仿生蝗虫机构着陆缓冲过程中的能量分配

着陆缓冲是仿生蝗虫跳跃机器人研究的重要问题之一,由于蝗虫的前腿、中腿和后腿尺寸不同,因此对缓冲过程中每条腿能量的分配直接影响到机器人受到地面冲击力和腿部肌肉力的大小,从而影响缓冲性能。在对蝗虫形态及着陆过程进行试验观测的基础上,采用弹簧等效代替蝗虫腿部肌肉,建立仿生蝗虫机构模型,并通过对机构进行受力分析,求得地面对机构各条腿支撑力与弹簧刚度系数之间的函数关系式。基于地面支撑力、腿部弹簧力以及每条腿的抗冲击能力的不同,提出了使得力的变化平缓、无冲击载荷的能量分配原则,根据该原则可求得各条腿的弹簧刚度系数。从算例中可以看出,此时仿生蝗虫机构所受到的地面支撑力和腿部弹簧力与不同着陆腿的抗冲击能力相吻合,且力的变化趋势平稳,可实现较好的缓冲效果。分析结果表明了分配方法的可行性,这为仿生蝗虫机构设计时腿部弹簧的选型提供了依据。     

四足并联腿步行机器人动力学

基于模块化和可重构理论,提出一种助老助残四足/两足可重构并联腿步行机器人。该机器人既可组合成两足步行机器人,亦可作为四足步行机器人使用。运用影响系数理论和虚功原理,对四足步行机器人静态步行时的摆动腿和机体机构进行动力学建模,导出摆动腿的动力学方程和机体机构超确定输入下的协调方程,按加权最小二乘法对四足并联腿步行机器人机体机构的动载进行最优协调分配,解决了机器人在行走过程中各分支运动约束而产生的动力耦合问题。     

基于3-UPU六足步行机器人的步态规划

提出一种基于非对称3-UPU并联机构的新型六足步行机器人,其具有承载能力大、通过能力强、控制容易等优势。首先,对六足步行机器人进行结构设计,然后,综合考虑机器人的稳定性和腿部干涉两种情况,设计了最大横向移动步幅。还对六足步行机器人进行了步态规划,包括机器人两组腿的占空系数、运动次序、运动步幅、运动轨迹及各分支等效杆长随机器人的移动的变化。     

新型四足步行机器人串并混联腿的运动学分析

针对串联四足机器人行走惯量大,自重/载重比大的问题,提出一种新型串并混联四足步行机器人,并对该机器人的串并混联腿进行运动学分析。该机器人由一个运载平台和四条结构相同的串并混联腿组成,每条腿均由髋关节、大腿、小腿顺次连接构成,其中髋关节为3-RRR并联机构。以能耗最小姿态为最优姿态,基于矢量法求解了该串并混联腿的运动学正解和反解,利用MATLAB和ADAMS软件验证了正解和反解的正确性;基于矢量法和微分变换法求出了该混联腿的速度雅克比矩阵和加速度矩阵,分析了其奇异性,并利用MATLAB软件绘制出该腿的工作空间。结果表明:该腿在髋关节连杆直径d=22mm,大腿杆件直径D=50mm,膝关节转角θ4∈[105°,155°]时,工作空间呈球冠形,最大内接圆半径R=400mm,高度为H∈[500mm,900mm]。本研究对该新型串并混联四足步行机器人的刚度分析、动态性能、机构优化设计和系统控制等的进一步研究具有重要意义。     

凸轮连杆组合机构驱动的四足仿生马机器人运动学建模与分析

提出了一种仿生马构型的四足步行机器人,以用于马术辅助治疗。其单腿系统利用凸轮连杆组合机构驱动。在论述该仿生马机器人结构与工作原理的基础上,进行了机器人的运动学建模与分析。利用环路矢量法建立各机构运动学方程,利用牛顿迭代法对非线性位移方程进行了求解。采用Matlab开发了求解机器人行走腿位移、速度、加速度运动的统一程序。通过实例计算,对采用电机等速驱动机器人产生的行走腿端点位移、加速度特性进行了分析。为后续优化机器人性能奠定了基础。     

带迟滞非线性环节二元机翼的气动弹性响应分析

基于Theodorsen非定常气动力理论,采用Roger拟合得到时域气动力表达式;针对二元机翼俯仰自由度带有迟滞非线性环节的情况,采用分段线性方式,建立了二元机翼气动弹性系统无量纲运动方程。通过数值仿真得到了系统极限环振动响应的时间历程和相轨迹,并与带中心间隙型非线性刚度环节二元机翼的气动弹性响应特性进行了比较;结果表明在一定的来流速度下,二元机翼俯仰自由度具有的迟滞特性会导致整个系统的极限环振动;最后用描述函数法给出了迟滞非线性环节的等效刚度及等效阻尼表达式,并进行了具有迟滞非线性环节二元机翼气动弹性系统颤振边界的等效线化分析,与直接数值仿真的计算结果吻合较好。     

