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徐州工程学院毕业设计（论文）任务书 机电工程 学院 机械设计制造及自动化 专业设计（论文）题目 随车起重机上车设计 学 生 姓 名 黄振家 班 级 04机本4班 起 止 日 期 2008.2.252008.6.2 指 导 教 师 李清伟 教研室主任 李志 发任务书日期 2008 年 2 月 25 日1.毕业设计的背景： 本课题来源于模拟生产实际,属于工程应用。起重机是当代最为得力的起重设备之一。随着国民经济的不断发展,多种类型的起重机广泛的运用于冶金、矿山、水泥、码头、化工、粮食等行业的各种场合。同时在各种场合对不同的工况所使用的起重机也不尽相同，近年来由于起重机的应用范围的扩大，品种的增多以及质量的不断提高， 对加工设计起重机提出了更高的要求。2.毕业设计(论文)的内容和要求： 通过分析和计算，确定每节臂的截面尺寸及截面形状，设计每节臂的具体结构和臂与臂之间的连接方式，设计整个起重臂的伸缩方式。并且设计随车起重机上车实现起重臂伸缩、变幅所需的上车液压系统，计算选择合适的泵、油缸及阀等液压元件。设计出具有一定起重量的随车起重机完整上车结构，绘制出上车装配图和每节臂的结构图。设计出上车液压系统，绘制上车液压系统原理图。3.主要参考文献：1湖北汽车学院.随车起重机新机型D.湖北：中国汽车工业出版社，2003.2谢开泉.前置式随车起重运输汽车的总体设计J.广西机械，2000，(3):33-36.3徐斌.QY25型随车起重机设计D.大连理工大学，2004.4顾迪民.工程起重机M.北京：中国建筑工业出版社，1981.5徐新才.机械设计手册M.北京：机械工业出版社，1992.4.毕业设计(论文)进度计划(以周为单位)：起 止 日 期工 作 内 容备 注第一周第二周第三周第四周第五周第六周第七周第八周第九周第十周第十一周第十二周第十三周第十四周第十五周第十六周调研、查阅相关文献，收集资料。调研、查阅相关文献，收集资料。综合分析文献资料，提出并论证上车整体设计方案。计算并确定每节臂的截面尺寸及形状。设计每节臂之间的连接方式。设计整个臂的伸缩方式。设计第一节臂的结构并绘制其结构图。设计第二节臂的结构并绘制其结构图。设计第三节臂的结构并绘制其结构图。确定上车液压系统整体结构，绘制上车液压系统原理图。根据上车液压系统原理图，计算选择液压元器件。根据上车液压系统原理图，计算选择液压元器件。绘制上车装配图，并根据装配图修改完善各节臂的结构图。绘制上车装配图，并根据装配图修改完善各节臂的结构图整理图纸资料，撰写毕业论文。整理图纸资料，撰写毕业论文。教研室审查意见： 室主任 年 月 日学院审查意见： 教学院长 年 月 日附录附录1 英文原文Introduction to Fluid Power1.1WHAT IS FLUID POWER?Fluid power is the technology that deals with the generation, control, and transmission of power-using pressurized fluids. It can be said that fluid power is the muscle that moves industry. This is because fluid power is used to push, pull, regulate, or drive virtually all the machines of modern industry. For example, fluid power steers and brakes automobiles, launches spacecraft, moves earth, harvests crops, mines coal, drives machine tools, controls airplanes, processes food, and even drills teeth. In fact, it is almost impossible to find a manufactured product that hasnt been “fluid-powered” in some way at some stage of its production or distribution.Since a fluid can be either a liquid or a gas, fluid power is actually the general term used for hydraulics and pneumatics. Hydraulic systems use liquids such as petroleum oils, water, synthetic oils, and even molten metals. The first hydraulic fluid to be used was water because it is readily available. However, water has many deficiencies. It freezes readily, is a relatively poor lubricant, and tends to rust metal components. Hydraulic oils are far superior and hence are widely used in lieu of water. Pneumatic systems use air as the gas medium because air is very abundant and can be readily exhausted into the atmosphere after completing its assigned task.It should be realized that there are actually two different types of fluid systems: fluid transport and fluid power.Fluid transport systems have as their sole objective the delivery of a fluid from one location to another to accomplish some useful purpose. Examples include pumping stations for pumping water to homes, Cross-country gas lines, and systems where chemical processing takes place as various fluids are brought together.Fluid power systems are designed specifically to perform work. The work is accomplished by a pressurized fluid bearing directly on an operating fluid cylinder or fluid motor. A fluid cylinder produces a force, whereas a fluid motor produces a torque. Fluid cylinders and motors thus provide the muscle to do the desired work. Of course, control components are also needed to ensure that the work is done smoothly, accurately, efficiently, and safely.Liquids provide a very rigid medium for transmitting power and thus can provide huge forces to move loads with utmost accuracy and precision. On the other hand, pneumatic systems exhibit spongy characteristics due to the compressibility of air. However, pneumatic systems are less expensive to build and operate. In addition, provisions can be made to control the operation of the pneumatic actuators that drive the loads.Fluid power equipment ranges in size from huge hydraulic presses to miniature fluid logic components used to build reliable control systems.How versatile is fluid power? In terms of brute power, a feather touch by an operator can control hundreds of horsepower and transmit it to any location where a hose or pipe can go. In terms of precision such as applications in the machine tool industry, tolerances of one ten-thousandth of an inch can be achieved and repeated over and over again. Fluid power is not merely a powerful muscle; it is a controlled, flexible muscle that provides power smoothly, efficiently, safely, and precisely to accomplish useful work.Figure 1-1 shows a pneumatically controlled dextrous hand designed to study machine dexterity and human manipulation in applications such as robotics and tactile sensing. Servo-controlled pneumatic actuators give the hand human-like grasping and manipulating capability. Key operating characteristics include high speed in performing