Design of perturbation signals for the estimation of proprioceptive reflexes

This study aimed to identify the functional contribution of reflexes to human motor control during posture maintenance. Continuous random force disturbances were applied at the hand while the subjects were instructed to minimize the deviation resulting from the force disturbances. The results were analyzed in the frequency domain with frequency response functions (FRFs). Two FRFs were evaluated: 1) the mechanical admittance and 2) the reflexive impedance, expressing the dynamic relation between position and muscle activation (assessed via electromyography, EMG). The reflexive impedance is a direct measure of the proprioceptive reflexes. To record all relevant dynamical characteristics of the arm, wide bandwidth signals were used as force disturbance. Distributing the power of the signal over fewer frequencies within the bandwidth improved the signal-to-noise-ratio SNR of the EMG recordings, facilitating reliable estimation of the reflexive impedance. The coherence indicated that the relation between force disturbance and EMG is linear under the given conditions and improved with the SNR. The method of designing disturbance signals and the estimation of the reflexive impedance are useful for studies aiming to quantify proprioceptive reflexes and to investigate its functionality.     

Postural control adaptation during galvanic vestibular and vibratory proprioceptive stimulation

The objective for this study was to investigate whether the adaptation of postural control was similar during galvanic vestibular stimulation and during vibratory proprioceptive stimulation of the calf muscles. Healthy subjects were tested during erect stance with eyes open or closed. An analysis method designed to consider the adaptive adjustments was used to evaluate the motion dynamics and the evoked changes of posture and stimulation response. Galvanic vestibular stimulation induced primarily lateral body movements and vibratory proprioceptive stimulation induced anteroposterior movements. The lateral body sway generated by the galvanic stimulation was proportionally smaller and contained more high-frequency movements (> 0.1 Hz) than the anteroposterior body sway induced by the vibratory stimulation. The adaptive adjustments of the body sway to the stimulation had similar time course and magnitude during galvanic and vibratory stimulation. The perturbations induced by stimulation were gradually reduced within the same time range (15-20 s) and both kinds of stimulation induced a body leaning whose direction was dependent on stimulus. The similarities in the adjustment patterns suggest that postural control operates in the same way independent of the receptor systems affected by the disturbance and irrespective of whether the motion responses were induced in a lateral or anteroposterior direction.     

Fuzzy sliding-mode control of a human arm in the sagittal plane with optimal trajectory

Patients with spinal cord injuries cannot move their limbs using their intact muscles. A suitable controller can be used to move their arms by employing the functional electrical stimulation method. In this article, a fuzzy exponential sliding-mode controller is designed to move a musculoskeletal human arm model to track an optimal trajectory in the sagittal plane. This optimal arm trajectory is obtained by developing a policy for the central nervous system. In order to specify the optimal trajectory between two points, two dynamic and static optimal criteria are applied simultaneously. The first dynamic objective function is defined to minimize the joint torques, and the second static optimization is offered to minimize the muscle forces at each moment. In addition, fuzzy logic is used to tune the sliding-surface parameter to enable an appropriate tracking performance. Simulation results are evaluated and compared with experimental data for upward and downward movements of the human arm.     

Modeling and control of a piezoelectric microactuator with proprioceptive sensing capabilities

In this paper, modeling and control strategies for a new observability-optimized piezoelectric microactuator are presented. The targeted applications mainly concern the design of microgripper for micromanipulation tasks. The device has been designed using a topological optimization method, which takes into account the optimal full integration of piezoelectric actuating and sensing elements within the device. It is achieved in link with modal controllability and observability considerations. The vibrational modes that govern the tip deflection of the monolithic compliant structure are proved to be fully observable by the integrated sensing area of the device. The proposed control strategy permits to simply reconstruct the deflection using electric charges measurement and modal state observer. Finally, the vibrations that are naturally induced by the flexible structure are successfully damped using robust and low order controller.     

