Impedance control of multi-arm space robot for the capture of non-cooperative targets

Robotic systems are expected to play an increasingly important role in future space activities. The robotic on-orbital service, whose key is the capturing technology, becomes a research hot spot in recent years. This paper studies the dynamics modeling and impedance control of a multi-arm free-flying space robotic system capturing a non-cooperative target. Firstly, a control-oriented dynamics model is essential in control algorithm design and code realization. Unlike a numerical algorithm, an analytical approach is suggested. Using a general and a quasi-coordinate Lagrangian formulation, the kinematics and dynamics equations are derived.Then, an impedance control algorithm is developed which allows coordinated control of the multiple manipulators to capture a target.Through enforcing a reference impedance, end-effectors behave like a mass-damper-spring system fixed in inertial space in reaction to any contact force between the capture hands and the target. Meanwhile, the position and the attitude of the base are maintained stably by using gas jet thrusters to work against the manipulators' reaction. Finally, a simulation by using a space robot with two manipulators and a free-floating non-cooperative target is illustrated to verify the effectiveness of the proposed method.

Output Feedback Control of Discrete-Time T-S Fuzzy Affine Systems Using Quantized Measurements

This paper investigates the problem of robust H!fixed-order dynamic output feedback( DOF)controller design for a class of Takagi-Sugeno( T-S) fuzzy affine systems using quantized measurements.Through a state-input augmentation method,some sufficient conditions for controller synthesis are developed based upon piecewise quadratic Lyapunov functions( PQLFs) in terms of LMIs. Two illustrative studies are conducted to verify the effectiveness of the proposed controller synthesis approach.

Reference tracking control for flexible air-breathing hypersonic vehicle with actuator delay and uncertainty

This paper considers the problem of reference tracking control for the flexible air-breathing hypersonic flight vehicle with actuator delay and uncertainty.By constructing the Lyapunov functional including the lower and upper bounds of the time-varying delay,the non-fragile controller is designed such that the resulting closed-loop system is asymptotically stable and satisfies a prescribed performance cost index.The simulation results are given to show the effectiveness of the proposed control method,which is validated by excellent output reference altitude and velocity tracking performance.

Propagation effects of low frequency electromagnetic waves in production well

The frequency domain electromagnetic method has already been widely used for tomographic imaging or electromagnetic well logging. However, different from open hole logging, the metal casing existing in production well logging has a strong shielding effect on the electromagnetic waves, thus bringing some difficulties to the application of the frequency domain electromagnetic method in production well logging. According to the relation of the field source geometry to the ring around the mandrel, the general expressions of frequency domain electromagnetic responses in axially symmetrical layered conductive medium are deduced. The propagation effects caused by the low-frequency electromagnetic waves in cased hole are also analyzed. The distribution curves of eddy current density and magnetic flux density along the radial direction in the mandrel indicate that the eddy loss within the mandrel is proportional to the transmission signal frequency and the mandrel conductivity. The secondary field responses of different casing materials show that the transmission frequency has an important effect on the ability of electromagnetic waves penetrating the metal casing. The transmission frequency should be ultra-low in order to enable the electromagnetic signal to penetrate the casing easily. The numerical results of frequency responses for different casing physical parameters show that the casing thickness has a significant impact on the choice of the transmission frequency. It is also found that the effect of the casing radius on the transmission frequency can be neglected.

Comparative Study on the Infrared Radiance Field of Building Surface under Sunshine Conditions and Rainfall Conditions

The Monte Carlo method and the region method are combined in this paper,where a high-rise building in Harbin were taken for example to investigate the infrared radiation field of building surface.The calculation models of temperature field and radiation transfer coefficient on the exterior surface were established.Through the self-built Bidirectional Reflectance Distribution Function(BRDF)experimental device,the BRDFs of moorstone,aluminum plate,coated glass and Ethylene-Propylene-Diene Monomer(EPDM)on the surfaces under dry and wet conditions were measured at different incidence angles with respective laser wavelengths of0.6328μm and 1.34μm.For the two wavelengths,the reflection ratios of the material surfaces under dry and wet conditions were calculated respectively.Based on some proper simplifications of the background condition,the simulation analysis of the radiation field of building surface was carried out according to the wetness theory and the measured data.Taking the situation at 9:00 a.m.on the day of summer solstice as an example,this paper made relevant quantitative calculation for the solar radiation,the self radiation of the surface units,the radiating projection between the surface units,and the general infrared radiation of the building surface.Comparisons on infrared radiance field of the building surface were obtained under cloud-free sunshine conditions and rainfall conditions respectively,and the rationality of the results was discussed.

