外文翻译--高架起重机桥架的建模与有限元分析 英文版

1 Solid Modeling and Finite Element Analysis of an Overhead Crane Bridge C. Alkin, C. E. Imrak, H. Kocabas Abstract The design of an overhead crane bridge with a double box girder has been investigated and a case study of a crane with 35 ton capacity and 13 m span length has been conducted. In the initial phase of the case study, conventional design calculations proposed by F. E.M Rules and DIN standards were performed to verify the stress and deflection levels. The crane design was modeled using both solids and surfaces. Finite element meshes with 4-node tetrahedral and 4-node quadrilateral shell elements were generated from the solid and shell models, respectively. After a comparison of the finite element analyses, the conventional calculations and performance of the existing crane, the analysis with quadratic shell elements was found to give the most realistic results. As a result of this study, a design optimization method for an overhead crane is proposed. Keywords: overhead crane, finite element method, solid modeling, box girder. Notation b distance between two side plates bk width of lower plate FAA static load due to the trolley FY load due to the working load h0 height of the girder end h2 height of the side plates LA distance between trolley wheels LK span of crane girder LP distance between two adjacent supports q weight of one meter platform qK weight of one meter maintenance platform qP uniformly distributed mass units of bridge t1 thickness of the upper and lower plates t2 thickness of the side plates x2 distance between center of gravity and the midpoint of the left side plate x4 distance between center of gravity and the midpoint of the rail y1 distance between neutral axis and the midpoint of the rail y3 distance between center of gravity and the midpoint of the top plate y5 distance between neutral axis and the midpoint of the top plate 2 WX1 moment of resistance on x-axis WY1 moment of resistance on y-axis C amplifying coefficient dynamic coefficient 1 Introduction Cranes are the best way of providing a heavy lifting facility covering virtually the whole area of a building. An overhead crane is the most important materials handling system for heavy goods. The primary task of the overhead crane is to handle and transfer heavy payloads from one position to another. Thus they are used in areas such as automobile plants and shipyards 1, 2. Their design features vary widely according to their major operational specifications, such as: type of motion of the crane structure, weight and type of the load, location of the crane, geometric features and environmental conditions. Since the crane design procedures are highly standardized with these components, most effort and time are spent on interpreting and implementing the available design standards 3. There are many published studies on structural and component stresses, safety under static loading and dynamic behavior of cranes 516. Solid modeling of bridge structures and finite element analysis to find the displacements and stress values has been investigated by Demirsoy 17.Solid modeling techniques applied for road bridge structures, and an analysis of these structures using the finite element method are provided in 18. In this study, stress and displacements were found using FEM90 software. Solid modeling of a crane bridge, the loading at different points on the bridge and then application of the finite element method have been studied by Celiktas 19. She presented the results of finite element methods for an overhead crane. DIN-Taschenbuch and F. E. M. (Federation Europenne de la Manutention) Rules offer design methods and empirical approaches and equations that are based on previous design experience and widely accepted design procedures. DIN-Taschenbuch 44 and 185 are a collection of standards related to crane design. DIN norms generally state standard values of design parameters. F. E. M Rules are mainly an accepted collection of rules to guide crane designers. It includes criteria for deciding on the external loads to select crane components 3, 20. In this study, the calculations apply the F. E. M. rules and DIN standards, which are used for box girder crane bridges. The calculation of the box girder uses the CESAN Inc. standard bridge tables. Then a solid model of the crane bridge is generated with the same dimensions as in the calculation results. Then static analysis is performed, using the Finite Element Method. Before starting the solution, the 3 boundary conditions are applied as in practice. 2 Overhead cranes with a double box girder Overhead travelling cranes with a double box girder not only hoist loads but also carry them horizontally. A double beam overhead crane is built of a trolley travelling on bridges, and bridges travelling on rails. The trolley hoists or lowers the loads and carries them on the bridge structure. The bridges carry the loads on a rail. As a result, three perpendicular movements are performed. The system is depicted in Fig. 1, where the payload of the mass is attached to the bridge with wire ropes 21, 22. The double box girders are subjected to vertical and horizontal loads by the weight of the crane, the working (hook) load and the dynamic loads. With a double box girder construction, the trolley runs above or between the girders. The acceptable construction requirements and values for a box girder bridge structure are shown in Fig.2. Fig. 1: Overall view of an overhead crane Fig. 2: Construction requirements for a box girder bridge 4 3 Application of FEM to an overhead crane