并联结构制造装备设计理论与建模方法研究

并联结构制造装备（Parallel Kinematic Machine简称PKM）是近年发展起来的一种新型制造装备，它以承载能力强、动态性能好、刚度重量比大等优点而受到广大学者及机床制造商的重视并正在成为制造领域的一个研究热点。本文就有关PKM的结构、位置分析、速度关系、工作空间分析、奇异位形分析以及标定方法等问题进行了深入的研究，具体内容包括以下几个方面：1．根据现有PKM的结构特点，将它们划分为“腿伸缩”的6条腿结构、“腿滑动’夕的6条腿结构、“腿伸缩”的3条腿结构、“腿滑动”的3条腿结构等类型，这种划分佩方面能够较准确地反映PK.M的结构特征以及复杂程度，另一方面也易于为广大工程技术人员理解和使用。2．将少自由度并联机构分为满阶机构以及欠阶机构，而欠阶机构又进一步分为非期望输出为常量和非期望输出为变量两种类型，这样的分类反映了机构的本质特征以及对其进行研究的复杂程度。3．提出利用演化关系研究各种典型并联机构之间的内在联系，建立了一些典型并联机构之间的演化关系，为利用演化关系进行并联机构的运动学性能分析奠定了基础。根据演化原理，提出了几种实现两维平动、两维转动的4自由度 (2T-2R, 4-DOF）并联机构新构型，并用杆一副关系图进行描述。4．基于机构演化关系建立了典型并联机构位置分析数学描述的统一表达形式，并对所提出的几种2T-2R, 4-DOF并联机构的位置正、逆解进行了详细的讨论。对并联机构速度、静力传递关系的对偶性以及串联与并联之间的对偶关系进行了总结。5．提出具有灵巧度指标要求的适用工作空间概念，对考虑灵巧度指标要求的全姿态工作空间的确定进行了详细分析，给出了几种机构工作空间求解的具体结果。分析了现有奇异位形分析方法应用于少自由度并联机构时可能会出现的问题，并基于前面所述机构演化关系，提出一种进行少自由度并联机构奇异位形分析的新途径。6.分析了PKM运动学标定的研究现状，提出了一种新的运动学参数识别方法。该方法利用运动学逆解模型建立目标函数，并且不需要测量运动平台的姿态参数。7.初步完成了一个适用于PKM的基于“IPC+PMAC”的双CPU开放式数控系统的开发。对于不同构型的PKM，可以方便地更换虚实空间映射模块，并方便地扩展各种新的功能模块。通过本文的工作，对并联结构制造装备的若干问题进行了系统的研究，为新型并联结构制造装备研究和走向工程应用提供了设计思想、建模方法和关键技术，对于推进并联结构制造装备的发展具有重要意义。

Kinetostatic-model-based Stiffness Analysis of Exechon PKM

As a comparative newly-invented PKM with over-constraints in kinematic chains, the Exechon has attracted extensive attention from the research society. Different from the well-recognized kinematics analysis, the research on the stiffness characteristics of the Exechon still remains as a challenge due to the structural complexity. In order to achieve a thorough understanding of the stiffness characteristics of the Exechon PKM, this paper proposed an analytical kinetostatic model by using the substructure synthesis technique. The whole PKM system is decomposed into a moving platform subsystem, three limb subsystems and a fixed base subsystem, which are connected to each other sequentially through corresponding joints. Each limb body is modeled as a spatial beam with a uniform cross-section constrained by two sets of lumped springs. The equilibrium equation of each individual limb assemblage is derived through finite element formulation and combined with that of the moving platform derived with Newtonian method to construct the governing kinetostatic equations of the system after introducing the deformation compatibility conditions between the moving platform and the limbs. By extracting the 6 x 6 block matrix from the inversion of the governing compliance matrix, the stiffness of the moving platform is formulated. The computation for the stiffness of the Exechon PKM at a typical configuration as well as throughout the workspace is carried out in a quick manner with a piece-by-piece partition algorithm. The numerical simulations reveal a strong position-dependency of the PKM's stiffness in that it is symmetric relative to a work plane due to structural features. At the last stage, the effects of some design variables such as structural, dimensional and stiffness parameters on system rigidity are investigated with the purpose of providing useful information for the structural optimization and performance enhancement of the Exechon PKM. It is worthy mentioning that the proposed methodology of stiffness modeling in this paper can also be applied to other overconstrained PKMs and can evaluate the global rigidity over workplace efficiently with minor revisions.

