LiDAR System

Abstract

The present invention relates to a laser radar system, comprising: a transmitting device for transmitting multiple groups of outgoing lasers with different frequencies; a transmitting optical system for directing the outgoing lasers to a detection area; a receiving device for receiving reflected lasers; the reflected lasers are lasers after the outgoing lasers are reflected by objects in the detection area; a receiving optical system for receiving the reflected lasers and directing them to the receiving device; and a processing system for obtaining the distance of objects in the detection area according to the frequency of each group of outgoing lasers and the phase difference between the outgoing lasers and the corresponding reflected lasers. The above-mentioned laser radar system can achieve detection at a relatively long distance, thereby meeting the use requirements of application scenarios with relatively long detection distances.

Description

Technical Field

[0001] The present invention relates to the field of laser detection technology, and in particular to a laser radar system. Background Art

[0002] LiDAR can measure the distance and test the target by emitting laser beams. LiDAR has been widely used in fields such as depth perception, mapping and ranging. Flash LiDAR (also called Flash LiDAR) is a non-scanning LiDAR. Depending on whether the light source is pulsed or continuous wave, the ranging principle corresponds to the pulse ranging based on time of flight (TOF) and the phase ranging based on continuous wave (AMCW). The light source of FLASH LiDAR "illuminates" the entire field of view at one time, and the energy decays quickly. In addition, it is limited by the ambiguous interval of its own ranging principle and is not suitable for long-distance detection applications. Summary of the invention

[0003] Based on this, it is necessary to provide a laser radar system to address the problem that FLASH laser radar is not suitable for long-distance detection.

[0004] A laser radar system, comprising:

[0005] A transmitting device, used for transmitting multiple groups of outgoing lasers with different frequencies;

[0006] An emission optical system, used for emitting the outgoing laser light toward a detection area;

[0007] A receiving device, used to receive reflected laser light; the reflected laser light is the laser light after the emitted laser light is reflected by an object in the detection area;

[0008] a receiving optical system, used for receiving the reflected laser light and emitting it toward the receiving device; and

[0009] The processing system obtains the distance of the object in the detection area according to the frequency of each group of emitted lasers and the phase difference between the emitted lasers and the corresponding reflected lasers.

[0010] In one of the embodiments, the transmitting device includes a laser and a modulator, and the modulator modulates the emitted laser.

[0011] In one embodiment, the laser emits two groups of outgoing lasers with different frequencies, the frequency of the first outgoing laser is f1, and the frequency of the second outgoing laser is f2.

[0012] In one embodiment, the frequency difference between the frequency f1 of the first emitted laser and the frequency f2 of the second emitted laser is Δf, and Δf is greater than the signal resolution of the processing system.

[0013] In one embodiment, the processing system obtains the distance of the object in the detection area based on the phase difference between the first outgoing laser and the corresponding first reflected laser, the phase difference between the second outgoing laser and the corresponding second reflected laser, and the frequency difference Δf between the first outgoing laser and the second outgoing laser.

[0014] In one embodiment, the modulator modulates the first output laser with a first carrier amplitude, and modulates the second output laser with a second carrier amplitude.

[0015] In one embodiment, the laser is a frequency-stabilized laser.

[0016] In one of the embodiments, the processing system further obtains the movement speed of the object in the detection area according to the frequency change of the reflected laser.

[0017] In one embodiment, the modulator modulates the multiple groups of outgoing lasers separately by time division multiplexing.

[0018] In one embodiment, the laser emits four groups of outgoing lasers with different frequencies, the frequencies of the first outgoing laser and the second outgoing laser are similar, and the frequencies of the third outgoing laser and the fourth outgoing laser are similar.

