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中英文文献翻译-压路机的仪器仪表在土方压实过程中对振动行为的监测
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中英文文献翻译-压路机的仪器仪表在土方压实过程中对振动行为的监测,振动压路机中英文
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压路机的仪器仪表在土方压实过程中对振动行为的监测Robert V. Rinehart , Michael A. Mooney美国科罗拉多矿业学院，金属工程部门、CO 80401美国科罗拉多矿业学院，金属工程分部、1610伊利诺伊州街，CO 80401摘要：智能土壤压实的目标之一是连续监测和鉴定及土壤参数的一个或多个以下的反馈控制：振动频率、力幅值，传输速度。持续的质量控制的反馈控制和土壤参数辨识的鲁棒模型结构的发展需要有关机器在行为操作期间的全面信息，例如，振动特性。本文介绍了装有综合测试仪监测系统的三维振动压路机组件和对偏心力的钢轮响应，压路机动力学的一个关键组成部分的位相滞后发展。测量技术详细阐述了实验数据表达出的在现场试验过程中观察到的反应性质。 2006年爱思唯尔BV公司保留所有权利。关键词：智能压实；振动监测；加速度仪；霍尔效应传感器；监测的土壤性质。引言：智能土壤压实涉及连续监测和查明的土壤性质，采用反馈控制的一个或多个以下：振动频率力幅值，传输速度优化的土壤压实，防止压实的破坏。持续质量控制的反馈控制和土壤参数辨识的鲁棒模型结构的发展需要全面了解机器的行为。在振动监测土壤压实中持续的信息，突出振动特性的滚子在操作期间对模型开发、参数估计和智能土壤紧实度至关重要。本文介绍使用开发和部署的综合测试仪系统来监测的振动压路机。本文所述的特定问题包括甄选和安置加速计来捕获关键滚子组件的三维响应和位置测量的旋转偏心质量内钢轮重现输入力的时程。并提出了一种实验数据来解释观察到的振动响应的性质和仪表的性能。1.仪表：这项振动压路机的调查是对英格索尔-兰德公司DD-138HFA双光轮压路机进行检测的（见图1）。仪表的设计和操作都直接适用于所有的单钢轮和凸块压实型压路机。DD 138HFA 整机质量为13752公斤，钢轮质量为2638公斤。每个钢轮直径1.4米，长度2.1米。在每一个钢轮严重偏心转动时，转动轴（见图2）提供了在垂直方向的振动和偏心力： 其中是圆形励磁频率(rad/s)，是偏心质量，是偏心力。偏心力幅值是和的乘积。励磁频率，或更普遍，是由操作员通过微机控制能从0调至70赫兹，但在实践中使用的更常见的频率范围是2050赫兹。偏心重块设置有八个可以改变的大约1千米到不少于2千米的重块，并且必须手动更改（如下所述）。仪表系统的概述如图1所示。为了解释目的，向前行驶如图1d所示，被视为图1a向右行驶和图1e向左行驶。右侧和左侧的机器取决于操作者他（她）自己前进行驶的方向。在三个方面利用加速计、钢轮和构件的振动进行了监测。如图 1 所示，钢轮框架连接是配置在不同的左、右两侧。因此，钢轮振动监测只对装载时非旋转的右侧进行检测（见图1d）。对左、右两侧框架的加速度进行了监测。对左侧的每个滚筒的传感器的位置使用霍尔效应（HE）对旋转偏心质量进行了监测。所有数据都通过一个16位，200千赫的数据采集系统(DAS)传感器取得。DAS，通过IOTech，inc.制造（克利夫兰，）配有一个用以太网端口提供连续数据流到车载笔记本电脑的压路机，和一个16位的可编程输入电压范围。因为信号采集的不同步，DAS使用多路复用器通过安装在压路机上的传感器完成样品模拟输入。然而，每5微秒相邻通道间的延迟时间差是远小于采样周期的（如2.5kHz采样频率的1.25%)。在一期280Hz振动中，每5微秒的最多延迟是0.14%，因此是被认为可以忽略不计的。抗锯齿硬件（即硬件实现低通滤波器），配合适当的采样频率，fs，确保被收购 DAS 的波形不包含从高频噪声源获得的任何能量（如电子噪声，高频率振动压路机压实机组件）。在本研究采用DAS，3杆巴特沃斯低通滤波器(LPF)实现了抗锯齿。该过滤器具有可编程截止频率的硬件，fLPF，通过改变电阻-电容模块在硬件设置。在本研究中使用的示例配置是fLPF等于500赫兹和fs等于2.5千赫。根据奈奎斯特采样定理，这一组合确保采样的信号是自由的别名组件，而且通过筛选允许最高频率信号是很好的解决3。 图1。（a）英格索兰DD 138HFA压路机系列，（b）钢轮和支架的加速度计坐落在右手边，（c）压路机系列从前面看出所有传感器位置，（d）压路机系列计划视图的示意图，（e）及（f）的支架加速度计安装在左侧，和手轮用于调整振动振幅和监测的旋转偏心质量状况。图2.前台的钢轮和支架显示轴方向、六自由度运动和传感器位置示意图。表一 加速度传感器规格Parameter参数DrumFrameRange范围10 g5 gSensitivity敏感性200 mV/g400 mV/gBandwidth频宽0400 Hz0300 HzNonlinearity非线性0.5% span0.5% spanTemperature error (20 to 85 C)温度误差2.0% span2.0% spanTransverse sensitivity横向敏感性1.0% span1.0% spanOutput noise输出噪音0.5 mV pp0.5 mV pp2.1.振动监测。 由于不对称在机器和潜在的非均匀土壤条件，每个钢轮及其周边框架及组件将可以体验自由运动（见图2）。引起这样的议案，由测量专业的三轴加速度计开发和制造的ICSensors (弗吉尼亚州汉普顿，/ icsensors /)被放置在图2中所示的钢轮和支架的位置。总结了采用ICSensors模型3140加速度计的规格。所用加速度计是压阻式传感器。传感元件是大规模暂停多束从硅支架的微机械硅。位于梁的压阻梁应变改变其电阻作为暂停的大规模变更的议案。临界加速度计规格包括范围、灵敏度、噪声地板、频率响应、非线性、横向灵敏度和温度误差。在测试过程中观察到典型的钢轮加速度幅值 (x和z方向) 范围从20-Hzvibrationto在70-Hzvibration。由于橡胶悬置，其框架连接每个钢轮，框架加速度幅值通常是 10-20%的钢轮加速度，因此可以从0.05 g至2 g的振幅范围 (x和z方向)。鉴于此范围和需要准确地捕获之间的山峰、高灵敏度、低噪音的加速度计为所需。例如，与200 mV/g的灵敏度和噪声 0.5 mVp-p，信噪比在钢轮加速度幅值的0.5 g信号将400。大量的带宽需要捕获0Hz (DC)响应和振动了to300Hz。直流能力提供援助，确保加速度计，真正面向在x、y和z方向，即在水平表面上0赫兹z加速度应改为1 g的安装过程中。高端的带宽允许捕获的谐波，即倍数的偏心的频率，振动响应。谐波含量提供的系统和土的非线性的措施，并形成了很多压路机4所使用的压实机计值的基础。谐波的最高300赫兹在振动压实已被观察到1，5。由于加速度在测试过程中观察到的大范围，高线性度所需。而且，温度对工作地点的潜在波动，低温度诱导漂移的灵敏度要求。