【正文】 a very fine mist of oil into the air discharging from the pressure regulator．This prevents wear of the closely fitting moving parts of pneumaticHydraulic systems ale used in industrial applications such as stamping presses，steel mills，and general manufacturing，agricultural machines，mining industry，aviation，space technology，deep—sea exploration, transportation，marine technology，and offshore gas and petroleum exploration．In short，very few people get through a day of their 1ives without somehow benefiting from the technology of hydraulics2．The principle of electricaldischarge machining also called electro is or sparkerosion machining, is based on the erosion of metals by spark discharges. We know that when two currentconduct in wires are allowed to touch each other, an arc is produced. If we look closely at the point of contact between the two wires, we note that a small portion of the metal has been eroded away, leaving a small crater.The basic EDM system consists of a shape tool and the workpiece, connected to a dc power supply and placed in a dielectric fluid this is one of the most widely used machining processes, particularly for diesinking operations when the potential difference between the tool and the work piece is sufficiently high, a transient spark discharges through the fluid, removing a very small amount of metal from the work piece surface.The capacitor discharge is repeated at rates of between 50,with voltages usually ranging between 50vand 380v and currents from to 500A.Mechanical control includes cams and governors. Although they have been used for the control of very plex machines, to be cost effectively, today they are used for simple and fixedcycle task control. Some automated machines, such as screw machines, still use cambased control. Mechanical control is difficult to manufacture and is subject to wear.Pneumatic control is still very popular for certain applications. It uses pressed air, valves, and switchs to construct simple control logic, but is easily slow. Because standard paonents are used to construct the logic, it is easier to build than a mechanical control . Pneumatic control parts are subject to wear.As does a mechanical control, an electromechanical control uses switches, relays, times counters, and so on, to construct logic, it is faster and more flexible. The controllers using electromechanical control are called relay devices.The values in the express the relative tool distance from the home position. This distance is shown in the relative or incremental coordinates, U and W. when reading the values in the not possible to know directly how far the tool is from the part origin. Just how far it is from the home position. mounted on exhaust ports of air valves and actuators to reduce noise and prevent operating personnel from possible injury resulting not only from exposure to noise but also from high—speed airborne sign of the coordinates is zero or negative because the tool cannot move farther than the machine origin . thus at present , the values are zero so the tool is at the home position. The values in the are normally used when setting up the tools in order to find the real tool distances from the part origin.The values in the absolute position express the absolute tool distance from the part origin. This distance is shown in shown in absolute coordinates, x and z .the sign may be positive or negative, depending on the quadrants in which the tool is moving. because of the pressibility of air，it is impossible to obtain precise controlled actuator velocities with pneumatic systems．a(chǎn)lso，precise positioning control is not obtainable．While pneumatic pressures are quite so far is to good. This is an important piece of information for the operator when maching, since any value in the absolute position is directly related to the part.The secret of hydraulic system’s SUCCESS and widespread use is its versatility and manageability．Fluid power is not hindered by the geometry operations when the potential difference between the tool and the work piece is sufficiently high, a transient spark discharges through the fluid, removing a very small amount of metal from the work piece of the machine as is the ease in mechanical systems．Also，power can be transmitted in almost limitless quantities because fluid systems are not so limited by the physical 1imitations 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 limit of fluid systems is 1imited only by the strength capacity of the material．In the express the relative tool distance from the home position. This distance is shown in the relative or incremental coordinates, U and W. when reading the values in the not possible to know directly how far the tool is from the part origin. Just how far it is from the home position. The sign of the coordinates is zero or negative because the tool cannot move farther than the machine origin . thus at present , the values are zero so the tool is at the home position. The values in the are normally used when setting up the tools in order to find the real tool distances from the part origin.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。 flow control valves including throttle, adjusting the valves, flow diversion valve sets, etc.。 載荷種類原動機(jī)電動機(jī)或汽輪機(jī)內(nèi)燃機(jī)載荷平穩(wěn)中等沖擊較大沖擊排數(shù)123456取，由機(jī)械設(shè)計手冊得，、則 A系列滾子鏈的許用功率曲線：雙排鏈。最小中心距受小鏈輪上包角的限制，通常?。海?4） 則 鏈條長度用鏈節(jié)數(shù)表示： （45）初取中心距，則鏈接數(shù)為：鏈接數(shù)必須取為整數(shù)，最好取為偶數(shù)，以避免使用過渡鏈節(jié)。滾子鏈傳動的傳動比為： （41） 式中 ——傳動比； ——小鏈輪轉(zhuǎn)速，； ——大鏈輪轉(zhuǎn)速，； ——小鏈輪齒數(shù)； ——大鏈輪齒數(shù)；因為所以得小鏈輪齒數(shù)為：