Unified Dynamic Model Research Articles

A unified dynamic model for locomotion and manipulation of a snake-like robot based on differential geometry

A snake-like robot, whose body is a seried-wound articulated mechanism, can move in various environments. In addition, when one end is fixed on a base, the robot can manipulate objects. A method of dynamic modeling for locomotion and manipulation of the snake-like robot is developed in order to unify the dynamic equations of two states. The transformation from locomotion to manipulation is a mechanism reconfiguration, that is, the robot in locomotion has not a fixed base, but it in manipulation has one. First, a virtual structure method unifies the two states in mechanism (e.g., an embedding in the configuration space); second, the product-of-exponentials formula describes the kinematics; third, the dynamics of locomotion and manipulation are established in a Riemannian manifold; finally, based on the analysis of the dynamic model, the dynamics of manipulation can be directly degenerated from those of locomotion, and this degeneration relation is proved through using the Gauss equations. In the differential geometry formulation, this method realizes the unification of the dynamics of locomotion and manipulation. According to a geometrical point of view, the unified dynamic model for locomotion and manipulation is considered as a submanifold problem endowed with geometric meaning. In addition, the unified model offers an insight into the dynamics of the snake-like robot beyond the dynamic model separately established for locomotion or manipulation.

Analysis of Stability Limitations of a VSC-HVDC Link Using Power-Synchronization Control

In this paper, the stability limitations are analyzed for a voltage-source converter (VSC) based high-voltage direct-current (HVDC) link using power-synchronization control for two feasible operation modes: alternating-voltage control and reactive-power control. As a comparison, the analysis has been done by the phasor approach and the space-vector approach. While the phasor approach is straightforward to apply and gives intuitive analytical results, the space-vector approach reflects more dynamic insights of the system. This is achieved by using a unified dynamic modeling of both the ac system and the VSC by means of a new introduced modeling approach Jacobian transfer matrices. This approach shows that non-minimum-phase phenomena due to competing effects between alternating voltages and currents following phase-angle changes impose a fundamental limitation on the achievable bandwidth of the VSC-HVDC link. At moderate voltage levels, a VSC-HVDC link operating in alternating-voltage control mode is able to achieve higher bandwidth than in reactive-power control mode since the right-half plane (RHP) zero is located further from the origin in the former mode.

Terrestrial Locomotion Modeling Bio-inspired by Elongated Animals

This paper presents a unified dynamic modeling approach of bio-inspired continuum robots. The resulting algorithm exploits a continuous version [1] of the Newton-Euler models of discrete structures and, is capable of computing the net motions as well as the internal control torques (and/or forces) of the continuum robot. The illustrative examples show that how this dynamic model work with the kinematic constraint model in order to produce locomotion. The efficiency of the algorithm is finally illustrated through examples related to the terrestrial locomotion of elongated animals such as snakes and worms.

A UNIFIED MODEL FOR ELECTRICITY AND HYDROGEN PRODUCTION IN MICROBIAL ELECTROCHEMICAL CELLS

AbstractThis work presents a unified dynamic model describing Microbial Fuel Cells and Microbial Electrolysis Cells (MxCs). The same set of kinetic equations is used to describe microbial activity in the anodic compartment of a microbial fuel cell and a microbial electrolysis cell, while cathodic reactions leading to electricity and hydrogen production are described by their respective dependencies. We present the results of parameter estimation and model validation, and an example of MxC model application for process control purposes.

Adaptive Integrated Control for Omnidirectional Mobile Manipulators Based on Neural-Network

An omnidirectional mobile manipulator, due to its large-scale mobility and dexterous manipulability, has attracted lots of attention in the last decades. However, modeling and control of such systems are very challenging because of their complicated mechanism. In this article, an unified dynamic model is developed by Lagrange Formalism. In terms of the proposed model, an adaptive integrated tracking controller, based on the computed torque control (CTC) method and the radial basis function neural-network (RBFNN), is presented subsequently. Although CTC is an effective motion control strategy for mobile manipulators, it requires precise models. To handle the unmodeled dynamics and the external disturbance, a RBFNN, serving as a compensator, is adopted. This proposed controller combines the advantages of CTC and RBFNN. Simulation results show the correctness of the proposed model and the effectiveness of the control approach.

Correlation effects on the weak response of nuclear matter

The consistent description of the nuclear response at low and high momentum transfer requires a unified dynamical model, suitable to account for both short- and long-range correlation effects. We report the results of a study of the charged current weak response of symmetric nuclear matter, carried out using an effective interaction obtained from a realistic model of the nucleon–nucleon force within the formalism of correlated basis functions. Our approach allows for a clear identification of the kinematical regions in which different interaction effects dominate.

