CN109696684B - Self-correlation laser radar device - Google Patents
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Abstract
The invention discloses an autocorrelation laser radar device, which comprises the steps of firstly obtaining a section of square wave signal through a laser pulse signal, wherein the starting time of the square wave signal is the starting time of a pulse, and the ending time of the square wave signal is the ending time of the laser pulse; and then, carrying out autocorrelation function processing on the square wave signal to obtain a bilaterally symmetrical triangle, wherein the moment when the triangle starts to generate is the starting moment of the square wave signal, the moment when the triangle reaches the highest point is the ending moment of the square wave, and the length of the bottom side of the left half triangle can be obtained by obtaining the highest point value of the triangle and the slope value of the left half of the triangle, wherein the length is the difference value of the starting moment and the ending moment of the square wave, and is the flight time of the pulse.
Description
Technical Field
The invention belongs to the technical field of radio waves, and particularly relates to an autocorrelation laser radar device for estimating square wave duration.
Background
Lidar has been used in a wide range of applications, ranging from ground to air, air to space, land to sea, sea to underwater, and in a number of disciplines. It has the advantages that the conventional radar can not compare with, and has wide application prospect in military affairs and civil use.
With the advancement of science and technology, people have higher and higher requirements on intelligence, and along with the development, the requirements on sensors are high. Different from the traditional camera vision imaging, the precision, distance and resolution of the laser radar measured data are much higher. In the future, the laser radar can be widely applied to various scenes, such as sweeping robots of families, vehicle-mounted automatic navigation systems, automatic surveying and mapping of airplanes and accurate ranging of satellites.
The method is characterized in that narrow-band pulse flight time ranging is adopted for most manufacturers of low-cost laser radar systems, namely a pulse laser of a transmitting module sends a section of narrow-pulse laser and sends an initial electric signal to a processor at the same time, an optical sensing device of a receiving module receives an echo reflected by a target object hit by the pulse laser and sends a cut-off electric signal to the processor, the processor calculates the flight time of the laser pulse by calculating the initial signal and the time difference of the cut-off signal, and the distance between the laser radar and the target object is calculated by multiplying the flight time measured by the system by the known light wave speed.
Because the light speed value is large, for some occasions (such as unmanned driving) with high requirements on data, the time resolution of the cut-off time at the starting time of the laser pulse is high (the distance error can reach 3cm due to the error of 100 ps). The traditional threshold value method, the constant ratio method and the like are difficult to meet the required requirements.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides an autocorrelation laser radar device, which utilizes an autocorrelation function to perform autocorrelation processing on a flight time square wave signal so as to obtain the duration time of the square wave.
To achieve the above object, an autocorrelation laser radar apparatus according to the present invention includes:
the central processing unit module is mainly responsible for sending instructions to each module in the system, receiving and processing feedback data of each module, and controlling the overall operation of the system;
the central processing unit module firstly sends an instruction to the laser pulse transmitting module to enable the laser pulse transmitting module to transmit a laser pulse signal; simultaneously sending an instruction to the laser pulse receiving module to prepare for receiving the echo pulse; then waiting for receiving a feedback signal sent by the flight time square wave generation module, sending an instruction to the triangular wave peak value calculation module by the central processing unit module after receiving the feedback signal, and waiting for the feedback signal of the triangular wave peak value calculation module; after the central processing unit receives the feedback signal of the triangular wave peak value calculation module, the square wave duration time is calculated through the autocorrelation function;
the laser pulse emitting module is internally provided with a laser, a light sensing unit and an electric signal amplifying unit; the laser is responsible for receiving the instruction sent by the central processing unit module and then emitting a laser pulse signal; the light sensing unit is used for generating an original pulse starting signal; the electric signal amplifying unit amplifies an original pulse starting signal;
the laser pulse emitting module receives an instruction emitted by the central processing unit module, activates the light sensing unit, then the laser emits a laser pulse signal to the space, the light sensing unit generates an original pulse starting signal after sensing the laser pulse signal, and the electric signal amplifying unit amplifies the original pulse starting signal and then inputs the amplified signal to the flight time square wave generating module;
