变长度柔性双足机器人行走控制及稳定性分析

针对传统双足机器人模型缺少脚质量和躯干的问题,提出考虑摆动腿动态及躯干影响的柔性双足机器人模型,并对其行走控制及稳定性进行研究。首先,建立系统的动力学模型并采用欧拉-拉格朗日法推导了系统的动力学方程;同时,在弹簧负载倒立摆（SLIP）模型的基础上添加刚性躯干、脚质量及采用变长度伸缩腿,充分考虑躯干及摆动腿动力学对机器人行走步态的影响;其次,设计基于变长度腿的反馈线性化控制器来跟踪目标轨迹,以及调节摆动腿和躯干的姿态;最后,利用Newton-Raphson迭代法和庞加莱映射分析机器人的不动点及轨道稳定性条件,并在理论分析的基础上进行仿真。仿真结果表明,所提控制器可以实现机器人的周期行走,对外界干扰具有良好的鲁棒性,且雅可比矩阵所有特征值的模均小于1,能形成稳定的极限环,证明系统是轨道稳定的。     

可侧向摆动的欠驱动双足机器人

为解决机器人的侧向平衡问题,同时为使机器人的行走空间由二维扩展到三维,确立了可以侧向周期稳定偏转的有弹性脚的欠驱动步行机器人模型。根据混合动力系统的特点,建立了侧向摆动方程及脚碰撞地面的方程,并利用数值仿真得到了不同初始状态下的稳定极限环。根据运动状态分析,找到了弹性脚的欠驱动步行机器人所允许的侧向偏转范围。施加基于能量的控制可以消除摆动过程中出现的干扰,使欠驱动步行机器人回归到稳定状态,稳定的侧向摆动保证了欠驱动步行机器人的稳定行走。     

伸缩腿双足机器人半被动行走控制研究

研究半被动伸缩腿双足机器人行走控制和周期解的全局稳定性问题.使用杆长可变的倒立摆机器人模型,以支撑腿的伸缩作为行走动力源,采用庞加莱映射方法分析了双足机器人行走的不动点及其稳定性.当脚与地面冲击时,假设两腿间的夹角保持为常数,设计了腿伸缩长度的支撑腿角度反馈控制率.证明了伸缩腿双足机器人行走过程不动点的全局稳定性.仿真结果表明,本文提出的腿伸缩长度反馈控制可以实现伸缩腿双足机器人在水平面上的稳定行走,并且周期步态对执行器干扰和支撑腿初始角速度干扰具有鲁棒性.     

下肢外骨骼机器人变步长步态规划方法

为了解决下肢外骨骼机器人连续步态规划问题,基于倒立摆模型提出了一种步态规划算法,并针对传统倒立摆模型无法变步长连续行走的问题提出了新的改进方法。将外骨骼机器人分成支撑腿和摆动腿两部分,分别采用D-H法进行运动学分析;利用倒立摆模型和固定函数法,进行等效质心与摆动腿末端轨迹规划;在相邻单脚支撑期之间插入双脚支撑期,使下肢外骨骼机器人在不断改变步行时,利用双脚支撑期进行位置和速度的切换,实现实时步态规划;将规划算法在SIMULINK中实现,并与ADAMS模型进行联合仿真,下肢外骨骼机器人在仿真环境下行走稳定,证明了算法的有效性。     

仿人机器人在复杂环境中的行走研究

在仿人机器人行走限定性的研究中,由于外界环境的复杂性,仿人机器人在行走过程中很容易失稳,导致不能稳定行走的问题.为了避免失稳摔倒,结合FZMP的在线调整策略,提出了通过调整直立姿态、调整落地角动量控制、落地减振控制和落地位置控制四种稳定行走控制方法,通过改变髋关节的高度来吸收由摆动腿提前着地而产生的垂直振动,给出了髋关节的高度补偿计算公式.使得机器人行走的整个过程,特别是在地面不平整以及摆动腿落地瞬间冲击力较大时也能保持良好的稳定性.通过ADAMS软件和虚拟仿真验证,改进方法能有效的实现机器人在复杂环境中的稳定行走.     

