毕业设计英文论文翻译,五千字,翻译原文

英文The road (highway)The road is one kind of linear construction used for travel。

It is made of the roadbed，the road surface, the bridge, the culvert and the tunnel. In addition, it also has the crossing of lines, the protective project and the traffic engineering and the route facility。

The roadbed is the base of road surface, road shoulder，side slope, side ditch foundations. It is stone material structure, which is designed according to route's plane position .The roadbed, as the base of travel, must guarantee that it has the enough intensity and the stability that can prevent the water and other natural disaster from corroding.The road surface is the surface of road. It is single or complex structure built with mixture。

The road surface require being smooth，having enough intensity，good stability and anti—slippery function. The quality of road surface directly affects the safe, comfort and the traffic。

金融体制、融资约束与投资——来自OECD的实证分析R．SemenovDepartment of Economics，University of Nijmegen，Nijmegen（荷兰内梅亨大学，经济学院）这篇论文考查了OECD的11个国家中现金流量对企业投资的影响.我们发现不同国家之间投资对企业内部可获取资金的敏感性具有显著差异,并且银企之间具有明显的紧密关系的国家的敏感性比银企之间具有公平关系的国家的低.同时，我们发现融资约束与整体金融发展指标不存在关系.我们的结论与资本市场信息和激励问题对企业投资具有重要作用这种观点一致，并且紧密的银企关系会减少这些问题从而增加企业获取外部融资的渠道。

一、引言各个国家的企业在显著不同的金融体制下运行。

金融发展水平的差别(例如，相对GDP的信用额度和相对GDP的相应股票市场的资本化程度），在所有者和管理者关系、企业和债权人的模式中，企业控制的市场活动水平可以很好地被记录.在完美资本市场,对于具有正的净现值投资机会的企业将一直获得资金。

然而，经济理论表明市场摩擦，诸如信息不对称和激励问题会使获得外部资本更加昂贵，并且具有盈利投资机会的企业不一定能够获取所需资本.这表明融资要素，例如内部产生资金数量、新债务和权益的可得性，共同决定了企业的投资决策.现今已经有大量考查外部资金可得性对投资决策的影响的实证资料（可参考，例如Fazzari（1998）、 Hoshi(1991)、 Chapman（1996）、Samuel(1998））.大多数研究结果表明金融变量例如现金流量有助于解释企业的投资水平。

这项研究结果解释表明企业投资受限于外部资金的可得性。

很多模型强调运行正常的金融中介和金融市场有助于改善信息不对称和交易成本，减缓不对称问题,从而促使储蓄资金投着长期和高回报的项目,并且提高资源的有效配置（参看Levine（1997)的评论文章）。

