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2011 | Buch

Geometric Design of Linkages

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This book is an introduction to the mathematical theory of design for articulated mechanical systems known as linkages. The focus is on sizing mechanical constraints that guide the movement of a work piece, or end-effector, of the system. The function of the device is prescribed as a set of positions to be reachable by the end-effector; and the mechanical constraints are formed by joints that limit relative movement. The goal is to find all the devices that can achieve a specific task. Formulated in this way the design problem is purely geometric in character. Robot manipulators, walking machines, and mechanical hands are examples of articulated mechanical systems that rely on simple mechanical constraints to provide a complex workspace for the end- effector. The principles presented in this book form the foundation for a design theory for these devices. The emphasis, however, is on articulated systems with fewer degrees of freedom than that of the typical robotic system, and therefore, less complexity. This book will be useful to mathematics, engineering and computer science departments teaching courses on mathematical modeling of robotics and other articulated mechanical systems.

This new edition includes research results of the past decade on the synthesis of multi loop planar and spherical linkages, and the use of homotopy methods and Clifford algebras in the synthesis of spatial serial chains. One new chapter on the synthesis of spatial serial chains introduces numerical homotopy and the linear product decomposition of polynomial systems. The second new chapter introduces the Clifford algebra formulation of the kinematics equations of serial chain robots. Examples are use throughout to demonstrate the theory.

