機(jī)械專業(yè)外文翻譯

1、第1頁(yè)外文翻譯英文原文Belt Conveying Systems Development of driving systemAmong the methods of material conveying employed belt conveyors play a very important part in the reliable carrying of material over long distances at competitive cost Conveyor systems have become larger and more complex and drive system

2、s have also been going through a process of evolution and will continue to do so. Nowadays, bigger belts require more power and have brought the need for larger individual drives as well as multiple drives such as 3 drives of 750 kW for one belt(this is the case for the conveyor drives in Chengzhuan

3、g Mine). The ability to control drive acceleration torque is critical to belt conveyors5 performance. An efficient drive system should be able to provide smooth, soft starts while maintaining belt tensions within the specified safe limits. For load sharing on multiple drives. torque and speed contro

4、l are also important considerations in the drive systems design. Due to the advances in conveyor drive control technology, at present many more reliable. Cost-effective and performance-driven conveyor drive systems covering a wide range of power are available for customers5 choicestAnalysis on conve

5、yor drive technologies1. 1 Direct drivesFull-voltage starters. With a full-voltage starter design, the conveyor head shaft is direct-coupled to the motor through the gear drive. Direct full-voltage starters are adequate for relatively low-power, simple-profile conveyors. With direct full-voltage sta

6、rters. no control is provided for various conveyor loads and. depending on the ratio between full-and no-load power requirements, empty starting times can be three or four times faster than full load.The maintenance-free starting system is simple, low-cost and very reliable. However, they cannot con

7、trol starting torque and maximum stall torque； therefore. they are第2頁(yè) limited to the low-power, simple-profile conveyor belt drives.Reduced-voltage starters. As conveyor power requirements increase, controlling the applied motor torque during the acceleration period becomes increasingly important. B

8、ecause motor torque 1s a function of voltage motor voltage must be controlled. This can be achieved through reduced-voltage starters by employing a silicon controlled rectifier(SCR). A common starting method with SCR reduced-voltage starters is to apply low voltage initially to take up conveyor belt

9、 slack. and then to apply a timed linear ramp up to full voltage and belt speed. However, this starting method will not produce constant conveyor belt acceleration. When acceleration is complete the SCRs, which control the applied voltage to the electric motor. are locked in full conduction, providi

10、ng fu11-line voltage to the motor Motors with higher torque and pulup torque, can provide better starting torque when combined with the SCR starters, which are available in sizes up to 750 KW.Wound rotor induction motors. Wound rotor induction motors are connected directly to the drive system reduce

11、r and are a modified configuration of a standard AC induction motor. By inserting resistance in series with the motors rotor windings. the modified motor control system controls motor torque For conveyor starting, resistance is placed in series with the rotor for low initial torque. As the conveyor

12、accelerates, the resistance is reduced slowly to maintain a constant acceleration torque. On multiple-drive systems. an external slip resistor may be left in series with the rotor windings to aid in load sharing The motor systems have a relatively simple design.However, the control systems for these

13、 can be highly complex,because they are based on computer control of the resistance switching. Today, the majority of control systems are custom designed to meet a conveyor systems particular specifications. Wound rotor motors are appropriate for systems requiring more than 400 kW .DC motor. DC moto

14、rs. available from a fraction of thousands of kW , are designed to deliver constant torque below base speed and constant kW above base speed to the maximum allowable revolutions per minute(r/min). with the majority of conveyor drives, a DC shunt wound motor is used.Wherein the motors rotating armatu

15、re is第3頁(yè) connected externally. The most common technology for controlling DC drives is a SCR device. which allows for continual variable-speed operation. The DC drive system is mechanically simple, but can include complex custom-designed electronics to monitor and control the complete system. This s

16、ystem option is expensive in comparison to other soft-start systems.but it is a reliable, cost-effective drive in applications in which torque,1oad sharing and variable speed are primary considerations. DC motors generally are used with higher-power conveyors, including complex profile conveyors wit

17、h multiple-drive systems, booster tripper systems needing belt tension control and conveyors requiring a wide variable-speed range. 1. 2 Hydrokinetic couplingHydrokinetic couplings, commonly referred to as fluid couplings. are composed of three basic elements; the driven impeller, which acts as a ce

18、ntrifugal pump the driving hydraulic turbine known as the runner and a casing that encloses the two power components.Hydraulic fluid is pumped from the driven impeller to the driving runner, producing torque at the driven shaft. Because circulating hydraulic fluid produces the torque and speed, no m

19、echanical connection is required between the driving and driven shafts. The power produced by this coupling is based on the circulated fluids amount and density and the torque in proportion to input speed.Because the pumping action within the fluid coupling depends on centrifugal forces.the output s

