CN107015215B

CN107015215B - High-repetition-frequency three-dimensional scanning laser radar scanning angle measuring circuit based on FPGA

Info

Publication number: CN107015215B
Application number: CN201710272498.0A
Authority: CN
Inventors: 徐立军; 李端; 李小路; 谢鑫浩; 杨炳伟
Original assignee: Beihang University
Current assignee: Beihang University
Priority date: 2017-04-24
Filing date: 2017-04-24
Publication date: 2020-11-24
Anticipated expiration: 2037-04-24
Also published as: CN107015215A

Abstract

The invention discloses a high repetition frequency three-dimensional scanning laser radar scanning angle measuring circuit based on an FPGA (field programmable gate array). the high repetition frequency three-dimensional scanning laser radar scanning angle measuring circuit based on the FPGA measures a zero position signal of a scanning motor in a vertical direction by utilizing an incremental encoder, measures angle data of the scanning motor in a horizontal direction by utilizing an absolute value encoder, and simultaneously realizes high-precision measurement of each outgoing laser pulse scanning angle in the vertical direction and the horizontal direction by combining a phase-locked loop module, a 2-to-1 switch module, a pulse-to-second counter module, an angle measuring module, a time measuring module and a USB (universal serial bus) interface module which are realized inside the FPGA. The FPGA-based high-repetition-frequency three-dimensional scanning laser radar scanning angle measuring circuit breaks through the defect that the scanning angle is obtained by a conventional interpolation method, and effectively improves the measuring precision of the scanning angle of the three-dimensional scanning laser radar.

Description

High-repetition-frequency three-dimensional scanning laser radar scanning angle measuring circuit based on FPGA

Technical Field

The invention relates to the field of laser radars, in particular to a high-repetition-frequency three-dimensional scanning laser radar scanning angle measuring circuit based on an FPGA.

Background

The laser radar is an active remote sensing technology combining the traditional radar technology and the advanced laser technology, the distance between the laser radar platform and the target is obtained based on the relation between the distance, the light speed and the time by measuring the time of the laser pulse between the target and the laser radar platform, and the laser radar can complete the three-dimensional scanning ranging of the surface of the target by matching the three-dimensional scanning of the scanning device or combining the two-dimensional scanning of the scanning device with the movement of the laser radar platform. Based on a laser radar imaging equation, three-dimensional coordinate calculation of each scanning point on the surface of the target is realized by using distance data between a laser radar platform and the scanned point of the target, scanning angle data of laser pulses and position and attitude data of the laser radar platform. Based on the three-dimensional coordinates obtained by resolving, a digital surface model and a digital elevation model of the target can be obtained by adopting an advanced filtering and classifying method, and finally, three-dimensional imaging and measurement of the target are realized. The three-dimensional scanning laser radar is a laser radar system with a scanning device capable of realizing three-dimensional scanning. From the measurement principle of the laser radar, it can be seen that the scanning angle of the laser pulse is the key data in the data processing of the laser radar, and therefore how to measure the scanning angle of each beam of the transmitted laser pulse with high precision is the key problem in the design of the laser system. Meanwhile, because the pulse emission frequency in the high-repetition-frequency three-dimensional scanning laser radar system is very high, and the response frequencies of the existing encoders which can be directly used for angle measurement are low, how to measure each laser pulse emission scanning angle of the high-repetition-frequency three-dimensional scanning laser radar with high precision is a difficult point in the design of the three-dimensional scanning laser radar system.

This paper is to laser scanning angle measurement problem among the three-dimensional scanning laser radar system of high repetition frequency, has proposed a high repetition frequency three-dimensional scanning laser radar scanning angle measuring circuit based on FPGA, high repetition frequency three-dimensional scanning laser radar scanning angle measuring circuit based on FPGA includes phase-locked loop module, 2 select 1 switch module, second pulse counter module, angle measurement module, time measurement module and USB interface module, all modules are all accomplished in FPGA is inside to and be used for horizontal direction scanning motor angle measurement's absolute value encoder and vertical direction scanning motor zero measurement's incremental encoder.

