大學畢業(yè)設計 外文翻譯 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 大學畢業(yè)設計 外文翻譯 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 大學畢業(yè)設計 外文翻譯 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 大學畢業(yè)設計 外文翻譯 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 大學畢業(yè)設計 外文翻譯 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 P the pressure drop across the valve and K0 is a constant If the pressure drop P 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 大學畢業(yè)設計 外文翻譯 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 大學畢業(yè)設計 外文翻譯 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 大學畢業(yè)設計 外文翻譯 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 大學畢業(yè)設計 外文翻譯 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 大學畢業(yè)設計 外文翻譯 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 大學畢業(yè)設計 外文翻譯 電液比例控制的雙缸液壓升降機 摘要 一個電液控制的液壓升降機的大型機車需要在這個機車的兩邊安裝 兩個對稱的油缸 摘要報道了一種電液系統(tǒng)的設計主要包括三個流體控制比例 閥 機車的速度調(diào)節(jié)和兩油缸的同步控制也是呈遞的 一個假微分反饋 PDF 控 制器以獲得一個機車的速度模式來證實和給定的這個接近 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拘泥每一步 一個電磁鐵操縱的單向 閥 即液壓鎖 被發(fā)明以防止機車下沉并允許反方向流體容易流動 關(guān)鍵詞 液壓升降機 速度跟蹤 同步化 液壓鎖 1 引言 現(xiàn)代液壓升降機目前有一個很優(yōu)秀的和低成本的方法來解決垂直運輸在低 或中高層建筑物的這一問題 在這些應用需要非常大的容量 緩慢的速度和短的 行進距離 這些包括風景名優(yōu)美的在超市連鎖店或歷史建筑電梯 舞臺升降機 船電梯和為殘疾人用的電梯等 在大多數(shù)情況下 液壓升降機能適應建筑設計要 求的前提下實現(xiàn)節(jié)能增效要求 另外 耐高溫流體的應用使液壓電梯有一個適當 的選擇當電梯不得不操縱在附近有的危險場合時如熔爐或明火 液壓傳動最好應用于需要進行大負荷運輸?shù)碾娨荷禉C 比如車輛升降機或 船舶升降機 在重負荷情況下 升降機的駕駛室通常有直接運行和輔助液壓缸 這直接的布置涉及一個大的凹陷 埋藏油缸腐蝕的大量危險和更換缸體出現(xiàn)故障 的零件困難 因此 在很多情形下輔助液壓缸是首選 盡管事實是它可能增加軌 道的磨損由于機車剛度不足 在極端的條件下 即當投入大型機車尺寸和不均勻 載荷時 機車的彈性甚至導致滑塊粘住兩橋底板的兩個邊 這是很危險的 因此 在這種情況下 一種可行的解決方案是直接安排兩個對稱的油缸在機車的每一邊 如圖1所示 應該指出的是 運轉(zhuǎn)平穩(wěn)不容忽視 因為人們可能是部分有效載荷伴 隨著貨運 在設計控制系統(tǒng)時的主要問題是確保兩油缸的同步運動 這個錯誤由于兩油缸運動的非同步性造成 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液壓缸 如圖2所示 很明顯 同等的壓力控制 不適合一個同步的液壓電梯 當載荷位于機車的右側(cè) 左邊的油缸有輕負荷 會 比右面的那個向上運動的速度快 兩油缸速度的不一致將不會停止 直到反作用 大學畢業(yè)設計 外文翻譯 力驅(qū)動通過欄桿上兩個比較低的左邊和右上方的導塊附著于機車來平衡液壓力 