NASA laboratory telerobotic manipulator control system architecture

In support of the National Aeronautics and Space Administration (NASA) goals to increase the utilization of dexterous robotic systems in space, the Oak Ridge National Laboratory (ORNL) has developed the Laboratory Telerobotic Manipulator (LTM) system. It is a dexterous, dual-arm, force-reflecting teleoperator system with robotic features for NASA ground-based research. This article describes the overall control system architecture, including both hardware and software. The control system is a distributed, modular, and hierarchical design with flexible expansion capabilities for future enhancements of both hardware and software.     

A kinematic analysis of the space station remote manipulator system (SSRMS)

An efficient reverse analysis of three 6-degree-of-freedom (dof) subchains of the 7-dof SSRMS is presented. The first subchain is formed by locking the seventh joint. The second subchain is formed by locking the second joint, while the third subchain is formed by locking the first joint (the grounded joint is counted as the first joint in the chain). There are a maximum of eight different arm configurations in each of the three subchains, and these were determined by employing a computer-efficient algorithm, which required the rooting of only at most quadratic polynomials. The algorithms were implemented, and the SSRMS was employed in an animated environment to perform and practice a number of useful tasks for space station servicing. The locking of the second joint has the advantage in that an operator could, at the outset, choose the orientation of the plane that contains the two longest links (the upper arm and forearm) so as to avoid collisions with obstacles. However, it has the disadvantage that when the second joint angle equals 0° or 180°, the manipulator is in a singularity configuration (a singularity analysis of the SSRMS is presented in a second article). It is interesting to note that this plane can also be oriented by specifying the first joint angle. This has the distinct advantage that the plane can be oriented arbitrarily and, in this way, the singularity is avoided.     

Tri-pyramid Robot: Design and kinematic analysis of a 3-DOF translational parallel manipulator

3-DOF translational parallel manipulators have been developed in many different forms, but they still have respective disadvantages in different applications. To overcome their disadvantages, the structure and constraint design of a 3-DOF translational parallel manipulator is presented and named the Tri-pyramid Robot. In the constraint design of the presented manipulator, a conical displacement subset is defined based on displacement group theory. A triangular pyramidal constraint is presented and applied in the constraint designs between the manipulator?s subchains. The structural properties including the decoupled motions, overconstraint elimination, singularity free workspace, fixed actuators and isotropic configuration are analyzed and compared to existing structures. The Tri-pyramid Robot is constrained and realized by a minimal number of 1-DOF joints. The kinematic position solutions, workspace with variation of structural parameters, Jacobian matrix, isotropic and dexterity analysis are performed and evaluated in the numerical simulations.     

A low-cost internet-based telerobotic system for access to remote laboratories

This paper presents an account of the design of a low-cost Internet-based teleoperation system implemented on China's Internet. Using a multimedia-rich human-computer interface, combining predictive displays and graphical overlays, a series of simple tasks were performed within a simulated space environment scenario. Internet clients anywhere can monitor the robotic workspace, talk with technicians, and control the Arm/Hand integrated system with 15 DOF located in lab to perform tasks (such as grasping a vessel, pouring a liquid, and peg-in-hole assembling, etc.). Our main contributions are to establish a foundation for teleoperated science and engineering research, and we have addressed some issues involving the time-delay associated with the Internet. We also developed several key software adaptation technologies and products used for Internet-Based teleoperation, compatible with the BH-III dexterous hand, BH1 6-DOF mechanical arm and five-finger 11-DOF data glove, constructed in our laboratory. This system has been successfully tested and applied in remote robotic education (Virtual Laboratories) system via China's Internet using our Master/Slave architecture, which combines mixed modes of remote monitor/manipulate and local autonomous control.     

Clamping weighted least-norm method for the manipulator kinematic control with constraints

One of the main challenges for kinematic control of manipulators is how to effectively address various constraints, such as obstacle avoidances. Most constraints can be converted into a virtual joint-limit problem by the general weighted least-norm method reported recently. However, a chattering of weighted factors might occur in the presence of disturbances. In this paper, in order to improve the robustness to disturbances, a clamping term forcing joints away from their limits is added to the solution of inverse kinematics, termed as the clamping weighted least-norm method. It is proved that the joint-limit constraint is always guaranteed. The proposed method is applicable to both non-redundant and redundant manipulators; the accuracy of main task is sacrificed only when there is confliction between main task and joint-limit constraint. Experiments on the seven-degree-of-freedom redundant manipulator illustrate the good performance for avoiding joint limits while tracking a given trajectory.     

The mechanical design of a seven-axes manipulator with kinematic isotropy

Discussed in this paper are the issues underlying the mechanical design of a seven-axes isotropic manipulator. The kinematic design of this manipulator was made based on one main criterion, namely, accuracy. Thus, the main issue determining the underlying architecture, defined by its Hartenberg—Denavit (HD) parameters, was the optimization of its kinematic conditioning. This main criterion led not to one set of HD parameters, but rather to a manifold of these sets, which allowed the incorporation of further requirements, such as structural behavior, workspace considerations and functionality properties. These requirements in turn allowed the determination of the link shapes and the selection of actuators. The detailed mechanical design led to heuristic rules that helped in the decision-making process in defining issues such as link sub-assemblies and motor location along the joint axes.     

