Abstract

Controlling a biped robot to walk through rough terrains is crucial to the robot’s field application. For a human in the workplace, the ability to flexibly transfer motion while walking in some urgent circumstances is necessary. Explicitly, the according scenario can be dodging an approaching object or instantly modifying the target place to step on. The function is also important for humanoid robot workers. Therefore, we proposed a walking control framework that achieves three-dimensional (3-D) walking and transfers the whole body motion when the target stepping location is urgently changed. The proposed framework contains a motion planner which outputs the desired center of mass (CoM) and center of pressure (CoP) trajectories in 3-D space and a hierarchical whole body controller (WBC) that outputs corresponding whole body joints’ trajectories. In the motion planner, the CoM jerk for each loop is calculated by the Linear-Quadratic-Tracker (LQT), a variation of the Linear-Quadratic-Regulator (LQR). The LQT coefficients adapt to the adjusted step length, making the desired CoM and CoP trajectories respond flexibly to the change of target step-stone. In WBC, three levels of tasks are defined, which meet dynamic, kinematic, and viable contact constraints, respectively. The optimal joints’ angular accelerations are obtained by exploiting the nullspace of the first two levels tasks and by quadratic programming (QP) for the third-level task. In the simulations, our method is demonstrated to be effective for the robot to transfer the motion under urgent change of the target step-stone.

中文翻译：

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三维双足行走过程中目标台阶紧急变化下的运动过渡

摘要

控制双足机器人在崎岖地形中行走对于机器人的现场应用至关重要。对于工作场所的人来说，在一些紧急情况下灵活地行走转移运动的能力是必要的。明确地说，相应的场景可以是躲避接近的物体或立即修改要踩踏的目标位置。该功能对于人形机器人工人也很重要。因此，我们提出了一种步行控制框架，可以实现三维（3-D）步行，并在目标步行位置紧急改变时转移全身运动。所提出的框架包含一个运动规划器，用于输出 3D 空间中所需的质心 (CoM) 和压力中心 (CoP) 轨迹，以及一个分层全身控制器 (WBC)，用于输出相应的全身关节轨迹。在运动规划器中，每个循环的 CoM 加加速度由线性二次跟踪器 (LQT)（线性二次调节器 (LQR) 的变体）计算。LQT系数适应调整后的步长，使得期望的CoM和CoP轨迹灵活响应目标阶梯石的变化。在WBC中，定义了三个级别的任务，分别满足动态、运动学和可行的接触约束。通过利用前两级任务的零空间和第三级任务的二次规划（QP）来获得最佳关节角加速度。在模拟中，我们的方法被证明对于机器人在目标台阶紧急变化的情况下转移运动是有效的。