Method for improving angular resolution of pulse type laser radar

Abstract

The invention discloses a method for improving the angular resolution of a pulse type laser radar. The method comprises the following steps: S1, starting a motor; s2, calculating the rotating speed of the motor; s3, judging whether the current rotating speed of the motor reaches the target speed or not; s4, light pulse emission; s5, reading a system counter, and calculating an accurate angle; s6, reading laser transmitting and receiving time difference; s7, calculating the obstacle distance; and S8, reading the current rough angle # imgabs0 # from the encoder interruption, if the current rough angle # imgabs0 # is zero, reporting point cloud data, and starting the next round of measurement, otherwise continuing the round of measurement, so that the angle resolution of the radar can be effectively improved, the radar performance can be improved, the identifiability of obstacles can be enhanced, the measurement precision can be improved, the hardware cost can be reduced, the flexibility is higher, and the real-time performance of the radar can be improved. The program stability is higher, the application prospect is wide, and application and popularization are facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of lidar, and particularly to a method for improving the angular resolution of a pulsed lidar. Background Art

[0002] A lidar is a radar system that detects the position, speed and other characteristic quantities of a target by emitting laser beams. Its working principle is to emit a detection signal (laser beam) to the target, and then compare the received signal (echo pulse signal) reflected from the target with the emitted signal. After appropriate processing, relevant information about the target can be obtained, such as parameters such as the target distance, azimuth, altitude, speed, attitude, and even shape, so as to detect, track and identify the target. With the development of lidar technology, the requirement for its resolution is getting higher and higher. Obtaining higher resolution is an important indicator for improving the performance parameters of lidar.

[0003] Currently, the angular resolution of lidar is limited by the number of grids of the optical encoder, and the angle value completely depends on the rising edge counting of the encoder; its laser emission process is completed in the encoder interrupt, and the interrupt frequency is very high. There is also a TDC interrupt in the interrupt, and the program may have an exception; after the motor speed of the lidar is stable, the encoder interrupt only retains the zero point detection function, and the angle calculation completely depends on the period of the laser PWM; this will cause problems such as inaccurate angle calculation and fluctuating measurement distance. Therefore, there is an urgent need to develop a method for improving the angular resolution of a pulsed lidar.

[0004] In view of this, the present invention is specifically proposed. Summary of the Invention

[0005] The object of the present invention is to provide a method for improving the angular resolution of a pulsed lidar, which can effectively improve the angular resolution of the lidar, improve the performance of the lidar, enhance the recognizability of obstacles, improve the measurement accuracy, reduce the hardware cost, have higher flexibility, higher program stability, have broad application prospects, and are conducive to popularization and application.

[0006] In order to achieve the above object, a method for improving the angular resolution of a pulsed lidar provided by the present invention includes the following steps: (1) Start the motor: When the lidar system is powered on and the power supply is stable, turn on the motor PWM, start the motor, set the motor speed and wait for the speed to be stable. The frame rate of the point cloud data of the lidar is equal to the motor speed; (2) Calculate the motor speed: After the motor starts and enters the acceleration stage, calculate the time interval between two rising edges of the encoder A phase as , the number of encoder lines is , then the time interval for the motor to rotate one circle , then the current motor speed ; (3) Determine whether the current motor speed has reached the target speed; (4) Optical pulse emission: After the actual speed reaches the target speed, turn on the laser PWM and set the PWM period; (5) Read the system counter and calculate the precise angle: Read the current count value of the system , and then read the count value at the last rising edge of phase A from the encoder interrupt , and obtain the precise angle from the equal-proportion conversion formula , is the angle corresponding to each grid of the encoder; read the rough angle through the encoder interrupt , the true angle ; (6) Read the time difference between laser transmission and reception: Wait for the occurrence of the TDC interrupt event, and read the time difference between the emission of the emitting diode and the reception of the receiving diode from the TDC ; (7) Calculate the distance to the obstacle: Calculate the distance to the obstacle through the formula , where c is the speed of light; (8) Report the point cloud data: Read the current rough angle from the encoder interrupt , if it is zero, report the point cloud data and start the next round of measurement, otherwise continue the current round of measurement.

[0007] Preferably, in step (3), if the current motor speed has not reached the target speed, calculate the difference err between the target speed and the current speed, and calculate the PWM duty cycle that should be set next through the PID algorithm until the difference between the target speed and the measured speed is not greater than 5%. If the difference between the target speed and the measured speed is not greater than 5% for 10 consecutive times, then start emitting optical pulses.

[0008] Preferably, in step (4), set the PWM period according to the angular resolution and rotation speed of the lidar , is the number of points to be scanned within 360 degrees.

