CN111366944B

CN111366944B - Distance measuring device and distance measuring method

Info

Publication number: CN111366944B
Application number: CN202010250865.9A
Authority: CN
Inventors: 顾可可; 马宁; 陈晓刚; 张合勇; 白云峰
Original assignee: Zhejiang Guangpo Intelligent Technology Co ltd
Current assignee: Zhejiang Guangpo Intelligent Technology Co ltd
Priority date: 2020-04-01
Filing date: 2020-04-01
Publication date: 2022-06-28
Anticipated expiration: 2040-04-01
Also published as: CN111366944A

Abstract

The invention relates to a distance measuring device and a distance measuring method, wherein the distance measuring device comprises an active light source, a light source and a light source, wherein the active light source is used for emitting measuring light which is periodically modulated to a target object; the receiving device is provided with at least one SPAD, the periodically modulated measuring light is configured into a pulse sequence with a plurality of periods, each period comprises a pulse period and a blank period, at least two light pulses are contained in one pulse period, the length of each period is larger than or equal to the single working time of the SPAD, and the SPAD only responds to one light pulse triggering event in a single pulse period. The invention can overcome the problem of inaccurate result caused by easy environmental noise interference of SPAD ranging in the prior art.

Description

Distance measuring device and distance measuring method

Technical Field

The invention relates to a distance measuring technology, in particular to a distance measuring device and a distance measuring method based on a single photon avalanche diode.

Background

In recent years, the field of unmanned driving or assisted driving is in a vigorous development period, and the vehicle-mounted laser radar technology is a link of great importance in the link of attack and defense. Due to the large demand, the great development of the laser radar is promoted, and the laser radar technology and related companies at home and abroad emerge in a large quantity.

In the existing laser ranging technology, a detector mostly adopts a common Avalanche Photodiode (APD), but after the APD detects an optical signal, an output signal of the APD is an analog quantity which is in positive correlation with the intensity of the light received by a light-sensitive surface, and in order to ensure the consistency of waveforms under different light intensities, a series of complex circuit structures are required to process the signal at the rear end. Meanwhile, the gain is limited, and the detection distance is greatly limited within a limited laser energy range.

The geiger mode APD, i.e., a Single Photon Avalanche Diode (SPAD), is based on internal photoelectric response and has the characteristic of high gain, and photoelectrons generated by a Single Photon can rapidly generate one-time Avalanche response (about 10 ps) under the action of a strong electric field. Therefore, the SPAD has single photon response capability and is beneficial to long-distance detection under the condition of lower laser energy. Meanwhile, the back end circuit is simple in structure, the waveform of the quenched avalanche signal is fixed after shaping, and measurement errors can be reduced.

Fig. 1 and 2 show the principle of laser ranging using SPAD. As shown in the figure, the laser emits a periodic pulse, and when the laser encounters an object to be measured, the pulse is reflected by the object and attenuated into a photon magnitude triggering SPAD. According to the working principle of the SPAD device, in a pulse period, the SPAD can be triggered by reflected light pulses (the probability is highest, and the trigger time is converted into the distance which is the position of the object to be detected) and can also be triggered by other noises (the probability is lower, and the trigger time is dispersed). The statistical map of fig. 2 is thus generated by statistical superposition of the N pulses. Wherein the abscissa is the time difference from the pulse emission to the SPAD trigger and the ordinate is the number of photons detected.

If a pulse sequence includes 200 pulses, ideally, when the laser returned from the measured object is strong enough, the total number of photons counted at this time point is the highest (for example, greater than 30), and is much greater than the number of times counted at other time points (that is, the number of times counted by the environmental noise is smaller than 10 at each time point), and then the flight time related to the corresponding obvious statistical peak is converted into the distance to obtain the position of the measured object.

However, the SPAD captures the reflected laser light with weak intensity and cannot obtain a clear statistical peak value under the following conditions:

1. the output laser power is not high

2. Low reflectivity of the measured object

3. The object is far away.

At this time, the peak in fig. 2 is weakened to cause the measurement signal to be annihilated in the environmental disturbance signal, so that the accuracy of measurement is degraded.

Disclosure of Invention

In view of the above, the present invention provides a new ranging device and a ranging method based on SPAD, which can overcome the problem of inaccurate result caused by the fact that SPAD ranging is easily interfered by environmental noise in the prior art.

