弹性接触对被动行走多体系统动力学与稳定性的影响研究

发布时间：2018-02-26 10:51

本文关键词： 多体动力学弹性接触被动行走稳定性吸引域　出处：《清华大学》2013年博士论文　论文类型：学位论文

【摘要】：被动行走是双足仿生行走的新概念。相比于传统的双足行走，其优点为能量消耗率很低。被动行走的仿真研究一般采用倒立摆模型假设，认为支撑足与地面铰接，足在地面上不发生弹起以及相对滑动。这种简化模型忽略了足与地面接触的过程。在各种多体系统中，碰撞与接触问题对于系统的动力学行为与稳定性有很重要的影响，实际的被动行走多体系统中足与地面接触也是行走过程的重要环节。为研究上述接触过程对行走的影响，本文首先建立了考虑足与地面弹性接触的二维被动行走模型，利用Hertz接触（弹簧阻尼）模型以及经过改进的Coulomb摩擦模型分别描述足与地面的法向接触力与切向摩擦力。通过动力学仿真，在寻找到周期行走步态的同时，得到了行走过程的接触力变化。通过改变模型的接触刚度系数、阻尼系数以及摩擦系数，发现接触阻尼系数与摩擦系数对于行走步态基本无影响，接触刚度系数对于行走的步态影响最大。接触刚度系数越大，，行走的平均速度和碰撞力峰值越大。通过增加仿真模型的斜面倾角，可得到单步周期、二步周期、多步周期等周期加倍的行走结果，这与Gacia等人的倒立摆模型结果类似。改变模型参数及接触参数，可得到参数对步态分岔点的影响。仿真结果表明接触刚度系数越大，步态分岔发生的倾角越小，其它接触参数对分岔点没有影响。进一步利用Floquet乘子以及胞映射方法对行走的稳定性研究。通过简单假设使动力学系统的状态空间降维，得到了3维胞空间下的被动行走吸引域。通过改变接触参数，发现接触刚度系数与接触阻尼系数对吸引域大小没有影响；摩擦系数越大，行走的吸引域越大。这说明摩擦力是考虑弹性接触的被动行走稳定性的决定因素。为验证仿真模型结果，建立了含有测试系统的简单直腿被动行走实验模型。利用陀螺仪测量双腿摆角，利用薄膜力传感器测量足地接触的法向力。在不同行走介质上测试的结果，说明了摩擦力对行走稳定性的决定作用。利用测试得到的行走步态以及接触法向力曲线，与仿真模型结果进行了对比，二者吻合较好。这说明考虑足与地面弹性接触的被动行走模型是更加接近真实物理模型的。
[Abstract]:Passive walking is a new concept of double foot bionic walking biped walking. Compared to the traditional, the utility model has the advantages of energy consumption rate is very low. Simulation Research on passive walking generally use the inverted pendulum model hypothesis, that the foot support is hinged with the ground, the foot does not occur on the ground bounce and relative sliding. This simplified model ignores the process of full contact with the ground. In a variety of multibody systems, collision and contact problem has an important effect on the dynamic behavior and stability of the system, the actual passive walking multi-body system midleg in contact with the ground. Walking is an important part of the process
For the process of the contact of walking effect, this paper consider the two-dimensional elastic contact of the foot and the ground passive walking model, using Hertz (contact spring damping) model and the Coulomb friction model is improved through the foot and the ground respectively describe the normal contact force and tangential friction force. Through dynamic simulation, looking into cycle walking at the same time, the contact force of the walking process changes. By changing the model of contact stiffness coefficient, damping coefficient, friction coefficient, damping coefficient and friction coefficient of contact found for gait has no effect, the contact stiffness coefficient has the greatest impact on the walking gait. The contact stiffness coefficient increases, the speed of walking the average and maximum impact force is greater.
The slant angle increase simulation model, can be obtained by single step cycle, two step cycle, the double step walking cycle cycle, and the Gacia's inverted pendulum model. Similar results change the model parameters and contact parameters, can get the influence of parameters on the gait of the bifurcation point. The simulation results show that the contact stiffness coefficient increases angle, gait bifurcation is small and the other contact parameters have no effect on the bifurcation point.
Study on the stability of the further use of Floquet multiplier and cell mapping method of walking. The state space dynamics system through simple hypothesis reduction, the passive walking 3 dimensional cellular space under the domain of attraction. By changing the contact parameters, found that the contact stiffness coefficient and contact damping coefficient has no effect on the size of the domain of attraction; friction coefficient large, walking more. This shows that the domain of attraction of the friction force is the decisive factor of passive walking stability considering elastic contact.
In order to verify the results of simulation models is established, containing the test system has the advantages of simple passive walking straight leg experimental model. Using the gyroscope to measure the swing angle of the legs, foot contact with film force sensor to measure the normal force. Test in different travel medium results illustrate the decisive role on the stability of walking friction. Using gait test get and contact normal force curve, compared with the simulation results of the model, two are in good agreement. This indicates that considering passive walking model of foot and ground elastic contact is more close to the real physical model.

【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TH113;TP242

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