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自动化控制中的特种电机目前以电路网络为中心的传统控制系统逐步被PLC控制系统所替代。
以PLC为核心的控制系统可以达到更精确的控制效果，能对复杂系统、非线性系统实现复杂、智能的控制算法，达到良好的效果。
通过网络也能实现远程控制。
特种电机的出现是社会对生产效率，产品质量，产品精度的要求提高的必然结果。
本文讨论的是特种电机中的步进电机与伺服电机。
标签：产生;原理;现状1970年，英国Leeds大学步进电机研究小组首创一个开关磁阻电机（Switchednbsp;Reluctancenbsp;Motor，nbsp;SRM）雏形，这是关于开关磁阻电机最早的研究。
1972年，进一步对带半导体开关的小功率电动机（10w～1kw）进行了研究。
到了1975年有了实质性的进展，并一直发展到可以为50kw的电瓶汽车提供装置。
上个世纪80年代初随着电力电子、微电脑和控制技术的迅猛发展而突飞猛进发展起来的一种新型调速驱动系统，具有结构简单、运行可靠及效率高等突出特点。
连续控制系统能反映信号的通与断，信号的大小和变化，使控制系统获得更好的静态与动态特性，完成更复杂的控制任务。
随着电力电子技术、控制理论以及微处理器技术的发展，电力电子变换器供电的连续控制系统使电力控制执行系统的性能指标出现了很大变化，不仅可以满足快速启、制动以及正、反转的要求（即四象限运行状态），而且可以确保整个电力控制执行系统工作在具有较高的调速、定位精度和较宽的调速范围内。
这些性能指标的提高，使得设备的生产率和产品质量大大提高。
不仅仅在电力系统，在复杂工件的加工，复杂轨迹的控制和实现里具有广泛应用。
在轻工业方面的用处更加广泛。
步进电动机（steppingmotor）步进电机是一种将电脉冲转化为角位移的执行机构。
当步进驱动器接收到一个脉冲信号，它就驱动步进电机按设定的方向转动一个固定的角度（称为“步距角”），它的旋转是以固定的角度一步一步运行的。
可以通过控制脉冲个数来控制角位移量，从而达到准确定位的目的;同时可以通过控制脉冲频率来控制电机转动的速度和加速度，从而达到调速的目的。
课程设计报告课题名称特种电机的结构、控制原理及应用目录摘要 (II)ABSTRACT........................................................................................................................................ I II 第1章绪论 . (1)1.1 课题背景 (1)1.2 课题意义及主要工作 (1)第2章步进电动机 (2)2.1步进电动机的分类、结构及特点 (2)2.1.1步进电动机的分类 (2)2.1.2步进电动机的结构及特点 (2)2.2步进电动机的工作原理、主要参数及特性 (4)2.2.1步进电动机的工作原理 (4)2.2.2主要参数及特性 (5)2.3步进电动机的应用 (6)第3章三相交流伺服电动机 (7)3.1交流伺服电动机结构 (7)3.2交流伺服电动机工作原理 (7)3.2.1交流伺服电动机工作原理 (7)3.2.2交流伺服电动机有以下三种转速控制方式 (8)3.3三相交流伺服电动机的应用 (8)第4章总结 (9)参考文献 (10)谢辞 .................................................................................................................. 错误！未定义书签。
摘要随着自动化技术、计算机技术、电力电子技术的发展，特别是高性能永磁材料的问世，电动机制造技术水平得到了极大的提高，也为特种电动机的制造、控制和应用提出了更高的要求，提供了更广阔的发展空间。
本旨在通过对特种电动机的构造、调速控制原理及应用的介绍，达到快速学习特种电动机控制技术及应用的目的。
本次课题设计着重介绍步进电动机、伺服电动机的的结构、控制原理及应用。
关键词：特种电机、步进电动机、伺服电动机ABSTRACTAlong with the automation technology, computer technology, the development of power electronic technology, especially the high performance permanent magnetic materials available, motor manufacturing technology level has been greatly improved, but also for the special motor manufacturing, control and application put forward higher request, provided more vast development space.This aims to construct special motor, speed control principle and application, achieve rapid learning special motor control technology and application for the purpose of. This design introduced the stepper motor, servo motor structure, control principle and application.Keywords:special motor, stepper motor, servo motor第1章绪论1.1 课题背景当今世界，各种先进的科学技术飞速发展，给人们的生活带来了深远的影响，它极大的改善我们的生活方式。
步进电机步进电动机（Stepping Motor，或Step Motor 、Stepper Motor）是一种可由电脉冲控制运动的特殊电动机，可以通过脉冲信号转换控制的方法将脉冲电信号变换成相应的角位移或线位移。
因此步进电动机也被称为脉冲电动机（Pulse Motor）。
步进电动机不能直接使用通常的直流或交流电源来驱动，而是需要使用专门的步进电动机驱动器通过一定的控制方式，可以使步进电动机运动时的角位移或线位移与脉冲数成正比，即其转速或线速度与输入控制脉冲的频率成正比。
在步进电动机所能承受的负载能力范围内，这种关系不会因电源电压、负载大小以及环境条件的波动而变化，因而在系统中可以采用开环的方式进行运动控制，从而使控制系统大为简化。
通常步进电动机可以在较宽的范围内通过改变输入控制脉冲的频率来实现调速，并能够做到快速起动、反转和制动。
另一种是由磁阻原理产生的。
作用力则是由定/转子间气隙磁阻的变化产生的，当定子绕组通电时，产生一个单相磁场作用于转子，由于磁场在转子与定子之间的分布要遵循磁阻最小原则（或磁导最大原则），即磁通总要沿着磁阻最小（磁导最大）的路径闭合，因此，当转子产生的磁场的磁极轴线与定子磁极的轴线不重合时，便会有磁阻力作用在转子上并产生转矩使其趋于磁阻最小的位置，即两轴线重合位置，这类似于磁铁吸引铁质物质的现象。
步进电动机的运动是受走步脉冲信号控制的，因此适合于作为数字控制系统的伺服元件。
它的直线位移量或角位移量与电脉冲数成正比，所以电机的线速度或转速与脉冲频率成正比。
通过改变脉冲频率的高低，就可以在很大的范围内调节电机的转速，并能实现快速启动、制动和反转。
步进电动机的运动是受（电脉冲）信号控制的，通过改变（脉冲频率）的高低，就可以在很大的范围内调节电机的转速，并能实现电机的（ABC）【A启动B制动C反转】。
步进电动机按产生转距的方式不同可分为反应式、激磁式及混合式三种。
反应式步进电动机的定转子都是凸极结构，是利用磁阻最小原理工作。
A stepper motor is an electromechanical device which converts electrical pulses into discrete mechanical movements. The shaft or spindle of a stepper motor rotates in discrete step increments when electrical command pulses are applied to it in the proper sequence. The motors rotation has several direct relationships to these applied input pulses. The sequence of the applied pulses is directly related to the direction of motor shafts rotation. The speed of the motor shafts rotation is directly related to the frequency of the input pulses and the length of rotation is directly related to the number of input pulses applied. Stepper Motor Advantages and Disadvantages Advantages1.The rotation angle of the motor isproportional to the input pulse. 