因而我们预期用于更加发达的金融体制的国家的企业将更容易获得外部融资.几位学者已经指出建立企业和金融中介机构可进一步缓解金融市场摩擦。

[1]. These brake systems use compressed air as the energy transmitting medium to actuate the foundation brakes mounted on the axles.The air brake system currently found in commercial vehicles is made up of two subsystems —the pneumatic subsystem and the mechanical subsystem. The pneumatic subsystem includes the compressor, storage reservoirs, treadle valve (or the brake application valve), brake lines, relay valves, quick release valve, brake chambers, etc. The mechanical subsystem starts from the brake chambers and includes push rods, slack adjusters, S-cams, brake pads and brake drums. One of the most important differences between a hydraulic brake system (found in passenger cars) and an air brake system is in their mode of operation. In a hydraulic brake system, the force applied by the driver on the brake pedal is transmitted through the brake fluid to the wheel cylinders mounted on the axles. The driver obtains a sensory feedback in the form of pressure on his/her foot. If there is a leak in the hydraulic brake system, this pressure will decrease and the driver can detect it through the relatively easy motion of the brake pedal. In an air brake system, the application of the brake pedal by the driver meters out compressed air from a supply reservoir to the brake chambers. The force applied by the driver on the brake pedal is utilized in opening certain ports in the treadle valve and is not used to pressurize air in the brake system. This leads to a lack of variation in the sensory feedback to the driver in the case of leaks, worn brake pads and other defects in the brake system.Air brake systems can degrade significantly with use and need periodic inspection and maintenance [2]. As a result, periodic maintenance inspections are performed by fleet owners and roadside enforcement inspections are carried out by state and federal inspection teams. The performance requirements of brakes in newly manufactured and “on-the-road”commercial vehicles in the United States are specified by the Federal Motor V ehicle Safety Standard (FMVSS) 121 [3]and the Federal Motor Carrier Safety Regulation (FMCSR) Part 393 [4], respectively. These regulations specify the stopping distance, deceleration and brake force that should be achieved when the vehicle is braked from an initial speed of 20 mph. Due to the difficulty in carrying out such tests on the road, equivalent methods have been developed to inspect the brake system. A chronology of the development of the various commercial vehicle brake testing procedures used in the United States can be found in [5].Inspection techniques that are currently used to monitor the air brake system can be broadly divided into two categories —“visual inspections”and “performance-based inspections”[6]. Visual inspections include observing the stroke of the push rod, thickness of the brake linings, checking for wear in other components and detecting leaks in the brake system through aural and tactile means. They are subjective, time-consuming and difficult on vehicles with a low ground clearance since an inspector has to go underneath a vehicle to check the brake system. In fact, the average time required for a typical current roadside inspection of a commercial vehicle is 30 min, with approximately half of the time spent on inspecting brakes [7]. Performance-based inspections involve the measurement of the braking force/torque, stopping distance, brake pad temperature, etc. A description of two performance-based brake testers —the roller dynamometer brake tester and the flat plate brake tester —and the associated failure criteria when an air brake system is tested with them can be found in [8]. It is appropriate to point out that, in an appraisal of the future needs of the trucking industry [9], the authors call for the development of improved methods of brake inspections.Also, in recent years, studies have been carried out to develop “Adaptive Cruise Control”(ACC)systems or “Autonomous Intelligent Cruise Control”(AICC) systems. The objective of these systems is to maintain a constant distance between two consecutive vehicles by mainly controlling the engine throttle and the brake system. While most of the research on ACC systems has focused on passenger cars, the benefits of implementing such systems on heavy trucks are significant [10].A typical ACC system for heavy trucks controls the engine throttle, the transmission and the brake system and will be interfaced with existing systems like the Antilock Braking System (ABS), Traction Control System (TCS), etc. A typical truck ABS monitors the speed of the wheels and modulates the brake system pressure in the event of an impending wheel lock-up [11]. The ABS consists of an Electronic Control Unit (ECU) that receives signals from the wheel speed sensors and processes this information to regulate the brake system pressure through modulator valves. It should be noted that ABS does not control the treadle valve to regulate the pressure in the brake system. It reduces the brake system pressure that is “commanded”by the driver when it senses an impending wheel lock-up. It cannot provide a higher pressure than that corresponding to the pedal input from the driver.It is important to note that the ABS modulates the brake system pressure only under conditions when a wheel lock-up is impending. The ABS is disengaged during “normal”braking operations. In fact, it has been pointed out in [12] that ABS is “passive during the vast majority of braking operations”. During such braking operations, the pressure of air in the brake system is the level that is commanded by the driver through the motion of the brake pedal. Hence, in order to implement ACC systems on commercial vehicles it is necessary to develop control schemes that will automatically regulate the brake system pressure during all braking operations.Motivated by the above issues, our overall objective is to develop model-based control and diagnostic systems for air brake systems. Such a model of the air brake system should correlate the pressure transients in all the brake chambers of the air brake system with the treadle valve plunger displacement (i.e., the displacement of the brake pedal) and the supply pressure of air provided from the reservoirs to the treadle and relay valves. We have already developed a model [13], and control and diagnostic schemes [14] and [15]based on this model, for the configuration of the air brake system where the primary circuit of the treadle valve is directly connected to one of the two front brake chambers. This model predicts the pressure transients in a front brake chamber during a given brake application with the input data being the treadle valve plunger displacement and the supply pressure to the treadle valve. In order to extend these control and diagnostic schemes, a model should be developed to predict the response of all the brake chambers in the air brake system. One of the steps involved in obtaining a model for the entire air brake system is to develop a model to predict the response of the relay valve, and this is the focus of this article.We will show in the subsequent sections that a relay valve has three phases (or modes) of operation and the evolution of pressure in each of the modes is different. The transition from one mode to another depends primarily on the pressure in the brake chamber and for this reason, it can be naturally modeled as a hybrid system.This article is organized as follows. In Section 2, we present a brief description of the air brake system and the experimental setup that has been constructed at Texas A&M University. A hybrid dynamical model of the relay valve to predict its pressure response is derived in Section 3. We present the equations governing the motion of the mechanical components in the relay valve and the flow of air in the system. This model is corroborated against experimental data and the resultsare provided in Section 4.2. A brief description of the air brake system and the experimental setupA layout of the air brake system found in a typical tractor is presented in Fig. 1. An engine-driven air compressor is used to compress air and the compressed air is collected in storage reservoirs. The pressure of the compressed air in the reservoirs is regulated by a governor. Compressed air is supplied from these reservoirs to the treadle and relay valves. The driver applies the brake by pressing the brake pedal on the treadle valve. This action meters the compressed air from the supply port of the treadle valve to its delivery port. Then, the compressed air travels from the delivery port of the treadle valve through air hoses to the relay valve (referred to as the service relay valve in Fig. 1) and the quick release valve and finally to the brake chambers mounted on the axles.Fig. 1. A general layout of a truck air brake system.View thumbnail imagesThe S-cam foundation brake, found in more than 85% of the air-braked vehicles in the United States [1], is illustrated in Fig. 2. Compressed air metered from the storage reservoirs enters the brake chamber and acts against the diaphragm, generating a force resulting in the motion of the push rod. The motion of the push rod serves to rotate, through the slack adjuster, a splined shaft on which a cam in the shape of an ‘S’is mounted. The ends of two brake shoes rest on the profile of the S-cam and the rotation of the S-cam pushes the brake shoes outwards so that the brake pads make contact with the rotating drum. This action results in the deceleration of the rotating drum. When the brake pedal is released by the driver, air is exhausted from the brake chamber and the push rod strokes back into the brake chamber thereby rotating the S-cam in the opposite direction. The contact between the brake pads and the drum is now broken and the brake is thus released.Fig. 2. The S-cam foundation brake.View thumbnail imagesA schematic of the experimental setup at Texas A&M University is provided in Fig. 3. Two “Type-20”brake chambers (having an effective cross-sectional area of 20 in2) are mounted on a front axle of a tractor and two “Type-30”brake chambers (having an effective cross-sectional area of 30 in2) are mounted on a fixture designed to simulate the rear axle of a tractor. The air supply to the system is provided by means of two compressors and storage reservoirs. The reservoirs are chosen such that their volume is more than twelve times the volume of the brake chambers that they provide air to, as required by the Federal Motor V ehicle Safety Standard (FMVSS) 121 [3]. Pressure regulators are mounted at the delivery ports of the reservoirs to control the supply pressure to the treadle valve and the relay valve. A cross-sectional view of the treadle valve used in the experiments is illustrated in Fig. 4. The treadle valve consists of two circuits —the primary circuit and the secondary circuit. The delivery port of the primary circuit is connected to the control port of the relay valve and the delivery ports of the relay valve are connected to the two rear brake chambers. The relay valve has a separate port for obtaining compressed air supply from the reservoir. The delivery port of the secondary circuit is connected to the Quick Release V alve (QRV) and the delivery ports of the QRV are connected to the two front brake chambers.Fig. 3. A schematic of the experimental facility.View thumbnail imagesFig. 4. A sectional view of the treadle valve.View thumbnail imagesThe treadle valve is actuated by means of a pneumatic actuator and compressed air is supplied to this actuator from the storage reservoirs through a pressure regulator. The displacement of the treadle valve plunger is measured by means of a displacement transducer. A pressure transducer is mounted at the entrance of each of the four brake chambers by means of a custom designed and fabricated pitot tube fixture. A displacement transducer is mounted on each of the two front brake chamber push rods through appropriately fabricated fixtures in order to measure the push rod stroke. All the transducers are interfaced with a connector block through shielded cables. The connector block is connected to a PCI-MIO-16E-4 Data Acquisition (DAQ) board [16] (mounted on a PCI slot inside a desktop computer) that collects the data during brake application and release. An application program is used to collect and store the data in the computer.3. Modeling the response of the relay valveIn this section, we shall present a description of the model of the relay valve. We adopt a lumped parameter approach in the development of this model. Friction at the sliding surfaces in the treadle and relay valves is neglected since they are well lubricated. The springs present in these valves have been experimentally found to be nearly linear in the range of their operation (except the rubber graduating spring used in the treadle valve, see Fig. 4) and the spring constants have been determined from experimental data. Other parameters such as areas, initial deflections, etc., are measured and used in the model.In this article, our objective is to develop a model for predicting the pressure transients in the rear brake chambers actuated by the relay valve during the brake application process. The relay valve is controlled by means of the compressed air delivered by the primary circuit of the treadle valve during a brake application. We shall consider the configuration of the brake system where the delivery port of the primary circuit of the treadle valve is connected to the control port of the relay valve. Compressed air is provided from the storage reservoirs to the relay valve at its supply port and one of the delivery ports of the relay valve is connected to a rear brake chamber. We shall measure the pressure transients at the primary delivery port of the treadle valve and in the rear brake chamber in our experiments. The pressure measured at the primary delivery port of the treadle valve will be provided as input to the numerical scheme that solves the model equations developed to predict the pressure transients in the rear brake chamber.When the driver presses