随车液压起重机的控制外文翻译@中英文翻译@外文文献翻译

附录 A 译文 随车液压起重机的控制 摘 要 ： 本文主要是描述随车液压起重机的控制过程。 这篇论文分为五个部分：需求分析，液压系统以及存在的问题的分析， 不同结构产生不同问题的分析，基于更加先进复杂电液比例控制阀的新技术的发展趋势的分析。 本文的研究工作是和实际的工业相结合的，比纯粹的研究理论更有意义。 关键字 ： 随车液压起重机，控制策略，电液比例控制阀 1.引言 本文主要叙述的是对随车起重机控制系统的改进方法 随车汽车起重机可以看成是一种大型柔性控制机械结构 。 这种控制系统把操作人员的命令由机械结构变为执行动作。 这样定义这种控制系统是为了避免在设计它事产生模糊的思想这是一种通过人的命令把能量转化成机械动作的控制系统 。 本文所写的就是这种控制系统。以这个目标为指导方针来分析怎样设计出新的控制系统。 文章分为五个部分： 1.分析这种控制系统必须据有易操作性，高强度，高效性，稳定性，安全性。 2.分析目前这种操作系统所存在的问题。 3.从不同的方面分析这种控制系统：不同的操作方式，不同的控制方法，不 同的组织结构。 4.介绍一种适合于未来工业的比较经济的新的控制系统。 5.分析一种据有高性能，高效率，易控制等的比较 好的控制系统。它将成为 今后研究的比较经济高效的一种方案。 2. 论文部分 2.1 对控制系统必备条件的分析 在一种新的操作系统开始正式投入工作之前，对这种控制系统据有严格的要求。对控制系统的影响有很多因素。例如：机械结构的可实行性因素，可操作性因素，效率因素，符合工业标准。 工业需求必须放在第一位。这与在控制系统中导管破裂保护和超载保护有同等的地位。其次稳定性要求也很重要；系统不稳定就没法正常工作。一旦稳定性要求得以确定，控制系统性能要求就可以进一步确定。机械结构决定了起重机的可操作性。机械机构是随 车起重机中可以往复转动固有频率低的大型柔性结构。 为了防止起重机振动，必须使起重机在固有频率下工作，或者提高起重机的固有频率。如果它的固有频率太低或者太高，操作人员将无法给它进行操作。最后传动效率可以在工业标准，稳定性，执行机构确定的基础上得到最优的方案。 2.2 对目前这种控制系统的分析 在设计一种新的起重机之前，研究目前起重机存在的问题是很有必要的。当前液压随车起重机主要存在以下三个问题： 1.不稳定性 2.不经济性 3.低效性 2.2.1 不稳定性 不稳定性是一个严重问题，他可能会损伤操作人员或 者会是设备受到毁坏。当一个系统不稳定时通常产生严重振动。为了消除当前系统的不稳定性，设计人员既花费了很多时间来研究又花费了很多财力设计出更加复杂的机构。如图 1所示为一种起重机，它适合于在高速下工作。但是为了可以安全的工作必须合理控制其运行速度。要提高它的控制速度又必须增加更加昂贵复杂的机械系统。 液压系统的参数，如温度或压力同样影响系统的稳定性。一个参数合理的液压系统比一个设计参数不合理的液压系统稳定，为了使整个系统运行稳定，有时必须降低次要的参数值。 2.2.2 不经济性 目前的液压系统是纯液压的机械系统 ，因此如果用户想实现一个功能，他就必须买一个能使现这个功能的液压机械组件。因为大多数用户又不同的使用要求，要求同一个设备可以进行升级。这就意味着这些标准设备可以人为的改造，这就增加了组件升级费用。 2.2.3 低效性 液体在液压系统的两个液压缸之间流动时效率较低。这是因为大多数液压阀都是用一个阀心来控制两个节流口，由于这个链接不可能使阀芯两侧的压力相等，因此在流出端就产生一个与液流方向相反的背压力，同时也增加了流入端的压力。由激励源产生的这个背压力与阀芯两端的压力差成正比的，给油缸的实际压力没有被有效的作用 在油缸上。例如，给液压缸的压力为 1000psi/1600psi传到液压缸时就只有 0psi/600 psi 了。无论如何，这样的话，提供的电量必须高于有效电量，这些额外的电量就被白白的浪费了 2.3 控制系统不同的控制方法 目前主要用电液比例控制阀来控制液压阀的运动。然而对控制筒有不同的控制方法。 电液比例控制阀对阀的关 /开，公共汽车系统，电源的智能激励，泵的调节方案控制精度都较高。必须对这种系统的优缺点进行分析，找出合理的方案。 2.4 近期方案 即使这种十分新的系统最佳外形的布局已经得以证明是可行的，但是起重 机制造商和配件商还不能立刻就接受这种技术。这是一个渐进的过程，所以提出了一种临时解决的方案。 这种方案是由微型计算机和升缩机构组成。这种离合阀可使这种更加高效稳定的执行控制机构得以实现。微型计算机可以对阀进行柔性控制。可以把这些变量编入软件。这样就消除了制造商许许多多不同的变量问题。起重机制造厂家可以根据产品功能选择不同型号的液压阀。配件商也将不得不生产这种型号的阀，这样不仅降低了制造成本，而且使起重机的性能得到提高。 2.5 更高效方案的分析 这种分析依赖于不同布局结果，液压泵控制的区域决定将要用的控制方 法，再依次对这个区域进行分析。不同的区域将用不同的方法探讨，用不同的刀具位置控制。 3. 实验设备 本文的中心是研究发展中的经济型机械控制方案的可实现问题，更多重点是先进的实验结果。实验结果由两种方法获得。第一种是通过研究单自由起重机实验台获得，第二种是通过研究一台由丹麦一家起重机厂送给英国的一所军校的起重机获得。如图 1 所示 图 1系统实验台 左：单自由度起重机模型 右：随车起重机实物 虽然目前这种升缩分离机构在生产商中没有被普遍接受，但是两分离阀将会被逐渐取代。如图 2所示是一种幅度 -脉冲变换液压 缸，它是通过数字信息处理器 /奔腾双信息处理器运行程序来控制液压阀的。由数字信号处理器运行控制代码，奔腾处理器来判断并提供图形用户界面。 4. 当前工作 4.1 直线轴流控法 当今市场常见的直线流控器都需要压力补偿。压力补偿器可以使阀芯突然受压时保持恒定的压力。但是新增加的压力补偿器会使阀的结构比简单的随动阀更加复杂。另一种解决方法是用流控器测量阀的压力降来调整阀芯的位置来实现。这种想法虽然简单，但是由于压力传感器和微控器的费用比较高，想普遍运用于商品上是很难的。然而目前这种利用微控器和压力传感器的思想对于生 产商来说是可以接受的。 虽然依据方程来看很简单，但是要实现却很难。流控器的位置精度取决于位置传感器的精度压力传感器的精度。噪声会影响位置传感器和压力传感器的稳定性。采用延时控制可以消除影响稳定性的噪声，这样，超过阀的运行范围的特征值用就不能用柏努力方程计算，应用更复杂的方程来计算。 图 3 起重机工作的不同情形 图 2升缩分离机构 4.2 液压缸控制方法 根据不同的受力方向和速度方向这种液压缸有四种工作情形。如图 3所示： 多数是普通的随动液压阀，它这种控制方法已经在文献中可以找到，依靠一般的测量 法测液压缸的速度位移相当复杂。它们也需要相当复杂的运算法则来控制。本文主要分析基于简单的 PI控制器和没有严格速度位移要求的液压缸的控制方法。这种系统的控制方法比复杂的控制方法简单得多，由于它不需要特殊的传感器而且容易被大多数工程师理解所以比较容易被厂商采用。 在设计一种控制方法时另一种特别的控制方法也需要了解，它也是液控中常用的一种方法。移动液压阀要求低泄漏，以前的液压阀大们通常有很大的交迭。然而，使生产商能够接受的这种线轴式液压缸的驱动性能相当慢。这种具有很大交迭的重合以及激发很慢的液压阀很难满足现在的 要求。交迭和较慢的驱动使压力控制变得相当困难。 新的控制方法可以用一个例子清楚简单的描述出来。从入口端实行流控制，出口端就实现液压力。流控制符合柏努力方程。液压控制过程中 PI控制器图 4 减压控制器 维持较小的压力来提高效率并且可以防止气穴现象。这些都是为了解决大交迭和较低的驱动所做的工作，压力控制器仅仅能排除控制中的一点问题。这就意味着如果控制人员想提高压力，却不能使液压缸移动，只能够降低控制口的开口量。这样做的作用只能使操作人员想改变活塞的方向时使它准时脱离零位。这种情况下外力方向和活塞运动仍然不能改变，这种方式需要改进 。既然这样，需要压力控制器在出口变大时提供与外力方向相反的有用压力，当已知入口端的压力下降的时候，它可以增加与外力相反的压力。这个压力也受 PI控制器控制，如图 4所示就是是一个这种控制系统的控制模型结构。 在写本文的时候这种控制的实验已经在图 1所示的实验台上完成了，由于起重机上安装了载荷单向阀，所以稳定性没有达到要求。然而，用液压单向阀取代这种载荷单向阀，可以使系统的稳定。在液压系统中，载荷闭式阀可以实现超载保护和卸载保护两种功能。由于在这种控制方法中使用伸缩阀机构对卸载保护很起作用，因此在起升机构中很有 必要使用有这种功能的单向阀。一个操作单向阀的驾驶员可以做这一点，没有增加复杂的动力来阻止起重机的倾。安装了这种单向阀，起重机操作人员不需要再增加更复杂的外力来防止起重机产生倾翻。 5. 结束语 即使没有大量的实验设施，但是实验还是完成了，一个好的开始是成功的一半。这个论文题的大轮阔已经确定，它是有意义而且合理的。这个工作分为需求分析、目前的系统分析、不同布局分析、近期的解决办法的分析和最优解决方案的发展趋势分析五个部分。在本论题的最后，液压随车起重机的控制模将会被修改。 6.感谢语 感谢 Danfoss Fluid Power A/S为这个研究提供了部分基金。也感谢 Hjbjerg Maskinfabrik (HMF) A/S愿意为这种起重机的测试提供技 术上的支 持 随车液压起重机的轨迹控制 问题描述 这项方案是根据如图 1所示的多自由度随车液压起重机控制问题提出来的。控制随车起重机要求操作人员技术相当高，它的操作机动范围很小。如果可以让现代的起重机实现遥控控制的话，操作人员只需要控制他手中的遥控器就可以控制起重机把重物放在他要求的任何地方。一个按钮控制一个自由度方向上 的转动。因此只需要让操作人员得到熟练的训练他就可以每次控制更多的按钮来实现多个自由度的转动。 图 1 所示为一台随车液压装载起重机部分液压系统控制图实例 这项工程的目标是设计一台非熟练操作人员都能够控制的移动式液压起重机。操作人员根据吊具总成的合成轨迹控制一根操纵杆。这样不同的自由度就可以同时被控制。 多数随车液压起重机的结构就像图 1所示的那样，大多数都是非常柔性化的，因此当受载时它们就会弯曲。这样做可以使起重机吊重比最低。事实上吊重顶端位置也是制约控制系统结构偏差的因素。这种问题可以通过一个好的位置 偏差补偿控制系统解决，这个系统还可以消除操作初期结构上发生的摆动。 继续使结构轨迹偏差补偿控制系统在起重机上进一步发展，起重机的装载能力将可以大大得到提高。