Active hip and spine ROM differs when comparing unconstrained motion with voluntary segmental constraint

2013 ◽  
Vol 18 (6) ◽  
pp. 557-561 ◽  
Author(s):  
Janice M. Moreside ◽  
David Barbado ◽  
Casto Juan-Recio ◽  
Francisco J. Vera-Garcia
Keyword(s):  
Unconstrained Motion

Uniaxial Stress Deformation Experiment for Validation of 3-D Dislocation Dynamics Simulations

2002 ◽  
Vol 124 (3) ◽  
pp. 290-296 ◽  
Author(s):  
David H. Lassila ◽  
Mary M. LeBlanc ◽  
Gregory J. Kay
Keyword(s):  
Experimental Data ◽  
Single Crystal ◽  
Single Crystals ◽  
High Purity ◽  
Axial Stress ◽  
Uniaxial Stress ◽  
Dislocation Dynamics ◽  
Uniform State ◽  
Dynamics Simulations ◽  
Unconstrained Motion

An apparatus has been developed for performing compression deformation experiments on oriented metallic single crystals to provide data for validation of 3-D dislocation dynamics simulations. The experiment is performed under conditions that allow unconstrained motion of the upper and lower compression platen, and thus a relatively uniform state of axial stress is maintained during the deformation. Experiments have been performed on high-purity Mo single crystal and polycrystalline Cu. Various aspects of the experimental procedures and results are presented. Possible usages of the experimental data for the validation of 3-D dislocation dynamics simulations are discussed.

Hamel Paradox and Rosenberg Conjecture in Analytical Dynamics

2013 ◽  
Vol 80 (4) ◽  
Author(s):  
Y. H. Chen
Keyword(s):  
Kinetic Energy ◽  
Fundamental Equation ◽  
Equation Of Motion ◽  
Analytical Dynamics ◽  
Constrained Motion ◽  
Embedding Method ◽  
Constrained Equation ◽  
Unconstrained Motion

Hamel proposed a seemingly intuitive, simple, straightforward, but incorrect, method of formulating the constrained equation of motion. The method has to do with the direct embedding of the constraint into the kinetic energy of the unconstrained motion. His intention was to caution against its possible adoption. Rosenberg echoed Hamel's warning and followed up to explore more insight of this method. He proposed a conjecture that the Hamel's embedding method would work if the constraint was holonomic. It would not work if the constraint was nonholonomic. We investigate the Hamel paradox and Rosenberg conjecture via the use of the Fundamental Equation of Constrained Motion.

Impedance Control: An Approach to Manipulation: Part III—Applications

1985 ◽  
Vol 107 (1) ◽  
pp. 17-24 ◽  
Author(s):  
Neville Hogan
Keyword(s):  
Feedback Control ◽  
Path Planning ◽  
Control Algorithm ◽  
Moving Objects ◽  
Impedance Control ◽  
Optimization Theory ◽  
Dynamic Interaction ◽  
Unified Approach ◽  
Simplified Analysis ◽  
Unconstrained Motion

This three-part paper presents a unified approach to the control of a manipulator applicable to free motions, kinematically constrained motions, and dynamic interaction between the manipulator and its environment. In Part I the approach was developed from a consideration of the fundamental mechanics of manipulation. Part II presented techniques for implementing a desired manipulator impedance. In Part III a technique for choosing the impedance appropriate to a given application using optimization theory is presented. Based on a simplified analysis it is shown that if the task objective is to tradeoff interface forces and motion errors, the manipulator impedance should be proportional to the environmental admittance. An application of impedance control to unconstrained motion is presented. The superposition properties of nonlinear impedances are used to develop a real-time feedback control algorithm which permits a manipulator to avoid unpredictably moving objects without explicit path planning.

