JP5206297B2 - Optical distance measuring apparatus and method - Google Patents

Description

  The present invention relates to an optical distance measuring apparatus and method, and in particular, an optical distance measuring device that measures a distance to an object based on a time until irradiation light irradiated on the object is reflected and returned on the object. The present invention relates to a distance measuring apparatus and method.

  2. Description of the Related Art Conventionally, there has been proposed an apparatus for measuring a distance to an object based on a time (TOF: time of flight) until irradiation light irradiated on the object is reflected on the object and returns. In such an apparatus, since the light other than the light emitted by itself is noise, it is necessary to remove the influence of disturbance light such as sunlight. By repeatedly measuring the TOF, creating a histogram of the TOF, and extracting the maximum value, it is possible to correctly extract the TOF even if ambient light is present. However, in order to extract the maximum value of the TOF histogram with high accuracy, a large number of TOF measurement times are required, and the measurement time becomes long. If the measurement time is long, an error occurs when a moving object is measured.

Therefore, for example, Patent Document 1 proposes a distance measuring device that performs preliminary measurement for perspective determination before the main measurement. In this apparatus, even in the preliminary measurement, the measurement is performed a plurality of times and a histogram of TOF is created. Distance determination unit of this apparatus, the inside of the histogram, by T ₁ or T _p the range, to determine whether there is to be a frequency threshold n or more frequencies have been defined. If there is something that is greater than or equal to the frequency threshold value n, the reflected light from the measurement object existing at a short distance is obtained, and the short distance mode is set. If there is no object whose frequency threshold value is n or more, it is determined that the object to be measured is not in a short distance and the long distance mode is set. In this measurement, in the short distance mode, the intensity of the reflected light is strong and it is difficult to be affected by the back light noise. Therefore, the distance measurement is performed with a smaller number of measurements than in the long distance mode.
JP 2006-322834 A

  The above technique is based on the idea that a predetermined accuracy can be obtained with a small number of measurements because the closer the distance to the object is, the less affected by the background noise. However, since the distance measurement accuracy depends on the optical signal-to-noise ratio and the number of measurements, it depends on the intensity of irradiation light, the reflectance of the object, and the intensity of background noise in addition to the distance to the object. Therefore, there is a problem that it is not possible to set an appropriate number of measurements when the background noise changes greatly or when the reflectance of the object is significantly different from normal.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an optical distance measuring apparatus and method that operate correctly even in an environment where there is a lot of disturbance light and fluctuates.

  The present invention includes a light projecting unit that repeatedly irradiates an object with pulsed light, a light receiving unit that repeatedly receives reflected pulsed light of the pulse light emitted from the object by the light projecting unit, and a light projecting unit that radiates pulse light. Histogram creation means for repeatedly measuring the time difference between the pulse light projecting time that is the time and the pulse light reception time that is the time when the light receiving means receives the reflected pulse light, and creating a histogram of the time difference, and the histogram creation means A distance calculation unit that calculates the distance to the object based on the maximum value of the created histogram, a reliability calculation unit that calculates the reliability of the histogram created by the histogram creation unit, and a histogram calculated by the reliability calculation unit A histogram creation stop means for causing the histogram creation means to stop creating a histogram when the reliability is equal to or greater than a threshold; Example was an optical rangefinder.

  According to this configuration, the histogram creation means repeatedly repeats the time difference between the pulse light projection time that is the time when the light projecting means radiates the pulsed light and the pulse light reception time that is the time when the light receiving means receives the reflected pulse light. In the optical distance measuring device that measures and creates a histogram of the time difference, and the distance calculation means calculates the distance to the object based on the maximum value of the histogram created by the histogram creation means, the reliability calculation means includes the histogram The histogram creation means calculates the reliability of the histogram created by the creation means, and the histogram creation stop means causes the histogram creation means to stop creating the histogram when the reliability of the histogram calculated by the reliability calculation means is equal to or higher than a threshold value. Even in environments with a lot of disturbance light and fluctuations, the histogram generation is stopped when the reliability of the histogram is high. By, it is possible to reduce unnecessary measurement and calculation.

  The present invention also provides a light projecting unit that repeatedly irradiates a target with pulsed light, a light receiving unit that repeatedly receives reflected pulsed light of the pulsed light emitted from the target by the light projecting unit, and a light projecting unit that emits pulsed light. Histogram creation means for creating a histogram of the time difference by repeatedly measuring the time difference between the pulse light projection time that is the irradiation time and the pulse light reception time that is the time when the light receiving means receives the reflected pulse light, and histogram creation Calculated by the distance calculation means for calculating the distance to the object based on the maximum value of the histogram created by the means, the reliability calculation means for calculating the reliability of the histogram created by the histogram creation means, and the reliability calculation means A non-measurable detecting means that makes it impossible to calculate the distance by the distance calculating means when the reliability of the histogram is equal to or less than a threshold value. An expression distance measuring apparatus.

  According to this configuration, the histogram creation means repeatedly repeats the time difference between the pulse light projection time that is the time when the light projecting means radiates the pulsed light and the pulse light reception time that is the time when the light receiving means receives the reflected pulse light. In the optical distance measuring device that measures and creates a histogram of the time difference, and the distance calculation means calculates the distance to the object based on the maximum value of the histogram created by the histogram creation means, the reliability calculation means includes the histogram The reliability of the histogram created by the creating means is calculated, and the measurement impossibility detecting means is unable to calculate the distance by the distance calculating means when the reliability of the histogram calculated by the reliability calculating means is less than or equal to a threshold value. Therefore, in an environment where there is a lot of disturbance light and fluctuates, it is impossible to calculate the distance when the histogram reliability is low. It is possible to prevent the output erroneous measurement results.

  Furthermore, the present invention provides a light projecting unit that repeatedly irradiates an object with pulsed light, a light receiving unit that repeatedly receives reflected pulsed light of the pulsed light emitted from the object, and the light projecting unit receives pulsed light. Histogram creation means for creating a histogram of the time difference by repeatedly measuring the time difference between the pulse light projection time that is the irradiation time and the pulse light reception time that is the time when the light receiving means receives the reflected pulse light, and histogram creation Calculated by the distance calculation means for calculating the distance to the object based on the maximum value of the histogram created by the means, the reliability calculation means for calculating the reliability of the histogram created by the histogram creation means, and the reliability calculation means Histogram creation that causes the histogram creation means to stop creating a histogram when the reliability of the histogram is greater than or equal to the first threshold And an unmeasurable detection means that makes it impossible to calculate the distance by the distance calculation means when the reliability of the histogram calculated by the reliability calculation means is less than or equal to the second threshold value. This is a distance measuring device.

  According to this configuration, the histogram creation means repeatedly repeats the time difference between the pulse light projection time that is the time when the light projecting means radiates the pulsed light and the pulse light reception time that is the time when the light receiving means receives the reflected pulse light. In the optical distance measuring device that measures and creates a histogram of the time difference, and the distance calculation means calculates the distance to the object based on the maximum value of the histogram created by the histogram creation means, the reliability calculation means includes the histogram The reliability of the histogram created by the creation unit is calculated, and the histogram creation stop unit stops the histogram creation unit from creating a histogram when the reliability of the histogram calculated by the reliability calculation unit is equal to or higher than the first threshold. Therefore, even in an environment with a lot of disturbance light and fluctuation, The by stopping, it is possible to reduce unnecessary measurement and calculation.

