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1、1,单词复习：1. engine lathe2. carriage/stop4. piston5. turret6. Cross slide7. forging/bar stock8. collet/chuck,上一课回顾,2,Lesson 10 Motors and Drivers 电机和驱动,重点词汇： diesel di:zl n.柴油机 synchronous /asynchronous eisikrns angular velocity strip 带、条 slider-crank 曲柄滑块 gasoline engines 汽油机 pneumatic nju(:)mtik 气动的,
2、3,Paragraph 1,All of the mechanisms will require some drivers to provide the input motion and energy.There are many possibilities. 所有机构都需要某种形式的驱动装置提供动力和运动。有许多种选择。If the design requires a continuous rotary input motion, such as for a slider-crank(曲柄滑块) or a cam-follower(凸轮随动件), then a motor is the lo
3、gical choice. 像曲柄滑块机构、凸轮机构，如果需要输入连续的旋转运动，那么选择发动机是合理的。,4,Paragraph 2:,Motors come in a wide variety of types.The most common energy source for a motor is electricity, but compressed air and pressurized hydraulic fluid are also used to power air and hydraulic motors.发动机有各种各样的类型。发动机最一般的能源是电，压缩空气和具有一定压力
4、的液体也常用于气动和液压马达。,5,Gasoline or diesel engines(汽油和柴油机) are another possibility. Electric motors are made in several designs, among which are AC, DC, servo, and stepping. 汽油机和柴油机是另一选择。电机也有像交流/直流电机、伺服电机步进电机几种形式。,6,Paragraph 3:,AC and DC refer to alternating current and direct current respectively. AC is
5、 typically supplied by the power company(动力公司) and, in the U. S., will be alternating at 60 hertz, at about 110volts or 220 volts.AC和DC分别指交流电和直流电。交流电一般由电厂（电力公司）提供，在美国交流电是60HZ、110V或 220V 。,7,Paragraph 4:,AC motors are the most inexpensive solution to continuous rotary motion, and there are a variety
6、of torque-speed curves(扭矩速度曲线) to suit various applications. 交流电机是得到连续旋转运动的最经济选择，有各种转矩速度曲线适应不同载荷。They are limited to a few speeds, which are a function of the 60 Hz AC line frequency. 交流电机有有限的几种速度，这是60HZ交流电源的作用结果。,8,The most common AC motor no load speeds are 1725 and 3450 revolution per minute (RPM
7、), which represent some slippage(转差率) from the more expensive synchronous AC motor speeds of 1800 and 3600 rpm.最普通的交流电机零负载时速度为1725和3450 rPm，这同较贵的速度为1800rPm和3600rPm的同步交流电机比有一定的转差率。 If other speeds are needed, a gearbox speed reducer(减速器) is attached to the motors output shaft. 如果需要输出其它速度，可在电机输出轴上装一齿轮
8、减速器来解决。,9,Paragraph 5,DC motors are made in different electrical configurations, which provide differing torque-speed characteristics. The torque-speed curve of a motor describes how it will respond to an applied load.直流电机有几种不同的配置，提供几种不同的转矩速度特性。转矩速度描述了直流电机如何与负载一致。,10,Figure 1a shows such a curve for
9、 a permanent magnet (PM永磁的) DC motor. Note that the torque varies greatly with speed, ranging from maximum torque at zero speed to zero torque at maximum speed. 图1a 所示为永磁直流电机特性曲线。转矩随速度变化较大，范围从零转速时最大转矩到最大转速时的零转矩。,(a)Speed-Torque characteristic of a PM electric motor,Figure 1 Speed-Torque curve,Paragr
10、aph 6,11,This relationship comes from the fact that Power =Torque Angular Velocity. Since the power available from the motor is limited, an increase in torque requires a decrease in angular velocity and vice versa.这种关系来自于关系式：动力 = 转矩 角速度 因为动力是一定的，转矩增大要求角速度减小，反之亦然。,vice versa vaisi v:s反之亦然We gossip ab