2.The motor has full torque at stand-still (if the windings are energized) 3.Precise positioning and repeat-ability of movement since goodstepper motors have an accuracy of3–5% of a step and this error isnon cumulative from one step tothe next.4.Excellent response to starting/stopping/reversing.5.Very reliable since there are no con-tact brushes in the motor.Therefore the life of the motor issimply dependant on the life of the bearing.6.The motors response to digitalinput pulses provides open-loopcontrol, making the motor simplerand less costly to control.7.It is possible to achieve very lowspeed synchronous rotation with aload that is directly coupled to theshaft.8.A wide range of rotational speedscan be realized as the speed isproportional to the frequency of the input pulses.Disadvantages1.Resonances can occur if notproperly controlled.2.Not easy to operate at extremelyhigh speeds.Open Loop OperationOne of the most significant advantagesof a stepper motor is its ability to beaccurately controlled in an open loopsystem. Open loop control means nofeedback information about position isneeded. This type of controleliminates the need for expensivesensing and feedback devices such asoptical encoders. Your position isknown simply by keeping track of theinput step pulses.Stepper Motor TypesThere are three basic stepper motortypes. They are :•Variable-reluctance•Permanent-magnet•HybridVariable-reluctance (VR)This type of stepper motor has beenaround for a long time. It is probablythe easiest to understand from astructural point of view. Figure 1shows a cross section of a typical V.R.stepper motor. This type of motorconsists of a soft iron multi-toothedrotor and a wound stator. When thestator windings are energized with DCcurrent the poles become magnetized.Rotation occurs when the rotor teethare attracted to the energized statorpoles.Permanent Magnet (PM)Often referred to as a “tin can” or“canstock” motor the permanentmagnet step motor is a low cost andlow resolution type motor with typicalstep angles of 7.5° to 15°. (48 – 24steps/revolution) PM motors as theFigure 1. Cross-section of a variable-reluctance (VR) motor.Industrial Circuits Application NoteStepper Motor Basicsmotor.1name implies have permanent magnets added to the motor structure. The rotor no longer has teeth as with the VR motor. Instead the rotor is magnetized with alternating north and south poles situated in a straight line parallel to the rotor shaft. These magnetized rotor poles provide an increased magnetic flux intensity and because of this the PM motor exhibits improved torque characteristics when compared with the VR type.Hybrid (HB)The hybrid stepper motor is more expensive than the PM stepper motor but provides better performance with respect to step resolution, torque and speed. Typical step angles for the HB stepper motor range from 3.6° to 0.9°(100 – 400 steps per revolution). The hybrid stepper motor combines the best features of both the PM and VR type stepper motors. The rotor is multi-toothed like the VR motor and contains an axially magnetized con-centric magnet around its shaft. The teeth on the rotor provide an even better path which helps guide the magnetic flux to preferred locations in the airgap. This further increases the detent, holding and dynamic torque characteristics of the motor when com-pared with both the VR and PM types.The two most commonly used types of stepper motors are the permanent magnet and the hybrid types. If a designer is not sure which type will best fit his applications requirements he should first evaluate the PM type as it is normally several times less expen-sive. If not then the hybrid motor may be the right choice.There also excist some special stepper motor designs. One is the disc magnet motor. Here the rotor is designed sa a disc with rare earth magnets, See fig. 5 . This motor type has some advantages such as very lowinertia and a optimized magnetic flowpath with no coupling between thetwo stator windings. These qualitiesare essential in some applications.Size and PowerIn addition to being classified by theirstep angle stepper motors are alsoclassified according to frame sizeswhich correspond to the diameter ofthe body of the motor. For instance asize 11 stepper motor has a body di-ameter of approximately 1.1 inches.Likewise a size 23 stepper motor has abody diameter of 2.3 inches (58 mm),etc. The body length may however,vary from motor to motor within thesame frame size classification. As ageneral rule the available torque out-put from a motor of