Disclosure of Invention

The invention discloses a high repetition frequency three-dimensional scanning laser radar scanning angle measuring circuit based on FPGA, which is characterized in that the high repetition frequency three-dimensional scanning laser radar scanning angle measuring circuit based on FPGA utilizes an incremental encoder to measure the zero position of a scanning motor in the vertical direction, a low response frequency absolute value encoder to measure the scanning angle of a scanning motor in the horizontal direction, and combines a high-precision time measuring module based on FPGA self-design to measure the time interval between a transmitting pulse signal and the zero position signal of the scanning motor in the vertical direction, so as to realize the measurement of the scanning angle of the high repetition frequency laser pulse in the three-dimensional scanning laser radar in the vertical direction and the scanning angle in the horizontal direction, and utilizes a second pulse signal and a self-designed USB interface module to orderly upload the measured angle data and time data to an upper computer through a USB interface, and in addition, by means of the self-designed USB interface, realize the alignment between scanning angle data and outside range finding module distance data, FPGA-based high repetition frequency three-dimensional scanning laser radar scanning angle measuring circuit includes phase-locked loop module, 2 select 1 switch module, angle measuring module, time measuring module, pulse per second counter module and USB interface module, all the module all accomplishes inside a slice FPGA, phase-locked loop moduleThe block generates respectively a second pulse with a frequency of 1 hz, a 50 mhz detection clock for the detection of the rising edge of the input signal of each module and a 500 mhz timing clock for the timing of the time measuring module, the 2-to-1 switch module is used for selecting whether the pulse per second signal input to the pulse per second counter module is generated by an external GPS or a phase-locked loop, the pulse per second counter measures the number of the input pulse per second signals, and controls the data in the USB interface module to be uploaded in order, the angle measurement module reads the angle data of the scanning motor in the horizontal direction under the control of the zero position signal of the scanning motor in the vertical direction to obtain the scanning angle theta in the horizontal direction corresponding to the zero position of the scanning motor in the vertical direction, and the time measuring module measures the time interval t between each transmission pulse signal and the zero signal of the previous vertical scanning motor._v-pThe scanning angle alpha in the vertical direction corresponding to each laser pulse can be obtained by using the measured time interval and the rotating speed of the scanning motor in the vertical direction

α＝t_v-p×s_v (1)

Simultaneously combining the horizontal scanning angle theta corresponding to the zero position of the motor and the time interval t between each transmission pulse signal and the zero position signal of the previous vertical scanning motor_v-pAnd the rotation speed s of the horizontal direction scanning motor_hThe horizontal scanning angle beta corresponding to each laser pulse can be obtained

β＝θ+t_v-p×s_h (2)

Thereby obtaining the scanning angle in the horizontal direction and the scanning angle in the vertical direction corresponding to each emitted laser pulse;

