电液比例控制的双缸液压升降机外文翻译

大学毕业设计（外文翻译）Electro-hydraulic proportional control of twin-cylinder hydraulic elevatorsAbstractThe 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 lock1. IntroductionThe 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 cabs 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 valves 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, 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 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 controlA 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 cabs 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 byThen 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 cabs 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 rowers unavoidably delayed response, the disparity between the boats 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 payloadfollowing cylinder. The backlash of valves 6 and 7 is similar to the rowers delayed response to the boats 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. 电液比例控制的双缸液压升降机 摘要:一个电液控制的液压升降机的大型机车需要在这个机车的两边安装两个对称的油缸。摘要报道了一种电液系统的设计主要包括三个流体控制比例阀。机车的速度调节和两油缸的同步控制也是呈递的。一个假微分反馈(PDF)控制器以获得一个机车的速度模式来证实和给定的这个接近。两油缸的非同步性的误差范围在2之内由于有比例控制器来拘泥每一步。一个电磁铁操纵的单向阀,即液压锁,被发明以防止机车下沉并允许反方向流体容易流动。关键词:液压升降机;速度跟踪;同步化;液压锁1、引言现代液压升降机目前有一个很优秀的和低成本的方法来解决垂直运输在低或中高层建筑物的这一问题,在这些应用需要非常大的容量,缓慢的速度和短的行进距离。这些包括风景名优美的在超市连锁店或历史建筑电梯、舞台升降机、船电梯和为残疾人用的电梯等。在大多数情况下,液压升降机能适应建筑设计要求的前提下实现节能增效要求。另外,耐高温流体的应用使液压电梯有一个适当的选择当电梯不得不操纵在附近有的危险场合时如熔炉或明火。液压传动最好应用于需要进行大负荷运输的电液升降机,比如车辆升降机或船舶升降机。在重负荷情况下,升降机的驾驶室通常有直接运行和辅助液压缸。这直接的布置涉及一个大的凹陷,埋藏油缸腐蚀的大量危险和更换缸体出现故障的零件困难。因此,在很多情形下辅助液压缸是首选,尽管事实是它可能增加轨道的磨损由于机车刚度不足。在极端的条件下,即当投入大型机车尺寸和不均匀载荷时,机车的弹性甚至导致滑块粘住两桥底板的两个边,这是很危险的。因此,在这种情况下,一种可行的解决方案是直接安排两个对称的油缸在机车的每一边如图1所示。应该指出的是,运转平稳不容忽视,因为人们可能是部分有效载荷伴随着货运。在设计控制系统时的主要问题是确保两油缸的同步运动。这个错误由于两油缸运动的非同步性造成，被相等压力控制下的不均匀荷载,这通常用于电梯的控制与多个液压缸,如图2所示。很明显,同等的压力控制不适合一个同步的液压电梯。当载荷位于机车的右侧,左边的油缸有轻负荷,会比右面的那个向上运动的速度快。两油缸速度的不一致将不会停止,直到反作用力驱动通过栏杆上两个比较低的左边和右上方的导块附着于机车来平衡液压力的差异。两油缸的非同步性只能用流量控制降低,即确保流体流入两油缸的单位时间是相同的。 图1 两个油缸安排一起运动图2 相同压力控制:不均匀放置静载荷导致非同步性本文提出了一种电液控制电梯有两缸,位于升降机驾驶室的两边。该系统包括三个流体控制比例阀。一个PDF控制器应用于速率控制然而一个约束一步的PD控制器可保证两油缸运动不同步的最小误差。一种新开发的设计电磁单向阀即液压锁也进行了介绍。在这个项目中,实验被引导用标准性机车代替大型建筑机车,由于费用的局限性。为了实现大型机车的灵活条件,轨道之间的距离与相应的导块侧向延伸,使机车在这个方向没有约束。与此同时,在前方向和后方向,机车被轨道制约,就像一个通用的乘客电梯。同步运动控制的两油缸在这里装配,就好比是比大的驾驶室有正常的约束更困难。2、电液控制系统设计有两种比较难的液压传动系统通常应用于液压升降机中。节流调速系统和容积调速系统。 在第一个系统中,泵运行以一个恒定的速度并且由阀门来控制和调节油缸上升和下降的速度。在后一种情况下,机车被变速泵操纵,这由速度控制的异步电机驱动。 图3 双缸液压升降机原理图液压系统应用两缸升降机的动作,根据节流调速,流体流入和流出两缸的多少是通过适当的阀门的设置来控制,与输出的泵保持在一个固定的水平。在这个系统中,有三种流体控制比例阀-5-7,如图3所示。流量控制比例阀就像节流阀,限制流体朝单一方向流动。他们能给一个平滑无级变化的流量控制从近零到阀门的最大容量。