Laser fuse has the advantages of good monochromaticity, high collimation and strong anti-electromagnetic interference ability. However, when passing through smoke and fog media, laser fuse will interact with suspended particles, causing part of the energy to be scattered by suspended particles to an angle different from the target direction, part of the energy to be absorbed by particles and other complex effects. Thus, attenuation of beam energy and false alarm are generated, and detection performance of laser fuse is reduced. When the target is in the smoke and fog background, it is difficult to recognize that the target echo overlaps with the smoke echo. To solve this problem, the target echo signal is recognized based on the Gaussian decomposition combined with SVM (Support Vector Machine) algorithm. The Gaussian waveform decomposition method is used to separate the echo signal of smoke and target, and the amplitude, center position and half wave width of the two waveforms are calculated. SVM algorithm is used for training. The signals of smoke and targets at different distances in different concentrations of smoke environment are collected, and the experimental verification shows that the recognition accuracy can reach 91.2%, which is compared with the existing KNN, K-Means, SAE algorithms. The results show that SVM algorithm has excellent recognition effect in smoke environment with different concentrations.
A high-speed real-time structured light imaging system is presented in this paper. The improved linear structured light imaging method is transplanted to the FPGA hardware system, and the imaging frequency is greatly increased. The best imaging effect can be obtained when imaging objects with different reflectivity. Experiments show that this method can achieve outstanding imaging effect for complex objects, and the imaging frame rate can reach 60 Fps.
Laser is another major invention of mankind since the 20th century, after atomic energy, computers, and semiconductors. Laser has the characteristics of high brightness, high direction, high monochrome and high incoality, which makes laser detection become one of the main detection systems for short-range target, and is widely used in military and civilian fields. In the military aspect, laser detection and identification of targets is a key technology of laser short-range detection. Laser detection can improve the hit probability to the target such as tank ,because it can provide accurate distance data for gun fire, detection and so on; in civilian use , Laser ranging is a key technology in 3D laser scanning. Improving the accuracy of laser ranging is beneficial to 3D reconstruction and point cloud data acquisition. Therefore, it is important to improve the performance of the range circuit. In order to improve the range measurement accuracy of pulse laser, a pulse laser range measurement receiver circuit is designed. Based on the operating conditions of photoelectric avalanche tube (APD), this paper analyzes the main performance parameters such as APD peak wavelength, minimum detection power, sensitivity, reaction time. APD500-9T has been selected as the photodetector, The voltage feedback APD bias circuit based on TPS40210 has been designed, which provides stable operating voltage for APD. This receiver circuit analyzes the input capacitor and GBP of the op-amp, OPA657 was selected as the amplifier of the amplification circuit and a reasonable circuit structure has been designed.The circuit model was built and the functional simulation has been performed in Multisim. Finally, through experimental verification, the highvoltage bias circuit can produce 95V high-voltage, meeting the APD500-9T operation requirements. The receiver circuit can fully receive the echo signal.
High precision time measurement technology is the basis of many scientific applications. It plays an important role in radar, sonar, laser ranging, particle physics and other advanced scientific fields. Meanwhile, the ability of high-precision time measurement is also an important factor limiting the development of these fields. Time to digital conversion (TDC) is a commonly used time interval measurement method, which is widely used in the above-mentioned advanced areas. This paper presents a new TDC design method based on the delay chain structure, and the measurement accuracy is further improved by the combination of rough and exquisite counting. The theoretical basis of the TDC is described. The calculation formula of the total time to be measured is given. Then, by combining the start and the stop signal reasonably, the time of gate signal is within an acceptable range, which reduces the instability of the signal and the number of input signal sources. The designed TDC achieves excellent delay uniformity and stability through the reasonable layout and routing of Carry4 delay chain module in FPGA. In addition, in the design of latch unit, a two-stage latch unit is designed according to the mean time between failures (MTBF) theorem, which ensures the consistency of delay and the correctness of timing, avoids the generation of metastable state, and improves the timing accuracy. Finally, in order to verify the performance of the proposed TDC design scheme, reasonable post simulation and board level verification are conducted under different clock frequencies. The verification results show that the maximum mean error of TDC is 3.99ps and the minimum is 2.82ps.
Polarization is steadily attracting attention in machine vision due to its ability to capture the information not readily available in standard color or greyscale camera. In this paper, the degree of polarization image and intensity image are used to calculate the position and posture of stamping parts. First, the degree of polarization image and intensity image were acquired from polarization camera. Canny edge operator is used to filter the polarization degree image to get the edge image. Morphological analysis and connected domain statistics are performed on the edge image, and location holes are extracted from the connected domain according to the geometric characteristics. Combined with the extracted location holes region, the obtained polarization intensity image is segmented by local threshold, and the edge contour of the location hole is extracted and the coordinates of the center point are calculated.
This paper proposes a method based on 3D version to recognize free-form objects in the complicated environment, which could be used in field of robot picking. The point cloud data is generated by binocular camera system. The depth map is employed to recover 3D point cloud of the scenario with the calibration method from the binocular camera. Segmentation algorithm is used to detect the object. Recognition is performed by using software libraries integrated with custom-developed segmentation algorithm and model database created by the same binocular camera system. Experiments are designed to verify the performance of the method by randomly placing different types of experimental objects in manipulator workspace. The preliminary results demonstrate the excellent ability of the system to perform object recognition and picking.
