Showing papers in "Chinese Journal of Mechanical Engineering in 2007"

Theoretical foundation of metamorphic mechanism and its synthesis

Abstract: The metamorphic mechanism is defined by three characteristics in multi-stage,multi-topological structure and multi-degree of freedom.The properties and boundary of metamorphic mechanism are discussed and clarified for the mechanism with multi-degree of freedom,combined symmetrical mechanisms,and kinematropic mechanisms.A way to describe a metamorphic mechanism is proposed.A new concept of the work-stage mechanism and the origin mechanism for metamorphic mechanism,which can be expressed by metrics,are presented.Meanwhile,a mathematic model of a metamorphic mechanism is set up by a metamorphic equation,which indicates the relationship among a work-stage matrix,an origin metamorphic matrix and a metamorphic matrix.The type synthesis of metamorphic mechanism can be converted into solving the group of metamorphic equations,which leads to form all work-stage matrices,an origin metamorphic matrix and metamorphic matrices.Therefore,the metamorphic mechanism, including the series work-stage mechanism and origin mechanism, is readily located by the corresponding matrices.An example is given to demonstrate the process of the synthesis of a metamorphic mechanism.A groundwork for the theoretical basis of synthesis of metamorphic mechanisms is presented.

New elastic-plastic model for the contact of rough surfaces

Abstract: A new elastic-plastic model for the contact of rough surfaces is presented.The model is developed based on contact mechanics and the assumption that the transitions from elastic, through elastic-plastic,to fully plastic deformation of a con- tacting asperity is continuous and smooth.The deformation behavior of a single contacting asperity is firstly modeled in detail,particularly,for the elastic-plastic deformation.The con- tact between the two rough flat surfaces is then modeled by using probability theory.The model developed is compared with the GW elastic model and CEB elastic-plastic model on their predicted real contact area and mean separation for a wide range of contact load and plasticity index.It is shown that the present model predicts larger real contact area and smaller mean separation than GW model under the same contact load and plasticity index.Besides,the difference of the predicted results based on the present model and GW model increases with the contact load and plasticity index.The comparison results strongly indicate that the present model is consistent with ex- perimental observation and physical intuition,and is more rea- sonable in describing the contact behavior between rough sur- faces.

Superposition throttle-slices opening size and characteristic test of telescope-damper

Abstract: The mechanics model of flexible ring throttle-slice and the differential equation of its deformation are established based on elastic mechanical principals. Utilizing the boundary condition, the general solution of elastic ring throttle-slice's deformation curved surface is obtained, and a deformation co-efficient of elastic throttle-slice is formed by identical transfor-mation of the general solution of elastic throttle-slice. Then a precise method for calculating ring throttle-slice deformation is put forward. The bending deformation of throttle-slice is ana-lyzed based on the deformation coefficient, and comparison with two common-used approaches is also performed about influence of calculation deviation on design and performance of damper. The effect of the equivalent thickness of superposition throttle-slices on throttle opening size is studied. Experimental results on telescope-damper performance at different superposi-tion throttle-slices show that the research can play an important role at damper valves design.

Nonlinear dynamic characteristics of moving hydraulic cylinder

Abstract: In terms of nonlinear dynamics, the actions of nonlinear spring force and nonlinear frictional force on dy-namic characteristics of moving hydraulic cylinder are em-phatically studied by means of theoretical analysis and experi-mental verification. Varying regularities of spring stiffness with piston displacement controlled by three types of hydraulic throttle-governing circuits are obtained. Soft spring property or hard spring property shown separately by above different working situations are found. The conclusions that the effect of nonlinear spring can be described by Duffing equation, the effect of nonlinear frictional force can be described by Van Der Pol equation, and their coupling effect can be described by Lienard equation are achieved. The reasons why hydraulic cylinder creeps in lower velocity are common acting results of the jump phenomenon caused by soft spring property and the self-excited vibration caused by nonlinear frictional force in specific working situation are expressed. Solutions of the equations are of different patterns in terms of different working conditions. All above illustrate that the nonlinear characteristics of moving hydraulic cylinder are complicated and changeable.

Analysis of the pump volume flow rate and tube property of the piezoelectric valveless pump with y-shape tubes

Abstract: There exists serious problems in the no-moving-part valves (NMPV) used by the piezoelectric pump presently: being complex in structure or bringing on huge vortex whose pressure and velocity vary dramatically in the tubes, which will go against the aim of transporting living cells and the long-chain-macromolecule cells in the areas of medical treat- ment, sanitation and health care. Aiming at these problems, a new type of the piezoelectric pump-valveless piezoelectric pump with Y-shape tubes is developed, and simulative and experimental researches are applied on the pump. Combined with the needs of transporting blood and fluid in the area of medical treatment, the advantages and disadvantages of several typical no-moving-part valves are analyzed, and the properties of the piezoelectric pump with Y-shape tubes and its tubes are introduced. Theoretical analysis is applied on the pump and the theoretical formula of the pump flow rate is established. Based on the finite element method (FEM), the numerical simulation of the fluid flow situation inside the Y-shape tubes is carried out, the law of pressure change of the Y-shape tubes along the positive and reverse directions are obtained, and the conclusion that the vortex occurs in the Y-shape tube is much more feeble than that in the taper tubes, is obtained, the flow resistances of the Y-shape tubes are also calculated. A comparison is made between the theoretical and experimental flow rate for the pie- zoelectric valveless pump with Y-shape tubes, the results indi- cate that the minimum and maximum relative errors between the two results tam out to be 7% and 13% respectively. There- fore, the validity and correctness of the theoretical analysis and the numerical simulation are proved.

