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生物启发的运动策略:在机器人和机构实验室开发的新型地面移动机器人生物启发的运动策略：在机器人和机构实验室开发的新型地面移动机器人摘要-本文介绍了一些地面移动机器人，它们的发展是基于弗吉尼亚理工大学RoMeLa（机器人技术和机械实验室）使用生物启发的新型运动策略。我们通过学习自然模型，然后模仿或获取来自这些设计和进程中的灵感，为移动机器人的移动，应用和实施了新的方式。不同于大多数地面移动机器人使用的常规手段的运动，如车轮或轨道，这些机器人展示独特的移动性特点，使在某些环境下运动困难的常规地面机器人变得适应。这些新型的地面机器人，包括：整个皮肤运动机器人，它从似变形虫的运动机械受到启发；三条腿的步行机器人STriDER（自激三足动态实验型机器人），利用驱动的被动式运动概念；六足机器人MARS（多附加的机器人系统）使用干粘合剂“壁虎脚”走在零重力的环境中；人形机器人DARwIn（动态拟人智能机器人）使用动态两足步态；移动性高的机器人IMPASS（拥有积极会话系统的智能移动平台）使用了一种新型车轮和腿混合运动的策略。对于上述每个机器人和所运用的新型运动策略，我们随后将对它们的性能以及面临的挑战进行讨论。关键词-生物的启发，运动，移动机器人。.导言9 / 11世界贸易中心的惨剧后，在归零地（911恐怖袭击中倒塌的世界贸易中心遗址），国防部联合机器人计划秘书办公室从机器人辅助搜索和努力救援中得到教训，并在为此准备的一份报告中指出，机器人的移动性是指作为目前机器人技术的一个主要限制性内容就是完成搜索和救援任务。该报告进一步指出，所有雇用机器人在归零地网站使用轨道驱动器一般都优于车轮在不平坦的地面，不过，其他更有效的运动策略必须作进一步调查。不同与空中或海上运输的车辆在他们的旅行区域内几乎可以达到任何一个目的地，今天使用的大部分地面车辆，在穿越大障碍和攀登陡坡时有困难，这是由于其有限的移动性，尤其是在非结构化环境下。 随着机器人智能技术的进步，和移动机器人在新的应用领域增加，机器人替换基础运动机械的需要，这可以使它们在被调遣到复杂的非结构化地形中时变得至关重要。目前地面车辆的运动的方法是基于车轮，铁轨或两条腿，每一个方法有其自身的长处和短处。为了使移动机器人适应一个地区的复杂地形，一种新的运动方法是必要的。例如，为了能够找到被困在倒塌大楼中的人，将需要身处狭窄拐角的机器人能够在瓦砾下或之间移动。目前的运动方法，可以做到这项工作的一部分，但在实现所有这些功能时，他们却只有有限的成功。 我们通过学习自然模型，然后模仿或获取来自这些设计和进程中的灵感，为移动机器人的移动，应用和实施了新的方式。在本文中，我们呈现了5个地面移动机器人，它们的发展是基于弗吉尼亚理工大学的RoMeLa（机器人技术和机械实验室）使用的生物启发的新型运动策略。不同于大多数地面移动机器人使用的常规手段的运动，如车轮或轨道，这些机器人展示独特的移动性特点，使在某些环境下运动困难的常规地面机器人变得适应。2.生物启发的新型运动的策略2.1从似变形虫的运动机械受到启发的运动WSL（整个皮肤运动）是指一个生物，有一细长圆环形状的身体用来作为表面为牵引，皮肤是用来驱动通过循环的收缩与扩张。图1.一个单轴的变形虫的动力机构这种启发的新型运动策略，来自某些单一方式的细胞生物体， 例如该变形虫 （巨变形虫）的运动。这些生物体的运动是由细胞质环流过程（图1 ）所造成的，液态形式的细胞质流在内外质管中流动，并转化为凝胶状的外质前端的表层皮肤，最后在细胞质的外皮肤后部回复到液态的形式。这连续细胞内外质的转化是该变形虫向前运动的有效动力。如果不可能的话，直接用机器人模仿这细胞质环流的过程是很困难的事。因此，代替使用细胞质液体凝胶转型的过程，WSL使用一个灵活的长圆环形状的皮肤膜。这种皮肤可以拉长，然后在一个单一连续的运动中随意内外旋转，在变形虫外质管中有效地生成整体的细胞质环流运动（图2 ）。图3和图4显示了一个简单的实验，它使用一个灌满水的长的有弹性的有机硅皮肤环形管，以演示运动机构的可行性。图2. 同心固体管整个皮肤运动模型 通过驱动环的收缩（1a，2a，3a ）及扩大（1b，2b，3b ）产生的反转运动。（ a ）在0.0秒 （ b ）在0.30秒 （ c ）在0.46秒图3.预拉力弹性皮肤模型运动的一系列照片图4. 拉紧的绳索驱动模型运动的一系列照片机器人使用整个皮肤运动可以在与机器人相接触的环境中的任何表面上移动，不论是地面，墙壁或两边的障碍物，或天花板，因为整个皮肤是用于运动。与一弹力膜或网状的链接作为其外部皮肤，机器人可以很容易挤压在障碍之间或在倒塌的天花板下，使用所有的接触面为牵引向前迈进，或甚至挤压本身通过直径小于其名义宽度的孔。2.2利用被动式运动驱动概念的三足运动图5. STriDER:自激三足动态实验型机器人STriDER（自激三足动态实验型机器人）是一种新型的三足步行机器（图五） ，利用被动动力驱动的运动概念，动态步行与高能源效率和最小控制使用其独特的三足步态（图6 ）。不像其他的被动动态行走的机器，这种独特的三足运动机器人，是以三脚架位置达到固有的稳定，它可以改变方向，和比较容易操作，使得它可实际地应用于现实生活中。图6.单步三足步态图6显示单步三足步态的概念。从开始的位置（图6 （ a ） ，机器人转变其重心，通过调整它的两个骨盆链接（图6 （ b ） ，机器人的身体能在跌倒的方向垂直于落地三角（图6（ c ） ，绕轴线旋转定义为由两个支持的双腿。正像在机器人跌倒时，中间的腿（摆动腿） 自然摆动到两落地腿之间（图6 （ d ）防止跌倒（图6 （ e ）。由于所有三腿接触地面，机器人重置姿态通过激励其连接，储存势能，为下次的步态（图6 （ f ）作准备 。三足步态的关键是自然摆动运动的摆动腿，和机构关于均衡骨盆关节连接的两个落地腿。适当的机械设计参数（质量和性能方面的联系），用其动态结构拓展驱动被动动力运动概念，以最低限度的控制和能源消耗进行反复运动。步态改变方向是在一个相当有趣的方式下执行：通过改变选择摆动腿的序列，三足步态可以在每一步60 区间的方向移动机器人（图7 ）图7. 转变方向的步态战略简单的三脚架配置和STriDER的三足步态有很多优势超过其它腿式机器人：它有一个简单的运动结构（对两足动物 ，四足动物 ，或六足动物）防止其双腿之间，一条腿和身体的冲突，相当稳定（如照相机三脚架）；简单的控制（对两足动物）正因该运动是一个在预定方向的简单下降及控制其下降；它又是高效能源，在动力学上用其内置开发驱动被动动力运动概念;它重量轻，使它能发射到难以进入的领域，例如，它使部署和定位传感器在高的位置进行监视变得非常理想。图8.一个单一步骤的三足步态的实验装备2.3步行在零重力环境下的干胶粘剂壁虎脚灵感来自美国航天局喷气推进实验室的LEMUR机器人（图9 ） ，在弗吉尼亚理工大学的机器人技术和机械实验室研制一种六足机器人的研究平台，多肢运动和操纵。如图10所示，MARS（多附庸的机器人系统）有6个4自由度的肢体轴对称布置，机器人本体与动球节点在肩膀上有一个大的工作空间。可互换的末端执行器/脚允许其用于研究各种研究方面例如走在非结构化环境，攀登，和灵巧的操控任务。图9. 美国航天局喷气推进实验室的LEMUR IIa 多附庸的机器人系统的六轴对称安排，四肢均连接到机构，由一个三自由度动球的联合提供了一个广泛的运动类似于肩髋关节。中途沿每个肢体是一种单自由度的联合它提供了一系列类似的运动类似于肘或膝关节。这种安排使每个肢体有广泛的工作空间。整个平台是大约16英寸，直径10英寸，身高与外表昆虫或蜘蛛一样。