JP7005994B2 - Distance measuring device and distance measuring method - Google Patents

Description

The present invention relates to a distance measuring device and a distance measuring method.

Conventionally, TOF (Time of) measures the distance to an object from the time difference between the irradiation timing of the emitted beam and the light receiving timing when the reflected light from the object is received by irradiating the object with a light emitting beam from a light emitting element or the like. Flight) The method is known.

One example is LIDAR (Light Detection and Ranging), which is widely used in aircraft, railways, vehicles, and the like. For example, as disclosed in Patent Documents 1 to 3, LIDAR scans a laser beam emitted from a light source with a rotating mirror, and detects light reflected or scattered by an object again through the rotating mirror. There is a scanning type LIDAR that can detect the presence or absence of an object in a desired range and the distance to the object by detecting with a device.

In distance measurement by LIDAR, it is important to separate noise from the signal from the object. Of the noise, shot noise is white noise associated with light quantity measurement, and the magnitude of shot noise is proportional to the square root of the time average of the light quantity, and when the sensitivity is high or the ambient light is strong, it is several tens of mV or more. Can also be. Therefore, shot noise is more likely to be a problem than circuit noise. As can be seen from the fact that the magnitude of noise is proportional to the square root of the time average of the amount of light, shot noise also occurs as white noise during DC light detection.

In the method of detecting the received signal based on the threshold voltage, it is necessary to set the threshold voltage sufficiently higher than the shot noise in order to prevent false detection due to noise, so the threshold voltage assumes the situation where the shot noise is the maximum. (See FIG. 1A). Therefore, when the shot noise is relatively small, the threshold value is set excessively large, and the detectable distance becomes smaller than necessary (see FIG. 1B). From the viewpoint of increasing the detection distance, it is preferable to set the threshold value small.

The present invention has been made in view of the above, and an object of the present invention is to accurately separate noise from a signal from an object while setting a small threshold value for detecting a signal.

In order to solve the above-mentioned problems and achieve the object, the distance measuring device according to the present invention receives a light projecting unit that projects light on an object and light reflected or scattered by the object. The light receiving unit, the scanning unit that scans the light projected from the light emitting unit into the scanning area, and the time from the light projected by the light emitting unit to the light reception by the light receiving unit are measured, and the distance to the object is measured. The scanning area is divided into a plurality of divided areas, and one scan is performed from the start of scanning of one of the divided areas to the end of scanning of all the divided areas. When defined as, the first measured value , which is the measured value of the first divided region, measured by the distance measuring unit during the one scan, and the second measured value measured before the first measured value. The second measured value, which is the measured value of the divided region, the first light receiving width, which is the time width during which the light receiving unit receives the light in the first divided region during the one scan, and the second divided region. Based on the second light receiving width, which is the time width during which the light receiving unit receives the light in the region, it is determined whether or not the first measured value can be the measurement result of the first divided region, and the first is determined. When it is determined that the measurement result of the divided region of 1 can be obtained, the first measured value is output as the distance to the object in the first divided region.

According to the present invention, it is possible to accurately separate noise from a signal from an object while setting a small threshold value for detecting a signal.

FIG. 1A is a diagram showing an example of a received light signal waveform when shot noise is large. FIG. 1B is a diagram showing an example of a received light signal waveform when shot noise is small. FIG. 2 is a block diagram showing a schematic configuration example of a distance measuring device according to an embodiment. FIG. 3A is a diagram schematically showing a floodlight optical system and a synchronous system according to an embodiment. FIG. 3B is a diagram schematically showing a light receiving optical system according to the embodiment. FIG. 3C is a diagram showing an example of an optical path from the LD to the reflection mirror and an optical path from the reflection mirror to the PD for time measurement according to the embodiment. FIG. 4 is a timing diagram showing an example of a synchronization signal and an LD drive signal. FIG. 5A is a timing diagram showing an example of an emitted light pulse and a reflected light pulse. FIG. 5B is a timing diagram showing an example of an emitted light pulse and a reflected light pulse after binarization. FIG. 6A is a schematic diagram showing an example of a received light signal waveform when sunlight does not enter. FIG. 6B is a schematic diagram showing an example of a received light signal waveform when sunlight enters. FIG. 6C is a schematic diagram showing an example of a received light signal waveform when sunlight enters when the DC component is removed. FIG. 6D is a schematic diagram showing an example of a received light signal waveform when strong sunlight enters when the DC component is removed. FIG. 7 is a diagram showing an example of the relationship between shot noise and a target peak. FIG. 8 is a diagram showing an example of the relationship between shot noise and a target peak. FIG. 9 is a diagram showing an example of the relationship between the actual distance to the object, the target peak intensity, and the shot noise. FIG. 10 is a schematic diagram showing an example of a light receiving signal waveform in which rain and an object are detected. FIG. 11 is a diagram showing an example in which the effective scanning region is divided into a plurality of regions (N division regions). FIG. 12 is a diagram illustrating an example of discrimination between noise and an object by the distance measuring device according to the embodiment. FIG. 13 is a diagram showing an example in which four N-divided regions are included in the M-divided region. FIG. 14 is a diagram illustrating an example in which optical scanning of an effective scanning region according to an embodiment is divided into a plurality of optical scans, distance measurement is performed at all scanning angles, and noise and an object are discriminated from each other. FIG. 15 is a diagram illustrating an example in which the pulse width of the pulsed light is used as a determination criterion. FIG. 16 is a flowchart showing an example of the flow of the target determination process according to the embodiment. FIG. 17 is a diagram showing an example of the relationship between the ranging value and the ranging range.

Hereinafter, embodiments of the distance measuring device and the distance measuring method according to the present invention will be described with reference to the accompanying drawings. The present invention is not limited to the following embodiments.

(Embodiment)
FIG. 2 is a block diagram showing a schematic configuration example of the distance measuring device 100 according to the embodiment. As an example, the distance measuring device 100 is mounted on a vehicle as a moving body, emits light, and receives light reflected (scattered) by an object (for example, a preceding vehicle, a stopped vehicle, an obstacle, a pedestrian, etc.). Then, it is a scanning type LIDAR that detects information about an object such as the presence or absence of the object and the distance to the object. For example, the distance measuring device 100 receives electric power from a vehicle battery (storage battery).

