Quadruped robots provide better stability and speed in comparison to other legged robots However, its joint actuator or sensor failure severely affects locomotion. Strategies for ac-tuator and sensor fault accommodation in a compliant legged quadruped are presented here. A pair of orthogonally mounted moving appendages mechanism is proposed here to accommodate locked joint failure. These appendages as rack mounted inertias perform controlled motion during actuator failure. A strategy for sensor fault accommodation is also presented. A three-dimensional multi-body dynamics model of quadruped robot and its fault accommodation strategies are developed using bond graph modeling approach The control performance is validated both through simulations and experiments.

1. Introduction

Mobile robots mostly follow three kinds of designs. The first kind is supported on wheels which allow high-speed motion on flat terrains but it is difficult to operate such a robot on uneven surfaces and to carry out specific tasks like step climbing.The second kind is based on anthropomorphic legs which offer better locomotion on uneven terrain, obstacle avoidance, etc.at the cost of speed. The third kind is a hybrid design which combines wheels at the leg tips to give a compromise design.The Cassino hexapod [1] is a hybrid mobile robot where rolling is possible on a flat ground and walking on irregular terrains.

In case of multi-legged robots, three appropriately placed legs are required to maintain static stability. Since at least one of the legs needs to be lifted-off the terrain for locomotion, the minimum number of legs required is four. As the number of legs increases, the stability during locomotion increases and the robot can remain operational in the presence of failure of a few legs [1]. Also, the redundant legs can be deployed as hands for manipulation purposes. This has motivated development of varieties of hexapod robots [2] and robots with still higher number of legs. However, the locomotion speed and agility of hexapod robots is less than quadruped robots. In the case of typical tasks like obstacle avoidance, step climbing, etc.,more legs means more complex gait patterns. One can think of an imagined horse-sized six legged animal trying to clear an equestrian huddle to understand the problems associated with too many limbs. The motion of legs should not interfere with each other and hence with more number of legs, the step size reduces and the length of the robot increases (such as in ants, centipedes and millipedes). In that respect, four-legged robots offer a good compromise between locomotion stability versus locomotion agility and speed. However, unlike a hexapod which can tolerate failure of up to two legs (excluding

摘  要：与其他腿部机器人相比，四足机器人提供了更好的稳定性和速度。然而，其关节执行器或传感器故障严重影响了运动。交流导航仪和传感器的策略本文提出了柔顺腿四足动物的错误调节。提出了一种正交安装的移动附件机构，以解决锁紧关节失效问题。这些附件作为机架安装的惯性，在执行器失效时执行受控运动。也提出了一种传感器故障调节策略。四足机器人的三维多体动力学模型利用键合图建模方法，提出了故障调节策略。通过仿真和实验验证了该控制系统的性能。

1. 介绍

移动机器人大多遵循三种设计方案。第一种机器人是由轮子支撑的，它允许在平坦的地形上高速运动，但是在不均匀的表面上操作这样的机器人并且完成攀爬等具体任务是困难的。第二种是以人形腿为基础，以速度为代价，在地形起伏、避障等方面提供更好的运动能力。第三种是一种混合设计，结合车轮在腿尖，以提供一个折衷的设计。卡西诺六足机器人[1]是一种混合移动机器人，可以在平坦的地面上滚动并且在不规则的地形上行走。对于多腿机器人，需要三条合适的腿来保持静态稳定性.。因为至少有一条腿需要从地形上抬起运动时，所需的最小腿数是四条。随着腿数的增加，机器人在移动过程中的稳定性增加，机器人可以在几条腿[1]出现故障的情况下继续工作。此外，多余的腿也可以作为手部署，以便进行操作。这推动了六足类机器人[2]和腿部数量更多的机器人的发展。然而，六足机器人的运动速度和灵活性都低于四足机器人。对于典型的任务，如避障、爬台阶等，腿越多意味着它的模式越复杂。人们可以想象出一种想象中的马匹大小的六条腿动物，试图清理马术圈，以理解与太多四肢相关的问题。腿的运动不应该在彼此干涉，因此越来越多的腿，步长减少，机器人的长度增加（如蚂蚁、蜈蚣、千足虫）。在这方面，四条腿的机器人它在运动稳定性与运动灵活性和速度之间提供了很好的折衷。然而，与六足类动物不同的是，六足类动物最多可以承受两条腿的失效(不包括某些特殊情况)，四足动物在一条腿故障时不能很好地操作。本文正是针对四足动物腿部的这种故障，提出了以移动附属物的形式来克服这个障碍的部署冗余硬件的建议。