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 時間是相同的 圖1 兩個油缸安排一起運動 圖2 相同壓力控制 不均勻放置靜載荷導致非同步性 本文提出了一種電液控制電梯有兩缸 位于升降機駕駛室的兩邊 該系統(tǒng)包 括三個流體控制比例閥 一個PDF控制器應用于速率控制然而一個約束一步的PD 控制器可保證兩油缸運動不同步的最小誤差 一種新開發(fā)的設計電磁單向閥即 液壓鎖也進行了介紹 在這個項目中 實驗被引導用標準性機車代替大型建筑機 車 由于費用的局限性 為了實現(xiàn)大型機車的靈活條件 軌道之間的距離與相應 的導塊側(cè)向延伸 使機車在這個方向沒有約束 與此同時 在前方向和后方向 機 車被軌道制約 就像一個通用的乘客電梯 同步運動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)設計 大學畢業(yè)設計 外文翻譯 有兩種比較難的液壓傳動系統(tǒng)通常應用于液壓升降機中 節(jié)流調(diào)速系統(tǒng)和容 積調(diào)速系統(tǒng) 在第一個系統(tǒng)中 泵運行以一個恒定的速度并且由閥門來控制和 調(diào)節(jié)油缸上升和下降的速度 在后一種情況下 機車被變速泵操縱 這由速度控 制的異步電機驅(qū)動 圖3 雙缸液壓升降機原理圖 液壓系統(tǒng)應用兩缸升降機的動作 根據(jù)節(jié)流調(diào)速 流體流入和流出兩缸的多 少是通過適當?shù)拈y門的設置來控制 與輸出的泵保持在一個固定的水平 在這個 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 他們能給一個平滑無級變化的流量控制從近零到閥 門的最大容量 通過閥門5的流量恒定不變 因為水壓調(diào)節(jié)器的組合能保持恒定 壓差穿過流量閥 不管系統(tǒng)或負載壓力的變化 節(jié)流閥門6和7的情況下 如圖3所 示 他們流量將會改變?nèi)绻到y(tǒng)或負載壓力發(fā)生變化 閥5 這里被稱為調(diào)速閥 可控制升降機的速度 機車的向上的運動是由定量柱塞泵1來控制 當電機2開 始工作時 二位電磁換向閥解除閥4對輸出泵1輸出的卸荷 到油箱20和打開的速 度保持在閥門5它的最大價值 閥4的電磁閥的自動供給能量 關(guān)閉閥門 并且安 裝一個減壓系統(tǒng) 在這一階段 機車的速度調(diào)節(jié)的校準的完成是通過調(diào)節(jié)通過閥 5線圈的電流 在關(guān)閉的閥5時 所有的流體流動進入油缸12和13 并且機車的速 度達到最大值 下行運動是由機車的靜載和它的有效載荷所引起 當控制面板 大學畢業(yè)設計 外文翻譯 收到一個向下的動作的信號 電磁控制單向閥10和11開啟 機車的速度控制是通 過閥門5來實現(xiàn) 閥5開口越大 機車獲得的速度就越快 閥門5引導高壓流體從 油缸到油箱20再到較低的機車 單向閥3阻止高壓流體反向流回 同步運動的油 缸12和13取決于流量控制閥6和7的組合調(diào)整 通過節(jié)流閥調(diào)節(jié)穩(wěn)態(tài)流動可以用 下式表示為 上式的Q代表流量 XV 活塞桿的位移 P通過閥門的壓降和K0是C常數(shù) 如 果壓力降的 P不變 流量和活塞桿的位移成正比 這也正比通過電磁閥線圈的電 流 流量變化所引起的壓降的變化也能因此得到補償 通過改變活塞桿的位移 如上所述 流體流過的流量控制比例閥只有一個方向 閥組8和9 其中的每一個 都由四個單向閥 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 門用于防止機車下沉 這通常是引起的泄漏的液壓元件當升降機停留在一平臺時 電磁單向閥的工作原理 將會在本文后面進一步敘說 當泵停止工作的時候他們 會鎖住升降機 因此這里被稱為液壓鎖 只有當他們的線圈通電升降機才會向下 移動 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 3 電液比例控制 預設一個合適的速度曲線 根據(jù)設計規(guī)范 如最大加速度 加速度改變的最 大比例和最大運行速度等 通常用來形容的運行模式的升降機 如果機車的速度 跟隨給定曲線 好的乘車舒適性是有保證的 開環(huán)控制不能達到足夠的跟蹤精度 因為有效載荷 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 