碳纤维复合体进行铝聚合物电池， PC104的单板电脑，以及可互换的传感器，包括立体视觉的接口相机。四肢由一个轻量级铝框架和碳纤维复合材料外骨骼皮肤建造。每一联合通过转口货品中最大芯直流电动机通过分布式可变方式控制驱动。在每个肢体端部，可互换末端执行器/脚允许它用于各种实验和应用。图10. MARS:多附庸的机器人系统与其他的机器人设计方法不同，它力求模仿生物学和工程两者统一，LEMUR的起源缺乏一些必要的生物分子;生物分子专门用于作为一个设计工具。机器人的目的是沿着表面结构移动，它的灵感来自于沿着底部和岩石之间移动的多肢灵巧的海洋生物。马上可举的例子便是章鱼和海星，其中他们的显著特点是轴对称，相对身体尺寸来说四肢较长。轴对称机器人是全方位的，面对一个特定方向的移动或操纵，节省其昂贵运动。此外，长的四肢又能产生一个广阔的工作空间。其中MARS的一个重要应用领域是在零重力情况下自主地在太空中检查维修车辆和结构。使用有肢的机器人是最有前途的技术，例如共聚物技术; 使用机器腿在空间车辆或结构的外表面爬行检查和维修操作。不过，使用有肢的机器人在零重力的环境中创造了一整套新的问题和要求。在零重力环境中运动需要使用确保其脚步行于表面的方法，这可能是通过抓住在表面上利用磁铁，吸杯的某些功能来完成。它的灵感来自壁虎在垂直墙壁上爬行和在天花板上下步行的能力，未来版本的MARS将使用干胶粘剂脚在零重力的环境下行走于表面，因为这是最有前途的技术，使机器人行走表面的运动和操作过程变的稳定。2.4一种新型车轮腿混合运动策略 智能平台的流动性与积极语言系统是一种非结构化环境无人系统，新型高流动性运动平台（图11 ） 。利用单独驱动无框车轮辐条，它可以按照轮廓不均匀的表面，如路轨，并越过大的障碍，如有腿车辆，保留简单的车轮（图12 ）。因为它缺乏复杂的腿和拥有一个大型有效的（轮）直径，这个高度自适应性系统可以轻易地移动到极端的地形，同时保持一定的运行速度，从而在搜索和救援任务，科学探索，和进行反恐的应用中有很大的潜力。图11.此渲染图象是IMPASS的版本，使用了两个驱动车轮，并进行模拟图12.IMPASS关于移动和适应地形的一些例子我们分析了运动学和模拟机器人用两个驱动车轮在平坦地形上的运动，它们利用每个车轮结构上的一个，两个，三个点相接触（图13 ）。这表明一个点接触模式有两个自由度，运动的输出可以任意选定。这种模式将允许机器人移动，同时为质量中心保持恒定的高度，我们已经通过模拟进行了证明。至于这个模式的结果表明，通过改变方位角发生离散，采取措施改变不同的长度和左右车轮。两个点的接触方式显示有一个自由度，选择一个步长，将径向平面的中心轴轨道视为确定的车轮角度函数。这种运动模式只用两个轮子便能静态地稳定行走，还可用于承受有效重载荷。 三点接触结构显示为零的自由度，但是在固定的任务中，它将有额外的稳定性，让机器人拥有更广泛的立足之地。图13.一个单一的驱动车轮及其自由度的不同模式的运动系统图关于瞬态转变的概念随后得到开发，在逐渐转变过程中有三个接触点，迫使基准线与机器人的轴线斜交（图14 ）。深入了解此结构，通过在此机构中分析机器人获得作为一个SPPS的空间机构。从空间分析获得的见解能形容一个更一般的运动学模型可以用来分析共面基准轴线和斜交基准线的两种情况，以及允许分析影响驾驶两个驱动轮辐车轮差异。图14.轮辐车轮驱动的转向策略 要验证我们的模型分析和在下一阶段项目的概念评估，我们已设计并制作了第一个轮辐车轮驱动的样机（图15 ）将用于IMPASS。图15.轮辐车轮驱动的样机2.5 两足运动的仿人机器人DARwIn（动态拟人机器人与情报）是一种仿人机器人能两足行走和表演，像人类一样，它已发展成一个为研究机器人运动的研究平台，同时也成为弗吉尼亚理工大学的首次进入2007年机器人世界杯竞争的基础平台（图16，17）。该高600毫米，重4公斤的机器人有21个自由度（DOF），每一关节通过分布式控制与可控顺序的无芯直流电动机进行驱动。利用计算机视觉系统对头部，在躯干上的惯性测量组合，和在脚上的多力传感器，DARwIn可以在超越障碍时完成人类一样的步态，能够越过不平坦的复杂地形，完成复杂行为，如踢足球。图16.运动系统图和DARwIn的CAD模型对这个项目的持续研究的目标是发展机器人平台，并研究与参加2007年机器人世界杯比赛相关的问题，（产生和实现一个动态步态，使用零力矩点控制，为了智能运动规划和避障，基于视觉的控制，在不平坦地形下散步，踢足球的复杂行为等发展算法和策略）。图17. DARwIn：动态拟人智能机器人DARwIn有一个轻巧的铝骨骼结构与快速成型塑胶皮肤表面。它的胳膊和腿连接到机构由三自由度动球节点提供了广泛的运动，与肩和髋关节类似。每一关节是Maxon的转口货品中最大芯直流电动机通过分布式控制与可变原则驱动。该机器人有两个2100 mAh/7.4v铝聚合物电池作为其电源， PC104的单板电脑处理，三率陀螺仪，跟踪机体的方向和各种传感器包括一个视觉接口相机和脚下八个力传感器。目前新版本的DARwIn正在发展，在弗吉尼亚理工大学，2007年机器人世界杯正在设计进行中，来自机械工程系和建筑设计学院的研究生和高级本科生相互协作。3.结论在本文中，我们呈现了5个独特的地面移动机器人，在RoMeLa的发展下，在弗吉尼亚理工大学使用了新型运动策略有高度的移动性。作为证明，为发展这些机器人使用生物灵感和仿生学是关键。通过学习自然模型，然后模仿或获取来自这些设计和进程中的灵感，为移动机器人在各种环境中具有独特移动性的移动，我们已经成功地应用和实施了新方式。 鸣谢作者想感谢美国国家科学基金会（No.IIS-0535012）、海军研究办公室（No.N00014-05-1-0828）、美国宇航局喷气推进实验室（美国航天局学院奖学金项目）以及弗吉尼亚理工大学办公室和副总统办公室负责人的研究（ASPIRES），感谢他们对军队的研究和开发， 感谢工程司令部（RDECOM）为继续支持这项工作，通过弗吉尼亚理工大学联合无人操作系统所做的测试、实验及研究（JOUSTER），并感谢作者的研究生道格拉内、马克英格拉姆、马克肖瓦尔特、杰里米西斯顿和卡尔米艾克就这些项目所做的工作。Biologically Inspired Locomotion Strategies: Novel Ground Mobile Robots at RoMeLaAbstract-This paper presents some of the ground mobile robots under development at the Robotics and Mechanisms Laboratory (RoMeLa) at Virginia Tech that use biologically inspired novel locomotion strategies. By studying natures models and then imitating or taking inspiration from these designs and processes, we apply and implement new ways for mobile robots to move. Unlike most ground mobile robots that use conventional means of locomotion such as wheels or tracks, these robots display unique mobility characteristics that make