20、peed is less than the input spee.d Referred to as slip.this normally is between l% and 3%. Basic hydrokinetic couplings are available in configurations from fractional to several thousand kW .Fixed-fill fluid couplings. Fixed-fill fluid couplings are the most commonly used soft-start devices for con

21、veyors with simpler belt profiles and limited convex/concave sections. They are relatively simple,1ow-cost,reliable,maintenance free devices that provide excellent soft starting results to the majority of belt conveyors in use today.Variable-fill drain couplings. Drainable-fluid couplings work on th

22、e same principle as fixed-fill couplings. The couplings impellers are mounted on the AC motor and the runners on the driven reducer high-speed shaf.t Housing mounted to the drive base encloses the working circuit.The couplings rotating casing contains第4頁(yè) bleed-off orifices that continually allow flu

23、id to exit the working circuit into a separate hydraulic reservoir. Oil from the reservoir is pumped through a heat exchanger to a solenoid-operated hydraulic valve that controls the filling of the fluid coupling. To control the starting torque of a single-drive conveyor system, the AC motor current

24、 must be monitored to provide feedback to the solenoid control valve. Variable fill drain couplings are used in medium to high-kW conveyor systems and are available in sizes up to thousands of kW . The drives can bemechanically complex and depending on the control parameters.the system can be electr

25、onically intricate. The drive system cost is medium to high, depending upon size specified.Hydrokinetic scoop control drive. The scoop control fluid coupling consists of the three standard fluid coupling components： a driven impeller, a driving runner and a casing that encloses the working circuit T

26、he casing is fitted with fixed orifices that bleed a predetermined amount of fluid into a reservoir.When the scoop tube is fully extended into the reservoir, the coupling is l00 percent filled. The scoop tube, extending outside the fluid coupling, is positioned using an electric actuator to engage t

27、he tube from the fully retracted to the fully engaged position.This control provides reasonably smooth acceleration rates.to but the computer-based control system is very complex. Scoop control couplings are applied on conveyors requiring single or multiple drives from l50 kW to 750 kW.1. 3 Variable

28、-frequency control(VFC)Variable frequency control is also one of the direct drive methods.The emphasizing discussion about it here is because that it has so unique characteristic and so good performance compared with other driving methods for belt conveyor. VFC devices Provide variable frequency and

29、 voltage to the induction motor, resulting in an excellent starting torque and acceleration rate for belt conveyor drives. VFC drives. available from fractional to several thousand(kW ), are electronic controllers that rectify AC line power to DC and, through an inverter, convert DC back to AC with

30、frequency and voltage control. VFC drives adopt vector control or direct torque control(DTC)technology, and can adopt different operating speeds according to different loads. VFC drives can make starting or stalling第5頁(yè) according to any given S-curves. realizing the automatic track for starting or st

31、alling curves. VFC drives provide excellent speed and torque control for starting conveyor belts. and can also be designed to provide load sharing for multiple drives. easily VFC controllers are frequently installed on lower-powered conveyor drives, but when used at the range of medium-high voltage

32、in the past. the structure of VFC controllers becomes very complicated due to the limitation of voltage rating of power semiconductor devices, the combination of medium-high voltage drives and variable speed is often solved with low-voltage inverters using step-up transformer at the output, or with

33、multiple low-voltage inverters connected in series. Three-level voltage-fed PWM converter systems are recently showing increasing popularity for multi-megawatt industrial drive applications because of easy voltage sharing between the series devices and improved harmonic quality at the output compare

34、d to two-level converter systems With simple series connection of devices. This kind of VFC system with three 750 kW /2 3kV inverters has been successfully installed in ChengZhuang Mine for one 2. 7-km long belt conveyor driving system in following the principle of three-level inverter will be discu

35、ssed in detail.Neutral point clamped(NPC)three-level inverter using IGBTsThree-level voltage-fed inverters have recently become more and more popular for higher power drive applications because of their easy voltage sharing features. lower dv/dt per switching for each of the devices, and superior ha

36、rmonic quality at the output. The availability of HV-IGBTs has led to the design of a new range of medium-high voltage inverter using three-level NPC topology. This kind of inverter can realize a whole range with a voltage rating from.23 kV to 4. 1 6 kV Series connection of HV-IGBT modules is used i

37、n the 3. 3 kV and 4. 1 6 kV devices. The 2. 3 kV inverters need only one HV-IGBT per switch2,3 2. 1 Power sectionTo meet the demands for medium voltage applications.a three-level neutral point clamped inverter realizes the power section.In comparison to a two-level inverter.the NPC inverter offers t