An abstract machine for restricted and-parallel execution of logic programs

Although the sequential execution speed of logic programs has been greatly improved by the concepts introduced in the Warren Abstract Machine (WAM), parallel execution represents the only way to increase this speed beyond the natural limits of sequential systems. However, most proposed parallel logic programming execution models lack the performance optimizations and storage efficiency of sequential systems. This paper presents a parallel abstract machine which is an extension of the WAM and is thus capable of supporting ANDParallelism without giving up the optimizations present in sequential implementations. A suitable instruction set, which can be used as a target by a variety of logic programming languages, is also included. Special instructions are provided to support a generalized version of "Restricted AND-Parallelism" (RAP), a technique which reduces the overhead traditionally associated with the run-time management of variable binding conflicts to a series of simple run-time checks, which select one out of a series of compiled execution graphs.

An abstract machine based execution model for computer architecture design and efficient implementation of logic programs in parallel.

The term "Logic Programming" refers to a variety of computer languages and execution models which are based on the traditional concept of Symbolic Logic. The expressive power of these languages offers promise to be of great assistance in facing the programming challenges of present and future symbolic processing applications in Artificial Intelligence, Knowledge-based systems, and many other areas of computing. The sequential execution speed of logic programs has been greatly improved since the advent of the first interpreters. However, higher inference speeds are still required in order to meet the demands of applications such as those contemplated for next generation computer systems. The execution of logic programs in parallel is currently considered a promising strategy for attaining such inference speeds. Logic Programming in turn appears as a suitable programming paradigm for parallel architectures because of the many opportunities for parallel execution present in the implementation of logic programs. This dissertation presents an efficient parallel execution model for logic programs. The model is described from the source language level down to an "Abstract Machine" level suitable for direct implementation on existing parallel systems or for the design of special purpose parallel architectures. Few assumptions are made at the source language level and therefore the techniques developed and the general Abstract Machine design are applicable to a variety of logic (and also functional) languages. These techniques offer efficient solutions to several areas of parallel Logic Programming implementation previously considered problematic or a source of considerable overhead, such as the detection and handling of variable binding conflicts in AND-Parallelism, the specification of control and management of the execution tree, the treatment of distributed backtracking, and goal scheduling and memory management issues, etc. A parallel Abstract Machine design is offered, specifying data areas, operation, and a suitable instruction set. This design is based on extending to a parallel environment the techniques introduced by the Warren Abstract Machine, which have already made very fast and space efficient sequential systems a reality. Therefore, the model herein presented is capable of retaining sequential execution speed similar to that of high performance sequential systems, while extracting additional gains in speed by efficiently implementing parallel execution. These claims are supported by simulations of the Abstract Machine on sample programs.

并联刨床刚度分析及实验研究

为了提高刨削加工能力,而采用考虑到并联机构的特点而提出了并联刨床的概念并对其进行了简单说明.采用对机床进行分解的方法对机床的各功能模块分别建立刚度模型,并利用变形线性叠加的原理对机床的并联部分刚度进行分析.采用有限元软件对机床的床身框架及平面约束机构部分的刚度进行分析.并以仿真和实验加工的方式进行了刚度特性研究.

