The Virtual Cam – Hexagon Method Authentication on Locating Key Instant Centers of All Planar Single Degree of Freedom Kinematically Indeterminate Linkages up to Ten-Bar

2018 ◽  
Author(s):  
Zhengqi Liu ◽  
Yin-ping Chang
Keyword(s):  
Degree Of Freedom ◽  
Universal Method ◽  
Single Degree Of Freedom ◽  
Graphical Approach ◽  
Single Degree ◽  
Wide Range ◽  
Different Types ◽  
Limited Application ◽  
Complete Sets ◽  
Improved Technique

At this moment all the methods which had been proposed have extremely limited application to only several specific constructions of kinematically indeterminate linkages, i.e. their complete sets of instant centers cannot be obtained simply from Kennedy Theorem due to lack of enough four-bar loop information in their constructions. Planar single degree of freedom linkages up to ten-bar include two different types of mechanisms, i.e. pure bar linkages, such as four-, six-, eight-, and ten-bar; and geared-bar linkages, i.e. geared-five, seven, and nine-bar. The huge varieties of different types and constructions can serve as great testbeds for these methods. This research systematically investigates and modifies the graphical approach, i.e. virtual cam method, whose employment will show it to be an almost-universal method which can be compliantly applied on very wide range of kinematically indeterminate linkages. The procedures and criteria of the methodology are proposed and examined thoroughly to help locate key instant centers of all planar single degree of freedom kinematically indeterminate linkages up to ten-bar so that their complete sets of instant centers can be located successfully. We call this modified and improved technique as Virtual Cam – Hexagon Method. The results are verified carefully against traditional Kennedy Theorem approach and CAD modeling.

The Virtual Cam Method Application and Verification on Locating Key Instant Centers of Ten-Bar 1-DOF Indeterminate Linkages

2017 ◽  
Author(s):  
Zhengqi Liu ◽  
Yin-ping Chang
Keyword(s):  
Degree Of Freedom ◽  
Single Degree Of Freedom ◽  
Graphical Approach ◽  
Cad Modeling ◽  
Single Degree ◽  
Complete Sets

Planar ten-bar single degree of freedom linkages have 230 valid isomers, 53 of them are kinematically indeterminate, i.e. their complete sets of instant centers cannot be obtained simply from Kennedy Theorem. This paper investigates a graphical approach, i.e. virtual cam method, to help locate the key instant centers of these kinematically indeterminate linkages, after that all the instant centers can be located by Kennedy Theorem accordingly. The criteria of application are proposed and examined carefully, the results are verified against traditional Kennedy Theorem approach and CAD modeling.

The Response of Nonlinear Systems to Modulated High-Frequency Input

1993 ◽  
Author(s):  
S. A. Nayfeh ◽  
A. H. Nayfeh
Keyword(s):  
Nonlinear Systems ◽  
Natural Frequency ◽  
Amplitude Modulation ◽  
Carrier Frequency ◽  
High Frequency ◽  
Degree Of Freedom ◽  
Resonant Excitation ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Different Types

Abstract We study the response of a single-degree-of-freedom system with cubic nonlinearities to an amplitude-modulated excitation whose carrier frequency is much higher than the natural frequency of the system. The only restriction on the amplitude modulation is that it contain frequencies much lower than the carrier frequency of the excitation. We apply the theory to different types of amplitude modulation and find that resonant excitation of the system may occur under some conditions.

The Measurement of Nonlinear Damping in Single-Degree-of-Freedom Systems

1991 ◽  
Vol 113 (1) ◽  
pp. 132-140 ◽  
Author(s):  
H. J. Rice ◽  
J. A. Fitzpatrick
Keyword(s):  
Nonlinear Distortion ◽  
Nonlinear Damping ◽  
Degree Of Freedom ◽  
Crucial Importance ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Wide Range ◽  
Impulse Excitation ◽  
Excitation Techniques ◽  
Quadratic Damping

The measurement and correct modelling of damping is of crucial importance in the prediction of the dynamical performance of systems for a wide range of engineering applications. In most cases, however, the experimental methods used to measure damping coefficients are extremely basic and, in general, poorly reported. This paper shows that damping is a deceptive parameter which is prone to subtle nonlinear distortion which often appears to satisfy general linear criteria. An efficient experimental method which provides for the measurement of both the linear and nonlinear damping for a single-degree-of-freedom system is proposed. The results from a numerical simulation study of a model with “drag” type quadratic damping are shown to give reliable estimates of parameters of the system when both random and impulse excitation techniques are used.

Effectiveness of neoprene pad vibration isolators at high frequencies

2021 ◽  
Vol 263 (4) ◽  
pp. 2172-2183
Author(s):  
Jerry Lilly
Keyword(s):  
Natural Frequency ◽  
Insertion Loss ◽  
Dynamic Stiffness ◽  
Degree Of Freedom ◽  
Frequency Wave ◽  
Single Degree Of Freedom ◽  
High Frequencies ◽  
Vibration Isolators ◽  
Single Degree ◽  
Wide Range

The natural frequency, dynamic stiffness, and insertion loss of commercially available neoprene pad vibration isolators have been measured in a simple, single degree of freedom system over a wide range of pad loadings out to a maximum frequency of 10 kHz. The results reveal that dynamic stiffness can vary significantly with pad loading as well as the durometer of the material. It will also be shown that insertion loss follows the theoretical single degree of freedom curve only out to a frequency that is about 5 to 10 times the natural frequency, depending upon the pad durometer rating. Above that frequency wave resonances in the material cause the insertion loss to deteriorate significantly out to a frequency near 1 kHz, above which the insertion loss maintains a relatively constant value, again depending upon the pad durometer rating. In some instances the insertion loss values can approach 0 dB or even become negative at specific frequencies in the frequency region that is 10 to 20 times the natural frequency of the system.

