The optimum design of 6‐DOF isotropic parallel manipulators

How to obtain 6‐DOF parallel manipulators with optimum global isotropy is investigated in this paper. A systematic method is first presented to get isotropic parallel designs. A measure for spatial isotropy is then proposed to evaluate and compare the global isotropy of obtained manipulators. Efficient methods to find the minimum and maximum singular values of matrices are developed to facilitate the evaluation process. © 2005 Wiley Periodicals, Inc.     

Kinematics of a parallel-serial (Hybrid) manipulator

Hybrid manipulators are parallel-serial connection robots that give rise to a multitude of highly articulate robotic manipulators. These manipulators are modular and can be extended by additional modules over large distances. Every module has a hemispherical work space and collective modules give rise to highly dexterous symmetrical work space. In this article, some basic designs and kinematical structures of these robot manipulators are discussed, the associated direct and the inverse kinematics formulations are presented, and solutions to the inverse kinematic problem are obtained explicitly and elaborated upon. These robot manipulators are shown to have a strength-to-weight ratio many times larger than the value currently available with industrial or research manipulators. This is due to the fact that these hybrid manipulators are stress compensated and have an ultralight weight, yet are extremely stiff due to the fact that the force distribution in their structure is mostly axial. The means of actuation in these manipulators are entirely prismatic and can be provided by ball-screws with antibacklash nuts or linear induction motors for maximum precision.     

Generating classes of locally orthogonal Gough-Stewart platforms

This paper develops methods for generating classes of orthogonal Gough-Stewart platforms (OGSPs). First, a new, two-parameter class of six-strut OGSPs which leads to isotropic manipulators are found. Next, this class is extended to include redundant Gough-Stewart platforms (GSPs). For an even number of struts, the same algorithm used to generate the six-strut case can be employed. For an odd number of struts, similar essential concepts are used to derive seven-strut and nine-strut OGSPs. Maximization of fault tolerance is implemented for a nine-strut isotropic OGSP. By exploiting invariant properties of the inverse Jacobian, new methods for favorably altering the center of gravity, strut attachment surface, and strut spatial distribution are developed.     

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.     

Realization of task-based designs involving DH parameters: a modular approach

Task-based designs—proven to be successful for constrained environments—may face challenges at prototype development phase. To assist in generalized design and development of task-based serial manipulators for cluttered environments, a parameters-based modular approach is proposed. First, a task-based design strategy for serial manipulators is exhibited, using all the robotic parameters (DH parameters) as variables. The flexibility in robotic parameters enhances the possibility of good designs even for highly cluttered workspaces, but the realization of the resulting complicated designs is challenging. This work is an attempt to develop modular manipulators in correspondence to the task-based designs. The DH parameters-based proposed link modules, with reconfigurable architecture, can be adjusted and assembled to acquire the serial manipulators with designed robotic parameters. To validate the concept, some standardized 3R-configurations have been modelled using the proposed link modules. Case studies are presented on task-based design of robotic manipulators, with six and eight degrees of freedom, for service applications in realistic environments. The selected case studies include the robot design processes for applications of cleaning solar panels, and for the maintenance of the nuclear plants.     

Design and analysis of kinematically redundant parallel manipulators with configurable platforms

Redundancy can, in general, improve the ability and performance of parallel manipulators by implementing the redundant degrees of freedom to optimize a secondary objective function. Almost all published researches in the area of parallel manipulators redundancy were focused on the design and analysis of redundant parallel manipulators with rigid (nonconfigurable) platforms and on grasping hands to be attached to the platforms. Conventional grippers usually are not appropriate to grasp irregular or large objects. Very few studies focused on the idea of using a configurable platform as a grasping device. This paper highlights the idea of using configurable platforms in both planar and spatial redundant parallel manipulators, and generalizes their analysis. The configurable platform is actually a closed kinematic chain of mobility equal to the degree of redundancy of the manipulator. The additional redundant degrees of freedom are used in reconfiguring the shape of the platform itself. Several designs of kinematically redundant planar and spatial parallel manipulators with configurable platform are presented. Such designs can be used as a grasping device especially for irregular or large objects or even as a micro-positioning device after grasping the object. Screw algebra is used to develop a general framework that can be adapted to analyze the kinematics of any general-geometry planar or spatial kinematically redundant parallel manipulator with configurable platform.     

Generation and forward displacement analysis of two new classes of analytic 6‐SPS parallel manipulators

Analytic manipulators are manipulators with a characteristic polynomial of fourth degree or lower. Using the component approach to generate analytic 6‐SPS parallel manipulators (PMs), the generation process is reduced to the generation of analytic components for 6‐SPS PMs. Two new classes of analytic components for 6‐SPS PMs are generated at first. Then, two new classes, IX and X, of analytic 6‐SPS PMs are generated. The forward displacement analysis (FDA) of the new analytic 6‐SPS PMs is also performed. The FDA of the 6‐SPS PMs of class IX is reduced to the solution of one univariate cubic equation and two univariate quadratic equations, in sequence, while that of the 6‐SPS PMs of class X is reduced to the solution of three univariate quadratic equations in sequence. Both of the new analytic 6‐SPS PMs have at most eight assembly modes. © 2001 John Wiley & Sons, Inc.     