the laser pulse receiving module is internally provided with a light sensing unit and an electric signal amplifying unit; the optical sensing unit is used for generating an original pulse cut-off signal, and the electric signal amplifying unit is used for amplifying the original pulse cut-off signal;
the laser pulse receiving module activates the light sensing unit after receiving an instruction transmitted by the central processing unit module, generates an original pulse cut-off signal when the light sensing unit senses an echo signal generated by the laser pulse signal after being reflected by a target object, amplifies the original pulse cut-off signal through the electric signal amplifying unit, and inputs the amplified signal to the flight time square wave generating module;
the flight time square wave generating module is internally provided with a threshold generator unit, two comparator units and an AND gate unit; the threshold generator unit provides thresholds for the two comparator units, the two comparator units are used for intercepting a pulse starting signal and a pulse stopping signal, and the AND gate unit is used for generating a flight time square wave signal;
after the flight time square wave generating module receives the instruction transmitted by the central processing unit module, a proper level is generated by the threshold value generator unit to be used as the threshold value of the two comparator units; the two comparator units intercept signals sent by the signal laser pulse transmitting module and the laser pulse receiving module according to the provided threshold, wherein one comparator unit is used for intercepting the amplified pulse starting signal and generating a square wave signal with the starting time as the starting time of the pulse starting signal, and the other comparator unit is used for intercepting the pulse stopping signal and generating a square wave signal with the ending time as the stopping time of the pulse stopping signal; then, the AND gate unit performs AND operation on the two square wave signals to generate a flight time square wave signal, inputs the flight time square wave signal to the triangular wave peak value calculation module, and simultaneously sends a feedback signal to the CPU module;
the triangular wave peak value calculation module is internally provided with an integrating circuit unit, a peak value holding circuit unit and an analog-digital sampling circuit unit;
after the triangular wave peak value calculation module receives the instruction transmitted by the central processing unit module, the integral circuit unit performs integral operation on the flight time square wave signal to generate a triangular wave signal; the peak value holding circuit unit carries out level holding on the peak value of the triangular wave signal to obtain the peak value level of the triangular wave signal; then the analog-digital sampling unit samples the peak value level to obtain a level value, and the level value is sent to the central processing unit module in the form of a feedback signal;
and the power supply module is mainly responsible for providing required electrical level and grounding interfaces for each module in the system and maintaining the normal operation of the system.
The invention aims to realize the following steps:
the invention relates to an autocorrelation laser radar device, which comprises the steps of firstly obtaining a section of square wave signal through a laser pulse signal, wherein the starting time of the square wave signal is the pulse starting time, and the ending time of the square wave signal is the laser pulse stopping time; and then, carrying out autocorrelation function processing on the square wave signal to obtain a bilaterally symmetrical triangle, wherein the moment when the triangle starts to generate is the starting moment of the square wave signal, the moment when the triangle reaches the highest point is the ending moment of the square wave, and the length of the bottom side of the left half triangle can be obtained by obtaining the highest point value of the triangle and the slope value of the left half of the triangle, wherein the length is the difference value of the starting moment and the ending moment of the square wave, and is the flight time of the pulse.
Meanwhile, the autocorrelation laser radar device also has the following beneficial effects:
(1) Compared with the traditional threshold method for calculating the square wave duration, the method can obtain better precision, the determination of the starting and ending time of the threshold method is very dependent on the trigger signal generated by the comparator, but even the comparator with excellent performance can generate 25ns of delay, because the light speed value is too large, which cannot be tolerated in the laser radar system (25 ns means 7.5 meters). The scheme can effectively eliminate the errors, two signals of the system can pass through the same comparator, the delay caused by the comparator can be effectively eliminated by the method, the finally intercepted and generated flight time square wave is generated by the AND gate circuit, compared with the 25ns delay of the comparator, the 100ps level delay of the AND gate can be completely ignored (100 ps means 3 cm), and compared with a threshold method, the method can obtain better measurement accuracy.
