步進電機和伺服電機的系統(tǒng)控制中英文翻譯資料

1、selecting the motor that suits your applicationmotion control, in its widest sense, could relate to anything from a welding robot to the hydraulic system in a mobile crane. in the field of electronic motion control, we are primarily concerned with systems falling within a limited power range, typica

2、lly up to about 10hp (7kw), and requiring precision in one or more aspects. this may involve accurate control of distance or speed, very often both and sometimes other parameters such as torque or acceleration rate. in the case of the two examples given, the welding robot requires precise control of

3、 both speed and distance; the crane hydraulic system uses the driver as the feedback system so its accuracy varies with the skill of the operator. this wouldnt be considered a motion control system in the strict sense of the term. our standard motion control system consists of three basic elements:f

4、ig. 1 elements of motion control systemthe motor，this may be a stepper motor (either rotary or linear), a dc brush motor or a brushless servo motor. the motor needs to be fitted with some kind of feedback device unless it is a stepper motor.fig. 2 shows a system complete with feedback to control mot

5、or speed. such a system is known as a closed-loop velocity servo system.fig. 2 typical closed loop (velocity) servo systemthe drive，this is an electronic power amplifier that delivers the power to operate the motor in response to low-level control signals. in general, the drive will be specifically

6、designed to operate with a particular motor type you cant use a stepper drive to operate a dc brush motor, for instance.application areas of motor typesstepper motorsstepper motor benefitsstepper motors have the following benefits: low cost ruggedness simplicity in construction high reliability no m

7、aintenance wide acceptance no tweaking to stabilize no feedback components are needed they work in just about any environment inherently more failsafe than servo motors.there is virtually no conceivable failure within the stepper drive module that could cause the motor to run away. stepper motors ar

8、e simple to drive and control in an open-loop configuration. they only require four leads. they provide excellent torque at low speeds, up to 5 times the continuous torque of a brush motor of the same frame size or double the torque of the equivalent brushless motor. this often eliminates the need f

9、or a gearbox. a stepper-driven-system is inherently stiff, with known limits to the dynamic position error.stepper motor disadvantagesstepper motors have the following disadvantages: resonance effects and relatively long settling times rough performance at low speed unless a micro step drive is used

10、 liability to undetected position loss as a result of operating open-loop they consume current regardless of load conditions and therefore tend to run hot losses at speed are relatively high and can cause excessive heating, and they are frequently noisy (especially at high speeds). they can exhibit

11、lag-lead oscillation, which is difficult to damp. there is a limit to their available size, and positioning accuracy relies on the mechanics (e.g., ball screw accuracy). many of these drawbacks can be overcome by the use of a closed-loop control scheme. note: the comp motor zeta series minimizes or

12、reduces many of these different stepper motor disadvantages. there are three main stepper motor types: permanent magnet (p.m.) motors variable reluctance (v.r.) motors hybrid motorswhen the motor is driven in its full-step mode, energizing two windings or “phases” at a time (see fig. 3), the torque

13、available on each step will be the same (subject to very small variations in the motor and drive characteristics). in the half-step mode, we are alternately energizing two phases and then only one as shown in fig. 4. assuming the drive delivers the same winding current in each case, this will cause

14、greater torque to be produced when there are two windings energized. in other words, alternate steps will be strong and weak. this does not represent a major deterrent to motor performancethe available torque is obviously limited by the weaker step, but there will be a significant improvement in low

15、-speed smoothness over the full-step mode.clearly, we would like to produce approximately equal torque on every step, and this torque should be at the level of the stronger step. we can achieve this by using a higher current level when there is only one winding energized. this does not over dissipat

16、e the motor because the manufacturers current rating assumes two phases to be energized the current rating is based on the allowable case temperature). with only one phase energized, the same total power will be dissipated if the current is increased by 40%. using this higher current in the one-phas

17、e-on state produces approximately equal torque on alternate steps (see fig. 5).fig. 3 full step currentfig. 4 half step currentfig.5 half step current, profiledwe have seen that energizing both phases with equal currents produces an intermediate step position half-way between the one-phase-one posit

18、ions. if the two phase currents are unequal, the rotor position will be shifted towards the stronger pole. this effect is utilized in the micro stepping drive, which subdivides the basic motor step by proportioning the current in the two windings. in this way, the step size is reduced and the low-sp

19、eed smoothness is dramatically improved. high-resolution micro step drives divide the full motor step into as many as 500 micro steps, giving 100,000 steps per revolution. in this situation, the current pattern in the windings closely resembles two sine waves with a 90 phase shift between them (see

20、fig. 6). the motor is now being driven very much as though it is a conventional ac synchronous motor. in fact, the stepper motor can be driven in this way from a 60 hz-us (50hz-europe) sine wave source by including a capacitor in series with one phase. it will rotate at 72 rpm.fig. 6 phase currents