Among numerical techniques, the finite element method is widely used due to the availability of many user-friendly commercial softwares. The finite element method can analyse any geometry, and solves both stresses and displacements 23. FEM approximates the solution of the entire domain under study as an assemblage of discrete finite elements interconnected at nodal points on the element boundaries. The approximate solution is formulated over each element matrix and thereafter assembled to obtain the stiffness matrix, and displacement and force vectors of the entire domain. In this study finite element modeling is carried out by means of the Cosmos Works and MSC commercial package. Patran and 4-node tetrahedral elements and 4-node quadrilateral shell elements have been used for modeling the overhead crane bridge. The four-node tetrahedral element is the simplest three-dimensional element used in the analysis of solid mechanics problems such as bracket stress analysis. This element has four nodes, with each node having three translational and three rotational degrees of freedom on the x, y, and z-axes. A shell element may be defined, which allows in the plane or curved surface of the element and posses both length. It width and may only be used in 3-D simulations. The four-node shell element is 5 obtained by assembling the bending element to the appropriate degrees of freedom. This is sufficient as long as the shell element deflection is within the predefined ratio of shell thickness, otherwise the system works as a large deflection. A typical four-node tetrahedral element and four-node quadratic shell element, and their coordinate systems are illustrated in Fig. 3 24. The four-node tetrahedral element chosen has six degrees of freedom at each node: translation in the nodal x, y, and z directions and rotations about the nodal x, y, and z directions. For the four-node quadratic shell element used to model the overhead crane girder, r and s denote the natural coordinates and is the thickness of the element. This system does not have any horizontal force. The axial displacements and rotations of the first and last faces are equal to zero. In addition, the transverse displacement is zero at the first and last face nodes. The external forces acting on the system are the mass of the main girder of the crane (distributed load) and the forces acting on the wheels of the trolley along the crane (active load). The forces acting on the trolley wheels are caused by the mass of the trolley, an the lifting load which will be moved on the crane. 4-node tetrahedral element 6 4-node quadratic shell element Fig. 3: Elements used to model an overhead crane girder 4 Solid and finite element modeling of an overhead crane bridge The finite element method is a numerical procedure that can be applied to obtain solutions to a variety of problems in engineering. Steady, transient, linear or nonlinear problems in stress analysis, heat transfer, fluid flow and electrome chanism problems may be analysed with finite element methods. The basic steps in the finite element method are defined as follows: preprocessing phase, solution phase, and post processing phase. Real crane data was gathered from CESAN Inc., a Turkish company involved in mass production of overhead cranes. First, the crane bridge is modeled as a surface. Bridge geometry is suitable for this, and long and thin parts should also be modeled as a surface. Later, a mesh is created. In this study, a quadratic element type is used. Solid modeling is generated for the calculated crane bridge and the solid model is shown in Fig. 4 20. 7 Solid model of a crane bridge Wireframe view of a crane bridge Fig. 4: Models of an overhead crane bridge 5 Numerical example of an overhead crane A 35-ton-capacity overhead crane of overall length 13 m and total weight 22.5 tons was selected as a study object. The configuration of the overhead crane is sho wn in Fig. 1.The overhead crane consists of two girders, two saddles to connect them, and a trolley moving in the longitudinal direction of the overhead crane and wheels. The driving unit is installed in one of the two girders. The overhead crane is supported by two rails and the runway girders installed in building. In order to calculate the stress in the structure, the rules of F. E. M 1.001 are applied. The design values used in the bridge analysis from the F. E.M and DIN standards are given in Table 1. Table 1: Bridge property values Handling Capacity : =35 ton Trolley Weight : =3 ton Bridge Length : =13 m Distance between wheels of trolley : =2m Trolley Velocity : =20 m/min. Crane Velocity : =15 m/min. Hoisting Velocit : =2.7 m/min Total duration of use : U4 Load spectrum class : Q3 8 First the maximum and minimum stresses and then the shear stress are calculated using the F. E. M. rules. Using the finite element method for the considered girder, we obtain the stress valnes. We obtain the static loads due to the dead weight, the loads due to the working load multiplied by the dynamic coefficient, and the two most unfavourable horizontal effects, excluding the buffer forces. The maximum stress consists of the stress on the bridge dead weights, the stress on the trolley dead weight, the stress from the hoisting load, stress from the inertia forces and the stress of the trolley contraction. The minimum stress includes the stress on the bridge dead weights and the stress on the trolley dead weight. The maximum and minimum stresses for the given values according to the F. E.M. rules 20 are written in standard form as and, Appliance group : A5 