Fluid moment and force measurement based on control surface integration

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

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

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.

The Advantages of Normalizing Electromyography to Ballistic Rather than Isometric or Isokinetic Tasks

Isometric tasks have been a standard for electromyography (EMG) normalization stemming from anatomic and physiologic stability observed during contraction. Ballistic dynamic tasks have the benefit of eliciting maximum EMG signals for normalization, despite having the potential for greater signal variability. It is the purpose of this study to compare maximum voluntary isometric contraction (MVIC) to nonisometric tasks with increasing degrees of extrinsic variability, ie, joint range of motion, velocity, rate of contraction, etc., to determine if the ballistic tasks, which elicit larger peak EMG signals, are more reliable than the constrained MVIC. Fifteen subjects performed MVIC, isokinetic, maximum countermovement jump, and sprint tasks while EMG was collected from 9 muscles in the quadriceps, hamstrings, and lower leg. The results revealed the unconstrained ballistic tasks were more reliable compared to the constrained MVIC and isokinetic tasks for all triceps surae muscles. The EMG from sprinting was more reliable than the constrained cases for both the hamstrings and vasti. The most reliable EMG signals occurred when the body was permitted its natural, unconstrained motion. These results suggest that EMG is best normalized using ballistic tasks to provide the greatest within-subject reliability, which beneficially yield maximum EMG values.

Hamel Paradox and Rosenberg Conjecture in Analytical Dynamics

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.

Semi-Autonomous Control of a Multi-Arm Telemanipulator With Adaptive Impedance

This paper addresses problems to achieve transparency and contact stability for Single Master Multi-Slave telemanipulation that consists of unconstrained and constrained motions. The adaptive bilateral control with a local force compensator is developed based on adaptive impedance control and contact force driven compensation with auto-switching functions. With a limited amount of knowledge about robotic and environment dynamics and a time-varying communication delay, the developed method guarantees good adaptive tracking performance in unconstrained motion and reduction of oscillating contacts to keep a balance of the system in constrained motion. Based on an actual haptic device and virtual robots, haptic simulations are presented to demonstrate adaptive transparency and contact stability in the presence of communication delays.

Adaptive force reflecting teleoperation with local force compensators

SUMMARYThis paper addresses problems to achieve transparency and contact stability for teleoperation that consists of unconstrained and constrained motions. The adaptive bilateral control with a local force compensator is developed, based on adaptive impedance control and contact force driven compensation with auto-switching functions. Without any knowledge about robotic and environment dynamics and with a communication delay, the developed method guarantees good adaptive tracking performance in unconstrained motion and reduction of oscillating contacts in constrained motion. Based on an actual haptic device and a virtual manipulator, haptic simulations are presented to demonstrate adaptive transparency and contact stability in the presence of communication delay.