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南京理工大学泰州科技学院毕业设计（论文）任务书系部：机械工程系专 业：机械工程及自动化学 生 姓 名：徐超学 号：05010243设计(论文)题目：两足行走机器人臂部结构部分设计起 迄 日 期:2009年 3月09 日 6月14日设计(论文)地点:南京理工大学泰州科技学院指 导 教 师:路建萍 刘 艳专业负责人:龚光容发任务书日期: 2009年 2月 26 日毕 业 设 计（论 文）任 务 书1本毕业设计（论文）课题应达到的目的： 通过本设计，使学生熟悉机械产品开发性设计的一般过程，培养学生综合运用所学基础理论、专业知识和各项技能，着重培养设计、计算、分析和解决问题的能力，进而总结、归纳和获得合理结论，进行较为系统的工程训练，初步锻炼科研能力，提高论文撰写和技术表述能力。为实际工作奠定基础，达到人才培养的目的与要求。2本毕业设计（论文）课题任务的内容和要求（包括原始数据、技术要求、工作要求等）：技术要求：本机器人的总体功能为模拟人体动作。设计两足行走机器人臂部结构，能够实现摆大臂和摆小臂的功能。工作任务：（1） 查阅资料15篇以上，翻译外文资料3000字，撰写文献综述和开题报告。（2） 完成行走结构总体设计，绘制功能原理图 1 份。（3） 绘制装配图 1 份 （0号图纸）；部件图 1份；零件图若干。（其中，至少有1张图纸使用计算机绘制）（4） 设计说明书1.5万字左右。(打印)毕 业 设 计（论 文）任 务 书3对本毕业设计（论文）课题成果的要求包括毕业设计论文、图表、实物样品等：(1)开题报告(含文献综述)；(2)外文资料翻译：3,000 汉字以上；(3)总体装配图： 1 张； (4)部件装配图1张；(5)主要零件图：若干张 (总图数约合2张0号图)；(6)毕业设计说明书,字数不少于10,000字,并附有200300汉字的中文摘要及相应的英文摘要。所有设计图表、论文撰写、参考文献标记等均应符合本院的规范化要求。4主要参考文献：1 马香峰. 机器人机构学M. 北京: 机械工业出版社, 1991.2 龚振邦等. 机器人机械设计M. 北京：电子工业出版社，1995年6月.3 吴瑞祥. 机器人技术及应用M. 北京：北京航空航天大学出版社，1994. 4 熊有伦.机器人技术基础M.武汉：华中理工大学出版社，1996.5 王志良.竞赛机器人制作技术M.北京：机械工业出版社，2007.6 马香峰 等. 工业机器人的操作机设计M. 北京：冶金工业出版社，1996年9月.7 余达太，马香峰. 工业机器人应用工程M. 北京：冶金工业出版社，1999年4月.8 机械设计手册编委会. 机械设计手册M. 北京：机械工业出版社，2007年7月.9 Ernest L. Hall et l. Robotics: A User-Friendly IntroductionM. New York:CBS College Publishing,1985.10 Yoram Koren. Robotics for EngineersM. McGraw-Hill Book Company, 1985.11 成大先.机械设计手册（第4版）.北京：化学工业出版社，2002.12 白井良明著. 王棣棠译. 机器人工程M. 北京：科学出版社，2001年2月.13 David Cook.机器人制作M.北京：北京航空航天大学出版社，2005. 14 费仁元等.机器人机械设计和分析.北京：北京工业大学出版社，1998. 毕 业 设 计（论 文）任 务 书5本毕业设计（论文）课题工作进度计划：起 迄 日 期工 作 内 容2009年 3月 9 日 3月15日 3月16日 3月22日3月23日 3月29日3月30日 4月5 日4月6 日 4月12日4月13日 4月26日4月27日 5月3 日5月4 日 5月10日5月11日 5月17 日5月18日 5月24 日5月25日 5月31 日6月1 日 6月7 日6月8 日 6月14 日选题，发放审题表及任务书，熟悉课题完成外文资料翻译完成开题报告(包含文献综述)查阅相关资料，提出几种可行性方案 确定合理方案，进行总体方案论证进行结构部分设计计算相关结构参数，选择标准部件，熟悉相关软件对设计方案进行评价与修改，使之完善绘制总装配图，绘制零件图整理相关资料，撰写并打印设计说明书初步提交设计成果（包括图纸及论文），整改正式提交设计成果和设计说明书准备论文答辩所在专业审查意见：负责人： 年 月 日系部意见：系部主任： 年 月 日 南京理工大学泰州科技学院毕业设计(论文)开题报告学 生 姓 名：徐超（大）学 号：05010243专 业：机械工程及自动化设计(论文)题目：两足行走机器人 臂部结构部分的设计 指 导 教 师:路建萍 刘 艳2009 年 3 月 22 日开题报告填写要求1。开题报告（含“文献综述”）作为毕业设计（论文）答辩委员会对学生答辩资格审查的依据材料之一。此报告应在指导教师指导下，由学生在毕业设计（论文）工作前期内完成，经指导教师签署意见及所在专业审查后生效；2。开题报告内容必须用黑墨水笔工整书写或按教务处统一设计的电子文档标准格式（可从教务处网页上下载）打印，禁止打印在其它纸上后剪贴，完成后应及时交给指导教师签署意见；3。“文献综述”应按论文的格式成文，并直接书写（或打印）在本开题报告第一栏目内，学生写文献综述的参考文献应不少于15篇科技论文的信息量，一般一本参考书最多相当于三篇科技论文的信息量（不包括辞典、手册）；4。有关年月日等日期的填写，应当按照国标GB/T 740894数据元和交换格式、信息交换、日期和时间表示法规定的要求，一律用阿拉伯数字书写。如“2009年3月15日”或“2009-03-15”。毕 业 设 计（论 文）开 题 报 告1结合毕业设计（论文）课题情况，根据所查阅的文献资料，每人撰写2000字左右的文献综述：文 献 综 述摘要 本文详细介绍了研究两足步行机器人的组成，机器人的原因，两足步行机器人的应用前景。国内外两足步行机器人的现状及发展趋势。关键词 两足机器人组成 研究原因 前景 现状及发展趋势1 机器人的硬体组成在种类繁多的机械人当中，最让人感兴趣的就是仿人类机械人了。因为人类是最高级的动物，能让机械人各项机能达到人类的高度是每一个从事此工作的科学家不断追求的梦想。人体外形各项器官基本可划分为动作器官、感觉器官、思维器官三部分，机械人套件里的电子模组也是按这三部分来划分的。动作器官包括：可以让我们机械人唱歌的发音模组、可以装饰和指示的发光模组、速度可以调节的马达模组等。感觉器官包括：可以分辨黑白甚至是不同颜色的灰度测量模组、可以检测碰撞的触碰检测模组等。思维器官包括：RCU，也就是中央控制器，整个机器人的核心模組。当然还有一些辅助功能的拼装配件等等1。2 研究两足步行机器人的原因世界著名机器人学专家，日本早稻田大学的加藤一郎教授说过：“机器人应当具有的最大特征之一是步行功能”。步行功能的具备为扩大机器人的应用领域开辟了无限广阔的前景研究两足步行机器人的原因，概括起来有如下4个：(1)我们希望研制出两足步行机构，使它们能在许多结构性和非结构性环境中行走，以代替人进行作业或延伸和扩大人类的活动领域。(2)我们希望更多地了解和掌握人类的步行特性，并利用这些特性为人类服务。(3)两足步行系统具有非常丰富的动力学特性，在这一方面的研究可以拓宽力学及机器人学的研究方向。(4)两足步行机器人可以作为一种智能机器人在人工智能中发挥重要的作用2。3 两足步行机器人应用前景实用的两足步行机器人由两条腿和一个平台(腰部)组成。腿的作用是为平台提供移动能力，而平台的作用则是提供一个基础，以便安装机械手、CCD摄象机、机载计算机控制系统和蓄电池。显然，这种带机械手的两足步行机器人能非常灵活地从事较多的工作。但是，对于这种两足步行机器人来说，平台的稳定性对于有效地控制机械手末端操作器的位置和姿态是至关重要的，而两条腿的步态又对平台的稳定性起决定作用。因此，如何规划好腿的步态，协调地控制两条腿的运动以保持平台及整个两足步行机器人的稳定就成为一个主要问题36。目前，两足步行机器人的应用领域主要是康复医学。从长远来看，两足步行机器人在无人工厂、核电站、海底开发、宇宙探索、康复医学以及教育、艺术和大众服务行业等领域都有着潜在而广阔的应用前景。4 两足步行机器人研究的现状从8O年代中期到现在，虽然理论研究和样机研制不象1985年以前那样丰富，但也颇具特色。重要的是，国内正是在这一时期全面开展了两足步行机器人的研究。下面，首先看看美国的有关情况。1985年，美国的Hodgins和Raibert等人研制了一个用来进行奔跑运动和表演体操动作的平面型两足步行机器人，这个机器人有3个自由度。1986年，他们用这个机器人进行奔跑实验，着重研究奔跑过程中出现的弹射飞行状态。在实验中，这个机器人的最大速度高达4.3米秒。1988年和1990年，他们又用这个机器人进行翻筋斗动作实验。Hodgins和Raibert研究这两种运动是因为它们含有丰富的动力学内容，尤其是两者都具有弹射飞行状态。在美国研究两足步行机器人的科学家中，郑元芳(YFZheng)博士是一个非常杰出的人物。他在80年代初由中国去了美国，并于1984年在俄亥俄州立大学获博士学位，然后一直在克莱姆森大学工作，最近又回到俄亥俄州立大学任职。在克莱姆森大学期间，他主持研制了两台步行机器人，分别命名为SD一1和SD一2。SDl具有4个自由度，SD一2则有8个自由度。其中，SD一2是美国第一台真正拟人的两足步行机器人。1986年，SD一2机器人成功地实现了平地上前进、后退以及左、右侧行。1987年，这个机器人又成功地实现了动态步行。郑元芳博士也因他在机器人领域的突出贡献而获得美国1987年度“总统青年研究员”奖 。1984年，郑元芳博士对两足步行机器人与环境接触时的碰撞效应进行了研究。1987年，他提出了一种用于两足步行机器人运动控制的监控系统。1989年，他研究了两足步行机器人的扰动抑制问题。1990年他首次提出了使两足步行机器人能走斜坡的控制方案，并利用SD一2机器人进行了成功的实验 。此外，郑元芳博士还从神经生理学的角度对人类肌肉的多级传感与多级驱动原理进行了研究，并提出了采用这种原理设计两足步行机器人的方法7。下面我们再看看国内在两足步行机器人方面的研究情况。我国从80年代中期才开始研究两足步行机器人，当时主要的研究单位是哈尔滨工业大学和国防科技大学。哈尔滨工业大学研制成功的第一台两足步行机器人重7Okg，高l10cm，有10个自由度，采用直流电机经谐波减速驱动，控制系统由一台IBMPCXT计算机和l0个MCS一51单片机系统组成。1989年l0月，这个机器人实现了平地上的前进，左、右侧行以及上、下楼梯的运动，步幅可达45cm，步速为l0秒步，为静态步行812。