Loading type : H (main load) Dynamic coefficient : =1.15 Amplifying coefficient := 1.11 9 , The value of the dynamic coefficient is applied to the loading arising from the working load. The value of the amplifying coefficient depends the group classification of the application, and the weight of one meter maintenance platform is zero in this work. 25. It is assumed that the total load (372780 N) is effected on the midpoint of the rail and each girder shares this total load equally. This load is applied via the contact points of the two trolley wheels in this system. Therefore the value of the acting force on each point is 93195 N. Applying the total load in the system, the value of the maximum stress according to Eq. (1) is 143.90 N/mm2 to two decimal places, and the value of the minimum stress according to Eq. (2) is 47.33 N/mm2 to two decimal places. According to Fig. 5, the permissible stress in shear consists of the shear stresses of the wheel forces, and is defined as 20 The value of the maximum shear stress is 24.82 N/mm2 to two decimal places from Eq. (5). Substituting Eq. (1)(3) the equivalent stress is given by. The value of the equivalent stress is 150.18 N/mm2 to two decimal places. Fig. 5: Inertia and moment of resistance in a box girder 10 6 Results from a girder model with a four-node tetrahedral element To model the overhead crane girder with a four-node tethrahedral element, Cosmosworks software was used for finite element analysis using the girder solid model generated by means of SolidWorks 2003. Youngs Modulus (E) is 2.1105 N/mm2 and the Poisson Ratio () is 0.3 for finite element analysis. The value of the maximum stress of the side plate is 12.07 N/mm2 to two decimal places and the value of the maximum stress of the bottom plate is 15.08N/mm2 to two decimal places from Fig. 6 20. The displacement of the modelled overhead crane girder was obtained from CosmosWorks, and is illustrated in Fig. 7. The value of maximum displacement of the girder is about 2.2 mm. Fig. 6: Stress values of an overhead crane girder with a four-node tetrahedral element 11 Fig. 7: Displacements of an overhead crane girder with a four-node tetrahedral element 7 Results from a girder model with a four-node quadratic shell element To model the overhead crane girder with a four-node quadratic shell element, MSC Patran software was used for the finite element analysis. Youngs Modulus (E) is 2.110 N/mm2 and the Poisson Ratio (_St) is 0.3 for finite element analysis. The value of the maximum stress of the side plate is 35.40 N/mm2 to two decimal places, and the value of the maximum stress of the bottom plate is 49.30 N/mm2 to two decimal places, from Fig. 8 20. The displacement of the modelled overhead crane girder was obtained from MSC Patran, and is illustrated in Fig. 9.The value of maximum displacement of the girder is about 3.89 mm. The value of the maximum stress according to Eq. (1) is calculated as 143.90 N/mm2 to two decimal places. The safety factor should be considered between 2 and 3 for overhead crane girder design. The maximum stress value of the side plate is between 24.14 and 36.21 N/mm2 to two decimal places, and the maximum stress value of the bottom plate is between 30.16 and 45.24 N/mm2 to two decimal places for a four-node tetrahedral element, taking into account the safety factor. The maximum stress value of the side plate is between 70.8 and 106.2 N/mm2 to two decimal places and the maximum stress value of the bottom plate is between 98.6 and 147.9 N/mm2 to two decimal places for a four-node quadratic shell element, 12 taking into account the safety factor. The permissible displacement of the girder is 13 mm according to F. E.M. rules. The maximum displacement obtained from the finite element model with a four-node tetrahedral element is between 4.40 and 6.60 mm, taking into account the safety factor. The maximum displacement obtained from the finite element model with a four-node quadratic shell element is between 7.78 and 11.67 mm, taking into account the safety factor. Fig. 8: Stress values of an overhead crane girder with a quadratic shell element 13 Fig. 9: Displacements of an overhead crane girder with a four-node quadratic shell element 8 Conclusion In this study, unlike the other studies carried out previously, shell elements in finite element modeling of an overhead box girder have been examined. In order to show the use of shell elements, one illustrative overhead crane bridge example is given. The maximum stress value is 143.90 N/mm2 and 45.24 N/mm2 for a four-node tetrahedral element and 147.9 N/mm2 for a four-node quadratic shell element using both calculations according to the F. E. M. Rules and finite element analysis. The value of the equivalent stress is 150.18 N/mm2 to two decimal places. Taking into account the safety factor, the stress value varies between 97145.5N/mm2, which is obtained from MSC Patran. The ratio of length to thickness of the element used in modelling the overhead crane box girder is higher than 20. Therefore, in order to show the accuracy of the 14 analysis of the overhead crane bridges, a four-node quadratic shell element is used instead of the four-node tetrahedral element for finite element analysis. Acknowledgment It is pleasure to acknowledge much stimulating correspondence with Dr. Haydar Livatyali and gratefully to acknowledge the support of CESAN Inc., which provided the design data. Machine tool numerical control reforms 1 CNC systems and the development trend of history 1946 birth of the worlds first electronic computer, which shows that human beings created to enhance and replace some of the mental work tools. It and human agriculture, industrial society in the creation of those who merely increase compared to manual tools, from a qualitative leap for mankinds entry into the information society laid the foundation. Six years later, in 1952, computer technology applied to the machine in the United States was born first CNC machine tools. Since then, the traditional machine produced a qualitative change. Nearly half a century since the CNC system has experienced two phases and six generations of development. 