Laser radar and light intensity calibration method and calibration device thereof

Abstract

The embodiment of the invention provides a laser radar and a light intensity calibration method and device thereof, and the laser radar comprises a laser device, and the light intensity calibration method comprises the steps: enabling the laser device to output a corresponding light signal based on a preset trigger signal and a first light intensity control signal; determining the actual light intensity of the optical signal in a preset time period; determining a light intensity feedback signal corresponding to the actual light intensity according to the actual light intensity of the light signal in a preset time period; and obtaining a calibrated second light intensity control signal based on the light intensity feedback signal and the first light intensity control signal. By adopting the above technical scheme, the light intensity of the laser radar can be calibrated, so that the laser can emit light stably, and the detection performance of the laser radar is improved.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of laser radar technology, and in particular to a laser radar and a light intensity calibration method and calibration device thereof. Background Art

[0002] The light emission characteristics of LiDAR are high peak power, short duration, and difficulty in measuring peak power. Currently, open-loop control is usually used to control the light emission power of LiDAR. When LiDAR is operated in different detection scenarios or after long-term operation, its light intensity will change, which will cause the light emission power to fluctuate and the performance of LiDAR ranging will be reduced.

[0003] Based on this, calibrating the light intensity of the laser radar to improve the detection performance of the laser radar is a technical problem that needs to be urgently solved by technical personnel in this field.

[0004] The contents of the background technology section are merely the technologies known to the public and do not represent the existing technologies in the field. Summary of the invention

[0005] In view of this, an embodiment of the present invention provides a laser radar and a light intensity calibration method and a calibration device thereof, which can calibrate the light intensity of the laser radar so that the laser can emit light stably and improve the detection performance of the laser radar.

[0006] First, an embodiment of the present invention provides a light intensity calibration method for a laser radar, wherein the laser radar includes a laser, and the light intensity calibration method includes:

[0007] Based on a preset trigger signal and a first light intensity control signal, the laser is caused to output a corresponding light signal;

[0008] Determining the actual light intensity of the light signal within a preset time period;

[0009] Determining a light intensity feedback signal corresponding to the actual light intensity according to the actual light intensity of the light signal within a preset time period;

[0010] A calibrated second light intensity control signal is obtained based on the light intensity feedback signal and the first light intensity control signal.

[0011] Optionally, determining the actual light intensity of the optical signal within a preset time period includes:

[0012] Detecting the optical signal and converting it into an electrical signal;

[0013] In the preset time period, the electrical signal is integrated to obtain a current integral value, which is used as the actual light intensity of the optical signal in the preset time period.

[0014] Optionally, the current integral value is converted into a digital form to obtain the current integral value in digital form, and the current integral value in digital form is used as the actual light intensity of the optical signal within a preset time period.

[0015] Optionally, the light intensity calibration method further includes: clearing the current integral value to zero.

[0016] Optionally, clearing the current integral value to zero includes at least one of the following:

[0017] After determining the actual light intensity of the light signal within a preset time period, outputting a reset signal to clear the current integral value;

[0018] Before the next light intensity calibration, a reset signal is output to clear the current integral value to zero.

[0019] Optionally, determining the light intensity feedback signal corresponding to the actual light intensity according to the actual light intensity of the light signal within a preset time period includes:

[0020] According to the pre-stored mapping relationship between the light intensity value and the light intensity feedback value, the light intensity feedback value corresponding to the actual light intensity is obtained, and the electrical signal corresponding to the light intensity feedback value is used as the light intensity feedback signal.

[0021] Optionally, obtaining a calibrated second light intensity control signal based on the light intensity feedback signal and the first light intensity control signal includes:

[0022] The light intensity feedback value corresponding to the feedback signal and the actual light intensity control value corresponding to the first light intensity control signal are accumulated to obtain the light intensity control value corresponding to the second light intensity control signal.

[0023] Optionally, the step of controlling the laser to output a corresponding optical signal based on a preset trigger signal and a first light intensity control signal includes:

[0024] Based on the current working mode of the laser radar, a trigger signal with corresponding pulse characteristics is output to drive the laser to output the optical signal under the action of the trigger signal with corresponding pulse characteristics.

[0025] Optionally, based on the current working mode of the laser radar, outputting a trigger signal with corresponding pulse characteristics to drive the laser to output the optical signal under the action of the trigger signal with corresponding pulse characteristics, includes:

[0026] When it is determined that the laser radar is in the first working mode, outputting a single pulse trigger signal to the driver to drive the laser to output the optical signal under the action of the single pulse trigger signal;

[0027] When it is determined that the laser radar is in the second working mode, output a multi-pulse trigger signal to the driver to drive the laser to output the optical signal under the action of the multi-pulse trigger signal;

[0028] Among them, the peak power of a single pulse of the laser radar in the first working mode is greater than the peak power of a single pulse in the second working mode.

[0029] Optionally, light intensity calibration is performed when the laser radar is in at least one of the following situations:

[0030] The laser radar is in a non-ranging state;

[0031] The laser radar is in a ranging gap.

[0032] Optionally, the laser radar includes a plurality of lasers;

[0033] The light intensity calibration method further includes: adjusting the first light intensity control signal corresponding to each laser in sequence according to a preset sequence.

[0034] Accordingly, an embodiment of the present invention further provides a light intensity calibration device for a laser radar, wherein the laser radar includes a laser, and the light intensity calibration device includes:

[0035] A control module, adapted to output a preset trigger signal and a first light intensity control signal; and adapted to obtain a calibrated second light intensity control signal based on a light intensity feedback signal and the first light intensity control signal;

[0036] A driving module, adapted to respond to a preset trigger signal and the first light intensity control signal to output a corresponding driving signal so that the laser outputs a corresponding light signal; and adapted to respond to the trigger signal and the second light intensity control signal so that the laser outputs a light signal with a desired light intensity;

[0037] The signal processing module is adapted to determine the actual light intensity of the optical signal within a preset time period, and determine a light intensity feedback signal corresponding to the actual light intensity according to the actual light intensity of the optical signal.

[0038] Optionally, the signal processing module includes:

[0039] A slave detector, adapted to detect the optical signal and convert it into an electrical signal;

[0040] A data processing unit, which integrates the electrical signal within the preset time period to obtain a current integral value and uses it as the actual light intensity of the optical signal within the preset time period;

[0041] The storage unit is suitable for storing the mapping relationship between the light intensity value and the light intensity feedback value.

[0042] Optionally, the signal processing module further includes:

[0043] The analog-to-digital conversion unit is coupled to the data processing unit and the storage unit respectively, and is suitable for performing analog-to-digital conversion on the current integral value to obtain the current integral value in digital form.

[0044] Optionally, the data processing unit includes an operational amplifier and an integrating capacitor, wherein:

[0045] The operational amplifier has a first input terminal coupled to the slave detector, a second input terminal coupled to the first terminal of the integrating capacitor, and an output terminal coupled to the second terminal of the integrating capacitor and the analog-to-digital conversion unit, respectively.

[0046] Optionally, the data processing unit further includes: a resetter, adapted to reset the current integral value to zero.

[0047] Optionally, the control module is further adapted to output a reset signal to the reset device after determining the actual light intensity of the light signal within a preset time period; or is adapted to output a reset signal to the reset device before the next light intensity calibration;

[0048] The resetter is adapted to clear the current integrated value to zero in response to the reset signal.

[0049] Optionally, the slave detector is placed on a direct light path or a scattered light path of the laser.

[0050] Optionally, the control module is adapted to accumulate the light intensity feedback value corresponding to the feedback signal and the actual light intensity control value corresponding to the first light intensity control signal as the light intensity control value corresponding to the second light intensity control signal.

[0051] Optionally, the control module is also suitable for outputting a trigger signal with corresponding pulse characteristics based on the current working mode of the laser radar, so as to drive the laser to output the light signal under the action of the trigger signal with corresponding pulse characteristics.

[0052] An embodiment of the present invention further provides a laser radar, comprising a laser, a main detector, and a processor. The light intensity calibration device described in any of the aforementioned embodiments, wherein:

[0053] The light intensity calibration device is adapted to output a preset trigger signal and a first light intensity control signal so that the laser outputs a corresponding light signal; and is adapted to determine the actual light intensity of the light signal within a preset time period, and determine a light intensity feedback signal corresponding to the actual light intensity according to the actual light intensity of the light signal; and is adapted to obtain a calibrated second light intensity control signal based on the light intensity feedback signal and the first light intensity control signal;

[0054] The laser is adapted to output the optical signal in response to the trigger signal and the first optical intensity control signal; and is adapted to output an optical signal having a desired optical intensity in response to the trigger signal and the second optical intensity control signal;

[0055] The main detector is adapted to receive a detection signal corresponding to the actual light signal as an echo signal;

[0056] The processor is adapted to output detection information based on the actual light signal and the echo signal.

[0057] Optionally, the laser radar also includes:

[0058] A scanning device, wherein the scanning device has a plurality of reflecting surfaces, each reflecting surface is adapted to rotate with the rotating device and change the transmission path of the optical signal;

[0059] The light intensity calibration device is also suitable for adjusting the first light intensity control signal during the ranging interval before the different reflective surfaces of the scanning device rotate to the target azimuth.

[0060] Optionally, the light intensity calibration device comprises a slave detector adapted to detect the light signal and convert it into an electrical signal;

[0061] The laser radar further comprises:

[0062] The scanning module is adapted to enable the optical signal emitted by the laser to directly enter the slave detector when the scanning module is rotated to a preset position.