[0019] The above-mentioned laser radar system measures the position information of objects in the detection area, such as the distance, based on the ranging principle of continuous wave amplitude modulation. During the entire detection process, multiple groups of outgoing lasers with different frequencies but similar frequencies are used for detection. The processing system obtains the distance of the object in the detection area according to the frequency of each group of outgoing lasers and the phase difference between the outgoing laser and the corresponding reflected laser. Using multiple groups of outgoing lasers with similar frequencies for detection, the frequency difference is used as the new measuring frequency. Since the frequency difference is small, a larger measuring length can be obtained, thereby greatly improving the detection distance of the laser radar. Compared with the use of a single-frequency outgoing laser, the use of multiple groups of outgoing lasers with different frequencies for detection can enable the entire laser radar system to achieve longer-distance detection, thereby meeting the use requirements of application scenarios with longer detection distances. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 4 is a structural block diagram of a laser radar system in one embodiment.

[0021] Figure 2 It is a basic principle diagram of ranging based on continuous wave amplitude modulation in one embodiment.

[0022] Figure 3 Schematic diagram of the position relationship between the laser radar system and the objects in the detection area when they move. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0024] In the description of the present application, it should be understood that the terms "center", "lateral", "up", "down", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In addition, it should be noted that when an element is referred to as being "formed on another element", it may be directly connected to the other element or there may be a centered element at the same time. When an element is considered to be "connected" to another element, it may be directly connected to the other element or there may be a centered element at the same time. In contrast, when an element is referred to as being "directly on" another element, there is no intermediate element.

[0025] Figure 1 FIG. 1 is a structural block diagram of a laser radar system in an embodiment. Figure 1 The laser radar system includes a transmitting device 110, a transmitting optical system 120, a receiving optical system 130, a receiving device 140 and a processing system 150.

[0026] The transmitting device 110 is used to transmit multiple groups of outgoing lasers with different frequencies. In the present embodiment, the outgoing laser emitted by the transmitting device 110 is a continuous wave laser. Among them, the frequencies of each group of outgoing lasers emitted by the transmitting device 110 are similar. The degree of similarity of the frequencies only requires that the difference in frequency is greater than the signal resolution of the processing system 150 and can be recognized by the processing system 150. The transmitting optical system 120 is arranged at the exit end of the transmitting device 110. The transmitting optical system 120 is used to direct the outgoing laser to the detection area. The transmitting optical system 120 may include optical elements such as a collimating lens and a reflector.

[0027] The receiving optical system 130 is used to receive the reflected laser light formed after the outgoing laser light is reflected by the object in the detection area, and project the reflected laser light to the receiving device. The receiving optical system 130 may include optical elements such as a focusing lens and a reflector.

[0028] The receiving device 140 is used to receive the reflected laser projected by the receiving optical system 130. The receiving device 140 is mainly used to realize the reception and photoelectric conversion of the optical signal, so as to obtain an electrical signal corresponding to the optical signal.

[0029] The processing system 150 is used to process and analyze the electrical signal output by the receiving device 140, so as to obtain the distance of the object in the detection area according to the frequency of each group of emitted lasers and the phase difference between the emitted lasers and the corresponding reflected lasers.

[0030] The above-mentioned laser radar system measures the position information of objects in the detection area, such as the distance, based on the ranging principle of continuous wave amplitude modulation. During the entire detection process, multiple groups of outgoing lasers with different frequencies but similar frequencies are used for detection. The processing system 150 obtains the distance of the object in the detection area according to the frequency of each group of outgoing lasers and the phase difference between the outgoing laser and the corresponding reflected laser. Using multiple groups of outgoing lasers with similar frequencies for detection, the processing system 150 is equivalent to using the frequency difference as the new measuring frequency in the calculation process. Since the frequency difference is small, a larger measuring length can be obtained, thereby greatly improving the detection distance of the laser radar. Compared with using an outgoing laser with a single frequency, using multiple groups of outgoing lasers with different frequencies for detection can enable the entire laser radar system to achieve detection at a longer distance, thereby meeting the use requirements of application scenarios with longer detection distances.

[0031] In one embodiment, the transmitting device 110 adopts a continuous wave amplitude modulation (Amplitude Modulation Continuous Wave, AMCW) mode to transmit an amplitude modulated continuous wave output laser. The transmitting device 110 can output multiple groups of output lasers with different frequencies alternately according to a preset rule. Specifically, the transmitting device 110 can use a single light source to emit multiple groups of output lasers with different frequencies using a time division multiplexing method. The transmitting device 110 can also use multiple light sources to emit output lasers of corresponding frequencies using different light sources.