the high-repetition-frequency three-dimensional scanning laser radar scanning angle measuring circuit based on the FPGA is characterized in that the high-repetition-frequency three-dimensional scanning laser radar scanning angle measuring circuit based on the FPGA adopts a USB interface module to realize the enabling control of an upper computer to a pulse per second counter module, the pulse per second counter module realizes the enabling control of an angle measuring module and a time measuring module, the angle measuring module realizes the enabling control of an external ranging module, and adopts a one-level and one-level enabling control mode to realize the vertical directionThe method comprises the steps of measuring scanning angles in the horizontal direction corresponding to the zero position of a scanning motor, measuring time intervals between each transmitted pulse signal and the zero position signal of the previous scanning motor in the vertical direction, aligning distance data, scanning angle data in the horizontal direction and time interval data of an external distance measuring module, detecting rising edges of input second pulses by using a detection clock when a USB interface module receives a start working flag bit from an upper computer, sending an enabling signal to a second pulse counter module by a control end of the USB interface module, detecting the rising edges of the input second pulses by using the detection clock when the second pulse counter module receives the enabling signal from the USB interface module, controlling a port to output the enabling signal to enable the angle measuring module and the time measuring module to start working when the first second pulse rising edge is detected, and simultaneously detecting the rising edges of the subsequent input second pulses by using the detection clock by the second pulse counter module, accumulating and counting detected pulse per second rising edges, detecting the rising edge of a zero position signal of a scanning motor in the vertical direction by using a detection clock after an angle measurement module receives an enabling signal of a pulse per second counter module, outputting the enabling signal by an angle measurement module control port to enable an external ranging module to start working when the angle measurement module detects the rising edge of the zero position signal of the scanning motor in the first vertical direction, simultaneously reading angle data of the scanning motor in the horizontal direction by the angle measurement module as a scanning angle in the horizontal direction when a three-dimensional scanning laser radar starts working, detecting the rising edge of each subsequent scanning motor in the vertical direction by using the detection clock, reading angle data of the scanning motor in the horizontal direction when the rising edge of the zero position signal of the scanning motor in the vertical direction is detected, wherein the read angle data is a scanning angle theta in the horizontal direction corresponding to the zero position of the scanning motor, when the time measuring module receives the enabling signal from the pulse per second counter module, the time measuring module detects the rising edge of the zero position signal of the scanning motor in the vertical direction by using the detection clock, when the rising edge of the zero position signal of the scanning motor in the vertical direction is detected, the time measuring module starts to count the rising edge of the timing clock, and when the time measuring module detects the rising edge of the emission pulse signal by using the detection clock, the time measuring moduleThe block puts the data of the number of rising edges of the current timing clock into a data bus of a time measuring module to wait for the USB interface module to read, the number of the rising edges of the current timing clock is the number of the timing clocks between the zero-position signal of the scanning motor in the vertical direction and the emission pulse signal at the same time, and the time interval t between the emission pulse signal and the zero-position signal of the scanning motor in the vertical direction can be obtained by multiplying the number of the timing clocks by the period of the timing clock_v-pIn summary, it can be seen that the transmission pulse signal corresponding to the first time interval measured by the time measurement module and the transmission pulse signal corresponding to the first distance data measured by the external ranging module are the same signal, so that alignment between the angle data measured by the high repetition frequency three-dimensional scanning lidar scanning angle measurement circuit based on the FPGA and the distance data measured by the external ranging module is achieved;

a high repetition frequency three-dimensional scanning laser radar scanning angle measuring circuit based on FPGA is characterized in that a USB interface module realizes the ordered transmission of the number of pulses per second measured by a pulse per second counter module, angle data measured by an angle measuring module, time data measured by a time measuring module and distance data measured by an external distance measuring module, when the USB interface module detects the rising edge of the pulse per second by using a detection clock, the USB interface module reads the data degree of the pulse per second counter and uploads the data degree to an upper computer through a USB interface, then waits for the angle data of the angle measuring module to be effective, reads the angle data and uploads the angle data to the upper computer through the USB interface after the angle data in the angle measuring module is effective, and when the module detects the rising edge of a transmitted pulse signal, the USB interface module reads the data measured on a data bus of the time measuring module and uploads the data to the upper computer through the USB interface, and then waiting for the distance data of the external ranging module to be effective, and after the distance data of the external ranging module is effective, reading the distance data of the external ranging module by the USB interface module and uploading the distance data to the upper computer through the USB interface, so that the data measured by the pulse-per-second counter, the data measured by the angle measuring module, the data measured by the time measuring module and the distance data measured by the external ranging module are sequentially uploaded to the upper computer.

Drawings

FIG. 1 is a schematic diagram of a high repetition frequency three-dimensional scanning lidar scanning angle measurement circuit based on FPGA

FIG. 2 is a complete block diagram of a high repetition frequency three-dimensional scanning lidar scanning angle measurement circuit based on FPGA

FIG. 3 is a working timing diagram of a high repetition frequency three-dimensional scanning lidar scanning angle measurement circuit based on FPGA