manipulation tasks, strength to easily grasp hand-sized objects that have varying densities, and force grasping control. The hand possesses three fingers and an opposing thumb, each with four degrees of freedom. Each joint is positioned by two pneumatic actuators (located in an actuator pack with the controlling servo valve) driving a high-strength tendon. Performance and configuration constraints concerning the weight, size, geometry, cleanliness, and availability of individual actuators led to the choice of pneumatic actuation.1.2HISTORY OF FLUID POWERFluid power is probably as old as civilization itself. Ancient historical accounts show that water was used for centuries to produce power by means of water wheels, and air was used to turn windmills and propel ships. However, these early uses of fluid power required the movement of huge quantities of fluid because of the relatively low pressures provided by nature.Fluid power technology actually began in 1650 with the discovery of Pascals law: Pressure is transmitted undiminished in a confined body of fluid.Pascal found that when he rammed a cork down into a jug completely full of wine, the bottom of the jug broke and fell out. Pascals law indicated that the pressures were equal at the top and bottom of the jug. However, the jug has a small opening area at the top and a large area at the bottom. Thus, the bottom absorbs a greater force due to its larger area.In 1750, Bernoulli developed his law of conservation of energy for a fluid flowing in a pipeline. Pascals law and Bernoullis law operate at the very heart of all fluid power applications and are used for analysis purposes. However, it was not until the Industrial Revolution of 1850 in Great Britain that these laws would actually be applied to industry. Up to this time, electrical energy had not been developed to power the machines of industry. Instead, it was fluid power that, by 1870, was being used to drive hydraulic equipment such as cranes, presses, winches, extruding machines, hydraulic jacks, shearing machines, and riveting machines. In these systems, steam engines drove hydraulic water pumps, which delivered water at moderate pressures through pipes to industrial plants for powering the various machines. These early hydraulic systems had a number of deficiencies such as sealing problems because the designs had evolved more as an art than a science.Then, late in the nineteenth century, electricity emerged as a dominant technology. This resulted in a shift of development effort away from fluid power. Electrical power was soon found to be superior to hydraulics for transmitting power over great distances. There was very little development in fluid power technology during the last 10 yr of the nineteenth century.The modern era of fluid power is considered to have begun in 1906 when a hydraulic system was developed to replace electrical systems for elevating and controlling guns on the battleship USS Virginia. For this application, the hydraulic system developed used oil instead of water. This change in hydraulic fluid and the subsequent solution of sealing problems were significant milestones in the rebirth of fluid power.In 1926 the United States developed the first unitized, packaged hydraulic system consisting of a pump, controls, and actuator. The military requirements leading up to World War II kept fluid power applications and developments going at a good pace. The naval industry had used fluid power for cargo handling, winches, propeller pitch control, submarine control systems, operation of shipboard aircraft elevators, and drive systems for radar and sonar.During and after World War lithe aviation and aerospace industry provided the impetus for many advances in fluid power technology. Examples include Hydraulic-actuated landing gears, cargo doors, gun drives, and flight control devices such as rudders, ailerons, and elevons for aircraft. Figure 1-2 shows the space shuttle Columbia, powered by fluid thrust forces, soaring from its launch pad. The space shuttle takes off like a rocket and the winged orbiter then maneuvers around Earth like a spaceship. After completing its mission it lands on a runway like an airplane. Unlike earlier manned space craft, which were good for only one flight, the shuttle orbiter and rocket boosters can be used again and again. Only the external tank is expended on each launch. Figure 1-3 provides a cutaway view of the shuttle vehicle, identifying its main components, many of which are hydraulically actuated.The expanding economy that followed World War II led to the present situation where there are virtually a limitless number of fluid power applications. Today fluid power is used extensively in practically every branch of industry. Some typical applications are in automobiles, tractors, airplanes, missiles, boats, and