当这种在起重机里的摆动可以被控制系统抑制的方法能够得到充分证明，在一个长的期限里可能有一个降低动力学安全系数的机会。这将使起重机生产商和用户节省一大笔费用。 吊具总成 图 2 测试起重机图片 方案内容 现以一台如图 2 所示的 HMF 680-4 型随车液压起重机来分析这些问题。在这台起重机的不同位置安装了传感器来监视系统上的不同参数值，它们都是一些起重机上很重要的不同连接位置的压力、流量 、应变参数值。实验测试可以证实起重机性能，所以可以通过精确的模型来测试起重机的性能。为了使所含盖的几个问题能够描述得更清楚，这些问题被简略的表述如下： 1. 分析系统要求说明书 系统的执行标准分析已被完成。基于系统的这种要求连同确保系统的执行的检验程序将被列入清单。 2. 机械子系统模型 许多技术模型已经存在，因此这些部件包括研究明确的模型局部动力学的表达方法。机械子系统的分析与局部模型偏差的详细分析相同。这样做是为了使计算的有效性能够明确表达出来，同时使系统的动作在控制过程中能够十分精确。基于这种非常有前 景的用公式表示一个数学子系统模型的方法已经完成，它将从起重机试验台的实验结果中得到校验。 3. 液压子系统模型 跟机械子系统建模一样，液压子系统模型由液压泵、不同的液压阀、激励源和液压导管组成。然而，并不是这些都要建模，只是那些对系统动力学部件影响比较大的成分才建模。液压子系统模型也需要用实验的方法来证明。除此之外是否在对偏差进行补偿时，系统中用了比重比较大的电液比例控制阀都必须被分析，即对机械结构的摆动进行分析。基于上述修正，对液压系统如果有必要都要做。 4.分析和标准的解决反转运动结构 起重机相对 于底部有一个可以操作的特定空间，即吊具总成能达到的范围。这是公认的起重机工作范围。有的部位要通过不同的路线才可以达到。因此有必要在这些区域确定最佳的运动结构。有不同的参数标准，习惯上用起重机上总负荷的最小值，也就是在临界状态点的最小压力值。为了做这个重要的结构压力分析，基于实现这个运算法则的控制系统将进一步得到发展。 5.载荷判断方案的发展 为了实现起重机结构偏转补偿，需要知道起重机承受的有效载荷。因此，有必要进行不同的载荷在线可能情况分析，这样就可以判断哪一个传感器需要进行载荷复合鉴定。基于这种鉴定 方案分析，可以实现最终的运算法则。 6. 控制运算法则的发展 基于这种机械液压子系统模型，一种吊具总成位置轨迹控制的控制规律将会得到发展。这种控制规律可以保证系统按照吊臂顶的运动轨迹运行，并且系统在工作情况下保持稳定。这包含在载荷判断和运动学最佳参数方案的分析中。 7. 控制系统的执行 最后系统的控制规律已经通过仿真试验得出，应该实现通过处理器或者数据信号处理检验系统实物了，即测试起重机。用这种测试方法将可以实现对系统制定测试，到测试结束的整个过程。这种测试技术还可以对一些典型系统进行控制。 机械化和自动化 自从 18 世纪末工业革命开始，工业机械化进程一直在不断地发展，并且变得越来越复杂。但目前的工业自动化过程较以前的工业自动化过程有很大的不同。 20 世纪的工业自动化之所以有别于 18、 19 世纪的机械化，是因为机械化仅应用于操纵（执行）机构，而自动化则涉及整个生产单元中的执行和控制两个（核心）部分。尽管不是所有的情况，但在大多数情况下，控制元件依然发挥着强大的力量，机械化已经代替了手工劳动，而自动化代替了脑力劳动。 机械化程度的发展在过去和现在的区别不是很明显 ，而在一端是具有强大辨别和控制功能的饿电子计算机，另一端是我们目前所说的“转换机构”正如传输带一样与其他设备简单的连接起来。自动调整机构能够自动调节系统，也就是说，它能在没有人干预和调整的情况下，自动对系统或生产过程进行控制和调节。现代工业技术的核心因素就是当前人们经常提起的反馈（控制），它是以自动调节系统为基础，借助于系统偏差与期望之间的偏差来控制，可由自动检测、测量、显示和校正方法得到。反馈控制应用于高速运转的大型数字计算机进行复杂运算时，对于输入的复杂问题，计算机通常会一直运行，直到求出与问题匹配的结 果。这或许于我们以前熟知的机器有很大的差别。同样的，反馈是我们所熟悉的机器概念。旧式的蒸汽机安装有离心传感器，控制杆上的两个小球不停的绕立轴旋转，气压升高，发动机转速变快，旋转控制器速度增加，使立杆上升，关闭阀门，切断蒸汽，从而发动机恢复到合适的速度。 随着工业革命的出现，机械化也随之产生，由于这时的机械化仅局限于单个生产过程。因此，需要使用人工控制每部机器及装卸材料，并把材料从一个地方运到另一个地方。仅仅在很少的情况下，这些生产过程才能够自动地衔接起来，形成连续的产品生产线。 一般而言，从 20 世纪 20 年代 以来，尽管现代工业已经实现了高度机械化，然而通常机械化的部分还没有联系在一起。机械化的工厂生产了光电灯泡、瓶子和大量生产的产品的元件，这些机械化工厂的自动化程度日益得到了加强。 20 世纪 40 年代电子计算机的发展，意味着在机械控制领域内将出现大量比计算机更简单、更廉价的产品。这些装 置 机械装置、气动装置、液压装置，在近些年内已有了很大的发展，并将继续发展下去，普通的观点认为这有利于自动控制的发展。当然不仅仅电子设备对目前自动控制的发展举足轻重，无疑在今后自动控制发展方面还继续会发挥不可估量的作用。 液压传动 对于两点之间较远的传动，不适合用传动带和传动链的机械系统，可优先考虑采用液压传动，液压传动的优点是：低速大力矩、机构紧密、稳定性高、无振动的平稳滑动，速度和方向能灵活控制，输出速度可实现无级快速变化。 由电力驱动的油泵提供有传递能量作用的油液，并可供给液压马达或油缸，从而将液压能转化成机械能。液压油流动是通过控制阀进行控制的，压力油的作用产生线性的或螺旋性的机械运动，此时的油液产生的动能相对低。因此，有时候使用静压传动。液压马达与液压泵的结构几乎是相同的，任何液压泵都可以当成马达应用，一定时间的流量可由调节 阀使用变量泵来控制。 一般来说液压传动可分为直线式的和旋转式的，旋转式传动产生旋转运动，而活塞及缸体部件产生往返的运动是线性运动。 所有液压马达的功能基于同一个原理，压力油被交换地挤入、挤出到油腔中，进油循环由最小的腔体注油开始，当油腔达到最大容积时，油腔和油路隔开，停止进油，然后通过回油路油液返回到油箱中，同时另一个油腔开始进油。 计算机辅助设计技术 在广义上讲，计算机辅助设计（ CAD）指的是计算机在解决设计问题中的应用。工程技术人员可以借助于直观显示屏幕、键盘、绘图仪和人机 接口等诸多方式与计算机通信。工程技术人员可以提出问题并能很快有计算机得到解答。更确切地说， CAD 是使工程技术人员和计算机系统工作，彼此发挥长处的技术。 过去，工程技术人员设计时所使用的传统工具是制图板、制图仪、计算器和技术数据图纸。后来，计算机的出现导致了工业中的巨大变化。随着数字控制、计算机数字控制、机床的引入，计算机在制造业中的应用在 20 世纪 50 年代末期首次有了实质性进展，通过磁带输入到机器中的数据控制了装配零件的机器运转。这一切对工程设计者并没有直接影响。 20 世纪 60 年代初随着计算机辅助设计的引入产 生了一场重大变革。 CAD 允许设计者以图形方式与计算机交互作用，工程技术人员能够检验一个设计思想，并很快地查看到设计效果，然后对其进行修改和重新评价。如此循环往复，直至形成一个合格的设计。每重复一次，设计方案都会得到一步的改善。因此，在时间、材料和资金允许的条件下所执行的循环次数越多，设计效果就越好。 计算机能加快设计进程，提高设计的精确程度。它能够在短时间内完成大量的、复杂的计算并得出准确可靠的结果。由于在有限的时间内某些设计所需要的大量计算不能简单的由人来完成，计算机的上述特征证明了作为一个设计工具的作用 是无法估量的。 计算机可在磁盘或直接存储器等永久性介质上保存大量的信息。因此，以数字形式描述一个工程图纸的细目或一个汽车车身的造型，并把信息存储在存储器中都是可以做到的。这些数据能从存储器中检索、快速转换并显示在 VDU（视频显示器）图形屏幕上，或交替地利用绘图仪绘制在图纸上。此外，设计者还可以迅速、容易地更新或修改图纸的任何部分。也能把修改后的图纸数据写回到存储器中。 计算机辅助设计在工程技术领域中有着重要的作用，例如，计算机系统生成工程图纸的应用；求解复杂构件的热应力问题的有限元技术的使用；机械装置和连接 的分析及大量的辅助工程应用。 附录 B 外文文献 CONTROL OF MOBILE HYDRAULIC CRANES Marc E. MNZER Aalborg University Institute of Energy Technology Pontoppidanstrde 101 DK-9220 Aalborg. Denmark Email: mmuniet. auc. dk The goal of the thesis described in this paper is to improve the control of mobile hydraulic cranes. The thesis is split into five parts: a requirements analysis, an analysis of the current systems and their problems, an analysis of different possibiilities for system topologies, development of a new control system for the near future based on electro-hydraulic separate meter in / separate meter out valves, and finally an analysis of more advanced and complex solutions which can be applied in the more distant future. The work of the thesis will be done in cooperation with industry so the thesis will have more of an industrial focus than a purely theoretical focus. Key words: Mobile Hydraulic Cranes, Control strategies, Separate Meter-in/Separate Meter-out. 1 INTRODUCTION