11、out them and vice versa (=they gossip about us).,12,Paragraph 7,Figure 1b show a family of load lines superposed on the torque speed curve of the motor. 图 1b 所示为在电机转矩速度曲线上的一组负载线。,(b) Load lines superposed on a speed-Torque curve,Figure 1 Speed-Torque curve,13,These load lines represent a changing lo
12、ad applied to a mechanism, which the motor must supply. 这些负载曲线表示电机提供的作用到机构上的载荷变化。 The problem comes from the fact that as the required torque (load) increase, the motor must reduce speed to supply it. 这一变化的根据是：随着需要的负载转矩增加，电机输出的速度必须减小来适应这种变化。,14,Thus the input speed will vary in response to load vari
13、ation. 这样速度将随着负载变化。If constant speed is desired, this is unacceptable.若需要速度恒定是不现实的。,15,One possible solution is to use a speed-controller DC motor which contains circuitry(回路) that increase and decrease the current to the motor in the face of changing load to try to maintain constant speed.一种可能的解决方案
14、是使用速度控制的直流电动机，它有一电路系统随着电机负载的变化增大或减小输入给电机的电流以试图保持恒定的速度。,Paragraph 8,16,These DC motor will run from an AC source since the controller converts AC to DC.The cost of this solution is high, however.控制器将交流电转化为直流电，因此这些直流电机的运行需要交流电源，成本较高。Another solution is to provide a flywheel on the input shaft, which w
15、ill store kinetic energy and help smooth out the speed variations introduced by the load variations. 另一种方案是在输入轴上安装飞轮，储存动能来平缓负载变化引起的速度波动。,17,Paragraph 9,These AC and DC motors are designed to provide continuous rotary output. Though they can be stalled against a load, they will not tolerate a full-cu
16、rrent, zero-velocity stall for more than a few minutes without overheating.这些交流和直流电机用于输出连续的旋转运动。虽然电机负载增大时速度可降低，但不可能实现全电流、零速度停车超过几分钟而不过热。,18,Paragraph 10,Servomotors are fast response, closed-loop(闭环) controlled motors capable of providing a programmed function of acceleration or velocity, as well as
17、 holding a fixed position against a load. 伺服电机是一种快速反应，闭环控制的电机，具有可编程控制速度、加速度的功能，也可以通过固定位置来应对载荷变化。,19,Closed loop means that sensors on the output device being moved feed back information on its position, velocity, and acceleration. 闭环的意思是移动输出装置上的传感器能给出位置、速度、加速度的反馈信息。Circuitry in the motor controller
18、responds to the fed back information by reducing or increasing (or reversing) the current flow to the motor. 电机控制装置中电路通过增加或减小（反向）进入电机的电流，对反馈信息作出反应。,20,Thus precise positioning of the output device is possible, as is control of the speed and the shape of its time responds to changes in load or input
19、commands. 这样输出装置处于精确的位置是可能的。同时控制了速度、对载荷变化和输入指令的反应时间。,21,These are very expensive devices and commonly used in applications such as moving the flight control surfaces in aircraft and guided missiles. 这是一种很昂贵的装置，一般用在像移动在飞行器和巡航导弹中的飞行控制操作台。These are relatively small and have lower power and torque capac
20、ity compared to larger AC/DC motors. 和大直流/交流电机相比，这种电机体积小、功率和输出转矩也较小。,22,Stepping motors are designed to position an output device. Unlike servomotors, these are open loop, meaning they receive no feedback as to（至于，关于） whether the output device has responded as required. 步进电机用于定位输出装置。不像伺服电机它是开环控制，意思是
21、无论输出装置是否按要求动作，都没有反馈。,Paragraph 11,23,Their internal construction consists of a number of magnetic strips（磁条） arranged around the circumference of both the rotor and the stator. 内部结构包括在定子和转子的圆周上分布的很多磁条。When energized, the rotor will move one step, to the next magnet, for each pulse received. 每接收一个脉冲，
