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关键词：: 带钢跑偏机分析设计图纸

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带钢跑偏机的分析设计

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前言1

1 绪论2

1.1 液压控制系统的组成2

1.2 液压控制系统的分类3

1.2.1 按偏差信号的产生和传递介质不同分类3

1.2.2 按液压控制元件不同分类3

1.2.3 按被控物理量的不同分类3

1.2.4 按输入信号的不同分类3

1.3 液压控制系统的特点4

1.4 电液伺服控制系统的发展概况4

2 设计要求及方案的选择7

2.1 设计要求7

2.2 方案选择7

2.2.1 方案一：机、液型带钢跑偏控制装置7

2.2.2 方案二：电、液型带钢跑偏控制装置9

3 电液伺服机构的分析11

3.1 电液伺服阀11

3.1.1 电液伺服阀的组成11

3.1.2 电液伺服阀的静态特性11

3.1.3 电液伺服阀的传递函数13

3.2 电液伺服液压缸的分析15

3.3 电液伺服系统的数学模型17

3.4 电液位置伺服系统的特点18

3.5 电液位置伺服系统的设计原则19

3.5.1 确定主要性能参数的原则19

3.5.2 确定参数间适当的比例关系20

3.5.3 应考虑的其它因素22

4 静、动态计算及分析23

4.1 静态计算23

4.1.1 确定供油压力23

4.1.2 根据负载轨迹或负载工况确定、23

4.1.3 选取伺服阀25

4.2 动态分析与计算26

4.2.1 求取各元件的传递函数26

4.2.2 绘制系统方块图26

4.2.3 根据系统精度或频宽要求初步确定开环增益27

5 系统的校正28

5.1 修改动力机构参数，改善系统性能28

5.1.1 确定活塞面积28

5.1.2 重新选择伺服阀28

5.1.3 系统稳定性和动态特性核验29

5.1.4 计算各项稳态误差30

5.2 系统的校正31

5.2.1 校正系统的动态分析32

5.2.2 校正后系统的误差33

6 液压能源参数选择34

7 系统的仿真35

7.1 系统PID控制器对系统的影响(I=0;D=0)36

7.1.1 取P=100时36

7.1.2 取P=150时36

7.1.3 取P=208.9时37

7.1.4 取P=300时37

7.2 改变液压缸阻尼比对系统的影响38

7.2.1 取=0.1时38

7.2.2 取=0.3时38

7.2.3 取=0.5时38

7.2.4 取=0.6时39

7.2.5 取=0.7时39

7.3 修改液压缸活塞面积对系统的影响40

7.3.1 取=1时40

7.3.2 取=时40

7.3.3 取= 3时40

7.4 无阻尼液压固有频率对系统的影响41

7.4.1 当=50时41

7.4.2 当=65.6时41

7.4.3 当=88时42

7.4.4 当=95时42

8 结论43

致谢44

参考文献45

摘要

目前，随着电脑技术，液压控制技术的发展，电液伺服控制系统也出现了突飞猛进的成果。

带钢经过连续轧制或酸洗等一系列加工处理后须卷成一定尺寸的钢卷，由于辊系的偏差及带材厚度不均和板材不齐等种种原因，使带材在作业线上产生随机偏离现象。它使卷取机卷成的钢卷边缘不齐，直接影响包装，运输及降低成品率。所以有必要做防跑偏的控制系统，以提高工作效率。

本文在通过对带钢跑偏机理的分析设计，阐述了有关电液伺服控制系统元件的组成、结构、工作原理及发展状况，并运用现代电液伺服控制技术设计控制方案，采用MATLAB仿真，不断调节使系统达到高效、稳定的自动跑偏控制的目的。

关键词：电液伺服控制系统；仿真

　　　液压控制技术在军事工业中，用于飞机的操作系统、雷达跟踪和舰船的舵机装置、导弹的位置控制、坦克火炮的稳定装置等。在民用工业中，用于仿形或数控机床，船舶舵机和消摆系统，冶金方面的带钢跑偏控制、张力控制、工程车辆转向系统，汽车的无人驾驶、自动变速、主动悬挂，试验装置方面的抗震试验台、材料试验机、道路模拟实验系统等。总之，液压控制技术应用愈来愈加广泛，在各个工业部门发挥着重要作用。尤其是在计算机的应用促使液压控制技术得到更迅速的发展和更广泛的应用。