them suitable for certain environments where conventional ground robots have difficulty moving. These novel ground robots include; the whole skin locomotion robot inspired by amoeboid motility mechanisms, the three-legged walking machine STriDER (Self-excited Tripedal Dynamic Experimental Robot) that utilizes the concept of actuated passive-dynamic locomotion, the hexapod robot MARS (Multi Appendage Robotic System) that uses dry-adhesive “gecko feet” for walking in zero-gravity environments, the humanoid robot DARwIn (Dynamic Anthropomorphic Robot with Intelligence) that uses dynamic bipedal gaits, and the high mobility robot IMPASS (Intelligent Mobility Platform with Active Spoke System) that uses a novel wheel-leg hybrid locomotion strategy. Each robot and the novel locomotion strategies it uses are described, followed by a discussion of their capabilities and challenges. Keywords - Bio-inspiration, locomotion, mobile robots. 1. Introduction In a report 1 prepared for the Office of the Secretary of Defense Joint Robotics Program on the lessons learned from the robot assisted search and rescue efforts at Ground Zero following the 9/11 World Trade Center tragedy, robot mobility is noted as one of the major limitations of current robotic technology for such missions. The report further states that all the robots employed at the Ground Zero site used track drives which are generally superior to wheels on uneven ground; however, other alternative locomotion strategies which are more effective must be further investigated. Unlike aerial or marine vehicles which can reach almost any destination point in their travel domain, most ground vehicles used today have difficulty traversing overobstacles and climbing steep inclines due to their limited mobility, especially in unstructured environments. As the technology of robotics intelligence advances, and new application areas for mobile robots increase, the need for alternative fundamental locomotion mechanisms for robots that can enable them to maneuver into complex unstructured terrain becomes critical. Current methods of ground vehicle locomotion are based on wheels, tracks or legs, and each of these methods has its own strengths and weaknesses 2, 3. In order to move a robot into an area of complex terrain a new method of locomotion is needed. For example, to be able to find people trapped in a collapsed building, a robot would need to be able to move over, under and between rubble, and maneuver itself into tight corners. Current methods of locomotion can do some part of this, but they have only had limited success in achieving all of these capabilities 4. By studying natures models and then imitating or taking inspiration from these designs and processes, we apply and implement new ways for mobile robots to move. In this paper we present five of the ground mobile robots under development at the Robotics and Mechanisms Laboratory (RoMeLa) at Virginia Tech that use biologically inspired novel locomotion strategies. Unlike most ground mobile robots that use conventional means of locomotion such as wheels or tracks, these robots display unique mobility characteristics that make them suitable for certain environments whereconventional ground robots have difficulty moving. 