the brake pedal, the primary piston in the treadle valve (see Fig. 4) first closes the primary exhaust port (by moving a distance equal to xpt) and then opens up the primary inlet port (xpp>xpt, xpp being the displacement of the primary piston from its initial position). This action serves to meter the compressed air from the reservoir to the primary delivery port. We shall refer to this phase as the “apply phase”. When the pressure in the primary circuit increases to a level such that it balances the force applied by the driver, the primary piston closes the primary inlet port with the exhaust port also remaining closed (xpp=xpt). We shall refer to this phase as the “hold phase”. When the driver releases the brake pedal, the primary piston return spring forces the primary piston to its initial position. This action opens the exhaust port (xpp<xpt) and air is exhausted from the primary delivery port to the atmosphere. We shall refer to this phase as the “exhaust phase”. A detailed derivation of the model of the treadle valve can be foundin [13].A schematic of the cross-sectional view of the relay valve used in our experimental setup is presented in Fig. 5. The compressed air from the delivery port of the primary circuit of the treadle valve enters the control port of the relay valve. The resulting force pushes the relay valve piston and the exhaust port of the relay valve is closed when the relay valve piston moves a distance equal to xrpt. Once the pre-loads on the relay valve assembly gasket are overcome, the inlet port of the relay valve is opened (xrpp>xrpt, xrpp being the displacement of the relay valve piston from its initial position). Compressed air is now metered from the supply port of the relay valve to its delivery port and subsequently to the rear brake chambers. This is the apply phase associated with the operation of the relay valve. When the pressure in the delivery port of the relay valve increases to a level such that it balances the forces acting on the relay valve piston due to the compressed air from the treadle valve, the inlet port of the relay valve is closed with its exhaust port also remaining closed (xrpp=xrpt). This is the hold phase associated with the operation of the relay valve. When the brake pedal is released by the driver, air is exhausted from the primary circuit of the treadle valve and consequently from the control port of the relay valve. Due to the presence of compressed air in the delivery port of the relay valve, the relay valve piston is pushed back to its initial position and this opens the exhaust port of the relay valve (xrpp<xrpt). Thus, air is exhausted from the delivery port of the relay valve to the atmosphere. This is the exhaust phase associated with the operation of the relay valve.Fig. 5. A sectional view of the relay valve.View thumbnail imagesThe equation of motion governing the mechanics of the operation of the relay valve piston and the relay valve assembly gasket during the apply and the hold phases is given by(1)where Mrpp and Mrv denote respectively the mass of the relay valve piston and the relay valve assembly gasket, xrpp denotes the displacement of the relay valve piston from its initial position, xrpt is the distance traveled by the relay valve piston before it closes the relay valve exhaust port, Krv is the spring constant of the relay valve assembly return spring, Fkrvi is the pre-load on the same, Arpp is the net area of the relay valve piston exposed to the pressurized air at the control port of the relay valve, Arpp1 is the net area of the relay valve piston exposed to the pressurized air at the delivery port of the relay valve, Arpp2 is the net area of the relay valve piston exposed to the exhaust port of the relay valve, Arv1 is the net cross-sectional area of the relay valve assembly gasket exposed to the pressurized air at the supply port of the relay valve, Arv2 is the net cross-sectional area of the relay valve assembly gasket exposed to the pressurized air at the delivery port of the relay valve, Ppd is the pressure of air at the delivery port of the primary circuit of the treadle valve, Prs is the pressure of air being supplied to the relay valve, Prd is the pressure of air at the delivery port of the relay valve and is the atmospheric pressure.The mass of the relay valve piston is of the order of around 0.1 kg and the magnitude of the spring and pressure forces is found to be of the order of 102 N. Thus, the acceleration required for the inertial forces to be comparable with the spring force and the pressure force terms has to be of theorder of 102–103 m/s2, which is not the case. Hence the inertial forces are neglected and the above equation reduces to(2)The equation of motion of the relay valve piston during the exhaust phase is given by(3)Neglecting inertial forces, the above equation reduces to(4)PpdArpp=Prd(Arpp1+Arpp2).Next, we will consider the flow of air in the portion of the brake system under study. The relay valve opening is modeled as a nozzle. For the flow through a restriction, if the ratio of the cross-sectional area of the upstream section to the cross-sectional area of the restriction is 4.4 or higher, the approach velocity to this restriction can be neglected and the upstream properties (such as pressure, enthalpy, temperature, etc.) can be taken to be the upstream total or stagnation properties [17]. In our case, the minimum ratio of the cross-sectional area of the supply chamber of the relay valve to the cross-sectional area of the relay valve opening (the restriction) is found to be more than this value. Hence, we can consider the valve opening as a nozzle and take the properties in the supply chamber of the valve as the stagnation properties at the inlet section of the nozzle. The flow through the nozzle is assumed to be one-dimensional and isentropic. We also assume that the fluid properties are uniform at all sections in the nozzle. Air is assumed to behave like an ideal gas with constant specific heats. Under the above assumptions, the part of the pneumatic subsystem under consideration can be visualized as illustrated in Fig. 6.Fig. 6. The simplified visualization of the pneumatic subsystem under consideration.View thumbnail imagesThe energy equation for the flow of air through the nozzle under the above assumptions can be written as [18](5)where ho is the specific stagnation enthalpy at the entrance section of the nozzle, h is the specific enthalpy at the exit section of the nozzle and u is the magnitude of the velocity of air at the exit section of the nozzle.For isentropic flow of an ideal gas with constant specific heats, the pressure (P), density (ρ) and temperature (T) are related by(6)where γis the ratio of specific heats.The mass flow rate of air from the relay valve opening at any instant of time (denoted by ) isgiven bywhere Ap is the cross-sectional area of the valve opening. This is the rate at which air is accumulating in the hoses and the brake chamber once the relay valve is actuated. Since we lump the properties of air inside the hose and the brake chamber, the mass of air in the brake chamber at any instant of time is obtained from the ideal gas equation of state as(8)where Vb is the volume of air in the brake chamber and Trd is the temperature of air in the brake chamber at that instant of time.Let us now consider the mechanics of the operation of the brake chamber. A cross-sectional view of the brake chamber is shown in Fig. 7. When the brake is applied, the brake chamber diaphragm starts to move only after a minimum threshold pressure is reached. This pressure is required to overcome the pre-loads on the diaphragm. When this pressure is attained in the brake chamber, the diaphragm moves such that the push rod is pushed out of the brake chamber. Once the brake pads contact the brake drum and steady state is reached, the volume of air in the brake chamber will be the maximum during that particular brake application. Thus, the volume of air in the brake chamber at any instant of time during the brake application process is given by(9)where V o1 is the initial volume of air in the brake chamber before the application of the brake, V o2 is the maximum volume of air in the brake chamber, Ab is the cross-sectional area of the brake chamber, xb is the displacement of the brake chamber diaphragm, i.e., the stroke of the push rod, and xbmax is the maximum stroke of the push rod.Fig. 7. A sectional view of the brake chamber.View thumbnail imagesIn our current experimental setup, the rear brake chambers are mounted on a fixture and the end of the push rod outside the brake chamber is not connected to a slack adjuster. The push rod is brought to rest during a given brake application when it strikes a plate mounted with its face perpendicular to the direction of motion of the push rod. The position of this plate can be adjusted to vary the push rod stroke. Hence, a reasonable model for the brake chamber is given by(10)where Mb is the mass of the brake chamber diaphragm, Kb is the spring constant of the brake chamber return spring and Fkbi is the pre-load on the brake chamber diaphragm return spring. It should be noted that the pressure of air in the rear brake chamber at any instant of time is assumed to be the same as the pressure of air at the delivery port of the relay valve at that instant of time. Neglecting inertial forces when compared to the force due to the pressure and spring forces, the above equation reduces toIn the case of a brake chamber mounted on an actual axle, the relationship between the push rod stroke and the brake chamber pressure has been found to be different than the one given by Eq.(11) due to the presence of additional components such as the slack adjuster, S-cam, brake pads and brake drum [15]. Thus, the model relating the push rod stroke and the brake chamber pressure for a rear brake chamber mounted on an actual rear axle should be developed as described in [15]. Differentiating Eq. (8) with respect to time and comparing the result with Eq. (7), and using Eqs.(5), (6), (9) and (11), we obtain the equation describing the pressure response of the relay valve during the apply and hold phases as(12)where Trs is the temperature of the air being supplied to the relay valve, CD is the discharge coefficient, R is the specific heat of air, γis the ratio of specific heats of air (both R and γare assumed to be constants) and(13)Ap=2πrrv(xrpp−xrpt),with rrv being the external radius of the relay valve inlet section. The discharge coefficient (CD) is used in order to compensate for the losses during the flow. Due to the complexity involved in calibrating the valve to determine the value of the discharge coefficient, we assumed a value of 0.82 for CD as recommended in [17]. The pressure transients in the brake chamber during the apply and hold phases are obtained by solving Eqs. (2) and (12) along with the initial condition that at the start of a given brake application, the brake chamber pressure is equal to the atmospheric pressure.4. Corroboration of the modelIn this section, we corroborate the model for the relay valve by comparing its predictions against experimental data obtained from various test runs carried out over a range of supply pressures. It should be noted that the typical supply pressure in air brake systems is usually between 825.3 kPa (105 psig) and 928.8 kPa (120 psig) and this is the pressure range provided by the compressor used in our experimental setup. Eqs. (2) and (12) are solved numerically to obtain the pressure transients in the rear brake chamber during the apply and hold phases of a given brake application. The pressure measured at the delivery port of the primary circuit of the treadle valveis given as the input data to the numerical scheme. The prediction of the model for a test run is compared with the data collected during that test run and the results from various test runs are presented in Fig. 8, Fig. 9, Fig. 10, Fig. 11 and Fig. 12. In these figures, time (in seconds) and brake chamber pressure (in Pa) have been plotted on the abscissa and the ordinate respectively. The value corresponds to that instant of time at which the computer program for collecting the data is started.Fig. 8. Pressure transients at 653 kPa (80 psig) supply pressure —apply phase.View thumbnail imagesFig. 9. Pressure transients at 722 kPa (90 psig) supply pressure —apply phase.View thumbnail imagesFig. 10. Pressure transients at 584 kPa (70 psig) supply pressure —apply and exhaust phases. View thumbnail imagesFig. 11. Pressure transients at 653 kPa (80 psig) supply pressure —apply and exhaust phases. View thumbnail imagesFig. 12. Pressure transients at 584 kPa (70 psig) supply pressure —repeated application.View thumbnail imagesIt can be observed from these figures that the model is able to predict the beginning and end of each brake application reasonably well. The steady state brake chamber pressure is also predicted well by the model in all the cases. The model has also captured the pressure transients well in the exhaust phase during a complete brake application and release cycle as shown in Fig. 10 and Fig. 11. It has also predicted the pressure transients well in the case of repeated brake applications as can be observed from Fig. 12.5. ConclusionsIn this article, we have developed a hybrid model for predicting the response of the relay valve used in air brake systems of commercial vehicles. The relay valve is actuated by the compressed air from the delivery port of the primary circuit of the treadle valve. We have presented the main governing equations for the pressure transients in a rear brake chamber attached to a delivery port of the relay valve. We have corroborated this model using data obtained from experimental test runs performed over a range of supply pressures. We plan to incorporate this model of the relay valve into an overall model of the air brake system which can be used in control and diagnostic applications.References[1]S.F. Williams, R.R. Knipling, Automatic slack adjusters for heavy vehicle air brake systems, Tech. Rep. DOT HS 807 724, National Highway Traffic Safety Administration, Washington, D. C., February 1991。

