Optical distance measuring device and optical distance measuring method

Abstract

Provided is an optical distance measurement device that makes it possible to appropriately correct a calculated distance while using a photon-counting light reception element and without increasing circuit size or determining a background light amount. A TOF optical distance measurement device 200 comprises a plurality of photon-counting light reception elements 3, measures a time of flight on the basis of the sum of the voltage pulses output by the light reception elements, and calculates the distance to an object on the basis of the time of flight. The TOF optical distance measurement device 200 generates a histogram indicating the frequencies at which times of flight calculated by a time-of-flight measurement circuit when measurement light is repeatedly output at a prescribed period are distributed in each time-axis area obtained by dividing same into a plurality of areas at prescribed time intervals, calculates a representative time-of-flight value for the object from the times of flight distributed in an area reaching a prescribed histogram threshold for the histogram frequency, and corrects the representative time-of-flight value on the basis of a frequency-to-error characteristic obtained in advance by the histogram generation circuit with varied reflection light intensity.

Description

[Technical Field]

[0001] The present invention relates to an optical distance measuring device and an optical distance measuring method that include a photon counting type light receiving element. [Background technology]

[0002] Patent document 1 discloses an optical distance measuring device that measures distance based on the difference between the time when irradiated light is projected and the time when reflected light is received, and includes a light source that projects pulsed light, a measurement light receiving means with variable sensitivity and a photon count type measurement light receiving element that receives light from an object, a scanning means that scans the light projection direction and the light receiving direction, a reference light receiving means that includes a reference light receiving element that receives light other than the projected light from the area that the measurement light receiving means will next measure using the scanning means, and a control means that controls the sensitivity of the measurement light receiving means according to the amount of light received by the reference light receiving means.

[0003] Patent Document 2 discloses a light source that irradiates laser light, a light receiving unit that includes a plurality of photon count type light receiving elements, a histogram generating unit that generates a histogram showing the relationship between the elapsed time and an integrated value obtained by integrating the response frequency of each of the plurality of light receiving elements for each consecutive predetermined time period during a period that includes a state in which the laser light is not being irradiated by the light source and a state in which the laser light is being irradiated, and a light receiving unit that estimates the amount of light received by the light receiving unit when the laser light is not being irradiated as a background light amount based on the response frequency of the histogram corresponding to the state in which the laser light is not being irradiated, and An optical measurement device is disclosed that includes: a light intensity estimation unit that estimates the amount of light received by subtracting the background light intensity from the amount of light received, which is estimated based on a response frequency corresponding to a state in which laser light is irradiated; and a distance estimation unit that, when an output signal becomes unstable due to characteristics of at least a part of the light receiving element and the histogram generation unit, derives a tentative distance to an object based on the time corresponding to the peak of the reflected light intensity estimated by the light intensity estimation unit in the histogram, and derives an offset amount due to the background light intensity estimated by the light intensity estimation unit and the unstable output signal corresponding to the reflected light intensity, and estimates the distance to the object based on the tentative distance and the offset amount. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-81254 [Patent Document 2] Japanese Patent Application Publication No. 2018-91760 Summary of the Invention [Problem to be solved by the invention]

[0005] The optical distance measuring device disclosed in Patent Document 1 aims to appropriately widen the dynamic range of brightness of the photodetector, but in addition to the photon-counting type measurement light-receiving element, it is necessary to further include a photon-counting type reference light-receiving element as a reference light-receiving means, which increases the number of components and the circuit size, driving up costs and limiting the miniaturization of the circuit.

[0006] The optical measuring device disclosed in Patent Document 2 needs to determine the amount of background light, and since the peak value of the amount of reflected light itself varies depending on the magnitude of the received light signal, further correction is required to accurately determine the distance.

[0007] An object of the present invention is to provide an optical distance measuring device and an optical distance measuring method that use a photon counting type light receiving element but do not increase the circuit size and can appropriately correct the calculated distance without calculating the amount of background light. [Means for solving the problem]

[0008] In order to achieve the above object, a first characteristic configuration of an optical distance measuring device according to the present invention comprises a light emitting element that outputs pulsed measurement light, a plurality of photon count type light receiving elements that detect reflected light from an object in response to the measurement light, an adding circuit that adds up voltage pulses output from each light receiving element, a time-of-flight measurement circuit that calculates the time from the point in time when the measurement light is output until the added value of the adding circuit reaches a predetermined addition threshold as the time-of-flight, a histogram generation circuit that generates a histogram showing the frequency of the time-of-flight calculated by the time-of-flight measurement circuit when the measurement light is repeatedly output at a predetermined period, distributed in each of a plurality of regions on a time axis divided into a plurality of regions at predetermined time intervals, and a histogram generation circuit that calculates the frequency of the time-of-flight calculated by the time-of-flight measurement circuit when the measurement light is repeatedly output at a predetermined period from the time-of-flight distributed in the region where the frequency reaches a predetermined histogram threshold based on the histogram, and a representative value calculation circuit that calculates a representative value of the time of flight relative to an object; and a distance calculation circuit that calculates a distance to the object based on the representative value of the time of flight calculated by the representative value calculation circuit, wherein the distance calculation circuit calculates an error correction value based on a power-error characteristic determined by an error obtained by the difference between the power and the actual distance obtained by the histogram generation circuit when the intensity of the reflected light is varied in advance, or the difference between the actual flight time and the representative value of the time of flight, and includes an error correction circuit that corrects the distance or the representative value of the time of flight with the error correction value, and the error correction circuit corrects the distance or the representative value of the time of flight with the error correction value, and It is determined by the error obtained by the difference between the time width and the actual distance and the distance, or the difference between the actual flight time and the representative value of the flight time. The error correction value is calculated based on the time width-error characteristic, and the representative value of the distance or the flight time is corrected with the error correction value.

[0009] Reflected light from a pulsed measurement light emitted from a light-emitting element toward an object is detected by multiple photon-counting light-receiving elements, and the voltage pulses output from each light-receiving element are added by an adder circuit. A time-of-flight measurement circuit calculates the time of flight from the time of emission of the measurement light to the time when the added value reaches a predetermined threshold value. A histogram generation circuit generates a histogram showing the frequency of the time of flight distributed in each region on a time axis divided into multiple regions at predetermined time intervals based on the time of flight calculated by the time-of-flight measurement circuit for the measurement light repeatedly output at a predetermined period. A representative value calculation circuit calculates a representative value of the time of flight to the object from the time of flight distributed in the region where the frequency reaches a predetermined histogram threshold, and a distance calculation circuit calculates the distance to the object based on the representative value of the time of flight. An error correction circuit included in the distance calculation circuit corrects the distance or the representative value of the time of flight with an error correction value. The error correction circuit calculates an error correction value based on the frequency-error characteristics determined by the frequency obtained by the histogram generation circuit when the intensity of reflected light is varied in advance, and the error obtained from the difference between the actual distance and the distance, or the difference between the actual flight time and the representative value of the flight time, and corrects the distance or the representative value of the flight time with the error correction value.Even though a photon-counting type light receiving element is used, it is possible to appropriately correct the calculated distance without increasing the circuit size and without calculating the amount of background light. Here, the frequency-error characteristic saturates when the frequency exceeds a certain value, and after saturation the error characteristic becomes unclear, making appropriate correction difficult. In such cases, appropriate correction becomes possible by utilizing the time width-error characteristic based on the time width, which is the period during which the sum of the adder circuit continues to be equal to or greater than a predetermined sum threshold.

