JP2019128221A - Time measurement device, distance measurement device, moving body device, time measurement method, and distance measurement method - Google Patents

Abstract

To provide a distance measurement device that can conduct a highly accurate and high-speed measurement, not relying on an amount of reception light by a light reception element of light projected and reflected upon an object.SOLUTION: A time measurement device measures a time from emission from an LD11 of light projected from a light projection system 10 including an LD 11 and reflected upon an object to reception of the light by a time measurement-purpose PD 42. The time measurement device comprises a time acquisition system that includes a control system 46 configured to, when a plurality of light projection are conducted in the same direction by the light projection system 10, classify a voltage signal in which a peak exceeds a threshold of voltage signals output from a waveform processing circuit 41 upon each light projection of the plurality of light projection or a value based on the voltage signal into a plurality of ranks corresponding to the time or a value based on the time; and acquire the time upon the light projection in the same direction on the basis of the classification result, in which a rank width for each rank is set based on a frequency characteristic (characteristic) of the waveform processing circuit 41.SELECTED DRAWING: Figure 1

Description

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

  Conventionally, a light projecting system including a light source, a light receiving element that receives and photoelectrically converts light projected from the light projecting system and reflected by an object, and at least one process for the output current of the light receiving element, A processing unit that outputs a signal obtained by the processing, and extracts a signal based on the light from a plurality of signals whose peaks exceed a threshold among the signals output from the processing unit, and based on the signal There is known an apparatus for measuring the time from when the light is emitted from the light source to when it is received by the light receiving element (see, for example, Patent Documents 1 and 2).

  However, the devices disclosed in Patent Documents 1 and 2 have room for improvement with respect to performing high-accuracy and high-speed measurement regardless of the amount of light received by the light-receiving element of the light projected and reflected by the object. .

  The present invention relates to a light projecting system including a light source, a light receiving system including a light receiving element that receives and photoelectrically converts light projected from the light projecting system and reflected by an object, and an electric signal output from the light receiving element. A processing system that performs at least one processing and outputs a signal obtained by the processing, and measures a time from when the light is emitted from the light source until it is received by the light receiving element. In the apparatus, when the light projecting system performs a plurality of times of light projecting in the same direction toward the object, the peak of the signals output from the processing system at the time of the plurality of times of light projecting has a threshold value. The time when the signal exceeding the value or the value based on the signal is classified into a plurality of classes corresponding to the time or the value based on the time, and the time at the time of light projection in the same direction is acquired based on the classification result An acquisition system, the processing system It is the time measurement device according to claim the class width of each of the classes based on the properties are set.

  According to the present invention, highly accurate and high-speed measurement can be performed regardless of the amount of light received by the light receiving element of the light projected and reflected by the object.

It is a figure which shows schematic structure of the object detection apparatus which concerns on one Embodiment. 2A is a diagram for explaining the light projecting optical system and the synchronization system, FIG. 2B is a diagram for explaining the light receiving optical system, and FIG. It is a figure which shows roughly the optical path of the light from to a reflective mirror, and the optical path of the light from a reflective mirror to PD for time measurement. It is a timing diagram which shows a synchronizing signal and LD drive signal. 4A is a timing chart showing the light emission pulse and the light reception pulse, and FIG. 4B is a timing chart showing the light emission pulse and the light reception pulse after binarization. FIG. 5A is a view showing a case where shot noise is larger than a threshold voltage, and FIG. 5B is a view showing a case where shot noise is smaller than a threshold voltage. It is a figure for demonstrating the difference of the pulse width of an object signal and noise. It is a figure for demonstrating the structural example of a waveform processing circuit. It is a figure which shows the structural example of a current-voltage converter and a signal amplifier. It is a figure for comparing an ideal sine wave and a light reception waveform. It is a figure which shows the change of the received light waveform according to the change of received light quantity. It is a figure for demonstrating rise time and fall time of a light reception signal. It is a figure which shows the change of the time when the rising of the received light signal crosses a threshold voltage according to the change of received light quantity. It is a figure which shows the pulse width of a light projection waveform. It is a figure for demonstrating the example which changes the class width of time class. It is a figure for demonstrating a sensing apparatus. 6 is a flowchart for explaining distance measurement processing 1; 6 is a flowchart for explaining distance measurement processing 2; 6 is a flowchart for explaining distance measurement processing 3; 10 is a flowchart for explaining distance measurement processing 4; It is a figure showing an example of composition of a control system.

  Hereinafter, an object detection apparatus 100 according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram illustrating a schematic configuration of the object detection apparatus 100.

For example, the object detection device 100 is mounted on a vehicle (for example, an automobile) as a moving body, and is projected and reflected (scattered) by an object (for example, a preceding vehicle, a stopped vehicle, an obstacle, a pedestrian, or the like). Is a scanning laser radar that detects information regarding an object (hereinafter also referred to as “object information”) such as the presence or absence of the object and the distance to the object. The object detection apparatus 100 receives power supply from, for example, a battery (storage battery) of a vehicle.
That is, the object detection device 100 functions as an object presence / absence determination device, a distance measurement device (distance measurement device), or an object recognition device (a device for recognizing the position, shape, size, etc. of an object).

  As shown in FIG. 1 as an example, the object detection apparatus 100 includes a light projecting system 10, a light receiving system 40, a waveform processing circuit 41 (processing system), a binarization circuit 44 (part of a time acquisition system), a control system. 46 (part of the time acquisition system), a synchronization system 50, an object recognition unit 47, and the like.

  The light projecting system 10 includes an LD 11 (laser diode) as a light source, an LD driving unit 12, and a light projecting optical system 20.

  The LD 11 is also called an edge emitting laser, and is driven by the LD driving unit 12 to emit laser light. The LD driving unit 12 lights (emits light) the LD 11 using the LD driving signal (rectangular pulse signal) output from the control system 46. The LD driver 12 includes, as an example, a capacitor connected so as to supply current to the LD 11, a transistor for switching between conduction / non-conduction between the capacitor and the LD 11, charging means capable of charging the capacitor, and the like. . The control system 46 starts and stops measurement in response to a measurement control signal (measurement start signal or measurement stop signal) from the ECU (Electronic Control Unit) of the automobile.

  In addition, although LD11 is used as the said light source, it is not restricted to this. For example, another light emitting element such as a VCSEL (surface emitting laser), an organic EL element, an LED (light emitting diode), an LD or a laser other than the VCSEL may be used.

  FIG. 2A schematically shows the light projecting optical system 20 and the synchronization system 50. FIG. 2B schematically shows the light receiving optical system 30. In the following, description will be made using an XYZ three-dimensional orthogonal coordinate system in which the Z-axis direction shown in FIG. 2A or the like is the vertical direction, as appropriate.

  As shown in FIG. 2A, the light projecting optical system 20 is disposed on the optical path of light through the coupling lens 22 and the coupling lens 22 disposed on the optical path of the light from the LD 11. And a rotating mirror 26 as a deflector disposed on the optical path of the light reflected by the reflecting mirror 24. Here, in order to reduce the size of the apparatus, a reflection mirror 24 is provided on the optical path between the coupling lens 22 and the rotating mirror 26 serving as a deflector, and the optical path is folded.

  Therefore, the light emitted from the LD 11 is shaped into light having a predetermined beam profile by the coupling lens 22, reflected by the reflecting mirror 24, and deflected around the Z axis by the rotating mirror 26.

  The light deflected to a predetermined deflection range around the Z axis by the rotating mirror 26 is the light projected from the light projecting optical system 20, that is, the light emitted from the object detection device 100.

  The rotating mirror 26 has a plurality of reflecting surfaces around the rotation axis (Z-axis), and reflects (deflects) the light from the reflecting mirror 24 while rotating around the rotation axis, thereby responding to the deflection range by the light. The effective scanning area to be scanned is one-dimensionally scanned in the horizontal one-axis direction (here, the Y-axis direction). Here, the deflection range and the effective scanning area are on the + X side of the object detection apparatus 100. Hereinafter, the rotation direction of the rotation mirror 26 is also referred to as “mirror rotation direction”.

  As can be seen from FIG. 2A, the rotating mirror 26 has two reflecting surfaces (two opposing surfaces), but is not limited thereto, and may be one surface or three or more surfaces. It is also possible to provide at least two reflecting surfaces and to incline them at different angles with respect to the rotation axis of the rotating mirror so as to switch the scanning / detection region in the Z-axis direction.

  As the deflector, other mirrors such as a polygon mirror (rotating polygon mirror), a galvano mirror, and a MEMS mirror may be used instead of the rotating mirror.

  As shown in FIGS. 2B and 1, the light receiving system 40 includes a light receiving optical system 30 on which light projected from the light projecting optical system 20 and reflected by an object in the effective scanning region is incident, It includes a time measurement PD 42 that receives and photoelectrically converts light via the light receiving optical system 30 and outputs an electrical signal. The electrical signal output from the time measurement PD 42 is a current (output current) and is sent to the waveform processing circuit 41. “PD” is an abbreviation for photodiode.

  As shown in FIG. 2B, the light receiving optical system 30 reflects the light projected from the light projecting optical system 20 and reflected by the object in the effective scanning area, and the rotating mirror 26 A reflection mirror 24 that reflects the light of the light, and an imaging optical system that is disposed on the optical path of the light from the reflection mirror 24 and forms an image on the time measurement PD 42 described later.

  Here, the light projecting optical system 20 and the light receiving optical system 30 are installed in the same casing. This housing has openings on the optical path of the emitted light from the light projecting 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 transmission window member). It is done. The window can be made of glass or resin, for example.

  FIG. 2C shows an optical path from the LD 11 to the reflection mirror 24 and an optical path from the reflection mirror 24 to the time measurement PD 42.

  As can be seen from FIG. 2C, the light projecting optical system 20 and the light receiving optical system 30 are arranged so as to overlap in the Z-axis direction, and the rotating mirror 26 and the reflecting mirror 24 are connected to the light projecting optical system 20 and the light receiving optical system. The optical system 30 is common. As a result, the relative positional deviation between the irradiation range of the LD 11 and the light receivable range of the time measurement PD 42 on the object can be reduced, and stable object detection can be realized.

  Therefore, the light projected from the light projecting 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 condensed on the time measurement PD 42 by the imaging optical system. (See FIG. 2 (B)). In FIG. 2B, in order to reduce the size of the apparatus, a reflection mirror 24 is provided between the rotating mirror 26 and the imaging optical system to return the optical path. Here, the imaging optical system is composed of two lenses (imaging lenses), but may be one lens, three or more lenses, or a mirror optical system. good.

