结论
步进电机的主要优点是定位精度高，无积累位置误差，其开环运行的机制大大减少了系统成本。但是存在着缺点:转速不够平稳运行会发生振荡现象。通过对步进电机的实测分析得知:
1.步进电机启动时突加高频脉冲信号，电机会产生啸叫、失步、甚至不能启动，而电机由高速运转突然停车时，即由高频脉冲骤然降至零脉冲，电机也会产生啸叫、振动。步进电机在输入脉冲200Hz左右时，处于振荡区容易损坏内部元器件，在2(X)F位以下运转速度慢、效率低，所以将350Hz作为脉冲低频起点，经测试，轻载时脉冲高频顶点可达到lOkHz，重载时脉冲高频顶点可达到6.6KHz
2.消除振荡的方法有阻尼法、多相励磁法、变频变压法、细分步法、反相阻尼法等。阻尼变化对低频振荡的影响可以看出，增大阻尼有利与振荡的衰减。低频振荡受升速频率的影响较小。降速过程的振荡小于升速过程的振荡，因此升速过程是引起振荡失步的主要环节
3.减小步进电机的步距角有利于提高步进电机的带负载能力。当电机和负载已经确定之后，整个驱动系统的性能就完全取决于驱动电源和控制方法。目前各种步进电机控制电路和方法很多，控制效果最好的应首推细分控制法，步进电机细分驱动可减少振动，提高步距精度。
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参 考 文 献
[1] 陈正宏，韩德源等.步进电机快速启停的一种新方法.电脑学习，1999,(3) [2] 王晓极，何捷.步进电机自动升降速及其单片机控制.微特电机，1998,(2) [3] 陈伯时.电力拖动自动控制系统[M].北京:机械工业出版社,1990 [4] 许大中.交流电机调速理论[M].杭州:浙江大学出版社，1991 [5] 车长征.PLC在步进电机位置控制中的应用.江苏电器，2002(4)
[6] 刘俊.两种PLC控制步进电机实现点位控制的比较与应用.上海高等电机技术专
科学校学报，2003 (3)
[7] 顾绳谷.电机及拖动基础.北京：机械工业出版社，1980 [8] 胡崇岳.现代交流调速技术.北京：机械工业出版社，,1998
[9] 常斗南，李全利，张学武.可编程控制器原理◎应用◎实验。北京：机械工业出
版社，1998.7
[10] 吴银庚，张彦斌。ENGLISH 4 上海交通大学科技外语系。北京：高等教育出版社.1981.9
[11] 戴文进，章卫国.Specialized English For Automation.武汉:：武汉理工大学出版社，2001.8
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英 文 资 料
The Position-Control System
The regulator, whose object is to maintain the value of some physical quantity at a fixed level in spite of disturbances, is an important example of a closed-loop system. Equally important and more challenging in engineering design is the servo-mechanism whose object is to follow input commands. An example of such a device is the motion applied to a handwheel located at a local command station. The output motion might be used to drive a heavy object (such as a missile launcher) into a required position; power amplification of the command and accurate reproduction are thus necessary.
The signals can be transmitted by direct mechanical linkage or by hydraulic, pneumatic, or electric conduit. Apart from mechanical linkage the most rapid transmission may be achieved with electrical connection and this is often but not always used. Where it is used, the mechanical input and output signals are first converted into proportional electrical signals and then transmitted through wires to a subtracting device which produces a signal proportional to the error.
The low-power error signal is used to drive an amplifier which also receives power from an external source and delivers controlled power to the room.
The combination of transducers and subtracting element from the error detector, the amplifier is the controller and the motor together with its gearbox from the output element.
The amplifier may be purely electrical if the motor is electrical but must be either electro-hydraulic or electro-pneumatic if the motor is either hydraulic or pneumatic.
It is emphasized that the object of the system is to make the relatable mass copy as nearly as possible the motion of the handwheel. Let us consider what will happen if the position of the handwheel is turned very rapidly through an angle i, the mass being initially at rest. Initially the mass has no velocity and the output position 0 is zero, thus a signal k i instantaneously appears at the terminals of the amplifier; power from the source is allowed to reach the motor which then begins to drive the mass so as reduce the error. As 0 approaches I the error gets smaller and thus less power is allowed to reach the motor. Systems are usually designed so that the mass just overshoots the required position; since 0 is then greater than I ,the error becomes negative and the motor forces the mass to stop and reverse direction. Some undershoots and further overshoots will then probably take place before the mass finally settles at the required position. Only when exact coincidence occurs does the amplifier receive zero signal and thus the motor is forced to move either one way or the other until all motion dies away. The motor can therefore only come to rest when the signal entering the amplifier is zero (i.e. when the output position is exactly equal to the command i) .
