Parametric fault diagnosis for electrohydraulic cylinder driveunits

A novel model-based methodology for fault diagnosis (FD) of nonlinear hydraulic drive systems is presented in this paper. Due to its linear dependence upon parameters, a second-truncated Volterra nonlinear model is first used to characterize such systems. The versatile order-recursive estimation scheme is employed to determine the values of parameters in the Volterra model. The scheme also avoids separate determination of the model order; thus, the complexity of the search process is reduced. Next, it is shown that the estimated parameters, representing different states of the system, normal as well as faulty conditions, can be used to detect and isolate system faults in a geometric domain. Very promising results are exhibited via simulations as well as laboratory experiments. It is concluded that the developed parametric FD technique has potential to provide efficient condition monitoring and/or preventive maintenance in hydraulic actuator circuits     

运动误差对双站SAR相位同步及成像的影响

收、发系统间的相位同步是双站合成孔径雷达的一项关键技术,采用锁相环接收机是实现双站SAR系统相位同步的一种可能方法.本文主要就锁相环接收机在运动误差条件下的相位同步问题进行了研究,并分析了锁相环相位误差对系统成像的影响,最后,给出了计算机仿真结果.     

网同步设备同步方式管理算法

针对专业通信网络的同步方式,提出了一种规划与调整网络中网同步设备同步方式的管理算法,并对其进行了仿真验证。文中提出了主从同步工作时时钟跟踪路经的择优原则以及对应算法,该算法可以用于同步管理方式的预先规划和运行中的调整。     

Modeling and identification of electrohydraulic servos

In general, design of adaptive controllers requires a proper model of the actual plant. This is normally done by considering a discrete-time linear model and estimating its unknown parameters, periodically. In this note, we discuss some practical issues concerning the identification of electrohydraulic actuators, using discrete-time linear models.     

Multi-cylinder electrohydraulic digital loading technology for reproduction of large load

To solve the problem of the control accuracy in electrohydraulic loading systems caused by load increment, this paper proposes a multi-cylinder electrohydraulic digital loading (MEDL) technology for accurate reproduction of large load. A traditionally used single cylinder loading (SCL) is replaced by a new hydraulic cylinders group that includes N hydraulic cylinders at each point, in which one is controlled by the electrohydraulic servo valve and the others (N-1) are controlled by the on-off valve. The areas of the on-off valve controlled (OVC) cylinders form an increasing geometric sequence with a common ratio of 2. In addition, the force of the servo valve controlled (SVC) cylinder can be regulated continuously, and the OVC cylinders have only two states of no force or maximum force. There should be no force tracking error caused by nonlinear factors for the OVC cylinders. Thus, a continuous accurate large loading can be achieved by changing the working area of the cylinders group. Moreover, an improved full closed-loop (FCL) control strategy is proposed to solve the load reverse sudden change caused by the asynchronous opening and closing of the servo valve and on-off valve. With a case of N = 4 for MEDL, AMESim simulation results illustrated that the tracking error of the 4-cylinder group was about 1/6 of the single cylinder under a case of 40 kN. Furthermore, extensive experiments conducted on a real full loading bench under the FCL control method indicated that compared with SCL, the tracking error of the 4-cylinder group with a multi-step signal and various-frequency sinusoidal signals were reduced by 73% and 46%, respectively. Both simulation and experimental results proved that the proposed MEDL technology improved the loading accuracy and optimized the dynamic performance of the system.     

控制网络的综合调度及其在双缸同步控制中的应用

为提高网络调度的工程可操作性,基于对传输任务与被控对象的分析提出一种不依赖于控制模型的综合调度方法.通过估计网络负载和引入频谱能量分析法粗拟出多个回路的采样周期范围,针对争用式网络协议采用非抢占RM算法进行带宽分配,采用带宽预留的概念全面考虑周期任务和猝发任务.最后以工程机械中常见的顶推系统双缸同步控制为例,对所提出的综合调度方法进行仿真研究,验证该方法的有效性.     

