1. The Robotics Research Group, College of Engineering, Peking University, Beijing, People's Republic of China
2. Beijing Engineering Research Center of Intelligent Rehabilitation Engineering, Beijing, People's Republic of China
3. Beijing Innovation Center for Engineering Science and Advanced Technology (BIC-ESAT), Peking University, Beijing, People's Republic of China
4. Beijing Advanced Innovation Center for Intelligent Robots and System, Beijing Institute of Technology, Beijing, People's Republic of China
5. Robotics and Rehabilitation (ROAR) Laboratory, Department of Mechanical Engineering, Columbia University, New York, NY, USA