The goal of the thesis described in this paper is to improve the control of mobile hydraulic cranes. A mobile hydraulic crane can be thought of as a large flexible mechanical structure which is moved by some sort of control system, The control system takes its input from a human operator and translates this command into the motion of actuators which move the mechanical structure. The definition of this control system is purposely left vague in order not to impose any constraints on its design. The control system consists of actuators which move the mechanical structure, a means of controlling the actuators, a means of supplying power to the actuators, and a way of accepting inputs from the operator. It is this control system which is the target of this thesis. The goal is to analyze the requirments made on the control system and present guidelines for the gesign of new control systems. The thesis will be split into five parts: 1. Analysis of the requirements of the control system, from the perspective of the operator, the mechanical system, efficiency, stability, and safety requirements. 2. Analysis of current control systems and what their problems are. 3. Analysis of the different options for the control system: different types of actuators different types of control strategies, and different ways of organizing components. 4. Presentation of a new type of control system, which is commercially implementable. A system that will meet the needs of industry in the near future. 5. Analysis of more optimized systems, with higher performance, better efficiency, more flexible control, etc. This will be less commercially applicable but will be a starting point for more research. 2 SECTIONS OF THE THESIS 2.1 Requirements Analysis of the Control System Before starting detailed work on developing new control systems, it is important to analyze what the exact demands are on the control system. The control system is influenced by many factors.For example: the mechanical structure it is controlling, the human operator, efficiency, stability, and industry requlations. Industry regulations are the first requirements that have to be addressed. Things like hose rupture protection and runaway load protection make a lot of demands on the control system. After regulations, stability is the next most important requirement； without stability the control system cant be used. Once stability has been assured, the performance requirements of the control system have to be set. They are determined by the mechanical structure of the crane and the human operator. The mechanical structure of a mobile hydraulic crane is a very necessary to keep the speed of the control system below this natural frequency or to develop a control system which can increase this frequency. The human operator also impossible limits on the control system. If the control system is too slow or too fast then it is impossible for a human operator to give it proper inputs. And finally, once the requlations have been met, stability is assured, and the performance is at the right level, the power efficiency of the control system has to be optimized. 2.2 Analysis of Current Control Systems Before designing a new control system it is good to analyze the current control systems to find out what their problems are. Current control systems are mainly hydraulic and can suffer from three main problems: 1. Instability 2. High cost 3. Inefficiency 2.2.1 Instability Instability is a serious problem as it can cause injury to human operators or damage to equipment. When a system becomes unstable it usually starts to oscillate violently. To avoid instability in current systems, the designers either sacrifice certain functions which are desirable, or add complexity and cost. For example, in the crane shown in Figure 1, it would be desirable to have control over the speed. But due to the safety system that cranes are required to have, standard speed control is not stable. To add speed control requires a more complex and more expensive mechanical system. The parameters of a hydraulic system, such as temperature or load force, also affect stability. A system that is stable with one set of parameters might be unstable with another set. To ensure stability over the entire operating range of the system, performance must sometimes be sacrificed at one of the parameter range. 