[0063] Optionally, the light intensity calibration device comprises a slave detector adapted to detect the light signal and convert it into an electrical signal;

[0064] The laser radar further includes: a scanning module and a reflector module, wherein:

[0065] The scanning module is adapted to change the angles of the light signal and the return light beam incident thereon;

[0066] The reflector module is used to change the transmission direction of the echo light beam deflected by the scanning module, so as to deflect the echo light beam to the main detector and transmit part of the echo light beam to the slave detector.

[0067] Optionally, the number of the slave detectors is related to the number of the lasers, the area of ​​the photosensitive surface of the slave detectors and the size of the laser radar.

[0068] By adopting the light intensity calibration scheme of the laser radar provided in the embodiment of the present invention, based on a preset trigger signal and a first light intensity control signal, the laser in the laser radar outputs a corresponding light signal, and then the light intensity feedback signal corresponding to the actual light intensity can be determined according to the actual light intensity of the light signal within a preset time period. Based on the light intensity feedback signal and the first light intensity control signal, a calibrated second light intensity control signal can be obtained, so that the actual light intensity output by the laser controlled by the second light intensity control signal is consistent with the expected light intensity, thereby being able to calibrate the light intensity of the laser radar, so that the laser can emit light stably, thereby improving the detection performance of the laser radar.

[0069] Furthermore, by converting the detected optical signal into an electrical signal, the anti-interference performance in the signal transmission process can be improved, and then the electrical signal is integrated within the preset time period, and the actual light intensity obtained can more accurately reflect the energy accumulated by the optical signal within the preset time, which can improve the accuracy of the subsequently acquired light intensity feedback signal, and the light intensity of the optical signal within the preset time period can be determined through signal type conversion and integration processing, and the implementation method is simple.

[0070] Furthermore, by performing analog-to-digital conversion on the current integral value, the current integral value in digital form can be obtained. Since the current integral value in digital form has good anti-interference performance during transmission, the stability of the current integral value during transmission can be improved.

[0071] Furthermore, the electrical signal is integrated and the current integral value obtained is cumulative. By clearing the current integral value to zero, on the one hand, the integral value obtained after the integration process reflects the energy integral of the light signal during this light intensity calibration, which can improve the accuracy of the light intensity calibration; on the other hand, it can avoid the subsequent light emission of the laser radar from interfering with the light intensity calibration process.

[0072] Furthermore, after determining the actual light intensity of the optical signal within a preset time period, a reset signal is output to clear the current integral value; or before the next light intensity calibration, a reset signal is output to clear the current integral value. By flexibly selecting the timing of clearing the current integral value, it can be applied to different application scenarios, thereby improving the universality of the calibration method.

[0073] Furthermore, according to the mapping relationship between the pre-stored light intensity value and the light intensity feedback value, the light intensity feedback value corresponding to the actual light intensity is obtained without manual processing, which can improve the calculation efficiency and the accuracy of the calculated light intensity feedback value, and thus improve the accuracy of the light intensity feedback signal.

[0074] Furthermore, by accumulating the light intensity feedback value corresponding to the feedback signal and the actual light intensity control value corresponding to the first light intensity control signal as the light intensity control value corresponding to the second light intensity control signal, the calculation complexity can be reduced and the calibration efficiency can be improved.

[0075] Furthermore, based on the current working mode of the laser radar, a trigger signal with corresponding pulse characteristics is output to drive the laser under the action of the trigger signal with corresponding pulse characteristics, so that the light intensity of the laser in the laser radar can be calibrated under different working modes.

[0076] Furthermore, by making the peak power of a single pulse of the trigger signal of the laser radar in the first working mode greater than the peak power of a single pulse in the second working mode, the light intensity of the laser in the laser radar can be calibrated within a wider power dynamic range.

[0077] Furthermore, by calibrating the light intensity of the laser radar when the laser radar is in a non-ranging state or in a ranging gap, it is possible to avoid affecting the ranging process of the laser radar, and both detection efficiency and calibration efficiency can be taken into account at the same time.

[0078] Furthermore, according to a preset order, the first light intensity control signal corresponding to each laser in the laser radar is adjusted in sequence, so that each laser of the laser radar can output a light signal with an expected light intensity, thereby improving the overall ranging performance of the laser radar.

[0079] Furthermore, the laser radar may also include a scanning device, which has multiple reflecting surfaces. Since each reflecting surface can rotate along with the rotating device, the transmission path of the optical signal can be changed. During the rotation of each reflecting surface, the light intensity calibration device can also adjust the first light intensity control signal in the ranging gap before the different reflecting surfaces of the scanning device rotate to the target azimuth, thereby avoiding affecting the ranging process and taking into account both detection efficiency and calibration efficiency.

[0080] Furthermore, the laser radar may also include a scanning module. When the scanning module is rotated to a preset position, the light signal emitted by the laser is directly incident on the slave detector in the light intensity calibration device. The slave detector can detect the light signal and convert it into an electrical signal. Therefore, the output light intensity of the laser radar can be calibrated during the ranging gap, which can avoid affecting the ranging process and take into account both the detection efficiency and the calibration efficiency.

[0081] Furthermore, the laser radar may also include a scanning module and a reflector module, wherein, since the reflector module can transmit part of the echo light beam to the slave detector, the slave detector can detect the optical signal and convert it into an electrical signal. Therefore, the output light intensity of the laser radar can be calibrated when it is in a non-ranging state, which can avoid affecting the ranging process and take into account both the detection efficiency and the calibration efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0082] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments of the present invention or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this specification. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0083] Figure 1 A schematic diagram of the structure of a driving circuit of a laser in a laser radar is shown;

[0084] Figure 2 A schematic diagram showing the change in the light intensity of a laser when a laser radar is in different ranging scenarios is shown;

[0085] Figure 3 A schematic diagram showing the change of laser light emitting power over time or temperature;

[0086] Figure 4 A flow chart of a method for calibrating light intensity of a laser radar in an embodiment of the present invention is shown;

[0087] Figure 5a and Figure 5b A schematic diagram of the light intensity calibration process of the laser radar in the first working mode and the second working mode in an embodiment of this specification is shown;

[0088] Figure 6 A flow chart showing a method for calibrating the light intensity of a laser radar in a specific application scenario in an embodiment of the present invention is shown;

[0089] Figure 7 A schematic structural diagram of a light intensity calibration device according to an embodiment of the present invention is shown;

[0090] Figure 8 A schematic diagram of the structure of a signal processing module in an embodiment of the present invention is shown;

[0091] Fig. 9 A schematic diagram of the structure of a laser radar in an embodiment of the present invention is shown;

[0092] Fig.10A schematic diagram of the specific structure of a laser radar in an embodiment of the present invention is shown;

[0093] Fig.11 A schematic diagram of the specific structure of another laser radar in an embodiment of the present invention is shown;

[0094] Fig.12 A schematic diagram of the specific structure of another laser radar in an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0095] In order to enable those skilled in the art to better understand the problems existing in the prior art, the working principle of the laser is first briefly introduced in conjunction with a driving circuit of a laser radar.

[0096] Reference Figure 1 The schematic diagram of the structure of the driving circuit of the laser in the laser radar shown in the figure, the driving circuit may include a driver 11, a driving switch 12 (specifically a power field effect transistor Power FET), a laser LD and an energy storage capacitor C.

[0097] When the driver 11 does not receive a trigger signal, the drive switch 12 is not turned on, the charging circuit (power supply HV→energy storage capacitor C→ground GND) is turned on, the energy storage capacitor C is charged by the power supply HV, and the laser LD does not emit light; when the gate driver 11 has a trigger signal input, the drive switch 12 is turned on, the discharge circuit (energy storage capacitor C→laser LD→drive switch 12→ground GND) is turned on, the energy storage capacitor C supplies power to the laser LD, and the laser LD emits light.

[0098] However, the inventors found that Figure 1 The driving circuit shown is an open-loop control and cannot adaptively adjust the light intensity of the laser, that is, it cannot adjust the light power of the LiDAR. When the LiDAR is operated in different environments or after long-term operation fatigue, its light power will fluctuate, resulting in a decrease in the performance of the LiDAR such as ranging.

[0099] For example, refer to Figure 2 The figure shows a schematic diagram of the change in the light intensity of a laser of a laser radar in different ranging scenarios, wherein the horizontal axis represents time t and the vertical axis represents power P.

[0100] like Figure 2 As shown in the figure, in order to take into account the laser radar's ability to detect objects with different reflectivity in different ranging scenarios, the laser radar needs to have a larger light intensity adjustment range (the light intensity can reflect the power). a to b During the period, the laser radar is in a close-range test scenario, and the laser only needs to emit a light signal with the first peak power P1; and at t cto d During the period, the laser radar is in a long-distance (for example, 200m) test scenario, and the laser needs to emit a light signal with a second peak power P2, over and over again, until the detection process is completed, wherein the second peak power P2 is much greater than the first peak power P1.

[0101] Therefore, the laser radar needs to emit light signals with different luminous powers in different ranging scenarios. However, during the light intensity adjustment process, the laser radar's luminous power will inevitably fluctuate, especially for some low-intensity luminous scenes. Power adjustment may cause the laser radar to fail to emit light, resulting in blind lines.

[0102] For example, refer to Figure 3 The figure shows a schematic diagram of the change of the luminous power of a laser radar with time or temperature, wherein the horizontal axis represents the usage time t or temperature T, and the vertical axis represents the luminous power P.