温度在一个建筑工地上很容易可以在白天相差30C。为了量化噪声目前在仪表控制系统，包括DAS的来源进行了几项研究。其中一项研究涉及获取来自使用不同的方法来提供力量给传感器和DAS固定加速度计的信号。这项研究的结果表明，直流电池等深循环船用蓄电池，是一个非常干净的动力源优于标准的直流电源。为加速度计和DAS直接从直流电池供电导致噪音水平受噪音楼的加速度计本身（见表1），而不是外部噪声源。其他的噪音来源包括电磁干扰的开销或埋电力线路和电子板上，从广播电台和手机波，地震振动从附近交通或其他设备和从发动机或传动电机高频振动的干扰。电子干扰减轻了确保仪器仪表和DAS中的所有元素都正确都封装与铝箔屏蔽。高频率信号是通过前面所述的硬件抗锯齿消除的。同在一个建筑工地上的机器，但转的时候（因此固定）加速度计数据采集的样品。这些样品的分析表明，在正常运行下的噪声地板（一个标准偏差）是大约1015毫克。2.2.偏心力知道的滚筒内旋转偏心位置使测定的强迫作用对土壤，以及重要的机器土壤系统参数包括的位相滞后的辊压实机投入钢轮偏心力位移。所示在图1f和在图3中详细的振幅调整手轮刚性地连接到偏心质量，并且因此自转在钢轮之外直接关系到旋转的滚筒内偏心。利用此机特点使偏心要监视的位置。为此，磁铁被放置在手轮在均匀间隔361的十处地点。肩并肩磁铁被用于在一个位置提供对一个已知的位置（即指0）的引用。他传感器被安装到固定的支架，如图3所示。他传感器输出高电压 (8.0-8.2 V) 和被认为是on时磁铁足够接近，和低电压输出(0.0-0.2 V)，和被认为是关闭时磁铁是不在范围内。由于传感器延迟和高采样频率，它是可能对于样本点之间全开和全存在。因此生他获得的DAS的传感器数据是大约一个离散的正方形的波（见图4a）。为方便和准确性他传感器的原始输出是卷积的阈值函数这样 0.5 V 以上任何样本点设置为 1.0，任何低于0.5 V的采样点设置为0.0。此阈值过程如图4所示。一旦他传感器数据已成离散方波解决，就可能重新创建由旋转偏心质量产生的强制作用。请注意，在这里我们只是关心与竖向力。使用10磁铁脉冲每偏心的偏心的重心在垂直位置的知识革命（见图3b）的偏心位置可以确定每革命10地点。鉴于的偏心旋转，预计强迫函数将正弦窗体。最大垂直力，看到方程(1)、 时发生偏心是在向下的位置，而竖向力偏心时水平是零。因此，如图5所示，适于已知偏心位置，使用最小二乘方法的一系列正弦波。这适合的结果证实强迫函数是正弦波，知道什么时候评价谐波含量的一个重要方面。然而，由于对偏心质量的液压控制，频率略有随着时间变化(如差10 HZ20 Hz振动每秒)。数据简约分析： 在野外施工检测的辊传播范围可以从0.5到2m/s的恒定的正向（或反向）速度。给出了典型工作频率范围在2050赫兹和假设 1 m/s，1 米长的底层土壤的前进速度会经历20到50次的循环压缩振动荷载，生产影响间距的 2-5 厘米。图 6 礼物一些示例加速度计数据，具体垂直钢轮加速收集在期间20 Hz振动1500赫兹采样频率 (75样品/周期) 和2.0m/s 转发速度。鉴于下签署公约和知道加速度和位移180的相位阳性，钢轮加速度峰值时发生钢轮在其最高的位置而负加速度峰值时是发生在钢轮最低的位置。给出了加速度计0-300Hz带宽，更高的频率响应是杂散噪声和被过滤。重力加速度被减去垂直加速度数据。达图 6 中所示的加速度响应的空间变化400毫克，远远大于噪声（在第2节中所述的1015毫克），并说明旅游性质的压路机，在底层土壤条件和瞬态振动的变化。时程分析方法，从数据（在图6中的实心圆）收集峰值。它是共同的分析原始数据，如图6所示。然而，在某些情况下，窗口化方法平均加速度峰值然后来平滑针对一些波动。窗口的长度可以各不相同；在图6中，窗口长度是2米或1.0米。如果长波长功能更感兴趣，开窗可以有助于顺利过渡辊压实机响应造成的短波长地下非均质性。窗口大小的选择可能取决于预期的反馈控制率和为质量控制的目的，与机器梯段位置精度而闻名。由于耦合辊/土壤系统的非线性特性，感光钢轮和钢架的加速反应不是纯粹的正弦曲线。非线性是由激发频率的谐波表现，率在图峰正和负加速度之间的差异。图6为此，由以下方法测定位移幅值一个/2仅提供真实位移的近似。图7示出的X，Y，Z前滚筒（右侧）和前车架（右侧）位移在宽范围的激励频率的决定的响应。如前面提到的，有可能改变在实时的DD-138的激发频率。在图中的数据呈现。图7是从一个单一的通其中频率是在定期加强。图。图7a示出了显著钢轮位移响应，有些下面的x钢轮位移响应，并且相当微不足道钢轮位移响应。右侧框架响应（图7b）显示出可比的x，y和z的位移在整个频域，尽管由于橡胶隔离器，比钢轮位移少得多。垂直FECC时间历史的样品示于图8与前右垂直钢轮位移响应（近似为A /2）在一起。积极的力量向下代表偏心位置和容积向下。这种反应是代表这将被视为略低于Z-翻译和摇摆谐振频率20赫兹振动。耦合的阻尼性质系统使得钢轮位移要出的相位与偏心力。更具体地说，土阻尼导致垂直位移钢轮落后于垂直偏心力激励。如在该特定样品组中所示，钢轮位移80滞后偏心力。这个相位滞后是频率比（激发频率/固有频率）和阻尼比的函数这两者的土壤的压实过程中改变并且因此改变土壤特性的一个非常有用的量度。如果一个人到辊式压实机作为2自由度集总参数系统2,6,8建模，传递到土壤FTR的力将被确定为：其中，铁是力振幅由于偏心（m0e02），是励磁频率，MD和MF是感光钢轮和分别帧的质量，g是重力加速度，并且ZD和ZF是的加速度分别在钢轮和支架。如果FTR否0，则钢轮与土壤相接触;否则，如果FTR B0，滚筒不与地面接触，并被认为是在接触操作的部分损失。还应当指出的是，比接触和接触的部分损失其它的操作模式在更高的振幅和频率比这里呈现（例如跳跃，混乱）存在。这些模式通常由运营商避免，因为它们加速机器磨损，往往导致机器操作性损失7。图9示出在等式四个力分量的区段。（2）一个数据具有21赫兹的激励频率，和低偏心力的幅度，（正力向下绘制）来设置。如示于图图9中，DD-138HFA的前滚筒的静态重量为70.6518千牛之间千牛和FECC振荡。滚筒惯量显著，变化之间22千牛和 19千牛，并且由于相位滞后，仅与偏心力部分添加剂。该框架的惯性是相当比其它三个力小。其结果是，FTR对于该特定数据集振荡千牛41和103之间，说明感光钢轮和土壤操作期间保持接触。相反地，图10给出了示出接触操作的部分损失的振动数据的一个片段。数据，并用27赫兹的激发频率和高偏心力的幅度，铁具有相对高的相移，这导致在滚筒惯性和FECC存在对立并部分地相互抵消。FECC66千牛之间振荡，钢轮惯性和127之间变化 17千牛 - 110千牛，和钢轮惯性之间变化。由此产生的振荡FTR之间0170千牛，具有FTR0指示钢轮和土壤之间的接触的损失。图3.（一）偏心幅度调节手轮用磁体和霍尔效应传感器，以及（b）传感器和磁铁设置可调偏心质量及其重心。 图4.（一）原料霍尔效应传感器数据和被阈值处理后的霍尔效应传感器数据。图5.最小二乘最适合的解决方案，为偏心旋转的两个时期的力的计算函数的数据。 图6.筛选有峰值得垂直钢轮加速度数据确定，示出了用于平滑时域加速度数据的平均化窗口。图7.钢轮位移与频率和支架位移与频率，请注意排量近似A /2。 