Multi-point substructure coupling method to compensate multi-accelerometer masses in measuring rotation-related FRFs

2021 ◽  
pp. 1-19
Author(s):  
YuLei Ji ◽  
Yanren Chen ◽  
Shaokun Zhang ◽  
Qingzhen Bi ◽  
Yuhan Wang
Keyword(s):  
Prediction Accuracy ◽  
Degrees Of Freedom ◽  
Measurement Data ◽  
Coupling Method ◽  
Multiple Point ◽  
Receptance Coupling ◽  
Rotational Vibration ◽  
Simulation And Experiment ◽  
Rotational Degrees Of Freedom ◽  
Milling Vibration

Abstract Tool-tip Frequency Response Functions (FRFs) are often required in milling vibration analysis. Receptance coupling substructures analysis (RCSA) affords an efficient analytical way for different tool-tip FRFs prediction with only one modal test. The coupling theory includes both translational and rotational degrees of freedom, so rotation-related FRFs are essential to know in the test. The finite-differential technique is generally used to measure these special FRFs due to the avoidance of specialist equipment. The technique uses several translational accelerometers spatially placed close to each other to approximate the rotational vibration. However, the added sensor masses lead to the frequency shift of the test structure, and the phenomenon would aggravate as the sensors increase. The polluted measurement data would subsequently decrease the tool-tip FRFs prediction accuracy. Addressing this problem, this paper introduces a multi-point substructure coupling method to simultaneously compensate the multi-accelerometer masses in a single experimental setup. The proposed method considers the installed accelerators as multiple point masses and then uses inverse coupling calculation to isolate their effect. The compensation procedure is first effectively validated in simulation and experiment, and then it is integrated into an RCSA-based application of predicting different tool-tip dynamics. Experimental results show that the compensated FRF data can improve prediction accuracy, especially when predicting tools shorter than the tested tool.

Kinematic calibration of the parallel Argos mechanism

Robotica ◽  
2000 ◽  
Vol 18 (6) ◽  
pp. 589-599 ◽  
Author(s):  
Peter Vischer ◽  
Reymond Clavel
Keyword(s):  
Degrees Of Freedom ◽  
Measurement Data ◽  
Spherical Model ◽  
Parallel Structure ◽  
Kinematic Calibration ◽  
End Effector ◽  
Calibration Models ◽  
Rotational Degrees Of Freedom ◽  
Set Up ◽  
Circle Model

This paper deals with the kinematic calibration of the Argos mechanism which is a novel, spherical parallel structure having 3 rotational degrees of freedom. Its design is based on 3 actuators carrying a pantograph each which are connected to the end-effector by means of 3 spherical joints. Two different calibration models are introduced. The first one models mechanical deviations in all parts except for the spherical joints and the assumption that they are moving on a perfect circle (“model 27”). The second model considers only deviations which affects the orientation of the end-effector but not its position assuming that the mechanism remains spherical (“model 9”). A measurement set-up allows to measure the full pose (position and orientation) of the end-effector with respect to its base. These measurement data are used to identify the parameters of the two calibration models resulting in an accuracy improvement of RMS (root mean squares errors) of a factor of 5.3 for the orientation and a factor of 3.4 for the prediction of the position.

Identification of a Lathe Spindle Dynamics Using Extended Inverse Receptance Coupling

2018 ◽  
Vol 140 (12) ◽  
Author(s):  
Marcin Jasiewicz ◽  
Bartosz Powałka
Keyword(s):  
Machine Tool ◽  
Degrees Of Freedom ◽  
Experimental Validation ◽  
Dynamic Properties ◽  
Measurement Procedure ◽  
Experimental Models ◽  
Analytical Models ◽  
Receptance Coupling ◽  
Spindle Dynamics ◽  
Rotational Degrees Of Freedom

In order to ensure machining stability, it is essential to properly determine the dynamic properties of machine tool–workpiece system. Experimental modal analysis provides good results; however, due to high time consumption, in some cases, its use is not practically justified. Then, a receptance coupling method can be used, that allows for the synthesis of the experimental models of the machine tool components and analytical models of the workpiece. However, a significant disadvantage of this method is the need for the experimental identification of the rotational degrees-of-freedom, fully defining dynamic properties of the spindle. This paper presents an improved method based on inverse receptance coupling, which enables effective identification of the spindle dynamics with the properties of the joint. Then, a measurement procedure and results of the experimental validation are presented.

