Attitude Angle Changes Research Articles

Integral Backstepping Control Algorithm for a Quadrotor Positioning Flight Task: A Design Issue Discussion

For quadrotor control applications, it is necessary to rely on attitude angle changes to indirectly achieve the position trajectory tracking purpose. Several existing literature studies omit the non-negligible attitude transients in the position controller design for this kind of cascade system. The result leads to the position tracking performance not being as good as expected. In fact, the transient behavior of the attitude tracking response cannot be ignored. Therefore, the closed-loop stability of the attitude loop as well as the position tracking should be considered simultaneously. In this study, the flight controller design of the position and attitude control loops is presented based on an integral backstepping control algorithm. This control algorithm relies on the derivatives of the associated virtual control laws for implementation. Examining existing literature, the derivatives of the virtual control law are realized approximated by numerical differentiations. Nevertheless, in practical scenarios, the numerical differentiations will cause the chattering phenomenon of control signals in the presence of unavoidable measurement noise. The noise-induced control signals may further cause damage to the actuators or even diverge the system response. To address this issue, the analytic form for the derivative of the virtual control law is derived. The time derivative virtual control law is analyzed and split into the disturbance-independent compensable and disturbance-dependent non-compensable terms. By utilizing the compensable term, the control chattering due to the differentiation of the noise can be avoided significantly. The simulation results reveal that the proposed control algorithm has a better position tracking performance than the traditional dual-loop control scheme. Meanwhile, a relatively smooth control signal can be obtained for a realistic control algorithm realization. Simulations are provided to illustrate the position tracking issue of a quadrotor and to demonstrate the effectiveness of the proposed compromised control scheme.

Automatic bridge crack detection using Unmanned aerial vehicle and Faster R-CNN

In order to improve the efficiency and accuracy of bridge crack detection, this paper introduces Deep Learning for bridge crack detection with Unmanned Aerial Vehicles (UAVs). In this study, a method for deciding the distance range for stable imaging was used, and we have done a set of verification experiments on three types of UAVs. Then a Two-RTSs system for UAV hovering accuracy was proposed, and the displacement and attitude angle changes of UAV were acquired. The results indicated that DJI M210-RTK could acquire high-quality images at longer distances and had better stability in hover mode. So, we decided to use the DJI M210-RTK for bridge crack recognition. Finally, the Faster Region Convolutional Neural Network (Fatesr R-CNN) algorithm based on VGG16 transfer learning is used for the apparent detection of a bridge located in Hunan Province. Our method can achieve precision, recall and F1-score of 92.03 %, 96.26 %, and 94.10 %, respectively. The outcome of this study shows that automatic bridge crack detection using UAVs and Faster R-CNN can be more efficient while maintaining high accuracy.

Experimental study on water-entry cavity and trajectory of vehicle with asymmetric nose shape

Different nose shape can cause a significant influence on the water entry trajectory and cavity. In order to study the evolution characteristics of cavity and trajectory of asymmetric nose in the process of water entry, based on the high-speed photography technology, the low-speed water entry comparative experiments were carried out for three different cut-angle nose types of 35°, 40° and 45° under different water entry angles. Through digital image processing technology, the contour of the water entry cavity and motion attitude information of the vehicle at different times are extracted, and the law of influence of the cut angle and entry angle on the cavity and trajectory is obtained. The experimental results show that: the cut angle side of the asymmetric nose can effectively promote the expansion of the cavity, thus forming the asymmetric water entry cavity; the expansion scale of the cavity is positively related to the initial horizontal expansion speed of the cavity and the area of the section of the head; the water entry trajectory of the asymmetric head will deflect to the cut angle side; the smaller the water entry angle is, the shorter the trajectory leveling time is, and the deeper the leveling depth is However, the change of attitude angle is almost independent of the entry angle.

ISAR Imaging of Maneuvering Target Based on the Estimation of Time Varying Amplitude With Gaussian Window

Due to the maneuverability of target’s motion in the inverse synthetic aperture radar (ISAR) imaging, the Doppler frequency of the received signal has the nonlinear time-varying characteristic. Under the circumstances, it is accurate enough to model the received signal of each range bin as a multicomponent quadratic frequency-modulated (QFM) signal. In this paper, the scaled Fourier transform (SCFT) is applied to obtain the phase parameters of the QFM signal. Owing to the phenomenon of the scatterers’ migration through resolution cell (MTRC) and the change of attitude angle, the amplitude of the received signal is no longer constant but time-varying. Thus, a novel and precise method using the adaptive Gaussian window is presented to estimate the time varying amplitude of the received signal. After that, the corresponding ISAR imaging algorithm is presented consequently. The validity of the proposed method is demonstrated by the simulated and real-data ISAR results.

