Augmented Virtual Stiffness Rendering of a Cable-driven SEA for Human-Robot Interaction

Human-robot interaction (HRI) is fundamental for human-centered robotics, and has been attracting intensive research for more than a decade. The series elastic actuator (SEA) provides inherent compliance, safety and further benefits for HRI, but the introduced elastic element also brings control difficulties. In this paper, we address the stiffness rendering problem for a cable-driven SEA system, to achieve either low stiffness for good transparency or high stiffness bigger than the physical spring constant, and to assess the rendering accuracy with quantified metrics. By taking a velocity-sourced model of the motor, a cascaded velocity-torque-impedance control structure is established. To achieve high fidelity torque control, the 2-DOF (degree of freedom) stabilizing control method together with a compensator has been used to handle the competing requirements on tracking performance, noise and disturbance rejection, and energy optimization in the cable-driven SEA system. The conventional passivity requirement for HRI usually leads to a conservative design of the impedance controller, and the rendered stiffness cannot go higher than the physical spring constant. By adding a phase-lead compensator into the impedance controller, the stiffness rendering capability was augmented with guaranteed relaxed passivity. Extensive simulations and experiments have been performed, and the virtual stiffness has been rendered in the extended range of 0.1 to 2.0 times of the physical spring constant with guaranteed relaxed passivity for physical humanrobot interaction below 5 Hz. Quantified metrics also verified good rendering accuracy.      

Variable stiffness control for SEAs in rehabilitation training

ABSTRACT

Series Elastic Actuator (SEA) with both security and high performance is used extensively for rehabilitation robots with physical interaction. Human joints applied for motion therapy show variable stiffness properties during the process of rehabilitation training. When using robot to do motion therapy, impedance control is one of the most popular methods for rehabilitation works. However, impedance control with constant stiffness usually produces rigidity in the body due to natural changes of muscle tension. It may seriously restrict the achievement of excellent training effect and may even cause harm to patients. In this study, a novel real-time parallel variable stiffness control method is proposed based on cascade impedance controller. First, an SEA joint is analyzed and the limit factor of the impedance frequency is discussed. Subsequently, cascade impedance controller scheme with stiffness adjustment regulator is utilized to achieve the stiffness and the passivity of the controller is proved. Based on the scheme, a novel stiffness self-adjustment algorithm is presented which can regulate the stiffness by impedance approximation. Finally, simulation and experimental results are provided to validate the stiffness adjustment method during the rehabilitation process.     

Reconfigurable bandpass filter with constant absolute bandwidth based on neural network

In this paper, a novel design method for reconfigurable bandpass filter (BPF) with constant absolute bandwidth (ABW) based on neural network is proposed. A lumped-element circuit is used to design the reconfigurable BPF, which consists five series LC tanks. Three series tanks can provide three transmission poles, while two parallel tanks can introduce two same transmission zeros (TZs). This method allows designing BPFs with tunable center frequency and constant ABW. A set of inductance and capacitance values for the center frequency and ABW requirements are optimized by using neural network. Then, optimize the capacitance values to adjust the center frequency with fixed inductance values by the three series tanks and the TZ by the parallel tanks. In order to verify this design method, three varactor diodes are employed to achieve the reconfigurable BPFs with the constant ABW under different work states. Experiments show that this method can optimize multiple LC circuit parameters of BPFs, which meet design requirements, with the same ABW and different center frequencies effectively and accurately     

刚度和等效质量对SEA能量放大特性的影响

对简单的SEA(series elastic actuator)模型采用解析法求解,得出了驱动器输出能量曲线,分析了其能量放大特性,解决了Paluska的SEA能量分析的无解析解问题.并针对Paluska分析中对动力学模型的过度简化,引入了传动机构的等效质量的概念,完善了SEA的能量放大作用模型.为了便于求解和分析,对SEA能量放大模型各参数进行归一化处理,并在归一化条件下通过频域转换方式进行数值求解,得出该条件下的驱动器输出能量曲线,从而得到了该模型下的SEA能量放大特性及其随系统参数(弹簧刚度、传动机构等效质量)的变化规律.     

