Search

In response to the problems of difficult identification of degradation stage start points and inadequate extraction of degradation features in the current rolling bearing remaining life prediction method, a rolling bearing remaining life prediction method based on multi-scale feature extraction and attention mechanism is proposed. Firstly, this paper takes the normalized bearing vibration signal as input and adopts a quadratic function as the RUL prediction label, avoiding identifying the degradation stage start point. Secondly, the spatial and temporal features of the bearing vibration signal are extracted using the dilated convolutional neural network and LSTM network, respectively, and the channel attention mechanism is used to assign weights to each degradation feature to effectively use multi-scale information. Finally, the mapping of bearing degradation features to remaining life labels is achieved through a fully connected layer for the RUL prediction of bearings. The proposed method is validated using the PHM 2012 Challenge bearing dataset, and the experimental results show that the predictive performance of the proposed method is superior to that of other RUL prediction methods.

This paper presents an improved adaptive sliding mode control method for soft Landing on the Asteroid, and addresses the problems of the unknown parameter of the upper bound of interference uncertainty and over-adaptation of switching gain. First, a three-dimensional dynamic model of asteroid probe, in which considering the interference uncertainty of the third-body gravitational perturbation and radiation pressure from the sun, is established in the fixed-body coordinate system. Second, an adaptive scheme is designed based on the degree of the system status deviating from the sliding surface to estimate the unknown parameter of the upper bound of system uncertainty, and the estimate value is used as the switch gain of sliding mode control to reduce the effects of uncertain dynamics. Besides, a monotone decreasing function is introduced in the sliding mode function to suppress the over-estimated value of the model-free interference which is resulted by system initial error. The stability of the closed-loop system is proved by using the Lyapunov theory. Finally, the simulation results of landing on the Eros are represented to illustrate the effectiveness of the proposed method.

Flexible double inverted pendulum system is a higher order, nonlinear and strong coupling unstable system. In order to achieve the steady control of the pendulum, an improved method of sliding mode control with boundary layer is put forward. Linear feedback is replaced with nonlinear feedback within the boundary layer. A mathematical model of flexible double inverted pendulum which is based on mechanism modeling method is established. Then the sliding mode controller is designed. The system has good stability control and robustness. The simulation results show that, the improved method not only realizes stable control of inverted pendulum but also ensures the system states reach sliding surface in a limited time. The robustness is stronger than the conventional boundary layer method.

An asteroid landing trajectory optimization method is studied based on Gauss Pseudo-spectral. Firstly, we analyze the characteristics of probe landing on asteroid, and put forward the initial conditions, process constraints, terminal constraints and the optimization performance index. The probe's landing trajectory optimization should meet the index. Secondly, Gauss Pseudo-spectral Method is used to disperse the optimal control problem into a nonlinear programming problem. Finally, SQP algorithm solves the nonlinear programming problem. We present the landing trajectory from the hover point to just a fix-point with leveled thrust. Simulation results show that the methodology proposed in this paper has good robustness and convergence.

At present, micrometer is used for measure the shape edge of automobile airbag. There are some shortcomings in this method. The number of test points is limited. Test data is not comprehensive. Detection speed is slow and a fixture can only test a kind of airbag. The method of airbag shape edge detection based on image processing is researched in this paper. The image of airbag is collected by CCD, and then it is sent to the computer to be processed and segmented. The edge of image is extracted through Canny edge detection algorithm in order to acquire shape edge of airbag in this paper, and the image similarity degree are calculated to provide the information of matching in the template matching process. Finally the comprehensive test shape edge of airbag is realized. The experimental results show that the detection method is effective feasible, intuitive and clear.

In this paper, an exact dynamic model of manipulator handling a flexible payload is derived by Hamiton's principle. On the basis of the distributed parameter model, a position controller is designed by using Lyapunov function related to the total energy of the system. The controller can achieve the given desired link angles and suppress the vibrations of flexible payload. Using the LaSalle's invariance principle and the characteristic of the differential operator, the asymptotic stability in the neighbor-hood of the desired states of the closed-loop system is proved. The effectiveness of the control strategy proposed is supported by some simulations.

The trajectory tracking control problem of the uncertain mobile robot with nonholonomic constraints is analyzed. Sliding mode control is presented based on the kinematics models analysis. Switching function of sliding model control is designed according to back-stepping method. Trending law control is selected to improve the system dynamic performance. In order to solve the constant speed problem caused by conventional trending law control, fuzzy control is used to adjust trending speed in the real time. The simulation results demonstrate that the fuzzy sliding mode controller improves the rapidity of trajectory tracking, and reduces the tracking error and the chattering of the control output.

In order to reduce the influence of azimuth effect in multi-position strap-down north seeking system, its cause of formation is studied based on the precession principle of the dynamically tuned gyro. A detecting system, composed by true north prism, two Leica theodolites and benchmark prism fixed in the strap-down north seeking system, was designed to calibrate the azimuth effect. By two steps, many measurements are gone on in every position to eliminate the random error. According to the homologous between the error and the position, a sinusoid is made a fit as compensate curve after the error of twelve positions is measured. Then the azimuth effect of the arbitrary position can be corrected by the curve. The experiment result shows that the seeking north standard deviation is only 11.77" after compensation, which is considerably less than the 87.75" without correction.

Space-based laser communication (LASERCOM) requires precision tracking and pointing in the microradian range. However, the angular vibrations of a satellite platform may be of the magnitude of milliradian and the frequency of 100 Hz or higher. For rejection of the platform vibrations there are two ways: line-of-sight stabilization technology or a fine steering mirror (control system with high closed-loop bandwidth. The former is much more complex in structure and difficult in implement than the latter. So, the latter is always adopted in actual space optical communication engineering. This paper describes a linear quadratic (LQ) optimal controller based on modern control theory for FSM system. Compared with classical controller, the proposed LQ has several advantages: (1) the LQ controller widens the system's closed loop bandwidth; (2) the large improvement in the system dynamic performance; (3) the significant improvement of the system rejection capability on high frequencies disturbance. The FSM system with the LQ controller have been designed and tested. The results confirm the advantages of the LQ controller above and show that it is an efficient control approach for FSM system in LASERCOM.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.