The waveform processing circuit 41 converts a current / voltage converter 43 that converts the output current output from the time measurement PD 42 into a voltage signal (light reception signal), and a signal that amplifies the output signal (voltage signal) of the current / voltage converter 43. And an amplifier 48.
The output signal of the waveform processing circuit 41, that is, the output signal of the signal amplifier 48 is sent to the binarization circuit 44 and the control system 46.
In the waveform processing circuit 41, the signal amplifier 48 is not essential.

  The binarization circuit 44 binarizes the output signal of the waveform processing circuit 41 with reference to the threshold voltage, and outputs a high level signal as a detection signal to the control system 46 while the output signal exceeds the threshold. The binarization circuit 44 includes a comparator.

  As shown in FIGS. 2A and 1, the synchronization system 50 is light emitted from the LD 11 and reflected by the reflection mirror 24 via the coupling lens 22, and is deflected by the rotation mirror 26 and reflected by the reflection mirror 24. The synchronous lens 52 disposed on the optical path of the light reflected again in the above, the synchronous detection PD 54 disposed on the optical path of the light passing through the synchronous lens 52, and the electric signal output from the synchronous detection PD 54 ( A current-voltage converter 53 for converting the output current) into a voltage signal, a signal amplifier 55 for amplifying the voltage signal from the current-voltage converter 53, and the voltage signal from the signal amplifier 55 is binarized based on a threshold value. And a binarization circuit 56 having a comparator that outputs a high level signal as a synchronization signal to the control system 46 while the voltage signal exceeds the threshold.

  More specifically, the reflection mirror 24 is arranged on the upstream side in the rotation direction of the rotary mirror 26 with respect to the deflection range, and the light deflected upstream of the deflection range by the rotary mirror 26 is incident thereon. Then, the light deflected by the rotation mirror 26 and reflected by the reflection mirror 24 is incident on the synchronization detection PD 54 through 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 deflection range. Then, the synchronization system 50 may be disposed on the optical path of the light deflected by the rotating mirror 26 and reflected by the reflecting mirror 24.

  Each time the light reflected by the reflecting surface of the rotating rotating mirror 26 is received by the synchronization detection PD 54, an electrical signal (output current) is output from the synchronization detection PD 54. As a result, a synchronizing signal is periodically output from the binarization circuit 56 (see FIG. 3).

  As described above, by performing synchronous lighting for irradiating the synchronization detection PD 54 with the light from the rotation mirror 26, the rotation timing of the rotation mirror 26 can be obtained from the light reception timing of the synchronization detection PD 54.

Therefore, the effective scanning area can be optically scanned by pulsing the LD 11 after a predetermined time has elapsed since the LD 11 is synchronously turned on. That is, the effective scanning region can be optically scanned by pulsing the LD 11 before and after the timing at which the synchronization detection PD 54 is irradiated with light.
Then, by generating a synchronization signal with the same cycle as the rotation cycle of the rotating mirror 26 and generating an LD drive signal for each synchronization signal, the effective scanning region can be repeatedly optically scanned.

  The synchronization system may not have a synchronization lens, or may have another optical element (for example, a light collecting mirror).

  Here, as a light receiving element used for time measurement and synchronization detection, in addition to PD (Photo Diode) described above, APD (Avalanche Photo Diode), Geiger mode APD SPAD (Single Photo Avalanche Diode), etc. can be used. It is. Since APD and SPAD are highly sensitive to PD, they are advantageous in terms of detection accuracy and detection distance.

  The control system 46 generates an LD drive signal based on the synchronization signal from the binarization circuit 56, and outputs the LD drive signal to the LD drive unit 12.

That is, the LD drive signal is a light emission signal (pulse signal for causing the LD to emit light) delayed with respect to the synchronization signal (see FIG. 3).
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 11, and pulsed light is output from the LD 11. Since the light emission duty of the LD 11 is limited from the viewpoint of the safety of the LD 11 and the durability of the LD 11, it is desirable that the pulse light output from the LD 11 has a narrow pulse width, and the pulse width is generally 10 ns to several It is set to about 10 ns. The pulse interval is generally about several tens of microseconds.

The control system 46 measures the distance to the object (object to be measured) based on the LD drive signal, the output signal of the waveform processing circuit 41, and the output signal of the binarization circuit 44, and uses the measurement result as distance data. Output to the object recognition unit 47.
The control system 46 includes, as an example, a control unit 46a, a storage unit 46b, an operation unit 46c, a histogram / frequency distribution table generation unit 46d, and a belonging class estimation unit 46e (see FIG. 20). In the control system 46, the storage unit 46b can be realized by, for example, a memory or a hard disk, and components other than the storage unit 46b can be realized by, for example, a central processing unit (CPU) or an integrated circuit (IC).
The function of each component of the control system 46 will be described later.

The object recognizing unit 47 recognizes the position, shape, size, etc. of the object based on a plurality of distance data acquired from one or more scans from the control system 46, and sends the object recognition result to the control system 46. Output. The control system 46 transfers the object recognition result to the ECU.
The object recognition unit 47 can be realized by, for example, a CPU (Central Processing Unit) or an IC (Integrated Circuit).

Based on the transferred object recognition result, the ECU performs, for example, vehicle steering control (for example, auto steering), speed control (for example, auto brake, auto accelerator, etc.), warning to the driver for visual and auditory senses, and the like.
Note that at least one of the functions of the control system 46 and the object recognition unit 47 may be performed by the ECU without providing at least one of the control system 46 and the object recognition unit 47.

  Here, when the effective scanning region is scanned by the rotating mirror 26, the LD driving unit 12 drives (emits light) the LD 11, and pulse light as shown in FIG. Emitting a pulse (also referred to as a “projected pulse”). Then, the pulse light (hereinafter also referred to as “received light pulse”) emitted from the LD 11 and reflected (scattered) by the object uses the APD instead of the PD as a light receiving element in the time measurement PD 42 (FIG. 4A) Light is received.

  The distance to the object can be calculated by measuring the time t from when the LD 11 emits the light emission pulse to when the APD receives the light reception pulse. With respect to time measurement, for example, as shown in FIG. 4B, a light emission pulse is received by a light receiving element such as a PD, subjected to photoelectric conversion, current-voltage conversion (and signal amplification as necessary). ) The obtained voltage signal is binarized into a rectangular pulse, the received light pulse is received by the APD, subjected to photoelectric conversion, current-voltage conversion (and further signal amplification as necessary), and the obtained voltage signal ( The light reception signal may be binarized to form a rectangular pulse, and the time t between the rising timings of both rectangular pulses may be measured by the control system 46, or the waveforms of the light emission pulse and the light reception pulse are A / D converted to digital data It is also possible to measure the time t by converting the digital data of both waveforms into a correlation calculation.

By the way, when light reflected from an object is received by the light receiving system 40, a shot noise (white noise accompanying disturbance light) is generated together with a signal (hereinafter, also referred to as "object signal" hereinafter) by light reflected from the object.
At this time, since the detection of the object signal is performed based on the threshold voltage set in the binarization circuit 44, if the peak intensity of the object signal is sufficiently larger than the peak intensity of the shot noise, for example, the threshold voltage By setting to a higher value, it is possible to detect only the object signal (see FIG. 5B).
However, if the peak intensity of the object signal becomes small enough to be about the same as the peak intensity of the shot noise (for example, when receiving reflected light from a distant object or an object with low reflectance), the object signal is detected. If the threshold voltage is set to a lower value in order to do this, both the object signal and the shot noise will be detected (see FIG. 5A). In this case, it is necessary to discriminate between the object signal and shot noise.
Therefore, regardless of the peak intensity of the object signal, in order to acquire the object signal with high accuracy, it is necessary to set the threshold voltage low and to discriminate the object signal from the shot noise.
Hereinafter, the object signal and the shot noise will be collectively referred to as a "signal" as appropriate.

Hereinafter, a method of determining an object signal and noise when the object signal and noise (for example, shot noise) exceed a threshold voltage will be described.
First, as shown in FIG. 6, the light is projected to an object, the reflected light from the object is received and photoelectrically converted, and the current generated by the photoelectric conversion is processed (for example, current voltage conversion, signal When a measurement including a series of steps of amplification and binarization is performed, from one light reception waveform (one light reception signal waveform), an object signal whose peak exceeds the threshold voltage (here, set to 120 mV) and at least one Two noises are detected here.

By performing such measurement a plurality of times, it is possible to create a histogram or frequency distribution table that represents the frequency of the signal for each class of time or distance. In the following, the class of time is also referred to as "time class" and the class of distance is also referred to as "distance class". One measurement is also called “one frame”.
That is, a plurality of detected signals (object signal and at least one noise) are classified into a plurality of classes, and the number of signals belonging to each class is counted.

Here, a plurality of detected signals are converted into a distance from the rise timing of the light emission signal to the timing at which the rise of the signal crosses the threshold voltage, and the converted value or 1/2 of the converted value is used. Classify into distance class.
Here, the distance is calculated based on the timing when the rising edge of the signal crosses the threshold voltage, but the distance is calculated based on the timing when the falling edge of the signal crosses the threshold voltage, and the rising and falling edges of the signal Various modifications can be made, such as calculating the distance from the timing of crossing the threshold voltage according to a predetermined conversion equation, or using another distance calculation method.
FIG. 6 shows a case where the class width of each time class (hereinafter collectively referred to as “time width tw” as appropriate) is constant (tw0 = tw1 = tw2 = tw3 = tw4 = tw5).

The following Table 1 is a frequency distribution table created by performing Experiment 1 which repeats the above measurement five times, and the distance to an object corresponding to a time width 20 ns shorter than the time width tw shown in FIG. It is a frequency distribution table of distance classes in which 3 m, which is a half of a value obtained by multiplying the width 20 ns by the luminous flux, is 3 m.

  First, in the first measurement, one signal is included in the distance class of 30 to 33 m. In the second measurement, one signal enters the distance class of 21 to 24 m, and one signal enters the distance class of 30 to 33 m. In the third measurement, one signal enters the distance class of 18 to 21 m, and one signal enters the distance class of 30 to 33 m. In the fourth measurement, one signal enters the distance class of 21 to 24 m, and one signal enters the distance class of 30 to 33 m. In the fifth measurement, one signal is contained in the distance class of 24 to 27 m, one signal is contained in the distance class of 30 to 33 m, and one signal is contained in the distance class of 42 to 45 m.

For example, the fact that the measurement is performed five times (the number of frames is 5) shows that noise is detected at random times for each measurement. Since the object signal is detected at a substantially constant time for each measurement (in contrast to the fact that the object signal reflects a substantially constant distance to the object in each measurement), the same measurement is repeated. To enter the distance class.
That is, since most signals (five signals) are contained in the distance class of 30 to 33 m, it is estimated that the signals in this distance class are object signals.
Then, a distance value is calculated for each signal in the distance class of 30 to 33 m, and an average value or median value (median) of the distance values can be obtained as the distance to the object.

