Improving EMG-based muscle force estimation by using a high-density EMG grid and principal component analysis

The accuracy of predictions of muscle force based on electromyography (EMG) is an important issue in biomechanics and kinesiology. Since human skeletal muscles show a high diversity and heterogeneity in their fiber architecture, it is difficult to properly align electrodes to the muscle fiber direction. Against this background, we analyzed the effect of different bipolar configuration directions on EMG-based force estimation. In addition, we investigated whether principal component analysis (PCA) can improve this estimation. High-density surface-EMG from the triceps brachii muscle and the extension force of the elbow were measured in 11 subjects. The root mean square difference (RMSD) between predicted and measured force was determined. We found the best bipolar configuration direction to cause a 13% lower RMSD relative to the worst direction. Optimal results were obtained with electrodes aligned with the expected main muscle fiber direction. We found that PCA reduced RMSD by about 40% compared to conventional bipolar electrodes and by about 12% compared to optimally aligned multiple bipolar electrodes. Thus, PCA contributes to the accuracy of EMG-based estimation of muscle force when using a high-density EMG grid.     

Use of extra degrees of freedom in multilevel drives

Multilevel converters with series connection of semiconductors allow power electronics to reach medium voltages (1-10 kV) with relatively standard components. The increase of the number of semiconductors provides extra degrees of freedom, which can be used to improve different characteristics. This paper is focused on variable-speed drives and it is shown that with the proposed multilevel direct torque control strategy (DiCoIF) the tradeoff between the performances of the drive (harmonic distortions, torque dynamics, voltage step gradients, etc.) and the switching frequency of the semiconductors is improved. Then, a slightly modified strategy reducing common-mode voltage and bearing currents is presented.     

Estimating effective degrees of freedom in motor systems.

Studies of the degrees of freedom and "synergies" in musculoskeletal systems rely critically on algorithms to estimate the "dimension" of kinematic or neural data. Linear algorithms such as principal component analysis (PCA) are the most popular. However, many biological data (or realistic experimental data) may be better represented by nonlinear sets than linear subspaces. We evaluate the performance of PCA and compare it to two nonlinear algorithms [Isomap and our novel pointwise dimension estimation (PD-E)] using synthetic and motion capture data from a robotic arm with known kinematic dimensions, as well as motion capture data from human hands. We find that PCA can lead to more accurate dimension estimates when considering additional properties of the PCA residuals, instead of the dominant method of using a threshold of variance captured. In contrast to the single integer dimension estimates of PCA and Isomap, PD-E provides a distribution and range of estimates of fractal dimension that identify the heterogeneous geometric structure in the experimental data. A strength of the PD-E method is that it associates a distribution of dimensions to the data. Since there is no a priori reason to assume that the sets of interest have a single dimension, these distributions incorporate more information than a single summary statistic. Our preliminary findings suggest that fewer than ten DOFs are involved in some hand motion tasks. Contrary to common opinion regarding fractal dimension methods, PD-E yielded reasonable results with reasonable amounts of data. Given the complex nature of experimental and biological data, we conclude that it is necessary and feasible to complement PCA with methods that take into consideration the nonlinear properties of biological systems for a more robust estimation of their DOFs.     

On the degrees of freedom of scattered fields

Starting from the observation that fields differing less than a prescribed error cannot be resolved as distinct entities, the degrees of freedom of the scattered field are introduced and then computed. The degrees of freedom are shown to be practically equal to the Nyquist number appropriate to the effective (spatial) bandwidth of the scattered field and to the extension of the observation domain. Accordingly, a finite number of elements of information can be used to determine the scattered field to a prescribed approximation error. It is also shown that the field representation can be made in terms of field values and simple sampling functions, provided that a marginal increase in the approximation error is tolerated. The results not only completely justify the use of sampling interpolation for representing scattering fields, but also demonstrate that such representation is practically an optimal one. An algorithm for the reconstruction of scattered fields, given the maximum allowed error, is then produced     

Three-dimensional input device with six degrees of freedom

Commodity priced PCs now come with powerful three-dimensional (3D) graphic capabilities that allow new applications to incorporate 3D interactivity. But, there are few low cost 3D input devices available for the desktop non-immersive virtual reality (VR) applications. Interactive systems that use a 3D world should ideally be complimented with a 3D input device. Such devices have previously been built mainly for immersive virtual reality systems and are not well suited for desktop systems. They are also expensive. Our device is intended to provide a low cost, intuitive full 3D input with six degrees of freedom. As well, it was to be used with the non-dominant hand, freeing the other hand for finer-motor skills to use a conventional mouse or the keyboard. We have built a prototype device that was inspired by the mechanics of the gimbal mount for a gyroscope. We used a field programmable gate array (FPGA) to provide rapid prototyping of the electronics from the sensors to the computer. Initial evaluation shows promise but also some problems together with suggestions for improvements.     

