proportion, so the shot noise and the reflected light pulse can be separated and distinguished. It turns out that distance measurement is difficult without technology.

  Further, as described above with reference to FIG. 15, in the problem of separating and discriminating the shot noise and the reflected light pulse, in the interframe processing, when the class interval is narrowed and the number of frames (the number of measurements) is reduced By chance, the count number of the shot noise detection pulse may be equal to the count number of the reflected light pulse in the other class, in which case the shot noise and the reflected light pulse can not be discriminated.

  In view of the above points, the distance measuring device 100a according to the present embodiment performs the pulse width censorship inter-frame process described with reference to FIGS. 29 and 30 below.

(Pulse width censorship inter-frame processing of distance measuring device)
FIG. 29 is a diagram for describing identification of the reflected light from the object by counting the signals exceeding the threshold for each classified histogram class and further obtaining the standard deviation of the pulse width. FIG. 30 is a flowchart showing an example of pulse width censorship inter-frame processing of the distance measuring device according to the second embodiment. Pulse width censorship inter-frame processing of the distance measurement device 100a according to the present embodiment will be described with reference to FIGS. 29 and 30. FIG.

  In the example shown in FIG. 30, as in the case of FIG. 15 described above, the class is divided every 1 [m], and the number of times of measurement is three, and the detected pulses are counted in each class. In FIG. 30, the pulse widths at the threshold of detected pulses exceeding the threshold are further summed up, the standard deviation σ thereof is calculated, and the distance of the true object is determined by the standard deviation σ.

  Since the shot noise exceeds the threshold with random magnitude, the standard deviation σ of the pulse width at the threshold is large, while the pulse width of the reflected light pulse of the object is stable and the standard deviation σ is small. is assumed. Therefore, in the pulse width censorship inter-frame processing according to the present embodiment, the class corresponding to the value with the smallest standard deviation σ of the pulse width is specified as the class including the reflected light pulse from the object. Further, in the example of FIG. 30, in order to specify the class in which the reflected light pulse from the object is included, the class having a standard deviation σ of pulse width of 1.0 or less is targeted. According to such a processing method (pulse width censorship inter-frame processing), even if the reflected light pulse is not detected and only shot noise is detected in a plurality of classes, if the value of the standard deviation σ of the pulse width is large. Since it can be determined that the noise is shot noise, it can be used to detect an erroneous distance measurement.

  In addition, in order to specify the class in which the reflected light pulse from the object is included, the pulse widths at the threshold of the detection pulses exceeding the threshold are summed, and the standard deviation σ is calculated. The dispersion of the pulse width (an example of the value indicating the dispersion) may be calculated. Since the shot noise exceeds the threshold with random magnitude, the dispersion of the pulse width at the threshold should be large, while it is assumed that the dispersion is small because the pulse width of the reflected light pulse of the object is stable. Be done.

  The pulse width censorship inter-frame processing for determining the standard deviation σ of the pulse width as described above and identifying the class including the reflected light pulse from the object based on the magnitude of the standard deviation σ in the present embodiment. Will be described with reference to FIG. In the example of the pulse width censorship inter-frame process shown in FIG. 30, the number of times of measurement will be described as being a predetermined number of times (for example, three times or the like).

<Step S31>
The light emitting unit 101 of the distance measuring device 100 a emits (projects) laser light (emission light pulse) in accordance with the LD drive signal output from the control unit 110 a. The light detection unit 102 of the distance measurement device 100a detects a pulse (detection) by receiving the reflected light that is emitted from the light emitter 101 and reflected by the object, and the other light (such as noise). As a signal). The light detection unit 102 outputs the detected detection pulse (detection signal) to the control unit 110 a and the determination unit 103. Then, the process proceeds to step S32.

<Step S32>
The determination unit 103 of the distance measurement device 100a determines whether or not the magnitude (for example, voltage) of the detection signal detected by the light detection unit 102 exceeds a predetermined threshold. If the threshold is exceeded (step S32: Yes), the measuring unit 104 of the distance measuring device 100a determines the light reception timing of the detection signal determined by the determination unit 103 to have exceeded the threshold, and the light reception timing and the control unit 110a. The reciprocation time of an object (object) or the like is measured based on the rise timing of the LD drive signal. The measurement unit 104 outputs measurement data indicating the measurement result of time to the control unit 110a. Then, the process proceeds to step S33.

  On the other hand, when the threshold is not exceeded (step S32: No), the process proceeds to step S44.

<Step S33>
The distance calculation unit 111 of the distance measurement device 100a converts the distance into a distance (calculates the distance) based on the measurement data of the time received from the measurement unit 104. Then, the process proceeds to step S34.