The following Table 2 is a frequency distribution table which is created by performing Experiment 2 repeating the above measurement three times, and the class width of the distance class is narrower than that of Table 1 above. Here, the class width is set to 1 m.
Here, when the class width is narrow, a plurality of distance values (hereinafter also referred to as “distance operation values”) calculated based on a plurality of object signals are dispersed near the boundary between two adjacent distance classes. In this case, there is a risk that a plurality of object signals that should originally enter the same class may enter different distance classes (one and the other of two adjacent distance classes).
In addition, when the distance value calculated based on the object signal and the distance value calculated based on the noise are distributed near the boundary between two adjacent distance classes, the object signal and noise that should originally be in different distance classes May enter the same class.
If the number of measurements (number of frames) is small, the number of distance class signals (number of object signals) containing object signals may be the same as the number of distance class signals (number of noises) containing noise. There is.

Therefore, in Experiment 2, in order to determine the distance class to which the object signal belongs and the distance class to which the noise belongs, the time during which the signal belonging to the distance class exceeds the threshold for each distance class containing a plurality of signals The values (pulse widths) converted into distances are summed up to calculate their standard deviation σ (variation).
Since the noise exceeds the threshold with random peak intensity, the standard deviation σ of the pulse width becomes large, and conversely, the pulse width of the object signal is stable and the standard deviation σ becomes small, so that both can be discriminated.

In Experiment 2, among classes in which a plurality of signals are contained, a class having a pulse width standard deviation σ of 1.0 or less is determined as a class in which an object signal is contained (a class to which an object signal belongs); A class higher than 0 is judged as a class containing noise (class to which noise belongs).
Specifically, two (most) signals are included in the distance class of 27 to 28 m and the distance class of 31 to 32 m, but since the standard deviation σ exceeds 1.0 for the 27 to 28 m distance class The distance class to which noise belongs is determined, and the distance class of 31 to 32 m is determined to be the distance class to which the object signal belongs because the standard deviation σ is 1.0 or less. Then, a distance value is calculated for each signal in the distance class of 31 to 32 m, and an average value or median value (median) of the distance values can be obtained as the distance to the object.
In Experiment 2, the standard deviation σ of the pulse width is used to discriminate the class to which the object signal belongs and the class to which the noise belongs, but an average value or median value (median) of the pulse width may be used.

実験３では、２６〜２７ｍの距離階級、２７〜２８ｍの距離階級、３０〜３１ｍの距離階級、３１〜３２ｍの距離階級に信号が１つずつ入っているが、２６〜２７ｍの距離階級に属する信号と２７〜２８ｍの距離階級に属する信号のパルス幅の標準偏差σが１．０を上回るのでノイズが属する距離階級と判断し、３０〜３１ｍの距離階級に属する信号と３１〜３２ｍの距離階級に属する信号のパルス幅の標準偏差σが１．０以下なので物体信号が属する距離階級と判断する。
すなわち、実験３では、一組の隣接する２つの距離階級にそれぞれ属する２つの信号のパルス標準偏差σと、別の組の隣接する２つの距離階級にそれぞれ属する２つの信号のパルス幅の標準偏差σを算出し、各標準偏差σが所定値（例えば１．０）以下であるか否かを判定することにより、物体信号が属する階級とノイズが属する階級を判別している。
そして、３０〜３１ｍの距離階級、３１〜３２ｍの距離階級に属する信号毎に距離値を算出し、該距離値の平均値や中央値（メジアン）を物体までの距離として求めることができる。 The following Table 3 is a frequency distribution table that is created by conducting Experiment 3 in which the above measurement is repeated twice and has a narrower class width than that of Table 1 above. Here, the class width is set to 1 m.

In Experiment 3, one signal is included in each of the distance classes of 26 to 27 m, 27 to 28 m, 30 to 31 m, and 31 to 32 m, but belongs to the 26 to 27 m distance class Since the standard deviation σ of the pulse width of the signal and the signal belonging to the distance class of 27 to 28 m exceeds 1.0, it is judged as a distance class to which noise belongs, and the signal belonging to the distance class of 30 to 31 m and the distance class of 31 to 32 m Since the standard deviation σ of the pulse width of the signal belonging to is 1.0 or less, it is determined that the object signal belongs to the distance class.
That is, in Experiment 3, the pulse standard deviation σ of two signals belonging to one set of two adjacent distance classes and the standard deviation of the pulse widths of two signals respectively belonging to another set of two adjacent distance classes By calculating σ and determining whether each standard deviation σ is equal to or less than a predetermined value (for example, 1.0), the class to which the object signal belongs and the class to which the noise belongs are determined.
Then, a distance value is calculated for each of the signals belonging to the distance class of 30 to 31 m and the distance class of 31 to 32 m, and an average value or median value (median) of the distance values can be obtained as the distance to the object.

  That is, when there are a plurality of distance classes to which the largest number of signals belong, by comparing the standard deviation σ of the pulse width of the signals belonging to each distance class, the object signal belongs to the plurality of distance classes to which the largest number of signals belong. A distinction can be made between a distance class and a distance class to which noise belongs.

  So far, the method of detecting the distance to the object while distinguishing the object signal and the noise at high speed with a smaller number of frames has been described. In the following, the class width (time width) of the time class will be described.

  The noise waveform among the light reception waveforms shown in FIG. 6 depends on the frequency characteristics of the waveform processing circuit 41 shown in FIGS. 1 and 7. The waveform processing circuit 41 is a circuit that converts a current generated by photoelectric conversion in the time measurement PD 42 into a voltage and amplifies the voltage. Here, in the waveform processing circuit 41, a TIA (Time Interval Analyzer) is used as the current-voltage converter 43, and a VGA (Variable Gain Amplifier) is used as the signal amplifier 48.

A specific circuit configuration example of the waveform processing circuit 41 is shown in FIG. Here, the cut-off frequencies fc (assumed to be substantially the same here) defined by the current-voltage converter 43 and the signal amplifier 48 respectively are operational amplifiers (here, the current-voltage converter 43 and the signal amplifier 48). If it is assumed that the bands substantially the same are assumed to be wide enough, the following equation (1) is obtained.
fc = GBW / G (1)
Here, GBW is a GB product (Gain Band width product) of the operational amplifier, and G is a gain of the operational amplifier expressed by the following equation (2).
G = −R2 / R1 = −R5 / R4 (2)

In particular, with respect to shot noise caused by disturbance light, the frequency of the fluctuation substantially coincides with the cut-off frequency fc of the waveform processing circuit 41 (see FIG. 9). In FIG. 9, the received light waveform is indicated by a solid line, and an ideal sine wave having a period of 12.5 MHz, that is, an 80 ns period is indicated by a broken line, but the frequency of the base level fluctuation is almost equal to 12.5 MHz. I do. For this reason, by setting the time width tw (class width of the time class) for creating the histogram and the frequency distribution table to be equal to or less than the time obtained by taking the reciprocal of the cutoff frequency fc (tw ≦ 1 / fc), Since a plurality of shot noise peaks rarely occur in one time class, it is possible to easily and clearly distinguish the object signal from the noise by comparing the signal count numbers between the time classes.
In the case where the distance class is used instead of the time class, the same argument is established by converting the time widths tw and 1 / fc into distances.
Here, fc = 12.5 MHz, and each time width tw is set to a constant time width shorter than 80 ns (12 m in distance conversion), which is the reciprocal thereof (tw0 = tw1 = tw2 = tw3 = tw4 = tw5 ). It is set as 20 ns (3 m in distance conversion) in Table 1, and 6.6 ns (1 m in distance conversion) in Table 2 and Table 3.

  Further, when the time width tw is a value of the reciprocal of the cut-off frequency fc of the waveform processing circuit 41 (tw = 1 / fc), the number of classes to be compared with the maximum time width tw within the above range is obtained. As a result, the amount of arithmetic processing for comparison and the number of memories accompanying it can be minimized.

  Further, it is preferable that the time width tw be equal to or more than the rise time tr of the signal output from the waveform processing circuit 41 (tw ≧ tr).

Here, although the cutoff frequency defined by each of the current-voltage converter 43 and the signal amplifier 48 has been described as the same “cut-off frequency fc”, the cutoff frequency of the current-voltage converter 43 and the signal amplifier 48, That is, it is also assumed that the cut-off frequencies of the operational amplifiers incorporated in the current-voltage converter 43 and the signal amplifier 48 are different from each other.
Therefore, let the cutoff frequencies defined by the current-voltage converter 43 and the signal amplifier 48 be cutoff frequencies fc1 and fc2, and let the GB product of the current-voltage converter 43 and the gain be GBW1, G1 = -R2 / R1, respectively. Assuming that the GB product and gain of the signal amplifier 48 are GBW2 and G2 = −R5 / R4, respectively, fc in the above equation (1) is replaced by fc1, GBW is replaced by GBW1, and G is replaced by G1; 1) An expression is established in which fc in the expression is replaced with fc2, GBW is replaced with GBW2, and G is replaced with G2.
Also in this case, it is preferable that tw ≦ 1 / fc1 or tw ≦ 1 / fc2, and that tw ≦ 1 / fc1 and tw ≦ 1 / fc2, that is, the reciprocal of tw which is not smaller than fc1 or fc2. It is more preferable that

FIG. 10 shows the waveform of the object signal for each received light amount when the amount of light reflected or scattered from the object (hereinafter also referred to as “received light amount”) received by the time measurement PD 42 changes. Yes.
In FIG. 10, the relationship of received light amount 1 <received light amount 2 <received light amount 3 <received light amount 4 is satisfied. As can be seen from FIG. 10, the peak voltage of the waveform of the object signal increases as the received light amount increases from the received light amount 1 to the received light amount 3, but when the received light amount increases to the received light amount 4, the time measurement PD 42 itself Alternatively, voltage saturation occurs in the waveform processing circuit 41, and the waveform of the object signal differs from the amount of received light 3, the peak voltage converges to a predetermined value, and the pulse width is extended.

Here, the rising time tr and the falling time tf of the object signal output from the waveform processing circuit 41 will be described with reference to FIG.
With respect to the voltage of the object signal, a voltage that is 90% of the peak voltage is V90, and a voltage that is 10% of the peak voltage is V10. The time for V10 when the object signal rises is tr10 and the time for V90 is tr90, and the time V10 when the object signal falls is tf10 and the time for V90 is tf90. Here, the rise time tr is defined as tr = tr90−tr10. Further, the falling time tf is defined as tf = tf10−tf90.