As shown in FIG. 2, the distance measuring device 100 includes a floodlight system 10, a light receiving optical system 30, a detection system 40, a time measurement unit 45, a synchronization system 50, a measurement control unit 46, and an object recognition unit. It has 47 and.

The floodlight system 10 includes an LD (Laser Diode) as a light source, an LD drive unit 12, and a floodlight optical system 20. The LD is also called an end face emission laser, and emits laser light by being driven by the LD drive unit 12. The LD drive unit 12 lights (lights) the LD using the LD drive signal (rectangular pulse signal) output from the measurement control unit 46. For example, the LD drive unit 12 includes a capacitor connected so as to be able to supply a current to the LD, a transistor for switching between conduction and non-conduction between the capacitor and the LD, a charging means capable of charging the capacitor, and the like. The measurement control unit 46 receives a measurement control signal (for example, a measurement start signal, a measurement stop signal, etc.) from the ECU (Electronic Control Unit) of the vehicle, and starts or stops the measurement.

FIG. 3A is a diagram schematically showing a floodlight optical system 20 and a synchronous system 50 according to an embodiment. FIG. 3B is a diagram schematically showing the light receiving optical system 30 according to the embodiment. FIG. 3C is a diagram showing an example of an optical path from the LD to the reflection mirror 24 and an optical path from the reflection mirror 24 to the PD 42 for time measurement according to the embodiment. Hereinafter, the XYZ three-dimensional Cartesian coordinate system in which the Z-axis direction shown in FIG. 3A or the like is the vertical direction will be described as appropriate.

As shown in FIG. 3A, the floodlight optical system 20 includes a coupling lens 22, a reflection mirror 24, and a rotary mirror 26. The coupling lens 22 is arranged on the optical path of the light from the LD. The reflection mirror 24 is arranged on the optical path of light through the coupling lens 22. The rotating mirror 26 is a deflector arranged on the optical path of the light reflected by the reflecting mirror 24. In FIG. 3A, in order to reduce the size of the device, a reflection mirror 24 is provided on the optical path between the coupling lens 22 and the rotary mirror 26, and the optical path is folded back. The light emitted from the LD is shaped into light having a predetermined beam profile by the coupling lens 22, then reflected by the reflection mirror 24 and deflected around the Z axis by the rotation mirror 26. The light emitted from the distance measuring device 100 is the light that is deflected to a predetermined deflection range around the Z axis by the rotating mirror 26 and is projected from the projection optical system 20.

In the above, the case where the LD is used as the light source is given as an example, but the present invention is not limited to this. For example, as the light source, another light emitting element such as a VCSEL (Vertical Cavity Surface Emitting Laser), an organic EL element, or an LED (Light Emitting Diode) may be used.

The rotary mirror 26 has a plurality of reflecting surfaces around the rotation axis (Z axis), and reflects (deflects) the light from the reflection mirror 24 while rotating around the rotation axis, so that the above-mentioned deflection range is obtained by the light. The effective scanning area corresponding to the above is scanned one-dimensionally in the horizontal one-axis direction (here, the Y-axis direction). The deflection range and the effective scanning area are on the + X side of the distance measuring device 100. As can be seen from FIG. 3A, the rotary mirror 26 has two reflecting surfaces (two facing surfaces). However, the rotary mirror 26 is not limited to this, and may have one reflecting surface or three or more reflecting surfaces. Further, the rotary mirror 26 may be provided with at least two reflective surfaces and arranged at different angles with respect to the rotary axis of the rotary mirror 26 to switch the scanning or detection area in the Z-axis direction.

As shown in FIG. 3B, the light receiving optical system 30 includes a rotating mirror 26, a reflection mirror 24, and a time measuring PD 42. The rotating mirror 26 reflects the light projected from the projection optical system 20 and reflected by the object existing in the effective scanning region. The reflection mirror 24 reflects the light from the rotary mirror 26. The time measurement PD 42 is arranged on the optical path of the light from the reflection mirror 24 and forms an image of the light. An imaging optical system for forming an image of light with the time measurement PD 42 is arranged on the optical path of the light from the reflection mirror 24. Here, the floodlight optical system 20 and the light receiving optical system 30 are installed in the same housing. Such a housing has an opening on the optical path of the emitted light from the projection optical system 20 and on the optical path of the incident light to the light receiving optical system 30, and the opening is closed by a window (light transmitting window member). It is missing. For example, the window can be made of glass or resin.

As shown in FIG. 3C, the floodlight optical system 20 and the light receiving optical system 30 are arranged so as to overlap each other in the Z-axis direction. Further, the rotary mirror 26 and the reflection mirror 24 are common to the light projecting optical system 20 and the light receiving optical system 30. As a result, the relative positional deviation between the LD irradiation range on the object and the light receiving range of the time measurement PD42 can be reduced, and stable object detection can be realized.

As shown in FIGS. 2 and 3B, the detection system 40 includes a time measurement PD 42 and a PD output detection unit 44. The time measurement PD 42 receives light projected from the projection optical system 20 and reflected by an object existing in the effective scanning region via the light receiving optical system 30. The PD output detection unit 44 detects a voltage signal (light receiving signal) based on the output current (photocurrent) of the time measurement PD 42. The light projected from the projection optical system 20 and reflected by the object is guided to the imaging optical system via the rotating mirror 26 and the reflecting mirror 24, and is focused on the time measurement PD 42 by the imaging optical system (FIG. 3B). reference). In FIG. 3B, in order to reduce the size of the device, a reflection mirror 24 is provided between the rotation mirror 26 and the imaging optical system, and the optical path is folded back. Here, the imaging optical system is composed of two lenses (imaging lenses), but may be composed of one lens or three or more lenses.

