scholarly journals Comparative Study of Two Pose Measuring Systems Used to Reduce Robot Localization Error

Sensors ◽  
2020 ◽  
Vol 20 (5) ◽  
pp. 1305
Author(s):  
Marek Franaszek ◽  
Geraldine S. Cheok ◽  
Jeremy A. Marvel
Keyword(s):  
Rigid Body ◽  
Body Condition ◽  
Degrees Of Freedom ◽  
Industrial Robot ◽  
Substantial Reduction ◽  
Three Dimensional ◽  
Robot Localization ◽  
Localization Error ◽  
Measuring Systems ◽  
The Difference

The performance of marker-based, six degrees of freedom (6DOF) pose measuring systems is investigated. For instruments in this class, the pose is derived from locations of a few three-dimensional (3D) points. For such configurations to be used, the rigid-body condition—which requires that the distance between any two points must be fixed, regardless of orientation and position of the configuration—must be satisfied. This report introduces metrics that gauge the deviation from the rigid-body condition. The use of these metrics is demonstrated on the problem of reducing robot localization error in assembly applications. Experiments with two different systems used to reduce the localization error of the same industrial robot yielded two conflicting outcomes. The data acquired with one system led to substantial reduction in both position and orientation error of the robot, while the data acquired with a second system led to comparable reduction in the position error only. The difference is attributed to differences between metrics used to characterize the two systems.

Validation of a Computational Musculoskeletal Model of the Elbow

2007 ◽  
Author(s):  
Justin P. Fisk ◽  
Jennifer S. Wayne
Keyword(s):  
Rigid Body ◽  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Rigid Body Dynamics ◽  
Clinical Tool ◽  
Element Analysis ◽  
Reconstructive Procedures ◽  
Biomechanical Models ◽  
Musculoskeletal Models ◽  
Body Dynamics

Musculoskeletal computational modeling can be a powerful and useful tool to study joint behavior, examine muscle and ligament function, measure joint contact pressures, simulate injury, and analyze the biomechanical results of reconstructive procedures. Commonly, biomechanical models are based on either finite element analysis (FEA) or three-dimensional rigid body dynamics. While each approach has advantages for specific applications, rigid body dynamics algorithms are highly efficient [1], thus significantly reducing solution time. Many musculoskeletal models of the elbow have been developed [2, 3], but all have constrained the articulations to have particular degrees of freedom and ignored the effects of ligaments. An accurate and robust model without these limitations has potential as a clinical tool to predict the outcome of injuries and/or surgical procedures. This work develops and validates an accurate computational model of the elbow joint whereby joint kinematics are dictated by three-dimensional bony geometry contact, ligamentous constraints, and muscle loading.

A Three-Dimensional Rigid-Body Model for Seismic Analysis of the Pebble-Bed HTR Graphite Core Structure

2013 ◽  
Author(s):  
Chuan Zeng ◽  
Haitao Wang
Keyword(s):  
Rigid Body ◽  
Degrees Of Freedom ◽  
Structural Integrity ◽  
Seismic Analysis ◽  
Three Dimensional ◽  
Computer Code ◽  
Seismic Load ◽  
Three Dimensional Model ◽  
Pebble Bed ◽  
Rigid Body Model

Graphite plays an important role in the pebble-bed high temperature gas-cooled reactors (HTR) as moderator, reflector as well as internal structural material. The HTR core consists of a large number of graphite bricks interconnected with keys. It is required that the structural integrity of the HTR core be maintained when subjected to the seismic load. Hence it is important from the viewpoint of seismic design to investigate the seismic responses of the graphite bricks. Considering the pebble-bed HTR has various graphite shapes, a generalized three-dimensional model with the associated computer code is developed to treat these interconnected graphite bricks with arbitrary shapes. In this model, each brick is treated as a rigid body with six degrees-of-freedom: three translational displacements and three rotations around the brick center of gravity. A nonlinear spring dashpot model is applied to present the collision between adjacent bricks and the interaction forces through the key systems. In the numerical tests, the code is verified by comparing predicted responses with exact solutions for two cases and good agreement is observed. The model is then used for the dynamic analysis of the side reflectors of the pebble-bed HTR core under a given seismic load. The calculated response behaviour of the side reflector column is summarized and discussed.