In FIG. 10, the object signal of received light amount 1, the object signal of received light amount 2, and the object signal of received light amount 3 have the same rise time tr and fall time tf, but the peak voltage is different. The timings are different from each other. For example, the case where the time axis of FIG. 10 is expanded and the threshold voltage is 0.75 V is shown in FIG.
This is the same distance when the time from when the light emission signal rises until the object signal rises exceeds the threshold, or when the number of signals is counted for each class by dividing the distance based on that time into a plurality of classes. It suggests that the class in which signals from the reflected light from a plurality of objects are counted may differ, and that the class in which signals from light reflected from a plurality of portions of the object at the same distance may be different.
From the received light amount 1 to the received light amount 3, as the received light amount increases, the timing at which the object signal exceeds the threshold becomes earlier. When the amount of light received reaches the amount of light received 4, the timing at which the object signal exceeds the threshold becomes earlier than the amount of light received 3.

That is, the amount of received light fluctuates due to the difference in reflectance and size even in a plurality of objects at the same distance and a plurality of portions at the same distance of the objects. Due to this variation, when the object signal exceeds the threshold value at different timings and the classes in which the object signal is counted are different, the object signals are counted in a plurality of classes, making it difficult to distinguish between the object signal and the noise.
Therefore, it is preferable that the time width tw be equal to or more than the rise time tr of the object signal so that the object signal is counted in the same class even if the amount of received light changes.
As described above, the rise time tr of the object signal is the same as long as the light reception signal is not saturated, and can be acquired in advance as a predetermined value.
Here, the rise time tr of the object signal is set to a time longer than 8 ns. In Experiment 1, tr = 20 ns (3 m in terms of distance), and in Experiment 2 and Experiment 3, 6.7 ns (1 m in terms of distance).

Moreover, tr is preferably equal to the rise time and fall time defined in the same manner as the object signal in the light emission pulse (projection pulse) from the LD 11.
If the waveform processing circuit 41 does not respond to the light emission pulse from the LD 11, the lighting of the LD 11 ends before the light reception signal reaches its peak, and as a result, the peak voltage of the light reception signal may decrease. Because.
Therefore, the time width tw may be set based on the pulse width of the light emission pulse from the LD 11, the rise time, and the fall time. For example, the time width tw is made equal to the pulse width of the light emission pulse or 1/4 to 1/2 of the pulse width, the time width tw is set to be longer than the rise time of the light emission pulse, or the time width tw is set to the fall time of the light emission pulse. It is good as above.
Here, the pulse width of the light emission pulse (light emission pulse) is, as shown in FIG. 13, the light emission at 50% of the light amount (light emission pulse 50% value) of the peak light amount of the light emission pulse (light emission pulse peak value) The width of the pulse is taken as the pulse width (projected pulse width Tpw). In FIG. 13, for convenience, the pulse width is expressed in time.
The waveform of the light reception pulse is a waveform in which the response characteristic of the time measurement PD 42 and the frequency characteristic of the waveform processing circuit 41 shown in FIGS. 7 and 8 are superimposed on the waveform of the light emission pulse.
The waveform of the light reception pulse is the same as the waveform of the light emission pulse if the characteristics are sufficiently fast, but actually, the waveform of the light reception pulse is higher than that of the light emission pulse depending on the response characteristics of the time measurement PD 42 and the frequency characteristics of the waveform processing circuit 41. It is often dull.

Further, the slower one of the response characteristic of the time measurement PD 42 and the frequency characteristic of the waveform processing circuit 41 is the rate-limiting and the final light reception waveform is determined, but in the above, the frequency characteristic of the waveform processing circuit 41 is the rate-limiting Have said.
The frequency characteristic of the waveform processing circuit 41 is restricted by the above-mentioned cut-off frequency fc. Since the gain decrease at the cut-off frequency fc is 3 dB, a high frequency signal is not transmitted as it is and is output from the waveform processing circuit 41 with the waveform being dull as a whole. FIG. 6 shows a received light waveform with the blunting.

Also, as described above, although the time width tw is the rise time tr or more, the detection timing of the reflected light from the plurality of objects at the same distance and the multiple portions at the same distance belongs to different classes. If the time from when the signal exceeds the threshold to the peak of the signal or when the relative velocity between the object detection apparatus 100 and the object is obtained, the relative speed is taken as the time width tw. It is also possible to use the frame rate, the resolution of speed detection related to it, or the like.
For example, when the relative velocity between the object detection device 100 and the object is obtained, the distance from the object detection device 100 to the object changes with time at that relative velocity. Since the time until the next detection at the same pixel (same scanning position) is decided by the frame rate etc., the time width and the distance width to the object to be counted in the same class are calculated by the resolution of the speed to be detected. The calculated value may be set as the class width.

In the above description, the time width tw is set in consideration of the rise time tr of the light reception signal. A method for setting the time width tw in consideration of the fall time tf of the light reception signal will be described below.
In some cases, not only the rising edge of the received light signal but also the falling edge is taken into account, the ranging accuracy may be improved.
In addition, in the characteristics of the waveform processing circuit 41, the LD 11, and the LD driving unit 12, the rising time tr and falling time tf of the light reception signal are often different (tr <tf). In this case, it is preferable to set the time width tw to be equal to or longer than the time from when the falling edge of the received light signal crosses V90 to the threshold voltage.
The timing at which the rising edge of the light reception signal crosses the threshold is distributed to a corresponding time class with a time width tw greater than tr, and the timing at which the falling crosses a threshold is distributed to a corresponding time class with a time width tw greater than tf. The number of signals may be counted for each, but the time width tw is set to be greater than tr, which is the shorter of tr and tf, and the timing at which the rising and falling edges of the received light signal cross the threshold value is assigned to the corresponding time class. Thus, the number of signals for each time class may be counted. In this way, although there is variation in counting at the falling edge of the light reception signal, it is not necessary to set the time width tw separately to create the histogram and the frequency distribution table separately, so measurement can be performed with simpler control. The distance can be measured.
Here too, as in the above, the method of time measurement and distance conversion can be variously modified.

Further, when the timing when the rising edge of the light reception signal exceeds the threshold is distributed to the corresponding time class with the time width tw and the number of signals is counted, the time width tw increases as the distance to the object increases, as shown in FIG. It is preferable to set the length to be longer (tw0 <tw1 <tw2 <tw3 <tw4 <tw5).
For example, when the object detection device 100 detects an object (another vehicle, a pedestrian, an obstacle, etc.) existing in front of the vehicle, it is desirable that the distance measurement accuracy is higher for an object at a short distance. Since the distance to the object is calculated using a signal belonging to the class having the highest signal frequency among a plurality of classes, the distance measurement accuracy becomes higher as the time width tw is shorter. For this reason, it is desirable to shorten the time width tw at a short distance.
On the other hand, at long distances, the peak voltage of the object signal is low, and the timing at which the object signal takes a peak tends to fluctuate due to the influence of noise or the like, and the histogram tends to be gentle. Even so, when performing multiple measurements, the pulse width of the object signal is more stable than the pulse width of noise (because the variation is small), so more counts can be accumulated faster to pulse each signal. It is desirable to make it easy to distinguish the object signal from the noise by comparing the standard deviation σ of the width. For this reason, it is desirable to increase the time width tw at a long distance.

  In FIG. 14, the time width tw of a plurality of (for example, six) time classes is set to become longer as the distance becomes longer (as time passes). For example, the detection distance required for the object detection device 100 Within the range (for example, 0 m to 210 m), the range of 0 m to 30 m is divided into a plurality of distance classes with a distance width of 1 m (time width 6.7 ns), and a range of 30 m to 90 m is a distance width 3 m (time width 20 ns) It may be divided into a plurality of distance classes, and the range of 90 m to 210 m may be divided into a plurality of distance classes with a distance width of 12 m (time width 80 ns), and each distance class may be further divided into a plurality of distance classes of a certain distance width. It may be divided. The "distance width" means the class width of the distance class.

  FIG. 15 shows a sensing device 1000 provided with an object detection device 100. The sensing device 1000 is mounted on a vehicle (moving body), and includes a monitoring control device 300 electrically connected to the object detection device 100 in addition to the object detection device 100. The object detection device 100 is attached in the vicinity of a vehicle bumper or in the vicinity of a rearview mirror. The monitoring control device 300 performs processing such as estimation of the shape and size of the object, calculation of the position information of the object, calculation of movement information, recognition of the type of the object, and the like based on the detection result of the object detection device 100. , Determine the presence or absence of danger. Then, when it is judged that there is a danger, an alarm such as an alarm is issued to alert the operator of the mobile body, or the steering control unit of the mobile body is instructed to turn off the steering wheel to avoid danger, or braking A command is issued to the ECU of the moving body. Sensing device 1000 receives supply of power, for example, from a battery of the vehicle.

  The monitoring control device 300 may be provided integrally with the object detection device 100 or may be provided separately from the object detection device 100. Moreover, the monitoring control apparatus 300 may perform at least one part of the control which ECU performs.

  Hereinafter, specific examples (ranging processes 1 to 4) of the ranging process performed by the object detection apparatus 100 will be described.

<Distance measurement process 1>
The ranging process 1 will be described with reference to FIG. The flowchart of FIG. 16 is based on a processing algorithm executed by the control system 46. Ranging process 1 is started when power is supplied to the object detection apparatus 100.

  In the first step S1, repeated scanning of the effective scanning area is started. Specifically, the control unit 46a outputs an LD drive signal (light emission signal) generated based on the input synchronization signal to the LD drive unit 12 and applies a drive current to the LD 11, thereby causing the LD 11 to emit light in pulses. The pulsed light is deflected by the rotating mirror 26 that rotates.

  In the next step S2, the count value k of the number of scans is initialized. Specifically, the control unit 46a sets the count value of the built-in counter to zero.

  In the next step S3, counting of the number of scans is started. Specifically, the control unit 46a starts counting by the counter using the input synchronization signal as a trigger, and thereafter increases the count value of the counter by 1 (counts up) each time the synchronization signal is input.

  In the next step S4, a voltage signal exceeding the threshold voltage among the voltage signals output from the waveform processing circuit 41 at the time of scanning for each scanning position in the effective scanning region is stored in the memory as the storage unit 46b. Specifically, the control unit 46a determines whether or not the peak of the voltage signal (analog signal) output from the waveform processing circuit 41 based on the output signal (digital signal) of the binarization circuit 44 exceeds the threshold voltage. A determination is made, and a positive voltage signal is stored in the memory in association with the scanning position at which the voltage signal is obtained.

  In the next step S5, the control unit 46a determines whether the count value k is less than K (K) 2). Here, “K” is a preset number of measurements until a measurement result is output. If the determination in step S5 is affirmed, the process returns to step S4. If the determination is negative, the process proceeds to step S5.5.

  In step S5.5, the control unit 46a ends the counting of the number of scans.

  At the next step S6, the control unit 46a sets 1 to n.

