Quadruped robots are machines intended for challenging and harsh environments. Despite the progress in locomotion strategy, safely recovering from unexpected falls or planned drops is still an open problem. It is further made more difficult when high horizontal velocities are involved. In this work, we propose an optimization-based reactive Landing Controller that uses only proprioceptive measures for torque-controlled quadruped robots that free-fall on a flat horizontal ground, knowing neither the distance to the landing surface nor the flight time. Based on an estimate of the Center of Mass horizontal velocity, the method uses the Variable Height Springy Inverted Pendulum model for continuously recomputing the feet position while the robot is falling. In this way, the quadruped is ready to attain a successful landing in all directions, even in the presence of significant horizontal velocities. The method is demonstrated to dramatically enlarge the region of horizontal velocities that can be dealt with by a naive approach that keeps the feet still during the airborne stage. To the best of our knowledge, this is the first time that a quadruped robot can successfully recover from falls with horizontal velocities up to 3 m/s in simulation. Experiments prove that the used platform, Go1, can successfully attain a stable standing configuration from falls with various horizontal velocity and different angular perturbations.

翻译：四足机器人是为应对复杂严峻环境而设计的机械装置。尽管运动控制策略已取得进展，如何安全地从意外摔倒或计划性纵跳中恢复仍是一个未解决难题，尤其是在涉及高水平速度时更具挑战性。本研究提出一种基于优化的反应式着陆控制器，该控制器仅利用本体感知测量值，适用于在平坦水平地面自由落体的扭矩控制型四足机器人，且无需预知着陆面距离或飞行时间。该方法基于质心水平速度估计值，采用变高度弹簧倒立摆模型在机器人下落过程中持续重新计算足部位置。通过这种方式，四足机器人能够在各个方向上实现成功着陆，即使存在显著水平速度也能应对。实验证明，该方法可显著扩展传统空中阶段固定足部姿态策略所能处理的水平速度范围。据我们所知，这是首次在仿真中实现四足机器人从高达3米/秒水平速度的坠落中成功恢复。实验表明，所用平台Go1能从不同水平速度和角度扰动的坠落中成功过渡到稳定站立构型。