  In addition, the measurement impossibility detecting means makes it difficult to calculate the distance by the distance calculating means when the reliability of the histogram calculated by the reliability calculating means is equal to or less than the second threshold value, and therefore there is a lot of disturbance light. By making it impossible to calculate the distance when the reliability of the histogram is low in a fluctuating environment, it is possible to prevent an erroneous measurement result from being output.

  In this case, the reliability calculated by the reliability calculation unit is preferably a value representing the sharpness of the maximum value of the histogram generated by the histogram generation unit.

  According to this configuration, the reliability calculation means uses the fact that the maximum value of the histogram becomes sharper when the optical SN is large and becomes unclear when the optical SN is small. Degree. For this reason, the reliability of the histogram can be calculated appropriately according to the ratio of the size of the irradiation light and the disturbance light.

  Further, it is preferable that the reliability calculation means calculates the reliability as the number of time difference measurements in the histogram created by the histogram creation means increases, and calculates the reliability as the time difference measurement number decreases.

  According to this configuration, since the reliability calculation means considers the measurement frequency, the reliability can be correctly calculated even if the maximum value of the histogram is accidentally sharpened with a small number of measurements.

  In addition, the reliability calculation unit measures the number A of bins indicating the maximum value in the histogram created by the histogram creating unit, any of the remaining bins excluding the bins indicating the maximum value from all bins and all bins. For the average value N of numbers, the reliability can be calculated as A / N.

  According to this configuration, the reliability calculation unit can calculate the reliability by a simple method.

Alternatively, the reliability calculation means may measure the number A of bins indicating the maximum value in the histogram created by the histogram creating means, or any of the remaining bins excluding the bins indicating the maximum value from all bins. For the average value N, 0.5 ≦ α ≦ 3, 0.5 ≦ β ≦ 3, and the number n of all bins, the reliability is expressed as reliability = (A−α · A ^1/2 ) / It can be calculated as [N + β · {(N / (n−1)} ^1/2 ].

  According to this configuration, since the reliability can be calculated based on the amount of shot noise, the reliability can be obtained more accurately even if the histogram is sharpened at an erroneous position when the number of detections is small. be able to.

  Furthermore, the bin showing the maximum value is composed of a plurality of adjacent bins, and the average value of the number of measurements of the plurality of bins can be the number of measurements A of the bin showing the maximum value.

  According to this configuration, even when the pulse time width of the pulse light is longer than the time width of the bin and the bin showing the maximum value is composed of a plurality of adjacent bins, the number A of measured bins showing the maximum value A Can be determined appropriately.

  On the other hand, the present invention includes a step of repeatedly irradiating an object with pulsed light, a step of repeatedly receiving reflected pulsed light of the pulsed light emitted from the object, and a pulsed light projection time that is the time of irradiation of the pulsed light. , A step of repeatedly measuring a time difference with a pulsed light receiving time which is a time when the reflected pulse light is received, a step of creating a histogram of the time difference, and a step of calculating a distance to the object based on the maximum value of the created histogram And a step of calculating the reliability of the created histogram, and a step of stopping the creation of the histogram when the calculated reliability of the histogram is equal to or greater than a threshold value.

  Alternatively, the present invention includes a step of repeatedly irradiating an object with pulsed light, a step of repeatedly receiving reflected pulsed light of the pulsed light emitted from the object, and a pulsed light projecting time that is the time when the pulsed light is irradiated, A step of repeatedly measuring a time difference with a pulsed light receiving time which is a time when the reflected pulsed light is received, and creating a histogram of the time difference, and a step of calculating a distance to an object based on a maximum value of the created histogram; The optical distance measuring method includes a step of calculating the reliability of the created histogram, and a step of disabling calculation of the distance when the reliability of the calculated histogram is equal to or less than a threshold value.

  Furthermore, the present invention includes a step of repeatedly irradiating an object with pulsed light, a step of repeatedly receiving reflected pulsed light of the pulsed light emitted from the object by the light projecting means, and a pulsed light that is the time when the pulsed light is irradiated. The process of creating a histogram of the time difference by repeatedly measuring the time difference between the projection time and the pulsed light reception time, which is the time when the reflected pulsed light was received, and the distance to the object based on the maximum value of the created histogram A step of calculating the reliability of the histogram, a step of calculating the reliability of the generated histogram, a step of stopping the generation of the histogram when the reliability of the calculated histogram is equal to or higher than the first threshold, and a reliability of the calculated histogram And a step of disabling the calculation of the distance when the value is equal to or smaller than a second threshold value.

  In this case, it is preferable that the calculated reliability is a value representing the sharpness of the maximum value of the created histogram.

  In addition, it is preferable to calculate the reliability higher as the number of time difference measurements in the created histogram is larger, and to calculate the reliability lower as the number of time difference measurements is smaller.

  In addition, the number A of bins indicating the maximum value in the generated histogram, the average value N of the number of measurements of all bins and the remaining bins excluding the bins indicating the maximum value from all bins are reliable. The degree can be calculated as A / N.

Alternatively, the measurement number A of bins indicating the maximum value in the generated histogram, the average value N of the measurement numbers of all bins and the remaining bins excluding the bins indicating the maximum value from all bins, 0.5 ≦ For α ≦ 3, 0.5 ≦ β ≦ 3 and the number n of all bins, the reliability is expressed as reliability = (A−α · A ^1/2 ) / [N + β · {(N / (n− 1)} ^1/2 ].

  Furthermore, the bin showing the maximum value is composed of a plurality of adjacent bins, and the average value of the number of measurements of the plurality of bins can be the number of measurements A of the bin showing the maximum value.

  According to the optical distance measuring apparatus and method of the present invention, an optical distance measuring apparatus that operates correctly even in an environment where there is a lot of disturbance light and fluctuates.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. First, the type of the optical distance measuring device according to the present invention will be described. Laser range finders (laser ranging devices) that measure the distance to an object with a laser beam include a scan type and a non-scan type.

  The scan type repeatedly irradiates an object while scanning a laser beam, and the reflected light is received by one light receiving element. Since the scan type emits collimated light, the power density on the object is relatively large, and the optical SN ratio can be increased. However, in order to obtain the spatial distribution of distance with high resolution, the scan type requires high-density scanning, and the scanning time increases. Therefore, in an automobile application where immediacy is required, the scan type generally scans with a high density in the horizontal direction and only a few lines in the vertical direction in order to shorten the scan time.

  On the other hand, the non-scan type irradiates light having a spread covering the measurement object, forms an image of the reflected light on a two-dimensional array of light receiving elements, and receives the light. The non-scan type has an advantage that a high-resolution spatial distribution can be obtained at a high speed because the distances of multiple points can be measured simultaneously with a single light irradiation. On the other hand, in the non-scan type, it is important to remove noise components such as irradiation light.