Singularities of a planar 3-RPR parallel manipulator with joint clearance

Robotica ◽  
2018 ◽  
Vol 36 (7) ◽  
pp. 1098-1109 ◽  
Author(s):  
Marise Gallant ◽  
Clément Gosselin
Keyword(s):  
Trajectory Planning ◽  
Parallel Manipulator ◽  
Joint Clearance ◽  
End Effector ◽  
Manipulator Design ◽  
Joint Clearances ◽  
Unconstrained Motion

SUMMARYIf the joint clearances of the joints of a manipulator are considered, an unconstrained motion of the end-effector can be computed. This is true for all poses of the manipulator, even with all actuators locked.This paper presents how this unconstrained motion can be determined for a planar 3-RPR manipulator. The singularities are then studied. It is shown that when clearances are considered, the singularity curves normally found in the workspace of such a manipulator become singular zones. These zones can be significant and greatly reduce the usable workspace of a manipulator. Since a prescribed configuration that would not, in theory, corresponds to a singular pose can become singular due to the unconstrained motion, the results of this paper are relevant to manipulator design and trajectory planning.

scholarly journals Fluid moment and force measurement based on control surface integration

2019 ◽  
Vol 61 (1) ◽  
Author(s):  
Diana D. Chin ◽  
David Lentink
Keyword(s):  
Particle Image ◽  
Force Measurement ◽  
Aerodynamic Force ◽  
Center Of Mass ◽  
Measurement Techniques ◽  
Control Surface ◽  
Fluid Forces ◽  
Surface Integration ◽  
Image Velocimetry ◽  
Unconstrained Motion

Abstract The moments and torques acting on a deforming body determine its stability and maneuverability. For animals, robots, vehicles, and other deforming objects locomoting in liquid or gaseous fluids, these fluid moments are challenging to accurately measure during unconstrained motion. Particle image velocimetry and aerodynamic force platforms have the potential to resolve this challenge through the use of control surface integration. These measurement techniques have previously been used to recover fluid forces. Here, we show how control surface integration can similarly be used to recover the 3D fluid moments generated about a deforming body’s center of mass. We first derive a general formulation that can be applied to any body locomoting in a fluid. We then show when and how this formulation can be greatly simplified without loss of accuracy for conditions commonly encountered during fluid experiments, such as for tests done in wind or water channels. Finally, we provide detailed formulations to show how measurements from an aerodynamic force platform can be used to determine the net instantaneous moments generated by a freely flying body. These formulations also apply more generally to other fluid applications, such as underwater swimming or locomotion over water surfaces. Graphic abstract

Robot Finger Stiffness Control in the Presence of Mechanical Nonlinearities

1988 ◽  
Vol 110 (3) ◽  
pp. 236-245 ◽  
Author(s):  
R. Vossoughi ◽  
M. Donath
Keyword(s):  
Controller Design ◽  
Contact Stiffness ◽  
Nonlinear Effects ◽  
Nonlinear Damping ◽  
Pole Placement ◽  
Robot Hand ◽  
Nonlinear Friction ◽  
Linear Subsystem ◽  
Stiffness Control ◽  
Unconstrained Motion

Stiffness control provides a mechanism for controlling finger position or force, and facilitates stable behavior during the transition between unconstrained motion and sudden contact with the environment. The method proposed here provides uniformity of response upon finger contact for any contact stiffness, as long as no separation occurs. The stiffness control system of a finger joint in a robot hand was partitioned into linear and nonlinear subsystems. The controller design used pole placement techniques based on the linear subsystem while the mechanical nonlinearities (i.e., load and velocity dependent nonlinear friction and nonlinear damping) in the drive were modeled separately. The parameters of the nonlinear model were experimentally identified off-line. These identified parameters were then used in a real-time estimator for compensation of the nonlinear effects while the system was under stiffness control. The technique was implemented successfully at 40 HZ on the actual finger under investigation. The results are a significant improvement on traditional techniques for nonlinear systems which result in large offsets or unstable behavior.

Sign in / Sign up

Export Citation Format

Share Document