scholarly journals Prediction of high-speed rigid body manoeuvring in air-water-sediment

2006 ◽  
Author(s):  
P. C. Chu ◽  
G. Ray
Keyword(s):  
Rigid Body ◽  
High Speed

Design of sliding mode flight control system for a flexible aircraft

2021 ◽  
pp. 095441002110455
Author(s):  
Majeed Mohamed ◽  
Madhavan Gopakumar
Keyword(s):  
Control System ◽  
Rigid Body ◽  
Flight Control ◽  
High Speed ◽  
Sliding Mode ◽  
Flight Mechanics ◽  
Frequency Separation ◽  
Flight Control System ◽  
Flexible Aircraft ◽  
Aircraft Dynamics

The evolution of large transport aircraft is characterized by longer fuselages and larger wingspans, while efforts to decrease the structural weight reduce the structural stiffness. Both effects lead to more flexible aircraft structures with significant aeroelastic coupling between flight mechanics and structural dynamics, especially at high speed, high altitude cruise. The lesser frequency separation between rigid body and flexible modes of flexible aircraft results in a stronger interaction between the flight control system and its structural modes, with higher flexibility effects on aircraft dynamics. Therefore, the design of a flight control law based on the assumption that the aircraft dynamics are rigid is no longer valid for the flexible aircraft. This paper focuses on the design of a flight control system for flexible aircraft described in terms of a rigid body mode and four flexible body modes and whose parameters are assumed to be varying. In this paper, a conditional integral based sliding mode control (SMC) is used for robust tracking control of the pitch angle of the flexible aircraft. The performance of the proposed nonlinear flight control system has been shown through the numerical simulations of the flexible aircraft. Good transient and steady-state performance of a control system are also ensured without suffering from the drawback of control chattering in SMC.

Using Dual Cam Tracks for High Speed Rigid Body Motion

1998 ◽  
Author(s):  
Clay Cooper ◽  
Stephen Derby
Keyword(s):  
Rigid Body ◽  
High Speed ◽  
Rigid Body Motion ◽  
Body Motion ◽  
Transfer Rates ◽  
Track System ◽  
Selection Of

Abstract Rigid Body Motion has long been one of the standard problems for kinematicians. For high speed transfer rates, an industrial example of using a dual cam track system to achieve better performance is documented. The dual track establishes both a positional and orientational location of the followers. The selection of this mechanism type is discussed.

Computation of Rigid-Body Rotation in Three-Dimensional Space From Body-Fixed Linear Acceleration Measurements

1979 ◽  
Vol 46 (4) ◽  
pp. 925-930 ◽  
Author(s):  
N. K. Mital ◽  
A. I. King
Keyword(s):  
Rigid Body ◽  
High Speed ◽  
Dimensional Space ◽  
Three Dimensional ◽  
Angular Acceleration ◽  
Linear Acceleration ◽  
Field Measurements ◽  
Moving Frame ◽  
Accelerometer Data ◽  
Hypothetical Data

The angular acceleration of a rigid body with respect to a body-fixed (moving) frame can be reliably computed from nine acceleration field measurements. Noncommutativity of finite rotations causes computational problems during numerical integration to obtain the transformation matrix, especially when the rotation is three-dimensional and there are errors in the measured linear accelerations. A method based on the orientation vector concept is formulated and tested against hypothetical data. The rigid-body rotations computed from linear accelerometer data from impact acceleration tests are compared against those obtained from three-dimensional analysis of high speed movie films.

Inverse Kinematics Analysis and Workspace of a New 3-RRRR Parallel Manipulator

Volume 2 ◽  
2004 ◽  
Author(s):  
Mohsen Bahrami ◽  
Iman Ebrahimi Moghaddam
Keyword(s):  
Rigid Body ◽  
Inverse Kinematics ◽  
Parallel Manipulator ◽  
High Speed ◽  
Analytic Solution ◽  
Kinematics Analysis ◽  
Electric Actuation ◽  
The One ◽  
Speed Accuracy ◽  
Robotic Applications

This paper presents a new 3-RRRR parallel manipulator. In the proposed mechanism, the revolute actuators are fixed to the base, which leads to a reduction of the inertia of the moving links and hence makes it attractive, particularly when high-speed motions are required and electric actuation is considered. This manipulator can be used in robotic applications involving the positioning and orientation of a rigid body in the space with high-speed, accuracy and high stiffness or as a simulator or others high-precision or high-speed devices. After introducing the mechanism, inverse kinematics analysis is presented. By the virtue of complexity of analytic solution, an algorithm is utilized which can numerically find possible of solutions and choose the one with applicable configuration. Then the workspace of manipulator is obtained by means of proposed numerical solution.

scholarly journals Accuracy Assessment of Pseudo-Rigid-Body Model for Dynamic Analysis of Compliant Mechanisms

2017 ◽  
Vol 9 (5) ◽  
Author(s):  
Na Li ◽  
Hai-Jun Su ◽  
Xian-Peng Zhang
Keyword(s):  
Rigid Body ◽  
Dynamic Analysis ◽  
Distribution Coefficient ◽  
Mass Distribution ◽  
High Speed ◽  
Compliant Mechanisms ◽  
Accuracy Assessment ◽  
Dynamic Responses ◽  
Dynamic Simulations ◽  
Rigid Body Model

