Method for Measuring Flight Time, Storage Medium and Device

Abstract

The present application discloses a device for measuring time of flight, a storage medium, and a device. The present application obtains a plurality of timestamp sets collected by a time-to-digital converter during an integration period, obtains a histogram based on the plurality of timestamp sets, slides a time window between a start time and an end time of the histogram, and counts the number of count values of all timestamps covered by the time window at each sliding position. The position with the largest total number of timestamps is the target position, that is, the time when the echo signal is received is within the range of the time window at the target position, and the time of flight is calculated accordingly. Therefore, the embodiments of the present application can make the timestamps of the echo signal easier to determine, so the signal-to-noise ratio SBNR of the distance detector can be improved, thereby effectively improving the accuracy of the distance detector in measuring the time of flight.

Description

Technical Field

[0001] This application relates to the field of measurement, and in particular, to a method for measuring time of flight, a storage medium, and a device. Background Art

[0002] Time of flight (TOF) measurement technology has important applications in various three-dimensional ranging and three-dimensional imaging fields, such as autonomous driving, face recognition, 3D games, and virtual reality. Specifically, the time of flight (TOF) measurement technology is that a light source emits a continuous or pulsed outgoing light beam, which is reflected by the target to be measured and then returns. The photoelectric sensor receives the returned echo photon beam, and the distance of the target to be measured, that is, the depth information, is converted by calculating the time difference between the emitted outgoing light beam and the received echo photon beam, or by calculating the phase difference between the outgoing light beam and the echo photon beam.

[0003] In the actual measurement process of time of flight, interference from ambient light and dark noise of the photoelectric sensor itself will cause a large amount of interference information, that is, noise signals, in the measurement system. Therefore, how to avoid the influence of noise signals to improve the accuracy of time of flight ranging is a technical problem that those skilled in the art need to solve urgently. Summary of the Invention

[0004] The technical problem to be solved by the embodiments of this application is to provide a method for measuring time of flight, a storage medium, and a device, which reduce the influence of noise signals on the measurement and improve the accuracy of measuring the time of flight.

[0005] In a first aspect, this application provides a method for measuring time of flight, including:

[0006] Obtaining N sets of timestamps; where N is an integer greater than 1, each set of timestamps includes multiple timestamps, and the integration periods of the respective sets of timestamps are equal;

[0007] Obtaining a histogram based on the N sets of timestamps; where the abscissa of the histogram includes multiple timestamps, the abscissa of the histogram includes the count values corresponding to the respective timestamps; obtaining multiple total timestamp numbers based on a preset time window and the histogram;

[0008] Taking the position with the largest total timestamp number as the target position;

[0009] Determining the time of flight according to the target position.

[0010] In a second aspect, this application provides a device for measuring time of flight, including:

[0011] An acquisition unit for acquiring N sets of timestamps; where N is an integer greater than 1, each set of timestamps includes multiple timestamps, and the integration periods of the respective sets of timestamps are equal;

[0012] A generation unit for obtaining a histogram data histogram based on the N sets of timestamps; where the abscissa data of the histogram includes multiple of the timestamps, and the abscissa of the histogram includes count values corresponding to the respective timestamps;

[0013] A obtaining unit for obtaining multiple total timestamp counts based on a preset time window and the histogram;

[0014] A first determination unit for taking the position with the largest total timestamp count as the target position;

[0015] A second determination unit for determining the flight time according to the target position.

[0016] Based on the same application concept, since the principle of problem-solving and the beneficial effects of this device can be seen in the method embodiments of the above-mentioned various possible flight time measurement devices and the beneficial effects brought about, the implementation of this device can refer to the implementation of the method, and the repeated parts will not be elaborated.

[0017] Another aspect of the present application provides a computer-readable storage medium, in which instructions are stored, and when it runs on a computer, it causes the computer to execute the methods described in the above aspects.

[0018] Another aspect of the present application provides a computer program product containing instructions, and when it runs on a computer, it causes the computer to execute the methods described in the above aspects.

[0019] In the embodiments of the present application, a plurality of timestamp sets collected by a time-to-digital converter during an integration period are obtained, a histogram is obtained based on the plurality of timestamp sets, a time window is slid between the start time and the end time of the histogram, and the number of count values of all timestamps covered by the time window is counted at each sliding position. The position with the largest total number of timestamps is the target position, that is, the time when the echo signal is received is within the range of the time window at the target position, and the flight time is calculated accordingly. Since the pulse of the transmitted pulse signal has a certain pulse width, that is, a certain duration; the echo signal returned after the transmitted pulse signal is reflected by an object has the same pulse width characteristic as the transmitted pulse signal. And the noise signal does not have such a pulse width characteristic. Therefore, the echo signal will be strengthened after being accumulated within the time window. Correspondingly, the noise signal does not have such a characteristic. By sliding the time window on the histogram in the embodiments of the present application, the timestamps of the echo signal can be included in a concentrated manner at a certain sliding position, so that the total number of timestamps after summation within the time window is significantly prominent, making it easier to accurately determine the timestamps of the echo signal. Therefore, the signal-to-noise ratio SBNR of the distance detector can be improved, and the accuracy of measuring the flight time by the distance detector can be effectively improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the background art, the following will describe the drawings required to be used in the embodiments of the present application or the background art.

[0021] Figure 1A is a schematic structural diagram of a detector in a flight time measurement device provided by an embodiment of the present application;

[0022] Figure 1B is a schematic diagram of the principle of generating a histogram provided by an embodiment of the present application;

[0023] Figure 1C and Figure 1D is a schematic diagram of the histogram;

[0024] Figure 2 is a schematic flowchart of a method for measuring flight time provided by an embodiment of the present application;

[0025] Figure 3 is a schematic diagram of a histogram before intra-group smoothing processing provided by an embodiment of the present application;

[0026] Figure 4 is a physical diagram of the histogram after smoothing processing provided by an embodiment of the present application;

[0027] Figure 5 is a schematic diagram of the principle of the time window sliding on the histogram provided by an embodiment of the present application;

[0028] Figure 6It is a schematic structural diagram of a flight time measurement device provided by an embodiment of the present application;

[0029] Figure 7 It is another schematic structural diagram of a flight time measurement device provided by an embodiment of the present application. Detailed implementation manners

[0030] To make the objectives, features, and advantages of the embodiments of the present application more obvious and understandable, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present application.

