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.     

A new approach for development of quadruped robot based on biological concepts

This paper proposes the design and development results of a new quadruped robot. The proposed new quadruped robot has a couple of advantages of flexible locomotion. The quadruped robot is designed and modeled based on a new concept that is the structure model with three segments of quadruped legs. New leg configuration with the simplified operation of four hip actuators is introduced. The posture of the new quadruped robot is more similar to the posture of dog than that of the previous quadruped robots. The objective of this paper is to develop a quadruped robot, which can walk and run in a trot gait with a simple PID controller. Numerical simulation and experimental results are shown to prove the locomotion performance of the proposed controller for the proposed quadruped robot.     

Effect of Spine Motion on Mobility in Quadruped Running

Most of current running quadruped robots have similar construction： a stiff body and four compliant legs. Many researches have indicated that the stiff body without spine motion is a main factor in limitation of robots’ mobility. Therefore, investigating spine motion is very important to build robots with better mobility. A planar quadruped robot is designed based on cheetahs’ morphology. There is a spinal driving joint in the body of the robot. When the spinal driving joint acts, the robot has spine motion; otherwise, the robot has not spine motion. Six group prototype experiments with the robot are carried out to study the effect of spine motion on mobility. In each group, there are two comparative experiments： the spinal driving joint acts in one experiment but does not in the other experiment. The results of the prototype experiments indicate that the average speeds of the robot with spine motion are 8.7%–15.9% larger than those of the robot without spine motion. Furthermore, a simplified sagittal plane model of quadruped mammals is introduced. The simplified model also has a spinal driving joint. Using a similar process as the prototype experiments, six group simulation experiments with the simplified model are conducted. The results of the simulation experiments show that the maximum rear leg horizontal thrusts of the simplified mode with spine motion are 68.2%–71.3% larger than those of the simplified mode without spine motion. Hence, it is found that spine motion can increase the average running speed and the intrinsic reason of speed increase is the improvement of the maximum rear leg horizontal thrust.     

Motion capability analysis of a quadruped robot as a parallel manipulator

This paper presents the forward and inverse displacement analysis of a quadruped robot MANA as a parallel manipulator in quadruple stance phase, which is used to obtain the workspace and control the motion of the body. The robot MANA designed on the basis of the structure of quadruped mammal is able to not only walk and turn in the uneven terrain, but also accomplish various manipulating tasks as a parallel manipulator in quadruple stance phase. The latter will be the focus of this paper, however. For this purpose, the leg kinematics is primarily analyzed, which lays the foundation on the gait planning in terms of locomotion and body kinematics analysis as a parallel manipulator. When all four feet of the robot contact on the ground, by assuming there is no slipping at the feet, each contacting point is treated as a passive spherical joint and the kinematic model of parallel manipulator is established. The method for choosing six non-redundant actuated joints for the parallel manipulator from all twelve optional joints is elaborated. The inverse and forward displacement analysis of the parallel manipulator is carried out using the method of coordinate transformation. Finally, based on the inverse and forward kinematic model, two issues on obtaining the reachable workspace of parallel manipulator and planning the motion of the body are implemented and verified by ADAMS simulation.     

Gait Analysis of Quadruped Robot Using the Equivalent Mechanism Concept Based on Metamorphosis

The previous research regarding the gait planning of quadruped robot focuses on the sequence for lifting o and placing the feet, but neglects the influence of body height. However, body height a ects gait performance significantly, such as in terms of the stride length and stability margin. We herein study the performance of a quadruped robot using the equivalent mechanism concept based on metamorphosis. Assuming the constraints between standing feet and the ground with hinges, the ground, standing legs and robot body are considered as a parallel mechanism, and each swing leg is regarded as a typical serial manipulator. The equivalent mechanism varies while the robot moves on the ground. One gait cycle is divided into several periods, including step forward stages and switching stages. There exists a specific equivalent mechanism corresponding to each gait period. The robot's locomotion can be regarded as the motion of these series of equivalent mechanisms. The kinematics model and simplified model of the equivalent mechanism is established. A new definition of the multilegged robot stability margin, based on friction coe cient, is presented to evaluate the robot stability. The stable workspaces of the equivalent mechanism in the step forward stage of trotting gait under di erent friction coe cients are analyzed. The stride length of the robots is presented by analyzing the relationship between the stable workspaces of the equivalent mechanisms of two adjacent step forward stages in one gait cycle. The simulation results show that the stride length is larger with increasing friction coe cient. We herein propose a new method based on metamorphosis, and an equivalent mechanism to analyze the stability margin and stable workspace of the multilegged robot.     