(2) The measurement of the thresholding method is very dependent on the threshold value, the trigger signal is generated when the level in the circuit is higher than the threshold value, and the noise has a very large influence on the level due to the influence of noise in the circuit, especially in high current high power systems such as laser radar systems. Some spike noise is likely to directly break the threshold, causing the comparator to misinterpret the signal coming, generating a trigger signal, and generating an erroneous result. In contrast, this method can effectively eliminate the effect of such spike noise, and the scheme calculates the square wave duration in an integral manner. Since the peak value of the spike noise is large but the duration is short, the integration method can effectively suppress the influence of the noise on the measurement. Not only the noise but also various noises can be suppressed by integral smoothing, so that the system has better robustness.
(3) For the threshold value method, a complex timing circuit is needed for measuring the flight time, particularly for a laser radar system, the accuracy of the circuit is extremely high, particularly in an outdoor motion state, the circuit is easy to be disturbed, and the errors generated by the micro-jitter of a high-frequency crystal oscillator are huge for the measurement. The time measurement of the method is completed through the integrating circuit, and compared with a high-precision timing circuit, the integrating circuit is simpler and more stable, and a series of sensitive devices such as a high-frequency crystal oscillator and the like are not provided.
Drawings
FIG. 1 is an architectural diagram of one embodiment of an autocorrelation lidar apparatus of the present invention;
FIG. 2 is a schematic diagram of a triangular wave peak calculation module;
FIG. 3 is a schematic diagram of a time-of-flight square wave generation module;
fig. 4 is a schematic diagram of the duration of a square wave signal through an autocorrelation function.
Detailed Description
The following description of the embodiments of the present invention is provided in order to better understand the present invention for those skilled in the art with reference to the accompanying drawings. It is to be expressly noted that in the following description, a detailed description of known functions and designs will be omitted when it may obscure the main content of the present invention.
Examples
Fig. 1 is a schematic diagram of an embodiment of an autocorrelation lidar apparatus of the present invention.
In this embodiment, as shown in fig. 1, an autocorrelation laser radar apparatus of the present invention includes: the device comprises a central processing unit module, a laser pulse transmitting module, a laser pulse receiving module, a flight time square wave generating module, a triangular wave peak value calculating module and a power supply module.
And the central processing unit module is mainly responsible for sending instructions to each module in the system, receiving and processing feedback data of each module, and controlling the overall operation of the system.
The central processing unit module firstly sends an instruction to the laser pulse transmitting module to enable the laser pulse transmitting module to transmit a laser pulse signal; simultaneously sending an instruction to a laser pulse receiving module to prepare for receiving the echo pulse; then waiting for receiving a feedback signal sent by the flight time square wave generation module, sending an instruction to the triangular wave peak value calculation module by the central processing unit module after receiving the feedback signal, and waiting for the feedback signal of the triangular wave peak value calculation module; after receiving the feedback signal of the triangular wave peak value calculation module, the central processing unit obtains a peak value level value sampled by the triangular wave peak value calculation module, and divides the level value by a square wave amplitude value obtained by looking up an electronic device manual, so that the square wave duration time is calculated.
In this embodiment, the central processor module may be a 51-chip microcomputer or an MP 430-chip microcomputer, or may be a raspberry pi for higher requirements.
The laser pulse emitting module is internally provided with a laser, a light sensing unit and an electric signal amplifying unit; the laser is used for receiving the instruction sent by the central processing unit module and then emitting a laser pulse signal; the light sensing unit is used for generating an original pulse starting signal; the electric signal amplifying unit amplifies the original pulse starting signal.
The laser pulse emitting module receives an instruction emitted by the central processing unit module, activates the light sensing unit, then the laser emits a laser pulse signal to the space, the light sensing unit generates an original pulse starting signal after sensing the laser pulse signal, and the electric signal amplifying unit amplifies the original pulse starting signal and then inputs the amplified signal to the flight time square wave generating module.
The laser pulse receiving module is internally provided with a light sensing unit and an electric signal amplifying unit; the optical sensing unit is used for generating an original pulse cut-off signal, and the electric signal amplifying unit is used for amplifying the original pulse cut-off signal.
