JP7388141B2 - distance measuring device - Google Patents

Description

The present disclosure relates to a distance measuring device that irradiates light and measures the distance to an object that reflects the light.

Patent Document 1 describes a distance method in which the time from irradiation to reception of light is measured by irradiating light and receiving reflected light from an object, and based on this time, the distance to the object that reflected the light is measured. It is described that in a measuring device, a plurality of avalanche photodiodes operating in Geiger mode are used to detect light.

Patent No. 5644294

When background light such as sunlight enters the distance measuring device, if the amount of background light increases, it becomes difficult to separate the background light from the light reflected from the object, and the background light becomes the light reflected from the object. If there is, there is a risk of false detection or failure to detect light reflected from the object, resulting in a decrease in distance measurement accuracy.

The present disclosure aims to improve distance measurement accuracy.

One aspect of the present disclosure includes an irradiation unit (2), a light receiving array unit (3), a histogram creation unit (4, S20, S30, S210 to S250), a noise floor calculation unit (S40, S280), and a A distance measuring device (1) includes a calculation section (S50, S290), a threshold calculation section (S60, S300, S305), and a distance calculation section (S70, S310).

The irradiation unit is configured to irradiate pulsed light. The light receiving array section includes a plurality of photodetectors (31) that output pulse signals upon incidence of photons.
The histogram creation section is configured to create a histogram showing a temporal change in the amount of light received by the light receiving array section in accordance with the plurality of pulse signals output from the light receiving array section.

The noise floor calculation unit is configured to calculate a background light noise floor indicating a level of background light detected by the light receiving array unit based on the histogram created by the histogram creation unit.

The variation calculation unit is configured to calculate a variation parameter indicating the degree of variation in the background light noise floor based on the histogram created by the histogram creation unit. The threshold calculation unit detects the pulsed light irradiated by the irradiation unit in the histogram by the light receiving array unit based on the background light noise floor calculated by the noise floor calculation unit and the variation parameter calculated by the variation calculation unit. The configuration is configured to calculate a threshold value for determining whether or not.

The distance calculation section is configured to calculate the distance to the object that reflected the pulsed light based on the threshold calculated by the threshold calculation section.
The distance measuring device of the present disclosure configured as described above calculates a threshold value based on the background light noise floor and the variation parameter of the background light noise floor. Therefore, the distance measuring device of the present disclosure can change the threshold value depending on the magnitude of the variation in the background light noise floor (that is, the magnitude of the standard deviation of the background light noise floor). As a result, the distance measuring device of the present disclosure may erroneously detect background light as pulsed light reflected by an object (hereinafter referred to as reflected light), or may fail to detect reflected light from an object. can be suppressed and distance measurement accuracy can be improved.

FIG. 2 is a block diagram showing the configuration of a distance measuring device. FIG. 3 is a diagram showing the configuration of a light receiving array section and a photodetector. It is a figure showing a specific example of the histogram of a 1st embodiment. It is a flowchart which shows distance measurement processing of a 1st embodiment. It is a flow chart which shows distance measurement processing of a 2nd embodiment. It is a figure which shows the specific example of the histogram of 2nd Embodiment. It is a flow chart which shows distance measurement processing of a 3rd embodiment. It is a figure showing the composition of the threshold value table of a 3rd embodiment. It is a figure which shows the structure of the threshold value table of another embodiment.

[First embodiment]
A first embodiment of the present disclosure will be described below with reference to the drawings.
The distance measuring device 1 of this embodiment is mounted on a vehicle and measures distances to various objects present around the vehicle.

As shown in FIG. 1, the distance measuring device 1 includes an irradiating section 2, a light receiving array section 3, a counting section 4, and a signal processing section 5.
The irradiation section 2 repeatedly irradiates pulsed laser light at preset intervals, and notifies the counting section 4 and the signal processing section 5 of the irradiation timing. Hereinafter, the period of laser light irradiation will be referred to as the measurement period.

The light receiving array section 3 includes a plurality of pixel units P1, P2, . . . , Pk. k is an integer of 2 or more. Each pixel unit Pi includes N photodetectors 31. N is an integer of 2 or more. When a photon is incident, the photodetector 31 outputs a pulse signal having a preset pulse width.