一种混合型4自由度并联机床的位置分析

针对原沈阳自动化研究所研制开发的五轴并联铣床的结构特点 ,提出了一种改进方案 ,并对这种新的构型的运动学进行了分析 ,针对其特点 ,从新的角度给出了位置正解及反解的方程。该构型的位置正解由于使用了附加传感器并充分考虑到机构特点而使得正解方程形式非常简单并且其中只存在一次项 ,从而避免了对复杂数值解法的采用

Improving the kinematic performance of the SCARA-Tau PKM

One well acknowledged drawback of traditional parallel kinematic machines (PKMs) is that the ratio of accessible workspace to robot footprint is small for these structures. This is most likely a contributing reason why relatively few PKMs are used in industry today. The SCARA-Tau structure is a parallel robot concept designed with the explicit goal of overcoming this limitation and developing a PKM with a workspace similar to that of a serial type robot of the same size. This paper shows for the first time how a proposed variant of the SCARA-Tau PKM can improve the usability of this robot concept further by significantly reducing the dependence between tool platform position and orientation of the original concept. The inverse kinematics of the proposed variant is derived and a comparison is made between this structure and the original SCARA-Tau concept, both with respect to platform orientation changes and workspace.

The Octahedral Hexarot - a novel 6-DOF parallel manipulator

A novel 6-DOF parallel kinematic manipulator named the Octahedral Hexarot is presented and analyzed. It is shown that this manipulator has the important benefits of combining a large positional workspace in relation to its footprint with a sizable range of platform rotations. These features are obtained by combining a rotation-symmetric actuating arm system with links in an octahedral-like configuration. Thus the manipulator consists of a central cylindrical column with six actuated rotating upper arms that can rotate indefinitely around the central column. Each upper arm is connected to a manipulated platform by one 5-DOF lower arm link. The link arrangement of the Octahedral Hexarot is inspired by the original Gough platform. The manipulated platform is an equilateral triangle and the joint positions on the upper arms approximately form an equilateral triangle. A task dependent optimization procedure for the structural parameters is proposed and the workspace of the resulting manipulator is analyzed in depth.

A contribution for developing more efficient dynamic modelling algorithms of parallel robots

Parallel kinematic structures are considered very adequate architectures for positioning and orienti ng the tools of robotic mechanisms. However, developing dynamic models for this kind of systems is sometimes a difficult task. In fact, the direct application of traditional methods of robotics, for modelling and analysing such systems, usually does not lead to efficient and systematic algorithms. This work addre sses this issue: to present a modular approach to generate the dynamic model and through some convenient modifications, how we can make these methods more applicable to parallel structures as well. Kane’s formulati on to obtain the dynamic equations is shown to be one of the easiest ways to deal with redundant coordinates and kinematic constraints, so that a suitable c hoice of a set of coordinates allows the remaining of the modelling procedure to be computer aided. The advantages of this approach are discussed in the modelling of a 3-dof parallel asymmetric mechanisms.

Design and implementation of a windows-based parallel computing environment for large scale optimization

A parallel computing environment to support optimization of large-scale engineering systems is designed and implemented on Windows-based personal computer networks, using the master-worker model and the Parallel Virtual Machine (PVM). It is involved in decomposition of a large engineering system into a number of smaller subsystems optimized in parallel on worker nodes and coordination of subsystem optimization results on the master node. The environment consists of six functional modules, i.e. the master control, the optimization model generator, the optimizer, the data manager, the monitor, and the post processor. Object-oriented design of these modules is presented. The environment supports steps from the generation of optimization models to the solution and the visualization on networks of computers. User-friendly graphical interfaces make it easy to define the problem, and monitor and steer the optimization process. It has been verified by an example of a large space truss optimization. (C) 2004 Elsevier Ltd. All rights reserved.

