弹簧刚度对被动步行的稳定性影响

由人类步行的生物力学研究得到启发，在被动双足步行机器人的髋关节处引入了扭簧，并通过仿真和试验研究了弹簧刚度对被动步行稳定性的影响.在仿真中，用胞映射方法计算被动步行机器人的吸引盆，并用吸引盆来衡量机器人的稳定性，研究了弹簧刚度对被动步行吸引盆大小的影响. 仿真结果表明, 吸引盆随着弹簧刚度的增大而增大. 在试验中，使机器人在各弹簧刚度参数下沿斜坡向下行走100次，记录下行走到头的次数作为稳定性的度量. 试验结果表明, 存在一个大小适中的弹簧刚度使机器人稳定性最大. 对弹簧提高机器人稳定性的原因进行了分析，对造成仿真与试验之间差异的原因进行了分析. 

THE EFFECT OF SPRING STIFFNESS ON THE STABILITY OF PASSIVE DYNAMIC WALKING

Compared with traditional biped robots, passive dynamic walker has simpler structure and higher energy efficiency. However, it has very weak tolerance for disturbances. Inspired by the biomechanics of human walking, we added a torsional spring at the hip of the passive dynamic walker to improve its stability. We studied the effect of spring stiffness on the stability of passive dynamic walking by simulations and experiments. In the simulations, the basin of attraction used as a measure for stability, was obtained with the cell mapping method. The effect of spring stiffness on the basin of attraction was then studied. The size of the basin of attraction increases with the increasing spring stiffness. In the experiments, we quantified the stability of each walker by observing passive walking trials down a gentle slope of finite length for 100 times and recording the fraction of trials which successfully walked to the end. The experimental results show that spring stiffness with a moderate value can induce maximal stability for passive dynamic walker. The hip moment contributed to the spring is quite similar to that of human in a walking cycle. This might indicate that the spring improves the stability. The spring torque in a whole walking cycle has positive effect on stability, which can be used to explain the simulation results. The discrepancy between simulations and experiments might be explained by the fact that the step length decreases with increasing spring stiffness, to induce the increasing chance of foot scuffing at mid-stance in experiments, which was ignored in simulations.