  FIG. 1 is a block diagram illustrating a configuration of a 3D camera 10 that is a non-scan type laser range finder according to an embodiment. The non-scanning laser range finder described above is also called a 3D camera, and as shown in FIG. 1, a light projecting unit 20 that irradiates the object O with the irradiation light L1 and a light receiving unit that receives the reflected light L2 from the object O. 30.

  The light projecting unit 20 includes a clock generation circuit 21, a circuit board 22, a drive circuit 23, a laser diode array including a plurality of laser diodes 24, a Fresnel lens 25, and a diffusion plate 26. The clock generation circuit 21 generates clock signals CLK1 and CLK2 for operating the light projecting unit 20 and the light receiving unit 30. Each laser diode 24 is arranged on a circuit board 22 and includes a drive circuit 23 and a Fresnel lens 25. The laser light generated by each laser diode 24 is diffused by the diffusion plate 26 and applied to the object O.

  The light receiving unit 30 includes an interference filter 31, a lens 32, and a two-dimensional light receiving element array 33. As shown in FIG. 2, the two-dimensional light receiving element array 33 includes pixels 330 each having an avalanche photodiode 332 having a light receiving portion 331 and its peripheral circuit 333 arranged in a grid pattern. FIG. 3 shows an example of the circuit configuration of each pixel 330. As shown in FIG. 3, the peripheral circuit 333 includes a resistor 334, a buffer 335, a TDC (Time Digital Converter) 336, a histogram circuit 337, and a signal processing circuit 338.

  The clock generation circuit 21 of the light projecting unit 20 generates a clock signal CLK1 having a period T and a clock signal CLK2 having a period MT (M is an arbitrary natural number of 1 or more). The clock signal CLK1 is a clock signal that defines the timing of pulse emission of the laser diode 24 of the light projecting unit 20, and the clock signal CLK2 is the distance of the signal processing circuit 338 of the light receiving unit 30 after the laser diode 24 has emitted M times. It is a clock signal that defines the timing for calculation. The clock signal CLK1 is input to the laser diode array of the light projecting unit 20, and the clock signal CLK1 and the clock signal CLK2 are input to the two-dimensional light receiving element array 33 of the light receiving unit 30.

  The clock signal CLK1 input to the laser diode array is distributed to each drive circuit 23, and a current signal for driving each laser diode 24 is generated. The laser diode 24 is driven by the current signal generated by the drive circuit 23, and emits pulses in synchronization with the clock signal CLK1. The advantage of using the laser diode 24 as a light-emitting element is due to high-speed response and single wavelength, but the laser diode 24 can be replaced with other light-emitting elements such as LEDs. The output light from the laser diode 24 is converted into parallel light by the Fresnel lens 25, is diffused by the diffusion plate 26, and is irradiated toward the object O. The diffusion plate 26 has a light distribution characteristic unique to the light emitting element, and the beam spreading angle is determined by the light distribution characteristic. The output light from each laser diode 24 is diffused by the diffusion plate 26 and added together to form one conical beam.

  As described above, in the present embodiment, the entire object O to be measured is illuminated at once with the irradiation light L1 which is a conical beam, and the reflected light L2 is simultaneously received by the two-dimensional light receiving element array 33 of the light receiving unit 30. Therefore, it is possible to acquire distance data with high spatial resolution. On the other hand, in this embodiment, since the irradiation range of the irradiation light L1 is wide, the power density of the irradiation light L1 is reduced, so the optical SN ratio is reduced.

  Another advantage of using the diffuser 26 is that the size of the apparent light source can be increased. “Aperent light source” is a term defined by the laser safety standard of JIS (Japanese Industrial Standards). It is a real or virtual object that connects the smallest retinal images. If the output is constant, the size of the apparent light source is large. Is safer for the eyes. In the present embodiment, by increasing the apparent light source size with the diffusion plate 26, the safety of the eyes can be made more reliable.

  The reflected light L2 reflected on the object O passes through the interference filter 31 of the light receiving unit 30 and is imaged on the two-dimensional light receiving element array 33 by the lens 32. The imaged light is received by each avalanche photodiode 332 on the two-dimensional light receiving element array 33. The interference filter 31 is a filter that transmits only light in a specific narrow wavelength range. By making the center wavelength of the laser light equal to the center wavelength of the interference filter 31, most of disturbance light such as sunlight is removed. can do. The bandwidth of laser light is generally several nm, but the center wavelength varies with temperature. In order to guarantee operation in a wide temperature range, the bandwidth of the interference filter 31 is set to about several tens to one hundred nm. For this reason, all the disturbance light cannot be removed by the interference filter 31, and noise removal by signal processing is required.

  The avalanche photodiode is a kind of photodiode and has a function related to application of a high electric field. Avalanche photodiodes include a linear mode in which a reverse bias voltage is operated at a breakdown voltage or lower and a Geiger mode in which the reverse bias voltage is operated at a breakdown voltage or higher. An avalanche photodiode generates an electron-hole pair when a photon is incident, and each electron and hole is accelerated by a high electric field to generate new electron-hole pairs one after another like an avalanche. ).

  In the linear mode, the proportion of electron-hole pairs that disappear (exit from a high electric field region) is larger than the proportion of generated electron-hole pairs, and the avalanche phenomenon stops naturally. Since the output current is substantially proportional to the amount of incident light, it can be used to measure the amount of incident light. While the photon count in the Geiger mode to be described later is digital, the light amount measurement in the linear mode is analog and is sometimes referred to as analog measurement.

  In the Geiger mode, an avalanche phenomenon can be caused even by the incidence of a single photon, and the avalanche phenomenon can be stopped by lowering the applied voltage to the breakdown voltage. Stopping the avalanche phenomenon by lowering the applied voltage is called quenching. The simplest quenching circuit can be realized by connecting a resistor 334 in series with an avalanche photodiode 332 as shown in FIG. 3, and the bias voltage decreases due to the voltage increase between the terminals of the resistor 334 due to the avalanche current. Then the avalanche current stops. With this quenching circuit, the peripheral circuit 333 can take out and count the incidence of photons as a voltage pulse. For this reason, Geiger mode is also called photon count mode.

The sensitivity of a light receiving element for analog measurement is generally expressed by quantum efficiency and dark current. Quantum efficiency is the ratio of the number of electrons generated per incident photon. The dark current is a current that flows due to electrons excited by heat in a state where no light is incident, and is the lowest level of thermal noise. The minimum input required to obtain an output of noise level (dark current) can be calculated from the quantum efficiency. If the dark current is 100 nA and the quantum efficiency is 50%, the charge of one electron is 1.6 × 10 ⁻¹⁹ C. Therefore, the minimum input required to obtain a noise level output is (100 [nA ] /1.6×10 ⁻¹⁹ [C]) / 0.5 = 1.25 × 10 ¹² [photons / second].

