Control design of a novel compliant actuator for rehabilitation robots

Rehabilitation robots have direct physical interaction with human body. Ideally, actuators for rehabilitation robots should be compliant, force controllable, and back drivable due to safety and control considerations. Series Elastic Actuators (SEA) offers many advantages for these applications and various designs have been developed. However, current SEA designs face a common performance limitation due to the compromise on the spring stiffness selection. This paper presents a novel compact compliant force control actuator design for portable rehabilitation robots to overcome the performance limitations of current SEAs. Our design consists of a servomotor, a ball screw, a torsional spring between the motor and the ball screw, and a set of translational springs between the ball screw nut and the external load. The soft translational springs are used to handle the low force operation, while the torsional spring with high effective stiffness is used to deal with the large force operation. It is a challenging task to design the controller for such a novel design as the control system needs to handle both the force ranges. In this paper, we develop the force control strategy for this actuator. First, two dynamical models of the actuator are established based on different force ranges. Second, we propose an optimal control with friction compensation and disturbance rejection which is enhanced by a feedforward control for the low force range. The proposed optimal control with feedforward term is also extended to the high force range. Third, a switching control strategy is proposed to handle a transition between low force and high force control. The mathematical proof is given to ensure the stability of the closed-loop system under the proposed switching control. Finally, the proposed method is validated with experimental results on a prototype of the actuator system and is also verified with an ankle robot in walking experiments.     

Dependable and reliable cloud-based architectures for vehicular communications: A systematic literature review

Traffic congestion, air pollution, fuel wastage, and car accidents are all exacerbated by increased traffic. Thus, vehicular communications, which refer to information transmission between cars, pedestrians, and infrastructures, have lately gained popularity and been extensively explored due to their enormous potential to enable intelligent transportation and various safety applications. Manually piloted cars and automated vehicles can acquire relevant information via vehicular communications to enhance traffic security and boost entertainment services. The basic concept of automobile clouds was originally published in the literature not long ago, and several suggested structural approaches have been presented in this study thus far. Several academics have concentrated on the structural layout to address various problems and, as a result, satisfy user expectations in order to give dependable services. We examined various vehicular cloud topologies in this study. We also offered a complete summary of current network layer research on allowing efficient vehicle communications and examined specific security, architectural, and reliability concerns in vehicular clouds. Also, the taxonomy of vehicular networks was discussed in terms of the service link between vehicular networks and cloud computing. Ultimately, we discussed the research prospects available. The results showed that security and privacy challenges are among the most important challenges.     

Voltage variable capacitor tuning: A review

This paper discusses the history, device theory, characteristics, applications, and future trends of voltage varible capacitor tuning. All equations are stated in terms of two general exponents of power law functions, namely the impurity distribution proportional to x^mand the differential capacitance proportional to (V + V0)^-n. The role of these exponents is shown in the device theory, the temperature drift, linearity in a VCO, and the cross modulation in an FM modulator. Important results from many papers and reports are cited to reinforce the ideas presented. Throughout the review, the desirability of the exponent n = 2 is reiterated.     

Closed-loop identification: application to the estimation of limb impedance in a compliant environment

The force and position data used to construct models of limb impedance are often obtained from closed-loop experiments. If the system is tested in a stiff environment, it is possible to treat the data as if they were obtained in open loop. However, when limb impedance is studied in a compliant environment, the presence of feedback cannot be ignored. While unbiased estimates of a system can be obtained directly using the prediction error method, the same cannot be said when linear regression or correlation analysis is used to fit nonparametric time- or frequency-domain models. We develop a prediction error minimization-based identification method for a nonparametric time-domain model augmented with a parametric noise model. The identification algorithm is tested on a dynamic mass-spring-damper system and returns consistent estimates of the system's properties under both stiff and compliant feedback control. The algorithm is then used to estimate the impedance of a human elbow joint in both stiff and compliant environments.     

A review:Photonics devices,architectures,and algorithms for optical neural computing

The explosive growth of data and information has motivated various emerging non-von Neumann computational approaches in the More-than-Moore era.Photonics neuromorphic computing has attracted lots of attention due to the fascinating advantages such as high speed,wide bandwidth,and massive parallelism.Here,we offer a review on the optical neural computing in our research groups at the device and system levels.The photonics neuron and photonics synapse plasticity are presented.In addition,we introduce several optical neural computing architectures and algorithms including photonic spiking neural network,photonic convolutional neural network,photonic matrix computation,photonic reservoir computing,and photonic reinforcement learning.Finally,we summarize the major challenges faced by photonic neuromorphic computing,and propose promising solutions and perspectives.     