2. Biologically Inspired Novel Locomotion Strategies 2.1 Locomotion inspired by amoeboid motility mechanisms Whole Skin Locomotion (WSL) 5, 6 is a biologically which has a body of a shape of an elongated torus, is used as a surface for traction and that the skin is used for the actuation by cycling through contraction and expansion.Fig. 1. Motility mechanism of a monopodial amoebaThe inspiration for this novel locomotion strategy comes from the way certain single celled organisms, such as the Amoeba proteus (giant amoeba) move. The motion of these organisms is caused by the process of cytoplasmic streaming (Fig. 1) where the liquid form endoplasm that flows inside the ectoplasmic tube transforms into the gel-like ectoplasm outer skin at the front, and the ectoplasm outer skin at the end transforms back into the liquid form endoplasm at the rear. The net effect of this continuous ectoplasm-endoplasm transformation is the forward motion of the amoeba 7, 8.Directly imitating this cytoplasmic streaming process with a robot is very difficult to do if not possiblee. Thus, instead of using the process of liquid to gel transformation of cytoplasm, the WSL is implemented by a flexible membrane skin in the shape of a long torus. The skin of this elongated torus can then rotate in a fashion of turning itself inside out in a single continuous motion, effectively generating the overall motion of the cytoplasmic streaming ectoplasmic tube in amoebae (Fig. 2). Fig. 2. Everting motion generated by the contracting (1a, 2a, 3a) and expanding (1b, 2b, 3b) actuator rings for the concentric solid tube WSL model. Figures 3 and 4 show simple experiments using a long elastic silicone skin toroid filled with water to demonstrate the feasibility of the locomotion mechanism. (a) At 0.0 sec (b) At 0.30 sec (c) At 0.46 sec Fig. 3. Sequence of pictures of the locomotion of the pre tensioned elastic skin model Fig. 4. Sequence of pictures of the tension cord actuated model locomotion A robot that uses WSL can move as long as any surface of the robot is in contact with the environment, be it the ground, walls or obstacles on the side, or the ceiling, since the entire skin is used for locomotion. With an elastic membrane or a mesh of links acting as its outer skin, the robot can easily squeeze between obstacles or under a collapsed ceiling, and move forward using all of its contact surfaces for traction, or even squeeze itself through holes with diameters smaller than its nominal width as demonstrated in 5. 2.2 Tripedal locomotion utilizing the concept of actuated passive-dynamic locomotion Fig. 5. STriDER: Self-excited Tripedal Dynamic Experimental Robot STriDER (Self-excited Tripedal Dynamic Experimental Robot) is a novel three-legged walking machine (Fig. 5) that exploits the concept of actuated passive dynamic locomotion 9 to 11, to dynamically walk with high energy efficiency and minimal control using its unique tripedal gait (Fig. 6). Unlike other passive dynamic walking machines, this unique tripedal locomotion robot is inherently stable with its tripod stance, can change directions, and is relatively easy to implement, making it practical to be used