低频重载下黏弹性减振器阻尼缓冲性能分析

为研究黏弹性减振器的非线性阻尼缓冲性能,根据其结构特点和非线性特征,建立单自由度分段非对称非线性振动模型,并由平均法推导出系统固有频率共振区附近的幅频特性方程。以安装在某300kW履式拖拉机的黏弹性减振器为应用对象进行研究,分析系统在固有频率共振区附近的非线性特性和阻尼减振性能。讨论了幅频特性分别和激励幅值、刚度系数、阻尼系数、质量之间的关系,并提出改善系统减振性能的建议。     

双曲轴驱动的八足趴卧式步行机器人设计分析

采用类似昆虫趴卧式关节腿结构,以2个电机分别独立驱动2条曲轴、进而分别带动与2条曲轴铰接的步行腿机构的技术,研发了一种八足趴卧式步行机器人。该机器人每条步行腿机构均是由曲柄连杆机构组成的大腿、小腿及胯关节和膝关节;且每条步行腿均是由2个曲柄控制,以实现其前后和上下摆动,能模拟昆虫类步行腿三维空间的爬行步态。通过对腿足结构原理的分析,建立爬行腿坐标系及其各连杆间空间变化矩阵的运动学模型;并以此分析了该机器人整机的爬行工作原理和典型爬行步态运动方式。最后,通过样机制作和行走试验表明：该机器人可以实现整机爬行运动要求,验证了其机械原理、运动学模型的正确性和设计方案可行性,其机械原理、曲轴结构设计、仿生步行腿设计和曲轴曲柄连杆驱动、传动系统的设计方案等,均可为将来更好的完善多足步行机器人开发应用提供参考依据。     

考虑时变间隙的并联指向机构非线性模态分析

针对复杂空间机构的振动模型难以建立的问题,基于数轴法提出一种简便的并联指向机构振动模型建模方法,利用ANSYS模态分析证明了该方法的可行性。为了研究运动副间隙对机构模态特性的动态影响规律,考虑运动副残余刚度,提出了含间隙运动副的改进非线性等效刚度系数建立方法。将改进的非线性等效刚度系数嵌入机构振动模型,建立了考虑时变运动副间隙的非线性振动模型。利用ADAMS对考虑间隙的机构动力学进行仿真分析,根据仿真得到的间隙数据对受时变间隙影响的机构非线性模态特性进行分析。研究结果可以为并联指向机构的动态性能优化、振动抑制和故障诊断提供理论依据。     

基于Adams的六足直立式步行机器人运动仿真分析

分析了一种以双电机为驱动力、以曲柄连杆机构为传动系统的六足直立式步行机器人的工作原理。首先,利用矢量解析法对步行腿机构建立相应运动数学模型并分析;再利用虚拟样机分析软件Adams对单侧步行腿机构进行运动轨迹建模仿真分析;最后,搭建实物样机验证了工作原理、方案设计、虚拟仿真结果的正确性和可行性。结果表明,步行腿机构的运动特性能够满足六足直立式步行机构的工作要求,设计方案可行,可为下一步的动力学分析和优化设计提供理论基础。     

Analysis on the performance of the SLIP runner with nonlinear spring leg

The spring-loaded inverted pendulum(SLIP) has been widely studied in both animals and robots.Generally,the majority of the relevant theoretical studies deal with elastic leg,the linear leg length-force relationship of which is obviously conflict with the biological observations.A planar spring-mass model with a nonlinear spring leg is presented to explore the intrinsic mechanism of legged locomotion with elastic component.The leg model is formulated via decoupling the stiffness coefficient and exponent of the leg compression in order that the unified stiffness can be scaled as convex,concave as well as linear profile.The apex return map of the SLIP runner is established to investigate dynamical behavior of the fixed point.The basin of attraction and Floquet Multiplier are introduced to evaluate the self-stability and initial state sensitivity of the SLIP model with different stiffness profiles.The numerical results show that larger stiffness exponent can increase top speed of stable running and also can enlarge the size of attraction domain of the fixed point.In addition,the parameter variation is conducted to detect the effect of parameter dependency,and demonstrates that on the fixed energy level and stiffness profile,the faster running speed with larger convergence rate of the stable fixed point under small local perturbation can be achieved via decreasing the angle of attack and increasing the stiffness coefficient.The perturbation recovery test is implemented to judge the ability of the model resisting large external disturbance.The result shows that the convex stiffness performs best in enhancing the robustness of SLIP runner negotiating irregular terrain.This research sheds light on the running performance of the SLIP runner with nonlinear leg spring from a theoretical perspective,and also guides the design and control of the bio-inspired legged robot.     