Quantifying relationship between relative position error of localization algorithms and object identification

Positioning of things, devices and people is the fundamental technology in ubiquitous computing. However, few literature has discussed the impact of positioning errors due to localization algorithm properties such as ranging noise and deployment of anchors on people’s identification of objects. Since several factors such as relative distance, relative angles and grouping of objects are intricately related with each other in such identification, it is not an easy task to investigate its characteristics. In this paper, we propose criteria to assess the “accuracy” of the estimated positions in identifying the objects. The criteria are helpful to design, develop and evaluate localization algorithms that are used to tell people the location of objects. Augmented reality is a typical example that needs such localization algorithms. To model the criteria without ambiguity, we prove that the Delaunay triangulation well-captures natural human behavior of finding similarity between estimated and true positions. We have examined different localization algorithms to observe how the proposed model quantifies the properties of those algorithms. Subjective testing has also been conducted using questionnaires to justify our quantification sufficiently renders human intuition.     

Intelligent optimal control of single-link flexible robot arm

This paper addresses the design and properties of an intelligent optimal control for a nonlinear flexible robot arm that is driven by a permanent-magnet synchronous servo motor. First, the dynamic model of a flexible robot arm system with a tip mass is introduced. When the tip mass of the flexible robot arm is a rigid body, not only bending vibration but also torsional vibration are occurred. In this paper, the vibration states of the nonlinear system are assumed to he unmeasurable, i.e., only the actuator position can be acquired to feed into a suitable control system for stabilizing the vibration states indirectly. Then, an intelligent optimal control system is proposed to control the motor-mechanism coupling system for periodic motion. In the intelligent optimal control system a fuzzy neural network controller is used to learn a nonlinear function in the optimal control law, and a robust controller is designed to compensate the approximation error. Moreover, a simple adaptive algorithm is proposed to adjust the uncertain bound in the robust controller avoiding the chattering phenomena. The control laws of the intelligent optimal control system are derived in the sense of optimal control technique and Lyapunov stability analysis, so that system-tracking stability can be guaranteed in the closed-loop system. In addition, numerical simulation and experimental results are given to verify the effectiveness of the proposed control scheme.     

欠驱动柔性机械臂的动力学建模与控制

针对欠驱动柔性机械臂建模、控制困难的问题,文中采用在第一关节安装轻质弹簧的方法来表示机械臂的柔性,从而得到柔性臂的简化模型。将其应用到两连杆欠驱动柔性机械臂中,建立欠驱动柔性机械臂的系统模型,并利用拉格朗日函数法,对该系统进行动力学建模。同时通过构造基于系统能量和驱动杆状态的李雅普诺夫函数,设计该欠驱动柔性机械臂系统的控制律。最后,使用Matlab对该系统及所设计的控制律进行数值仿真。仿真结果表明,所构建的动力学模型以及设计的控制规则具有良好的有效性,且同时具备响应速度快、控制输入小的优点。     

手臂电磁通道特征研究

依据现有研究结果和未来体域网发展趋势研究了手臂电磁通道特征.将两个同样工作在5.8 GHz、尺寸为4 cm×4 cm的全织物贴片天线作为收发两端,研究竖直状态下手臂的传输特征;再依据自然行走状态,模拟前摆最大值位置、自然下垂和后摆最大值位置手臂的动态过程.通过对天线在空气和手臂不同位置上传输特征的对比分析,确定表面波对传输特征的影响,并采用曲线拟合方法获得相对路径损耗预测模型;通过对比手臂三种自然状态的实测结果,建立路径损耗的预测模型.研究表明,对自然下垂状态下的预测模型进行简单的修正即可较好地预测前摆和后摆时的路径损耗.     

Humanoid motion planning of robotic arm based on human arm action feature and reinforcement learning

The use and application of robotic arms in helping the aged and vulnerable persons are increasing gradually. In order to achieve safer and reliable human-robot interaction and its wider adoption, the requirements for the humanoid motion of robotic arms are becoming more stringent. This paper presents a humanoid motion planning method for a robotic arm based on the physics of human arm and reinforcement learning. Firstly, the humanoid motion rules are extracted by analyzing and learning the action data of human arm, which is collected using the VICON optical motion capture system. Then, according to the acquired features and rules, the corresponding reward functions are proposed and the humanoid motion training of the robotic arm is carried out by using the reinforcement learning based on Deep Deterministic Policy Gradient (DDPG) and Hindsight Experience Replay (HER) algorithm. Finally, the experiments are carried out to verify whether the robotic arm motions planned by the proposed approach are humanoid, and the observed results show its feasibility and effectiveness in planning the humanoid motion of the robotic arm.     

