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大學(xué)畢業(yè)設(shè)計(jì)（外文翻譯）
剪式汽車舉升機(jī)設(shè)計(jì)
Electro-hydraulic proportional control of twin-cylinder hydraulic elevators
Abstract
The large size of the cab of an electro-hydraulic elevator necessitates the arrangement of two cylinders located symmetrically on both sides of the cab. This paper reports the design of an electro hydraulic system which consists of three flow-control proportional valves. Speed regulation of the cab and synchronization control of the two cylinders are also presented. A pseudo-derivative feedback (PDF) controller is applied to obtain a velocity pattern of the cab that proves to be close to the given one. The non-synchronous error of the two cylinders is kept within ±2mm with a constrained step proportional-derivative (PD) controller. A solenoid actuated non-return valve, i.e. a hydraulic lock, is also developed to prevent cab sinking and allow easy inverse-fluid flow.
Keywords: Hydraulic elevator; Velocity tracking; Synchronization; Hydraulic lock
1. Introduction
The modern hydraulic elevator is currently an excellent and low-cost solution to the problem of vertical transportation in low or mid-rise buildings, and in those applications requiring very large capacities, slow speeds and short travel distances. These include scenic elevators in superstores or historical buildings, stage elevators, ship elevators and elevators for the disabled, etc. In most cases, hydraulic elevators can be adapted to architectural design requirements without compromising energy saving and efficiency requirements.In addition, the use of fire-resistant fluid makes the hydraulic elevator a suitable choice when elevators have to operate near hazards such as furnaces or open fires.
Hydraulic drives are used preferably in elevators where large payloads need to be carried, such as for car elevators or marine elevators. In heavy load cases, an elevator cab usually has directly acting or side-acting hydraulic cylinders. The direct-acting arrangement involves a deep pit, substantial risk of corrosion of the buried cylinders and the difficulty of replacing failed cylinder parts. Thus, in many situations the side-acting hydraulic cylinder is preferred, despite the fact that it probably increases rail wear due to insufficient cab stiffness. In the extreme conditions, i.e. when large cab sizes and uneven payloads are involved, the cab's flexibility may even cause the guide shoes to stick to the rails, which is very dangerous. Therefore, in such cases, a feasible solution is to arrange two directly acting cylinders symmetrically on each side of the cab, as shown in Fig. 1. It should be noted that smooth running cannot be ignored because people may be part of the payloads that accompany the freight. The major issue when designing a control system is to ensure the synchronous motion of the two cylinders.
The error due to the non-synchronous motion of the two cylinders caused, by an uneven load under equal pressure-control, which is generally used for elevator control with multiple hydraulic cylinders, is schematically shown in Fig. 2. It is obvious from Fig. 2 that equal pressure-control is not suitable for a synchronized hydraulic elevator. When the payload is located on the right side of the cab, the left cylinder, with a lighter load, will move upward faster than the right one. The speed disparity between the two cylinders will not cease until the reaction forces actuated by the rails on both the lower left and upper right guide shoes attached on the cab are balanced by the hydraulic force difference. The non-synchronisation of the two cylinders can only be reduced by flow control, i.e. by ensuring that the fluid flows into the two cylinders per unit time are the same.
This paper presents an electro-hydraulic system for the control of an elevator with twin cylinders that are located on each side of the elevator cab. The designed system consists of three flow-control proportional valves. A PDF controller is applied to velocity control whereas a constrained step PD controller guarantees the minimum non-synchronous error between the motion of two cylinders. The design of a newly developed solenoid-actuated non-return valve i.e. a hydraulic lock is also presented in this paper. In this project, experiments are conducted with a normal size passenger cab instead of building a new large-size cab due to cost limitations. In order to achieve the flexible condition of a larger cab, the distance between the rails and their corresponding guide shoes in the side direction is extended so that the cab has no constraints in this direction. Meanwhile, in the forward and backward direction, the cab is constrained by the rails just like a general passenger elevator. The synchronous motion control of the two cylinders in such an assembly is analogous to and even more difficult than that of a larger cab with normal constraints.