最近哈尔滨工业大学又研制了一台l2自由度的两足步行机器人，井正在进行动态步行的实验。我们南京航空学院从1989年秋天起也开展了一个两足步行机器人的研究计划，现在已研制出一台8自由度空间运动型的两足步行机器人，命名为NAIWR1。目前，这一计划正在实施中。总观起来，两足步行机器人研究的现状是：国外，主要是日本和美国，对两足步行机器人的研究已经达到了相当高的水平，研制出了能静态或动态行走的多种样机。国内由于起步较晚，前一段刚完成静态稳定步行的研究，目前，正处于准动态和动态稳定步行的研究阶段。虽然国内的研究水平还不象国外那样高，但在短短的五六年时间能达到今天的水平，已经是相当惊人的了！5 两足步行机器人研究的发展趋势概括起来，两足步行机器人的发展趋势包括如下l0个方面：(1)能动态稳定地高速步行。(2)能以自由步态全方位灵活行走。(3)具有良好的地形适应性。(4)具有极强的越障和回避能力。(5)具有很高的载重自重比。(6)可靠性高、工作寿命长。(7)具有丰富的内感知和外感知系统。(8)控制系统和能源装置机载化。(9)具有完全的自律能力。(10)具有灵活的操作能力(安装一个或多个机械手) 13,14。6 结束语本文较详细地介绍了国内外两足步行机器人研究的主要情况。我们相信，随着整个机器人技术及相关技术的发展，在不久的将来，两足步行机器人一定能够真正进入实用化阶段，在各行各业中发挥重要作用。参考文献1 Todd D J .Walking machines ,an introduction to legged robots Kogan Page Ltd.London,1985.2 Hemamu H , Weimer F C.Koozekananit S H .Some aspects of the inverted pendulurn problem for modelling of Iocomotion systemr. Proc of 1973 JACC.3 白井良明著. 王棣棠译. 机器人工程M. 北京：科学出版社，2001.2.4 熊有伦.机器人技术基础M.武汉：华中理工大学出版社，1996.5 王志良.竞赛机器人制作技术M.北京：机械工业出版社，2007.6 成大先.机械设计手册（第4版）M.北京：化学工业出版社，2002.7 熊有伦.机器人技术基础M.武汉：华中理工大学出版社，1996.8 机械设计手册编委会. 机械设计手册M. 北京：机械工业出版社，2007.7.9 马香峰. 机器人机构学M. 北京: 机械工业出版社, 1991.10 龚振邦等. 机器人机械设计M. 北京：电子工业出版社，1995.6.11 吴瑞祥. 机器人技术及应用M. 北京：北京航空航天大学出版社，1994. 12 熊有伦.机器人技术基础M.武汉：华中理工大学出版社，1996.13 David Cook.机器人制作M.北京：北京航空航天大学出版社，2005. 14 费仁元等.机器人机械设计和分析.北京：北京工业大学出版社，1998. 毕 业 设 计（论 文）开 题 报 告本课题要研究或解决的问题和拟采用的研究手段（途径）：本课题是设计两足行走机器人臂部结构，能够实现摆大臂、摆小臂的功能。主要设计难点是重心前后移动与身体左右平衡难以协调的问题，尤其是正步行走、身体不倾斜的前提下更难以实现。我们设计小组选择简单的控制系统实现模仿人类行走的机器人，以此提高我们的机械设计创新能力。 我们采用以下创新点： (1) 先是用3D软件PRO/E设计出机器人的总体结构和各个零件的结构，直观的展现了我们所设计的双足行走机器人。(2) 采用了17台舵机，腿部共有8台舵机每条腿个有4个舵机，臂部共有4台舵机，每条手臂个2个，躯干4台舵机还有头1台，合理控制，以此解决了简单控制条件下机器人难以实现正步行走的难点问题。（3）大小臂均可沿锥面做往复回转运动，可组合出多种姿态。（4）充分体现了以机为主、机电结合的特色。 毕 业 设 计（论 文）开 题 报 告指导教师意见：1对“文献综述”的评语：该生的文献综述结合所要研究地课题比较紧密，从文中可以看出该生对所要做地工作进行了较深入地学习。2对本课题的深度、广度及工作量的意见和对设计（论文）结果的预测：本课题要做什么步骤叙述很清楚，设计思路正确，工作量合理，预计该生能顺利并很好地完成该课题。 指导教师： 年 月 日所在专业审查意见： 负责人： 年 月 日 A Power Autonomous Monopedal Robot Benjamin T. Kruppa, Jerry E. Prattb bkrupp, jprattihmc.us aYobotics, Inc, Cincinnati, OH bFlorida Institute for Human and Machine Cognition, Pensacola, FL ABSTRACT We present the design and initial results of a power-autonomous planar monopedal robot. The robot is a gasoline powered, two degree of freedom robot that runs in a circle, constrained by a boom. The robot uses hydraulic Series Elastic Actuators, force-controllable actuators which provide high force fidelity, moderate bandwidth, and low impedance. The actuators are mounted in the body of the robot, with cable drives transmitting power to the hip and knee joints of the leg. A two-stroke, gasoline engine drives a constant displacement pump which pressurizes an accumulator. Absolute position and spring deflection of each of the Series Elastic Actuators are measured using linear encoders. The spring deflection is translated into force output and compared to desired force in a closed loop force-control algorithm implemented in software. The output signal of each force controller drives high performance servo valves which control flow to each of the pistons of the actuators. In designing the robot, we used a simulation-based iterative design approach. Preliminary estimates of the robots physical parameters were based on past experience and used to create a physically realistic simulation model of the robot. Next, a control algorithm was implemented in simulation to produce planar hopping. Using the joint power requirements and range of motions from simulation, we worked backward specifying pulley diameter, piston diameter and stroke, hydraulic pressure and flow, servo valve flow and bandwidth, gear pump flow, and engine power requirements. Components that meet or exceed these specifications were chosen and integrated into the robot design. Using CAD software, we calculated the physical parameters of the robot design, replaced the original estimates with the CAD estimates, and produced new joint power requirements. We iterated on this process, resulting in a design which was prototyped and tested. The Monopod currently runs at approximately 1.2 m/s with the weight of all the power generating components, but powered from an off-board pump. On a test stand, the eventual on-board power system generates enough pressure and flow to meet the requirements of these runs and we are currently integrating the power system into the real robot. When operated from an off-board system without carrying the weight of the power generating components, the robot currently runs at approximately 2.25 m/s. Ongoing work is focused on integrating the power system into the robot, improving the control algorithm, and investigating methods for improving efficiency. 