Nonlinear model identification for Artemia population motion

In this paper, two different nonlinear models for Artemia swarming are derived. In order to generate the data suitable for identification, a robot driving the Artemia population has been built. The obtained data have been then used to identify the parameters of a model based on Newton??s equations and a black-box NARX model implemented by neural networks. The performances obtained validate the physical hypotheses underlying the gray-box model.     

Nonlinear robust and optimal control of robot manipulators

In this paper, we propose a new optimal control method for robust control of nonlinear robot manipulators. Many industrial robot systems are required to perform relatively large angular movement with sufficient accuracy. In real circumstances, highly nonlinear manipulator dynamics and uncertainties such as unknown load placed on the manipulator, external disturbance, and joint friction make the precise control of manipulators a very challenging task. The main contribution of this work is to develop a new robust control strategy to accomplish the precise control of robot manipulators under load uncertainty using a nonlinear optimal control formulation and solution. This methodology is based on the underlying relation between the robust stability and performance optimality. A class of robust control problems can be transformed to an equivalent optimal control problem by incorporating the uncertainty bounds into the cost functional. The θ-D optimal control approach is utilized to find an approximate closed-form feedback solution to the resultant nonlinear optimal control problem via a perturbation process. Numerical simulations show that the proposed robust controller is able to control the robot manipulator precisely under large load variations.     

L'espace articulaire de la Robotique Industrielle est un espace vectorielIndustrial Robotics joint space is a vector space

The mathematical modelling of industrial robots is based on the vectorial nature of the n-dimensional joint space of the robot, defined as a kinematic chain with n degrees of freedom. However, in our opinion, the vectorial nature of the joint space has been insufficiently discussed in the literature. We establish the vectorial nature of the joint space of an industrial robot from the fundamental studies of B. Roth on screws. To cite this article: B. Tondu, C. R. Mecanique 331 (2003).     

Explicit dynamics equations of the constrained robotic systems

Recursive matrix relations concerning the kinematics and the dynamics of a constrained robotic system, schematized by several kinematical chains, are established in this paper. Introducing frames and bases, we first analyze the geometrical properties of the mechanism and derive a general set of relations. Kinematics of the vector system of velocities and accelerations for each element of robot are then obtained. Expressed for every independent loop of the robot, useful conditions of connectivity regarding the relative velocities and accelerations are determined for direct or inverse kinematics problem. Based on the general principle of virtual powers, final matrix relations written in a recursive compact form express just the explicit dynamics equations of a constrained robotic system. Establishing active forces or actuator torques in an inverse dynamic problem, these equations are useful in fact for real-time control of a robot.     

Layer-specific population rate coding in a local cortical model with a laminar structure

Uncovering the principle of neural coding is essential for understanding how our mysterious brain works. Recent studies have reported the laminar differences of alpha-beta and gamma rhythms in the sensory cortex, yet it remains unclear about the underlying function role of frequency-dependent interlaminar interactions in neural coding. Using a rate-based network model to simulate the cortical laminar under the external time-varying stimuli, we showed that the physiological specificity of rhythms for layers enables the cortical laminae to preferentially encode information in different frequency ranges. The interplay of the supragranular layer and infragranular layer contributes significantly to improving the neural representation of external time-varying input at the population level. Further investigations revealed the essential role of recurrent connections of the cortical laminae in regulating the population rate coding. In particular, the laminar network optimally encodes the time-varying input at intermediate strengths of intralaminar excitatory–inhibitory circuits and interlaminar connections. Additionally, we verified the crucial role of adaptation in improving population coding by introducing slow dynamics and suppressing the noise-like excitatory activity in the laminar network. These findings highlight the crucial role of frequency-dependent interlaminar interactions in encoding time-varying stimuli and may shed light on the underlying function of cortical structural specificity in neural information processing.

     

On human–robot interaction of a 3-DOF decoupled parallel mechanism based on the design and construction of a novel and low-cost 3-DOF force sensor

This paper addresses the extension of a 3-degrees-of-freedom (3-DOF) decoupled parallel mechanism for human–robot interaction purposes. To this end, a low-cost 3-DOF force sensor for human–robot interaction applications is proposed, designed and constructed. In the latter force sensor, five load cells are placed in order to identify the amount of the applied force along each Cartesian direction. In addition, an experimental identification procedure based on least square method is carried out in order to obtain the first and third degree polynomial models of the sensor output model. From the practical tests it has been reveled that the force sensor has a reasonable precision of 0.1 N in both x and y-axes and 0.2 N in z-axis, within a range of 5 N which is suitable for human–robot interaction applications. Then, using the proposed force sensor, two control methods, namely “position control” and “speed control” are applied for human–robot interaction purposes and their performances are compared.     