[0010] The second characteristic configuration is, in addition to the first characteristic configuration described above, that the power-error characteristic is defined based on an intensity-power characteristic that indicates the correlation between an index related to the intensity of the reflected light and the power obtained by the histogram generation circuit when the measurement light is repeatedly output at a predetermined period in advance, and an intensity-error characteristic that indicates the correlation between an index related to the intensity of the reflected light and the error.

[0011] When the measurement light is repeatedly output at a predetermined cycle and the intensity of the reflected light is varied, an intensity-frequency characteristic that indicates the correlation between an index related to the intensity of the reflected light and the frequency obtained by the histogram generation circuit, and an intensity-error characteristic that indicates the correlation between an index related to the intensity of the reflected light detected by the light receiving element and the error are calculated, and the frequency-error characteristic is obtained by combining both characteristics based on the intensity of the reflected light.

[0012] The third characteristic configuration is that, in addition to the second characteristic configuration described above, the power-error characteristic exhibits a monotonically decreasing characteristic in which the error decreases as the power increases.

[0013] The intensity-power characteristic shows a monotonically increasing characteristic in which the power increases as the intensity of the reflected light increases up to a certain value. The intensity-error characteristic shows a monotonically decreasing characteristic in which the delay time shortens as the intensity of the reflected light increases. When these two characteristics are combined based on the intensity of the reflected light, a monotonically decreasing characteristic is obtained in which the error decreases as the power increases.

[0014] The fourth characteristic configuration of the same is that, in addition to any one of the first to third characteristic configurations described above, the time width-error characteristic is a characteristic that is defined based on the intensity-error characteristic that indicates a correlation between the index related to the intensity of the reflected light and the error when the measurement light is repeatedly output in advance at a predetermined period, and the intensity-time width characteristic that indicates a correlation between the index related to the intensity of the reflected light and the time width at which the added value of the adder circuit is equal to or greater than the addition threshold value.

[0015] The time width-error characteristic is obtained by repeatedly outputting measurement light at a predetermined cycle and varying the intensity of the reflected light, and then calculating the intensity-error characteristic, which shows the correlation between the intensity of the reflected light and the error, and the intensity-time width characteristic, which shows the correlation between the intensity of the reflected light and the time width at which the added value of the adding circuit becomes equal to or greater than the predetermined addition threshold, and combining the two characteristics based on the intensity of the reflected light.

[0016] The fifth characteristic configuration is that, in addition to the fourth characteristic configuration described above, the time width is a value obtained by dividing the sum of the time widths obtained in the region reaching a predetermined histogram threshold by the histogram generation circuit, by the sum of the frequencies in the region.

[0017] The duration of the intensity-duration characteristics can be smoothed by dividing the sum of the durations obtained in the region up to a predetermined histogram threshold by the sum of the frequencies in that region in the histogram generation circuit. The duration here can be the average value of the histogram distribution.

[0018] A sixth characteristic configuration of the same is that, in addition to any one of the first to fifth characteristic configurations described above, the time width-error characteristic exhibits a monotonically increasing characteristic in which the error increases as the time width increases.

[0019] The intensity-error characteristic exhibits a monotonically decreasing characteristic in which the error decreases as the intensity of the reflected light increases. The intensity-duration characteristic exhibits a characteristic in which the time width gradually increases from the low to the intermediate region of the reflected light intensity, and gradually shortens from the intermediate to the high region, with the time width being the largest in the intermediate region. When both characteristics are combined based on the reflected light intensity, the result is a monotonically decreasing characteristic in which the error decreases with increasing time width from the low to the intermediate region of the reflected light intensity, and a monotonically decreasing characteristic in which the delay time decreases with decreasing time width from the intermediate to the high region of the reflected light intensity. In other words, the result is a monotonically increasing characteristic in which the error increases with increasing time width. The received light intensity at which this time width is maximized corresponds to the received light intensity at which the frequency of the histogram saturates. Therefore, once the frequency saturates in the frequency-error characteristic, correction can be made based on the time width-error characteristic.

[0020] The seventh characteristic configuration is that, in addition to any one of the first to sixth characteristic configurations described above, the representative value calculation circuit calculates the representative value of the flight time for the object by dividing the total sum of the flight times distributed in the region where the frequency reaches the histogram threshold based on the histogram by the sum of each frequency in the region.

[0021] As an error absorption algorithm, it is preferable to divide the total sum of the flight times distributed in the area where the frequency reaches a predetermined histogram threshold by the sum of the frequencies in the corresponding area, and use this value as the representative value of the flight time for the object.

[0022] The eighth characteristic configuration of the same is that, in addition to any of the first to sixth characteristic configurations described above, the representative value calculation circuit calculates, based on the histogram, a value obtained by dividing the total sum of flight times distributed in the area where the frequency reaches the histogram threshold and in the area adjacent to that area by the sum of the frequencies in the corresponding area, as the representative value of the flight time for the object.

[0023] Although it is conceivable that the histogram frequency may exist across multiple regions on a time axis divided into multiple regions, even in such cases, a more accurate representative value can be obtained by dividing the total sum of the flight times distributed in the region where the frequency reaches a predetermined histogram threshold and in the region adjacent to that region by the sum of the frequencies in the corresponding region, thereby reducing the effect of chattering, which is the dispersion of frequencies between adjacent bins in the histogram.

[0024] The ninth characteristic configuration is that, in addition to any one of the first to sixth characteristic configurations described above, the representative value calculation circuit calculates, for a region where the total sum of the frequencies distributed in a plurality of adjacent regions based on the histogram reaches the histogram threshold, a value obtained by dividing the total sum of the flight times distributed in the plurality of regions by the sum of the frequencies in the corresponding region, as the representative value of the flight time for the object.

[0025] Even if the frequency in a single region does not reach a predetermined histogram threshold, if the total sum of the frequencies distributed across multiple regions reaches the histogram threshold, a more accurate representative value can be obtained by dividing the total sum of the times of flight distributed across multiple regions by the sum of the frequencies in the corresponding regions to obtain a representative value of the time of flight for the object. This can reduce the effect of chattering, which is the dispersion of frequencies across adjacent bins in the histogram.

[0026] a time-of-flight measurement circuit that calculates a time-of-flight from a time point from when the measurement light is output to when an added value of the adder circuit reaches a predetermined addition threshold; a histogram generation circuit that generates a histogram showing a frequency distribution of the time-of-flight calculated by the time-of-flight measurement circuit in each of a plurality of regions on a time axis divided into a plurality of regions at predetermined time intervals when the measurement light is repeatedly output at a predetermined period; a representative value calculation circuit that calculates a representative value of the time-of-flight to the object from the time-of-flight distributed in the region where the frequency reaches a predetermined histogram threshold based on the histogram; and a distance calculation circuit that calculates a distance to the object based on the representative value of the time-of-flight calculated by the representative value calculation circuit, wherein the distance calculation circuit calculates a difference between the frequency and an actual distance obtained by the histogram generation circuit when the intensity of the reflected light is changed in advance, or includes an error correction circuit that calculates an error correction value based on a frequency-error characteristic determined by an error obtained by the difference between the actual flight time and the representative value of the flight time, and corrects the distance or the representative value of the flight time with the error correction value, the flight time measurement circuit is configured to calculate, as the flight time, the flight time from the time of output of the measurement light to each time point when the output value of the addition circuit reaches a first addition threshold and a second addition threshold higher than the first addition threshold, the histogram generation circuit is configured to generate a histogram showing the frequency of the flight time calculated by the flight time measurement circuit distributed in each region on a time axis divided into a plurality of regions at predetermined time intervals when the measurement light is repeatedly output at a predetermined period, the representative value calculation circuit calculates, based on the histogram based on the first addition threshold, a value obtained by dividing all the added values ​​of the flight times corresponding to the first addition threshold by the frequency corresponding to the first addition threshold among the flight times distributed in the region where the frequency reaches the histogram threshold, as the representative value of the flight time for the object, the error correction circuitThe error correction value is calculated based on the frequency-error characteristic determined by the frequency obtained in the histogram based on the first addition threshold and the second addition threshold and the error obtained due to the difference between the actual distance and the distance, and the representative value of the distance or the flight time is corrected with the error correction value.