一种新的六自由度机械臂运动学反解方法研究

针对运用解析法对机械臂进行运动学反解仅适用于具有特定结构机械臂的不足,提出能量优化的遗传算法进行机械臂运动学反解的方法。为便于能量的量化计算,在进行机械臂运动学分析的基础上,建立四连杆简化模型。采用实数编码方式,以机械臂各关节角上下限为依据,建立与之相对应的染色体。以机械臂各连杆势能变化及机械臂末端与期望值之差作为适应度函数,评估个体的适应度。通过概率的方法实现选择、交叉和变异操作。实验结果证明了该方法的正确性。     

Development of a vision non-contact sensing system for telerobotic applications

The study presented here describes a novel vision-based motion detection system for telerobotic operations such as distant surgical procedures. The system uses a CCD camera and image processing to detect the motion of a master robot or operator. Colour tags are placed on the arm and head of a human operator to detect the up/down, right/left motion of the head as well as the right/left motion of the arm. The motion of the colour tags are used to actuate a slave robot or a remote system. The determination of the colour tags’ motion is achieved through image processing using eigenvectors and colour system morphology and the relative head, shoulder and wrist rotation angles through inverse dynamics and coordinate transformation. A program is used to transform this motion data into motor control commands and transmit them to a slave robot or remote system through wireless internet. The system performed well even in complex environments with errors that did not exceed 2?pixels with a response time of about 0.1?s. The results of the experiments are available at: http://www.youtube.com/watch?v=yFxLaVWE3f8 and http://www.youtube.com/watch?v=_nvRcOzlWHw     

Optimizing the kinematic chains for a spatial parallel manipulator via searching the desired dexterous workspace

This paper exploits a new algorithm to optimize the length of the legs of a spatial parallel manipulator for the purpose of obtaining a desired dexterous workspace rather than the whole reachable workspace. With the analysis of the degree of freedom (DoF) of a manipulator, we can select the least number of variables to depict the kinematic constraints of each leg of a manipulator. The optimum parameters can be obtained by searching the extreme values of the objective functions with the given adroit workspace. Example is utilized to demonstrate the significant advantages of this method in the dexterous workspace synthesis. In applications, this method can be widely used to synthesize, optimize and create all kinds of new spatial parallel manipulator with a desired dexterous workspace.     

Workspace analysis for haptic feedback manipulator in virtual cockpit system

To obtain natural space experience of haptic interaction for users in virtual cockpit systems (VCS), a haptic feedback system and a workspace analysis framework for haptic feedback manipulator (HFM) are presented in this paper. Firstly, improving the classical three-dimensional workspace obtained by the Monte Carlo method, a novel workspace representation method, oriented workspace, is presented, which can indicate both the position and the orientation of the end-effector. Then, aimed at the characters of HFMs, the oriented workspace is divided into the effective workspace and the prohibited area by extracting the control panel area. At last, the effective workspace volume and the control panel area are calculated by the double-directed extremum method, with the accuracy improved by repeatedly adding and extracting boundary points. By simulation, the area in which interactions between the manipulator and users hand performed is determined and accordingly the effective workspace along with its boundary and volume are obtained in a relative high precision, which lay a basis for haptic interaction in VCS.     

A modified Hopfield neural networks model for graphs-based kinematic structure design

Graph theory can be used efficiently for both kinematic and dynamics analysis of mechanical structures. One of the most important and difficult issues in graphs theory-based structures design is graphs isomorphism discernment. The problem is vital for graph theory-based kinematic structures enumeration, which is known to be nondeterministic polynomial-complete problem. To solve the problem, a Hopfield neural networks (HNN) model is presented and some operators are improved to prevent premature convergence. By comparing with genetic algorithm, the computation times of the HNN model shows less affection when the number of nodes were enhanced. It is concluded that the algorithm presented in this paper is efficient for large-scale graphs isomorphism problem.     

力反馈水下遥操作系统稳定性分析

在遥操作系统中, 为了提高操作者的交互感知能力, 通常将与环境的接触力反馈回主端. 然而, 反馈力会导 致主端机器人的诱导运动, 使得主端机器人发出不准确的运动指令, 甚至导致闭环系统不稳定. 此外, 在作业过程 中, 水下机械臂不可避免地受到洋流和海浪带来的外部干扰. 针对带有接触力反馈的水下遥操作系统, 本文设计了 一种补偿主端位置漂移的辅助系统, 构造了有限时间干扰观测器, 并讨论了观测时间内系统状态的有界性, 进一步 证明了整个闭环系统是指数输入–状态稳定的. 仿真结果表明, 该方法能够保证变时延和外部干扰条件下水下遥操 作系统跟踪性能.     

