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Calculated journal bearing lubrication of non-Newtonian medium with surface roughness effects
CHEN Hao-sheng, CHEN Da-rong, WANG Jia-dao, LI Yong-jian
Front. Mech. Eng.. 2006, 1 (3): 270-275.
https://doi.org/10.1007/s11465-006-0028-9
To analyze the effects of non-Newtonian lubricants and surface roughness in journal bearing lubrication, a modified Reynolds equation is derived. In the equation, differential viscosity and the first normal stress function are defined to specify the rheological properties of non- Newtonian medium. Flow factors are used to specify the effect of surface roughness. The modified Reynolds equation is numerically calculated using super over relaxation method. Numerical results of the lubrication show that the differential viscosity is the principal non-Newtonian property affecting the lubrication, it is determined by the material parameters of the lubricant and is affected by the shearing rate. Under its effect, the load capacity of non-Newtonian lubricants is not always higher or lower than that of Newtonian lubricants . The effect of the first normal stress difference increases under the conditions of dynamic loading. Surface roughness shows an obvious effect on load capacity when it is greater than one-tenth of the film thickness, and the surface with longitudinal pattern affects the load capacity most. However, surface roughness has less effect on lubrication results than lubricants non-Newtonian property.
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Virtual reality system of manned maneuvering unit taking into consideration the disturbance from an astronaut’s limbs
CHENG Jian, FAN Xiu-min, XU An, HONG Xin, HUANG Wei-dong
Front. Mech. Eng.. 2006, 1 (3): 282-287.
https://doi.org/10.1007/s11465-006-0042-y
This paper describes a manned maneuvering unit (MMU) virtual reality system. Based on the dynamics/kinematics model of an astronaut equipped with an MMU, a disturbance model of the astronaut s arms under zero gravity conditions is developed. After measuring three initial-position information, the astronaut s arms tracking information is inputted by some tracker setting on an operator using real-time emendation and correction. Finally, the paper presents two different results between loading and unloading the disturbance model within the progress of simulation. From the different results, we find that the motion of an astronaut s arms has greater influence over space walking with the same control mode. The MMU virtual reality provides a new method for the simulation of real space walking, and also a perfect method for developing prototype MMU.
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Manufacturing error analysis of compliant 3-DOF microrobot
CHAO Dai-hong, LIU Rong, WU Yue-min, SHI Long, ZONG Guang-hua
Front. Mech. Eng.. 2006, 1 (3): 299-304.
https://doi.org/10.1007/s11465-006-0030-2
In the fields of micro/nanopositioning application, error analysis is an effective way to enhance the precision of micromanipulators. Manufacturing imperfections, which are inevitable, are the most important factors influencing the accuracy. Therefore, various manufacturing imperfections were studied by taking a planar 3 degrees of freedom (3-DOF) flexure hinge based microrobot as a case. By formulating static stiffness of the robot, mapping between manufacturing imperfections and end-effector positioning accuracy was obtained. Using the theoretical calculation and finite element method (FEM), effects of various machining imperfection types on end-effector positioning accuracy were evaluated. The results showed that errors of the radium of the hinges and angular differences of the centerline of the hinges were dominant factors resulting in output errors. Conclusions drawn from the experiments can be used to instruct the design of compliant parallel mechanisms by distributing various manufacturing differences of configurable parameters to guarantee precision in the positioning of the end-effector within the required range; they may also be helpful while calibrating this kind of manipulator.
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Computer aided process planning system based on workflow technology and integrated bill of material tree
LU Chun-guang, MENG Li-li
Front. Mech. Eng.. 2006, 1 (3): 305-312.
https://doi.org/10.1007/s11465-006-0039-6
It is extremely important for procedure of process design and management of process data for product life cycle in Computer Aided Process Planning (CAPP) system, but there are many shortcomings with traditional CAPP system in these respects. To solve these questions, application of workflow technology in CAPP system based on web-integrated Bill of Material (BOM) tree is discussed, and a concept of integrated BOM tree was brought forward. Taking integrated BOM as the thread, CAPP systematic technological process is analyzed. The function, system architecture, and implementation mechanism of CAPP system based on Browser/Server and Customer/Server model are expatiated. Based on it, the key technologies of workflow management device were analyzed. Eventually, the implementation mechanism of integrated BOM tree was analyzed from viewpoints of material information encoding, organization node design of integrated BOM tree, transformation from Engineering BOM (EBOM) to Process BOM(PBOM), and the programming implementation technology.
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A new slicing method of reverse engineering based on the principle of refraction and reflection
LIU Ya-xiong, ZONG Xue-wen, TANG Yi-ping, LU Bing-heng
Front. Mech. Eng.. 2006, 1 (3): 323-328.
https://doi.org/10.1007/s11465-006-0041-z
The traditional slicing method of reverse engineering has been used in product measure from time immemorial. This method however has the disadvantage of low contrast of the cross-sectional pictures of an object. In order to overcome the said shortcoming, a new slicing method of reverse engineering, based on the principle of refraction and reflection of a prism, has been propounded. According to the reflectivity of the object, one of the illuminating methods straight illuminating or inclined illuminating is adopted. These methods can enable one to obtain the image of the cross-section of a bright object with a dark background or the opposite. Experiments have proved to show the advantages of this new slicing method for high contrast of the cross-sectional pictures. To eliminate geometrical distortions caused by the refraction and reflection of the prism, a mathematical transformation model can be set up to correct the image by using relevant software. Eventually, a RP model of a temporomandibular joint fabricated according to its slicing pictures is illustrated.
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A new acoustic emission source location technique based on wavelet transform and mode analysis
JIAO Jing-pin, HE Cun-fu, WU Bin, FEI Ren-yuan, WANG Xiu-yan
Front. Mech. Eng.. 2006, 1 (3): 341-345.
https://doi.org/10.1007/s11465-006-0006-4
For wave propagation in dispersive media, the arrival time of the acoustic emission signal to the sensor is dependent on the setting of the threshold voltage, which results in the inaccuracy of the acoustic emission location. Based on the wavelet transform and the theory of modal acoustic emission, a new method is proposed to improve the accuracy of acoustic emission source location. It is believed that the acoustic emission signal propagation in the structure has the characteristics of multi-mode and dispersion, and the acoustic emission source location should use the arrival time to sensors obtained from the output signals not only at the same mode but also at the same frequency. The wavelet transform is used to resolve the problem. By utilizing the time-frequency data of the wavelet, the frequency-dependent arrival time traveling is easily obtained; by numerical computation of the wave s propagation in structure, the group velocity of the guided mode is also obtained, therefore the accuracy source location is realized. The acoustic emission source location experiments were conducted in a thin steel plate and results show that the technique is an effective tool for acoustic emission source location.
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22 articles
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