Mapping similarity between parallel and serial architecture kinematics

First the principles of mapping spatial points to surfaces is introduced in the context of the inverse kinematics of a general six revolute serial wrist partitioned robot. Then the advantage of choosing ideal frames is illustrated by showing that in the case of some architectures an image space formulation, though possible, may be an impediment to clear geometric insight and a satisfactory and much simpler solution. After showing how the general point mapping transformation is reduced to classical Blaschke-Grünwald planar mapping a novel three legged planar robot??s direct kinematics is solved in image space and then using conventional ??distance?? constraints. The purpose is to show why the latter approach yields spurious solutions and how the displacement pole rotation performed with kinematic mapping reliably avoids this problem. In conclusion certain other new and/or interesting reduced mobility parallel robots are discussed briefly to point out some advantages and insights gained with an image space approach. Particular effort is made to expose in detail how mapping simplifies and extends the solution of direct kinematics pertaining to Calvel??s ??Delta?? 3D translational robot.     

Adaptive fuzzy formation control for a swarm of nonholonomic differentially driven vehicles

In this paper, an adaptive fuzzy robust H ^∞ controller is proposed for formation control of a swarm of differential driven vehicles with nonholonomic dynamic models. Artificial potential functions are used to design the formation control input for kinematic model of the robots and matrix manipulations are used to transform the nonholonomic model of each differentially driven vehicle into equivalent holonomic one. The main advantage of the proposed controller is the robustness to input nonlinearity, external disturbances, model uncertainties, and measurement noises, in a formation control of a nonholonomic robotic swarm. Moreover, robust stability proof is given using Lyapunov functions. Finally, simulation results are demonstrated for a swarm formation problem of a group of six unicycles, illustrating the effective attenuation of approximation error and external disturbances, even in the case of robot failure.     

Analysis on nonlinear turning motion of multi-spherical soft robots

A modular multi-spherical soft robot, which consists of five deformable spherical cells, two friction feet, the electromagnetic valves and the control systems, is constructed. According to the deflating action and the inflating action of the spherical cells, the size and the shape of each spherical cell can be changed. With two friction feet sticking with the ground in turn, the soft robot can move forwards, make a turning motion and avoid the obstacle. This paper creates a nonlinear relation between the pressure P and the inflation radius \(\left( r \right) \) at different original radii \(\left( {r_0 } \right) \) and obtains the inflation or deflation velocity \(v_r \). Six inflating and deflating steps to finish the turning motion are presented. Based on the geometric relationship between the inflation radius (r) and the original radius \((r_0 )\) of each cell, the nonlinear turning process is described to control the center positions (x, y, z) of the spherical cell. Last, a simulation and an experiment of five spherical cells are shown to emulate the turning process. Experiment results show that the robot has a maximum turning capability of \(20{^{\circ }}\) in one period.     

Experimental investigation on the effect of vibration on flow of liquid film in a horizontal duct

Effect of vibration on characteristics of a thin liquid film in a horizontal rectangular duct was studied experimentally in two flow regions viz, prebreak-up and break-up for Re _f =400–900. The lower surface of the duct on which liquid film flows was subjected to external vibration in the range of 25–1000 Hz. The instantaneous film thickness which was recorded by conductivity measurement gauges was analysed statistically. Results of structural changes in liquid film due to external vibration and without it are reported in this paper.     

Evoking complex neuronal networks by stimulating a single neuron

The responses of electrically coupled neuronal network to external stimulus injected on a single neuron are investigated. Stimulating the largest-degree neuron in the network, it is found that as the intensity of the stimulus increases, the network will be transiting from the resting to firing states and then restoring to the resting state, thereby showing a bounded firing region in the parameter space. Furthermore, it is found that as the coupling strength among the neurons decreases, the firing region is gradually expanded and, at the weak couplings, it could be separated into several disconnected subregions. By a simplified network model, we conduct a detailed analysis on the bifurcation diagram of the network dynamics in the two-dimensional parameter space spanned by stimulating intensity and coupling strength, and, by introducing a new coefficient named effective stimulus, explore the underlying mechanisms for the modified firing region. It is revealed that the coupling strength and stimulating intensity are equally important in evoking the network, but with different mechanisms. Specifically, the effective stimuli are shifted up globally by increasing the stimulating intensity, while are drawn closer by increasing the coupling strength. The dynamical responses of small-world and random complex networks to external stimulus are also investigated, which confirm the generality of the observed phenomena. The findings shed new lights on the collective behaviors of complex neuronal networks and might help our understandings on the recent experimental results.     