2. Electro-hydraulic control system design
There are two different fluid power systems generally used in hydraulic elevators. the flow-restriction speed-regulation system and variable-delivery speed-regulation system. In the former system, the pump runs at a constant speed and the valve regulates the speed of the cylinder in both the upward and downward directions. In the latter case, the cab is operated by varying the speed of the pump, which is driven by a speed-controlled induction motor.
The hydraulic system employed in this twin-cylinder elevator works according to the flow-restricted speed regulation principle, in which the fluid flow into and out of the two cylinders is controlled by appropriate valve settings, with the output of the pump kept at a fixed level. In this system, there are three flow-control proportional valves -5-7 as shown in Fig. 3. Flow-control proportional valves act as throttle valves that restrict the fluid flow to a single direction. They can give a smooth stepless variation of flow control from near zero up to the valve's maximum capacity. The flow rate through valve 5 remains almost invariable because a combination hydrostat maintains a constant level of pressure difference across the proportional valve, irrespective of system or load pressure changes. In the case of throttle valves, 6 and 7 in Fig. 3, their fluid flows will change with system or load pressure changes. Valve 5, here called velocity valve, controls the velocity of the elevator. The upward motion of the cab is driven by fixed-displacement piston pump 1. When motor 2 starts to work, the solenoid-actuated twin-position relief- valve 4 unloads the output from pump 1 to tank 20 and the opening of velocity valve 5 is kept at its maximum value. The solenoid of valve 4 is automatically energised, shifting the valve to its closed position and thus setting a relief pressure for the system. At this stage, the regulation of the cab velocity is achieved by adjusting the electric current through the coil of valve 5. At the closing of valve 5, all the fluid flows into cylinders 12 and 13 and thus the cab velocity reaches its maximum value. The downward motion is caused by the dead load of the cab and its payloads. When the control panel receives a downward call, solenoid-actuated non-return valves 10 and 11 open and the cab velocity is controlled by valve 5. The larger the opening of valve 5, the higher the cab velocity. Velocity valve 5 directs pressurised fluid from the cylinders to tank 20 to lower the cab. Check valve 3 prevents pressurised fluid from driving the pump in its reverse working direction. Synchronous motion of cylinders 12 and 13 depends on the combined adjustment of the flow control valves 6 and 7. The steady-state flow through a throttle valve can be represented as
where Q denotes the flow, Xv the spool displacement, ΔP the pressure drop across the valve and K0 is a constant. If the pressure drop ΔP remains constant, Q is in direct proportion to Xv, which is in direct proportion to the electric current through the solenoid coil. The flow variations that are caused by the pressure drop variations can thus be compensated for by changing Xv. As mentioned above, fluid flows through the flow control proportional valves in only one direction. Valve groups 8 and 9, each of which consists of four check valves, are used to ensure that valves 6 and 7 work in their normal directions.
Solenoid-actuated non-return valves 10 and 11 are specially designed to prevent the cab from sinking, which is normally caused by the leakage of the hydraulic components when the cab stops at a landing. The working principle of the solenoid-actuated non-return valve will be further expanded later in this paper. They lock the cab when the pump stops and thus can be called hydraulic locks here. Only when their solenoids are energized will the cab move downward. In case of power breaks or other hydraulic element failures, emergency valve 14 lowers the cab at a lower speed.
3. Electro-hydraulic proportional control
A suitable velocity curve, preset according to design specifications such as maximum acceleration, maximum rate of acceleration change and maximum running velocity, etc., is usually used to describe the running pattern of an elevator. If the cab velocity follows the given curve well, good riding comfort is assured. Open-loop control cannot achieve sufficient tracking accuracy because of variations in payloads, fluid volume in cylinders and fluid viscosity. Therefore, speed feedback is needed to attenuate the influence of the various disturbances on the performance of an elevator. Furthermore, without closed-loop control, the non-synchronous motion of the two cylinders is inevitable due to the differences in payload, friction and hydraulic flow resistance between the two cylinders. Consequently, two closed loops are required to attain speed regulation and synchronization control at the same time. The control block diagram of the whole system is shown in Fig. 4, which represents the elevator motion in upward direction. A similar block diagram can easily be deduced for downward motion. The cab velocity is measured by an encoder. The translational movement of the cab is transferred to rotation of the rotor of an encoder by a pulley. A two-element synchro-system is used to measure the relative angles between the rotors of control transmitter CX and control transformer CT. Thus, the relative angle
measured by the synchro-system is proportional to the height error between the two cylinders. As discussed above, the cab velocity is only determined by velocity valve 5 in Fig. 3, provided the synchronization valves 6 and 7 work in strict proportion to valve 5. In turn, under the same condition, the adjustment of valves 6 and 7 will not influence the cab's velocity. Hence, speed regulation and synchronization control can be realized separately, i.e. velocity controller 1 and synchronization controller 2 can work independently. A pseudo-derivative feedback (PDF) controller, i.e. controller 1 as shown in Fig. 4 is applied to suppress the adverse effects of internal parameter changes such as fluid volume in cylinders and external disturbances such as payload and fluid-temperature variations.