Detailed Description

Fig. 2 is a complete block diagram of a high repetition frequency three-dimensional scanning lidar scanning angle measurement circuit system based on an FPGA. As shown in fig. 2, the FPGA-based high repetition frequency three-dimensional scanning lidar scanning angle measurement circuit includes a phase-locked loop module, a 1-out-of-2 switch module, a pulse-per-second counter module, an angle measurement module, a time measurement module, and a USB interface module, all of which are completed inside one FPGA, and an absolute value encoder for measuring the angle of the horizontal scanning motor and an incremental encoder for measuring the zero position of the vertical scanning motor. The phase-locked loop module is used for generating a second pulse with the frequency of 1 Hz, a detection clock with the frequency of 50 MHz and a timing clock with the frequency of 500 MHz, which are required by other modules to work. The 1-out-of-2 switch is used for selecting whether the pulse per second signal used by the pulse per second counting module is from an external GPS or an internal phase-locked loop. The angle measurement module is used for measuring the scanning angle of the scanning motor in the horizontal direction corresponding to the zero position of each scanning motor in the vertical direction. The time measuring module is used for measuring the time interval between the zero position signal and the emission pulse signal of the scanning motor in the vertical direction. The USB interface module is used for controlling the enabling of the measuring circuit and transmitting data of each module to the upper computer. The external ranging module measures the distance between a target and the laser radar, and is not included in a high-repetition-frequency three-dimensional scanning laser radar scanning angle measuring circuit based on an FPGA (field programmable gate array), but is required to be used in the working description of the measuring circuit, so that the distance is represented by a dotted frame.

Fig. 3 is a working timing diagram of the high repetition frequency three-dimensional scanning lidar scanning angle measurement circuit based on the FPGA. As shown in FIG. 3, after the three-dimensional scanning laser radar system starts to work, the software of the upper computer is used for being based on the USB interface of the upper computerThe high repetition frequency three-dimensional scanning laser radar scanning angle measuring circuit of FPGA sends a start working flag bit, a USB interface module waits for an upper computer to send the start working flag bit, after the USB interface module receives the start working flag bit, a USB interface module control end signal is changed from low level to high level, so that a pulse per second counter module is enabled to start working, the pulse per second counter module detects the rising edge of input pulse per second by using a detection clock, when the pulse per second counter module detects the rising edge of the pulse per second, the pulse per second counter module control end outputs enabling signals to respectively enable an angle measuring module and a time measuring module, the angle measuring module detects the rising edge of a zero position signal of a scanning motor in the vertical direction by using the detection clock, when the angle measuring module detects the rising edge of the zero position signal of a first scanning motor, the angle measuring module control end outputs enabling signals to respectively enable an emission pulse counter and an external ranging module to start working, and simultaneously, the angle measurement module reads the angle data of the absolute value encoder, and in subsequent work, the angle measurement module detects the rising edge of the zero-position signal of each vertical scanning motor and reads the angle data of the absolute value encoder after detecting the rising edge of the zero-position signal of the vertical scanning motor, wherein the angle data is the horizontal scanning angle of the emergent laser pulse corresponding to the zero position of the motor. After the time measurement module is enabled by a control signal of the pulse per second counter module, a detection clock is used for detecting the rising edge of a zero position signal of the scanning motor in the vertical direction, after the time measurement module detects the rising edge of the zero position signal of the scanning motor in the vertical direction, the time measurement module starts to count the rising edges of the clock during counting, the time measurement module simultaneously detects the rising edge of each emission pulse signal by the detection clock, when the time measurement module detects the rising edge of the emission pulse signal, the time measurement module places the number of the rising edges of the timing clock on a data bus of the time measurement module to wait for the USB interface module to read, so that the time between the zero position of the scanning motor in the vertical direction and each emission pulse signal is obtained, and the ith interval

Wherein the content of the first and second substances,

timing the number of clock pulses, T, for the rising edge of the ith transmit pulse signal_cClock cycles are clocked. Thereby obtaining the scanning angle alpha of the ith laser pulse in the vertical direction_i

Wherein s is_vIs the rotation speed of the scanning motor in the vertical direction, and the scanning angle beta of the ith emitted laser pulse in the horizontal direction_i

Wherein, theta_iScanning the horizontal direction scanning angle s corresponding to the rising edge time of the zero position signal of the ith vertical direction scanning motor_hIs the rotation speed of the horizontal direction scanning motor.