2 设计要求及方案的选择

2.1 设计要求

　　　已知条件与要求：

　　　机组最大卷取速度 =5

　　　最大钢卷质量 =15000

　　　卷取机移动部分质量 =20000

　　　卷取误差

　　　移动距离

　　　导轨摩擦系数

　　　工作环境冷轧车间

　　　根据对同类机组的实测数据及统计资料，经分析确定系统的性能指标为

　　　系统误差

　　　系统频宽

　　　最大工作速度

　　　最大加速度

2.2 方案选择

　　　根据主机参数及其控制系统要求，现在对现有两种控制方案进行对比：

2.2.1方案一：机、液型带钢跑偏控制装置

　　　该跑偏控制装置由两个先导阀、主阀(液动型零开口四通滑阀)、双出杆对称液压缸、无外动力液压油源等组成。其工作原理如图2-1所示。

　　　两个锥阀既作为检测带钢对中与否的传感器, 又是主阀的先导阀。其结构见图2-2。先导阀阀芯为带平衡活塞式结构, 靠弹簧复位; 滑轮及连杆靠螺纹与阀芯相联并可调零; 主阀为液动型零开口四通滑阀, 其结构见图2-3。

内容简介：: 修改参数后得到的方块图1-开环频率特性；2-闭环频率特性图5-2 修改参数后系统的博德图图5-3 修改参数后系统的阶跃特性跑偏系统方块图原系统的简化方块图带压力反馈电液伺服阀系统原理图带压力反馈的跑偏系统方块图电液控制阀电液阀是机械运动的组成部分，其运动直接受电子电路的影响。对于液油压系统设计者来说，它已成为了一个流行的部分。电子阀门的主要类型是开关，比例，伺服阀和数字阀。根据1995年美国科学作家沙利文估计，电子IC与常规液压阀需求预计年均增长速度在5%左右。销售比例和伺服阀据估计会在3个主要应用领域增加，这3个领域分别是移动机械、机械工业、航天设备.一般而言，有液压阀的综合电子电路会增加机器的准确性和速度。运用电子系统也会有一些缺点。在一些应用中，由于热，部分效率会丧失。Vickers公司已经设计出了能代表未来电子系统的。它是专门的机器，其主要组成部分是比例阀、缸和数码控制。1993在美国获专利的机械工程师jun是液油压系统设计者。他们工作时是否使用机器人或自行移动机器和对于它们已经开始使用电脑和廉价的电子元件，这会改善液压系统性能还可以省钱。电子阀是机械的组成部分，其运动直接受电子线路影响。它已成为系统设计者设计的一个流行的部分了。液压控制是反过来受电子部分控制的。象扭矩马达或螺线管，通常是用电流通过一个有距离的比例阀来使它的线圈阀运动的电子阀的主要类型是开关、比例阀、伺服阀和数字阀. 该装置是固定在流体之间来提供动力和驱动源泉的，如扶轮摩托以及控制流体的压力、方向和曲率的。它能使机器控制驱动器组成部分的加速、速度、位置和力量的。在 Bethlehem, Pa.Rexroth公司的产品开发部门的经理 Paul Stavrou说：“电子控制液压系统在20世纪40年代已经有了，但是直到80年代初期具有微型化,降低成本和高可靠性优点的它才蓬勃运用于工业。主要生产电子阀的公司包括Rexroth，Vickers公司，总部设在Troy, Mich；Parker Hannifin Corp. of Cleveland, Ohio; and Eaton Corp. of Eden Prairie等等这些地方。每阀有截然不同的作用，取决于它的类型。最简单的就是开关阀。它的开关转换是通过前后来回转换线圈来实现的。在on的位置上，线圈于阀位置的排成一条直线通道，它允许一定量流体流动通过装置。在“off”位置上，线圈隔开连通渠道。通过调节电子控制螺线管流通速度可以使同一个阀的开关有不同的速率。这类型的控制有时也叫做“bangbang控制”，因为高强度的阀会过度震荡产生噪音。一般而言，比例阀会比较精确的按照流体的速度和压力来控制并对电子输入信号迅速做出反应。Stavrou说道：“电子控制已经给予比例阀精确度和信号反应时间，所以它适合应用于大多数工业。”比例阀运行时,线圈运动是靠一个有距离的直接成正比的有电螺线管来实现的。比如说在Rexroth公司生产的一个比例阀中，电动放大器接收到的信号为9伏特,它转换成当前高达1.5安培的电流.电流到达了一个有可以往返移动活塞的电动螺线管，被发送到螺线形电导管的定量电流控制着活塞移动线圈阀移动一段距离。随着时间的推移，流动量也改变。阀有变化地控制速度和驱动的力量。简单的说，一个比例阀可以改变流体的流动方向，也可以在一个驱动构件中控制输出部件的方向。比例阀通常被用在工作时无感应反馈的中开放性系统。不过,他们有时也被纳入封闭性的系统中。封闭性系统就是在其中一个传感器,通常是有差别的可变线性变压器传送可以告知控制者在每一个反复运动中螺线管活塞的位置的信号的。传感器也可以发出衡量驱动构件输出的信号。现在包含比例阀的封闭性系统，曾经是伺服阀的领域。伺服阀通常比比例阀制作的更精确，通常有两三个阶段。通常第一阶段，在试验电路中螺线管或扭矩马达控制流体流动。（一些扭矩马达在不是试验电路中有足够的力量去直接控制阀。）第二阶段中，试验电路控制能调节流体流动到驱动构件的活塞阀的运动。当使用扭矩发动机时, 电流被输送到其旋管使转子转动。转子与一个可在孔中来回转动的挡板连接。在实验电路中，这些孔是到达两个相分离渠道的通道。另外，通向线圈相反端的渠道控制阀的第二阶段。在接到电流时,扭矩马达会调整flapper板的位置。不同压力情况下，流体会流向线圈相反的方向。然后线圈会移动一段距离，这个距离与不同的压力和输送到发动机的电流有关。在线圈位置上的反馈通常是由一个线性的变数差别的变压器提供的。比例阀和伺服阀通常是由放大器和滑向系统控制架的控制卡来控制的。当一些还在被传统的软件和硬件控制时，最先进的伺服阀已经与规划和电脑数值控制相联系了。安装阀的时间应该保持到最小值，而且机器空间是紧的，控制卡应直接固定到阀的位置。应用及滥用伺服阀比比例阀性能跟高, 但他们是更加昂贵的。根据美国Frost & Sullivan公司的市场调查，与它的复杂性有关，每个伺服阀的价格大约在$1000 到 $2000之间。电子控制器价格可能会增加超过$500。然而，比例阀平均会是那些花费的一半。据Frost & Sullivan公司.1995年估计，美国对电子和常规水力阀的需求预计以每年5%的年率增长。比例阀和伺服阀的销售量预计会在三个主要应用领域增加: 移动机械、工业机械, 和航空航天设备。例如,在移动机械市场上,电动液压阀必须有多功能而且坚固。他们必须适合机器, 包括垃圾车, 铲车, 和挖掘机。阀经常在户外使用，这样会导致振动。电动液压的阀门的一个好处是, 他们在操作重设备时能增加安全性。例如，大多数起重机,禁止了一些区域。这些区域是机器不能设法运载重的装载或它也许下落的区域。然而在过去五年里, 为了使操作人员更好的操作机器以及限定危险的区域，起重机制造商开始对他们的常规液压系统增加传感器。根据Vickers公司的先进技术经理弗雷德菲利普所估计，如果起重机制作商最终决定使用微处理器控制, 安全系统将是更加有效的。他说：微处理器使设计一个系统成为可能。这个系统就是能够自动使起重机在被禁止的区域外部的系统。Vickers 公司把电动液压阀投入到新用途的使用中。例如在Burbank和Calif.的娱乐业, 他们把那个公司的电液比例阀运用在行动模拟器上。这个机器包括震动模仿运动譬如加速度、减速, 和自转。电动液压阀也使用在转台式行动控制上。Eaton 流体分裂制作了一个电子速度控制系统来提高使用在建筑业搅拌混凝土的运输搅拌器的耐久性。由于电液阀为混合鼓自动速度控制提供独立发动机速度，因此机器的使用寿命被提高了。引擎驱动鼓通过一个水力泵、马达, 和齿轮还原剂。当混凝土搅拌时，鼓每分钟转动在1 和17 转之间。