基于FPGA实现的10Gbps高速转发引擎设计分析

高速特发引擎的设计是T比特路由器设计中的关键和难点,本文围绕传输带宽需求、查表时间需求和包头处理时间需求以及器件水平等方面对基于FPGA实现的10Gbps高速转发引擎进行了详细的分析,讨论了高速转发引擎各功能模块的设计可行性,并给出了一种可行的实现方案。     

Parallel fiber-optic SCI links

Parallel fiber-optic links promise to be a key enabling technology for distributed computing, substantially increasing transmission distance and bandwidth. The drive to include more and more processors and I/O devices in parallel-processor complexes has created a need for box-to-box interconnection links capable of delivering bandwidth comparable to system backplanes. Point-to-point links overcome the speed and cost constraints of shared buses. However, copper-based point-to-point links can reliably carry high-speed data only a limited distance. Parallel fiber-optic links substantially increase transmission distance and surpass copper's bandwidth capability. Our research addresses the integration of parallel fiber-optic data links into system designs that require a high-bandwidth link over moderate distances. To demonstrate the feasibility of using parallel fiber-optic technology as a fundamental building block in large-scale commercial and parallel machines, we constructed a link testbed     

The effects of variable mechanical parameters on peak power and energy consumption of ankle-foot prostheses at different speeds

In recent years, powered ankle-foot prostheses are developed to restore human ankle behaviour. Compared with common passive ankle prostheses, a powered ankle-foot prosthesis can provide amputees with better performance on walking gait by providing additional energy. However, the electrical peak power of powered ankle-foot prostheses at high speed is still a big challenge for the current actuation system. While most researchers focus on the energy consumption on one walking speed, we investigate the influences of several variable mechanical parameters to reduce electrical peak power during different locomotion speeds. Then we apply this concept to current ankle-foot models. It's found that the variable mechanical parameters can significantly reduce the demand of electrical peak power at different speeds. Meanwhile, the reduction of the electrical peak power does not lead to a large increment of the energy consumption. The results also show that every variable mechanical parameter has a different influence on the peak power and energy consumption of the ankle-foot prosthesis. It means the most effective and sensitive variable mechanical parameter need to be found for a specific ankle prosthesis system.     

Modeling and analysis of nano-sized GMRs based on Co,NiFe and Ni materials

Magnetic simulation method is introduced to analyze giant magnetoresistances(GMRs)in nanoscale for nano-sized biosensors.A spin valve model with special gridding corresponding to the exchange interaction length is proposed to study the influence of easy axes,exchange coefcients,pinning fields and feature widths on magnetization reversals and hysteresis characteristics of nano-sized GMRs with diferent pinned layer and free layer materials of Co,NiFe and Ni.The switching field is found to be almost linear with the pinning field and decrease with the absolute exchange coefcients and the feature widths for the nano-sized GMRs.The increase rate of each depends on the spin valve stacks.Further investigations into variations of the magnetization distribution reveal that the initial magnetization distribution and the magnetization reversal mode depend greatly on easy axes and materials The dependence on easy axes based mainly on the magnetocrystalline anisotropy is illustrated in detail.     

串联弹性驱动器设计、建模及在机器人上的应用

相比于传统的刚性驱动器, 串联弹性驱动器(Series elastic actuator, SEA)具有被动柔顺性、阻抗低、抗冲击、力感知等诸多优点, 因而已被广泛应用于各种机器人系统中. 首先根据弹性和阻尼特性将串联弹性驱动器分为弹性型、阻尼型和弹性?阻尼型串联弹性驱动器, 介绍不同类型串联弹性驱动器的优缺点, 并详细概述弹性和阻尼特性的机械实现方式; 然后对各类串联弹性驱动器作为力传感器的建模方法进行介绍; 接着叙述串联弹性驱动器在机器人系统中的主要应用, 如力传感器、安全保护、降低能耗; 最后展望串联弹性驱动器未来的发展方向.     

针对串联弹性驱动器抖动抑制的轨迹规划和跟踪控制

针对串联弹性驱动器（Series elastic actuator,SEA）的位置控制问题,本文提出了一种"规划+控制"的策略.首先根据连杆端运动学约束方程,基于数字滤波器对电机位置进行轨迹规划;为了使电机能够准确跟踪期望轨迹,根据电机端的动力学模型设计位置跟踪控制器.理论分析证明了规划的抖动抑制作用和跟踪控制系统的稳定性,随后的实验结果也表明了这种"规划+控制"方法在使连杆到达期望位置的前提下,能够有效地抑制残余抖动.     