for real life applications.Fig. 6. Single step tripedal gait Fig. 6 shows the concept of the single step tripedal gait. From its starting position (Fig. 6 (a), as the robot shifts its center of gravity by aligning two of its pelvis links (Fig. 6 (b), the body of the robot can fall over in the direction perpendicular to the stance triangle (Fig. 6 (c), pivoting about the line defined by the two supporting legs. As the robot falls over, the leg in the middle (swing leg) naturally swings between the two stance legs (Fig. 6 (d)and catches the fall (Fig. 6 (e). As all three legs contact the ground, the robot resets its posture by actuating its joint, storing potential energy for its next gait (Fig. 6 (f). The key to this tripedal gait is the natural swinging motion of the swing leg, and the flipping of the body about the aligned pelvis joints connecting the two stance legs. With the appropriate mechanical design parameters (mass properties and dimension of the links), this motion is repeated with minimal control and power consumption exploiting the actuated passive dynamic locomotion concept utilizing its built in dynamics. Gaits for changing directions are implemented in a rather interesting way: by changing the sequence of choice of the swing leg, the tripedal gait can move the robot in 60interval directions for each step (Fig. 7)Fig. 7. Gait strategies for changing directions The simple tripod configuration and tripedal gait of STriDER has many advantages over other legged robots; it has a simple kinematic structure (vs. bipeds, quadrupeds, or hexapods) that prevents conflicts among its legs and between a leg and the body; it is inherently stable (like a camera tripod); it is simple to control (vs. bipeds) as the motion is a simple falling in a predetermined direction and catching its fall; it is energy efficient, exploiting the actuated passive dynamic locomotion concept utilizing its built in dynamics; it is lightweight enabling it to be launched to difficult to access areas; and it is tall making it ideal for deploying and positioning sensors at high position for surveillance, for example.Fig. 8. Experiment setup for a single step tripedal gait 2.3 Dry-adhesive gecko feet for walking in zero gravity environments Inspired by NASA JPLs LEMUR class robots 12, 13 (Fig. 9), RoMeLa at Virginia Tech is developing a hexapod robotic platform for research in multi-limbed ocomotion and manipulation. Shown in figure 10, the Multi Appendage Robotic System (MARS) has six 4-degree-of-freedom (DOF) limbs arranged xi-symmetrically about the robot body with kinematically spherical joints at the shoulder for a large workspace. Interchangeable end-effector/feet allow it to be used for studying various research areas such as walking in unstructured environments, climbing, and for dexterous manipulation tasks.Fig. 9. NASA JPLs LEMUR IIa MARSs six axi-symmetrically arranged limbs are each connected to the body by a 3 DOF kinematically spherical joint which provides a wide range of motion similar to a shoulder of hip joint. Midway along each limb is a single DOF joint which provides a range of motion similar to an elbow or knee joint. This arrangement allows each limb to have a wide workspace. The