在泵内，二个伺服阀控制流体流入一台流体伺服机。二条螺线管致力不同的流程方向，使每个阀都接收到从计算机控制器发出的信号并允许液压机液体转动的流动以使混合鼓以渴望的速度转动。计算机接收来自泵输出轴的一个霍尔效应传感器的鼓速度的连续的测量。没有电子控制, 在机器内当速度增加和减少时，搅拌器也跟着加速和减速。发动机的转动速度的比例会影响搅拌器的耐久性, 主要取决于在它的使用期间混凝土鼓转动多少次。鼓的转动也会影响引擎消耗的燃料量。使用电子速度控制系统, 机器操作员能使混合鼓的速度降低到1 转每分钟, 有效地打破搅拌器的和那引擎之间速度的连接。因而，混合鼓在工作的地方会更多的减少转动次数。在这个过程中节省下来的机器能量可以更好的利用到它工作的地方。Eaton 声称电子系统会使搅拌器的使用寿命增加一年。而且这个公司的研究表明由于引擎产生较少马力，对于混凝土的每一次装载，电子系统会减少引擎0.8 加仑的燃料消耗量。在众多优点中, 速度控制系统会自动地控制混凝土的混合速度。计算机系统也会存储以往每批混凝土的资料, 包括在混合期间鼓的转动数和自鼓转动开始消耗的时间多少。这些数据对于评估已完成的混凝土结构的完整性的房屋检查员是有价值。是否要使用电液通常,电子线路和流体阀的综合会增加机器的运转的速度和精确度。譬如执行一项特殊任务,在挖掘机里转动桶。电液会比传统无电的阀控制使用较少能量和有更好的精确度。传统方法包括直接给螺线管通电而使机械和自动控制连接，从而手工阀。在许多应用中，机电系统可以代替电液系统。例如, ac 马达会给予退弹管道系统的机器工具轴以能量。在许多情况下，机电系统与电动液压相比较，它们不会漏油, 通常更加安静,较不昂贵，对时尚模式和数字控制的反应更加直接。而且使用电动液压的系统也会有一些缺点。例如, 在某些应用中,由于热构件的效率会流失。另外, 对电子使用会使设计,应用和维护的液压机构的复杂性增加。例如,一位电液系统设计师必须使电子元件在苛刻的操作条件譬如到处温度和过份振动中，受到保护。电动液压的系统经常用于控制移动机械的行动。这里, 液压构件的优点就是依照设计者的意愿，它们能用机器相对小的空间来移动高而且重的装载。设计怎样去控制机器的行动经常取决于系统设计师是否了解应用和维护各个系统的细微差异。因为用户可能更了解传统液压系统的操作, 他们害怕无法改正电子问题，这是电液制造商面对的一个障碍。所以，电液构件制作商决定设计容易使用和维护的产品。Eaton 公司的运输搅拌器有一个诊断的特点，它允许卡车司机精确定位和确定电子失误的原因。当有问题时, 代码会出现在小室的一个诊断盘区，司机可以跟踪代码查明故障以及根据提示作出处理。对电液系统的采纳是用户关于构件的性能怎样与一种特殊应用匹配，这是很重要的。根据电液系统制作商所说, 随着时间的推移用户会发现有流体构件的连接电子的优点。但是, 一些用户对于由控制传统方法的转换持有怀疑态度。Vickers公司机械系统经理Paul Smith说：“我们的顾客应该肯定对液压系统增加复杂性的价值。他们会认识到产品会回报他们投资在它上面的额外金钱。回报来自更多地方,例如，减少在设施和维修方面的费用。 Smith说：“发展趋向是首先为用户实施一个开放的环形系统。然后, 当他们与它相适应时,再使他们转向更加复杂但更加准确的闭环系统。”发展中的改善Vickers公司的先进技术小组正致力于对电液系统的一系列改善。例如, 工程师正对用于特定产品和多用途产品的控制器进行改善。另外, 他们正设法提高能量利用率，减少噪声和挖掘电液系统的潜力。进一步,这个公司设计了他们认为能代表未来的电液系统:一台专业的发动机。他的主要构件是比例阀、圆筒和一位数字式控制器。除了减少液压系统的构件数量以外, 这种专业的发动机还有其它的优点。例如,在设计一个液压系统时, 为了符合应用要求，许多工作会进行优化。在这种专业的发动机里，为了一系列应用，获取到的它的工作情况会被编程到控制器里。因此, 系统设计师就节省了花费在调整控制系统的时间。没有一台专门的发动机，系统设计师设置的在电子控制器里的决定它效率工作情况的获取将会是错误的。发动机里开发软件的应用也使记录运转控制的工作情况变得容易了。最具代表性的就是程序员用一台个人计算机就可以连接发动机的控制器。软件和它的帮助菜单随后被一步步用到审阅编程处理中, 省去了在操作指南中的查找。Vickers公司的Phillips说：“系统设计师的一个目标就是选择能在运用中带来良好结果的构件。”设计师必须记住逻辑上什么零件在一起运作得最好。同时, 他们设法使零件数量减到最少而仍然达到必需的效果。使系统变的更灵活，要想达到那样的目的才更容易。Electrohydraulic valves take controlCopyright American Society of Mechanical Engineers Jun 1993The electrohydraulic valve, a mechanical component whose movements are directly influenced by electronic circuits, has become a popular part for system designers of hydraulic fluid systems. The main types of electrohydraulic valves are on-off, proportional, servo, and digital valves. The demand for electronic and conventional hydraulic valves is expected to grow at an annual rate of 5% in the US through 1995, according to Frost & Sullivan. Sales of proportional and servo valves are expected to increase in the 3 primary areas of application: mobile machinery, industrial machinery, and aerospace equipment. Generally, the integration of electronic circuits with hydraulic valves increases the precision and speed of a machines motion. There are also a few drawbacks associated with using electrohydraulic systems. In some applications, component efficiency is lost because of heat. Vickers Inc. has designed what it feels represents the electrohydraulic system of the future: an expert actuator whose primary components are a proportional valve, a cylinder, and a digital controller.Designers of hydraulic fluid systems, whether they are working with robots or mobile earth movers, are