1. INTRODUCTION Practical legged robots are challenging for a number of reasons, including dynamic balance requirements, design complexity, and power requirements. To investigate power-autonomous legged robots we have been developing a power-autonomous Monopedal robot that is powered from a two stroke engine, which drives a high-pressure hydraulic system. The Monopod is a planar robot, confined to the surface of a sphere by a 12 foot radius boom. It has two degrees of freedom: a hip and a knee. Hydraulic Series Elastic Actuators are located in the body and transmit power to the hip and knee through cables. The Monopod is intended to be a test platform for a variety of technologies including: Hydraulic Series Elastic Actuators. Series Elastic Actuators 1-3 allow for high fidelity, moderate bandwidth force control. While several robots have utilized Series Elastic Actuators that use DC motors, the Monopod is the first robot that uses hydraulic versions of the actuators. Virtual running springs. The support phase of running is often modeled as a mass bouncing on a spring, and it is argued that the efficiency of running animals is due in part to springy muscles and tendons 4. To both gain efficiency and simplify control, most running robots utilize a physical leg spring 5. The Monopod is a test Sensors, and Command, Control, Communications, and Intelligence (C3I) Technologies for Homeland Securityand Homeland Defense V, edited by Edward M. Carapezza, Proc. of SPIE Vol. 6201, 620112, (2006)0277-786X/06/$15 doi: 10.1117/12.666253Proc. of SPIE Vol. 6201 620112-1 platform to determine if one can use a virtual leg spring instead of a real leg spring in a running robot. With the current implementation of the Monopod, we simulate a virtual leg spring using the force-controllable properties of the Series Elastic Actuators. While we do not get the efficiency benefits of real springs, we retain control flexibility, rather than having the spring bounce fully dictate the resultant dynamics. High density, mobile, hydraulic power system. In order for legged robots to be practical, high power-density and high energy-density systems must be developed. Combustion-driven hydraulic systems are an appealing choice. However, lightweight off-the-shelf solutions are lacking, and expert knowledge tends to be concentrated in domains that have differing requirements than legged robots. Therefore, the Monopod is intended to be a development and test platform for mobile hydraulic power systems that can later be extended to other robots. In the design of the robot, we used an iterative simulation-based design process. We performed physically realistic simulations of the robot running at various speeds with various total mass and extracted joint torque, speed, and range of motion requirements. Using these joint power specifications, we were able to calculate pressure and flow requirements of the system and choose individual components (pulley diameters, piston diameters, gear pump, engine, accumulator, servo valves, radiators) to meet those specifications. These components were then modeled in SolidWorks, along with the robot structure. New mechanical properties of the robot were extracted from SolidWorks to update the simulation model. This process was iterated several times until prototype design components were selected. 2. SIMULATIONS To determine the power requirements for the monopod, we performed physically realistic dynamic simulations of the robot using the Yobotics Simulation Construction Set software. For our simulations, we assumed zero energy recapture through the use of springy legs. This is an extremely conservative assumption as springy legs provide a very large energy return in running animals and almost all running robots built to date. We plan to eventually modify the design to incorporate springy legs. However, we make the assumption of zero energy return 1) to ensure that our power system exceeds the final requirements of the robot and 2) since it is difficult to model the springy leg and determine exactly what power savings it would provide. We developed a control algorithm for the simulated Monopod for running up to 3.5 m/s (Figure 1). The algorithm is similar to the 3-part hopping algorithm of Raibert 5, but contains a few modifications. Hopping height is controlled by controlling the vertical take-off velocity during the thrusting phase of stance, rather than through a step change