通过阀门5的流量恒定不变,因为水压调节器的组合能保持恒定压差穿过流量阀,不管系统或负载压力的变化。节流阀门6和7的情况下,如图3所示。他们流量将会改变如果系统或负载压力发生变化。阀5,这里被称为调速阀可控制升降机的速度。机车的向上的运动是由定量柱塞泵1来控制。 当电机2开始工作时,二位电磁换向阀解除阀4对输出泵1输出的卸荷，到油箱20和打开的速度保持在阀门5它的最大价值。阀4的电磁阀的自动供给能量,关闭阀门,并且安装一个减压系统。在这一阶段,机车的速度调节的校准的完成是通过调节通过阀5线圈的电流。在关闭的阀5时,所有的流体流动进入油缸12和13，并且机车的速度达到最大值。下行运动是由机车的静载和它的有效载荷所引起。当控制面板收到一个向下的动作的信号,电磁控制单向阀10和11开启，机车的速度控制是通过阀门5来实现。阀5开口越大，机车获得的速度就越快。阀门5引导高压流体从油缸到油箱20再到较低的机车。单向阀3阻止高压流体反向流回。同步运动的油缸12和13取决于流量控制阀6和7的组合调整。通过节流阀调节稳态流动可以用下式表示为上式的Q代表流量,XV 活塞杆的位移、P通过阀门的压降和K0是C常数。如果压力降的P不变,流量和活塞杆的位移成正比,这也正比通过电磁阀线圈的电流。流量变化所引起的压降的变化也能因此得到补偿,通过改变活塞杆的位移。如上所述,流体流过的流量控制比例阀只有一个方向。阀组8和9,其中的每一个都由四个单向阀,用于确保阀门6和7工作在正常的方向。电磁单向阀10和11是专门用于防止机车下沉,这通常是引起的泄漏的液压元件当升降机停留在一平台时。电磁单向阀的工作原理,将会在本文后面进一步叙说。当泵停止工作的时候他们会锁住升降机,因此这里被称为液压锁。只有当他们的线圈通电升降机才会向下移动。如果发生电源的中断或其它液压元件的损坏,紧急阀14以较低的速度降下升降机。3、电液比例控制预设一个合适的速度曲线,根据设计规范,如最大加速度、加速度改变的最大比例和最大运行速度等,通常用来形容的运行模式的升降机。如果机车的速度跟随给定曲线,好的乘车舒适性是有保证的。开环控制不能达到足够的跟踪精度因为有效载荷，缸内流体体积和流体粘度的变化。因此，速度反馈需要衰减的影响的升降机性能的各种干扰。此外,没有闭环控制,两油缸的非同步性运动的差异是不可避免的,由于载荷、摩擦力和两油缸之间液压力的变化。因此,两个闭合环路需要在同一时间内达到的速度调节和同步控制。控制系统的总体框图如图4所示。 图4 升降机控制系统方框图它代表了电梯的向上运动。一个类似的框图可以很容易被演绎出为向下运动。驾驶室的速度是衡量一个编码器。驾驶室的平移运动是通过一个编码器控制的滑轮的旋转运动来转变的。一个二元同步是用来测量转子控制变送器CX和控制变压器CT相对转角之间的角度。因此,通过测量的相对角度与两油缸之间的高度误差成正比。如上所述,机车的速度是只取决于速度阀5，如图3所示,给出了同步阀6和7与比例阀5成严格的比例动作。反过来,在同等条件下,调整阀6、7,不会影响机车的速度。因此,速度调节和同步控制可以单独来实现,即速度控制器1和同步控制器2可以独立工作。一个微分反馈控制器,即控制器1,如图4所示。是适用于抑制内部参数变化所造成的副作用如油缸液体体积的变化和外部干扰如油缸内有效载荷和流体温度的变化。如图5所示。 图5 PDF格式的控制系统PDF格式的控制器易于实现，并且对参数变化和外部干扰不敏感。 当m1(t)足够小,饱和非线性可简化为工作在它的线性范围,然后PDF格式的控制器参数可以很容易被获得。假设这个系统可以用下式表达三个控制器参数如下：这里的是7.5167/ ts,ts是停留时间和KH调整控制器输出幅度常数。原位调谐控制器参数是要保障性能最优。 图6 空载速度曲线（虚线：预期 实线：实测） 图7 满载下速度曲线（虚线：预期 实线：实测）如图6、7展示了机车的速度跟踪性能，接着分别给出了满载荷和空载情况的速度曲线。速度图案之间的差异和实际速度模式主要是由于电液比例阀5的非线性特性。然而,整个速度模式非常接近设计模式,因此令人满意的舒适性仍然可以得到保障。一个约束步骤的PD控制器,即(PD)控制器2。如图2是用来获取两油缸的同步运动。PD控制器后面的理论和一艘小船转向相同。当划一艘船,以保持它沿着直线运动,划船人每次都是用力控制船桨根据船离开直线的远近和快慢。因为划船人不可避免延迟反应,船的真实路线和被给的路线不一致，不能保持很小差距。一种有效替代的方法包含桨手每当桨被操作之时申请估计能力的小部分。船将逐步的靠近被给路线，直到错误路线的方法可接受的价值。缸 12被当作参考油缸,其运动必须遵循油缸13。阀6和7的后座,类似于运动员的延迟反应使船的路线错误。在控制器是2每一段调整期的实际输出,只有一小部分所要求的价值,采用PD控制器。那是,大型的错误是在每一个采样周期的情况下,降低到一个可以接受的一个约束步直到一个被接受的高度误差达到了。该控制方案已经被证明是有效的在保持非同步性误差在2毫米范围,如图8和9。 图8 无效载荷下的非同步高度误差曲线 图9 1吨载荷下的非同步性高度不均匀误差曲线应该指出的是,如果最初的非同步性误差在采样周期是相当大的,将需要一些时间来达到可接受的错误的水平。如果升降机运行结束时的非同步误差能保留下次运作将要发生的错误,该过程可以避免非同步性的错误并保留整个动作过程的小的有价值的部分。为了达到这一目的,一个过滤装置是必要的,因为不同的泄漏率的两油缸将直接增加初始误差的升降机。4、结论电液控制系统与三流量控制比例阀已被推荐用于控制升降机速度和非同步性之间的误差的一个双缸液压升降机。一个假微分反馈控制方案已证明是一个适当的技术来实现一个理想的速度模式。此外,该系统保证低的非同步性误差通过PD控制器拘泥的一步。试验结果表明,该非同步性误差能被保存在2毫米范围。一定模式之间的差异和实际所需的速度模式滞后原因主要是电液比例阀的磁滞。一种新的电磁驱动的单向阀已设计,装配和测试,并证明了要成为一名优良的液压装置,为防止机车下沉。