[0103] like Figure 3 As shown in the figure, if the horizontal axis represents time t, after the laser radar has been running for a long time, its internal components will age and its corresponding luminous power will also produce different drifts; or, if the horizontal axis represents temperature T, as the temperature changes, its corresponding luminous power will also produce different drifts. That is, during the use of the laser radar, the luminous power P will produce unpredictable drifts as the temperature T or the use time t changes, which will affect the detection accuracy of the laser radar, for example, it will affect the measurement of reflectivity, because the reflectivity is related to the measured light intensity.

[0104] In order to solve the above technical problems, the technical solution of the embodiment of the present invention provides a light intensity calibration method for a laser radar. Based on the actual light intensity of the laser in the laser radar within a preset time period, the light intensity of the laser can be feedback controlled to achieve calibration of the first light intensity control signal, and obtain a calibrated second light intensity control signal, so that the actual light intensity output by the laser controlled by the second light intensity control signal is consistent with the expected light intensity, thereby being able to calibrate the light intensity of the laser radar, so that the laser can emit light stably, thereby improving the detection performance of the laser radar.

[0105] In order to enable those skilled in the art to better understand the inventive concept, working principle and advantages of the embodiments of the present invention, the light intensity calibration scheme of the laser radar in the embodiments of the present invention is described in detail below.

[0106] Reference Figure 4 The flowchart of a method for calibrating the light intensity of a laser radar in an embodiment of the present invention is shown. In some embodiments of this specification, the laser radar includes a laser. Specifically, the light intensity of the laser radar can be calibrated according to the following steps:

[0107] S11, based on a preset trigger signal and a first light intensity control signal, causing the laser to output a corresponding light signal.

[0108] Specifically, the trigger signal can control the light-emitting moment of the laser, and the first light intensity control signal can control the intensity of the light signal output by the laser. Therefore, the moment of the trigger signal and the light intensity corresponding to the first light intensity control signal can be set to adapt to different detection requirements of the laser radar.

[0109] In some embodiments of this specification, the laser may be a laser emitting device such as a semiconductor laser, a solid laser, etc. The embodiments of the present invention do not limit the specific structure of the laser, as long as the laser can output an optical signal (also referred to as a detection signal).

[0110] S12, determining the actual light intensity of the light signal within a preset time period.

[0111] Specifically, the laser is affected by various factors (for example, temperature changes, device aging, etc.), and the actual light intensity of the optical signal it outputs may differ from the expected light intensity (the expected light intensity can be controlled by the first light intensity control signal). Therefore, the actual light intensity of the laser radar within a preset time period can be obtained.

[0112] In some embodiments of the present specification, the preset time period is related to the light emission duration of the laser. In some embodiments, the preset time period may be equal to the light emission duration of the laser. In other embodiments, the preset time period may be greater than the light emission duration of the laser. The embodiments of the present invention are not limited to this, as long as the light intensity of the optical signal can be obtained in the preset time period.

[0113] S13, determining a light intensity feedback signal corresponding to the actual light intensity according to the actual light intensity of the light signal within a preset time period.

[0114] Specifically, when the actual light intensity of the optical signal within a preset time period is determined, a light intensity feedback signal corresponding to the actual light intensity can be obtained according to a preset mapping relationship, wherein the light intensity feedback signal can characterize the difference between the actual light intensity of the optical signal and the expected light intensity.

[0115] S14, obtaining a calibrated second light intensity control signal based on the light intensity feedback signal and the first light intensity control signal.

[0116] In a specific implementation, a preset device or functional module may be used according to the light intensity feedback signal and the first light intensity control signal to obtain a calibrated second light intensity control signal.

[0117] Therefore, based on the light intensity feedback signal and the first light intensity control signal, a calibrated second light intensity control signal can be obtained, so that the actual light intensity output by the laser controlled by the second light intensity control signal is consistent with the expected light intensity, thereby calibrating the light intensity of the laser radar, so that the laser can emit light stably and improve the detection performance of the laser radar.

[0118] In order to enable those skilled in the art to better understand and implement the embodiments of the present invention, some specific examples are given below for the specific implementation of the light intensity calibration method of the laser radar in the embodiments of the present invention.

[0119] In some embodiments of the present specification, the actual light intensity of the optical signal may be determined in a variety of ways.

[0120] As a specific example, the optical signal can be detected and converted into an electrical signal, and then the electrical signal is integrated within the preset time period to obtain a current integral value, which is used as the actual light intensity of the optical signal within the preset time period.

[0121] Specifically, considering that the optical signal is easily affected by external ambient light, before determining the actual light intensity of the optical signal, the optical signal can be converted into a corresponding electrical signal to improve the anti-interference performance during the transmission of the optical signal; and the optical signal output by the laser can be regarded as a pulse signal. As time changes, the energy of the optical signal will gradually increase, reach a peak value, and then gradually decrease. By integrating the optical signal, the actual light intensity obtained can accurately reflect the energy integral of the optical signal within a preset time period, which can improve the accuracy of the subsequently obtained light intensity feedback signal, and the light intensity of the optical signal within a preset time period can be determined through signal type conversion and integration processing, and the implementation method is simple.

[0122] In some other embodiments, the optical signal may be directly processed to determine its actual light intensity within a preset period of time. For example, optical frequency coherence detection may be used to determine the actual light intensity of the optical signal within a preset period of time. This specification does not limit this, as long as the light intensity of the optical signal can be determined.

[0123] In a specific implementation, the actual light intensity of the optical signal within a preset time period may be determined by the following steps:

[0124] A1): In the preset time period, the electrical signal is integrated to obtain a current integral value, which is used as the actual light intensity of the optical signal in the preset time period.

[0125] In a specific implementation, the current integral value obtained through the integration processing is in analog form, which is susceptible to interference from other signals during the transmission process. Therefore, in some embodiments of the specification, step A2) can also be performed: the current integral value is converted into a digital form to obtain the current integral value in digital form, and the current integral value in digital form is used as the actual light intensity of the optical signal within a preset time period.

[0126] Specifically, since the current integral value in digital form has good anti-interference performance during transmission, by converting the current integral value in analog form into an integral value in digital form, the stability of the current integral value during transmission can be improved, thereby improving the accuracy of the current integral value.

[0127] In a specific implementation, the actual light intensity obtained by integrating the light signal is the energy accumulated by the light signal in a preset period of time, which is cumulative. As the light intensity calibration proceeds, the integrated light pulses may continue to increase, and the current integral value obtained by the integration processing continues to increase, which cannot correctly reflect the actual light intensity of the light signal in a light intensity calibration process.

[0128] Based on this, in some embodiments of this specification, the current integral value can be cleared to zero. By clearing the current integral value to zero, on the one hand, the integral value obtained by the integration process reflects the energy integral of the light signal during the current light intensity calibration, which can improve the light intensity calibration accuracy; on the other hand, it can avoid the subsequent light emission of the laser radar from interfering with the current light intensity calibration process.

[0129] In a specific implementation, based on actual detection requirements, the current integral value may be cleared to zero at different times.

[0130] As an optional example, after determining the actual light intensity of the light signal within a preset time period, a reset signal is output to clear the current integral value.

[0131] Specifically, when the actual light intensity of the optical signal within the preset time period is determined, the light intensity calibration process is completed, and the current integral value can be cleared to prepare for the next light intensity calibration.

[0132] It should be noted that the "current light intensity calibration process" is a calibration of the light emission process corresponding to when one of the lasers of the lidar completes a measurement. The laser's one measurement light emission and the corresponding light intensity calibration process can emit one pulse or multiple pulses.

[0133] As another optional example, before the next light intensity calibration, a reset signal is output to clear the current integrated value to zero.

[0134] Specifically, before the next light intensity calibration, the current integral value is cleared to zero, so that when the next light intensity calibration is performed, the integral value obtained after the integration processing is only the actual light intensity value corresponding to the light signal during the next light intensity calibration, and is not affected by the previous light intensity calibration.

[0135] It can be seen from the above that the above method can be applied to different application scenarios by flexibly selecting the time to clear the current integral value, thereby improving the universality of the calibration method.

[0136] It can be understood that the description of clearing the current integral value to zero in the above example is only an example, and the embodiment of the present invention does not impose any limitation on this, as long as it can be determined that the actual light intensity of the optical signal can be used.

[0137] By adopting the above method, the actual light intensity of the light signal corresponding to the trigger signal and the first light intensity control signal can be determined, and then based on the actual light intensity of the light signal and the light intensity control value corresponding to the first light intensity control signal, the light intensity of the laser radar can be calibrated so that the laser can output a light signal with the expected light intensity.

[0138] In some embodiments of the present specification, a light intensity feedback value corresponding to the actual light intensity can be obtained according to a pre-stored mapping relationship between light intensity values ​​and light intensity feedback values, and an electrical signal corresponding to the light intensity feedback value can be used as the light intensity feedback signal.

[0139] Among them, the mapping relationship between the light intensity value and the light intensity feedback value can be established before the laser radar leaves the factory, by sensing the laser output with light signals of different powers through the detector, and obtaining the light intensity corresponding to the light signals of different powers sensed by the detector, and comparing the light intensity with its expected light intensity to obtain the light intensity feedback value corresponding to the light intensity of the light signals of different powers, thereby establishing a mapping relationship between the light intensity value and the light intensity feedback value.