一种基于SDN和MPTCP的多径并行传输技术

本文提出了根据网络信息状态通过SDN控制器来控制MPTCP流量以提高并行传输速率。利用本文所提出的最宽不相交选路算法,为每个MPTCP连接选择一组可用带宽最宽且链路差距较小的路径集。然后使用可用路径容量的比例作为流量分配到该路径上的概率,进一步减小子流的带宽差距。最后,通过搭建Floodlight仿真实验平台,证明本方案能够避免MPTCP的不同子流经过同一路径,并有效的利用路径提升并行传输效率。     

一种路由交换阵列节点芯片及其系统的设计与实现

介绍一种面向大数据处理数据中心应用的计算/控制/网络存储的路由交换阵列节点芯片及其所组成的安全交换阵列原型机的设计与实现;该路由交换阵列系统通过因特网远程使用软件定义网络(SDN)方式对高速安全交换网络的内部路由控制和安全等模块进行集中编程控制,满足数据中心对数据传输带宽容量的需求;同时并行计算过程中消除网络传输瓶颈,避免了数据中心网络等资源的长期占用浪费,为下一代数据中心解决方案的形成打下基础。另外还简述了其在金融交易系统领域大数据应用尝试的研究近况。     

一种面向密码SoC的高性能全双工DMA设计

在密码SoC等数据密集型应用中,数据传输速度成为制约密码处理性能提升的瓶颈。结合密码SoC的数据流处理特点,提出一种面向密码SoC的高性能DMA优化设计方法。对特定模块的DMA传输开辟专用通道,利用并行读写数据提高特定模块DMA传输的总线带宽利用率。添加特殊工作模式用于自主控制重复任务传输以提升传输的带宽利用率。在此基础上,采用多通道优先级动态调整技术实现多任务下效率较高的自适应传输。仿真结果表明,该DMA在55 nm工艺下的最高频率达910 MHz,总线利用率和协处理器利用率的平均值分别高达91%和54%,相对通用DMA,其对密码SoC的ZUC、SNOW、SM3、SM4和AES算法的性能分别提升216%、222%、123%、69%和221%。     

Cell处理器访存特征研究

Cell处理器是一款异构多核处理器,拥有强大的计算能力。但是,在进行应用并行化时,却受到本地存储器容量、访存带宽和数据传输延时等的限制。DMA传输是隐藏长延时、提高存储带宽利用率的有效方法。本文在分析Cell处理器结构基础上,进行了一系列详细的DMA测试,并利用指数拟合技术得到DMA平均带宽模型,发现参与DMA传输的SPE数量和每次DMA传输规模是影响DMA访存带宽的主要因素。     

Signal strength based routing for power saving in mobile ad hoc networks

The transmission bandwidth between two nodes in mobile ad hoc networks is important in terms of power consumption. However, the bandwidth between two nodes is always treated the same, regardless of what the distance is between the two nodes. If a node equips a GPS device to determine the distance between two nodes, the hardware cost and the power consumption increase. In this paper, we propose using a bandwidth-based power-aware routing protocol with signal detection instead of using GPS devices to determine the distance. In our proposed routing protocol, we use the received signal variation to predict the transmission bandwidth and the lifetime of a link. Accordingly, the possible amount of data that can be transmitted and the remaining power of nodes in the path after data transmission can be predicted. By predicting the possible amount of data that can be transmitted and the remaining power of nodes after data transmission, we can design a bandwidth-based power-aware routing protocol that has power efficiency and that prolongs network lifetime. In our simulation, we compare our proposed routing protocol with two signal-based routing protocols, SSA and ABR, and a power-aware routing protocol, MMBCR, in terms of the throughput, the average transmission bandwidth, the number of rerouting paths, the path lifetime, the power consumed when a byte is transmitted, and the network lifetime (the ratio of active nodes).     