四足机器人腿部运动空间和足端运动轨迹研究

机器人的单腿的运动空间及足端点运动轨迹决定了所设计的机器人的应用范围。为了研究四足步行机器人摆动腿在一定参数条件下的运动空间大小及足端的运动轨迹,通过对机器人摆动腿正运动学方程,足端点轨迹在y、z轴上对时间的函数进行计算,并将计算结果运用MATLAB软件进行仿真,不仅直观地观测到机器人的运动情况,还得到所需的数据,且以图形的形式显示出来,达到了预期目的。     

四足机器人被动跳跃步态动力学分析与仿真

在四足机器人被动跳跃步态分析模型的基础上,采用拉格朗日法推导了该步态中各运动相的动力学方程,并根据跳跃步态特征给出了基于事件的运动相转换方程。定义了四足机器人被动跳跃步态的庞加莱映射,利用牛顿迭代法获得了庞加莱映射的某个固定点。在MATLAB中以该固定点为初始条件对各运动相动力学方程进行了数值积分,得到了被动跳跃步态的周期性运动曲线,证明了四足机器人在某个初始条件下能够实现稳定的被动跳跃步态。
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基于螺旋理论的冗余液压驱动四足机器人运动学分析

四足机器人的各种研究大多基于四条腿弯曲方向一致展开的。对于液压驱动且具有冗余度的四足机器人,静止姿态下,其前面两条腿与后面两条腿成对称弯曲状。为了研究这种机器人单腿运动和躯体运动状态,文中建立了基于螺旋理论的液压驱动四足机器人运动学模型,包括给出了单腿串联运动学逆解和躯体并联运动学正解。然后根据机器人行走过程设计出后面两条腿的髋关节与膝关节摆幅角度,通过建立的运动学模型,得到前面两条腿的关节变量及躯体姿态。最后通过MATLAB数值仿真和ADAMS虚拟样机实验,对机器人在一种行走方案下的躯体运动姿态进行仿真对比,验证了所建运动学模型的可靠性。     

一种六足仿生机器人的研究

基于仿生学原理,应用连杆机构学中的Robert原理,设计出一连杆轨迹能较好地近似于机器人理想足部轨迹的六杆机构.并通过ADAMS动力学仿真软件,对用这一连杆机构作为腿部机构的六足机器人进行了前进和转弯步态仿真.仿真结果表明该机器人具有良好的移动性能.     

液压四足机器人单腿竖直跳跃步态规划

针对机器人跳跃运动落地时冲击力大的问题,面向竖直跳跃运动,以液压四足机器人单腿为研究对象,建立液压驱动四足机器人单腿运动学模型,并分别对机器人单腿处于起跳相、落地相和腾空相时进行轨迹规划;根据关节参数,通过运动学逆解求得驱动函数,利用仿真软件ADAMS进行竖直跳跃步态仿真;搭建单腿实验平台,进行实验验证,依据得到的动态特性,分析步态规划的准确性及合理性,为后续液压四足机器人动步态的研究提供设计和控制依据。     

四足步行机器人腿机构及其稳定性步态控制

结合实际 ,详细地分析了四足步行机器人的步态和腿机构的运动关系 ,并在此基础上给出了四足步行机器人腿部机构和驱动控制方案。     

单腿跳跃机器人的被动周期运动研究

单腿跳跃机器人系统是一个非线性系统,其是否存在被动周期运动,关系着单腿跳跃机器人是否能以最小能耗实现跳跃运动。文中采用Brute-force方法研究了最简跳跃机器人模型的被动周期运动,但Brute-force方法的最大一个缺点就是其初始条件是手动修改,这种手动修改初始条件的方法具有盲目性,即经过无数次的尝试,才能找到满意的初始条件,效率低下。文中最后提出设想,如果在确定初始条件前采用优化方法,找到合适的初始条件,那么就可以提高效率,避免了盲目性。     

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.     