2.2.2 High cost Current systems are purely hydraulic-mechanical, so if the user wants a certain function, the user buys a certain hydraulic-mechanical component. Because most user have different requirements, there are many different variations of the same basic component. This means that many specialized components must be manufactured rather than one standard product. This drives up the cost of components. 2.2.3 Inefficiency One form of inefficiency in current systems is due to the link between the flows of the two ports of the cylinder. This is because most valves use a single spool to control the flow in both ports. Because of this link, it is impossible to set the pressure levels in the two sides of the cylinder independently. Therefore, the outlet side will develop a back pressure which acts in opposition to the direction of travel, which increases the pressure required on the inlet side to maintain motion. Since the force generated by the actuator is proportional to the pressure difference between the two sides, the actual pressures in the cylinder dont affect the action of the cylinder. For example, the action of the cylinder for 0psi/600psi would be the same as 1000psi/1600psi. However, in the second case, the power supply would have to supply much more power. This extra power is wasted. 2.3 Different Options for Control Systems Current control systems use hydraulic actuators with directional/proportional valves to control the movement. However there are many different options for controlling a cylinder. Options range from new high performance electro-hydraulic valves, to separate meter in / separate meter out (SMISMO) valves, to hydraulic bus systems, to intelligent actuators with built in power supplies, to pump based control strategies. These systems all have advantages and disadvantages which need to be analyzed if the most optimum solution is to be chosen. 2.4 Near Future Solution It is expected that even if it is proven that a completely new system topology is the optimum configuration, the crane manufacturers and component manufacturers will not accept the new technology overnight. This will most likely take time, so an interim solution will be developed. This solution will be made up of micro computer controlled Separate Meter In / Separate Meter Out (SMISMO) valves (Elfving, Palmberg 1997； Jansson, Palmberg, 1990； Mattila, Virvalo 1997). SMISMO valves will make it possible to implement new control strategies which are more efficient and stable. The micro computer will make it possible to introduce flexibility to valves. Variants can be programmed in software. This eliminates the need to manufacture hundreds of different variants. The crane manufacturer will be able to choose the exact functions he wants in his valve, while the component manufacturer will have to manufacture only one valve. This will lower the cost, even though the performance will have increased. 2.5 Analysis of Higher Performance Solutions This analysis will depend on the results of the analysis of different topologies. If it is shown that pump based control is to be the way of the future for example, then analysis will be performed in this area. Another area which will also be explored, is tool position control. 3 LABORATORY FACILITIES As the focus of this thesis is on developing control strategies that can be implemented on commercial machinery, much emphasis will be placed on experimental results. Experimental results will be obtained from two systems. The first, a simple one degree of freedom crane, was designed as an experimental platform. The second is a real crane which was donated to the University by Hojbjerg Maskinfabrik (HMF) a Danish crane manufacturer. Refer to Figure 1. Figure 1 Experimental Systems in Laboratory. Left: One DOF crane model. Right: Real Mobile Hydraulic Crane As there are currently no commercially available separate meter-in/separate meter-out valves, two separate valves will be used instead. A sample circuit of one cylinder is shown in Figure 2. The control algorithms which control the valves, will be programmed on a Digital Signal Processor (DSP)/Pentium dual processor system. The DSP will run the control code and the Pentium will do diagnostics and provide a graphical user interface. Figure 2 Separate Meter In / Separate Meter Out Setup 4 CURRENT WORK 4.1 Flow Control by Direct Actuation of the Spool Most flow control valves on the market today work with a pressure compensator (Andersen； Ayers 1997). The pressure compensator keeps a constant pressure drop across the main spool of