[0031] When the following description refers to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The implementation manners described in the following exemplary embodiments do not represent all the implementation manners consistent with the present application. On the contrary, they are only examples of devices and methods consistent with some aspects of the present application as detailed in the appended claims.

[0032] In the description of the present application, it should be understood that terms such as "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific situations.

[0033] See Figure 1A , which is an architecture diagram of a flight time measurement device provided by an embodiment of the present application. In the embodiment of the present application, the flight time measurement device may include: a transmitter and a detector. The transmitter is used to emit pulse signals; the detector includes a pixel unit, a time-to-digital converter (TDC), and a random access memory (RAM). Further, the flight time measurement device can measure the distance between the flight time measurement device and the object to be measured by measuring the time interval between the pulse signal emitted by the laser pulse and the echo signal received by the detector.

[0034] The basic process of DTOF (direct time of flight) measurement is as follows: DTOF will emit N pulse signals and receive N echo signals within a single-frame measurement time, and then perform a histogram statistics on the flight times of the recorded N echo signals. The flight time with the highest frequency of occurrence is used to calculate the distance between the lidar and the target object.

[0035] Specifically, the transmitter emits a pulse signal towards the target object. The pulse signal is reflected when it encounters the target object. The pixel unit or pixel array receives the echo signal reflected by the target object, converts the echo signal into an electrical signal, the TDC records the generation time of the electrical signal (also known as the timestamp), and this generation time serves as the arrival time of the echo signal. The RAM stores the arrival time of the echo signal. Based on the emission time of the pulse signal and the arrival time of the echo signal, the time of flight TOF can be obtained, and then the distance of the target object can be calculated according to the constant speed of light and the time of flight.

[0036] However, in the actual measurement process, due to the high-sensitivity characteristics of the detector, in addition to the echo signal reflected by the target object, the signal received by the detector may also include noise signals. The sources of the noise signals include the components inside the detector or the incidence of ambient light. The detector cannot effectively distinguish which of the received signals are noise signals and which are echo signals. To reduce the influence of the noise signals on the DTOF measurement result, the related technology uses time-correlated single photon counting (TCSPC) to measure the time of flight. Its main principle is that the transmitter emits laser pulse signals multiple times within a time frame. Since the moving speed of the target object is much lower than the speed of light, the arrival times of the echo signals have the characteristics of coherence or consistency, while the arrival times of the noise signals are random. Thus, after experiencing multiple integration periods, the SiPM (Silicon photomultiplier) can stand out from the noise signals based on the echo signals accumulated by multiple SPADs (Single Photon Avalanche Diodes) within each integration period.

[0037] For example: Refer to Figure 1B As shown, the time frame consists of N integration periods, where N is an integer greater than 1. The echo signals received by the detector from the target object within each integration period are represented by rectangles filled with diagonal lines, and the received noise signals are represented by rectangles filled with gray. The transmitter emits laser pulse signals at the start times of the 1st integration period to the Nth integration period. It can be seen from the figure that in addition to receiving echo signals, the detector will also receive multiple noise signals within each integration period. The positions of the echo signals basically remain unchanged, while the positions of the individual noise signals are relatively random. The position of the signal (noise signal or echo signal) on the horizontal axis represents the arrival time. Based on the emission time of the pulse signal and the arrival time of the echo signal, the time of flight (TOF) of each echo signal can be calculated, and then the count value (cumulative number of times) of the echo signals corresponding to the same time of flight is statistically counted, and Figure 1BThe histogram below, where the horizontal axis of the histogram represents time and the vertical axis represents the count value, and the time corresponding to the maximum count value in the histogram is the flight time.

[0038] It can be seen that for the current measurement method based on DTOF flight time, the measured flight time depends on whether the peak position of the count value in the histogram can be effectively identified, and then the flight time can be identified. When the ambient light is weak and the target distance is small, the signal-to-background noise ratio (SBNR) is large, and the peak of the histogram corresponding to the echo signal is easily obtained after multiple integration periods, as follows Figure 1C shown. However, when the intensity of the ambient light is strong or the distance of the target object is large, the echo signal received by the detector becomes less as the distance increases, while the received ambient photons remain unchanged, the SBNR will be small, and the randomness of the noise signal may cause some peaks of the noise signal on the histogram to fluctuate more than the peak corresponding to the echo signal, resulting in incorrect peak recognition by the backend circuit and causing detection errors, as follows Figure 1D shown. Moreover, when the ambient light is stronger and the distance of the measured target is farther, the probability that the peak of the noise signal masks the peak of the echo signal is greater, thereby greatly reducing the accuracy of the detected distance.

[0039] Please refer to Figure 2 , Figure 2 which is a schematic flowchart of a method for measuring flight time provided by an embodiment of the present application. The method includes but is not limited to the following steps:

[0040] S201. Obtain N sets of timestamps.

[0041] Among them, 1 set of timestamps is used to represent the photon events corresponding to 1 integration period, which may include noise events and echo signal events. The integration periods corresponding to each set of timestamps are equal. The TDC records the reception time of the echo photons (pulse signals reflected by the target object) and stores the timestamps of the echo signals recorded within each integration period in the memory. The timestamps of multiple echo signals recorded by the TDC within one integration period form a set of timestamps. The specific process of recording the timestamps of the echo signals within the integration period can refer to Figure 1A and Figure 1B for description, which will not be elaborated here. The measurement device of the present application obtains N sets of timestamps recorded by the TDC within N integration periods. Each set of timestamps includes at least one timestamp, and the number of timestamps in each set of timestamps may be equal or unequal.