The invention provides a distance measuring device, which comprises an active light source, a light source and a controller, wherein the active light source is used for emitting measuring light which is periodically modulated to a target object; the receiving device is provided with at least one SPAD, the periodically modulated measuring light is configured into a pulse sequence with a plurality of periods, each period comprises a pulse period and a blank period, at least two light pulses are contained in one pulse period, the length of each period is larger than or equal to the single working time of the SPAD, and the SPAD only responds to one light pulse triggering event in a single pulse period.

Preferably, the receiving device further comprises a signal recording unit, the signal processing device comprises a statistical unit, the signal recording unit responds to the detection event of the SPAD and records the detection event as a measurement signal, and the statistical unit performs statistics on the measurement signal according to a time sequence distribution.

Preferably, the signal processing apparatus further includes a result identification unit, and according to the statistical result of the statistical unit, the result identification unit identifies the statistical result in one pulse sequence, and determines whether there is a corresponding number of statistical peak values corresponding to the at least two optical pulses in the pulse sequence.

Preferably, the optical fiber detection device further comprises a control device for providing a pulse driving signal to the active light source and providing optical pulse timing information to the signal identification unit, and the signal identification unit judges whether the at least two statistical peak values correspond to the at least two optical pulses according to the pulse timing information.

Preferably, the distance calculating device is further included, and when the signal identifying unit identifies the at least two statistical peaks, the distance of the target object is calculated according to the time sequence positions of the at least two peaks.

Preferably, the receiving device is a SPAD array.

According to an object of the present invention, there is also provided a ranging method using the ranging apparatus as described above, comprising the steps of:

providing an active light source for emitting periodically modulated measuring light to the target,

providing a receiving device for receiving the measuring light returned from the target object and forming a measuring signal,

providing a signal processing device for processing the measurement signal to generate a statistical result, wherein

The receiving device has at least one SPAD, the periodically modulated measuring light is configured as a pulse train having a number of periods, each period comprising a pulse period and a blank period, at least two light pulses within a pulse period, and each period having a length greater than or equal to a single on-time of the SPAD, the SPAD responding to only one light pulse triggering event within a single pulse period.

Preferably, the step of generating statistical results for the measurement signal processing comprises: and counting the time-sequence distribution of the measurement signals.

Preferably, the method further includes identifying a statistical result in one pulse sequence, and determining whether at least two statistical peaks having a correspondence with the at least two optical pulses exist in the pulse sequence, where the correspondence includes that a time interval between the at least two statistical peaks is consistent with a time interval between the at least two optical pulses.

Preferably, the statistics further includes convolving the statistical result with the light source signal sequence to obtain the time offset.

Preferably, after identifying the at least two statistical peaks, the method further includes calculating a distance of the target object according to time-series positions of the at least two peaks.

According to the object of the invention, a distance measuring device as described above is proposed for use in measuring the reflectivity of an object.

According to the purpose of the invention, the application of the distance measuring device is provided for judging the distance interval of the object.

Compared with the existing counting, the distance measuring device and the distance measuring method have the following counting effects:

1. by setting a multi-pulse mode, the original finding of a photon number peak value is changed into finding of a plurality of peak values at corresponding intervals, so that the probability of positioning errors caused by noise interference is reduced;

2. at the same distance, the reflectivity of the reflector at the position can be judged by judging the corresponding ratio of the peak values of the number of the photons;

3. at different distances, the distance of the object can be judged by calculating the flight time and the corresponding ratio of a plurality of photon number peak values.

Drawings

Fig. 1 is a schematic diagram of a measurement light signal of a conventional laser ranging.

Fig. 2 is a graph of statistical results obtained from the measured optical signals in fig. 1.

FIG. 3 is a schematic diagram of a measuring optical signal of the distance measuring device of the present invention.

Fig. 4 is a graph of statistical results obtained from the measured optical signals in fig. 3.

Fig. 5 is a schematic structural diagram of the distance measuring device of the present invention.

FIG. 6 is a diagram illustrating statistical results of a second technique according to the present invention.

Fig. 7 is a diagram illustrating statistical results of a third technique according to the present invention.

Fig. 8 is a flow chart of the ranging method of the present invention.

Detailed Description

The present invention will be described in detail with reference to the specific embodiments shown in the drawings, which are not intended to limit the present invention, and structural, methodological, or functional changes made by those skilled in the art according to the specific embodiments are included in the scope of the present invention.

