Improving myoelectric pattern recognition robustness to electrode shift by changing interelectrode distance and electrode configuration

Pattern recognition of myoelectric signals for prosthesis control has been extensively studied in research settings and is close to clinical implementation. These systems are capable of intuitively controlling the next generation of dexterous prosthetic hands. However, pattern recognition systems perform poorly in the presence of electrode shift, defined as movement of surface electrodes with respect to the underlying muscles. This paper focused on investigating the optimal interelectrode distance, channel configuration, and electromyography feature sets for myoelectric pattern recognition in the presence of electrode shift. Increasing interelectrode distance from 2 to 4 cm improved pattern recognition system performance in terms of classification error and controllability (p < 0.01). Additionally, for a constant number of channels, an electrode configuration that included electrodes oriented both longitudinally and perpendicularly with respect to muscle fibers improved robustness in the presence of electrode shift (p < 0.05). We investigated the effect of the number of recording channels with and without electrode shift and found that four to six channels were sufficient for pattern recognition control. Finally, we investigated different feature sets for pattern recognition control using a linear discriminant analysis classifier and found that an autoregressive set significantly (p < 0.01) reduced sensitivity to electrode shift compared to a traditional time-domain feature set.     

Signal processing for the multistate myoelectric channel

In the multistate myoelectric channel, a single myoelectric signal source is used to control a multifunction powered prosthesis. The selection of a prosthesis function requires a receiver to process the myoelectric signal, contaminated with noise, and to decide on the basis of the received signals which function is desired. Thus the channnel cleady presents a problem of choice of receiver and of decision strategy. Previous sotutions to this problem have been basically empirical. In this paper we seek the optimum receiver where optimum is in the minimum probability of error sense. First a model is developed for the bipolar myoelectric signal to provide information about the relevant signal parameters and statistics. Using this information the Bayes minimum probability of error receiver is derived for an orbitrary signal parameter set. The optimum signal parameter set is then found for the Bayes receiver, and the receiver performance calculated. The receiver performance is measured and compared with the calculated performance. A significant performance improvement is seen in the optimum receiver over a more conventional receiver.     

Two-channel enhancement of a multifunction control system

The enhancement of an existing myoelectric control system has been investigated. The original one-channel system used an artificial neural network to classify myoelectric patterns. This research shows that a two-channel control system can improve the classification accuracy of the pattern classifier significantly, thus improving the reliability of the prosthesis     

A Procedure for Decomposing the Myoelectric Signal Into Its Constituent Action Potentials-Part II: Execution and Test for Accuracy

The scheme for decomposing a myoelectric signal into its constituent motor unit action potential trains described in the paper [3] requires interaction from the human operator. In this paper, guidelines to be employed by the operator in assisting the computerized algorithms in identifying (classifying) a motor unit action potential are presented. The accuracy of the decomposition scheme was evaluated by decomposing a mathematically synthesized myoelectric signal. This signal was constructed by linearly superimposing eight mathematically generated motor unit action potential trains along with Gaussian noise. A skilled operator was able to decompose this signal with an accuracy of 99.8 percent, incurring one error in a total of 435 classifications. The decomposition reproducibility was evaluated by having two experienced operators independently decompose the same record of empirically obtained myoelectric signal. Their results were in total agreement for 479 motor unit action potential classifications belonging to five motor unit action potential trains. Up to eight motor unit action potential trains have been decomposed from one myoelectric signal.     

协作通信网络中的合作编码技术

未来觅带无线通信系统要支持高达1 Gb／s的峰值无线传输速率,就必须考虑利用协作通信技术,充分复用频率、时间、空间等多维资源,改善网络覆盖性能。合作编码将协作信号处理和信道编码技术有机地结合在一起,是实现高性能合作通信的重要保障,合作编码将成为未来觅带无线通信技术的一项关键技术。合作编码技术必须适应节点的双工或半双工通信方式,采用适应不同的协同通信网络环境要求的合作编码技术方案。未来的合作编码技术的发展方向是自适应的合作编码技术和网络编码协作技术。     

A new strategy for multifunction myoelectric control

A novel approach to the control of a multifunction prosthesis based on the classification of myoelectric patterns is described. It is shown that the myoelectric signal exhibits a deterministic structure during the initial phase of a muscle contraction. Features are extracted from several time segments of the myoelectric signal to preserve pattern structure. These features are then classified using an artificial neural network. The control signals are derived from natural contraction patterns which can be produced reliably with little subject training. The new control scheme increases the number of functions which can be controlled by a single channel of myoelectric signal but does so in a way which does not increase the effort required by the amputee. Results are presented to support this approach     

Functional assessment of control systems for cybernetic elbowprostheses. II. Application of the technique

This paper (Part II of II) presents application of the technique described in Part I to functional assessment of two myoelectric elbow-prosthesis controllers: the controller implemented in the Boston Elbow, a state-of-the-art elbow prosthesis, and a proposed control scheme that, to a crude degree, mimics control of the intact elbow. Assessment of the controllers was achieved by evaluating an amputee subject's functional capability as he performed a constrained motion task with a prosthesis that implemented each control scheme. Evaluation of the amputee's capability was accomplished off line using sampled values of his myoelectric activity, his limb kinematics, and the interface forces at the constraint. Superior performance was observed with the proposed scheme. Namely, the subject exhibited better synergy among his elbow and shoulder muscles. Furthermore, when using the proposed controller, he exhibited some natural patterns of muscle coordination.     