The USB interface module is used for receiving a start working identification position of the upper computer and enabling control of the pulse-per-second counter module, and is also used for transmitting pulse-per-second number data measured by the pulse-per-second counter module, angle data of a scanning motor in the horizontal direction at the moment of the rising edge of a zero-position signal of the scanning motor in the vertical direction measured by the angle measuring module, time interval data between the rising edge of the zero-position signal of the scanning motor in the vertical direction and the rising edge of a transmitting pulse signal measured by the time measuring module and distance data measured by the external distance measuring module to the upper computer through the USB interface. When the USB interface module detects the rising edge of the pulse per second signal, the USB interface module reads the pulse per second number data measured by the pulse per second counter module and uploads the read pulse per second number data to the upper computer through the USB interface. When the USB interface module detects the rising edge of the zero position signal of the scanning motor in the vertical direction and judges that the data measured by the angle measuring module is valid, the USB interface module reads the scanning angle in the horizontal direction measured by the angle measuring module and uploads the scanning angle to the upper computer through the USB interface. When the USB interface module detects the rising edge of the emission pulse signal, the USB interface module reads data on a data bus of the time measurement module and uploads the data to an upper computer through a USB interface. And then, the USB interface module waits for the data of the external ranging module to be valid, and when the data of the external ranging module is valid, the USB interface module reads the data of the external ranging module and uploads the data to the upper computer through the USB interface. In summary, the USB interface module realizes the orderly uploading of data of each module.

The above description is only a basic scheme of the specific implementation method of the present invention, but the protection scope of the present invention is not limited thereto, and any changes or substitutions that can be conceived by those skilled in the art within the technical scope of the present invention disclosed herein are all covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims

1. A high repetition frequency three-dimensional scanning laser radar scanning angle measuring circuit based on FPGA is characterized in that an incremental encoder is used for measuring the zero position of a scanning motor in the vertical direction by the FPGA-based high repetition frequency three-dimensional scanning laser radar scanning angle measuring circuit, a low response frequency absolute value encoder is used for measuring the scanning angle of a scanning motor in the horizontal direction, a time interval between a transmitting pulse signal and a zero position signal of the scanning motor in the vertical direction is measured by combining a high-precision time measuring module based on FPGA, the measurement of the scanning angle of the high repetition frequency laser pulse in the vertical direction and the scanning angle in the horizontal direction in the three-dimensional scanning laser radar is realized, meanwhile, a GPS second pulse signal and a USB interface module are used for orderly uploading measured angle data and time data to an upper computer through a USB interface, and meanwhile, the alignment between the scanning angle data and distance data is realized by means of the USB interface, the high repetition frequency three-dimensional scanning laser radar scanning angle measurement based on the FPGAThe circuit comprises a phase-locked loop module, a 2-to-1 switch module, an angle measuring module, a time measuring module, a pulse-per-second counter module and a USB interface module, wherein all the modules are completed in an FPGA (field programmable gate array), the phase-locked loop module respectively generates pulse-per-second with the frequency of 1 Hz and is used for 50 MHz detection clock for detecting the rising edge of input signals of the angle measuring module, the time measuring module, the pulse-per-second counter module and the USB interface module and 500 MHz timing clock for timing the time measuring module, the 2-to-1 switch module is used for selecting whether pulse-per-second signals input to the pulse counter module are generated by an external GPS (global positioning system) or a phase-locked loop, the pulse-per-second counter measures the number of the input pulse-per-second signals and controls the data in the USB interface module to be sequentially uploaded, and the angle measuring module reads angle data of a horizontal scanning motor under the control, obtaining a horizontal scanning angle theta corresponding to the zero position of the scanning motor in the vertical direction, and measuring the time interval t between each transmission pulse signal and the zero position signal of the scanning motor in the previous vertical direction by the time measuring module_v-pBy using the time interval measured and the speed s of the scanning motor in the vertical direction_vThe scanning angle alpha in the vertical direction corresponding to each laser pulse can be obtained

α＝t_v-p×s_v (1)

β＝θ+t_v-p×s_h (2)

Thereby obtaining the horizontal direction scanning angle and the vertical direction scanning angle corresponding to each emitted laser pulse.