Inverse kinematics of variable-geometry truss manipulators

A new class of robotic arm consists of a periodic sequence of truss substructures, each of which has several variable-length members. Such variable-geometry truss manipulators (VGTMs) are inherently highly redundant and promise a significant increase in dexterity over conventional anthropomorphic manipulators. This dexterity may be exploited for both obstacle avoidance and controlled deployment in complex workspaces. The inverse kinematics problem for such unorthodox manipulators, however, becomes complex because of the large number of degrees of freedom, and conventional solutions to the inverse kinematics problem become inefficient because of the high degree of redundancy. This paper presents a solution to this problem based on a spline-like reference curve for the manipulator's shape. Such an approach has a number of advantages: (1) direct, intuitive manipulation of shape; (2) reduced calculation time; and (3) direct control over the effective degree of redundancy of the manipulator. Furthermore, although the algorithm has been developed primarily for variable-geometry-truss manipulators, it is general enough for application to other manipulator designs.     

Active isotropic compliance in redundant manipulators

Multibody System Dynamics - The isotropic compliance property is examined in the Special Euclidean Group SE(3) in the case of redundant manipulators. The redundancy problem is solved by means of...     

Conformational Modeling of Continuum Structures in Robotics and Structural Biology: A Review

Hyper-redundant (or snakelike) manipulators have many more degrees of freedom than required to position and orient an object in space. They have been employed in a variety of applications ranging from search-and-rescue to minimally invasive surgical procedures, and recently they even have been proposed as solutions to problems in maintaining civil infrastructure and the repair of satellites. The kinematic and dynamic properties of snakelike robots are captured naturally using a continuum backbone curve equipped with a naturally evolving set of reference frames, stiffness properties, and mass density. When the snakelike robot has a continuum architecture, the backbone curve corresponds with the physical device itself. Interestingly, these same modeling ideas can be used to describe conformational shapes of DNA molecules and filamentous protein structures in solution and in cells. This paper reviews several classes of snakelike robots: (1) hyper-redundant manipulators guided by backbone curves; (2) flexible steerable needles; and (3) concentric tube continuum robots. It is then shown how the same mathematical modeling methods used in these robotics contexts can be used to model molecules such as DNA. All of these problems are treated in the context of a common mathematical framework based on the differential geometry of curves, continuum mechanics, and variational calculus. Both coordinate-dependent Euler–Lagrange formulations and coordinate-free Euler–Poincaré approaches are reviewed.     

High-speed positioning of an industrial robot based on Preview-Learning control

In this study, a numerical procedure for designing kinematic parameters of SCARA-type manipulators is proposed to yield such a design that the resulting manipulator has the fastest cycle time for a given task. To achieve this goal, an optimization problem is formulated to minimize the cycle time by determining geometric parameters such as the link lengths and the locations of manipulators as well as the trajectory. The representative task to get the cycle time is defined as CP (continuous path) motion along the path crisscrossing the standard working area. A gradient projection algorithm is used to obtain the optimal design with the assumption that each actuator should exert a torque and angular velocity within the capacity of specific commercially available direct-drive motors. SCARA-type manipulators of both absolute coordinate and relative coordinate types are designed to reduce the cycle times. The results show that the absolute coordinate manipulator produces a shorter cycle time than the relative coordinate manipulator in optimal designs.     

A Geometric Theory for Analysis and Synthesis of Sub-6 DoF Parallel Manipulators

Mechanism synthesis is mostly dependent on the designer's experience and intuition and is difficult to automate. This paper aims to develop a rigorous and precise geometric theory for analysis and synthesis of sub-6 DoF (or lower mobility) parallel manipulators. Using Lie subgroups and submanifolds of the special Euclidean group SE(3), we first develop a unified framework for modelling commonly used primitive joints and task spaces. We provide a mathematically rigorous definition of the notion of motion type using conjugacy classes. Then, we introduce a new structure for subchains of parallel manipulators using the product of two subgroups of SE(3) and discuss its realization in terms of the primitive joints. We propose the notion of quotient manipulators that substantially enriches the topologies of serial manipulators. Finally, we present a general procedure for specifying the subchain structures given the desired motion type of a parallel manipulator. The parallel mechanism synthesis problem is thus solved using the realization techniques developed for serial manipulators. Generality of the theory is demonstrated by systematically generating a large class of feasible topologies for (parallel or serial) mechanisms with a desired motion type of either a Lie subgroup or a submanifold.     

Kinematic and dynamic design and optimization of a parallel rehabilitation robot

In this paper, a method for concurrent optimum design of a complex parallel manipulator is introduced. The manipulator is a three-degree-of-freedom mechanism used as a walking rehabilitation device. The proposal deals with several optimization issues; firstly, the methodology is applied to a system recently designed and, in the best of our knowledge, the control policy, and dynamic model have not been published before, secondly, we propose an objective function which considers dexterity and singular manipulators, as well as energy and position error, and thirdly, we propose an optimization algorithm which successfully approximates the optimum solution, delivering low-cost feasible designs with fewer function evaluations than a comparing Genetic Algorithm. A set of numerical simulations validate the methodology and evidence its robustness since it delivers quite similar designs in several independent executions.