entire platform is approximately 16 inches in diameter standing 10 inches tall with the appearance of an insect or spider. The carbon fiber composite body carries Li-Poly batteries, a PC104 single board computer, and interchangeable sensors including stereovision Firewire cameras. The limbs are constructed with a lightweight aluminum frame and carbon fiber composite exoskeleton skin for stiffness. Each joint is actuated by Maxons RE-max coreless DC motors via distributed control withvariable compliance. At the end of each limb, interchangeable end-effector/feet allow it to be used for various experiments and applications. Fig. 10. MARS: Multi Appendage Robotic System Unlike other robot design approaches that seek to mimic biology and engineering together, LEMURs origins lack any necessary biological elements 12; biological elements are used exclusively as a design tool. As the robot is intended to move along the surface of the structure, inspiration was taken from multi-limbed, dexterous sea creatures that tend to move along the bottom and among rocks. Immediately applicable examples are octopi and starfish which are notable for their axi-symmetry. The creatures limbs are long relative to body size. Being axi-symmetric, the robot is omni directional, saving operationally expensive movement to face a particular direction for mobility or manipulation. Also, the long limbs generate a generous workspace. One of the key application areas of MARS is autonomous in-space inspection and maintenance of space vehicles and structures in zero gravity. Using limbed robots is the most promising technology for such EVA tasks; to crawl outside on the outer surface of space vehicles or structures using legs for inspection and maintenance operations. However using limbed robots in zero gravity environments creates a whole new set of problems and requirements. Locomotion in zero gravity environments requires using methods of securing its feet to the walking surface. This may be accomplished by grabbing certain features on the surface, using magnets, suction cups. Inspired by the ability of geckos to climb vertical walls and walk upside down on the ceiling, future version of MARS will be using dry adhesive feet to walk on surfaces in zero gravity environments as this is the most promising technology for stabilizing the robot on its walking surface for locomotion and for manipulation tasks. 2.4 A novel wheel-leg hybrid locomotion strategy IMPASS (Intelligent Mobility Platform with Active Spoke System) is a novel high mobility locomotion platform for unmanned systems in unstructured environments 14 to 16 (Fig. 11). Utilizing rimless wheels with individually actuated spokes, it can followthe contour of uneven surfaces like tracks and step over large obstacles like legged vehicles while retaining the simplicity of wheels (Fig. 12). Since it lacks the complexity of legs and has a large effective (wheel) diameter, this highly adaptive system can move over extreme terrain with ease while maintaining respectable travel speeds, and thus has great potential for search-and-rescue missions, scientific exploration, and anti-terror response applications. Fig. 11. Rendered image of a version of IMPASS using two actuated spoke wheels and a mock up of the systemFig. 