图8.垂直偏心力和垂直钢轮位移之间的相位差。图9.发送到土壤力由于压实机和所得的传递的力为接触操作的四个组成部分。图10.对传送到土壤力由于压实机和所得的传递的力为接触操作的损失的四个组成部分。4.结束语。实现智能压实，其中机准米是通过反馈控制，适用于所有土壤的压实过程是一个复杂的问题。反馈控制和系统识别都需要耦合系统的有效模式，而这又需要对机器的行为全面连续的信息。通过安装到钢轮和支架都以及监控三轴加速计提供此信息eccen- TRIC位置经由何传感器本文已证明是有效的。这里介绍的仪表辊压机提供了有关本机的振动特性和有关偏心强制功能全面的数据。当选择加速度计，考虑钢轮和支架加速度的预期水平以及感兴趣的频率范围是很重要的。此外，噪音水平，横向灵敏度和温度影响也必须加以考虑。这个仪器系统和随后的数据分析表明两种不同的基本波振动模式，即翻译围绕z轴和摆动关于x轴。作为钢轮框架上都这样，加速度计的位置是重要的，并且可以进行选择以强调（或弱化）一个给定的基本模式。最后，偏心位置的测量和相位滞后的确定被认为是在正确表征钢轮和土壤之间的接触力和理解基波辊和土壤的反应很重要。5.致谢：这项研究是由美国国家科学基金会（CMS-0327509）的支持，他们的支持大大激励了我们。作者还非常感谢交通运输的科罗拉多部门的合作和英格索兰公司提供的设备。作者还感谢保罗范和帕特里克米勒的贡献和反馈。6.参考文献：1 M.A.穆尼，P.B.戈尔曼，J.N.冈萨雷斯，土方施工过程中的振动基于健康监测，结构健康监测2（4）（2005）137-152。2 R.安德瑞格，K.考夫曼，“智能压实振动压路机。”交通运输研究记录1868年，交通运输研究委员会，华盛顿，2004年，第124-134。3 D.K. Lindler，介绍信号与系统，麦格劳 - 希尔，纽约，1999年，第739-741。4 H.F.尔纳，A。桑德斯特伦，连续压实控制，CCC，土壤欧洲车间压实颗粒物质，压力机路桥，法国巴黎，2000年，页237-246。5 M.A.穆尼，P.B.戈尔曼，G.B.陈C. Srour，观察土壤板结，PROC过程中振动压路机签名的变化。第一届欧洲CONF。在结构健康监测，法国巴黎，2002年。6 T.S.柳，T.塞利格，振动，碾压的动力，岩土工程事业部，ASCE 105（GT10）（1979）1211年至1231年的。7 D.亚当F.科夫，压实优化和质量控制（连续压实控制与轻落锤式设备）操作设备，PROC。国际研讨会在岩土工程和路面铁路设计与施工，希腊雅典，2004年，第97-106。8 M.A.穆尼，R.V.莱因哈特，“路基土压实过程振动压路机的现场监测，”岩土地质环境的工程，ASCE，2007，133（2），257-265。11Instrumentation of a roller compactor to monitor vibration behavior during earthwork compaction Robert V. Rinehart a, Michael A. Mooneyb, a Colorado School of Mines, Division of Engineering Golden, CO 80401, United States b Colorado School of Mines, Division of Engineering, 1610 Illinois Street, Golden, CO 80401, United States Abstract Among the goals of intelligent soil compaction are continuous monitoring and identification of soil parameters and the feedback control of one or more of the following: vibration frequency, force amplitude, and forward velocity. The development of a robust model structure for feedback control and/or soil parameter identification for continuous quality control/quality assurance requires comprehensive information about the machines behavior during operation, e.g., vibration characteristics. This paper describes the development of a comprehensive instrumentation system to monitor the three-dimensional vibration of roller compactor components and the phase lag of the drum response with respect to the eccentric force, a key component of roller compactor dynamics. The measurement techniques are explained in detail, and experimental data is presented to demonstrate the nature of the responses observed during field testing. 2006 Elsevier B.V. All rights reserved. Keywords: Intelligent compaction; Vibration monitoring; Accelerometers; Hall Effect sensors; Soil properties monitoring 1. Introduction Intelligent soil compaction involves the continuous moni- toring and identification of soil properties and employs feedback control of one or more of the following: vibration frequency, force amplitude, and forward velocity to optimize the compaction of soil and to prevent damaging over compaction. The development of a robust model structure for feedback control and/or soil parameter identification for continuous quality control/quality assurance