The counting section 4 includes a plurality of adders A1, A2, . . . , Ak and a plurality of histogram memories M1, M2, . . . , Mk.
Adders A1, A2, . . . , Ak are connected to pixel units P1, P2, . . . , Pk, respectively. The adder Ai outputs an addition signal indicating the total value (hereinafter referred to as the number of input pulses) of the pulse signals input from the N photodetectors 31 constituting the pixel unit Pi. i is an integer from 1 to k.

Histogram memories M1, M2, . . . , Mk are connected to adders A1, A2, . . . , Ak, respectively. Then, the histogram memory Mi calculates the number of pulse inputs indicated by the addition signal input from the adder Ai every time a preset acquisition period elapses starting from the most recent irradiation timing notified from the irradiation unit 2. The information is stored in association with the number of times the acquisition period has arrived since the irradiation timing. Further, the histogram memories M1, M2, . . . , Mk are connected to the signal processing section 5.

The signal processing unit 5 is an electronic control device mainly composed of a microcomputer including a CPU 51, a ROM 52, a RAM 53, and the like. Various functions of the microcomputer are realized by the CPU 51 executing programs stored in a non-transitive physical recording medium. In this example, the ROM 52 corresponds to a non-transitional physical recording medium that stores a program. Furthermore, by executing this program, a method corresponding to the program is executed. Note that some or all of the functions executed by the CPU 51 may be configured in hardware using one or more ICs. Furthermore, the number of microcomputers constituting the signal processing section 5 may be one or more.

As shown in FIG. 2, the light receiving array section 3 includes a light receiving surface 3a formed by arranging a plurality of pixel units P1, P2, . . . , Pk in a two-dimensional matrix.
The photodetector 31 includes a SPAD 61, a quench resistor 62, an inversion circuit 63, a D flip-flop circuit (hereinafter referred to as a DFF circuit) 64, and a delay circuit 65. SPAD is an abbreviation for Single Photon Avalanche Diode.

SPAD 61 is an avalanche photodiode that operates in Geiger mode and can detect the incidence of a single photon. The SPAD 61 has an anode connected to a negative power source and a cathode connected to a positive power source via a quench resistor 62. The quench resistor 62 applies a reverse bias voltage to the SPAD 61. Furthermore, the quench resistor 62 stops the Geiger discharge of the SPAD 61 due to the voltage drop generated by the current flowing through the SPAD 61 when a photon is incident on the SPAD 61 and the SPAD 61 breaks down. Note that for the quench resistor 62, a resistor element having a predetermined resistance value, a MOSFET whose on-resistance can be set by a gate voltage, or the like is used.

An inversion circuit 63 is connected to the cathode of the SPAD 61. When the SPAD 61 is not broken down, the input of the inversion circuit 63 is at a high level. When the SPAD 61 is in a broken down state, current flows through the quench resistor 62, causing the input of the inversion circuit 63 to change to a low level. The output of the DFF circuit 64 changes to high level at the rising edge when the output of the inverting circuit 63 changes from low level to high level. The output of the DFF circuit 64 is connected to a reset terminal of the DFF circuit 64 via a delay circuit 65. The delay circuit 65 inverts the signal level of the output of the DFF circuit 64, delays it by a preset delay time, and inputs the signal to the reset terminal. As a result, when the delay time elapses after the output of the DFF circuit 64 changes to high level, the DFF circuit 64 is reset and changes to low level.

The pixel histogram created from the stored data stored in the histogram memory Mi is, as shown in FIG. It is a histogram showing changes over time. The maximum value on the vertical axis is N.

The pixel histogram shows the number of pulse inputs for each time bin Tbin. The time bin Tbin is a time range that is a unit scale of the pixel histogram. The length of the time bin Tbin is equal to the acquisition period described above.

The time bins Tbin are assigned identification numbers 1, 2, 3, . . . in order from the most recent irradiation timing. The time bins Tbin with identification numbers from 1 to m correspond to the background light noise floor calculation period Tb. The time bin Tbin whose identification number is after (m+1) corresponds to the distance calculation period Tr. m is an integer of 2 or more.