  On the other hand, the sensitivity of the photon counter is expressed by detection efficiency and dark count rate. In an avalanche photodiode in the Geiger mode, electron-hole pairs continue to be generated one after another unless the avalanche current is stopped by a quenching circuit, so that the quantum efficiency becomes infinite. The generation of an avalanche current with respect to the incidence of photons is a stochastic phenomenon, and this probability is called detection efficiency. Similar to the dark current in the linear mode, an avalanche current may be generated due to the thermal motion of electrons in the Geiger mode, and the amount of thermal noise is expressed by the number of avalanche generation (dark count rate) per hour.

  In this embodiment, an avalanche photodiode 332 that operates in Geiger mode is used. C. Niclass, A. Rochas, PABesse, and E. Charbon, “Design and Characterization of a CMOS 3-D Image Sensor Based on Single Photon Avalanche Diodes”, IEEE Journal of Solid-State Circuits, vol.40, n. 9, Sep. 2005. In recent years, a technology to realize Geiger mode avalanche photodiodes using a standard CMOS process has been developed, which makes it possible to form a two-dimensional array of avalanche photodiodes at low cost. It was.

  In this embodiment, the TDC 336, the histogram circuit 337, and the signal processing circuit 338 included in each pixel 330 can all be mounted on the same LSI by a CMOS process. As shown in FIG. 3, clock signals CLK1 and CLK2 input to the two-dimensional light receiving element array mounted on the LSI are distributed to the TDC 336 and the signal processing circuit 338 of each pixel 330, respectively.

  Hereinafter, the operation of each pixel when light, that is, photons are incident on the avalanche photodiode will be described with reference to FIG. When photons enter the avalanche photodiode 332, an avalanche current flows, and the voltage at the terminal A increases. Due to the voltage rise, a pulse PLS is generated via the buffer 335 and input to the TDC 336. The TDC 336 converts the time from the input time point of the clock signal CLK1 to the input time point of the pulse PLS into a digital value and outputs the digital value to the histogram circuit 337. When the pulse PLS is not input, the TDC 336 outputs a predetermined maximum value.

  The histogram circuit 337 increments the memory value of the address corresponding to the output value of the TDC 336 by 1 at the timing of the clock signal CLK1. The histogram circuit 337 does not increment the memory value when the value of the TDC 336 is a value indicating that the pulse PLS has not been input. After a series of operations from the generation of the clock CLK1 to the increment of the histogram memory is repeated M times, the signal processing circuit 338 reads the value of the histogram memory at the timing of the clock CLK2, and corresponds to the address where the maximum value is stored. The distance is calculated and output from the time to light and the speed of light. The distance value calculated for each pixel is sequentially read out of the two-dimensional light receiving element array 33 through a reading circuit.

  As described above, since all the disturbance light cannot be removed by the interference filter 31, the light received by the avalanche photodiode 332 includes the irradiation light L1 from the laser diode 24 of the light projecting unit 20 and the disturbance light. . Hereinafter, it will be described with reference to FIG. 4 that TOF can be detected correctly even when disturbance light is included in the received light.

  The pulse PLS output from the avalanche photodiode 332 includes one that reacts to photons of the irradiation light L1 and one that reacts to photons of disturbance light. If it is assumed that the object O and the 3D camera 10 do not move relative to each other during the measurement, the light reception timing of the reflected light L2 by the irradiation light L1 is constant. Therefore, the detection timing of the pulse PLS is repeatedly measured many times to obtain the maximum frequency. By selecting the measured value, the TOF of the reflected light L2 can be obtained. When the histogram circuit 337 measures the detection timing of the repetitive pulse PLS with respect to many (M) times of pulse emission and creates a histogram, the measurement corresponding to the reflected light L2 forms a peak (maximum value) in the histogram. .

  On the other hand, the light reception timing of disturbance light such as sunlight is uncorrelated with the timing of the clock signal CLK1, which is the pulse emission timing of the irradiation light L1, and is therefore uniformly distributed on the histogram. By detecting the peak position of the histogram by the signal processing circuit 338, the influence of disturbance light can be removed and the correct TOF, that is, the distance can be detected. The histogram of FIG. 4 is an actual measurement example when the optical SN ratio is 0.01, and it can be seen that a peak can be correctly extracted even when the disturbance light component is large. In the two-dimensional light receiving element array 33, since the distance to the object O corresponding to each pixel 330 is different, the light reception timing of the reflected light L2 corresponding to the irradiation light L1 is different for each pixel 33. In this embodiment, since a histogram is created independently for each pixel 33 and a peak is extracted, a distribution of different distances for each pixel 33 can be obtained.

  In the present embodiment, the simplest example of detecting the peak position of the histogram has been shown, but various modifications can be made to the method of detecting the peak position. For example, the peak position can be detected by obtaining the maximum value after smoothing the bin values of the histogram. When each bin time interval is short, the relative fluctuation amount of each bin value increases, but the peak position can be detected robustly against the fluctuation by smoothing. After obtaining the peak position, the TOF can be obtained with higher accuracy by obtaining the position of the center of gravity in the vicinity of the peak position. This TOF detection is based on the fact that the frequency of light reception increases in the vicinity of the TOF on the histogram, and the TOF can also be detected by other histogram processing methods that take into account the peak shape.

  In the above description, it is assumed that the movement between the 3D camera 10 and the object O during the creation of the histogram is sufficiently small. On the other hand, in automobile applications such as driving support control and collision prevention system, if the measurement time becomes long, the influence of the movement between the 3D camera 10 and the object O cannot be ignored. For example, if the update rate of distance data is 15 times / second, the measurement time per time is 66 msec. In this case, when the relative speed between the 3D camera 10 and the object O is 100 km / h, the relative movement distance within the measurement time is 1.8 m. This means that a large error corresponding to the movement distance occurs in the measurement distance. Therefore, when there is a relative movement between the 3D camera 10 and the object O, the measurement time must be shortened.

  However, if the measurement time is shortened, there is a problem that the probability that a peak can be correctly detected from the histogram decreases. The average value of the number of photons detected within a predetermined time varies statistically, and the amount of variation is called shot noise. Shot noise follows a Poisson distribution, and its standard deviation is the square root of the number of detections. Even when the local maximum value is extracted from the histogram, it is affected by the shot noise, so that the measurement accuracy decreases as the number of photon detections decreases.

Here, the case where the bin with the highest frequency is extracted from the histogram is specifically considered. If the number of detected bins with the maximum number of detection is A, the amount of fluctuation is A ^1/2 which is the square root. For example, when A is 100, the fluctuation amount is 10 and the SN ratio is 10, and when A is 10,000, the fluctuation amount is 100 and the SN ratio is 100. Therefore, it can be seen that when the measurement time is shortened, the number of detected photons is decreased and the robustness against fluctuation is decreased.

  From the above, it is necessary to shorten the measurement time in order to reduce the influence of the movement between the 3D camera 10 and the object, but there is a trade-off relationship that the accuracy of peak extraction is reduced when the measurement time is shortened. In the present embodiment, a TOF is detected by creating a histogram with a minimum measurement time required to maintain a peak extraction system. In the present embodiment, the signal processing circuit 338 obtains the reliability of the histogram, and the histogram circuit 337 completes the creation of the histogram when the reliability reaches or exceeds the threshold value, thereby realizing a minimum measurement time.