in spring set point at the bottom of stance. This is possible, since the Monopods leg spring is virtual and arbitrary forces can be applied to the hip and knee. In contrast, the leg spring in most running robots is real and dictates much of the dynamic hopping response. Also, in addition to controlling forward velocity through foot placement, we added a speed control mechanism in which thrust is delayed if the actual velocity is less than the desired velocity. We ran simulations at various body masses to aid in the design of the robot. While our lightweight (94 pound) simulations ran up to 3.5 m/s, our heavier simulations have only run up to 2.5 m/s to date. Figure 1 shows a stop frame animation of a 94 pound simulation running at 3.5 m/s. Figure 1: Stop frame animation from a 43 kg (94 pound) Monopod simulation running at a speed of 3.5 m/s. Frames are captured at 0.05 second increments. Motion is from right to left. Proc. of SPIE Vol. 6201 620112-2V During running, the joint torque, speed, and power vary during a complete cycle. The maximum values for torque, velocity, power, and range of motions are shown in Table 1 for a typical simulation run. These joint power numbers were used to select components for the hydraulic system. Table 1: Summary of Joint Power requirements from a typical simulation running at maximum speed. Max Hip Torque 360 Nm 266 ft-lb Max Knee Torque 360 Nm 263 ft-lb Max Hip Velocity 24 rad/sec 224 RPM Max Knee Velocity 28 rad/sec 264 RPM Max Hip Power 4450 W 5.96 HP Max Knee Power 4205 W 5.63 HP Max Total Power 6025 W 8.07 HP Average Power 1550 W 2.08 HP Max Hip Rotation 1.70 rad 97.3 deg Max Knee Rotation 1.12 rad 63.7 deg 3. HYDRAULIC SYSTEM DESIGN Before designing the hydraulic system, we made a few assumptions regarding the overall Monopod design architecture: 1) The actuators would be mounted rigidly in the body of the robot and would be connected to the joints using a cable and pulley system. By placing the actuators in the body of the robot (as opposed to mounting them directly on the leg of the robot) we can minimize the leg mass, allowing for very fast movements. 2) The actuators would be linear, as opposed to rotary. Linear hydraulic pistons are more readily available, less expensive and are lighter than rotary hydraulic motors. Furthermore, it is difficult to implement Series Elastic Actuation using rotary actuators. This is due to the poor performance specifications of torsional springs as compared to compression springs, and due to the difficulty of instrumenting a torsional spring. Figure 2: Hydraulic system layout for the Monopedal robot. Figure 2 shows the hydraulic circuit designed for the Monopod. High pressure supply lines are shown in red and low pressure return lines are shown in blue. A constant displacement pump, driven by an engine, draws low pressure fluid out of the reservoir pressurizing and distributing the flow downstream to the manifold block. Once inside the manifold block, the flow normally passes through a check valve where it pressurizes an accumulator. Alternately, a computer Proc. of SPIE Vol. 6201 620112-3 controlled solenoid valve can shunt flow back to the reservoir through an oil cooler. This alternate path is taken when the accumulator has reached the maximum desired operating pressure as measured by a pressure sensor. High pressure fluid is stored in the accumulator until there is a demand from one of two servo valves. Alternately, if the pressure becomes too high in the accumulator, a pressure relief valve will divert flow back to the reservoir. The servo valves control the pressure and flow rates to each piston. As the pistons are cycled, return flow is sent back to the reservoir through the oil cooler, thus completing the cycle. 3.1. Hydraulic Component Selection The hydraulic system layout is quite standard. The difficulty lies in appropriately sizing components to meet the power requirements of the Monopod without over specifying the design, which would produce excess weight. Figure 3 is a schematic representation of the component selection process. Figure 3: Diagram of simulation-based iterative design process. 