同时测量物体六自由度的方法

对目前国内外发展的同时测量物体六自由度的方法进行了较为详细的介绍,并给出了每种测量原理和发展现状,比较了各种方法的优缺点,讨论了其发展趋势。     

Fractional order multifunction filter with 3 degrees of freedom

In this paper the design procedure and performance of the third order multifunction filter based on Current Differencing Buffered Amplifier (CDBA) using Fractional Elements of Different Order (FOE) is presented. Three fractional elements of different order α, β, γ are used and peak value frequencies and cut-off frequencies are computed for the multifunction filter from the fractional order transfer function. The frequency response of the filters is obtained using FOMCON toolbox of MATLAB and also with PSPICE using fractional order elements. Stability and sensitivity analysis are also examined. The Power dissipation, Total Harmonic Distortion (THD), and Noise Analysis demonstrate a very good agreement between the theoretical and simulation results. It is also observed from the simulations that the CDBA based third order multifunction filter in fractional domain is suitable for integrated circuits.     

四自由度模块化机械臂运动学建模

首先根据四自由度(MT-R)模块化机械臂的结构特点和运动学约束,利用D-H算法对机械臂进行表示和建模,得到了以关节角度为变量的正运动学模型。利用矩阵逆乘的解析法求解机械臂逆运动学的完整解析解;最后通过仿真和实验验证了正运动学模型及运动学逆解的正确性。验证结果为机械臂末端执行器的精确定位和轨迹规划提供了理论依据。     

多天线认知网络自由度的上界及实现方法

认知无线电技术源于频谱资源的短缺,并极大提高了无线通信网络的频谱效率。针对经典的多天线认知网络的容量上界问题,从自由度角度出发,提出了新的自由度上界,并设计实现方法达到这一上界。该方法基于干扰对齐方法,通过主用户对认知用户采取主动频谱共享实现了认知网络自由度上界的提高。结果表明,利用新的方法,自由度上界远远优于之前的研究。     

汽车驾驶模拟器二自由度运动系统

为汽车驾驶模拟器设计了一种二自由度运动系统。该系统采用电动驱动方式,提供仰俯、侧倾两个自由度运动。介绍了该系统软、硬件结构和相关控制算法。其中硬件系统由运动平台和电控系统构成,执行机构采用伺服电机及电动缸。软件系统将汽车运行参数解算成电动缸的控制参数,控制电动缸完成运动控制。平台可以实现汽车运行过程中的大部分体感模拟。     

Decomposition of intramuscular EMG signals using a heuristic fuzzy expert system

Although increasingly sophisticated algorithms have been proposed to decompose intramuscular electromyography signals into the concurrent activities of individual motor units (MUs), the human operator is still able to improve decomposition results by visual inspection. The rationale for this paper was to combine components from previous decomposition procedures in an expert systems approach utilizing fuzzy logic and attempting to replicate the thought process of an accomplished decomposer in order to minimize the user interaction subsequently needed to enhance decomposition results. The decomposition procedure is discussed and examples are given of the type of information it can yield. The method has been used to identify the discharge activities of up to 15 MUs with up to 95$%$ accuracy.      

Quasi-multi-pulse voltage source converter design with two control degrees of freedom

In this article, the design details of a quasi-multi-pulse voltage source converter (VSC) switched at line frequency of 50 Hz are given in a step-by-step process. The proposed converter is comprised of four 12-pulse converter units, which is suitable for the simulation of single-/multi-converter flexible alternating current transmission system devices as well as high voltage direct current systems operating at the transmission level. The magnetic interface of the converter is originally designed with given all parameters for 100 MVA operation. The so-called two-angle control method is adopted to control the voltage magnitude and the phase angle of the converter independently. PSCAD simulation results verify both four-quadrant converter operation and closed-loop control of the converter operated as static synchronous compensator (STATCOM).     

Vibration-free position control for a two degrees of freedom flexible-beam sensor

This work presents a position control for a two degree of freedom flexible-beam made of a composite material, whose aim is to control the tip of the flexible-beam by decreasing the vibration when the beam moves. A mechatronic unit that uses a multi-axis force/torque sensor has been specially designed and we propose to control the system by using a reduced dynamic model. The control method makes use of an inner-loop to control the position of two servo-motors, by means of PID regulators, and an outer-loop that cancels the tip vibration. Moreover, the closed-loop motor dynamics has been reduced by using a series connection of filters that invert its dynamics. The motor controllers have proved to be fast and precise, and cancel the non-modelled components of the motor friction without the need for a previous estimation. The flexible-beam vibration has been controlled by implementing an input-state feedback linearisation which includes compensation terms for the nonlinear beam dynamics, a linear feedback control law and a full state estimator. The experimental validation of the complete control method showed a significant trajectory tracking of the tip, while vibrations were prevented.     

