液壓比例控制雙語課件匯總?cè)譸pt完整版課件最全教學(xué)教程整套課件全書電子教案

1、1/34電液比例控制技術(shù)Electro-hydraulic proportional control第一章 概述第二章 比例電磁鐵第三章 電液比例控制閥第四章 電液比例容積控制第五章 電液比例控制基本回路第六章 比例放大器第七章 電液比例控制系統(tǒng)的分析 與設(shè)計(jì)第八章 電液比例控制技術(shù)的工程 應(yīng)用Chapter 1 IntroductionChapter 2 The proportional electromagnetChapter 3 Electro-hydraulic Proportional Control ValveChapter 4 Electro-hydraulic proporti

2、onal volume controlChapter 5 Basic Electro-hydraulic Proportional Control CircuitsChapter 6 proportional amplifierChapter 7 Analysis and Design of Electro- hydraulic Proportional Control SystemChapter 8 Engineering application of Electro-hydraulic proportional control technology目錄catalogue 3/34第一章 概

3、述Chapter 1 Introduction第一章 概述Chapter 1 Introduction 1.1 The overview of the development of Electro- hydraulic proportional technology1.2 The concept of Electro-hydraulic proportional control1.3 Basic principal of Electro-hydraulic proportional control system and its constitution1.4 Classification of

4、 Electro-hydraulic proportional control system1.5 Characteristics and applications of Electro-hydraulic proportional control system1.1 電液比例技術(shù)的發(fā)展概況1.2 電液比例控制的概念1.3 電液比例控制系統(tǒng)的工作 原理及組成1.4 電液比例控制系統(tǒng)的分類1.5 電液比例控制的特點(diǎn)及應(yīng)用 傳統(tǒng)的液壓控制方式是開關(guān)型控制，它通過電磁驅(qū)動(dòng)或手動(dòng)驅(qū)動(dòng)來實(shí)現(xiàn)液壓流體的通、斷和方向控制，從而實(shí)現(xiàn)被控對(duì)象的機(jī)械化和自動(dòng)化。但是這種方式無法實(shí)現(xiàn)對(duì)液流流量、壓力連續(xù)地按比例地控

5、制，同時(shí)控制的速度比較低、精度差、換向時(shí)沖擊比較大。 The traditional way of hydraulic control is switch control. In this switch control method, there are two ways to control the hydraulic fluidthe electronagnetic drive way and manual drive way. The hydraulic fluid can be controlled to be through or off, thus the controlled o

6、bject can be achieve as mechanization and automation. However, in this switch control method, it is hardly to make sure that the flow rate and the pressure of the hydraulic fluid is controlled to be continuously and proportionally. Besides, in this switch control method, the response speed is slow,

7、the control accuracy is low, and in the case of hydraulic fluid direction changing , the impact is large. 1.1 電液比例技術(shù)的發(fā)展概況The overview of the development of electro-hydraulic proportional technology 第二次世界大戰(zhàn)期間，由于以飛機(jī)、火炮等軍事裝備為對(duì)象的控制系統(tǒng)，要求快速響應(yīng)、高精度等高性能指標(biāo)，在這個(gè)背景下迅速發(fā)展了電液伺服控制。這種控制方式可根據(jù)輸入信號(hào)(如電流)的大小連續(xù)、按比例地改變液流的流量

8、、壓力和方向，克服開關(guān)型控制的缺點(diǎn)，實(shí)現(xiàn)高性能的控制要求。 During the Second World War, the control systems of aircraft, artillery and other military equipment require high-performance indicators such as fast response and high precision, then it cause rapid development of Electro-hydraulic servo control. In Electro-hydraulic se

9、rvo control system, the flow rate, pressure and direction of the fluid can be controlled to be continously and proportionally, according to the strength of the input signal (such as the current). This Electro-hydraulic servo control system overcomed the shortcomings of the switch control method , an

10、d achieved the requirements of high performance control. 60年代電液伺服控制日趨成熟 ，向民用工業(yè)推廣。同時(shí)，液壓伺服系統(tǒng)暴露出了它致命的弱點(diǎn)：元件的制造精度要求過高，成本昂貴；對(duì)油液污染十分敏感，因此系統(tǒng)的維護(hù)成本高；能量損失(閥壓降)較大。因?yàn)橐话愎I(yè)控制系統(tǒng)，它要求精度不太高，響應(yīng)也不需要太快。 In the 1960s, the use of electro-hydraulic servo control became matured day by day, and it was rapidly promoted to the