The heights of bars B1, B2, and B3 in the pixel histogram shown in FIG. 3 indicate the number of input pulses due to the light reflected by the object and the background light. On the other hand, the heights of bars other than bars B1, B2, and B3 indicate the number of input pulses due to background light.

Next, the procedure of distance measurement processing executed by the CPU 51 of the signal processing section 5 will be explained. The distance measurement process is a process that is repeatedly executed every time a measurement period elapses while the irradiation unit 2 is emitting laser light.

When the distance measurement process is executed, the CPU 51 stores 1 in the pixel instruction value i provided in the RAM 53 in S10, as shown in FIG.
In S20, the CPU 51 acquires stored data from the histogram memory Mi.

In S30, the CPU 51 creates a pixel histogram of the i-th pixel unit Pi using the stored data acquired in S20.
The CPU 51 calculates the background light noise floor BGND in S40. The background light noise floor is the light reception level of light (that is, background light) detected by the light receiving array section 3 when the laser light emitted from the irradiating section 2 is not received by the light receiving array section 3. Specifically, the CPU 51 calculates the background light noise floor BGND using the following equation (1), with the number of pulse inputs corresponding to the time bin Tbin of identification number j being BGND_j.

In S50, the CPU 51 calculates the background light standard deviation σ_BGND using the following equation (2).

Here, the reason why the background light standard deviation σ_BGND can be calculated using equation (2) will be explained.
The parameters of the photodetector 31 used in the background light standard deviation σ_BGND are theoretically based on the defining equation of the binomial distribution.

The probability density function of the binomial distribution determined by two parameters n and p is expressed by the following equation (3). Equation (3) below indicates the probability of success k times when independent Bernoulli trials with success probability p are attempted n times.

The expected value E[X], variance V[X], and standard deviation σ[X] in this binomial distribution are expressed by the following equations (4), (5), and (6), respectively.

When the success probability p is the probability that the SPAD 61 reacts with light, the response probability p of one SPAD 61 is expressed by the following equation (7). Further, the number of trials n is expressed by the following formula (8). In equation (7) or equation (8) below, r is the ideal count rate, τP, τ _NP is the dead time of SPAD61, A is the number of SPADs that responded (i.e., the expected value of background light), and N is the number of SPADs per pixel. SPAD number.

As shown in equation (7) below, the response probability p of one SPAD 61 can be replaced with "probability that A SPADs 61 respond among N SPADs 61".

From equations (4), (7), and (8), the expected value E[X] is expressed by the following equation (9). Equation (1) indicates the average value of the number of pulse inputs in time bins Tbin with identification numbers from 1 to m, and Equation (1) corresponds to Equation (9) below.

From equations (6), (7), and (8), the standard deviation σ[X] is expressed by the following equation (10). The standard deviation σ[X] shown in equation (10) below corresponds to the background light standard deviation σ_BGND shown in equation (2).

Next, in S60, the CPU 51 calculates the threshold Th using the following equation (11). In the following formula (11), a is a preset false detection tolerance coefficient. As the erroneous detection tolerance coefficient a becomes larger, the frequency of erroneously detecting that background light is detected as light reflected by an object decreases.

Note that the curve D1 shown in FIG. 3 shows a normal distribution in which the average value is the background light noise floor BGND and the standard deviation is the background light standard deviation σ_BGND.

In S70, the CPU 51 calculates the distance to the object that reflected the light (hereinafter referred to as object distance) using the pixel histogram created in S30 and the threshold Th calculated in S60.
Specifically, as shown in FIG. 3, the CPU 51 first performs a transition from a state in which the number of pulse inputs is less than the threshold Th to a state in which the number of pulse inputs is equal to or greater than the threshold Th during the distance calculation period Tr. Identify time bin Tbin as a rise time bin. In the pixel histogram shown in FIG. 3, the time bin Tbin corresponding to bar B1 is the rise time bin.

