Chunsheng Hu

High-precision rolling angle measurement for a three-dimensional collimator.

We propose a precise rolling angle measurement for a collimator to extend its application in 3D angular deformation measurement, with performance significantly superior to that of the traditional 2D technique. The rolling angle measurement is realized by taking full advantage of the point array image, which is projected in terms of the collimated beam. The measurement error is estimated according to the proposed algorithm. The characteristics of the point array are analyzed to optimize the point array for precise measurement, including the point distribution, the point array resolution, and the point array area. Both simulations and experiments demonstrate that subarcsecond precision rolling angle measurement is achieved by our method, which is superior to those attained by other proposed targets.

A new time discrimination circuit for the 3D imaging Lidar

In order to enhance the time discrimination precision in the 3D imaging lidar, we propose a new time discrimination circuit, which improves both the delayer and the attenuator in the previous CFD (Constant Fraction Discriminator) circuit. The proposed circuit mainly includes a delayer, a low-pass filter, and a comparator. The delayer is implemented with a series of inductors and capacitors, which has some advantages: low signal distortion, small volume, easy adjustment, etc. The low-pass filter attenuates the signal amplitude and broadens the signal width, as well as reduces the noise by decreasing the equivalent noise bandwidth, and increases the signal slope at the discrimination time. Therefore, the time discrimination error is reduced significantly. This paper introduces the proposed circuit in detail, carries out a theoretical analysis for the noise and time discrimination error in the proposed circuit and compares them with the previous CFD circuit. The comparison results show that the proposed circuit can reduce the time discrimination error by about 50% under the same noise level. In addition, some experiments have been carried out to test the performances of the circuit. The experiments show that the time delay of the circuit is about 14ns, the time discrimination error is less than 150 ps when the voltage SNR ranges from 18.2 to 81.8, and the time discrimination error is less than 100 ps when the signal amplitude ranges from 0.2 V to 1.86 V. The tested time discrimination error is well in accordance with the theoretical calculation.

Precise optical method for three dimensional ship deformations measurement

We present an optical method to measure three dimensional (3D) ship deformations. This method is based on optical collimation theory and thereby, with a crosshairs image projected and captured in a collimation optical path, the 3D deformation angles, including the pitching angle, the yawing angle and the rolling angle, could be calculated by image’ variation. In order to improve the measurement precision, sub-pixel location algorithm is adopted in image processing. Particularly, given that the rolling angle is the most difficult to measure in a collimation optical path, numerical simulation is carried out to analysis the error characteristics of this angular measurement. Experimental results indicate that this 3D ship deformations measurement achieve the precision of several arcsecs in the distance of 25m and in the deformation range of -120″~120″.

A new 3D imaging lidar based on the high-speed 2D laser scanner

In order to enhance the imaging speed of the 3D imaging lidar (light detection and ranging) and implement high-speed 3D imaging under static conditions, we propose a new 3D imaging lidar based on a laser diode and a high-speed 2D laser scanner. The proposed 3D imaging lidar is mainly composed of a transmitter, a laser scanner, a receiver and a processor. This paper introduces the components and principle of the proposed 3D imaging lidar first. And then some experiments have been carried out to evaluate the performance of the 3D imaging lidar, in terms of scanning field, measuring precision, scanning speed, image resolution and etc. The results show that the scanning field of the 3D imaging lidar is about 26°×12°, the measuring precision is better than 5 cm (4 m distance), the scanning speed is greater than 30 fps (frame per second) and the image resolution can reach 16×101. In addition, the 3D imaging lidar can obtain both the 3D image and intensity image for the given target at the same time.

A novel high-speed 2D laser scanner for the 3D imaging lidar

In order to enhance the imaging speed of the 3D imaging lidar (light detection and ranging) and implement high-speed 3D imaging under static conditions, we propose a novel high-speed 2D laser scanner with an asymmetric 16-plane rotating mirror. Firstly, this paper analyzes the principles and characteristics of common laser scanners used in 3D imaging lidars, which mainly include a symmetric rotating mirror scanner, a vibrating mirror scanner, a oval line scanner and a double optical wedge scanner. And then we propose an asymmetric 16-plane rotating mirror with a novel structure, which can carry out faster scanning in 2D field with only one rotating mirror. The scanning principle and main structure of the rotating mirror is introduced in detail. Based on the proposed asymmetric rotating mirror, a new high-speed laser scanner for the 3D imaging lidar is implemented with some advantages: high scanning speed, large scanning field and high reflectivity. Finally, the laser scanning experiment has been carried out with the proposed laser scanner. The experimental results show that the scanning speed is above 30 frames per second, the scanning field is about 32°×12°, the vertical resolution of each frame is 16, and the laser reflectivity is above 0.9. The proposed laser scanner can be applied to areas such as groundborne, vehicleborne and airborne 3D imaging lidars.