1.1 Numerical Control (NC) phase (1952 to 1970) Early computers computational speed low and the prevailing scientific computing and data processing is not affected, but can not meet the requirements of real-time control machine. People have to use digital logic circuit tied into a single machine as a dedicated computer numerical control system, known as the hardware connection NC (HARD-WIRED NC), called the Numerical Control (NC). With the development of components of this phase after three generations, that is, in 1952 the first generation - tube； 1959 of the second generation - transistor； 1965 of the third generation - small-scale integrated circuits. 1.2 Computer Numerical Control (CNC) phase (1970 to present) 15 To 1970, GM has been a small computer and mass-produced. So it transplant system as the core component of NC, have entered a Computer Numerical Control (CNC) stage(in front of the computer should be universal word omitted). To 1971, the United States INTEL company in the world will be the first time the two most core computer components - computing and controller, a large-scale integrated circuit technology integration in a chip, called the microprocessor (MICROPROCESSOR) , also known as the central processing unit (CPU). 1974 microprocessor to be used in CNC system. This is because the function of the computer is too small to control a machine tool capacity affluent (the time has been used to control more than one machine, called Group Control), as a reasonable economic use of the microprocessor. Minicomputer reliability and then not ideal. Early microprocessor speed and functionality while still not high enough, but can be adopted to solve the multi-processor architecture. As microprocessor core is a general computer components, it is still known as the CNC. By 1990, PC machines (personal computers, domestic habits that computer) performance has been developed to a high stage, as a CNC system to meet the requirements of the core components. NC system based on PC has now entered the stage. In short, CNC has also experienced a stage three generations. That is, in 1970s fourth generation - small computer； 1974 of the fifth generation - microprocessors and the sixth-generation 1990 - Based on the PC (called PC-BASED abroad). Also pointed out that, although the foreign computer has been renamed NC (CNC), but China still customary said Numerical Control (NC). Therefore, we stress the day-to-day NC, in essence, is that computer numerically controlled. 1.3 the trend of future development of NC 1.3.1continue to open, the sixth generation of PC-based development Based on the PC with the open, low-cost, high reliability, rich in resources such as hardware and software features, and more CNC system manufacturers will embark on this path. At least it used PC as a front-end machine, to deal with the human-machine interface, programming, networking and communications problems, the former NC Some systems have the mandate. PC machine with the friendly interface, will be universal to all CNC system. Remote communications, remote 16 diagnostics and maintenance will be more widespread. 1.3.2high-speed and high-precision Development This is to adapt to high-speed and high-precision machine tools to the needs of the development direction. 1.3.3intelligent direction to the development With artificial intelligence in the computer field infiltration and the continuing development of the intelligent numerical control system will be continuously improved. （ 1） adaptive control technology CNC system can detect some important information in the process, and automatically adjust system parameters to improve the system running state purposes. （ 2） the introduction of expert guidance processing system the experience of skilled workers and experts, processing and the general rules of law of special deposit system, the process parameters to the database as the foundation, and establish artificial intelligence expert system. （ 3） introduction of Fault Diagnosis Expert System （ 4） intelligent digital servo drives Automatic Identification can load, and automatically adjust parameters to get the best drive system operation. 2 CNC of the need for transformation 2.1 microscopic view of the necessity of From the micro perspective, CNC machine tools than traditional machines have the following prominent superiority, and these advantages are from the NC system includes computer power. 2.1.1can be processed by conventional machining is not the curve, surface and other complex parts Because computers are superb computing power can be accurately calculated instantaneous each coordinate axis movement exercise should be instantaneous, it can compound into complex curves and surfaces. 2.1.2automated processing can be achieved, but also flexible automation to increase machine efficiency than traditional 3 to 7 times. 