Noise-assisted MEMD based relevant IMFs identification and EEG classification

Noise-assisted multivariate empirical mode decomposition(NA-MEMD) is suitable to analyze multichannel electroencephalography(EEG) signals of non-stationarity and non-linearity natures due to the fact that it can provide a highly localized time-frequency representation.For a finite set of multivariate intrinsic mode functions(IMFs) decomposed by NA-MEMD,it still raises the question on how to identify IMFs that contain the information of inertest in an efficient way,and conventional approaches address it by use of prior knowledge.In this work,a novel identification method of relevant IMFs without prior information was proposed based on NA-MEMD and Jensen-Shannon distance(JSD) measure.A criterion of effective factor based on JSD was applied to select significant IMF scales.At each decomposition scale,three kinds of JSDs associated with the effective factor were evaluated:between IMF components from data and themselves,between IMF components from noise and themselves,and between IMF components from data and noise.The efficacy of the proposed method has been demonstrated by both computer simulations and motor imagery EEG data from BCI competition IV datasets.

Fast Algorithm for Nonsubsampled Contourlet Transform

多尺度的几何分析(MGA ) 为图象处理作为有效策略被认出了。作为 MGA 的分离工具之一， nonsubsampled contourlet 变换(NSCT ) 广泛地被使用了图象降噪，图象熔化，图象改进，特征抽取等等。然而，处理表演由于它的高冗余性被限制，并且导致集中的计算效率。因此，它的快算法在实践被需要。在这份报纸，我们采用一个优化方向性的过滤器银行(DFB ) 并且把它嵌进 NSCT 当使重建的表演的损失细微时，显著地加速计算速度。试验性的结果证明重建的图象质量能满足人的视觉系统。而且，改进 NSCT 有速度关于若干次比传统的的。图象降噪上的试验性的结果也验证建议方法的可行性和效率。

Deep Learning Based Data Fusion for Sensor Fault Diagnosis and Tolerance in Autonomous Vehicles

Environmental perception is one of the key technologies to realize autonomous vehicles.Autonomous vehicles are often equipped with multiple sensors to form a multi-source environmental perception system.Those sensors are very sensitive to light or background conditions,which will introduce a variety of global and local fault signals that bring great safety risks to autonomous driving system during long-term running.In this paper,a real-time data fusion network with fault diagnosis and fault tolerance mechanism is designed.By introducing prior features to realize the lightweight network,the features of the input data can be extracted in real time.A new sensor reliability evaluation method is proposed by calculating the global and local confidence of sensors.Through the temporal and spatial correlation between sensor data,the sensor redundancy is utilized to diagnose the local and global confidence level of sensor data in real time,eliminate the fault data,and ensure the accuracy and reliability of data fusion.Experiments show that the network achieves state-of-the-art results in speed and accuracy,and can accurately detect the location of the target when some sensors are out of focus or out of order.The fusion framework proposed in this paper is proved to be effective for intelligent vehicles in terms of real-time performance and reliability.

Non-fragile control of fuzzy affine dynamic systems via piecewise Lyapunov functions

This paper addresses the robust static out- put feedback （SOF） controller design problem for a class of uncertain fuzzy affine systems that are robust against both the plant parameter perturbations and controller gain variations. More specifically, the purpose is to synthesize a non-fragile piecewise affine SOF controller guaranteeing the stability of the resulting closed-loop fuzzy affine dynamic system with certain performance index. Based on piecewise quadratic Lyapunov functions and applying some convexification pro- cedures, two different approaches are proposed to solve the robust and non-fragile piecewise affine SOF controller syn- thesis problem. It is shown that the piecewise affine controller gains can be obtained by solving a set of linear matrix in- equalities （LMIs）. Finally, simulation examples are given to illustrate the effectiveness of the proposed methods.

Novel video coding algorithmbased on 3D-binDCT

In this paper we propose a three dimensional multiplierless discrete cosine transform(DCT) with lifting scheme called 3D-binDCT.Based on 3D-binDCT,a novel video coding algorithm without motion estimation/compensation is proposed.It uses the 3D-binDCT to exploit spatial or temporal redundancy.The computation of binDCT only needs shift and addition operations,thus the computational complexity is minimized.DC coefficient prediction,modified scan mode and arithmetic coding techniques are also adopted.Extensive simulation results show that the proposed coding scheme provides higher coding efficiency and improves visual quality, and it is easy to be realized by software and hardware.