A Hierarchical Hashing Scheme for Nearest Neighbor Search and Broad-Phase Collision Detection

Increasing computational power allows computer graphics researchers to model spectacular phenomena such as fluids and their interactions with deformable objects and structures. Particle-based (or Lagrangian) fluid and solid simulations are commonly managed separately and mixed together for the collision detection phase. We present a unified dynamic acceleration model to be used for particle neighborhood queries and broad-phase collision detection, based on a hierarchical hash table data structure. Our method is able to significantly reduce computations in large, empty areas, and thus gives better results than existing acceleration techniques, such as multilevel hashing schemes or KD-trees, in most situations.

Determination of spacecraft and phobos parameters of motion in the Phobos-Grunt project

For the needs of the upcoming flight to Phobos within the framework of the project Phobos-Grunt, a dynamical numerical theory of the motion of Phobos is developed on the basis of Earth-based and spacecraft (SC) optical measurements and Earth-based radio observations of the SC motion. The theory uses the most reliable astronomical constants. Within the framework of a unified dynamical model, an algorithm is proposed for the joint correction of Phobos and the spacecraft parameters of motion, among which are the secular acceleration of Phobos and its gravitational constant. The accuracy of the obtained ephemeris is estimated for the time of the SC arrival to Phobos.

A Unified Dynamic Model and Control for the Voltage-Sourced Converter Under Unbalanced Grid Conditions

This paper introduces and develops i) a novel unified dynamic model, and ii) new control schemes for a grid-connected static energy conversion system that is based on the voltage-sourced converter (VSC) configuration. The model and the controls are applicable to both the conventional two-level and the three-level neutral point diode clamped (NPC) VSCs. The model is unified since it represents the dynamic behavior of the with respect to both positiveand negative-sequence components, due to unbalanced grid conditions and disturbances. To develop the unified model, the concepts of generalized sinusoidal pulse-width modulation (SPWM) and VSC sequence subsystems are presented. Based on the negative-sequence subsystem control, a new control strategy, to either balance the ac line currents or to mitigate dc-bus voltage ripples, is introduced. Application of the developed model and the controls to a variable-speed wind-power unit is presented in the paper.

Dynamical systems modelling of turbulence-shear flow interactions in magnetized fusion plasmas

A study of the qualitative structure and stability properties of a unified dynamical model for confinement transitions in fusion plasmas yields substantial new global and predictive information. Physics-based conditions are used to unfold trapped or persistent degenerate singularities in a simple model. Structural characterization of the resulting enhanced model achieves unification of previous disparate views of confinement transition physics, supplies valuable intelligence on the big issues of shear flow suppression of turbulence, multiple equilibria and oscillatory régimes, and suggests targeted experimental design, control and optimization strategies for new-generation fusion experiments.

A Unified Dynamic Model Formulation for Robotic Manipulator Systems

AbstractThis paper addresses the problem of the formulation of a unified dynamic model for sundry robotic manipulator systems derived from the first principle of mechanics instead of the existing formulation based on linear separability principle. It provides a systematic derivation, evaluation, and subsequent conceptual interpretation of manipulator dynamics model. Further, it analyzes the generality of the unified model over a wide range of manipulator configurations. In addition, it describes the implementation aspects of the unified model. © 2003 Wiley Periodicals, Inc.

THE NON-LINEAR DYNAMIC BEHAVIOR OF AN ELASTIC LINKAGE MECHANISM WITH CLEARANCES

In terms of Newton two-state model, by choosing two sets of generalized co-ordinates, this paper develops a unified dynamic model between the separation and collision process for the elastic linkage mechanism. This model incorporates the effects of rigidity and elasticity coupling and the angular velocity of crank is assumed to be variable in the operation. In addition, this paper provides a more simple and practical numerical solution method for convenient analysis. Through an example, the dynamic responses of the elastic linkage mechanism with clearances are analyzed, both the effects of elasticity and clearance on the dynamic behaviors of the mechanism are analyzed simultaneously and the non-linear behaviors caused by the clearance joints are analyzed by the dynamic model of rigid mechanism.