22、转子转动一步（一定角度）到达下一个磁体。,24,Thus these are intermittent motion devices and do not provide continuous rotary motion like other motors. 这样它成为一个间歇运动装置，不像其它电机一样提供连续的旋转运动。The number of magnetic strips determines the resolution (typically a few degrees per step). 磁条的数量决定了分度大小。,25,They are relatively small com
23、pared to AC/DC motors and have low torque capacity. They are moderately expensive and require special controllers. 和交直流电机相比，体积小、输出转矩小。它不算太贵，要求特殊的控制器。,26,Paragraph 12,Air and hydraulic motors have more limited application than electric motors, simply because they require the availability of compresse
24、d air or hydraulic source. 气动和液压马达和电机相比应用很有限，是因为它需要压缩空气和液压源。,27,Both of these devices are less energy efficient than direct electric to mechanical conversion of electric motors, because of losses associated with the conversion of the energy first from chemical or electric to fluid pressure and then
25、to mechanical form. 同利用电机直接转化为机械能相比，这些装置的能量利用率较低，这是因为首先化学的或电的能量转化为流体压力，然后转化为机械能，这些相关的转换会有损耗。,28,Every energy conversion involves some losses. Air motors find widest application in factories and shops, where high-pressure compressed air is available for other reasons. 每种能量转换都会有一些损失。在工厂和车间里，高压空气因有其它用途
26、，可以方便获取，所以气动马达得到广泛应用。A common example is the air impact wrench used in automotive repair shop. 一个最普通的例子是在自动化维修车间使用的气动扳手。,29,Although individual air motors and air cylinders are relatively cheap, these pneumatic systems（气动系统） are quite expensive when the cost of all the ancillary equipment is include
27、d. 虽然气压缸和气动马达都比较便宜，但计入所有辅助装置的成本，这些气动系统是很贵的。,30,Hydraulic motors are most often found within machines or systems such as construction equipment (cranes), aircraft, and ships, where high-pressure hydraulic fluid is provided for many purposes. 液压马达常用于像建筑设备（起重机）、飞行器和轮船等机器和系统中，在这些系统中高压液体有多种用途。,31,Hydraul
28、ic systems are very expensive when the cost of all the ancillary equipment is included. 计入所有辅助设备的成本，液压系统也是很贵的。,32,Paragraph 13,Air and hydraulic cylinder are liner actuators (piston in cylinder), which provide a limited stroke, straight line output from a pressurized fluid input of either compressed
29、 air or hydraulic fluid (oil). 气压和液压缸是一线性执行机构（活塞在缸体内），它可实现有限行程的直线运动，由工作介质为压缩空气或液压油的加压流体驱动。,33,They are the method of choice if you need a linear motion input. However, they share the same high cost, low efficiency, and complication factors as listed under their motor equivalents above. 如果你需要直线运动这是一种
30、选择。然而它们都是成本高、效率低、具有像上述电机一样的复杂因素。,34,Another problem is that of control. Most motors will tend to run at a constant speed. 另一个问题是它们的控制。大多数发动机倾向于恒速运行。A linear actuator，when subjected to a constant pressure source, typical of most compressors, will respond with more nearly constant acceleration, which
31、means its velocity will increase linearly with time. 在恒压流体源典型的如大多数压缩机作用下，执行机构将得到一个几乎恒定的加速度，这意味着速度将随时间线性增加。,Paragraph 14,35,This can result in severe impact loads on the driven mechanism when the actuator comes to the end of its stroke at maximum velocity. 执行机构以最高速到达行程末端时，对驱动机构产生剧烈的冲击。Servo-valve(伺服阀) control of the fluid flow, to slow the actuator at the end of its stroke, is possible but quite expensive. 为了放慢执行机构在行程末端的速度，用伺服阀控制流体流动是可行的，但是很昂贵。,36,课后作业：,1、复习本课单词，预习下一课单词,