多级平行轴齿轮传动系统动力学仿真

为分析多级平行轴齿轮传动系统内部难以直接测量的振动信号,建立了4级齿轮传动系统非线性动力学46自由度仿真模型,并基于势能法对时变啮合刚度进行精确求解,采用4阶Runge-Kutta法对集中参数模型进行Matlab编程,进而分析时变啮合刚度对模型响应结果的影响.基于分析结果,探究了引起多级平行轴齿轮传动系统振动的重要原因.同时,通过模型振动时域响应及频谱分析,发现各级传动齿轮之间存在耦合振动现象,能够为实际多级平行轴齿轮传动系统健康监测与故障诊断提供理论支撑与科学指导.     

Non-back-drivable rotary mechanism with intrinsic compliance for robotic thumb abduction/adduction

Duplicating the complexity of the human thumb with a robotic one is a difficult task for engineers, when taking into consideration the necessary miniaturization and robustness requirements. Miniaturization is required to fit all the components within the size of a human hand; however, the reduction in size of the components affects the strength of the transmission. Several robotic hands with active thumbs were designed. Most of these had the abduction/adduction joint rigidly connected to the electrical motor and gearhead. This is a non-optimal solution because although miniaturized, the transmission is back-drivable and thus the motor gearhead is exposed to shocks. In this paper, we present the design of a non-back-drivable rotary mechanism with intrinsic compliance for a robotic thumb ab/adduction joint. The mechanism enables switch off of the power supply once a desired posture is stable, thus avoiding accidental dangerous releases of the grasped object, absorbs the impact forces generated at the instant of grasping and dissipates the repeated strains that are induced during manipulation. The mechanism was developed and tested. Detailed kinematic, static and stiffness analyses are presented as well as experimental measurements which demonstrate suitable performance for our application (max efficiency ~0.85, critical load 1.2 Nm, energy absorbed 1.5 J).     

A power efficiency routing and maintenance protocol in wireless multi-hop networks

In wireless multi-hop networks, selecting a path that has a high transmission bandwidth or a high delivery rate of packets can reduce power consumption and shorten transmission delay during data transmission. There are two factors that influence the transmission bandwidth: the signal strength of the received packets and contentions in the contention-based MAC layer. These two factors may cause more power to be consumed during data transmission. We analyze these two factors and propose a power-aware routing protocol called MTPCR. MTPCR discovers the desired routing path that has reduced power consumption during data transmission. In addition to finding a desired path to reduce power consumption, MTPCR also takes into account the situations in which the transmission bandwidth of the routing path may decrease, resulting in much power consumption during data transmission because of the mobility of nodes in a network. MTPCR is thus useful in a network: it analyzes power consumption during data transmission with the help of neighboring nodes, and it uses a path maintenance mechanism to maintain good path bandwidth. The density of nodes in a network is used to determine when to activate the path maintenance mechanism in order to reduce the overhead of this mechanism. With the proposed path maintenance mechanism, power consumption during data transmission can be efficiently reduced, as well as the number of path breakages. In our simulation, we compared our proposed routing protocol, MTPCR, with the following protocols: two classical routing protocols, AODV and DSR; two power-aware routing protocols, MMBCR and xMBCR; and one multiple path routing protocol, PAMP. The comparisons are made in terms of throughput of the routing path, power consumption in path discovery, power consumption in data transmission, and network lifetime.     

Parallel solution of contact shape optimization problems based on Total FETI domain decomposition method

An application of a variant of the parallel domain decomposition method that we call Total FETI or TFETI (Total Finite Element Tearing and Interconnecting) for the solution of contact problems of elasticity to the parallel solution of contact shape optimization problems is described. A unique feature of the TFETI algorithm is its capability to solve large contact problems with optimal, i.e., asymptotically linear complexity. We show that the algorithm is even more efficient for the solution of the contact shape optimization problems as it can exploit effectively a specific structure of the auxiliary problems arising in the semi-analytic sensitivity analysis. Thus the triangular factorizations of the stiffness matrices of the subdomains are carried out in parallel only once for each design step, the evaluation of the components of the gradient of the cost function can be carried out in parallel, and even the evaluation of each component of the gradient itself can be further parallelized using the standard TFETI scheme. Theoretical results which prove asymptotically linear complexity of the solution are reported and documented by numerical experiments. The results of numerical solution of a 3D contact shape optimization problem confirm the high degree of parallelism of the algorithm.