本科生毕业设计（论文）外文翻译毕业设计（论文）题目：电力系统检测与计算外文题目：The development of the single chipmicrocomputer译文题目：单片机技术的发展与应用学生姓名： XXX专业： XXX指导教师姓名： XXX评阅日期：单片机技术的发展与应用从无线电世界到单片机世界现代计算机技术的产业革命，将世界经济从资本经济带入到知识经济时代。

在电子世界领域，从 20 世纪中的无线电时代也进入到 21 世纪以计算机技术为中心的智能化现代电子系统时代。

现代电子系统的基本核心是嵌入式计算机系统(简称嵌入式系统)，而单片机是最典型、最广泛、最普及的嵌入式系统。

一、无线电世界造就了几代英才。

在 20 世纪五六十年代，最具代表的先进的电子技术就是无线电技术，包括无线电广播，收音，无线通信(电报)，业余无线电台，无线电定位，导航等遥测、遥控、遥信技术。

早期就是这些电子技术带领着许多青少年步入了奇妙的电子世界，无线电技术展示了当时科技生活美妙的前景。

电子科学开始形成了一门新兴学科。

无线电电子学，无线通信开始了电子世界的历程。

无线电技术不仅成为了当时先进科学技术的代表，而且从普及到专业的科学领域，吸引了广大青少年，并使他们从中找到了无穷的乐趣。

从床头的矿石收音机到超外差收音机；从无线电发报到业余无线电台；从电话，电铃到无线电操纵模型。

无线电技术成为当时青少年科普、科技教育最普及，最广泛的内容。

至今，许多老一辈的工程师、专家、教授当年都是无线电爱好者。

无线电技术的无穷乐趣，无线电技术的全面训练，从电子学基本原理，电子元器件基础到无线电遥控、遥测、遥信电子系统制作，培养出了几代科技英才。

二、从无线电时代到电子技术普及时代。

早期的无线电技术推动了电子技术的发展，其中最主要的是真空管电子技术向半导体电子技术的发展。

半导体电子技术使有源器件实现了微小型化和低成本，使无线电技术有了更大普及和创新，并大大地开阔了许多非无线电的控制领域。

Environmental problems caused by Istanbul subway excavation and suggestionsfor remediation伊斯坦布尔地铁开挖引起的环境问题及补救建议Ibrahim Ocak Abstract：Many environmental problems caused by subway excavations have inevitably become an important point in city life. These problems can be categorized as transporting and stocking of excavated material, traffic jams, noise, vibrations, piles of dust mud and lack of supplies. Although these problems cause many difficulties,the most pressing for a big city like Istanbul is excava tion,since other listed difficulties result from it. Moreover, these problems are environmentally and regionally restricted to the period over which construction projects are underway and disappear when construction is finished. Currently, in Istanbul, there are nine subway construction projects in operation, covering approximately 73 km in length; over 200 km to be constructed in the near future. The amount of material excavated from ongoing construction projects covers approximately 12 million m3. In this study, problems—primarily, the problem with excavation waste(EW)—caused by subway excavation are analyzed and suggestions for remediation are offered.摘要：许多地铁开挖引起的环境问题不可避免地成为城市生活的重要部分。

华南理工大学广州学院本科生毕业设计(论文）翻译英文原文名Review of Vibration Analysis Methods for Gearbox Diagnostics and Prognostics中文译名对变速箱振动分析的诊断和预测方法综述学院汽车工程学院专业班级车辆工程七班学生姓名刘嘉先学生学号201130085184指导教师李利平填写日期2015年3月15日英文原文版出处：Proceedings of the 54th Meeting of the Society for Machinery Failure Prevention Technology, Virginia Beach，V A, May 1-4，2000，p. 623-634译文成绩：指导教师(导师组长）签名：译文：简介特征提取技术在文献中有描述;然而，大多数人似乎掩盖所需的特定的预处理功能。