requires compre- hensive information about the machines behavior. In the case of vibration monitoring of soil compaction 1,2, continuous information about the salient vibration characteristics of the roller during operation is critical to model development, parameter estimation, and intelligent soil compaction. This paper describes the development and deployment of a comprehensive instrumentation system to monitor the vibration of a roller compactor. Specific issues addressed in this paper include the selection and placement of accelerometers to capture the three-dimensional response of critical roller components, and the measurement of the rotating eccentric mass position within the drum to reproduce the input force time history. Experimental data is presented to explain the nature of vibration response observed and performance of the instrumentation. 2. Instrumentation The vibratory roller compactor instrumented for this investigation was an Ingersoll-Rand DD-138HFA double smooth drum roller (see Fig. 1). The instrumentation design and operation are directly applicable to all single drum and padfoot rollers. The DD-138HFA has a machine mass of 13,752 kg and a drum mass of 2638 kg. Each drum is 1.4 m in diameter and 2.1 m in length. Within each drum, an eccentric mass configuration rotating about the drum axle (see Fig. 2) provides the vibratory or eccentric force in the vertical direction: fecct m0e0x2cosxt1 where is the circular excitation frequency (rad/s), m0is the eccentric mass, and e0is the eccentricity. The eccentric force amplitude is the product of m0e0and 2. The excitation Automation in Construction 17 (2008) 144150 /locate/autcon Corresponding author. Tel.: +1 303 384 2498; fax: +1 303 273 3602. E-mail addresses: rrinehar (R.V. Rinehart), mooney (M.A. Mooney). 0926-5805/$ - see front matter 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.autcon.2006.12.006 frequency , or more commonly f=/2, is computer- controlled by the operator and can vary from 0 to 70 Hz, though the more common range of frequency used in practice is 2050 Hz. The eccentric mass m0e0has eight settings varying from approximately 1 kg m to more than 2 kg m, and must be changed manually (described below). An overview of the instrumentation system is illustrated in Fig. 1. For explanation purposes, forward travel is shown in Fig. 1d, and would be considered to the right in Fig. 1a and to the left in Fig. 1e. Right side and left side of the machine are taken with respect to the operator as he/she is traveling in the forward direction. Drum and frame vibration was monitored in three dimensions using accelerometers. As shown in Fig. 1, the drumframe connection configuration is different on the right and left sides. As such, drum vibration was monitored on the right side only where there was access to a non-rotating mount (see Fig. 1d). Frame acceleration was monitored on both the right and left sides. The position of the rotating eccentric mass was monitored from the left side of each drum using Hall Effect (HE) sensors. All