11、civilian industry. But at the same time, hydraulic servo system exposed its biggest weakness: high precision, expensive cost of components manufacturing and sensitiveness to oil pollution. All of these shortcomings means that it requires high cost of maintenance. Besides the loss in energy (such as

12、valve pressure drop) is also large. However, in most industrial control system, neither the precision is required so high nor the speed of respond is required so quickly. 卻要求系統(tǒng)對(duì)油液污染和善通液壓系統(tǒng)差不多，維護(hù)簡(jiǎn)單，成本低廉，于是人們就想到如何發(fā)展一種廉價(jià)的伺服控制，這便導(dǎo)致研究和發(fā)展電液比例控制技術(shù)。比例技術(shù)的發(fā)展大致可以劃分為三個(gè)階段：第一階段：液壓比例技術(shù)的誕生第二階段：比例技術(shù)日趨成熟第三階段：比例技術(shù)飛速發(fā)展

13、requires that the controlled system is not sensitive to oil pollution and easy maintenance and low cost. Hence people turned to develop a low-cost servo control system. And it caused the research and development of Electro-hydraulic proportional control technology. Proportional control technology ca

14、n be divided into three stages:The first stage: the birth of hydraulic proportional technology The second stage:proportional control technology is matured day by dayThe third stage:proportional technology entered into the rapid development第一階段：1967年瑞士Beoringer公司率先生產(chǎn)出KL型比例復(fù)合閥，標(biāo)志液壓比例技術(shù)的誕生。到70年代初日本油研公司

15、研制壓力和流量兩種比例閥并獲得了專利。這段時(shí)間，主要是以比例型電-機(jī)械變換器，例如比例電磁鐵、伺服電機(jī)、動(dòng)圈式力矩馬達(dá)等取代普通液壓閥中的手動(dòng)調(diào)節(jié)裝置和普通電磁鐵，實(shí)現(xiàn)電液比例控制，而閥內(nèi)的結(jié)構(gòu)和設(shè)計(jì)準(zhǔn)則幾乎沒有什么變化。從性能上說，頻寬約15Hz，滯環(huán)約47，多數(shù)只用于開環(huán)控制。 The first stage: In 1967, the Swiss Beoringer company firstly produced the KL type proportional composite valve, which was marked as the birth of hydraulic pr

16、oportional technology. In the early 1970s, Japanese YUKEN company produced two kinds of proportional valve (pressure and flow), and applied them for patent. In this period of time, manual adjustment device and ordinary electromagnet was mainly replaced by proportional electro - mechanical converter

17、such as proportional solenoid, servo motor, dynamic torque motor, etc. to realize electro hydraulic proportional control. And the structure and design standards almost kept the same. In terms of performance , the bandwidth is about 15Hz and hysteresis is about 47%, most are only used for switch cont

18、rol.第二階段：從1975年到1980年，比例技術(shù)進(jìn)入發(fā)展的第二階段，比例器件普遍采用了各種內(nèi)反饋回路，同時(shí)研制了耐高壓的比例電磁鐵，與之配套的比例放大器也日趨成熟，從性能上說，比例閥的頻寬已達(dá)515Hz，滯環(huán)縮小到3左右，不僅用于開環(huán)控制，也廣泛地用于各種閉環(huán)控制系統(tǒng)中。The second stage: From 1975 to 1980, proportional control technology entered into its second stage. The proportional devices had commonly used variety of internal

19、 feedback loops. Meanwhile, high pressure solenoid is developed and the development of amplifier is matured day by day. In the term of the performance, the bandwidth of proportional valves had reached to 515Hz and hysteresis had been narrowed to 3%, proportional technology had begun to be not only u

20、sed for open loop control system, but also widely used in a variety of closed-loop control system.第三階段：1980年以來，比例技術(shù)進(jìn)入了飛速發(fā)展階段，并取得了長足的進(jìn)步，具體體現(xiàn)如下： 設(shè)計(jì)原理進(jìn)一步完善，通過液壓、機(jī)械以及電氣的各種反饋手段，使比例閥的性能如滯環(huán)、頻寬等，同工業(yè)伺服閥接近，只是因制造成本所限，尚存在一定的中位死區(qū)；比例技術(shù)同插裝技術(shù)結(jié)合，開發(fā)出二通、三通比例插裝閥； The third stage: Since the 1980s, proportional technolog