beginning to use compact and inexpensive electronic components to both improve the performance of the hydraulic systems and save money.The electrohydraulic valve, a mechanical component whose movements are directly influenced by electronic circuits, has become a popular part for system designers. This regulator of fluids is in turn regulated by an electric component, such as a solenoid or torque motor, that typically moves the spool of the valve through a distance proportional to an electric current.The main types of electrohydraulic valves are on-off, proportional, servo, and digital valves. The devices are mounted between the fluid supply source and a driven actuator, such as a rotary motor, and control a fluids pressure, direction, and Bow rate. They enable the actuator to control the acceleration, velocity, position, and force of the driven machine component.Electronic controls for hydraulic systems have been around since the 1940s, but it was not until the early 80s, with their miniaturization, lower costs, and improved reliability that they began to flourish in industry, said Paul Stavrou, manager of systems and product development at Rexroth Corps. servo and proportional controls group in Bethlehem, Pa.The leading producers of electrohydraulic valves include Rexroth; Vickers Inc., based in Troy, Mich.; Parker Hannifin Corp. of Cleveland, Ohio; and Eaton Corp. of Eden Prairie, Minn. Each valve has a distinctly different level of performance depending on its type (see table on page 56 ). (Table omitted)The simplest is the on-off valve, which turns the valve on and off by shuttling a spool back and forth. In the on position, channels in a spool align with ports in the valve housing and allow the flow of a defined volume of fluid through the device. In the off position, the spool blocks off the port. The same valve may be turned on and off at varying rates b an electronically controlled solenoid to modulate the rate of flow. This style of regulation is sometimes called bang-bang control because at high power the valves often vibrate excessively and are noisy.The proportional valve is generally more precise in terms of the rate and pressure of flow that it controls, and faster in its response to electronic input signals. Electronic controls have given proportional valves accuracy and signal-response times that are adequate in most industrial applications, Stavrou said.When a proportional valve is operating, its spool moves through a distance directly proportional to the current received by a solenoid. In one of Rexroths proportional valves, for example, an electric amplifier receives a signal of up to 9 volts, which it converts into a current of up to 1.5 amps. The current reaches an electric solenoid, which has a plunger that moves back and forth. The plunger moves the valve spool through a distance defined by the measure of current sent to the solenoid.By changing the volume of flow over time, the valve variably controls the speed and force of a driven unit. Similarly, a proportional valve that changes the direction of flow also controls the direction of output components on a driven unit.Proportional valves are often used in an open-loop system that works without sensor