38、he benefit that three voltage levels can be supplied to the output terminals,so for the same output current quality,only第6頁(yè) 1/4 of the switching frequency is necessary Moreover the voltage ratings of the switches in NPC inverter topology will be reduced to 1/2. and the additional transient voltage s

39、tress on the motor can also be reduced to 1/2 compared to that of a two-level inverter.The switching states of a three-level inverter are summarized in Table 1. U. V and W denote each of the three phases respectively； P N and O are the dc bus points. The phase U, for example, is in state P(positive

40、bus voltage)when the switches S1 and S2 are closed, whereas it is in state N (negative bus voltage) when the switches and S4 are closed. At neutral point clamping the phase is in O state when either or S3 conducts depending on positive or negative phase current polarity, respectively. For neutral po

41、int voltage balancing, the average current injected at O should be zero.2. 2 Line side converterFor standard applications. a l2-pulse diode rectifier feeds the divided DC-link capacitor. This topology introduces low harmonics on the line side. For even higher requirements a 24-pulse diode rectifier

42、can be used as an input converter. For more advanced applications where regeneration capability is necessary, an active front. end converter can replace the diode rectifier, using the same structure as the inverter.2. 3 Inverter controlMotor Contro1.Motor control of induction machines is realized by

43、 using a rotor flux.oriented vector controller.Fig.2 shows the block diagram of indirect vector controlled drive that incorporates both constant torque and high speed field-weakening regions where the PW M modulator was used. In this figure, the command flux is generated as function of speed.The fee

44、dback speed is added with the feed forward slip command signal .the resulting frequency signal is integrated and then the unit vector signals(cos，,： and sin )are generated. The vector rotator generates the voltage1 and angle H commands for the PW M as shown.PWM Modulator. The demanded voltage vector

45、 is generated using an elaboratePWM modulator. The modulator extends the concepts of space-vector modulation to the three-level inverter. The operation can be explained by starting from a regularly sampled sine-triangle comparison from two-level inverter. Instead of using one set of reference wavefo

46、rms and one triangle defining the switching frequency, the three-level modulator uses two sets of reference waveforms U 1 and U 2 and just one triangle. Thus, each switching transition is used in an optimal way so that several objectives are reached at the same time.Very low harmonics are generated.

47、 The switching frequency is low and thus switching losses are minimized. As in a two-level inverter, a zero-sequence component can be added to each set of reference waveform s in order to maximize the fundamental voltage component. As an additional degree of freedom, the position of the reference wa

48、veform s within the triangle can be changed This can be used for current balance in the two halves of the DCTink.Testing resultsAfter Successful installation of three 750 kW /2 3 kV three-level inverters for one 2. 7 km long belt conveyor driving system in Chengzhuang Mine. The performance of the wh

49、ole VFC system was tested. Fig. 3 is taken from the test, which shows the excellent characteristic of the belt conveyor driving system with VFC controller.Fig. 3 includes four curves. The curve 1 shows the belt tension. From the curve it can be find that the fluctuation range of the belt tension is

50、very small. Curve 2 and curve 3 indicate current and torque separately Curve 4 shows the velocity of the controlled belt. The belt velocity have the s shape characteristic. All the results of the test show a very satisfied characteristic for belt driving system.ConclusionsAdvances in conveyor drive

51、control technology in recent years have resulted in many more reliable. Cost-effective and performance-driven conveyor drive system choices for users. Among these choices, the Variable frequency control (VFC) method shows promising use in the future for long distance belt conveyor drives due to its

52、excellent performances. The NPC three-level inverter using high voltage IGBTs第8頁(yè) make the Variable frequency control in medium voltage applications become much more simple because the inverter itself can provide the medium voltage needed at the motor terminals， thus eliminating the step-up transform

53、er in most applications in the past.The testing results taken from the VFC control system with NPC three. level inverters used in a 2. 7 km long belt conveyor drives in Chengzhuang Mine indicates that the performance of NPC three-level inverter using HV-IGBTs together with the control strategy of ro

54、tor field-oriented vector control for induction motor drive is excellent for belt conveyor driving system.中文譯文:帶式輸送機(jī)及其牽引系統(tǒng)在運(yùn)送大量的物料時(shí)，帶式輸送機(jī)在長(zhǎng)距離的運(yùn)輸中起到了非常重要的競(jìng)爭(zhēng)作用。 輸送系統(tǒng)將會(huì)變得更大、更復(fù)雜，而驅(qū)動(dòng)系統(tǒng)也已經(jīng)歷了一個(gè)演變過(guò)程，并將繼續(xù)這樣下 去。如今，較大的輸送帶和多驅(qū)動(dòng)系統(tǒng)需要更大的功率，比如3驅(qū)動(dòng)系統(tǒng)需要給輸送帶 750KW (成莊煤礦輸送機(jī)驅(qū)動(dòng)系統(tǒng)的要求)。控制驅(qū)動(dòng)力和加速度扭矩是輸送機(jī)的關(guān)鍵。一 個(gè)高效的驅(qū)動(dòng)系統(tǒng)應(yīng)該能順利的運(yùn)行,同