As mentioned in the background, with the existing SPAD ranging scheme, the measurement signal is easily annihilated in the background noise due to the ambient light interference and the crosstalk signal between the devices during the signal readout, thereby affecting the measurement accuracy of the SPAD device.

The invention provides an active light source with a coding scheme, which enables measuring light to emit light pulses with specific codes in one period, enables only 1 light pulse in one period to be sensed by an SPAD device by controlling the time interval between the light pulses, counts the measuring results according to time sequence according to the receiving probability returned by each light pulse, if the statistical peak values corresponding to the number and the time interval of the light pulses can be found, shows that the statistical peak values are correct signals reflected by an object, and then calculates the distance of the object according to the signals to ensure the correctness of the measuring results.

For the sake of easy understanding, the technical principle of the present invention will be described below. Referring to fig. 3, the upper light pulse in fig. 3 is a simple periodic light pulse, and a certain interval period is set between each pulse, and the interval period enables the SPAD device to be reset after being excited by one pulse, so that the SPAD device can be restored to the working state before the next pulse arrives. The invention modulates the light pulse in one period on the basis of the general periodic pulse to generate a plurality of pulses, and transmits 3 pulses with equal intervals and equal amplitudes as shown in the lower part of figure 3. Of course, other numbers or at least two or more light pulses arranged at equal amplitudes and unequal intervals are also possible. It should be noted that the example in fig. 3 does not have the same pulse width as the signal in fig. 1, but only schematically shows the comparison between the pulse setting method of the present invention and the conventional pulse setting method. The pulses of light are spaced apart at short intervals, typically shorter than the recovery period of the SPAD device, so that only one pulse of light in a set of pulses of light within a period T triggers the SPAD device to respond and be recorded. At this time, if the laser reflected back by the measured object is strong enough, the SPAD has the largest probability of being triggered by the first pulse reflected back, then the second pulse, then the third pulse, and finally the situation of being triggered by noise. In one measurement, a group of pulse sequences is transmitted, and a statistical result graph distributed in time series in fig. 4 can be obtained by collecting feedback signals under the duration of the pulse sequences and then performing statistical processing. It can be seen from the figure that the SPAD is started by the first light pulse the most times, and the highest statistical peak is obtained, then the second light pulse, and then the third light pulse, and the intervals of the three statistical peaks are the same as the time intervals of the light pulses in a single period, which shows that the actual result is consistent with the theoretical expectation.

According to this principle, if a plurality of statistical peaks corresponding to the number of pulses and time intervals can be read in one ranging action, it can be determined that these peaks are measurement results caused by measurement light reflected by an object, thereby excluding the background interference signal. On the contrary, if the statistical result shows that the distribution of each signal is uniform, or although there is a statistical peak, the distribution of the statistical peak does not correspond to the distribution of the light pulse, it can be determined that the measurement is invalid. By utilizing the mechanism, the influence of ambient light on the SPAD device can be eliminated, and the accuracy and the reliability of the SPAD distance measurement are greatly improved.

Hereinafter, the technical solution of the present invention will be described in detail by specific embodiments.

Referring to fig. 5, fig. 5 is a schematic structural diagram of a distance measuring device according to the present invention. As shown in the figure, the distance measuring device 10 includes a housing 11, which has a hollow accommodating cavity 12 inside, and mechanical and electronic components required by the device are placed inside. In the illustrated embodiment, one working surface 13 of the housing 11 is provided with a light exit hole 14 and a light entrance hole 15. In other embodiments, the light exit and/or light entrance holes may be formed in other working surfaces of the housing 11, and for example, in order to increase the measurement circumferential angle of the distance measuring device 10, a plurality of working surfaces may be formed to scan from different directions.

The distance measuring device 10 comprises, seen from the inside, an active light source 19 for emitting periodically modulated measuring light towards a target 20; a receiving device 18 for receiving the measuring light returned from the target 20, and a signal processing device 16 for processing the measuring signal of the receiving device to generate a statistical result.

In one embodiment, the active light source 19 includes a laser light source and a modulation valve, and the laser light source is made to show a periodically modulated pulse laser by controlling the on/off of the modulation valve. The receiver 18 uses a Single Photon Avalanche Diode (SPAD) 28 as the photoelectric conversion element in the present invention, and in one embodiment the SPAD element 28 is an SPAD array of a plurality of SPAD devices.

