Humanoid robots are at high risk of hardware damage due to falls over. We have proposed the novel shock mitigation approach using a folding umbrella for humanoid robots, which offers both reversibility and compactness. In this study, we design umbrella closing and opening mechanisms to enable rapid opening of the umbrella, which is essential for shock mitigation when the robot falls over. We implement a mechanism that employs a clutch system activated by a vertical motion of a motor-driven rack, achieving both closing and rapid opening of an umbrella.