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恶劣环境而设计的机器装置。尽管运动控制策略已取得显著进展，但在意外跌落或规划弹跳场景中实现安全恢复仍是一个开放性问题，尤其当涉及高速水平运动时更为困难。本文提出一种基于优化的反应式落地控制器，该控制器仅利用本体感知信息，适用于在平坦水平地面自由落体的力矩控制型四足机器人，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，采用可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端位置。通过这种方式，四足机器人可随时准备在所有方向实现成功着陆，即使存在显著水平速度。实验表明，该方法能显著扩展传统空中阶段保持足端不动策略可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成功恢复水平速度达3米/秒的跌落。实验证明，本研究所用平台Go1能够从不同水平速度及多种角度干扰的跌落场景中成功恢复至稳定站立姿态。