feedback. However, they are sometimes integrated into closed-loop systems in which a sensor, usually a linear variable differential transformer, sends signals that tell the controller where the solenoid plunger is during each stroke. The sensor can also send signals that measure the output of the driven unit.Closed-loop systems, which now incorporate proportional valves, were once the domain of servo valves. The servo devices are machined more precisely than proportional valves and usually have two or three stages.Typically, in the first-stage a solenoid or torque motor controls the flow of fluid in a pilot circuit. (Some torque motors are powerful enough to directly control valves without a pilot circuit.) In the second stage, the pilot circuit controls the movement of the valve spool, which itself regulates fluid flowing to the driven unit.When a torque motor is used, an electrical current is sent to its coils to move an armature. The armature is connected to a flapper plate that moves back and forth between orifices. These orifices are entry ports to two separate channels within the pilot circuit.Separately, the channels run to the opposite ends of a spool that controls the second stage of the valve. Upon receiving the electric current, the torque motor adjusts the position of the flapper plate. A difference in pressure emerges between the fluid flowing to opposite ends of the spool. Then the spool moves through a distance that is related to the pressure difference and electric current sent to the motor. Feedback on the position of the spool is often provided by a linear variable differential transformer.Proportional and servo valves are usually controlled from amplifier and control cards that slide into system control racks. The most sophisticated servo valves are often linked to programmable and computer numerical controllers, while some are controlled by custom software and hardware. In applications where time spent installing the valve needs to be kept to a minimum and machine space is tight, control cards are mounted directly into the valves housing.USE AND ABUSEServo valves hare higher performance than proportional valves, but they are more expensive. The average servo valve costs between $1000 and $2000, depending on its complexity according to the research firm Frost & Sullivan Market Intelligence in New York. Electronic controllers can add more than $500 to the price. The average proportional valve, however, can cost half that much.The demand for electronic and conventional hydraulic valves is expected to grow at an annual rate of 5 percent in the United States through 1995, according to Frost & Sullivan. Sales of proportional and servo valves are expected to increase in the three primary areas of application: mobile machinery, industrial machinery, and aerospace equipment.In the mobile machinery market, for example, electrohydraulic valves must be versatile and rugged. They have to fit in a range of machines, including garbage trucks, forklifts, and excavators. The valves are often used outdoors and in conditions that induce vibrations.One benefit of electrohydraulic valves is that they can increase safety in operating heavy equipment. Most large cranes, for example, have