Non-unique turbulent boundary layer flows having a moderately large velocity defect: a rational extension of the classical asymptotic theory

The classical analysis of turbulent boundary layers in the limit of large Reynolds number Re is characterised by an asymptotically small velocity defect with respect to the external irrotational flow. As an extension of the classical theory, it is shown in the present work that the defect may become moderately large and, in the most general case, independent of Re but still remain small compared to the external streamwise velocity for non-zero pressure gradient boundary layers. That wake-type flow turns out to be characterised by large values of the Rotta–Clauser parameter, serving as an appropriate measure for the defect and hence as a second perturbation parameter besides Re. Most important, it is demonstrated that also this case can be addressed by rigorous asymptotic analysis, which is essentially independent of the choice of a specific Reynolds stress closure. As a salient result of this procedure, transition from the classical small defect to a pronounced wake flow is found to be accompanied by quasi-equilibrium flow, described by a distinguished limit that involves the wall shear stress. This situation is associated with double-valued solutions of the boundary layer equations and an unconventional weak Re-dependence of the external bulk flow—a phenomenon seen to agree well with previous semi-empirical studies and early experimental observations. Numerical computations of the boundary layer flow for various values of Re reproduce these analytical findings with satisfactory agreement.     

Razor clam-inspired burrowing in dry soil

RoboClam is a biomimetic burrowing robot that imitates the valve expansion/contraction digging pattern of the Atlantic razor clam, Ensis directus, to dig into submerged soil using an order of magnitude less energy than would be required to push into the soil with brute force. This paper examines whether it would theoretically be possible to use the same method to dig into dry soil. The stress state of the soil around the contracting robot was analyzed, and a target zero-stress state for dry soil digging was found. Then, the two possible modes of soil collapse were investigated and used to determine how quickly the robot would have to contract to achieve the target zero-stress state. It was found that for most dry soils, a RoboClam-like device would have to contract in 0.02 s, a speed slightly faster than the current robot is capable of, but still within the realm of possibility for a similar machine. These results suggest that the biomimetic approach successfully used by RoboClam to dig into submerged soil could feasibly be used to dig into dry soil as well.     

The plane elasticity problem of an isotropic wedge under normal and shear distributed loading––application in the case of a multi-material problem

The problem of a multi-material composite wedge under a normal and shear loading at its external faces is considered with a variable separable solution. The stress and displacement fields are determined using the equilibrium conditions for forces and moments and the appropriate Airy stress function. The infinite isotropic wedge under shear and normal distributed loading along its external faces is examined for different values of the order n of the radial coordinate r. The proposed solution is applied to the elastostatic problem of a composite isotropic k-materials infinite wedge under distributed loading along its external faces. Applications are made in the case of the two-materials composite wedge under linearly distributed loading along its external faces and in the case of a three-materials composite wedge under a parabolically distributed loading along its external faces.     

A note on the “nonlinear control of electrical flexible-joint robots”

Robust tracking control of electrically flexible-joint robots is addressed in this paper. Two important practical situations are considered. The fact that robot actuators have limited voltage and that current measurement is subjected to noise. Let us notice that a few solutions for the voltage-bounded robust tracking control have been proposed. In this paper, we contribute to this subject by presenting a new form of voltage-based control strategy. It proves that the closed loop system is BIBO stable, while actuator/link position errors are uniformly–ultimately bounded stable in agreement with Lyapunov’s direct method in any finite region of the state space. As a second contribution of this paper, we present a robust adaptive control scheme without the need for computation of regressor matrix and current measurement, with the same result on the closed loop system stability. This novelty gives a simple robust tracking control scheme for both structured and unstructured uncertainties based on the function approximation technique. The analytical studies as well as experimental results produced using MATLAB/Simulink external mode control on a flexible-joint electrically driven robot demonstrate high performance of the proposed control scheme.

     

Transient radiation by a submerged fluid-filled cylindrical shell

The radiation by a submerged fluid-filled cylindrical shell in response to a transient external pressure pulse is considered, and a semi-analytical model based on the Reissner–Mindlin shell theory is employed to simulate the interaction numerically. Two types of radiated waves that have been previously seen in experimental images for a submerged evacuated cylindrical shell are observed in both the external and internal fluids, the symmetric Lamb waves S₀ and the antisymmetric Lamb (or pseudo-Rayleigh) waves A₀. The third type of radiated waves is also observed that has not been explicitly imaged either experimentally or numerically for a submerged evacuated cylindrical shell, and it is demonstrated that these waves are the Scholte–Stoneley waves A. The effect that the complex structure of the radiated field has on the wave phenomena in the internal fluid is analyzed for shells of several different thicknesses, and the results of this analysis are summarized in the form of diagrams suitable for the use at the pre-design stage.     

