Spatial Mechanisms and Robot Manipulators

摘要

The subject of spatial mechanisms and robot manipulators continues to see sensational theoretical advances and exciting practical applications in fields ranging from product engineering, manufacturing, military applications, space exploration, rescue and recovery operations in hazardous environments, and of course, the rapidly growing area of medical robotics. Each new application raises numerous theoretical and experimental challenges. These open questions have attracted the attention of the best and brightest researchers, working in the general areas of mechanisms and robotics. The field of robotics, in particular, is interdisciplinary, with a constant flow of theories from many areas, including kinematics, statics and dynamics, computer graphics, control, and programming. The theories are used to provide a working and consistent approach to the interesting problem of robot manipulator control.This special supplement attempts to share with the readership of the ASME Journal of Mechanical Design some of the exciting new advances proposed by these researchers. The Guest Editors have collected a number of recent submissions to the journal in these subject areas and attempted to include a mix of basic theoretical research and practical applications of well-known principles to new and challenging problems. To further solidify the value of this special issue, we approached several distinguished scholars to submit invited papers. They agreed to provide articles based on some of their most recent and original work. The manuscripts were peer reviewed and found to be outstanding. Therefore, we anticipate that this special issue will be a widely-sought reference for students, educators, and researchers in the areas of spatial mechanisms and robotics.To whet the appetite of the reader, the Guest Editors will touch upon some of the highlights of the invited papers in this supplement.The invited paper by Wampler investigates the interesting problem of the location of a rigid body such that N specified points of the body lie on N given planes in space. Variants of this problem arise in kinematics, metrology, and computer vision, including some, such as the motion of a spherical four-bar, which are not at first glance point-plane contact problems. The case N=6 (i.e., the minimum number to fully constrain the body) is of special interest. The paper presents an eigenvalue method for finding all solutions, which may number up to eight. For N⩾7 there are, in general, no solutions, but if the constraints are compatible and not degenerate, the paper shows how to find the unique solution by a linear least-squares method. For N⩽5, the body is underconstrained, having in general 6−N degrees of freedom; the paper determines the degree of the general motion for each case. The article also examines the workspace of a particular three-degree-of-freedom parallel-link tripod mechanism.The invited paper by Stump and Kumar develops analytical techniques to delineate the workspace boundaries for parallel mechanisms with cables. In such mechanisms, it is not only necessary to solve the closure equations but it is also essential to verify that equilibrium can be achieved with non-negative actuator (cable) forces. The authors use tools from convex analysis and linear algebra to derive closed-form expressions for the workspace boundaries and illustrate the applications using planar and spatial examples.The invited paper by Khan and Angeles describes the optimum dimensioning of a robotic manipulator. The design of a robotic manipulator begins with the dimensioning of its various links to meet performance specifications. However, the authors believe that a methodology for the determination of the manipulator architecture (i.e., the fundamental geometry of the links, regardless of their shapes) is still lacking. Attempts have been made to apply the classical paradigms of linkage synthesis for motion generation, as in Burmester Theory. The problem with this approach