[0140] Specifically, when determining the actual light intensity value of the optical signal, a corresponding light intensity feedback value may be obtained according to the mapping relationship, and the light intensity feedback value may represent the difference between the actual light intensity of the optical signal and the expected light intensity.

[0141] Therefore, based on the pre-stored mapping relationship between the light intensity value and the light intensity feedback value, the light intensity feedback value corresponding to the actual light intensity can be automatically obtained without manual processing, which can improve the calculation efficiency and the accuracy of the calculated light intensity feedback value, and then use the electrical signal corresponding to the light intensity feedback value as the light intensity feedback signal to improve the accuracy of the light intensity feedback signal.

[0142] Afterwards, a calibrated second light intensity control signal may be obtained according to the light intensity feedback signal and the first light intensity control signal.

[0143] As an optional example, the light intensity feedback value corresponding to the feedback signal and the actual light intensity control value corresponding to the first light intensity control signal may be accumulated to serve as the light intensity control value corresponding to the second light intensity control signal.

[0144] For example, assuming that based on the preset trigger signal and the first light intensity control signal, the expected light intensity of the light signal output by the laser is E3, and the actual light intensity of the light signal is determined to be E4 after integration processing and data conversion, that is, the actual light intensity control value corresponding to the first light intensity control signal is E4. According to the mapping relationship, the corresponding light intensity feedback value can be determined to be E f , the actual light intensity control value E4 and the light intensity feedback value E f By accumulating, the light intensity control value corresponding to the second light intensity control signal can be obtained.

[0145] It is understandable that the above calculation method is only an example, and the embodiment of the present invention does not limit the specific calculation method for obtaining the second light intensity control signal, as long as the calibrated second light intensity control signal can be obtained according to the light intensity feedback signal and the first light intensity control signal.

[0146] As mentioned above, based on different ranging scenarios, the light intensity of the laser radar is not the same, that is, it can be considered that the laser radar is in different working modes. At this time, based on the current working mode of the laser radar, a trigger signal with corresponding pulse characteristics can be output to drive the laser to output the light signal under the action of the trigger signal with corresponding pulse characteristics, so that the light intensity of the laser in the laser radar can be calibrated under different working modes.

[0147] Specifically, when it is determined that the laser radar is in the first working mode, a single pulse trigger signal is output to the driver to drive the laser to output the optical signal under the action of the single pulse trigger signal;

[0148] When it is determined that the laser radar is in the second working mode, output a multi-pulse trigger signal to the driver to drive the laser to output the optical signal under the action of the multi-pulse trigger signal;

[0149] Among them, the peak power of a single pulse of the laser radar in the first working mode is greater than the peak power of a single pulse in the second working mode.

[0150] By adopting the above-mentioned light emission control method, the peak power of a single pulse of the trigger signal of the laser radar in the first working mode is made greater than the peak power of a single pulse in the second working mode, so that the light emission intensity of the laser in the laser radar can be calibrated within a wider power dynamic range.

[0151] It should be noted that the first working mode and the second working mode of the laser radar are only examples, which are only used to illustrate that when the laser radar is in different operating states, a trigger signal with corresponding pulse characteristics can be used to drive the laser to emit light.

[0152] It is understandable that, in the actual light intensity calibration process, a trigger signal with the same pulse characteristics can be used to drive the laser to emit light.

[0153] As a specific example, refer to Figure 5a Schematic diagram of the light intensity calibration process of the laser radar in the first working mode, wherein the horizontal axis represents time t and the vertical axis represents the actual light intensity E i (i.e. the current integral value obtained after integration) and the expected light intensity E d (related to the first light intensity control signal).

[0154] like Figure 5a As shown, at t a1 to a2 During the period, the trigger signal Tr obtained by the driver is a single pulse.

[0155] Under the drive of the single pulse trigger signal Tr, the laser can be controlled according to the expected light intensity E corresponding to the first light intensity control signal. d1 In this process, the light signal can be integrated to obtain the corresponding actual light intensity E a1 , according to the actual light intensity E a1 and the expected light intensity E d1 , the light intensity of the laser radar can be calibrated. The specific calibration process can be found in the above embodiment and will not be elaborated here.

[0156] In t a2 to a3 During this period, the single pulse trigger signal Tr is at a low level, the laser does not emit light, and the corresponding actual light intensity is still E a1 .

[0157] Continue to refer to Figure 5a , at t a3 At or after the moment, the reset signal Rs jumps from low level to high level, and the current integral value E a1 is cleared.

[0158] use Figure 5a In the light emission control method shown, the laser only needs to emit light once to complete the light intensity calibration process, and the calibration efficiency is high.

[0159] As another specific example, refer to Figure 5b The schematic diagram of the light intensity calibration process of the laser radar in the second working mode is shown in FIG. Figure 5bAs shown, the driver can now obtain multiple pulses (for example Figure 5a The three-pulse trigger signal Tr is shown in FIG. 1 , specifically:

[0160] From time 0 to t6, the driving signal includes three cycles of pulse signals, each of which includes a low level segment in the first half cycle and a high level segment in the second half cycle, wherein:

[0161] The time period from t0 to t2 is the first pulse signal of the first cycle, and at time t1, the first pulse signal jumps from a low level to a high level. Driven by the first pulse signal and the first light intensity control signal, the laser can be operated at the expected light intensity E d2 In this process, the light signal is integrated to obtain the corresponding light intensity E b1 .

[0162] The period from t2 to t4 is the second pulse signal of the second cycle, and at time t3, the second pulse signal jumps from a low level to a high level. Driven by the second pulse signal and the first light intensity control signal, the laser can be operated at the expected light intensity E d2 In this process, the light signal is integrated to obtain the corresponding light intensity E b2 .

[0163] Similarly, when the laser experiences all pulses, for example, the third pulse signal of the third cycle in the period from t4 to t6, the optical signal is integrated to obtain the corresponding light intensity E b3 Then according to the actual light intensity E b3 and the expected light intensity E d2 , the light intensity of the laser radar can be calibrated. The specific calibration process can be found in the above embodiment and will not be elaborated here.

[0164] Continue to refer to Figure 5b At or after time t7, the reset signal Rs changes from low level to high level, and the current integral value E b3 is cleared.

[0165] For lasers with lower peak power, the integral value within the preset period is also smaller, so Figure 5b The light emission control method shown in the figure is to make the laser emit light multiple times ( Figure 5b It is shown as 3 times. In the specific implementation, it can be flexibly set according to actual needs. The embodiment of the present invention does not impose any restriction on the number of times the laser emits light. It can increase the effective number of bits of the integral output, and the actual light intensity of the obtained optical signal is more accurate.

[0166] Combined with reference Figure 5a and Figure 5b , t a1 toa2 The duration corresponding to the time period is greater than the duration corresponding to the time period from t1 to t2, that is, the pulse width when the laser radar is in the first operating mode is greater than the pulse width when the laser radar is in the second operating mode. When the pulse amplitude is the same, the peak power of a single pulse of the laser radar in the first operating mode is greater than the peak power of a single pulse in the second operating mode.

[0167] It should be noted that, first of all, Figure 5a and Figure 5b It is just used to illustrate that when the laser radar is in different working modes, different control methods can be used to control the laser emission. Figure 5a and Figure 5b The light intensity value, the pulse characteristics of the trigger signal (such as pulse amplitude, width, and number of pulses), and the level jump time of the reset signal shown in the figure are only examples. Different waveform diagrams can be obtained for different light intensity calibration scenarios, and the embodiment of the present invention does not limit this. Secondly, Figure 5a and Figure 5b After the current light intensity calibration is completed (or it can also be considered that before the next light intensity calibration), the current integral value of the calculated light signal is cleared to zero. In the actual calibration process, the current integral value can also be cleared to zero when the current integral is determined. For example, Figure 5a As shown, the level of the reset signal Rs can be a3 The instant at which the current integral value jumps from a low level to a high level, the embodiment of the present invention does not impose any restriction on the instant at which the current integral value is cleared.

[0168] It is understandable that for the same laser, when the laser radar is in the first working mode and the second working mode, the laser radar can be operated in the following manner: Figure 5a and Figure 5b The light intensity calibration process shown in the figure is to perform at least two consecutive calibrations on the light intensity. For example, the light intensity can be first calibrated by Figure 5a The first light intensity calibration is performed using the lighting method shown. Figure 5b Perform a second light intensity calibration using the lighting method shown.

[0169] In a specific implementation, considering that the light intensity of the laser is affected by the external environment and fluctuates for a relatively long time, the light intensity can be calibrated at an appropriate time during the laser radar detection process. For example, the laser can be calibrated when the laser radar is just turned on, and then detection can be performed; or the laser can be calibrated during the laser radar detection process.

[0170] As a specific example, when the laser radar is in a non-ranging state, its light intensity is calibrated.

[0171] As another specific example, when the laser radar is in a ranging gap, its light intensity is calibrated.

[0172] Therefore, the above calibration process can avoid affecting the ranging process, and can take into account both detection efficiency and calibration efficiency.

[0173] It is understandable that the calibration moments described above are all examples, and this specification does not impose any limitations on this, as long as the light intensity calibration method of the embodiment of the present invention can be used to calibrate the laser radar.

[0174] In a specific application scenario, a laser radar may generally include multiple lasers, each of which may constitute a corresponding transmitting array, and the lasers in the transmitting array may emit light in a patrol manner according to a preset timing to complete the detection process.