An Investigation on the Issues in Modelling of Free Flight in Animal Locomotion

2011 ◽  
Author(s):  
Masateru Maeda ◽  
Toshiyuki Nakata ◽  
Hao Liu
Keyword(s):  
Rigid Body ◽  
Degrees Of Freedom ◽  
Aerodynamic Force ◽  
Three Dimensional ◽  
Micro Air Vehicles ◽  
Rigid Body Dynamics ◽  
Free Flight ◽  
Comprehensive Investigation ◽  
Body Dynamics ◽  
Generation Mechanisms

Aiming at establishing an effective computational framework to accurately predict free-flying dynamics and aerodynamics we here present a comprehensive investigation on some issues associated with the modelling of free flight. Free flight modelling/simulation is essential for some types of flights e.g. falling leaves or auto-rotating seeds for plants; unsteady manoeuvres such as take-off, turning, or landing for animals. In addition to acquiring the deeper understanding of the flight biomechanics of those natural organisms, revealing the sophisticated aerodynamic force generation mechanisms employed by them may be useful in designing man-made flying-machines such as rotary or flapping micro air vehicles (MAVs). The simulations have been conducted using the coupling of computational fluid dynamics (CFD) and rigid body dynamics, thus achieving the free flight. The flow field is computed with a three-dimensional unsteady incompressible Navier-Stokes solver using pseudo-compressibility and overset gird technique. The aerodynamic forces acting on the flyer are calculated by integrating the forces on the surfaces. Similarly, the aerodynamic torque around the flyer’s centre of mass is obtained. The forces and moments are then introduced into a six degrees-of-freedom rigid body dynamics solver which utilises unit quaternions for attitude description in order to avoid singular attitude. Results are presented of a single body model and some insect-like multi-body models with flapping wings, which point to the importance of free-flight modelling in systematic analyses of flying aerodynamics and manoeuvrability. Furthermore, a comprehensive investigation indicates that the framework is capable to predict the aerodynamic performance of free-flying or even free-swimming animals in an intermediate range of Reynolds numbers (< 105).

Analysis of a 3-DOF Micro-Positioning Stage

2014 ◽  
Vol 620 ◽  
pp. 234-239 ◽  
Author(s):  
De De Zhai ◽  
Shi Xun Fan ◽  
Da Peng Fan
Keyword(s):  
Theoretical Basis ◽  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Theory Analysis ◽  
Stage Design ◽  
Flexure Hinges ◽  
Positioning Stage ◽  
Effect Curve ◽  
The Difference ◽  
Three Degrees Of Freedom

Firstly a three degrees of freedom micro-positioning stage constructed by flexure hinges is designed, and the simplified model of the stage is established. Secondly, the stiffness of the stage along X, Y direction or around Z direction is deduced by structural mechanics. The difference between finite element method and theory value is less than 7%, so it shows the theory analysis is feasible, further more, stress of the moving stage is analyzed, and the effect curve of the key parameters to the stiffness and stress is obtained. It can be concluded that the stiffness and stress mainly related with the flexure hinge length L and width t, thus it provide a theoretical basis for three-dimensional micro-positioning stage design.

scholarly journals Identification of Three-Dimensional Equivalent Material Properties for Laminated Disks Pack of Electric Machine Stators: Application in Reciprocal Compressors

2019 ◽  
Vol 2019 ◽  
pp. 1-18
Author(s):  
Jean C. Marcon ◽  
Olavo M. Silva ◽  
Thiago A. Fiorentin ◽  
Arcanjo Lenzi
Keyword(s):  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Magnetic Core ◽  
Synthesis Methods ◽  
Equivalent Material ◽  
The Difference ◽  
Three Dimensional Models ◽  
Orthotropic Properties ◽  
Definition Of ◽  
Laminated Structures