[0027] Since the time of flight is calculated up to each time point when a second threshold value higher than the first threshold value is reached, the histogram frequency increases when the threshold value used for correction is high, which is equivalent to increasing the dynamic range of the histogram, and a more appropriate representative value of the time of flight can be obtained.

[0028] The eleventh characteristic configuration is that, in addition to any one of the first to tenth characteristic configurations described above, the device is equipped with an optical deflection device that deflects the measurement light output from the light-emitting element in a predetermined direction, and / or an optical scanning device that scans the measurement light in a predetermined direction.

[0029] The measurement light can be deflected or scanned towards the space where the object needs to be detected.

[0030] A first characteristic configuration of the optical distance measuring method according to the present invention includes a reflected light detection step of detecting reflected light from an object in response to pulsed measurement light output from a light-emitting element using a plurality of photon-counting light-receiving elements; a time-of-flight measurement step of calculating the time from the point of output of the measurement light to the point of time when the sum of voltage pulses output from each light-receiving element reaches a predetermined sum threshold as a time-of-flight; a histogram generation step of generating a histogram showing the frequency of the time-of-flight calculated in the time-of-flight measurement step when the measurement light is repeatedly output at a predetermined period, distributed in each of a plurality of regions on a time axis divided into a plurality of regions at predetermined time intervals; and a histogram generation step of generating a histogram showing the frequency of the time-of-flight for the object from the time-of-flight distributed in the region where the frequency reaches a predetermined histogram threshold based on the histogram. The method includes a representative value calculation step of calculating a representative value, and a distance calculation step of calculating a distance to the object based on the representative value of the time of flight calculated in the representative value calculation step, wherein the distance calculation step includes an error correction step of calculating an error correction value based on the power-error characteristic determined by an error obtained by the difference between the power obtained in the histogram generation step and the actual distance or the difference between the actual flight time and the representative value of the time of flight when the intensity of the reflected light is changed in advance, and correcting the representative value of the distance or the time of flight with the error correction value, and the error correction step is a period after the power of the power-error characteristic is saturated, during which the added value becomes equal to or greater than the predetermined addition threshold when the intensity of the reflected light is changed in advance. It is determined by the error obtained by the difference between the time width and the actual distance and the distance, or the difference between the actual flight time and the representative value of the flight time. The error correction value is calculated based on the time width-error characteristic, and the representative value of the distance or the flight time is corrected with the error correction value.

[0031] The second characteristic configuration includes a reflected light detection step of detecting reflected light from an object in response to pulsed measurement light output from a light-emitting element using a plurality of photon-counting light-receiving elements; a time-of-flight measurement step of calculating, as a time-of-flight, a time from the output of the measurement light to the time when an added value of voltage pulses output from each light-receiving element reaches a predetermined addition threshold; a histogram generation step of generating a histogram showing the frequency of the time-of-flight calculated in the time-of-flight measurement step distributed in each of a plurality of regions on a time axis divided into a plurality of regions at predetermined time intervals when the measurement light is repeatedly output at a predetermined period; a representative value calculation step of calculating, based on the histogram, a representative value of the time-of-flight to the object from the time-of-flight distributed in the region where the frequency reaches a predetermined histogram threshold; and a distance calculation step of calculating a distance to the object based on the representative value of the time-of-flight calculated in the representative value calculation step, the representative value of the time of flight for the object is calculated by dividing the total sum of the times of flight calculated in the time of flight measurement step by the number of times of flight corresponding to the first addition threshold, based on the histogram based on the first addition threshold, by the number of times of flight corresponding to the first addition threshold; and the error correction step includes: calculating an error correction value based on a frequency-error characteristic determined by an error obtained by a difference from the representative value of the time of flight; and correcting the representative value of the distance or the time of flight with the error correction value; the time of flight measurement step includes calculating, as the time of flight, the time of flight from the time of output of the measurement light to each time point when the added value of the voltage pulse reaches a first addition threshold and a second addition threshold higher than the first addition threshold; the histogram generation step includes generating a histogram showing the number of times of flight calculated in the time of flight measurement step when the measurement light is repeatedly output at a predetermined cycle, the number of times of flight corresponding to the first addition threshold, based on the histogram based on the first addition threshold, distributed in the region where the number of times of flight reaches the histogram threshold; and the error correction step includes:The method includes a step of calculating the error correction value based on the frequency-error characteristic determined by the frequency obtained in the histogram based on the first addition threshold and the second addition threshold and the error obtained due to the difference between the actual distance and the distance, and correcting the representative value of the distance or the flight time with the error correction value. [Effects of the Invention]

[0032] As described above, according to the present invention, it is possible to provide an optical distance measuring device and an optical distance measuring method that use a photon-counting type light receiving element without increasing the circuit size and that can appropriately correct the calculated distance without calculating the amount of background light. [Brief explanation of the drawings]

[0033] [Figure 1] FIG. 1 is an explanatory diagram of the configuration of an optical distance measuring device according to the present invention. [Figure 2] FIG. 2 is an explanatory diagram of the light receiving circuit. [Figure 3] FIG. 3 is an explanatory diagram of the main circuit. [Figure 4] FIG. 4 is a diagram illustrating the operation of the histogram generating circuit and the representative value calculating circuit. [Figure 5] FIG. 5 is a diagram illustrating the operation of a histogram generating circuit and a representative value calculating circuit showing another embodiment. [Figure 6] FIG. 6(a) is an explanatory diagram of the waveform at the light receiving section, and FIG. 6(b) is an explanatory diagram showing the characteristics of the error, histogram frequency, and time width with respect to the intensity of received light. [Figure 7] FIG. 7 is an explanatory diagram of the power-error characteristic. [Figure 8] FIG. 8 is an explanatory diagram of the time width-error characteristic. [Figure 9] FIG. 9 is a flowchart showing the procedure of the TOF optical distance measuring method. DETAILED DESCRIPTION OF THE INVENTION

[0034] An optical distance measuring device and an optical distance measuring method according to the present invention will be described below. As shown in Figure 1, the optical distance measuring device 200 is a TOF type optical distance measuring device housed in a casing C with a translucent window, and includes a light-emitting element 2 that outputs pulsed measurement light, multiple photon-counting type light-receiving elements 3 that detect reflected light from an object in response to the measurement light, an optical scanning device 10 that scans the measurement light output from the light-emitting element 2 toward the measurement space and directs the reflected light diffused from the surface of an object present in the measurement space to the light-receiving element 3, and a control circuit 100 that drives the light-emitting element 2 while operating the optical scanning device 10, processes the signal corresponding to the reflected light detected by the light-receiving element 3, and calculates the distance to the object.