a particular framesize will increase with increased bodylength.Power levels for IC-driven steppermotors typically range from below awatt for very small motors up to 10 –20 watts for larger motors. The maxi-mum power dissipation level orthermal limits of the motor are seldomclearly stated in the motor manu-facturers data. To determine this wemust apply the relationship P␣=V ×I.For example, a size 23 step motor maybe rated at 6V and 1A per phase.Therefore, with two phases energizedthe motor has a rated power dissipa-tion of 12 watts. It is normal practiceto rate a stepper motor at the powerdissipation level where the motor caserises 65°C above the ambient in stillair. Therefore, if the motor can bemounted to a heatsink it is oftenpossible to increase the allowablepower dissipation level. This isimportant as the motor is designed tobe and should be used at its maximumpower dissipation ,to be efficient froma size/output power/cost point of view.When to Use a StepperMotorA stepper motor can be a good choicewhenever controlled movement isrequired. They can be used to advan-tage in applications where you need tocontrol rotation angle, speed, positionand synchronism. Because of the in-herent advantages listed previously,stepper motors have found their placein many different applications. Someof these include printers, plotters,highend office equipment, hard diskdrives, medical equipment, faxmachines, automotive and many more.The Rotating Magnetic FieldWhen a phase winding of a steppermotor is energized with current amagnetic flux is developed in thestator. The direction of this flux isdetermined by the “Right HandRule” which states:“If the coil is grasped in the righthand with the fingers pointing in thedirection of the current in the winding(the thumb is extended at a 90° angleto the fingers), then the thumb willpoint in the direction of the magneticfield.”Figure 5 shows the magnetic fluxpath developed when phase B is ener-gized with winding current in thedirection shown. The rotor then alignsitself so that the flux opposition isminimized. In this case the motorwould rotate clockwise so that itssouth pole aligns with the north poleof the stator B at position 2 and itsnorth pole aligns with the south poleof stator B at position 6. To get themotor to rotate we can now see thatwe must provide a sequence ofenergizing the stator windings in sucha fashion that provides a rotatingmagnetic flux field which the rotorfollows due to magnetic attraction.Torque GenerationThe torque produced by a steppermotor depends on several factors.• The step rate• The drive current in the windings• The drive design or typeIn a stepper motor a torque is devel-oped when the magnetic fluxes of therotor and stator are displaced fromeach other. The stator is made up of ahigh permeability magnetic material.The presence of this high permeabilitymaterial causes the magnetic flux tobe confined for the most part to thepaths defined by the stator structurein the same fashion that currents areconfined to the conductors of an elec-tronic circuit. This serves to concen-trate the flux at the stator poles. Thedeveloped by Portescap.23two-pole stepper motor with a lag between the rotor and stator.stepper motors.torque output produced by the motor is proportional to the intensity of the magnetic flux generated when the winding is energized.The basic relationship which defines the intensity of the magnetic flux is defined by:H = (N ×i)÷l where:N =The number of winding turnsi =currentH =Magnetic field intensity l =Magnetic flux path length This relationship shows that the magnetic flux intensity and conse-quently the torque is proportional to the number of winding turns and the current and inversely proportional to the length of the magnetic flux path.From this basic relationship one can see that the same frame size stepper motor could have very different torque output capabilities simply by chang-ing the winding parameters. More detailed information on how the winding parameters affect the output capability of the motor can be found in the application note entitled “Drive Circuit Basics”.Phases, Poles and Stepping AnglesUsually stepper motors have two phases, but three- and five-phase motors also exist.A bipolar motor with two phases has one winding/phase and a unipolar motor has one winding, with a center tap per