According to the inventive idea of the invention, the measuring light emitted by the active light source 19 is configured as a pulse train having several periods, each period comprising a pulse period and a blank period, with at least two light pulses within a pulse period, and each period having a length greater than or equal to the single on-time of the SPAD, and the interval time between at least two light pulses being less than the single on-time of the SPAD. Through the configuration, in the process of one-time measurement, a pulse sequence containing a plurality of periods is emitted, is reflected back by a target and is sensed by the SPAD device, and a background signal processing device is triggered to count the measurement signals to form a statistical result.

Further, the receiving device 18 also comprises a signal recording unit 38, the signal recording unit 38 being responsive to detection events of the SPAD28 and recording as a measurement signal. The signal processing device 16 includes a statistical unit 26 and a result identification unit 36, the statistical unit 26 counts the measurement signals according to the time-series distribution, and the result identification unit 36 identifies the statistical result in one pulse sequence according to the statistical result of the statistical unit 26, and determines whether there is a statistical peak value corresponding to the light pulse emitted by the active light source 19 in one pulse sequence.

Further, a control device 17 is also included in the distance measuring device 10. The control device 17 supplies pulse drive signals to the active light source 19 on the one hand, and supplies light pulse timing information to the signal recognition unit 36 on the other hand. Thus, the signal identification unit 36 can obtain information such as the emission time and the time interval of the light pulse according to the pulse timing information, and then judge whether a plurality of statistical peak values appearing in the statistical result correspond to the light pulse emitted by the active light source according to the received statistical result.

Further, a distance calculating device 27 is included in the distance measuring device 10. When the signal identifying unit 36 identifies a plurality of correct statistical peaks, the distance to the target object is calculated according to the time-series positions of the peaks. A specific calculation method is, for example, a time of flight (TOF) method, which calculates the distance between the target object 20 and the ranging apparatus 10 by calculating the difference between the time of transmission of one pulse and the time of reception of the signal reflected by the pulse.

Referring to fig. 6, fig. 6 is a schematic diagram illustrating statistical results of a second technique according to the present invention. As shown, the magnitudes of the three statistical peaks are close to each other, that is, the probabilities that the three light pulses emitted by the active light source 19 are received and trigger SPAD counting are close and not very prominent compared with the background light (compare with fig. 4). In this case, the reflected measuring light is generally weakened due to the low reflectivity of the object surface, which reduces the sensitivity of SPAD detection, so that the probability of three light pulses being detected is close. According to the principle, after the statistical result is read, a group of threshold values can be set, and the reflectivity of the surface of the object can be roughly judged by comparing the threshold values, so that the distance measuring device of the invention has the function of judging the reflectivity of the target object besides the basic function of measuring the distance of the object.

Referring to fig. 7, fig. 7 is a schematic diagram of statistical results of another application of the present invention. As shown, the three statistical peaks are far from the target, which indicates that the target is far away, and the three statistical peaks have weak amplitudes and are close to each other, because when measuring a target at a long distance, the measurement light reflected from the target is relatively weak, and the detection sensitivity of the SPAD is reduced, so that the reception probabilities of the three light pulses are close. According to the characteristic, under the condition that the distance is only required to be used qualitatively and the accurate distance is not required to be obtained accurately, for example, under the condition that unmanned driving is in a pre-judging priority level, a short-distance target is judged firstly, a long-distance target can be delayed properly, at the moment, the distance interval of each object is judged firstly through the distance measuring device, and then the distance of the target object in the short-distance interval is calculated preferentially according to the rule, so that the processing capacity and the processing efficiency of the device can be improved.

Referring to fig. 8, fig. 8 is a schematic flow chart of a ranging method of the present invention, and as shown in the figure, the method includes the steps of:

s1: the active light source in the distance measuring device is used for emitting measuring light which is periodically modulated to a target object. Wherein the periodically modulated measuring light is configured as a pulse train having a number of periods, each period comprising a pulse period and a blank period, at least two light pulses within a pulse period, and each period having a length greater than or equal to a single on-time of the SPAD, the interval time between the at least two light pulses being less than the single on-time of the SPAD.

S2: the measuring light returned from the target is received by the receiving device, and a measuring signal is formed.

S3: and processing the measurement signal by using a signal processing device to generate a statistical result. Wherein the step of processing the measurement signal to generate a statistical result comprises: and counting the time-sequence distribution of the measuring signals.