As shown in FIGS. 2 and 3A, the synchronization system 50 includes a synchronization lens 52, a synchronization detection PD 54, and a PD output detection unit 56. The synchronous lens 52 is the light emitted from the LD and reflected by the reflection mirror 24 via the coupling lens 22, and is arranged on the optical path of the light deflected by the rotary mirror 26 and reflected again by the reflection mirror 24. Ru. The synchronization detection PD 54 is arranged on the optical path of light through the synchronization lens 52. The PD output detection unit 56 detects a voltage signal (light receiving signal) based on the output current (photocurrent) of the synchronization detection PD 54.

Specifically, the reflection mirror 24 is arranged on the upstream side in the rotation direction of the rotation mirror 26 with respect to the above-mentioned deflection range, and the light deflected by the rotation mirror 26 on the upstream side of the deflection range is incident. Then, the light deflected by the rotation mirror 26 and reflected by the reflection mirror 24 is incident on the synchronization detection PD 54 via the synchronization lens 52. The reflection mirror 24 may be arranged on the downstream side in the rotation direction of the rotation mirror 26 with respect to the above-mentioned deflection range. Then, the synchronization system 50 may be deflected by the rotation mirror 26 and arranged on the optical path of the light reflected by the reflection mirror 24.

FIG. 4 is a timing diagram showing an example of a synchronization signal and an LD drive signal. As shown in FIG. 4, the synchronization detection PD 54 outputs a current each time the light reflected by the reflecting surface of the rotating mirror 26 is received by the rotation of the rotating mirror 26. That is, the synchronization detection PD 54 periodically outputs a current. In this way, by performing synchronous lighting for irradiating the PD 54 for synchronization detection with the light from the rotation mirror 26, it is possible to obtain the rotation timing of the rotation mirror 26 from the light receiving timing of the PD 54 for synchronization detection. Become. Therefore, the effective scanning region can be optically scanned by lighting the LD in a pulsed manner after a predetermined time has elapsed from the synchronous lighting of the LD. That is, the effective scanning region can be optically scanned by lighting the LD in a pulse during the period before and after the timing when the PD 54 for synchronization detection is irradiated with light.

Here, as the light receiving element used for time measurement and synchronization detection, in addition to the PD described above, an APD (Avalanche Photo Diode), a Geiger mode APD SPAD (Single Photon Avalanche Diode), or the like can be used. Since APD and SPAD have high sensitivity to PD, they are advantageous in terms of detection accuracy and detection distance.

When the PD output detection unit 56 detects a voltage signal (light receiving signal) based on the output current of the synchronization detection PD 54, the PD output detection unit 56 outputs the synchronization signal to the measurement control unit 46. Specifically, the PD output detection unit 56 converts the output current from the synchronization detection PD 54 into a voltage signal by a current-voltage converter, amplifies the voltage signal by a signal amplifier, and compares the amplified voltage signal with a comparator or the like. It is binarized with a threshold using a device, and the binarized signal is output to the measurement control unit 46 as a synchronization signal.

The measurement control unit 46 generates an LD drive signal based on the synchronization signal from the PD output detection unit 56, and outputs the generated LD drive signal to the LD drive unit 12 and the time measurement unit 45. That is, the LD drive signal is a light emission control signal (periodic pulse signal) delayed with respect to the synchronization signal.

When the LD drive signal is input to the LD drive unit 12, a drive current is applied to the LD from the LD drive unit 12, and a light emitting pulse is output from the LD. From the viewpoint of LD safety and LD durability, the emission duty of LD is limited, so it is desirable that the emission pulse has a narrow pulse width. Generally, the pulse width is set to about 10 ns to several tens of ns. The pulse interval is about several tens of microseconds.

The time measuring unit 45 obtains the light receiving timing in the time measuring PD 42 based on the detection signal from the PD output detecting unit 44 (the detection timing of the light receiving signal in the PD output detecting unit 44), and obtains the light receiving timing and the LD drive signal. The round-trip time to the object is measured based on the rising timing of. Then, the time measurement unit 45 outputs the round-trip time to the object to the measurement control unit 46 as a time measurement result.

The measurement control unit 46 calculates the round-trip distance to the object by converting the time measurement result from the time measurement unit 45 into a distance, and outputs 1/2 of the round-trip distance as distance data to the object recognition unit 47. The object recognition unit 47 recognizes where an object exists based on a plurality of distance data acquired by one scan or a plurality of scans from the measurement control unit 46, and outputs the object recognition result to the measurement control unit 46. do. The measurement control unit 46 transfers the object recognition result from the object recognition unit 47 to the ECU.

The ECU performs, for example, steering control of an automobile (for example, auto steering) and speed control (for example, auto braking) based on the object recognition result transferred from the distance measuring device 100. Further, as the deflector, for example, a polygon mirror (rotating polymorphic mirror), a galvano mirror, a MEMS mirror, or another mirror may be used instead of the rotating mirror 26. Further, the synchronization system 50 does not have to have the synchronization lens 52, and may have another optical element (for example, a condenser mirror or the like).

FIG. 5A is a timing diagram showing an example of an emitted light pulse and a reflected light pulse. When the effective scanning area is scanned by the rotary mirror 26, the LD drive unit 12 drives the LD to emit pulsed light (hereinafter, may be referred to as “emission light pulse”) as shown in FIG. 5A. .. Then, the pulsed light emitted from the LD and reflected (scattered) by the object (hereinafter, may be referred to as “reflected light pulse”) is detected by the time measurement PD42. Note that FIG. 5A gives an example in which APD is used instead of PD as the light receiving element.

FIG. 5B is a timing diagram showing an example of an emitted light pulse and a reflected light pulse after binarization. It is possible to calculate the distance to the object by measuring the time t from the time when the LD emits the emitted light pulse until the time t when the reflected light pulse is detected by the APD. For example, as shown in FIG. 5B, for time measurement, the emitted light pulse is received by a light receiving element such as a PD to form a binarized rectangular pulse, and the reflected light pulse is binarized by the PD output detection unit 44. The pulse may be used, and the time difference t of the rising timing of these two rectangular pulses may be measured by the time measuring unit 45. It is also possible to measure the time t by A / D converting the waveforms of the emitted light pulse and the reflected light pulse and converting them into digital data, and performing a correlation calculation between the LD output signal and the APD output signal. be.