[0032] In one embodiment, the laser generating device 110 includes a laser 112 and a modulator 114. The laser 112 is used to emit a laser beam. The laser beam emitted by the laser 112 is a continuous wave. The wavelength of the laser beam emitted by the laser 112 can be set as needed. The wavelength of the laser beam emitted by the laser 112 is a wavelength that meets the safety of human eyes, such as 940nm or 1550nm. The laser 112 can be one or a laser array, so as to form a multi-path laser beam.

[0033] In one embodiment, the laser radar system is a FLASH laser radar system (also known as a flash laser radar system), which is a non-scanning laser radar. At this time, the laser 112 is a planar array light source, and its emitted laser "illuminates" the entire detection area at the same time. The use of a planar array light source can cover the entire detection field of view at one time without any scanning device, which can simplify the structure of the entire laser radar system, reduce costs, and improve the reliability and stability of the laser radar system; it can quickly record the entire scene and avoid various interferences caused by the movement of the target or the laser radar system during the scanning process.

[0034] The modulator 114 is used to perform amplitude modulation on the laser beam emitted by the laser 112. Since the laser beam emitted by the laser 112 is a continuous wave, the modulated outgoing laser is an amplitude modulated continuous wave. In one embodiment, the laser 112 emits laser beams of two frequencies alternately, and the frequency of the laser beam emitted in each time period is fixed. The modulator 114 uses the same modulation carrier to amplitude modulate laser beams of the same frequency, and the amplitude modulation carriers of laser beams of different frequencies are different. In one embodiment, the modulator 114 modulates the first outgoing laser with a first carrier amplitude, and modulates the second outgoing laser with a second carrier amplitude. The modulated carrier may be a sine wave or a triangular wave, etc. In this embodiment, the carrier signal is taken as an example of a sine wave.

[0035] In one embodiment, the same modulator 114 may be used to alternately generate multiple groups of amplitude modulated carriers with different amplitudes through time division multiplexing, or different modulators 114 may be used to perform modulation respectively.

[0036] In one embodiment, the laser 112 emits two groups of outgoing lasers with different frequencies. The frequency of the first outgoing laser is f1, and the frequency of the second outgoing laser is f2. In one embodiment, the frequency f1 of the first outgoing laser and the frequency f2 of the second outgoing laser are relatively close, and the frequency difference between the two is Δf. Δf is greater than the signal resolution of the processing system 150. If the difference between f1 and f2 is less than the signal resolution of the processing system 150, the processing system 150 will not be able to identify the modulation frequencies f1 and f2, and thus the two outgoing lasers will be processed as one outgoing laser. At this time, the modulator 114 modulates the first outgoing laser with a first carrier amplitude and modulates the second outgoing laser with a second carrier amplitude, so that the processing system 150 can effectively identify the lasers of the two frequencies.

[0037] In one embodiment, the processing system 150 includes a photoelectric conversion circuit and a processing circuit (not shown). The photoelectric conversion circuit is used to convert the reflected laser received by the receiving device 140 into a corresponding electrical signal. The processing circuit can determine the light intensity, phase, direction and other information of the reflected laser according to the electrical signal. The receiving device 140 can use a planar array detector array, and the detector can use a photodiode.