<Step S34>
The signal information acquisition unit 112a of the distance measurement device 100a extracts and acquires the pulse width of the detection signal (detection pulse) determined by the determination unit 103 as having exceeded the threshold value among the detection signals detected by the light detection unit 102. Do. Then, the process proceeds to step S35.

<Step S35>
The count unit 114 of the distance measuring device 100a sets the number of detection pulses (detection signals) determined to have exceeded the threshold with respect to the class for the distance divided to create a histogram at an arbitrary distance interval. Count by rank of Then, the process proceeds to step S36.

<Step S36>
When calculation of the distance by the distance calculation unit 111 and the process of counting by the counting unit 114 have been performed by the predetermined number of times of measurement (step S36: Yes), the process proceeds to step S37, and is not performed (step S36: No), the process returns to step S31.

<Step S37>
The standard deviation calculating unit 117 of the distance measuring device 100a determines whether or not there is a class having a total value (total number) of 2 or more in each measurement of the count value of each class counted by the counting unit 114. Here, it is determined by the standard deviation calculation unit 117 whether or not there is a class having a total value (total number) of 2 or more. If there is no data of 2 or more pulse widths, the standard deviation of the pulse widths is calculated. It is because you can not do it. If there is a class having a total value of 2 or more (step S37: Yes), the process proceeds to step S38, and if there is no class having a total value of 2 or more (step S37: No), the process proceeds to step S46.

<Step S38>
The standard deviation calculation unit 117 of the distance measuring device 100a sets the standard deviation of the pulse width corresponding to all the classes having the largest total value (total number) in each measurement of the count value of each class counted by the counting section 114. calculate. Then, the process proceeds to step S39.

<Step S39>
If there is one or more classes having a standard deviation of 1 or less calculated by the standard deviation calculation unit 117 (step S39: Yes), the process proceeds to step S40, and one or more classes have a standard deviation of 1 or less (step S39: No), the process proceeds to step S46.

<Step S40>
If there is only one class having a standard deviation of 1 or less (step S40: Yes), the process proceeds to step S41. If two or more classes having a standard deviation of 1 or less exist (step S40: No), the process proceeds to step S42. Do.

<Step S41>
When there is only one class having a standard deviation of 1 or less calculated by the standard deviation calculating section 117, the specifying unit 115a of the distance measuring device 100a specifies the class as a class related to the object. That is, the identifying unit 115a identifies a detection signal (detection pulse) belonging to the class as a reflected light signal (reflected light pulse) from the object. Then, the process proceeds to step S43.

<Step S42>
If two or more classes having a standard deviation of 1 or less calculated by the standard deviation calculation section 117, the identifying unit 115a of the distance measuring device 100a determines the class having the smallest standard deviation among the classes, the class associated with the object Identify as That is, the identifying unit 115a identifies a detection signal (detection pulse) belonging to the class as a reflected light signal (reflected light pulse) from the object. Then, the process proceeds to step S43.

<Step S43>
The final distance calculation unit 116 of the distance measurement device 100 a targets the average value of the distances calculated by the distance calculation unit 111 for each reflected light signal (reflected light pulse) from the object specified by the specifying unit 115 a. Calculated as the distance from the object. The final distance calculation unit 116 transmits, to the ECU 200, the distance data on the calculated distance from the target, for example, included in the object recognition data via the communication unit 122. Then, the pulse width censorship inter-frame process ends.

<Step S44>
If the magnitude of the detection signal detected by the light detection unit 102 does not exceed the threshold value by the determination unit 103, the control unit 110a of the distance measurement device 100a does not have an object or a collision due to another object or the like It is determined that there is no risk of Then, the process proceeds to step S45.

<Step S45>
The control unit 110 a discards the information of the detection pulse received from the light detection unit 102. Then, the process returns to step S31.

<Step S46>
If the control unit 110a determines that the total value (total number) in each measurement of the count value of each class counted by the count unit 114 is not two or more by the standard deviation calculation unit 117, and the standard When the standard deviation calculated by the deviation calculation unit 117 does not have one or more classes equal to or less than one, it is determined that distance measurement is not possible. Then, the pulse width censorship inter-frame process ends.

  By the above steps S31 to S46, the pulse width censorship inter-frame process is executed, and the distance to the object (object) is calculated.

  In steps S39 to S42 in FIG. 30, the class having a standard deviation of 1 or less and the smallest standard deviation is specified as the class relating to the object, but the invention is not limited thereto. Absent. For example, the class corresponding to the smallest standard deviation among the standard deviations calculated in step S38 may be specified as the class of the object. Further, although the standard deviation is determined for the class having a standard deviation of 1 or less in step S39, the standard deviation may be determined based on a value other than one.

