Three-link System Research Articles

OBJECTS OF FORENSIC LINGUISTIC EXAMINATION: NEW CHALLENGES OF CRIMINOGENIC INTERNET COMMUNICATION

The article is devoted to the system of objects of forensic linguistic examination at the present stage of its development. The relevance of the study is tied with the activation of criminogenic Internet communication, which implements defamatory, extremist and other aggressive speech acts that create threats to the information and worldview security of Web users. The essence of the object of forensic linguistic examination is considered from the following points of view: the theory of confl ict, the criminalistic understanding of the object of forensic examination as a complex three-link dynamic system, the concept of speech traces, the language form of the speech products, the material storage mediums, etc. Defi nitions of the diagnosed and diagnosing objects of the forensic linguistic examination are proposed. The article focuses on creolized and multicode texts, their multimodal perception. The correlation of speech traces of criminogenic Internet communication and digital traces is considered.

Kinematic Cartography and the Efficiency of Viscous Swimming

The apparent “distance” between two configurations of a system and the “length” of trajectories through its configuration space can be significantly distorted by plots that use “natural” or intuitively selected coordinates. This effect is similar to the way that a latitude–longitude plot of the Earth distorts the size and shape of the continents. In this paper, we explore how ideas from cartography can be used to identify system parameterizations that better reflect the effort costs of changing configuration. We then apply these new parameters to provide geometric insight about two aspects of moving in dissipative environments such as low Reynolds number fluids: The shape of the optimal gait cycle for a three-link swimmer and the fundamentally superior efficiency of a serpenoid swimmer as compared to the classic three-link system.

Stable Control Strategy for Planar Three-Link Underactuated Mechanical System

A stable-control strategy for a planar three-link passive–active–active underactuated mechanical system not subject to gravity constraints has been devised. The control objective is to move the end effector from any initial position to any target position. First, a dynamic model of the system is built, and its properties are analyzed. Next, based on the complete integrability of an underactuated planar acrobot (UPA), the control of a planar three-link system is divided into two stages. In each stage, keeping the angle of one active link constant reduces the planar three-link system to a UPA, thereby enabling the use of quadrature to obtain the angle constraint relationships between the passive and active links. Then, the target angles associated with the target position are calculated by particle swarm optimization based on the angle constraint relationships. Finally, a controller for each stage is designed, ensuring that the control objective will be reached. Simulation results demonstrate the validity of this control method.

Decentralized adaptive sliding mode control of a space robot actuated by control moment gyroscopes

An adaptive sliding mode control (ASMC) law is proposed in decentralized scheme for trajectory tracking control of a new concept space robot. Each joint of the system is a free ball joint capable of rotating with three degrees of freedom (DOF). A cluster of control moment gyroscopes (CMGs) is mounted on each link and the base to actuate the system. The modified Rodrigues parameters (MRPs) are employed to describe the angular displacements, and the equations of motion are derived using Kane’s equations. The controller for each link or the base is designed separately in decentralized scheme. The unknown disturbances, inertia parameter uncertainties and nonlinear uncertainties are classified as a “lumped” matched uncertainty with unknown upper bound, and a continuous sliding mode control (SMC) law is proposed, in which the control gain is tuned by the improved adaptation laws for the upper bound on norm of the uncertainty. A general amplification function is designed and incorporated in the adaptation laws to reduce the control error without conspicuously increasing the magnitude of the control input. Uniformly ultimate boundedness of the closed loop system is proved by Lyapunov’s method. Simulation results based on a three-link system verify the effectiveness of the proposed controller.

State Space Methods and Examples for Computational Models of Human Movement

<p>In the past, multi-rigid-body systems have been formulated by Lagrangian and Hamiltonian dynamics, the Newton-Euler method and Kane’s dynamic equations. Availability of large computers and versatile software systems enables us to formulate larger systems and analyze them computationally. In such circumstances, the probability of human error grows with the size of the system. The purpose of this work is to provide state space formulations that allow verification of computational results and be able to transport Lyapunov stability results across the these dynamics disciplines. The formulations are presented with matrices for all transformations and projections.</p><p>This work also investigates the constraint forces and their computation or elimination by different methods. A one-link constrained rigid body is considered first. The results are summarily extended to a three-link system. Six three-link rigid body sub modules are interconnected to describe, control and simulate many different maneuvers and activities of humans.</p><p>The actuators have alpha and gamma inputs, and pull but cannot push. The control strategy is based on Evarts’ “attention set,”, and is applied to the movement of one arm in a computational experiment.</p>