[0175] In a specific implementation, when the laser radar includes multiple lasers, the first light intensity control signal corresponding to each laser can be adjusted in sequence according to a preset order. In some embodiments, the preset order can be the light emission timing of each laser, or it can be a self-set order. The embodiment of the present invention does not impose any restrictions on this, as long as each laser can be adjusted so that each laser can output a light signal with the expected light intensity.

[0176] In order to enable those skilled in the art to better understand and implement the light intensity calibration method in the embodiment of the present invention, a specific example is used to describe it in detail below.

[0177] Reference Figure 6 The flowchart of the light intensity calibration method of the laser radar in a specific application scenario in an embodiment of the present invention is shown. In some embodiments of this specification, the light intensity calibration process can be performed according to the following steps:

[0178] S61, based on the current working mode of the laser radar, output a trigger signal with corresponding pulse characteristics to drive the laser to output the optical signal under the action of the trigger signal with corresponding pulse characteristics.

[0179] Among them, the laser radar can have a first working mode and a second working mode. Among them, the specific implementation scheme of driving the laser to emit light based on the trigger signal in each working mode can be found in the above content and will not be described in detail here.

[0180] S62, detecting the optical signal and converting it into an electrical signal.

[0181] S63, performing integration processing on the electrical signal within the preset time period to obtain a current integration value.

[0182] S64, performing analog-to-digital conversion on the current integral value to obtain the current integral value in digital form, and using the current integral value in digital form as the actual light intensity of the optical signal within a preset time period.

[0183] S66, obtaining a light intensity feedback value corresponding to the actual light intensity according to a pre-stored mapping relationship between the light intensity value and the light intensity feedback value, and using an electrical signal corresponding to the light intensity feedback value as the light intensity feedback signal.

[0184] S67, accumulating the light intensity feedback value corresponding to the feedback signal and the actual light intensity control value corresponding to the first light intensity control signal as the light intensity control value corresponding to the second light intensity control signal.

[0185] In a specific implementation, the optical signal is integrated, and the actual light intensity obtained is the energy integral value of the optical signal in a preset time period, which is cumulative. Therefore, during the light intensity calibration process, the current integral value can be cleared.

[0186] For example, continue to refer to Figure 6 After determining the actual light intensity of the optical signal within the preset time period, the current integral value may be cleared, that is, after executing step S64 and before executing step S66, step S65 may be executed; or, before the next light intensity calibration, the current integral value may be cleared, that is, after executing step S67, step S68 may be executed.

[0187] The embodiment of the present invention further provides a laser radar light intensity calibration device corresponding to the laser radar light intensity calibration method, and the light intensity calibration device can calibrate the light intensity of the laser radar.

[0188] Reference Figure 7 The structure diagram of a light intensity calibration device in an embodiment of the present invention is shown in FIG. Figure 7 As shown, in some embodiments of the present specification, the laser radar L0 may include a laser LD, and the light intensity calibration device U may include a control module U1, a driving module U2 and a signal processing module U3, wherein:

[0189] The control module U1 is adapted to output a preset trigger signal Tr and a first light intensity control signal E c1 ; and adapted to be based on the light intensity feedback signal and the first light intensity control signal E c1 , and obtain the calibrated second light intensity control signal E c2 ;

[0190] The driving module U2 is adapted to respond to a preset trigger signal Tr and the first light intensity control signal E c1, outputting a corresponding driving signal to make the laser LD output a corresponding optical signal; and being adapted to respond to the trigger signal Tr and the second light intensity control signal E c2 , so that the laser outputs an optical signal with a desired light intensity;

[0191] The signal processing module U3 is adapted to determine the actual light intensity of the optical signal within a preset time period, and determine a light intensity feedback signal corresponding to the actual light intensity according to the actual light intensity of the optical signal.

[0192] The following combination Figure 7 , briefly describe the working principle of the light intensity calibration device U:

[0193] In response to the preset trigger signal Tr output by the control module U1 and the first light intensity control signal E c1 The driving module U2 can generate a corresponding driving signal and output it to the laser LD, and the laser LD can output a corresponding optical signal.

[0194] The signal processing module U3 can process the optical signal output by the laser LD, determine the actual light intensity of the optical signal within a preset time period, and output the actual light intensity to the control module U1. The control module U1 can obtain a calibrated second light intensity control signal E based on the light intensity feedback signal and the first light intensity control signal. c2 The driving module U2 can respond to the trigger signal Tr and the second light intensity control signal E c2 , so that the laser LD outputs an optical signal with a desired light intensity.

[0195] Therefore, the control module can obtain a calibrated second light intensity control signal based on the light intensity feedback signal and the first light intensity control signal, so that the actual light intensity output by the laser controlled by the second light intensity control signal is consistent with the expected light intensity, thereby calibrating the light intensity of the laser radar, allowing the laser to emit light stably and improving the detection performance of the laser radar.

[0196] In order to enable those skilled in the art to better understand and implement the embodiments of the present invention, some specific examples are given below for the specific implementation of the light intensity calibration device of the laser radar in the embodiments of the present invention.

[0197] In some embodiments of this specification, the control module can be implemented by a processing chip such as a central processing unit (CPU), a field programmable gate array (FPGA), or an application specific integrated circuit (ASIC) or one or more integrated circuits configured to implement the embodiments of the present invention. As a specific example, the control module can be an FPGA.

[0198] Combination Figure 7 , refer to Figure 8 FIG. 1 is a schematic diagram of a structure of a signal processing module in an embodiment of the present invention. In some embodiments of this specification, for example Figure 8 As shown, the signal processing module U3 may specifically include: a slave detector SD, a data processing unit DPU and a storage unit SC, wherein:

[0199] The slave detector SD is adapted to detect the optical signal and convert it into an electrical signal;

[0200] A data processing unit DPU is adapted to perform integration processing on the electrical signal within the preset time period to obtain a current integral value and use it as the actual light intensity of the optical signal within the preset time period;

[0201] The storage unit SC is suitable for storing the mapping relationship between the light intensity value and the light intensity feedback value.

[0202] Specifically, before determining the actual light intensity of the optical signal, the detected optical signal can be converted from the detector SD into a corresponding electrical signal and output to the data processing unit DPU. The data processing unit DPU can integrate the electrical signal within a preset time period to obtain a corresponding integral value, and then according to the mapping relationship between the stored light intensity value and the light intensity feedback value of the storage unit SC, a light intensity feedback value corresponding to the actual light intensity can be obtained. The electrical signal corresponding to the light intensity feedback value is used as a light intensity feedback signal and output to the control module U1.

[0203] In some embodiments of this specification, continue to refer to Figure 8, the slave detector SD may be a photodiode PD. In some other embodiments, the slave detector SD may also be other devices or equipment that can convert optical signals into electrical signals, for example, the slave detector SD may be an avalanche photodiode (APD), a single photon avalanche diode (SPAD) and a silicon photomultiplier (SiPM).

[0204] In a specific implementation, based on laser radars with different structures, the slave detector SD can be placed on the corresponding output light path of the laser radar. For example, the slave detector SD can be placed on the direct light path or scattered light path of the laser to detect the optical signal output by the laser LD.

[0205] It is understandable that the placement position of the slave detector described above is only an example, and the embodiment of the present invention does not limit this, as long as the slave detector can detect the optical signal output by the laser.

[0206] In a specific implementation, the current integral value obtained by the data processing unit DPU integration processing is an analog form, which is easily interfered by other signals during the transmission process. In some embodiments of this specification, continue to refer to Figure 8 The signal processing module U3 may further include an analog-to-digital conversion unit ADC0, which is coupled to the data processing unit DPU and the storage unit SC respectively, and is suitable for performing analog-to-digital conversion on the current integral value to obtain the current integral value in digital form.

[0207] In some embodiments of the present specification, the data conversion unit ADC0 may specifically be an analog to digital converter (ADC), and the analog to digital converter ADC may be capable of converting a current integral value in analog form into a corresponding current integral value in digital form.

[0208] In a specific implementation, the data processing unit DPU may specifically include an operational amplifier OA and an integrating capacitor C, wherein:

[0209] The operational amplifier OA has a first input terminal coupled to the slave detector SD, a second output terminal coupled to the first terminal of the integrating capacitor C, and an output terminal coupled to the second terminal of the integrating capacitor C and the data conversion unit ADC0 respectively.

[0210] Specifically, the operational amplifier OA and the integrating capacitor C can form an integrating circuit, and can obtain the energy integral of the electrical signal within a preset time.

[0211] In a specific implementation, the actual light intensity obtained by integrating the light signal is the energy accumulated by the light signal in a preset period of time, which is cumulative. As the light intensity calibration proceeds, the current integral value obtained by the integration processing continues to increase, and thus cannot correctly reflect the actual light intensity of the light signal in this light intensity calibration process.

[0212] Based on this, in some embodiments of this specification, continue to refer to Figure 8 The data processing unit DPU may further include: a resetter S, a first end of which is respectively coupled to the second end of the operational amplifier OA and the first end of the integrating capacitor C, and a second end of which is respectively coupled to the output end of the operational amplifier OA and the second end of the integrating capacitor C, suitable for clearing the current integrated value.

[0213] In a specific implementation, based on actual detection requirements, the current integral value may be cleared to zero at different times.

[0214] As an optional example, Figure 8 As shown, the control module U1 is further adapted to output a reset signal to the resetter S after determining the actual light intensity of the light signal within a preset time period, and the resetter S may be adapted to clear the current integral value to zero in response to the reset signal.