一些文件没有提供足够的细节重现他们的结果，并没有一个全面的比较传统的功能过渡齿轮箱数据。

常用术语,如“残差信号”,是指在不同的文件不同的技术.试图定义了状态维修社区中的常用术语和建立所需的特定的预处理加工特性。

本文的重点是对所使用的齿轮故障检测功能。

功能分为五个不同的组基于预处理的需要。

论文的第一部分将提供预处理流程的概述和其中每个特性计算的处理方案。

在下一节中，为特征提取技术描述，将更详细地讨论每一个功能。

最后一节将简要概述的宾夕法尼亚州立大学陆军研究实验室的CBM工具箱用于齿轮故障诊断。

特征提取概述许多类型的缺陷或损伤会增加机械振动水平。

这些振动水平，然后由加速度转换为电信号进行数据测量。

原则上,关于受监视的计算机的健康的信息被包含在这个振动签名。

因此，新的或当前振动签名可以与以前的签名进行比较,以确定该元件是否正常行为或显示故障的迹象。

在实践中，这种比较是不能奏效的。

由于大的变型中,签名的直接比较是困难的。

相反,一个涉及从所述振动署名数据特征提取更多有用的技术也可以使用。

CLUTCHThe engine produces the power to drive the vehicle. The drive line or drive train transfers the power of the engine to the wheels. The drive train consists of the parts from the back of the flywh eel to the wheels. These parts include the clutch, th e transmission, the drive shaft, and the final drive assembly (Figure 8-1).The clutch which includes the flywheel, clutch disc, pressure plate, springs, pressure plate cover and the linkage necessary to operate the clutch is a rotating mechanism between t he engine and the transmission (Figure 8-2). It operates through friction which comes from contact between the parts. That is the reason why the clutch is called a friction mechanism. After engagement, the clutch must continue to transmit all the engine torque to the transmission depending on the friction without slippage. The clutch is also used to disengage the engine from the drive train whenever the gears in the transmission are being shifted from one gear ratio to another.To start the engine or shift the gears, the driver has to depress the clutch pedal with the purpose of disengagement the transmission from the engine. At that time, the driven members connected to the transmission input shaft are either stationary or rotating at a speed that is slower or faster than the driving members connected to the engine crankshaft. There is no spring pressure on the clutch assembly parts. So there is no friction between the driving members and driven members. As the driver lets loose the clutch pedal, spring pre ssure increases on the clutch parts. Friction between the parts also increases. The pressure exerted by the springs on the driven members is controlled by the driver through the clutch pedal and linkage. The positive engagement of the driving and driven members is made possible by the friction between the surfaces of the members. When full spring pressure is applied, the speed of the driving and driven members should be the same. At themoment, the clutch must act as a solid coupling device and transmit al l engine power to the transmission, without slipping.However, the transmission should be engaged to the engine gradually in order to operate the car smoothly and minimize torsional shock on the drive train because an engine at idle just develops little power. Otherwise, the driving members are connected with the driven members too quickly and the engine would be stalled.The flywheel is a major part of the clutch. The flywheel mounts to the engine’s crankshaft and transmits engine torque to the clutch assembly. The flywheel, when coupled with the clutch disc and pressure plate makes and breaks the flow of power from the engine to the transmission.The flywheel provides a mounting location for the clutch assembly as well. When the clutch is applied, the flyw heel transfers engine torque to the clutch disc. Because of its weight, the flywheel helps to smooth engine operation. The flywheel also has a large ring gear at its outer edge, which engages with a pinion gear on the starter motor during engine cranking.The clutch disc fits between the flywheel and the pressure plate. The clutch disc has a splined hub that fits over splines on the transmission input shaft. A splined hub has grooves that match splines on the shaft. These splines fit in the grooves. Thus, t he two parts are held together. However, back-and-forth movement of the disc on the shaft is possible. Attached to the input shaft, At disc turns at the speed of the shaft.The clutch pressure plate is generally made of cast iron. It is round and about the same diameter as the clutch disc. One side of the pressure plate is machined smooth. This side will press the clutch disc facing are against the flywheel. The outer side has various shapes to facilitate attachment of spring and release mechanisms. The two primary types of pressure plate assemblies are coil spri ng assembly and diaphragmspring (Figure 8-3).In a coil spring clutch the pressure plate is backed by a number of coil springs and housed with them in a pressed-steel cover bolted to the flywheel. The springs push against the cover. Neither the driven plate nor the pressure plate is connected rigidly to the flywh eel and both can move either towards it or away. When the clutch pedal is depressed a thrust pad riding on a carbon or ball thrust bearing i s forced towards the flywheel. Levers pivoted so that they engage with the thrust pad at one end and the pressure plate at the other end pull the pressure plate ba ck against its springs. This releases pressure on the driven plate disconnecting the gearbox from the engine (Figure 8-4).Diaphragm spring pressure plate assemblies are widely used in most modern cars. The diaphragm spring is a single thin sheet of metal which yields when pressure is applied to it. When pressure is removed the metal springs back to its original shape. The centre portion of the diaphragm spring is slit into numerous fingers that act as release levers. When the clutch assembly rotates with the engine these weights are flung outwards by centrifugal forces and cause the levers to pre ss against the pressure plate. During disengagement of the clutch the fingers are moved forward by the release bearing. The spring pivots over the fulcrum ring and its outer rim moves away from the flywheel. The retracting spring pulls the pressure plate a way from the clutch plate thus disengaging the clutch (Figure 8-5).When engaged the release bearing and the fingers of the diaphragm spring move towards the transmission. As the diaphragm pivots over the pivot ring its outer rim forces the pressure plate against the clutch disc so that the clutch plate is engaged to the flywheel.The advantages of a diaphragm type pres sure plate assembly are its compactness, lower weight, fewer moving parts, less effort to engage, reduces rotational imbalance by providin g a balanced force around the pressure plate and less chances of clutch slippage.The clutch pedal is connected to the disengagement mechanism either by a cable or, more com monly, by a hydraulic system. Either way, pushing the pedal down operates the dise ngagement mechanism which puts pressure on the fingers of the clutch diaphragm via a release bearing and causes the diaphragm to release the clutch plate. With a hydraulic mechanism, the clutch pedal arm operates a piston in the clutch master cylinder. Thi s forces hydraulic fluid through a pipe to the clutch release cylinder where another piston operates the clutch disengagement mechanism. The alternative is to link the clutch pedal to the disengagement mechanism by a cable.The other parts including the cl utch fork, release bearing, bell-housing, bell housing cover, and pilot bushing are needed to couple and uncouple the transmission. The clutch fork, which connects to the linkage, actually operates the clutch. The release bearing fits between the clutch fork and the pressure plate assembly. The bell housing covers the clutch assembly. The bell housing c over fastens to the bottom of the bell housing. This removable cover allows a mechanic to inspect the clutch without removing the transmission and bell housing. A pilot bushing fits into the back of th e crankshaft and holds the transmission input shaft.A Torque ConverterThere are four components inside the very strong housing of the torque converter:1. Pump;2. Turbine;3. Stator;4. Transmission fluid.The housing of the torque converter is bolted to the flywheel of the engine, so it turns at what ever speed the engine is running at. The fins that make up the pump of the torque converter are at tached to the housing, so they also turn at the same speed a s the engine. The cutaway below shows how everything is connected inside the torque converter (Figure 8-6).The pump inside a torque converter is a type of centrifugal pump. As it spins, fluid is flung to the outside, much as the spin cycle of a washing machine flings water and clothes to the outside of the wash tub. As fluid is flung to the outside, a vacuum is created that draws more fluid in at the center.The fluid then enters the blades of the turbine, which is connected to the transmission. The turbin e causes the transmission to spin, which basically moves the car. The blades of the turbine are curved. This means that the fluid, which enters the turbine from the outside, has to change direction before it exits the center of the turbine. It is this directional change that causes the turbine to spin.The fluid exits the turbine at the center, moving in a different direction than when it entered. The fluid exits the turbine moving opposite the direction that the pump (and engine) is turning. If the fluid were allowed to hit the pump, it would slow the engine down, wasting power. This is why a torque converter has a stator.The stator resides in the very center of the torque converter. Its job is to redirect the fluid returning from the turbine before it hits the pump again. This dramatically increases the efficiency of the torque converter.The stator has a very aggressive blade design that almost completely reverses the direction of the fluid. A one-way clutch (inside the stator) connects the stator to a fixed shaft in the transmission. Because of this arrangement, the stator cannot spin with the fluid - i tc a n s p i n o n l y i n t h e o p p o s i t ed i re c t i o n,f o r c i ng th e f l ui d t oc h a n g ed i re c t i o n a s i t h i t s t h e s t a t o r b l a d e s.Something a little bit tricky happens when the car gets moving. There is a point, around 40 mph (64 kph), at which both the pump and the turbine are spinning at almost the same speed (the pump alwaysspins slightly faster). At this point, the fluid returns from the turbine, entering the pump already moving in the same direction as the pump, so the stator is not needed.Even though the turbine changes the direction of the fluid and flings it out the back, the fluid still ends up moving in the direction that the turbine is spinning because the turbin e is spinning faster in one direction than the fluid is being pumped in the other direction. If you were standing in the back of a pickup moving at 60 mph, and you threw a ball out the back of that pickup at 40 mph, the ball would still be going forward at 20 mph. This is similar to what happens in the tur bine: The fluid is being flung out the back in one direction, but not as fast as it was going to start with in the other direction.At these speeds, the fluid actually strikes the back sides of the stator blades, causing the stator to freewheel on its one-way clutch so it doesn’t hinder the fluid moving through it.Benefits and Weak PointsIn addition to the very important job of allowing a car come to a complete stop without stalling the engine; the torqu e converter actually gives the car more torque when you accelerate out of a Stop. Modern torque converters can multiply the torque of the engine by two to three times. This effect only happens when the engine is turning much faster than the transmission.At higher speeds, the transmission catches up to the engine, eventually moving at almost the same speed. Ideally, though, the transmission would move at exactly the same speed as the engine, because this difference in speed wastes power. This is part of th e reason why cars with automatic transmissions get worse gas mileage than cars with manual transmissions.To counter this effect, some cars have a torque converter with alockup clutch. When the two halves of the torque converter get up to speed, this clutch locks them together, eliminating the slip page and improving efficiency.。

大学毕业论文英文翻译中文译文计算机网络每个一个世纪都有一种主导地位的技术。

18世纪伴随着工业革命的到来的是大型机械系统的时代；19世纪是蒸汽机的时代，而20世纪的发展历程中，关键的技术是信息收集、处理和分发。

在其他的发展方面，我们还可以看到：遍布全球的电话网络的建立起来了，无线电广播和电视的出现了，计算机工业诞生了，并且以超乎想象的速度在成长；另外通信卫星也发射上天了。