Laminated structures can be represented computationally by the finite element method (FEM) using the homogenization procedure, which consists of the adjustment of equivalent orthotropic properties to a homogeneous structure. The application occurs in stators of electric machines composed of stacked laminated disks connected to each other through windings and other fastening components. This paper describes a method to the dynamic characterization of a typical laminated stator through the application of the homogenization technique to the magnetic core and consideration of the effect of winding contour conditions and screw joints. Two simplified three-dimensional models for the stator were compared. The first considers the application of a typical tightening of the fastening screws and the presence of a homogeneous isotropic volume representing the winding. The second considers the effect of the boundary condition of the winding on the region of the teeth of the nucleus in order to reduce the degrees of freedom of the complete model. The coupling between the components is accomplished through the application of modal synthesis methods, which require the definition of the surfaces and the type of connection between the components. The obtainment of the set of equivalent orthotropic properties is based on the minimization of residues related to the difference between the natural and experimental frequencies in the range of 0 to 10 kHz. This was carried out using the multiobjective genetic algorithm (MOGA) method used in conjunction with commercial Ansys® software. Both models presented satisfactory experimental correlation. The simplified model demonstrated limitations of representativeness emphasized in specific frequency bands.

scholarly journals A 3-D Pseudo-Rigid Body Model for Rectangular Cantilever Beams With an Arbitrary Force End-Load

2014 ◽  
Author(s):  
Jairo Chimento ◽  
Craig Lusk ◽  
Ahmad Alqasimi
Keyword(s):  
Rigid Body ◽  
Cross Sections ◽  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Neutral Axis ◽  
Spatial Behavior ◽  
Model Parameters ◽  
Cantilever Beams ◽  
Body Model ◽  
Rigid Body Model

This paper presents the first three-dimensional pseudo-rigid body model (3-D PRBM) for straight cantilever beams with rectangular cross sections and spatial motion. Numerical integration of a system of differential equations yields approximate displacement and orientation of the beam’s neutral axis at the free-end, and curvatures of the neutral axis at the fixed-end. This data was used to develop the 3-D PRBM which consists of two torsional springs connecting two rigid links for a total of 2 degrees of freedom (DOF). The 3-D PRBM parameters that are comparable with existing 2-D model parameters are characteristic radius factor (means: γ = 0.8322), bending stiffness coefficient (means: KΘ = 2.5167) and parametric angle coefficient (means: cΘ = 1.2501). New parameters are introduced in the model in order to capture the spatial behavior of the deflected beam including two parametric angle coefficients (means: cΨ = 1.0714; cΦ = 1.0087).

A quaternion-based simulation of multirotor dynamics

2015 ◽  
Vol 06 (01) ◽  
pp. 1550009 ◽  
Author(s):  
Valeria Artale ◽  
Cristina L. R. Milazzo ◽  
Angela Ricciardello
Keyword(s):  
Rigid Body ◽  
Euler Equations ◽  
Body Condition ◽  
Rotational Motion ◽  
Three Dimensional ◽  
Euler Angle ◽  
Dynamical Model ◽  
Control Technique ◽  
Coordinate Space ◽  
And Control

The main problem addressed in this paper is the quaternion-based trajectory control of a microcopter consisting of six rotors with three pairs of counter-rotating fixed-pitch blades, known as hexacopter. If the hypothesis of rigid body condition is assumed, the Newton–Euler equations describe the translational and rotational motion of the drone. The standard Euler-angle parametrization of three-dimensional rotations contains singular points in the coordinate space that can cause failure of both dynamical model and control. In order to avoid singularities, all the rotations of the microcopter are thus parametrized in terms of quaternions and an original proportional derivative (PD) regulator is proposed in order to control the dynamical model. Numerical simulations will be performed on symmetrical flight configuration, proving the reliability of the proposed PD control technique.