[0038] In this embodiment, after the emitting device 110 emits the first outgoing laser and the second outgoing laser, they are emitted through the emitting optical system 120. After the outgoing laser encounters the object in the detection area, it is reflected, thereby obtaining the first reflected laser corresponding to the first outgoing laser and the second reflected laser corresponding to the second outgoing laser. The first reflected laser and the second reflected laser are received by the receiving optical system 130 and projected to the receiving device 140. The receiving device 140 receives the first reflected laser and the second reflected laser and converts them into corresponding electrical signals and then outputs them to the processing system 150. At this time, the processing system 150 obtains the distance of the object in the detection area according to the phase difference between the first outgoing laser and the first reflected laser, the phase difference between the second outgoing laser and the second reflected laser, and the frequency difference Δf between the first outgoing laser and the second outgoing laser. That is, in this embodiment, two groups of lasers with different frequencies are used for independent distance measurement during the detection process. When the processing system 150 calculates the distance, it does not only calculate the distance based on the outgoing laser of one frequency, but uses the frequency difference Δf between the two as a measuring scale to calculate the distance. According to the ranging principle of continuous wave amplitude modulation, the smaller the frequency, the longer the detectable distance. Since the frequency difference Δf of the two groups of lasers is small compared to a single frequency, the entire laser radar system can achieve detection at a longer distance, thereby meeting the use requirements of longer distance detection. For example, the measuring length of f1 is L1, and the measuring length of f2 is L2. When the distance of the object in the detected area is greater than L1 or L2, the distance detection cannot be completed by using the outgoing laser with a frequency of f1 or f2 alone. Usually, to achieve long-distance detection, a low-frequency laser is required, and the smaller the frequency, the lower the accuracy, and the detection distance and detection accuracy cannot meet the use requirements at the same time. This case can solve this problem very well. In this case, it is not necessary to control f1 and f2 to be small enough, but only to ensure that the two are close and greater than the signal resolution of the processing system 150, so there is no need to sacrifice accuracy to increase the detection distance.

[0039] In order to better reflect the advantages of the laser radar system in this embodiment, the following is an explanation of the specific working principle of the laser radar system:

[0040] The amplitude of the emitted laser is modulated (such as a sine wave) so that a phase difference is formed on the light intensity waveform when the emitted laser is reflected by an object in the detection area and returns to the processing system 150. Based on the measured phase difference, the flight time of the carrier signal (the time from emission to reception) can be calculated. The basic principle of continuous wave phase ranging is to obtain the distance information of the target by demodulating the phase change of the light. When a single emitted laser is used for detection, assuming that the frequency of the emitted laser is f0 and L0 is the length of the measuring scale, the following relationship is satisfied:

[0041]

[0042] Where λ0 is the wavelength corresponding to the modulation frequency f0. The formula for calculating the distance based on the flight time is as follows:

[0043]

[0044] Where L represents the distance between the detected object in the detection area and the laser radar system, c represents the speed of light in a vacuum, t represents the flight time, L0 represents the length of the scale, N is an integer that refers to the maximum multiple of 2π contained in the phase change of the reflected laser relative to the outgoing laser, and ΔN refers to the part of the phase change of the reflected laser relative to the outgoing laser that is less than 2π, that is, is the mantissa of the phase shift less than 2π. In one embodiment, the modulator 114 controls the phase of the two while performing amplitude modulation, so that the phase difference between the reflected laser and the emitted laser is less than 2π, that is, N in the above formula is 0, so that the distance L can be calculated based on the measured phase difference ΔN. The fuzzy distance Δr and the ranging accuracy σ based on this ranging principle are:

[0045]

[0046] Among them, F AM and λ AM They represent modulation frequency and wavelength respectively, SNR is signal-to-noise ratio, and f is also the modulation frequency.

[0047] Figure 2The figure shows a schematic diagram of the laser radar principle based on AMCW ranging. Assume that the amplitude of the emitted laser is a sinusoidal signal s(t), the modulation frequency is f, the signal of the reflected laser received after △t is r(t), the attenuated amplitude is A, and the intensity offset (caused by ambient light) is B. The M sampling time intervals are equal, all T / 4, that is, one quarter of a period. The sampling time of different laser radar systems varies, and can be adjusted accordingly according to the test environment and the working state of the chip used (such as frame rate). In this embodiment, 4 sampling times are used, and each sampling time is one quarter of the corresponding continuous wave period, so that as complete information as possible can be collected within one signal period, so that information such as distance can be accurately calculated. The specific calculation formula and algorithm are well known to those skilled in the art, so they will not be repeated here. Four sets of equations can be listed through 4 samplings, so that the phase offset of the emitted and reflected sinusoidal signals can be calculated, and the distance between the object in the detection area and the laser radar system can be calculated accordingly. The values ​​of A and B indirectly reflect the measurement accuracy.

