Typical gait analysis of a six-legged robot in the context of metamorphic mechanism theory

The equivalent mechanism of the system is often considered as one specific mechanism in most existing studies of multi-legged robots, however the equivalent mechanism is varying while the robot moves on the ground. Four typical tripod period gaits of a radial symmetrical six-legged robot are analyzed. Similar to the metamorphic mechanism, the locomotion of multi-legged robot is considered as a series of varying hybrid serial-parallel mechanisms by assuming the constraints of the feet on the ground with hinges. One gait cycle is divided into several periods, and in different walking period there is a specific equivalent mechanism corresponding to it, and the walking process of multi-legged robot is composed by these series of equivalent mechanisms. Walking performance can be got by analyzing these series of equivalent mechanisms. Kinematics model of the equivalent mechanism is established, workspaces of equivalent mechanisms are illustrated by simulation and a concept of static stability workspace is proposed to evaluate the static stability of these four gaits. A new method to calculate the stride length of multi-legged robots is presented by analyzing the relationship between the workspace of two adjacent equivalent parallel mechanisms in one gait cycle. The stride lengths of four gaits are given by simulations. Comparison of stride length and static stability among these four typical tripod gaits are given. It has been proved that mixed gait and insect-wave gait II have better static stability than mammal kick-off gait and insect-wave gait I. Insect-wave gait II displays its advantage on stride length while the height of robot body lower than 87 mm, mammal kick-off gait has superiority on stride length while the height of robot body higher than 115 mm, and insect-wave gait I shows its shortcoming in stride length. The proposed method based on metamorphic theory and combining the footholds and body height of robot provides a new method to comprehensive analyze the performance of multi-legged robot.     

Gait Analysis of a Radial Symmetrical Hexapod Robot Based on Parallel Mechanisms

Most gait studies of multi-legged robots in past neglected the dexterity of robot body and the relationship between stride length and body height.This paper investigates the performance of a radial symmetrical hexapod robot based on the dexterity of parallel mechanism.Assuming the constraints between the supporting feet and the ground with hinges,the supporting legs and the hexapod body are taken as a parallel mechanism,and each swing leg is regarded as a serial manipulator.The hexapod robot can be considered as a series of hybrid serial-parallel mechanisms while walking on the ground.Locomotion performance can be got by analyzing these equivalent mechanisms.The kinematics of the whole robotic system is established,and the influence of foothold position on the workspace of robot body is analyzed.A new method to calculate the stride length of multi-legged robots is proposed by analyzing the relationship between the workspaces of two adjacent equivalent parallel mechanisms in one gait cycle.Referring to service region and service sphere,weight service sphere and weight service region are put forward to evaluate the dexterity of robot body.The dexterity of single point in workspace and the dexterity distribution in vertical and horizontal projection plane are demonstrated.Simulation shows when the foothold offset goes up to 174 mm,the dexterity of robot body achieves its maximum value 0.164 4 in mixed gait.The proposed methods based on parallel mechanisms can be used to calculate the stride length and the dexterity of multi-legged robot,and provide new approach to determine the stride length,body height,footholds in gait planning of multi-legged robot.     

基于地面反力检测的四足马机器人适应步行法

为适应国内外对四足马机器人进行的广泛研究,根据四足马机器人的结构模型和步行稳定性分析,对其适应步行法进行了研究。首先,介绍了具有12个运动关节和球形脚部的四足马机器人结构模型,并求出了其运动学反解;其次,在分析步行稳定性和检测地面反力的基础上,提出了一种四足马机器人适应步行的实现方法;最后,通过自制的小型四足马机器人进行了适应步行实验。实验结果表明,所提出的四足马机器人适应步行法具有可行性。     

