Virtual Model Control of a Hexapod Walking Robot

Since robots are typically designed with an individual actuator at each joint, the control of these systems is often difficult and non-intuitive. This thesis explains a more intuitive control scheme called Virtual Model Control. This thesis also demonstrates the simplicity and ease of this control method by using it to control a simulated walking hexapod. Virtual Model Control uses imagined mechanical components to create virtual forces, which are applied through the joint torques of real actuators. This method produces a straightforward means of controlling joint torques to produce a desired robot behavior. Due to the intuitive nature of this control scheme, the design of a virtual model controller is similar to the design of a controller with basic mechanical components. The ease of this control scheme facilitates the use of a high level control system which can be used above the low level virtual model controllers to modulate the parameters of the imaginary mechanical components. In order to apply Virtual Model Control to parallel mechanisms, a solution to the force distribution problem is required. This thesis uses an extension of Gardner`s Partitioned Force Control method which allows for the specification of constrained degrees of freedom. This virtual model control technique was applied to a simulated hexapod robot. Although the hexapod is a highly non-linear, parallel mechanism, the virtual models allowed text-book control solutions to be used while the robot was walking. Using a simple linear control law, the robot walked while simultaneously balancing a pendulum and tracking an object.

Exercise sheet 5 pdf

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Exercise sheet 5

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Evaluación de la mecánica ventricular izquierda mediante speckle tracking en pacientes sanos en la Clínica Shaio

Introducción: La ecocardiografía es actualmente la técnica de imagen diagnóstica más utilizada para la evaluación de la anatomía y la función cardiovascular. En la actualidad se está utilizando la ecocardiografía por speckle tracking la cual permite una evaluación mas objetiva y confiable de la función ventricular, sin embargo se requieren valores de referencia que hagan que los valores obtenidos sean válidos y útiles para determinar en forma mas oportuna conductas previas al deterioro de su función. Objetivo general: Determinar los valores de referencia para mecánica ventricular izquierda mediante ecocardiografía bidimensional por speckle tracking con equipo Toshiba Artida con transductor multifrecuencia de 3 megahertzios en pacientes sin patología cardiaca conocida en la Fundación Clínica Shaio en el año 2014. Metodología: Análisis de una cohorte prospectiva de todos los pacientes que ingresaron a la Fundación Clínica Shaio para evaluación ecocardiográfica sin patología cardiaca conocida entre los meses Agosto y Diciembre del 2014. Resultados: Se presenta este estudio de la evaluación de la mecánica ventricular izquierda en adultos sanos, los resultados son similares a los obtenidos en estudios de referencia, sin embargo se consideran de gran importancia ya que de acuerdo a la guía actual de evaluación de la mecánica ventricular por strain rate es importante que cada equipo se encuentre estandarizado con el fin de tener resultados válidos de acuerdo a las diferentes patologías en las que se puede aplicar y a nuestra población.

Mecánica ventricular izquierda en pacientes con infarto agudo del miocardio

RESUMEN Introducción El papel de las nuevas técnicas ecocardiográficas para el diagnóstico de infarto agudo del miocardio se encuentra en desarrollo y la realización de mecánica ventricular izquierda podría sugerir la presencia de enfermedad coronaria hemodinámicamente significativa. Objetivos Determinar si en pacientes con infarto agudo del miocardio la medición de strain longitudinal global y regional sirve para predecir la presencia de enfermedad coronaria significativa. Métodos Es un estudio de pruebas diagnósticas en el que se evaluaron las características operativas de la mecánica ventricular izquierda para la detección de enfermedad coronaria significativa comparado contra el cateterismo cardiaco, considerado el patrón de oro. Se analizaron 54 pacientes con infarto agudo del miocardio llevados a cateterismo cardiaco, a quienes se les realizó un ecocardiograma transtorácico con medición de strain longitudinal global y regional. Resultados De los 54 pacientes analizados, el 83% tenía enfermedad coronaria significativa. El hallazgo de un strain longitudinal global < -17.5 tuvo una sensibilidad del 85% y una especificidad del 78% para predecir la presencia de enfermedad coronaria; para la arteria descendente anterior un strain longitudinal regional < – 17.4 tuvo una sensibilidad de 82% y una especificidad de 44%, para la arteria circunfleja una sensibilidad del 87% y una especificidad del 37% y para la arteria coronaria derecha una sensibilidad de 73% y una especificidad de 32%. Conclusiones La realización de ecocardiografía con mecánica ventricular en pacientes con infarto agudo del miocardio es útil para predecir la presencia de enfermedad coronaria hemodinámicamente significativa.