Symmetries and Gaits for Purcell's Three-Link Microswimmer Model

Robotic locomotion typically involves using gaits—periodic changes of kinematic shape, which induce net motion of the body in a desired direction. An example is robotic microswimmers, which are inspired by motion of swimming microorganisms. One of the most famous theoretical models of a microswimmer is Purcell's planar three-link swimmer, whose structure possesses two axes of symmetry. Several works analyzed gaits for robotic three-link systems based on body-fixed velocity integrals. Using this approach, finite motion in desired directions can only be obtained approximately. In this study, we propose gaits which are based on analysis of the system's structural symmetries, and generate exact motion along principal directions without net rotation. Another gait that produces almost pure rotation is presented, and bounds on the small-amplitude residual translation are obtained by using perturbation expansion. Next, the theory is extended to more realistic swimmers which have only one symmetry axis. Gaits for such swimmers which generate net translation are proposed, and their small-amplitude motion is analyzed using perturbation expansion. The theoretical results are demonstrated by using numerical simulations and conducting controlled motion experiments with a robotic macroswimmer prototype in a highly viscous fluid.

Modelling and monitoring of passive control structures in human movement

Passive tissues, ligaments and cartilage are vital to human movement. Their contribution to stability, joint function and joint integrity is essential. The articulation of their functions and quantitative assessment of what they do in a healthy or injured state are important in athletics, orthopaedics, medicine and health. In this paper, the role of cartilage and ligaments in stability of natural contacts, connections and joints is articulated by including them in two very simple skeletal systems: one- and three-link rigid body systems. Based on the Newton–Euler equations, a state space presentation of the dynamics is discussed that allows inclusion of ligament and cartilage structures in the model, and allows for Lyapunov stability studies for the original and reduced systems. The connection constraints may be holonomic and non-holonomic depending on the structure of the passive elements. The development is pertinent to the eventual design of a computational framework for the study of human movement that involves computer models of all the relevant skeletal, neural and physiological elements of the central nervous system (CNS). Such a structure also permits testing of different hypotheses about the functional neuroanatomy of the CNS, and the study of the effects and dynamics of disease, deterioration, aging and injuries. The formulation here is applied to one- and three-link systems. Digital computer simulations of a two rigid body system are presented to demonstrate the feasibility and effectiveness of the approach and the methods.

Determination of dynamic accuracy of manipulation systems of robots with elastic hinges

Two mathematical models for determining the dynamic accuracy of manipulation systems of robots with elastic hinges are considered. Mathematical models are the implementation of the method based on the Lagrange equation and using the transformation matrices of elastic coordinates. Mathematical models make it possible to determine the elastic deviations of manipulation systems of robots from programmed motion trajectories caused by elastic deformations in hinges, which are taken into account in directions of change of the corresponding generalized coordinates. One model is the exact implementation of the Lagrange method and makes it possible to determine the total elastic deviation of the manipulation system from the programmed motion trajectory. Another mathematical model is approximated and makes it possible to determine small elastic quasi-static deviations and elastic vibrations. The results of modeling the dynamics by two models are compared to the example of a three-link manipulation system. The considered models can be used when performing investigations of the mathematical accuracy of the manipulation systems of robots.

Geometric nonlinear formulation for thermal-rigid-flexible coupling system

This paper develops geometric nonlinear hybrid formulation for flexible multibody system with large defor- mation considering thermal effect. Different from the con- ventional formulation, the heat flux is the function of the ro- tational angle and the elastic deformation, therefore, the cou- pling among the temperature, the large overall motion and the elastic deformation should be taken into account. Firstly, based on nonlinear strain-displacement relationship, varia- tional dynamic equations and heat conduction equations for a flexible beam are derived by using virtual work approach, and then, Lagrange dynamics equations and heat conduction equations of the first kind of the flexible multibody system are obtained by leading into the vectors of Lagrange mul- tiplier associated with kinematic and temperature constraint equations. This formulation is used to simulate the thermal included hub-beam system. Comparison of the response be- tween the coupled system and the uncoupled system has re- vealed the thermal chattering phenomenon. Then, the key parameters for stability, including the moment of inertia of the central body, the incident angle, the damping ratio and the response time ratio, are analyzed. This formulation is also used to simulate a three-link system applied with heat flux. Comparison of the results obtained by the proposed for- mulation with those obtained by the approximate nonlinear model and the linear model shows the significance of con- sidering all the nonlinear terms in the strain in case of large deformation. At last, applicability of the approximate non- linear model and the linear model are clarified in detail.