Energy Expenditure of Trotting Gait Under Different Gait Parameters

Robots driven by batteries are clean, quiet, and can work indoors or in space. However, the battery endurance is a great problem. A new gait parameter design energy saving strategy to extend the working hours of the quadruped robot is proposed. A dynamic model of the robot is established to estimate and analyze the energy expenditures during trotting. Given a trotting speed, optimal stride frequency and stride length can minimize the energy expenditure. However, the relationship between the speed and the optimal gait parameters is nonlinear, which is difficult for practical application. Therefore, a simplified gait parameter design method for energy saving is proposed. A critical trotting speed of the quadruped robot is found and can be used to decide the gait parameters. When the robot is travelling lower than this speed, it is better to keep a constant stride length and change the cycle period. When the robot is travelling higher than this speed, it is better to keep a constant cycle period and change the stride length. Simulations and experiments on the quadruped robot show that by using the proposed gait parameter design approach, the energy expenditure can be reduced by about 54% compared with the 100 mm stride length under 500 mm/s speed. In general, an energy expenditure model based on the gait parameter of the quadruped robot is built and the trotting gait parameters design approach for energy saving is proposed.     

四足爬行机器人步态分析与运动控制

为了实现液压作动的四足步行机器人的稳定行走,根据运动稳定裕量原则规划四足机器人的直行步态,保证三足支撑机体时稳定裕量为100 mm;针对液压缸运动加速度突变导致机体冲击振动的问题,提出了利用S型曲线作为各自由度的运动位移控制规律的方法。按照JQRI00型四足步行机器人原理样机的结构建立了虚拟样机模型,应用仿真软件对所设计步态进行了仿真,分析了步态的运动学、动力学特征和位移控制方法的运动特征;在四足步行机器人原理样机上进行了试验,并将试验与仿真结果进行了比较。研究结果表明,所设计的机器人步态可行,保证了机器人具有较好的行走稳定性;将S型曲线用于位移控制,消除了液压缸运动加速度的突变,进一步提高了机体运行的平稳性。     

四足步行机弯道行走步态

弯道行走是四足步行机步态拟定中还未被研究的问题,可它对研制衫的四足步行机十分重要。根据地面情况先拟定出使步行机稳定而不会跌倒的行走步态,然后依可行性条件来检查步态是否可行。依据步行机的结构参数找出该步行机的稳定可行步长的转角集。只要在这个稳定可行集内选择步态的步长和转角,按本文方法拟定转弯步态,该步态必能保证步行机平衡行步。     

Energy efficiency analysis of quadruped robot with trot gait and combined cycloid foot trajectory

Quadruped robots consume a lot of energy, which is one of the factors restricting their application. Energy efficiency is one of the key evaluating indicators for walking robots. The relationship between energy and elastic elements of walking robots have been studied, but different walking gait patterns and contact status have important influences on locomotion energy efficiency, and the energy efficiency considering the foot-end trajectory has not been reported. Therefore, the energy consumption and energy efficiency of quadruped robot with trot gait and combined cycloid foot trajectory are studied. The forward and inverse kinematics of quadruped robot is derived. The combined cycloid function is proposed to generate horizontal and vertical foot trajectory respectively, which can ensure the acceleration curve of the foot-end smoother and more successive, and reduce the contact force between feet and environment. Because of the variable topology mechanism characteristic of quadruped robot, the leg state is divided into three different phases which are swing phase, transition phase and stance phase during one trot gait cycle. The non-continuous variable constraint between feet and environment of quadruped robot is studied. The dynamic model of quadruped robot is derived considering the variable topology mechanism characteristic, the periodic contact and elastic elements of the robot. The total energy consumption of walking robot during one gait cycle is analyzed based on the dynamic model. The specific resistance is used to evaluate energy efficiency of quadruped robot. The calculation results show the relationships between specific resistance and gait parameters, which can be used to determine the reasonable gait parameters.     