Calculation of Franck-Condon factors including anharmonicity: simulation of the C2 H4+ X̃2B 3u←C2 H4X̃1 Ag band in the photoelectron spectrum of ethylene

Our new simple method for calculating accurate Franck-Condon factors including nondiagonal (i.e., mode-mode) anharmonic coupling is used to simulate the C2H4+X2B 3u←C2H4X̃1 Ag band in the photoelectron spectrum. An improved vibrational basis set truncation algorithm, which permits very efficient computations, is employed. Because the torsional mode is highly anharmonic it is separated from the other modes and treated exactly. All other modes are treated through the second-order perturbation theory. The perturbation-theory corrections are significant and lead to a good agreement with experiment, although the separability assumption for torsion causes the C2 D4 results to be not as good as those for C2 H4. A variational formulation to overcome this circumstance, and deal with large anharmonicities in general, is suggested

The dark side of the Mediterranean : expression of fear from the inquisition to the present

Inside the stones of its most famous buildings, Évora keeps mysteries and secrets which constitute the most hidden side of its cultural identity. A World Heritage site, this town seems to preserve, in its medieval walls, a precious knowledge of the most universal and ancient human emotion: fear. Trying to transcend many of its past and future fears, some of its historical monuments in Gothic style were erected against the fear of death, the most terrible of all fears, which the famous inscription, in the Bones Chapel of the Church of São Francisco, insistently reminds us, through the most disturbing words: “Nós ossos que aqui estamos pelos vossos esperamos”. If the first inquisitors worked in central Europe (Germany, northern Italy, eastern France), later the centres of the Inquisition were established in the Mediterranean regions, especially southern France, Italy, Portugal, and Spain. Consequently, the roots of fear in Évora are common to other towns, where the Inquisition developed a culture of fear, through which we can penetrate into the dark side of the Mediterranean, where people were subjected to the same terrifying methods of persecution and torture. This common geographical and historical context was not ignored by one of the most famous masters of American gothic fiction, Edgar Allan Poe. Through the pages of The Pit and the Pendulum, readers get precise images of the fearful instruments of terror that were able to produce the legend that has made the first grand inquisitor, Tomas de Torquemada, a symbol of ultimate cruelty, bigotry, intolerance, and religious fanaticism, which unfortunately are still the source of our present fears in a time when religious beliefs can be used again as a motif of war and destruction. As Krishnamurti once suggested, only a fundamental realization of the root of all fear can free our minds.

Latitude and longitude vertical disparities

The literature on vertical disparity is complicated by the fact that several different definitions of the term “vertical disparity” are in common use, often without a clear statement about which is intended or a widespread appreciation of the properties of the different definitions. Here, we examine two definitions of retinal vertical disparity: elevation-latitude and elevation-longitude disparities. Near the fixation point, these definitions become equivalent, but in general, they have quite different dependences on object distance and binocular eye posture, which have not previously been spelt out. We present analytical approximations for each type of vertical disparity, valid for more general conditions than previous derivations in the literature: we do not restrict ourselves to objects near the fixation point or near the plane of regard, and we allow for non-zero torsion, cyclovergence, and vertical misalignments of the eyes. We use these expressions to derive estimates of the latitude and longitude vertical disparities expected at each point in the visual field, averaged over all natural viewing. Finally, we present analytical expressions showing how binocular eye position—gaze direction, convergence, torsion, cyclovergence, and vertical misalignment—can be derived from the vertical disparity field and its derivatives at the fovea.

A tungsten complex containing a highly delocalized metal-ligand system

Nucleophilic attack of (triphenylphosphonio) cyclopentadienide on the dichlorodiazomethane-tungsten complex trans[ BrW(dppe)(2)(N2CCl2)]PF6 [dppe is 1,2-bis(diphenylphosphino) ethane] results in C-C bond formation and affords the title compound, trans-[W(C24H18ClN2P)Br(C26H24P2)(2)]PF6 center dot 0.6CH(2)Cl(2). This complex, bis[1,2- bis(diphenylphosphino)ethane] bromido{chloro[3-(triphenylphosphonio) cyclopentadienylidene] diazomethanediido} tungsten hexafluorophosphate dichloromethane 0.6-solvate, contains the previously unknown ligand chloro[3-(triphenylphosphonio) cyclopentadienylidene] diazomethane. Evidence from bond lengths and torsion angles indicates significant through-ligand delocalization of electron density from tungsten to the nominally cationic phosphorus(V) centre. This structural analysis clearly demonstrates that the tungsten-dinitrogen unit is a powerful pi-electron donor with the ability to transfer electron density from the metal to a distant acceptor centre through an extended conjugated ligand system. As a consequence, complexes of this type could have potential applications as nonlinear optical materials and molecular semiconductors.