3.2. Pulley and Piston Diameters From simulations we extracted estimates of joint torques, speeds and ranges of motions for the Monopod. Power is transmitted to the joints through steel cables running over pulleys and these steel cables are actuated by hydraulic pistons. In selecting the piston and pulley diameters, we assumed an operating pressure of 3000 PSI, which is a widely accepted standard for off the shelf hydraulic components. At pressure ratings significantly higher than 3000 PSI, components become very heavy as well as exceedingly expensive. When considering pulley diameter, one must also consider cable life. Very small pulleys produce significant bending stresses on steel cable and thus degraded cable life. According to our cable manufacturer, the pulley diameter should be about 25 times the diameter of the cable being wrapped around it. Preliminarily, we chose a .188 inches cable diameter because its breaking strength (2000lbs) appeared to be in the range we required. Using the 25X factor from the manufacturer, we arrived at a pulley diameter of 4.68 inches. For round numbers, we decided to use a 4.75 inches pulley diameter. Using this pulley diameter and 3000 PSI design pressure we calculated the required piston diameter to produce 266ft-lbs of torque to be 0.770 inches. In order to use an off the shelf item, we selected a piston diameter of 0.75 inches. Note that the actuator force (thus cable force) for the 0.75 inch diameter piston is 1324lbs, less than the rated strength of the cable of 2000lbs. With cylinder diameters of 0.75 inches and pulley diameters of 4.75 inches, the simulation produced the maximum pressures and flow rates at the actuators as shown in Table 2. Proc. of SPIE Vol. 6201 620112-4Hip Actuator Flow-Load Characteristics. Supply = 3200P51Pressure (PSI)Knee Actuator Flow-Load Characteristics. Supply = 3200P5102000Pressure (PSI)2500 Table 2: Maximum pressure and flow rates from a typical simulation using inch piston diameter and 4.75” pulley diameter. Max Hip Actuator Pressure 20.68 MPa 3000 PSI Max Knee Actuator Pressure 20.68 MPa 3000 PSI Max Hip Actuator Flow Rate 4.02e-4 m3/s 6.38 GPM (24.5 in3/s) Max Knee Actuator Flow Rate 3.895e-4 m3/s 6.17 GPM (23.8 in3/s) Max Total Actuator Flow Rate 6.385e-4 m3/s 10.12 GPM (39.0 in3/s) Average Flow Rate 1.98e-4 m3/s 3.14 GPM (12.1 in3/s) With the cylinder and pulley diameters selected, we used the simulation model to generate the pressure and flow requirements for the Monopod over and extended period of time. From this pressure and flow data we extracted the average flow, peak flow, and pressure drop. This information was then used to select the major system components including servo valves, radiator, accumulator, and gear pump. 3.3. Servo Valve Selection Figure 4 shows the flow versus pressure history of the hip and the knee actuators during a typical simulation run, along with the flow-load characteristics of the Moog Series 32 Servo valve, with a 3200 PSI Supply Pressure. We see that if the pressure can be maintained at 3200 PSI, then the valve will be able to produce the required flow. Figure 4: Hip and Knee actuator flow and load characteristics recorded during a typical simulation, compared to the fully open response of the servo valves. Both simulation curves are strictly under the servo valve curves, indicating that the estimated flows and pressures are feasible. 3.4. Accumulator An accumulator typically uses air to act as a spring, maintaining pressure in the system. In sizing an accumulator, one needs to select the pre-charge pressure and the accumulator volume. Since the Monopod uses short bursts of energy, we assume adiabatic (no heat exchange) compression and expansion. The accumulator is pre-charged with nitrogen at pressure P0 and has volume V0. The minimum operating pressure is P1 when the air volume is at V1. The maximum operating pressure is P2 when the air volume is at V2. With adiabatic expansion, we have 4 . 12214 . 114 . 100VPVPVP= We can solve for V1 and V2 in terms of V0: Proc. of SPIE Vol. 6201 620112-5 04 . 1/1101VPPV=, 04 . 1/1202VPPV= Subtracting and solving for V0, we get 4 . 1/1204 . 1/110210=PPPPVVV Parker-Hannifin recommends that the pre-charge pressure be 90 percent the minimum pressure. However, to ensure that the system pressure never falls below pre-charge, we set it a little below that. If we set the minimum pressure to 3000 PSI, the maximum to 3400 PSI, and the pre-charge pressure to 2500 PSI, then we get ()2103 .13VVV= To sustain the maximum combined flow rate of 10.12 GPM over the contact period of 0.2 seconds, we need an accumulator volume of 0.854 gallons (1.7 Liters) with these values. To be conservative, we chose a 2.0 Liter accumulator, which should be able to sustain 0.2 seconds of max flow at over 3000 PSI if we charge it to at least 3400 PSI. This choice also provides 2.9 seconds of operation at our average flow rate of 3.14 GPM. 3.5. Pump