As shown in Fig. 5, the PDF controller is easy to realize and insensitive to system-parameter changes and external disturbances . When m1(t) is small enough, the saturated non-linearity can be simplified as working in its linear segment, then the PDF controller parameters can easily be obtained.
Suppose the system can be described by
Then the three controller parameters are:
where is 7.5167/ts, ts the settling time and kH the constant for adjusting the output amplitude of the controller.
In situ tuning of controller parameters is required to ensure the optimal performance. Figs. 6 and 7 show the tracking performance of the cab's velocity following the given velocity curve with a full payload and with no payload, respectively. The difference between the desired velocity pattern and the actual velocity pattern is mainly due to the non-linear characteristics of the electro-hydraulic proportional valve 5. However, the whole velocity pattern is very close to the designed pattern, and thus satisfactory riding comfort can still be guaranteed.
A constrained step proportional-derivative (PD) controller, i.e. controller 2 in Fig. 2, is used to obtain synchronous motion of the two cylinders. The idea behind this PD controller is similar to the steering of a boat. When rowing a boat to keep it along a straight line, the rower exerts force on oars each time according to how far and how fast the boat is getting away from the line. Because of the rower's unavoidably delayed response, the disparity between the boat's real route and the given route cannot be kept small. An effective alternative method involves the rower applying a fraction of the estimated forces each time the oars are operated. The boat will thus approach the given route step by step till the route error approaches an acceptable value.
Cylinder 12 is taken as the reference cylinder, whose movement has to be followed by cylinder 13, say, the
Fig.8. Non-synchronous height error curve under void payload.
Fig.9. Non-synchronous height error curve under one ton unevenly placed payload
following cylinder. The backlash of valves 6 and 7 is similar to the rower's delayed response to the boat's route error. In each adjustment period of controller 2, its real output is only a fraction of the required value calculated by the PD controller. That is, the large error is reduced in each sampling period at a constrained step until an acceptable height error is reached. This control scheme has proven to be effective in keeping the non-synchronous error within ±2mm, as shown in Figs. 8 and 9. It should be noted that if the initial non-synchronous error during a sampling period is rather large, it would take some time to reach an acceptable level of error. If the non-synchronous error at the end of one elevator run can be retained at the beginning error of the next run, this process can be avoided and the non-synchronous error will remain at small values throughout all the runs. To attain this goal, a sink-proof device is needed since the different leakage rates of the two cylinders will directly increase the initial error of an elevator.
4. Conclusion
An electro-hydraulic control system with three flow control proportional valves has been proposed for the control of elevator velocity and non-synchronous error between the cylinders of a twin cylinder hydraulic elevator. A pseudo-derivative feedback control scheme has shown to be an appropriate technique to achieve a desired velocity pattern. Furthermore, this system guarantees low non-synchronous error by applying a constrained step PD controller. The test results show that the non-synchronous error can be kept within ±2 mm. A certain discrepancy between the desired pattern and the actual velocity pattern is due mainly to the hysteresis of the electro-hydraulic proportional valves. A new solenoid actuated non-return valve has been designed, fabricated and tested, and proves to be a good hydraulic device for preventing cab sinking.
