CN118483712A - Distance measuring method, detector array and distance measuring module - Google Patents
Distance measuring method, detector array and distance measuring module Download PDFInfo
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
- G01S17/06—Systems determining position data of a target
- G01S17/08—Systems determining position data of a target for measuring distance only
- G01S17/10—Systems determining position data of a target for measuring distance only using transmission of interrupted, pulse-modulated waves
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/483—Details of pulse systems
- G01S7/486—Receivers
- G01S7/4861—Circuits for detection, sampling, integration or read-out
- G01S7/4863—Detector arrays, e.g. charge-transfer gates
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/483—Details of pulse systems
- G01S7/486—Receivers
- G01S7/4865—Time delay measurement, e.g. time-of-flight measurement, time of arrival measurement or determining the exact position of a peak
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- Electromagnetism (AREA)
- Optical Radar Systems And Details Thereof (AREA)
Abstract
The application discloses a ranging method, which comprises the following steps: acquiring dark count data of a detector array and photon flight time data of photons reflected back by a target to be detected, wherein the photons are received by the detector array; calibrating the time width of each time box by using the dark count data, and determining the calibrated width of each time box; and determining the distance of the target to be measured according to the photon flight time data and the calibration width of each time bin. The application also provides a detector array and a ranging module, which can correct the distance calculation error caused by the jitter deviation of the periodic phase/delay unit of the time-to-digital conversion unit, improve the measurement precision and improve the reliability of the ranging method.
Description
Technical Field
The invention relates to the technical field of ranging, in particular to a ranging method, a ranging module and ranging equipment.
Background
The direct time of flight (DTOF) technique is a ranging technique based on the principle of photon time of flight measurement. The DTOF ranging module generally comprises at least a light source, a photosensitive unit and a time-to-digital conversion unit (TIME DIGITAL Converter, TDC), and the ranging principle is as follows: the light pulse emitted by the light source irradiates the object to be detected, the light pulse is received by the photosensitive unit after being reflected by the object to be detected, the time-to-digital conversion unit records the time of emitting and receiving the light pulse, the flight time t of the light reciprocating in the air is calculated, and the distance s=c×t/2 of the object is obtained, wherein c is the light speed.
The DTOF ranging module generally measures photon flight time of a large number of light pulses, performs statistics and drawing to form a histogram, wherein the histogram is composed of a plurality of time boxes with certain time width, the height of each time box reflects the number of photons with flight time falling into the time box, and the distance of a target to be measured is obtained by searching a peak value from the histogram and determining the time in the time box where the peak value is located as the photon flight time reflecting the distance of the target to be measured. The time-to-digital conversion unit divides the time boxes according to the periodic phase/delay units and allocates corresponding storage spaces to store photon numbers in each time box, and the dividing precision of the time-to-digital conversion unit is the ranging precision of the ranging system, which is equal to the time width of the time boxes.
However, due to the non-ideal semiconductor manufacturing process, layout, design and other aspects and the influence of temperature, certain jitter deviation exists among the periodic phase/delay units of the time-to-digital conversion unit, so that the time width of each time box is not equal. The time width of all time bins is equal when the distance is calculated, which is equal to the distance measurement precision of the distance measurement system, so that the distance calculation has errors.
Disclosure of Invention
In view of the foregoing, an object of the present invention is to provide a ranging method, a ranging module and a ranging device.
According to a first aspect of the present invention, there is provided a ranging method comprising: acquiring dark count data of a detector array, and acquiring photon flight time data of photons reflected back by a target to be detected received by the detector array; calibrating the time width of each time box by using the dark count data, and determining the calibrated width of each time box; and determining the distance of the target to be measured according to the photon flight time data and the calibration width of each time bin.
Preferably, calibrating the time width of each time bin by using the dark count data, determining the calibrated width of each time bin includes: determining a dark count rate of the detector array and dark count values within each time bin; and determining the calibration width of each time box according to the dark count value in each time box and the dark count rate of the detector array.
