Mechanism Dynamics Sequence-Solution Method and Its Application

2006 ◽  
Vol 2 (2) ◽  
pp. 105-113 ◽  
Author(s):  
Zhao Yun ◽  
Yu Gao-Hong ◽  
Chen Jian-Neng ◽  
Li Ge
Keyword(s):  
High Speed ◽  
Solution Process ◽  
Normal Pressure ◽  
Moment Equation ◽  
Test Results ◽  
Test Bed ◽  
Linkage Mechanism ◽  
Compression Mechanism ◽  
Consistency Of The Test ◽  
Four Bar Linkage

In order to eliminate the interference of reverse-driving and the positive or negative value of normal pressure on the direction of frictional force, in solving mechanism dynamics equations, a dynamics sequence solution (DSS) is proposed. For this purpose a moment equation about joints for links is proposed, and it, together with the traditional mechanics equation of links, forms a dynamic-equation set, to provide a basic equation set of mechanism dynamics. In order to explain DSS, the force at a particular joint is considered in terms of the normal and tangential directions, and the resolution of the problem using a four-bar linkage mechanism as an example, are explained. The solution procedures diagrams for different driving types of reverse-driving force, as well as the solution process for friction force under normal pressure, are described. With a dry-straw-compression mechanism as the example, a dynamic model of the mechanism is established, and the above proposed DSS is used to find unknown forces. Finally, the dynamic characteristics of rotary-transplanting mechanisms (the key component of high-speed rice transplanter) are analyzed, through the proposed DSS, and the results are verified in a test-bed situation. The consistency of the test results with the theoretical ones shows that the proposed DSS is able to effectively solve the dynamics equations of complicated mechanisms. In this part, the authors introduced DSS and discussed the feasibility of its application.

Optimal Control of a Flexible Mechanism Using a Combined Feedforward-Feedback Strategy: Simulation and Experiment

1999 ◽  
Author(s):  
Hubertus v. Stein ◽  
Heinz Ulbrich
Keyword(s):  
Optimal Control ◽  
Control Strategy ◽  
System Performance ◽  
High Speed ◽  
Time Varying ◽  
Linkage Mechanism ◽  
Additional Degree ◽  
Control Approach ◽  
Feedback Optimal Control ◽  
Four Bar Linkage

Abstract Due to the elasticity of the links in modern high speed mechanisms, increasing operating speeds often lead to undesirable vibrations, which may render a required accuracy unattainable or, even worse, lead to a failure of the whole process. The dynamic effects e.g. may lead to intolerable deviations from the reference path or even to the instability of the system. Instead of suppressing the vibration by a stiffer design, active control methods may greatly improve the system performance and lead the way to a reduction of the mechanism’s weight. We investigate a four-bar-linkage mechanism and show that by introducing an additional degree of freedom for a controlled actuator and providing a suitable control strategy, the dynamically induced inaccuracies can be substantially reduced. The modelling of the four-bar-linkage mechanism as a hybrid multi body system and the modelling of the complete system (including the actuator) is briefly explained. From the combined feedforward-feedback optimal control approach presented in (v. Stein, Ulbrich, 1998) a time-varying output control law is derived that leads to a very good system performance for this linear discrete time-varying system. The experimental results show the effectiveness of the applied control strategy.

scholarly journals Feeding mechanics and bite force modelling of the skull of Dunkleosteus terrelli , an ancient apex predator

2006 ◽  
Vol 3 (1) ◽  
pp. 77-80 ◽  
Author(s):  
Philip S.L Anderson ◽  
Mark W Westneat
Keyword(s):  
High Speed ◽  
Prey Capture ◽  
Mouth Opening ◽  
Biomechanical Model ◽  
Bite Force ◽  
Rapid Expansion ◽  
Large Individual ◽  
Linkage Mechanism ◽  
Feeding Mechanics ◽  
Four Bar Linkage

Placoderms are a diverse group of armoured fishes that dominated the aquatic ecosystems of the Devonian Period, 415–360 million years ago. The bladed jaws of predators such as Dunkleosteus suggest that these animals were the first vertebrates to use rapid mouth opening and a powerful bite to capture and fragment evasive prey items prior to ingestion. Here, we develop a biomechanical model of force and motion during feeding in Dunkleosteus terrelli that reveals a highly kinetic skull driven by a unique four-bar linkage mechanism. The linkage system has a high-speed transmission for jaw opening, producing a rapid expansion phase similar to modern fishes that use suction during prey capture. Jaw closing muscles power an extraordinarily strong bite, with an estimated maximal bite force of over 4400 N at the jaw tip and more than 5300 N at the rear dental plates, for a large individual (6 m in total length). This bite force capability is the greatest of all living or fossil fishes and is among the most powerful bites in animals.