  Next, it will be described that there is a problem in that an erroneous measurement distance is output when the maximum value is obtained by the above-described method in a situation where the histogram does not form a peak and measurement is impossible. The following cases can be considered as specific situations that cannot be measured. In other words, the situation where measurement is impossible is when the morning sun or the sun is directly incident, when operating in a high temperature environment and the dark count rate is high, when the reflected light is scattered and attenuated by rain fog, and the object is in the measurable area. Is not present. The former two are cases where noise increases, and the latter two are cases where the signal becomes small.

  The technique described in Japanese Patent Application Laid-Open No. 5-297140 detects a small amount of received light and does not handle it as measurement data. The technique described in Japanese Patent Application Laid-Open No. 7-167955 increases noise. In this case, the distance is not calculated. However, whether or not it is measurable is determined by the ratio of the relative magnitude of the signal and noise, that is, the signal-to-noise ratio, and the determination based on the signal and / or noise is not appropriate. Absent. In the present embodiment, whether or not measurement is possible is appropriately determined based on the reliability of the maximum value of the histogram. When the SN ratio of the measurement result is large, the reliability of the maximum value of the histogram becomes high.

  Hereinafter, a specific method for obtaining the reliability of the histogram in the present embodiment will be described with reference to FIGS. 5 to 7 are histograms of the number of bins n. In the case illustrated in FIG. 5, the signal processing circuit 338 first obtains the bin i having the maximum number of detections in the histogram created by the histogram circuit 337. In FIG. 5, the bin i indicated by diagonal lines has the maximum number of detections, and the number of detections is A. Next, the signal processing circuit 338 calculates the average detection number N of all bins except the bin i. Here, the signal processing circuit 338 may set the average of all bins to N when the number of bins is large.

  When the difference between A and N is large, the photon detection is concentrated on the time corresponding to the bin i, and it can be said that the reliability that the time is TOF is high. Therefore, by defining the reliability as A / N, an evaluation value that does not depend on the total number of detections can be obtained. The signal processing circuit 338 calculates the reliability A / N at a predetermined time interval during the histogram creation of the histogram circuit 337, and when the reliability A / N becomes equal to or higher than a predetermined threshold (first threshold). The histogram circuit 337 stops the histogram creation and obtains the TOF. In the present embodiment, this makes it possible to reduce the measurement time to the minimum necessary level, maintain the accuracy of peak extraction, and reduce the influence of the movement between the 3D camera 10 and the object O.

  In addition, the signal processing circuit 338 determines that a signal indicating that measurement cannot be performed, for example, a distance, when the reliability A / N is equal to or lower than a predetermined threshold (second threshold) after K measurements (K is an arbitrary natural number). A signal indicating zero is output. A value indicating that measurement is impossible when the readout circuit of the subsequent stage of the peripheral circuit 333 not shown in FIG. 3 reads the output of the signal processing circuit 338 every N measurements and the reliability A / N does not reach the threshold during that time. Zero is read. Thereby, it is possible to prevent an erroneous distance from being output due to a small SN ratio of the measurement signal. Thereby, it is possible to prevent an erroneous distance from being output due to a small SN ratio of the measurement signal.

Next, a definition example of reliability taking photon shot noise into consideration is shown. When the number of detected bins is A, the standard deviation of the fluctuation amount is A ^1/2 . Further, the fluctuation amount of N is {(N / (n-1)} ^1/2 . Therefore, the reliability can be determined by the following equation.
Reliability = (A−α · A ^1/2 ) / [N + β · {(N / (n−1)} ^1/2 ] (1)

  Here, α and β are constants and have a value of about 0.5 to 3. As described above, n is the total number of bins. With such a definition, when the number of detections is small, the reliability can be obtained correctly even if the histogram is sharpened at an erroneous position due to shot noise. For example, for simplicity, assuming that n = 32 and α = β = 1, the number of detections of bin 1 is 2, and the number of detections of other bins is 1, the number of detections is too small and the histogram The reliability is clearly low. In this case, if reliability = A / N, the reliability is as high as reliability = 2. However, when the reliability is calculated by the above equation (1), the reliability becomes a value of about 0.6, and it can be seen that the reliability is correct considering the number of detections. Note that the determination of the reliability can be performed only after detecting a certain number of detections.

  In the example of FIG. 5, the maximum number of detection bin i is compared with the average of all other bins. As shown in FIG. 6, the bin i can be compared with some other bins. For example, bin i and bin j can be compared with bin i being bin j, which is the detection number B having the second largest detection number. Further, the bin i can be compared with the average of the bin k, which is the detection number C, which is the third largest detection number, and the bin j, which is the second largest detection number. Conversely, the average value M can also be obtained from bins excluding bins i, j, and k of exceptional values as described above from all bins.

  Next, consider a case where the pulse time width of the pulsed light to be projected is longer than the time width of the bin. In such a case, a histogram shape as shown in FIG. 7 is typical. In such a case, considering the pulse shape, for example, the maximum value A is obtained from the average or weighted average of the hatched bins shown in FIG. 7, and the average value M is obtained from the bins excluding the hatched bins in FIG. be able to.

  It should be noted that the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

It is a block diagram which shows the structure of the 3D camera which concerns on embodiment. It is a figure which shows the structure of the two-dimensional light receiving element array which concerns on embodiment. It is a figure which shows the structure of the circuit of each pixel of a two-dimensional light receiving element array. It is a figure which shows the principle of TOF detection by the histogram process which concerns on embodiment. It is a figure which shows the peak sharpness of a histogram. It is a figure which shows the peak sharpness of a histogram. It is a figure which shows the peak sharpness of a histogram.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... 3D camera, 20 ... Light emission part, 21 ... Clock generation circuit, 22 ... Circuit board, 23 ... Drive circuit, 24 ... Laser diode, 25 ... Fresnel lens, 26 ... Diffusing plate, 30 ... Light-receiving part, 31 ... Interference Filter, 32 ... lens, 33 ... two-dimensional light receiving element array, 330 ... pixel, 331 ... light receiving unit, 332 ... avalanche photodiode, 333 ... peripheral circuit, 334 ... resistor, 335 ... buffer, 336 ... TDC, 337 ... histogram circuit 338... Signal processing circuit.