[0042] For example, N = 4, and the set of timestamps corresponding to the first integration period includes 2 timestamps: t 11, t 12 , the set of timestamps corresponding to the second integration period includes 4 timestamps: t 21 , t 22 , t 23 , t 24 , the set of timestamps corresponding to the third integration period includes 4 timestamps: t 31 , t 32 , t 33 , t 34 , the set of timestamps corresponding to the fourth integration period includes 7 timestamps: t 41 , t 42 , t 43 , t 44 , t 45 , t 46 , t 47 .

[0043] It can be understood that the time interval between two adjacent timestamps within the same set of timestamps is greater than or equal to the minimum time resolution of the TDC, which is determined by the hardware capabilities of the TDC.

[0044] S202. Obtain a histogram based on N sets of timestamps.

[0045] Among them, the histogram may include multiple timestamps and the count values of each timestamp. The count value represents the statistical times of the timestamp. For example: Refer to Figure 1B the shown histogram. The histogram may include 16 timestamps: t1 to t16, and each timestamp corresponds to its respective count value.

[0046] In a possible embodiment, obtaining a histogram based on N sets of timestamps can be achieved in the following manner:

[0047] Possibly, since the N integration periods in the embodiments of the present application are one detection period, therefore, the N sets of timestamps can be accumulated to obtain a histogram, and thus a histogram of a complete detection period can be obtained.

[0048] Possibly, the embodiments of the present application can also select K sets of timestamps from the N sets of timestamps; where K < N and K is an integer greater than 2; and then accumulate and process the selected K sets of timestamps to obtain a histogram.

[0049] Specifically, since the embodiments of the present application select K sets of timestamps from the N sets of timestamps and the value of K is less than N, therefore, it does not need to process all the sets of timestamps, which can reduce the amount of data for accumulation processing and thus reduce the duration consumed by the operation.

[0050] It can be understood that the time lengths of the N integration periods in the embodiments of the present application are the same. And when selecting the K timestamp sets, the integration periods of each timestamp set need to be aligned, that is, the start times and end times of each integration period are aligned, and then the K timestamp sets are subjected to an accumulation process. The specific accumulation process can refer to Figure 1B the description, which will not be elaborated here.

[0051] Further, the method for selecting K timestamp sets from the N timestamp sets in the embodiments of the present application includes:

[0052] Method 1: Randomly select K timestamp sets from the N timestamp sets.

[0053] Specifically, for the process of selecting K timestamp sets, the measuring device obtains the current time value as the initial input quantity. The current measuring device can also obtain other types of initial input quantities, such as variables like longitude and latitude coordinates. Then, the current time value is subjected to a hash operation to obtain a hash value, and then the hash value is modulo-divided by the quantity N to obtain a remainder i. The value range of the remainder i is 0 to N - 1. This remainder i is used as the serial number of the timestamp set, and the timestamp set corresponding to the remainder i is used as the reference timestamp set. The reference timestamp set and the first K - 1 timestamp sets before this reference timestamp set are used as the K timestamp sets selected this time. If the number of timestamp sets before the reference timestamp set is less than K - 1, the remaining number of timestamp sets is taken from the tail of the N timestamp sets. Alternatively, the reference timestamp set and the last K - 1 timestamp sets after this reference timestamp set are used as the K timestamp sets selected this time. If the number of timestamp sets after the reference timestamp set is less than K - 1, the remaining number of timestamp sets is taken from the head of the N timestamp sets.

[0054] Possibly, during the process of randomly selecting K timestamp sets, the current time value obtained is 13:39:00 on November 7, 2020. The hash operation on the current time value yields a hash value of 65538. Let N = 10 and K = 4. The serial numbers of timestamp sets 1 to 10 are 0 to 9 respectively. The hash value 65538 calculated is modulo-divided by 10 to obtain a remainder of 8, that is, the serial number of the reference timestamp set is 8. The timestamp set with serial number 8 and the 3 timestamp sets with serial numbers 5 to 7, namely timestamp set 6, timestamp set 7, timestamp set 8, and timestamp set 9, are used as the 4 timestamp sets selected this time.

[0055] Possibly, during this random selection process, the current time value is obtained as 13:44:01 on November 7, 2020. The current time value is subjected to a hashing operation to obtain 62539. Let N = 10 and K = 4. The serial numbers of the timestamp sets from 1 to 10 are 0 to 9 respectively. Taking the remainder of the hash value 62539 modulo 10 gives a remainder of 9. There are no 3 timestamp sets after the timestamp set with serial number 9. So, take the remaining 3 timestamp sets from the head. Then, the timestamp set 10, the timestamp set 1, the timestamp set 2, and the timestamp set 3 are used as the 4 selected timestamp sets for this time.

[0056] It should be noted that the above embodiments of randomly selecting K timestamp sets from N timestamp sets are only for illustrative purposes. Any method can also be used to randomly select K timestamp sets. For example: using a numerical probability algorithm, a Monte Carlo algorithm, a Las Vegas algorithm, or a Sherwood algorithm to randomly select a specified number of timestamp sets. The embodiments of this application are not limited.

[0057] Method 2: Select the K timestamp sets with the fewest number of timestamps from N timestamp sets.

[0058] It can be understood that since the number of pulse signals emitted in each integration period is unique, when selecting the timestamp sets with fewer timestamps in the integration period, the number of timestamps of the noise signals therein is correspondingly less. For example, N = 10 and K = 4. The 10 timestamp sets are: timestamp set 1 to timestamp set 10. The number of timestamps in timestamp set 1 is 100, the number of timestamps in timestamp set 2 is 122, the number of timestamps in timestamp set 3 is 123, the number of timestamps in timestamp set 4 is 102, the number of timestamps in timestamp set 5 is 98, the number of timestamps in timestamp set 6 is 90, the number of timestamps in timestamp set 7 is 80, the number of timestamps in timestamp set 8 is 85, the number of timestamps in timestamp set 9 is 89, and the number of timestamps in timestamp set 10 is 84. The 4 timestamp sets with the fewest number of timestamps selected from the 10 timestamp sets are: timestamp set 7, timestamp set 8, timestamp set 9, and timestamp set 10.

[0059] Method 3: Select K timestamps with odd serial numbers from N timestamp sets.