17 Because computers are memory and storage capacity, can be imported and stored procedures remember down, and then click procedural requirements to implement the order automatically to achieve automation. CNC machine tool as a replacement procedures, we can achieve another work piece machining automation, so that single pieces and small batch production can be automated, it has been called flexible automation. 2.1.3high precision machining parts, the size dispersion of small, easy to assemble, no longer needed repair. 2.1.4processes can be realized more focused, in part to reduce the frequent removal machine. 2.1.5have automatic alarm, automatic control, automatic compensation, and other self-regulatory functions, thus achieving long unattended processing. 2.1.6derived from the benefits of more than five. Such as: reducing the labor intensity of the workers, save the labor force (one can look after more than one machine), a decrease of tooling, shorten Trial Production of a new product cycle and the production cycle, the market demand for quick response, and so on. These advantages are our predecessors did not expect, is a very major breakthrough. In addition, CNC machine tools or the FMC (Flexible Manufacturing Cell), FMS (flexible manufacturing system) and CIMS (Computer Integrated Manufacturing System), and other enterprises, the basis of information transformation. NC manufacturing automation technology has become the core technology and basic technology. 2.2 the macro view of the necessity From a macro perspective, the military industrial developed countries, the machinery industry, in the late 1970s, early 1980s, has begun a large-scale application of CNC machine tools. Its essence is the use of information technology on the traditional industries (including the military, the Machinery Industry) for technological transformation. In addition to the manufacturing process used in CNC machine tools, FMC, FMS, but also included in the product development in the implementation of CAD, CAE, CAM, virtual manufacturing and production management in the implementation of the MIS (Management Information System), 18 CIMS, and so on. And the products that they produce an increase in information technology, including artificial intelligence and other content. As the use of information technology to foreign forces, the depth of Machinery Industry (referred to as information technology), and ultimately makes their products in the international military and civilian products on the market competitiveness of much stronger. And we in the information technology to transform traditional industries than about 20 years behind developed countries. Such as possession of machine tools in China, the proportion of CNC machine tools (CNC rate) in 1995 to only 1.9 percent, while Japan in 1994 reached 20.8 percent, every year a large number of imports of mechanical and electrical products. This also explains the macro CNC transformation of the need. 3 CNC machine tools and production lines of the transformation of the market 3.1 CNC transformation of the market My current machine total more than 380 million units, of which only the total number of CNC machine tool 113,400 Taiwan, or that Chinas CNC rate of less than 3 percent. Over the past 10 years, Chinas annual output of about 0.6 CNC machine tools to 0.8 million units, an annual output value of about 1.8 billion yuan. CNC machine tools annual rate of 6 per cent. Chinas machine tool easements over age 10 account for more than 60% below the 10 machines, automatic / semi-automatic machine less than 20 per cent, FMC / FMS, such as a handful more automated production line (the United States and Japan automatic and semi-automatic machine, 60 percent above). This shows that we the majority of manufacturing industries and enterprises of the production, processing equipment is the great majority of traditional machine tools, and more than half of military age is over 10 years old machine. Processing equipment used by the prevalence of poor quality products, less variety, low-grade, high cost, supply a long period, in view of the international and domestic markets, lack of competitiveness, and a direct impact on a companys products, markets, efficiency and impact The survival and development of enterprises. Therefore, we must vigorously raise the rate of CNC machine tools. 3.2 import equipment and production lines of the transformation of NC market Since Chinas reform and opening up, many foreign enterprises from the introduction of technology, equipment and production lines for technological 19 transformation. According to incomplete statistics, from 1979 to 1988 10, the introduction of technological transformation projects are 18,446, about 16.58 billion US dollars. These projects, the majority of projects in Chinas economic construction play a due role. Some, however, the introduction of projects due to various reasons, not equipment or normal operation of the production line, and even paralyzed, and the effectiveness of enterprises affected by serious enterprise is in trouble. Some of the equipment, production lines introduced from abroad, the digestion and absorption of some bad, spare parts incomplete, improper maintenance, poor operating results； only pay attention to the introduction of some imported the equipment, apparatus, production lines, ignore software, technology, and management, resulting in items integrity, and potential equipment can not play, but some can not even start running, did not play due role, but some production lines to sell the products very well, but not because of equipment failure production standards； because some high energy consumption, low pass rate products incur losses, but some have introduced a longer time, and the need for technological upgrading. Some of the causes of the equipment did not create wealth, but consumption of wealth. These can not use the equipment, production lines is a burden, but also a number of significant assets in stock, wealth is repaired. As long as identifying the main technical difficulties, and solve key technical problems, we can minimize the investment and make the most of their assets in stock, gain the greatest economic and social benefits. This is a great transformation of the market. 