  In the next step S7, time calculation is performed for each voltage signal that exceeds the threshold voltage during each scan for the n-th scanning position, and the time calculation value that is the calculation result is stored in the memory as the storage unit 46b. Specifically, the control unit 46a scans each time for the nth scanning position which is the nth scanning position in the effective scanning region (the scanning position corresponding to the nth pulse of the LD driving signal for one scan). Sometimes, the time from the rising timing of the light emission signal to the predetermined timing based on the timing at which the voltage signal crosses the threshold voltage is calculated, and the calculation result is stored in the memory as a time calculation value in association with the voltage signal.

  In the next step S8, a histogram or a frequency distribution table representing the frequency of the voltage signal exceeding the threshold voltage for each time class is created. Specifically, the histogram / frequency distribution table generation unit 46d divides the voltage signals corresponding to the respective time operation values stored in the memory in step S7 into the corresponding time classes, and creates a histogram or a frequency distribution table.

  In the next step S9, the time class having the highest frequency of the voltage signal exceeding the threshold voltage (hereinafter also referred to as “frequency most frequent time class”) is extracted. Specifically, the control unit 46a extracts the most frequent time class from the plurality of time classes of the histogram or the frequency distribution table created in step S8.

  In the next step S10, the control unit 46a determines whether or not the highest frequency time class extracted in step S9 is plural. If the determination here is affirmed, the process proceeds to step S11. If the determination is negative, the process proceeds to step S16.

  In step S11, the belonging class estimation unit 46e calculates the standard deviation σ of the pulse widths of the plurality of voltage signals belonging to the most frequent time classes.

  In the next step S12, the belonging class estimation unit 46e estimates the most frequent time class having a standard deviation σ of 1.0 or less as the class to which the object signal belongs (hereinafter also referred to as "object signal belonging class"), The result is output to the calculation unit 46c.

  In the next step S13, the operation unit 46c refers to the estimation result from the belonging class estimation unit 46e and the time operation value corresponding to each voltage signal stored in the memory to determine the object signal belonging class most frequently. The average value of the time operation value for each voltage signal belonging to the time class (when the time operation value is 1, the time operation value itself is calculated), and 1/2 of the value obtained by converting the average value to the distance is n Output as the measurement result of the scanning position. In addition, instead of the average value of the above-mentioned time operation value, the median value (median) of the time operation value or a representative value of the most frequent time class estimated to be the object signal belonging class, for example, class value (class width (class width) The middle value may be used.

  In the next step S14, it is determined whether n <N. Here, “N” is the total number of scan positions in the effective scan area (the total number of pulses of the LD drive signal for one scan). If the determination in step S14 is affirmed, the process proceeds to step S17. If the determination in step S14 is negative, the process proceeds to step S15.

  In step S15, it is determined whether or not the measurement is finished. Specifically, the determination here is affirmed when the supply of power to the object detection apparatus 100 is stopped, and is denied when the supply is not stopped. If the determination in step S15 is affirmed, the flow ends. If the determination is negative, the process returns to step S2.

In step S17, n is incremented. When step S17 is executed, the process returns to step S7.
Note that the series of processing from step S5.5 to step S17 is performed between scans (from the end of the K scans to the start of the first scan of the next K scans). .

  In the distance measuring process 1 described above, among the voltage signals output from the waveform processing circuit 41, the voltage signal whose peak exceeds the threshold value is distributed to the time class corresponding to the time calculation value calculated based on the voltage signal. The histogram and the frequency distribution table are created, but the voltage signal may be distributed to a time class corresponding to 1/2 of the time calculation value to create the histogram and the frequency distribution table.

<Distance measurement process 2>
The distance measurement process 2 will be described with reference to FIG. The flowchart in FIG. 17 is based on a processing algorithm executed by the control system 46. The ranging process 2 is started when the object detection apparatus 100 is supplied with power.

  In the first step S21, repeated scanning of the effective scanning area is started. Specifically, the control unit 46a outputs an LD drive signal (light emission signal) generated based on the input synchronization signal to the LD drive unit 12 and applies a drive current to the LD 11, thereby causing the LD 11 to emit light in pulses. The pulsed light is deflected by the rotating mirror 26 that rotates.

  In the next step S22, the count value k of the number of scans is initialized. Specifically, the control unit 46a sets the count value of the built-in counter to zero.

  In the next step S23, counting of the number of scans is started. Specifically, the control unit 46a starts counting by the counter using the input synchronization signal as a trigger, and thereafter increases the count value of the counter by 1 (counts up) each time the synchronization signal is input.

  In the next step S24, the voltage signal exceeding the threshold voltage among the voltage signals output from the waveform processing circuit 41 at the time of scanning for each scanning position in the effective scanning region is stored in the memory as the storage unit 46b. Specifically, the control unit 46a determines whether or not the peak of the voltage signal (analog signal) output from the waveform processing circuit 41 based on the output signal (digital signal) of the binarization circuit 44 exceeds the threshold voltage. A determination is made, and a positive voltage signal is stored in the memory in association with the scanning position at which the voltage signal is obtained.

  In the next step S25, control unit 46a determines whether count value k is less than K (K (2). Here, “K” is a preset number of measurements until a measurement result is output. If the determination in step S25 is affirmed, the process returns to step S24, and if denied, the process proceeds to step S25.5.

  In step S25.5, the control unit 46a ends the count of the number of scans.

  At the next step S26, the control unit 46a sets 1 to n.

  In the next step S27, distance calculation is performed for each voltage signal exceeding the threshold voltage at each scan with respect to the n-th scan position, and the distance calculation value as the calculation result is stored in the memory as the storage unit 46b. Specifically, the control unit 46a performs each scan with respect to the nth scan position, which is the nth scan position in the effective scan area (a scan position corresponding to the nth pulse of the LD drive signal for one scan). Sometimes the time from the rise timing of the light emission signal to the predetermined timing based on the timing at which the voltage signal crosses the threshold voltage is calculated, and a distance calculation is performed by associating 1/2 of the calculated result into a distance to the voltage signal. Save to memory as a value.

  In the next step S28, a histogram or frequency distribution table representing the frequency of the voltage signal exceeding the threshold voltage for each distance class is created. Specifically, the histogram / frequency distribution table generation unit 46d creates a histogram or frequency distribution table by distributing the voltage signal corresponding to each distance calculation value stored in the memory in step S27 to the corresponding distance class.

  In the next step S29, the distance class with the largest number of frequencies of the voltage signal exceeding the threshold voltage (hereinafter, also referred to as "frequency largest class") is extracted. Specifically, the control unit 46a extracts the most frequent distance class from the plurality of distance classes of the histogram or the frequency distribution table created in step S28.

  In the next step S30, the control unit 46a determines whether or not the frequency largest distance class extracted in step S29 is plural. If the determination here is affirmed, the process proceeds to step S31. If the determination is denied, the process proceeds to step S36.

  In step S31, the belonging class estimation unit 46e refers to the memory to calculate the standard deviation σ of the pulse widths of the plurality of voltage signals belonging to the largest frequency classes.

  In the next step S32, the affiliation class estimation unit 46e estimates the most frequent frequency class with a standard deviation σ of 1.0 or less as the class to which the object signal belongs (hereinafter also referred to as “object signal affiliation class”), and the estimation. The result is output to the calculation unit 46c.

  In the next step S33, the calculation unit 46c refers to the estimation result from the affiliation class estimation unit 46e and the distance calculation value corresponding to each voltage signal stored in the memory, so that the frequency most frequently estimated as the object signal affiliation class is obtained. The average value of the distance calculation value for each voltage signal belonging to the distance class (if the distance calculation value is one, the distance calculation value itself) is output as the measurement result of the n-th scanning position. In place of the average value of the distance calculation values, a median value (median) of the distance calculation values or a representative value of the most frequent distance class estimated as the object signal affiliation class, for example, a class value (the frequency maximum) The middle value of the distance class) may be used.

  In the next step S34, the control unit 46a determines whether n <N. Here, “N” is the total number of scan positions in the effective scan area (the total number of pulses of the LD drive signal for one scan). If the determination in step S34 is affirmed, the process proceeds to step S37. If the determination in step S34 is negative, the process proceeds to step S35.

  In step S35, it is determined whether or not the measurement is finished. Specifically, the determination here is affirmed when the supply of power to the object detection apparatus 100 is stopped, and is denied when the supply is not stopped. If the determination in step S35 is affirmed, the flow is ended, and if denied, the process returns to step S22.

In step S37, n is incremented. When step S37 is executed, the process returns to step S27.
A series of processing from step S25.5 to step S37 is performed between scannings (after the end of K scannings and before the start of the first scanning of the next K scannings). .

  In the distance measurement process 2 described above, among the voltage signals output from the waveform processing circuit 41, the voltage signal whose peak exceeds the threshold value is distributed to the distance class corresponding to the distance calculation value calculated based on the voltage signal. The histogram and the frequency distribution table are created, but the voltage signal may be distributed to the time class corresponding to the distance calculation value to create the histogram and the frequency distribution table.

<Ranging process 3>
The distance measurement process 3 will be described with reference to FIG. The flowchart in FIG. 18 is based on a processing algorithm executed by the control system 46. Ranging process 3 is started when the object detection apparatus 100 is supplied with power.

  In the first step S41, repeated scanning of the effective scanning area is started. Specifically, the control unit 46a outputs the LD drive signal generated based on the input synchronization signal to the LD drive unit 12 and applies a drive current to the LD 11, thereby causing the LD 11 to emit light, and the pulse light. Is deflected by a rotating mirror 26 that rotates.

  In the next step S42, the count value k of the number of scans is initialized. Specifically, the control unit 46a sets the count value of the built-in counter to zero.

  In the next step S43, counting of the number of scans is started. Specifically, the control unit 46a starts counting by the counter using the input synchronization signal as a trigger, and thereafter increases the count value of the counter by 1 (counts up) each time the synchronization signal is input.

  In the next step S44, of the voltage signals output from the waveform processing circuit 41 at the time of scanning with respect to each scanning position in the effective scanning region, voltage signals exceeding the threshold voltage are stored in the memory as the storage unit 46b. Specifically, the control unit 46a determines whether or not the peak of the voltage signal (analog signal) output from the waveform processing circuit 41 based on the output signal (digital signal) of the binarization circuit 44 exceeds the threshold voltage. A determination is made, and a positive voltage signal is stored in the memory in association with the scanning position at which the voltage signal is obtained.

  In the next step S45, control unit 46a determines whether count value k is smaller than K (K22). Here, “K” is the preset number of measurements before outputting the measurement result. If the determination in step S45 is affirmed, the process returns to step S44. If the determination in step S45 is negative, the process proceeds to step S45.5.

  In step S45.5, the control unit 46a ends the count of the number of scans.