圆周对称分布六腿机器人三种典型行走步态步长及稳定性分析

针对现有圆周对称分布六腿步行机器人步长研究中存在的缺点和不足,提出了并联机构支链工作空间相交法,将由机器人本体、支撑腿和地面组成的并联机构分割成不同的分支,利用各分支工作空间求交,从而确定机器人在某一本体高度上的步长和稳定裕度.该方法可在已知机器人立足点和本体高度的情况下求得机器人的最大可行步长和稳定裕度,也可以求得机器人在某一本体高度上的极限可行步长和在这种情况下的立足点的位置,还可以根据已知步长和机器人本体高度来确定最大稳定裕度和最大稳定裕度下的立足点的位置.这种方法为圆周对称分布六腿机器人采用不同步态行走过程中立足点、本体高度和步长的选取提供重要参考.     

无动力双足步行机器人控制策略与算法

本文研究无动力双足步行机器人的建模、分析与控制问题. 基于能量的控制增加了机器人行走极限环的稳定性、鲁棒性, 扩大了极限环的收敛域; 角度不变控制使机器人的稳定行走步态摆脱了地面倾斜角度的限制; 把基于能量的控制与角度不变控制结合起来, 可以实现在不同倾斜角度地面上行走模式的切换. 基于能量的行走平均速度控制方法在平均速度与目标能量之间建立了联系, 能使机器人的行走产生新的稳定步态. 最后, 对无动力双足步行机器人的研究前景做了展望.     

基于反向迭代学习控制的工业机器人应用研究

针对一类具有对称期望轨迹跟踪的工业机器人系统,提出一种新的迭代学习控制方法,即反向型迭代学习控制方法。通过利用这类轨迹固有的特征,将其以中心点为界分解为前后两个独立的轨迹,利用两段轨迹的镜像对称特征,不断交替优化调整下次迭代周期的控制量,使得跟踪当前轨迹的工业机器人系统每次迭代时不必再从轨迹的初始点学习,从而有效加快了系统的学习速度。对具有镜像对称特征的期望轨迹进行交替利用控制信息,实现了工业机器人对期望轨迹的快速跟踪、减小系统的跟踪误差,从而达到了机器人跟踪效率的较大提升。收敛性分析和机器人的仿真实例验证了所提控制方法的有效性。     

基于迭代学习控制的鳗鱼机器人切向速度跟踪控制

鳗鱼机器人的动力学模型非线性强、高度欠驱动,导致多关节鳗鱼机器人的切向速度跟踪控制极具挑战．本文采用P型迭代学习控制与步态生成器相结合的方法对多关节鳗鱼机器人的切向速度进行跟踪控制．首先,采用解析牛顿-欧拉法建立非惯性系下的鳗鱼机器人动力学模型,直接获得切向速度子动力学模型;然后,利用带饱和函数的P型迭代学习控制器控制步态参数,并且利用复合能量函数和切向速度子动力学模型分析该控制器的收敛性,得到切向速度跟踪误差的收敛条件;最后,提出鳗鱼机器人的运动控制框架,并对多模块的鳗鱼机器人进行仿真和实验．实验结果表明,实际的切向速度随着迭代次数的增加而逐渐跟踪上了期望的切向速度,故而验证了鳗鱼机器人切向速度跟踪控制器的有效性．     

具有屈膝行为的双足被动行走模型

参考人类下坡行走运动特点,提出一种具有屈膝行为的双足被动行走模型.采用5质点4杆被动行走模型,设计支撑腿在行走过程中弯曲,通过对支撑腿膝关节弯曲时刻的调整,求解得到模型在不同斜面上的稳定周期行走步态.仿真结果表明,模型实现了在坡度范围小于0.39 rad的斜面上稳定行走步态.与传统步态相比,稳定行走的坡度范围显著提高,在较大坡度上也具有很好的稳定性.     