판재를 이용한 초고속 위협체의 방호성능에 대한 해석적 연구

We investigated the protection capability of a plate against high speed projectiles demonstrating collision and penetration behaviors by finite element analysis. The element erosion method was used for penetration analysis, which showed that the speed of the projectile was slightly reduced by the collision with the protection plate. Protection capability was measured by the projectile’s attitude angle change because the damage of our tanks by projectiles was also dependent on the projectile-tank collision angle. When the length of the protection plate was sufficiently long, the projectile was severely deformed and incapacitated. In the case of a small plate, the projectile was deformed only in the collision region. Thus, projection capability was investigated by the change of attitude angle. The effect of collision angle, velocity, and length of the plate on the rotational and vertical velocities of the projectile was investigated.

A New Star Identification Algorithm based on Improved Hausdorff Distance for Star Sensors

High accuracy attitude for spacecraft can be determined by star sensors. The key technology is star pattern recognition. Based on the Hausdorff distance (HD) algorithm, a robust identification algorithm has been used for matching point-sets, which does not require absolute point correspondence. HD identification is not suitable for large attitude angle changes around the boresight, which usually results in a low recognition rate and low speed of identification. A new image similarity measure combined with an improved HD algorithm is proposed for recognizing stellar maps. An improved HD based on scalar distances is implemented to guarantee an acceptable success rate of recognition for large attitude changes around the boresight, which is noise resistant. Another improved HD based on vector distances is constructed to guarantee the recognition speed using a star dimensional configuration. Appropriate gray and matching thresholds are selected to improve recognition speed. Results of the semiphysical simulation show that the proposed algorithm is better than the HD identification method in terms of noise resistance, recognition rate, and speed of operation.

Duct Cleaning Robot Comprehensive Kinematics Modeling and Analysis Considering the Complex Terrain

Complex terrain conditions greatly influences the movement of mobile robot,which should not be neglected.In this paper,a novel motion modeling idea is proposed, in which the robot chassis attitude angle changes caused by topographic changes was real-timely measured and be input into the robot kinematic modeling process to establish the overall kinematic model of robot. This modeling method reflect the various parts of the robot motion relations, and also display the complex topography of the robot trajectory of the end of the actuator.Finally,validated and analyzed the feasibility of the modeling method.

Study on the Performance of Gas Journal Bearings for Power MEMS

Gas journal bearings, which are used to support radial loads in a rotating machine, have somewhat unusual requirements in Power MEMS deriving from the extremely shallow structures. With the reference Knudsen number being included, the modified Reynolds equation for gas journal bearings based on Burgdorfer’s first order slip boundary condition is put forward. The boundary condition for modified Reynolds equation is given. The numerical method is employed to solve the modified Reynolds equation to obtain the pressure profiles, load capacities and attitude angles of gas journal bearings for Power MEMS under different reference Knudsen numbers and eccentricity ratios. Numerical analysis shows that the pressure profiles and non-dimensional load capacities decrease obviously with the reference Knudsen number increasing, and the attitude angle changes conversely. Moreover, when the eccentricity ratio is smaller, the effect of gas rarefaction on the attitude angle is less.

Characteristics of Micro Gas Journal Bearings Based on Effective Viscosity

According to the first order slip velocity boundary, a modified Reynolds equation for micro gas journal bearings is presented with consideration of effective viscosity under a rarefied flow condition. A modified Reynolds equation is attained and solved using the finite difference method. The nondimensional pressure, load capacity, and attitude angle for micro gas journal bearings under different reference Knudsen numbers (the ratio of ambient molecular mean free path to the average radial clearance), bearing numbers, and eccentricity ratios are obtained. The numerical analysis demonstrates that the slip model with effective viscosity is in a better agreement with the FK model derived by Fukui and Kaneko than that without effective viscosity. When the bearing number is constant, the pressure and load capacity decrease, and the attitude angle changes inversely with the increasing reference Knudsen number. The larger the eccentricity ratio, the larger change in attitude angle from effective viscosity. When eccentricity ratio is less than 0.6, the attitude angle changes softly, and the effect of effective viscosity is unobvious. When the eccentricity ratio is constant, the influence of effective viscosity on nondimensional load capacity and attitude angle becomes larger with the increasing bearing number, and the influence is more prominent with a larger reference Knudsen number.

The corrections for significant wave height and attitude effects in the TOPEX radar altimeter

The routine ground processing of data from the NASA radar altimeter of TOPEX/POSEIDON includes instrument corrections for the effects of significant wave height and attitude angle changes on the altimeter's estimates of range, backscattered power, and significant wave height. This paper describes how these instrument corrections were generated and how they are applied. Detailed waveform fitting to telemetered waveform samples is used to assess the effectiveness of the corrections. There are several altimeter hardware‐caused small waveform departures from the model waveforms and these departures, designated waveform “features,” are described in detail. A consequence of the waveform features, and their positioning relationship to range rate, is that range data for ground tracks moving toward the equator may differ systematically by about a centimeter compared to range data for ground tracks moving away from the equator. The results and discussion are limited to side A of the redundant altimeter, as only side A has been operated on orbit.