Simultaneous motion estimation and segmentation

We present a Bayesian framework that combines motion (optical flow) estimation and segmentation based on a representation of the motion field as the sum of a parametric field and a residual field. The parameters describing the parametric component are found by a least squares procedure given the best estimates of the motion and segmentation fields. The motion field is updated by estimating the minimum-norm residual field given the best estimate of the parametric field, under the constraint that motion field be smooth within each segment. The segmentation field is updated to yield the minimum-norm residual field given the best estimate of the motion field, using Gibbsian priors. The solution to successive optimization problems are obtained using the highest confidence first (HCF) or iterated conditional mode, (ICM) optimization methods. Experimental results on real video are shown.     

航空相机大面阵CCD多自由度拼接方法研究

随着科学技术的进步,航空相机向着高分辨率、大视场方向发展,现有单片CCD 不能满足大视场的要求,高精度、多自由度的CCD拼接技术已成为当前发展的迫切需求.通过对比现有拼接技术的优劣,提出了一种新的大面阵CCD多自由度机械交错拼接技术,采用三点凸轮式多自由度拼接机构,取代传统修磨垫片方式,拼接时可在线实时调整.对拼接精度进行分析,结果表明,该方法的搭接误差 2m,共面误差 4m,满足航空相机大视场和高分辨率要求;对拼接结构进行模态仿真分析与模态测试实验,拼接机构一阶谐振频率大于390 Hz,满足使用要求.     

基于用户协作的认知MIMO干扰网络自由度上界研究

在K+1用户认知MIMO干扰网络中,传统算法区分对待主/次用户干扰,将其对齐压缩到不同的干扰空间上,导致空间自由度的浪费。从复用干扰空间的角度出发,推导了新的自由度上界及其必要条件。为了验证其合理性和正确性,设计了联合干扰对齐指标,并结合范数理论和Rayleigh-Ritz定理提出一种协作联合干扰对齐算法,并对算法的有效性进行了分析。理论分析和仿真结果表明,新的自由度上界突破了已有文献所给上界,且可通过所提算法达到。     

Simulation of intramuscular EMG signals detected using implantable myoelectric sensors (IMES)

The purpose of this study was to test the feasibility of recording independent electromyographic (EMG) signals from the forearm using implantable myoelectric sensors (IMES), for myoelectric prosthetic control. Action potentials were simulated using two different volume conductor models: a finite-element (FE) model that was used to explore the influence of the electrical properties of the surrounding inhomogeneous tissues and an analytical infinite volume conductor model that was used to estimate the approximate detection volume of the implanted sensors. Action potential amplitude increased progressively as conducting electrodes, the ceramic electrode casing and high resistivity encapsulation tissue were added to the model. For the muscle fiber locations examined, the mean increase in EMG root mean square amplitude when the full range of material properties was included in the model was 18.2% (+/-8.1%). Changing the orientation of the electrode with respect to the fiber direction altered the shape of the electrode detection volume and reduced the electrode selectivity. The estimated detection radius of the IMES electrode, assuming a cylindrical muscle cross section, was 4.8, 6.2, and 7.5 mm for electrode orientations of 0 degree, 22.5 degrees, and 45 degrees with respect to the muscle fiber direction.     

Isotropic fading vector broadcast Channels:The scalar upper bound and loss in degrees of freedom

We propose a scalar upper bound on the capacity region of the isotropic fading vector broadcast channel in terms of the capacity region of a scalar fading broadcast channel. The scalar upper bound is applicable to the broad class of isotropic fading broadcast channels regardless of the distribution of the users' channel magnitudes, the distribution of the additive noise experienced by each user, or the amount of channel knowledge available at the receiver. Using this upper bound, we prove the optimality of the Alamouti scheme in a broadcast setting, extend the recent results on the capacity of nondegraded, fading scalar broadcast channels to nondegraded fading vector broadcast channels, and determine the capacity region of a fading vector Gaussian broadcast channel with channel magnitude feedback. We also provide an example of a Rayleigh-fading broadcast channel with no channel state information available to the receiver (CSIR), where the bound on the capacity region obtained by a naive application of the scalar upper bound is provably loose, because it fails to account for the additional loss in degrees of freedom due to lack of channel knowledge at the receiver. A tighter upper bound is obtained by separately accounting for the loss in degrees of freedom due to lack of CSIR before applying the scalar upper bound.