The detectable distance in such a distance measuring method is required to be on the order of 100 m. Further, in general, the amount of light reflected and returned from an object 100 m away is about several nW to several tens of nW. That is, the light receiving system is required to be able to detect a light receiving signal of several nW without error. Since the received signal for weak light of about several nW has a small signal intensity, it is easily affected by random noise, which affects the distance measurement accuracy and the reliability of object detection.

Random noise can be broadly divided into circuit noise and shot noise. The circuit noise is mainly the thermal noise generated from the resistor and the noise generated by the substrate picking up the radiated noise. Such circuit noise is generally about several mV. On the other hand, shot noise is mainly white noise associated with light quantity measurement, and its magnitude is proportional to the square root of the time average of light quantity, and is several tens of mV or more when the sensitivity is high or the disturbance light is strong. Can also be. Therefore, in the present embodiment, shot noise is more likely to be a problem than circuit noise among random noise. Shot noise also occurs as white noise during DC light detection, as can be seen from the fact that the magnitude of the noise is proportional to the square root of the time average of the amount of light.

FIG. 6A is a schematic diagram showing an example of a received light signal waveform when sunlight does not enter. FIG. 6B is a schematic diagram showing an example of a received light signal waveform when sunlight enters. FIG. 6C is a schematic diagram showing an example of a received light signal waveform when sunlight enters when the DC component is removed. FIG. 6D is a schematic diagram showing an example of a received light signal waveform when strong sunlight enters when the DC component is removed. Note that FIG. 6D means that it is stronger than the sunlight of FIGS. 6B and 6C.

Compared to the case where sunlight does not enter (see FIG. 6A), when sunlight enters, not only the DC component increases, but also random noise (shot noise) increases (see FIG. 6B). The DC component can be removed by a high-pass filter or the like, but random noise cannot be removed by a high-pass filter or the like (see FIG. 6C). For example, in the actual traveling environment of a vehicle, sunlight may be reflected by a highly reflective object such as a window glass or a bonnet of the vehicle, and strong sunlight may enter the light receiving element. In such a case, as shown in FIG. 6D, shot noise increases and the noise exceeds the detection threshold. If the noise exceeds the detection threshold, it becomes difficult to distinguish between the signal and the noise, resulting in erroneous detection. Further, when a highly reflective object exists at a short distance, the sunlight entering the light receiving element becomes stronger, so that the shot noise becomes larger, the phenomenon that the noise exceeds the detection threshold is more likely to occur, and the false detection increases.

In the method of detecting the received signal based on the threshold voltage, it is usually necessary to set the threshold voltage sufficiently higher than the shot noise in order to prevent erroneous detection due to noise, so the threshold voltage has the maximum shot noise. Determined assuming the situation (see Figure 1A). Therefore, when the shot noise is relatively small, the threshold voltage is set excessively large, and the detectable distance becomes smaller than necessary (see FIG. 1B). From these, it is desirable to set the threshold voltage small in order to increase the detectable distance.

Based on these, the relationship between shot noise and the peak of the reflected pulse from the object signal (target peak) will be described. FIG. 7 is a diagram showing an example of the relationship between shot noise and a target peak. As shown in FIG. 7, when the ambient illuminance is very bright, the shot noise is large. However, as shown in FIG. 7, when the distance to the object is short or the reflectance of the object is large, it is easy to distinguish it from shot noise, and it is easy to set the threshold voltage for detecting the target peak. be.

FIG. 8 is a diagram showing an example of the relationship between shot noise and a target peak. Note that FIG. 8 is different from FIG. 7, and the case where the distance to the object is long is taken as an example. As shown in FIG. 8, when the distance from the object is long or the reflectance of the object is small, the target peak becomes small and it becomes difficult to distinguish it from shot noise.

FIG. 9 is a diagram showing an example of the relationship between the actual distance to the object, the target peak intensity, and the shot noise. In FIG. 9, shot noise showing a maximum value assuming strong sunlight such as the west sun is taken as an example. Further, in FIG. 9, the shot noise is displayed by an error bar from 0 mV. As shown in FIG. 9, the voltage of the target peak intensity is saturated in the distance measurement at a short distance (up to the vicinity of 25 m). When setting the threshold value to avoid erroneous distance measurement due to shot noise, for example, the threshold value is set to 400 mV. However, in this case, it can be seen that the peak intensity becomes smaller than the threshold value in the distance measurement at a long distance of 50 m or more, so that the distance measurement cannot be performed. That is, in order to measure a distance farther, a technique that can set a low threshold value and separate shot noise and a target peak is required.

By the way, other factors such as erroneous detection of a received signal from an object include rain and fog. In these cases as well, as with shot noise, there is a high possibility that the threshold voltage for detecting a received signal from an object will be exceeded, and it will not be possible to know which signal is due to reflection from the object.

FIG. 10 is a schematic diagram showing an example of a light receiving signal waveform in which rain and an object are detected. As shown in FIG. 10, three rains (rain 1, rain 2, rain 3) and one object are detected, assuming that the pulse is emitted at time 0. When the detection threshold value for detecting the received light signal is set to the level of the broken line shown in FIG. 10, four rain 1 to rain 3 and an object are detected. Although we want to recognize an object as danger information without recognizing rain as danger information, we cannot determine which is rain and which is an object even by looking at the detection result. Therefore, it is not possible to know where the position of the object to be used as dangerous information is.