the valve, which keeps the flow constant. However, the addition of a pressure compensator makes the valve more complicated than a simple single spool valve. Another way of doing flow control is to measure the pressure drop across the valve and adjust the spool position to account for this (Back； Feigel 1990). This is not a new idea but has not been implemented commercially because of the high cost of pressure transducers and micro controllers. However, with the current drop in cost of micro controllers and pressure transducers this idea is now commercially feasible. The concept is very simple, spool position is calculated from the Bernoulli equation using the pressure drop across the spool and reference flow. Even though this is a simple equation, it is not easy to implement. The accuracy of the flow control is dependent on the precision of the position sensors and of the pressure transducers. Noise on the pressure or the position signals can cause stability problems. Filtering the noise, introduces delays in the control which can also affect stability. In addition the Bernoulli equation is not followed exactly over the entire operating range of the valve, so it may be necessary to store the valve characteristics as a data table or develop a more complex equation. 4.2 Cylinder Control Strategy To control a hydraulic cylinder, the strategy has to be able to handle four different situations depending on the directions of the load and the velocity of the cylinder. Refer to Figure 3. Figure 3 Different Situations in Crane Operation The control strategies that have appeared in the literature are usually quite complex and depend on measurements of the cylinder position and velocity (Elfving, Palmberg 1997； Mattila； Virvalo 1997). They are also based on rather complex control algorithms. It is the goal of this thesis to start with a control strategy which is based on simple PI controllers and makes no demands for position and velocity of the cylinder. The performance of this system will be lower than a complex control strategy, but it may be easier to implement commercially because it has no need for special sensors and is easier to understand for the average engineer. Another feature which needs to be acknowledged when designing a control strategy, is the type of valve used. Mobile hydraulic valves demand low leakage and since most mobile valves are spool valves, they usually have large overlaps. In addition, to make the cost of the valve acceptable to industry, the actuation stage on the spool is usually quite slow. This combination of large overlap and slow actuation makes it hard to implement many of the strategies that have been presented. Pressure control especially becomes difficult when there is an overlap and a slow actuator. One example of a new strategy which is simple and robust is described as follows. Flow control is implemented on the inlet side and pressure control is implemented on the outlet side. The flow control is based on the Bernoulli equation. Pressure control is done by PI controller which maintains a low constant pressure to increase the efficiency and prevent cavitation. To work around large overlaps and slow actuation stage, the pressure controller only does meter out control. This means that if the controller wishes to raise the pressure, it cant add flow to the cylinder, it can only decrease the opening of the meter out port. The benefit of this is that the only time that the spool has to cross the zero position is when the operator wishes to change the direction of motion of the cylinder. For the case where the load force and the velocity are in the same direction, this strategy has to be modified. In this case, the pressure reference of the pressure controller at the outlet is increased to a value which opposes the load force. The pressure reference is increased when it is noticed that the pressure of the inlet side is dropping. The pressure reference is also controlled by a PI controller. A schematic model of the controller system for the load lowering case is shown in Figure 4. At the time of writing this paper the initial experimental tests had performed on the real crane shown in Figure 1. Stability was not achieved because the crane is equipped with a load holding valve. However, the load holding valve will be replaced with a pilot operated check valve, which should make it possible to stabilize the system. In current systems, the load holding valve serves two