Preferably, the ranging method includes at least a first frame data acquisition including acquiring dark count data and a second frame data acquisition including acquiring photon time-of-flight data; the time interval between the first frame data acquisition and the second frame data acquisition is smaller than a time threshold, or the difference of environmental parameters during the first frame data acquisition and the second frame data acquisition is smaller than a difference threshold.
Preferably, the ranging method includes one frame data acquisition including acquiring dark count data and acquiring photon time-of-flight data simultaneously.
Preferably, the ranging method further comprises: acquiring environmental parameters of a current frame, and judging whether the difference between the environmental parameters of the current frame and the environmental parameters of a previous frame is larger than a difference threshold; if the difference between the environmental parameter of the current frame and the environmental parameter of the previous frame is smaller than or equal to a difference threshold value, photon flight time data of the current frame are obtained, and the calibrated width of each time box of the previous frame is adopted; and if the difference between the environmental parameter of the current frame and the environmental parameter of the previous frame is larger than a difference threshold, acquiring dark count data and the photon flight time data again, calibrating the time width of each time box once according to the acquired dark count data, and determining the calibrated width of each time box.
Preferably, the environmental parameter includes at least one of a temperature parameter, a humidity parameter, a brightness parameter, a position parameter, and a voltage parameter.
According to a second aspect of the present invention, there is provided a detector array for generating dark count data and acquiring photon time-of-flight data of photons reflected back from an object to be measured, applying the ranging method described above; the detector array includes at least a first type of detector and a second type of detector, the dark count rate of the first type of detector being different from the dark count rate of the second type of detector.
Preferably, the detector array comprises a first detector element for generating dark count data and a second detector element for responding to photons reflected back from the object to be measured and generating photon time of flight data; wherein the dark count rate of the first detector element is greater than the dark count rate of the second detector element.
Preferably, in the detector array, the first detector element is located at a periphery of the second detector element, and the first detector element is light-shielded.
According to a third aspect of the present invention, there is provided a ranging module for ranging by using the ranging method described above, where the ranging module includes the detector array described above.
Advantageous effects
According to the ranging method, the detector array and the ranging module, dark count data of the detector array and photon flight time data of photons reflected by the to-be-measured object are obtained, then the time width of each time bin is calibrated according to the dark count data of the detector array, the calibration width of each time bin is determined, and then the distance of the to-be-measured object is calculated according to the photon flight time data of photons reflected by the to-be-measured object and the calibration width of each time bin, so that the distance calculation error caused by jitter deviation of a periodic phase/delay unit of the time-to-number conversion unit can be corrected, the measurement accuracy is improved, and the reliability of the ranging method is improved.
Furthermore, the ranging module utilizes the dark count data to calibrate the time width of each time box, so that the ranging module can meet the calibration requirement at any time and any place without being influenced by external environment, and the calibration is more convenient; moreover, when the external environment is unchanged or the change is very small, the calibration width of the time box can be recycled, the ranging efficiency is improved, and the ranging module does not need to set the light environment condition required by additionally setting the calibration time box width, so that the manufacturing cost is reduced and the volume of the ranging equipment is reduced.
Further, the detector array at least comprises a first type detector and a second type detector, the dark count rate of the first type detector is different from that of the second type detector, the first type detector and the second type detector are respectively used for generating dark count data and acquiring photon flight time data of photons reflected by a target to be detected, and the first type detector and the second type detector can work independently, so that calibration and ranging can be performed simultaneously, and the ranging efficiency is improved.
Further, whether the environmental parameters change or not is monitored in real time, if the difference between the environmental parameters of the current frame and the environmental parameters of the previous frame is larger than a preset threshold value, dark count data and photon flight time data are acquired again, the time width of each time box is calibrated once according to the acquired dark count data, and the calibration width of each time box is determined. If the difference between the environmental parameters of the current frame and the environmental parameters of the previous frame is smaller than or equal to a preset threshold value, the calibration result obtained by the previous frame is directly multiplexed to perform distance calculation, so that the accuracy of distance calculation is ensured, repeated calibration is avoided, the distance measurement effect is improved, and the operation load of the distance measurement module is reduced.