Therefore, as described below, the noise component and the object are discriminated from each other. In the following description, when performing optical scanning, the effective scanning area is divided into a plurality of (N) areas, and optical scanning is performed for each divided area (N divided area). Then, the period from the start of optical scanning for one N-divided region of all N-divided regions in the effective scanning region to the end of optical scanning for all N-divided regions is defined as one-optical scanning. FIG. 11 is a diagram showing an example in which the effective scanning region is divided into a plurality of regions (N division regions). Then, in one optical scan, the distance measurement value (for example, distance measurement value B) measured by lightly scanning a certain N division region (for example, N division region B) is N adjacent to the division region B. The value of the distance measurement value (for example, distance measurement value A) measured by performing optical scanning of the division region (for example, N division region A) at a timing prior to the optical scan to the N division region B. By referring to and determining the certainty of the distance measurement value B based on the distance measurement value A and the distance measurement value B, the noise component and the object are discriminated. That is, the effective scanning area is divided into a plurality of areas, and the period from the start of optical scanning for one of the divided areas to the end of optical scanning for all the divided areas is defined as one optical scanning. However, in the method of measuring the distance of the effective scanning area by single-light scanning, the distance measurement result measured by only one divided area is treated as noise, and the distance measured by two or more adjacent divided areas is measured. When the results are approximately the same distance, it is adopted as the distance measurement value. In order to realize this, the distance measurement is performed by performing optical scanning on the N division area A adjacent to the N division area B where the distance measurement value B is measured at a timing prior to the optical scan to the N division area B. The distance measurement value A is referred to, and the distance measurement value B is adopted when the distance measurement value A and the distance measurement value B are substantially the same distance.

As described above, when the effective scanning region is deflected to perform optical scanning, the effective scanning region can be expressed by the deflection angle. That is, for each divided region in which the effective scanning area for optical scanning is divided into a plurality of (N) regions, the deflection angle required for optical scanning of the entire effective scanning region is divided into a plurality of (N) angles. However, this divided angle (deflection angle or scanning angle) may be used for expression.

Here, if it is determined that the distance measurement value A and the distance measurement value B are not related to each other, the adoption of the distance measurement value B is suspended. Then, the N-divided region (for example, the N-divided region C) adjacent to the distance measurement value B and located on the opposite side of the N-divided region A is optical-scanned at a timing after the optical scan to the N-divided region B. With respect to the distance-measured distance-measured value C, the reserved distance-measured value B is referred to, and the certainty of the distance-measured value C is determined based on the distance-measured value B and the distance-measured value C. When it is determined that the relationship between the distance measurement value B and the distance measurement value C is low, the distance measurement value B is approximately the same distance as both the distance measurement value A and the distance measurement value C in the adjacent N division region. It means that there is no value. The holding of the distance measurement value B at this time is released, and it is treated as noise. Then, the adoption of the distance measurement value C is put on hold, and the information indicating that the distance measurement value C has been put on hold is stored.

Further, when the distance measurement value C is considered to be highly related to the distance measurement value B, the distance measurement value B and the distance measurement value C in the adjacent N division region are substantially the same distance. These are adopted as distance measurement values. That is, the distance measurement value C is first adopted by determining the relationship between the distance measurement value B and the distance measurement value C, and the information indicating that the distance measurement value C is adopted is fed back, and the distance measurement value B is adopted. Will be.

FIG. 12 is a diagram illustrating an example of discrimination between noise and an object by the distance measuring device 100 according to the embodiment. Here, the N-divided region in the effective scanning region will be described using the expression of scanning angle. The upper part of FIG. 12 is a schematic diagram showing an example in which an object or noise exists at a certain distance at each scanning angle. Here, an object or noise is collectively referred to as a target. The middle part of FIG. 12 scans the existing target as shown in the upper part of FIG. 12 from the right side of the figure, and shows how the judgment is made for the result measured at each angle. It is a figure. The lower part of FIG. 12 is a diagram showing the content of the judgment. The white circle and the white triangle mean that the target is an object, and the cross mark means that the target is noise. In this embodiment, if the distance is within ± 50 cm from the distance measurement value at the adjacent scanning angle, it is determined that the distance is the same.

As shown in FIG. 12, first, the distance measurement result “6 m” having a scanning angle of “0.1 °” is temporarily put on hold because there is no value before it. Then, at the scanning angle "0.2 °", the same distance measurement result "6 m" as the scanning angle "0.1 °" was confirmed. Therefore, at this point, the distance measurement result at the scanning angle "0.1 °" was confirmed. For "6m", the judgment is a white triangle (after the temporary judgment is suspended, the white circle is judged by the feedback from the data behind). Subsequently, up to the scanning angle "0.6 °", the white circles are judged (white circles are judged by comparison with the previous data).

After that, the distance measurement result "3 m" with the scanning angle "0.7 °" is temporarily put on hold because the distance is different from the distance measurement result "6 m" with the scanning angle "0.6 °". .. Then, at the scanning angle "0.8 °", the same distance measurement result "3 m" as the scanning angle "0.7 °" was confirmed. Therefore, at this point, the distance measurement result at the scanning angle "0.7 °" was confirmed. For "3m", the judgment is a white triangle.

Further, the scanning angle "1.8 °" is temporarily put on hold because there is no distance measurement result at the scanning angle "1.7 °". Since there is no distance measurement result even at the scanning angle "1.9 °", the target with the distance measurement result "5 m" at the scanning angle "1.8 °" is judged by the cross mark (after the temporary judgment is suspended). It will be judged by the cross mark based on the feedback from the back data). That is, the target with the distance measurement result “5 m” with the scanning angle “1.8 °” is treated as noise.

By the way, as shown in FIG. 12, it is desirable that distance information of all scanning angles can be obtained by one scanning from the scanning start position to the scanning end position in the effective scanning region. However, if an attempt is made to shorten the scanning time, the scanning speed becomes high, the time for emitting light at one scanning angle becomes very short, and a high transfer rate is required for the signal to be processed. growing. Then, it becomes difficult to continuously emit the laser that emits the pulsed light at each scanning angle. Therefore, for example, Japanese Patent Application Laid-Open No. 2016-133341 proposes to divide the optical scan of the effective scan region into a plurality of scans and perform distance measurement at all scan angles. Hereinafter, the discrimination between noise and an object in the divided ranging distance measurement in which the optical scan of the effective scanning region is divided into a plurality of optical scans will be described.