Furthermore, the CPU 51 specifies, as a falling time bin, a time bin Tbin when the number of pulse inputs changes from a state where the number of pulse inputs is equal to or greater than the threshold value Th to a state where the number of pulse inputs is less than the threshold value Th during the distance calculation period Tr. In the pixel histogram shown in FIG. 3, the time bin Tbin corresponding to bar B4 is the falling time bin.

Further, the CPU 51 calculates the intermediate time between the rise time corresponding to the rise time bin and the fall time corresponding to the fall time bin as the signal detection time. In the pixel histogram shown in FIG. 3, the time Tu from the irradiation timing to the time bin Tbin corresponding to bar B1 is the rise time, and the time Td from the irradiation timing to the time bin Tbin corresponding to bar B4 is the fall time. .

Then, the CPU 51 calculates the object distance based on the calculated signal detection time.
When the process of S70 is completed, as shown in FIG. 4, the CPU 51 determines in S80 whether the value stored in the pixel instruction value i is greater than or equal to the total number of pixels k. Here, if the value stored in the pixel instruction value i is less than the total number of pixels k, the CPU 51 in S90 adds an additional value of 1 to the value stored in the pixel instruction value i. The pixel instruction value i is stored and the process moves to S20.

On the other hand, if the value stored in the pixel instruction value i is greater than or equal to the total number of pixels k, the CPU 51 ends the distance measurement process.
The distance measuring device 1 configured in this manner includes an irradiating section 2, a light receiving array section 3, a counting section 4, and a signal processing section 5.

The irradiation unit 2 irradiates pulsed light. The light receiving array section 3 includes a plurality of photodetectors 31 that output pulse signals upon incidence of photons.
The counting section 4 and the signal processing section 5 create a pixel histogram showing a temporal change in the amount of light received by the light receiving array section 3 in accordance with the plurality of pulse signals output from the light receiving array section 3.

The signal processing unit 5 calculates a background light noise floor BGND indicating the level of background light detected by the light receiving array unit 3 based on the created pixel histogram. Note that the signal processing unit 5 calculates the light reception level of light detected by the light receiving array unit 3 as the background light noise floor BGND when the pulsed light irradiated by the irradiating unit 2 is not received by the light receiving array unit 3. .

The signal processing unit 5 calculates the background light standard deviation σ_BGND based on the created pixel histogram. Based on the calculated background light noise floor BGND and the calculated background light standard deviation σ_BGND, the signal processing unit 5 determines whether the light receiving array unit 3 has detected the pulsed light irradiated by the irradiation unit 2 in the pixel histogram. A threshold value Th for determining whether or not the

The signal processing unit 5 calculates the distance to the object that reflected the pulsed light based on the calculated threshold Th.
In this way, the distance measuring device 1 calculates the threshold Th based on the background light noise floor BGND and the background light standard deviation σ_BGND. Therefore, the distance measuring device 1 can change the threshold Th depending on the magnitude of the variation in the background light noise floor BGND (that is, the magnitude of the background light standard deviation σ_BGND). This prevents the distance measuring device 1 from erroneously detecting background light as pulsed light reflected by an object (hereinafter referred to as reflected light) or from failing to detect reflected light from an object. However, distance measurement accuracy can be improved.

Further, the light receiving array section 3 is configured such that a plurality of photodetectors 31 form one pixel, and includes k pixels. The signal processing unit 5 calculates the background light standard deviation σ_BGND based on the calculated background light noise floor BGND and the number N of photodetectors 31 forming one pixel. Thereby, the distance measuring device 1 can easily calculate the background light standard deviation σ_BGND, and can reduce the processing load on the signal processing unit 5.

In the embodiment described above, the counting section 4, S20, and S30 correspond to processing as a histogram creation section, the pixel histogram corresponds to a histogram, S40 corresponds to processing as a noise floor calculation section, and S50 corresponds to processing as a variation calculation section. The background light standard deviation σ_BGND corresponds to a variation parameter.

Further, S60 corresponds to processing as a threshold calculation section, S70 corresponds to processing as a distance calculation section, and the pixel unit Pi corresponds to a pixel.
[Second embodiment]
A second embodiment of the present disclosure will be described below with reference to the drawings. Note that in the second embodiment, different parts from the first embodiment will be explained. Common configurations are given the same reference numerals.