Cells as strain-cued automata

We argue in favor of representing living cells as automata and review demonstrations that autonomous cells can form patterns by responding to local variations in the strain fields that arise from their individual or collective motions. An autonomous cell's response to strain stimuli is assumed to be effected by internally-generated, internally-powered forces, which generally move the cell in directions other than those implied by external energy gradients. Evidence of cells acting as strain-cued automata have been inferred from patterns observed in nature and from experiments conducted in vitro. Simulations that mimic particular cases of pattern forming share the idealization that cells are assumed to pass information among themselves solely via mechanical boundary conditions, i.e., the tractions and displacements present at their membranes. This assumption opens three mechanisms for pattern formation in large cell populations: wavelike behavior, kinematic feedback in cell motility that can lead to sliding and rotational patterns, and directed migration during invasions. Wavelike behavior among ameloblast cells during amelogenesis (the formation of dental enamel) has been inferred from enamel microstructure, while strain waves in populations of epithelial cells have been observed in vitro. One hypothesized kinematic feedback mechanism, “enhanced shear motility”, accounts successfully for the spontaneous formation of layered patterns during amelogenesis in the mouse incisor. Directed migration is exemplified by a theory of invader cells that sense and respond to the strains they themselves create in the host population as they invade it: analysis shows that the strain fields contain positional information that could aid the formation of cell network structures, stabilizing the slender geometry of branches and helping govern the frequency of branch bifurcation and branch coalescence (the formation of closed networks). In simulations of pattern formation in homogeneous populations and network formation by invaders, morphological outcomes are governed by the ratio of the rates of two competing time dependent processes, one a migration velocity and the other a relaxation velocity related to the propagation of strain information. Relaxation velocities are approximately constant for different species and organs, whereas cell migration rates vary by three orders of magnitude. We conjecture that developmental processes use rapid cell migration to achieve certain outcomes, and slow migration to achieve others. We infer from analysis of host relaxation during network formation that a transition exists in the mechanical response of a host cell from animate to inanimate behavior when its strain changes at a rate that exceeds 10⁻⁴–10⁻³ s⁻¹. The transition has previously been observed in experiments conducted in vitro.     

Output feedback controller for hysteretic time-delayed MIMO nonlinear systems

In this paper, an H ^?? output feedback controller is developed for a class of time-delayed MIMO nonlinear systems, containing backlash as an input nonlinearity. Particularly, a state observer is proposed to estimate unmeasurable states. The control law can be divided into two elements: An adaptive interval type-2 fuzzy part which approximates the uncertain model. The second part is an H ^??-based controller, which attenuates the effects of external disturbances and approximation errors to a prescribed level. Furthermore, the Lyapunov theorem is used to prove stability of proposed controller and its robustness to external disturbance, hysteresis input nonlinearity, and time varying time-delay. As an example, the designed controller is applied to address the tracking problem of 2-DOF robotic manipulator. Simulation results not only verify the robust properties but also in comparison with an existing method reveal the ability of the proposed controller to exclude the effects of unknown time varying time-delays and hysteresis input nonlinearity.     

Nonlinear magneto-mechanical-thermo coupling characteristic analysis for transport behaviors of carriers in composite multiferroic piezoelectric semiconductor nanoplates with surface effect

In this paper, to better reveal the surface effect and the screening effect as well as the nonlinear multi-field coupling characteristic of the multifunctional piezoelectric semiconductor (PS) nanodevice, and to further improve its working performance, a magneto-mechanical-thermo coupling theoretical model is theoretically established for the extensional analysis of a three-layered magneto-electro-semiconductor coupling laminated nanoplate with the surface effect. Next, by using the current theoretical model, some numerical analyses and discussion about the surface effect, the corresponding critical thickness of the nanoplate, and the distributions of the physical fields (including the electron concentration perturbation, the electric potential, the electric field, the average electric displacement, the effective polarization charge density, and the total charge density) under different initial state electron concentrations, as well as their active manipulation via some external magnetic field, pre-stress, and temperature stimuli, are performed. Utilizing the nonlinear multi-field coupling effect induced by inevitable external stimuli in the device operating environment, this paper not only provides theoretical support for understanding the size-dependent tuning/controlling of carrier transport as well as its screening effect, but also assists the design of a series of multiferroic PS nanodevices.

     

One-dimensional nonlinear induced dynamics of acoustic waves in a finite three-dimensional domain

The problem of the time-dependent viscous compressible gas flow excited by a small external time-dependent space-and time-periodic force is considered within the framework of the Navier-Stokes equations on a finite interval with periodic boundary conditions. The investigation is carried out numerically for a periodicity interval L, divided by the viscous length, from 10² to 2 × 10³ and external force amplitudes from 10^?4 to 0.1. The nonlinear dynamics of the wave processes are investigated within the framework of this problem. It is shown that nonlinear steady-state oscillations with sharp variation of the quantities in space and time develop when L is greater than or of the order of 10³. This leads to the onset of a continuous spectrum.