machine tools. In the automobile alone, fluid power is utilized in hydraulic brakes, automotive transmissions, power steering, power brakes, air conditioning, lubrication, water coolant, and gasoline pumping systems. The innovative use of modern technology such as electro-hydraulic closed-loop systems, microprocessors, and improved materials for component construction will continue to advance the performance of fluid power systems.Relative to automotive applications, Fig. 1-4 is a diagram showing the Bendix Hydro-Boost Power Brake System. The basic system consists of an open center spool valve and hydraulic cylinder assembled in a single unit (see Fig. 1-5). Operating pressure is supplied by the power steering pump. Hydro-Boost provides a power assist to operate a dual master-cylinder braking system. Normally mounted on the engine compartment fire wall, it is designed to provide specific “brake-feel” characteristics throughout a wide range of pedal forces and travel. A spring accumulator stores energy for reverse stops. From one to three stops are available depending on the magnitude and duration of the brake application. This system was developed by Bendix Corporation as an answer to crowded engine compartments and replaces the large vacuum units.1.3ADVANTAGES OF FLUID POWERThere are three basic methods of transmitting power: electrical, mechanical, and fluid power. Most applications actually use a combination of the three methods to obtain the most efficient overall system. To properly determine which principle method to use, it is important to know the salient features of each type. For example, fluid systems can transmit power more economically over greater distances than can mechanical types. However, fluid systems are restricted to shorter distances than are electrical systems.The secret of fluid powers success and widespread use is its versatility and manageability. Fluid power is not hindered by the geometry of the machine, as is the case in mechanical systems. Also, power can be transmitted in almost limitless quantities because fluid systems are not so limited by the physical limitations of materials as are the electrical systems. For example, the performance of an electromagnet is limited by the saturation limit of steel. On the other hand, the power capacity of fluid systems is limited only by the physical strength of the material (such as steel) used for each component.Industry is going to depend more and more on automation in order to increase productivity. This includes remote and direct control of production operations, manufacturing processes, and materials handling. Fluid power is the muscle of automation because of advantages in the following four major categories.1. Ease and accuracy of control. By the use of simple levers and push buttons, the operator of a fluid power system can readily start, stop, speed up or slow down, and position forces that provide any desired horsepower with tolerances as precise as one ten-thousandth of an inch. Figure 1-6 shows a fluid power system that allows an aircraft pilot to raise and lower his landing gear. When the pilot moves a small control valve in one direction, oil under pressure flows to one end of the cylinder to lower the landing gear. To retract the landing gear, the pilot moves the valve lever in the opposite direction, allowing oil to flow into the other end of the cylinder.2. Multiplication of force. A fluid power system (without using cumbersome gears, pulleys, and levers) can multiply forces simply and efficiently from a fraction of an ounce to several hundred tons of output. Figure 1-7 shows an application where a rugged, powerful drive is required for handling huge logs. In this case, a turntable, which is driven by a hydraulic motor, can carry a 20,000-lb load at a loft radius (a torque of 200,000 ft ib) under rough operating conditions.3. Constant force or torque. Only fluid power systems are capable of providing constant force or torque regardless of speed changes. This is accomplished whether the work output moves a few inches per hour, several hundred inches per minute, a few revolutions per hour, or thousands of revolutions per minute. Figure 1-8 depicts an application in oceanography that involves the exploration and development of the oceans resources for the benefit of humankind. In this instance, it is important for the operator to apply a desired constant grabbing force through the use of the grappling hooks.4. Simplicity, safety, economy. In general, fluid power systems use fewer moving parts than comparable mechanical or electrical systems. Thus, they are simpler to maintain and operate. This, in turn, maximizes safety, compactness, and reliability. Figure 1-9 shows a power steering control designed for off-highway vehicles. The steering unit (shown attached to the steering