It becomes evident from the above discussion that unless very great care is taken in the design, it is quite possible that the oscillation about the desired position will build up instead of dying a away quickly. A system in which oscillations build up is said to be unstable and much of the design work in control engineering is associated with producing a stable system. Adequate stability is, of course, only one of several requirements. Another requirement is faithful reproduction of a variety of input signals. Another type of input command might consist of handwheel motion of constant velocity. The system would then respond with an oscillatory transient and the mass would finally settle down with a velocity equal to the command but with a position lagging the
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command by a small angle. The slight difference between input and output position would be of such magnitude as to produce an output torque from the motor sufficient to drive the mass at the required velocity against frictional torques. The error could not be zero otherwise the motor would stop and the error would then build up.
It is thus apparent that whilst the output 0 will automatically align itself with the command I under static Conditions, under dynamic conditions the output motion only approximates to that of the command. The closeness of the approximation can however usually be made as good as is necessary to overcome most physical problems; for example, in certain types of automatically controlled profile milling machines a tracking accuracy to 0.0001 inch has been achieved.
Another object of the position control system is that it must be capable of holding the output position equal to the command in the presence of severe load disturbances. For example, a launcher must remain pointing in the desired direction regardless of random gusts of wind.
Feed----The Action Correcting System
You have known for a long time that engineering education includes subjects like chemistry and physics and,
in fact you probably know a fair amount about these subjects. Beyond that, however, your picture of what engineers must know in order to create complex systems is probably not very clear. This will be remedied in part by an introduction to the important subject of feedback control systems. Control systems have extensive significance in economic and biological systems, as well as in engineered systems.
It is impossible, for example, to drive your automobile down the highway, take your hands off the wheel, and get very far without something exciting happening. This is so even on a straight stretch mainly because there are bumps and many other factors that force the car off course. What is needed is a means of detecting drift of the car toward either side and a way of correcting for that drift as soon as it is detected. The means for accomplishing this are familiar: your eyes enable you to decide what remedial action is called for; your arms and the steering mechanism are used to carry out those decisions. These parts of you and the automobile constitute what engineers call a feedback control system.
This is a familiar process, indeed. It is a feedback control system that enables you to catch a ball, learn any motor skill, and keep your body temperature close to constant. Even the simple act of reaching to the top corner of this page before turning it involves a rather elaborate control system. The human body contains a remarkable series of such systems.
There are several characteristics of feedback control systems worthy of special mention, one of which is the closed loop. By “closing the loop”, effect is connected with cause,, so that the cause-effect relationship is now one of interdependence. Of course, it is feedback that closes the loop. Feedback is information characterizing the actual situation, which the processor, the brain for example, compares with the intended state of affairs. The difference between intended and actual becomes the basis of corrective action.
Another feature worth noticing is the role of information throughout a feedback control system. The system must be given a desired condition (intended state of affairs, goal, set point). This is information. The processor
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converts information from one form into another, the effecter converts information into action; the sensor converts action into information. No wonder information is sometimes called the lifeblood of a control system. Feedback, which one-way communication like the printed page fails to provide, makes learning easy and, in the case of motor skills, is essential. Picture a blindfold dart thrower, who throws darts indefinitely and shows no improvement as long as he knows nothing about the effectiveness of his efforts.
