Nina Robson

Kinematic Synthesis With Contact Direction and Curvature Constraints on the Workpiece

In this paper, we consider the synthesis of a planar RR chain that guides a rigid body, or workpiece, such that it does not violate normal direction and curvature constraints imposed by contact with objects in the environment. These constraints are transformed into conditions on the velocity and acceleration of points in the moving body. We use this to formulate the synthesis equations for an RR chain, which are solved by algebraic elimination. An example of the design of a planar RR linkage and a four-bar chain in which the coupler maintains in contact with two objects in two locations is used to illustrate the results.Copyright

GEOMETRIC DESIGN OF SPHERICAL SERIAL CHAINS WITH CURVATURE CONSTRAINTS IN THE ENVIRONMENT

ABSTRACT This paper builds up on recent results on planar kinematicsynthesis with contact direction and curvature constraints on theworkpiece. We consider the synthesis of spherical serial chainsto guide a rigid body, such that it does not violate normal direc-tionandcurvatureconstraintsimposedbycontactwithobjectsinthe environment. We show how to derive these constraints fromthe geometry of the task and transform them into conditions onvelocity and acceleration of points in the moving body to obtainsynthesis equations which can be solved by algebraic elimina-tion. Trajectoryinterpolationformulasyieldthemovementofthechainwiththedesiredcontactpropertiesineachofthetaskposi-tions. An example shows the application of the developed theoryto the failure recovery of a robot manipulator, using kinematicsynthesis techniques. 1 INTRODUCTION Recent results on planar kinematic synthesis with contactdirections and curvature constraints on a work piece [1] are ex-pandeduponinthispaper. Thedesignofsphericallinkagesbasedon the contact and curvature constraints imposed on the workpiece is considered. The specifications on the end points of theend effector which are in contact with objects in the environmentare derived from the task geometry and transformed into speci-fications on the end effector origin and frame orientation. ThesespecificationsarethenusedtosynthesizeaserialTSchain,where

Applications of the Geometric Design of Mechanical Linkages With Task Acceleration Specifications

This paper formulates the kinematic specification of the synthesis problem for planar and spatial open serial chains in which the acceleration of the end-effector is specified. While the planar RR synthesis has been reported by the authors in some of their previous work, the synthesis of the spatial perpendicular RRS mechanical linkage with prescribed acceleration task is described in details in this paper and is a new contribution. Applications of this research focus on the design of planar RR and four-bar linkages to maintain specified local motion. In extending the research to spatial applications, a new strategy for failure recovery of a general six degree of freedom TRS robot arm is presented. It combines the second order effects of the task with the particular joint failure to yield free parameters that allow reconfiguration of the system to accommodate the failure.Copyright

Experimental observations on the human arm motion planning under an elbow joint constraint

This paper seeks to define the governing strategies by which the human central nervous system (CNS) finds optimal solutions for an arm reaching motion, when an elbow joint is constrained. The compensated arm reaching motion under the joint kinematic constraint is observed by human experiments. We present an experimental protocol, where subjects perform point-to-point reaching tasks with a lightweight elbow brace to restrict the elbow kinematics with minimal effect on the arm dynamics. The human compensatory strategy is analyzed in terms of hand path kinematics (i.e. spatial and temporal characteristics) and the arm postural configuration. The spatial and temporal characteristics of hand path are approximated by the Euclidean geodesic curves and the well known bell-shaped smooth profile, respectively. Furthermore, the contribution of each joint degree-of-freedom (DOF) motion is discussed and its relation to the arm posture selection is elaborated.

THE SYNTHESIS OF PLANAR 4R LINKAGES WITH THREE TASK POSITIONS AND TWO SPECIFIED VELOCITIES

In this paper, we consider the complete synthesis of planar 2R chains, in which the five design parameters of the chain are determined using kinematic specifications on the movement of the floating link. We use three positions and two velocities to define algebraic design equations which are solved to obtain multiple solutions. Our primary concern is how to ensure that a 4R chain constructed from two of these solutions moves smoothly through the given task. This is achieved by mapping the design data to an image space of planar displacements and comparing it to the curve traced by the movement of the coupler of the resulting design. Examples show that a designer can work in this image space to adjust the task specification to obtain an effective linkage design.Copyright

Development of Underactuated Mechanical Fingers Based on Anthropometric Data and Anthropomorphic Tasks

