The different kinds of singularities encountered in closed-loop kinematics chains are analyzed. A general classification of these singularities in three main groups, which is based on the properties of the Jacobian matrices of the chain, is described. The identification of the singular configurations is particularly relevant for hard automation modules or robotic devices based on closed kinematic chains, such as linkages and parallel manipulators. Examples are given to illustrate the application of the method to these mechanical systems. >

Singularity analysis of closed-loop kinematic chains

In this paper, we survey the field of robotic grasping and the work that has been done in this area over the last two decades, with a slight bias toward the development of the theoretical framework and analytical results in this area.

Robotic grasping and contact: a review

In this paper, a novel performance index for the kinematic optimization of robotic manipulators is presented. The index is based on the condition number of the Jacobian matrix of the manipulator, which is known to be a measure of the amplification of the errors due to the kinematic and static transformations between the joint and Cartesian spaces. Moreover, the index proposed here, termed global conditioning index (CGI), is meant to assess the distribution of the aforementioned condition number over the whole workspace. Furthermore, the concept of a global index is applicable to other local kinematic or dynamic indices. The index introduced here is applied to a simple serial two-link manipulator, to a spherical three-degree-of-freedom serial wrist, and to three-degree-of-freedom parallel planar and spherical manipulators. Results of the optimization of these manipulators, based on the GCI, are included.

A Global Performance Index for the Kinematic Optimization of Robotic Manipulators

The Stewart Platform is one example of a parallel connection robot manipulator. This paper summarizes work that has been done at Oregon State University over the past several years on this topic. T...

A Stewart-Platform based manipulator: general theory and practical construction

In this paper, an attempt at summarizing the evolution and the state of the art in the field of robot hands is made. In such exposition, a critical evaluation of what in the author's view are the leading ideas and emerging trends is privileged with respect to exhaustiveness of citations. The survey is focused mainly on three types of functional requirements a machine hand can be assigned in an artificial system, namely, manipulative dexterity, grasp robustness, and human operability. A basic distinction is made between hands designed for mimicking the human anatomy and physiology,and hands designed to meet restricted, practical requirements. In the latter domain, arguments are presented in favor of a -minimalistic" attitude in the design of hands for practical applications, i.e., use the least number of actuators, the simplest set of sensors, etc., for a given task. To achieve this rather obvious engineering goal is a challenge to our community. The paper illustrates some of the new sometimes difficult, problems that are brought about by building and controlling simpler, more practical devices.

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Hands for dexterous manipulation and robust grasping: a difficult road toward simplicity

Structural Kinematics of In-Parallel-Actuated Robot-Arms

Special configurations of spatial mechanisms and robot arms

A deep symmetry between serial chain manipulators and fully parallel systems such as the Stewart platform is dem onstrated. This symmetry is shown to be a result of the well-known duality of motion screw axes and wrenches. The appearance of the inverse of the Jacobian matrix in force decomposition in the same role as the Jacobian in rate decomposition is also a consequence of this same duality and of the reciprocity relationship between the motion screw system and the wrench system of a kine matic joint. A geometric meaning of the columns of the Jacobian is demonstrated. A simple example of the appli cation of the ideas presented here to the understanding of the complex combinations of serial and parallel chains found in vehicle and multifingered hand problems is also presented.

Kenneth H. Hunt

Papers

Structural Kinematics of In-Parallel-Actuated Robot-Arms

Special configurations of spatial mechanisms and robot arms

Series-parallel dualities in actively coordinated mechanisms

Assembly configurations of some in-parallel-actuated manipulators

Geometry of screw systems—1: Screws: Genesis and geometry