Drawings
The above and other objects, features and advantages of the present invention will become more apparent from the following description of embodiments of the present invention with reference to the accompanying drawings, in which:
fig. 1 shows a flowchart of a ranging method provided by an embodiment of the present invention;
FIG. 2 illustrates a histogram of first photon time-of-flight data provided by an embodiment of the present invention;
FIG. 3 illustrates a histogram of second photon time-of-flight data provided by an embodiment of the present invention;
FIG. 4 is a flow chart of another ranging method provided by an embodiment of the present invention;
fig. 5 shows a schematic structural diagram of a ranging module according to an embodiment of the present invention.
Detailed Description
Various embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. The same reference numbers will be used throughout the drawings to refer to the same or like parts. For clarity, the various features of the drawings are not drawn to scale.
The following describes in further detail the embodiments of the present invention with reference to the drawings and examples.
In the prior art, a time-to-digital conversion unit in a ranging module divides time boxes according to periodic phase/delay units and allocates corresponding storage spaces to store photon numbers in each time box, and the division precision of the time-to-digital conversion unit is equal to the time width of the time boxes. However, the time-to-digital conversion unit has a certain jitter deviation due to the non-ideal and temperature influence of the semiconductor manufacturing process, layout, design and the like according to the periodic phase/delay unit, so that the time width of each time box is not equal, and the distance calculation is error.
Dark Count Rate (DCR for short): the dark count refers to the number of times of dark count pulses per second, and the dark count refers to the phenomenon that carriers in a photosensitive material thermally excite to cause avalanche due to thermal motion under the action of reverse bias voltage in the absence of illumination, and one avalanche phenomenon generates one dark count pulse. In general, dark counts are mixed in photon counts of signal light, indistinguishable interference is generated on statistical data of photon flight time, and especially under the condition of weak light, dark counts can lead to higher noise points, and the signal to noise ratio is obviously reduced.
Based on the technical problems, the application utilizes the dark count with negative influence on the ranging effect to calibrate the periodic phase/delay unit of the time-to-digital conversion unit in the ranging module, thereby eliminating or reducing the ranging error caused by the jitter of the periodic phase/delay unit of the time-to-digital conversion unit. The following describes the technical scheme of the application in detail:
fig. 1 shows a flowchart of a ranging method provided by an embodiment of the present invention. As shown in fig. 1, the ranging method includes the following steps.
Step S110: dark count data of the detector array is acquired, and photon time-of-flight data of photons reflected back by the object to be measured is acquired by the detector array.
Step S120: and calibrating the time width of each time box by using the dark count data, and determining the calibrated width of each time box.
Step S130: and determining the distance of the target to be measured according to the photon flight time data and the calibration width of each time bin.
According to the ranging method, the dark count data of the detector array and the photon flight time data of photons reflected by the to-be-measured object are obtained, then the time width of each time bin is calibrated according to the dark count data of the detector array, the calibrated width of each time bin (namely the actual width of each time bin) is determined, and then the distance of the to-be-measured object is calculated according to the photon flight time data of photons reflected by the to-be-measured object and the calibrated width of each time bin, so that the distance calculation error caused by the jitter deviation of the periodic phase/delay unit of the time-to-number conversion unit can be corrected, the measurement accuracy is improved, and the reliability of the ranging method is improved.
In the application, the principle of calibrating the time width of each time box by using dark count data is as follows: the dark count characteristic of the detector array is related to factors such as internal structural defects of the detector, temperature and the like, and the detector array can be regarded as uniformly generating dark counts in the time dimension under the condition that the influencing factors are kept unchanged, namely the dark count rate is a fixed value. When the dark count rate of the detector array is a fixed value, the probability of generating dark counts in unit time is a fixed value, and if the dark counts are counted through a dark count-time histogram, the dark count value in each time box in the histogram is positively correlated with the time width of the time box, namely, the larger the time width of the time box is, the larger the dark count value in the time box is; and vice versa. Therefore, the actual width of each time bin, namely the calibration width, can be reversely deduced according to the dark count value in each time bin in the dark count data and the dark count rate.