data were acquired from the sensors via a 16-bit, 200- kHz data acquisition system (DAS). The DAS, manufactured by IOTech, Inc. (Cleveland OH, ) is equipped with an Ethernet port which provides continuous data streaming to a laptop PC onboard the roller compactor, and has 16 programmable input voltage ranges. The DAS uses a multi- plexer to sample analog inputs from the sensors installed on the roller compactor and therefore signals are not sampled simultaneously. However, the 5 s delay between adjacent channels is much less than the sampling period (e.g. 1.25% for a sampling frequency of 2.5 kHz). Past research has shown that up to the fourth harmonic of the excitation frequency is of interest, and given that the maximum excitation frequency possible with the DD-138 is 70 Hz, the highest frequency of interest is 280 Hz 1. The multiplex delay of 5 s is 0.14% of one period of 280-Hz vibration and was therefore considered to be negligible. Anti-aliasing hardware (i.e. hardware implemented low pass filters), in conjunction with an appropriate sampling frequency, fs, ensures that the waveform being acquired by the DAS does not contain any energy from high frequency noise sources (e.g. electronic noise, high frequency vibration of roller compactor components). In the case of the DAS employed in this research, anti-aliasing is achieved with a 3-pole Butterworth low pass filter (LPF). The filter has a hardware programmable cutoff frequency, fLPF, which is set by varying a resistorcapacitor module in the hardware. An example configuration used in this study is fLPFequal to 500 Hz and fsequal to 2.5 kHz. Based on Fig. 1. (a) The Ingersoll-Rand DD-138HFA roller compactor viewed from the right, (b) the drum and frame accelerometer mounts on the right side, (c) the roller compactor viewed from the front, (d) a plan view schematic summarizing all sensor locations, (e) the roller compactor viewed from the left, and (f) the frame accelerometer mounts on the left side, and the hand wheel used to adjust the vibration amplitude and monitor the position of the rotating eccentric mass. Fig. 2. Schematic of the front drum and frame showing axis orientation, six degree-of-freedom motion, and sensor locations. 145R.V. Rinehart, M.A. Mooney / Automation in Construction 17 (2008) 144150 the Nyquist sampling theorem, this combination ensures that the sampled signal is free of aliased components, and that the highest frequency signal allowed to pass through the filter is well resolved 3. In addition to the accelerometers and Hall Effect (HE) sensors described in detail below,the DAS acquired information from the roller compactors vehicle network. Parameters include eccentric excitation frequency and forward velocity which can be acquired at the same sampling frequency as the rest of the signal from the accelerometers and HE sensors. 