四足步行机的全方位行走探讨

本文对缩放式四足步行机器人(简称步行机)的全方位行走问题进行了探讨。给出了一种拟定全方位行走的方法,同时,给出了用该方法拟定出步态的可行性条件和垂直方向稳定性条件。举例摸拟了步行机按拟定出的全方位步态的行走。     

四足轮腿式移动机器人的步态分析及轨迹规划

针对外星复杂的地表环境,基于2-UPS/(S+SPR)R闭环并联机构,设计了一种四足轮腿式移动机器人。通过对比机器人在运动过程中的稳定裕度与重心调整量得到最优步态,利用ZMP法衡量了机器人在静步态下的稳定性,并用改进的复合摆线法规划了足端的运动轨迹。在整个运动过程中,机械腿运动平稳,速度、加速度变化较为平滑,不会出现对机械腿造成损坏的较强冲击;且在抬腿和着地瞬间,速度、加速度均为0,不会对机身产生冲击。分析结果表明,该四足轮腿式移动机器人运动灵活且平稳,适用于外太空的探测。     

基于稳定阈度分析的外骨骼动态步长规划方法

在医疗领域,康复外骨骼机器人能够帮助下肢瘫痪的患者重新行走,因此得到广泛的关注。由于下肢截瘫患者身体的特殊性,针对该类患者使用的外骨骼机器人大多使用拐杖作为平衡辅助工具。在固定步长的情况下,不同的拐杖支撑点位置,会很大程度影响步行稳定阈度。通过分析穿戴者拄拐步态所形成的多边形支撑面,利用零力矩点(ZMP)理论计算相应的压力中心位置,从而得到四足步态的稳定阈度表达式;并在此基础上提出动态调整步长的方法,得到拐杖支撑点与步长的拟合曲面,对步长进行实时、适当调整;最后通过外骨骼机器人的运动学模型,规划相应的步态轨迹。通过在课题组自主研发的外骨骼机器人样机上进行大量对比实验,证明了在每个步态周期中,针对不同的拐杖支撑位置,提出的方法可以有效增加系统步态的稳定阈度,降低拐杖支撑点的随机性对系统稳定性的影响。     

单自由度腿部机构的四足机器人稳定性研究

以基于切比雪夫连杆腿部机构的四足机器人为原型,建立了其足端的运动轨迹方程,并推导出速度方程; 分别从静态及动态两种步态对单自由度四足机器人的稳定性进行研究,给出了各种步态下保持平衡行进的稳定判据; 并通过Adams仿真进行了验证。     

基于ADAMS的液压驱动四足机器人步态规划与仿真

为实现机器人的高负载、不平地面的高适应性运动要求,设计了一种液压驱动的四足机器人。分析了四足机器人的机械结构,机器人腿结构具有运动关节少、运动空间范围大特点,利用ADAMS规划设计了四足运动步态,并在ADAMS中进行动力学仿真。仿真分析了对角步态下机器人质心位移、液压缸驱动力以及与地面的接触力等参数,获得了液压缸工作流量、功率参数。仿真结果验证了机器人结构设计、步态规划的可行性,为液压缸、发动机选型提供了参考依据。     

NOVEL FORMULATION OF STATIC STABILITY FOR A WALKING QUADRUPED ROBOT

By defining the static stable area for foot placement, a new approach to analysis of quadruped robot stability is presented. Unlike conventionally, the method avoids solving complicated direct kinematics of quadruped robot and shows the information on the robot stability and the selection of swing leg. Especially, the proposed algorithm can be used as real-time operation for on-line gait generation and control for quadruped robots. The effectiveness of the proposed approach is shown through a practical crawling experiment of the quadruped robot TITAN-VIII.     