According to the invention, the time width of each time box is calibrated by using the dark count data, so that the calibration requirement at any time and any place can be met without being influenced by external environment, and the calibration is more convenient; moreover, when the external environment is unchanged or the change is very small, the calibration width of the time box can be recycled, the ranging efficiency is improved, and the ranging module does not need to set the light environment condition required by additionally setting the calibration time box width, so that the manufacturing cost is reduced and the volume of the ranging equipment is reduced.
Specifically, referring to fig. 2, the larger the dark count value in each time bin is counted in the statistical histogram of the dark count data, the longer the time represented by the time bin (bin), the wider the time width of the time bin divided by the instant digital conversion unit. Referring to fig. 3, photon counts in each time bin are counted in a statistical histogram of photon flight time data, and a time bin (bin) corresponding to a peak value in the histogram is a target time bin reflecting a target distance to be measured. And after the widths of the time boxes are calibrated by using the dark count data, calculating the distance of the measured object according to the target time box and the widths of the time boxes before the target time box. It should be noted that, since the photon flight time t and the distance s from the measured object to the ranging device have a one-to-one correspondence, that is, s=c×t/2, c is the light velocity, the time bin in the statistical histogram may also be correspondingly converted into the distance bin, so as to obtain the same statistical result.
It should be noted that, there is a related art that uses dark counts to calibrate the gain of a Time-to-Digital Converter (TDC), which is mainly used to solve the problem of the uniformity of the TDC gain corresponding to multiple channels. Specifically, in the related art, the ranging module includes a plurality of detector elements, each detector element corresponds to a TDC, and the TDC is configured to acquire photon flight times of response of the detector element and divide a time bin to store photon counts corresponding to different photon flight times. Therefore, each detector element of the ranging module correspondingly outputs a photon time-of-flight statistical histogram, if the TDC gains corresponding to the detector elements are inconsistent or have large fluctuation difference, the time bin width in each statistical histogram is difficult to achieve high consistency, so that the statistical data of the statistical histograms are difficult to integrate into a total histogram, and the detection precision of the target object is reduced. To solve this problem, the related art calibrates the TDC gains of the channels (i.e., the detector elements) with the dark counts, so that the variation of the TDC gain of the channels is within a small range, the variation of the TDC gain of each channel is small, and the detection of the target object is more accurate. In other words, the calibration of the TDC gains of the multiple channels in the related art can be understood as calibrating the average ranging accuracy of the TDCs corresponding to the multiple channels, that is, the related art regards the TDC dividing time bins as uniform division, and the width of each time bin (bin) is the same, and the width of each bin is binsize. By calibrating the TDC gains of the channels, the average precision fluctuation difference of the TDCs of the channels is smaller, so that the detection precision of the target object is improved. The application aims at the problems that the TDC circuit has jitter caused by conditions such as a manufacturing process, temperature and the like of the single-channel TDC, the width division of each bin is uneven, and the calculation of a ranging result has errors.
The application is described below with reference to specific embodiments:
step S110: dark count data of the detector array is acquired, and photon time-of-flight data of photons reflected back by the object to be measured is acquired by the detector array.
In this embodiment, the dark count data may include dark count rate and dark count time distribution data for the detector array. If the dark count time distribution data is presented in the form of a histogram, the abscissa of the histogram is the time at which the detector array generates dark current, and the ordinate is the dark count value. In particular, the histogram may be constituted of a plurality of time bins representing time intervals having a time width, dark currents generated at different times will generate one count in the corresponding time bin, and the height of the time bin represents the number of dark counts whose generated time falls within the time bin. In other words, the dark count data may include the dark count rate of the detector array and the dark count values within the respective time bins.