位置控制系统
器的任务是在扰动条件下将某物理量的值维持在一个规定的范围内，因此它是一类重要且典
型的闭环系统。伺服机构的任务就是跟踪输入指令信号，在工程设计中，它与调节器具有同等的重要性并且更具有挑战性。
这种装置中的一个例子就是位置控制伺服机构，它必须将施加在当地指挥站里操纵轮上的运动在某个遥远的地方再现出来。输出运动可被用来将一个很重的物体（如导弹发射架）移动到一个期望的位置上，于是指令的功率放大与精确是必不可少的。
信号可以通过机械连接或通过液压导管，气动导管或电缆直接传诵。与机械连接不同，最迅速的传送方式是电连接，这是非常普遍的，尽管并不总是如此。当它被应用时，机械输入与输出信号首先被转换成一定比例的电信号，然后通过导线将其传送到比较装置上，比较装置会产生一个正比于误差的信号。
低功率的误差信号被送回到放大器，放大器从外部电源获得功率并将可控的功率传送到电动机。
传感器与比较器元件的组合构成了误差检测器，放大器就是控制器，电动机与它的变速箱构成了输出元件。
如果电动机是用电的，那么放大器可以是纯电的。若电动机是液压的或气动的，那么放大器必须是电-液的或电-气的。
需强调的是，这个系统的任务就是供可旋转的物体尽可能地复现操纵轮的运动。让我们考虑当物体一开始处于静止状态，操纵轮的位置被非常快的转动了一个角度 I后将会出现什么情况。该物体一开始处于没有速度并且输出位置 0是零，于是一个信号K I 立刻会出现在放大器的输入端上；放大器的输出被传送到电动机的功率也随着减少。所设计的系统通常是物体恰好超过所要求的位置；既然 0 此时比 I 大，误差变负，电动机使物体停止并且改变方向。在物体最终稳定在所要求的位置之前，可能会产生达到给定值或进一步超过给定值的现象。只有当完全一致时，放大器的输入才为零，电动机被迫朝一个方向或另一个方向转动直至所有的运动停止。因此只有放大器的输入信号为零时（即当输出位量全与指令一样时），电动机才会停止工作。
从上面的讨论我们可以知道，除非精心设计，否则相当有可能在期望位置附近振荡加剧而不是快速衰减。振荡加剧的系统是不稳定的，因此在控制过程中的许多设计工作都与产生一个稳定的系统有关。当然，适当的稳定性仅仅是几个要求中的一个。另一项要求是如实的复现各类输入信号。另一类输入指令可能由恒角速度的操纵轮构成。那么这个系统将具有振荡的瞬态响应，物体终会稳定在与指令相同的速度上，但是在位置上较输入有一个小的角度滞后。输入与输出位置
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之间的细微差别将具有这样的数量级，使得电机产生一个足以使物体克服摩擦力矩并以所需要的速度转动的输出力矩。误差不能为零，否则电动机将会停止并且新的误差又会重新产生。
因此很明显，在静止条件下当输出 0 自动地与指令 I 一致时，在电台条件下，输出运动只会靠近指令的运动。然而这个逼近程度通常相当高，足以克服许多物理问题。例如，某类型自动控制的仿行铣床的跟踪精度已达到0.0001英寸。
定位控制系统的另一项任务是在负载剧烈变化干扰下。它必须有能力保持输出位置与指令相等。例如，无论是否存在随机阵风，发射架必须要与期望方向保持一致。
反馈----行动校正系统
你早知道工程技术教育包括化学，物理这样的课程。事实上，你可能对这些课程已经了解得相当多了。不过除此之外，工程技术人员为了创造各种复杂的系统应该了解些什么，你也许并不是非常清楚。这一点，可以通过反馈控制系统这门重要课程的介绍得到部分的弥补。控制系统在经济体系和生物系中，同在工程系统中一样，具有广泛的意义。例如，当你在公路上驾驶一辆汽车，让双手离开方向盘。行驶的很远而不发生一些令人惊慌不安的事情，那是不可能的。甚至在一段笔直的道路上，这也是做不到的，因为颠簸和许多其他因素会迫使汽车偏离行车路线。为此需要有一种能测出汽车向两旁偏移的设备，以及一旦测出这种情况就能加以校正的方法。完成这个任务的仪器是大家所熟悉的：你的眼睛能使你察觉必须采取校正动作；你的大脑能使你决定需要采取什么样的补救动作；你的手臂以及驾驶机构可以用来执行这个决定。人体的这些部分和汽车就构成了工程师们所说的反馈控制系统。
的确，这样的过程你们是熟悉的。正是反馈控制系统使你能抓住一个球，学驾驶摩托车的技术，以及使你的体温接近恒定。甚至在你想翻过这一页书面而把手伸向书页上角这样一个简单的动作，也涉及到一个相当复杂的控制系统。人体就包含着一系列这样奇妙的系统。
在反馈控制系统中有几个特点值得专门提出来。其中之一就是闭合回路。通过“使回路闭合”，可以把结果和原因联系在一起。因此，原因和结果就成了相互依存的关系。当然，是反馈使得这个回路闭合起来。反馈是一种表示实际情况的信息；而处理机构，例如人脑，把这种信息和预定的状况进行比较。预定状况和实际情况之间的差异就成为校正动作基础。
另外一个值得指出的特点就是信息在整个反馈控制系统中的作用。必须给这个系统一个理想的条件（预定的状况，目标，给定值），这就是信息。信息处理机构把一种信息转换成另一种信息，而操纵装置则将信息转换成动作；传感器又将动作转换成信息。难怪信息有是称作控制系统的生命线。
反馈能使学习变的方便，而像印刷之类的单向信息传递就没有反馈。在学习驾驶摩托车时，反馈更必不可少。你可以想象一下，一个蒙住眼睛的标枪投手，只要对自己的努力所产生的效果一无所知，那他就是不断地投掷下去，成绩也不可能提高。
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