  In the next step S46, the control unit 46a sets n to n.

  In the next step S47, a time calculation is performed for each voltage signal that exceeds the threshold voltage during each scan for the n-th scanning position, and a time calculation value that is the calculation result is stored in a memory as the storage unit 46b. Specifically, the control unit 46a performs each scan with respect to the nth scan position, which is the nth scan position in the effective scan area (a scan position corresponding to the nth pulse of the LD drive signal for one scan). Sometimes, the time from the rising timing of the light emission signal to the predetermined timing based on the timing at which the voltage signal crosses the threshold voltage is calculated, and the calculation result is stored in the memory as a time calculation value in association with the voltage signal.

  In the next step S48, a histogram or frequency distribution table representing the frequency of the time operation value for each time class is created. Specifically, the histogram / frequency distribution table generating unit 46d creates a histogram or a frequency distribution table by assigning each time calculation value stored in the memory in step S47 to the corresponding time class.

  In the next step S49, the time class with the largest frequency of the time operation value (hereinafter, also referred to as "the most frequency class") is extracted. Specifically, the control unit 46a extracts the most frequent time class from the plurality of time classes in the histogram or the frequency distribution table created in step S48.

  In the next step S50, the control unit 46a determines whether or not there is a plurality of most frequent time classes extracted in step S49. If the determination here is affirmed, the process proceeds to step S51. If the determination is denied, the process proceeds to step S56.

  In step S51, the affiliation class estimation unit 46e refers to the memory and calculates the standard deviation σ of the pulse widths of the plurality of voltage signals respectively corresponding to the plurality of time calculation values belonging to each frequency most frequent time class.

  In the next step S52, the affiliation class estimation unit 46e assigns the most frequent time class having a standard deviation σ of 1.0 or less to the class to which the time operation value calculated based on the object signal belongs (hereinafter referred to as “TOF operation time affiliation class” And the estimation result is output to the calculation unit 46c. "TOF" is an abbreviation of Time of Flight.

  In the next step S53, the calculation unit 46c refers to the estimation result from the affiliation class estimation unit 46e and the time calculation value stored in the memory, and the time belonging to the most frequent time class estimated as the TOF calculation time affiliation class. An average value of the calculation values (if the time calculation value is one, the time calculation value itself) is calculated, and ½ of the value obtained by converting the average value into a distance is output as the measurement result of the nth scanning position. Instead of the average value of the time calculation values, a median value (median) of the time calculation values or a representative value of the most frequent time class estimated as the TOF calculation time affiliation class, for example, a class value (the frequency) The middle value of the most frequent time class) may be used.

  In the next step S54, it is determined whether n <N. Here, N is the total number of scan positions in the effective scan area (the total number of pulses of the LD drive signal for one scan). If the determination in step S54 is affirmed, the process proceeds to step S57. If the determination in step S54 is negative, the process proceeds to step S55.

  In step S55, it is determined whether or not the measurement is finished. Specifically, the determination here is affirmed when the supply of power to the object detection apparatus 100 is stopped, and is denied when the supply is not stopped. If the determination in step S55 is affirmed, the flow is ended, and if denied, the process returns to step S42.

In step S57, n is incremented. When step S57 is executed, the process returns to step S47.
Note that a series of processes from step S45.5 to step S57 is performed between scannings (from the end of K scans to the start of the first scan of the next K scans). .

  In the distance measuring process 3 described above, a time calculation value calculated based on a voltage signal whose peak exceeds a threshold value among the voltage signals output from the waveform processing circuit 41 is distributed to the corresponding time class, and a histogram or frequency distribution. Although a table is created, one-half of the time operation value may be distributed to the corresponding time class or the corresponding distance class to create a histogram or a frequency distribution table.

<Distance measurement process 4>
The distance measurement process 4 will be described with reference to FIG. The flowchart in FIG. 19 is based on a processing algorithm executed by the control system 46. The ranging process 4 is started when the object detection apparatus 100 is supplied with power.

  In the first step S61, repeated scanning of the effective scanning area is started. Specifically, the control unit 46a outputs an LD drive signal (light emission signal) generated based on the input synchronization signal to the LD drive unit 12 and applies a drive current to the LD 11, thereby causing the LD 11 to emit light in pulses. The pulsed light is deflected by the rotating mirror 26 that rotates.

  In the next step S62, the count value k of the number of scans is initialized. Specifically, the control unit 46a sets the count value of the built-in counter to zero.

  In the next step S63, counting of the number of scans is started. Specifically, the control unit 46a starts counting by the counter using the input synchronization signal as a trigger, and thereafter increases the count value of the counter by 1 (counts up) each time the synchronization signal is input.

  In the next step S64, of the voltage signals output from the waveform processing circuit 41 at the time of scanning with respect to each scanning position in the effective scanning area, voltage signals exceeding the threshold voltage are stored in the memory as the storage unit 46b. Specifically, the control unit 46a determines whether or not the peak of the voltage signal (analog signal) output from the waveform processing circuit 41 based on the output signal (digital signal) of the binarization circuit 44 exceeds the threshold voltage. A determination is made, and a positive voltage signal is stored in the memory in association with the scanning position at which the voltage signal is obtained.

  In the next step S65, control unit 46a determines whether count value k is less than K (K ≧ 2). Here, “K” is the preset number of measurements before outputting the measurement result. If the determination in step S65 is affirmative, the process returns to step S64, and if the determination is negative, the process proceeds to step S65.5.

  In step S65.5, the control unit 46a ends the counting of the number of scans.

  In the next step S66, the control unit 46a sets 1 to n.

  In the next step S67, a distance calculation is performed for each voltage signal that exceeds the threshold voltage during each scan for the n-th scanning position, and a distance calculation value that is the calculation result is stored in a memory as the storage unit 46b. Specifically, the control unit 46a performs each scan with respect to the nth scan position, which is the nth scan position in the effective scan area (a scan position corresponding to the nth pulse of the LD drive signal for one scan). Sometimes the time from the rise timing of the light emission signal to the predetermined timing based on the timing at which the voltage signal crosses the threshold voltage is calculated, and a distance calculation is performed by associating 1/2 of the calculated result into a distance to the voltage signal. Save to memory as a value.

  In the next step S68, a histogram or frequency distribution table representing the frequency of the distance operation value for each distance class is created. Specifically, the histogram / frequency distribution table generating unit 46d assigns each distance calculation value stored in the memory in step S67 to the corresponding distance class, and creates a histogram or a frequency distribution table.

  In the next step S69, the distance class having the largest frequency of the distance operation value (hereinafter, also referred to as "frequency largest distance class") is extracted. Specifically, the control unit 46a extracts the most frequent distance class from the plurality of distance classes of the histogram or the frequency distribution table created in step S68.

  In the next step S70, control unit 46a determines whether or not the frequency largest distance class extracted in step S69 is plural. If the determination here is affirmed, the process proceeds to step S71. If the determination is denied, the process proceeds to step S76.

  In step S71, the belonging class estimation unit 46e refers to the memory to calculate the standard deviation σ of the pulse widths of the plurality of voltage signals belonging to the largest frequency classes.

  In the next step S72, the class to which the distance calculation value calculated based on the object signal belongs to the class rank estimation unit 46e based on the object signal is the class with the highest frequency class having a standard deviation σ of 1.0 or less (hereinafter And the estimation result is output to the calculation unit 46c.

  In the next step S73, the calculation unit 46c refers to the estimation result from the belonging class estimation unit 46e and the distance calculation value stored in the memory to determine that the voltage belongs to the highest distance class estimated as the TOF calculation distance belonging class. The average value of the distance calculation value for each signal (if the distance calculation value is one, the distance calculation value itself) is output as the measurement result of the n-th scanning position. In addition, instead of the average value of the distance calculation value, a median value (median) of the distance calculation value or a representative value of the most frequent distance class estimated to be a TOF calculation distance belonging class, for example, a class value The middle value of the largest distance class may be used.

  In the next step S74, the control unit 46a determines whether n <N. Here, “N” is the total number of scan positions in the effective scan area (the total number of pulses of the LD drive signal for one scan). If the determination in step S74 is affirmed, the process proceeds to step S77. If the determination in step S74 is negative, the process proceeds to step S75.

  In step S75, it is determined whether the measurement is completed. Specifically, the determination here is affirmed when the supply of power to the object detection apparatus 100 is stopped, and is denied when the supply is not stopped. If the determination in step S75 is affirmed, the flow ends. If the determination is negative, the process returns to step S62.

In step S77, n is incremented. When step S77 is executed, the process returns to step S67.
Note that a series of processes from step S65.5 to step S77 is performed between scannings (after the completion of K scannings and before the start of the first scanning of the next K scannings). .

  In the distance measurement process 4 described above, among the voltage signals output from the waveform processing circuit 41, the distance operation value calculated based on the voltage signal whose peak exceeds the threshold is distributed to the corresponding distance class to be used as a histogram or frequency distribution Although a table is created, the distance calculation values may be distributed to corresponding time classes to create a histogram or a frequency distribution table.

  The time measurement apparatus which constitutes a part of the object detection apparatus 100 of the present embodiment described above includes a light projection system 10 including an LD 11 (light source) that emits light based on an LD drive signal (light emission signal); A light receiving system 40 including a time measuring PD 42 (light receiving element) for receiving and photoelectrically converting light projected from 10 and reflected by the object, and at least one process on the output current of the time measuring PD 42; And a waveform processing circuit 41 (processing system) for outputting a voltage signal (signal) obtained by the processing, and a time for measuring a time from when the light is emitted from the LD 11 to when it is received by the time measuring PD 42 In the measurement apparatus, when the light projecting system 10 performs light projection a plurality of times in the same direction toward the object (to the same scanning position), the light is output from the waveform processing circuit 41 at the plurality of times of light projection. Voltage signal The voltage signal whose peak exceeds the threshold voltage (threshold value) or the value based on the voltage signal is classified into a plurality of classes corresponding to the time or the value based on the time, and the same direction based on the classification result Characterized in that a time acquisition system including a control system 46 for acquiring the above time at the time of light projection is provided, and the class width for each class is set based on the frequency characteristic (characteristic) of the waveform processing circuit 41 Time measuring device.

  Here, if the class width is too narrow, the number of classes, that is, the number of objects to be compared increases, and the amount of calculation processing increases. On the contrary, if the class width is too wide, the number of noises (for example, shot noises) whose peak exceeds the threshold value that enter the same class at each light projection increases, and the discrimination accuracy between the object signal and the noise decreases.

  Therefore, focusing on the fact that the pulse period of noise is related to the frequency characteristic of the waveform processing circuit 41 that processes the output current of the light receiving element, the threshold voltage can be lowered by setting the class width based on the frequency characteristic. Even when the number of scans (the number of times of light projection) required for one measurement is small when setting to, the accuracy of discrimination between an object signal and noise can be improved, and the amount of arithmetic processing can be reduced.