4 NC transformation of the content and gifted missing 4.1 the rise of foreign trade reform In the United States, Japan and Germany and other developed countries, and their machine transformation as new economic growth sector, the business scene, is in a golden age. The machine, as well as technology continues to progress, is a machine of the eternal issue. Chinas machine tool industry transformation, but also from old industries to enter the CNC technology mainly to the new industries. In the United States, Japan, Germany, with CNC machine tools and technological transformation of production lines vast market, has formed a CNC machine tools and production lines of the new industry. In the United States, transforming machine tool industry as 20 renewable (Remanufacturing) industry. Renewable industry in the famous companies: Borsches engineering company, atoms machine tool company, Devlieg-Bullavd (Bo) services group, US equipment companies. Companies in the United States-run companies in China. In Japan, the machine tool industry transformation as machine modification (Retrofitting) industry. Conversion industry in the famous companies: Okuma engineering group, Kong 3 Machinery Company, Chiyoda Engineering Company, Nozaki engineering company, Hamada engineering companies, Yamamoto Engineering Company. 4.2 the content of NC Machine tools and production line NC transformation main contents of the following: One is the restoration of the original features of the machine tools, production line of the fault diagnosis and recovery； second NC, in the ordinary machine augends significant installations, or additions to NC system, transformed into NC machine tools, CNC machine tools； its Third, renovation, to improve accuracy, efficiency and the degree of automation, mechanical, electrical part of the renovation, re-assembly of mechanical parts processing, restore the original accuracy of their production requirements are not satisfied with the latest CNC system update； Fourth, the technology updates or technical innovation, to enhance performance or grades, or for the use of new technology, new technologies, based on the original technology for large-scale update or technological innovation, and more significantly raise the level, and grades of upgrading. 4.3 NC transformation of the gifted missing 4.3.1reduce the amount of investment, shorter delivery time Compared with the purchase of new machine, the general can save 60% to 80% of the costs and transforming low-cost. Especially for large, special machine tools particularly obvious. General transformation of large-scale machine, spent only the cost of the new machine purchase 1 / 3, short delivery time. But some special circumstances, such as high-speed spindle, automatic tray switching systems and the production of the installation costs too costly and often raise the cost of 2 to 3 times compared with the purchase of new machine, only about 50 percent of savings investment. 21 4.3.2stable and reliable mechanical properties, structure limited By the use of bed, column, and other basic items are heavy and solid casting components, rather than kind of welding components of the machine after the high-performance, quality, and can continue to use the new equipment for many years. But by the mechanical structure of the original restrictions, it is not appropriate to the transformation of a breakthrough. 4.3.3become familiar with the equipment, ease of operation and maintenance The purchase of new equipment, new equipment do not know whether to meet the processing requirements. Transformation is not, can be used to calculate the machine processing capacity； In addition, since the use of many years, the operator of the machine has long been understood that in the operation, use and maintenance of the training time is short, quick. Transformation of the machine tools installed, we can achieve full load operation. 4.3.4can take full advantage of the existing conditions Take full advantage of the existing foundation, not like buying new equipment as necessary to build a foundation. 4.3.5can be used as control technology According to the development speed of technological innovation and in a time ly manner increased level of automation in production equipment and efficiency, improve the quality of equipment and grades, and the old machine will be replaced by the current level of machine. 5 the choice of NC System NC system are the three major types of transformation, in accordance with specific circumstances Choose. 5.1 stepper motor drive the open-loop system The servo drive system is stepper motor, stepper motor power, such as electro-hydraulic pulse motor. NC system by sending commands to the progress of pulse, the drive control and power amplifier circuit, the stepper motor rotate through the gears with ball screw drive of the implementation of parts. As long as control 22 commands the number of pulses, frequency and electricity sequence can control the implementation of parts of the displacement movement, speed and direction of movement. Such a system does not require the test will be the actual position and velocity feedback to the input, so called open-loop system, the system accuracy of the displacement in the major decisions of the stepper motor angular displacement accuracy, transmission gear and other components of the leads crew pitch accuracy, the accuracy of the lower displacement. The system is simple, convenient debugging maintenance, reliable, low cost, easy modification success. 