[0035] The optical scanning device 10 includes a deflection mirror 11 that deflects the measurement light output from the light-emitting element 2 toward the measurement space and guides the reflected light from the object to the light-receiving element 3, a motor 13 that rotates the deflection mirror 11 around a rotation axis P, and an encoder 14 that detects the rotation speed and rotation position of the motor 13.

[0036] The encoder 14 is composed of a disk 14A that rotates around a rotation axis P and has slits formed at predetermined intervals on its outer periphery, and a transmission-type photointerrupter 14B that detects light that passes through the slits formed in the disk 14A.

[0037] The deflection mirror 11 is fixed at an angle of 45 degrees relative to the rotation axis P, and the light receiving element 3, condenser lens 12, light emitting element 2, and projection lens 15 are arranged on the axis of the rotation axis P. The pulsed measurement light output from the light emitting element 2 passes through the projection lens 15 and is shaped into parallel light, then propagates along the light guide 16, is deflected at a right angle by the deflection mirror 11, is deflected and scanned as the deflection mirror 11 rotates, and is output to the monitoring area.

[0038] Light reflected from an object propagates through the space surrounding the light guide 16, enters the deflection mirror 11, is deflected in the axial direction of the rotation axis P, passes through the condenser lens 12, and enters the light-receiving element 3. Note that the above-described optical scanning device 10 is an example, and the configuration is not limited to this, as long as the optical scanning device can scan or deflect the measurement light output from the light-emitting element 2 in a predetermined direction and guide the reflected light to the light-receiving element 3. For example, a configuration including a polygon mirror that rotates at a constant speed, a deflection mirror that oscillates by a driving force such as a piezoelectric element, a configuration in which the entire optical system is rotationally driven, or a configuration in which the entire optical system including the light-emitting element 2 and the light-receiving element 3 is rotationally driven may be employed.

[0039] A laser diode that outputs a laser in the near-infrared region is used as the light-emitting element 2, and a silicon photomultiplier (SiPM) in which multiple single photon avalanche diodes (SPADs) are arranged in a matrix is ​​used as the light-receiving element 3.

[0040] When a photon is incident on an avalanche photodiode (APD), electron-hole pairs are generated. The electrons and holes are then accelerated by a high electric field, causing a series of avalanche-like collision ionizations, generating new electron-hole pairs.

[0041] Avalanche photodiodes (APDs) have two operating modes: linear mode, which operates at a reverse bias voltage below the breakdown voltage, and Geiger mode, which operates at a voltage above the breakdown voltage. In linear mode, the gain can be variably controlled by applying and controlling a reverse bias voltage below the breakdown voltage. The output current is roughly proportional to the amount of incident light, and the gain, or sensitivity, can be changed by adjusting the reverse bias voltage, making it useful for measuring the amount of incident light. In Geiger mode, applying a reverse bias voltage above the breakdown voltage can cause an avalanche phenomenon even with the incidence of a single photon, hence the name Single Photon Avalanche Diode (SPAD).

[0042] When using a photon-counting light-receiving element that outputs a voltage pulse in response to incident photons, such as a single-photon avalanche diode (SPAD), the effects of ambient light can be eliminated by repeatedly measuring the arrival time of the voltage pulse to create a histogram and extracting the maximum value.

[0043] A single photon avalanche diode (SPAD) can stop avalanche by reducing the applied voltage to its breakdown voltage. Reducing the applied voltage to stop the avalanche phenomenon is called quenching. The simplest quenching circuit is realized by connecting a quenching resistor in series with an avalanche photodiode (APD). When avalanche current occurs, the voltage across the quenching resistor terminals rises, causing the bias voltage of the avalanche photodiode (APD) to drop, and when it falls below the breakdown voltage, the avalanche current stops. After that, when the applied voltage to the single photon avalanche diode (SPAD) exceeds the breakdown voltage again, it becomes capable of detecting light, but until then, there is a dead period during which the single photon avalanche diode (SPAD) does not respond.

[0044] The control circuit 100 includes a motor drive circuit 20, a light emission control circuit 30, a light receiving circuit 40, a time-of-flight measurement circuit 50, a histogram generation circuit 60, a representative value calculation circuit 70, a distance calculation circuit 80, and an error correction circuit 90. It is preferable that the error correction circuit 90 is configured integrally with the distance calculation circuit 80, but in this embodiment, it may be configured so that its function is separated from that of the distance calculation circuit 80, as shown in Figures 1 and 3.

[0045] The motor drive circuit 20 drives the motor 13 so that the deflection mirror 11 rotates at a predetermined speed based on the pulse signal output from the encoder 14. As the motor 13, a brushless DC motor, a stepping motor, or the like is suitably used.

[0046] The light emission control circuit 30 controls the light emitting element 2 to output pulsed measurement light at a predetermined period based on the pulse signal output from the encoder 14. For example, if the rotation speed of the deflection mirror 11 (motor 13) is 1200 rpm (one rotation is 50 msec) and the resolution of the scanning angle of the measurement light, i.e., the unit scanning angle, is 0.25°, then outputting pulsed measurement light at 28.8 kHz will output measurement light in 0.25° increments. Note that the above numerical values ​​are merely examples, and the present invention is not limited to these numerical values. The same applies to the following numerical values.

[0047] In practice, as will be described later, pulsed light with a pulse width of 1 nsec is output 16 times at intervals of approximately 2 μsec during a unit scan angle of 0.25°, and based on the output from each light-receiving element 3 which detects the reflected light from each pulsed light, the time-of-flight measurement circuit 50 calculates the time-of-flight, i.e., the time from when the measurement light is output until it is reflected by an object and returns, and the histogram generation circuit 60 generates a histogram.

[0048] 1 and 2, a light-receiving circuit 40 includes a quenching resistor 41 that converts the current pulses output from each light-receiving element (single photon avalanche diode (SPAD)) 3 into a voltage; a pulse shaping circuit 42 that is a differential circuit including a capacitor that shapes the output of each light-receiving element 3 and quenching resistor 41 into a short pulse wave; an adder circuit 43 that adds the short pulse waves output from each pulse shaping circuit 42; and a comparator circuit 44 that outputs a pulse when the output of the adder circuit 43 reaches a predetermined addition threshold. The number of single photon avalanche diodes (SPADs) that make up a silicon photomultiplier (SiPM) is generally about 130 to 6,000 per pixel, and the quenching resistors 41 and pulse shaping circuits 42, as well as the adder circuits 43, in numbers corresponding to the number of elements, are integrated into an integrated circuit that makes up the silicon photomultiplier (SiPM).

[0049] The time-of-flight measurement circuit 50 is composed of a TDC circuit (TDC: Time-to-Digital Converter) that calculates the time of flight from the rising point of the light emission control signal output from the light emission control circuit 30 to the rising point of the output signal of the comparison circuit 44 (specifically, from the point of output of the measurement light to the point at which the added value of the addition circuit (SiPM output) reaches a predetermined addition threshold), that is, the time from the point of output of the measurement light to the point at which the reflected light is detected.

[0050] As shown in Figures 1 and 3, the histogram generation circuit 60 generates a histogram showing the frequency with which the time of flight calculated by the time-of-flight measurement circuit 50 is distributed in each region on a time axis divided into multiple regions at predetermined time intervals when the measurement light is repeatedly output at a predetermined period.