技术的快速发展的一个直接结果是，这些领域正在快速地融合，信息收集、传输、存储和处理之间的差别正在迅速地消失。

对于具有数百个办公室的大型组织来说，尽管这些办公室分布在广阔的地理区域中，但未来期望的情景是，工作人员只要单击一下按钮，就可以查看最远处分部的状态。

随着信息收集、处理和分发能力的不断提高，我们对于更加复杂的信息处理技术的需求也增长得更快。

与其他的工业(比如汽车和航空运输业)相比，计算机工业还是非常年轻，尽管如此，计算机技术却在很短的时间内有了惊人的进展。

在计算机诞生之初的20年间，计算机系统是高度集中化的，通常位于一个很大的房间中。

该房间通常配有玻璃墙，参观的人透过玻璃墙可以欣赏到里边伟大的电子奇迹。

中等规模的公司或者大学可能会有一台或者两台计算机，而大型的研究机构最多也就几十台计算机。

要在20年内生产出大量同样功能但是体积比邮票还小的计算机，在当时的人们看来纯属科学幻想。

计算机和通信的结合对于计算机系统的组织方式产生了深远的影响。

把一台大型的计算机放在一个单独的房间中，然后用户带着他们的处理任务去房间里上机，这种"计算机中心"的概念现在已经完全过时了。

由一台计算机来处理整个组织中所有的计算需求，这种老式的模型已经被新的模型所取代，在新的模型下，由大量独立的，但相互连接起来的计算机来共同完成计算任务。

这些系统称为计算机网络(computer networks)。

如何设计这些网络，并且将这些网络组织起来，这就是本书的主题。

5000字英文论文篇一：论文用5000字中英文翻译MCU DescriptionSCM is also known as micro-controller (Microcontroller Unit), commonly used letters of the acronym MCU that it was first used in industrial control. Only a single chip by the CPU chip developed from a dedicated processor. The first design is by a large number of peripherals and CPU on a chip in the computer system, smaller, more easily integrated into a complex and demanding on the volume control device which. INTEL s Z80 is the first designed in accordance with this idea processor, then on the development of microcontroller and dedicated processors have parted ways.Are 8-bit microcontroller early or 4 bits. One of the most successful is the INTEL 8031, for a simple, reliable and good performance was a lot of praise. Then developed in 8031 out of MCS51 MCU Systems. SCM systems based on this system until now are still widely used. With the increased requirements of industrial control field, began a 16-bit microcontroller, because the cost is not satisfactory but have not been very widely used. After 90 years with the great development of consumer electronics, microcontroller technology has been a huge increase. With INTEL i960 series, especially the later series of widely used ARM, 32-bit microcontroller quickly replace high-end 16-bit MCU status and enter the mainstream market. The traditional 8-bit microcontroller performances have been the rapid increase capacity increase compared to 80 the number of times. Currently, high-end 32-bit microcontroller clocked over 300MHz, the performance catching the mid-90 s dedicated processor, while the average model prices fall to one U.S. dollars; the most high-end model only 10 dollars. Modern SCM systems are no longer only in the developmentand use of bare metal environment, a large number of proprietary embedded operating system is widely used in the full range of SCM. The handheld computers and cell phones as the core processing of high-end microcontroller can even use a dedicated Windows and Linux operating systems.SCM is more suitable than the specific processor used in embedded systems, so it was up to the application. In fact the number of SCM is the world s largest computer. Modern human life used in almost every piece of electronic and mechanical products will be integrated single chip. Phone, telephone, calculator, home appliances,electronic toys, handheld computers and computer accessories such as a mouse with a 1-2 in both the Department of SCM. Personal computer will have a large number of SCM in the work. General car with more than 40 SCM, complex industrial control systems may even have hundreds of SCM in the same time work! SCM is not only far exceeds the number of PC and other computing the sum, or even more than the number of human beingsSingle chip, also known as single-chip microcontroller, it is not complete a certain logic chips, but to a computer system integrated into a chip. Equivalent to a micro-computer, and computer than just the lack of a microcontroller I / O devices. General talk: a chip becomes a computer. Its small size, light weight, cheap, for the study, application and development of facilities provided. At the same time, learning to use the MCU is to understand the principle and structure of the computer the best choice. SCM and the computer functions internally with similar modules, such as CPU, memory, parallel bus, the same effect as well, and hard disk memory devices, and different is its performance of these components were relatively weak many of our home computer, but the price is low , usually not more than 10 yuan you can do with it ...... some control for a class is not very complicated electrical work is enough of. We are usingautomatic drum washing machine, smoke hood, VCD and so on appliances which could see its shadow! ...... It is primarily as a control section of the core componentsIt is an online real-time control computer, control-line is that the scene is needed is a stronger anti-jamming ability, low cost, and this is, and off-line computer (such as home PC), the main difference.Single chipMCU is through running, and can be modified. Through different procedures to achieve different functions, in particular special unique features, this is another device much effort needs to be done, some great efforts are very difficult to do. A not very complex functions if the 50 s with the United States developed 74 series, or the 60 s CD4000 series of these pure hardware buttoned, then the circuit must be a large PCB board! But if the United States if the 70 s with a series of successful SCM market, theresult will be a drastic change! Just because you are prepared by microcomputer programs can achieve high intelligence, high efficiency and high reliability!As the microcontroller on the cost-sensitive, so now the dominant software or the lowest level assembly language, which is the lowest level in addition to more than binary machine code language, and as so low why is the use? Many high-level language has reached the level of visual programming Why is not it? The reason is simply that there is no home computer as a single chip CPU, not as hard as a mass storage device. A visualization of small high-level language program which even if only one button, will reach tens of K of size! For the home PC s hard drive in terms of nothing, but in terms of the MCU is not acceptable. SCM in the utilization of hardware resources to be very high for the job so although the original is still in the compilation of a lot of use. The same token,if the giant computer operating system and applications run up to get home PC, home PC, also can not afford to.Can be said that the twentieth century across the three power era, that is, the age of electricity, the electronic age and has entered into the computer age. However, this computer, usually refers to the personal computer, referred to as PC. It consists of the host, keyboard, monitor and other components. Another type of computer, most people do not know how. This computer is to give all kinds of intelligent machines single chip (also known as micro-controller). As the name suggests, this computer system took only a minimal integrated circuit, can be a simple operation and control. Because it is small, usually hidden in the charged mechanical stomach in. It is in the device, like the human brain plays a role, it goes wrong, the whole plant was paralyzed. Now, this microcontroller has a very broad field of use, such as smart meters, real-time industrial control, communications equipment, navigation systems, and household appliances. Once all kinds of products were using SCM, can serve to upgrade the effectiveness of products, often in the product name preceded by the adjective - intelligent, such as intelligent washing machines. Now some technical personnel of factories or other amateur electronics developers to engage in out of certain products, not the circuit is too complicated, that function is too simple and can easily be copied. The reason may be stuck in the product did not use a microcontrolleror other programmable logic device.SCM historySCM was born in the late 20th century, 70, experienced SCM, MCU, SoC three stages.First model1.SCM the single chip microcomputer (Single Chip Microcomputer) stage, mainly seeking the best of the best single form of embedded systemsarchitecture. Innovation model success, laying the SCM and general computer completely different path of development. In the open road of independent development of embedded systems, Intel Corporation contributed.2.MCU the micro-controller (Micro Controller Unit) stage, the main direction of technology development: expanding to meet the embedded applications, the target system requirements for the various peripheral circuits and interface circuits, highlight the object of intelligent control. It involves the areas associated with the object system, therefore, the development of MCU s responsibility inevitably falls on electrical, electronics manufacturers. From this point of view, Intel faded MCU development has its objective factors. In the development of MCU, the most famous manufacturers as the number of Philips Corporation. Philips company in embedded applications, its great advantage, the MCS-51 single-chip micro-computer from the rapid development of the micro-controller. Therefore, when we look back at the path of development of embedded systems, do not forget Intel and Philips in History.Embedded SystemsEmbedded system microcontroller is an independent development path, the MCU important factor in the development stage, is seeking applications to maximize the solution on the chip; Therefore, the development of dedicated single chip SoC trend of the natural form. As the microelectronics, IC design, EDA tools development, application system based on MCU SOC design have greater development. Therefore, the understanding of the microcontroller chip microcomputer can be, extended to the single-chip micro-controller applications.MCU applicationsSCM now permeate all areas of our lives, which is almost difficult to find traces of the field without SCM. Missile navigation equipment,aircraft, all types of instrument control, computer network communications and data transmission, industrial automation, real-time process control and data processing, extensive use of various smart IC card, civilian luxury car security system, video recorder, camera, fully automatic washing machine control, and program-controlled toys, electronic pet, etc., which are inseparable from the microcontroller. Not to mention the area of robot control, intelligent instruments, medical equipment was. Therefore, the MCU learning, development and application of the large number of computer applications and intelligent control of the scientists, engineers.SCM is widely used in instruments and meters, household appliances, medical equipment, aerospace, specialized equipment, intelligent management and process control fields, roughly divided into the following several areas:1. In the application of Intelligent InstrumentsSCM has a small size, low power consumption, controlling function, expansion flexibility, the advantages of miniaturization and ease of use, widely used instrument, combining different types of sensors can be realized Zhuru voltage, power, frequency, humidity, temperature, flow, speed, thickness, angle, length, hardness, elemental, physical pressure measurement. SCM makes use of digital instruments, intelligence, miniaturization, and functionality than electronic or digital circuits more powerful. Such as precision measuring equipment (power meter, oscilloscope, various analytical instrument).2. In the industrial control applicationWith the MCU can constitute a variety of control systems, data acquisition system. Such as factory assembly line of intelligent control 3. In Household AppliancesCan be said that the appliances are basically using SCM, praise from the electric rice, washing machines, refrigerators, air conditioners, color TV, and other audio video equipment, to the electronic weighing equipment, varied, and omnipresent.篇二：毕业论文5000字英文文献翻译(c++)┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ 装┊ ┊ ┊ ┊ ┊ 订┊ ┊ ┊ ┊ ┊ 线┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊安徽工业大学毕业设计（论文）说明书英文翻译英语原文：. Introducing ClassesThe only remaining feature we need to understand before solving our bookstore problem is how to write a data structure to represent our transaction data. In C++ we define our own data structure by defining a class. The class mechanism is one of the most important features in C++. In fact, a primary focus of the design of C++ is to make it possible to define class types that behave as naturally as the built-in types themselves. The library types that we ve seen already, such as istream and ostream, are all defined as classesthat is,they are not strictly speaking part of the language.Complete understanding of the class mechanism requires mastering a lot of information. Fortunately, it is possible to use a class that someone else has written without knowing how to define a class ourselves. In this section, we ll describe a simple class that we canuse in solving our bookstore problem. We ll implement this class in the subsequent chapters as we learn more about types,expressions, statements, and functionsall of which are used in defining classes.To use a class we need to know three things:What is its name? Where is it defined?What operations does it support?For our bookstore problem, we ll assume that the class is named Sales_item and that it is defined in a header named Sales_item.h.The Sales_item ClassThe purpose of the Sales_item class is to store an ISBN and keep track of the number of copies sold, the revenue, and average sales price for that book. How these data are stored or computed is not our concern. To use a class, we need not know anything about how it is implemented. Instead, what we need to know is what operations the class provides.As we ve seen, when we use library facilities such as IO, we must include the associated headers. Similarly, for our own classes, we must make the definitions associated with the class available to the compiler. We do so in much the same way. Typically, we put the class definition into a file. Any program that wants to use our class must include that file. Conventionally, class types are stored in a file with a name that, like the name of a program source file, has two parts: a file name and a file suffix. Usually the file name is the same as the class defined in the header. The suffix usually