基于曲柄摇杆机构的新型六足爬行机器人的设计

六足爬行机器人在理论上可以实现向前向后稳定行走.对驱动足采用了曲柄摇杆机构,将腿放在四杆机构的摇杆上,实现了腿前后摇摆行走.此外,由于是通过连杆曲线图谱选择腿部运动轨迹,从连杆曲线图谱上可以看到,整条曲线都是很平滑的,因此,机器人在行走过程中也会非常稳定,而不至于出现冲击载荷.对六足机器人的行进机构、运动设计与分析、机器人的运动轨迹和六足机器人的控制系统进行了详细阐述.     

Kinematics and dynamics analysis of a quadruped walking robot with parallel leg mechanism

It is desired to require a walking robot for the elderly and the disabled to have large capacity,high stiffness,stability,etc.However,the existing walking robots cannot achieve these requirements because of the weight-payload ratio and simple function.Therefore,Improvement of enhancing capacity and functions of the walking robot is an important research issue.According to walking requirements and combining modularization and reconfigurable ideas,a quadruped/biped reconfigurable walking robot with parallel leg mechanism is proposed.The proposed robot can be used for both a biped and a quadruped walking robot.The kinematics and performance analysis of a 3-UPU parallel mechanism which is the basic leg mechanism of a quadruped walking robot are conducted and the structural parameters are optimized.The results show that performance of the walking robot is optimal when the circumradius R,r of the upper and lower platform of leg mechanism are 161.7 mm,57.7 mm,respectively.Based on the optimal results,the kinematics and dynamics of the quadruped walking robot in the static walking mode are derived with the application of parallel mechanism and influence coefficient theory,and the optimal coordination distribution of the dynamic load for the quadruped walking robot with over-determinate inputs is analyzed,which solves dynamic load coupling caused by the branches’ constraint of the robot in the walk process.Besides laying a theoretical foundation for development of the prototype,the kinematics and dynamics studies on the quadruped walking robot also boost the theoretical research of the quadruped walking and the practical applications of parallel mechanism.     

Method for six-legged robot stepping on obstacles by indirect force estimation

Adaptive gaits for legged robots often requires force sensors installed on foot-tips, however impact, temperature or humidity can affect or even damage those sensors. Efforts have been made to realize indirect force estimation on the legged robots using leg structures based on planar mechanisms. Robot Octopus III is a six-legged robot using spatial parallel mechanism(UP-2UPS) legs. This paper proposed a novel method to realize indirect force estimation on walking robot based on a spatial parallel mechanism. The direct kinematics model and the inverse kinematics model are established. The force Jacobian matrix is derived based on the kinematics model. Thus, the indirect force estimation model is established. Then, the relation between the output torques of the three motors installed on one leg to the external force exerted on the foot tip is described. Furthermore, an adaptive tripod static gait is designed. The robot alters its leg trajectory to step on obstacles by using the proposed adaptive gait. Both the indirect force estimation model and the adaptive gait are implemented and optimized in a real time control system. An experiment is carried out to validate the indirect force estimation model. The adaptive gait is tested in another experiment. Experiment results show that the robot can successfully step on a 0.2 m-high obstacle. This paper proposes a novel method to overcome obstacles for the six-legged robot using spatial parallel mechanism legs and to avoid installing the electric force sensors in harsh environment of the robot’s foot tips.     

Adjustable Mechanism for Walking Robots with Minimum Number of Actuators

Recent literature on walking robots deals predominantly with multi-degrees-of-freedom leg mechanisms and machines capable of adopting several gaits.This paper explores the other end of the spectrum suggesting mechanisms derived from a four bar coupler curve for a one degree of freedom walking robot.Simulation of the walk indicates that body of the robot is able to move with low variation in velocity.The best strategy for changing the gait to enable the robot to walk over obstacles and the effect of change i...     

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.     

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 generation and change of direction for the underactuated three-legged robot

This paper describes a three-legged robot that consists of one actuated leg and two passive legs. The active leg has a knee joint and an ankle joint. The passive legs have no knee joint, although they have a passive ankle joint respectively. The passive leg part and the actuated leg part are linked by a hip part. The robot behavior is passive while the robot is supported by its passive legs and swings the actuated leg part. Generally, in the event that an actuator or a transmitting mechanism fails, robots cannot apply torques to the joint. We therefore took up a walking robot with passive knee joints not only for the energy-efficient walking but also with a view to making ambulation failsafe in case of mechanical failures.     

Biped Robot with Triangle Configuration

A new biped robot with a triangle configuration is presented and it is a planar closed chain mechanism.The scalability of three sides of the triangle is realized by three actuated prismatic joints.The three vertexes of the triangle are centers of three passive revolute joints coincidently.The biped mechanism for straight walking is proposed and its walking principle and mobility are explained.The static stability and the height and span of one step are analyzed.Kinematic analysis is performed to plan the gaits of walking on an even floor and going upstairs.A prototype is developed and experiments are carried out to validate the straight walking gait.Two additional revolute joints are added to form a modified biped robot which can follow the instruction of turning around.The turning ability is verified by experiments.As a new member of biped robots,its triangle configuration is used to impart geometry knowledge.Because of its high stiffness,some potential applications are on the way.