影響的升降機性能的各種干擾 此外 沒有閉環(huán)控制 兩油缸的非同步性運動的 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 閉合環(huán)路需要在同一時間內(nèi)達到的速度調(diào)節(jié)和同步控制 控制系統(tǒng)的總體框圖 如圖4所示 大學畢業(yè)設計 外文翻譯 圖4 升降機控制系統(tǒng)方框圖 它代表了電梯的向上運動 一個類似的框圖可以很容易被演繹出為向下運 動 駕駛室的速度是衡量一個編碼器 駕駛室的平移運動是通過一個編碼器控 制的滑輪的旋轉(zhuǎn)運動來轉(zhuǎn)變的 一個二元同步是用來測量轉(zhuǎn)子控制變送器CX和 控制變壓器CT相對轉(zhuǎn)角之間的角度 因此 通過測量的相對角度與兩油缸之間的 高度誤差成正比 如上所述 機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成嚴格的比例動作 反過來 在同等條件下 調(diào)整閥6 7 不 會影響機車的速度 因此 速度調(diào)節(jié)和同步控制可以單獨來實現(xiàn) 即速度控制器1 和同步控制器2可以獨立工作 一個微分反饋控制器 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現(xiàn) 并且對參數(shù)變化和外部干擾不敏感 當m1 t 足夠小 飽和非線性可簡化為工作在它的線性范圍 然后PDF格式的控制器參數(shù)可 大學畢業(yè)設計 外文翻譯 以很容易被獲得 假設這個系統(tǒng)可以用下式表達 三個控制器參數(shù)如下 這里的 是7 5167 ts ts 是停留時間和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 預期 實線 實測 大學畢業(yè)設計 外文翻譯 圖7 滿載下速度曲線 虛線 預期 實線 實測 如圖6 7展示了機車的速度跟蹤性能 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 整個速度模式非常接近設計模式 因此令人滿意的舒適性仍然 可以得到保障 一個約束步驟的PD控制器 即 PD 控制器2 如圖2是用來獲取兩 油缸的同步運動 PD控制器后面的理論和一艘小船轉(zhuǎn)向相同 當劃一艘船 以保 持它沿著直線運動 劃船人每次都是用力控制船槳根據(jù)船離開直線的遠近和快慢 因為劃船人不可避免延遲反應 船的真實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槳被操作之時申請估計能力的小部 分 船將逐步的靠近被給路線 直到錯誤路線的方法可接受的價值 缸 12被當 作參考油缸 其運動必須遵循油缸13 閥6和7的后座 類似于運動員的延遲反應 使船的路線錯誤 在控制器是2每一段調(diào)整期的實際輸出 只有一小部分所要求 的價值 采用PD控制器 那是 大型的錯誤是在每一個采樣周期的情況下 降低到 一個可以接受的一個約束步直到一個被接受的高度誤差達到了 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 無效載荷下的非同步高度誤差曲線 大學畢業(yè)設計 外文翻譯 圖9 1噸載荷下的非同步性高度不均勻誤差曲線 應該指出的是 如果最初的非同步性誤差在采樣周期是相當大的 將需要一 些時間來達到可接受的錯誤的水平 如果升降機運行結(jié)束時的非同步誤差能保 留下次運作將要發(fā)生的錯誤 該過程可以避免非同步性的錯誤并保留整個動作過 程的小的有價值的部分 為了達到這一目的 一個過濾裝置是必要的 因為不同 的泄漏率的兩油缸將直接增加初始誤差的升降機 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速度和非同步 性之間的誤差的一個雙缸液壓升降機 一個假微分反饋控制方案已證明是一個 適當?shù)募夹g(shù)來實現(xiàn)一個理想的速度模式 此外 該系統(tǒng)保證低的非同步性誤差通 過PD控制器拘泥的一步 試驗結(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)動的單向閥已設計 裝配和測試 并證明了要成為一名優(yōu) 良的液壓裝置 為防止機車下沉 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