phase. Sometimes the unipolar stepper motor is referred to as a “four-phase motor”, even though it only has two phases.Motors that have two separate windings per phase also exist—these can be driven in either bipolar or unipolar mode.A pole can be defined as one of the regions in a magnetized body where the magnetic flux density is con-centrated. Both the rotor and the stator of a step motor have poles.Figure 2 contains a simplified picture of a two-phase stepper motor having 2poles (or 1 pole pairs) for each phase on the stator, and 2 poles (one pole pair) on the rotor. In reality several more poles are added to both the rotor and stator structure in order toincrease the number of steps per revolution of the motor, or in other words to provide a smaller basic (full step) stepping angle. The permanent magnet stepper motor contains an equal number of rotor and stator pole pairs. Typically the PM motor has 12pole pairs. The stator has 12 pole pairs per phase. The hybrid type stepper motor has a rotor with teeth. The rotor is split into two parts, separated by a permanant magnet—making half of the teeth south poles and half north poles.The number of pole pairs is equal to the number of teeth on one of the rotor halves. The stator of a hybrid motor also has teeth to build up a higher number of equivalent poles (smaller pole pitch, number of equivalent poles = 360/teeth pitch)compared to the main poles, on which the winding coils are wound. Usually 4 main poles are used for 3.6 hybrids and 8 for 1.8- and 0.9-degree types.It is the relationship between the number of rotor poles and the equival-ent stator poles, and the number the number of phases that determines the full-step angle of a stepper motor.Step angle=360÷(N Ph ×Ph)=360/N N Ph =Number of equivalent poles perphase = number of rotor poles Ph =Number of phases N=Total number of poles for all phases togetherIf the rotor and stator tooth pitch is unequal, a more-complicated relation-ship exists.Stepping ModesThe following are the most common drive modes.• Wave Drive (1 phase on)• Full Step Drive (2 phases on)• Half Step Drive (1 & 2 phases on)• Microstepping (Continuously varying motor currents)For the following discussions please refer to the figure 6.In Wave Drive only one winding is energized at any given time. The stator is energized according to the sequence A → B →A → B and the rotor steps from position 8 → 2 → 4→ 6. For unipolar and bipolar woundmotors with the same winding param-eters this excitation mode would result in the same mechanical position. The disadvantage of this drive mode is that in the unipolar wound motor you are only using 25% and in the bipolar motor only 50% of the total motor winding at any given time. This means that you are not getting the maximum torque output from the motor4Table 1. Excitation sequences for different drive modesFigure 7. Torque vs. rotor angular position.Figure 8. Torque vs. rotor angle position at different holding torque.In Full Step Drive you are ener-gizing two phases at any given time.The stator is energized according to the sequence AB →A B →A B →A B and the rotor steps from position 1 → 3 → 5 → 7 . Full step mode results in the same angular movement as 1 phase on drive but the mechanical position is offset by one half of a full step. The torque output of theunipolar wound motor is lower than the bipolar motor (for motors with the same winding parameters) since the unipolar motor uses only 50% of the available winding while the bipolar motor uses the entire winding.Half Step Drive combines both wave and full step (1&2 phases on)drive modes. Every second step only one phase is energized and during the other steps one phase on each stator.The stator is energized according to the sequence AB → B →A B →A →A B → B → A B → A and the rotor steps from position 1 → 2 → 3→ 4 → 5 → 6 → 7 → 8. This results in angular movements that are half of those in 1- or 2-phases-on drive modes. Half stepping can reduce a phenomena referred to as resonance which can be experienced in 1- or 2-phases-on drive modes.The displacement angle is deter-mined by the following relationship:X = (Z ÷2π)×sin (T a ÷T h )where:Z =rotor tooth pitch T a =Load torqueT h =Motors rated holding torque X =Displacement angle.Therefore if you have a problem with the step angle error of the loaded motor at rest