Combination of energy minimizations and rigid-body Rietveld refinement: the structure of 2,5-dihydroxybenzo[de]benzo[4,5]imidazo[2,1-a]isoquinolin-7-one

1999 ◽  
Vol 32 (2) ◽  
pp. 178-186 ◽  
Author(s):  
Martin U. Schmidt ◽  
Robert E. Dinnebier
Keyword(s):  
Crystal Structure ◽  
Rigid Body ◽  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Rietveld Analysis ◽  
Hydrogen Bond Network ◽  
Intermolecular Energy ◽  
Planar Molecules ◽  
Bond Network ◽  
Random Packings

The crystal structure of the yellow pigment 2,5-dihydroxybenzo[de]benzo[4,5]imidazo[2,1-a]isoquinolin-7-one (C18H10N2O3) was determined from powder data. The crystal structure was solved by minimizing the intermolecular energy starting from random packings. Subsequently, the structure was refined by rigid-body Rietveld analysis, using synchrotron powder data. The refinement included several intramolecular degrees of freedom. The compound crystallizes inPna21,Z\,=\,4, with lattice parametersa\,=\,13.2759 (3),b\,=\,20.9561 (5),c\,=\,4.7798 (1) Å, andV\,=\,1329.79 (5) Å3. The crystal consists of planar molecules, connected by hydrogen bonds of the types O–H...OH and O–H...N, which form a three-dimensional hydrogen-bond network.

Defocus ramp correction in spot-scan imaging

1992 ◽  
Vol 50 (1) ◽  
pp. 130-131
Author(s):  
Kenneth H. Downing
Keyword(s):  
Computer Control ◽  
Three Dimensional ◽  
Sufficient Accuracy ◽  
Objective Lens ◽  
Electron Crystallography ◽  
Contrast Transfer Function ◽  
Tilt Axis ◽  
Specimen Height ◽  
The Difference ◽  
Envelope Functions

Three-dimensional structures of a number of samples have been determined by electron crystallography. The procedures used in this work include recording images of fairly large areas of a specimen at high tilt angles. There is then a large defocus ramp across the image, and parts of the image are far out of focus. In the regions where the defocus is large, the contrast transfer function (CTF) varies rapidly across the image, especially at high resolution. Not only is the CTF then difficult to determine with sufficient accuracy to correct properly, but the image contrast is reduced by envelope functions which tend toward a low value at high defocus.We have combined computer control of the electron microscope with spot-scan imaging in order to eliminate most of the defocus ramp and its effects in the images of tilted specimens. In recording the spot-scan image, the beam is scanned along rows that are parallel to the tilt axis, so that along each row of spots the focus is constant. Between scan rows, the objective lens current is changed to correct for the difference in specimen height from one scan to the next.

On the Use of Quantum Thermal Bath in Unimolecular Fragmentation Simulations

2019 ◽  
Author(s):  
Riccardo Spezia ◽  
Hichem Dammak
Keyword(s):  
Degrees Of Freedom ◽  
Molecular Simulations ◽  
Zero Point ◽  
Thermal Bath ◽  
Unimolecular Dissociation ◽  
Point Energy ◽  
Rotational Degrees Of Freedom ◽  
The Difference ◽  
Nuclear Effects

<div> <div> <div> <p>In the present work we have investigated the possibility of using the Quantum Thermal Bath (QTB) method in molecular simulations of unimolecular dissociation processes. Notably, QTB is aimed in introducing quantum nuclear effects with a com- putational time which is basically the same as in newtonian simulations. At this end we have considered the model fragmentation of CH4 for which an analytical function is present in the literature. Moreover, based on the same model a microcanonical algorithm which monitor zero-point energy of products, and eventually modifies tra- jectories, was recently proposed. We have thus compared classical and quantum rate constant with these different models. QTB seems to correctly reproduce some quantum features, in particular the difference between classical and quantum activation energies, making it a promising method to study unimolecular fragmentation of much complex systems with molecular simulations. The role of QTB thermostat on rotational degrees of freedom is also analyzed and discussed. </p> </div> </div> </div>

Sign in / Sign up

Export Citation Format

Share Document