5.2 or asynchronous motor DC Motor Drive, grating feedback loop measurement NC system And the open-loop system is the difference between a system: from the grating, such as position sensors for simultaneous detection device measured the actual position feedback signals, at any time and to compare the value will be the difference between the two enlarge and change, driven implementing agencies , given the speed of elimination of bias towards the direction of movement, until a given position feedback and the actual location of the margin of zero. Feed the closed-loop system in the structure than to the open-loop system into the complex, high-cost, strict requirements on the environment at room temperature. Design and debugging difficult than open-loop system. However, can be compared to the open-loop system into higher accuracy, faster speed, greater power drive characteristic indicators. Under the technological requirements and decide whether or not to adopt this system. 5.3 AC / DC servo motor drive, the semi-encoder feedback loop NC system Semi-closed-loop system detection devices installed in the middle of transmission, the implementation of indirect measurement components position. It can only be part of the internal loop compensation system components of the error and, therefore, it compared the accuracy of the closed-loop system of low accuracy, but its structure and debug than simple closed-loop system. Will be in the angular displacement detection devices and speed detection devices and make a servo motor when there was no need to consider the overall position of the installation of detection devices. NC system for the current production companies more manufacturers, such as the famous German company SIEMENS, Japan FANUC companies； Everest domestic 23 companies such as China, Beijing Aerospace CNC System Corporation, Shenyang and the central high-grade companies NC National Engineering Research Center. NC selection system is based mainly CNC machine modified to achieve the various precision, motor-driven power and user requirements. 6 the transformation of NC modification of the main mechanical components A new CNC machine tools in the design to achieve: a high static and dynamic stiffness of movement of the friction coefficient between small, transmission without clearance； big power； easy operation and maintenance. CNC transformation should be possible to achieve the above requirements. NC devices that can not be connected together with the general machine tools to reach the requirements of the NC machine tool, should also be major components corresponding to the transformation of up to a certain design requirements can be anticipated adaptation. 6.1 sliding Guideway On the NC lathe, in addition to a general guide lathes and precision of sexual orientation, but also a good Naimaca, wear characteristics, and reduce the frictional resistance to the death zone. At the same time there must be enough stiffness to reduce rail deformation on the impact of machining accuracy, a reasonable guide protection and lubrication. 6.2 deputy Gear General Machine concentrated in the main gear box and gearbox in the spindle. In order to ensure transmission accuracy, the use of CNC machine tool accuracy of gear higher grades than the general machine tools. In the structure must be able to achieve seamless transmission, thus transforming, machine main gear must meet the requirements of CNC machine tools, in order to ensure accuracy machining. 6.3 and the ball screw sliding leadscrew Screw-drive directly related to the transmission chain accuracy. Screw selection depends largely on the accuracy of the processing of requests and drag torque requirements. Accuracy is the main requirement of processing may be sliding Screw, but should check the leadscrew wear, such as pitch and pitch error accumulated error 24 and match Nut Gap. Sliding leadscrew general should not be less than six, the nut is too large gap replacement nut. The use of a sliding leadscrew relatively lower prices of ball screw, but it is difficult to meet the high precision machining. Ball screw friction losses small, high efficiency, the transmission efficiency of more than 90% of high accuracy, long life； starting torque and the torque of close campaigns, starting torque motor can be reduced. So to meet high precision machining requirements. 6.4 security Efficiency must be security as the prerequisite. Machine transformation in the light of the actual situation, we should take corresponding measures must not be ignored. Ball screw is sophisticated components, work to prevent dust particular chip and hard sand into the raceway. Screw in the vertical can also increase overall plate shields. And the extension units at both ends of the sliding contact surface Guide to seal well, absolutely rigid Coarse prevent the entry of foreign matter sliding surface damage Guide. 7 the main steps of CNC machine tools 7.1 for the determination of transformation Through analysis of the feasibility of transforming the future, we can against a Taiwan or a few machines determine the current status of reform programmes, which are generally incl