A computationally efficient method for manipulator dynamic analysis

A computationally efficient method for manipulator dynamic analysis is presented. This method adopts two schemes to improve the computational efficiency. First, it takes the advantage of the following geometric feature of most manipulators: For the first three-degree-of-freedom (DOF) mechanism (positioning mechanism), all the links are moving in a principal plane that is rotating about the base axis with respect to the ground. With this geometry, only three equations of motion per link, two equations for the forces in the principal plane and one equation for the moments which are perpendicular to the principal plane, are needed for the inverse dynamic analysis of the first three-DOF motion. Thus, the number of equations can be reduced to half. Second, this method adopts longitudinal and transverse force components at certain joints in the formulation of equations of motion. This eliminates the need of a simultaneous solution of many equations, which is necessary in conventional Newton-Euler method. Hence, this method is more computationally efficient than the many existing dynamic analysis methods. Two examples, one is closed-chain type and the other is open-chain type, are used as illustrations.     

A kinematic, kinetic and electromyographic comparison of stooped sheep shearing techniques and shearing with a sheep manipulator

Traditional sheep shearing methods require workers to adopt postures where the trunk is approximately horizontal and held in that position against gravity for long periods of time. The objective of this study was to examine the biomechanics of stooped shearing techniques and to compare the effectiveness of a new sheep manipulator in reducing the frequency of these postures and the changes in low back forces and electromyographic (EMG) activity. Five male shearers were filmed using three video cameras and EMG and three-dimensional (3D) kinematic data were derived during seven segments of the shearing action. Kinematic data were used to calculate the L5/S1 compressive and shear forces using the 3D Static Strength Prediction Program(TM). Results showed the low back forces in stooped shearing were typically between 2200 and 3000N. Also, the sheep manipulator effectively allowed the shearers to maintain a more upright posture (mean trunk angle >65 degrees) which decreased the compressive (maximum <1350N) and shear (maximum <260N) forces at L5/S1.     

Dynamics analysis of the Star parallel manipulator

Matrix relations in kinematics and dynamics of the Star parallel manipulator are established in this paper. The prototype of the manipulator is a three-degree-of-freedom mechanism, which consists of a system of parallel kinematical chains connecting to a moving platform. Knowing the translation motion of the platform, we develop first the inverse kinematics problem and determine the position, velocity and acceleration of each robot’s link. Further, the inverse dynamics problem is solved using an approach based on the principle of virtual work, but it has been verified the results in the framework of the Lagrange equations with their multipliers. Recursive formulae offer expressions and graphs for the power requirement comparison of each of three actuators in two computational complexities: complete dynamic model and simplified dynamic model.     

A kinematic analysis of directional effects on mouse control

The directional effects associated with cursor movement controlled by a computer mouse have long been studied to improve mouse performance during precise tasks. However, those studies have rarely considered the kinematic variables associated with directional effects and have only analysed the projection of trajectories along the main axes of movement, eventually reducing the original dimensions of the data. In addition, as the angle of approach has a limited number of levels, it has been difficult to observe singular behaviour in the horizontal directions. In this study, we investigated the directional effects on kinematic variables when using a mouse to select circular targets. In this experiment, the measured trajectory of 16 different angles of approach was measured after separating the x and y components. The results revealed interesting biomechanical and cognitive features of mouse control and led to the suggestion of two improvements to be made upon the typical mouse design.     

A kinematic model for dynamic analysis of space frames

This paper presents a kinematic model for dynamic analysis of framed structures. The accuracy of the proposed method is demonstrated by analyzing the dynamic responses of two space frames of varying stiffness properties.     

The s-ethos system: A methodology for systematic flight analysis centered on human factors

The aeronautics community needs several alternative methods and tools to describe and analyze interactions between human operators and systems, according to some constraints (e.g., human factors, air safety, etc.). Hence, it needs to build models from the observation of real interactions, especially piloting, and to use extant theories from several fields: cognitive ergonomics and artificial intelligence, mainly. S-ETHOS sketches out a knowledge-based system that analyzes human pilot activities and provides feedback to improve air safety by giving measured appraisal of pilot error. The core of S-ETHOS is the ETHOS model that depicts the standard behavior based on the human pilot. S-ETHOS helps any air safety expert to simulate the pilot behavior during his mission and then will compare behavior between the simulation and real situations. It allows the air safety expert to know how the pilot assesses each situation. We implemented the ETHOS model according to an object-oriented approach, relying on a knowledge modeling language called OBJLOG II+. This model provides a first keystone to understanding how the human pilot captures and builds his environment through complex states. We will discuss the identified behaviors and potential deviations and associated situations.     

多功能智能操作器的设计

介绍基于单片机设计的多功能智能操作器原理及软硬件实现方法，该系统可完成操作器和伺服放大器两者的功能，控制电动执行机构或调节阀动作。实际使用说明，该系统具有优良的控制效果和极高的可靠性。     

简化Lorenz混沌系统的非线性动力学分析

借助Lyapunov函数稳定性理论研究了简化Lorenz混沌系统的全局吸引集,得到了它的界估计。通过了计算机模拟,数值模拟验证了计算理论的可行性。