基于ADAMS的四足仿生机器人单腿结构设计

利用ADAMS软件虚拟样机技术,设计了液压驱动的四足仿生机器人单腿机械结构。通过分析四足哺乳类动物身体结构及运动特性,设计了仿生机器人的机械机构,确定了机器人腿部自由度配置,建立了仿真模型。根据动物的实际运动步态,规划并设计了静步态及对角小跑两种步态,进行了逆动力学仿真,得到关节等关键部位输出数据。在仿真实验的基础上,设计了液压作动器的关键参数及四足仿生机器人单腿机械结构。     

液压四足机器人机身扰动抑制及实验研究

针对液压四足机器人在运动过程中的机身扰动较大的问题,提出基于运动学和虚拟模型的液压四足机器人机身扰动抑制策略。分析机器人机身扰动产生的机理及其影响,建立四足机器人整机运动学方程,根据机器人实时姿态反馈抑制机身扰动。同时在机器人机身横滚和俯仰自由度上引入弹簧阻尼虚拟元件,通过调整虚拟力的大小控制机身姿态。面向机器人对角小跑步态,对机器人摆动相和支撑相进行足端轨迹规划。通过液压四足机器人平台进行实验验证,实验结果表明,该扰动抑制策略能够根据机器人的机身姿态调整关节角度,机器人机身起伏小,机器人实际运动轨迹与理论运动轨迹接近,验证了所提方法的有效性。     

四足机器人的腿部拓扑结构研究及其动力学仿真

对一种四足机器人的腿部机构设计方法进行探究。简析哺乳动物腿部关节分布,确立了四足机器人拓扑结构与自由度数目,用拉格朗日方程对其动力学简略推导,并建立虚拟样机。借助ADAMS动力学仿真软件,验证四足机器人虚拟样机在起立过程和对角步态的动力学规律。     

Design of a slider-crank leg mechanism for mobile hopping robotic platforms

Legged locomotion has been widely researched due to its effectiveness in overcoming uneven terrains. Due to previous efforts there has been much progress in achieving dynamic gait stability and as the next step, mimicking the high speed and efficiency observed in animals has become a research interest. The main barrier in developing such a robotic platform is the limitation in the power efficiency of the actuator: the use of pneumatic actuators produce sufficient power but are heavy and big; electronic motors can be compact but are disadvantageous in producing sudden impact from stall which is required for high speed legged locomotion. As a new attempt in this paper we suggest a new leg design for a mobile robot which uses the slider-crank mechanism to convert the continuous motor rotation into piston motion which is used to impact the ground. We believe this new mechanism will have advantage over conventional leg mechanism designs using electronic motors since it uses the continuous motion of the motor instead of sudden rotation movements from stall state which is not ideal to draw out maximum working condition from an electronic motor. In order to control impact timing from the periodic motion of the piston a mechanical passive clutch trigger mechanism was developed. Dynamic analysis was performed to determine the optimal position for the mechanical switch position of the clutch trigger mechanism, and the results were verified through simulation and experiment. Development of a legged locomotion with two degrees of freedom, slider-crank mechanism for impact and additional actuation for swing motion, is proposed for future work.     

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。     

液压四足机器人足端的力预测控制与运动平稳性

针对液压四足机器人在坚硬路面行走时,足端位置易受刚性冲击,导致运动姿态平稳性差的问题,提出一种液压四足机器人足端力预测控制方法。在分析液压四足机器人结构的基础上,根据运动学与力学模型构建了液压伺服系统的力控制模型;采用改进自适应布谷鸟优化BP神经网络算法建立足端力预测控制模型,通过仿真对比分析验证了该算法的可行性。最后通过液压四足机器人KL样机进行足端力及刚性地面行走测试,结果表明该方法能有效增强液压四足机器人腿部的力柔顺性,提高运动姿态平稳性。     

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。