  As a result, according to the time measurement device of the present embodiment, the amount of light received by the time measuring PD 42 for the light reflected and reflected by the object is high (regardless of the distance to the object and the reflectance of the object) Accurate and high-speed measurement can be performed.

On the other hand, in Patent Documents 1 and 2, since the class width is not set based on the frequency characteristic of the circuit that processes the output current of the light receiving element, noises with peaks exceeding the threshold value enter the same class at each light projection. There was room for improvement in terms of reducing the number and the amount of calculation processing.
That is, in Patent Documents 1 and 2, high-precision and high-speed measurement is possible regardless of the amount of light received by the light receiving element of the light that is projected and reflected by the object (regardless of the distance to the object or the reflectance of the object). There was room for improvement.

  The waveform processing circuit 41 further includes a current-voltage converter 43 (current-voltage conversion circuit) that converts the output current of the time measurement PD 42 into a voltage, and the class width is based on the cut-off frequency fc1 of the current-voltage converter 43. Is preferably set. This is because the pulse period of noise is particularly related to the cutoff frequency fc1.

  The class width is preferably equal to or less than the reciprocal of the cutoff frequency fc1. In this case, a plurality of noises can be prevented from entering one class, and the discrimination accuracy between the object signal and the noise can be further improved.

  Further, the waveform processing circuit 41 includes a signal amplifier 48 (signal processing circuit) that processes the output signal of the current-voltage converter 43, and the class width is set based on the cut-off frequency fc2 of the signal amplifier 48. preferable. This is because the pulse period of noise is particularly related to the cutoff frequency fc2.

  Further, it is more preferable that the class width is equal to or less than the reciprocal of the cut-off frequencies fc1 and fc2 of the current-voltage converter 43 and the signal amplifier 48 which is not smaller. In this case, it is possible to more reliably prevent a plurality of noises from entering one class, and it is possible to further improve the determination accuracy of the object signal and the noise.

  In addition, it is preferable that the class width be set to be equal to or more than the rise time tr of the object signal (a signal by light emitted from the light projection system 10 and reflected by the object). In this case, even if there are variations in the object signal due to differences in the amount of light received by the time measurement PD 42 for each light projection, the object signal or the value based on the object signal falls in the same class, so the object signal and noise It is possible to further improve the determination accuracy of

In addition, the class width is preferably set to be equal to or longer than the fall time of the object signal (a signal generated by light projected from the light projecting system 10 and reflected by the object).
If the object signal not only rises but also falls is considered, distance measurement accuracy may be improved. Even in that case, even when there are variations in the object signal when counting the fall timing, Since the object signal or a value based on the object signal falls in the same class, it is possible to further improve the determination accuracy of the object signal and the noise.

  Also, the class width may be different among the classes. For example, the class width is preferably wider as the class is higher (as time and distance are longer). In this case, it is possible to easily distinguish the object signal and the noise in the far distance range while improving the distance measurement accuracy in the short distance range.

  The class width is preferably set based on any of the pulse width of the light (emission pulse) emitted from the LD 11, the rise time, and the fall time. In general, the cutoff frequency of the waveform processing circuit 41 is set to a predetermined value in order to obtain an object signal having the same pulse width as the pulse width of the light emission pulse (pulse width of the LD drive signal). By setting the class width based on the pulse width of the pulse, the rise time and the fall time, as a result, the class width can be set based on the pulse width of the object signal, the rise time and the fall time.

  In addition, the time acquisition system includes a binarization circuit 44 that binarizes the voltage signal output from the waveform processing circuit 41 with a threshold, and the rising timing of the LD drive signal (the light emission timing of the LD 11, More specifically, it is preferable to calculate the time difference between the light emission start timing of the LD 11 and the timing based on the output signal of the binarization circuit 44 or a value based on the time difference, and perform the above classification based on the calculation result.

  In addition, the time acquisition system is a signal having a peak exceeding a threshold or a peak belonging to the largest number of values based on the signal among a plurality of classes, a signal having a peak exceeding a threshold or a value based on the signal It is preferable to calculate the time at the time of light projection in the same direction based on the value).

  In addition, when there are a plurality of the above-mentioned largest classes, the time acquisition system is an object signal or a signal among the plurality of classes based on the time from when the signal whose peak exceeds the threshold first crosses the threshold to the next. Preferably, the class to which the value based on the object signal belongs is estimated.

  In addition, in the time acquisition system, a time when the signal whose peak exceeds the threshold first crosses the threshold and then crosses the threshold among a plurality of classes, or a value based on the time (a value obtained by converting the time into a distance) It is preferable to estimate a class having a standard deviation σ of a predetermined value (for example, 1.0) or less as a class to which an object signal or a value based on the object signal (for example, TOF operation time or TOF operation distance) belongs.

  The light projecting system 10 includes a rotating mirror 26 (deflector) that deflects and scans the light from the LD 11. In this case, a plurality of scans are required for the light projecting system 10 to emit light a plurality of times in the same direction, but the object detection apparatus 100 detects an object signal even with a small number of scans while the threshold voltage is set lower. Since noise can be distinguished, high-precision and high-speed measurement is possible regardless of the distance to the object and the reflectance of the object.

Further, according to the object detection device 100 that includes the time measurement device of the present embodiment and calculates the distance to the object based on the acquisition result of the time acquisition system of the time measurement device, the light that is projected and reflected by the object It is possible to realize a distance measurement device that enables high-accuracy and high-speed measurement regardless of the amount of light received by the time measurement PD 42.
The object detection device 100 does not calculate the distance to the object based on the output of the time measurement device, and the ECU of the vehicle on which the object detection device 100 is mounted determines the distance to the object based on the output of the time measurement device. It may be calculated.

  Moreover, according to the vehicle apparatus (mobile body apparatus) provided with the object detection apparatus 100 and the vehicle (mobile body) on which the object detection apparatus 100 is mounted, a vehicle apparatus having excellent collision safety can be realized.

  In addition, an object detection apparatus 100 and a monitoring control apparatus 300 for obtaining object information (at least one of presence / absence of an object, position of an object, moving direction of an object, and moving speed of an object) based on an output of the object detection apparatus 100. , The object information can be stably acquired with high accuracy and high speed.

  In addition, the sensing device 1000 is mounted on a moving object, and the monitoring control device 300 determines the presence or absence of a danger based on at least one of position information and movement information of an object. Can provide useful information for risk avoidance.

  Further, according to the vehicle apparatus (mobile apparatus) including the sensing apparatus 1000 and the vehicle (mobile body) on which the sensing apparatus 1000 is mounted, a vehicle apparatus having excellent collision safety can be realized.

  In the time measurement method of the present embodiment, a light emitting process of emitting light, a photoelectric conversion process of receiving and photoelectrically converting light reflected by the object and emitted in the light emitting process, and generated in the photoelectric conversion process Performing at least one processing on the current, and outputting a voltage signal (signal) obtained by the processing, and measuring a time from the projection of the light to the reception of the light In the time measurement method, when light is projected a plurality of times in the same direction toward the object in the light projection step, a peak among the voltage signals output in the processing step at the time of each plural times of light projection The exceeded voltage signal or the value based on the voltage signal is classified into a plurality of classes corresponding to the time or the value based on the time, and based on the classification result, the time at the time of light projection in the same direction is obtained Including the time acquisition step A time measurement method, wherein a class width of each class is set based on the characteristic.

  According to the time measurement method of the present embodiment, high accuracy and high speed are achieved regardless of the amount of light received in the photoelectric conversion step of the light projected and reflected by the object (regardless of the distance to the object and the reflectance of the object) Measurement can be performed.

  In the distance measuring method of the present embodiment, a light emitting process of emitting light, a photoelectric conversion process of receiving and photoelectrically converting light reflected by the object and emitted in the light emitting process, and generated in the photoelectric conversion process Performing at least one processing on the current, and outputting a voltage signal (signal) obtained by the processing, and measuring a time from the projection of the light to the reception of the light In the distance measuring method, when light is projected a plurality of times in the same direction toward the object in the light projecting step, a peak among the voltage signals output in the processing step at each of the plurality of times of light projecting The exceeded voltage signal or the value based on the voltage signal is classified into a plurality of classes corresponding to the time or the value based on the time, and based on the classification result, the time at the time of light projection in the same direction is obtained Time acquisition process and time acquisition process It includes a distance calculation step of calculating the distance to the object based on the acquisition result, the distance measurement method, wherein a class width of each class based on the characteristics of the processing is set.

  According to the distance measurement method of the present embodiment, high accuracy and high speed can be achieved regardless of the amount of light received in the photoelectric conversion step of the light projected and reflected by the object (regardless of the distance to the object and the reflectance of the object) Measurement can be performed.

  The configuration of the object detection device 100 according to the above embodiment can be changed as appropriate.

  For example, a filter such as a low-pass filter or a high-pass filter may be incorporated in the waveform processing circuit as a signal processing circuit. Such a filter is preferably connected between the signal amplifier and the binarization circuit when the signal amplifier is incorporated in the waveform processing circuit, and a current-voltage converter when the signal amplifier is not incorporated in the waveform processing circuit. It is preferable to connect between the signal and the binarization circuit.

The light projecting system 10 is a scanning type that uses a rotating mirror 26 as a deflector, but may be a non-scanning type that does not use a deflector. That is, the light projection system only needs to have at least a light source, and a lens for adjusting the light projection range may be provided at a later stage of the light source. For the non-scanning light projecting system, it is preferable to use a light source array in which a plurality of light sources are arranged in an array.
Examples of such a light source array include an LD11 array in which a plurality of LDs 11 are arranged one-dimensionally or two-dimensionally, and a VCSEL array in which VCSELs are arranged one-dimensionally or two-dimensionally. Examples of the LD11 array in which a plurality of LD11 are one-dimensionally arranged include a stacked LD11 array in which a plurality of LD11 are stacked and an LD11 array in which a plurality of LD11 are arranged horizontally.
In addition, if VCSEL is used as each light source in a light source array, it can arrange | position more densely than the case where LD is used (the number of the light emission points in an array can be increased more).

  Further, the light projecting optical system may not have a coupling lens, and may have another lens.

  Further, the light projecting optical system and the light receiving optical system may not have the reflection mirror. That is, the light from the LD 11 may be incident on the rotating mirror without folding the optical path.

  The light receiving optical system may not have the light receiving lens, or may have another optical element (for example, a light collecting mirror).

  Also, as the deflector, in place of the rotating mirror, for example, another mirror such as a polygon mirror (rotating polygon mirror), a galvano mirror, a MEMS mirror, etc. may be used.