Input impedance and reflection coefficient in fractal-like modelsof asymmetrically branching compliant tubes

A mathematical model is described, based on linear transmission line theory, for the computation of hydraulic input impedance spectra in complex, dichotomously branching networks similar to mammalian arterial systems. Conceptually, the networks are constructed from a discretized set of self-similar compliant tubes whose dimensions are described by an integer power law. The model allows specification of the branching geometry, i.e., the daughter-parent branch area ratio and the daughter-daughter area asymmetry ratio, as functions of vessel size. Characteristic impedances of individual vessels are described by linear theory for a fully constrained thick-walled elastic tube. Besides termination impedances and fluid density and viscosity, other model parameters included relative vessel length and phase velocity, each as a function of vessel size (elastic nonuniformity). The primary goal of the study was to examine systematically the effect of fractal branching asymmetry, both degree and location within the network, on the complex input impedance spectrum and reflection coefficient. With progressive branching asymmetry, fractal model spectra exhibit some of the features inherent in natural arterial systems such as the loss of prominent, regularly-occurring maxima and minima; the effect is most apparent at higher frequencies. Marked reduction of the reflection coefficient occurs, due to disparities in wave path length, when branching is asymmetric. Because of path length differences, branching asymmetry near the system input has a far greater effect on minimizing spectrum oscillations and reflections than downstream asymmetry. Fractal-like constructs suggest a means by which arterial trees of realistic complexity might be described, both structurally and functionally     

A 256K CMOS SRAM with variable impedance data-line loads

A 256K (32K/spl times/8) CMOS SRAM utilizing variable impedance loads and a pulsed word-line (PWL) technique is described. In the WRITE cycle, the variable impedance loads of the data lines enter a high impedance state and reduce the operating power. During the READ cycle, the PWL technique is used to achieve high-speed operation and low power dissipation. The internal clocks generated by the address transition detectors activate word-line and sense amplifiers for READ operation and disable them after the data are sent to D/SUB out/ buffers. This PWL technique eliminates the precharge time of 20 ns, which corresponds to 30% of the access time. The RAM offers 45-ns address access time and 40-mW operating power in the WRITE cycle of 1 MHz.     

An adaptive composite control for a hydraulic actuator impedance system of legged robots

The hydraulic drive unit (HDU) is the actuator of a legged robot joint, whose control affects the robot's motion performance. Impedance control is one of the essential control methods for the legged robot, which can reduce the collision force in foot-ground contact and improve the robot's stability. However, hydraulic systems are strongly nonlinear and have time-varying parameters, particularly when the robot is in different environments. Therefore, the impedance control of the HDU should be adaptive to parameter and environmental changes. A novel adaptive control combining polynomial nonlinear extended state observer (PNLESO) and adaptive feedback linearization control (AFLC) for the HDU is designed in this study called the PNLESO-AFLC. The main aspects of this study are as follows: (i) A polynomial based error function is designed to form the PNLESO, which observes system disturbances and improves observer chattering; (ii) AFLC is designed to compensate for the PNLESO's observation error, improving adaptability to changing parameters and different working conditions. Finally, the effectiveness of the PNLESO−AFLC is verified by comparative experiments. Experimental results show that the PNLESO−AFLC has good adaptability to different working conditions and can significantly improve the impedance control performance of HDU.     

变阻抗TEM喇叭天线设计中末端端口阻抗问题的研究

恒阻抗TEM喇叭天线的上、下板之间的间距、板的宽度沿天线轴向呈线性渐变,且喇叭天线的驱动端口、末端端口的宽高比相同。与恒阻抗TEM喇叭天线不同,指数渐变型TEM喇叭天线上下极板之间的间距沿轴向呈指数渐变。研究发现,当指数渐变型TEM喇叭的极板宽度采用不同的渐变形式时,极板宽度线性变化型TEM喇叭天线的驻波比最佳,主射方向远场脉冲峰峰值最大。当天线轴向长度、末端端口高度一定时,天线主射方向远场脉冲峰峰值随着天线末端端口宽度的增大而增大;当末端端口宽度达到一定值时,脉冲峰峰值达到最大值,继续增大末端端口宽度,脉冲峰峰值减小;当天线主射方向远场脉冲峰峰值达到最大值时,天线末端端口阻抗值为215Ω。     

A new MEMS based variable capacitor with wide tunability,high linearity and low actuation voltage