     

Geometrical conditions for the design of partial or full isotropic hexapods

This paper presents a methodology for the design of PKMs (parallel kinematic machines) with defined isotropy and stiffness. Partial isotropy or full isotropy can be achieved by suitable design choices. The former is useful for five axis applications, while the latter for six axis manipulators. The paper summarizes the concept of full and partial isotropy, and for a wide class of hexapods defines in analytical form the conditions to achieve it exactly. These conditions can be used to design isotropic parallel manipulators. The methodology requires that the six legs have to be divided into two groups (terns). The legs belonging to one tern are mutually identical and are positioned with radial symmetry with respect to the TCP (tool center point). The paper shows that the manipulator structure can be defined in term of 13 design parameters, the value of six of them are chosen in order to achieve the required isotropy and stiffness properties, while the remaining seven parameters can be used to optimize the structure. The design criterion here presented assures that stiffness isotropy, force, and velocity isotropy are all achieved contemporarily. This methodology can be practically applied to a large family of hexapods. © 2005 Wiley Periodicals, Inc.     

Adaptive fuzzy control of mechanicalbehavior for a two degree-of-freedomrobotic manipulator

Active compliance control of robotic manipulators is useful in making robots perform precision assembly operations. The essential requirement here is mechanical isotropy of the robot end-point. In this paper the problem of how to achieve this kind of mechanical behaviour is considered from aspects of impedance control and fuzzy set theory. The new fuzzy–impedance control law, which is suitable for real-time applications, is proposed for a two degree-of-freedom (2-d.o.f.) robotic manipulator. According to simulation results, the proposed control law can provide approximately isotropic behaviour of the robot end-point in the whole workspace.     

基于非线性H_∞状态反馈的机器人鲁棒控制

针对机器人存在参数不确定性以及外界未知干扰的情况 ,运用反推 (backstepping)设计方法 ,通过求解非线性 H∞ 状态反馈控制问题 ,设计了一种鲁棒控制器 ,实现了对外界未知干扰的有效衰减 ,以及只考虑参数不确定性时系统跟踪误差的渐近收敛性 .最后给出了对两连杆刚性机器人的仿真 ,验证了控制效果 .     

基于非线性H∞状态反馈的机器人鲁棒控制

针对机器人存在参数不确定性以及外界未知干扰的情况,运用反推(backstepping)设计方法 ,通过求解非线性H∞状态反馈控制问题,设计了一种鲁棒控制器,实现了对外界未 知干扰的有效衰减,以及只考虑参数不确定性时系统跟踪误差的渐近收敛性．最后给出了对 两连杆刚性机器人的仿真,验证了控制效果．     

Translational Parallel Manipulators: New Proposals

Translational parallel manipulators are parallel manipulators wherein the end‐effector performs only spatial translations. This paper presents a new family of translational parallel manipulators. The manipulators of this family are independent constraint manipulators. They have three limbs that are topologically identical and have no rotation singularity. The limbs of these manipulators feature five one‐degree‐of‐freedom kinematic pairs in series. Four joints are revolute pairs and the remaining one, called T‐pair, is a kinematic pair that can be manufactured in different ways. In each limb, three adjacent revolute pairs have parallel axes and the remaining revolute pair has an axis that is not parallel to the axes of the other revolute pairs. The mobility analysis of the manipulators of this new family is addressed by taking into account two different choices for the actuated pairs. One of the results of this analysis is that the geometry of a translational parallel manipulator free from singularities can be defined for a particular choice of the actuated pairs. © 2002 Wiley Periodicals, Inc.     

冗余机械臂运动学优化设计

该文主要从机械臂运动学的角度,定义了故障容错机械臂,巧妙地论证了冗余故障容错机械臂应该具备的自由度数,以及针对不同的任务要求,设计故障容错机械臂的方法。通过将任务空间抽象简化为一系列的特征点,建立机械臂参数与理想值相关的罚函数,选择有效的优化算法,设计出了通用一阶故障容错平面位置机械臂,通用一阶故障容错空间位置机械臂,以及特定任务一阶故障容错平面位置机械臂。建立起完整的故障容错机械臂的设计方法。     

化工过程模拟类库的设计

将面向对象思想应用于化工过程模拟软件的开发中,为实现化工过程模拟软件的资源重用,提出了建立化工过程模拟类库的思想。类库的采用为各个类的应用与维护提供了一种有效的方法,有利于采用面向对象思想进行化工模拟软件的开发、升级与维护。本文采用分析与综合的方法,将化工过程模拟领域涉及的各种要领进行抽象,获得相应的类,对这些类统一组织、管理形成类库。类库中的类主要分为基础类和过程单元类。基础类包括组份类、混合物