2.1. Vibration monitoring Due to asymmetry in the machine and the potential non- uniform soil conditions, each roller drum and its surrounding frame assembly will potentially experience six degree-of- freedom motion (see Fig. 2). To capture such motion, ICSensors triaxial translation accelerometers developed and manufactured by Measurement Specialties (Hampton VA, / icsensors/) were placed at the drum and frame locations shown in Fig. 2. The specifications of the ICSensors model 3140 accelerometers employed are summarized in Table 1. The accelerometers used are piezoresistive type sensors. The sensing element is a micro-machined silicon mass suspended by multiple beams from a silicon frame. Piezoresistors located in the beams change their resistance as the motion of the suspended mass changes the strain in the beams. The critical accelerometer specifications included range, sen- sitivity, noise floor, frequency response, nonlinearity, transverse sensitivity, and temperature error. Typical drum acceleration amplitudes observed during testing (x and z directions) range from0.5gat20-Hzvibrationto9gat70-Hzvibration.Dueto the rubber mounts that connect each drum to its frame, frame acceleration amplitudes are typically 1020% of the drum acce- leration and hence can range in amplitude from 0.05 g to 2 g (x and z direction). Given this range and the need to accurately capture accelerations between peaks, a high sensitivity and low noise accelerometer was desired. For example, with a sensitivity of 200 mV/g and a noise of 0.5 mV pp, the signal to noise ratio at a drum acceleration amplitude of 0.5 g would be 400. A significantbandwidth was neededto capture boththe 0-Hz (DC) responseandvibrationupto300Hz.TheDCcapabilityprovides assistance during installation to ensure that the accelerometers are truly oriented in the x, y, and z directions, i.e., at 0 Hz on a horizontal surface the z acceleration should read 1 g. The high end of the bandwidth permits the capture of harmonics, i.e., multiples of the eccentric frequency, in the vibration response. Harmonic content provides a measure of system and soil nonlinearity and forms the basis of the compactor meter value usedonmanyrollercompactors4.Harmoniccontentashighas 300 Hz has been observed during vibratory compaction 1,5. Due to the large range of accelerations observed during testing, a high degree of linearity was required. And, due to the potential fluctuations in temperature on job sites, a low temperature-induced drift of the sensitivity was required. Temperature can very easily vary by 30 C on a construction site during the day. In order to quantify the sources of noise present in the instrumentation system, including the DAS, several studies were performed. One such study involved acquiring a signal from a stationary accelerometer using different methods to supply power to the sensor and the DAS. The results of this study revealed that a DC battery, such as a deep cycle marine battery, is a very clean power source and is preferable to a standard DC power supply. Powering the accelerometers and the DAS directly from a DC battery led to noise levels being controlled by the noise floor of the accelerometers themselves (see Table 1), rather than external noise sources. Other