Here, an effective scanning area including a plurality of the above-mentioned N-divided areas will be defined as an M-divided area. When lightly scanning the effective scanning region, first, the Nth N-divided region in the M-th M-divided region is optical-scanned, and then the N-th N-divided region in the M + 1-th M-divided region is optical-scanned. do. This operation is performed for all M division areas. After that, the N + 1st N division region in the Mth M division region is lightly scanned, and then the N + 1th N division region in the M + 1th M division region is lightly scanned. By performing this order for all N-divided regions in all M-divided regions, optical scanning for all N-divided regions in the effective scanning region is realized. As is clear from this description, the number of scan divisions in the effective scanning region is determined by the number of N division regions included in the M division region. For example, when the M division region includes four N division regions, the number of divisions of optical scanning in the effective scanning region is four. FIG. 13 is a diagram showing an example in which four N-divided regions are included in the M-divided region. As described above, even when the optical scan of the effective scanning region is divided into a plurality of optical scans and distance measurement is performed at all scanning angles, one of the N-divided regions in the effective scanning region is N-divided region. The period from the start of optical scanning to the end of optical scanning for all N-divided regions is defined as one-optical scanning.

FIG. 14 is a diagram illustrating an example in which optical scanning of an effective scanning region according to an embodiment is divided into a plurality of optical scans, distance measurement is performed at all scanning angles, and noise and an object are discriminated from each other. Here, the N-divided region and the M-divided region in the effective scanning region will be described using the expression of scanning angle. In FIG. 14, the effective scanning area is optically scanned in units of 0.1 °. That is, the N division area is obtained by dividing the effective scanning area every 0.1 °. Further, the effective scanning area is divided into M division areas by 0.4 °. That is, in FIG. 14, four N-divided regions are included in the M-divided region. The number of divisions of optical scanning in the effective scanning region is four.

The upper part of FIG. 14 is a schematic diagram showing an example in which an object or noise exists at a certain distance at each scanning angle. As described above, objects or noise are collectively referred to as targets. The middle part of FIG. 14 is a diagram showing how the target existing as shown in the upper part of FIG. 14 is judged based on the result of repeating distance measurement by four divisions of optical scanning. Is. The lower part of FIG. 14 is a diagram showing the content of the judgment. In this embodiment, if the distance is within ± 50 cm from the distance measurement value at the adjacent scanning angle, it is determined that the distance is the same.

That is, the distance measurement at the scanning angle “0.1 °” shown in FIG. 14 was performed by the divisional scanning immediately before the scanning at the scanning angle “0.2 °”. Similarly, the distance measurement at the scanning angle "0.3 °" is performed by the divided scanning one after the scanning at the scanning angle "0.2 °". In this way, the M-divided region in which the effective scanning region is divided into 0.4 ° intervals is divided into four, and the N-divided region in 0.1 ° intervals is set as the minimum optical scanning unit, and the optical scanning of the effective scanning region is performed. Distance measurement is performed by dividing into a plurality of optical scans.

As shown in FIG. 14, first, the distance measurement result “6 m” having a scanning angle of “0.1 °” is temporarily put on hold because there is no value before it. Then, at the scanning angle "0.2 °", the same distance measurement result "6 m" as the scanning angle "0.1 °" was confirmed. Therefore, at this point, the distance measurement result at the scanning angle "0.1 °" was confirmed. For "6m", the judgment is a white triangle (after the temporary judgment is suspended, the white circle is judged by the feedback from the data behind). Subsequently, up to the scanning angle "0.6 °", the white circles are judged (white circles are judged by comparison with the previous data).

After that, the distance measurement result "3 m" with the scanning angle "0.7 °" is temporarily put on hold because the distance is different from the distance measurement result "6 m" with the scanning angle "0.6 °". .. Then, at the scanning angle "0.8 °", the same distance measurement result "3 m" as the scanning angle "0.7 °" was confirmed. Therefore, at this point, the distance measurement result at the scanning angle "0.7 °" was confirmed. For "3m", the judgment is a white triangle.

Further, the scanning angle "1.8 °" is temporarily put on hold because there is no distance measurement result at the scanning angle "1.7 °". Since there is no distance measurement result even at the scanning angle "1.9 °", the target with the distance measurement result "5 m" at the scanning angle "1.8 °" is judged by the cross mark (after the temporary judgment is suspended). It will be judged by the cross mark based on the feedback from the back data). That is, the target with the distance measurement result “5 m” with the scanning angle “1.8 °” is treated as noise. As described above, in FIG. 14, the determination of the target at each position is performed across a plurality of divided optical scans.

As described above, in FIGS. 12 and 14, the distance measurement value at a scanning angle (N division area) adjacent to the distance measurement value measured at a certain scanning angle (N division area) using the distance measurement value. Judging the certainty of. By determining whether or not the difference in distance between adjacent scanning angles (N-divided area) is within a predetermined range, the standard adopted as the distance-finding value is to measure an object having the same adjacent scanning angles (N-divided area). It is possible to efficiently judge whether or not it is done. It is desirable that the range of the difference in distance used for the judgment is within the range of the distance measurement value set by investigating the distance range of the same object in advance.

Furthermore, in order to make a reliable judgment in determining whether or not adjacent scanning angles (N division regions) are measuring the same object, the pulse width of the scattered pulsed light at a certain scanning angle is determined. You may use it. That is, in consideration of the case where noises are accidentally generated at substantially the same distance, each pulse width of the pulsed light corresponding to the targets existing at substantially the same distance at adjacent scanning angles is a preset constant pulse. Whether or not it is within the width range is also set as a criterion. This makes it possible to reduce the probability of erroneous determination that noise is adopted as an object. For example, the pulse width range can be within ± 20%.