  The synchronization system may not have a synchronization lens, or may have another optical element (for example, a focusing mirror).

  Further, in the above embodiment, a vehicle is described as an example of a mobile body on which the object detection apparatus 100 is mounted, but the mobile body may be, for example, an aircraft, a ship, a robot or the like.

  Further, it is needless to say that the specific numerical values, shapes and the like used in the above description are merely examples and can be suitably changed without departing from the scope of the present invention.

  As is apparent from the above description, the object detection apparatus 100 (distance measurement apparatus) including the time measurement apparatus of the above embodiment, the sensing apparatus 1000, the mobile apparatus, the time measurement method, the distance measurement method, the distance measurement processes 1 to 4 Is a technology that uses the so-called Time of Flight (TOF) method to measure the distance to an object, and in industrial fields such as motion capture technology, range finder, three-dimensional shape measurement technology, etc. It can be used widely. That is, the time measurement device, the distance measurement device, and the sensing device 1000 according to the present invention may not necessarily be mounted on a moving body.

Below, the thought process in which inventors came to draft the said embodiment is demonstrated.
As an object detection device, for example, in an on-vehicle application, a laser radar (also referred to as “LIDAR”) is known which detects the presence or absence of an object in front of a traveling vehicle and the distance to the object. Laser radar irradiates an object with laser light emitted from a laser light source, and receives light reflected or scattered from the object with a light receiving element, thereby determining the presence or absence of an object in a desired range and the distance to the object. To detect.

  What is important in ranging with such a laser radar is separation of noise and signals from objects. Among noises, shot noise is white noise accompanying disturbance light. The magnitude of the shot noise is proportional to the square root of the time average of the light quantity of the disturbance light, and becomes more problematic than the circuit noise when the sensitivity of the light receiving element is high or the disturbance light is strong. Noise can also be generated when an object that is unnecessary to avoid, such as rain or fog, is detected.

In the method of detecting the light reception signal (signal based on the output current of the light receiving element) on the basis of the threshold voltage, basically, in order to prevent false detection due to shot noise, the threshold voltage has a maximum shot noise. The voltage value is determined to be sufficiently high (see FIG. 5A). For this reason, when the shot noise is relatively small, the threshold voltage becomes excessively large and the signal due to the reflected light from the object at a long distance does not exceed the threshold voltage, so the maximum detection distance becomes very short (see FIG. 5 (B)).
Therefore, in order to increase the maximum detection distance, it is desirable to set the threshold voltage to the minimum within the range where false detection does not occur.

  According to Patent Document 1, it is determined to which class of the histogram having the class of distance and time the measured distance corresponds, and an output voltage signal in a predetermined range centered on the class where the frequency of the measured distance is maximum A distance measuring device is disclosed that calculates the distance to an object based on the average value of This distance measuring device is said to be able to accurately calculate the distance to an object while suppressing noise components even in a bad environment such as rainy weather.

  Patent Document 2 discloses a method of creating a histogram similar to that of Patent Document 1 and calculating the distribution of disturbance light with a histogram excluding the bins that are the maximum. In this method, the intensity of the pulsed light can be changed according to the distance to the object, so it is possible to acquire an image of the object independent of the distance to the object.

However, in Patent Documents 1 and 2, a TOF (Time Of Flight) having a sensor and an integrated circuit that acquire a 2D image of an object illuminated with a plurality of pulsed lights by simultaneously lighting a plurality of light sources arranged two-dimensionally. ) The use of sensors is assumed.
This TOF sensor obtains the time for the pulsed light to reciprocate between the object and the distance to the object based on the time for each pixel of the sensor.
Since each light source used in this TOF sensor is repeatedly lit at a high speed of, for example, a 10 ns cycle (100 MHz), such a histogram can be generated in a short time.

On the other hand, in a scanning time measurement device or distance measurement device that repeats light emission of one shot at each angle, the light emission cycle (period of one scan) at each angle (every pixel, every scanning position) is, for example, about 60 ms. Become.
In this case, as in Patent Documents 1 and 2, a histogram is created in distance measurement, and the measurement is repeated 30 times to perform accurate distance measurement, for example, once the dispersion is statistically reliable. It takes 1.8 seconds.
For this reason, when the scanning type time measurement device or distance measurement device is mounted on a moving object such as a vehicle that needs to detect a moving object or the like, noise such as shot noise or rain may be measured at least several times. It is required to accurately measure the distance by distinguishing it from the object signal.

  Therefore, the inventors have made a scanning time measurement apparatus, distance measurement apparatus, and time measurement method capable of discriminating noise and object signal at high speed and with high accuracy even if threshold voltage for detecting object signal is set low. In order to realize the distance measuring method, the time measuring device, the sensing device including the distance measuring device, the time measuring device, the distance measuring device, and the mobile device including the sensing device, the above embodiment is proposed.

  DESCRIPTION OF SYMBOLS 10 ... Projection system, 11 ... LD (light source, a part of projection system), 26 ... Rotation mirror (part of a projection system), 30 ... Light reception optical system (part of light reception system), 40 ... Light reception system 41: waveform processing circuit (processing system) 42: PD for measuring time (light receiving element, part of light receiving system) 43: current / voltage converter (current voltage conversion circuit, part of processing system) 48: signal Amplifier (signal processing circuit, part of processing system), 44: binarization circuit (part of time acquisition system), 46: control system (part of time acquisition system), 100: object detection apparatus (time measurement apparatus) Devices, including distance measuring devices).

Patent 3771346 Patent 6020547

Claims (20)

A light projection system including a light source,
A light receiving system including a light receiving element for receiving and photoelectrically converting light emitted from the light emitting system and reflected by the object;
A processing system which performs at least one process on the electrical signal output from the light receiving element and outputs a signal obtained by the process;
In a time measuring device for measuring a time from when the light is emitted from the light source to when it is received by the light receiving element,
Among the signals output from the processing system during each of a plurality of times of light emission when the light emission system performs light emission in the same direction toward the object, a signal whose peak exceeds a threshold Alternatively, a time acquisition system that classifies values based on the signal into the time or a plurality of classes corresponding to the values based on the time, and acquires the time at the time of light projection in the same direction based on the classification result. Prepared,
A time measuring apparatus characterized in that a class width for each class is set based on the characteristics of the processing system. The electrical signal is a current,
The processing system includes a current-voltage conversion circuit that converts the current into a voltage,
The time measuring apparatus according to claim 1, wherein the class width is set based on a cut-off frequency of the current-voltage conversion circuit.   The time measuring apparatus according to claim 2, wherein the class width is equal to or less than an inverse number of the cutoff frequency. The processing system includes a signal processing circuit that processes an output signal of the current-voltage conversion circuit,
The time measuring apparatus according to claim 2 or 3, wherein the class width is set based on a cut-off frequency of the signal processing circuit.   5. The time measuring device according to claim 4, wherein the class width is equal to or less than the reciprocal of the non-smaller one of the cut-off frequencies of the current-voltage conversion circuit and the signal processing circuit.   The time measurement apparatus according to any one of claims 1 to 5, wherein the class width is set to be equal to or more than a rise time of the signal by the light.   The time measurement apparatus according to any one of claims 1 to 6, wherein the class width is set to be equal to or more than a fall time of the signal due to the light.   The time measurement apparatus according to any one of claims 1 to 7, wherein the class width is different among the classes.   The time measuring device according to claim 8, wherein the class width increases as the class increases.   10. The time according to any one of claims 1 to 9, wherein the class width is set based on any one of pulse width, rise time and fall time of light emitted from the light source. measuring device.   The time acquisition system includes a binarization circuit that binarizes the signal output from the processing system with the threshold value, and the light emission timing of the light source and the output of the binarization circuit at the time of each light projection The time measurement apparatus according to any one of claims 1 to 10, wherein a time difference with a timing based on a signal or a value based on the time difference is calculated, and the classification is performed based on the calculation result.   In the time acquisition system, a signal having the peak exceeding a threshold or a number of values based on the signal among the plurality of classes belongs to a class having the largest number of signals or a value based on the signal. The time measuring apparatus according to any one of claims 1 to 11, wherein the time at the time of light projection in the same direction is calculated based on the time.   In the time acquisition system, when there are a plurality of the largest classes, the signal among the plurality of classes is based on the time from when the signal with the peak exceeding the threshold first crosses the threshold to the next. 13. The time measuring apparatus according to claim 12, wherein a class to which a signal based on light or a value based on the signal belongs is estimated.   In the time acquisition system, in the plurality of classes, a time when a signal whose peak exceeds the threshold first crosses the threshold to the next or a standard deviation of a value based on the time is less than or equal to a predetermined value. The time measuring apparatus according to claim 13, wherein the class is estimated as a class to which the light signal or the value based on the signal belongs.   The time measuring apparatus according to any one of claims 1 to 14, wherein the light projection system includes a deflector that deflects and scans light from the light source.   A distance measuring device comprising the time measuring device according to any one of claims 1 to 15, wherein the distance to the object is calculated based on the output of the time measuring device. The distance measuring device according to claim 16;
A moving body device comprising: a moving body on which the distance measuring device is mounted. The time measuring device according to any one of claims 1 to 15,
A moving body device comprising: a moving body on which the time measuring device is mounted. A floodlighting process to floodlight,
A photoelectric conversion step of receiving and photoelectrically converting the light projected in the light projection step and reflected by the object; and
A process of performing at least one process on the electrical signal generated by the photoelectric conversion process and outputting a signal obtained by the process, and a time from when the light is projected until the light is received In the time measurement method of measuring
When the light projecting step is performed a plurality of times in the same direction toward the object, a signal whose peak has exceeded a threshold among the signals output in the processing step at the time of each of the plurality of times of light projecting, or Classifying the value based on the signal into the time or a plurality of classes corresponding to the value based on the time, and acquiring the time at the time of light projection in the same direction based on the classification result; and Including
A time measurement method, wherein a class width for each class is set based on the characteristics of the processing. A floodlighting process to floodlight,
A photoelectric conversion step of receiving and photoelectrically converting the light projected in the light projection step and reflected by the object; and
Performing at least one process on the electrical signal generated by the photoelectric conversion process, and outputting a signal obtained by the process, wherein the distance measurement method measures the distance to the object,
When the light projecting step is performed a plurality of times in the same direction toward the object, a signal whose peak has exceeded a threshold among the signals output in the processing step at the time of each of the plurality of times of light projecting, or The value based on the signal is classified into a plurality of classes corresponding to the time or the value based on the time, and based on the classification result, the light is projected when the light is projected in the same direction, and then received. A time acquisition step of acquiring time until
A distance calculating step of calculating the distance based on an acquisition result in the time acquiring step;
A distance measuring method, wherein a class width for each class is set based on the characteristics of the processing.

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