An Experimental Study of a Single-Degree-of-Freedom Impact Oscillator

2021 ◽  
Author(s):  
Shun Zhong ◽  
Jingyuan Tan ◽  
Zhicheng Cui ◽  
Tanghong Xu ◽  
Liqing Li
Keyword(s):  
Dynamical Behavior ◽  
Degree Of Freedom ◽  
Experimental Results ◽  
Physical Parameters ◽  
Impact Oscillator ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Design Choice ◽  
Wide Range ◽  
Simulation Results

Purpose. Impacts appear in a wide range of mechanical systems. To study the dynamical behavior introduced by impact in practical way, a single-degree-of-freedom impact oscillator rig is designed. Originality. A simple piece-wise linear system with symmetrical flexible constraints is designed and manufactured to carry out a wide range of experimental dynamic analysis and ultimately to validate piece-wise models. The new design choice is based on the following criteria: accuracy in representing the mathematical model, manufacturing simplicity, flexibility in terms of parameter changes and cost effectiveness as well avoidance of the delay introduced by the structure. Meanwhile, the new design provides the possibility of the applications of the complex control algorithms. Design/methodology/approach. The design process is described in detail. The initial experimental results of the rig as well as numerical simulation results are given. In this rig, the mass driven force is generated by electromagnet, which can be adjusted and control easily. Also, most of the physical parameters can be varied in a certain range to enhance flexibility of the system allowing to observe subtle phenomena. Findings. Compared with the simulation results, the designed rig is proved to be validated. Then, the initial experimental results demonstrate potentials of this rig to study fundamental impact phenomena, which have been observed in various engineering systems. They also indicate that this rig can be a good platform for investigating nonlinear control methods.

Detection of Improper General Spatial Kinematic Chains With Different Types of Pairs

1994 ◽  
Author(s):  
Xian-Wen Kong ◽  
Ting-Li Yang
Keyword(s):  
Unsolved Problem ◽  
Degree Of Freedom ◽  
Sufficient Condition ◽  
Necessary And Sufficient Condition ◽  
Single Degree Of Freedom ◽  
Kinematic Chains ◽  
Single Degree ◽  
Different Types ◽  
Necessary And Sufficient ◽  
Topological Synthesis

Abstract Improper general spatial kinematic chains (GSKCs) due to the effect of pair types may be generated during the process of topological synthesis of GSKCs with different types of pairs. Thus, detection of improper GSKCs is necessary in topological synthesis of GSKCs with different types of pairs. Unfortunately, it is still an unsolved problem. In this paper, a method for detecting improper GSKCs is presented. Both a necessary and sufficient condition and a sufficient condition for proper GSKCs with R, P, H, T and C pairs are introduced at first. Based on these two conditions, an algorithm to detect improper GSKCs is then developed which is very efficient and suitable for topological synthesis of GSKCs with R, P, H, T and C pairs. The proposed algorithm has been applied to topological synthesis of 1- and 2-loop, single degree of freedom GSKCs with R, P, H, T and C pairs and the corresponding atlas is obtained.

Aspects of creep buckling II. The effects of small deflexion approximations on predicted behaviour

1978 ◽  
Vol 364 (1718) ◽  
pp. 415-433 ◽  
Keyword(s):  
Constant Load ◽  
Buckling Analysis ◽  
Degree Of Freedom ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Creep Buckling ◽  
Different Types ◽  
Post Buckling

In creep buckling analysis, small deflexion approximations generally influence the calculated displacement‒time relations and may also result in the prediction of different phenomena from those indicated by exact analyses. Part II examines the nature of these approximations and the effects of using them. As in Part I, much significance is attached to the link between a structure’s creep buckling behaviour at constant load and its instantaneous buckling and post-buckling behaviour under varying load. Analyses of simple single degree of freedom models are used for illustration. Some general conclusions are drawn which permit a better understanding of the relationships between the different types of analysis that have been used in previous creep buckling studies.

Design of a Single Degree-of-Freedom, Adaptable Electromechanical Gait Trainer for People With Neurological Injury

2018 ◽  
Vol 10 (4) ◽  
Author(s):  
Sung Yul Shin ◽  
Ashish D. Deshpande ◽  
James Sulzer
Keyword(s):  
Low Cost ◽  
Degree Of Freedom ◽  
Neurological Injury ◽  
Link Length ◽  
Gait Patterns ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Wide Range ◽  
Robotic Gait ◽  
Gait Trainer

The cost of therapy is one of the most significant barriers to recovery after neurological injury. Robotic gait trainers move the legs through repetitive, natural motions imitating gait. Recent meta-analyses conclude that such training improves walking function in neurologically impaired individuals. While robotic gait trainers promise to reduce the physical burden on therapists and allow greater patient throughput, they are prohibitively costly. Our novel approach is to design a new single degree-of-freedom (DoF) robotic trainer that maintains the key advantages of the expensive trainers but with a simplified design to reduce cost. Our primary design challenge is translating the motion of a single actuator to an array of natural gait trajectories. We address this with an eight-link Jansen mechanism that matches a generalized gait trajectory. We then optimize the mechanism to match different trajectories through link length adjustment based on nine different gait patterns obtained from gait database of 113 healthy individuals. To physically validate the range in gait patterns produced by the simulation, we tested kinematic accuracy on a motorized wooden proof-of-concept of the gait trainer. The simulation and experimental results suggested that an adjustment of two links can reasonably fit a wide range of gait patterns under typical within-subject variance. We conclude that this design could provide the basis for a low-cost, patient-based electromechanical gait trainer for neurorecovery.

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