变长度弹性伸缩腿双足机器人半被动起步行走仿人控制

传统双足机器人行走使用轨迹跟踪控制,而人类行走大部分时间处于被动状态.针对半被动变长度弹性伸缩腿双足机器人从静止状态开始起步行走的问题,提出了一种起步行走仿人控制方法.首先,使用串联弹性驱动双足弹簧负载倒立摆(B-SLIP)模型;然后,利用拉格朗日方法建立行走动力学方程,并利用模型的自稳定性在双支撑阶段采用能量误差比例...     

Efficiency analysis of telescopic-legged bipedal robots

This paper investigates the stability of underactuated bipedal walking incorporating telescopic-leg actuation. In human walking, knee joints of swing and support legs are bent and stretched. The telescopic legs mimic the motion of the center of mass of human legs via their telescopic motion during the stance phase. First, underactuated telescopic-legged biped robot models are introduced. Second, an output-following control law is applied to the linearized equation of motion of the robot, and the controlled robot’s equation is then specified as a linear time-varying system. The error transition equation is developed to evaluate the stability during the stance phase. Numerical calculations are performed to show the influences of leg telescopic motion on the stability.     

Passive joint stiffness in the hip and knee increases the energy efficiency of leg swinging

In the field of minimally-actuated robots, energy efficiency and stability are two of the fundamental criteria that can increase autonomy and improve task-performance capabilities. In this paper, we demonstrate that the energetic cost of leg swinging in dynamic robots can be reduced without significantly affecting stability by emulating the physiological use of passive joint stiffness, and we suggest that similar efficiency improvements could be realized in dynamic walking robots. Our experimental model consists of a two-segment dynamically swinging robotic leg with hip and knee joints. Closed-loop control is provided to the hip using neurally inspired, nonlinear oscillators that do not override the leg’s natural dynamics. We examined both linear and nonlinear, physiologically based stiffness profiles at the hip and knee and a hyperextension-preventing hard stop at the knee. Our results indicate that passive joint stiffness applied at one or both joints can improve the energy efficiency of leg swinging by reducing the actuator work required to counter gravitational torque and by promoting kinetic energy transfer between the shank and thigh. Energetic cost reductions (relative to the no-stiffness case) of approximately 25% can be achieved using hip stiffness, provided that the hip actuation bias angle is not coincident with gravity, and cost reductions of approximately 66% can be achieved using knee stiffness. We also found that constant stiffness combined with a limit on knee hyperextension produces comparable results to the physiological stiffness model without requiring complex implementation techniques. Although this study focused on the task of leg swinging, our results suggest that passive-stiffness properties could also increase the energy efficiency of walking by reducing the cost of forward leg swing by up to 66%. We also expect that the energetic cost of walking could be further reduced by adding stiffness to the ankle to assist in the propulsive portion of stance phase.     

双足机器人动态步行实时步态生成

针对双足机器人动态步行生成关节运动轨迹复杂问题,提出了一种简单直观的实时步态生成方案。建立了平面五杆双足机器人动力学模型,通过模仿人类步行主要运动特征并根据双足机器人动态步行双腿姿态变化的要求,将动态步行复杂任务分解为顺序执行的四个过程,在关节空间相对坐标系下设计了躯干运动模式、摆动腿和支撑腿动作及步行速度调整模式,结合当前步行控制结果反馈实时产生稳定的关节运动轨迹。仿真实验验证了该方法的有效性,简单易实现。     

Feedforward and Feedback Dynamic Trot Gait Control for Quadruped Walking Vehicle

To realize dynamically stable walking for a quadruped walking robot, the combination of the trajectory planning of the body and leg position (feedforward control) and the adaptive control using sensory information (feedback control) is indispensable. In this paper, we propose a new body trajectory, the 3D sway compensation trajectory, for a stable trot gait; we show that this trajectory has a lower energy consumption than the conventional sway trajectory that we have proposed. Then, for the adaptive attitude control method during the 2-leg supporting phase, we consider four methods, that is, a) rotation of body along the diagonal line between supporting feet, b) translation of body along the perpendicular line between supporting feet, c) vertical swing motion of recovering legs, and d) horizontal swing motion of recovering legs; we then describe how we verify the stabilization efficiency of each method through computer simulation, stabilization experimentation, and experimenting in walking on rough terrain using the quadruped walking robot, TITAN-VIII.     