Geometric Swimming at Low and High Reynolds Numbers

Several efforts have recently been made to relate the displacement of swimming three-link systems over strokes to geometric quantities of the strokes. In doing so, they provide powerful, intuitive representations of the bounds on a system's locomotion capabilities and the forms of its optimal strokes or gaits. While this approach has been successful for finding net rotations, noncommutativity concerns have prevented it from working for net translations. Our recent results on other locomoting systems have shown that the degree of this noncommutativity is dependent on the coordinates used to describe the problem and that it can be greatly mitigated by an optimal choice of coordinates. Here, we extend the benefits of this optimal-coordinate approach to the analysis of swimming at the extremes of low and high Reynolds numbers.

Dynamic Characteristic Analysis of Electric Actuator for 1 kV/3.2 kA Air Circuit Breaker Based on the Three-link Structure

In the present paper, a new type of electrical actuator, an electromagnetic force driving actuator (EMFA), applicable to air circuit breaker is developed and analyzed. Transient analysis is performed to obtain the dynamic characteristics of EMFA. The distribution of static magnetic flux is obtained using the finite element method. The coupled problems of electrics and mechanics governing equations are solved using the time-difference method. According to the interception rate of each contactor, investigation of the contactor spring load condition is conducted and applied to the threelink system. Comparisons of the dynamic characteristics of the three-link simulation and experimental data are performed.

Mechanical Impedance Control in the Human Arm While Manually Transporting an Open-Top Fluid Filled Dish

The present study deals with stabilizing aspects of a hand-held dish filled with liquid while walking steadily. This is an attempt to decipher the neuro-muscular strategies employed and the mechanical responses of the arm during certain tasks of manual materials handling. The experimental configuration included a cup and the test-subject’s hand as an ‘end-effector’ of a serial three-link system representing the upper limb. These links are connected together by the wrist, elbow and shoulder joints. The tested subjects walked at constant speed on a treadmill while aiming to minimize liquid spillage from the cup. The motion of the limb and shoulder girdle served as inputs to a model to reveal the impedance adjustments during the simultaneous control of grasping and walking under ordinary conditions, and when one of the joints is affected. A regressive function used to express stiffness, included first-order dependence on angle and on angular velocity. The function used for damping included first-order dependence on angular velocity. Redundancies in the numerical solution were eliminated using multicollinearity diagnostic algorithms. The results revealed that the wrist joint was found to have constant stiffness and damping and no regulation of these coefficients was necessary during gait. Both in the elbow and shoulder joints stiffness included a constant coefficient as well as an angular velocity-dependent coefficient. Although all tested subjects demonstrated ability to prevent spillage of liquid, there was a considerable variability among the results obtained, indicating that the compensatory mechanisms employed by each subject to regulate the mechanical impedance were subjective. These results can help in the optimization of manual materials handeling tasks in industrial settings as well as future design of prosthetic arms, robotic appliances and man machine interfacing devices.

Mechanical impedance control in the human arm while manually transporting an open-top fluid filled dish

The present study deals with stabilizing aspects of a hand-held dish filled with liquid while walking steadily. This is an attempt to decipher the neuro-muscular strategies employed and the mechanical responses of the arm during certain tasks of manual materials handling. The experimental configuration included a cup and the test-subject's hand as an 'end-effector' of a serial three-link system representing the upper limb. These links are connected together by the wrist, elbow and shoulder joints. The tested subjects walked at constant speed on a treadmill while aiming to minimize liquid spillage from the cup. The motion of the limb and shoulder girdle served as inputs to a model to reveal the impedance adjustments during the simultaneous control of grasping and walking under ordinary conditions, and when one of the joints is affected. A regressive function used to express stiffness, included first-order dependence on angle and on angular velocity. The function used for damping included first-order dependence on angular velocity. Redundancies in the numerical solution were eliminated using multicollinearity diagnostic algorithms. The results revealed that the wrist joint was found to have constant stiffness and damping and no regulation of these coefficients was necessary during gait. Both in the elbow and shoulder joints stiffness included a constant coefficient as well as an angular velocity-dependent coefficient. Although all tested subjects demonstrated ability to prevent spillage of liquid, there was a considerable variability among the results obtained, indicating that the compensatory mechanisms employed by each subject to regulate the mechanical impedance were subjective. These results can help in the optimization of manual materials handeling tasks in industrial settings as well as future design of prosthetic arms, robotic appliances and man machine interfacing devices.