The laser pulse receiving module activates the light sensing unit after receiving an instruction transmitted by the central processing unit module, generates an original pulse cut-off signal when the light sensing unit senses an echo signal generated by the laser pulse signal reflected by a target object, amplifies the original pulse cut-off signal through the electric signal amplifying unit, and then inputs the amplified signal to the flight time square wave generating module.
In this embodiment, the positions of the laser pulse emitting module and the laser pulse receiving module are adjusted before the first use, and for a target in a predicted measurement range, the positions of the two modules are adjusted so that the reflected light of the laser emitted by the laser pulse emitting module after hitting the target can hit the light sensing unit of the laser pulse receiving module. In the adjusting process, not only the lens of the laser pulse transmitting module and the lens of the light sensing unit of the laser pulse receiving module need to be designed and analyzed, but also a visible continuous light laser source needs to be used for simulating a light path, and then manual or mechanical fine adjustment is carried out to enable the light path to reach the optimal working state; secondly, the light sensing unit of the laser pulse transmitting module and the light sensing unit of the laser pulse receiving module need to adopt different designs. For the light sensing module of the laser pulse emitting module, because the light sensing module is closer to the laser light source, the light sensing module can sense larger laser pulse energy, so that a smaller amplification factor is needed to prevent the laser pulse energy from being broken down by excessive energy, and similarly, the subsequent amplification unit needs to take the point into consideration and amplify the laser pulse energy to a proper size. In addition, the light sensing unit of the module only needs to be triggered by a small amount of laser energy divided by the light splitter, so that excessive pulse laser energy is not wasted in the part, and the pulse laser emitted by the laser is not directly blocked. Most of the energy of the laser light generated by the laser is emitted into space for time-of-flight ranging based on the reflected light. For the laser pulse receiving module, propagation attenuation of laser in a space is affected by the square of the distance, so that great energy attenuation is achieved for a long distance, the requirement for the light sensing unit is high, the weak light signals radiated back can be sensed by high amplification factors, and a filtering function is needed to filter noise light of other wave bands. Generally, there is a high requirement for the subsequent amplification unit of the module, and it is necessary to amplify the weak electrical signal to a sufficient size. Therefore, the amplification factor of the electric signal amplification unit in the laser pulse transmitting module is much smaller than that of the electric signal amplification unit in the laser pulse receiving module.
As shown in fig. 3, the time-of-flight square wave generating module is internally provided with a threshold generator unit, two comparator units and an and gate unit; the threshold generator unit provides threshold values for two comparator units, the two comparator units are used for intercepting the pulse start signal and the pulse stop signal, and the AND gate unit is used for generating a flight time square wave signal.
After receiving the instruction transmitted by the central processing unit module, the flight time square wave generating module generates a proper level as the threshold value of the two comparator units through the threshold value generator unit; and the two comparator units intercept signals sent by the signal laser pulse transmitting module and the laser pulse receiving module according to the provided threshold value to obtain a section of flight time square wave signal.
As shown in fig. 2 (a), one of the comparator units is used to intercept the amplified pulse start signal and generate a square wave signal with the start time being the start time of the pulse start signal, and the other comparator unit is used to intercept the pulse stop signal and generate a square wave signal with the end time being the stop time of the pulse stop signal; in this embodiment, the square wave signal is not a smooth square wave due to the delay of the comparator unit (about 5ns for high performance), which is one of the causes of error in the conventional pulse measurement method, and the comparator generates the trigger signal in advance due to the fluctuation of the pulse around the threshold, so that the measured start time of the pulse is advanced from the real time. The ns-level time error can cause the distance error of a decimeter level, which is intolerable to application scenes such as unmanned driving and the like with higher requirements on precision, and the invention can eliminate the error.
Then, the AND gate unit performs AND operation on the two square wave signals to generate a flight time square wave signal, inputs the flight time square wave signal to the triangular wave peak value calculation module, and simultaneously sends a feedback signal to the CPU module; in this embodiment, unlike the previous comparator, the delay of the and circuit is very low, which can reach 10ps, and most application scenarios can completely tolerate the time error.