functions, load holding and runaway load protection. Due to the use of a SMISMO valve setup, the runaway load protection is built into the control strategy, therefore the only function which is necessary for the load holding valve to perform is load holding. A pilot operated check valve will be able to do this, without adding complex dynamics which upset the stability of the system. Figure 4 Controller Strategy for Lowering of Load 5 CONCLUSION Even though not much experimental work has been finished, a good start has been made and initial tests have been promising. The outline of the thesis has been developed and organized in a logical manner. The work is split into five parts, requirements analysis, analysis of current systems, analysis of different topologies, development of a near future solution, and development of a more optimum solution. At the end of the thesis, the control of mobile hydraulic cranes will have been improved. 6 ACKNOWLEDGEMENTS This project is being funded in part by Danfoss Fluid Power A/S. The author would also like to thank Hojbjerg Maskinfabrik (HMF) A/S for the donation of the test crane. 7 REFERENCES Andersen, B. R.； Ayres, J. L. (1997). Load Sensing Directional Valves, Current Technology and Future Development, The Fifth Scandinavian International Conference on Fluid Power Back, W.； Feigel, H. (1990). Neue Mglichkeiten Beim Elektrohydraulischen Load-Sening, O+P lhydraulik und Pneumatik 34 Elfving, M.； Palmberg, J. O. (1997). Distributed Control of Fluid Power Actuators-Experimental Verification of a Decoupled Chamber Pressure Controlled Cylinder, 4th International Conference on Fluid Power Jansson, A.； Palmberg, J. O. (1990). Separate Controls of Meter-in and Meter-Out Orifices in Mobile Hydraulic Systems, International Off-Highway and Powerplant Congress and Exposition Mattila, J.； Virvalo, T. (1997). Computed Force Control of Hydraulic Manipulators, 5th Scandinavian International Conference On Fluid Power Trajectory Control of Mobile Hydraulic Crane EMSD 9/10 - 69C Problem Description This project takes its base in the problem of controlling mobile hydraulic cranes with multiple degrees of freedom, such as the one shown in figure 1. Controlling a mobile hydraulic crane takes a highly trained operator as it is often operated in areas with little space for maneuverability. Modern cranes are sometimes fitted with radio control so that if possible, the operator can be placed close at hand of where the load must be positioned. Still only one degree of freedom is controlled per button/handle. Therefore only if the operator has been sufficiently trained he/she may control two or more degrees of freedom at a time by operating more buttons. Figure1 Drawing showing a example of a hydraulic loader crane, for mounting on lorry. Only parts of the hydraulical system is sketched. The aim of this project is to develop a control system for a mobile hydraulic crane so that less training of the operator is needed. This is incorporated through trajectory control of the tool center of the crane by operating a joystick only. In this way multiple degrees of freedom are controlled simultaneously. Mobile hydraulic crane structures like the one depicted in figure 1 are normally also very flexible, i.e. they bend when they are loaded. This is due to highly optimized constructions regarding material usage, in order to keep the weight down. As it is the position of the tool center that is controlled the control system should also compensate for this structural deflection. This way by having an adequately good control system Which compensates for deflection, the system may also eliminate the possibilities for the operator to initialize oscillations in the structure. Making use of a trajectory control system with compensation for structural deflection will therefore expand the possibility of utilising the crane to its maximum regarding loading capability. In long term this may give the opportunity to lower the crane will be damped by the control system. All together this results in advantages for both manufacturer and end user advantages through a higher cost/capacity-ratio and a more easily controlled system. Project Contents The problem described will practically be delt with using a HMF 680-4 mobile hydraulic crane, a picture of this may be seen in figure 2. The crane is mounted with sensors for monitoring different parameters in the system, which are the most important pressures, flows, strains and relative link positions of the crane. This crane will be the basis for the experimental testing and verification, and therefore also for the mathematical models derived. In order to fulfil the above described problem several subjects has to be covered, in short these are: Figure 2 Picture of the text crane. 