forbidden zones into which the machine must not try to carry heavy loads or it may fall over.Within the past five years, however, crane makers have begun adding sensors to their conventional hydraulic systems to keep the operator better informed of the outline and limits of the danger zone. If crane makers eventually decide to use microprocessor controls, the safety system will be even more effective, according to Fred Phillips, manager of advanced technology at Vickers. A microprocessor makes it possible to design a system that automatically keeps the crane outside the forbidden zone, he said.Vickers electrohydraulic valves are being put to novel uses. For example, Iwerks Entertainment in Burbank, Calif., uses the companys electrohydraulic proportional valves in a motion simulator used in the entertainment industry. This machine consists of a seat that shakes to simulate movements such as acceleration, deceleration, and rotation.Electrohydraulic valves are also used in the control of rotary motion. The hydraulics division of Eaton makes an electronic speed-control system that improves the durability of transit mixers used in the construction industry to mix concrete. The lifetime of the machine is improved because electrohydraulic valves provide for the automatic control of speed of the mixing drum, independent of engine speed.The engine drives the drum through a hydraulic pump, motor, and gear reducer. The drum rotates at between 1 and 17 rpm when concrete is mixing. Two servo valves control the flow of fluid into a hydraulic servo in the pump. Two solenoids dedicated to different flow directions and mounted to each valve take signals from a computer controller and allow the hydraulic fluid to flow at a rate and pressure that rotates the mixing drum at the desired speed. The computer receives continuous measurements of the drums speed from a Hall-effect sensor mounted at the output shaft of the pump.Without electronic controls, the mixer accelerates and decelerates as speed increases and decreases in the engine. Rotating in proportion to engine speed influences the mixers durability, a characteristic that largely depends on how many times the concrete drum turns during a lifetime. The drums rotation also influences the amount of fuel the engine consumes.With the electronic speed-control system, the machine operator can reduce the speed of the mixing drum to 1 rpm, effectively breaking the link between the speed of the mixing machine and that of the engine. The mixing drum, consequently, turns far fewer times on its way to a work site. Mechanical energy saved on the journey is put to better use at the work site.Eaton claims the electronic system adds a year to the life of a transit mixer. Further, a study conducted by the company shows that the electronic system reduces the engines fuel consumption by 0.8 gallon for each load of concrete due to the engine generating less horsepower.Among other benefits, the speed-control system automatically controls the speed at which concrete is mixed. The systems computer also stores historical information on each batch of concrete, including the number of drum turns during mixing and the length of time that has elapsed since the procedure took