2. The FPGA-based high repetition frequency three-dimensional scanning lidar scanning angle measurement circuit of claim 1, whereinThe FPGA-based high-repetition-frequency three-dimensional scanning laser radar scanning angle measuring circuit adopts a USB interface module to realize the enabling control of an upper computer on a pulse per second counter module, the pulse per second counter module realizes the enabling control of an angle measuring module and a time measuring module, the angle measuring module realizes the enabling control of an external ranging module, adopts a one-stage and one-stage enabling control mode to realize that the zero position of an incremental encoder corresponds to the horizontal scanning angle, the time interval between the zero position of the incremental encoder and each transmitted pulse signal is measured, and simultaneously, the alignment of distance data, angle data and time interval data is realized, when the USB interface module receives a start working mark position from the upper computer, a control end of the USB interface module sends an enabling signal to the pulse per second counter module, when the pulse counter module receives the enabling signal from the USB interface module, the pulse per second counter module detects the rising edge of input pulse per second by using a detection clock, when the rising edge of the first pulse per second is detected, the pulse per second counter module controls a port to output an enabling signal to enable the angle measurement module and the time measurement module to start working, meanwhile, the pulse per second counter module starts to detect the rising edge of the subsequently input pulse per second by using the detection clock, the detected rising edge of the pulse per second is accumulated and counted, after the angle measurement module receives the enabling signal of the pulse per second counter module, the rising edge of a zero position signal of a vertical scanning motor is detected by using the detection clock, when the angle measurement module detects the rising edge of the zero position signal of the first vertical scanning motor, the angle measurement module controls the port to output the enabling signal to enable a transmitting pulse counting module and an external ranging module to start working, and simultaneously, the angle measurement module reads angle data of an absolute value encoder as the horizontal scanning module when the three-dimensional scanning laser radar Angle tracing, detecting rising edge of each subsequent vertical scanning motor zero position signal by using detection clock, reading absolute value encoder angle data when rising edge of vertical scanning motor zero position signal is detected, wherein the read angle data is horizontal scanning angle theta corresponding to vertical scanning motor zero position, and the time measuring module receives enable signal from the pulse per second counter moduleThe time measuring module detects the rising edge of the zero-position signal of the vertical scanning motor by using the detection clock, when the rising edge of the zero-position signal of the vertical scanning motor is detected, the time measuring module starts counting the rising edge of the timing clock, when the time measuring module detects the rising edge of the emission pulse signal by using the detection clock, the time measuring module puts the counting data of the rising edge of the current timing clock into a data bus of the time measuring module to wait for the USB interface module to read, the number of the rising edges of the current timing clock is the number of the timing clocks between the zero-position signal of the vertical scanning motor and the emission pulse signal at the moment, and the time interval t between the emission pulse signal and the zero-position signal of the vertical scanning motor can be obtained by multiplying the number of the timing clocks_v-pAnd the transmitting pulse signal corresponding to the first time interval measured by the time measuring module and the transmitting pulse signal corresponding to the first distance data measured by the external ranging module are the same signal, so that alignment between the angle data measured by the high-repetition-frequency three-dimensional scanning laser radar scanning angle measuring circuit based on the FPGA and the distance data measured by the external ranging module is realized.

3. The FPGA-based high repetition frequency three-dimensional scanning lidar scanning angle measurement circuit of claim 1, wherein the USB interface module realizes the ordered transmission of the number of pulses per second measured by the pulse per second counter module, the angle data measured by the angle measurement module, the time data measured by the time measurement module, and the distance data measured by the external ranging module, when the USB interface module detects the rising edge of the pulse per second by using the detection clock, the USB interface module reads the data degree of the pulse per second counter and uploads the data to the host computer through the USB interface, then waits for the angle data of the angle measurement module to be valid, reads the angle data and uploads the data to the host computer through the USB interface after the angle data in the angle measurement module is valid, and when the rising edge of the transmitted pulse signal is detected by the time measurement module, the USB interface module reads the data on the data bus of the time measurement module, and uploading the data to an upper computer through a USB interface, then waiting for the data of the external ranging module to be valid, and after the external data is valid, reading the distance data of the external ranging module by the USB interface module and uploading the distance data to the upper computer through the USB interface, thereby realizing that the data measured by the pulse-per-second counter, the data measured by the angle measuring module, the data measured by the time measuring module, the data of the number of pulses measured by the transmitted pulse counter module and the distance data measured by the external ranging module are sequentially uploaded to the upper computer.