Deterministic process‐based generative models for characterizing packet‐level bursty error sequences

Errors encountered in digital wireless channels are not independent but rather form bursts or clusters. Error models aim to investigate the statistical properties of bursty error sequences at either packet level or bit level. Packet‐level error models are crucial to the design and performance evaluation of high‐layer wireless communication protocols. This paper proposes a general design procedure for a packet‐level generative model based on a sampled deterministic process with a threshold detector and two parallel mappers. In order to assess the proposed method, target packet error sequences are derived by computer simulations of a coded enhanced general packet radio service system. The target error sequences are compared with the generated error sequences from the deterministic process‐based generative model using some widely used burst error statistics, such as error‐free run distribution, error‐free burst distribution, error burst distribution, error cluster distribution, gap distribution, block error probability distribution, block burst probability distribution, packet error correlation function, normalized covariance function, gap correlation function, and multigap distribution. The deterministic process‐based generative model is observed to outperform the widely used Markov models. Copyright © 2013 John Wiley & Sons, Ltd.     

Signal processing for proportional myoelectric control

Proportional myoelectric control of powered prostheses requires the estimation of a time-varying control signal from the patient's myoelectric signal. Since the myoelectric signal is a zero-mean stochastic process, a nonlinearity is a necessary element of the estimator. Typically, a full-wave rectifier is used for this nonlinearity, followed by a low-pass filter to complete the estimation of the control signal. In this work, it is proposed to use a logarithmic nonlinearity, followed by a linear minimum mean-square error estimator. The logarithmic nonlinearity maps the myoelectric signal into an additive control signal-plus-noise domain in which the Kalman filter is employed to estimate the control signal. The theoretical performance of this estimator is obtained and verified by experiments.     

无人作战飞机任务系统技术研究

先进的任务系统是UCAV执行作战任务的核心。本文从功能层、物理层和技术实现层三个层面论述了UCAV任务系统方案：在功能层上,该方案采用操控／自主攻击方式,既可由地面控制站操作员操纵,执行作战任务,也可由UCAV任务系统对目标进行自动识别、威胁判断、攻击排序及火力分配,自主完成攻击及对威胁的规避任务;或者由操作员指定攻击目标后,任务系统自动规划飞行轨迹和飞行操作指令,由飞控系统控制UCAV自主飞行到最佳攻击区域完成对目标的攻击。在物理层上,任务系统由机载任务系统、地面控制站两大部分组成。在技术实现层上,涉及的关键技术主要有任务规划技术、传感器数据处理与信息融合技术、传感器管理技术、态势评估与战术决策技术、自主攻击技术等。     

基于自适应学习的多传感器融合时间管理

由于多传感器测量不同步,需要将各传感器时间校准到融合时间;以往采用的时间管理方法应用条件有限,且带入了较大的校准误差;为了减小校准误差,在内插和外推预测算法的基础上,引入自适应学习控制算子,利用学习算子的适应性能力调节估计参数;并利用时间序列预报,将内插和外推两个相反方向的估计值进行加权,进一步减小校准误差.最后以目标位置测量为例,对该方法进行仿真验证.     

基于水平集算法后向散射的运动目标轮廓提取

基于距离选通的激光主动成像系统在大气条件下对运动目标成像时,为了在更大范围内搜索跟踪目标,距离选通初始门宽通常在微秒量级,进而引起后向散射,严重影响了系统对目标的识别与提取。文中首先分析了基于距离选通的激光主动成像系统,在此基础上引入距离信息实时跟踪运动目标,研究了不同选通门宽引起的后向散射对图像质量的影响,提出了一种基于Sobel 算子和 GAC 模型的目标轮廓提取算法,将 Sobel 边缘检测的结果引入水平集边界停止函数,为水平集的曲线演化提供参考依据。实验结果表明,提出的水平集算法能够克服严重后向散射干扰影响提取目标轮廓,目标提取精度在0.9以上,高于 GAC、LIF、LBF 等经典水平集算法。     