The distance measuring device 1 of the second embodiment differs from the first embodiment in that the distance measuring process is changed.
Next, the procedure of distance measurement processing according to the second embodiment will be explained.

When the distance measurement process of the second embodiment is executed, the CPU 51 adds 1 to the value stored in the addition count provided in the RAM 53 in S210, as shown in FIG. Store in the addition number Count.

In S220, the CPU 51 acquires stored data from all histogram memories M1, M2, . . . , Mk.
In S230, the CPU 51 creates integrated pixel histograms for all pixel units P1, P2, . . . , Pk using the stored data acquired in S220.

Specifically, first, a pixel histogram of the pixel unit P1 is created using the data stored in the histogram memory M1 acquired in S220. Then, the created pixel histogram of the pixel unit P1 is added to the integrated pixel histogram of the pixel unit P1 stored in the RAM 53. That is, for the pixel histogram of pixel unit P1 and the integrated pixel histogram of pixel unit P1, the number of pulse inputs of the time bin Tbin with the same identification number is added, and this added value is used as the number of pulse inputs of the new integrated pixel histogram. shall be. Then, the new integrated pixel histogram created for the pixel unit P1 is stored in the RAM 53. Note that if the integrated pixel histogram of the pixel unit P1 is not stored in the RAM 53, the created pixel histogram of the pixel unit P1 is stored in the RAM 53 as a new integrated pixel histogram.

The CPU 51 also creates integrated pixel histograms for the pixel units P2, . . . , Pk in the same manner as the pixel unit P1, and stores them in the RAM 53.
In S240, the CPU 51 determines whether the value stored in the number of additions Count is equal to or greater than the upper limit number n. Here, if the value stored in the number of additions Count is less than the upper limit number n, the CPU 51 ends the distance measurement process.

On the other hand, if the value stored in the number of additions Count is greater than or equal to the upper limit number of times n, the CPU 51 stores 0 in the number of additions Count in S250.
As a result, an integrated pixel histogram is created by adding the pixel histograms repeatedly for the upper limit number of times n.

As shown in FIG. 6, the integrated pixel histogram of all the pixel units P1, P2, ..., Pk has the time starting from the irradiation timing on the horizontal axis and the number of pulse inputs on the vertical axis. It is a histogram showing a change in the number of objects over time. The maximum value on the vertical axis is N×n.

The integrated pixel histogram shows the number of pulse inputs for each time bin Tbin. The time bins Tbin are assigned identification numbers 1, 2, 3, . . . in order from the most recent irradiation timing. The time bins Tbin with identification numbers from 1 to m correspond to the background light noise floor calculation period Tb. The time bin Tbin whose identification number is after (m+1) corresponds to the distance calculation period Tr. m is an integer of 2 or more.

The heights of bars B11, B12, and B13 in the pixel histogram shown in FIG. 6 indicate the number of pulse inputs due to the light reflected by the object and the background light. On the other hand, the heights of bars other than bars B11, B12, and B13 indicate the number of input pulses due to background light.

When the process of S250 is completed, the CPU 51 stores 1 in the pixel instruction value i provided in the RAM 53 in S260, as shown in FIG.
In S270, the CPU 51 acquires the integrated pixel histogram of the pixel unit Pi from the RAM 53.

In S280, the CPU 51 calculates the background light noise floor BGND_n of the integrated pixel histogram of the pixel unit Pi. Specifically, the CPU 51 calculates the background light noise floor BGND_n using the following equation (12), setting the number of pulse inputs corresponding to the time bin Tbin with the identification number j as BGND_n_j.

In S290, the CPU 51 calculates the background light standard deviation σ_BGND_n using the following equation (13).

Here, the reason why the background light standard deviation σ_BGND_n can be calculated by the following equation (13) will be explained.
In the second embodiment, since an integrated pixel histogram is created by repeating and integrating the number of pulse inputs a plurality of times, the number of trials n is expressed by the following equation (14). Count in equation (14) is the number of additions described above.