[0051] A representative value calculation circuit 70 calculates a representative value of the time of flight to the object from the time when the frequency is distributed in a region where the frequency reaches a predetermined histogram threshold based on the histogram. A distance calculation circuit 80 calculates the distance to the object based on the representative value of the time of flight calculated by the representative value calculation circuit 70. An error correction circuit 90 calculates an error correction value based on the frequency obtained by the histogram generation circuit 60 when the intensity of the reflected light is changed in advance, and on the frequency-error characteristics determined by the error obtained due to the difference between the actual distance and the distance, or the difference between the actual flight time and the representative value of the time of flight, and corrects the distance with the error correction value.

[0052] The actual distance is the value of the actual physical distance from the optical distance measuring device 200 to the object reflecting the reflected light, and the error is defined as the difference from the distance value calculated by the distance calculation circuit 80. Similarly, the actual flight time is the value of the actual physical flight time of light, and the error may be defined as the difference between the actual flight time and the representative value of the flight time calculated by the representative value calculation circuit 70. Based on the error characteristics of this error value, an error correction value corresponding to the unit of distance or time can be calculated.

[0053] The reflected light of the pulsed measurement light output from the light-emitting element 2 toward the object is detected by a plurality of photon-counting light-receiving elements 3, and the voltage pulses output from each light-receiving element 3 are added by an adder circuit 43. The time-of-flight measurement circuit 50 calculates the time of flight from the time the measurement light is output to the time the added value by the adder circuit 43 reaches a predetermined addition threshold.

[0054] As shown in FIG. 4, based on each time-of-flight (denoted as "TDC count value Tm,n in FIG. 4, where m is the light emission number and n is the edge detection number") calculated by the time-of-flight measurement circuit 50 for the measurement light that is repeatedly output (repeatedly output 16 times in this embodiment) at a predetermined cycle (approximately 500 kHz in this embodiment) within a unit scan angle (0.25° in this embodiment), a histogram is generated by the histogram generation circuit 60, which generates a histogram showing the frequency (maximum value is 16) of distribution of the time-of-flight corresponding to each region on the time axis divided into a plurality of regions (denoted as "bins" in FIG. 4) at predetermined time intervals (0.5 nsec in FIG. 4).

[0055] Specifically, the time of flight is the time from the time the measurement light is output to the time when the output of the addition circuit 43 (SiPM output) reaches a predetermined addition threshold, and the TDC edge histogram, i.e., the frequency Hn, is obtained by adding up the number of times of flight present in each region (bin), and the TDCSUM histogram, i.e., the total time of flight Sn, is obtained by adding up the times of flight present in each region (bin).

[0056] The representative value calculation circuit 70 calculates a representative value of the time-of-flight for the object (Sn / Hn) from the times-of-flight distributed in the region (bin) where the frequency Hn reaches a predetermined histogram threshold. The distance calculation circuit 80 then calculates the distance to the object based on the representative value of the time-of-flight calculated by the representative value calculation circuit 70. The error correction circuit 90 then corrects the distance. As will be described in detail later, the error correction circuit 90 calculates a known error, which is the difference between the actual distance to the object for each frequency obtained by the histogram generation circuit 60 when the intensity of the reflected light is varied in advance and the distance based on the representative value of the time-of-flight obtained by measurement. Therefore, the error correction value for the distance is calculated based on the frequency-error characteristics obtained thereby, and the distance calculated by the distance calculation circuit 80 is corrected.

[0057] The representative value calculation circuit 70 calculates the total flight time Sn, which is the sum of all flight times distributed in the region where the frequency Hn is a predetermined histogram threshold based on the histogram, divided by the value of the frequency Hn, as the representative value of the flight time for the object. In the example of Figure 4, Sn = T 1,1 +T 2,1 +T 3,1 +···+T *,* The representative value is obtained by dividing by the frequency Hn.

[0058] In the example of Figure 4, the representative value is calculated only for areas (bins) where the frequency reaches a predetermined histogram threshold, but the representative value calculation circuit 70 may also calculate a representative value of the flight time for an object by dividing the total sum of the flight times distributed in areas (bins) where the frequency reaches a predetermined histogram threshold and areas (bins) adjacent to the area based on the histogram by the sum of the frequencies in the corresponding areas (bins).

[0059] It is possible that the histogram frequency exists across multiple regions (bins) on a time axis divided into multiple regions (bins), but even in such cases, a more accurate representative value can be obtained by dividing the total sum of the flight times distributed in the region (bin) where the frequency reaches a predetermined histogram threshold based on the histogram and the regions (bins) adjacent to that region (bin) by the sum of the frequencies in the corresponding regions (bins) to calculate a representative value of the flight time for the object. In this case, the region adjacent to the region where the frequency reaches the predetermined histogram threshold may be the region with the higher frequency adjacent to either the left or right of the region with the highest frequency, or both adjacent regions may be used.

[0060] Furthermore, even if the frequency in a single region does not reach a predetermined histogram threshold, if the sum of all frequencies distributed across multiple regions reaches the histogram threshold, the sum of all the times of flight distributed across multiple regions may be divided by the sum of the frequencies in the corresponding regions to calculate a representative value of the time of flight for the object. As a result, a more accurate representative value can be obtained. An accurate representative value can be obtained by reducing the effect of chattering, which occurs when frequencies are dispersed across adjacent bins in the histogram.

[0061] Furthermore, as shown in Figure 5, the time-of-flight measurement circuit 50 may be configured to calculate the time from the time of output of the measurement light to each time point when the added value (SiPM output) of the addition circuit 43 reaches a predetermined addition threshold (first addition threshold), and the time to each time point when it reaches an addition threshold (second addition threshold) higher than the predetermined addition threshold, as the time-of-flight.

[0062] In this case, the histogram generation circuit 60 is configured to generate a histogram showing the frequency with which each time of flight calculated by the time-of-flight measurement circuit 50 when the measurement light is repeatedly output at a predetermined period is distributed in each area on a time axis divided into multiple areas (bins) at predetermined time intervals.

[0063] The representative value calculation circuit 70 may be configured to calculate a representative value of the flight time for the object by dividing the total sum of the flight times corresponding to a predetermined addition threshold among the flight times distributed in a region (bin) where the frequency reaches a predetermined histogram threshold based on the histogram by the frequency corresponding to the predetermined addition threshold.

[0064] Furthermore, the error correction circuit 90 may be configured to calculate an error correction value based on the frequency obtained from a histogram based on the first and second summation thresholds and the frequency-error characteristic determined by the error resulting from the difference between the actual distance and the distance, and to correct the representative value of the distance or time-of-flight using the error correction value. In this case, as shown in Figure 5, the maximum value (Max) of the edge detection number n indicated by the "TDC count value Tm,n" is 32, which has the same effect as expanding the dynamic range of the histogram and results in a more appropriate frequency-delay characteristic. Note that in this case, the frequency-delay characteristic must be calculated separately based on the frequency corresponding to the two summation thresholds.

[0065] The above-mentioned error correction circuit 90 will now be described. As explained in FIG. 2, the output of each single photon avalanche diode (SPAD) is shaped into a short pulse wave by a pulse shaping circuit 42 and added by an adding circuit 43. When the output reaches the adding threshold, a pulse signal is output from a comparison circuit 44, and the time of flight including the delay time is calculated by a time-of-flight measurement circuit 50.

[0066] FIG. 6(a) shows the response characteristics of a silicon photomultiplier (SiPM) that is the light receiving element 3 and each single photon avalanche diode (SPAD) that constitutes the silicon photomultiplier (SiPM) to a received light signal.