電液比例控制的雙缸液壓升降機(jī)
摘要:一個(gè)電液控制的液壓升降機(jī)的大型機(jī)車需要在這個(gè)機(jī)車的兩邊安裝兩個(gè)對(duì)稱的油缸。摘要報(bào)道了一種電液系統(tǒng)的設(shè)計(jì)主要包括三個(gè)流體控制比例閥。機(jī)車的速度調(diào)節(jié)和兩油缸的同步控制也是呈遞的。一個(gè)假微分反饋(PDF)控制器以獲得一個(gè)機(jī)車的速度模式來(lái)證實(shí)和給定的這個(gè)接近。兩油缸的非同步性的誤差范圍在±2之內(nèi)由于有比例控制器來(lái)拘泥每一步。一個(gè)電磁鐵操縱的單向閥,即液壓鎖,被發(fā)明以防止機(jī)車下沉并允許反方向流體容易流動(dòng)。
關(guān)鍵詞:液壓升降機(jī);速度跟蹤;同步化;液壓鎖
1、引言
現(xiàn)代液壓升降機(jī)目前有一個(gè)很優(yōu)秀的和低成本的方法來(lái)解決垂直運(yùn)輸在低或中高層建筑物的這一問(wèn)題,在這些應(yīng)用需要非常大的容量,緩慢的速度和短的行進(jìn)距離。這些包括風(fēng)景名優(yōu)美的在超市連鎖店或歷史建筑電梯、舞臺(tái)升降機(jī)、船電梯和為殘疾人用的電梯等。在大多數(shù)情況下,液壓升降機(jī)能適應(yīng)建筑設(shè)計(jì)要求的前提下實(shí)現(xiàn)節(jié)能增效要求。另外,耐高溫流體的應(yīng)用使液壓電梯有一個(gè)適當(dāng)?shù)倪x擇當(dāng)電梯不得不操縱在附近有的危險(xiǎn)場(chǎng)合時(shí)如熔爐或明火。
液壓傳動(dòng)最好應(yīng)用于需要進(jìn)行大負(fù)荷運(yùn)輸?shù)碾娨荷禉C(jī),比如車輛升降機(jī)或船舶升降機(jī)。在重負(fù)荷情況下,升降機(jī)的駕駛室通常有直接運(yùn)行和輔助液壓缸。這直接的布置涉及一個(gè)大的凹陷,埋藏油缸腐蝕的大量危險(xiǎn)和更換缸體出現(xiàn)故障的零件困難。因此,在很多情形下輔助液壓缸是首選,盡管事實(shí)是它可能增加軌道的磨損由于機(jī)車剛度不足。在極端的條件下,即當(dāng)投入大型機(jī)車尺寸和不均勻載荷時(shí),機(jī)車的彈性甚至導(dǎo)致滑塊粘住兩橋底板的兩個(gè)邊,這是很危險(xiǎn)的。因此,在這種情況下,一種可行的解決方案是直接安排兩個(gè)對(duì)稱的油缸在機(jī)車的每一邊如圖1所示。應(yīng)該指出的是,運(yùn)轉(zhuǎn)平穩(wěn)不容忽視,因?yàn)槿藗兛赡苁遣糠钟行лd荷伴隨著貨運(yùn)。在設(shè)計(jì)控制系統(tǒng)時(shí)的主要問(wèn)題是確保兩油缸的同步運(yùn)動(dòng)。
這個(gè)錯(cuò)誤由于兩油缸運(yùn)動(dòng)的非同步性造成，被相等壓力控制下的不均勻荷載,這通常用于電梯的控制與多個(gè)液壓缸,如圖2所示。很明顯,同等的壓力控制不適合一個(gè)同步的液壓電梯。當(dāng)載荷位于機(jī)車的右側(cè),左邊的油缸有輕負(fù)荷,會(huì)比右面的那個(gè)向上運(yùn)動(dòng)的速度快。兩油缸速度的不一致將不會(huì)停止,直到反作用力驅(qū)動(dòng)通過(guò)欄桿上兩個(gè)比較低的左邊和右上方的導(dǎo)塊附著于機(jī)車來(lái)平衡液壓力的差異。兩油缸的非同步性只能用流量控制降低,即確保流體流入兩油缸的單位時(shí)間是相同的。
圖1 兩個(gè)油缸安排一起運(yùn)動(dòng)
圖2 相同壓力控制:不均勻放置靜載荷導(dǎo)致非同步性