Torsional interactions between mooring line components

Six strand ropes generate torque under tension. This can lead to transfer of twist to other mooring line components, either permanently, or dynamically. The effects of this imposed twist can seriously affect strength and fatigue endurance. In order to predict the torsional interactions between components it is necessary to quantify the tension/torsion behavior of all the different categories of mooring line component, not just the six strand rope. This paper discusses the problems of torsional interaction and presents results of measurements of tension/torsion behavior of six strand rope, stud link chain and a PET fiber rope.

Preliminary results from a real time control system using optical information

Successful results from training an adaptive controller to use optical information to balance an inverted pendulum are presented in comparison to the training requirements using traditional controller inputs. Results from research into the psychology of the sense of balance in humans are presented as the motivation for the investigation of this new type of controller. The simulated model of the inverted pendulum and the virtual reality environments used to provide the optical input are described The successful introduction of optical information is found to require the preservation of at least two of the traditional input types and entail increased training time for the adaptive controller and reduced performance (measured as the time the pendulum remains upright).

Results of applying sensor fusion to a control system using optic flow

The results from applying a sensor fusion process to an adaptive controller used to balance all inverted pendulum axe presented. The goal of the sensor fusion process was to replace some of the four mechanical measurements, which are known to be sufficient inputs for a linear state feedback controller to balance the system, with optic flow variables. Results from research into the psychology of the sense of balance in humans were the motivation for the investigation of this new type of controller input. The simulated model of the inverted pendulum and the virtual reality environments used to provide the optical input are described. The successful introduction of optical information is found to require the preservation of at least two of the traditional input types and entail increased training till-le for the adaptive controller and reduced performance (measured as the time the pendulum remains upright)

Singularities of optimal control problems on some 6-D lie groups

This paper considers the motion planning problem for oriented vehicles travelling at unit speed in a 3-D space. A Lie group formulation arises naturally and the vehicles are modeled as kinematic control systems with drift defined on the orthonormal frame bundles of particular Riemannian manifolds, specifically, the 3-D space forms Euclidean space E-3, the sphere S-3, and the hyperboloid H'. The corresponding frame bundles are equal to the Euclidean group of motions SE(3), the rotation group SO(4), and the Lorentz group SO (1, 3). The maximum principle of optimal control shifts the emphasis for these systems to the associated Hamiltonian formalism. For an integrable case, the extremal curves are explicitly expressed in terms of elliptic functions. In this paper, a study at the singularities of the extremal curves are given, which correspond to critical points of these elliptic functions. The extremal curves are characterized as the intersections of invariant surfaces and are illustrated graphically at the singular points. It. is then shown that the projections, of the extremals onto the base space, called elastica, at these singular points, are curves of constant curvature and torsion, which in turn implies that the oriented vehicles trace helices.

Three dimensional picture of the local structure of 1,4-Polybutadiene from a complete atomistic model and neutron scattering data

An efficient method of combining neutron diffraction data over an extended Q range with detailed atomistic models is presented. A quantitative and qualitative mapping of the organization of the chain conformation in both glass and liquid phase has been performed. The proposed structural refinement method is based on the exploitation of the intrachain features of the diffraction pattern by the use of internal coordinates for bond lengths, valence angles and torsion rotations. Models are built stochastically by assignment of these internal coordinates from probability distributions with limited variable parameters. Variation of these parameters is used in the construction of models that minimize the differences between the observed and calculated structure factors. A series of neutron scattering data of 1,4-polybutadiene at the region 20320 K is presented. Analysis of the experimental data yield bond lengths for C-C and C=C of 1.54 and 1.35 Å respectively. Valence angles of the backbone were found to be at 112 and 122.8 for the CCC and CC=C respectively. Three torsion angles corresponding to the double bond and the adjacent R and β bonds were found to occupy cis and trans, s(, trans and g( and trans states, respectively. We compare our results with theoretical predictions, computer simulations, RIS models, and previously reported experimental results.

Measuring motion with kinematically redundant accelerometer arrays: theory, simulation and implementation

This work presents two schemes of measuring the linear and angular kinematics of a rigid body using a kinematically redundant array of triple-axis accelerometers with potential applications in biomechanics. A novel angular velocity estimation algorithm is proposed and evaluated that can compensate for angular velocity errors using measurements of the direction of gravity. Analysis and discussion of optimal sensor array characteristics are provided. A damped 2 axis pendulum was used to excite all 6 DoF of the a suspended accelerometer array through determined complex motion and is the basis of both simulation and experimental studies. The relationship between accuracy and sensor redundancy is investigated for arrays of up to 100 triple axis (300 accelerometer axes) accelerometers in simulation and 10 equivalent sensors (30 accelerometer axes) in the laboratory test rig. The paper also reports on the sensor calibration techniques and hardware implementation.