We have proposed a new RF MEMS variable capacitor to achieve high linearity, wide tunability and low actuation voltage. The idea is based on increasing the linear region in the gap between the plates of the capacitor. It is done by adding a fixed-fixed beam below the fixed-free beam. The fixed-free beam is one plate of the capacitor. The voltage is applied to the fixed-free beam. In the vicinity of the pull-in voltage, the fixed-free beam losses its equivalent stiffness. The fixed-fixed beam is located in the vicinity of pull in situation of the fixed-free beam. This condition increases the equivalent stiffness of the fixed-free beam and allows the beam to continue moving down linearly and consequently increases the maximum capacitance of the structure. Geometrical and material property effects of the second beam on the linearity, tunability and voltage are investigated. The governing nonlinear equation for static deflection of the beam based on the Euler–Bernoulli beam theory has been presented.     

Synchronized motion and compliant control for dual control moment gyroscopes by realizing the impedance transformation matrix

In this paper, dual control moment gyroscopic actuators (CMG) were formed in a scissored-pair configuration to maximize the induced torque in the desired direction. A robust synchronizing motion control method was proposed to regulate the directional gyroscopic torque. In order for the two CMGs to form a scissored-pair structure having opposite angular momentum vectors, the synchronization of two CMGs was done without losing the control capability due to axial drift. A transformation matrix was designed for the robust synchronization control performance by realizing the empirically discovered impedance models of CMGs. Three different control modes were realized by selecting the components of the impedance transformation matrix (ITM): a robustly independent control mode, a synchronized motion control mode, and a mixed motion control mode. Each CMG played the role of either a master or a slave and copied the motion from another to follow it under the synchronization mode. The experimental results show that two CMGs can generate a robust and directional torque under the mixed control mode of both robust and synchronization control.     

Development of a new fully flexible hydraulic variable valve actuation system for engines using rotary spool valves

In this paper, a new hydraulic variable valve actuation (VVA) system is proposed and designed. The VVA system can significantly improve the engine performance in terms of the power density, volumetric efficiency, emission, and fuel consumption. In this system, each engine valve is actuated by a hydraulic cylinder which is charged and discharged using two rotary spool valves. The rotary spool valves are rotated by the engine crankshaft while their phases are controlled by hydraulic or electric phase shifters. Similar to camless valvetrains, the new engine valve system is capable of flexible engine valve timing and lift at any engine speed without the drawbacks of existing camless valvetrains including high control complexity, low reliability, and slow actuator response. The mathematical model of the system is derived and verified by comparing simulation and experimental results. Two feedback controllers are designed and implemented for precise valve opening and closing timing and valve lift control. Experiments are performed to validate the mathematical model and evaluate the proposed system's performance. The results show excellent system repeatability and controllability at different operating conditions.     

A method for partitioning applications in hybrid reconfigurable architectures

In this paper, we propose a methodology for accelerating application segments by partitioning them between reconfigurable hardware blocks of different granularity. Critical parts are speeded-up on the coarse-grain reconfigurable hardware for meeting the timing requirements of application code mapped on the reconfigurable logic. The reconfigurable processing units are embedded in a generic hybrid system architecture which can model a large number of existing heterogeneous reconfigurable platforms. The fine-grain reconfigurable logic is realized by an FPGA unit, while the coarse-grain reconfigurable hardware by our developed high-performance data-path. The methodology mainly consists of three stages; the analysis, the mapping of the application parts onto fine and coarse-grain reconfigurable hardware, and the partitioning engine. A prototype software framework realizes the partitioning flow. In this work, the methodology is validated using five real-life applications. Analytical partitioning experiments show that the speedup relative to the all-FPGA mapping solution ranges from 1.5 to 4.0, while the specified timing constraints are satisfied for all the applications.     

A simple active damping control for compliant base manipulators

When a robotic manipulator is mounted to a crane, boom or mobile platform, it loses its accuracy and speed due to the compliance of the base. This paper presents a simple robust control strategy that will reduce mechanical vibrations and enable better tip positioning. The control algorithm uses the sensory feedback of the base oscillation to modulate the manipulator actuator input to induce the inertial damping forces. The authors' previous work (1999) demonstrated the feasibility of the proposed concept using linear analysis. This work extends the concept to a more general case of a nonlinear multiple link manipulator using acceleration feedback and one sample delayed torque. A simulation and an experimental study show very promising results for a test bed consisting of a two-link manipulator and a compliant base     

Radio wave propagation over a rough variable impedance boundary: Part I--Full-wave analysis

A full-wave solution is developed for problems of radio wave propagation over rough surfaces characterized by variable impedance and height parameters. The analysis, which is suitable for problems involving both the radiation fields as well as the ground waves, is compared with earlier solutions to these problems. The full-wave solutions which satisfy the exact boundary conditions are shown to be consistent with the reciprocity relationships for the general case.     