Redundancy resolution of the human arm and an upper limb exoskeleton

The human arm has 7 degrees of freedom (DOF) while only 6 DOF are required to position the wrist and orient the palm. Thus, the inverse kinematics of an human arm has a nonunique solution. Resolving this redundancy becomes critical as the human interacts with a wearable robot and the inverse kinematics solution of these two coupled systems must be identical to guarantee an seamless integration. The redundancy of the arm can be formulated by defining the swivel angle, the rotation angle of the plane defined by the upper and lower arm around a virtual axis that connects the shoulder and wrist joints. Analyzing reaching tasks recorded with a motion capture system indicates that the swivel angle is selected such that when the elbow joint is flexed, the palm points to the head. Based on these experimental results, a new criterion is formed to resolve the human arm redundancy. This criterion was implemented into the control algorithm of an upper limb 7-DOF wearable robot. Experimental results indicate that by using the proposed redundancy resolution criterion, the error between the predicted and the actual swivel angle adopted by the motor control system is less then 5°.     

Digital control of shaft speed and position

Where speed accuracies within 0.1 percent are desired over a wide speed range, the digital approach has proved superior to the analog method. This article describes a typical hybrid digital/analog servo system used to control the speed of a dc motor. A vital part of the system is the comparator, which must combine the functions of frequency and phase discrimination and perform the transition smoothly. It is also shown how precise synchronism between two or more rotating systems, with respect to both speed and position, can be maintained, giving the effect of a ``synchronous link.'     

Sensorless position control of induction motors-an emergingtechnology

Concepts for the sensorless position control of induction motor drives rely on anisotropic properties of the machine rotor. Such anisotropies can be incorporated as periodic variations of magnetic saliencies in various ways. The built-in spatial anisotropy is detected by injecting a high-frequency flux wave into the stator. The resulting stator current harmonics contain frequency components that depend on the rotor position. Models of the rotor saliency serve to extract the rotor position signal using phase-locked loop techniques. A different approach makes use of the parasitic effects that originate from the discrete winding structure of a cage rotor. It has the merit of providing high spatial resolution for incremental positioning without sensor. The practical implementation of sensorless position identification and of a high-accuracy position control system are reported     

Compensator-based position control of an electrorheological actuator

This paper addresses the question of whether compensator-based controllers can be used to successfully control the position of a model scale robot arm attached to the output shaft of an electrorheological (ER) actuator, with a view of recommending the actuator for robotic applications and providing an alternative control strategy to proportional plus integral plus derivative, (PID), control. An ER actuator is a device that uses a ‘smart’ material, called an ER fluid or suspension, as a coupling medium between the prime mover running at a constant speed and a load. Three compensator-based controllers—the phase-lag, the phase-lead and lead-lag compensators—were designed and implemented on the ER actuator-arm system. The phase-lead and phase-lag compensators gave reasonable performance. The lead-lag compensator, on the other hand, was impossible to implement.     

Passivity-based reinforcement learning control of a 2-DOF manipulator arm

Passivity-based control (PBC) is commonly used for the stabilization of port-Hamiltonian (PH) systems. The PH framework is suitable for multi-domain systems, for example mechatronic devices or micro-electro-mechanical systems. Passivity-based control synthesis for PH systems involves solving partial differential equations, which can be cumbersome. Rather than explicitly solving these equations, in our approach the control law is parameterized and the unknown parameter vector is learned using an actor–critic reinforcement learning algorithm. The key advantages of combining learning with PBC are: (i) the complexity of the control design procedure is reduced, (ii) prior knowledge about the system, given in the form of a PH model, speeds up the learning process, (iii) physical meaning can be attributed to the learned control law. In this paper we extended the learning-based PBC method to a regulation problem and present the experimental results for a two-degree-of-freedom manipulator. We show that the learning algorithm is capable of achieving feedback regulation in the presence of model uncertainties.     

