Case Of Free Motion Research Articles

Analyzing the Performance Limits of Articulated Soft Robots Based on the ESPi Framework: Applications to Damping and Impedance Control

In situations of harsh impacts, damping injection directly on the link of an articulated soft robot is challenging and usually requires high actuator torques at the moment of impact. In this work, we discuss the underlying reasons and analyze the performance limitations arising in the implementation of basic impedance elements, such as springs and dampers, through the elastic structure preserving impedance (ESPi) control framework. Using the insights obtained, we present a way to design impedance controllers with a damping design based on dynamic extensions. Inspired by the design of shock absorbers and the muscle-tendon model, the presented damping layout requires substantially smaller actuator torques in situations where the robot is subject to harsh impacts. The implementation is facilitated through the ESPi control framework resulting in a physically intuitive impedance design. The resulting closed-loop system can be interpreted as an interconnection of passive Euler Lagrange systems, which again, yields a passive system. The design's passive nature ensures stability in the free motion case and enables the robot to interact robustly and safely with its environment. The work focuses on robotic systems with no inertial coupling between the motor and link dynamics. Experimental results, obtained with the presented design on a dedicated series elastic actuator (SEA) test bed, are reported and discussed.

A parallel algorithm for the simulation of controlled motion of space tether systems

Simulation of the controlled motion of space tether systems differs significantly from the free motion case. Tether deployment increases its length and adds new points into the discrete model of the tether. A set of dynamic equations is expanded with equations that describe the motion of the new points. The necessary condition at each step is the consistency of the system. Tether deployment is supervised by the control system which limits the tether length. The problem arises of solving a system of differential equations with variable and increasing number of equations. In this paper a parallel algorithm for simulating the controlled motion of space tether systems is designed. The parallel algorithm provides an ability to split the tether to such number of points that the model becomes similar to the model with distributed parameters. As a result, the simulation of several modes of tether motion unavailable for other methods becomes possible. The estimation of speedup provided by the algorithm is implemented. It shows that the speedup is comparable with the more simple case of the free motion simulation. Computational experiments have been carried out for the algorithm performance evaluation.

H ∞ -Based Robust Torque Control of Harmonic Drive Systems

In this paper, the torque control of a harmonic drive system for constrained-motion and free-motion applications is examined in detail. A nominal model for the system is obtained in each case from experimental frequency responses of the system, and the deviation of the system from the model is encapsulated by a multiplicative uncertainty. Robust torque controllers are designed using this information in an H∞-framework, and implemented on two different setups. From time and frequency domain experiments, it is shown that the closed-loop system retains robust stability, while improving the tracking performance exceptionally well. To further improve the performance of the system for free-motion case, a feedforward friction-compensation algorithm is implemented in addition to the robust torque control. It is shown that friction-compensation will shrink the model uncertainty at low frequencies and hence, the performance of the closed-loop system will be improved at those frequencies.

On a quantum-mechanical description of motion with friction

A method for the quantum treatment of motion in a dissipative system is considered. The one-dimensional problem is described by a nonlinear integro-differential generalization of the Schrodinger equation. An exact solution is found for the case of free motion with friction. The problem of the infinite-wall potential is considered and an approximate solution is obtained. The solution provides an example of a system with friction, having parameters that depend on the amount of time that has passed from the moment the system was created. This effect can be tentatively applied to the interpretation of experimental indications of the effective time dependence of hadron cross-sections.

CONVERGENCE TO AN EQUILIBRIUM STATE FOR A ONE-DIMENSIONAL QUANTUM SYSTEM OF HARD RODS

In this paper a theorem is proved on the convergence to an equilibrium state during the course of the time evolution of an infinite, one-dimensional system of quantum particles interacting by means of a hard-rod potential. The basic idea consists in the reduction of the time evolution of the system of hard rods to the time evolution of free particles. The case of free motion was studied earlier by O. Lanford and D. Robinson. Bibliography: 23 titles.