Dynamic simulation of multi-fingered robot hands based on a unified model

In dextrous manipulation of multi-fingered robot hands, the contact motions between the fingers and the grasped object may frequently change between sticking, rolling, and sliding. Furthermore, when a robot hand is to re-grasp an object, the number of fingers in contact with the grasped object will change and impulsive collisions will occur. In order to cope with these different cases, this paper proposes a unified framework to model the dynamics of a multi-fingered hand in free motion, collision, and different contact motions including sticking, rolling, sliding, and their combinations. The introduction of a contact motion selection matrix enables us to unify dynamic equations for different motions into a single model. To calculate the collision response, we adopt the impulse-based method proposed by Mirtich. A new contact transition model is also developed to identify the type of contact motion between a finger and the grasped object. Based on the unified dynamic model, we have developed a 3D dynamic simulator to simulate dextrous manipulation of a five-fingered robot hand. The validity of the dynamic simulator is verified by examples.

A unified dynamic model and control synthesis for robotic manipulators with geometric end-effector constraints

A compact dynamic model and a hybrid position/force controller for a constrained robot manipulator, subject to a set of holonomic (integrable) constraints have been developed in this study. The joint-space dynamics (DAEs) has been transformed into the constraint-space model in which the system dynamics can be readily decomposed into two orthogonal subsystems; the motion-controlled subsystem is specified in the direction tangential to the known constraint surfaces, and the force-controlled subsystem is regulated in the orthogonal direction. Also utilizing the transformed dynamics, we have presented a hybrid adaptive control law to simultaneously manipulate the end-effector position and the contact force. Further, by a Lyapunov theory, it has been shown that the corresponding closed-loop system is globally stable under the parametric uncertainties.

Electric fields and potential patterns in the high-latitude ionosphere for different situations in interplanetary space

The potential ϑ of the electric field at high latitudes has been obtained by solving numerically the second order differential equation in spherical coordinates: − 1 2 (rσ Hϕ θ) θ+ 1 r (σ Hϑλ) λ + 1 r (σ Pϑ λ) θ−(σ Pϑ θ) λ = 1 r (rψ θ) θ+ 1 r 2 ψ λλ , where θ is colatitude, λ is longitude, σ H and σ P are the height-integrated Hall and Perdersen ionospheric conductivities, r = sin θ, and ψ is the current function. The boundary condition is ϑ = 0 on the geomagnetic parallel θ = 34°. Values of ψ are determined from geomagnetic field variations at the Earth's surface from geomagnetic field variations at the Earth's surface for various conditions in interplanetary space. σ P and σ H are taken to vary with season, local time, tilt of the geomagnetic dipole axis (UT), and intensity of corpuscular precipitation (the model proposed by Wallis and Budzinski, 1981). The model distributions of ϑ M and E M = -▽ ϑ m so obtained are compared with observational results. The feasibility has been demonstrated of interpreting the statistical results and individual measurement data in terms of a unified dynamic model of ionospheric electric fields. The model makes allowance for the changes of electromagnetic “weather” in interplanetary space.

Josephson Junctions as Narrow-Linewidth Tunable Microwave Oscillators

Extensive measurements of radiation emitted from long Josephson junctions d.c.-current biased on zero-field and Fiske-steps are reported. The measurements were made in the band 8-10 GHz on long Nb-Nb oxide-Pb overlap tunnel junctions with the lengths 0.5 mm and 1.0 mm having fundamental frequencies of 10 GHz and 5 GHz, respectively. Depending on the fundamental frequency of the junction 1st or 2nd harmonic detection was employed. In the fundamental scheme the frequency fn vs. the d.c.-voltage Vn along the steps follows a modified Josephson voltage/frequency relation fn/Vn = 2e/nh, where n is the step-number n = 1, 2, 3,... for Fiske-steps and n = 2, 4, 6,... for zero-field steps. On a given step the frequency could be tuned (200-500 MHz) by varying the bias point. The linewidth was measured to be less than 5 kHz. All the observed phenomena are consistent with a novel unified dynamic bunched fluxon model applicable to both zero-field and Fiske-steps and are in good agreement with recent numerical solutions of the perturbed sine-Gordon equation with proper boundary conditions. Taking advantage of operation on higher order steps and strong harmonic generation the present upper frequency limit for the Josephson fluxon oscillator is above 200 GHz. The maximum power observed so far is only 5 pW, but the estimated available power is of the order 1 μW, which is quite sufficient to pump other Josephson devices.

A unified model for multiple photon dissociation of SF 6

A unified dynamical model is used to calculate laser frequency response, absorption cross section and dissociation rates for SF 6 pumped by CO 2 laser radiation.