21、y had entered into the rapid development stage, and made great progress. For example: 1) Design principles have been improved. And the performances of proportional valve such as hysteresis,bandwidth, etc. was more and more approach to the servo valves, though there still existed some median dead zon

22、e because of the limit of manufacturing cost;2) Proportional technology was combined with the cartridge technology, and two and three proportional cartridge valves had been developed； 第三階段：80年代以來，比例技術(shù)進(jìn)入了飛速發(fā)展階段，并取得了長足的進(jìn)步，具體體現(xiàn)如下： 3) 設(shè)計(jì)原理進(jìn)一步完善，通過液壓、機(jī)械以及電氣的各種反饋手段，使比例閥的性能如滯環(huán)、頻寬等，同工業(yè)伺服閥接近，只是因制造成本所限，尚存在一定的

23、中位死區(qū)；4) 比例技術(shù)同插裝技術(shù)結(jié)合，開發(fā)出二通、三通比例插裝閥； The third stage: Since the 1980s, proportional technology had entered into the rapid development stage, and made great progress. For example: 3) Electro-mechanical devices had appeared, in which devices it combined proportional valve, sensors, electronic amplifier

24、and digital display into one piece； 4) The proportional valves were combined with hydraulic pumps and hydraulic motors, and that constitutes energy-saving proportional volume devices. 近年來比例控制技術(shù)被迅速、廣泛地應(yīng)用于各種工業(yè)控制，各種比例器件在許多國家形成了系列化、標(biāo)準(zhǔn)化的產(chǎn)品，例如西德已有30普通閥的市場(chǎng)被比例閥取代。除了模擬式的電液比例元件外，人們也注重于開發(fā)出各種數(shù)字式的比例元件。數(shù)字式液壓元件也是今

25、后比例技術(shù)發(fā)展的一個(gè)重要分支。 In recent years, the proportional control technology has been rapidly and widely used in various industrial control systems. And the proportional devices have been developed in serial and standardly in many countries. For example, over 30% of the market of the normal valves have been

26、 replaced by proportional valves in West Germany. And people have paid more attention to the development of various digital proportional components besides the analogous electro-hydraulic proportional components. Digital hydraulic components will become one of most important branches of proportional

27、 control technology in the future. 電液比例技術(shù)還出現(xiàn)了很多所謂整體閉環(huán)控制，即全程電反饋的電液比例元件。其中有各種比例閥、比例容積控制、恒功率控制、恒流量控制、恒壓力控制動(dòng)力源等。 Electro-hydraulic proportional components with overall closed-loop control which means the electrical feedback in the whole course such as various proportional valves, proportional volume con

28、trol, constant power control, constant flow control, constant pressure control,etc. also appear in the field of Electro-hydraulic proportional technology. 從廣義上講，凡是輸出量，如壓力、流量、位移、速度、加速度等，能隨輸入信號(hào)連續(xù)地按比例地變化的控制系統(tǒng)，都稱為比例控制系統(tǒng)。從這個(gè)意義上說，伺服控制也是一種比例控制。 但是通常所說的比例控制系統(tǒng)是特指介于開關(guān)控制和伺服控制之間的一種新型控制系統(tǒng)。與開關(guān)控制系統(tǒng)比較，它能實(shí)現(xiàn)連續(xù)、比例控制，并

29、且控制精度高、反應(yīng)速度快；Generally speaking, proportional control system is the one that output signal such as pressure, flow, displacement, velocity and acceleration, etc. can change continuously and proportionally with the input signal. In this sense, servo control is also a kind of proportional control. Howe

30、ver, normally, proportional control system is considered as a new kind of control system between the on-off control and servo control. Compared with the on-off control system, it can achieve the continuous and proportional control, and it has high control accuracy and quick response.1.2電液比例控制的概念The

31、concept of electro-hydraulic proportional control 此外，以德國Bosch公司為代表推出的高性能閉環(huán)比例閥。由于采用了高響應(yīng)直流比例電磁鐵和相應(yīng)的放大器，含內(nèi)置位置檢測(cè)電子裝置和反饋閉環(huán)，采用零開口四邊滑閥，其輸出穩(wěn)態(tài)特性中無中位死區(qū)滯環(huán)僅0.3%，頻寬達(dá)200Hz，其性能與伺服閥無異。 In addition, as a representative, the German Bosch company has introduced high-performance closed-loop proportional valves, which u