Modeling and control of the Mitsubishi PA-10 robot arm harmonic drive system

The purpose of this paper is to present our results in developing a dynamic model of the Mitsubishi PA-10 robot arm for the purpose of low-velocity trajectory tracking using low-feedback gains. The PA-10 is ideal for precise manipulation tasks because of the backdrivability, precise positioning capabilities, and zero backlash afforded by its harmonic drive transmission (HDT). However, the compliance and oscillations inherent in harmonic drive systems, and the lack of any technical information on the internal dynamics of the transmission, make the development of an accurate dynamic model of the robot extremely challenging. The novelty of this research is therefore the development of a systematic algorithm to extract the model parameters of a harmonic drive transmission in the robot arm to facilitate model-based control. We have modeled all seven joints of the Mitsubishi PA-10, and we have done several experiments to identify the various parameters of the harmonic drive system. We conclude with a sample trajectory-tracking task that demonstrates our model-based controller for the Mitsubishi PA-10 robot arm.     

An airjet actuator system for identification of the human arm jointmechanical properties

A system is described for determining the mechanical properties of the human arm during unconstrained posture and movement. An airjet perturbation device is attached to the wrist with a special cuff, and provides high-frequency stochastic perturbations in potentially three orthogonal directions. The airjet operates as a fluidic flip-flop utilizing the Coanda effect, and generates binary force sequences with a steady-state thrust of 4 N, a flat frequency response to 75 Hz, usable thrust to 150 Hz, and a rise time of 1 ms, when the static pressure at the nozzle inlet is 5.5 x 10(5) Pa (80 psi). These operating characteristics are adequate to identify the arm's mechanical properties efficiently and robustly.     

Identification of human control law during physical Human–Robot Interaction

With the growing interest in applications involving humans and robots teaming together, the need to understand each other’s intentions and behavior arises. This work presents a method to online identify the time-varying human feedback control law during physical Human–Robot Interaction. The robot motion is implemented as a Cartesian impedance, and the interaction with the human happens by force exchange. The coupled system is modeled with a state-space formulation. The state vector is augmented with the unknown parameters, and an Extended Kalman Filter (EKF) is implemented for online identification. This approach is compared with the Least Squares (LS) and the Recursive Least Squares (RLS) methods. Both simulation and experimental results are provided, showing the presented approach’s feasibility in identifying the parameters and reconstructing the control inputs.     

多点步进电机的远程位置控制系统

步进电机的远程多点位置控制系统,利用TCP协议将服务器端控制中心和客户端控制器接入因特网,可实现控制数据和位置监控数据的远程同步传输。系统采用NI公司的CompactRIO作为核心控制器;通过LabVIEW编写改进专家PID控制算法,可根据设定位置与实时位置的偏差动态设定输出控制器参数,有效防止过冲现象,实现步进电机的精确位置控制。步进电机的驱动控制电路由单片机和LM298构成,结合多级细分控制方法可有效抑制步进电机的震动和失步。     

Chattering reduction in the position control of induction motorusing the sliding mode

An induction motor position control system based on the sliding mode control is presented. In the sliding mode control, the control function is discontinuous on the hyperplane, which causes harmful effects such as current harmonics and acoustic noise in the motor drive application. A low-pass filter is introduced between the sliding mode controller output and the motor controller input to reduce these effects. Although the filter smooths the motor input current and alleviates the vibration at the final reference position, it may cause sluggish response in transient condition. To overcome the problem, a variable-bandwidth filter is proposed. In steady state, the bandwidth of the filter is made to be narrow to mitigate the ripple components while it is widened during the transient to improve the response. To achieve such an operation, the bandwidth of the filter is adjusted according to the error function. The proposed method shows good performance, which is confirmed through computer simulation and experiments     

模糊控制在焊接机器人位置跟随系统上的应用

介绍了一种基于ARM处理器与模糊控制算法的焊接机器人位置随动跟踪系统。在论述了模糊控制规律实现方法的基础上,提出了采用模糊控制法来实现焊接机器人与控制箱的精确同步运行,最后通过MATLAB搭建仿真平台,并验证了模糊控制方法在位置随动跟踪系统上的可行性和稳定性,从而可以在一定程度上提高了工业焊接技术水平。