[0060] Among them, the N timestamp sets are numbered starting from 1. The serial numbers of the N timestamp sets are: 1, 2, 3,..., N. The serial numbers of odd numbers are 1, 3, 5,....

[0061] For example, N = 10 and K = 4. The 10 timestamp sets are: timestamp set 1 to timestamp set 10. The 4 timestamp sets with odd serial numbers selected from the 10 timestamp sets are: timestamp set 1, timestamp set 3, timestamp set 5, and timestamp set 7.

[0062] Method 4: Select K timestamp sets with even serial numbers from N timestamp sets.

[0063] Among them, the N timestamp sets are numbered starting from 1, and the serial numbers of the N timestamp sets are: 1, 2, 3,..., N. The serial numbers of even numbers are 2, 4, 6, 8.

[0064] For example, N = 10 and K = 4. The 10 timestamp sets are: timestamp set 1 to timestamp set 10. The 4 timestamp sets with even serial numbers selected from the 10 timestamp sets are: timestamp set 2, timestamp set 4, timestamp set 6, and timestamp set 8.

[0065] In another possible implementation, obtaining a histogram based on N timestamp sets may include:

[0066] Perform smoothing processing on each of the N timestamp sets to obtain the processed N timestamp sets;

[0067] Perform accumulation processing on the processed N timestamp sets to obtain the final histogram.

[0068] Among them, the integration periods of the N timestamp sets are aligned, that is, the start times and end times of each integration period are aligned. Then, perform accumulation processing on the N timestamp sets to obtain an intermediate histogram. The specific accumulation process can refer to Figure 1B 's description, which will not be elaborated here. Then, perform smoothing processing on the intermediate histogram to obtain the final histogram.

[0069] As Figure 3 shown, when the data in the N timestamp sets is not smoothed in the embodiment of the present application, the histogram obtained after accumulating the N timestamp sets. The histogram includes m timestamps and the count values corresponding to each timestamp. m is an integer greater than 2. In the histogram, the abscissa represents time, and the ordinate represents the count value. The m count values are bin1, bin2,..., bin k 、…、bin m ,..., bin m , and the timestamps corresponding to the m count values are t1, t2,..., t m , and the time interval between two adjacent count values in the histogram is greater than the minimum time resolution of the TDC. As Figure 4As shown, after the data in the N timestamp sets are smoothed respectively in the embodiments of the present application, the histograms of the processed N timestamp sets are accumulated to obtain m filtered values.

[0070] Possibly, as Figure 4 shown, the embodiments of the present application can use a digital filter for smoothing. When the digital filter is an FIR filter, the order of the FIR filter is n - 1. Before smoothing, the m count values are respectively: bin1, bin2,... bin m , after smoothing, the m count values are respectively: S1, S2,... S m .

[0071] It can be understood that S1 is the data obtained by accumulating the count values at the t1 moment in the N timestamp sets after the data in the N timestamp sets are smoothed respectively. By analogy, S m is the data obtained by accumulating the count values at the t m moment in the N timestamp sets after the data in the N timestamp sets are smoothed respectively. The digital filter performs digital filtering on the m count values in the N timestamp sets according to the equivalent sampling clock period, and performs digital filtering once per clock period. The digital filtering of the m count values is completed in m clock periods. Thus, the embodiments of the present application can suppress the timestamps of noise signals through smoothing, so that the timestamps of echo signals can be determined quickly.

[0072] It can be understood that the smoothing may include but is not limited to FIR digital filtering, FIIR digital filtering, interpolation processing, etc.

[0073] S203. Obtain multiple total timestamp numbers based on a preset time window and histogram.

[0074] Among them, the time interval of the histogram is the same as the integration period of the N timestamp sets. The length of the time window is greater than the minimum time resolution of the TDC, and is generally an integer multiple of the minimum time resolution of the TDC. For example, the minimum time resolution of the TDC is 1 ns, and the length of the time window is 3 ns.

[0075] Possibly, multiple consecutive time windows with the same width are set between the start time and the end time of the histogram based on the preset time window; the count values of the timestamps covered on each time window are summed to obtain multiple total timestamp numbers.

[0076] Specifically, in the embodiments of the present application, the time length between the start time and the end time of the histogram can be divided into multiple time windows, and there is no overlap between two adjacent time windows, that is, the start time of the current time window is the end time of the previous time window, and the end time of the current time window is the start time of the next time window. For each time window, count the number of timestamps covered by the time window to obtain multiple total timestamp numbers.

[0077] Possibly, control the time window to slide between the start time and the end time of the histogram at a preset sliding step; sum up the count values of the timestamps covered by the time window at each sliding position to obtain multiple total timestamp numbers.

[0078] Optionally, the length of the time window can be equal to the width of the laser pulse. The transmitter emits laser pulses within the integration period of each of the N timestamp sets. The laser pulse has a certain duration, and this duration is the width of the laser pulse. Further, since the length of the time window in the embodiments of the present application is equal to the width of the laser pulse, the slidable time window can concentrate the echo signals within the same time window, which not only reduces the time for searching for the peak timestamp but also improves the accuracy of searching for the peak timestamp.

[0079] It can be understood that the sliding step represents the time interval between two adjacent sliding positions. The sliding step can be K times greater than or equal to the minimum time resolution of the TDC, where K is an integer greater than 1. In this way, the embodiments of the present application can effectively identify each time window in the N timestamp sets using the TDC. The measuring device controls the time window to slide between the start time and the end time of the histogram. The time window has multiple different sliding positions during the sliding process. Further, for each sliding position of the time window, count the count values of all the timestamps covered by the time window, and then sum up the count values of all the timestamps to obtain the total timestamp number corresponding to this sliding position.

[0080] S204. Take the position with the largest total timestamp number as the target position.

[0081] Among them, after the sliding of the time window from the start time to the end time of the histogram is completed, the total number of timestamps at each sliding position is obtained, and the sliding position with the largest total number of timestamps is determined. For example: The time window slides 5 times between the start time and the end time of the histogram. The total number of timestamps covered by the time window is counted as 12 at the first sliding position, 15 at the second sliding position, 27 at the third sliding position, 10 at the fourth sliding position, and 8 at the fifth sliding position. Then the total number of timestamps at the third sliding position is the largest, and the third sliding position is determined as the target position.