is .h, but some programmers use .H, .hpp, or .hxx. Compilers usually aren t picky about header file names, but IDEs ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊┊ ┊ ┊ 装┊ ┊ ┊ ┊ ┊ 订┊ ┊ ┊ ┊ ┊ 线┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊安徽工业大学毕业设计（论文）说明书sometimes are. We ll assume that our class is defined in a file named Sales_item.h.Operations on Sales_item ObjectsEvery class defines a type. The type name is the same as the name of the class. Hence, our Sales_item class defines a type namedSales_item. As with the built-in types, we can define a variable of a class type. When we write Sales_item item we are saying that item is an object of type Sales_item. We often contract the phrase an object of type Sales_item to aSales_ item object or even more simply to a Sales_item. In addition to being able to define variables of type Sales_item, we can perform the following operations on Sales_item objects:Use the addition operator, +, to add two Sales_items,Use the input operator, to read a Sales_item object,Use the output operator, to write a Sales_item object,Use the assignment operator, =, to assign one Sales_item object to another,Call the same_isbn function to determine if two Sales_items refer to the same book.Classes are central to most C++ programs: Classes let us define our own types that are customizedfor the problems we need to solve, resulting in applications that are easier to write andunderstand.Well-designed class types can be as easy to use as the built-in types.A class defines data and function members: The data members store the state associated with objectsof the class type, and the functions perform operations that give meaning to the data. Classeslet us separate implementation and interface. The interface specifies the operations that the classsupports. Only the implementor of the class need know or care about the details of the implementation. This separation reduces the bookkeeping aspects that make programming tedious anderror-prone.Class types often are referred to as abstract data types. An abstract data type treats the data(state) and operations on that state as a single unit. We can think abstractly about what the classd oes, rather than always having to be aware of how the class operates. Abstract data types arefundamental to both object-oriented and generic programming.Data abstraction is a programming (and design) technique that relies on the separation of interfaceand implementation. The class designer must worry about how a class is implemented, but programmersthat use the class need not know about these details. Instead, programmers who use a type need to know only the type s interface; they can think abstractly about what the type does rather than concretely about how the type works. Encapsulation is a term that describes the technique of combining lower-level elements to forma new, higher-level entity. A function is one form of encapsulation: The detailed actions performedby the function are encapsulated in the larger entity that is the function itself. Encapsulated elements hide the details of their implementationwe may call ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ 装┊ ┊ ┊ ┊ ┊ 订┊ ┊ ┊ ┊ ┊ 线┊ ┊ ┊ ┊┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊安徽工业大学毕业设计（论文）说明书a function but have no access to the statements that it executes. In the same way, a class is an encapsulated entity: It represents an aggregation of several members, and most (well-designed) class types hide the members that implement the type.If we think about the library vector type, it is an example of both data abstraction and encapsulation. It is abstract in that to use it, we think about its interfaceabout the operations that it can perform. It is encapsulated because we have no access to the details of how the type is representated nor to any of its implementation artifacts. An array, on the other hand, is similar in concept to a vector but is neither abstract nor encapsulated. We manipulate an array directly by accessing the memory in which the array is stored.Not all types need to be abstract. The library pair class is a good example of a useful, well-designed class that is concrete rather thanabstract. A concrete class is a class that exposes, rather than hides, its implementation.Some classes, such as pair, really have no abstract interface. The pair type exists to bundle two data members into a single object. There is no need or advantage to hiding the data members. Hiding the members in a class like pair would only complicate the use of the type.Even so, such types often have member functions. In particular, it is a good idea for any class that has data members of built-in or compound type to define constructor(s) to initialize those members. The user of the class could initialize or assign to the data members but it is less error-prone for the class to do so.Programmers tend to think about the people who will run their applications as users. Applicationsare designed for and evolve in response to feedback from those who ultimately use the applications. Classes are thought of in a similar way: A class designer designs and implements a class for users of that class. In this case, the user is a programmer, not the ultimate user of the application.Authors of successful applications do a good job of understanding and implementing the needs ofthe application s users. Similarly,well-designed, useful classes are designed with a close attention to the needs of the users of the class.In another way, the division between class designer and class user reflects the division betweenusers of an application and the designers and implementors of the application. Users care only if the application meets their needs in a cost-effective way. Similarly, users of a class care only about its interface. Good class designers define a class interface that is intuitive and easy to use. Users care about the implementation only in so far as the implementation affects their use of the class. If the implementation is too slow or puts burdens on users ofthe class, then the users must care. In well-designed classes, only the class designer worries about the implementation.In simple applications, the user of a class and the designer of the class might be one┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ 装┊ ┊ ┊ ┊ ┊ 订┊ ┊ ┊ ┊ ┊ 线┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊安徽工业大学毕业设计（论文）说明书and the same person. Even in such cases, it is useful to keep the roles distinct. When designing the interface to a class, the class designer should think about how easy it will be to use the class. When using the class, the designer shouldn t think about how the class works.When referring to a user, the context makes it clear which kind of user is meant. If we speak of user code or the user of the Sales_item class, we mean a programmer who is using a class in writing an application. If we speak of the user of the bookstore application, we mean the manager of the store who is running the application.Data abstraction and encapsulation provide two important advantages: 1.Class internals are protected from inadvertent user-level errors, which might corrupt the state of the object.2.The class implementation may evolve over time in response to changing requirements or bug reports without requiring change inuser-level code.By defining data members only in the private section of the class, the class author is free to make changes in the data. If the implementation changes, only the class code needs to be examined to see what affect the change may have. If data are public, then any function that directly accesses the data members of the old representation might be broken. Itwould be necessary to locate and rewrite all those portions of code that relied on the old pesentation before the program could be used again. Similarly, if the internal state of the class is private, then changes to the member data can happen in only a limited number of places. The data is protected from mistakes that users might introduce. If there is a bug that corrupts the object s state, the places to look for the bug are localized: When data are private, only a member function could be responsible for the error. The search for the mistake is limited, greatly easing the problems of maintenance and program correctness.If the data are private and if the interface to the member functions does not change, then user functions that manipulate class objects require no change.Because changing a class definition in a header file effectively changes the text of every source file that includes that header, code that uses a class must be recompiled when the class changes.Classes are the most fundamental feature in C++. Classes let us define new types that are tailored to our own applications, making our programs shorter and easier to modify.Data abstractionthe ability to define both data and function membersand encapsulationthe ability to protect class members from general accessare fundamental to classes. Member functions define the interface to the class. We encapsulate the class by making the data and functions used by the implementation of a class private.Classes may define constructors, which are special member functions that control how┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ 装┊ ┊ ┊ ┊ ┊ 订┊ ┊ ┊ ┊ ┊ 线┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊ ┊安徽工业大学毕业设计（论文）说明书objects of the class are initialized. Constructors may be verloaded. Every constructor should initialize every data member. Constructors should use a constructor initializer list to initialize the data members. Initializer lists are lists of namevalue pairs where the name is a member and the value is an initial value for that member.Classes may grant access to their nonpublic members to other classes or functions. A class grants access by making the class or function a friend.Classes may also define mutable or static members. A mutable member is a data member that is never const; its value may be changed inside a const member function. A static member can be either function or data; static members exist independently of the objects of the class type. Copy ControlEach type, whether a built-in or class type, defines the meaning of a (possibly empty) set of operations on objects of that type. We can add two int values, run size on a vector, and so on. These operations define what can be done with objects of the given type.Each type also defines what happens when objects of the type are created. Initialization of objects of class type is defined by constructors. Types also control what happens when objects of the type are copied, assigned, or destroyed. Classes control these actions through special member functions: the copy constructor, the assignment operator, and the destructor. This chapter covers these operations.When we define a new type, we specifyexplicitly or implicitlywhat happens when objects of that type are copied, assigned, and destroyed. We do so by defining special members: the copy constructor, the assignment operator, and the destructor. If we do not explicitly define the copy constructor or the assignment operator, the compiler will (usually) define them for us.The copy constructor is a special constructor that has a single parameter that is a (usually const) reference to the class type. The copy constructor is used explicitly when we define a new object and initialize it from an object of the same type. It is used implicitly when we pass or return objects of that type to or from functions.Collectively, the copy constructor, assignment operator, and destructor are referred to as copy control. The compiler automatically implements these operations, but the class may define its own versions. Copy control is an essential part of defining any C++ class. Programmers new to C++ are often confused by having to define what happens when objects arecopied, assigned, or destroyed. This confusion is compounded because if we do not explicitly define these operations, the compiler defines them for usalthough they might not behave as we intend.Often the compiler-synthesized copy-control functions are finethey do exactly the篇三：毕业设计的5000字英文文献翻译外文及翻译英语原文 Android Application FundamentalsAndroid applications are written in the Java programming language. The Android SDK tools compile the code—along with any data and resource files—into an Android package, an archive file with an .apk suffix. All the code in a single .apk file is considered to be one application and is the file that Android-powered devices use to install the application. Once installed on a device, each Android application lives in its own security sandbox: ? The Android operating system is a multi-user Linux system in which eachapplication is a different user.? By default, the system assigns each application a unique Linux user ID (the ID is used only by the system and is unknown to the application). The system setspermissions for all the files in an application so that only the user ID assigned to that application can access them.? Each process has its own virtual machine (VM), so an application s code runs in isolation from other applications.? By default, every application runs in its own Linux process. Android starts the process when any of the application s components need to be executed, then shuts down the process when it s no longer needed or when the system must recovermemory for other applications.In this way, the Android system implements the principle of least privilege. That is, each application, by default, has access only to the components that it requires to do its work and no more. This creates a very secure environment in which an application cannot access parts of the system for which it is not given permission.However, there are ways for an application to share data with other applications and for an application to access system services:? It s possible to arrange for two applications to share the same Linux user ID, in whichcase they are able to access each other s files. To conserve system resources,applications with the same user ID can also arrange to run in the same Linux processand share the same VM (the applications must also be signed with the samecertificate).。