Preferably, the method further comprises the step S4: and identifying a statistical result in a pulse sequence, and judging whether at least two statistical peaks which have a corresponding relation with the at least two optical pulses exist in the pulse sequence, wherein the corresponding relation comprises that a time sequence interval between the at least two statistical peaks is consistent with a time sequence interval between the at least two optical pulses.

Preferably, the statistics further includes convolving the statistics with the light source signal sequence to obtain the time offset.

Preferably, after identifying the at least two statistical peaks, the method further includes step S5: and calculating the distance of the target object according to the time sequence positions of the at least two peak values.

In summary, the present invention provides a ranging apparatus and a ranging method based on SPAD, which further divide the periodically modulated measuring light into a plurality of optical pulses in one period, then count the times of forming feedback signals by each optical pulse in a period time range, form a statistical result distributed according to time sequence, and determine whether each statistical peak corresponds to each optical pulse, thereby determining whether the measuring signals are true. By utilizing the technical scheme of the invention, the problem of inaccurate result caused by easy environmental noise interference of SPAD ranging in the prior art can be solved.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

1. A distance measuring device comprises an active light source for emitting periodically modulated measuring light to a target; receiving means for receiving the measurement light returned from the target object, and signal processing means for processing the measurement signal of the receiving means to generate a statistical result, characterized in that: the receiving device comprises at least one SPAD detector, the periodically modulated measuring light is configured to be a pulse sequence with a plurality of periods, each period comprises a pulse period and an empty period, at least two light pulses are provided in one pulse period, the length of each period is larger than or equal to the single working time of the SPAD detector, only 1 light pulse in the at least two light pulses in one pulse period can trigger the SPAD detector, so that the SPAD detector only responds to one light pulse triggering event in a single pulse period, the receiving device further comprises a signal recording unit, the signal processing device comprises a statistical unit, the signal recording unit responds to the detection events of the SPAD detector and records the detection events as a measuring signal, the statistical unit counts the measuring signal according to time sequence distribution, and the signal processing device, the device also comprises a result identification unit which identifies the statistical result in one pulse sequence according to the statistical result of the statistical unit and judges whether the corresponding number of statistical peak values corresponding to the at least two light pulses exist in the pulse sequence or not, and a distance calculation device which calculates the distance of the target object according to the time sequence positions of the at least two peak values when the signal identification unit identifies the at least two statistical peak values.

2. A ranging apparatus as claimed in claim 1, wherein: the control device is used for providing a pulse driving signal for the active light source and providing synchronous light pulse time sequence information for the signal identification unit, and the signal identification unit judges whether the at least two statistical peak values correspond to the at least two light pulses or not according to the pulse time sequence information.

3. A ranging apparatus as claimed in claim 1, characterized in that: the receiving device is a stand-alone SPAD detector or a SPAD array.

4. A distance measurement method is characterized in that: ranging using a ranging device according to any of claims 1 to 3, comprising the steps of:

emitting periodically modulated measuring light to a target object using the active light source,

receiving, by the receiving device, measurement light returned from the target object and forming a measurement signal,

processing the measurement signals using the signal processing means to generate statistical results, wherein

The receiving device has at least one SPAD, the periodically modulated measuring light is configured as a pulse train having a number of periods, each period comprising a pulse period and a blank period, at least two light pulses within a pulse period, and each period having a length greater than or equal to a single on-time of the SPAD, the SPAD responding to only one light pulse triggering event within a single pulse period,

The step of processing the measurement signals to generate statistical results comprises: counting the time-sequence distribution of the measuring signals,

further comprising identifying statistical results within a pulse sequence and determining whether there are at least two statistical peaks within the pulse sequence that have a correspondence with the at least two optical pulses, the correspondence comprising a time interval between the at least two statistical peaks being consistent with a time interval between the at least two optical pulses,

after the at least two statistical peaks are identified, the method further comprises calculating the distance of the target object according to the time sequence positions of the at least two peaks.

5. The ranging method of claim 4, wherein: the statistics also comprises the convolution of the statistical result and the light source signal sequence to obtain the time offset.

6. Use of a distance measuring device according to any of claims 1-3 for measuring the reflectivity of an object.

7. Use of a distance measuring device according to any of claims 1-3 for determining the distance interval of an object.