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معرفی و راهنمای استفاده از ساینس دایرکت (ScienceDirect)

manufacturemajlesi — Tue, 09 Mar 2010 14:03:41 GMT

معرفی و راهنمای استفاده از ساینس دایرکت (ScienceDirect)

نام شرکت Elsevier در سال 1580، زمانی که لوئیس الزویر(Lowys Elsevier) شروع به فروختن کتاب به دانشجویان کرد مطرح شد. Elsevier یکی از اولین ناشرانی است که به چاپ مجلات علمی و شرح وقایع علمی پرداخته است. شعبه اصلی Elsevier Science در آمستردام هلند می باشد.
Elsevier یک ناشر چند رسانه ای پیشرو می باشد که محصولات و خدمات علمی، فنی و پزشکی را در سراسر دنیا منتشر می کند. Elsevier بیش از 200000 محصول و خدمات ارائه می دهد که شامل مجلات، کتابها، محصولات و خدمات الکترونیکی و پایگاههای اطلاعاتی می باشد و هر سال بیش از 1600 نشریه و 1200 کتاب را منتشر می نماید.
دو Brand از معروف ترین Brand های اصلی ElsevierScience، ناشرین Academic Press و ScienceDirect می باشند.
ScienceDirect :
یک سرویس اطلاعاتی الکترونیکی پیشرو می باشد که بوسیله آن به بیش از 1700 مجله علمی، فنی و پزشکی به صورت تمام متن(Fulltext) دسترسی پیدا می کنید. به بیش از 59 میلیون چکیده مقالات علمی دسترسی پیدا می کنید. با مقالات بیش از 120 ناشر دیگر ارتباط برقرار می کنید.
Academic Press :
در حدود 60 سال است که اطلاعات مورد نیاز دانشمندان، محققان، مهندسان و متخصصان در صنعت و دانشگاه را ارائه می نماید و شامل بیش از 167000 مقاله از حدود 250 نشریه می باشد.

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منبع۱ و منبع ۲

Kinematic optimization of ball-screw transmission mechanisms

manufacturemajlesi — Tue, 09 Mar 2010 13:55:18 GMT

Kinematic optimization of ball-screw transmission mechanisms

Abstract :
The paper proposes a method for the kinematic optimization of transmission mechanisms, where non-circular (NC) gears are used to perform a mechanical control on the output motion. The investigation presented here deals with the motion control of a ball-screw transmission mechanism. The objective is lowering the peak acceleration value of the screw, by designing a pair of variable radius gears as a driving mechanism. The kinematic characteristics of the ball-screw mechanism are analyzed by means of non-dimensional motion equations in order to formulate the optimization problem. A genetic algorithm (GA) is then implemented to optimize the objective function, and a penalty method is used to fulfil thedesign rules. The kinematic analysis of the optimal mechanism revealed a 37% reduction of the peak acceleration of the screw in comparison with a constant pitch screw, operated at a constant speed. A kinematic simulation is used to validate the method.

Source : www.sciencedirect.com

A ballscrew drive mechanism

manufacturemajlesi — Tue, 09 Mar 2010 13:47:52 GMT

A ballscrew drive mechanism with piezo-electric nut for preload

and motion control

Abstract :
This work reports the development of a ballscrew drive mechanism equipped with a piezo-electric nut for active ballscrew preload and fine motion control. This mechanism is intended for a motion stage of long-stroke, high-speed and ultra-precision applications. Motion of the piezo-electric nut ballscrew drive system consists of a high-speed coarse positioning and an ultra-fine positioning. Coarse positioning is done by a conventional servo motor and ballscrew where the piezo-electric nut exerts a light ballscrew preload in order to reduce the friction torque and wear at high speed motion. After the coarse positioning, a fine position adjustment is actuated by three piezo-electric actuators to get very precise positioning. Test results show that the positioning error can be fine-adjusted to the nanometer level. The low speed stability of the ballscrew drive mechanism has also been improved using the piezo-electric actuators by applying a dither signal to the ballscrew preload. The dither action can smooth and reduce the ballscrew friction force and consequently reduce the stick–slip phenomenon at low speed motion.
Keywords: Ultra-precision positioning; Ballscrew preload control; Piezo-electric actuator

Source : www.sciencedirect.com

A new method for measuring circular motion error of NC machine tools

manufacturemajlesi — Tue, 09 Mar 2010 13:46:41 GMT

A new method and instrument for measuring circular motion error of NC machine tools

Abstract :

A new method and instrument for measuring circular motion error of numerical control (NC) machine tools are described in this paper. The instrument consists of a linear displacement transducer bar with two balls at each end and a high accuracy rotary encoder. The radius variations are detected by the transducer and the rotation angle of the bar is measured by the rotary encoder while the machine is moving in a circular path. The measuring area is circular except for a small area around the center of the disc. The bar can be expanded and contracted along its axis for different application. The instrument has a compact structure and can be installed on a machine tool simply and quickly. It is shown by the experimental results that the instrument has good repeatability and high precision of measuring circular motion trajectories. The instrument can be widely used especially in the error-compensation and error-source project in the industrial application.
Keywords : NC machine tool; Motion error; Measurement instrument; Circular measurement