本文提出了一種電液控制電梯有兩缸,位于升降機(jī)駕駛室的兩邊。該系統(tǒng)包括三個(gè)流體控制比例閥。一個(gè)PDF控制器應(yīng)用于速率控制然而一個(gè)約束一步的PD控制器可保證兩油缸運(yùn)動(dòng)不同步的最小誤差。一種新開(kāi)發(fā)的設(shè)計(jì)電磁單向閥即液壓鎖也進(jìn)行了介紹。在這個(gè)項(xiàng)目中,實(shí)驗(yàn)被引導(dǎo)用標(biāo)準(zhǔn)性機(jī)車代替大型建筑機(jī)車,由于費(fèi)用的局限性。為了實(shí)現(xiàn)大型機(jī)車的靈活條件,軌道之間的距離與相應(yīng)的導(dǎo)塊側(cè)向延伸,使機(jī)車在這個(gè)方向沒(méi)有約束。與此同時(shí),在前方向和后方向,機(jī)車被軌道制約,就像一個(gè)通用的乘客電梯。同步運(yùn)動(dòng)控制的兩油缸在這里裝配,就好比是比大的駕駛室有正常的約束更困難。
2、電液控制系統(tǒng)設(shè)計(jì)
有兩種比較難的液壓傳動(dòng)系統(tǒng)通常應(yīng)用于液壓升降機(jī)中。節(jié)流調(diào)速系統(tǒng)和容積調(diào)速系統(tǒng)。 在第一個(gè)系統(tǒng)中,泵運(yùn)行以一個(gè)恒定的速度并且由閥門來(lái)控制和調(diào)節(jié)油缸上升和下降的速度。在后一種情況下,機(jī)車被變速泵操縱,這由速度控制的異步電機(jī)驅(qū)動(dòng)。
圖3 雙缸液壓升降機(jī)原理圖
液壓系統(tǒng)應(yīng)用兩缸升降機(jī)的動(dòng)作,根據(jù)節(jié)流調(diào)速,流體流入和流出兩缸的多少是通過(guò)適當(dāng)?shù)拈y門的設(shè)置來(lái)控制,與輸出的泵保持在一個(gè)固定的水平。在這個(gè)系統(tǒng)中,有三種流體控制比例閥-5-7,如圖3所示。流量控制比例閥就像節(jié)流閥,限制流體朝單一方向流動(dòng)。他們能給一個(gè)平滑無(wú)級(jí)變化的流量控制從近零到閥門的最大容量。通過(guò)閥門5的流量恒定不變,因?yàn)樗畨赫{(diào)節(jié)器的組合能保持恒定壓差穿過(guò)流量閥,不管系統(tǒng)或負(fù)載壓力的變化。節(jié)流閥門6和7的情況下,如圖3所示。他們流量將會(huì)改變?nèi)绻到y(tǒng)或負(fù)載壓力發(fā)生變化。閥5,這里被稱為調(diào)速閥可控制升降機(jī)的速度。機(jī)車的向上的運(yùn)動(dòng)是由定量柱塞泵1來(lái)控制。 當(dāng)電機(jī)2開(kāi)始工作時(shí),二位電磁換向閥解除閥4對(duì)輸出泵1輸出的卸荷，到油箱20和打開(kāi)的速度保持在閥門5它的最大價(jià)值。閥4的電磁閥的自動(dòng)供給能量,關(guān)閉閥門,并且安裝一個(gè)減壓系統(tǒng)。在這一階段,機(jī)車的速度調(diào)節(jié)的校準(zhǔn)的完成是通過(guò)調(diào)節(jié)通過(guò)閥5線圈的電流。在關(guān)閉的閥5時(shí),所有的流體流動(dòng)進(jìn)入油缸12和13，并且機(jī)車的速度達(dá)到最大值。下行運(yùn)動(dòng)是由機(jī)車的靜載和它的有效載荷所引起。當(dāng)控制面板收到一個(gè)向下的動(dòng)作的信號(hào),電磁控制單向閥10和11開(kāi)啟，機(jī)車的速度控制是通過(guò)閥門5來(lái)實(shí)現(xiàn)。閥5開(kāi)口越大，機(jī)車獲得的速度就越快。閥門5引導(dǎo)高壓流體從油缸到油箱20再到較低的機(jī)車。單向閥3阻止高壓流體反向流回。同步運(yùn)動(dòng)的油缸12和13取決于流量控制閥6和7的組合調(diào)整。通過(guò)節(jié)流閥調(diào)節(jié)穩(wěn)態(tài)流動(dòng)可以用下式表示為