  As described above, the distance measuring device 100a according to the present embodiment adds up the pulse widths at the threshold of the detected pulses exceeding the threshold, calculates the standard deviation thereof, and the class corresponding to the value with the smallest standard deviation. Between the pulse width censorship which identifies as a class that includes the reflected light pulse from the object. That is, since the shot noise exceeds the threshold with random magnitude, the standard deviation of the pulse width at the threshold is large, while the pulse width of the reflected light pulse of the object is stable and the standard deviation is small. As it is assumed, the class corresponding to the value with the smallest standard deviation is specified as the class that includes the reflected light pulse from the object. By this, it is possible to accurately distinguish the detection signal of the reflected light from the object and the noise and to improve the accuracy of the measurement of the distance to the object.

  In addition, in order to specify the class including the reflected light pulse from the object, the class whose standard deviation of the pulse width is equal to or less than a predetermined value (for example, 1 or the like) is targeted. As a result, even if the reflected light pulse is not detected and only shot noise is detected in a plurality of classes, if the value of the standard deviation of the pulse width is large, it can be determined as shot noise and erroneous distance measurement is detected. can do.

  Also, the reflected light from the object such as distance measurement of the object under a long distance, distance measurement for an object with low reflectance, or distance measurement of an object under a strong ambient light such as a west sun In a situation where the magnitude of the noise is not negligible with respect to the magnitude of the pulse, the class including the reflected light pulse from the object is identified based on the standard deviation indicating the variation of the pulse width. The noise and the reflected light pulse can be discriminated with high accuracy even if the threshold value for detecting H is set low. In addition, since the standard deviation can be calculated if the number of measurements is at least two, processing between pulse width censorship frames can be performed by at least two measurements, and discrimination between noise and a reflected light pulse becomes possible.

(Comparison between pulse width censorship interframe processing and interframe processing and single frame processing)
FIG. 31 is a diagram for explaining the variation in the distance measurement success rate due to the difference in the threshold in the case of performing the pulse width censorship inter-frame process according to the second embodiment. FIG. 32 is a diagram for explaining the variation in the distance measurement success rate due to the difference in the threshold when inter-frame processing is performed. FIG. 33 is a diagram for explaining the variation in the ranging success rate due to the difference in the threshold when single frame processing is performed. A comparison result of the pulse width censorship inter-frame processing, the inter-frame processing, and the single-frame processing according to the present embodiment will be described with reference to FIGS. 31 to 33. Here, single-frame processing refers to processing of distance measurement based on only normal threshold determination, with one measurement (ie, a single frame) without using multiple measurements.

  In pulse width censorship inter-frame processing, inter-frame processing, and single inter-frame processing shown in FIGS. 31 to 33, threshold values (voltages) are set to 100, 200, 300, and 400 [mV], respectively, It verified about how ranging success rate changes according to the actual distance to. In the oscilloscope used, shot noise was calculated with a sampling rate of 4 GSa / S and a horizontal axis of 2 μs / div. Each process was performed at intervals of 10 m in a range of 10 to 100 m, and the number of measurements in the pulse width censorship interframe process and the interframe process was three. Further, in the pulse width censorship interframe processing, the class including the reflected light pulse from the object is specified for the class whose standard deviation σ of the pulse width is 1.0 or less. If two or more classes have a pulse width standard deviation σ of 1.0 or less, the class having the smallest standard deviation σ is specified as the class including the reflected light pulse from the object. In addition, the interval of the classes of the histogram is 1 [m], and the N number for calculating the distance measurement success rate is 100 times.

  As a result of the pulse width censorship inter-frame processing shown in FIG. 31, 80 [%] or more is obtained at thresholds 100 [mV] and 200 [mV] buried in shot noise even in a large shot noise environment assuming west day The success rate of ranging was shown. In addition, if it is possible to set a low threshold such as the threshold 100 [mV] and 200 [mV] in this way, the distance that can be measured is extended, and in particular, 100 [m] when the threshold is 100 [mV]. It can be seen that the distance measurement success rate is 50% or more for the distance measurement up to the point.

  As a result of the inter-frame processing shown in FIG. 32, even in the environment of a large shot noise assuming west sun, distance measurement of 50% or more is achieved at the thresholds 100 [mV] and 200 [mV] buried in shot noise. The success rate is shown, and it is understood that the distance which can be measured is extended when it is possible to set a low threshold such as the threshold of 100 [mV] and 200 [mV]. However, in the inter-frame processing of pulse width censorship shown in FIG. 31, a high ranging success rate is obtained.