The average flow rate of the system is calculated by integrating the absolute values of the flows over the hip and knee, and dividing by time. Our pump needs to supply the average flow rate of 3.14 GPM at the maximum pressure of 3400 PSI. To be conservative and account for losses, we selected a constant displacement pump rated at 3.5 GPM at 3500 PSI. 3.6. Internal Combustion Engine The chosen pump needs a continuous input power of 7.2kW (9.65 HP) to conservatively drive 3.5GPM, 3500PSI. Because of its high power density, we chose a two cycle engine over a four cycle engine. In an effort to further reduce weight, we chose a 16 horse power, 150cc hobby aircraft engine designed specifically for “giant scale” hobby aircraft. The engine was oversized in an effort to avoid a condition of maximum load 100% of the time. Because of its use in model aircraft, the engine we chose was air cooled. As one would expect, a tremendous amount of heat is generated by the high RPM two stroke engine. This heat must be removed to prevent seizing of the pistons. Since the Monopod was not expected to achieve the speeds of hobby aircraft (upwards of 120mph) we knew air cooling would be a challenge. Several tests were performed to determine if air cooling would be possible using on board fans or blowers. We determined that it would be very difficult to achieve air cooling under our load conditions and therefore decided to liquid cool the engine. In order to liquid cool the engine, the cylinder heads were modified to accept liquid tight jackets. Next, we devised a test to measure the amount of heat generated by the combustion engine. This information would be required to properly size a radiator to remove the heat from the coolant. During the tests, the engine was cooled by a reservoir containing four liters of water, which was circulated through water jackets encapsulating the cylinder heads. The temperature of the reservoir was measured and recorded once every 60 seconds. The results of two tests (one under light load and one under heavy load) can be seen in Figure 5 below. Proc. of SPIE Vol. 6201 620112-6 IC Engine Heat Generation with Circulating Reservior8090100110120130140150160170180190200210220024681012141618202224262830Time (minutes)Temperature (deg F) 0 psi, 3gpm2500 psi, 3gpm Figure 5: Heat generation of two cycle, 16 horsepower, 150cc hobby aircraft engine. Engine cooling was achieved by circulating four liters of water, in a closed loop, through water jackets encasing the cylinder heads. Tests were conducted under hydraulic loads of 0 PSI at 3 GPM and 2500 PSI at 3 GPM (4.4 horsepower). Using the Specific Heat of water, the mass of the water, change in temperature and time, we can calculate the power generated to heat water according to Equation 1, where the specific heat of water is 4.19 Joules/gramC. From this data and Equation 1, we found that the approximately 1021 Watts of heat is generated at 0 PSI, 3 GPM while 2322 Watts of heat is generated at 2500 PSI, 3 GPM. ()()()()ondstCTgramsMassCgramsJoulesatSpecificHeWattsPowersec=oo (Equation 1) It should be noted that tremendous amounts of heat can be removed from this system by vaporizing the water. Once the temperature reaches the boiling point, the formula changes to that shown in Equation 2, where the heat of vaporization of water is 2260 J/gram. Thus, heating water from room temperature to boiling (80C temp change) requires approximately 335 Joules per gram, whereas evaporating the water requires 2260 Joules per gram, or about 6.7 times more energy. Naturally this leads one to believe that evaporative cooling might be a good approach. However, in evaporative cooling, you are limited by the amount of water you carry on board. For this reason, we choose a more conventional approach: using a radiator to prevent the water from boiling. ()()()ondstgramsMassgramsJoulesonVaporizatiofHeatWattsPowersec= (Equation 2) From the two test conducted above, it is clear that we can cool the engine using a circulated water cooling method if we are able to remove approximately 2500 Watts of energy from the coolant. If the outside temperature is 32C (90 F) and we assume that the operating temperature of the water cooler is 225F (107C). (250F is possible with a 50% water 50% Ethylene Glycol mixture), for a difference of 75C, then we need 35 W/C cooling rate for the water. A radiator meeting these specifications was chosen, along with a circulating pump to move water through the closed loop. The temperature vs. time history of two load conditions with water cooling through the chosen radiator can be seen in Figure 6. Proc. of SPIE Vol. 6201 620112-7 IC Engine Heat Generation with Radiant Heat Exchanger8090100110120130140150160170180190200210220024681012141618202224262830Time (minutes)Temperature (deg F)0 psi, 3 gpm3000 psi, 3 gpm Figure 6: Heat generation of two cycle, 16 horsepower, 150cc hobby aircraft engine. Engine cooling is achieved by circulating a 1:1 mix of Ethylene Glycol and water in a closed loop with an air cooled radiator. Tests were conducted under hydraulic loads of 0 PSI at 3 GPM and 3000 PSI at 3 GPM (5.3 horsepower). 