wheel column in Fig. 1-9) consists of a manually operated directional control valve and meter in a single body. See Fig. 1-10 for a cutaway of this steering unit. Because the steering unit is fully fluid-linked, mechanical linkages, universal joints, bearings, reduction gears, etc., are eliminated. This provides a simple, compact system. In addition, very little input torque is required to produce the control needed for the toughest applications. This is important where limitations of control space require a small steering wheel and it becomes necessary to reduce operator fatigue. The compact design and versatility of the control system allow the unit to control many large and high-powered systems with a high degree of reliability. The steering unit shown in Fig. 1-10 contains a check valve that converts the unit to a hand-operated pump for emergency power-off steering.Additional benefits of fluid power systems include instantly reversible motion, automatic protection against overloads, and infinitely variable speed control. Fluid power systems also have the highest horsepower-per-weight ratio of any known power source.Drawbacks of Fluid PowerIn spite of all these highly desirable features of fluid power, it is not a panacea for all power transmission problems. Hydraulic systems also have some drawbacks. Hydraulic oils are messy, and leakage is impossible to eliminate completely. Hydraulic lines can burst, possibly resulting in injuries to people due to high-speed oil jets and flying pieces of metal, if proper design is not implemented. Prolonged exposure to loud noise such as that emanating from pumps, can result in loss of hearing. Also, most hydraulic oils can cause fires if an oil leak occurs in an area of hot equipment. Therefore, each application must be studied thoroughly to determine the best overall design. It is hoped that this book will not only assist the reader in developing the ability to make these types of system selection decisions but also present in a straightforward way the techniques for designing, analyzing, and troubleshooting basic fluid power systems.1.4APPLICATIONS OF FLUID POWERAlthough a number of cases of fluid power have already been presented in this chapter, the following additional applications should give the reader a broader view of the widespread use of fluid power in todays world.1. fluid power drives high-wire overhead tram. Most overhead trams require a haulage or tow cable to travel up or down steep inclines. However, the 22-passenger, 12,000-lb hydraulically powered and controlled Sky-tram shown in Fig. 1-11 is unique. It is self-propelled and travels on a stationary cable. Because the tram moves instead of the cable, the operator can stop, start, and reverse any one car completely independently of any other car in the tram system. Integral to the design of the Sky-tram drive is a pump (driven by a standard eight-cylinder gasoline engine), which supplies pressurized fluid to four hydraulic motors. Each motor drives two friction drive wheels.Eight drive wheels on top of the cables support and propel the tram car. On steep inclines, high driving torque is required for ascent and high braking torque for descent. Dual compensation of the four hydraulic motors provides efficient proportioning of available horsepower to meet the variable torque demands.2.fluid power is applied to harvesting corn. The worlds dependence on the United States for food has resulted in a great demand for agricultural equipment development. Fluid power is being applied to solve many of the problems dealing with the harvesting of food crops. Figure 1-12 shows a hydraulically driven elevator conveyor system, which is used to send harvested, husked ears of corn to a wagon trailer. Mounted directly to the chain-drive conveyor, a hydraulic motor delivers full-torque rotary power from start-up to full rpm.3Hydraulics power brush drives. Figure 1-13 shows a fluid powerdriven brush drive used for cleaning roads, floors, etc., in various industrial locations. Mounted directly at the hub of the front and side sweep-scrub brushes, compact hydraulic motors place power right where its needed. They eliminate bulky mechanical linkages for efficient, lightweight machine design. The result is continuous, rugged industrial cleaning action at the flip of a simple valve.4.fluid power positions and holds parts for welding. In Fig. 1-14, we see an example of a welding operation in which a farm equipment manufacturer applied hydraulics for positioning and holding parts while welding is done. It is a typical example of how fluid power can be used in manufacturing and production operations to reduce costs and increase production. This particular application required a sequencing system for fast, positive holding. This was accomplished by placing a restrictor (sequence