上式的Q代表流量,XV 活塞桿的位移、ΔP通過(guò)閥門的壓降和K0是C常數(shù)。如果壓力降的ΔP不變,流量和活塞桿的位移成正比,這也正比通過(guò)電磁閥線圈的電流。流量變化所引起的壓降的變化也能因此得到補(bǔ)償,通過(guò)改變活塞桿的位移。如上所述,流體流過(guò)的流量控制比例閥只有一個(gè)方向。閥組8和9,其中的每一個(gè)都由四個(gè)單向閥,用于確保閥門6和7工作在正常的方向。電磁單向閥10和11是專門用于防止機(jī)車下沉,這通常是引起的泄漏的液壓元件當(dāng)升降機(jī)停留在一平臺(tái)時(shí)。電磁單向閥的工作原理,將會(huì)在本文后面進(jìn)一步敘說(shuō)。當(dāng)泵停止工作的時(shí)候他們會(huì)鎖住升降機(jī),因此這里被稱為液壓鎖。只有當(dāng)他們的線圈通電升降機(jī)才會(huì)向下移動(dòng)。如果發(fā)生電源的中斷或其它液壓元件的損壞,緊急閥14以較低的速度降下升降機(jī)。
3、電液比例控制
預(yù)設(shè)一個(gè)合適的速度曲線,根據(jù)設(shè)計(jì)規(guī)范,如最大加速度、加速度改變的最大比例和最大運(yùn)行速度等,通常用來(lái)形容的運(yùn)行模式的升降機(jī)。如果機(jī)車的速度跟隨給定曲線,好的乘車舒適性是有保證的。開(kāi)環(huán)控制不能達(dá)到足夠的跟蹤精度因?yàn)橛行лd荷，缸內(nèi)流體體積和流體粘度的變化。因此，速度反饋需要衰減的影響的升降機(jī)性能的各種干擾。此外,沒(méi)有閉環(huán)控制,兩油缸的非同步性運(yùn)動(dòng)的差異是不可避免的,由于載荷、摩擦力和兩油缸之間液壓力的變化。因此,兩個(gè)閉合環(huán)路需要在同一時(shí)間內(nèi)達(dá)到的速度調(diào)節(jié)和同步控制。控制系統(tǒng)的總體框圖如圖4所示。
圖4 升降機(jī)控制系統(tǒng)方框圖
它代表了電梯的向上運(yùn)動(dòng)。一個(gè)類似的框圖可以很容易被演繹出為向下運(yùn)動(dòng)。駕駛室的速度是衡量一個(gè)編碼器。駕駛室的平移運(yùn)動(dòng)是通過(guò)一個(gè)編碼器控制的滑輪的旋轉(zhuǎn)運(yùn)動(dòng)來(lái)轉(zhuǎn)變的。一個(gè)二元同步是用來(lái)測(cè)量轉(zhuǎn)子控制變送器CX和控制變壓器CT相對(duì)轉(zhuǎn)角之間的角度。因此,通過(guò)測(cè)量的相對(duì)角度與兩油缸之間的高度誤差成正比。如上所述,機(jī)車的速度是只取決于速度閥5，如圖3所示,給出了同步閥6和7與比例閥5成嚴(yán)格的比例動(dòng)作。反過(guò)來(lái),在同等條件下,調(diào)整閥6、7,不會(huì)影響機(jī)車的速度。因此,速度調(diào)節(jié)和同步控制可以單獨(dú)來(lái)實(shí)現(xiàn),即速度控制器1和同步控制器2可以獨(dú)立工作。一個(gè)微分反饋控制器,即控制器1,如圖4所示。是適用于抑制內(nèi)部參數(shù)變化所造成的副作用如油缸液體體積的變化和外部干擾如油缸內(nèi)有效載荷和流體溫度的變化。如圖5所示。
圖5 PDF格式的控制系統(tǒng)
PDF格式的控制器易于實(shí)現(xiàn)，并且對(duì)參數(shù)變化和外部干擾不敏感。 當(dāng)m1(t)足夠小,飽和非線性可簡(jiǎn)化為工作在它的線性范圍,然后PDF格式的控制器參數(shù)可以很容易被獲得。