Claims (30)

A light projecting means for repeatedly irradiating an object with pulsed light;
A light receiving means for repeatedly receiving reflected pulsed light of the pulsed light emitted by the light projecting means from the object;
The time difference is measured repeatedly by measuring the time difference between the pulse light projecting time that is the time when the light projecting means irradiates the pulse light and the pulse light receiving time that is the time when the light receiving means receives the reflected pulse light. A histogram creation means for creating a histogram of
Distance calculating means for calculating a distance to the object based on the maximum value of the histogram created by the histogram creating means;
Reliability calculation means for calculating the reliability of the histogram created by the histogram creation means;
A histogram creation stop means for causing the histogram creation means to stop creating the histogram when the reliability of the histogram calculated by the reliability calculation means is equal to or greater than a threshold;
Equipped with a,
The reliability calculation means includes any one of a bin measurement number A indicating the maximum value in the histogram generated by the histogram generation means, all bins, and the remaining bins excluding the bin indicating the maximum value from all the bins. An optical distance measuring device that calculates the reliability as A / N for the average value N of the number of measurements . A light projecting means for repeatedly irradiating an object with pulsed light;
A light receiving means for repeatedly receiving reflected pulsed light of the pulsed light emitted by the light projecting means from the object;
The time difference is measured repeatedly by measuring the time difference between the pulse light projecting time that is the time when the light projecting means irradiates the pulse light and the pulse light receiving time that is the time when the light receiving means receives the reflected pulse light. A histogram creation means for creating a histogram of
Distance calculating means for calculating a distance to the object based on the maximum value of the histogram created by the histogram creating means;
Reliability calculation means for calculating the reliability of the histogram created by the histogram creation means;
When the reliability of the histogram calculated by the reliability calculation means is less than or equal to a threshold value, measurement inability detection means that the distance calculation means cannot calculate the distance;
Equipped with a,
The reliability calculation means includes any one of a bin measurement number A indicating the maximum value in the histogram generated by the histogram generation means, all bins, and the remaining bins excluding the bin indicating the maximum value from all the bins. An optical distance measuring device that calculates the reliability as A / N for the average value N of the number of measurements . A light projecting means for repeatedly irradiating an object with pulsed light;
A light receiving means for repeatedly receiving reflected pulsed light of the pulsed light emitted by the light projecting means from the object;
The time difference is measured repeatedly by measuring the time difference between the pulse light projecting time that is the time when the light projecting means irradiates the pulse light and the pulse light receiving time that is the time when the light receiving means receives the reflected pulse light. A histogram creation means for creating a histogram of
Distance calculating means for calculating a distance to the object based on the maximum value of the histogram created by the histogram creating means;
Reliability calculation means for calculating the reliability of the histogram created by the histogram creation means;
A histogram creation stop means for causing the histogram creation means to stop creating the histogram when the reliability of the histogram calculated by the reliability calculation means is equal to or higher than a first threshold;
A non-measurable detection means that makes it impossible to calculate the distance by the distance calculation means when the reliability of the histogram calculated by the reliability calculation means is less than or equal to a second threshold;
Equipped with a,
The reliability calculation means includes any one of a bin measurement number A indicating the maximum value in the histogram generated by the histogram generation means, all bins, and the remaining bins excluding the bin indicating the maximum value from all the bins. An optical distance measuring device that calculates the reliability as A / N for the average value N of the number of measurements . A light projecting means for repeatedly irradiating an object with pulsed light;
A light receiving means for repeatedly receiving reflected pulsed light of the pulsed light emitted by the light projecting means from the object;
The time difference is measured repeatedly by measuring the time difference between the pulse light projecting time that is the time when the light projecting means irradiates the pulse light and the pulse light receiving time that is the time when the light receiving means receives the reflected pulse light. A histogram creation means for creating a histogram of
Distance calculating means for calculating a distance to the object based on the maximum value of the histogram created by the histogram creating means;
Reliability calculation means for calculating the reliability of the histogram created by the histogram creation means;
A histogram creation stop means for causing the histogram creation means to stop creating the histogram when the reliability of the histogram calculated by the reliability calculation means is equal to or greater than a threshold;
Equipped with a,
The reliability calculation means includes any one of a bin measurement number A indicating the maximum value in the histogram generated by the histogram generation means, all bins, and the remaining bins excluding the bin indicating the maximum value from all the bins. For the average value N of the number of measurements, 0.5 ≦ α ≦ 3, 0.5 ≦ β ≦ 3, and the number n of all the bins, the reliability is expressed as reliability = (A−α · A ^An optical distance measuring device which calculates as ^1/2 ) / [N + β · {(N / (n−1)} ^1/2 ] . A light projecting means for repeatedly irradiating an object with pulsed light;
A light receiving means for repeatedly receiving reflected pulsed light of the pulsed light emitted by the light projecting means from the object;
The time difference is measured repeatedly by measuring the time difference between the pulse light projecting time that is the time when the light projecting means irradiates the pulse light and the pulse light receiving time that is the time when the light receiving means receives the reflected pulse light. A histogram creation means for creating a histogram of
Distance calculating means for calculating a distance to the object based on the maximum value of the histogram created by the histogram creating means;
Reliability calculation means for calculating the reliability of the histogram created by the histogram creation means;
When the reliability of the histogram calculated by the reliability calculation means is less than or equal to a threshold value, measurement inability detection means that the distance calculation means cannot calculate the distance;
Equipped with a,
The reliability calculation means includes any one of a bin measurement number A indicating the maximum value in the histogram generated by the histogram generation means, all bins, and the remaining bins excluding the bin indicating the maximum value from all the bins. For the average value N of the number of measurements, 0.5 ≦ α ≦ 3, 0.5 ≦ β ≦ 3, and the number n of all the bins, the reliability is expressed as reliability = (A−α · A ^An optical distance measuring device which calculates as ^1/2 ) / [N + β · {(N / (n−1)} ^1/2 ] . A light projecting means for repeatedly irradiating an object with pulsed light;
A light receiving means for repeatedly receiving reflected pulsed light of the pulsed light emitted by the light projecting means from the object;
The time difference is measured repeatedly by measuring the time difference between the pulse light projecting time that is the time when the light projecting means irradiates the pulse light and the pulse light receiving time that is the time when the light receiving means receives the reflected pulse light. A histogram creation means for creating a histogram of
Distance calculating means for calculating a distance to the object based on the maximum value of the histogram created by the histogram creating means;
Reliability calculation means for calculating the reliability of the histogram created by the histogram creation means;
A histogram creation stop means for causing the histogram creation means to stop creating the histogram when the reliability of the histogram calculated by the reliability calculation means is equal to or higher than a first threshold;
A non-measurable detection means that makes it impossible to calculate the distance by the distance calculation means when the reliability of the histogram calculated by the reliability calculation means is less than or equal to a second threshold;
Equipped with a,