FIG. 15 is a diagram illustrating an example in which the pulse width of the pulsed light is used as a determination criterion. As shown in FIG. 15, the pulse width of the target peak shows a stable width. On the other hand, shot noise and the like have a random pulse width. By investigating the value of the pulse width σ of the target peak of the object in advance and setting the pulse width range based on the pulse width σ in advance, if the range is exceeded, it will be a signal from the same object. I will not adopt it. That is, even if noise at adjacent scanning angles (N division regions) is observed at substantially the same position, it can be judged that the relationship between the two is low because the pulse width in that case is different than the set width. That is, by adding the pulse width to the determination criterion, it is possible to more reliably discriminate between noise and an object. The pulse width represents the width from the rising edge to the falling edge of the signal when the signal is received.

FIG. 16 is a flowchart showing an example of the flow of the target determination process according to the embodiment. As shown in FIG. 16, the distance measuring device 100 acquires the data (for example, the distance measuring result) obtained by scanning (optical scanning) (step S101). Then, the distance measuring device 100 determines whether or not the distance measuring result exists at the adjacent scanning angle with respect to the distance measuring result at a certain position in the one-light scanning (step S102).

At this time, when the distance measurement result does not exist at the adjacent scanning angles (step S102: No), the distance measuring device 100 temporarily puts the distance measurement result at its own position on hold (step S103). After putting it in the hold state, the distance measuring device 100 executes the process of step S101 again and acquires the distance measurement result of the next position. On the other hand, when the distance measurement result exists in the adjacent scanning angles (step S102: Yes), the distance measuring device 100 has the distance measurement result of the adjacent scanning angles within 50 cm of its own distance measurement result, and It is determined whether the pulse width corresponding to the distance measurement result of the adjacent scanning angle is within ± 20% of the pulse width corresponding to the own distance measurement result (step S104). That is, the distance measuring device 100 has a pulse width of pulsed light corresponding to a target within the range of the difference in distance between adjacent scanning angles (for example, within 50 cm) or at substantially the same distance at adjacent scanning angles. Check if is within a certain pulse width range (for example, within ± 20%).

At this time, if any of the conditions is not satisfied (step S104: No), the distance measuring device 100 temporarily puts the distance measurement result of its own position on hold (step S103). After putting it in the hold state, the distance measuring device 100 executes the process of step S101 again and acquires the distance measurement result of the next position. On the other hand, when any of the conditions is satisfied (step S104: Yes), the distance measuring device 100 outputs the distance measurement result of its own position as being adopted (step S105).

Further, the distance measuring device 100 determines whether or not the distance measuring result of the adjacent scanning angle has been output (step S106). At this time, when the distance measurement result of the adjacent scanning angles has not been output (step S106: No), the distance measuring device 100 outputs the distance measurement result of the adjacent scanning angles as being adopted (step S107). After that, the distance measuring device 100 executes the process of step S101 again, and acquires the distance measuring result of the next position. On the other hand, when the distance measurement result of the adjacent scanning angle has already been output (step S106: Yes), the distance measuring device 100 re-executes the process of step S101 and acquires the distance measurement result of the next position. The distance measuring device 100 ends the target determination process when the determination of all the distance measurement results is completed.

In the present embodiment, the case where the distance range from the adjacent scanning angles regarded as the same object is within ± 50 cm is given as an example, but the present invention is not limited to this. When the distance range is reduced, noise removal can be realized more effectively. For example, an object existing at a position of 10 m is scanned with an angle resolution of 0.1 ° to measure a distance, and when the object faces the distance measuring device 100, the adjacent scanning angle is used. The scanning direction resolution of the object is 1.7 cm. That is, even if an object is installed at an angle of 45 ° with respect to the distance measuring device 100, the difference in the distance is only 1.7 cm, and it is sufficient to set the distance range with the adjacent scanning angle to ± 10 cm. It turns out that there is. Therefore, even noise that appears in a place where the difference in distance from the object is only 20 cm can be removed as noise.

However, the resolution in the scanning direction for an object existing at a position of 100 m is 17 cm. At this time, if an object is installed at an angle of 45 ° with respect to the distance measuring device 100, the difference in distance is 17 cm, and if it is set within a distance range of ± 10 cm, this object will be treated as noise. .. Further, in reality, considering the variation in distance measurement, there is a high possibility that the object will be erroneously processed as noise. Therefore, in the present embodiment, the ranging range of the object at the adjacent scanning angle may be changed according to the distance measured.

For example, the distance measured is "A", the angular resolution in the scanning direction is "θ1", the standard deviation of the distance measurement variation of the object at the reference distance is "σobj", the multiple of the standard deviation is "n", and the distance measuring device 100. The upper limit of the expected angle of the object that can be measured is "θ2". Of these, values other than "A" are values that can be determined in advance, and by applying the value "A" measured in real time to the following (Equation 1), for example, the adjacent scanning angles. The range of the object in can be applied immediately.

Distance measurement range of objects at adjacent scanning angles = (n ・ σobj ^ 2) ^ 0.5 + A ・ sinθ1 ・ tanθ2 ・ ・ ・ (Equation 1)

Here, assuming that θ1 = 0.1 °, σobj = 10 cm (reference distance 50 m), n = 2, and θ2 = 60 °, the distance measured value A and the distance measured value of the object at an adjacent angle are used. The relationship with the distance measurement range adopted is as shown in FIG. FIG. 17 is a diagram showing an example of the relationship between the ranging value and the ranging range. As shown in FIG. 17, it can be seen that the larger the distance measurement value, the wider the distance measurement range of the object.

As described above, in the distance measuring device 100, based on the relationship between the distance measurement value of an object and the distance measurement value scanned at a scanning angle adjacent to the object, the object is noisy or Determine that it is an object. As a result, it is possible to accurately determine whether an object is noise or an object. Further, since the threshold value for detecting the signal can be set small, the detection distance can be increased.

In the above embodiment, the case of rotational scanning using the rotary mirror 26 has been described as an example, but a configuration may be configured in which a plurality of light sources are arranged on an arc, for example, and sequentially irradiated with light. ..