[0215] As another alternative example, Figure 8 As shown, the control module U1 is further adapted to output a reset signal to the resetter S before the next light intensity calibration, and the resetter S may be adapted to clear the current integral value to zero in response to the reset signal.

[0216] Specifically, before the next light intensity calibration, the current integral value is cleared to zero, so that when the next light intensity calibration is performed, the integral value obtained after the integration processing is only the actual light intensity value corresponding to the light signal during the next light intensity calibration, and is not affected by the previous light intensity calibration.

[0217] Using the above method, the signal processing module can determine the actual light intensity of the optical signal corresponding to the trigger signal and the first light intensity control signal, and then the control module can calibrate the light intensity of the laser radar based on the actual light intensity of the optical signal and the light intensity control value corresponding to the first light intensity control signal, so that the laser can output a light signal with the expected light intensity.

[0218] In some embodiments of the present specification, based on the mapping relationship between the light intensity value and the light intensity feedback value stored in the storage unit and the actual light intensity, a light intensity feedback value corresponding to the actual light intensity can be obtained, and the electrical signal corresponding to the light intensity feedback value can be output to the control module as the light intensity feedback signal. The control module can accumulate the light intensity feedback value corresponding to the feedback signal and the actual light intensity control value corresponding to the first light intensity control signal as the light intensity control value corresponding to the second light intensity control signal.

[0219] Among them, the mapping relationship between the light intensity value and the light intensity feedback value can be established before the laser radar leaves the factory, by sensing the laser output with light signals of different powers through the detector, and obtaining the light intensity corresponding to the light signals of different powers sensed by the detector, and comparing the light intensity of the light signal with its expected light intensity to obtain the light intensity feedback value corresponding to the light intensity of the light signals of different powers, so as to establish a mapping relationship between the light intensity value and the light intensity feedback value.

[0220] It is understandable that the above calculation method is only an example, and the embodiment of the present invention does not limit the specific calculation method for obtaining the second light intensity control signal, as long as the calibrated second light intensity control signal can be obtained according to the light intensity feedback signal and the first light intensity control signal.

[0221] As mentioned above, based on different ranging scenarios, the light intensity of the laser radar is not the same, that is, it can be considered that the laser radar is in different working modes. At this time, the control module can also output a trigger signal with corresponding pulse characteristics based on the current working mode of the laser radar to drive the laser to output the light signal under the action of the trigger signal with corresponding pulse characteristics, so that the light power of the laser radar can be adjusted within different power dynamic ranges.

[0222] Specifically, when the control module determines that the laser radar is in the first working mode, it can output a single pulse trigger signal to the driver to drive the laser to output the optical signal under the action of the single pulse trigger signal. The specific calibration process can be found in Figure 5a , which will not be described in detail here.

[0223] When the control module determines that the laser radar is in the second working mode, it can output a multi-pulse trigger signal to the driver to drive the laser to output the optical signal under the action of the multi-pulse trigger signal. The specific calibration process can be found in Figure 5b , which will not be described in detail here.

[0224] In a specific implementation, considering that the light intensity of the laser is affected by the external environment and fluctuates for a relatively long time, the light intensity can be calibrated at an appropriate time during the laser radar detection process. For example, the laser can be calibrated when the laser radar is just turned on, and then detection can be performed; or the laser can be calibrated during the laser radar detection process.

[0225] As a specific example, when the control module determines that the laser radar is in a non-ranging state, its light intensity is calibrated.

[0226] As another specific example, when the control module determines that the laser radar is in a ranging gap, its light intensity is calibrated.

[0227] Therefore, by calibrating the light intensity of the laser radar when the laser radar is in a non-ranging state or the laser radar is in a ranging gap, both detection efficiency and calibration efficiency can be taken into account at the same time.

[0228] In a specific application scenario, a laser radar may generally include multiple lasers, each of which may constitute a corresponding transmitting array, and the lasers in the transmitting array may emit light in a patrol manner according to a preset timing to complete the detection process.

[0229] In a specific implementation, when the laser radar includes multiple lasers, the first light intensity control signal corresponding to each laser can be adjusted in sequence according to a preset order. In some embodiments, the preset order can be the light emission timing of each laser, or it can be a self-set order. The embodiment of the present invention does not impose any restrictions on this, as long as each laser can be adjusted so that each laser can output a light signal with the expected light intensity.

[0230] In order to enable those skilled in the art to better understand and implement the working principle of the light intensity calibration device in the embodiment of the present invention, the following is combined with Figure 7 and Figure 8 Provide detailed explanation.

[0231] First, the control module U1 can output a trigger signal with corresponding pulse characteristics based on the current working mode of the laser radar L0, so that the driving module U2 can produce a corresponding driving signal under the action of the trigger signal with corresponding pulse characteristics. Under the action of the driving signal, the laser LD can output an optical signal.

[0232] The light signal can be detected by the detector SD and converted into an electrical signal. The integrating capacitor C can integrate the electrical signal within the preset time period to obtain a current integral value of the light signal within the preset time period. The analog-to-digital conversion unit ADC0 can be suitable for performing analog-to-digital conversion on the current integral value to obtain a current integral value in digital form, and use the current integral value in digital form as the actual light intensity of the light signal within the preset time period.

[0233] According to the mapping relationship between the light intensity value and the light intensity feedback value stored in the storage unit SC, the light intensity feedback value corresponding to the actual light intensity can be obtained, and the electrical signal corresponding to the light intensity feedback value is output to the control module U1 as the light intensity feedback signal.

[0234] The control module U1 can add the light intensity feedback value corresponding to the feedback signal and the actual light intensity control value corresponding to the first light intensity control signal as the light intensity control value corresponding to the second light intensity control signal, and then the driving unit U2 can drive the laser LD to output a light signal with the expected light intensity according to the calibrated second light intensity signal and the trigger signal.

[0235] In a specific implementation, the optical signal is integrated, and the actual light intensity obtained is the energy integral value of the optical signal in a preset time period, which is cumulative. Therefore, during the light intensity calibration process, the current integral value can be cleared.

[0236] For example, the current integral value may be cleared after the actual light intensity of the optical signal within a preset time period is determined; or the current integral value may be cleared before the next light intensity calibration.

[0237] Therefore, by using the light intensity calibration device in the above embodiment, the light intensity of the laser can be calibrated, and by clearing the current integral value to zero, the light intensity of the laser can be calibrated multiple times, thereby improving the detection accuracy of the laser radar.

[0238] An embodiment of the present invention further provides a laser radar, which may include the light intensity calibration device described in any of the aforementioned embodiments. The light intensity calibration device can calibrate the output light intensity of the laser in the laser radar, which is described in detail below with reference to specific examples.

[0239] Reference Fig. 9 The structure diagram of a laser radar in an embodiment of the present invention is shown in FIG. Fig. 9 As shown, in some embodiments of the present specification, the laser radar 100 may include: a laser 110, a main detector 120, a processor 130, and a light intensity calibration device 140 as described in any of the above embodiments, wherein:

[0240] The light intensity calibration device 140 is adapted to output a preset trigger signal and a first light intensity control signal so that the laser 110 outputs a corresponding light signal; and is adapted to determine the actual light intensity of the light signal within a preset period of time, and determine a light intensity feedback signal corresponding to the actual light intensity according to the actual light intensity of the light signal; and is adapted to obtain a calibrated second light intensity control signal based on the light intensity feedback signal and the first light intensity control signal;

[0241] The laser 110 is adapted to output the optical signal in response to the trigger signal and the first optical intensity control signal; and is adapted to output an optical signal having a desired optical intensity in response to the trigger signal and the second optical intensity control signal;

[0242] The main detector 120 is adapted to receive a detection signal corresponding to the actual optical signal as an echo signal;

[0243] The processor 130 is adapted to output detection information based on the actual optical signal and the echo signal.

[0244] The specific implementation method and working principle of the light intensity calibration device 140 can be found in the above content and will not be elaborated here.

[0245] Specifically, in response to a preset trigger signal and a first light intensity control signal output by the light intensity calibration device 140, the laser 110 can emit a light signal (a detection beam or a laser signal) to the outside world. At the same time, the light intensity calibration device 140 can determine the actual light intensity of the light signal within a preset time period. According to the actual light intensity of the light signal, a light intensity feedback signal corresponding to the actual light intensity can be determined. Then, the light intensity calibration device 140 can obtain a calibrated second light intensity control signal based on the light intensity feedback signal and the first light intensity control signal.

[0246] Under the action of the trigger signal and the second light intensity control signal, the laser 110 can output a light signal with an expected light intensity, and the main detector 120 can detect the echo signal (reflection signal) reflected by the light signal from the obstacle A0. The processor 130 can determine the flight time difference and power and other parameters of the detection signal based on the detection signal and the echo signal, and then obtain relevant information about the obstacle A0, such as the distance of the obstacle A0 relative to the laser radar 100, the reflectivity of the obstacle A0 and other parameters, thereby completing the detection, tracking and identification of the obstacle A0.

[0247] Since the light intensity calibration device can obtain a calibrated second light intensity control signal based on the light intensity feedback signal and the first light intensity control signal, the laser can emit light according to the expected light intensity, thereby calibrating the light emitting power of the laser radar and improving the detection performance of the laser radar.

[0248] In order to enable those skilled in the art to better understand and implement the laser radar in the embodiment of the present invention, a detailed description is given below with reference to specific examples.