[0082] For example, see Figure 5 As shown, the start time of the histogram is 450 nanoseconds, the end time is 490 nanoseconds, and the length of the time window is 3 nanoseconds ( Figure 5 as shown by the dashed box in). Specifically, the first sliding position of the time window is 450 nanoseconds to 453 nanoseconds, the second sliding position is 451 nanoseconds to 454 nanoseconds, and so on, and all sliding positions on the histogram can be determined. The count values of all timestamps covered by the time window at each sliding position are summed. For example: The count values of all timestamps covered by the time window at the first sliding position are summed to obtain a total number of timestamps of 13. Determine the sliding position with the largest total number of timestamps. As Figure 5 shown, the sliding position with the largest total number of timestamps is 466 nanoseconds to 469 nanoseconds. The time window covers 11 timestamps at this sliding position. The 11 timestamps are denoted as timestamp 1 to timestamp 11. The count value of timestamp 1 is 2, the count value of timestamp 2 is 3, the count value of timestamp 3 is 3, the count value of timestamp 4 is 2, the count value of timestamp 5 is 3, the count value of timestamp 6 is 2, the count value of timestamp 7 is 2, the count value of timestamp 8 is 4, the count value of timestamp 9 is 2, the count value of timestamp 10 is 2, and the count value of timestamp 11 is 2. The sum of the count values of the above 11 timestamps is 27 to obtain the total number of timestamps.

[0083] S205. Determine the flight time according to the target position.

[0084] In this embodiment, the number of count values of all timestamps covered by the time window can be counted at each sliding position. The position with the largest total number of timestamps is the target position, that is, the time when the echo signal is received is within the range of the time window at the target position, and the flight time is calculated accordingly. Among them, the method for determining the flight time according to the target position includes:

[0085] Method 1: Obtain the count values of each timestamp covered by the time window at the target position;

[0086] Use the timestamp with the largest count value as the peak timestamp;

[0087] Calculate the flight time based on the peak timestamp.

[0088] For example, refer to Figure 5 As shown, the time window covers 11 timestamps at the target position. The 11 timestamps are denoted as Timestamp 1 to Timestamp 11. The count value of Timestamp 1 is 2, the count value of Timestamp 2 is 3, the count value of Timestamp 3 is 3, the count value of Timestamp 4 is 2, the count value of Timestamp 5 is 3, the count value of Timestamp 6 is 2, the count value of Timestamp 7 is 2, the count value of Timestamp 8 is 4, the count value of Timestamp 9 is 2, the count value of Timestamp 10 is 2, and the count value of Timestamp 11 is 2. It can be seen that the count value of Timestamp 8 is the largest, and the value of Timestamp 8 is used as the peak timestamp. The peak time is the signal reception time detected. Then, calculate the flight time based on the photon signal emission time and the peak timestamp. For example: if the peak timestamp is t1 and the preset signal emission time is t0, then the flight time is t1 - t0. Then, the distance between the detector and the target object can be calculated based on the flight time and the speed of light.

[0089] Method 2: Obtain the count values of each timestamp covered by the time window at the target position;

[0090] Sort each timestamp in ascending order according to the count value;

[0091] Average the last N timestamps in the sorted order to obtain the peak timestamp; where N is an integer greater than 1;

[0092] Calculate the flight time based on the peak timestamp.

[0093] For example, refer to Figure 5As shown, the time window covers 11 timestamps at the target position. The 11 timestamps are denoted as Timestamp 1 to Timestamp 11. The count value of Timestamp 1 is 2, the count value of Timestamp 2 is 3, the count value of Timestamp 3 is 3, the count value of Timestamp 4 is 2, the count value of Timestamp 5 is 3, the count value of Timestamp 6 is 2, the count value of Timestamp 7 is 2, the count value of Timestamp 8 is 4, the count value of Timestamp 9 is 2, the count value of Timestamp 10 is 2, and the count value of Timestamp 11 is 2. The above 11 timestamps are sorted in ascending order according to the count values as: Timestamp 1, Timestamp 4, Timestamp 6, Timestamp 7, Timestamp 9, Timestamp 10, Timestamp 11, Timestamp 8, Timestamp 2, Timestamp 3, Timestamp 5. Take the average of the last 4 timestamps to obtain the peak timestamp. The methods for calculating the average include, but are not limited to: weighted average, arithmetic average, or geometric average, etc. For example: if the peak timestamp is t1 and the emission time of the pulse signal is t0, then the flight time is t1 - t0, and then the distance between the detector and the target object can be calculated based on the flight time and the speed of light.

[0094] Method 3: Obtain the count values of each timestamp covered by the time window at the target position;

[0095] Sort each timestamp in descending order according to the count value;

[0096] Take the average of the first N timestamps to obtain the peak timestamp; where N is an integer greater than 1;

[0097] Calculate the flight time based on the peak timestamp.

[0098] For example, referring to Figure 5 As shown, the time window covers 11 timestamps at the target position. The 11 timestamps are denoted as Timestamp 1 to Timestamp 11. The count value of Timestamp 1 is 2, the count value of Timestamp 2 is 3, the count value of Timestamp 3 is 3, the count value of Timestamp 4 is 2, the count value of Timestamp 5 is 3, the count value of Timestamp 6 is 2, the count value of Timestamp 7 is 2, the count value of Timestamp 8 is 4, the count value of Timestamp 9 is 2, the count value of Timestamp 10 is 2, and the count value of Timestamp 11 is 2. The above 11 timestamps are sorted in descending order according to the count values as: Timestamp 8, Timestamp 2, Timestamp 3, Timestamp 5, Timestamp 1, Timestamp 4, Timestamp 6, Timestamp 7, Timestamp 9, Timestamp 10, Timestamp 11. Take the average of the first 4 timestamps to obtain the peak timestamp. The methods for calculating the average include, but are not limited to: weighted average, arithmetic average, or geometric average, etc. For example: if the peak timestamp is t1 and the emission time of the pulse signal is t0, then the flight time is t1 - t0, and then the distance between the detector and the target object can be calculated based on the flight time and the speed of light.