100 Distance measuring device 10 Floodlight system 12 LD drive unit 20 Floodlight optical system 22 Coupling lens 24 Reflection mirror 26 Rotating mirror 30 Light receiving optical system 40 Detection system 42 Time measurement PD
44 PD output detection unit 45 time measurement unit 46 measurement control unit 47 object recognition unit 50 synchronization system 52 synchronization lens 54 synchronization detection PD
56 PD output detector

Japanese Unexamined Patent Publication No. 2004-184333 Japanese Unexamined Patent Publication No. 11-038137 Japanese Unexamined Patent Publication No. 08-304535

Claims (11)

A light projecting unit that emits light to an object,
A light receiving unit that receives light reflected or scattered by the object, and a light receiving unit.
A scanning unit that scans the light projected from the projection unit into the scanning region, and a scanning unit.
A distance measuring unit that measures the time from the light projected by the light projecting unit to the light receiving by the light receiving unit and measures the distance to the object.
Equipped with
When the scanning area is divided into a plurality of divided areas and the period from the start of scanning of one of the divided areas to the end of scanning of all the divided areas is defined as one scan.
Measurement of the first measured value, which is the measured value of the first divided region measured by the distance measuring unit during the one scan, and the measurement of the second divided region measured before the first measured value. The second measured value, which is the value, and
During the one scan, the first light receiving width, which is the time width during which the light receiving unit receives the light in the first divided region, and the time width during which the light receiving unit receives the light in the second divided region. Based on the second light receiving width, it is determined whether or not the first measured value can be the measurement result of the first divided region.
A distance measuring device, characterized in that, when it is determined that the measurement result of the first divided region can be obtained, the first measured value is output as a distance to an object in the first divided region. When the relationship between the first measured value and the second measured value does not satisfy the first predetermined criterion, and when
In either case, the first light receiving width and the second light receiving width do not satisfy the second predetermined criterion.
The first measured value measured by the distance measuring unit during the one scan, the third measured value which is the measured value of the third divided region measured after the first measured value, and the third measured value.
The first light receiving width, which is the time width during which the light receiving unit receives the light during the one scan, and the third light receiving width, which is the time width during which the light receiving unit receives the light in the third divided region. The distance measuring device according to claim 1, wherein it is determined whether or not the first measured value can be a measurement result of the first divided region based on the width. When the relationship between the first measured value and the third measured value does not satisfy the first predetermined criterion, and when
In either case, the first light receiving width and the third light receiving width do not satisfy the second predetermined criterion.
The first measured value is not used as the measurement result of the first divided region.
When the relationship between the first measured value and the third measured value satisfies the first predetermined standard, and the first light receiving width and the third light receiving width satisfy the second predetermined standard, the said. The distance measuring device according to claim 2, wherein the first measured value is a measurement result of the first divided region. A scan area divided into M areas (M ≧ 1) is defined as an M division area.
When the M division area is further divided into N (N ≧ 1) areas, it is defined as an N division area.
The scanning unit is
The operation of scanning the N-th N-divided region in the M + 1-th M-divided region after scanning the N-th N-divided region in the M-th M division region is performed in all the scanning regions. Do about the M division area,
Next, the operation of scanning the N + 1th N-divided region in the M + 1-th M-divided region after scanning the N + 1-th N-divided region in the M-th M-divided region is performed in the scanning region. Scan all the N-divided areas in the scanning area in the order of performing all M-divided areas.
The first division region is the Nth N division region in the M division region, and the second division region is the N-1th N division region in the M division region. The distance measuring device according to claim 1. A scan area divided into M areas (M ≧ 1) is defined as an M division area.
When the M division area is further divided into N (N ≧ 1) areas, it is defined as an N division area.
The scanning unit is
The operation of scanning the N-th N-divided region in the M + 1-th M-divided region after scanning the N-th N-divided region in the M-th M division region is performed in all the scanning regions. Do about the M division area,
Next, the operation of scanning the N + 1th N-divided region in the M + 1-th M-divided region after scanning the N + 1-th N-divided region in the M-th M-divided region is performed in the scanning region. Scan all the N-divided areas in the scanning area in the order of performing all M-divided areas.
The first divided region is the Nth N-divided region in the M-divided region, and the second divided region is the N-1th N-divided region in the M-divided region. The division area 3 is the N + 1th N division area in the M division area.
The distance measuring device according to claim 2 or 3. The distance measuring device according to claim 2, 3 or 5, wherein the first predetermined standard is such that both measured values are within a predetermined range. The distance measuring device according to claim 6, wherein the predetermined range becomes wider as the distance represented by the measured value becomes longer. The distance measuring device according to any one of claims 2, 3, 5 to 7, wherein the second predetermined reference is such that the ratio of both light receiving widths to the first light receiving width is larger than a certain reference value. The distance measuring device according to any one of claims 2, 3, 5 to 7, wherein the second predetermined standard is a light receiving width of both within a certain width range. The light receiving unit outputs a light receiving signal having a voltage corresponding to the amount of the received light.
The distance measuring unit detects the light when the voltage of the received light signal exceeds the detection threshold voltage.
The distance measuring device according to any one of claims 1 to 9, wherein the detection threshold voltage is smaller than the voltage of the shot noise included in the received light signal. A floodlight step that casts light on an object,
A light receiving step that receives light reflected or scattered by the object, and
A scanning step of scanning the light projected by the projection step into the scanning area, and a scanning step.
A distance measurement step that measures the time from the light projection by the light projection step to the light reception by the light reception step and measures the distance to the object.
Including
When the scanning area is divided into a plurality of divided areas and the period from the start of scanning of one of the divided areas to the end of scanning of all the divided areas is defined as one scan.
The first measured value, which is the measured value of the first divided region measured by the distance measuring step during the one scan, and the measured value of the second divided region measured before the first measured value. The second measured value is
During the one scan, the first light receiving width, which is the time width during which the light receiving unit receives the light in the first divided region, and the time width during which the light receiving unit receives the light in the second divided region. Based on the second light receiving width, it is determined whether or not the first measured value can be the measurement result of the first divided region.
A distance measuring method characterized by outputting the first measured value as a distance to an object in the first divided region when it is determined that the measurement result of the first divided region can be obtained.

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