Technology of optical azimuth transmission

It often needs transfer a reference from one place to another place in aerospace and guided missile launching. At first, principles of several typical optical azimuth transmission methods are presented. Several typical methods are introduced, such as Theodolite (including gyro-theodolite) collimation method, Camera series method, Optical apparatus for azimuth method and polarization modulated light transmission method. For these typical azimuth transmission methods, their essential theories are elaborated. Then the devices, the application fields and limitations of these typical methods’ are presented. Theodolite (including gyro-theodolite) collimation method is used in the ground assembly of spacecraft. Camera series method and optical apparatus for azimuth method are used in azimuth transmission between different decks of ship. Polarization modulated light transmission method is used in azimuth transmission of rocket and guided missile. At the last, the further developments of these methods are discussed.

Coordinates calibration in precision detection of 3D optical deformation measurement system

In order to validate the detection precision of a three Dimensions Optical Deformation Measure System (3D-OMS), a calibration method of auxiliary coordinate and the optical coordinate base on theodolites has been proposed. The installation method by using theodolites to calibrate the auxiliary coordinate and the optical coordinate has been proposed. Specifically, after the auxiliary mirrors installed, the installation accuracy is detected, then we analyzed the influence of Axis-Error of theodolite under the practical condition of our experiment. Furthermore, the influence of validation precision for the 3D-OMS caused by the misalignment of auxiliary coordinate and optical coordinate is analyzed. According to our theoretical analysis and experiments results, the validation precision of the 3D-OMS can achieve an accuracy of 1″ at the conditions of the coordinate alignment accuracy is no more than 10′ and the measuring range of 3D-OMS within ±3′. Therefore, the proposed method can meet our high accuracy requirement while not sensitive to the installation error of auxiliary mirrors. This method is also available for other similar work.

A wideband low-noise pulsed laser detection circuit for the 3D imaging lidar

In order to enhance the measurement precision and detection range of the 3D imaging lidar (light detection and ranging), we propose a new broadband low-noise detection circuit for the pulse laser, which mainly includes a high-speed APD (Avalanche Photodiode) detector and a broadband low-noise transimpedance amplifier. In the detection circuit, a high negative bias voltage is applied to the APD detector and used to set the static input current of the amplifier NE5210 to 200 μA with a proper bias method. By this bias method, the allowable input current range of the amplifier NE5210 is enhanced by about 1 time. This paper introduces the main framework and performance of the detection circuit. The output noise voltage, output signal voltage and voltage SNR (Signal-to-noise Ratio) of the detection circuit are analyzed and calculated as well. Some experiments have been carried out with the proposed detection circuit, showing that the detection circuit can detect a narrow pulse laser with about 4 ns pulse width. Based on our experiments and analyses, the pass band of the detection circuit ranges from 0.56 MHz to 200MHz approximately, the allowable input current of the amplifier NE5210 varies from -460 μA to 0, and the effective output differential voltage ranges from -1.6 V to 1.4 V. The proposed detection circuit is implemented and tested in a high-speed 3D imaging lidar. As well as 3D imaging lidars, the detection circuit can be applied to the pulse laser range finder and other pulse laser detection system.

A new gain control and amplifying circuit for the 3D imaging lidar

In order to avoid the shortcoming of the passive gain control method in the 3D imaging lidar (light detection and ranging), we propose a new gain control method, which can adjust the gain of the amplifying circuit according to the target distance. This method complies with the principle that the laser echo amplitude is inversely proportional to the square of the target distance. In addition, to simplify the complexity of the gain control module, we propose a simple implementation method based on the charging process of a capacitor. Firstly, the theoretical waveform of the proposed gain control method and the gain control error are analyzed and simulated. The results indicates that when the gain ranged from 1 to 100, the maximum of gain error is less than 28% in the whole target distance range, and the gain error is less than 5% in the most target distance range. Based on this method, a new gain control and amplifying circuit has been developed, which is mainly composed of an amplifying module and a gain control module. The gain control module is used to generate a gain control voltage and apply the voltage to the gain control of the amplifying module. Finally, some experiments have been carried out to verify the entire circuit functions and performances. The experimental results show that the output signal amplitude keep constant on the whole when the target distance is changing. The pass band of the circuit ranges from 0.33 MHz to 150 MHz, and the maximum gain is 316.

A new time-to-digital converter for the 3D imaging Lidar

In order to reduce the negative influence caused by the temperature and voltage variations of the FPGA (Field Programmable Gate Array), we propose a new FPGA-based time-to-digital converter. The proposed converter adopts a high-stability TCXO (Temperature Compensated Crystal Oscillator), a FPGA and a new algorithm, which can significantly decrease the negative influence due to the FPGA temperature and voltage variations. This paper introduces the principle of measurement, main framework, delayer chain structure and delay variation compensation method of the proposed converter, and analyzes its measurement precision and the maximum measurement frequency. The proposed converter is successfully implemented with a Cyclone I FPGA chip and a TCXO. And the implementation method is discussed in detail. The measurement precision of the converter is also validated by experiments. The results show that the mean measurement error is less than 260 ps, the standard deviation is less than 300 ps, and the maximum measurement frequency is above 10 million times per second. The precision and frequency of measurement for the proposed converter are adequate for the 3D imaging lidar (light detection and ranging). As well as the 3D imaging lidar, the converter can be applied to the pulsed laser range finder and other time interval measuring areas.