Three-dimensional contour imaging is used to reconstruct the surface of complex contour. Line-structured light is characterized by fast measurement, large amount of data and nondestructive to contour surface and is widely used in 3-D imaging. Therefore, a series of calibration methods for line-structured light are also produced, such as cross-ratio invariance, triangulation method, polynomial and so on. However, the traditional calibration methods are complex and take a long time, so a simplified method is proposed. This method omits the complicated process of calculating the cross-ratio and obtains the equation of light plane by accurately calculating the external parameters between the target and the camera and get the 3-D points of the line-structured light by the pinhole camera model. What’s more, RANSAC is applied to get the more precious line-structured light plane by eliminating the wrong points. Moreover, errors are measured and analyzed during the process of structure light calibration.
In this paper, a two-dimensional (2D) laser radar system is designed. The working principle of pulsed two-dimensional laser radar is introduced. The driving circuit of laser emitting system is designed and simulated. The suitable parameters are acquired. Afterwards, the ranging result is calculated by the TDC-GP22, and the azimuth angle is acquired based on the encoder. The experiments are carried out, and the echo signals are measured at different distances. It provides the basis for unmanned aerial vehicle technology.
KEYWORDS: LIDAR, 3D image processing, Clouds, 3D acquisition, 3D modeling, 3D scanning, Radar imaging, Laser imaging, Laser development, Control systems
In this paper, we propose a three-dimensional (3D) laser imaging method. The working principle of laser radar is introduced, and three scanning strategies are proposes based on low-cost two-dimensional (2D) laser radar. Three dimensional point cloud images under different strategies are simulated and analyzed. Combined with the advantages of the three strategies, a 3D laser radar scheme with pitch and rotation function is designed, and the coordinate transformation of 3D laser radar data point cloud display is established. Three-dimensional imaging experiments on real environment scenes are carried out. The experimental results show that the designed 3D laser radar can get 3D point cloud data in real time. It provides support for low cost 3D laser radar to realize 3D reconstruction and image fusion.
Aiming at the low precision of small pulse laser ladar in practical application, the wavelet threshold de-noising algorithm is adopted to extract the echo signal. According to the echo signal equation and the ladar noise characteristics, a noisy echo model is established. In order to extract the echo signal, the wavelet threshold de-noising algorithm is used. Select the best wavelet basis and decomposition scale. According to the simulation results, the actual echo signal is processed, and the noise is effectively improved. The detection accuracy improves effectively.
Aiming at the difficult problem of high precision frequency stabilization of semiconductor laser diode, the laser frequency control is realized through the design of the semiconductor drive system. Above all, the relationship between the emission frequency and the temperature of LD is derived theoretically. Then the temperature corresponding to the stable frequency is obtained. According to the desired temperature stability of LD, temperature control system is designed, which is composed of a temperature setting circuit, temperature gathering circuit, the temperature display circuit, analog PID control circuit and a semiconductor refrigerator control circuit module. By sampling technology, voltage of platinum resistance is acquired, and the converted temperature is display on liquid crystal display. PID analog control circuit controls speed stability and precision of temperature control. The constant current source circuit is designed to provide the reference voltage by a voltage stabilizing chip, which is buffered by an operational amplifier. It is connected with the MOSFET to drive the semiconductor laser to provide stable current for the semiconductor laser. PCB circuit board was finished and the experimental was justified. The experimental results show that: the design of the temperature control system could achieve the goal of temperature monitoring. Meanwhile, temperature can be stabilized at 40°C ± 0.1°C. The output voltage of the constant current source is 2 V. The current is 35 mA.
According to the problem of the high-precision ranging in the circumferential scanning probe laser proximity fuze, a new type of pulsed laser ranging system has been designed. The laser transmitting module, laser receiving module and ranging processing module have been designed respectively. The factors affecting the ranging accuracy are discussed. And the method of improving the ranging accuracy is studied. The high-precision ranging system adopts the general high performance microprocessor C8051FXXX as the core. And the time interval measurement chip TDC-GP21 was used to implement the system. A PCB circuit board was processed to carry on the experiment. The results of the experiment prove that a centimeter level accuracy ranging system has been achieved. The works can offer reference for ranging system design of the circumferential scanning probe laser proximity fuze.
According to the requirement of the long range detection of the circumferential detection system of the laser fuze, a hybrid modulated pulsed laser driving power supplying for APD avalanche photodiode is designed. The working principle of the laser circumferential detection system is analyzed, and the APD is selected as the photoelectric detector according to the measurement equation of the circumferential detection system. According to the different kinds of APD requirements for high voltage power supply, the principle of boost converter is analyzed. By using PWM and PFM hybrid modulation type power supply technology, PWM modulation is applied in low rising voltage. When the voltage is required to achieve more than 100V, PFM mode boost is chosen. Simulation of the output voltages which are 85V and 200V of the two modes respectively is made. The PCB circuit board is processed to verify the experiment. The experimental results show that the hybrid modulation pulse laser drive power supply can meet the requirements of all kinds of APD power supply. The circuit board can be used in the detection of laser fuze with different target distance, and has wide application prospect.
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