The reliability calculation means includes any one of a bin measurement number A indicating the maximum value in the histogram generated by the histogram generation means, all bins, and the remaining bins excluding the bin indicating the maximum value from all the bins. For the average value N of the number of measurements, 0.5 ≦ α ≦ 3, 0.5 ≦ β ≦ 3, and the number n of all the bins, the reliability is expressed as reliability = (A−α · A ^An optical distance measuring device which calculates as ^1/2 ) / [N + β · {(N / (n−1)} ^1/2 ] . A light projecting means for repeatedly irradiating an object with pulsed light;
A light receiving means for repeatedly receiving reflected pulsed light of the pulsed light emitted by the light projecting means from the object;
The time difference is measured repeatedly by measuring the time difference between the pulse light projecting time that is the time when the light projecting means irradiates the pulse light and the pulse light receiving time that is the time when the light receiving means receives the reflected pulse light. A histogram creation means for creating a histogram of
Distance calculating means for calculating a distance to the object based on the maximum value of the histogram created by the histogram creating means;
Reliability calculation means for calculating the reliability of the histogram created by the histogram creation means;
A histogram creation stop means for causing the histogram creation means to stop creating the histogram when the reliability of the histogram calculated by the reliability calculation means is equal to or greater than a threshold;
Equipped with a,
The reliability calculation means includes a measurement number A of bins indicating the maximum value in the histogram generated by the histogram generation means, and a part of the remaining bins excluding the bin indicating the maximum value from all bins. An optical distance measuring device that calculates the reliability as A / N with respect to the average value N of the number of measurements . A light projecting means for repeatedly irradiating an object with pulsed light;
A light receiving means for repeatedly receiving reflected pulsed light of the pulsed light emitted by the light projecting means from the object;
The time difference is measured repeatedly by measuring the time difference between the pulse light projecting time that is the time when the light projecting means irradiates the pulse light and the pulse light receiving time that is the time when the light receiving means receives the reflected pulse light. A histogram creation means for creating a histogram of
Distance calculating means for calculating a distance to the object based on the maximum value of the histogram created by the histogram creating means;
Reliability calculation means for calculating the reliability of the histogram created by the histogram creation means;
When the reliability of the histogram calculated by the reliability calculation means is less than or equal to a threshold value, measurement inability detection means that the distance calculation means cannot calculate the distance;
Equipped with a,
The reliability calculation means includes a measurement number A of bins indicating the maximum value in the histogram generated by the histogram generation means, and a part of the remaining bins excluding the bin indicating the maximum value from all bins. An optical distance measuring device that calculates the reliability as A / N with respect to the average value N of the number of measurements . A light projecting means for repeatedly irradiating an object with pulsed light;
A light receiving means for repeatedly receiving reflected pulsed light of the pulsed light emitted by the light projecting means from the object;
The time difference is measured repeatedly by measuring the time difference between the pulse light projecting time that is the time when the light projecting means irradiates the pulse light and the pulse light receiving time that is the time when the light receiving means receives the reflected pulse light. A histogram creation means for creating a histogram of
Distance calculating means for calculating a distance to the object based on the maximum value of the histogram created by the histogram creating means;
Reliability calculation means for calculating the reliability of the histogram created by the histogram creation means;
A histogram creation stop means for causing the histogram creation means to stop creating the histogram when the reliability of the histogram calculated by the reliability calculation means is equal to or higher than a first threshold;
A non-measurable detection means that makes it impossible to calculate the distance by the distance calculation means when the reliability of the histogram calculated by the reliability calculation means is less than or equal to a second threshold;
Equipped with a,
The reliability calculation means includes a measurement number A of bins indicating the maximum value in the histogram generated by the histogram generation means, and a part of the remaining bins excluding the bin indicating the maximum value from all bins. An optical distance measuring device that calculates the reliability as A / N with respect to the average value N of the number of measurements .   The reliability calculation means includes the number A of measured bins indicating the maximum value in the histogram created by the histogram creating means, and the number of measurements in the remaining bins excluding the bin indicating the maximum value from all the bins. The optical system according to any one of claims 7 to 9, wherein the reliability is calculated as A / N with respect to an average value N of bins up to the top n-th place (n is an arbitrary integer). Distance measuring device.   The reliability calculation means includes the number A of measured bins indicating the maximum value in the histogram created by the histogram creating means, and the number of measurements in the remaining bins excluding the bin indicating the maximum value from all the bins. 10. The method according to claim 7, wherein the reliability is calculated as A / N with respect to an average value N of bins excluding bins with a size of the top n (n is an arbitrary integer). The optical distance measuring device described. Bin indicating the maximum value of a plurality of bins adjacent, the measurement average number of the plurality of bins, and measuring the number A bottle showing the maximum value, any one of claims 1 to 11 The optical distance measuring device described in 1. The optical distance measuring device according to claim 12, wherein the reliability is calculated as A / N with respect to an average value N of the number of measurements of the remaining bins excluding a plurality of bins indicating the maximum value. The optical measurement according to any one of claims 1 to 13 , wherein the reliability calculated by the reliability calculation means is a value representing a sharpness of a maximum value of the histogram created by the histogram creation means. Distance device. The reliability calculation means calculates the reliability larger as the number of measurement of the time difference in the histogram created by the histogram creation means is larger, and calculates the reliability smaller as the measurement number of the time difference is smaller. Item 15. The optical distance measuring device according to any one of Items 1 to 14 . A step of repeatedly irradiating an object with pulsed light;
Repeatedly receiving reflected pulsed light of the pulsed light emitted from the object;
Repeatedly measuring a time difference between a pulsed light projecting time that is the time of irradiation of the pulsed light and a pulsed light receiving time that is the time of receiving the reflected pulsed light, and creating a histogram of the time difference;
Calculating the distance to the object based on the maximum value of the created histogram;
Calculating the reliability of the created histogram;
Stopping the creation of the histogram when the calculated reliability of the histogram is equal to or greater than a threshold;
Equipped with a,
With respect to the average value N of the number of measurements of any one of the bins indicating the local maximum value in the created histogram, all bins and the remaining bins excluding the bin indicating the local maximum from the bins, An optical distance measuring method for calculating the reliability as A / N. A step of repeatedly irradiating an object with pulsed light;
Repeatedly receiving reflected pulsed light of the pulsed light emitted from the object;
Repeatedly measuring a time difference between a pulsed light projecting time that is the time of irradiation of the pulsed light and a pulsed light receiving time that is the time of receiving the reflected pulsed light, and creating a histogram of the time difference;
Calculating the distance to the object based on the maximum value of the created histogram;
Calculating the reliability of the created histogram;
A step of disabling the calculation of the distance when the calculated reliability of the histogram is equal to or less than a threshold;
Equipped with a,
With respect to the average value N of the number of measurements of any one of the bins indicating the local maximum value in the created histogram, all bins and the remaining bins excluding the bin indicating the local maximum from the bins, An optical distance measuring method for calculating the reliability as A / N. A step of repeatedly irradiating an object with pulsed light;
Repeatedly receiving reflected pulsed light of the pulsed light emitted from the object;
Repeatedly measuring a time difference between a pulsed light projecting time that is the time of irradiation of the pulsed light and a pulsed light receiving time that is the time of receiving the reflected pulsed light, and creating a histogram of the time difference;