valve) on the flow of oil in the line leading to the second of the two cylinders (rams), as illustrated in Fig. 1-15. The first cylinder extends to the end of its stroke. Oil pressure then builds up, overcoming the restrictor setting, and the second cylinder extends to complete the “hold” cycle. This unique welding application of hydraulics was initiated to increase productivity by making more parts per hour. In addition, the use of hydraulics reduced scrap rates and operator fatigue as well as increasing productivity from 5 pieces per shift to more than 20a 400 % increase.5.Fluid power performs bridge maintenance. A municipality had used fluid power for years as a means for removing stress from structural members of bridges, making repairs, and replacing beams. As many as four or five bulky, low-pressure hand pumps and jacking ram setups were used to remove stress from beams needing replacement. Labor costs were high, and no accurate methods existed for recording pressures. An excessive downtime problem dictated that a new system be designed for the job. A modern fluid power system was designed that located several 100-ton rams on the bridge structure, as illustrated in Fig. 1-16. One portable pump was used to actuate all of the rams by the use of a special manifold. This made it easy to remove stress from members needing repair or replacement. This new fluid power system cut the setup time and labor costs for each repair job to one-third that required with the hand pump and jacking ram setups previously used6.Fluid power is the muscle in industrial lift trucks. Figure 1-17 shows an industrial hydraulic lift truck with a 5000-lb capacity. The hydraulic system includes dual-action tilt cylinders and a hoist cylinder. Tilting action is smooth and sure for better load stability and easier load placement. A lowering valve in the hoist cylinder controls the speed of descent even if the hydraulic circuit is broken. Hydrostatic power steering is available as an optional feature.7. Fluid power drives front-end loaders. Figure 1-18 shows a front-end loader filling a dump truck with soil scooped up by a .large hydraulic-powered bucket. Excellent load control is made possible with a specially designed flow control valve. The result is low effort and precise control; this keeps the operator working on the job longer and more efficiently. Thus, reduced operator fatigue results in increased production8. Hydraulics power robotic dextrous arm. Figure 1-19 shows a hydraulically powered robotic arm that has the strength and dexterity to torque down bolts with its fingers and yet can gingerly pick up an eggshell. This robotic arm is adept at using human tools such as hammers, electric drills, and tweezers and can even bat a baseball. The arm has a hand with a thumb and two fingers, as well as a wrist, elbow, and shoulder. It has ten degrees of freedom, including a three-degree-of-freedom end effector (hand) designed to handle human tools and other objects with human-like dexterity. The servo control system is capable of accepting computer or human operator control inputs. The system can be designed for carrying out hazardous applications in the subsea, utilities, or nuclear environments, and it is also available in a range of sizes from human proportions to 6 ft long.1.5COMPONENTS OF A FLUID POWER SYSTEMHydraulic SystemThere are six basic components required in a hydraulic system:1. A tank (reservoir) to hold the liquid, which is usually hydraulic oil.2. A pump to force the liquid through the system.3. An electric motor or other power source to drive the pump.4. Valves to control liquid direction, pressure, and flow rate.5. An actuator to convert the energy of the liquid into mechanical force or torque to do useful work. Actuators can either be cylinders to provide linear motion, as shown in Fig. 1-20, or motors (hydraulic) to provide rotary motion, as shown in Fig. 1-21.6. Piping, which carries the liquid from one location to another.Of course, the sophistication and complexity of hydraulic systems will vary depending on the specific applications. This is also true of the individual components that comprise the hydraulic system. As an example, refer to Fig. 1-22, which shows two different-sized, complete, hydraulic power units designed for two uniquely different applications. Each unit is a complete, packaged power system containing its own electric motor, pump, shaft coupling, reservoir and miscellaneous piping, pressure gages, valves, and other components as required for proper operation. These hydraulic components and systems are studied in detail in subsequent chapters.Pneumatic SystemPneumatic systems have components that are similar to those used in hydraulic systems. Essentially the following six basic components are required for pneumatic systems:1. An air tank to store