Design of a new high-performance electrohydraulic actuator

This paper describes the design and prototyping of a new high-performance actuation system that combines the benefits of conventional hydraulic systems and direct-drive electrical actuators, namely high torque/mass ratio and modularity. It is referred to as the electrohydraulic actuator (EHA) and results from the fusion of the above-mentioned technologies. The EHA is a unique device with its own characteristics and requires hydraulic components that are specifically tailored to its needs and requirements. Based on a mathematical model of the EHA, the requirements for its components are determined. These requirements are used as a basis for component selection, component modification, and design of a customized new symmetrical linear actuator. The analysis of the EHA presented is supported by experimental data and explains the extremely high level of performance attained by a prototype of the EHA     

DAB接收机RF模块灵敏度与同步速度优化方法的研究

对DAB接收机灵敏度与同步速度的电路优化主要通过对RF模块外围电路的优化来实现。在研究DAB接收机RF模块的中频反馈电路和DAB信号同步控制原理的基础上,研究了反馈电路的优化方法,分析了同步慢的原因,提出了解决方案。测试记录表明：增加一条快速泄放电路可改善同步速度,提高反馈电压增加下信号的增长率益。     

一种适用于BICM-ID系统的迭代载波同步算法

在比特交织编码调制迭代译码(BICM-ID)系统中,针对低信噪比条件下传统的同步算法对频偏和相差估计精度较低的问题,提出了一种码辅助的迭代载波同步算法。该算法基于最大期望(EM)算法,并在此基础上加以改进,利用译码器输出的软信息,迭代的在载波同步和译码之间相互交换信息,实现同步和译码的联合处理。仿真结果表明,在译码器收敛的允许范围之内,提出的算法能够大幅提高同步参数的估计精度,在迭代次数达到8次时,BICM-ID系统的误比特率性能基本接近理想同步条件下的译码性能。     

Multimedia synchronization protocols for broadband integratedservices

Protocols to provide synchronization of data elements with arbitrary temporal relationships of both stream and non-stream broadband traffic types are proposed. It is specified that the provision of a synchronization function be performed within a packet switched network, and, accordingly, a two-level communication architecture is presented. The lower level, called the network synchronization protocol (NSP), provides the ability to establish and maintain individual connections with specified synchronization characteristics. The upper level, the application synchronization protocol (ASP), supports an integrated synchronization service for multimedia applications. The ASP identifies the temporal relationships among an application's data objects and manages the synchronization of arriving data for playout. The proposed NSP and ASP are mapped to the session and application layers of the open-systems-interconnection (OSI) reference model, respectively     

Feedback frequency synchronization for OFDM applications

Maximum-likelihood estimation methods are often used to derive carrier frequency recovery schemes for digital receivers. Unfortunately, their rigorous application is generally hindered by analytical difficulties and, in consequence, some approximations must be made to achieve practical results. In this paper we concentrate on frequency recovery for orthogonal frequency division multiplexing signals. Following Daffara and Chouly (see Proc. ICC, p.766-71, June 1993), we derive a feedback synchronizer based on maximum-likelihood methods. Making different approximations, however, we come up with a scheme that is superior in terms of estimation accuracy. Comparisons are also made with other feedback schemes based on heuristic reasoning     

A frequency synchronization for TDMA system

A frequency synchronization algorithm utilizing the peak phase error detection and frequency offset smoother is proposed for burst data transmission. The basic idea of frequency offset estimator (FOE) is to use a curve fitting method. The proposed peak phase error detection avoids a large phase error giving a bad value for FOE. For the purpose of controlling the automatic frequency control (AFC), frequency offset smoother by a simple filter is used. Simulation results show that the proposed algorithm is adequate for frequency synchronization of burst data transmission     

Carrier phase synchronization for GMSK signals

Several carrier phase recovery schemes for Gaussian minimum shift keying (GMSK) modulated signals are derived and analysed in terms of squaring loss and acquisition time. Two bandwidths are considered for the GMSK signal: BT_b=0.5 and 0.25, following the recommendations of the Consultative Committee for Space Data Systems. Pre‐encoding is assumed to remove the inherent differential encoding of the GMSK modulations. The carrier phase recovery schemes are derived from the approximate expression of the GMSK signal as an OQPSK signal or as the superposition of two OQPSK signals maximum a posteriori/maximum likelihood phase estimation is considered, with perfect clock reference; both non‐data‐aided and decision–directed schemes are analysed. Moreover, in the case of GMSK with BT_b=0.25, an equalizer is also included in the synchronizer loop to remove inter‐symbol interference. High and low signal to noise ratio (SNR) approximations are considered to simplify the structure of the synchronizers. It is shown that, for the considered BT_b values, the complex synchronizers initially derived do not provide any improvements over their simplified versions; the introduction of the equalizer for GMSK with BT_b=0.25 leads to a better performance. Moreover, it is shown that GMSK with BT_b=0.5 has a better performance than unfiltered OQPSK, which is better than GMSK with BT_b=0.25. The SNR values above which the high SNR approximation turns out to be convenient with respect to the low SNR approximation are also given. Copyright © 2002 John Wiley & Sons, Ltd.     

