As the subway roared into Tokyo’s Tsukishima Station a gust of wind tossed up a stray face mask, sending it sailing above the platform.

Hisashi Taniguchi watched the piece of fabric fluttering about. He immediately pictured in his mind a microscopic view in which the wind dispersed — in the air he was breathing — countless viral particles that had been trapped between the mask’s filters.

There needs to be an efficient system to disinfect these public spaces, he thought. This was back in March, when the spread of COVID-19 was just starting to pick up speed in the capital. Taniguchi, founder and CEO of Tokyo-based robotics firm ZMP Inc., immediately got to work.