[0099] It can be understood that in the above embodiments of the present application, by arranging the timestamps in ascending or descending order, the amount of data for calculating the peak timestamp is reduced. This not only effectively improves the efficiency of determining the peak timestamp but also improves the accuracy of measuring the flight time.

[0100] Therefore, in the embodiments of the present application, multiple timestamp sets collected by a time-to-digital converter during an integration period can be obtained. A histogram is obtained based on the multiple timestamp sets. A time window is slid between the start time and the end time of the histogram, and the number of count values of all timestamps covered by the time window is counted at each sliding position. The position with the largest total number of timestamps is the target position, that is, the time when the echo signal is received is within the range of the time window at the target position, and the flight time is calculated accordingly. Since the pulse of the transmitted pulse signal has a certain pulse width, that is, a certain duration; the echo signal returned after the pulse signal is reflected by an object has the same pulse width characteristic as the transmitted pulse signal. And the noise signal does not have such a pulse width characteristic. Therefore, the echo signal will be strengthened after being accumulated within the time window. Correspondingly, the noise signal does not have such a characteristic. By sliding the time window on the histogram in the embodiments of the present application, the timestamps of the echo signal can be concentrated and included at a certain sliding position, making the total number of timestamps after summation within the time window significantly prominent, making it easier to accurately determine the timestamps of the echo signal. Therefore, the signal-to-noise ratio SBNR of the distance detector can be improved, effectively improving the accuracy of the distance detector in measuring the flight time.

[0101] The above has elaborated in detail a flight time measurement device in the embodiments of the present application. Below, a flight time measurement device in the embodiments of the present application (hereinafter referred to as device 6) is provided.

[0102] Figure 6 The shown device 3 can implement Figure 2 the flight time measurement device of the shown embodiment. Device 6 includes an acquisition unit 601, a generation unit 602, a obtaining unit 603, a first determination unit 604, and a second determination unit 605.

[0103] The acquisition unit 601 is configured to acquire N timestamp sets; where N is an integer greater than 1, each of the timestamp sets includes multiple timestamps, and the integration periods of the respective timestamp sets are equal;

[0104] The generation unit 602 is configured to obtain a histogram based on the N timestamp sets; where the abscissa data of the histogram includes multiple timestamps, and the abscissa of the histogram includes count values corresponding to the respective timestamps;

[0105] The obtaining unit 603 is configured to obtain multiple total timestamp numbers based on a preset time window and the histogram;

[0106] A first determination unit 604, configured to use the position with the largest total number of timestamps as the target position;

[0107] A second determination unit 605, configured to determine the flight time according to the target position.

[0108] In one or more embodiments, the obtaining unit 603 includes:

[0109] A first setting subunit, configured to set a plurality of consecutive time windows with the same width between the start time and the end time of the histogram based on a preset time window;

[0110] A second setting subunit, configured to sum the count values of the timestamps covered by all the timestamps on each time window to obtain a plurality of total timestamp numbers;

[0111] The first determination unit 604 is specifically configured to: use the position of the time window with the largest total number of timestamps as the target position.

[0112] In one or more embodiments, the obtaining unit 603 includes:

[0113] A third setting unit, configured to control the time window to slide between the start time and the end time of the histogram with a preset sliding step;

[0114] A fourth setting unit, configured to sum the count values of the timestamps covered by the time window at each sliding position to obtain a plurality of total timestamp numbers;

[0115] The first determination unit 604 is specifically configured to: use the sliding position with the largest total number of timestamps as the target position.

[0116] In one or more embodiments, the second determination unit 605 includes:

[0117] A first acquisition subunit, configured to acquire the count values of the timestamps covered by the time window at the target position;

[0118] A first peak timestamp determination subunit, configured to use the timestamp with the largest count value as the peak timestamp;

[0119] A first calculation subunit, configured to calculate the flight time according to the peak timestamp.

[0120] In one or more embodiments, the second determination unit 605 includes:

[0121] A second acquisition subunit, configured to acquire the count values of the timestamps covered by the time window at the target position;

[0122] An ascending sub-unit for arranging the respective timestamps in ascending order according to the count values;

[0123] A first obtaining sub-unit for obtaining an average value of the last M timestamps to obtain a peak timestamp; where M is an integer greater than 1 and M < N;

[0124] A second peak timestamp determining sub-unit for using the peak timestamp as the signal reception time;

[0125] A second calculating sub-unit for calculating the flight time according to the transmission time of the pulse signal and the reception time of the echo signal.

[0126] In one or more embodiments, the second determining unit 605 includes:

[0127] A third obtaining sub-unit for obtaining the count values of the respective timestamps covered by the time window at the target position;

[0128] A descending sub-unit for arranging the respective timestamps in descending order according to the count values;

[0129] A second obtaining sub-unit for obtaining an average value of the first M timestamps to obtain a peak timestamp; where M is an integer greater than 1 and M < N;

[0130] A third peak timestamp determining sub-unit for using the peak timestamp as the signal reception time;

[0131] A third calculating sub-unit for calculating the flight time according to the transmission time of the pulse signal and the reception time of the echo signal.

[0132] In one or more embodiments, the generating unit 602 includes:

[0133] A selecting sub-unit for selecting K timestamp sets from the N timestamp sets; where K < N and K is an integer greater than 2;

[0134] An accumulating unit for performing an accumulating process on the selected K timestamp sets to obtain a histogram.

[0135] In one or more embodiments, the selecting sub-unit is specifically configured to:

[0136] Randomly select K timestamp sets from the N timestamp sets; or

[0137] Select the K timestamp sets with the least number of timestamps from the N timestamp sets; or

[0138] Select the K timestamp sets with odd serial numbers from the N timestamp sets; or

[0139] Select K sets of timestamps with even serial numbers from the N sets of timestamps.

