Laser active imaging is fit to conditions such as no difference in temperature between target and background, pitch-black night, bad visibility. Also it can be used to detect a faint target in long range or small target in deep space, which has advantage of high definition and good contrast. In one word, it is immune to environment. However, due to the affect of long distance, limited laser energy and atmospheric backscatter, it is impossible to illuminate the whole scene at the same time. It means that the target in every single frame is unevenly or partly illuminated, which make the recognition more difficult. At the same time the speckle noise which is common in laser active imaging blurs the images . In this paper we do some research on laser active imaging and propose a new target recognition method based on multi-frame images . Firstly, multi pulses of laser is used to obtain sub-images for different parts of scene. A denoising method combined homomorphic filter with wavelet domain SURE is used to suppress speckle noise. And blind deconvolution is introduced to obtain low-noise and clear sub-images. Then these sub-images are registered and stitched to combine a completely and uniformly illuminated scene image. After that, a new target recognition method based on contour moments is proposed. Firstly, canny operator is used to obtain contours. For each contour, seven invariant Hu moments are calculated to generate the feature vectors. At last the feature vectors are input into double hidden layers BP neural network for classification . Experiments results indicate that the proposed algorithm could achieve a high recognition rate and satisfactory real-time performance for laser active imaging.
By summarizing the corresponding parameters 0f the driving system of a 4-m Alt-azimuth telescope, some unit
techniques like the driving modes and structure, angular position measurement methods in detail. have been analyzed in
the paper. A set of primary schemes for astronomical applications, including the altitude axes being driven by 2 DC
torque motors, the azimuth by 4 DC torque motors using helical gears, and two pieces of the 27-bit segment tape
encoders for each set of axes is proposed. To meet practical engineering needs, the shafting motion parameters are
designed and motor elementary parameters are primarily calculated to offer the important references for further study on
system driving model and prototype development.
When a motion control system tracks a fast moving target, the over-tune is the main part of the dynamic tracking
error. The speed delay compensation may be used to decrease the error but the stability is sacrificed. We put
forward the Differential Position Feedback control, and discuss its effects and control mechanism through
simulation. With transfer function identification, we find that the Differential Position Feedback(DPF) control is
based on internal model principle. The simulation results show that DPF can improve the tracking ability for the
fast moving target but lower the tracking precision at low frequency region. If it is combined with the dynamic
integral control, better tracking precision can be obtained.
The servo control system of the optoelectronic tracking equipment usually is a kind of SISO. When the fast moving target is tracked, the over-tune of the servo system is the main representation for the dynamic tracking error. As the result, the tracking ability may be improved by limiting the over-tune. We put forward a method, the advanced position compensation (called as APC in short), which is to check the speed-overtune by applying the advanced position information. For the large accelerate target, small over-tune tracking is achieved, but it lowers the ability for tracking the sine signal at low frequency area. While the dynamic high-type can improve the tracking precision for the sine signal at low frequency area, we work out a brand-new method, which combines the advantages of the both. It increases the tracking precision in the whole frequency band at large scale for the optoelectronic tracking system. The simulation results show that when the target moves with the largest accelerate 120°/s2, 120°/s, the maximum static tracking error is about 0.6".
Acquisition is defined as identification for a fixed target in the related field of sight (FOS), while tracking means the sway of the telescope's axis of sight (AOS). The automatic acquisition and tracking is a process in which the operating way of the telescope should be switched from guiding to automatic tracking. There are some kinds of method to improve the acquisition and tracking ability for fast moving targets: to extend the acquisition and tracking FOS with memory and storage information of the sensor system; the multimode control to improve the dynamic property of the servo system; to choose an opportune time for acquisition and tracking; to select the control regulator parameter in every working states. If the processor of the CCD sensor can temporarily remember and save the information of the target before it moves out of the FOS, correspondingly, the FOS may be extended. The data forecast technology is used to store the target information. The automatic interception experiments are carried out to verify the control strategy.
Optoelectronic theodolite has the highest measuring precision for space target positioning and flight-path measurements
among the measuring instruments. With the advantages of real-time, high precision, dynamic tracking property and
image reproduction, it is widely used in the areas of aerospace and weapon experiments. Now, to meet the new
challenges, the measuring system should be changed from singe theodolite to a network, and from manual operation
tracking to multi-source automatic tracking. So that, the technology of multi-source information fusion is highly needed
to realize real-time guide for the theodolite.