21、in micro step modestandard 200-step hybrid motorthe standard stepper motor operates in the same way as our simple model, but has a greater number of teeth on the rotor and stator, giving a smaller basic step size. the rotor is in two sections as before, but has 50 teeth on each section. the half-too

22、th displacement between the two sections is retained. the stator has 8 poles each with 5 teeth, making a total of 40 teeth (see fig. 7).fig.7 200-step hybrid motorif we imagine that a tooth is placed in each of the gaps between the stator poles, there would be a total of 48 teeth, two less than the

23、number of rotor teeth. so if rotor and stator teeth are aligned at 12 oclock, they will also be aligned at 6 oclock. at 3 oclock and 9 oclock the teeth will be misaligned. however, due to the displacement between the sets of rotor teeth, alignment will occur at 3 oclock and 9 oclock at the other end

24、 of the rotor.the windings are arranged in sets of four, and wound such that diametrically-opposite poles are the same. so referring to fig. 7, the north poles at 12 and 6 oclock attract the south-pole teeth at the front of the rotor; the south poles at 3 and 9 oclock attract the north-pole teeth at

25、 the back. by switching current to the second set of coils, the stator field pattern rotates through 45. however, to align with this new field, the rotor only has to turn through 1.8. this is equivalent to one quarter of a tooth pitch on the rotor, giving 200 full steps per revolution.note that ther

26、e are as many detent positions as there are full steps per rev, normally 200. the detent positions correspond with rotor teeth being fully aligned with stator teeth. when power is applied to a stepper drive, it is usual for it to energize in the “zero phase” state in which there is current in both s

27、ets of windings. the resulting rotor position does not correspond with a natural detent position, so an unloaded motor will always move by at least one half steps at power-on. of course, if the system was turned off other than in the zero phase state, or the motor is moved in the meantime, a greater

28、 movement may be seen at power-up.another point to remember is that for a given current pattern in the windings, there are as many stable positions as there are rotor teeth (50 for a 200-step motor). if a motor is de-synchronized, the resulting positional error will always be a whole number of rotor

29、 teeth or a multiple of 7.2. a motor cannot “miss” individual steps position errors of one or two steps must be due to noise, spurious step pulses or a controller fault.fig. 8 digital servo drivedigital servo drive operationfig.8 shows the components of a digital drive for a servo motor. all the mai

30、n control functions are carried out by the microprocessor, which drives a d-to-a converter to produce an analog torque demand signal. from this point on, the drive is very much like an analog servo amplifier.feedback information is derived from an encoder attached to the motor shaft. the encoder gen

31、erates a pulse stream from which the processor can determine the distance traveled, and by calculating the pulse frequency it is possible to measure velocity.the digital drive performs the same operations as its analog counterpart, but does so by solving a series of equations. the microprocessor is

32、programmed with a mathematical model (or “algorithm”) of the equivalent analog system. this model predicts the behavior of the system. it also takes into account additional information like the output velocity, the rate of change of the input and the various tuning settings.to solve all the equation

33、s takes a finite amount of time, even with a fast processor this time is typically between 100ms and 2ms. during this time, the torque demand must remain constant at its previously-calculated value and there will be no response to a change at the input or output. this “update time” therefore becomes

34、 a critical factor in the performance of a digital servo and in a high-performance system it must be kept to a minimum.the tuning of a digital servo is performed either by pushbuttons or by sending numerical data from a computer or terminal. no potentiometer adjustments are involved. the tuning data

35、 is used to set various coefficients in the servo algorithm and hence determines the behavior of the system. even if the tuning is carried out using pushbuttons, the final values can be uploaded to a terminal to allow easy repetition.some applications, the load inertia varies between wide limits thi

36、nk of an arm robot that starts off unloaded and later carries a heavy load at full extension. the change in inertia may well be a factor of 20 or more, and such a change requires that the drive is re-tuned to maintain stable performance. this is simply achieved by sending the new tuning values at th

37、e appropriate point in the operating cycle. 步進電機和伺服電機的系統(tǒng)控制運動控制，在其最廣泛的意義上說，可能與任何移動式起重機中焊接機器人液壓系統(tǒng)有關(guān)。在電子運動控制領(lǐng)域，我們的主要關(guān)切系統(tǒng)范圍內(nèi)的有限功率的大小，通常高達約10hp（7千瓦），并要求在一個或多個方面有嚴(yán)格精密。這可能涉及精確控制的距離或速度，但很多時候是雙方的，有時還涉及其它參數(shù)如轉(zhuǎn)矩或加速率。在以下所舉的兩個例子中，焊接機器人，需要精確的控制雙方的速度和距離;吊臂液壓系統(tǒng)采用驅(qū)動作為反饋系統(tǒng)，因此，它的準(zhǔn)確度會隨著操作者的技能的不同而不同。在嚴(yán)格意義上來說，這將不會被視為一項運動控