[0067] The upper graph in Figure 6(a) shows the relative relationship between the light-receiving signals of each single photon avalanche diode (SPAD) and the light-receiving threshold (binary threshold) of the pulse shaping circuit 42. The light-receiving thresholds of each pulse shaping circuit 42 configured as an integrated circuit are all set to the same value, but since the light detection of the single photon avalanche diode (SPAD) actually reacts with a certain probability, it is schematically represented as a fixed width, as shown in the figure as a gray band.

[0068] Therefore, for each of the following conditions, there is a certain degree of probabilistic variation in the output timing of each single photon avalanche diode (SPAD): "small" when the received light signal is weak and the received light intensity is about the same as the light receiving threshold; "medium" when the received light intensity is somewhat higher than the light receiving threshold; and "large" when the received light intensity is sufficiently higher than the light receiving threshold.

[0069] The graph in the middle of Figure 6(a) shows the output characteristics of several individual single photon avalanche diodes (SPADs). When the received light intensity is "low," the output timing of the pulse shaping circuits 42 varies, and some elements do not output. When the received light intensity is "medium," output is produced from all pulse shaping circuits 42, but there is variation in the output timing. When the received light intensity is "high," output is produced from all pulse shaping circuits 42 at approximately the same time.

[0070] The lower graph in Figure 6(a) shows the relationship between the output of the silicon photomultiplier (SiPM), i.e., the output of the adder circuit 43, and the summation threshold. When the output of the adder circuit 43 reaches the summation threshold, a pulse is output from the comparator circuit 44. However, due to variations in the rise characteristics of the received light signal and the response time of the single photon avalanche diode (SPAD), an error (delay time) occurs between the arrival time of the received light signal and the pulse rise time determined by the summation threshold. Therefore, to determine the time of flight with higher accuracy, a delay time correction process is required in which the delay time is subtracted from the time of flight / representative value of the time of flight calculated from the time from the departure point of the measurement light to the pulse rise time, or a process is required in which the error corresponding to the delay time is corrected for the distance corresponding to the representative value of the time of flight.

[0071] The error (delay time) tends to become shorter in the order of "low" → "medium" → "high" received light intensity, and the frequency at which the output of adder circuit 43 exceeds the summation threshold increases as the received light intensity increases when the received light intensity is low, reaching nearly 100% once a certain level of received light intensity is exceeded. Also, the time width during which the output of adder circuit 43 exceeds the summation threshold is short when the peak value of the output of the silicon photomultiplier (SiPM) is a "low" received light intensity near the summation threshold, and as the received light intensity increases, the output signal of the silicon photomultiplier (SiPM) becomes larger and the time width increases, and then when the received light intensity becomes "high" and the output of the silicon photomultiplier (SiPM) rises in a short period of time, the time width decreases.

[0072] That is, the frequency of the time-of-flight histogram generated by the histogram generation circuit 60 tends to change from "low" to "saturated" to "saturated" in the order of received light intensity "low" to "medium" to "high," and the time width exceeding the summation threshold at that time tends to exhibit a mountain-shaped pattern of "low" to "high" to "small" in the order of received light intensity "low" to "medium" to "high." Here, the time width is the sum of the time widths obtained in the region reaching the predetermined histogram threshold obtained by the histogram generation circuit 60 (calculated by the pulse width summation circuit shown in FIG. 3) divided by the frequency. Saturation means reaching or being filled up to a predetermined frequency, which is the maximum limit. Saturation of the histogram may be determined by whether the frequency of the histogram is equal to or greater than a predetermined value.

[0073] The duration of the intensity-duration characteristics can be smoothed by dividing the sum of the durations obtained in the region reaching a predetermined histogram threshold in the histogram generation circuit 60 by the sum of the frequencies in that region.

[0074] Based on this trend, Figure 6( a ) are obtained. In other words, even if the light is reflected from the same object, if the received light intensity differs, the flight time will differ, and as a result, an error will occur between the distance calculated by distance calculation circuit 80 and the actual distance to the object to be measured.

[0075] Therefore, if the intensity-error characteristics, intensity-frequency characteristics, and intensity-time duration characteristics are derived based on the intensity-error characteristics, intensity-frequency characteristics, and intensity-time duration characteristics obtained using a histogram generation circuit 60 or the like when the intensity of the reflected light is varied in advance, and these are stored as a correction table in a memory provided in the control circuit 100, the error correction circuit 90 can refer to the correction table and correct the distance based on the representative value of the flight time with an error.

[0076] The error is calculated as the difference between the actual distance to the target object and the distance based on the representative value of the flight time before correction. The delay time is calculated as the difference between the theoretical flight time calculated from the actual distance to the target object and the representative value of the flight time before correction measured by actual measurement.

[0077] To vary the intensity of the reflected light, the emission intensity of the measurement light can be variably set, various attenuation filters can be placed on the light receiving section of the light receiving element 3, or the reflection characteristics of the object onto which the measurement light is irradiated can be varied. Examples of objects with different reflection characteristics that can be used include white paper, black paper, gray paper, metal foil coated paper, and retroreflective sheets.

[0078] The power-error characteristic is obtained by combining, based on intensity, the intensity-power characteristic that indicates the correlation between the intensity of the reflected light and the power obtained by the histogram generation circuit 60 when the measurement light is repeatedly output at a predetermined period, and the intensity-error characteristic that indicates the correlation between the intensity of the reflected light and the error (delay time).

[0079] Figure 7 shows an image of how the power-error characteristic is generated. It is obtained by relating the power of the intensity-power characteristic and the error (delay time) of the intensity-error characteristic with respect to the intensity. The power-error characteristic obtained in this way becomes the histogram correction table shown in Figure 3.

[0080] The power-error characteristic shows a monotonically decreasing characteristic in which the error (delay time) decreases as the power increases. The intensity-power characteristic shows a monotonically increasing characteristic in which the power increases as the intensity of the reflected light increases up to a certain value. The intensity-error characteristic shows a monotonically decreasing characteristic in which the error (delay time) decreases as the intensity of the reflected light increases. When both characteristics are combined using the intensity of the reflected light as a reference, a monotonically decreasing characteristic is obtained in which the error decreases as the power increases.

[0081] As shown in Figures 6(b) and 7, the frequency-error characteristics exhibit a monotonically decreasing characteristic, and when the amount of received light exceeds a certain value, the histogram frequency saturates and it becomes impossible to associate the histogram frequency with the delay time, making further correction impossible.

[0082] To prepare for such a case, the error correction circuit 90 corrects the representative value of the time of flight with the error correction value using the above-mentioned time width-error characteristic after the frequency of the frequency-error characteristic has saturated.

[0083] The time width-error characteristic is obtained by combining, based on the intensity of the reflected light, the intensity-error characteristic, which shows the correlation between the intensity of the reflected light and the error (delay time), and the intensity-time width characteristic, which shows the correlation between the intensity of the reflected light and the time width at which the added value of the addition circuit (SiPM output) is equal to or greater than a predetermined addition threshold, when the measurement light is repeatedly output at a predetermined period.

[0084] The time width-error characteristic is obtained by repeatedly outputting the measurement light at a predetermined cycle and varying the intensity of the reflected light, and then calculating the intensity-error characteristic, which shows the correlation between the intensity of the reflected light and the error (delay time), and the intensity-time width characteristic, which shows the correlation between the intensity of the reflected light and the time width at which the added value of the adder circuit becomes equal to or greater than the predetermined addition threshold, and combining both characteristics based on the intensity. The time width-error characteristic uses a region where the error (delay time) increases monotonically as the time width increases.