32、sed high response DC proportional solenoids, corresponding amplifiers, built-in position detection electronic devices and feedback loops, with zero-opened four-sided slide valve. There is no dead zone in its steady-state characteristics and the hysteresis is just 0.3% and the bandwidth is 200Hz, whi

33、ch has the same performance as servo valves. 現(xiàn)在比例閥已有些是把傳感器、測(cè)量放大器、控制放大器和閥復(fù)合在一起的機(jī)電一體化的元件，使得結(jié)構(gòu)更緊湊，性能進(jìn)一步提高。 Nowadays, some proportional valves are Electro-mechanical components which combine the sensors, measuring amplifiers and control amplifiers with valves. This makes the structure more compact and i

34、mproves the performance. 與伺服控制系統(tǒng)比較，由于比例閥是在普通工業(yè)用閥的基礎(chǔ)上改造而成的，因此加工精度不高，成本低廉，抗污染性能好，幾乎同開關(guān)型控制差不多，控制精度、反應(yīng)速度等控制性能雖然比伺服閥和伺服系統(tǒng)差，但能滿足大多數(shù)工業(yè)控制的要求，并且閥內(nèi)壓降小，因此能節(jié)省能耗，降低發(fā)熱量。Compared with the servo control system, the proportional control system is almost similar with the on-off control. Since proportional valves are

35、transformed from common industrial valves, so they have low cost and good anti-pollution performance, but their machining accuracy are not so good. Though proportional valves and systems have lower control performances such as control precision, response speed, etc. than servo valves and servo syste

36、ms, they still can meet the requirements of most industrial control systems. Besides, the valve pressure drop is low, so it saves energy and reduces heat. 比例控制主要用于開環(huán)系統(tǒng)，伺服控制主要用于閉環(huán)系統(tǒng)。伺服控制裝置總是帶有內(nèi)反饋，任何檢測(cè)到的誤差都會(huì)引起系統(tǒng)狀態(tài)的改變，而這種改變正是強(qiáng)迫這個(gè)誤差為零。誤差為零時(shí)伺服系統(tǒng)處于平衡狀態(tài)，直到新的誤差檢測(cè)出來。在伺服控制系統(tǒng)中，平衡狀態(tài)控制信號(hào)（誤差）理論上為零，而比例控制系統(tǒng)卻永遠(yuǎn)不會(huì)為零。

37、The proportional control system is mainly used in open-loop control system, and the servo control system is mainly used in closed-loop system. Servo control devices always have internal feedback. Any error detected can cause the change of system state, and this change is to force the error to zero.

38、When the error is zero, servo system is in balance until a new error is detected.In servo control system,the error of control signal in balance is zero,but proportional control system is never be zero. 比例系統(tǒng)中的主控元件可以有無限種狀態(tài)，分別對(duì)應(yīng)受控對(duì)象的無限種運(yùn)動(dòng)，而開關(guān)控制中控制元件只有兩種狀態(tài)。在工程實(shí)際應(yīng)用中，由于多數(shù)被控對(duì)象僅需要有限的幾種狀態(tài)，因而開關(guān)控制也有可取之處。開關(guān)元件通常

39、簡(jiǎn)單可靠，不存在系統(tǒng)的不穩(wěn)定性。 在模擬比例控制中，如果需要用計(jì)算機(jī)來控制，則必須具有A/D、D/A接口元件與計(jì)算機(jī)連接。In the proportional system, the main control elements may have infinite states, in corresponding to infinite states of controlled elements. However, in on-off control system, the control elements only have two states. In actual engineering

40、 application, as most controlled elements only need several states, on-off control does have its merits, with simple and reliable on-off elements, while without instability in the system. In the analog signal proportional control system, if the computer is needed, A/D, D/A interface elements must be

41、 connected with the computer. 近年來已經(jīng)開發(fā)出了一些比例元件（電液數(shù)模轉(zhuǎn)換器），其輸出量與脈沖數(shù)、脈寬或脈沖頻率成比例。其優(yōu)點(diǎn)是抗污染能力強(qiáng)，滯后時(shí)間短，重復(fù)性好，能與數(shù)字計(jì)算機(jī)直接連接，是電液比例技術(shù)中的一個(gè)新領(lǐng)域。In recent years, some proportional elements such as electro-hydraulic analog-to-digital converter have been invented, whose outputs are proportional to pulse number, pulse widt