This paper describes a systematic method for the kinematic synthesis of one degree-of-freedom robotic fingers that incorporate multi-loop kinematic structures with second order task specifications, such that the fingers do not violate normal direction and curvature constraints imposed by contact with objects. We show how to use these contact and curvature effects to formulate the synthesis equations for the design of a planar index finger, based on anthropomorphic back-bone chain and anthropomorphic task. The prototype of the finger is described in the end of the paper.It is important to note, that the theoretical foundation presented in this paper, assists in solving some of the open problems of the field, providing preliminary results on the synthesis of one degree-of-freedom kinematic chains, based on human’s finger dimensions and novel task specifications that incorporate curvature constraints, with future applications in grasping and object manipulation.Copyright

Kinematic Synthesis of Minimally Actuated Multi-Loop Planar Linkages With Second Order Motion Constraints for Object Grasping

In this paper, we consider the dimensional synthesis of one degree-of-freedom multi-loop planar linkages such that they do not violate normal direction and second order curvature constraints imposed by contact with objects. Our goal is in developing minimally actuated multi-loop mechanical devices for human-robot interaction, that is, devices whose tasks will happen in a human environment.Currently no systematic method exists for the kinematic synthesis of robotic fingers that incorporate multi-loop kinematic structure with second order task constraints, related to curvature. We show how to use these contact and curvature effects to formulate the synthesis equations for the design of a planar one-degree-of-freedom six-bar linkage. An example for the design of a finger that maintains a specified contact with an object, for an anthropomorphic task, is presented at the end of the paper.It is important to note, that the theoretical foundation presented in this paper, assists in solving some of the open problems of this field, providing preliminary results on the synthesis of kinematic chains with multi-loop topology and the use of novel task specifications that incorporate curvature constraints with future applications in grasping and object manipulation.© 2013 ASME

An experimental study on redundancy resolution scheme of postural configuration in human arm reaching with an elbow joint kinematic constraint

This paper studies the redundancy resolution strategy of the central nervous system (CNS) in selecting an arm posture during reaching motions. Based on the assumption that such governing rules are preserved against any joint constraint condition, an elbow joint DOF was fixed during the experiments with a light weight elbow brace. Two different coordinate systems are defined to interpret kinematics and dynamics of motion in a task-oriented space and an internal body space. The kinematic and dynamic contributions of the internal body frame on the task frame, is quantified by mappings. The experimental results show that the core principle of the CNS to determine the arm posture is to minimize the kinetic energy cost.

Reconstructing Humans’ Hand Motion: Preliminary Results and Applications in the Design of Mechanical Fingers for Anthropomorphic Tasks

This paper reports the development of a low-cost sensor-based glove device using commercially available components that can be used to obtain position, velocity and acceleration data for individual fingers of the hand. Optical tracking of the human hand and finger motion is a challenging task due to the large number of degrees of freedom (DOFs) packed in a relatively small space. We propose methods to simplify the hand motion capture by utilizing accelerometers and adopting a reduced marker protocol.The preliminary results show that the use of relative position, velocity and acceleration homogeneous transformations enable us in getting improved finger motion data with respect to those obtained from a Vicon system. This data is directly related to contact and curvature constraints between the fingers and the grasped object. Once obtained from the glove, the higher derivative specifications are used in formulating the synthesis task for the design of robotic fingers.Copyright

Experimental Observations on the Central Nervous System’s Governing Strategies on the Arm Reaching With Reduced Mobility

For the motion planning of a point–to–point reaching task with a healthy arm, the CNS tends to plan the shortest hand path between two task points with a bell–shaped velocity profile. If any kinematic or dynamic constraints are imposed on the arm, the CNS adapts to the changes by incorporating learning mechanism into the motion planning. This paper seeks to identify the modified motion planning strategies of the CNS when the elbow joint is constrained to move. We present an experimental protocol, where subjects perform point–to–point reaching tasks with a lightweight elbow brace to restrict the joint kinematics with a minimal effect on the arm dynamics. From the experimental observations, the human strategies on each aspect of motion planning (i.e. hand path geometry, speed of the motion, and the arm posture selection) are hypothesized. The hypothesized strategies are developed as models and compared with the experimental data. As a result, we found that the hand path follows the rhumb line on the constraint workspace while the speed profile preserves a bell–shape, which can be roughly approximated by the minimum jerk model. In addition, by comparing the joint contributions data with and without the elbow constraint, it is hypothesized that the CNS resolves the redundancy of the inverse kinematics problem by reducing the kinetic energy of the limbs.Copyright