a given volume of compressed air2. A compressor to compress the air that comes directly from the atmosphere3. An electric motor or other prime mover to drive the compressor4. Valves to control air direction, pressure, and flow rate5. Actuators, which are similar in operation to hydraulic actuators6. Piping to carry the pressurized air from one location to anotherFigure 1-23 shows a compact, self-contained pneumatic power unit complete with tank, compressor, electric motor, and miscellaneous components such as valves, piping, and pressure gages.It should be noted in pneumatic systems that after the pressurized air is spent driving actuators, it is then exhausted back into the atmosphere. On the other hand, in hydraulic systems the spent oil drains back to the reservoir and is repeatedly reused after being repressurized by the pump as needed by the system.1.6CLOSED-LOOP VERSUS OPEN-LOOP SYSTEMSFluid power systems can be either the closed-loop or open-loop type. The following describes these two types of fluid power systems.Closed-Loop SystemA closed-loop system is one that uses feedback. This means that the state of the output from the system is automatically sampled and compared (fed back) to the input or command signal by means of a device called a feedback transducer. If there is a difference between the command and feedback signals, action is taken to correct the system output until it matches the requirement imposed on the system. Closed-loop systems are frequently called servo systems, and the valves used to direct fluid to the actuators are typically called servo valves.Open-Loop SystemAn open-loop system does not use feedback. The output performance of the system therefore depends solely on the characteristics of the individual components and how they interact in the circuit. Most hydraulic circuits are of the open-loop type, which are generally not so complex or so precise as closed-loop systems. This is because any errors such as slippage (oil leakage past seals, the magnitude of which depends on system pressure and temperature) are not compensated for in open-loop systems. For example, the viscosity of a hydraulic fluid decreases (fluid becomes thinner) as its temperature rises. This increases oil leakage past seals inside pumps, which, in turn, causes the speed of an actuator, such as a hydraulic motor, to drop. In a closed-loop system, a feedback transducer (for example, a tachometer, which generates a signal proportional to the speed at which it is rotated) would sense this speed reduction and feed a proportional signal back to the command signal. The difference between the two signals is used to control a servo valve, which would then increase the fluid flow rate to the hydraulic motor until its speed is at the required level.1.7 TYPES OF FLUID POWER CONTROL SYSTEMSFluid power systems are also classified by the type of control system utilized. There are three basic types of fluid power control systems: electrical, fluid logic, and programmable logic. The following is a brief description of each of these three control systems.Electrical Control SystemThis type of fluid power control system is characterized by the fact that the fluid power system interacts with a variety of electrical components for control purposes. For example, electrical components such as pressure switches, limit switches, and relays can be used to operate electrical solenoids to control the operation of valves that direct fluid to the hydraulic actuators. An electrical solenoid control system permits the design of a very versatile fluid power circuit. Automatic machines such as those used in the machine-tool industry rely principally on electrical components to control the hydraulic muscles for doing the required work. The aircraft and mobile equipment industries have also found that fluid power and electricity work very well together, especially where remote control is needed. By merely pressing a simple push-button switch, an operator can control a very complex machine to perform hundreds of machinery operations to manufacture a complete product. An electrically controlled fluid power system can be either of the open-loop or closed-loop type, depending on the precision required.Fluid Logic Control SystemThis type is characterized by the fact that the fluid power system interacts with fluid logic devices instead of with electrical devices for control purposes. Two such fluid logic systems are called “moving-part logic (MPL)” and “fluidics,” which perform a wide variety of sensory and control functions. Fluid logic devices switch a fluid, usually air, from one outlet of the device to another outlet. Hence an output of a fluid logic device is either ON or OFF as it rapidly switches from one state to the other by the application of a control signal.MPL devices are miniature valve-type