A Low Power/Area Digital FIR Filter Design Based on PRF Framework

A novel DSP to ASIC (Application Specific Integrated Circuit) architecture design methodology is presented in this paper for reducing power/area consumption. Traditional methods always focus on optimizing hardware structure or algorithm separately. The authors propose a new method called PRF (Paralleling Reducing Folding) framework to combine hardware optimization with algorithm simplification. In the first step, paralleling, unfolding technology is applied to divide one data path into several channels and expose the redundancy of the algorithm. In the second step, reducing, decoupling theory is used to reduce computational complexity. In the last step, folding, time multiplexing method is used to merge similar components. As an exoteric methodology framework, many optimization methods can be integrated into the PRF framework. To optimize a 3N taps FIR (Fincte Impact Response) and obtain a content result, PRF methodology framework is applied.

Controller Optimization for Multirate Systems Based on Reinforcement Learning

The goal of this paper is to design a model-free optimal controller for the multirate system based on reinforcement learning.Sampled-data control systems are widely used in the industrial production process and multirate sampling has attracted much attention in the study of the sampled-data control theory.In this paper,we assume the sampling periods for state variables are different from periods for system inputs.Under this condition,we can obtain an equivalent discrete-time system using the lifting technique.Then,we provide an algorithm to solve the linear quadratic regulator(LQR)control problem of multirate systems with the utilization of matrix substitutions.Based on a reinforcement learning method,we use online policy iteration and off-policy algorithms to optimize the controller for multirate systems.By using the least squares method,we convert the off-policy algorithm into a model-free reinforcement learning algorithm,which only requires the input and output data of the system.Finally,we use an example to illustrate the applicability and efficiency of the model-free algorithm above mentioned.

Non-fragile Observer Design for Fractional-order One-sided Lipschitz Nonlinear Systems

This paper is concerned with the problem of the full-order observer design for a class of fractional-order Lipschitz nonlinear systems. By introducing a continuous frequency distributed equivalent model and using an indirect Lyapunov approach, the sufficient condition for asymptotic stability of the full-order observer error dynamic system is presented. The stability condition is obtained in terms of LMI, which is less conservative than the existing one. A numerical example demonstrates the validity of this approach.

Rotation,scaling and translation invariant image watermarking using feature points

In this article, a novel robust image watermarking scheme is presented to resist rotation, scaling, and translation （RST）. Initially, the original image is scale normalized, and the feature points are then extracted. Furthermore, the locally most stable feature points are used to generate several nonoverlapped circular regions. These regions are then rotation normalized to generate the invariant regions. Watermark embedding and extraction are implemented in the invariant regions in discrete cosine transform domain. In the decoder, the watermark can be extracted without the original image. Simulation results show that the proposed scheme is robust to traditional signal processing attacks, RST attacks, as well as some combined attacks.

Event-triggered state estimation for T-S fuzzy affine systems based on piecewise Lyapunov-Krasovskii functionals

This paper investigates the problem of event-triggered H∞state estimation for Takagi-Sugeno (T-S) fuzzy affine systems. The objective is to design an event-triggered scheme and an observer such that the resulting estimation error system is asymptotically stable with a prescribed H∞performance and at the same time unnecessary output measurement transmission can be reduced. First, an event-triggered scheme is proposed to determine whether the sampled measurements should be transmitted or not. The output measurements, which trigger the condition, are supposed to suffer a network-induced time-varying and bounded delay before arriving at the observer. Then, by adopting the input delay method, the estimation error system can be reformulated as a piecewise delay system. Based on the piecewise Lyapunov-Krasovskii functional and the Finsler's lemma, the event-triggered H∞observer design method is developed. Moreover, an algorithm is proposed to co-design the observer gains and the event-triggering parameters to guarantee that the estimation error system is asymptotically stable with a given disturbance attenuation level and the signal transmission rate is reduced as much as possible. Simulation studies are given to show the effectiveness of the proposed method.

Synchronising second-order multi-agent systems under dynamic topology via reference model-based algorithm

This paper revisits the synchronisation problem for second-order multi-agent systems(MASs)under dynamically changing communication topology.By employing the reference model-based synchronisation algorithm,it is finally shown that synchronisation for both the position and velocity states can be achieved if the union of the communication topologies has a directed spanning tree frequently enough.This extends the existing results obtained for second-order MASs which exploits mild communication topology condition guaranteeing the synchronisation to a more general case.Convergence analysis is successfully performed by exploiting the product properties of row-stochastic matrices,which can also provide us with an estimate the convergence rate towards the synchronisation.