12. Some examples of the mobility and terrain adaptability of IMPASS We have analyzed the kinematics and simulated the motion of a robot using two actuated spoke wheels on flat terrain using a one-, two-, and three-point contact per wheel scheme (Fig. 13). It is shown that the one-point contact mode has two degrees of freedom and that the motion output can be arbitrarily selected. This mode would allow for moving while maintaining a constant height for the center of mass, which we have demonstrated by simulation. Turning for this mode is shown to occur discretely by changing the heading angle for every step by taking steps of different lengths with the right and left wheels. The two-point contact mode is shown to have one degree of freedom, and that by choosing a step length, the path of the center of the axle in the sagittal plane is determined as a function of the wheel angle. This mode of locomotion allows for statically stable walking with only two wheels, and could be used for carrying heavy payloads. The three-point contact scheme is shown to have zero degrees of freedom,but would allow for additional stability during stationary tasks by letting the robot assume a wide stance. Fig. 13. Kinematic diagram of a single actuated spoke wheel and its degrees of freedom for different modes The concept for transient turning was then developed by having three contact points at the step transition, forcing the pivot line to be skew with the axle of the robot (Fig. 14). Insight into this configuration was gained by analyzing the robot in this configuration as an SPPS spatial mechanism. The insight gained from the spatial analysis is used to describe a more general kinematic model that could be used to analyze both cases of the coplanar pivot line and the skew pivot line, as well as allow analysis of the effects of differentially driving the two actuated spoke wheels.Fig. 14. Turning strategy for the actuated spoke wheel To verify our analytical model and to evaluate the concept in the next phase of the project, we have designed and fabricated our first prototype of the actuated spoke wheel (Fig. 15) to be used for IMPASS. Fig. 15. Prototype of the actuated spoke wheel2.5 Bipedal locomotion for humanoid robots DARwIn (Dynamic Anthropomorphic Robot with Intelligence) is a humanoid robot capable of bipedal walking and performing human like motions, developed as a research platform for studying robot locomotion and also as the base platform for Virginia Techs first entry to the 2007 Robocup competition (Fig.s 16, 17). The 600 mm tall, 4 Kg robot has 21 degree-of-freedom (DOF) with each joint actuated by coreless DC motors via distributed control with controllable compliance. Using a computer vision system on the head, IMU in the torso, and multiple force sensors on the foot, DARwIn can implement human-like gaits while navigating obstacles and will be able to traverse uneven terrain while implementing complex behaviors such as playing soccer. Fig. 16. Kinematic diagram and the CAD model of DARwIn The goal of this on going research project is to develop the roboti
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