Walking and steering control for a 3D biped robot considering ground contact and stability

This paper presents a stable walking control method for a 3D bipedal robot with 14 joint actuators. The overall control law consists of a ZMP (zero moment point) controller, a swing ankle rotation controller and a partial joint angles controller. The ZMP controller guarantees that the stance foot remains in flat contact with the ground. The swing ankle rotation controller ensures a flat foot impact at the end of the swinging phase. Each of these controllers creates 2 constraints on joint accelerations. As a consequence, the partial joint angles controller is implemented to track only 10 independent outputs. These outputs are defined as a linear combination of the 14 joint angles. The most important question addressed in this paper is how this linear combination can be defined in order to ensure walking stability. The stability of the walking gait under closed loop control is evaluated with the linearization of the restricted Poincare map of the hybrid zero dynamics. As a result, the robot can achieve an asymptotically stable and periodic walking along a straight line. Finally, another feedback controller is supplemented to adjust the walking direction of the robot and some examples of the robot steered to walk along different paths with mild curvature are given.     

Walking of biped with passive exoskeleton: evaluation of energy consumption

The paper aims to theoretically show the feasibility and efficiency of a passive exoskeleton for a human walking and carrying a load. The human is modeled using a planar bipedal anthropomorphic mechanism. This mechanism consists of a trunk and two identical legs; each leg consists of a thigh, shin, and foot (massless). The exoskeleton is considered also as an anthropomorphic mechanism. The shape and the degrees of freedom of the exoskeleton are identical to the biped (to human)—the topology of the exoskeleton is the same as of the biped (human). Each model of the human and exoskeleton has seven links and six joints. The hip-joint connects the trunk and two thighs of the two legs. If the biped is equipped with an exoskeleton, then the links of this exoskeleton are attached to the corresponding links of the biped and the corresponding hip, knee, and ankle joints coincide. We compare the walking gaits of a biped alone (without exoskeleton) and of a biped equipped with exoskeleton; for both cases the same load is transported. The problem is studied in the framework of a ballistic walking model. During ballistic walking of the biped with exoskeleton, the knee of the support leg is locked, but the knee of the swing leg is unlocked. The locking and unlocking can be realized in the knees of the exoskeleton by any mechanical brake devices without energy consumption. There are no actuators in the exoskeleton. Therefore, we call it a passive exoskeleton. The walking of the biped consists of alternating single- and double-support phases. In our study, the double-support phase is assumed instantaneous. At the instant of this phase, the knee of the previous swing leg is locked and the knee of the previous support leg is unlocked. Numerical results show that during the load transport the human with the exoskeleton spends less energy than human alone. For transportation of a load with mass 40 kg, the economy of the energy is approximately 28%, if the length of the step and its duration are equal to 0.5 m and 0.5 s, respectively.     

Design and Control of 6-DOF Mechanism for Twin-Frame Mobile Robot

A new lightweight six-legged robot that uses a simple mechanism and can move and work with high efficiency has been developed. This robot consists of two leg-bases with three legs each, and walks by moving each leg-base alternately. These leg-bases are connected to each other with a 6 degrees of freedom (DOF) mechanism. While designing this robot, the output force, velocity, and workspace of various connection mechanisms were compared, and the results showed that good performance could be achieved with a serial/parallel hybrid mechanism. The serial/parallel hybrid mechanism consists of three 6-DOF serially linked arms positioned with radial symmetry about the center of each leg-base; each leg-base is composed of two active and four passive joints. Walking experiments with this robot confirmed that this mechanism has satisfactory performance not only as a walking robot, but also as an active walking platform. Furthermore, in this robot, the entire leg-drive mechanism acts as a 6-axis force sensor, and individual sensors at the feet are not necessary. The forces and moments can be calculated from the changes in the joint angles. Experiments conducted verified that smooth contact with the ground by the swing-leg and successful switching from swing to support leg can be achieved using this force control and force measurement method.