[0085] Figure 8 shows an image of how the time width-error characteristics are generated. They are obtained by relating the error correction value (delay time) of the intensity-error characteristics and the time width of the intensity-time width characteristics based on the intensity. The time width-error characteristics obtained in this way become the pulse width table shown in Figure 3.

[0086] The intensity-error characteristic shows a monotonically decreasing characteristic in which the error decreases as the intensity of the reflected light increases. The intensity-duration characteristic shows a mountain-shaped characteristic in which the duration gradually increases from the low to the intermediate range of the reflected light intensity, and gradually decreases from the intermediate to the high range, with the duration being at its maximum in the intermediate range.

[0087] When these two characteristics are combined based on the intensity of the reflected light, they show a monotonically decreasing characteristic in which the error (delay time) decreases as the time width increases from the low to the intermediate range of the intensity of the reflected light, and a monotonically decreasing characteristic in which the error (delay time) decreases as the time width decreases from the intermediate to the high range of the intensity of the reflected light.The received light intensity at which this time width is at its maximum corresponds to the received light intensity at which the frequency in the histogram saturates, so once the frequency in the frequency-error characteristic saturates, correction can then be made based on the time width-delay time characteristic.

[0088] In the above explanation and in Figure 6, we explained that the error (= delay time), histogram frequency, and time width are synthesized / integrated based on the received light intensity. However, synthesis / integration based on the received light intensity itself is not necessary; any index correlated with the received light intensity can be used instead. For example, if it is difficult to measure the received light intensity itself, synthesis based on another index that is correlated with the received light intensity can be used. For example, under the same measurement conditions, it is expected that the received light intensity will increase as the measured light intensity increases. By varying the measured light intensity and measuring the delay time, histogram frequency, and time width corresponding to each measured light intensity, it is possible to determine the correlation between the error (= delay time) and histogram frequency, and the error (= delay time) and time width. This allows for the use of a photon-counting light-receiving element without increasing the circuit size and without calculating the amount of background light, making it possible to appropriately correct the calculated distance.

[0089] As shown in Figure 9 and as described above, the optical distance measuring method of the present invention is a TOF type optical distance measuring method, and is configured to include: a reflected light detection step in which reflected light from an object in response to pulsed measurement light output from a light-emitting element is detected using multiple photon-counting light-receiving elements; a time-of-flight measurement step in which a time-of-flight from the output of the measurement light to the time when the added value of the voltage pulses output from each light-receiving element reaches a predetermined addition threshold; a histogram generation step in which a histogram is generated in which the time-of-flight calculated in the time-of-flight measurement step when the measurement light is repeatedly output at a predetermined period is shown, showing the frequency of distribution in each region on a time axis divided into multiple regions at predetermined time intervals; a representative value calculation step in which a representative value of the time-of-flight to the object is calculated from the time-of-flight distributed in the region where the frequency reaches a predetermined histogram threshold based on the histogram; and a distance calculation step in which a distance to the object is calculated based on the representative value of the time-of-flight calculated in the representative value calculation step, wherein the distance calculation step further includes an error correction step in which the distance is corrected with an error correction value.

[0090] The error correction step corrects the distance with an error correction value based on the frequency obtained in the histogram generation step when the intensity of the reflected light is varied in advance and the frequency-error characteristic determined by the error obtained from the difference between the actual distance and the distance. When the frequency of the frequency-error characteristic is saturated, the added value becomes equal to or greater than a predetermined addition threshold when the intensity of the reflected light is varied in advance. It is determined by the error obtained by the difference between the time width, which is the period, and the actual distance and the distance, or the difference between the actual flight time and the representative value of the flight time. The representative value of the time of flight is corrected by the error correction value based on the time width-error characteristic. Whether the frequency is saturated may be determined by whether the frequency of the histogram is equal to or greater than a predetermined value.

[0091] In the above-described embodiment, a representative value of the time of flight for an object is calculated, the distance to the object is calculated based on the representative value of the time of flight, and this distance is corrected by the error correction value. However, the representative value of the time of flight may be corrected by a delay time equivalent to the error, and the distance may be calculated from the corrected representative value of the time of flight.

[0092] The above-described embodiment is merely an example of the present invention, and the scope of the present invention is not limited to the description of the embodiment. [Explanation of symbols]

[0093] 2: Light-emitting element 3: Light receiving element 10: Optical scanning device 20: Motor drive circuit 30: Light emission control circuit 40: Light receiving circuit 50: Time-of-flight measurement circuit 60: Histogram generation circuit 70: Representative value calculation circuit 80: Distance calculation circuit 90:Error correction circuit 100: Control circuit 200: Optical ranging device

Claims

1. a light emitting element that outputs pulsed measurement light; a plurality of photon counting light receiving elements that detect reflected light from an object in response to the measurement light; an adder circuit that adds up the voltage pulses output from the light receiving elements; a time-of-flight measurement circuit that calculates the time from when the measurement light is output to when the added value of the adder circuit reaches a predetermined addition threshold as a time-of-flight; a histogram generating circuit for generating a histogram showing the frequency of distribution of the time of flight calculated by the time-of-flight measuring circuit in each of a plurality of regions on a time axis divided into a plurality of regions at predetermined time intervals when the measurement light is repeatedly output at a predetermined cycle; a representative value calculation circuit that calculates a representative value of the flight times for the object from the flight times distributed in the region where the frequency reaches a predetermined histogram threshold based on the histogram; a distance calculation circuit that calculates a distance to the object based on the representative value of the flight time calculated by the representative value calculation circuit; Equipped with the distance calculation circuit includes an error correction circuit that calculates an error correction value based on a frequency-error characteristic determined by an error obtained by the frequency obtained by the histogram generation circuit when the intensity of the reflected light is varied in advance, the difference between the actual distance and the distance, or the difference between the actual flight time and the representative value of the flight time, and corrects the distance or the representative value of the flight time with the error correction value; The error correction circuit calculates the error correction value based on a time width-error characteristic that is determined by the error obtained from the difference between the actual distance and the distance, or the difference between the actual flight time and the representative value of the flight time, and the time width that is the period during which the added value of the addition circuit is greater than or equal to the addition threshold when the intensity of the reflected light is changed in advance after the power of the power-error characteristic has saturated, and corrects the distance or the representative value of the flight time with the error correction value.

2. The optical distance measuring device of claim 1, wherein the power-error characteristic is determined based on an intensity-power characteristic that indicates the correlation between an index related to the intensity of the reflected light and the power obtained by the histogram generation circuit when the measurement light is repeatedly output at a predetermined period, and an intensity-error characteristic that indicates the correlation between an index related to the intensity of the reflected light and the error.

3. 3. The optical distance measuring device according to claim 2, wherein the power-error characteristic exhibits a monotonically decreasing characteristic in which the error decreases as the power increases.

4. An optical distance measuring device as described in any one of claims 1 to 3, wherein the time width-error characteristic is a characteristic that is defined based on the intensity-error characteristic that shows the correlation between an index related to the intensity of the reflected light and the error when the measurement light is repeatedly output at a predetermined period, and the intensity-time width characteristic that shows the correlation between the index related to the intensity of the reflected light and the time width at which the added value of the addition circuit is greater than or equal to the addition threshold.

5. 5. The optical distance measuring device according to claim 4, wherein the time width is a value obtained by dividing the sum of the time widths obtained in the region reaching a predetermined histogram threshold by the sum of the frequencies in the region.