[0140] In one or more embodiments, the generating unit 602 includes:

[0141] A smoothing subunit, configured to perform smoothing processing on the N sets of timestamps to obtain N processed sets of timestamps;

[0142] A histogram obtaining unit, configured to perform accumulation processing on the N processed sets of timestamps to obtain a final histogram.

[0143] In one or more embodiments, the length of the time window is greater than or equal to an integer multiple of the minimum time resolution of the TDC.

[0144] In one or more embodiments, the length of the time window is equal to the width of the laser pulse.

[0145] The embodiments of the present application and Figures 1A - 5 The method embodiments thereof are based on the same concept and have the same technical effects. The specific process can be referred to the description of the method embodiments in Figures 1A - 5 and will not be elaborated here.

[0146] The device 6 may be a field-programmable gate array (FPGA), an application-specific integrated chip, a system on chip (SoC), a central processing unit (CPU), a network processor (NP), a digital signal processing circuit, a microcontroller unit (MCU) for implementing related functions, and may also adopt a programmable logic device (PLD) or other integrated chips.

[0147] The above details a method for measuring the time of flight in the embodiments of the present application. The following provides a device for measuring the time of flight in the embodiments of the present application (hereinafter referred to as device 7).

[0148] Figure 7 FIG. is a schematic structural diagram of a device provided for an embodiment of the present application, hereinafter referred to as device 7. Device 7 may be integrated into the lidar or the carrier platform in the above embodiment, such as Figure 7 shown. The device includes: a memory 702 and a processor 701.

[0149] The memory 702 can be an independent physical unit, connected to the processor 901 via a bus. The memory 702 and the processor 701 can also be integrated together and implemented through hardware, etc.

[0150] Optionally, the device 7 may further include a transmitter and a receiver. The transmitter is used to transmit laser signals, and the receiver is used to receive laser signals.

[0151] The memory 702 is used to store programs for implementing the above method embodiments or each module of the device embodiments. The processor 701 calls the program and executes the operations of the above method embodiments:

[0152] Obtain N sets of timestamps; where N is an integer greater than 1, each set of timestamps includes multiple timestamps, and the integration periods of each set of timestamps are equal;

[0153] Obtain a histogram based on the N sets of timestamps; where the abscissa of the histogram includes multiple timestamps, and the abscissa of the histogram includes the count values corresponding to each timestamp; obtain multiple total timestamp numbers based on a preset time window and the histogram;

[0154] Take the position with the largest total timestamp number as the target position;

[0155] Determine the time of flight according to the target position.

[0156] In one or more embodiments, when the processor 701 executes the operation of obtaining multiple total timestamp numbers based on a preset time window and the histogram, it includes:

[0157] Set multiple consecutive time windows with the same width between the start time and the end time of the histogram based on the preset time window;

[0158] Sum up the count values of all the timestamps covered by each time window to obtain multiple total timestamp numbers;

[0159] The operation of taking the position with the largest total timestamp number as the target position includes: taking the time window position with the largest total timestamp number as the target position.

[0160] In one or more embodiments, when the processor 701 executes the operation of obtaining multiple total timestamp numbers based on a preset time window and the histogram, it includes:

[0161] Control the time window to slide between the start time and the end time of the histogram with a preset sliding step;

[0162] Sum up the count values of all the timestamps covered by the time window at each sliding position to obtain multiple total timestamp numbers;

[0163] Taking the position with the largest total timestamp number as the target position includes: taking the sliding position with the largest total timestamp number as the target position.

[0164] In one or more embodiments, the processor 701 executes determining the time of flight according to the target position, including:

[0165] Obtaining the count values of each timestamp covered by the time window at the target position;

[0166] Taking the timestamp with the largest count value as the peak timestamp;

[0167] Calculating the time of flight according to the peak timestamp.

[0168] In one or more embodiments, the processor 701 executes determining the time of flight according to the target position, including:

[0169] Obtaining the count values of each timestamp covered by the time window at the target position;

[0170] Sorting the timestamps in ascending order according to the count values;

[0171] Taking the average of the M timestamps arranged at the back to obtain the peak timestamp; where M is an integer greater than 1, and M < N;

[0172] Taking the peak timestamp as the signal reception moment;

[0173] Calculating the time of flight according to the transmission moment of the pulse signal and the reception moment of the echo signal.

[0174] In one or more embodiments, the processor 701 executes determining the time of flight according to the target position, including:

[0175] Obtaining the count values of each timestamp covered by the time window at the target position;

[0176] Sorting the timestamps in descending order according to the count values;

[0177] Taking the average of the M timestamps arranged at the front to obtain the peak timestamp; where M is an integer greater than 1, and M < N;

[0178] Taking the peak timestamp as the signal reception moment;

[0179] Calculating the time of flight according to the transmission moment of the pulse signal and the reception moment of the echo signal.

[0180] In one or more embodiments, the processor 701 executes obtaining the histogram based on the N timestamp sets, including:

[0181] Select K sets of timestamps from the N sets of timestamps; where K < N and K is an integer greater than 2;

[0182] Perform an accumulation process on the selected K sets of timestamps to obtain a histogram.

[0183] In one or more embodiments, the processor 701 executes the selection of K sets of timestamps from the N sets of timestamps, including:

[0184] Randomly select K sets of timestamps from the N sets of timestamps; or

[0185] Select the K sets of timestamps with the least number of timestamps from the N sets of timestamps; or

[0186] Select the K sets of timestamps with odd serial numbers from the N sets of timestamps; or

[0187] Select the K sets of timestamps with even serial numbers from the N sets of timestamps.

[0188] In one or more embodiments, the processor 701 executes the obtaining of the histogram based on the N sets of timestamps, including:

[0189] Perform a smoothing process on the N sets of timestamps to obtain the processed N sets of timestamps;

[0190] Perform an accumulation process on the processed N sets of timestamps to obtain the final histogram.

[0191] In one or more embodiments, the length of the time window is greater than or equal to an integer multiple of the minimum time resolution of the TDC.