假設(shè)這個(gè)系統(tǒng)可以用下式表達(dá)
三個(gè)控制器參數(shù)如下：
這里的是7.5167/ ts,ts是停留時(shí)間和KH調(diào)整控制器輸出幅度常數(shù)。原位調(diào)諧控制器參數(shù)是要保障性能最優(yōu)。
圖6 空載速度曲線（虛線：預(yù)期 實(shí)線：實(shí)測(cè)）
圖7 滿載下速度曲線（虛線：預(yù)期 實(shí)線：實(shí)測(cè)）
如圖6、7展示了機(jī)車的速度跟蹤性能，接著分別給出了滿載荷和空載情況的速度曲線。速度圖案之間的差異和實(shí)際速度模式主要是由于電液比例閥5的非線性特性。然而,整個(gè)速度模式非常接近設(shè)計(jì)模式,因此令人滿意的舒適性仍然可以得到保障。一個(gè)約束步驟的PD控制器,即(PD)控制器2。如圖2是用來(lái)獲取兩油缸的同步運(yùn)動(dòng)。PD控制器后面的理論和一艘小船轉(zhuǎn)向相同。當(dāng)劃一艘船,以保持它沿著直線運(yùn)動(dòng),劃船人每次都是用力控制船槳根據(jù)船離開(kāi)直線的遠(yuǎn)近和快慢。因?yàn)閯澊瞬豢杀苊庋舆t反應(yīng),船的真實(shí)路線和被給的路線不一致，不能保持很小差距。一種有效替代的方法包含槳手每當(dāng)槳被操作之時(shí)申請(qǐng)估計(jì)能力的小部分。船將逐步的靠近被給路線，直到錯(cuò)誤路線的方法可接受的價(jià)值。缸 12被當(dāng)作參考油缸,其運(yùn)動(dòng)必須遵循油缸13。閥6和7的后座,類似于運(yùn)動(dòng)員的延遲反應(yīng)使船的路線錯(cuò)誤。在控制器是2每一段調(diào)整期的實(shí)際輸出,只有一小部分所要求的價(jià)值,采用PD控制器。那是,大型的錯(cuò)誤是在每一個(gè)采樣周期的情況下,降低到一個(gè)可以接受的一個(gè)約束步直到一個(gè)被接受的高度誤差達(dá)到了。該控制方案已經(jīng)被證明是有效的在保持非同步性誤差在±2毫米范圍,如圖8和9。
圖8 無(wú)效載荷下的非同步高度誤差曲線
圖9 1噸載荷下的非同步性高度不均勻誤差曲線
應(yīng)該指出的是,如果最初的非同步性誤差在采樣周期是相當(dāng)大的,將需要一些時(shí)間來(lái)達(dá)到可接受的錯(cuò)誤的水平。如果升降機(jī)運(yùn)行結(jié)束時(shí)的非同步誤差能保留下次運(yùn)作將要發(fā)生的錯(cuò)誤,該過(guò)程可以避免非同步性的錯(cuò)誤并保留整個(gè)動(dòng)作過(guò)程的小的有價(jià)值的部分。為了達(dá)到這一目的,一個(gè)過(guò)濾裝置是必要的,因?yàn)椴煌男孤┞实膬捎透讓⒅苯釉黾映跏颊`差的升降機(jī)。
4、結(jié)論
電液控制系統(tǒng)與三流量控制比例閥已被推薦用于控制升降機(jī)速度和非同步性之間的誤差的一個(gè)雙缸液壓升降機(jī)。一個(gè)假微分反饋控制方案已證明是一個(gè)適當(dāng)?shù)募夹g(shù)來(lái)實(shí)現(xiàn)一個(gè)理想的速度模式。此外,該系統(tǒng)保證低的非同步性誤差通過(guò)PD控制器拘泥的一步。試驗(yàn)結(jié)果表明,該非同步性誤差能被保存在±2毫米范圍。一定模式之間的差異和實(shí)際所需的速度模式滯后原因主要是電液比例閥的磁滯。一種新的電磁驅(qū)動(dòng)的單向閥已設(shè)計(jì),裝配和測(cè)試,并證明了要成為一名優(yōu)良的液壓裝置,為防止機(jī)車下沉。