Nonlinear Feedback Control of a Gravity-Assisted Underactuated Manipulator With Application to Aircraft Assembly

A nonlinear feedback scheme for a gravity-assisted underactuated manipulator with second-order nonholonomic constraints is presented in this paper. The joints of the hyper articulated arm have no dedicated actuators but are activated by gravity. By tilting the base link appropriately, the gravitational torque drives the unactuated links to a desired angular position. With simple locking mechanisms, the hyperarticulated arm can change its configuration using only one actuator at the base. This underactuated arm design was motivated by the need for a compact snake-like robot that can go into aircraft wings and perform assembly operations using heavy end-effectors. The dynamics of the unactuated links are essentially second-order nonholonomic constraints for which there are no general methods to design closed-loop control. We propose a nonlinear closed-loop control law that is guaranteed to be stable in positioning one unactuated joint at a time. We synthesize a Lyapunov function to prove the convergence of this control scheme. The Lyapunov function also generates estimates of the domain of convergence of the control law for various control gains. The control algorithm is implemented on a prototype three-link system. Finally, we provide some experimental results to demonstrate the efficacy of the control scheme.

Stationary Configurations of a Tetrahedral Tethered Satellite Formation

O RBITAL dynamics analysis of a connected multibody system is relevant for several missions, including tethered systems, space robots and manipulators, telescopes, space stations, etc. It is important to determine stationary motions of such structures due to their possible use as nominal motions in energy-saving mode. The study of the behavior of multibody systems in the orbital environment continues to grow since its beginning in the 1960s. Sarychev [1] and Wittenburg [2] investigate the equilibria of two connected rigid bodies in circular orbit with respect to the orbital reference frame. Cheng and Liu [3] consider the in-plane dynamics of a three-body systemwith two equal extreme bodies, examining the equilibrium orientations, bifurcations, and stability with respect to in-plane perturbations. Lavagna and Ercoli Finzi describe planar equilibrium configurations [4] and study their stability [5] for an extended rigid body with two pendulums attached either in a sequence or in a parallel scheme. Quite frequently, the orbital dynamics of multibody systems is studied for models that approximate connected satellites by an open chain of material points linked by weightless straight rods with spherical hinges. Misra and Modi [6] develop the general threedimensional formulation for an n-link chain. For twoand three-link systems, they determine the libration frequencies and study the control laws. In [7,8] this model is used to determine in-plane equilibrium configurations of a two-link chain and to study their stability. Sarychev [9] finds all spatial equilibrium orientations of a two-link chain in a circular orbit and describes their number as a function of problem parameters. Continued interest in such studies was confirmed recently by Correa and Gomez [10], who numerically study the equilibrium configurations of a three-link chain in the plane of the orbit and analyze their stability with respect to in-plane perturbations. An analytical study of chains with arbitrary number of links can be found in [11,12]. The center ofmass of the chain (CMC)moves along a circular orbit. All in-plane equilibrium configurations are described in [11]. All spatial equilibria are listed in [12], in which it is shown that each connecting rod can be oriented with respect to the tangent, normal and binormal to the CMC orbit in one of the following ways: 1) A rod is aligned with the tangent axis. 2) A rod belongs to an NBN group, that is, to a subchain of rods that lies in the plane parallel to normal and binormal so that its center of mass is on the tangent axis. 3) A rod links two NBN groups or an end of an NBN group with the tangent axis. Some of these equilibrium configurations are actually twodimensional, with all the system lying in one of the coordinate planes of the orbital reference frame. Yet, there exist essentially threedimensional configurations, for example, with masses placed at the vertices of a tetrahedron. Tetrahedral satellite formations are of significant interest due to numerous applications and many projects under development, including NASA research programs in formation flying [13–15]. Tetrahedral configuration has been successfully implemented in the Cluster mission to study three-dimensional structure of the Earth’s magnetosphere [16]. Being the simplest spatial configuration, a tetrahedral formation is a natural tool in experiments of this kind, because it enables one to execute simultaneous measurements at points of a large-span three-dimensional basis. In the present article, we apply the general results of [12] to study tetrahedral equilibrium configurations of a tethered satellite system. We identify the spectrum of spatial equilibrium configurations that can be achieved by varying the masses of the bodies and lengths of the rods.We determine the links that can be replacedwith tethers.We study the possibility of controlling such a system and of stabilizing its orientation.