In this embodiment, the photon time-of-flight data may include both the time-of-flight of the photons and the number of photons. If the photon time-of-flight data is presented in the form of a histogram, the abscissa of the histogram is the photon time-of-flight and the ordinate is the photon number. Every time a photon is captured by the detector array, photon counting is carried out at a corresponding abscissa position according to the flight time of the photon determined by the time-to-digital conversion unit, and the value of the photon number corresponding to the abscissa is increased by 1. It should be noted that, because the storage space of the ranging module is limited, the time-to-digital conversion unit generally divides the abscissa of the histogram into a plurality of time intervals according to the clock signal to allocate the storage space, where one time interval corresponds to the width of one time bin in the histogram and one storage entry; the height of the bin then reflects the number of photons whose time of flight falls within the bin.
In some embodiments, the ranging method includes at least a first frame data acquisition including acquiring dark count data and a second frame data acquisition including acquiring photon time-of-flight data; the time interval between the first frame data acquisition and the second frame data acquisition is smaller than a time threshold, or the difference of environmental parameters during the first frame data acquisition and the second frame data acquisition is smaller than a difference threshold.
Specifically, the first frame data acquisition and the second frame data acquisition are acquired by the same detector array under different time and different conditions, and the time interval between the first frame data acquisition and the second frame data acquisition is very small (less than a time threshold), or the environmental parameter variation between the first frame data acquisition and the second frame data acquisition is very small (the environmental parameter difference between the first frame and the second frame is less than a difference threshold). Therefore, the time-to-digital converter (TDC) in the two frames has similar working performance, and the widths of time boxes divided by the TDC in the two frames of data acquisition process are basically the same, so that the dark count data of the first frame can be utilized to calibrate the widths of the time boxes divided by the TDC and applied to photon flight time data processing of the second frame.
It should be noted that, in the first frame data acquisition, the detector array needs to be subjected to shading treatment, so that the acquired dark count data is free from photon count interference of ambient light. And the second frame data acquisition is performed without shading the detector array, so that the detector array can receive photons reflected by the object to be detected, and photon flight time data are acquired.
In this embodiment, dark count data and photon flight time data are acquired through at least two frames respectively, so that storage resources in the ranging module can be reused, that is, after the width calibration of the time box is completed by using the dark count data of the first frame, photon flight time data of the second frame can cover the dark count data obtained by the first frame, and the data obtained by the first frame and the second frame can be stored in the same storage space in sequence, thereby reducing storage space occupation and hardware resource allocation requirements.
In some embodiments, the ranging method includes a frame data acquisition including acquiring dark count data and acquiring photon time-of-flight data simultaneously. Specifically, the detector array includes at least a first type of detector and a second type of detector, the first type of detector having a dark count rate different from the dark count rate of the second type of detector. One type of detector is used to acquire dark count data and the other type of detector is used to acquire photon time-of-flight data. The two types of detectors can work independently and do not interfere with each other, so that calibration and ranging can be performed simultaneously, and the ranging efficiency is improved. Wherein the dark count rate of the detector for acquiring dark count data is greater and the dark count rate of the detector for acquiring photon time-of-flight data is less.
In this embodiment, the first type of detector for acquiring dark count data needs to perform shading treatment so as to avoid external ambient light interference; the second type of detector does not need to carry out shading treatment, and can normally receive photons reflected by the object to be detected.
Step S120: and calibrating the time width of each time box by using the dark count data, and determining the calibrated width of each time box.
In the present embodiment, step S120 includes the following steps.
Step S121: the dark count rate of the detector array and the dark count values within each time bin are determined. In this embodiment, the detector array may include a plurality of detectors arranged in an array. Thus, the dark count rate of the detector array (i.e., the probability of the detector array generating dark counts per unit time) may be determined based on the dark count rates of the plurality of detectors and the number of detectors on in the detector array.
Step S122: and determining the calibration width of each time box according to the dark count value in each time box and the dark count rate of the detector array.