Towards the design of monolithic decoupled XYZ compliant parallel mechanisms for multi-function applications

This paper deals with the monolithic decoupled XYZ compliant parallel mechanisms (CPMs) for multi-function applications, which can be fabricated monolithically without assembly and has the capability of kinetostatic decoupling. At first, the conceptual design of monolithic decoupled XYZ CPMs is presented using identical spatial compliant multi-beam modules based on a decoupled 3-PPPR parallel kinematic mechanism. Three types of applications: motion/positioning stages, force/acceleration sensors and energy harvesting devices are described in principle. The kinetostatic and dynamic modelling is then conducted to capture the displacements of any stage under loads acting at any stage and the natural frequency with the comparisons with FEA results. Finally, performance characteristics analysis for motion stage applications is detailed investigated to show how the change of the geometrical parameter can affect the performance characteristics, which provides initial optimal estimations. Results show that the smaller thickness of beams and larger dimension of cubic stages can improve the performance characteristics excluding natural frequency under allowable conditions. In order to improve the natural frequency characteristic, a stiffness-enhanced monolithic decoupled configuration that is achieved through employing more beams in the spatial modules or reducing the mass of each cubic stage mass can be adopted. In addition, an isotropic variation with different motion range along each axis and same payload in each leg is proposed. The redundant design for monolithic fabrication is introduced in this paper, which can overcome the drawback of monolithic fabrication that the failed compliant beam is difficult to replace, and extend the CPM’s life.

Diseño, fabricación y montaje de un robot de cinemática paralela de dos grados de libertad

[ES]Este Trabajo consiste en diseñar un robot de cinemática paralela de dos grados de libertad partiendo de unos requisitos mínimos necesarios que habrán de verificarse. A continuación, se fabricará siguiendo dicho diseño para finalmente montarlo sobre unas guías lineales constituyendo así una máquina de cinemática paralela, objetivo final conjunto de este Trabajo añadido al mencionado control de las guías. Resulta de especial interés su particular arquitectura, aspecto clave cuando se pretende un sistema preciso y reducir las vibraciones.

Diseño, fabricación y control de un sistema neumático de agarre de 1 grado de libertad

[ES]El presente Trabajo de Fin de Grado tiene la finalidad de contribuir al desarrollo de una línea de investigación mediante la implementación de un sistema neumático de agarre al mecanismo de cinemática paralela 5R. Dicho proyecto se integra dentro de una línea de investigación basada en el desarrollo y estudio de mecanismos de este tipo. Así, este Trabajo supone una pequeña parte de un proyecto de mayor envergadura, para cuyo éxito será necesaria la colaboración con otros investigadores y la integración de este trabajo al realizado por ellos. Consiste en diseñar, fabricar y controlar un sistema neumático de agarre al mecanismo 5R. El diseño se realizará sopesándose las distintas alternativas que existen, teniéndose en cuenta las limitaciones impuestas por el 5R. En el diseño se escogen los componentes correctos para conseguir que el sistema realice sus dos funciones:  Agarrar piezas.  Movimiento en el eje z que le permita desplazar el objeto. Antes del ensamblaje de los componentes neumáticos, y teniendo en cuenta el diseño realizado, se fabricarán las piezas necesarias para poder integrarlo al 5R y para, a su vez, juntar los componentes entre sí. A continuación, se desarrollará un programa informático para poder controlar el sistema. Finalmente, para verificar su correcto funcionamiento, se realizarán las pruebas pertinentes.

Diseño y evaluación de un sistema de medida de aceleración en el elemento terminal de un manipulador de cinemática paralela

[ES]Este proyecto tiene como objetivo desarrollar una línea de investigación de opciones de sensorización de un mecanismo mediante acelerómetros. Se construirá para ello un sistema de adquisición y tratamiento de señales destinado a la sensorización de un mecanismo de cinemática paralela en base a los conocimientos adquiridos durante el curso. Se trabajará además con otros alumnos para llevar a cabo el diseño y montaje de un robot prototipo de cinemática paralela de dos grados de libertad sobre el que se experimentará y llevará a cabo el proyecto. Se plantean de este modo dos líneas de trabajo que se desarrollarán en este proyecto: Elaboración de un sistema de adquisición y tratamiento de señales adaptable a distintos sensores. Utilización de señales de múltiples acelerómetros para conocer en primer lugar aceleración, y de ser posible, posición de puntos de interés del mecanismo.