[0249] In a specific implementation, according to detection requirements, the laser radar may include multiple lasers and multiple main detectors, each laser may emit a detection beam individually or simultaneously, and the corresponding main detectors may be turned on at the same time to receive the detection beam.

[0250] According to the specific configuration, a laser and one or more main detectors can form a detection channel, a main detector can also form a detection channel with one or more lasers, and multiple detection channels can detect simultaneously or in a patrol. As an optional example, according to the perceived environmental characteristic information (such as the reflectivity characteristics of the detected object, at least one of the distance and ambient light intensity), the pulse energy or emission power of the detection beam emitted by the laser can be selectively adjusted by dynamically adjusting the number of on and off of the laser; accordingly, the number of on and off of the main detector can be dynamically adjusted according to the environmental information (such as at least one of the reflectivity, distance, ambient light intensity, etc. of the object) to ensure the distance measurement capability required by the laser radar and take into account the power consumption requirements.

[0251] In a specific implementation, the laser may be a laser emitting device such as a semiconductor laser, a solid laser, etc. The embodiment of the present invention does not limit the specific structure of the laser, as long as the laser can emit a detection beam.

[0252] In a specific implementation, the main detector may be a photodetector. As an optional example, the photodetector may be a photodetector such as an avalanche photodiode APD, a single photon avalanche photodiode SPAD, a silicon photomultiplier SiPM, etc. The embodiment of the present invention does not limit the specific structure of the main detector, as long as the main detector can detect the light spot formed by the detection beam incident thereon.

[0253] In some embodiments of the present specification, based on the specific structure of the laser radar, during the detection process of the laser radar, the light intensity calibration device can calibrate its light intensity at the corresponding time.

[0254] In a specific implementation, the laser radar may further include a scanning device, and the scanning device may have multiple reflective surfaces, each of which is suitable for rotating with the rotating device and changing the transmission path of the optical signal. Accordingly, the light intensity calibration device is also suitable for adjusting the first light intensity control signal in the ranging gap before the different reflective surfaces of the scanning device rotate to the target azimuth.

[0255] As a specific example, Fig. 9, refer to Fig.10 A schematic diagram of a specific structure of a laser radar in an embodiment of the present invention is shown in FIG. Fig.10 As shown, the laser radar includes a laser 110 ( Fig.10 Only one laser is shown for ease of understanding) and the main detector 120 ( Fig.10 Only some of the main detectors are shown in the figure for easier understanding).

[0256] The laser 110 may be integrated on a laser chip 111. In other implementations, the laser 110 may be disposed on a laser emitting board.

[0257] In a specific implementation, the laser chip 111 can be coupled to a light intensity calibration device 140, and the laser emission of the laser 110 can be controlled by the light intensity calibration device 140, and its laser emission control parameters may include at least one or more of the emission period, emission power, pulse duration, number of pulses, etc.

[0258] Similarly, the main detector 120 may be integrated on a detector chip 121, and the detector chip 121 may include one or more main detectors 120. In other implementations, the main detector 120 may be disposed on a receiving circuit board.

[0259] The embodiment of the present invention does not limit the specific structure and process of the laser 110 and the main detector 120, as long as the emission of the detection beam and the detection of the corresponding echo beam can be achieved.

[0260] In a specific implementation, the laser radar may further include a collimating unit 161 (e.g., a collimating lens) and a light splitting unit 162, wherein:

[0261] The collimating unit 161 can be disposed on the output light path of the laser 110 to collimate the optical signal emitted by the laser 110 and then input it to the spectroscopic unit 162. The spectroscopic unit 162 can fold the optical signal to the scanning device 150 to further improve its light output efficiency.

[0262] In a specific implementation, the scanning device 150 can be a multi-faceted rotating mirror, which can detect the angle position through a code disk (not shown in the figure). As an optional example, the scanning device 150 rotates around the rotating shaft 155, which includes four reflecting surfaces, such as Fig.10 As shown, it includes a first reflective surface 151, a second reflective surface 152, a third reflective surface 153 and a fourth reflective surface 154. As an optional example, in order to enhance the reflection performance of the scanning device 150, a high reflection film can be set on the first reflective surface 151, the second reflective surface 152, the third reflective surface 153 and the fourth reflective surface 154.

[0263] In the idle gaps when the various reflective surfaces of the scanning device 150 are switched, such as the gap when the first reflective surface 151 turns to the second reflective surface 152, a part of the lasers can be selected for calibration, and then in the gap when the second reflective surface 152 turns to the third reflective surface 153, another part of the lasers can be selected for calibration. In this way, the calibration of all the lasers can be completed step by step in the multiple switching processes.

[0264] After the light intensity of the laser is calibrated, the scanning device 150 can transmit the optical signal to the external environment. When the light beam transmitted to the outside encounters an obstacle, light reflection will occur, and part of the reflected light beam will be transmitted to the scanning device 150. The light beam deflected by the scanning device 150 passes through the gap beside the spectroscopic unit 162 and is converged by the converging unit 163. It is then detected by the main detector 120, thereby realizing the detection, tracking and identification of obstacles.

[0265] Therefore, when the laser radar is Fig.10 In the structure shown, by calibrating the light intensity of the laser radar when the laser radar is in the ranging gap, it is possible to avoid affecting the ranging process while taking into account both the detection efficiency and the calibration efficiency.

[0266] In a specific implementation, the light intensity calibration device may include a slave detector, which can detect the light signal and convert it into an electrical signal. Correspondingly, the laser radar may also include a scanning module, and when the scanning module is rotated to a preset position, the light signal emitted by the laser is directly incident on the slave detector. In this process, the slave detector can detect the light signal emitted by the laser to calibrate the light intensity of the laser.

[0267] As a specific example, Fig. 9 , refer to Fig.11 The specific structural diagram of another laser radar in the embodiment of the present invention, the laser radar 100 may also include a scanning module 170. When the scanning module 170 is in a first position (the position of the scanning module is represented by a solid line frame), the optical signal (detection signal) output by the laser 110 is completely deflected to the outside of the laser radar by the scanning module 170, and the optical signal output by the laser 110 is not detected by the detector 141.

[0268] When the scanning module 170 rotates to a preset position (the position of the scanning module is indicated by a dotted box), part of the light signal output by the laser 110 is not deflected to the outside by the scanning module 170, and at least part of the light signal output by the laser 110 can be detected from the detector 141, and the light intensity calibration device 140 can calibrate the light intensity of the light signal output by the laser 110.

[0269] It is understandable that the movement process of the above-mentioned scanning module is only an example, and the embodiment of the present invention does not limit the specific rotation method of the scanning module. As long as the scanning module is in a certain position, at least part of the optical signal of the laser is not incident on the scanning module.

[0270] In both of the above examples, the laser light intensity is calibrated by a light intensity calibration device during the intervals when the laser radar is measuring distance. In the actual calibration process, the laser light intensity can be directly calibrated after the laser radar is started, and the detection process can be carried out after the calibration is completed.

[0271] Specifically, the light intensity calibration device may include a slave detector, which can detect the light signal and convert it into an electrical signal. Correspondingly, the laser radar also includes: a scanning module and a reflector module, wherein: the scanning module is suitable for changing the angle of the light signal and the echo light beam incident thereon; the reflector module is used to change the transmission direction of the echo light beam folded by the scanning module, so as to fold the echo light beam to the main detector, and transmit part of the light signal to the slave detector. In this process, the slave detector can detect the light signal emitted by the laser to calibrate the light intensity of the laser.

[0272] As a specific example, Fig. 9 , refer to Fig.12 The specific structure diagram of another laser radar in the embodiment of the present invention, the laser radar 100 may also include a scanning module 180 and a reflector module 190, wherein:

[0273] The reflector module 190 is arranged on the output light path of the laser 110, and can redirect the light signal output by the laser 110 to the scanning module 180. During the light signal redirection process, the reflector module 190 can transmit part of the light signal, and the slave detector 141 arranged above the reflector module 190 can detect the light signal. Since the transmission component of the light signal is constant, the light signal output by the laser 110 can be calibrated by detecting the light intensity of the transmitted light signal until the laser 110 outputs a light signal with an expected light intensity.

[0274] When the optical signal output by the laser 110 meets the requirements, the scanning module 180 can reflect the optical signal to the external environment. When the light beam reflected to the outside encounters an obstacle, light reflection will occur, and part of the reflected light beam will be transmitted to the scanning module 180. The light beam deflected by the scanning module 180 passes through the gap beside the reflector module 190 and is converged by the converging unit 163 before being detected by the main detector 120.

[0275] Therefore, by calibrating the output light intensity of the laser radar when it is in a non-ranging state, it is possible to avoid affecting the ranging process, while taking into account both detection efficiency and calibration efficiency. Detection can be performed after the laser is calibrated, which can improve the overall detection accuracy of the laser radar.

[0276] It is understandable that the relative positions of the detector and the reflector module are only illustrative, and the embodiment of the present invention does not impose any limitation on this, as long as the position of the detector can detect the light signal transmitted by the reflector module.

[0277] In a specific implementation, a laser radar generally has multiple lasers. For example, for a laser radar with 320 channels, the number of corresponding lasers is also 320, so the light intensity of these 320 lasers needs to be calibrated. Therefore, it is necessary to set the number of slave detectors, or the photosensitive surface area of ​​at least one of the slave detectors, or the total photosensitive surface area of ​​multiple slave detectors, so that the photosensitive surface of the slave detector can receive the light directly or scattered by all lasers of the laser radar to meet the light intensity calibration requirements.