Safety and reliability of synchronizable digital coding in railwaytrack-circuits

The incorporation of digital error-control coding into railway track circuits represents a new approach for track-train data transmission for automatic train control. Methods based on error probability analysis are presented for assessing the safety and reliability of synchronizable error control coding in this application. The results for a sample coding scheme have been verified by experimentation using a calibrated source injecting audio-frequency Gaussian noise into a practical track circuit. Safety and reliability must be traded off, although the safety can be increased by incorporating dictionary checking in the code-receiver algorithm and the reliability can be enhanced by allowing single synchronization error correction. The technique demonstrates the possibility of designing a track-circuit data transmission system to given target safety and reliability levels of the same order of magnitude as the known failure rates of existing equipment     

TD-SCDMA中基于信息融合技术的外环功率控制算法

An outer loop power control algorithm based on triangle norm (t norm) information fusion technology is proposed in this paper. According to the difference between block error rate and bit error rate with target values, the membership function calculation and level dividing of the two differences are dealt with. And then t norm operator is used to fuse the two membership function values to determine the adjustment step size. The algorithm can acquire the optimal adjustment step size in the light of the channel status and avoid the overshoot phenomenon of the existing outer power control methods. As a result, the block error rate can converge to the target value quickly. Experiment results verify the excellent property of the algorithm.     

Vibrotactile Guidance Cues for Target Acquisition

Three experiments examined the use of vibrotactile cues to guide an operator toward a target. Vibrotactile stimulation on the hand can provide spatially stabilizing cues for feedback of subtle changes in position. When such feedback is present, a deviation from the point of origin results in tactile stimulation indicating the direction and magnitude of the positional error. Likewise, spatial deviation from a desired position displayed tactually can provide robust position guidance and stabilization sufficient to improve the acquisition time and accuracy of fine cursor control. A major advantage of this mode of information representation is that it can be present at the same time as visual cues with minimal cross-modal interference. Our findings suggest that performance is actually enhanced when both tactile and visual cues are present. Although previous studies have suggested that various forms of tactile feedback can provide position guidance and stabilization, to our knowledge, this work is the first that details the effect of tactile feedback on target acquisition directly.     

Quantification of Man-Machine System Reliability in Process Control

Application of reliability engineering to process plant design, operation and control has led to a demand for estimates of `human reliability,' or `human error.' However, it is desirable to treat the concept of `human error' with caution and to avoid an approach in which the operator appears to be held solely responsible or even blamed; in reality the error arises out of a quite specific combination of conditions in the man-machine system and it is on the total system that attention should be centered. Problems such as performance of discrete tasks and vigilance tasks or behavior in emergencies have been widely studied. While some of this work appears applicable to process control, there remain significant gaps. A more comprehensive taxonomy of process operator error seems to be needed. Systems exist for reporting incidents in process plants, each with a particular objective such as improvement of personal safety, estimation of insurance rates, or reduction of maintenance costs. Data produced are specialized and often useless for other purposes. In particular, it is difficult to abstract data on malfunction involving the operator. A taxonomy suitable for process control is suggested and a scheme for collection of data on reliability in process plants is outlined. Attention is drawn to the relevance of the process and control system characteristics and to their variability. The importance of the process computer is emphasized, both in its impact on the control system and as a research tool.     

差错控制编码差分酉空时调制系统迭代检测法

针对采用差错控制编码的差分酉空时调制系统,在平坦及频率选择性衰落瑞利信道下提出了一种迭代检测法。差分酉空时调制可视为递归卷积码,使用差错控制编码后的差分酉空时调制可视为一种串行级联码。提出了一种差分酉空时调制的软输出后验概率译码器以及迭代检测法,以获得附加的编码增益。仿真结果表明,在平坦及频率选择性衰落瑞利信道下,所提方案均可得到优异的系统性能。     

基于极化码的无线光通信副载波误码性能分析

提出了一种基于极化码的无线光信道副载波调制方法,给出了极化编译码的具体算法过程,并将其应用于无线光通信系统。在不同大气湍流强度下,对系统的差错性能进行了仿真分析,其重对基于极化码的二相相移键控和四相相移键控两种调制方法的误码率进行了对比,结果表明,采用极化码的副载波二相相移键控调制系统的性能优于四相相移键控系统。最后,实验比较分析了极化编码前后副载波调制系统的误比特率,结果表明,在无线光通信大气湍流信道模型下,采用副载波极化码编码调制技术可使误码率性能改善一个量级。     

Selective classification for improved robustness of myoelectric control under nonideal conditions

Recent literature in pattern recognition-based myoelectric control has highlighted a disparity between classification accuracy and the usability of upper limb prostheses. This paper suggests that the conventionally defined classification accuracy may be idealistic and may not reflect true clinical performance. Herein, a novel myoelectric control system based on a selective multiclass one-versus-one classification scheme, capable of rejecting unknown data patterns, is introduced. This scheme is shown to outperform nine other popular classifiers when compared using conventional classification accuracy as well as a form of leave-one-out analysis that may be more representative of real prosthetic use. Additionally, the classification scheme allows for real-time, independent adjustment of individual class-pair boundaries making it flexible and intuitive for clinical use.