The triangular wave peak value calculation module is internally provided with an integrating circuit unit, a peak value holding circuit unit and an analog-digital sampling circuit unit;
after the triangular wave peak value calculation module receives the instruction transmitted by the central processing unit module, the flight time square wave signal is subjected to autocorrelation function processing, and the specific process is as follows:
first, as shown in fig. 2 (b), the integrating circuit unit performs an integrating operation on the flight time square wave signal, and it is assumed that the square wave signal generated by the flight time square wave generating module is:
wherein A is the amplitude of the time-of-flight square wave, and since the square wave signal is directly generated by the AND gate circuit, the amplitude is a fixed value obtained by referring to the handbook of the relevant electronic device, i.e., A is a known quantity, t is t 0 ，t 1 Start and off times of square wave signals, unknown quantities, t 1 -t 0 I.e. the required time difference. After the square wave signal is subjected to integral operation, a triangular wave signal is generated:
wherein f is 2 (t) is a square wave f 1 (t) signal integrated, f 1 (t) is the square wave signal described above, S is the signal f 1 (t) area. Despite the square wave signal f due to the previous time of flight 1 And (t) more burrs exist, but the burrs of the square wave signals can be smoothed by the processing of the integrating circuit to obtain a smoother pseudo right-angled triangle, and because the duration of the burrs is shorter and the burrs can be smoothed well in the integrating process, the obtained pseudo right-angled triangle has few burrs and smoother sides, and can be similar to a right-angled triangle.
Next, as shown in fig. 2 (c), the peak hold circuit unit holds the peak level of the triangular wave signal to obtain the peak level of the triangular wave signal, that is:
f 3 ＝max(f 2 )＝S；
then, as shown in fig. 2 (d), the analog-digital sampling unit samples the peak level to obtain a level value, i.e., S, and sends the level value to the central processor module in the form of a feedback signal;
as shown in fig. 4, the process uses the principle of autocorrelation function in time domain to perform calculation, and for convenience of description, the square wave amplitude is first normalized, that is, the square wave signal amplitudes described below are all 1. The principle is as follows:
as shown in fig. 4 (a), for a section of square wave signal containing a spur, an autocorrelation function operation is performed to obtain a left-right symmetrical graph, as shown in fig. 4 (b); since the autocorrelation function has a good smoothing effect, it is a good approximation to consider the graph as a left-right symmetric triangle. Considering only the left half triangle, the slope of the hypotenuse of the triangle is 1 because the amplitude of the square wave is 1;
the square wave is subjected to integral operation, and an approximate triangle can be obtained due to the restraining effect of the integral on the burrs. Due to the integral operation, the size (namely the height) of the peak value of the triangle is the size of the whole area of the original square wave; here, the amplitude of the square wave is 1, so the maximum value of the overlapping area is the area of the original square wave, so the peak value of the autocorrelation function is exactly the peak value of the integral function, and since the slope of the autocorrelation function triangle is 1, the peak value of the integral function is equal to half the length of the base of the autocorrelation function, i.e. the duration of the square wave. The duration of the flight pulse square wave, i.e. the pulse flight time, can be derived from the peak of the integration function.
And the power supply module is mainly responsible for providing required electrical level and grounding interfaces for each module in the system and maintaining the normal operation of the system.
Although illustrative embodiments of the present invention have been described above to facilitate the understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the embodiments, and various changes may be made apparent to those skilled in the art as long as they are within the spirit and scope of the present invention as defined and defined by the appended claims, and all matters of the invention which utilize the inventive concepts are protected.