Library of C the CNC industrialdeveloped tens of thousands and educational field, he hasNUMERICAL CONTROLNumerical Control technology as it is known today, emerged in the mid 20th century. It can be traced to the year of 1952, the U.S. Air Force, and the names of John Parsons and the Massachusetts Institute of Technology in Cam-bridge, MA, USA. It was not applied in production manu-facturing until the early 1960's. The real boom came in the form of CNC, around the year of 1972, and a decade later with the introduction of affordable micro computers. The history and development of this fascinating technology has been well documented in many publications.In the manufacturing field, and particularly in the area of metal working, Numerical Control technology has caused something of a revolution. Even in the days before comput-ers became standard fixtures in every company and in many homes, the2machine tools equipped with Numerical Control system found their special place in the machine shops. The recent evolution of micro electronics and the never ceasing computer development, including its impact on Numerical Control, has brought significant changes to the manufacturing sector in general and metalworking in-dustry in particular.DEFINITION OF NUMERICAL CONTROLIn various publications and articles, many descriptions have been used during the years, to define what Numerical Control is. It would be pointless to try to find yet another definition, just for the purpose of this handbook. Many of these definitions share the same idea, same basic concept, just use different wording.The majority of all the known definitions can be summed up into a relatively simple statement:Numerical Control can be defined as an operation of machine tools by the means of specifically coded instructions to the machine control systemThe instructions are combinations of the letters of alpha-bet, digits and selected symbols, for example, a decimal point, the percent sign or the parenthesis symbols. All in-structions are written in a logical order and a predetermined form. The collectionNUMERICAL CONTROLof all instructions necessary to ma-chine a part is called an NC Program, CNC Program, or a Part Program. Such a program can be stored for a future use and used repeatedly to achieve identical machining re-sults at any time.♦ NC and CNC TechnologyIn strict adherence to the terminology, there is a differ-ence in the meaning of the abbreviations NC and CNC. The NC stands for the older and original Numerical Control technology, whereby the abbreviation CNC stands for the newer Computerized Numerical Control technology, a modem spin-off of its older relative. However, in practice, CNC is the preferred abbreviation. To clarify the proper us-age of each term, look at the major differences between the NC and the CNC systems.Both systems perform the same tasks, namely manipula-tion of data for the purpose of machining a part. In both cases, the internal design of the control system contains the logical instructions that process the data. At this point the similarity ends. The NC system (as opposed to the CNC system) uses a fixed logical functions, those that are built-in and perma-nently wired within the control unit. These functions can-not be changed by the programmer or the machine opera-tor. Because of the fixed4wiring of the control logic, the NC control system is synonymous with the term 'hardwired'. The system can interpret a part program, but it does not al-low any changes to the program, using the control features. All required changes must be made away from the control, typically in an office environment. Also, the NC system re-quires the compulsory use of punched tapes for input of the program information.The modem CNC system, but not the old NC system, uses an internal micro processor (i.e., a computer). This computer contains memory registers storing a variety of routines that are capable of manipulating logical functions. That means the part programmer or the machine operator can change the program on the control itself (at the ma-chine), with instantaneous results. This flexibility is the greatest advantage of the CNC systems and probably the key element that contributed to such a wide use of the tech-nology in modern manufacturing. The CNC programs and the logical functions are stored on special computer chips, as software instructions, rather than used by the hardware connections, such as wires, that control the logical func-tions. In contrast to the NC system, the CNC system is syn-onymous with the term 'softwired'.NUMERICAL CONTROLWhen describing a particular subject that relates to the numerical control technology, it is customary to use either the term NC or CNC. Keep in mind that NC can also mean CNC in everyday talk, but CNC can never refer to the older technology, described in this handbook under the abbrevia-tion ofNC. The letter 'C 'stands for Computerized, and it is not applicable to the hardwired system. All control systems manufactured today are of the CNC design. Abbreviations such as C&C or C'n 'C are not correct and reflect poorly on anybody that uses them.CONVENTIONAL AMD CNC MACHININGWhat makes the CNC machining superior to the conven-tional methods? Is it superior at all? Where are the main benefits? If the CNC and the conventional machining pro-cesses are compared, a common general approach to ma-chining a part will emerge: Obtain and study the drawingSelect the most suitable machining methodDecide on the setup method (work holding)Select the cutting toolsEstablish speeds and feedsMachine the part6This basic approach is the same for both types of machin-ing. The major difference is in the way how various data are input. A feedrate of 10 inches per minute (10 in/min) is the same in manual or CNC applications, but the method of applying it is not. The same can be said about a coolant - it can be activated by turning a knob, pushing a switch or programming a special code. All these actions will result in a coolant rushing out of a nozzle. In both kinds of machin-ing, a certain amount of knowledge on the part of the user is required. After all, metal working, particularly metal cut-ting, is mainly a skill, but it is also, to a great degree, an art and a profession of large number of people. So is theappli-cation of Computerized Numerical Control. Like any skill or art or profession, mastering it to the last detail is neces-sary to be successful. It takes more than technical knowl-edge to be a CNC machinist or a CNC programmer. Work experience and intuition, and what is sometimes called a 'gut-feel', is a much needed supplement to any skill.In a conventional machining, the machine operator sets up the machine and moves each cutting tool, using one or both hands, to produce the required part. The design of a manual machine tool offers many features that help the process of machining a part -NUMERICAL CONTROLlevers, handles, gears and di-als, to name just a few. The same body motions are re-peated by the operator for every part in the batch. However, the word 'same 'in this context really means'similar 'rather than 'identical'. Humans are not capable to repeat every process exactly the same at all times - that is the job ofma-chines. People cannot work at the same performance level all the time, without a rest. All of us have some good andsome bad moments. The results of these moments, when*applied to machining a part, are difficult to predict. There will be some differences and inconsistencies within each batch of parts. The parts will not always be exactly the same. Maintaining dimensional tolerances and surface fin-ish quality are the most typical problems in conventional machining. Individual machinists may have their own time 'proven' methods, different from those of their fellow col-leagues. Combination of these and other factors create a great amount of mconsistency.The machining under numerical control does away with the majority of inconsistencies. It does not require the same physical involvement as manual machining. Numerically controlled machining does not need any levers or dials or handles, at least8not in the same sense as conventional ma-chining does. Once the part program has been proven, it can be used any number of times over, always returning consistent results. That does not mean there are no limiting factors. The cutting tools do wear out, the material blank in one batch is not identical to the material blank in another batch, the setups may vary, etc. These factors should be considered and compensated for, whenever necessary.The emergence of the numerical control technology does not mean an instant, or even a long term, demise of all man-ual machines. There are times when a traditional machin-ing method is preferable to a computerized method. For ex-ample, a simple one time job may be done more efficiently on a manual machine than a CNC machine. Certain types of machining jobs will benefit from manual or semiauto-matic machining, rather than numerically controlled ma-chining. The CNC machine tools are not meant to replace every manual machine, only to supplement them.In many instances, the decision whether certain machin-ing will be done on a CNC machine or not is based on the number of required parts and nothing else. Although the volume of partsNUMERICAL CONTROLmachined as a batch is always an important criteria, it should never be the only factor. Consideration should also be given to the part complexity, its tolerances, the required quality of surface finish, etc. Often, a single complex part will benefit from CNC machining, while fifty relatively simple parts will not.Keep in mind that numerical control has never machined a single part by itself. Numerical control is only a process or a method that enables a machine tool to be used in a pro-ductive, accurate and consistent way.NUMERICAL CONTROL ADVANTAGESWhat are the main advantages of numerical control?It is important to know which areas of machining will benefit from it and which are better done the conventional way. It is absurd to think that a two horse power CNC mill will win over jobs that are currently done on a twenty times more powerful manual mill. Equally unreasonable are ex-pectations of great improvements in cutting speeds and feedrates over a conventional machine. If the machining and tooling conditions are the same, the cutting time will be very close in both cases.Some of the major areas where the CNC user can and should expect improvement:10Setup time reductionLead time reductionAccuracy and repeatabilityContouring of complex shapesSimplified tooling and work holdingConsistent cutting timeGeneral productivity increaseEach area offers only a potential improvement. Individ-ual users will experience different levels of actual improve-ment, depending on the product manufactured on-site, the CNC machine used, the setup methods, complexity of fixturing, quality of cutting tools, management philosophy and engineering design, experience level of the workforce, individual attitudes, etc.Setup Time ReductionIn many cases, the setup time for a CNC machine can be reduced, sometimes quite dramatically. It is important to realize that setup is a manual operation, greatly dependent on the performance of CNC operator, the type of fixturing and general practices of the machine shop. Setup time is unproductive, but necessary - it is a part of the overhead costs of doing business. To keep the setupNUMERICAL CONTROLtime to a mini-mum should be one of the primary considerations of any machine shop supervisor, programmer and operator. Because of the design of CNC machines, the setup time should not be a major problem. Modular fixturing, standard tooling, fixed locators, automatic tool changing, pallets and other advanced features, make the setup time more efficient than a comparable setup of a conventional machine. With a good knowledge of modern manufacturing, productivity can be increased significantly.The number of parts machined under one setup is also important, in order to assess the cost of a setup time. If a great number of parts is machined in one setup, the setup cost per part can be very insignificant. A very similar re-duction can be achieved by grouping several different oper-ations into a single setup. Even if the setup time is longer, it may be justified when compared to the time required to setup several conventional machines.Lead Time ReductionOnce a part program is written and proven, it is ready to be Bsed again in the future, even at a short notice. Although the lead time for the first run is usually longer, it is virtually nil for any subsequent run. Even if an engineering change of the part design12requires the program to be modi tied, it can be done usually quickly, reducing the lead time.Long lead time, required to design and manufacture sev-eral special fixtures for conventional machines, can often be reduced by preparing a part program and the use of sim-plified fixturing. Accuracy and RepeatabilityThe high degree of accuracy and repeatability of modern CNC machines has been the single major benefit to many users. Whether the part program is stored on a disk or in the computer memory, or even on a tape (the original method), it always remains the same. Any program can be changed at will, but once proven, no changes are usually required any more. A given program can be reused as many times as needed, without losing a single bit of data it contains. True, program has to allow for such changeable factors as tool wear and operating temperatures, it has to be stored safely, but generally very little interference from the CNC pro-grammer or operator will be required. The high accuracy of CNC machines and their repeatability allows high quality parts to be produced consistently time after time. Contouring of Complex ShapesNUMERICAL CONTROLCNC lathes and machining centers are capable of con-touring a variety of shapes. Many CNC users acquired their machines only to be able to handle complex parts. A good examples are CNC applications in the aircraft and automo-tive industries. The use of some form of computerized pro-gramming is virtually mandatory for any three dimensional tool path generation.Complex shapes, such as molds, can be manufactured without the additional expense of making a model for trac-ing. Mirrored parts can be achieved literally at the switch of a button. Storage of programs is a lot simpler than storage of patterns, templates, wooden models, and other pattern making tools.Simplified Tooling and Work HoldingNonstandard and 'homemade' tooling that clutters the benches and drawers around a conventional machine can be eliminated by using standard tooling, specially designed for numerical control applications. Multi-step tools such as pilot drills, step drills, combination tools, counter borers and others are replaced with several individual standard tools. These tools are often cheaper and easier to replace than special and nonstandard tools.Cost-cutting measures have forced many tool suppliers to keep a low or even a nonexistent inventory, increasing the delivery lime14to the customer. Standard, off-the-shelf tooling can usually beob-tained faster then nonstandard tooling.Fixturing and work holding for CNC machines have only one major purpose - to hold the part rigidly and in the same position for all parts within a batch. Fixtures designed for CNC work do not normally require jigs, pilot holes and other hole locating aids.♦ Cutting Time and Productivity IncreaseThe cutting time on the CNC machine is commonly known as the cycle time - and is always consistent. Unlike a conventional machining, where the operator's skill, experi-ence and personal fatigue are subject to changes, the CNC machining is under the control of a computer. The small amount of manual work is restricted to the setup andload-ing and unloading the part. For large batch runs, the high cost of the unproductive time is spread among many parts, making it less significant. The main benefit of a consistent cutting time is for repetitive jobs, where the production scheduling and work allocation to individual machine tools can be done very accurately.The main reason companies often purchase CNCma-chines is strictly economic - it is a serious investment. Also, having a competitive edge is always on the mind of every plant manager. The numerical control teclmology offers excellent means to achieve a significant improvement in the manufacturing productivity and increasing the overall quality of the manufactured parts. Like any means, it has to be used wisely and knowledgeably. When more and more companies use the CNCtechnology, just having a CNC machine does not offer the extra edge anymore. Thecom-panies that get forward are those who know how to use the technology efficiently and practice it to be competitive in the global economy.To reach the goal of a major increase in productivity, it is essential that users understand the fundamental principles on which CNC technology is based. These principles take many forms, for example, understanding the electronic cir-cuitry, complex ladder diagrams, computer logic, metrol-ogy, machine design, machining principles and practices and many others. Each one has to be studied and mastered by the person in charge. In this handbook, the emphasis is on the topics that relate directly to the CNC programming and understanding the most common CNC machine tools, the Machining Centers and the lathes (sometimes also called the Turning Centers). The part quality consideration should be very important to every programmer and ma-chine tool operator and this goal is also reflected in the handbook approach as well as in the numerous examples.TYPES OF CNC MACHINE TOOLSDifferent kinds of CNCmachines cover an extremelylarge variety. Their numbersare rapidly increasing, as thetechnology developmentadvances. It is impossible toiden-tify all the applications,they would make a long list.Here is a brief list of some ofthe groups CNC machines canbe part of: *Mills and Machining centersLathes and Turning CentersDrilling machines CNC machining centers andlathes dominate the number ofinstallations in industry. Thesetwo groups share the marketjust about equally. Someindustries may have a higherneed for one group ofmachines, depending on their □ Boring mills and Profilers □ EDM machines □ Punch presses and Shears □ Flame cutting machines □ Routers □ Water jet and Laser profilers □ Cylindrical grinders □ Welding machines □ Benders, Winding and Spinning machines, etc.needs. One must remember that there are many different kinds of ladies and equally many different kinds ofma-chining centers. However, the programming process for a vertical machine is similar to the one for a horizontalma-chine or a simple CNC mill. Even between differentma-chine groups, there is a great amount of general applica-tions and the programming process is generally the same. For example, a contour milled with an end mill has a lot in common with a contour cut with a wire.♦ Mills and Machining Centers Standard number of axes on a milling machine is three - the X, Y and Z axes. The part set on a milling system is al-ways stationary, mounted on a moving machine table. The cutting tool rotates, it can move up and down (or in and out), but it does not physically follow the tool path.CNC mills - sometimes called CNC milling machines - are usually small, simple machines, without a tool changer or other automatic features. Their power rating is often quite low. In industry, they are used for toolroom work, maintenance purposes, or small part production. They are usuallydesigned for contouring, unlike CNC drills.CNC machining centers are far more popular and effi-cient than drills and mills, mainly for their flexibility. The main benefit the user gets out of a CNC machining center is the ability to group several diverse operations into a single setup. For example, drilling, boring, counter boring, tap-ping, spot facing and contour milling can be incorporated into a single CNC program. In addition, the flexibility is enhanced by automatic tool changing, using pallets to minimize idle time, indexing to a different side of the part, using a rotary movement of additional axes, and a number of other features. CNC machining centers can be equipped with special software that controls the speeds and feeds, the life of the cutting tool, automatic in-process gauging and offset adjustment and other production enhancing and time saving devices.There are two basic designs of a typical CNC machining center. They are the vertical and the horizontal machining centers. The major difference between the two types is the nature of work that can be done on them efficiently. For a vertical CNC machining center, the most suitable type of work are flat parts, either mounted to the fixture on the ta-ble, or held in a vise or a chuck. The work that requires ma-chining on two or more faces m a single setup is more de-sirable to be done on a CNC horizontal machining center. An good example is a pump housing and other cubic-like shapes. Some multi-face machining of small parts can also be done on a CNC vertical machining center equipped with a rotary table.The programming process is the same for both designs, but an additional axis (usually a B axis) is added to the hori-zontal design. This axis is either a simple positioning axis (indexing axis) for the table, or a fully rotary axis for simul-taneous contouring. This handbook concentrates on the CNC vertical ma-chining centers applications, with a special section dealing with the horizontal setup and machining. The program-ming methods are also applicable to the small CNC mills or drilling and/or tapping machines, but the programmer has to consider their restrictions.♦ Lathes and Turning CentersA CNC lathe is usually a machine tool with two axes, the vertical X axis and the horizontal Z axis. The main feature of a lathe that distinguishes it from a mill is that the part is rotating about the machine center line. In addition, the cut-ting tool is normally stationary, mounted in a sliding turret. The cutting tool follows the contour of the programmed tool path. For the CNC lathes with a milling attachment, so called live tooling, the milling tool has its own motor and rotates while the spindle is stationary.The modem lathe design can be horizontal or vertical. Horizontal type is far more common than the vertical type, but both designs have their purpose in manufacturing. Sev-eral different designs exist for either group. For example, a typical CNC lathe of the horizontal group can be designed with a flat bed or a slant bed, as a bar type, chucker type or a universal type. Added to these combinations are many ac-cessories that make a CNC lathe an extremely flexible ma-chine tool. Typically, accessories such as a tailstock, steady rests or follow-up rests, part catchers,pullout-fingers and even a third axis milling attachment are popular compo-nents of the CNC lathe. ?CNC lathe can be veiy versatile - so versatile in fact, that it is often called a CNC TurningCenter. All text and program examples in this handbook use the more traditional term CNC lathe, yet still recogniz-ing all its modern functions.中文翻译：数控正如我们现在所知，数控技术出现于20世纪中叶。