3.7. Hydraulic Heat Generation and Removal Primarily due to the large pressure drops over the servo valves during high speed, low force motions, there will be large amounts of power dissipated into the hydraulic fluid. Simulation results show approximately 2600 Watts of average heat generation while running at speeds between 1.5m/s and 3.5 m/s. We need to remove this heat from the system to prevent overheating. If the outside temperature is 32 C (90 F) and the oil temperature is 79.4 C (175 F), or a difference of 47.4C, then we need 52.7 W/C cooling rate for the oil. A radiator meeting these specifications was chosen. 3.8. Reservoir Reservoirs in hydraulic systems are important for allowing air bubbles to come out of the fluid and for allowing particles to settle. Various hydraulics applications engineers that we spoke to recommended a minimum reservoir size of one minute of fluid flow. However, for the Monopod that would require an approximately 3.5 gallon reservoir at a weight of 28 pounds. Therefore, we performed some tests using an off-board hydraulic system and ran hydraulic fluid through a pressure relief valve and radiator at 3500 PSI, 3.5 GPM with approximately 1.5 gallons of fluid in the reservoir. After 15 minutes, there were no noticeable bubbles and we determined that 20 seconds of fluid flow may be acceptable for our application. 3.9. Series Elastic Actuators Series Elastic Actuators 1-3 provide many benefits in force control of robots in unconstrained environments. These benefits include high force fidelity, low impedance, low friction, and good force control bandwidth. Series Elastic Actuators employ a novel mechanical design architecture which goes against the common machine design principal of “stiffer is better”. A compliant element is placed between the gear train and driven load to intentionally reduce the stiffness of the actuator. A position sensor measures the deflection, and the force output is accurately calculated using Hookes Law (F=Kx). A control loop then servos the actuator to the desired output force. The resulting actuator has inherent shock tolerance, high force fidelity and extremely low impedance. These characteristics are desirable in many applications including legged robots, exoskeletons for human performance amplification, robotic arms, haptic interfaces, and adaptive suspensions. The Monopod is the first legged robot that uses hydraulic Series Elastic Actuators. A CAD model of the actuator design is shown in Figure 7. Four pre-compressed die compression springs lie between the hydraulic piston and the output. A linear encoder measures the spring deflection, which is used in a PI force-control loop implemented in software and Proc. of SPIE Vol. 6201 620112-862OMFUTER SYSTEMCCUMULATORSpI-HYDEA U LbF ILTEEANIFOLD ELOCKNEE ACTUATOE updated at 1000 Hz. This actuator produces over 1300 pounds of force, with a force-control bandwidth of approximately 40 Hz. Figure 7: CAD model of hydraulic Series Elastic Actuator used in the Monopod. 4. MECHANICAL DESIGN The body of the robot consists of two 1/8th inch thick carbon fiber plates separated by aluminum cross members for rigidity. Individual components specified above are mounted between the carbon fiber plates. The center of mass of the robot is approximately 12 inches directly above the hip joint. The upper and lower legs consist of four 1” diameter carbon fiber tubes which are permanently mounted to machined aluminum joints using high strength epoxy. The center of mass of each leg falls just above the mind point of the link. A SolidWorks model of the final mechanical design, including overall dimensions and primary system components is shown in Figure 8. Figure 9 shows photographs of the completed Engine-Pump Assembly as well as the complete Monopod Robot. Figure 8: SolidWorks design drawings showing overall size of the Monopod and layout of major components. Units are in inches. Proc. of SPIE Vol. 6201 620112-9 Figure 9: Photographs of completed engine and pump assembly (left) and Monopod with carbon body plate removed (right). The engine and pump assembly has a total dry weight of 22lbs. and is capable of hydraulic pressure up to 4000 PSI at 4.5 GPM which is equivalent to 10.5 horsepower. Pressure and flow rate are limited by gear pump specifications. The total dry weight of the Monopod is 115 pounds. With hydraulic fluid, engine cooling fluid, and gasoline, the full weight is approximately 125 pounds. 