devices that, by the action of internal moving parts, perform switching operations in fluid logic systems. These MPL devices can be actuated by means of mechanical displacement, electric voltage, or fluid pressure. Figure 1-24 shows an electronic-driven MPL valve that readily interfaces with electric and electronic circuits. This valve converts low-voltage (12 to 24 V) signals into high-pressure (100 psi ) pneumatic outputs. The total travel of the poppet (the only moving part) is a mere 0.007 in. As a result, low power consumption (0.67 W) and long life are major benefits of this design. Additionally, the very fast response time (5-10 ms) and small size make this MPL valve well suited for a wide range of applications in biomedical, environmental test equipment, textile machines, packaging machinery, computerized industrial automation, and portable systems.Figure 1-25 shows how either 8 or 12 of the electronic valves of Fig. 1-24 can be mounted on a manifold card to provide added convenience in interfacing electronics with pneumatics. The self-contained card includes a manifold mount for single air supply, a fully wired circuit board, and instant plug-in with a 25-pin RS-232 connector. This system allows low-voltage signals from controllers, computers, or other sources to operate pneumatic valves with a minimum of piping and hookup.The second fluid logic system, fluidics, utilizes fluid flow phenomena in components and circuits also to perform a wide variety of sensory and control functions. Fluidic components (when kept free of contaminants, which can obstruct critical air passageways) are reliable because they contain no moving parts.Fluidics is an offshoot of fluid power technology and is equivalent to electronics as an offshoot of the technology of electrical power. Just as electronic devices use tiny currents as opposed to the huge currents flowing in electrical power lines, fluidic devices use small flow rates at low pressures in contrast to the high pressure and large flow rates required to operate a huge hydraulic press. Fluidic systems (unlike electrical controls) cannot cause fire hazards due to sparks in a potentially explosive environment. Because they operate with fluids, fluidic components also interface readily within fluid power systems.Programmable Logic Control SystemIn this type, programmable logic controllers (PLCs) are used to control system operation. In recent years, PLCs have increasingly been used in lieu of electromechanical relays to control fluid power systems. A PLC is a user-friendly electronic computer designed to perform logic functions for controlling the operation of industrial equipment and processes. A PLC consists of solid-state digital logic elements for making logic decisions and providing corresponding outputs. Unlike general-purpose computers, a PLC is designed to operate in industrial environments where high ambient temperature and humidity levels may exist. PLCs offer a number of advantages over electromechanical relay control systems. Unlike electro-mechanical relays, PLCs are not hard-wired to perform specific functions. Thus, when system operation requirements change, a software program is readily changed instead of having to physically rewire relays. In addition, PLCs are more reliable, faster in operation, smaller in size, and can be readily expanded.Figure 1-26 shows a PLC-based synchronous lift system used for precise lifting and lowering of high-tonnage objects on construction jobs. Unlike complex and costly electronic lift systems, this hydraulic system has a minimum number of parts and can be run effectively and efficiently by one person. The PLC enables the operator to quickly and easily set the number of lift points, stroke limit, system accuracy, and other operating parameters from a single location. The PLC receives input signals from electronic sensors located at each lift point, and in turn sends output signals to the solenoid valve that controls fluid flow to each hydraulic cylinder to maintain the relative position and accuracy selected by the operator. Because the sensors are attached directly to the load, they ensure more exact measurement of the load movement. The system accommodates a wide range of loads and is accurate to 0.040 in. (1 mm).The PLC unit of this system (see Fig. 1-27) contains a LCD display that shows the position of the load at each lift point and the status of all system operations so the operator can stay on top of every detail throughout the lift. The PLC unit, which weighs only 37 pounds and has dimensions of only 16 in. by 16 in. by 5 in., can control up to eight lifting points. The system diagram is shown in Fig. 1-28, in which components are identified using letters as follows:A: Programmable logic controllerB: Solenoid directional control valveC: Electronic load displacement sensorsD: Sensor cablesE: Hydraulic cylinders with flow control valves to regulate movement.