The secant compensation must be applied in the servo system of the azimuth axis for the altitude-azimuth pedestal. The secant compensation value changes acutely while the elevation goes high. The pedestal can't follow the target smoothly so as to lose the target near the zenith. The zenith exclusion region, as is the main shortage of the altitude-azimuth pedestal, was analyzed. The conclusion is that the scope of the zenith exclusion region was restricted by three parameters; maximum azimuth angular velocity of tracking mount, flight level and airspeed of the target. And then, the factors that influence high-elevation tracking performance are analyzed. The dynamic delay is usually regarded as the main influencing factor. The effect of equivalent insensitive-zone and random tracking error are often neglected. Nevertheless, it is clearly important to be aware of them in some case. The factors discussed above were tested with the experiment. The actual track data draw a conclusion that the last two factors become the main influencing factors in the case of tracking slow-moving targets. It verified that the theoretical analysis is correct and is very valuable for engineering.
The tracking servo system of an optoelectronic tracking system that is driven by unipolar PWM power amplifier has the features of high efficiency, wide speed regulation range. But the phenomena such as instability at low-speed and positioning exist in the system because of dead-zone nonlinearity, which result in steady error and low tracking precision. A method for improving low-speed performance of an optoelectronic Tracking System is given in the paper: using bipolar PWM power amplifier to replace unipolar PWM power amplifier and we did some comparative experiments. The experimental results showed that using bipolar PWM power amplifier to replace unipolar PWM power amplifier is an effective method for improving the low-speed performance of the optoelectronic tracking system.
Concerning the disturbances at low speed, such as friction at zero crossings and the moment fluctuation of the motor, we explore the repeat control method rooted in study law to compensate the low-speed-disturbances, and the system's properties at low speed are improved greatly. Here we present our works. Section 1 is the introduction. The friction and moment fluctuation of the motor at low speed for the optoelectronic system are tested out which are shown in section 2. We introduce a repeat controller to the system to compensate the low-speed disturbances in section 3. Concerning the stability, a filter is added to the repeat controller. The experimental results are discussed in section 4. Not only the repeat control can overcome some low-speed-disturbances, but is more useful when tracking a periodic input signal.
The research, on the damage mechanism to the high-space target by the ground laser, aims to determine the saturation or damage threshold of optic-electro sensors on the target. The laser beam to the target is relationship with the following features: The speediness of the energy accumulation and the laser tracking stability in long distance. The speediness needs high peak-power in the shortest time, while the stability needs high speed-precision ability to the servo system on earth. Obviously, the pulse laser is more effective than the continuous laser when considering the speediness. Here for the 10.6 ? m CO2 laser, the interfering effects are dealt with to the target in 500km space. Provided that the turbulent air does not influence the laser beam, the power of periodic rectangle-pulse laser arriving on the space object is evaluated first. Then the laser staring time on the object is calculated. Third, the laser energy accumulation on the space object is analyzed, and last the saturation or damage threshold ofthe object is determined.
At low speed or zero crossings, the existed nonlinear effects such as friction, the fluctuation of the motor moment will make the system jitter heavily. Our researches focus on the analysis and compensation of the motor moment fluctuation when the optoelectronic tracking system works at low speed. Actually, other nonlinear factors at low speed are also checked. As the fluctuation is always presented in sine orderliness, a repeat controller that bases on the study law is applied to the tracking system. Both simulations and experiments show that with the repeat controller, the tracking precision increase about 3 times comparing to the PID one.
A stable adaptive controller is reported here for a class of system with state dependent parasitic effects such as friction. The methodology is constructive, and ensures stable and convergent performance. The control design is applicable to a class of dynamic systems working at low speed with the cited parasitic effects. The design is verified by simulation and a hardware example case.
Model Reference Adaptive Control (MRAC) technique is applied to our practical optoelectronic tracking system. Comparing with tradition corrective method, MRAC effectively increases the tracking precision when the system works in low speed area. The low speed jitter phenomenon is decreased obviously.
First, the stationary time is calculated, and accordingly, the minimum stable speed or the speed resolving power of the Ground Servo System is discussed. Through simulation we analyze the interfering result and tracking effect.
In this paper, the principle of fiber Bragg gratings (FBG) are briefly described. The formation technologies of FBG are systematically given and analyzed. In addition, we will describe in detail the experiment in which we applied phase mask method to write directly the period Bragg gratings into the single mode of Ge-doped fiber with KrF excimer UV laser. Comparing with other methods, this one involves a lot of advantages. The results of experiment will also be presented and analyzed.
For the detection of methane (CH4) gas concentration in some mining complexes, the paper studies and discusses two kinds of easily-realized CH4 gas opticfiber sensor, that is infrared absorption CH4 gas optic fiber sensor and thin film transmission CH4 gas optic fiber sensor. The optic structure of the sensor is discussed, and the paper compares the difference between the single optic structure system and the double one. It puts forward a multipoint long-distance detection system constructed by the micro- computer small system and the upper computer, and discusses the hardware and software system.