5. PRELIMINARY RUNNING RESULTS The Monopod currently runs at approximately 1.2 m/s with the weight of all the power generating components, but powered from an off-board pump. Video images are shown in Figure 10, while data is shown in Figure 11. On a test stand, the eventual on-board power system generates enough pressure and flow to meet the requirements of these runs and we are currently integrating the power system into the real robot. When operated from an off-board system without carrying the weight of the power generating components, the robot currently runs at approximately 2.25 m/s. The control algorithm used for both weights was identical, indicating that with further algorithm development we should be able to achieve faster and more efficient running. Figure 10: Monopod running with full component weight of approximately 125 pounds, but powered from off-board hydraulic source. Images are spaced at 0.1 seconds. Robot runs from left to right. Proc. of SPIE Vol. 6201 620112-10 353637383940353637383940353637383940353637383940- 53637383940- 3536373839403637383940353637383940353637383940 Figure 11: Data from the Monopod running with full component weight of approximately 125 pounds, but powered from an off-board hydraulic source. The leftmost graphs show robot velocity, body height, body pitch, and accumulator pressure. The middle graphs show hip position, velocity, torque, and mechanical power. The right graphs show knee position, velocity, torque, and mechanical power. 6. DISCUSSION: HYDRAULIC SYSTEMS AND EFFICIENCY We chose the hydraulic system layout shown in Figure 2 due to the high power densities we could achieve and the low complexity. However, with our application, using a single accumulator charged to a high pressure is extremely inefficient. Particularly, during high speed, low force motions, there is a high flow rate out of the accumulator and high pressure drop over the actuator servo valves, generating large amounts of heat. In fact, given the same amount of actuator stroke motion, a low force motion, such as leg swing, requires the same energy as a high force motion, such as stance. Since running requires alternating periods of high force and low force motions, this hydraulic system layout is ill suited to running robots if efficiency, and hence time between refueling is important. Despite these inefficiencies, many robots and exoskeletons 5-7 use similar hydraulic layouts where a single accumulator is charged to a high pressure. The main reasons are low weight, low complexity, and high bandwidth. However, time between refueling of these systems may be too frequent for practical use. Song, Waldron and colleagues 8 recognized the low efficiency of single pressure valve-controlled systems during the design of the Adaptive Suspension Vehicle. To avoid these inefficiencies, they instead opted for a hydrostatic system in which each actuator has a variable displacement pump. All of the pumps are driven by a single engine and their displacements are controlled by swashplate control actuators. Despite requiring motion of significant swashplate masses, they reported position control bandwidths up to 20Hz. They also investigated several other alternatives, including drawing flow from multiple pressure sources, depending on the demands of each actuators. They rejected that possibility due to the required addition of extra hydraulic lines and manifold blocks, and the extra servo valves required. Except for the cost of the extra servo valves (approximately $4000 each), we think that a multi-pressure system may be an attractive option. A single engine could drive either multiple pumps or a variable displacement pump which pressurizes each of the accumulators depending on their need. Each actuator could pull from any of the accumulators through a network of switches. If there were M pressures, M-1 switches would be required per actuator (the lowest pressure source could always be connected). For N actuators, (M-1) * N switches plus N servo valves would be require