Bi-directionally fed phased-array antenna downsized with variable impedance phase shifter for ISM band

A novel bi-directionally fed phased-array antenna (BiPA) is presented. A BiPA can operate at half the phase shift of the conventional antenna with the same performance, leading to smaller size and lower cost. Main components of a BiPA are antenna elements and variable impedance phase shifters (VIPSs). The VIPS consists of three resonant circuits that include variable capacitors, it is applicable for both functions as a power divider and as an impedance-matching device, since the input/output impedance and the phase shift can be independently varied. The BiPA with a VIPS is simulated and evaluated at a 2.45-GHz industrial-scientific-medical band. The measured results agree well with the simulated ones. The performances of the VIPSs are confirmed as 1.4 dB in insertion loss, and -17dB in return loss for a phase shift of 0/spl sim/80/spl deg/ with the control voltage from 0- to 3.5-V DC, and the measured radiation pattern of the BiPA is /spl plusmn/30/spl deg/ in the steering angle, 24/spl deg/ in beamwidth, and -9dB in the sidelobe. Furthermore, an enhancement of the sidelobe suppression can be expected by changing the power ratio of each antenna element.     

一种适用于激光共焦扫描显微镜的体绘制

激光共聚焦扫描显微镜(LCSM)主要运用于生物医学研究,利用其采集的序列二维断层图像重构三维图形是LCSM系统的重要组成部分。主要研究了LCSM系统数据场的体绘制方法,根据其数据场特点,提出了最大值绘制算法。实验结果表明,此方法适用于LCSM系统,能够生成逼真的三维图形。     

Adaptive fuzzy impedance control of exoskeleton robots with electromyography-based convolutional neural networks for human intended trajectory estimation

Among various uses of exoskeleton robots, the rehabilitation of stroke patients is a more recent application. There is, however, considerable environmental uncertainty in such systems including uncertain robot dynamics, unwanted user reflexes, and, most importantly, uncertainty in user intended trajectory. Hence, it is challenging to develop transparent, stable, and wide-scale exoskeleton robots for rehabilitation. This paper proposes an adaptive fuzzy impedance controller (AFIC) and a convolutional neural network (CNN) which uses electromyographic (EMG) signals for early detection of human intention and better integration with a lower limb exoskeleton robot. Specifically, the primary purpose of the AFIC is to manage the mechanical interaction between human, robot, and environment and to deal with uncertainties in internal control parameters. CNN uses EMG signals, inertial measurement units, foot force sensing resistors, joint angular sensors, and load cells to deal with signal uncertainties and noise through automatic feature processing in order to detect user’s desired joint angles with high accuracy. EMG is particularly effective here since it reflects the human intention to move faster than the other mechanical sensors. In the experimental procedure, signals were sampled at 500 Hz as two healthy individuals walked normally at 0.3, 0.4, 0.5, and 0.6 m/s for eight minutes while wearing a robot with zero inertia. Approximately 70% of the data is used for training and 30% for testing the network. The estimated angle from the trained network is then used as the desired angle in the AFIC loop, which controls the robot online as the desired trajectory. Pearson correlation coefficient and normalized root mean square error are computed to evaluate the accuracy and robustness of the proposed angle estimation with CNN and AFIC algorithms. Experimental results show that the proposed approach successfully obtains the torque of the robot joints despite uncertainties in changing the walking speed.     

A stable transition controller for constrained robots

This paper addresses the problem of contact transition from free motion to constrained motion for robots. Stability of transition from free motion to constrained motion is essential for successful operation of a robot performing general tasks such as surface following and surface finishing. Uncertainty in the location of the constraint can cause the robot to impact the constraint surface with a nonzero velocity, which may lead to bouncing of the robot end-effector on the surface. A new stable discontinuous transition controller is proposed to deal with contact transition problem. This discontinuous transition control algorithm is used when switching from free motion to constrained motion. Control algorithm for a complete robot task is developed. Extensive experiments with the proposed control strategy were conducted with different levels of constraint uncertainty and impact velocities. Experimental results show much improved transition performance and force regulation with the proposed controller. Details of the experimental platform and typical experimental results are given