The motion of a three-link system along a plane

Controllable motions of a three-link system along a horizontal plane when there is dry friction are considered. Previously obtained results are generalized and refined.

Trophic-dynamic modeling in a shallow eutrophic river ecosystem

In this study, eutrophication control in shallow streams is analyzed from the viewpoint of a trophic chain. A trophic-dynamic model for aquatic ecosystems is established to resolve the interactions between all trophic species. The simulated taxa are algae, aquatic insects and fish, and the major relationship among them is predation. The trophic-dynamic model is built on the mass balance of each trophic level in terms of growth, respiration, and predation. The results of simulation show that algae are limited by nutrients in one-link and three-link systems and by predators in a two-link food chain. These conclusion is in good agreement with other theoretical predictions. As a result, bio-management of predators to regulate excessive algae only works in two-link and four-link food chains. The impact of the trophic cascade on dissolved oxygen (DO) level also is simulated. DO variation is greatly affected by the population of algae.

Optimum search speed and activity: a dynamic game in a three-link trophic system

Optimum search speed and activity: a dynamic game in a three-link trophic system

Trophic interactions in two northern wolf-ungulate systems

Four population models for northern ungulates are formulated based on specific regulatory mechanisms: FOOD model, PREDATION-FOOD one-state model, PREDATION-FOOD two-state model and PREDATION model. In this paper I contrast the dynamics of the North American moose (Alces alces), a non-migrant ungulate, with the dynamics of the barren-ground caribou (Rangifer tarandus), a migrant ungulate. Predation by the grey wolf (Canis lupus) and by bears (Ursus arctos and U. americanus) is considered. Moose densities in North America are generally below 0.5 animals km-*2. In most areas, density-dependent food exploitation seems to operate at densities greater than 1.0 moose km-*2. Results from 27 studies were used to assess the functional and numerical responses of wolves to changing moose density. Per capita killing rate and wolf density were related (P = 0.01) to moose density following a Type I1 response. Wolf predation rate proved to be density dependent from 0 to 0.65 moose km", and inversely density dependent at higher moose densities. An empirical model based on these results suggests that moose would stabilise at high densities in the absence of predators (FOOD model) or in the presence of wolves only (PREDATION-FOOD one-state model). If moose productivity level is diminished through deteriorating habitat quality, or if bear predation is added, then a low-density equilibrium (0.2-0.4 moose km*2) is predicted (PREDATION model). The demography of the George River caribou herd in northern QukbecILabrador is reviewed for the period 1955-93. The herd increased from 5000 animals in 1955 to 644000 (c. 1.5 animals km-*2) in 1984, following an exponential growth rate (r) of 0.16. The herd reached a plateau of c. 725 000 animals in early 1990. A decline is predicted for the near future because of severe habitat degradation. In the 1980s, nutritional stress has been documented, especially in summer when caribou used traditional ranges depleted of key forage resources such as lichens and tundra shrubs. Food competition is viewed as the dominant regulatory factor (FOOD model), although the nature of caribou-habitat interactions may generate longterm fluctuations in numbers because of a time-delay effect. Wolf predation does not appear to be an important mortality factor capable of regulating the George River herd. The above case studies can be interpreted within the context of the 'food chain dynamics' theory. For the non-migrant ungulate (moose), a three-link system is proposed where predators hold down grazers, which in turn use only a small fraction of annual forage production. For the migrant ungulate (caribou), a two-link system is proposed where high-density grazers exert a strong regulatory control on plant productivity and where predators have minimal effect on grazers.

Modal Analysis of a Flexible Three-Link System in Variable Configurations

In this paper, some experimental results of modal tests performed on a large three-link flexible system are reported. These modal tests were conducted at the NASA’s LSS GTF (Large Space Structures Ground Test Facility) located at MSFC (Marshall Space Flight Center). The experimental results were obtained for various configurations and compared with those obtained using the Component Mode Synthesis technique. The mode functions were selected to keep the computation as simple as possible without compromising the accuracy. The results obtained from the dynamic software simulation package called TREETOPS have also been included for completeness. It is found that the experimental results are in excellent agreement with those obtained by the use of component mode techniques for the aforementioned structures. The average percent change in the frequencies is observed to be 6.09%, while the average mode shape correspondence is noted as 94.5%.