Inhaltsverzeichnis

Frontmatter
Chapter 1. Introduction
Abstract
A mechanical system, or machine, generally consists of a power source and a mechanism for the controlled use of this power. The power may originate as the flow of water or the expansion of steam that drives a turbine and rotates an input shaft to the mechanism. It may be that instead the turbine rotates a generator and the resulting electricity is used to actuate a distant electric motor connected to the mechanism input. Another power source is the expansion of pressurized fluid or burning air–fuel mixture against a piston in order to drive its linear movement inside a cylinder. The purpose of the mechanism is to transform this input power into a useful application of forces combined with a desired movement. For this reason, machines are often defined abstractly as devices that transform energy from one form, such as heat or chemical energy, into another form, usually work.
J. Michael McCarthy, Gim Song Soh
Chapter 2. Analysis of Planar Linkages
Abstract
In this chapter we consider assemblies of links that move in parallel planes. Any one of these planes can be used to examine the movement since the trajectories of points in any link can be projected onto this plane without changing their properties. Our focus is on linkages constructed from revolute joints with axes perpendicular to RR, PR, and RP open chains and the closed chains constructed from them, as well as the 3R and RPR planar robots. We determine the configuration of the linkage as a function of the independent joint parameters and the physical dimensions of the links.
J. Michael McCarthy, Gim Song Soh
Chapter 3. Graphical Synthesis in the Plane
Abstract
The geometric principles that are fundamental to linkage design can be found in simple and efficient graphical constructions for RR and PR chains. As the floating link of one of these chains reaches various task positions, points in it define sets of corresponding points in the fixed frame. The design problem is to find a circle for the RR chain and a straight line for the PR chain that passes through these corresponding points. This usually results in multiple RR and PR chains that can be combined to form slider-crank or four-bar linkages.
J. Michael McCarthy, Gim Song Soh
Chapter 4. Planar Kinematics
Abstract
In this chapter we study the geometry of planar displacements. The position of a moving body is defined by a coordinate transformation. Associated with each of these transformations is an invariant point called the pole of the displacement. We examine the relationship between relative positions of points in the moving body and the location of this pole. We also consider the triangle formed by the poles of two displacements and the pole of their composite displacement. The geometry of this triangle describes the relationship between the three displacements.
J. Michael McCarthy, Gim Song Soh
Chapter 5. Algebraic Synthesis of Planar Chains
Abstract
In this chapter we examine the design of RR, PR and RP planar open chains that reach a specified set of task positions. A constraint equation is defined for each chain that characterizes the set of positions that it can reach. This relationship is inverted by considering the positions as known and the fixed and moving pivots of the chain as unknowns. The result is a set of design equations that are solved to design the chain.
J. Michael McCarthy, Gim Song Soh
Chapter 6. Multiloop Planar Linkages
Abstract
In this chapter, we will formulate the systematic design of multiloop planar linkages in a way that combines with traditional robotics and four-bar linkage synthesis theory to obtain innovative articulated robotic systems. First, we will show how mechanical constraints can be introduced to a planar 3R serial chain to guide the movement of its end effector through a set of five specified task positions to obtain a six-bar linkage, as illustrated in Figure 6.1.
J. Michael McCarthy, Gim Song Soh
Chapter 7. Analysis of Spherical Linkages
Abstract
In this chapter we examine spherical linkages. These linkages have the property that every link in the system rotates about the same fixed point. Thus, trajectories of points in each link lie on concentric spheres with this point as the center. Only the revolute joint is compatible with this rotational movement and its axis must pass through the fixed point. We study the spherical RR and 3R open chains and the 4R closed chain and determine their configuration as a function of the joint variables and the dimensions of the links.
J. Michael McCarthy, Gim Song Soh
Chapter 8. Spherical Kinematics
Abstract
In this chapter we consider spatial displacements that are pure rotations in threedimensional space. These are transformations that have the property that one point of the moving body M has the same coordinates in F before and after the displacement. Because the distance between this fixed point and points in M are constant, each point in the moving body moves on a sphere about this point. If the origins for both the fixed and moving frames are located at this fixed point, then the spatial displacement is defined by a 3x3 rotation matrix. The study of spherical kinematics benefits from both the properties of linear transformations and the geometry of a sphere.
J. Michael McCarthy, Gim Song Soh
Chapter 9. Algebraic Synthesis of Spherical Chains
Abstract
In this chapter we formulate the design theory for spherical RR chains. The axes of the two revolute joints must lie in the same plane, and therefore intersect in a point. The floating link of this system moves in pure rotation about this point.
J. Michael McCarthy, Gim Song Soh
Chapter 10. Multiloop Spherical Linkages
Abstract
In this chapter, the design procedure introduced for the synthesis of planar six- and eight-bar linkages is applied to the synthesis of spherical six- and eight-bar linkages. The process begins with the specification of a spherical 3R chain or a spherical 6R loop and five task orientations. The synthesis equations for RR chains are solved to constrain the spherical 3R serial chain to design a spherical six-bar linkage, and to constrain the 6R loop to design an eight-bar linkage. The result is one degree-offreedom spherical linkages that move through the five task positions.
J. Michael McCarthy, Gim Song Soh
Chapter 11. Analysis of Spatial Chains
Abstract
In this chapter we study spatial linkages. These systems have at least one link that moves through a general spatial displacement. We examine the TS and CC chains that are important to our design theory, as well as the TPS and TRS chains that appear in robotics. In addition, we study the 3R wrist which is actually a spherical linkage, however, it provides a convenient parameterization of the S-joint that is an important part of our spatial open chains. We determine the joint angles for these chains that position the end-effector in a desired location.
J. Michael McCarthy, Gim Song Soh
Chapter 12. Spatial Kinematics
Abstract
In this chapter we develop the geometry of spatial displacements defined by coordinate transformations consisting of spatial rotations and translations. We consider the invariants of these transformations and find that there are no invariant points. Instead there is an invariant line, called the screw axis. Thus, the geometry of lines becomes important to our study of spatial kinematics.We find that a configuration of three lines, called a spatial triangle, generalizes our results for planar and spherical triangles to three-dimensional space.
J. Michael McCarthy, Gim Song Soh
Chapter 13. Algebraic Synthesis of Spatial Chains
Abstract
In this chapter we consider the design of spatial TS, CC, and RR chains. Our approach is the same as that used to design planar and spherical linkages. For each chain we determine the geometric constraints that characterize the chain, and formulate design equations that are solved for a given set of task positions.
J. Michael McCarthy, Gim Song Soh
Chapter 14. Synthesis of Spatial Chains with Reachable Surfaces
Abstract
In this chapter, we consider the design of spatial serial chains that guide a body such that a point in the body moves on a specific algebraic surface. The problem originates with Schoenflies [113], who sought points that remained in a given configuration for a given set of spatial displacements. Burmester [7] applied this idea to planar mechanism design by seeking the points in a planar moving body that remain on a circle. Chen and Roth [10] generalized this problem to find points and lines in a moving body that take positions on surfaces associated with the articulated chains used to build robot manipulators.
J. Michael McCarthy, Gim Song Soh
Chapter 15. Clifford Algebra Synthesis of Serial Chains
Abstract
In this chapter we formulate design equations for a spatial serial chain using the matrix exponential form of its kinematics equations. These equations define the position and orientation of the end effector in terms of rotations about the joint axes of the chain. Because the coordinates of these axes appear explicitly, we can specify a set of task positions, and solve these equations to determine the location of the joints. At the same time we are free to specify joint parameters or certain dimensions to ensure that the resulting robotic system has certain features.
J. Michael McCarthy, Gim Song Soh
Chapter 16. Platform Manipulators
Abstract
In this chapter we consider six-degree-of-freedom systems consisting of a platform supported by multiple serial chains, called parallel, or platform, manipulators.Walking machines, mechanical fingers manipulating an object, and vehicle simulator platforms are all examples of platform manipulators. The Jacobian of these systems defines the contribution of each actuator to the resultant force and torque applied to the platform.
J. Michael McCarthy, Gim Song Soh
Backmatter
Metadaten
Titel
Geometric Design of Linkages
verfasst von
J. Michael McCarthy
Gim Song Soh
Copyright-Jahr
2011
Verlag
Springer New York
Electronic ISBN
978-1-4419-7892-9
Print ISBN
978-1-4419-7891-2
DOI
https://doi.org/10.1007/978-1-4419-7892-9

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