In the present embodiment, the dark count value in each time bin is positively correlated with the time width of the time bin, and the larger the dark count value in the time bin is, the larger the time width of the time bin (bin) is (the longer the time represented by the time bin (bin)) is; and vice versa. The calibration width of each time bin can be calculated by the dark count value and the dark count rate of the corresponding time bin. For example, the dark count rate (i.e., the number of dark counts generated per nanosecond ns) of the detector array is 0.5, if the dark count value in time bin1 is 3, the nominal width a 1 =3/0.5=6 ns of time bin1, and so on, to obtain the nominal widths a 2、a3、……、a14 corresponding to time bins bin2-bin14, respectively.
Step S130: and determining the distance of the target to be measured according to the photon flight time data and the calibration width of each time bin.
In this embodiment, the calibration width of each time bin determined based on the dark count data is assigned to each time bin in the histogram corresponding to the photon time of flight data, and then the target time bin with the highest height (the maximum photon count value) is determined in the histogram corresponding to the photon time of flight data, so as to determine the distance of the target to be measured. According to the embodiment, the calibration width of each time bin determined in the dark count data is assigned to each time bin in the photon flight time data, so that distance calculation errors caused by jitter deviation of the time-to-digital conversion unit can be avoided, measurement accuracy is improved, and reliability of a ranging method is improved.
Specifically, referring to fig. 3, assuming that the statistical histogram of the second photon time-of-flight data includes time bins bin1, bin2, … …, bin14, the calibration widths a 1、a2、……、a14 corresponding to the respective time bins obtained from the dark count data are respectively assigned to bin1, bin2, … …, bin14. As shown in fig. 3, in the statistical histogram of the photon flight time data, the target time bin reflecting the distance of the target to be measured is bin5, and the photon flight time reflecting the distance of the target to be measured can be calculated by t=a 1+a2+a3+a4+a5. In some embodiments, centroid calculation may also be performed on t, improving accuracy.
Fig. 4 shows a flowchart of another ranging method provided by an embodiment of the present invention.
In some embodiments, whether to repeatedly perform TDC calibration may be determined according to whether the environmental parameter of the environment where the ranging module is located changes, that is, whether to perform calibration may be determined according to the difference between the environmental parameter of the ranging module and the environmental parameter of the previous frame before each frame of measurement. Specifically:
the ranging method may include:
step S140: and acquiring the environmental parameters of the current frame, and judging whether the difference between the environmental parameters of the current frame and the environmental parameters of the previous frame is larger than a preset threshold value.
In this embodiment, the environmental parameters may include at least one of a temperature parameter, a humidity parameter, a brightness parameter, a position parameter, and a voltage parameter of the ranging module, and the preset thresholds corresponding to different environmental parameters may be different. The preset threshold can be determined according to a large number of ranging experiments, and the working performance of the TDC is basically unchanged or very small under the condition that the change amplitude of the environmental parameter is smaller than the preset threshold, so that the TDC can be regarded as basically stable.
In this embodiment, step S140 may include two determination results:
judgment result 1: the difference between the environmental parameter of the current frame and the environmental parameter of the previous frame is larger than a preset threshold;
Judgment result 2: the difference between the environmental parameter of the current frame and the environmental parameter of the previous frame is less than or equal to a preset threshold.
For the judgment result 1, the ranging method of the present embodiment may further include:
step S150: and re-acquiring dark count data and the photon flight time data, calibrating the time width of each time box once according to the re-acquired dark count data, and determining the calibrated width of each time box.
In this embodiment, the determination result 1 may indicate that the ranging environment of the current frame has changed greatly compared with the ranging environment of the previous frame, and therefore, the working performance of the TDC may also change greatly, so that the TDC calibration result of the previous frame is not suitable for the ranging process of the current frame, and therefore, it is necessary to perform TDC calibration once again in the current frame to ensure that the ranging distance calculation is accurate.