42、h or pulse frequency. With the advantages in contamination resistance, shorter delay time, excellent repeatability and connection to the computer directly, it is a new field in electro-hydraulic proportional technology.1.3 電液比例控制系統(tǒng)的工作原理及組成Basic principal of electro-hydraulic proportional control sys

43、tem and its constitution 圖1.1 電液比例開環(huán)控制系統(tǒng)方框圖 電液比例控制可以分為開環(huán)控制和閉環(huán)控制。開環(huán)控制如圖1.1所示，輸入電壓 U 經(jīng)電子放大器放大后，驅(qū)動(dòng)比例電磁鐵，使之產(chǎn)生一個(gè)與驅(qū)動(dòng)電流 I成比例的力Fd，去推動(dòng)液壓控制閥，液壓控制閥輸出一個(gè)強(qiáng)功率的液壓信號(hào)（壓力 P 和流量 Q ），使執(zhí)行元件拖動(dòng)負(fù)載以所期望的速度 v 運(yùn)動(dòng)。 Electro-hydraulic control can be divided into open-loop control and closed loop control.As in Fig 1.1, in open-loop

44、 control, the input voltage U is amplified by the amplifier, and drives the proportional electromagnet, to create a force Fd which is proportional to the driving electricity I, and push the hydraulic control valve. Then the hydraulic control valve outputs a high power hydraulic signal（pressure P and

45、 flow Q） to drive the load with an expected velocity. We can change the velocity of load through changing the input signal U. Fig. 1.1 Block Diagram (BD) of Electro-Hydraulic open-loop control system 若需提高控制性能，可以采用閉環(huán)控制，如圖1.2。這時(shí)，可在開環(huán)控制的基礎(chǔ)上增加一個(gè)測(cè)量反饋元件，不斷測(cè)量系統(tǒng)的輸出量v，并將它轉(zhuǎn)換成一個(gè)與之成比例的電壓U2 ，反饋到系統(tǒng)的輸入端，同輸入信號(hào)U1比較，

46、形成偏差e。圖1.2 電液比例閉環(huán)控制系統(tǒng)方框圖Fig. 1.2 Block Diagram (BD) of Electro-Hydraulic closed loop control system If we want to improve the control performance, we can use closed loop control system, as shown in Figure 1.2. Then, based on the open-loop control system, a measuring and feedback element will be adde

47、d, which measures the output v and transforms it into voltage U2 proportionally. The voltage U2 returns to the input, compares with the input signal U1, and deviation signal e is formed. 此偏差信號(hào)e經(jīng)放大、校正后，加到電液比例閥上，放大成強(qiáng)功率的液壓信號(hào)P和Q，去驅(qū)動(dòng)執(zhí)行元件，以拖動(dòng)負(fù)載朝著消除偏差的方向運(yùn)動(dòng)，直到偏差e趨近于零為止。從圖可知，電液比例控制系統(tǒng)同電液伺服系統(tǒng)相似，只不過用電液比例閥取代了伺服系

48、統(tǒng)中的電液伺服閥而已。 電液比例控制系統(tǒng)，盡管其結(jié)構(gòu)各異，功能也不相同，但都可歸納為由功能相同的基本單元組成的系統(tǒng)，如圖1.3所示。After the deviation signal was amplified and corrected, it will be added to the electro-hydraulic proportional valve. Then, the signal is converted to hydraulic signal P and Q , driving the power element to eliminate the deviation unt

49、il the deviation tends to be 0. From the figure, the electro-hydraulic proportional control system is similar to the electro-hydraulic servo control system, merely substituting the electro-hydraulic proportional valve for the electro-hydraulic servo valve.In the electro-hydraulic proportional contro

50、l system, though differing in structures and functions, it can be categorized to the system comprised by basic units of the same function, as shown in figure 1.3. 圖中虛線所示為可能實(shí)現(xiàn)的檢測(cè)與反饋。包含了外反饋回路控制系統(tǒng)的才稱為閉環(huán)控制系統(tǒng)，不包含外反饋的稱為開環(huán)系統(tǒng)。如果存在比例閥本身的內(nèi)反饋，也可以構(gòu)成實(shí)際的局部小閉環(huán)控制。但一般這不稱為閉環(huán)系統(tǒng)。In the figure, the dashed line represent