A New Method for Determining the Effects of Structural Flexibility on the Dynamic Behavior of High Speed Mechanisms

1999 ◽  
Author(s):  
L. Yuan ◽  
J. Rastegar
Keyword(s):  
Dynamic Behavior ◽  
High Speed ◽  
New Method ◽  
Structural Flexibility ◽  
Structural Elements ◽  
Dynamics Modeling ◽  
Linkage Mechanism ◽  
Active Materials ◽  
Response Characteristics ◽  
Four Bar Linkage

Abstract A new method for the analysis of the effects of structural flexibility on the dynamic behavior of mechanical systems is presented. The developed method is in most part based on “tracing” the “propagation” of the effects of the high frequency motion requirements on the dynamic response characteristics of machines with structural flexibilities, particularly those with closed-loop kinematic structures. The method considers the “filtering” action of structural elements with flexibility. Such filtering of higher frequency motions is shown to have a predictable effect on the steady state motion of such mechanical system. The main advantage of the developed method is that the effects of such flexibilities can be determined without the need to perform the usual dynamics modeling and computer simulations. The method is shown to be very simple and readily implementable. The method is applied to a four-bar linkage mechanism with a longitudinally flexible coupler link. The obtained results are shown to be highly accurate as compared to those obtained by computer simulation. The application of the method to systematic design of machines with structural flexibility for high speed and precision operation, optimal integration of smart (active) materials into the structure of such machines, and some related issues are discussed.

Four-Bar Linkage Mechanism for Insectlike Flapping Wings in Hover: Concept and an Outline of Its Realization

2005 ◽  
Vol 127 (4) ◽  
pp. 817-824 ◽  
Author(s):  
Rafał Z˙bikowski ◽  
Cezary Galin´ski ◽  
Christopher B. Pedersen
Keyword(s):  
Insect Flight ◽  
Micro Air Vehicles ◽  
Flapping Wing ◽  
Flapping Wings ◽  
Test Bed ◽  
Linkage Mechanism ◽  
Actual Design ◽  
Straight Line Mechanism ◽  
Four Bar Linkage ◽  
Air Vehicles

This paper describes the concept of a four-bar linkage mechanism for flapping wing micro air vehicles and outlines its design, implementation, and testing. Micro air vehicles (MAVs) are defined as flying vehicles ca. 150 mm in size (handheld), weighing 50–100 g, and are developed to reconnoiter in confined spaces (inside buildings, tunnels, etc.). For this application, insectlike flapping wings are an attractive solution and, hence, the need to realize the functionality of insect flight by engineering means. Insects fly by oscillating (plunging) and rotating (pitching) their wings through large angles, while sweeping them forward and backward. During this motion, the wing tip approximately traces a figure eight and the wing changes the angle of attack (pitching) significantly. The aim of the work described here was to design and build an insectlike flapping mechanism on a 150 mm scale. The main purpose was not only to construct a test bed for aeromechanical research on hover in this mode of flight, but also to provide a precursor design for a future flapping-wing MAV. The mechanical realization was to be based on a four-bar linkage combined with a spatial articulation. Two instances of idealized figure eights were considered: (i) Bernoulli’s lemniscate and (ii) Watt’s sextic. The former was found theoretically attractive, but impractical, while the latter was both theoretically and practically feasible. This led to a combination of Watt’s straight-line mechanism with a drive train utilizing a Geneva wheel and a spatial articulation. The actual design, implementation, and testing of this concept are briefly described at the end of the paper.

Verification of a ground-based method for simulating high-altitude, supersonic flight conditions

2018 ◽  
Vol 07 (01n02) ◽  
pp. 1850005
Author(s):  
Xuewen Zhou ◽  
Jian Xu ◽  
Shuiyan Lv
Keyword(s):  
High Altitude ◽  
High Speed ◽  
Test Method ◽  
Wind Tunnels ◽  
Test Results ◽  
Atmospheric Conditions ◽  
Test Bed ◽  
Supersonic Flight ◽  
Important Research Topic ◽  
Sled System

Ground-based methods for accurately representing high-altitude, high-speed flight conditions have been an important research topic in the aerospace field. Based on an analysis of the requirements for high-altitude supersonic flight tests, a ground-based test bed was designed combining Laval nozzle, which is often found in wind tunnels, with a rocket sled system. Sled tests were used to verify the performance of the test bed. The test results indicated that the test bed produced a uniform-flow field with a static pressure and density equivalent to atmospheric conditions at an altitude of 13–15[Formula: see text]km and at a flow velocity of approximately M 2.4. This test method has the advantages of accuracy, fewer experimental limitations, and reusability.

