Study on principle of optimal control for energy-efficient walking systems

从理论和实验两方面研究了机器人两足步态的动力学生成和步态效率的提高。经验表明，作为被动动态步行者特征的足部凹凸曲线对提高步行速度有重要作用。我们从数学上阐明了半圆形脚的影响；在站立阶段充当虚拟踝关节力矩，减少足跟撞击造成的能量耗散，并通过数值模拟证实了它们显著提高了步态效率。参数激励动态双足行走也是我们的主要研究课题。我们最终完成了一个实验步行机，并通过调整物理参数和控制参数，实现了其稳定的水平行走。实验结果在国际上得到了高度评价。在理论研究中，我们考虑通过驱动膝关节来实现参数化激励，并成功地将其应用于水平步态生成中。我们进一步提出了几种先进的方法；基于机器人质心上下运动的参数激励和膝关节逆弯曲的鸟状体行走，比较了它们的步态效率。此外，我们还从机械能平衡的角度研究了极限环步行者的步态稳定性。然后，我们确定了系统地实现这种能量平衡所需的条件，并阐明了它们的物理意义。我们还考虑了采用髋部二分机制（BHM），在不破坏其自然动力的情况下为被动动力步行者增加上半身。通过阐明结合BHM的机器人驱动机构，我们成功地实现了其高效水平的动态行走。在整个研究过程中，我们对节能和无zmp机器人如何产生动态双足步态提供了新颖的见解和深刻的理解。

We have studied robotic biped gait generation based on its dynamics and improvement of the gait efficiency theoretically and experimentally. It is empirically known that the convex curve of the foot, which characterizes passive-dynamic walkers, has important effects on increasing the walking speed. We mathematically clarified the effects of semicircular feet; acting as the virtual ankle-joint torque during the stance phase and reducing the energy dissipation caused by heel strikes, and confirmed that they dramatically improve the gait efficiency through numerical simulations. Parametrically excited dynamic bipedal walking is also our main research subject. We finally completed an experimental walking machine and succeeded its stable level walking by adjusting the physical and control parameters. The experimental result was highly-appraised internationally. In the theoretical investigation, we have considered to achieve parametrically excitation by actuating the knee joint, and successfully applied the effect to level gait generation. We further proposed several advanced methods; parametric excitation based on up-and-down motion of robot's center of mass and ornithoid walking by inverse knee-joint bending, and compared their gait efficiency. Furthermore, we have investigated the gait stability of limit cycle walkers from the viewpoint of mechanical energy balance. We then identified the conditions necessary to systematically achieve this energy balance and clarified their physical meanings. We also considered applying a bisecting hip mechanism (BHM) for adding an upper body to passive-dynamic walkers without destroying their natural dynamics. By clarifying the robot's driving mechanism incorporating the BHM, we successfully achieved its efficient level dynamic walking. Throughout our investigations, we provided novel insights and deep understandings into how energy-efficient and ZMP-free robots can generate a dynamic bipedal gait.