sources of noise include electromagnetic interference from overhead or buried power lines and onboard electronics, interference from radio and cellular phone waves, seismic vibrations from nearby traffic or from other equipment, and high frequency vibrations from the engine or drive motors. Electronic interference was mitigated by ensuring that all elements within the instrumentation and the DAS were properly encapsulated with foil shielding. Higher frequency signals are eliminated via the anti-aliasing hardware described earlier. With the machine on a construction site, but turned off (and therefore stationary) several samples of accelerometer data were acquired. Analysis of these samples revealed that the noise floor (one standard deviation) under normal operation is approximately 1015 mg. 2.2. Eccentric force Knowing the location of the rotating eccentric inside the drum enables the determination of the forcing function that the roller compactor inputs to the soil, as well as important machinesoil system parameters including the phase lag of drum displacement with respect to eccentric force. The Table 1 Accelerometer specifications ParameterDrumFrame Range10 g5 g Sensitivity200 mV/g400 mV/g Bandwidth0400 Hz0300 Hz Nonlinearity0.5% span0.5% span Temperature error (20 to 85 C)2.0% span2.0% span Transverse sensitivity1.0% span1.0% span Output noise0.5 mV pp0.5 mV pp Fig. 3. (a) Eccentric amplitude adjustment hand wheel with magnets and Hall Effect sensor, and (b) sensor and magnet setup with adjustable eccentric mass and its center of gravity. 146R.V. Rinehart, M.A. Mooney / Automation in Construction 17 (2008) 144150 amplitude adjustment hand wheel shown in Fig. 1f and in more detail in Fig. 3 is rigidly connected to the eccentric mass, and therefore its rotation outside the drum is directly related to the rotation of the eccentric inside the drum. Taking advantage of this machine characteristic enables the position of the eccentric to be monitored. To this end, magnets were placed on the hand wheel itself in ten locations evenly spaced at 361 intervals. Side by side magnets were used at one location to provide a reference to a known location (i.e. a reference to 0). The HE sensor was mounted to a fixed bracket as shown in Fig. 3. The HE sensor outputs a high voltage (8.08.2 V) and is considered “on” when a magnet is sufficiently close, and outputs a low voltage (0.00.2 V), and is considered “off” when a magnet is not in range. Due to sensor latency and high sampling frequencies, it is possible for a sample point to exist between fully offand fully on. Therefore the raw HE sensor data acquired by the DAS is approximately a discrete square wave (see Fig. 4a). For convenience and accuracy the raw HE sensor output was convolved with a thresholding function such that any sample point at or above 0.5 V is set to 1.0 and any sample point below 0.5 V is set to 0.0. This thresholding process is illustrated in Fig. 4. Once the HE sensor data has been resolved into a discrete square wave, it is possible to re-create