1. Analysis and specification of the demands for the system An analysis of performance criterias for the system is to be made. Based on this demands for the system will be specified along with testing procedures for the system to ensure the system fulfil the demands. 2. Modelling of the mechanical subsystem Many different modelling techniques exist, and therefore this part includes studying formulations methods for modelling multi-body dynamics. In particular an analysis of how to model the deflections in the mechanical subsystem should be made. The purpose is to arrive at a formulation which is computational efficient, but at the same timesufficiently accurate in describing the behaviour of the mechanical system, in order to include it in the control strategy. Based on the most promising formulation a mathematical model of the subsystem will be made, and it will be verified through experimental results obtained from the test crane. 3. Modelling of the hydraulic subsystem As well as mechanical system should be modeled, so shall the hydraulic subsystem, which consists of a pump, different valves, actuators and hoses. However, not all of these will be modeled, but only the components which have significant influence on the dynamical properties of the system. Also the model of the hydraulic subsystem shall be verified experimentally. Besides this it must be analysed whether or not the bandwidth of the controlling proportional valves are sufficiently high for using these in the control system when compensating for deflections, i.e. oscillations in the mechanical structure. Based on the above modifications to the hydraulic systems must be made if it is found necessary. 4. Analysis and criterias for solving inverse kinematic configurations The crane has a given space, measured relative to its base, in which it can operate, i.e. which the tool center can reach. This is known as the workspace of the crane. Some parts of the workspace may be reached in several different ways. Therefore it is necessary to determine the optimal kinematic configuration of the crane for these areas. There may be different criterias for optimisation, here one is sued which minimises the overall load on the crane, i.e. minimizes stress at critical points. In order to do this an analysis of the stress in the structure must be made and based on this an algorithm for implementing in the control system will be developed. 5. Development of load identification scheme In order to compensate for the structural deflections in the crane, the payload carried by the crane needs to be known. Therefore an analysis of the different possibilities for online identification of the load is necessary, this includes considering which sensors are needed and how complex the load identification will be. Based on the analysis an identification scheme is to be made, which may be implemented in the final control algorithm. 6. Development of control algorithm Based on the models of the mechanical and hydraulic subsystems a control law for the position trajectory control of tool center shall be developed. This control law must ensure that the system behaves as specified through control of the toll center, and that the system will be stable under all working conditions. Included in this is also the inclusion of the load identification and the kinematic optimization schemes. 7. Implementation of the control system Finally the control law developed for the system which has been tested through simulations, should be implemented in a microprocessor of DSP and verified on the physical system, i.e. the text crane. This will be done by experimentally testing it against the demands through the specified test procedure for the system. Based on these experiments it will be determined, what is attainable with the given technology for these type of systems, regarding control possibilities. Mechanization and Automation Processes of mechanization have been developing and becoming more complex ever since the beginning of the Industrial Revolution at the end of the 18th century . The current developments of automatic processes are , however , different from the old