中文翻译液压动力的介绍1.1什么是液压动力?液压动力是应用世代的, 控制以及传递被压液体力量的使用的技术。也可以说动力是移动产业的肌肉。这是因为液压动力被用于推, 拉, 控制, 或驱动实际上现代产业所有机器。例如, 液压动力操舵和闸汽车, 发射航天器, 收获庄稼, 开采煤炭, 驾驶机械工具, 控制飞机, 处理食物, 甚至钻牙。实际上, 几乎不可能发现在某个方面某一阶段不是流压动力 生产或发行的一件工业制造品。因为流体可能是液体也可能是气体, 液压动力实际上是通常规定被使用。液压机构使用液体譬如石油, 水, 综合性油, 甚至熔融金属。水作为第一液压机液体被使用是因为它是简单可利用的。但是, 水有许多缺点。它容易结冰，是相对较差的润滑剂, 并且倾向于锈蚀金属成分。水力油是因为优越性因此被广泛代替水来使用。气动系统使用空气作为气体媒介是因为空气是非常丰富的, 可能容易被用尽而进入大气。我们应该体会,实际上有二不同类型可变的系统: 液压运输和液压动力。液压运输系统它们的唯一宗旨是流体从一个地点到另一个的传递来实现一些有用的目的。例子包括泵站为家庭抽水，连接横穿全国的天然气管道, 并且会从系统化学制品处理发生的地方把各种各样的流体被带来。液压动力系统为进行具体的工作而设计。工作由被一个运行的液压泵或液压马达直接承载的被压液体完成。一个液压泵产生力量, 而一个液压马达产生扭矩。液压泵或液压马达提供力量完成预期的工作。当然, 控制组分也需要必要保证, 工作能被顺利地，准确地, 高效率地, 并且安全地完成。液体为传送力量和因提供巨大的力量来最大准确性和精确度供给一个非常刚性的媒介。另一方面, 气动系统表现出吸水的特征是由于空气的压缩性。而且, 气动系统修造和运行是较不昂贵的，另外用于添加供应可能被做控制驾驶装载气动力学的作动器的操作。液压动力设备排列范围大小从巨大的水力信息到用于建立可靠的控制系统的微型液压逻辑元件。什么是液压动力的多样性？一种多功能多种使用方法的液压动力是根据畜生力量, 是操作员用羽毛接触可能控制上百马力和把它传达给水喉或管子的任一个地点。用精确度譬如应用在机械工具产业, 容忍一英寸的一千分之十可能多次达到和被重复。液压动力不仅仅是一块强有力的系统; 它是受控的, 能顺利地提供力量的灵活地，系统地, 高效率地, 安全地, 并且精确地完成有用的工作。通常显示一只气动力学地受控灵巧手用于设计学习机器手巧和人的操作在应用譬如机器人学和有触觉感觉。伺服气动力学的作动器给类似人手掌握的和操作的能力。关键工作特征包括高速在执行操作任务, 掌握手的力量很容易的估量了有变化的密度的对象, 还有力量掌握控制手拥有三个手指和一个反对的拇指, 每个以四个自由程度。各联接由二台气动力学的作动器安置(位于作动器叠板与控制的伺服阀门) 驾驶高强度腱。表现和配置限制关于重量, 大小, 几何, 洁净, 并且各自的作动器的可及性引导了气动力学的驱动选择。1.2 液压动力的历史液压动力大概是一老的象文明样。古老历史记录可被表明, 是通过水被使用在几个世纪中通过水轮产生力量, 还有空气被使用于转动风车和推进船。但是, 这些对液压动力早期应用同为自然提供的相对低压而需要大量液体。液压动力技术实际上开始在1650 年的帕斯卡定律的发现上: 压力被未衰减地传送于流体的一个约束体上。帕斯卡发现于，当他把软木塞塞入装满水的水罐, 水罐的底部被打破掉下来了。帕斯卡定律表明, 压力在水罐的上面和底部是相等的。但是, 水罐有一个小口和一个大区域在底部。因而, 底部吸收更加巨大的力量作用于它的更大的区域。1750 年, 比牛里发现了在管道中的流动流体能量守恒定律。帕斯卡的定律和比牛里的定律作用在所有液压动力应用的核心和被使用为分析目的。但是, 不是直到1850 的在英国工业革命年, 这些定律对于产业没有实际上的运用。由这时间决定, 电能未被发展供给产业动力机器。 反而, 这时的液压动力在1870 年以前, 被使用于驱驶水力设备譬如起重机, 水轮, 绞盘, 挤压来启动各种各样的机器的机器, 水力起重器, 剪切机器, 还有铆定机器。在这些系统, 蒸汽引擎驱驶水力水泵,以适度压力通过管子投递水作用于工厂设备。这些早期的液压机构有一定数量的缺点譬如密封问题因为设计更演变为艺术而非科学。然后, 在19 世纪, 电作为一种统治技术。这导致开发努力从液压动力转移。电能很快被发现在远距离传动上比动水学优越。因此在19 世纪的最后10 年间液压动力技术有很少发展。现代液压动力液压动力被认为开始于1906年美国弗吉尼亚在战舰上被开发替换电气系统的为举起和控制火炮上的一种液压机的应用, 液体系统开发了废旧石油代替水。这个变化在液压机液体上和密封问题的相应解答是在液压动力的重生的重大里程碑。美国在1926首先开发统一化, 被包装的水力系统包括泵，控制器, 还有制动器。军方要求主导由第二次世界大战被保留的液压动力应用和发展去努力。海军工业使用了液压动力来提升货物, 绞盘, 推进器控制, 水下控制系统, 舰上航空器电梯的操作液压动力技术, 并且为雷达和声纳系统驱动。在世界大战中和之后航空和航天工业的前进提供了动力。例子包括水力开动的起落架, 货物门, 枪驱动, 并且飞行控制从它的发射台设备譬如为航空器的船舵, 飞机辅翼, 还有升降舵补腾飞助翼。它可以显示哥伦比亚空间站由流体推力力量供给动力。 航天飞机象火箭离开并且飞过轨道后更换位置后象太空飞船一样在地球附近环绕。在完成它的使命以后它象飞机一样降落在跑道上。不同于更加早期的只能飞行一次的人造飞行器, 人造卫星和火箭助推器可以多次使用。唯一外在动力被消费在各次发射上。它可以提供航天飞机的一张局部剖视图, 辨认它的主要组分, 以及许多水力开动。跟随着第二次世界大战后经济的发展导致了今天液压动力被广泛地使用在每个实际产业部门。一些典型的应用是在汽车里, 拖拉机, 飞机, 导弹, 船舶, 并且机械工具。在汽车中, 液压动力被运用在水力闸, 汽车传动, 力量指点, 力量闸, 空调, 润滑, 水蓄冷剂, 还有汽油泵装置。对现代技术的创新用途譬如电动液压的闭环系统, 微处理器, 还有改善的材料为构建建筑将继续推进液压动力系统表现。工作压力由力量指点泵浦提供，与氢结合促进提供力量协助操作为一个双重大师圆筒制动系统。通常登上在引擎隔间防火墙, 它被设计提供具体闸感觉 特征在大范围脚蹬力量过程中和旅行中。春天积蓄存放能量为反向中止。从一到三中止是可利用闸应用的依存在巨大和期间。 这个系统由比那思公司开发了作为对拥挤引擎隔间的一个答复和替换大真空单位。1.3 液压动力好处有传送功率三个基本的方法: 电子, 机械, 还有液压动力。多数应用实际上使用三个方法的组合获得最高效率的整个系统。适当地确定原则方法使用, 它重要的是知道各型明显特点。举个例子, 液压动力系统比能机械型可能更加经济。但是, 液压动力系统比电气系统被限于更短的距离。液压动力的成功和普遍用途秘密是它的通用性和可管理性。液压动力不被机器的几何形状所妨碍, 象在机械系统一样。并且, 功率象电气系统可能以几乎不可限量传送因为液压动力系统不是那么由材料的物理局限限制。例如,电磁是由钢饱和极限限制表现。另一方面, 可变的系统功率容量只由材料的物质各个组分限制(譬如钢)。产业越来越自动化是为了提高生产力。这包括生产操作远程和直接控制, 制造过程, 及原材料处理。液压动力在自动化的系统有以下四个主要作用：1. 限制和控制准确度。由对简单的杠杆和推挤键的用途, 一个液压动力系统的操作员能简单开始, 停止, 加速或减速, 并且向一英寸的一千分之十提供任一期望的马力来移动到精确位置。可用图显示为航空器飞行员升高和降低他的起落架的一个液压动力系统。当飞行员移动一个小控制阀在一个方向, 油在压力下流动到液压缸的一个末端来降低起落架。缩回起落架, 飞行员在相反方向移动阀门杠杆, 允许油流动入液压缸的另一末端。2. 力量的增植。一个液压动力系统(没有使用笨重齿轮, 滑轮, 及杠杆) 可能简单和高效率地倍增力量从一盎司的十分之一到几百吨的力量增值为处理巨大的日志的一种强有力的坚固性的应用驱动。在这种情况下, 转盘, 被水力马达驱动, 可能用于运载20,000 磅（装载在200,000 牛.米扭矩）概略的操作条件。3. 恒定的力量或扭矩。只有液压动力系统即使在速度变动的情况下提供恒定的力量或扭矩。 这可成功确定是否将工作产品每小时移动几英寸, 每分钟几百英寸, 每小时旋转几次, 或数以万计转每分钟。我们可以描述一种使用在对海洋的资源勘探和发展为人类的目的海洋学方面。在这种场合, 它是为操作员应用恒定的绝对的力量通过对揪打的勾子的重要用途。4. 朴素, 安全, 经济。总之, 液压动力系统使用少移动的部份比可比较的机械或电气系统。因而, 他们更加容易简单维护和经营。这, 反过来,是最大化安全, 机秘, 并且可靠的。图样显示功率指点控制被设计为高速公路车。由于指点单位充分地流体连接, 机械联结, 普遍联接, 轴承, 减少齿轮, 等。这提供一简单, 紧凑系统。另外, 很少输入扭矩必将引起控制需要成为最坚韧的应用。这重要控制空间的局限要求在一个小方向盘的地方并且它变得必要减少操作员疲劳。液压动力缺点：尽管液压动力所有这些高度集中的特点, 这不是只概括为为所有输电问题，液压机构有一些缺点。水力油杂乱, 并且漏出无法完全地消除。水力线可能破裂, 可能由于产生高速油喷气机和飞行金属伤害人民,。譬如对从泵浦发出喧闹声长时期的暴露, 能导致听力损失。并且, 多数水力油罐起因火如果石油泄漏发生在热的设备区域。所以, 各配置必须周到地被学习确定最佳的整体设计。预期, 这本书不仅将协助读者在开发能力做这些型系统选择决定而且提出用一个直接的方式技术为设计, 分析, 并且查明故障基本的液压动力系统。1.4 液压动力的应用虽然液压动力一定数量的案件已经被提出在这个章节里, 以下另外的应用应该给读者对液压动力的普遍用途在今日世界里的一个大观。1. 液压动力驾驶高导线顶上的电车。 多数顶上的电车要求货车使用费或拖曳缆绳旅行或下来陡峭的斜面。 但是, 22 个乘客, 12000 磅水力供给动力和受控天空电车被显示无结果是独特的。它自走和旅行在一固定式缆绳，由于电车行动代替缆绳, 操作员能停止, 开始, 并且完全地独立地扭转任一一辆汽车其他汽车在电车系统。积分式对天空电车驱动的设计是泵浦(被一个标准八缸引擎驾驶),供应加压了流体对四个水力马达。各自动驾驶两个摩擦驱动轮。八个驱动轮在缆绳支持顶部和推进电车汽车。在陡峭的斜面, 高驾驶扭矩必需为上升并且高刹车的扭矩为下降。四个水力马达的双重报偿提供高效率适宜可利用的马力适应易变的扭矩需要。2.液压动力申请收获玉米。对美国的世界的食物依赖性导致对农业设备发展的巨大需求。 液压动力被申请解决许多问题应付收获食用农作物。对无盖货车拖车一个水力被驾驶的提升传动机系统,使用于收获, 剥壳的玉米穗。登上直接地对链子驾驶传动机, 水力马达从起动把充分的动力投递于充分扭矩转台式功率。3.动水学功率刷子驱动。各种各样的工业地点可变的电力带动的刷子驱动被使用为清洁路, 地板, 等。登上直接地在前线和边的插孔清扫洗刷刷子, 紧凑水力马达安置功率权利于需要它
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