  In the result of single frame processing shown in FIG. 33, if the threshold value is set sufficiently higher than the shot noise, the distance measurement success rate at a short distance is almost the same as in FIG. 31 and FIG. In the case of the above, it can be seen that the ranging success rate drops sharply and it is not possible to perform ranging. In addition, when the threshold value is lowered to measure distance, the shot noise and the reflected light pulse can not be distinguished, and the distance measurement success rate is extremely lowered.

  It is also possible to combine the number setting inter-frame processing according to the first embodiment and the pulse width censorship inter-frame processing according to the second embodiment. That is, the number of measurements is determined based on the peak value, the pulse width is extracted in the determined number of measurements, the standard deviation of the pulse width is calculated, and the reflected light pulse from the object is calculated based on the standard deviation. It may be specified as a class that includes

  In addition, the distance measurement device 100 (100a) according to each of the above-described embodiments and the modifications may be mounted on a mobile body such as a car, a vehicle other than a car, an aircraft, a ship, and a robot. As a result, by using the distance measuring devices 100 and 100a, in which the accuracy of the measurement of the distance to the object is improved, it is possible to obtain a mobile body with excellent safety.

  In each of the above-described embodiments and modifications, when at least one of the functional units of the distance measuring device 100 (100a) is realized by execution of a program, the program is incorporated in advance in a ROM or the like. Provided. Further, the program executed by the distance measurement device 100 (100a) according to each of the above-described embodiments and each modification is a file in an installable format or an executable format, and a compact disc read only memory (CD-ROM), It may be configured to be provided by being recorded on a computer readable recording medium such as a flexible disk (FD), a CD-R (Compact Disk-Recordable), or a DVD (Digital Versatile Disc). In addition, the program executed by the distance measurement device 100 (100a) according to each of the above-described embodiments and the respective modifications is stored on a computer connected to a network such as the Internet and provided by downloading via the network. It may be configured as follows. Further, the program executed by the distance measurement device 100 (100a) according to each of the above-described embodiments and the respective modifications may be provided or distributed via a network such as the Internet. Moreover, the program executed by the distance measurement device 100 (100a) of each of the above-described embodiments and each modification has a module configuration including at least one of the above-described respective functional units, and as an actual hardware The control unit 46 reads and executes a program from the storage device (for example, the storage unit 48) described above, and the functional units described above are loaded on the main storage device and generated.

10 LD
12 LD drive unit 20 projection optical system 22 coupling lens 24 reflection mirror 26 rotation mirror 30 light receiving optical system 32 imaging optical system 40 detection system 42 PD for reflection detection
44 detection circuit 45 time measurement unit 46 control unit 47 object recognition unit 48 storage unit 49 communication unit 50 synchronization system 52 synchronization lens 54 PD for synchronization detection
56 binarization circuit 61 light emitting window 62 light receiving window 100, 100a distance measuring device 101 light emitting unit 102 light detecting unit 103 determining unit 104 measuring unit 110, 110a control unit 111 distance calculating unit 112, 112a signal information acquiring unit 113 measurement Number of times determination unit 114 Count unit 115, 115a Identification unit 116 Final distance calculation unit 117 Standard deviation calculation unit 121 Storage unit 122 Communication unit 200 ECU
300, 300a error bar T predetermined interval t time difference tf falling time tr, tr1, tr2 rising time Vth1 to Vth4 threshold Δt, Δt1, Δt2 signal waveform width

JP, 2004-184333, A JP, 2015-108539, A

Claims (13)