Energy consumption assessment and energy loss analysis in pneumatic system

Abstract: Compared with the traditional energy consumption assessment method based on air flow rate,a new method using air power is presented.The air power is defined as the flux of the available energy of flowing compressed air.The available energy is the work-producing potential of compressed air under a surrounding of the atmospheric pressure and temperature.Air power is a relative potential in the atmospheric environment, because pneumatic systems work in the same environment. With air power,mechanism and factors making energy loss are discussed and some data of energy losses in pneumatic system are shown,which will make objective of energy savings clear.

Bilevel genetic algorithm for the flexible job-shop scheduling problem

Abstract: The multi-objective optimization of the flexible job-shop scheduling problem (FJSP) is studied. According to the characteristics of the FJSP, two effective crossover operators and mutation operators are designed for the genetic algorithm. In order to preserve the good characteristics of the previous generation and reduce the disruptive effects of genetic operators, a multistage-based generation alteration model of genetic algo- rithm is proposed to solve the FJSP. The approach is tested on two instances taken from the literature and compared with other approaches. The computation results validate the effectiveness of the proposed algorithm.

Function-oriented active tooth surface design of spiral bevel gears

Abstract: Transmission errors and contact pattern have de- terminative effects on the gearing performances of a gear drive, so a new approach for design of spiral bevel gears is proposed, based on a predesigned parabolic function of transmission er- rors with limited magnitude of maximal transmission errors and a predesigned linear function of contact path.This approach is based on three meshing points.By controlling their magnitudes of transmission errors and the positions on the tooth surface,the allover control of engagement quality is realized.The advan- tages of the function-oriented active tooth surface design are the reduction of level of noise and the obtaining of favorable shape and dimensions of contact pattern,and moreover,the gearing performance in whole tooth contact could be controlled directly in design.The goals are achieved by application of local syn- thesis algorithm,local conjugate theory and machining princi- ple of spiral bevel gears.Function-oriented active tooth surface design provides an innovative desiring approach for the spiral bevel gears and is quite important for the gears in high speed, heavy duty or with special requirements.

Some basic concepts in modern design theory

Abstract: In the long march of development of design theories, many terms have been coined for explaining their new ideas. Some times one term is used by different authors with different definitions or different means, say concepts, Other times dif- ferent terms are used by different authors with the same mean or concept. It is rational and necessary for the modem design theory in the way of its growth to examine the definitions, means and concepts of all these terms. In considering the char- acter of global economy and the change in manufac~ring, some new definitions, means and concepts have been given to the terms for working with the theory and related methodology, and form a base of the development of the theory. The purpose of the paper is to summarize existed results and call further study on the definitions, means and concepts of such terms to match the state-of-the-art requirements. Insufficient in precision use of a term will occasionally lead to a different result in theoretical research. The concepts of performance, function, quality, con- strain, requirements, features, requirement driving, state etc. studied and used previously in the modern design theory are collected and discussed.

Kinematic design of 5-dof hybrid robot with large workspace/limb-stroke ratio

Abstract: This paper deals with the conceptual and kinematic designs of a 5-degree of freedom (DOF) reconfigurable hybrid robot. The robot is composed of a 2-DOF parallel spherical mechanism that is serially connected with a 3-DOF open loop kinematic chain via a prismatic joint. Somewhat similar to the well-known Tricept robot, this design has the merit that a relatively large workspace/limb-stroke ratio can be achieved thanks to the decomposition of the motions of the output link into the 2-DOF rotation and 1-DOF translation. As with the Tricept, the robot is well suited for use as a plug-and-play module to configure different machines. The dimensional synthesis of the 2-DOF spherical parallel mechanism is carried out by the monotonical analysis of the design variables versus a global conditioning index represented by the mean of the minimum singular value of the Jacobian, leading to the solution of two nonlinear equations due to the limb length constraint and nearly axial symmetry requirement of the kinematic performance. The results of the dimensional synthesis are given via examples.

Simulation and experimental analysis of electro-hydraulic steering control system for tlc900 transporting girder vehicle

Abstract: Aimed at the key part for TLC900 transporting girder vehicle applied in constructing high-speed railroads,the operational principle of steering system is explained and the mathematical model of steering control is set up.Based on the steering theory and requirement of steering capability for transporting girder vehicle,the control policy of subsection PID is adopted.In this foundation,the Simulink software package of Matlab is utilized to simulate the dynamic characteristics of the system.Comparison and analysis of the test data and the simu- lation result to prove the feasibility of the method,which bene- fits to improve the control capability of steering system of the transporting girder vehicle more.

Multi-objective optimization for crash safety design of vehicles using stepwise regression model

Abstract: In the automotive industry,structural optimization related to erashworthiness and energy absorption capability is of great importance,which involves highly nonlinear computational analysis and design with many material and structural parameters.Unfortunately,conventional design, analysis techniques and the experiments can only improve the structural crashworthiness to a limited extent,and in most engineering design problems there are several conflicting objectives that have to be considered for optimization.In order to improve crashworthiness design,a method using a multi-objective optimization technique based on stepwise regression model is presented through the applications of design of experiments and response surface models and finite element simulation technique.The method is applied for the multi- objective optimization design of the reinforced members of a vehicle,where the mass,toe board intrusion,and the integrated value of collision acceleration are chosen as the objective functions.The results show the new computational design method is a practical tool for the crash safety design of vehicles.