From equations (4), (7), and (14), the expected value E[X] is expressed by the following equation (15). Equation (12) indicates the average value of the number of pulse inputs in time bins Tbin with identification numbers from 1 to m, and Equation (12) corresponds to Equation (15) below.

From formulas (6), (7), and (14), the standard deviation σ[X] is expressed by the following formula (16). The standard deviation σ[X] shown in equation (16) below corresponds to the background light standard deviation σ_BGND_n shown in equation (13).

Next, in S300, the CPU 51 calculates the threshold Th_n using the following equation (17). Note that the curve D2 shown in FIG. 6 shows a normal distribution in which the average value is the background light noise floor BGND_n and the standard deviation is the background light standard deviation σ_BGND_n.

In S310, the CPU 51 calculates the object distance using the integrated pixel histogram of the pixel unit Pi acquired in S270 and the threshold Th_n calculated in S300.
Specifically, as shown in FIG. 6, the CPU 51 first performs a transition from a state in which the number of pulse inputs is less than the threshold value Th_n to a state in which the number of pulse inputs is equal to or greater than the threshold value Th_n during the distance calculation period Tr. Identify time bin Tbin as a rise time bin. In the integrated pixel histogram shown in FIG. 6, the time bin Tbin corresponding to bar B11 is the rise time bin.

Further, the CPU 51 specifies, as a falling time bin, a time bin Tbin when the number of pulse inputs changes from a state where the number of pulse inputs is equal to or greater than the threshold value Th_n to a state where the number of pulse inputs is less than the threshold value Th_n during the distance calculation period Tr. In the integrated pixel histogram shown in FIG. 6, the time bin Tbin corresponding to bar B14 is the falling time bin.

Further, the CPU 51 calculates the intermediate time between the rise time corresponding to the rise time bin and the fall time corresponding to the fall time bin as the signal detection time. In the integrated pixel histogram shown in FIG. 6, the time Tu from the irradiation timing to the time bin Tbin corresponding to bar B11 is the rise time, and the time Td from the irradiation timing to the time bin Tbin corresponding to the bar B14 is the fall time. be.

Then, the CPU 51 calculates the object distance based on the calculated signal detection time.
When the process of S310 is completed, as shown in FIG. 5, the CPU 51 determines in S320 whether the value stored in the pixel instruction value i is greater than or equal to the total number of pixels k. Here, if the value stored in the pixel instruction value i is less than the total number of pixels k, the CPU 51 in S330 adds an additional value of 1 to the value stored in the pixel instruction value i. The pixel instruction value i is stored, and the process moves to S270.

On the other hand, if the value stored in the pixel instruction value i is greater than or equal to the total number of pixels k, the CPU 51 in S340 selects all pixel units P1, P2, ..., Pk stored in the RAM 53. The accumulated pixel histogram is deleted from the RAM 53, and the distance measurement process is ended.

The distance measuring device 1 configured in this manner includes an irradiating section 2, a light receiving array section 3, a counting section 4, and a signal processing section 5.
The irradiation unit 2 irradiates pulsed light. The light receiving array section 3 includes a plurality of photodetectors 31 that output pulse signals upon incidence of photons.

The counting section 4 and the signal processing section 5 create an integrated pixel histogram showing a temporal change in the amount of light received by the light receiving array section 3 according to the plurality of pulse signals output from the light receiving array section 3.

The counting unit 4 and the signal processing unit 5 detect n times obtained by performing a photodetection operation n times from when the irradiation unit 2 irradiates the pulsed light until the light receiving array unit 3 detects the pulsed light. By integrating the results, an integrated pixel histogram is created.

The signal processing unit 5 calculates a background light noise floor BGND_n indicating the level of background light detected by the light receiving array unit 3 based on the created integrated pixel histogram.
The signal processing unit 5 calculates the background light standard deviation σ_BGND_n based on the created integrated pixel histogram. Based on the calculated background light noise floor BGND_n and the calculated background light standard deviation σ_BGND_n, the signal processing unit 5 detected the pulsed light irradiated by the irradiation unit 2 in the integrated pixel histogram using the light receiving array unit 3. A threshold value Th_n for determining whether or not is calculated.