55、時(shí)保持輸送帶張緊力在指定的安全極限負(fù)荷內(nèi)。為 了負(fù)載分配在多個(gè)驅(qū)動(dòng)上，扭矩和速度控制在驅(qū)動(dòng)系統(tǒng)的設(shè)計(jì)中也是很重要的因素。由于 輸送機(jī)驅(qū)動(dòng)系統(tǒng)控制技術(shù)的進(jìn)步，目前更多可靠的低成本和高效驅(qū)動(dòng)的驅(qū)動(dòng)系統(tǒng)可供顧客 選擇1。1帶式輸送機(jī)驅(qū)動(dòng)1.1帶式輸送機(jī)驅(qū)動(dòng)方式全電壓?jiǎn)?dòng) 在全電壓?jiǎn)?dòng)設(shè)計(jì)中，帶式輸送機(jī)驅(qū)動(dòng)軸通過(guò)齒輪傳動(dòng)直接連接到電 機(jī)。直接全壓驅(qū)動(dòng)沒(méi)有為變化的傳送負(fù)載提供任何控制,根據(jù)滿載和空載功率需求的比率， 空載啟動(dòng)時(shí)比滿載可能快34倍。此種方式的優(yōu)點(diǎn)是:免維護(hù),啟動(dòng)系統(tǒng)簡(jiǎn)單，低成本，可 靠性高。但是，不能控制啟動(dòng)扭矩和最大停止扭矩。因此，這種方式只用于低功率結(jié)構(gòu)簡(jiǎn) 單的傳送驅(qū)動(dòng)中。降壓?jiǎn)?dòng)隨著

56、傳送驅(qū)動(dòng)功率的增加，在加速期間控制使用的電機(jī)扭矩變得越來(lái)越重要。由于電機(jī)扭矩是電壓的函數(shù)，電機(jī)電壓必須得到控制，一般用可控硅整流器(SCR)構(gòu) 成的降壓?jiǎn)?dòng)裝置，先施加低電壓拉緊輸送帶，然后線性的增加供電電壓直到全電壓和最大 帶速。但是，這種啟動(dòng)方式不會(huì)產(chǎn)生穩(wěn)定的加速度，當(dāng)加速完成時(shí)，控制電機(jī)電壓的SCR鎖 定在全導(dǎo)通，為電機(jī)提供全壓。此種控制方式功率可達(dá)到750kW。繞線轉(zhuǎn)子感應(yīng)電機(jī)繞線轉(zhuǎn)子感應(yīng)電機(jī)直接連接到驅(qū)動(dòng)系統(tǒng)減速機(jī)上，通過(guò)在電機(jī)轉(zhuǎn)子繞組中串聯(lián)電阻控制電機(jī)轉(zhuǎn)矩。在傳送裝置啟動(dòng)時(shí)，把電阻串聯(lián)進(jìn)轉(zhuǎn)子產(chǎn)生較低的轉(zhuǎn) 矩，當(dāng)傳送帶加速時(shí)，電阻逐漸減少保持穩(wěn)定增加轉(zhuǎn)矩。在多驅(qū)動(dòng)系統(tǒng)中，一個(gè)外加的滑

57、 差電阻可能將總是串聯(lián)在轉(zhuǎn)子繞組回路中以幫助均分負(fù)載。該方式的電機(jī)系統(tǒng)設(shè)計(jì)相對(duì)簡(jiǎn) 單，但控制系統(tǒng)可能很復(fù)雜，因?yàn)樗鼈兪腔谟?jì)算機(jī)控制的電阻切換。當(dāng)今，控制系統(tǒng)的 大多數(shù)是定制設(shè)計(jì)來(lái)滿足傳送系統(tǒng)的特殊規(guī)格。繞線轉(zhuǎn)子電機(jī)適合于需要400kW以上的系 統(tǒng)。直流(DC)電機(jī)大多數(shù)傳送驅(qū)動(dòng)使用DC并勵(lì)電機(jī)，電機(jī)的電樞在外部連接?？刂艱C驅(qū)動(dòng)技術(shù)一般應(yīng)用SCR裝置，它允許連續(xù)的變速操作。DC驅(qū)動(dòng)系統(tǒng)在機(jī)械上是簡(jiǎn)單 的，但設(shè)計(jì)的電子電路，監(jiān)測(cè)和控制整個(gè)系統(tǒng)，相比于其他軟啟動(dòng)系統(tǒng)的選擇是昂貴的，但 在轉(zhuǎn)矩、負(fù)載均分和變速為主要考慮的場(chǎng)合，它又是一個(gè)可靠的，節(jié)約成本的方式。DC電 機(jī)一般使用在功率較大的輸送裝置