6. 6. The optical distance measuring device according to claim 1, wherein the time width-error characteristic exhibits a monotonically increasing characteristic in which the error increases as the time width increases.

7. An optical ranging device as described in any one of claims 1 to 6, wherein the representative value calculation circuit calculates the representative value of the flight time for the object by dividing the total sum of the flight times distributed in the region where the frequency reaches the histogram threshold based on the histogram by the sum of each frequency in the region.

8. An optical ranging device as described in any one of claims 1 to 6, wherein the representative value calculation circuit calculates the representative value of the flight time for the object by dividing the total sum of the flight times distributed in the area where the frequency reaches the histogram threshold and the area adjacent to that area based on the histogram by the sum of the frequencies in the corresponding area.

9. An optical ranging device as described in any one of claims 1 to 6, wherein the representative value calculation circuit calculates, for a region where the total sum of the frequencies distributed in a plurality of adjacent regions based on the histogram reaches the histogram threshold, a value obtained by dividing the total sum of the flight times distributed in the plurality of regions by the sum of the frequencies in the corresponding region, as the representative value of the flight time for the object.

10. a light emitting element that outputs pulsed measurement light; a plurality of photon counting light receiving elements that detect reflected light from an object in response to the measurement light; an adder circuit that adds up the voltage pulses output from the light receiving elements; a time-of-flight measurement circuit that calculates the time from when the measurement light is output to when the added value of the adder circuit reaches a predetermined addition threshold as a time-of-flight; a histogram generating circuit for generating a histogram showing the frequency of distribution of the time of flight calculated by the time-of-flight measuring circuit in each of a plurality of regions on a time axis divided into a plurality of regions at predetermined time intervals when the measurement light is repeatedly output at a predetermined cycle; a representative value calculation circuit that calculates a representative value of the flight times for the object from the flight times distributed in the region where the frequency reaches a predetermined histogram threshold based on the histogram; a distance calculation circuit that calculates a distance to the object based on the representative value of the flight time calculated by the representative value calculation circuit; Equipped with the distance calculation circuit includes an error correction circuit that calculates an error correction value based on a frequency-error characteristic determined by an error obtained by the frequency obtained by the histogram generation circuit when the intensity of the reflected light is varied in advance, the difference between the actual distance and the distance, or the difference between the actual flight time and the representative value of the flight time, and corrects the distance or the representative value of the flight time with the error correction value; the time-of-flight measurement circuit is configured to calculate, as the time-of-flight, a time of flight from a point in time at which the measurement light is output to a point in time at which the output value of the addition circuit reaches a first addition threshold and a second addition threshold higher than the first addition threshold, the histogram generation circuit is configured to generate a histogram showing the frequency of distribution of the time of flight calculated by the time-of-flight measurement circuit in each of a plurality of regions on a time axis divided into a plurality of regions at predetermined time intervals when the measurement light is repeatedly output at a predetermined cycle, the representative value calculation circuit calculates, as the representative value of the flight times for the object, a value obtained by dividing all the added values ​​of the flight times corresponding to the first addition threshold by the frequency corresponding to the first addition threshold, among the flight times distributed in the region where the frequency reaches the histogram threshold based on the histogram based on the first addition threshold; The error correction circuit calculates the error correction value based on the power-error characteristic determined by the power obtained in the histogram based on the first addition threshold and the second addition threshold and the error obtained due to the difference between the actual distance and the distance, and corrects the representative value of the distance or the time of flight with the error correction value.

11. An optical distance measuring device as described in any one of claims 1 to 10, comprising an optical deflection device that deflects the measurement light output from the light-emitting element in a predetermined direction, and / or an optical scanning device that scans the measurement light in a predetermined direction.

12. a reflected light detection step of detecting reflected light from an object in response to pulsed measurement light output from a light emitting element using a plurality of photon counting light receiving elements; a time-of-flight measurement step of calculating a time from the time when the measurement light is output until the time when the sum of the voltage pulses output from each light-receiving element reaches a predetermined sum threshold as a time-of-flight; a histogram generating step of generating a histogram showing the frequency of distribution of the time of flight calculated in the time of flight measuring step in each of a plurality of regions on a time axis divided into a plurality of regions at predetermined time intervals when the measurement light is repeatedly output at a predetermined cycle; a representative value calculation step of calculating a representative value of the flight times for the object from the flight times distributed in the region where the frequency reaches a predetermined histogram threshold based on the histogram; a distance calculation step of calculating a distance to the object based on the representative value of the time of flight calculated in the representative value calculation step, the distance calculation step includes an error correction step of calculating an error correction value based on the frequency-error characteristic determined by an error obtained by the frequency obtained in the histogram generation step and a difference between the actual distance and the distance or a difference between the actual flight time and the representative value of the flight time when the intensity of the reflected light is varied in advance, and correcting the distance or the representative value of the flight time with the error correction value; The error correction step is an optical ranging method in which, after the power of the power-error characteristic has saturated, the error correction value is calculated based on a time width, which is the period during which the added value is greater than or equal to the predetermined addition threshold when the intensity of the reflected light is changed in advance, and a time width-error characteristic determined by the error obtained by the difference between the actual distance and the distance, or the difference between the actual flight time and the representative value of the flight time, and the error correction value is corrected based on the error correction value.

13. a reflected light detection step of detecting reflected light from an object in response to pulsed measurement light output from a light emitting element using a plurality of photon counting light receiving elements; a time-of-flight measurement step of calculating a time from the time when the measurement light is output until the time when the sum of the voltage pulses output from each light-receiving element reaches a predetermined sum threshold as a time-of-flight; a histogram generating step of generating a histogram showing the frequency of distribution of the time of flight calculated in the time of flight measuring step in each of a plurality of regions on a time axis divided into a plurality of regions at predetermined time intervals when the measurement light is repeatedly output at a predetermined cycle; a representative value calculation step of calculating a representative value of the flight times for the object from the flight times distributed in the region where the frequency reaches a predetermined histogram threshold based on the histogram; a distance calculation step of calculating a distance to the object based on the representative value of the time of flight calculated in the representative value calculation step, the distance calculation step includes an error correction step of calculating an error correction value based on the frequency-error characteristic determined by an error obtained by the frequency obtained in the histogram generation step and a difference between the actual distance and the distance or a difference between the actual flight time and the representative value of the flight time when the intensity of the reflected light is varied in advance, and correcting the distance or the representative value of the flight time with the error correction value; the time-of-flight measuring step includes a step of calculating, as the time-of-flight, a time of flight from a point in time at which the measurement light is output to a point in time at which the sum of the voltage pulses reaches a first summation threshold and a second summation threshold higher than the first summation threshold, the histogram generating step includes a step of generating a histogram showing the frequency of distribution of the time of flight calculated in the time of flight measuring step in each of a plurality of regions on a time axis divided into a plurality of regions at predetermined time intervals when the measurement light is repeatedly output at a predetermined cycle, the representative value calculation step includes a step of calculating, as the representative value of the flight times for the object, a value obtained by dividing all added values ​​of the flight times corresponding to the first addition threshold among the flight times distributed in the region where the frequency reaches the histogram threshold based on the first addition threshold, by the frequency corresponding to the first addition threshold; The optical ranging method includes a step of calculating the error correction value based on a power-error characteristic determined by the power obtained in the histogram based on the first addition threshold and the second addition threshold and the error obtained due to the difference between the actual distance and the distance, and correcting the representative value of the distance or the time of flight with the error correction value.

Images