Dynamic characteristics analysis is very important for the design and application of compliant mechanisms, especially for dynamic and control performance in high-speed applications. Although pseudo-rigid-body (PRB) models have been extensively studied for kinetostatic analysis, their accuracy for dynamic analysis is relatively less evaluated. In this paper, we first evaluate the accuracy of the PRB model by comparing against the continuum model using dynamic simulations. We then investigate the effect of mass distribution on dynamics of PRB model for compliant parallel-guided mechanisms. We show that when the beam mass is larger than 10% of the motion stage, the error is significant. We then propose a new PRB model with a corrected mass distribution coefficient which significantly reduces the error of the PRB model. And the dynamic responses are also analyzed according to the corrected mass distribution coefficient. At last, a compliant double parallel-guiding mechanism is used as a case study for validation of the new PRB model for dynamics of compliant mechanisms.

scholarly journals Rigid-body fitting to atomic force microscopy images for inferring probe shape and biomolecular structure

2021 ◽  
Vol 17 (7) ◽  
pp. e1009215
Author(s):  
Toru Niina ◽  
Yasuhiro Matsunaga ◽  
Shoji Takada
Keyword(s):  
Atomic Force Microscopy ◽  
Rigid Body ◽  
Correlation Coefficient ◽  
High Speed ◽  
Similarity Score ◽  
Molecular Structures ◽  
Cosine Similarity ◽  
Force Microscopy ◽  
Atomic Force ◽  
Dynamics Simulations

Atomic force microscopy (AFM) can visualize functional biomolecules near the physiological condition, but the observed data are limited to the surface height of specimens. Since the AFM images highly depend on the probe tip shape, for successful inference of molecular structures from the measurement, the knowledge of the probe shape is required, but is often missing. Here, we developed a method of the rigid-body fitting to AFM images, which simultaneously finds the shape of the probe tip and the placement of the molecular structure via an exhaustive search. First, we examined four similarity scores via twin-experiments for four test proteins, finding that the cosine similarity score generally worked best, whereas the pixel-RMSD and the correlation coefficient were also useful. We then applied the method to two experimental high-speed-AFM images inferring the probe shape and the molecular placement. The results suggest that the appropriate similarity score can differ between target systems. For an actin filament image, the cosine similarity apparently worked best. For an image of the flagellar protein FlhAC, we found the correlation coefficient gave better results. This difference may partly be attributed to the flexibility in the target molecule, ignored in the rigid-body fitting. The inferred tip shape and placement results can be further refined by other methods, such as the flexible fitting molecular dynamics simulations. The developed software is publicly available.

Development of a Low Cost High-Speed Video Motion Capture System for Planar Motion

2020 ◽  
Author(s):  
Heather L. Lai ◽  
Susan Ko
Keyword(s):  
Rigid Body ◽  
Motion Capture ◽  
High Speed ◽  
Field Of View ◽  
High Speed Camera ◽  
Motion Capture System ◽  
Position Sensing ◽  
High Speed Video ◽  
Acceleration Data ◽  
Position Data

Abstract This project focuses on the development and characterization of a high speed video motion capture system for the measurement of planar, rigid body motions. The ability to collect information related to the accelerations, velocities and positions of points on a rigid body as it moves in planar space is very important in the fields of science and engineering. Traditional techniques, including the use of accelerometers, extensors and lasers, either rely on contact between the rigid body and the sensor or only measure out of plane motion. In this project, an inexpensive monochromatic high speed camera was used in conjunction with markers adhered to the objects under investigation to measure the planar displacement of a point on a moving object. The high speed camera is able to capture video at a rate of up to 20,000 frames per second, however, at this speed the field of view is very small. For a larger field of view, the frames per second is diminished to close to 3,000 frames per second. The goal of this project was to develop the hardware parameters and software necessary to collect and process 2D motion data at different frequencies and then evaluate the efficacy of video motion capture through comparison with simultaneously captured acceleration data. The efficacy was evaluated over a range of accelerations using variable frequency oscillations. The video footage was processed, frame by frame in order to extract x and y position for the center of the marker. Extraction of the position data was completed using the MATLAB computer vision toolbox, which provides tools for identifying the x and y locations of corners, circle centers and other defining features. The project began by identifying size, shape, color and material of markers for effective data collection using the motion capture system. Additionally, camera settings, field of view, capture rate, lighting and mounting conditions were evaluated to determine what conditions would result in the most accurate position sensing. In order to validate the measurements from the motion capture system, position data were correlated with accelerations measured from a traditional accelerometer located on the object under test. In order for the position data collected through the high speed video capture to be compared with the acceleration data collected using measurement from accelerometers, numerical differentiation of the position signals gathered from the high speed footage was performed. The efficacy of different shape and size markers, along with other camera settings, will be demonstrated for specific oscillatory test profiles.

A Finite Element Formulation of Flexible Slider Crank Mechanism Using Local Coordinates

1994 ◽  
Author(s):  
Behrooz Fallahi ◽  
S. Lai ◽  
C. Venkat
Keyword(s):  
Rigid Body ◽  
Coordinate System ◽  
High Speed ◽  
Displacement Vector ◽  
Lagrange Equation ◽  
Local Coordinate System ◽  
Body Motion ◽  
Elastic Displacement ◽  
Global Coordinate System ◽  
Element Formulation

Abstract The need for higher productivity has lead to the design of machines operating at higher speeds. At high speed the rigid body assumption is no longer valid and the links should be considered flexible. In this work a method which is based on Modified Lagrange Equation for modeling flexible mechanism is presented. The method posses a more computational efficiency for not requiring the transformation from the local coordinate system to the global coordinate system. Also an approach using the homogeneous coordinate for element matrices generation is presented. The approach leads to a formalism where the displacement vector is expressed as a product of two matrices and a vector. The first matrix is a function of rigid body motion. The second matrix is a function of rigid body configuration. The vector is a function of elastic displacement. This formal separation helps to facilitate the generation of element matrices using symbolic manipulations.

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