the forcing function produced by the rotating eccentric mass. Note that here we are only concerned with the vertical force. Using the 10 magnet pulses per revolution of the eccentric along with the knowledge of the position of the eccentrics center of gravity with respect to vertical (see Fig. 3b) the position of the eccentric can be determined at 10 locations per revolution. Given the rotation of the eccentric, it was expected that the forcing function would be of a sinusoidal form. The maximum vertical force, see Eq. (1), occurs when the eccentric is in the downward position, whereas the vertical force is zero when the eccentric is horizontal. Accordingly, as shown in Fig. 5, a sinusoid is fit to the series of known eccentric locations using a least squares approach. The results of this fit confirm that the forcing function is sinusoidal, an important aspect to know when evaluating harmonic content. However, due to hydraulic control of the eccentric mass, the frequency varies slightly with time (e.g. 0.25 Hz for 10 s of 20-Hz vibration). 3. Field data reduction During field operation, the instrumented roller travels at a constant forward (or reverse) velocity that can range from 0.5 to 2 m/s. Given the typical operating frequency range of 20 50 Hz and assuming a forward velocity of 1 m/s, a 1-m length of underlying soil will experience 20 to 50 cycles of compressive vibratory loading, producing an impact spacing of 25 cm. Fig. 6 presents some sample accelerometer data, specifically vertical drum acceleration collected at a sampling frequency of 1500 Hz during 20-Hz vibration (75 samples/ cycle) and 2.0 m/s forward velocity. Given the positive down sign convention and knowing that acceleration and displace- ment are 180 out of phase, a positive drum acceleration peak occurs when the drum is in its highest position whereas a negative drum acceleration peak occurs when the drum is in its lowest position. Given the 0300-Hz accelerometer Fig. 4. (a) Raw Hall Effect sensor data, and (b) Hall Effect sensor data after being thresholded. Fig. 5. The least squares best fit solution to the calculated forcing function data for two periods of eccentric rotation. Fig. 6. Filtered vertical drum acceleration data with peaks identified, illustrating the averaging window used to smooth time domain acceleration data. 147R.V. Rinehart, M.A. Mooney / Automation in Construction 17 (2008) 144150 bandwidth, higher frequency response is spurious noise and was filtered. The acceleration of gravity is subtracted from the vertical acceleration data. The spatial variation in acceleration response shown in Fig. 6, up to 400 mg, is much greater than the noise (1015 mg as described in Section 2), and is indicative of the traveling nature of the roller compactor, variation in underlying soil conditions, and transient vibrations. For time history analysis, peak values were gleaned from the data (filled circles in Fig. 6). It is common to analyze raw data as presented in Fig. 6. However,
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