ones . The “automation” of the 20th century is distinct from the mechanization of the 18th and 19th centuries in as much as mechanization was applied to individual operations , whereas “automation” is concerned with the operation and control of control is go great that whereas And in many ,though not all , instances the element of control is so great that whereas mechanization displaces muscle , automation displeases brain as well . The distinction between the mechanization of the past and what is happening now is , however , not a sharp one . At one extreme we have the electronic computer with its quite remarkable capacity for discrimination and control , while at the other end of the scale are “transfer machines” , as they are now called , which may be as simple as a convey or belt to another . An automatic mechanism is one which has a capacity for self-regulate ； that is , it can regulate or control the system or process without the need for constant human attention or adjustment . Now people often talk about “feedback” as being an essential factor of the new industrial techniques , upon which is based an automatic self-regulating system and by virtue of which any deviation in the system from desired conditions can be detected, measured , reported and corrected . When “feedback” is applied to the process by which a large digital computer runs at the immense speed through a long series of sums , constantly rejecting the answers until it finds one to fit a complex set of facts that have been put to it , it is perhaps different in degree from what we have previously been accustomed to machines . But “feedback”, as such , is a familiar mechanical conception . The old-fashioned steam engine was fitted with a centrifugal governor , two balls on levers spinning round and round an upright shaft . If the steam pressure rose and the engine started to go too fast , the increased speed of the spinning governor caused it to rise up the vertical rod and shut down a valve . This cut off some of the steam and thus the engine brought itself back to its proper speed . The mechanization , which was introduced with the Industrial Revolution , because it was limited to individual processes , required the employment of human labor to control each machine as well as to load and unload materials and transfer them from one place to another . Only in a few instances were processes automatically linked together and was production organized as a continuous flow . In general , however , although modern industry has been highly mechanized ever since the 1920s , the mechanized parts have not as a rule been linked together . Electric-light bulbs , bottles and the components of innumerable mass-produced articles are made in mechanized factories in which a degree of automatic control has gradually been building up . The development of the electronic computer in the 1940s suggested that there were a number of other devices less complicated and expensive than the computer which could share the field of mechanical control . These devices mechanical , pneumatic and hydraulic have been considerably developed in recent years and will continue to advance now that the common opinion is favoring the extension of “automation” . Electronic devices , of course , although not the sole cause of what is happening , are nevertheless in a key position . They are gaining in importance and unquestionably hold out exceptional promise for development in the future . Hydraulic Power Transmission Hydraulic drives are used in preference to mechanical system when power is to be transmitted between points too far apart for chains or belts ； high torque at low speed is required ； a very compact unit is needed ； a smooth transmission , free of vibration , is required ； easy control of speed and direction is necessary ； or output speed must be varied steplessly . Electrically driven oil pressure pumps establish an oil flow for energy transmission , which is fed to hydraulic motor or hydraulic cylinder , converting it into mechanical energy . The control of the oil flow is by means of valves .The pressurized oil flow produces linear or rotary mechanical motion . The kinetic energy of the oil flow is comparatively low , and therefore the term hydrostatic driver is sometimes used . There is little constructional difference between hydraulic motor and pumps . Any pump may be used as a motor . The quantity of oil flowing at any given time may be varied by means