Source : www.sciencedirect.com

Method for the evaluation of optical encoders performance under vibration

manufacturemajlesi — Tue, 09 Mar 2010 13:39:18 GMT

Method for the evaluation of optical encoders performance under vibration

Abstract :
Optical encoders are the preferred choice for position measurement, both linear and angular, when high accuracy is required. Their performance is widely affected by deformation, temperature and vibration. This last aspect is analysed, showing the limitations found in conventional methods of performance evaluation. The determining parameters, such as sweep type, sampling rate, trigger etc. are examined and a final diagram of measuring accuracy versus frequency is presented, where aspects as resonance effects and measuring uncertainty are identified and discussed. Experimental analyses have been made in a commercial linear optical encoder and show that its measuring error is three times its precision, and wide areas of large measuring uncertainty are present in the frequency span. The information obtained through this method can be used to improve encoder design and mounting conditions in the machine, reducing the total error.
Source : www.elsevier.com/locate/precision

A study on hydrodynamic deep drawing equipment

manufacturemajlesi — Tue, 09 Mar 2010 13:36:18 GMT

A study on hydrodynamic deep drawing equipment

Abstract :
In this paper, a new model of general super-pressure hydrodynamic deep drawing (HDD) equipment is studied and developed. Theoverall plan, the structured features of general die sets with liquid inside, the hydraulic system, the CNC system and experimental results are described.
Source : www.elsevier.com/locate/jmatprotec

Ensuring the integrity in clinching process

manufacturemajlesi — Tue, 09 Mar 2010 13:30:46 GMT

Ensuring the integrity in clinching process

Abstract :
Clinching is a mechanical joining method, especially for sheet metal parts. The process is perceived as being a simple method that is based on only the accurate movement of a punch into a die. During the process, sheet metals are deformed locally without the use of any additional elements. Precisely selected tools are a requirement for an acceptable joint. The two most frequently used geometries in clinching tools are round and square. When round tools are used, the joint has a uniform shear load capacity in all the horizontal directions. Many papers have been written on the clinching process itself, including the tool geometries, parameter optimisation, joint strengths, simulation and FE analysis of the process, but few articles discuss the significance of anticipatory maintenance or continuous follow-up while using clinching in a mass-production process. This paper points out several problems encountered in the long-term use of a clinching process. Both the lack of systematic maintenance and continuous follow-up are discussed. The significance of changes in the construction are also evaluated in this presentation that is based on a real case study. This paper also offers proposals for improvements.
Source : www.elsevier.com/locate/jmatprotec

An experimental study of cold formed steel trusses using

manufacturemajlesi — Tue, 09 Mar 2010 13:27:18 GMT

An experimental study of cold formed steel trusses using
mechanical clinching

Abstract :
The paper describes an investigation into the use of mechanical clinching in cold-formed steel trusses. A series of full-scale tests on trusses with varying configurations of chord and internal members was undertaken. In addition a series of small-scale tests was carried out on samples replicating the nodal connections between the chord and the tie elements of the truss. The results of the small-scale tests are compared with the behaviour of the trusses. The number of clinches has a marked influence on the strength, deformation and failure mode of the trusses.

Stability-based spindle speed control during flexible workpiece high-speed milling

manufacturemajlesi — Tue, 09 Mar 2010 13:26:18 GMT

Stability-based spindle speed control during flexible workpiece high-speed milling

Abstract :
High-speed machining (HSM) is a technology used to increase productivity and reduce production costs. The prediction of stable cutting regions represents an important issue for the machining process, which may otherwise give rise to spindle, cutter and part damage. In this paper, the dynamic interaction of a spindle-tool set and a thin-walled workpiece is analysed by a finite element approach for the purpose of stability prediction.
The gyroscopic moment of the spindle rotor and the speed-dependent bearing stiffness are taken into account in the spindle-tool set finite element model and induce speed-dependent dynamic behaviour. A dedicated thin-walled workpiece is designed whose dynamic behaviour interacts with the spindle-tool set. During the machining of this flexible workpiece, chatter vibration occurs at some stages of machining, depending on the cutting conditions and also on the tool position along the machined thin wall.
By coupling the dynamic behaviour of the machine and the workpiece, respectively, dependent on the spindle speed and the relative position of both the systems, an accurate stability lobes diagram is elaborated.
Finally, the proposed approach indicates that spindle speed regulation is a necessary constraint to guarantee optimum stability during machining of thin-walled structures.

low-noise high endurance spiral bevel gears

manufacturemajlesi — Mon, 08 Mar 2010 13:54:18 GMT

Design, manufacture, stress analysis, and experimental tests of low-noise high endurance spiral bevel gears

Abstract :
The contents of the paper cover the design, manufacturing, stress analysis, and results of experimental tests of prototypes of spiral bevel gears with low levels of noise and vibration and increased endurance. The main goals are the improvement of the bearing contact, the achievement of a predesigned parabolic function of transmission errors, reduction of the magnitude of transmission errors as the precondition of reduction of noise and vibration, and avoidance of areas of severe contact stresses for the increase of the endurance of the gear drives. The goals are achieved by application of local synthesis algorithm, tooth contact analysis, and stress analysis by application of finite element method. The proposed ideas have been proven by the manufacturing and test of prototypes of spiral bevel gear drives. An example of design and optimization of a spiral bevel gear drive for the illustration of the developed theory is represented.

Source : www.Sciencedirect.com