The signal processing unit 5 calculates the distance to the object that reflected the pulsed light based on the calculated threshold Th_n.
In this way, the distance measuring device 1 calculates the threshold Th_n based on the background light noise floor BGND_n and the background light standard deviation σ_BGND_n. Therefore, the distance measuring device 1 can change the threshold Th_n depending on the magnitude of the variation in the background light noise floor BGND_n (that is, the magnitude of the background light standard deviation σ_BGND_n). As a result, the distance measuring device 1 can suppress the occurrence of situations in which background light is mistakenly detected as reflected light or cannot detect reflected light from an object, and can improve distance measurement accuracy. can.

Further, the light receiving array section 3 is configured such that a plurality of photodetectors 31 form one pixel, and includes k pixels. The signal processing unit 5 calculates the calculated background light noise floor BGND_n, the number N of photodetectors 31 constituting one pixel, and the n detection results obtained by performing the photodetection operation n times. The background light standard deviation σ_BGND_n is calculated based on the number of integrations n of the integrated pixel histogram created by the integration. Thereby, the distance measuring device 1 can easily calculate the background light standard deviation σ_BGND_n, and can reduce the processing load on the signal processing unit 5.

Further, the distance measuring device 1 creates an integrated pixel histogram by integrating n pixel histograms. In this way, by increasing the number of pulsed lights used in one distance measurement, the SN ratio in the integrated pixel histogram can be improved, and the distance measurement accuracy can be further improved.

In the embodiment described above, the counting unit 4 and S210 to S250 correspond to processing as a histogram creation unit, the integrated pixel histogram corresponds to a histogram, S280 corresponds to processing as a noise floor calculation unit, and S290 corresponds to processing as a noise floor calculation unit. This corresponds to processing as a calculation unit, and the background light standard deviation σ_BGND_n corresponds to a variation parameter.

Further, S300 corresponds to processing as a threshold value calculation section, and S310 corresponds to processing as a distance calculation section.
[Third embodiment]
A third embodiment of the present disclosure will be described below with reference to the drawings. Note that in the third embodiment, parts different from the second embodiment will be explained. Common configurations are given the same reference numerals.

The distance measuring device 1 of the third embodiment differs from the second embodiment in that the distance measuring process is changed.
The distance measurement process of the third embodiment differs from the second embodiment in that, as shown in FIG. 7, the process of S305 is executed instead of S300.

That is, when the process of S290 is completed, the CPU 51 refers to the threshold value table TB1 stored in the ROM 52 in S305, calculates the threshold value Th_n, and proceeds to S310.

As shown in FIG. 8, the threshold table TB1 sets the correspondence between the background light noise floor BGND_n and the threshold Th_n. Specifically, the threshold table TB1 stores thresholds Th_n when the background light noise floor BGND_n is 0, 1, ..., N×n as thresholds th_BGND_0, th_BGND_1, ..., th_BGND_N×n, respectively. do. The threshold value th_BGND_x is a value calculated by the following formula (18). x is an integer from 0 to N×n.

In the embodiment described above, S305 corresponds to processing as a threshold value calculation unit.
Although one embodiment of the present disclosure has been described above, the present disclosure is not limited to the above embodiment, and can be implemented with various modifications.

[Modification 1]
For example, in the above embodiment, the background light noise floor BGND, BGND_n is calculated as the average value of the number of input pulses in the background light noise floor calculation period Tb. However, the background light noise floors BGND and BGND_n may be calculated as the median value of the number of input pulses during the background light noise floor calculation period Tb.

[Modification 2]
In the third embodiment, the threshold Th_n is calculated by referring to the threshold table TB1. However, the threshold Th in the first embodiment may be calculated by referring to the threshold table TB2 shown in FIG. As shown in FIG. 9, the threshold table TB2 sets the correspondence between the background light noise floor BGND and the threshold Th. Specifically, the threshold table TB1 stores thresholds Th when the background light noise floor BGND is 0, 1, . . . , N as thresholds th_BGND_0, th_BGND_1, . . . , th_BGND_N. The threshold value th_BGND_y is a value calculated by the following formula (19). y is an integer from 0 to N.