一种新型四足变胞爬行机器人的步态规划研究

随着移动机器人在探测救援中的应用逐渐增多,活动灵巧、环境适应能力强的多足机器人越来越受到国内外学者的关注。介绍一种腰部可以活动的四足机器人的设计及其步态生成,并展示了活动腰部可提升机器人对极端环境的适应性。提出三个基本假设以简化机构模型,提出腰部构态变换规则,并用几何方法说明了腰部构型变化可扩大机器人腿部活动空间,从而提升对复杂环境的适应性。另外,腰部运动与步态融合,生成了两种新的基本步态——扭腰直行步态和原地旋转步态。基于提出的两种步态,对比了固定腰部与可动腰部条件下运动稳定裕度的变化,分别计算了狭窄弯道通过条件,并分析了所设计步态对头部视觉的影响,从而证明所设计机器人具有较高的极端环境适应能力。     

四足机器人对角小跑步态动态稳定步行足端非连续约束及动力学建模

将四足机器人对角小跑步态周期分为摆动相和支撑相,采用D-H坐标法进行四足机器人运动学建模分析,提出基于质心运动定理分析腿机构处于支撑相的足端非连续约束力,通过力雅可比矩阵建立足端约束力与关节广义驱动力的映射关系。考虑足端与环境间的非连续约束,建立了具有变拓扑机构、非连续约束等特征的四足机器人非线性动力学模型,并通过虚拟样机仿真验证了动力学理论分析的正确性,为提高四足机器人非结构环境的机动性和动态稳定性研究提供了参考。     

四足步行机器人关节位姿和稳定性研究

四足机器人爬行控制的关键是关节位姿的确定、机器人稳定性的判断和摆动腿顺序的选择.提出了一种求解关节位姿驱动变量的有效方法,此方法能获得满意的四足机器人步行步态.通过定义立足点的静态稳定区域提出了一种机器人稳定性分析的新方法,该方法不仅避免了复杂的机器人正动力学求解问题,同时还可给出机器人稳定性和立足点稳定范围的信息.实际爬行实验验证了所提方法的有效性.     

一种四足马机器人的结构模型及其步行控制

参照马的生理结构,对四足马机器人的一种结构及其步行控制方法进行了研究。为验证该方法的有效性,首先,根据仿生原理设计出具有12个运动关节和4个球形脚部的四足马机器人结构模型,并求出了其运动学反解;其次,基于提出的结构模型,设计并实现了四足马机器人行走步态和对角小跑步态,并对步行稳定性进行了分析。步行实验表明,所提出的四足马机器人仿生结构及两种步态的实现方法具有可行性。     

复合运动模式四足机器人机构设计及分析

研制了一种轮足复合运动的四足智能移动机器人,该机器人可以步行前进,原地转弯,楼梯爬越,也可在良好路面利用足底轮以较高速度滚动前进。阐述了机器人的机械结构和参数,运动学分析和运动空间描述。利用ADAMS建立了三维仿真模型,进行了多种步态的仿真。得出稳定裕度合适的步态,实验验证了机器人的性能。     

四足机器人改进型对角小跑步态研究

传统的四足机器人对角小跑步态一般在机体坐标系中进行规划,在实际应用中存在着摆动腿无法同时着地、机体翻转无法有效抑制等问题,这些都降低了机器人运动的稳定性和精确性。针对以上问题,提出了一种在世界坐标系下规划的改进型对角小跑步态方法,该方法通过浮动机体运动学对摆动相进行规划,在足端的雅可比矩阵中引入机体姿态相关项,从而保证了摆动腿能同时着地,同时在支撑相和摆动相之间增加了四腿同时着地的调整相,对机器人机体位姿进行调整。对比仿真和样机试验结果表明：与传统方法相比,所提方法能够使摆动腿同时着地并能连续调整机体位姿,使机器人获得更好的运动稳定性和更高的位移控制精度。     

适应不同重力环境的仿壁虎机器人运动仿真

针对不同重力环境下仿壁虎机器人的运动稳定性、运动高效协调性等问题,基于四足机器人的步态规划现状和仿壁虎机器人自身特定的机械结构,设计了仿壁虎机器人在g、0、-g 3种环境下的足端轨迹和运动步态。在ADAMS仿真软件中研究了机器人的运动学和动力学特性,得到了仿壁虎机器人稳定爬行与脚掌黏附力、足端轨迹和运动步态的关系。探讨了仿真结果的合理性和局限性,为仿壁虎机器人在实际环境中的稳定运动奠定了理论基础。