51、s possible measuring and feedback. Those systems including external feedback are called closed-loop control system, otherwise open-loop control system. If the proportional valve has internal feedback itself, it can also constitute local small closed-loop control. But in general, it can not be called

52、 closed-loop control system.圖1.3 電液比例控制系統(tǒng)Fig. 1.3 Electro-hydraulic proportional control system 組成電液比例控制系統(tǒng)的基本元件有：指令元件、比較元件、電控器、比例閥、液壓執(zhí)行器、檢測(cè)反饋元件。(1)指令元件 它是給定控制信號(hào)的產(chǎn)生與輸入的元件。也叫編程器或輸入電路。在有反饋信號(hào)存在的情況下，它給出與反饋信號(hào)有相同形式和量級(jí)的控制信號(hào)。它也可以是信號(hào)發(fā)生裝置或程序控制器。(2)比較元件 它的功用是把給定輸入與反饋信號(hào)進(jìn)行比較，得出偏差信號(hào)作為電控器的輸入。進(jìn)行比較的信號(hào)必須是同類型的，當(dāng)信號(hào)類型不同時(shí)

53、，在比較前要進(jìn)行信號(hào)類型轉(zhuǎn)換。Basic elements of Electro-hydraulic proportional control system: order element,comparison element,electric controller,proportional valve,Hydraulic actuator,measuring and feedback element.(1)Order Element It is the generating and inputting element of the given control signal, also know

54、n as the programming unit or input circuit. With the feedback signal, it will give the control signal with the same type and order as that feedback signal. It can be either signal generator or programming controller.(2)Comparison Element Its function is to compare the input signal and feedback signa

55、l, with the deviation as the input of electric controller. The signals compared should be in the same type. Otherwise before the comparison, a transformation of signal type is needed.(3)電控器 電控器通常被稱作比例放大器。它的作用是對(duì)輸入的信號(hào)進(jìn)行加工、整形和放大，使達(dá)到電-機(jī)械轉(zhuǎn)換裝置的控制要求。(4)比例閥 它作為整個(gè)系統(tǒng)的功率放大部分，可分為兩部分：電-機(jī)械轉(zhuǎn)換器、液壓放大元件。還可能帶有閥內(nèi)的檢測(cè)反饋元

56、件。(5)液壓執(zhí)行器 通常指液壓缸或液壓馬達(dá)，它是系統(tǒng)的輸出裝置，用于驅(qū)動(dòng)負(fù)載。(3)Electric Controller Generally, electric controller is called proportional amplifier, with the function of processing, shaping and amplifying the input signal and meeting the control requirement of electro-mechanical conversion device.(4)Proportional Valve A

57、s the part of power amplification of the whole system, it can be divided into two categories: electro-mechanical transformer and hydraulic amplifier (some even with a measuring and feedback element inside).(5)Hydraulic Actuator Generally, known as the hydraulic cylinder or the hydraulic motor, it is

58、 the system output unit, used for driving the load.(6)檢測(cè)反饋元件 對(duì)于閉環(huán)控制需要加入檢測(cè)反饋元件。它檢測(cè)被控量或中間變量的實(shí)際值，得出系統(tǒng)的反饋信號(hào)。從框圖中可見，檢測(cè)元件還有內(nèi)、外環(huán)之分。內(nèi)環(huán)檢測(cè)元件通常包含在比例閥內(nèi)，用于改善比例閥的動(dòng)、靜態(tài)特性；外環(huán)檢測(cè)元件直接檢測(cè)輸出量，用于提高整個(gè)系統(tǒng)的性能和控制精度。(6)Measuring and Feedback Element In closed-loop control system, a measuring and feedback element is needed, which

59、 will measure the controlled object or the actual value of intermediate variable and get the feedback signal of system. From the block diagram, the measuring elements are classified into external and internal loop. For internal loop measuring elements, they are inside the proportional valves, to imp

60、rove the dynamic and static characteristics of the valves. For external measuring elements, they are used for measuring the output directly, to improve performance and control accuracy of the whole system.1.4 電液比例控制系統(tǒng)的分類Classification of electro-hydraulic proportional control system被控量是否有反饋控制信號(hào)比例元件類