[0278] In some embodiments of the present specification, the number of slave detectors is related to the number of lasers, the area of ​​the photosensitive surface of the slave detectors, and the size of the laser radar, and the number of slave detectors to be used can be determined based on the above parameters.

[0279] For example, the more lasers there are, the smaller the area of ​​the photosensitive surface of the slave detector, and the larger the size of the lidar, the more slave detectors are required.

[0280] In a specific implementation, in order to reduce the number of slave detectors used, a detector with a larger photosensitive surface may be used. For example, a photodiode PD may be used as a slave detector.

[0281] Although the embodiments of the present invention are disclosed above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A method for calibrating the light intensity of a laser radar, wherein the laser radar comprises a laser, characterized in that: The light intensity calibration method comprises: Based on a preset trigger signal and a first light intensity control signal, the laser is caused to output a corresponding light signal; Determining the actual light intensity of the light signal within a preset time period; Determining a light intensity feedback signal corresponding to the actual light intensity according to the actual light intensity of the light signal within a preset time period; A calibrated second light intensity control signal is obtained based on the light intensity feedback signal and the first light intensity control signal.

2. The light intensity calibration method according to claim 1, characterized in that: The determining the actual light intensity of the light signal within a preset time period includes: Detecting the optical signal and converting it into an electrical signal; In the preset time period, the electrical signal is integrated to obtain a current integral value, which is used as the actual light intensity of the optical signal in the preset time period.

3. The light intensity calibration method according to claim 2, characterized in that: Also includes: The current integral value is converted into digital form to obtain the current integral value in digital form, and the current integral value in digital form is used as the actual light intensity of the light signal in a preset time period.

4. The light intensity calibration method according to claim 2, characterized in that: Also includes: The current integral value is cleared to zero.

5. The light intensity calibration method according to claim 4, characterized in that: The clearing the current integral value to zero includes at least one of the following: After determining the actual light intensity of the light signal within a preset time period, outputting a reset signal to clear the current integral value; Before the next light intensity calibration, a reset signal is output to clear the current integral value to zero.

6. The light intensity calibration method according to claim 1, characterized in that: The step of determining a light intensity feedback signal corresponding to the actual light intensity according to the actual light intensity of the light signal within a preset time period includes: According to the pre-stored mapping relationship between the light intensity value and the light intensity feedback value, the light intensity feedback value corresponding to the actual light intensity is obtained, and the electrical signal corresponding to the light intensity feedback value is used as the light intensity feedback signal.

7. The light intensity calibration method according to claim 6, characterized in that: The step of obtaining a calibrated second light intensity control signal based on the light intensity feedback signal and the first light intensity control signal comprises: The light intensity feedback value corresponding to the feedback signal and the actual light intensity control value corresponding to the first light intensity control signal are accumulated to obtain the light intensity control value corresponding to the second light intensity control signal.

8. The light intensity calibration method according to claim 1, characterized in that: The method of controlling the laser to output a corresponding optical signal based on a preset trigger signal and a first light intensity control signal includes: Based on the current working mode of the laser radar, a trigger signal with corresponding pulse characteristics is output to drive the laser to output the optical signal under the action of the trigger signal with corresponding pulse characteristics.

9. The light intensity calibration method according to claim 8, characterized in that: The step of outputting a trigger signal having a corresponding pulse characteristic based on the current working mode of the laser radar, so as to drive the laser to output the optical signal under the action of the trigger signal having the corresponding pulse characteristic, comprises: When it is determined that the laser radar is in the first working mode, outputting a single pulse trigger signal to the driver to drive the laser to output the optical signal under the action of the single pulse trigger signal; When it is determined that the laser radar is in the second working mode, output a multi-pulse trigger signal to the driver to drive the laser to output the optical signal under the action of the multi-pulse trigger signal; Among them, the peak power of a single pulse of the laser radar in the first working mode is greater than the peak power of a single pulse in the second working mode.

10. The light intensity calibration method according to claim 1, characterized in that: Light intensity calibration is performed when the laser radar is in at least one of the following situations: The laser radar is in a non-ranging state; The laser radar is in a ranging gap.

11. The light intensity calibration method according to claim 1, characterized in that: The laser radar includes a plurality of lasers; The light intensity calibration method also includes: According to a preset sequence, the first light intensity control signal corresponding to each laser is adjusted in turn.

12. A light intensity calibration device for a laser radar, the laser radar comprising a laser, characterized in that: The light intensity calibration device comprises: A control module, adapted to output a preset trigger signal and a first light intensity control signal; and adapted to obtain a calibrated second light intensity control signal based on a light intensity feedback signal and the first light intensity control signal; A driving module, adapted to respond to a preset trigger signal and the first light intensity control signal to output a corresponding driving signal so that the laser outputs a corresponding light signal; and adapted to respond to the trigger signal and the second light intensity control signal so that the laser outputs a light signal with a desired light intensity; The signal processing module is adapted to determine the actual light intensity of the optical signal within a preset time period, and determine a light intensity feedback signal corresponding to the actual light intensity according to the actual light intensity of the optical signal.

13. The light intensity calibration device according to claim 12, characterized in that: The signal processing module comprises: A slave detector, adapted to detect the optical signal and convert it into an electrical signal; A data processing unit, which integrates the electrical signal within the preset time period to obtain a current integral value and uses it as the actual light intensity of the optical signal within the preset time period; The storage unit is suitable for storing the mapping relationship between the light intensity value and the light intensity feedback value.

14. The light intensity calibration device according to claim 13, characterized in that: The signal processing module also includes: The analog-to-digital conversion unit is coupled to the data processing unit and the storage unit respectively, and is suitable for performing analog-to-digital conversion on the current integral value to obtain the current integral value in digital form.

15. The light intensity calibration device according to claim 14, characterized in that: The data processing unit includes an operational amplifier and an integrating capacitor, wherein: The operational amplifier has a first input terminal coupled to the slave detector, a second input terminal coupled to the first terminal of the integrating capacitor, and an output terminal coupled to the second terminal of the integrating capacitor and the analog-to-digital conversion unit, respectively.

16. The light intensity calibration device according to claim 14 or 15, characterized in that: The data processing unit also includes: A resetter is adapted to reset the current integral value to zero.

17. The light intensity calibration device according to claim 16, characterized in that: The control module is further adapted to output a reset signal to the reset device after determining the actual light intensity of the light signal within a preset time period; or is adapted to output a reset signal to the reset device before the next light intensity calibration; The resetter is adapted to clear the current integrated value to zero in response to the reset signal.

18. The light intensity calibration device according to any one of claims 13 to 15, characterized in that: The slave detector is placed on the direct light path or scattered light path of the laser.

19. The light intensity calibration device according to claim 12, characterized in that: The control module is adapted to accumulate the light intensity feedback value corresponding to the feedback signal and the actual light intensity control value corresponding to the first light intensity control signal as the light intensity control value corresponding to the second light intensity control signal.

20. The light intensity calibration device according to claim 12, characterized in that: The control module is also suitable for outputting a trigger signal with corresponding pulse characteristics based on the current working mode of the laser radar, so as to drive the laser to output the optical signal under the action of the trigger signal with corresponding pulse characteristics.

21. A laser radar, characterized in that: The device comprises a laser, a main detector, a processor and a light intensity calibration device according to any one of claims 12 to 20, wherein: The light intensity calibration device is adapted to output a preset trigger signal and a first light intensity control signal so that the laser outputs a corresponding light signal; and is adapted to determine the actual light intensity of the light signal within a preset time period, and determine a light intensity feedback signal corresponding to the actual light intensity according to the actual light intensity of the light signal; and is adapted to obtain a calibrated second light intensity control signal based on the light intensity feedback signal and the first light intensity control signal; The laser is adapted to output the optical signal in response to the trigger signal and the first optical intensity control signal; and is adapted to output an optical signal having a desired optical intensity in response to the trigger signal and the second optical intensity control signal; The main detector is adapted to receive a detection signal corresponding to the actual light signal as an echo signal; The processor is adapted to output detection information based on the actual light signal and the echo signal.

22. The laser radar according to claim 21, characterized in that: Also includes: A scanning device, wherein the scanning device has a plurality of reflecting surfaces, each reflecting surface is adapted to rotate with the rotating device and change the transmission path of the optical signal; The light intensity calibration device is also suitable for adjusting the first light intensity control signal during the ranging interval before the different reflective surfaces of the scanning device rotate to the target azimuth.

23. The laser radar according to claim 21, characterized in that: The light intensity calibration device comprises a slave detector adapted to detect the light signal and convert it into an electrical signal; The laser radar also includes: The scanning module is adapted to enable the optical signal emitted by the laser to directly enter the slave detector when the scanning module is rotated to a preset position.

24. The laser radar according to claim 21, characterized in that: The light intensity calibration device comprises a slave detector, which is suitable for detecting the light signal and converting it into an electrical signal; The laser radar further includes: a scanning module and a reflector module, wherein: The scanning module is adapted to change the angles of the light signal and the return light beam incident thereon; The reflector module is used to change the transmission direction of the echo light beam deflected by the scanning module, so as to deflect the echo light beam to the main detector and transmit part of the echo light beam to the slave detector.

25. The laser radar according to claim 23 or 24, characterized in that: The number of the slave detectors is related to the number of the lasers, the area of ​​the photosensitive surface of the slave detectors and the size of the laser radar.

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