Claims (3)
1. An autocorrelation lidar apparatus, comprising:
the central processing unit module is mainly responsible for sending instructions to each module in the system, receiving and processing feedback data of each module, and controlling the overall operation of the system;
the central processing unit module firstly sends an instruction to the laser pulse transmitting module to enable the laser pulse transmitting module to transmit a laser pulse signal; simultaneously sending an instruction to a laser pulse receiving module to prepare for receiving the echo pulse; then waiting for receiving a feedback signal sent by the flight time square wave generation module, sending an instruction to the triangular wave peak value calculation module by the central processing unit module after receiving the feedback signal, and waiting for the feedback signal of the triangular wave peak value calculation module; after the central processing unit receives the feedback signal of the triangular wave peak value calculation module, the square wave duration is calculated through an autocorrelation function;
the laser pulse emitting module is internally provided with a laser, a light sensing unit and an electric signal amplifying unit; the laser is responsible for receiving the instruction sent by the central processing unit module and then emitting a laser pulse signal; the light sensing unit is used for generating an original pulse starting signal; the electric signal amplifying unit amplifies an original pulse starting signal;
the laser pulse emitting module receives an instruction emitted by the central processing unit module, activates the light sensing unit, then the laser emits a laser pulse signal to the space, the light sensing unit generates an original pulse starting signal after sensing the laser pulse signal, and the electric signal amplifying unit amplifies the original pulse starting signal and then inputs the amplified signal to the flight time square wave generating module;
the laser pulse receiving module is internally provided with a light sensing unit and an electric signal amplifying unit; the optical sensing unit is used for generating an original pulse cut-off signal, and the electric signal amplifying unit is used for amplifying the original pulse cut-off signal;
the laser pulse receiving module activates the light sensing unit after receiving an instruction transmitted by the central processing unit module, generates an original pulse cut-off signal when the light sensing unit senses an echo signal generated by the laser pulse signal after being reflected by a target object, amplifies the original pulse cut-off signal through the electric signal amplifying unit, and inputs the amplified signal to the flight time square wave generating module;
the flight time square wave generating module is internally provided with a threshold value generator unit, two comparator units and an AND gate unit; the threshold generator unit provides thresholds for the two comparator units, the two comparator units are used for intercepting a pulse starting signal and a pulse stopping signal, and the AND gate unit is used for generating a flight time square wave signal;
after receiving the instruction transmitted by the central processing unit module, the flight time square wave generating module generates a proper level as the threshold value of the two comparator units through the threshold value generator unit; the two comparator units intercept signals sent by the signal laser pulse transmitting module and the laser pulse receiving module according to the provided threshold, wherein one comparator unit is used for intercepting the amplified pulse starting signal and generating a square wave signal with the starting time as the starting time of the pulse starting signal, and the other comparator unit is used for intercepting the pulse cut-off signal and generating a square wave signal with the ending time as the cut-off time of the pulse cut-off signal; then, the AND gate unit performs AND operation on the two square wave signals to generate a flight time square wave signal, inputs the flight time square wave signal to the triangular wave peak value calculation module, and simultaneously sends a feedback signal to the CPU module;
the triangular wave peak value calculation module is internally provided with an integrating circuit unit, a peak value holding circuit unit and an analog-digital sampling circuit unit;
after the triangular wave peak value calculation module receives the instruction transmitted by the central processing unit module, the integral circuit unit performs integral operation on the flight time square wave signal to generate a triangular wave signal; the peak value holding circuit unit carries out level holding on the peak value of the triangular wave signal to obtain the peak value level of the triangular wave signal; then the analog-digital sampling unit samples the peak value level to obtain a level value, and the level value is sent to the central processing unit module in the form of a feedback signal;
and the power supply module is mainly responsible for providing required electrical level and grounding interfaces for each module in the system and maintaining the normal operation of the system.
2. The autocorrelation lidar apparatus of claim 1, wherein the laser pulse transmitting module and the laser pulse receiving module satisfy: when the self-correlation laser radar system is used for the first time, the positions of the laser pulse transmitting module and the laser pulse receiving module are adjusted, so that reflected light of a laser pulse signal transmitted by the laser pulse transmitting module after hitting a target can hit a light sensing unit in the laser pulse receiving module.
3. The autocorrelation lidar apparatus of claim 1, wherein the electrical signal amplification units in the laser pulse transmitting module and the laser pulse receiving module satisfy: the amplification factor of the electric signal amplification unit in the laser pulse transmitting module is far smaller than that of the electric signal amplification unit in the laser pulse receiving module.
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| CN110687545B (en) * | 2019-09-27 | 2022-03-25 | 电子科技大学中山学院 | High-precision laser radar system |
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