you can improve this by changing the “stiffness” of the motor.This is done by increasing the holding torque of the motor. We can see this effect shown in the figure 5.Increasing the holding torque for a constant load causes a shift in the lag angle from Q 2 to Q 1.Step Angle AccuracyOne reason why the stepper motor has achieved such popularity as a position-ing device is its accuracy and repeat-ability. Typically stepper motors will have a step angle accuracy of 3–5%of one step. This error is also non-cumulative from step to step. The accuracy of the stepper motor is mainly a function of the mechanical precision of its parts and assembly.Figure 9 shows a typical plot of the positional accuracy of a stepper motor.Step Position ErrorThe maximum positive or negative position error caused when the motor has rotated one step from the previous holding position.Step position error = measured step angle - theoretical anglePositional ErrorThe motor is stepped N times from an initial position (N = 360°/step angle)and the angle from the initial positionTorque Angle T LoadT H1T H2O O 12ONormal Wave Drive full step Half-step drive Phase 1234123412345678A ••••••B ••••••A ••••••B••••••The excitation sequences for the above drive modes are summarized in Table 1.In Microstepping Drive the currents in the windings arecontinuously varying to be able to break up one full step into many smaller discrete steps. Moreinformation on microstepping can be found in the microstepping chapter.Torque vs, Angle CharacteristicsThe torque vs angle characteristics of a stepper motor are the relationship between the displacement of the rotor and the torque which applied to the rotor shaft when the stepper motor is energized at its rated voltage. An ideal stepper motor has a sinusoidal torque vs displacement characteristic as shown in figure 8.Positions A and C represent stable equilibrium points when no external force or load is applied to the rotor shaft. When you apply an external force T a to the motor shaft you in essence create an angulardisplacement, Θa . This angular displacement, Θa , is referred to as a lead or lag angle depending on wether the motor is actively accelerating or decelerating. When the rotor stops with an applied load it will come to rest at the position defined by this displacement angle. The motordevelops a torque, T a , in opposition to the applied external force in order to balance the load. As the load isincreased the displacement angle also increases until it reaches themaximum holding torque, T h , of the motor. Once T h is exceeded the motor enters an unstable region. In this region a torque is the opposite direction is created and the rotor jumps over the unstable point to the next stable point.5Figure 9. Positional accuracy of a stepper motor.Figure 10. Torque vs. speed characteristics of a stepper motor.is measured at each step position. If the angle from the initial position to the N-step position is ΘN and the error is ∆ΘN where:∆ΘN = ∆ΘN - (step angle) × N.The positional error is the difference of the maximum and minimum but is usually expressed with a ± sign. That is:positional error = ±1⁄2(∆ΘMax - ∆ΘMin )Hysteresis Positional ErrorThe values obtained from the measure-ment of positional errors in both directions.Mechanical Parameters,Load, Friction, InertiaThe performance of a stepper motor system (driver and motor) is also highly dependent on the mechanical parameters of the load. The load is defined as what the motor drives. It is typically frictional, inertial or a combination of the two.Friction is the resistance to motion due to the unevenness of surfaces which rub together. Friction is constant with velocity. A minimum torque level is required throughout the step in over to overcome thisfriction ( at least equal to the friction).Increasing a frictional load lowers the top speed, lowers the acceleration and increases the positional error. The converse is true if the frictional load is loweredInertia is the resistance to changes in speed. A high inertial load requires a high inertial starting torque and the same would apply for braking. In-creasing an inertial load will increase speed stability, increase the amount of time it takes to reach a desired speed and decrease the maximum self start pulse rate. The converse is again true if the inertia is decreased.The