[0009] Preferably, the function of the encoder interrupt is: perform a rising edge detection on the optical point encoder, count, and calculate the rough angle ; record the system count when the rising edge arrives and the previous system count , which are used to calculate the motor speed and calculate the precise angle to improve the angular resolution.

[0010] Preferably, in the step (1), the lidar system includes an optical encoder, a motor, a mirror, and a base. The black part of the optical encoder is opaque and is used to mark the zero point of the angle. The rest is an equally spaced grid for calculating the rotated angle. Above the optical encoder is the motor, which drives the optical encoder to rotate. The base is integrated with a light-emitting diode, a light-receiving diode, and the corresponding control circuit. After the obstacle is irradiated by the laser, diffuse reflection occurs. The mirror is used to change the emission path of the laser diode and the diffuse reflection reception path of the light.

[0011] Preferably, the mirror is a 905nm mirror.

[0012] A method for improving the angular resolution of a pulsed lidar provided by the present invention has the following beneficial effects.

[0013] 1. The present invention improves the angular resolution of the lidar at the software level. Without replacing the optical encoder with a higher grid number, the angular resolution can be made independent of the grid number of the optical encoder, which has higher flexibility.

[0014] 2. The present invention does not require changing the original assembly structure. While improving the performance of the lidar, it does not increase additional costs and reduces the hardware cost.

[0015] 3. The present invention can dynamically adjust the motor speed. The encoder interrupt and the TDC interrupt are executed independently without interference, and the program runs with higher stability.

[0016] 4. The present invention solves the problems of inaccurate angle calculation and fluctuating measurement distance of the lidar, and has higher measurement accuracy and accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a flowchart of a method for improving the angular resolution of a pulsed lidar provided by the present invention.

[0018] Figure 2 It is a structural diagram of the lidar system.

[0019] In the figure: 1. Optical encoder 2. Mirror 3. Base 4. Diffuse reflection reception path of light 5. Emission path of laser diode 6. Obstacle 7. Motor. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] The following further describes the present invention in conjunction with specific embodiments and drawings to help understand the content of the present invention.

[0021] Such as Figure 1As shown in the figure, it is a flowchart of a method for improving the angular resolution of a pulsed lidar provided by the present invention. The method for improving the angular resolution of a pulsed lidar includes the following steps: (1) Start the motor: After the lidar system is powered on and the power supply is stable, turn on the motor PWM to start the motor, set the motor speed and wait for the speed to stabilize. The frame rate of the lidar point cloud data is equal to the motor speed; (2) Calculate the motor speed: After the motor starts and enters the acceleration stage, calculate the time interval between two rising edges of the encoder A phase as , the number of encoder lines is , then the time interval for the motor to rotate one circle , then the current motor speed ; (3) Determine whether the current motor speed reaches the target speed. If the current motor speed does not reach the target speed, calculate the difference err between the target speed and the current speed, and calculate the PWM duty cycle that should be set next through the PID algorithm until the difference between the target speed and the measured speed is not greater than 5%. If the difference between the target speed and the measured speed is not greater than 5% for 10 consecutive times, start emitting optical pulses.

[0022] (4) Optical pulse emission: After the actual speed reaches the target speed, turn on the laser PWM, set the PWM period, and set the PWM period according to the angular resolution and speed of the lidar, , is the number of points to be scanned within 360 degrees.

[0023] (5) Read the system counter and calculate the precise angle: Read the current count value of the system , and then read the count value of the previous A-phase rising edge from the encoder interrupt . Obtain the precise angle from the equal-proportion conversion formula , is the angle corresponding to each grid of the encoder; read the approximate angle through the encoder interrupt, and the real angle ; (6) Read the laser transceiver time difference: Wait for the occurrence of the TDC interrupt event, and read the time difference between the emission of the emitting diode and the reception of the receiving diode from the TDC; (7) Calculate the distance to the obstacle: Calculate the distance to the obstacle through the formula , where c is the speed of light; (8) Report the point cloud data: Read the current approximate angle from the encoder interrupt. If it is zero, report the point cloud data and start the next round of measurement. Otherwise, continue with the current round of measurement.

[0024] The function of the encoder interruption is: to perform rising edge detection on the optical encoder, count, and calculate the rough angle. ; Record the system count when the rising edge arrives. And the previous system count. These are used to calculate the motor speed and the precise angle to improve the angular resolution.