place. These data are valuable to building inspectors, who evaluate the integrity of the finished concrete structure.USING ELECTROHYDRAULICS OR NOTGenerally, the integration of electronic circuits with hydraulic valves increases the precision and speed of a machines motion. A particular task, such as rotating the bucket on an excavator, can be performed using less energy and with greater precision than by traditional nonelectronic methods of valve control. The traditional methods include manual control of a valve through mechanical links and automatic control by directly energizing a solenoid.Electromechanical systems can take the place of electrohydraulic systems in many applications, however. For example, ac motors often power machine-tool axes with ball-screw feed systems. Electromechanical systems in many cases are competitive with their electrohydraulic counterparts; they cannot leak oil, are often quieter, can be less expensive, and respond in a more linear fashion to analog and digital control.There are also a few drawbacks associated with using electrohydraulic systems. For example, in certain applications, component efficiency is lost because of heat. Additionally, the use of electronics may increase the complexity of designing, applying, and maintaining hydraulic systems. An electrohydraulic system designer, for example, may have to shield electronic components from harsh operating conditions, such as high and low temperatures and excessive vibration.Electrohydraulic systems are often used to control the motion of mobile machinery. Here, the defining advantage of hydraulic systems, their ability to move high loads using a relatively small volume of the machines space, weighs heavily in the designers decision.The decision of how to control machine motion often depends on whether the system designer is familiar with the nuances of applying and maintaining each system. Since the user is likely to be more familiar with the operation of traditional hydraulic systems, the fear of being unable to correct electronic problems is one obstacle faced by makers of electrohydraulic systems.As a result, makers of electrohydraulic components are designing products that are easy to use and maintain. Eatons transit mixer has a diagnostic feature that allows a truck driver to pinpoint the location and reason for an electronic failure. When there is a problem, a code appears on a diagnostic panel in the cab and the driver can track the code to a troubleshooting procedure in a manual.Just as important to the acceptance of electrohydraulic systems is the users knowledge of how the performance of a component matches a particular application. According to makers of electrohydraulic systems, over time users become more aware of the benefits of linking electronics with hydraulic components. Still, some users are skeptical of switching from traditional methods of control. Our customers have to determine the value of adding sophistication to the hydraulic system, said Paul Smith, a manager of systems engineering at Vickers. They have to see that the product will pay back the extra money they have invested in it. Payback may come, for example, from more

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