1. Humanoid Robot Innovation Center, UBTECH Robotics, Shenzhen, Guangdong 518000, P. R. China
2. Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, P. R. China
3. School of Artificial Intelligence, Faculty of Electronic Information and Electronic Engineering, Dalian University of Technology, Dalian 116000, P. R. China
4. Research Institute, UBTECH Robotics, Shenzhen 518000, P. R. China