[Modification 3]
In the embodiment described above, the background light noise floors BGND and BGND_n are calculated based on the number of input pulses in the background light noise floor calculation period Tb. However, the background light noise floors BGND and BGND_n may also be calculated using the number of pulse inputs during the distance calculation period Tr.

The signal processing unit 5 and its method described in the present disclosure are implemented by a dedicated computer provided by configuring a processor and memory programmed to perform one or more functions embodied by a computer program. , may be realized. Alternatively, the signal processing unit 5 and its techniques described in this disclosure may be implemented by a dedicated computer provided by a processor configured with one or more dedicated hardware logic circuits. Alternatively, the signal processing unit 5 and its method described in the present disclosure may include a processor configured to execute one or more functions, a memory, and one or more hardware logic circuits. It may also be realized by one or more dedicated computers configured in combination. The computer program may also be stored as instructions executed by a computer on a computer-readable non-transitory tangible storage medium. The method for realizing the functions of each section included in the signal processing section 5 does not necessarily need to include software, and all the functions may be realized using one or more pieces of hardware.

A plurality of functions of one component in the above embodiment may be realized by a plurality of components, and a function of one component may be realized by a plurality of components. Further, a plurality of functions possessed by a plurality of constituent elements may be realized by one constituent element, or one function realized by a plurality of constituent elements may be realized by one constituent element. Further, a part of the configuration of the above embodiment may be omitted. Further, at least a part of the configuration of the above embodiment may be added to or replaced with the configuration of other embodiments.

In addition to the distance measuring device 1 described above, a system including the distance measuring device 1 as a component, a program for making a computer function as the distance measuring device 1, and a non-transitional physical record such as a semiconductor memory in which this program is recorded. The present disclosure can also be implemented in various forms such as media, distance measurement methods, etc.

DESCRIPTION OF SYMBOLS 1... Distance measuring device, 2... Irradiation part, 3... Light receiving array part, 4... Counting part, 5... Signal processing part, 31... Photodetector

Claims (3)

an irradiation unit (2) configured to irradiate pulsed light;
a light receiving array section (3) comprising a plurality of photodetectors (31) that output pulse signals upon incidence of photons;
a histogram creation unit (4, S20, S30, S210 to S250) and
a noise floor calculation unit (S40, S280) configured to calculate a background light noise floor indicating a reception level of background light detected by the light receiving array unit based on the histogram created by the histogram creation unit; and,
a variation calculation unit (S50, S290) configured to calculate a variation parameter indicating a degree of variation in the background light noise floor based on the histogram created by the histogram creation unit;
Based on the background light noise floor calculated by the noise floor calculation unit and the variation parameter calculated by the variation calculation unit, the pulsed light irradiated by the irradiation unit is applied to the light receiving array unit in the histogram. a threshold value calculation unit (S60, S300, S305) configured to calculate a threshold value for determining whether or not it has been detected;
a distance calculation unit (S70, S310) configured to calculate a distance to an object that reflects the pulsed light based on the threshold calculated by the threshold calculation unit ;
The light receiving array section is configured such that a plurality of the photodetectors form one pixel, and includes one or more of the pixels,
The variation calculation unit sets the background light noise floor calculated by the noise floor calculation unit as BGND_n, the number of the photodetectors forming one pixel as N, and the irradiation unit irradiates the pulsed light. Let n be the number of times the histogram is integrated, which is created by integrating the detection results obtained by performing the light detection operation once or multiple times until the light receiving array section detects the pulsed light. , a distance measuring device (1) that calculates the variation parameter by the following equation (13), where the variation parameter is σ_BGND_n.

The distance measuring device according to claim 1,
The noise floor calculation unit calculates, as the background light noise floor, a light reception level of light detected by the light reception array unit when the pulsed light irradiated by the irradiation unit is not received by the light reception array unit. Distance measuring device. The distance measuring device according to claim 1 or 2 ,
The histogram creation unit (4, S210 to S250) is configured to obtain a histogram by performing a photodetection operation multiple times from when the irradiation unit irradiates the pulsed light to when the light receiving array unit detects the pulsed light. A distance measuring device that creates the histogram by integrating the detection results of the plurality of times.