Clock synchronization for wavelet-based multirate transmissions

This paper deals with symbol timing recovery for multirate transmission systems employing wavelets as signaling pulses either at baseband or with linear bandpass modulation. Our analysis is twofold. First, we investigate the impact of clock errors on the bit-error rate of the optimum receiver for a wavelet-based multirate signal. Second, we consider a nondata-aided maximum-likelihood clock synchronization scheme implemented as a multiple delay-locked loop. We derive a linearized loop model and assess its performance in terms of tracking jitter variance. The analytical results are contrasted with those obtained by simulation and with the relevant modified Cramer-Rao bound     

Soft-decision-based node synchronization for Viterbi decoders

Optimum decision methods are employed to discriminate between in-sync and out-of-sync operations in Viterbi decoders when the received data sequence is given in analog form (soft decisions). The exact solution to this discrimination problem, however, appears too complex in many practical cases. A suboptimum algorithm is then proposed that can be implemented as a hardware device, external to the decoder. This algorithm is recognized as a modified version of an earlier technique known as the “reencoding method”. Analysis and simulations indicate that the modification produces remarkably good results not only in comparison with the reencoding method but also with previous techniques discussed in literature     

Blind phase synchronization for VSB signals

Starting out with a strong justification for phase synchronization, we derive the symbol error probability for 8-vestigial sideband (VSB) in the presence of phase errors and compare it with the symbol error rates for 8-PAM and 64-QAM. Monte Carlo simulations support the theoretical expressions. Phase misadjustments lead to error floors, which are computed, and which further reveal the susceptibility of VSB signals to phase errors. Phase synchronizers can either work in a data-aided manner or blindly. We focus on the latter and show the relationship between phase synchronization and blind source separation (BSS). Finally, a method suitable for the phase synchronization of VSB signals as used by the ATSC DTV transmission system is presented and evaluated. Its performance is measured against that of the decision-directed approaches that have been suggested in the literature. Depending on the SNR of the VSB signal, either blind or decision-directed approaches exhibit superior performance. A semiblind method, which combines the advantages of the decision-directed and the blind mode in their respective SNR regions, is introduced and set in perspective with the other algorithms     

Two-dimensional synchronization patterns for minimum ambiguity

A number of closely related combinatorial problems corresponding to specific assumptions about the type of time-frequency sequence which may be appropriate in a particular application, are formulated in terms of square or rectangular arrays of dots with appropriate constraints on the two-dimensional correlation function. The current state of knowledge concerning each of these problems is summarized. It is hoped that more general constructions may be found, leading to larger families of solutions, as well as better computational algorithms for finding individual solutions which may lie outside of the general families.     

The conservative code for bit synchronization

A novel coding scheme for bit synchronization, the conservative code, is presented and analyzed. Each codeword is characterized by having a predefined number of transitions, with a known delimiting transition at the end, i.e. the number of transitions is conserved. As a result, it is possible to decode the incoming serial bit-stream without explicitly recovering the receiving clock with a phase-locked loop. Thus, it is possible to receive messages from asynchronous sources without any training period. This code can be extremely useful in communication over a passive optical star. In the analysis, the efficiency or capacity of the code is computed with two additional constraints: limited run-length and balancing. It is shown that this coding scheme is efficient when both constraints are applied. The objective of this analysis is to show that the additional constraints imposed on the encoding do not cause a significant reduction in its efficiency. The design of a serial electronic interface is described. Its goal is to maximize the interface bandwidth (greater than 1/Gb/s with GaAs technology), which is usually the bottleneck of an optical communication system. It is achieved by reducing the critical timing path to one flipflop and one NOR gate, and by having a hierarchical interface design     

Frequency synchronization for TD-LTE-A downlink receiver

A high accuracy frequency synchronization method is proposed for the 3rd generation partnership project (3GPP) long term evolution advanced (LTE-A) downlink receiver in time division duplexing (TDD) mo...     

Two-stage carrier synchronization techniques for nonselectivefading

Transmitted reference carrier synchronization techniques can potentially provide near-coherent performance in the presence of time-varying fading. Such techniques are spectrally not as efficient as nonreference-based architectures and can have performance several dB worse than ideal coherent in higher order modulations (e.g., 64-QAM). This paper presents a two-stage demodulator that facilitates improved spectral efficiency or provides better performance (or sometimes both). The two-stage architecture results from examining the optimal detector for M-QAM. The first stage produces tentative decisions and removes the modulation from the received signal. The second stage implements a smoothing filter for the resulting signal, providing an improved carrier estimate. Monte Carlo simulation results demonstrate the improved performance For 4-QAM, 16-QAM, and 64-QAM