Light is emitted from the light emitting unit to the scanning area, and the light is received by the light detecting section so that the light is reflected by the object present in the scanning area to obtain a detection signal, and the light is emitted from the light emitting section. A distance measuring device for measuring a distance to the object based on time until acquisition of a detection signal,
A first acquisition unit that acquires information related to the detection signal;
The light emitting unit emits the light to the object based on the information on the detection pulse acquired by the first acquiring unit, and the light detecting unit detects the reflected light reflected by the object. A determination unit that determines the number of times of detection;
The number of times of detection is an operation of emitting the light from the light emitting unit to the object, and obtaining a time from detection of the reflected light reflected by the object by the light detection unit or a value based on the time The measuring unit to be
The time or a value based on the time is taken as a class, and the number of detection signals corresponding to the time determined by the measuring unit or the value based on the time with respect to the class divided at an arbitrary interval, The count part which counts every class,
An identifying unit for identifying the class corresponding to the largest one of the total values of the measurement values of the count values of the classes counted by the counting unit;
The distance measuring device which calculates | requires the distance to the said target object based on the value based on the said time corresponding to the said class specified by the said specification part or the said time. A second acquisition unit that acquires a waveform width of the detection signal as a first waveform width based on a first threshold;
A third calculation unit that calculates the variation of the first waveform width acquired by the second acquisition unit for each of the classes having the largest total value in each of the measurements;
And further
The distance measuring apparatus according to claim 1, wherein the specifying unit specifies, from among the classes, the variation calculated by the third calculating unit from among the classes having a predetermined value or less.   The distance measuring apparatus according to claim 2, wherein the identification unit identifies a class having the smallest variation among the classes. The first acquisition unit acquires a peak value of the detection signal as information on the detection signal,
The distance determination apparatus according to any one of claims 1 to 3, wherein the determination unit determines the number of times of detection based on the peak value acquired by the first acquisition unit. The first acquisition unit acquires, as information related to the detection signal, a second waveform width that is a waveform width based on a second threshold in the detection signal,
The distance measuring device according to any one of claims 1 to 3, wherein the determination unit determines the number of times of detection based on the second waveform width acquired by the first acquisition unit. The first acquisition unit acquires, as information on the detection signal, information on which one of a plurality of thresholds the detection signal has exceeded,
The said determination part determines the said frequency | count of a detection based on the information about whether the said detection signal exceeded which threshold among the said some threshold acquired by the said 1st acquisition part. The distance measuring device according to any one of the preceding claims. The first acquisition unit acquires, as information related to the detection signal, inclinations at two points in time when the waveform of the detection signal exceeds two threshold values,
The distance measurement device according to any one of claims 1 to 3, wherein the determination unit determines the number of times of detection based on the inclination acquired by the first acquisition unit. The first acquisition unit acquires, as information related to the detection signal, a difference between respective waveform widths of two threshold values of the detection signal,
The distance determination apparatus according to any one of claims 1 to 3, wherein the determination unit determines the number of times of detection based on the difference acquired by the first acquisition unit. The first acquisition unit acquires information on a scanning angle of view when the detection signal is acquired,
The distance measuring apparatus according to any one of claims 1 to 8, wherein the determination unit determines the number of times of detection based on information on the detection signal corresponding to the scanning angle of view for each scanning angle of view. .   The distance measurement according to any one of claims 1 to 9, wherein a distance to the object is determined based on the time corresponding to the class specified by the specifying unit or an average value of values based on the time. apparatus.   The mobile provided with the distance measurement apparatus as described in any one of Claims 1-10. Light is emitted from the light emitting unit to the scanning area, and the light is received by the light detecting section so that the light is reflected by the object present in the scanning area to obtain a detection signal, and the light is emitted from the light emitting section. A distance measuring method of measuring a distance to the object based on time until acquisition of a detection signal,
An acquisition step of acquiring information on the detection signal;
A determining step of emitting the light from the light emitting unit to the object based on the acquired information on the detection signal, and determining the number of times of detection of the reflected light reflected by the object by the light detecting unit; When,
The number of times of detection is an operation of emitting the light from the light emitting unit to the object, and obtaining a time from detection of the reflected light reflected by the object by the light detection unit or a value based on the time Measurement steps to be performed,
The time or the value based on the time is a class, and the number of detection signals corresponding to the time determined by the measuring step or the value based on the time is determined for each of the classes divided by an arbitrary interval. Counting steps to
Identifying the class corresponding to the largest one of the total values of the measured count values of each class at each measurement;
A distance measuring method for determining a distance to the object based on the time corresponding to the specified class or a value based on the time. In the computer, light is emitted from the light emitting unit to the scanning area to the computer, and the light is received by the light detecting unit so that the light is reflected by the object present in the scanning area, and a detection signal is acquired. A program for performing distance measurement to the object based on time from emission of light to acquisition of the detection signal,
An acquisition step of acquiring information on the detection signal;
A determining step of emitting the light from the light emitting unit to the object based on the acquired information on the detection signal, and determining the number of times of detection of the reflected light reflected by the object by the light detecting unit; When,
The number of times of detection is an operation of emitting the light from the light emitting unit to the object, and obtaining a time from detection of the reflected light reflected by the object by the light detection unit or a value based on the time Measurement steps to be performed,
The time or the value based on the time is a class, and the number of detection signals corresponding to the time determined by the measuring step or the value based on the time is the class for the class divided at an arbitrary interval Count step to count each
Identifying the class corresponding to the largest one of the total values of the measured count values of each class at each measurement;
A program for determining a distance to the object based on the time corresponding to the specified class or a value based on the time.

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