Calculating the distance to the object based on the maximum value of the created histogram;
Calculating the reliability of the created histogram;
Stopping the creation of the histogram when the calculated reliability of the histogram is greater than or equal to a first threshold;
A step of disabling the calculation of the distance when the calculated reliability of the histogram is equal to or less than a second threshold;
Equipped with a,
With respect to the average value N of the number of measurements of any one of the bins indicating the local maximum value in the created histogram, all bins and the remaining bins excluding the bin indicating the local maximum from the bins, An optical distance measuring method for calculating the reliability as A / N. A step of repeatedly irradiating an object with pulsed light;
Repeatedly receiving reflected pulsed light of the pulsed light emitted from the object;
Repeatedly measuring a time difference between a pulsed light projecting time that is the time of irradiation of the pulsed light and a pulsed light receiving time that is the time of receiving the reflected pulsed light, and creating a histogram of the time difference;
Calculating the distance to the object based on the maximum value of the created histogram;
Calculating the reliability of the created histogram;
Stopping the creation of the histogram when the calculated reliability of the histogram is equal to or greater than a threshold;
Equipped with a,
The measured number A of bins indicating the maximum value in the generated histogram, the average value N of the measured numbers of any bin and the remaining bins excluding the bins indicating the maximum value from all the bins, 0.5 ≦ α ≦ 3, 0.5 ≦ β ≦ 3, and for the number n of all the bins, the reliability is expressed as reliability = (A−α · A ^1/2 ) / [N + β · {(N / (N-1)} ^1/2 ] is calculated as an optical distance measuring method. A step of repeatedly irradiating an object with pulsed light;
Repeatedly receiving reflected pulsed light of the pulsed light emitted from the object;
Repeatedly measuring a time difference between a pulsed light projecting time that is the time of irradiation of the pulsed light and a pulsed light receiving time that is the time of receiving the reflected pulsed light, and creating a histogram of the time difference;
Calculating the distance to the object based on the maximum value of the created histogram;
Calculating the reliability of the created histogram;
A step of disabling the calculation of the distance when the calculated reliability of the histogram is equal to or less than a threshold;
Equipped with a,
The measured number A of bins indicating the maximum value in the generated histogram, the average value N of the measured numbers of any bin and the remaining bins excluding the bins indicating the maximum value from all the bins, 0.5 ≦ α ≦ 3, 0.5 ≦ β ≦ 3, and for the number n of all the bins, the reliability is expressed as reliability = (A−α · A ^1/2 ) / [N + β · {(N / (N-1)} ^1/2 ] is calculated as an optical distance measuring method. A step of repeatedly irradiating an object with pulsed light;
Repeatedly receiving reflected pulsed light of the pulsed light emitted from the object;
Repeatedly measuring a time difference between a pulsed light projecting time that is the time of irradiation of the pulsed light and a pulsed light receiving time that is the time of receiving the reflected pulsed light, and creating a histogram of the time difference;
Calculating the distance to the object based on the maximum value of the created histogram;
Calculating the reliability of the created histogram;
Stopping the creation of the histogram when the calculated reliability of the histogram is greater than or equal to a first threshold;
A step of disabling the calculation of the distance when the calculated reliability of the histogram is equal to or less than a second threshold;
Equipped with a,
The measured number A of bins indicating the maximum value in the generated histogram, the average value N of the measured numbers of any bin and the remaining bins excluding the bins indicating the maximum value from all the bins, 0.5 ≦ α ≦ 3, 0.5 ≦ β ≦ 3, and for the number n of all the bins, the reliability is expressed as reliability = (A−α · A ^1/2 ) / [N + β · {(N / (N-1)} ^1/2 ] is calculated as an optical distance measuring method. A step of repeatedly irradiating an object with pulsed light;
Repeatedly receiving reflected pulsed light of the pulsed light emitted from the object;
Repeatedly measuring a time difference between a pulsed light projecting time that is the time of irradiation of the pulsed light and a pulsed light receiving time that is the time of receiving the reflected pulsed light, and creating a histogram of the time difference;
Calculating the distance to the object based on the maximum value of the created histogram;
Calculating the reliability of the created histogram;
Stopping the creation of the histogram when the calculated reliability of the histogram is equal to or greater than a threshold;
Equipped with a,
For the measurement number A of bins indicating the maximum value in the created histogram, the average value N of the measurement numbers of some of the remaining bins excluding the bins indicating the maximum value from all bins, An optical distance measuring method for calculating reliability as A / N. A step of repeatedly irradiating an object with pulsed light;
Repeatedly receiving reflected pulsed light of the pulsed light emitted from the object;
Repeatedly measuring a time difference between a pulsed light projecting time that is the time of irradiation of the pulsed light and a pulsed light receiving time that is the time of receiving the reflected pulsed light, and creating a histogram of the time difference;
Calculating the distance to the object based on the maximum value of the created histogram;
Calculating the reliability of the created histogram;
A step of disabling the calculation of the distance when the calculated reliability of the histogram is equal to or less than a threshold;
Equipped with a,
For the measurement number A of bins indicating the maximum value in the created histogram, the average value N of the measurement numbers of some of the remaining bins excluding the bins indicating the maximum value from all bins, An optical distance measuring method for calculating reliability as A / N. A step of repeatedly irradiating an object with pulsed light;
Repeatedly receiving reflected pulsed light of the pulsed light emitted from the object;
Repeatedly measuring a time difference between a pulsed light projecting time that is the time of irradiation of the pulsed light and a pulsed light receiving time that is the time of receiving the reflected pulsed light, and creating a histogram of the time difference;
Calculating the distance to the object based on the maximum value of the created histogram;
Calculating the reliability of the created histogram;
Stopping the creation of the histogram when the calculated reliability of the histogram is greater than or equal to a first threshold;
A step of disabling the calculation of the distance when the calculated reliability of the histogram is equal to or less than a second threshold;
Equipped with a,
For the measurement number A of bins indicating the maximum value in the created histogram, the average value N of the measurement numbers of some of the remaining bins excluding the bins indicating the maximum value from all bins, An optical distance measuring method for calculating reliability as A / N.   The number A of bins indicating the maximum value in the created histogram, and the average value of bins where the size of the number of the remaining bins excluding the bins indicating the maximum value from all the bins is the top n The optical ranging method according to any one of claims 22 to 24, wherein the reliability is calculated as A / N with respect to N (n is an arbitrary integer).   The number A of bins indicating the maximum value in the created histogram, and the bins where the number of measurement numbers in the remaining bins excluding the bins indicating the maximum value from all the bins are excluded to the top nth. The optical distance measuring method according to any one of claims 22 to 24, wherein the reliability is calculated as A / N with respect to an average value N of bins (n is an arbitrary integer). 27. The bin according to any one of claims 16 to 26 , wherein the bin indicating the maximum value includes a plurality of adjacent bins, and an average value of the number of measurements of the plurality of bins is defined as a measurement number A of the bin indicating the maximum value. The optical distance measuring method described in 1. 28. The optical distance measuring method according to claim 27, wherein the reliability is calculated as A / N with respect to an average value N of the number of measurements of the remaining bins excluding a plurality of bins indicating the maximum value. The optical distance measuring method according to any one of claims 16 to 28 , wherein the reliability calculated is a value representing a sharpness of a maximum value of the created histogram. 30. The reliability according to any one of claims 16 to 29 , wherein the greater the number of measurements of the time difference in the created histogram, the greater the reliability, and the smaller the number of measurements of the time difference, the smaller the reliability. Optical ranging method.

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