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.     

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.     

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.     

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.     

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.     

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.     

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, 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.     

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.     

Topology design and kinematic optimization of cyclical 5-DoF parallel manipulator with proper constrained limb

This paper proposes topology design and kinematic optimization of cyclical 5-degree-of-freedom (DoF) parallel manipulator with proper constrained limb. Firstly, a type of cyclical 5-DoF parallel manipulators with proper constrained limb is proposed by analyzing DoF of the proper constrained limb within workspace. Exampled by a cyclical 5-DoF parallel manipulator with the topology 4-UPS&1-RPS, its motion mapping model is formulated. By taking the reciprocal product of a wrench on a twist as the generalized virtual power, the local and global kinematic performance indices are provided. Then, on the basis of the actuated and constrained singularity analysis of the 4-UPS&1-RPS parallel manipulator within the position and pose workspace, the topology design of the manipulator without singularity is carried out, and its reachable and prescribed workspaces are obtained. Finally, by maximizing the global kinematic performance index and subjecting to a set of appropriate constraint conditions, the kinematic optimal design of the 4-UPS&1-RPS parallel manipulator is carried out utilizing the genetic algorithm of MATLAB optimization toolbox.     

Duty-cycle analysis of a human-controlled manipulator

The duty cycles of a human-controlled servomanipulator system have been experimentally measured revealing how humans use manipulators to perform tasks. The use of the kinematic ranges, in both joint and Cartesian space is valuable to engineers in the kinematic design of servomanipulators. The working volume of human manipulation presented here is also of interest to designers of prosthetic systems. These results illuminate the relative merits of various system drive configurations. A graphical representation of mechanical power usage, which displays the total operation time as a function of torque and velocity, is presented for each manipulator joint. These data are compared with data representing idealized joint performance resulting in design criteria for quantitative improvements in joint torque and velocity capacities. A generalized method for applying this representation to any robotic system is discussed.     

Formulation of the kinematic model of a general (6 DOF) robot manipulator using a screw operator

In general, the manipulator's end-effector can be located in a desired position and orientation in its work-space through angular and/or linear displacements of its joints. These joint coordinates can be obtained by solving the loop-closure equation of the manipulator's kinematic model. The most common method for obtaining this equation is based on the point coordinates 4×4 homogeneous transformation matrix. This method uses a special set of frames which are adapted to the manipulator's configuration. Within the last few years there has been some interest in the use of screw operators (line transformations) to model the kinematic configuration of manipulators and to form the loop-closure equation. In this article, a kinematic model of a general (6 DOF) manipulator is obtained through the application of a screw operator (dual-unit quaternion) to represent the screw displacements of the line coordinates of the manipulator link and joint axes. The loop-closure equation of the closed kinematic chain is obtained by introducing a hypothetical link/joint at the manipulator's end-effector location. The resultant non-linear loop-closure equation is then solved for the joint coordinates using a numerical technique. The method is illustrated with an example.     

一种六自由度机械臂的控制系统设计

针对机械臂在工业自动化等方面的需求,在分析了传统机械臂控制系统的基础上提出了一种以STM32F4为主控制器、陀螺仪传感器为关节状态检测器、舵机驱动模块为机械臂运动单元的六自由度控制系统。该系统采用扩展卡尔曼滤波算法(EKF算法),将陀螺仪采集的关节状态参数传递给EKF核心算法进行预估机械臂的运动状态,实现对机械臂运动过程中的偏差调控。实验表明,该控制系统的运动精度误差最大不超过18 mm,能够快速、准确地调控机械臂的运动轨迹。     

应用网络数据通信的飞行模拟系统

介绍了一种应用网络进行数据通信的飞行模拟系统，由于本系统实时性要求强，在两站之间使对等通讯，阐述了应用网间数据包交换协议进行网络数据通信的通信过程，实现了目标投影系统和天地景系统的要求功能，获得满意的控制效果。