In this embodiment, when the difference between the ambient temperature of the current frame and the ambient temperature of the previous frame is greater than a first preset threshold, or the difference between the ambient humidity of the current frame and the ambient humidity of the previous frame is greater than a second preset threshold, or the difference between the ambient brightness of the current frame and the ambient brightness of the previous frame is greater than a third preset threshold, or the difference between the operating voltage (especially the operating voltage of the TDC) of the ranging module of the current frame and the operating voltage (especially the operating voltage of the TDC) of the ranging module of the previous frame is greater than a fourth preset threshold, or the difference between the position of the ranging module of the current frame and the position of the ranging module of the previous frame is greater than a fifth preset threshold, the time width of each time bin is calibrated once according to the first photon flight time data of the current frame, and the calibrated width of each time bin is determined. The position parameter of the ranging module can be determined through a positioning system.
For the judgment result 2, the ranging method of the present embodiment may further include:
Step S160: and acquiring photon flight time data of the current frame, and adopting the calibration width of each time box of the previous frame.
In other words, if the ranging environment of the current frame is unchanged or has a smaller range than that of the previous frame, the operation performance of the TDC is stable, which can be regarded as that the operation performance of the TDC is basically unchanged, i.e. the jitter deviation of the periodic phase/delay unit of the TDC is basically the same as that of the previous frame. Therefore, the TDC calibration result of the previous frame can be repeatedly utilized in the current frame, and the TDC calibration result of the previous frame is endowed to a time bin in a statistical histogram corresponding to photon flight time data of the current frame, so that more accurate distance information of a target to be measured can be calculated, and the distance measurement efficiency is improved.
In this embodiment, when the difference between the ambient temperature of the current frame and the ambient temperature of the previous frame is less than or equal to a first preset threshold, or the difference between the ambient humidity of the current frame and the ambient humidity of the previous frame is less than or equal to a second preset threshold, or the difference between the ambient brightness of the current frame and the ambient brightness of the previous frame is less than or equal to a third preset threshold, or the difference between the operating voltage of the ranging module of the current frame and the operating voltage of the ranging module of the previous frame is less than or equal to a fourth preset threshold, or the difference between the position of the ranging module of the current frame and the position of the ranging module of the previous frame is less than or equal to a fifth preset threshold, the calibration width of each time bin of the previous frame is adopted.
According to the ranging method provided by the embodiment of the invention, whether the environmental parameters change or not is monitored in real time, if the difference between the environmental parameters of the current frame and the environmental parameters of the previous frame is larger than the preset threshold value, the calibration can be carried out by re-acquiring the dark count data to calibrate the time-to-digital conversion unit so as to dynamically start the calibration in real time, and the calibration width of each time box is the actual width of the time box actually divided by the time-to-digital conversion unit, so that the actual distance represented by the time box where the peak value in the histogram is located can be accurately calculated through the calibration width of each time box, and the measurement accuracy is improved. If the difference between the environmental parameters of the current frame and the environmental parameters of the previous frame is smaller than or equal to a preset threshold value, the calibration result obtained by the previous frame is directly multiplexed to perform distance calculation, so that the accuracy of distance calculation is ensured, repeated calibration is avoided, the distance measurement effect is improved, and the operation load of the distance measurement module is reduced.
The application also provides a detector array 210, and the detector array 210 applies the ranging method of the above embodiment to perform ranging.
In this embodiment, the detector array 210 is used to generate dark count data and to acquire photon time-of-flight data for photons reflected back by the object under test.
In this embodiment, the detector array 210 includes at least a first type of detector 211 and a second type of detector 212, where the dark count rate of the first type of detector 211 is different from the dark count rate of the second type of detector 212.
In this embodiment, the detector array 210 includes a first detector element 211 and a second detector element 212, wherein the first detector element 211 is configured to generate dark count data and the second detector element 212 is configured to respond to photons reflected back from an object to be measured and generate photon time-of-flight data.
Wherein the dark count rate of the first detector element 211 is greater than the dark count rate of the second detector element 212.
In some embodiments, in the detector array 210, the first detector element 211 is located at the periphery of the second detector element 212, and the first detector element 211 is shielded from light. So that the first detector element 211 and the second detector element 212 can operate independently of each other without interfering with each other.