A New Approach for the Reduction of Vibrational Excitation in Kinematics Synthesis of High Speed Linkages

2000 ◽  
Author(s):  
L. Yuan ◽  
J. Rastegar
Keyword(s):  
High Speed ◽  
Closed Loop ◽  
Vibrational Excitation ◽  
High Harmonic ◽  
Harmonic Component ◽  
Primary Source ◽  
Linkage Mechanism ◽  
New Approach ◽  
Function Generation ◽  
Four Bar Linkage

Abstract A new method is presented for the modification of the output motion of linkage mechanisms with closed-loop chains using cams positioned at one or more of its joints. In particular, the method is applied to a four-bar linkage mechanism that is synthesized for function generation for the purpose of eliminating the high harmonic component of the output link motion. By eliminating the high harmonic component of the output motion of a mechanism, the potential vibrational excitation that the mechanism can impart on the overall system, including its own structure, is greatly reduced. The resulting system should therefore be capable of operating at higher speeds with increased precision. For mechanisms with rigid links, the primary source of high harmonic motions is the nonlinearity of the kinematics of closed-loop chains. With the present method, the higher harmonic motions generated due to such nonlinearities are eliminated by the integration of appropriately designed cams that are used to vary the effective link lengths. A numerical example is provided together with a discussion of the related topics of interest.

A Systematic Method for Kinematics Synthesis of High-Speed Mechanisms With Optimally Integrated Smart Materials

2000 ◽  
Author(s):  
J. Rastegar ◽  
L. Yuan
Keyword(s):  
Smart Materials ◽  
High Speed ◽  
Vibrational Excitation ◽  
High Harmonic ◽  
Harmonic Component ◽  
Linkage Mechanism ◽  
Output Link ◽  
Mechanism Synthesis ◽  
Systematic Method ◽  
Four Bar Linkage

Abstract A systematic method is presented for kinematics synthesis of high-speed mechanisms with optimally integrated smart materials based actuators for the purpose of modifying the output link motion. As an example, the method is applied to a four-bar linkage mechanism that is synthesized for function generation to eliminate the high harmonic component of the output link motion. For mechanisms with rigid links, the high harmonic motions are generated due to the nonlinearity of the kinematics of their closed-loop chains. By eliminating the high harmonic component of the output motion, the potential vibrational excitation that the mechanism can impart on the overall system and its own structure is greatly reduced. The resulting system should therefore be capable of operating at higher speeds with increased precision. A numerical example is provided together with a discussion of the application of the method to other mechanism synthesis problems and some related topics of interest.

A Systematic Method for Kinematics Synthesis of High-Speed Mechanisms With Optimally Integrated Smart Materials

2000 ◽  
Vol 124 (1) ◽  
pp. 14-20 ◽  
Author(s):  
J. Rastegar ◽  
L. Yuan
Keyword(s):  
Smart Materials ◽  
High Speed ◽  
Vibrational Excitation ◽  
High Harmonic ◽  
Harmonic Component ◽  
Linkage Mechanism ◽  
Output Link ◽  
Mechanism Synthesis ◽  
Systematic Method ◽  
Four Bar Linkage

A systematic method is presented for kinematics synthesis of high-speed mechanisms with optimally integrated smart materials based actuators for the purpose of modifying the output link motion. As an example, the method is applied to a four-bar linkage mechanism that is synthesized for function generation to eliminate the high harmonic component of the output link motion. For mechanisms with rigid links, the high harmonic motions are generated due to the nonlinearity of the kinematics of their closed-loop chains. By eliminating the high harmonic component of the output motion, the potential vibrational excitation that the mechanism can impart on the overall system and its own structure is greatly reduced. The resulting system should therefore be capable of operating at higher speeds and with greater precision. A numerical example is provided together with a discussion of the application of the method to other mechanism synthesis problems and some related topics of interest.

Analysis of a Gravity Compensated Four-Bar Linkage Mechanism With Linear Spring Suspension

2007 ◽  
Vol 130 (1) ◽  
Author(s):  
Theeraphong Wongratanaphisan ◽  
Matthew O. T. Cole
Keyword(s):  
Potential Energy ◽  
High Speed ◽  
Vertical Plane ◽  
Potential Energy Function ◽  
Linkage Mechanism ◽  
Wide Range ◽  
Spring Suspension ◽  
Linear Spring ◽  
Four Bar Linkage ◽  
Load Mass

This paper presents the analysis of a gravity compensated four-bar linkage mechanism with zero-free-length linear spring suspension. The objective of the study is to seek the possibility of employing the four-bar linkage or similar mechanisms for assisting vertical planar motion of a load mass in a gravitational field. The analysis is based on the system potential energy framework. Firstly, an arrangement of springs for gravity compensation in a four-bar linkage mechanism is proposed. It is then shown that for a four-bar linkage with symmetric geometric and mass properties the potential energy of the system has interesting and useful characteristics near the configuration at which the middle link is horizontal: an ideal operating configuration. The study also covers more practical cases where there is asymmetry in the mass distribution. The potential use of the mechanism in these cases is validated through a study of the sensitivity of the system potential energy function around the equilibrium point. Finally, based on the results obtained a novel mechanism is proposed for achieving gravity compensated vertical plane motion of a load mass. The proposed mechanism can have a wide range of travel and has significant potential for use not only in low-speed mechanical systems but also in high-speed heavy automated systems, where operating accelerations are of the order of 1g or less.

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