rotor oscillations of a stepper motor will vary with the amount of friction and inertia load. Because of this relationship unwanted rotor oscil-lations can be reduced by mechanical damping means however it is more often simpler to reduce theseunwanted oscillations by electrical damping methods such as switch from full step drive to half step drive.Torque vs, Speed CharacteristicsThe torque vs speed characteristics are the key to selecting the right motor and drive method for a specificapplication. These characteristics are dependent upon (change with) the motor, excitation mode and type of driver or drive method. A typical “speed – torque curve” is shown in figure9.To get a better understanding of this curve it is useful to define the different aspect of this curve.Holding torqueThe maximum torque produced by the motor at standstill.Pull-In CurveThe pull-in curve defines a area refered to as the start stop region. This is the maximum frequency at which the motor can start/stop instantaneously,with a load applied, without loss of synchronism.Maximum Start RateThe maximum starting step frequency with no load applied.Pull-Out CurveThe pull-out curve defines an area refered to as the slew region. It defines the maximum frequency at which the motor can operate without losing syn-chronism. Since this region is outside the pull-in area the motor must ramped (accelerated or decelerated)into this region.Maximum Slew RateThe maximum operating frequency of the motor with no load applied.The pull-in characteristics vary also depending on the load. The larger the load inertia the smaller the pull-in area. We can see from the shape of the curve that the step rate affects the torque output capability of stepper motor The decreasing torque output as the speed increases is caused by the fact that at high speeds the inductance of the motor is the dominant circuit element.TorqueSpeedP.P.S.Start-Stop RegionPull-in Torque curveSlew RegionHolding TorquePull-out Torque Curve Max Start Rate Max Slew RateThe shape of the speed - torque curve can change quite dramatically depending on the type of driver used.The bipolar chopper type drivers which Ericsson Components produces will maximum the speed - torque performance from a given motor. Most motor manufacturers provide these speed - torque curves for their motors.It is important to understand what driver type or drive method the motor manufacturer used in developing their curves as the torque vs. speed charac-teristics of an given motor can vary significantly depending on the drive method used.Stepper motors can often exhibit a phenomena refered to as resonance at certain step rates. This can be seen as a sudden loss or drop in torque at cer-tain speeds which can result in missed steps or loss of synchronism. It occurs when the input step pulse rate coin-cides with the natural oscillation frequency of the rotor. Often there is a resonance area around the 100 – 200 pps region and also one in the highstep pulse rate region. The resonance phenomena of a stepper motor comes from its basic construction and there-fore it is not possible to eliminate it completely. It is also dependent upon the load conditions. It can be reduced by driving the motor in half or micro-stepping modes.Figure 11. Single step response vs. time.Single Step Response and ResonancesThe single-step response character-istics of a stepper motor is shown in figure 11.When one step pulse is applied to a stepper motor the rotor behaves in a manner as defined by the above curve. The step time t is the time it takes the motor shaft to rotate one step angle once the first step pulse is applied. This step time is highly dependent on the ratio of torque to inertia (load) as well as the type of driver used.Since the torque is a function of the displacement it follows that the accel-eration will also be. Therefore, when moving in large step increments a high torque is developed and consequently a high acceleration. This can cause overshots and ringing as shown. The settling time T is the time it takes these oscillations or ringing to cease. In certain applications this phenomena can be undesirable. It is possible to reduce or eliminate this behaviour by microstepping the stepper motor. For more information on microstepping please consult the microstepping note.Anglet TTime O6。