[0048] Generally speaking, the maximum detectable distance of a radar based on the AMCW ranging principle is limited by the length of the measuring ruler. Therefore, in this embodiment, two indirect measuring ruler frequencies f1 and f2 with very close frequencies are selected, namely the frequencies of the first emitted laser and the second emitted laser. Then, the processing system 150 can obtain the same detection distance L corresponding to the two measuring rulers, and obtain the detectable distance L of the system after a simple calculation:

[0049]

[0050] Since Δf is small, when N=0, the detectable distance is much greater than the fuzzy distance when using a single frequency for detection. Two groups of laser beams with similar frequencies are used for detection. The frequency of the first laser beam is f1, and the frequency of the second laser beam is f2. Since the frequencies are very close, the detection distances of the two groups of laser beams are the same. The equation for the detection distance is listed. It can be seen from the above calculation formula that it is equivalent to calculating the detection distance by Δf.

[0051] The above-mentioned laser radar system adopts two output lasers with similar frequencies to measure distance, and uses a light source wavelength that is relatively safe for the human eye, which improves the theoretical maximum detection distance of the laser radar system and can be used in outdoor environments such as autonomous driving.

[0052] In one embodiment, the laser 112 emits four groups of outgoing lasers with different frequencies. The four groups of outgoing lasers with different frequencies include a first outgoing laser, a second outgoing laser, a third outgoing laser, and a fourth outgoing laser. Among them, the frequencies of the first outgoing laser and the second outgoing laser are similar, which is a first combination; the frequencies of the third outgoing laser and the fourth outgoing laser are similar, which is a second combination. At this time, the first combination can calculate the frequency difference according to the frequencies of the first laser and the second laser, and then obtain the detection distance through the phase difference between the first outgoing laser and the corresponding first reflected laser, the phase difference between the second outgoing laser and the corresponding second reflected laser, and the frequency difference calculated previously; the second combination can calculate the frequency difference according to the frequencies of the third laser and the fourth laser, and then obtain the detection distance through the phase difference between the third laser and the corresponding third laser, the phase difference between the fourth laser and the corresponding fourth laser, and the frequency difference calculated previously; in this way, multiple distances can be detected simultaneously.

[0053] In one embodiment, the laser 112 is a frequency-stabilized laser. A frequency-stabilized laser refers to a laser that uses frequency stabilization technology to stabilize the output frequency at a certain value. Generally speaking, the frequency of a laser will jitter within a certain range, which is determined by the principle or nature of the laser source itself. In this embodiment, by using a frequency-stabilized light source, the speed of a moving object can be measured through the Doppler effect. Specifically, when the object in the detection area is a moving object, the processing system 150 is also used to obtain the moving speed of the object in the detection area based on the frequency change of the reflected laser. Specifically, based on the frequency change of the reflected laser and the emitted laser, the Doppler frequency shift f caused by the movement of the object is obtained. Dopp The processing system 150 can perform a frequency discrimination operation on the received reflected laser and obtain the Doppler frequency shift f caused by the object movement according to the frequency changes of the emitted laser and the reflected laser. Dopp . Through the Doppler frequency shift f Dopp The velocity v of an object within the detection area can be determined by the following calculation formula:

[0054]

[0055] Where f is the frequency of the emitted laser, c is the speed of light in a vacuum, and α is the angle between the object's direction of motion and the laser radar system-object connection line, as Figure 3 As shown. According to the above formula, the object's moving speed v can be calculated.

[0056] In one embodiment, the Doppler frequency shift generated by the object's motion is generally greater than the modulation frequency of the carrier wave, and the Doppler frequency shift information can be obtained by frequency discrimination. In one embodiment, the Doppler frequency shift generated by the object's motion is greater than the frequency of each group of emitted lasers. In other embodiments, the frequency shift amount can be obtained by ensuring that the Doppler frequency shift generated by the object's motion and the frequency of each group of emitted lasers can be distinguished, thereby realizing the resolution of the velocity information.