[0025] As Figure 2 shown, it is the structural diagram of the lidar system. In the step (1), the lidar system includes an optical encoder disk 1, a motor 7, a mirror 2, and a base 3. The black part of the optical encoder disk 1 is opaque and is used to mark the zero point of the angle. The rest is an equally spaced grid used to calculate the rotated angle. Above the optical encoder disk 1 is the motor 7, which drives the optical encoder disk 1 to rotate. The base 3 is integrated with a light-emitting diode, a light-receiving diode, and the corresponding control circuits. After the obstacle 6 is irradiated by the laser, diffuse reflection occurs. The mirror 2 is used to change the emission path 5 of the laser diode and the diffuse reflection reception path 4 of the light. Preferably, the mirror 2 is a 905nm mirror.

[0026] The present invention improves the angular resolution of the lidar at the software level. Without replacing the optical encoder with a higher grid count, it can make the angular resolution independent of the grid count of the optical encoder, having higher flexibility. The present invention does not need to change the original assembly structure. While improving the performance of the lidar, it does not increase additional costs and reduces the hardware cost. The present invention can dynamically adjust the motor speed. The encoder interruption and the TDC interruption are executed independently without interference, and the program operation has higher stability. The present invention solves the problems of inaccurate angle calculation and fluctuating measurement distance of the lidar, having higher measurement accuracy and accuracy.

[0027] Specific examples are applied in this article to elaborate on the inventive concept in detail. The description of the above embodiments is only used to help understand the core idea of the present invention. It should be pointed out that for those of ordinary skill in the art of this technology, any obvious modification, equivalent replacement, or other improvement made without departing from the inventive concept should be included within the protection scope of the present invention.

Claims

1. A method for improving the angular resolution of a pulsed lidar, characterized in that, It includes the following steps: (1) Start the motor: Power on the lidar system. After the power supply is stable, turn on the motor PWM to start the motor, set the motor speed and wait for the speed to stabilize. The frame rate of the lidar point cloud data is equal to the motor speed; (2)Calculate the motor speed: After the motor starts and enters the acceleration stage, calculate the time interval between two rising edges of the encoder's phase A as , the number of encoder lines is , then the time interval for the motor to make one revolution , then the current motor speed ; (3) Determine whether the current motor speed reaches the target speed; (4) Optical pulse emission: After the actual speed reaches the target speed, turn on the laser PWM and set the PWM period; (5) Read the system counter and calculate the precise angle: Read the current count value of the system , then read the count value at the previous rising edge of phase A from the encoder interrupt . Use the equal ratio conversion formula to obtain the precise angle, being the angle corresponding to each grid of the encoder; Read the approximate angle through the encoder interrupt , and the true angle ; (6) Read the time difference of laser transceiver: Wait for the occurrence of the TDC interrupt event, and read the time difference between the emission of the emitting diode and the reception of the receiving diode from the TDC ; (7) Calculate the distance to the obstacle: Through the formula calculate the distance to the obstacle, where c is the speed of light; (8) Report point cloud data: Read the current rough angle from the encoder interrupt. If it is zero, report the point cloud data and start the next round of measurement; otherwise, continue the current round of measurement.

2. The method for improving the angular resolution of a pulsed lidar according to claim 1, characterized in that, In step (3), if the current motor speed does not reach the target speed, calculate the difference err between the target speed and the current speed, and calculate the PWM duty cycle to be set next time through the PID algorithm until the difference between the target speed and the measured speed is not greater than 5%. If the difference between the target speed and the measured speed is not greater than 5% for 10 consecutive times, then start to emit optical pulses.

3. The method for improving the angular resolution of a pulsed lidar according to claim 2, characterized in that, In the step (4), set the PWM period according to the angular resolution and rotation speed of the lidar. , is the number of points to be scanned within 360 degrees.

4. The method for improving the angular resolution of a pulsed lidar according to claim 3, characterized in that, The function of the encoder interruption is to perform a rising edge detection on the optical encoder, count, and calculate the rough angle. ; Record the system count when the rising edge arrives. And the previous system count. These are used to calculate the motor speed and the precise angle to improve the angular resolution.

5. The method for improving the angular resolution of a pulsed lidar according to claim 4, characterized in that, In step (1), the lidar system includes an optical encoder, a motor, a mirror and a base. The black part of the optical encoder is opaque and is used to mark the zero point of the angle. The rest is an equally spaced grid used to calculate the rotated angle. Above the optical encoder is the motor, which drives the optical encoder to rotate. The base is integrated with a light-emitting diode, a light-receiving diode and the corresponding control circuit. After the obstacle is irradiated by the laser, diffuse reflection occurs. The mirror is used to change the emission path of the laser diode and the diffuse reflection reception path of the light.

6. The method for improving the angular resolution of a pulsed lidar according to claim 5, characterized in that, The mirror is a 905nm mirror.

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