38、制系統(tǒng)。 我們的標(biāo)準(zhǔn)運動控制系統(tǒng)由以下三個基本要素組成：圖1運動控制系統(tǒng)組成元件電機，可能是一個步進電機（要么旋轉(zhuǎn)或線性），也可能是直流無刷電機或無刷伺服馬達。電機必須配備一些種回饋裝置，除非它是一個步進電機。圖 2顯示了一個完善地反饋控制電機轉(zhuǎn)速的系統(tǒng)。這樣一個具有閉環(huán)控制系統(tǒng)的速度伺服系統(tǒng)。圖2 典型的閉環(huán)（速度）伺服系統(tǒng)驅(qū)動器是一個電子功率放大器，以提供電力操作電動機來回應(yīng)低層次的控制信號。一般來說，驅(qū)動器將特別設(shè)計，其操作與特定電機類型相配合。例如，你不能用一個步進驅(qū)動器來操作直流無刷電機。不同電機適應(yīng)的不同領(lǐng)域步進電機：步進電機的好處。（1）成本低廉（2）堅固耐用（3）結(jié)構(gòu)簡單（4）

39、高可靠性（5）無維修（6）適用廣泛（7）穩(wěn)定性很高（8）無需反饋元件（8）適應(yīng)多種工作環(huán)境（9）相對伺服電機更具有保險性。因此，幾乎沒有任何可以想象的失敗使步進驅(qū)動模塊出錯。步進電機驅(qū)動簡單，并且驅(qū)動和控制在一個開放的閉環(huán)系統(tǒng)內(nèi)。他們只需要4個驅(qū)動器。低速時，驅(qū)動器提供良好的扭矩，是有刷電機同一幀大小5倍連續(xù)力矩，或相當(dāng)于無刷電機一倍扭矩。這往往不再需要變速箱。步進驅(qū)動系統(tǒng)遲緩，在限定的范圍內(nèi)，可以更好的減少動態(tài)位置誤差。步進電機弊端。步進電機有下列缺點：（1）共振效應(yīng)和相對長的適應(yīng)性（2）在低速，表現(xiàn)粗糙，除非微驅(qū)動器來驅(qū)動（3）開環(huán)系統(tǒng)可能導(dǎo)致未被查覺的損失（4）由于過載，他們消耗過多電流

40、。因此傾向于過熱運行。（5）虧損速度比較高，并可產(chǎn)生過多熱量因此，他們噪音很大（尤其是在高速下）。（6）他們的滯后現(xiàn)象導(dǎo)致振蕩，這是很難抑制的。對他們的可行性，這兒有一個限度，而他們的大小，定位精度主要依靠的是機器（例如，滾珠絲杠的精確度） 。許多這些缺點是可以克服的，通過使用一個閉環(huán)控制方案。注：comp motor系列很多地減小或降低了這些不同的步進電機不利之處。主要有3類步進電機：（1）永磁式步進電機 ，（2）可變磁阻式步進電動機，（3）混合式步進電機汽車。當(dāng)電動機驅(qū)動，給兩個繞組通電時或2相通電的時候（見圖 3），扭矩可于每一個步將是相同（除極少數(shù)的變異和傳動特性）。在半步模式下，我們

41、交替改變兩相電流，如圖4所示。假設(shè)該驅(qū)動器在每種情況下提供了相同的繞組電流，再通電時，這將導(dǎo)致更大的轉(zhuǎn)矩。換句話說，交替的步進距將時強時若。對電動機表現(xiàn)來說，這并不代表著一個重大的威懾。扭矩明顯受制于較弱的一步，低速平滑有一個顯著的改善。顯然，我們想在每一個步驟實現(xiàn)約相等扭矩對時，這扭矩應(yīng)該在水平較強的一步。們可以實現(xiàn)這個，當(dāng)只有一個繞組通電時，通過用高電流水平。這并不過度消耗電機，因為該電機的額定電流假定兩個階段被激活（目前的評級是基于許可的情況溫度） 。只有一相通電，如果目前是增加了40的功率，同樣的總功率將會消散。利用這種更高的電流在一相中產(chǎn)生大致相等的扭矩，在交替的步進距中。（見圖5 ）圖3半步電流圖4 全步電流 圖5 側(cè)面全步電流我們已經(jīng)看到，給兩相都通與相同的電流產(chǎn)生的一個中間的步進，居于每一相的中間位置。如果兩相電流是不相等的，轉(zhuǎn)子位置將轉(zhuǎn)向更強的一極。這種作用是利用細分驅(qū)動，其中細分的大小基于兩個繞組中的電流的大小。以這種方式，步長是減少了，而低速平滑度得到大幅度提高。高細分驅(qū)動電動機細分整步步進到多達500個細分步，轉(zhuǎn)一圈可細分十萬步。在這種情況下，繞