[0057] Assuming that the wavelength of the laser beam generated by the laser radar system is 940nm, for most outdoor objects, such as moving pedestrians or vehicles, the movement speed range is 1m / s to 34m / s (120km / h), and the corresponding Doppler frequency shift range is 1.06MHz to 35MHz. At this time, the two sets of output laser frequencies f1 and f2 can be selected as 0.9MHz and 1MHz, and the theoretical maximum detection distance of the corresponding laser radar system can reach 1500m. In other embodiments, the frequencies f1 and f2 of the two sets of output lasers can be set according to the object's movement speed range, application scenario, maximum detection distance, and the system's light source power (limited by cost, safety and other factors), etc., and are not limited to the above-mentioned specific embodiments.

[0058] The above-mentioned laser radar system has the advantages of low cost and long ranging range, and can realize the functions of ranging, speed measurement and imaging at the same time.

[0059] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0060] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A laser radar system, characterized in that: include: A transmitting device, used for transmitting multiple groups of outgoing lasers with different frequencies; An emission optical system, used for emitting the outgoing laser light toward a detection area; A receiving device, used to receive reflected laser light; the reflected laser light is the laser light after the emitted laser light is reflected by an object in the detection area; A receiving optical system, used for receiving the reflected laser and emitting it toward the receiving device; as well as A processing system, which obtains the distance of the object in the detection area according to the frequency of each group of emitted lasers and the phase difference between the emitted lasers and the corresponding reflected lasers; The transmitting device includes a laser and a modulator, and the modulator modulates the emitted laser; The laser emits two groups of outgoing lasers with different frequencies. The frequency of the first outgoing laser is , the frequency of the second emitted laser is ; The frequency of the first emitted laser and the frequency of the second emitted laser The frequency difference between , Greater than the signal resolution of the processing system; The distance is calculated as: Wherein, f1 is the first emitted laser frequency, f2 is the second emitted laser frequency, c is the speed of light in a vacuum, N1 is the multiple of 2π contained in the phase change between the first emitted laser and the corresponding first reflected laser, N2 is the multiple of 2π contained in the phase change between the second emitted laser and the corresponding second reflected laser, and is the part of the phase change of the first reflected laser light relative to the first emitted laser light that is less than 2π; The phase change of the second reflected laser light relative to the second emitted laser light is less than 2π.

2. The laser radar system according to claim 1, characterized in that The emission optical system includes a collimating lens and a reflecting mirror.

3. The laser radar system according to claim 2, characterized in that The receiving optical system includes a focusing lens and a reflecting mirror.

4. The laser radar system according to claim 3, characterized in that The transmitting device transmits the output laser in a continuous wave amplitude modulation mode.

5. The laser radar system according to claim 1, characterized in that The processing system processes the first emitted laser light and the corresponding first reflected laser light according to the phase difference between the first emitted laser light and the corresponding second reflected laser light, the phase difference between the second emitted laser light and the corresponding second reflected laser light, and the frequency difference between the first emitted laser light and the second emitted laser light. , get the distance of the object in the detection area.

6. The laser radar system according to claim 1, characterized in that The modulator modulates the first emitted laser light with a first carrier amplitude, and modulates the second emitted laser light with a second carrier amplitude.

7. The laser radar system according to claim 1, characterized in that The laser is a frequency-stabilized laser.

8. The laser radar system according to claim 1, characterized in that The processing system also obtains the moving speed of the object in the detection area according to the frequency change of the reflected laser.

9. The laser radar system according to claim 1, characterized in that: The modulator modulates the multiple groups of emitted lasers respectively in a time division multiplexing manner.

10. The laser radar system according to claim 1, characterized in that: The laser emits four groups of outgoing lasers with different frequencies, the frequencies of the first outgoing laser and the second outgoing laser are similar, and the frequencies of the third outgoing laser and the fourth outgoing laser are similar.

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