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>

Effect of Rotational Degrees of Freedom on Molecular Mobility

2013 ◽  
Vol 117 (13) ◽  
pp. 6800-6806 ◽  
Author(s):  
M. Jafary-Zadeh ◽  
C. D. Reddy ◽  
Yong-Wei Zhang
Keyword(s):  
Molecular Mobility ◽  
Degrees Of Freedom ◽  
Rotational Degrees Of Freedom

Dynamic Modeling of a High-Dynamic Flight Simulator

2014 ◽  
Vol 687-691 ◽  
pp. 610-615 ◽  
Author(s):  
Hui Liu ◽  
Li Wen Guan
Keyword(s):  
Dynamic Modeling ◽  
Degrees Of Freedom ◽  
Flight Simulator ◽  
Inverse Dynamic ◽  
Dynamic Formulation ◽  
Time Histories ◽  
Rotational Degrees Of Freedom ◽  
High Dynamic ◽  
Euler Approach ◽  
Simulation Results

High-dynamic flight simulator (HDFS), using a centrifuge as its motion base, is a machine utilized for simulating the acceleration environment associated with modern advanced tactical aircrafts. This paper models the HDFS as a robotic system with three rotational degrees of freedom. The forward and inverse dynamic formulations are carried out by the recursive Newton-Euler approach. The driving torques acting on the joints are determined on the basis of the inverse dynamic formulation. The formulation has been implemented in two numerical simulation examples, which are used for calculating the maximum torques of actuators and simulating the time-histories of kinematic and dynamic parameters of pure trapezoid Gz-load command profiles, respectively. The simulation results can be applied to the design of the control system. The dynamic modeling approach presented in this paper can also be generalized to some similar devices.

Nonlinear Six-Degree-of-Freedom Dynamic Model for Risers, Pipelines, and Beams

1986 ◽  
Vol 30 (03) ◽  
pp. 177-185
Author(s):  
Michael M. Bernitsas ◽  
John E. Kokarakis
Keyword(s):  
Cross Sections ◽  
Degrees Of Freedom ◽  
Nonlinear Effects ◽  
Nonlinear Formulation ◽  
Marine Risers ◽  
Internal Fluid ◽  
Rotational Degrees Of Freedom ◽  
Six Degree Of Freedom ◽  
Structural Imperfections ◽  
Inertia Forces

A nonlinear model for the dynamic behavior of tubular beams such as marine risers, pipelines, legs of tension leg platforms, and drill strings is developed. The formulation includes three translational degrees of freedom of the riser cross section and three rotational degrees of freedom for shear and torsion. Nonlinear constitutive equations for cross sections of unequal principal stiffnesses and extensible material are derived. Initial structural imperfections which are inherent in long risers are modeled in the form of initial curvature and geometric torsion which do not induce strains. The inertia forces due to the motion of the riser and internal fluid motions are formulated. The external hydrodynamic and hydrostatic forces are integrated on the riser surface as pressure and traction forces. The model is a comprehensive consistent nonlinear formulation of the riser dynamics and can be used for evaluation of the significance of nonlinear effects.

ROTATIONS AND VIBRATIONS OF FULLERENES IN THE MOLECULAR COMPLEX C20@C80

2021 ◽  
pp. 35-48
Author(s):  
M.A. Bubenchikov ◽  
◽  
A.M. Bubenchikov ◽  
D.V. Mamontov ◽  
◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Equations Of Motion ◽  
Classical Mechanics ◽  
Rotation Frequency ◽  
Dynamic State ◽  
Large Molecules ◽  
Rotational Degrees Of Freedom ◽  
Rotational Motions ◽  
Centers Of Mass ◽  
The Moment

The aim of this work is to apply classical mechanics to a description of the dynamic state of C20@C80 diamond complex. Endohedral rotations of fullerenes are of great interest due to the ability of the materials created on the basis of onion complexes to accumulate energy at rotational degrees of freedom. For such systems, a concept of temperature is not specified. In this paper, a closed description of the rotation of large molecules arranged in diamond shells is obtained in the framework of the classical approach. This description is used for C20@C80 diamond complex. Two different problems of molecular dynamics, distinguished by a fixing method for an outer shell of the considered bimolecular complex, are solved. In all the cases, the fullerene rotation frequency is calculated. Since a class of possible motions for a single carbon body (molecule) consists of rotations and translational displacements, the paper presents the equations determining each of these groups of motions. Dynamic equations for rotational motions of molecules are obtained employing the moment of momentum theorem for relative motions of the system near the fullerenes’ centers of mass. These equations specify the operation of the complex as a molecular pendulum. The equations of motion of the fullerenes’ centers of mass determine vibrations in the system, i.e. the operation of the complex as a molecular oscillator.

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