The application also provides a ranging module 200 for ranging by using the ranging method described in the above embodiment, where the ranging module 200 includes the detector array 210 described in the above embodiment.
Fig. 5 shows a schematic structural diagram of a ranging module according to an embodiment of the present invention. Referring to fig. 5, the ranging module includes a detector array 210, a light source 220, and a time-to-digital conversion unit 230.
The incident light pulse emitted by the light source 220 is reflected to the second detector through the object to be detected, and photon flight time data can be obtained.
In this embodiment, the time-to-digital conversion unit 230 is configured to obtain dark count data and photon time-of-flight data of photons reflected by the object to be measured onto the detector array, and store the dark count data and the photon time-of-flight data by dividing the time bins.
The ranging module 200 also includes a processor 240 and a memory 250. The processor 240 is configured to perform the ranging method provided in the above embodiment, process the data, and calculate the distance between the objects to be measured. The memory 250 is used to provide storage space for dark count data and photon time-of-flight data, respectively.
Embodiments in accordance with the present invention, as described above, are not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention and various modifications as are suited to the particular use contemplated. The invention is limited only by the claims and the full scope and equivalents thereof.
Claims (10)
1. A ranging method, comprising:
Acquiring dark count data of a detector array, and acquiring photon flight time data of photons reflected back by a target to be detected received by the detector array;
Calibrating the time width of each time box by using the dark count data, and determining the calibrated width of each time box;
and determining the distance of the target to be measured according to the photon flight time data and the calibration width of each time bin.
2. The ranging method as defined in claim 1 wherein calibrating the time width of each time bin using the dark count data, determining the calibrated width of each time bin comprises:
determining a dark count rate of the detector array and dark count values within each time bin;
And determining the calibration width of each time box according to the dark count value in each time box and the dark count rate of the detector array.
3. The ranging method as defined in claim 1 wherein the ranging method comprises at least a first frame data acquisition comprising acquiring dark count data and a second frame data acquisition comprising acquiring photon time-of-flight data;
The time interval between the first frame data acquisition and the second frame data acquisition is smaller than a time threshold, or the difference of environmental parameters during the first frame data acquisition and the second frame data acquisition is smaller than a difference threshold.
4. The ranging method as defined in claim 1 wherein the ranging method comprises a frame data acquisition comprising acquiring dark count data and acquiring photon time-of-flight data simultaneously.
5. The ranging method according to claim 3 or 4, further comprising:
Acquiring environmental parameters of a current frame, and judging whether the difference between the environmental parameters of the current frame and the environmental parameters of a previous frame is larger than a difference threshold;
If the difference between the environmental parameter of the current frame and the environmental parameter of the previous frame is smaller than or equal to a difference threshold value, photon flight time data of the current frame are obtained, and the calibrated width of each time box of the previous frame is adopted;
And if the difference between the environmental parameter of the current frame and the environmental parameter of the previous frame is larger than a difference threshold, acquiring dark count data and the photon flight time data again, calibrating the time width of each time box once according to the acquired dark count data, and determining the calibrated width of each time box.
6. The ranging method as recited in claim 5 wherein the environmental parameter comprises at least one of a temperature parameter, a humidity parameter, a brightness parameter, a location parameter, and a voltage parameter.
7. A detector array applying the ranging method of any of claims 1 to 6 for generating dark count data and acquiring photon time of flight data of photons reflected back by an object to be measured;
The detector array includes at least a first type of detector and a second type of detector, the dark count rate of the first type of detector being different from the dark count rate of the second type of detector.
8. The detector array of claim 7, comprising a first detector element for generating dark count data and a second detector element for responding to photons reflected back from an object to be measured and generating photon time of flight data;
wherein the dark count rate of the first detector element is greater than the dark count rate of the second detector element.
9. The detector array of claim 8, wherein in the detector array the first detector element is located at a periphery of the second detector element, and the first detector element is masked.
10. A ranging module for ranging by the ranging method according to any one of claims 1 to 6, comprising: the detector array of any of claims 7-9.
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