58、上，包括需要輸送帶張力控制的多驅(qū)動(dòng)系統(tǒng)和需要寬變 速范圍的輸送裝置上。1. 2液力偶合器流體動(dòng)力偶合器通常被稱為液力偶合器，由三個(gè)基本單元組成：充當(dāng)離心泵的葉輪， 推進(jìn)水壓的渦輪和裝進(jìn)兩個(gè)動(dòng)力部件的外殼。流體從葉輪到渦輪，在從動(dòng)軸產(chǎn)生扭矩。由 于循環(huán)流體產(chǎn)生扭矩和速度，在驅(qū)動(dòng)軸和從動(dòng)軸之間不需要任何機(jī)械連接。這種連接產(chǎn)生 的動(dòng)力決定于液力偶合器的充液量，扭矩正比于輸入速度。因在流體偶合中輸出速度小于 輸入速度，其間的差值稱為滑差,一般為1 %3 %。傳遞功率可達(dá)幾千千瓦。固定充液液力偶合器固定充液液力偶合器是在結(jié)構(gòu)較簡(jiǎn)單和僅具有有限的彎曲部分的輸送裝置中最常用的軟啟動(dòng)裝置，其結(jié)構(gòu)相對(duì)比較簡(jiǎn)單，

59、成本又低，對(duì)現(xiàn)在使用的 大多數(shù)輸送機(jī)能提供優(yōu)良的軟啟動(dòng)效果?？勺兂湟阂毫ε己掀饕卜Q為限矩型液力偶合器。偶合器的葉輪裝在AC電機(jī)上，渦輪裝在從動(dòng)減速器高速軸上，包含操作部件的軸箱安裝在驅(qū)動(dòng)基座。偶合器的旋轉(zhuǎn)外殼 有溢出口,允許液體不斷地從工作腔中流出進(jìn)入一個(gè)分離的輔助腔，油從輔助腔通過(guò)一個(gè)熱 交換器泵到控制偶合器充液量的電磁閥。為了控制單機(jī)傳動(dòng)系統(tǒng)的啟動(dòng)轉(zhuǎn)矩，必須監(jiān)測(cè)AC 電機(jī)電流，給電磁閥的控制提供反饋?？勺兂湟阂毫ε己掀骺墒褂迷谥写蠊β瘦斔拖到y(tǒng)中， 功率可達(dá)到數(shù)千千瓦。這種驅(qū)動(dòng)無(wú)論在機(jī)械，或在電氣上都是很復(fù)雜的，其驅(qū)動(dòng)系統(tǒng)成本中 等。勺管控制液力偶合器也稱為調(diào)速型液力偶合器。此種液力偶合器同

60、樣由三個(gè)標(biāo)準(zhǔn)的液力偶合單元構(gòu)成，即葉輪、渦輪和一個(gè)包含工作環(huán)路的外殼。此種液力偶合器需要在 工作腔以外設(shè)置導(dǎo)管(也稱勺管)和導(dǎo)管腔，依靠調(diào)節(jié)裝置改變勺管開度(勺管頂端與旋轉(zhuǎn) 外殼間距)人為的改變工作腔的充液量,從而實(shí)現(xiàn)對(duì)輸出轉(zhuǎn)速的調(diào)節(jié)。這種控制提供了合理 的平滑加速度，但其計(jì)算機(jī)控制系統(tǒng)很復(fù)雜。勺管控制液力偶合器可以應(yīng)用在單機(jī)或多機(jī) 驅(qū)動(dòng)系統(tǒng)，功率范圍為150kW750kW。1. 3變頻控制(VFC)變頻控制也是一種直接驅(qū)動(dòng)方式，它具有非常獨(dú)特的高性能。VFC裝置為感應(yīng)電機(jī)提 供變化的頻率和電壓，產(chǎn)生優(yōu)良的啟動(dòng)轉(zhuǎn)矩和加速度VFC設(shè)備是一個(gè)電力電子控制器，首先第11頁(yè)把AC整流成DC，然后利用逆