[0192] In one or more embodiments, the length of the time window is equal to the width of the laser pulse.

[0193] The embodiments of the present application and Figure 2 The embodiments are based on the same concept, and the technical effects brought by them are also the same. The specific process can refer to the description of the Figure 2 embodiments and will not be elaborated here.

[0194] Among them, when part or all of the time-of-flight measurement method in the above embodiments is implemented by software, the device may also only include a processor. The memory for storing the program is located outside the device, and the processor is connected to the memory through a circuit / wire for reading and executing the program stored in the memory.

[0195] The processor can be a central processing unit (CPU), a network processor (NP), or a combination of a CPU and an NP.

[0196] The processor may further include a hardware chip. The above-mentioned hardware chip can be an application-specific integrated circuit (ASIC), a programmable logic device (PLD), or a combination thereof. The above-mentioned PLD can be a complex programmable logic device (CPLD), a field-programmable gate array (FPGA), a generic array logic (GAL), or any combination thereof.

[0197] The memory can include volatile memory, such as random-access memory (RAM); the memory can also include non-volatile memory, such as flash memory, a hard disk drive (HDD), or a solid-state drive (SSD); the memory can further include a combination of the above types of memory.

[0198] In the above embodiments, the sending unit or transmitter executes the sending steps of the above various method embodiments, and the receiving unit or receiver executes the receiving steps of the above various method embodiments, and other steps are executed by other units or processors. The sending unit and the receiving unit can form a transceiver unit, and the receiver and the transmitter can form a transceiver.

[0199] An embodiment of the present application also provides a computer storage medium storing a computer program for executing the method for measuring the time of flight provided in the above embodiments.

[0200] An embodiment of the present application also provides a computer program product containing instructions, which when running on a computer, causes the computer to execute the method for measuring the time of flight provided in the above embodiments.

[0201] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0202] The present application is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to the embodiments of the present application. It should be understood that each flow and / or block in the flowchart and / or block diagram, and the combination of flows and / or blocks in the flowchart and / or block diagram, can be realized by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing devices produce a device for realizing the functions specified in one or more flows in the flowchart and / or one or more blocks in the block diagram.

[0203] These computer program instructions can also be stored in a computer-readable memory capable of guiding a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory produce a manufactured article including an instruction device that realizes the functions specified in one or more flows in the flowchart and / or one or more blocks in the block diagram.

[0204] These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process, so that the instructions executed on the computer or other programmable device provide steps for realizing the functions specified in one or more flows in the flowchart and / or one or more blocks in the block diagram.

Claims

1. A method for measuring the flight time, characterized in that, including: Obtain N sets of timestamps; where N is an integer greater than 1, each set of timestamps includes multiple timestamps, and the integration periods of each set of timestamps are equal; Based on the N sets of timestamps, obtain a histogram; where the abscissa of the histogram includes multiple timestamps, and the ordinate of the histogram includes the count values corresponding to each timestamp; Control a time window to slide between the start time and the end time of the histogram at a preset sliding step; sum up the count values of all timestamps covered by the time window at each sliding position to obtain multiple total timestamp numbers; where the length of the time window is equal to the width of the laser pulse, and the sliding step represents the time interval between two adjacent sliding positions; Take the sliding position with the largest total timestamp number as the target position; Obtain the count values of each timestamp covered by the time window at the target position; Arrange each timestamp in ascending order according to the count value of each timestamp; Average the last M timestamps to obtain a peak timestamp; where M is an integer greater than 1 and M < N; Calculate the flight time according to the peak timestamp.

2. The method according to claim 1, characterized in that, The obtaining the histogram based on the N sets of timestamps includes: Select K sets of timestamps from the N sets of timestamps; where K < N and K is an integer greater than 2; Perform an accumulation process on the selected K sets of timestamps to obtain a histogram.

3. The method according to claim 2, characterized in that, The selecting K sets of timestamps from the N sets of timestamps includes: Randomly select K sets of timestamps from the N sets of timestamps; or Select the K sets of timestamps with the least number of timestamps from the N sets of timestamps; or Select K sets of timestamps with odd serial numbers from the N sets of timestamps; or Select K sets of timestamps with even serial numbers from the N sets of timestamps.

4. The method according to claim 1, characterized in that, The obtaining the histogram based on the N sets of timestamps includes: Perform a smoothing process on the N sets of timestamps to obtain N processed sets of timestamps; Perform an accumulation process on the processed N sets of timestamps to obtain a final histogram.

5. The method according to claim 1, wherein The length of the time window is greater than or equal to an integer multiple of the minimum time resolution of the TDC.

6. A device for measuring the time of flight, characterized in that, including: An obtaining unit for obtaining N sets of timestamps; where N is an integer greater than 1, each set of timestamps includes multiple timestamps, and the integration periods of each set of timestamps are equal; A generating unit for obtaining a histogram data histogram based on the N sets of timestamps; where the abscissa data of the histogram includes multiple timestamps, and the ordinate of the histogram includes the count values corresponding to each timestamp; A obtaining unit for controlling a time window to slide between the start time and the end time of the histogram at a preset sliding step; sum up the count values of all timestamps covered by the time window at each sliding position to obtain multiple total timestamp numbers; where the length of the time window is equal to the width of the laser pulse, and the sliding step represents the time interval between two adjacent sliding positions; A first determination unit, configured to use the sliding position with the largest total timestamp number as the target position; A second determination unit, configured to obtain the count values of the timestamps covered by the time window at the target position; sort the timestamps in ascending order according to the count values of the timestamps; obtain an average value of the last M timestamps to obtain a peak timestamp; where M is an integer greater than 1 and M < N; calculate the flight time according to the peak timestamp.

7. A computer storage medium, characterized in that, The computer storage medium stores a computer program, and when the computer program runs on a computer, the computer is caused to execute the method according to any one of claims 1 to 5.

8. A device for measuring the flight time, characterized in that Comprising: A processor and a memory, the memory is used to store a computer program or instruction, and the processor is used to execute the computer program or instruction in the memory to implement the method according to any one of claims 1 to 5.

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