Multi-Axis Force-Torque Sensors for Measuring Zero-Moment Point in Humanoid Robots: A Review

Recent advances in mobility, manipulation, and intelligence of robots have promoted the usability of humanoid robots to support humans in their daily lives in the future. The multi-axis force-torque sensor is an essential sensor for the biped humanoid robot to maintain balance during walking and running since it is used to calculate the zero-moment point, the criterion of dynamic stability. Forcetorque sensors will be widely used in the future because they are essential for service robots to interact with people in unstructured environments. However, due to special design considerations and requirements, it is difficult to find a suitable commercial force-torque sensor for biped humanoid robots and the price is very expensive. This paper reviews the multi-axis force-torque sensor used in current state-of-the-art humanoid robots based on the understanding of biped walking, zero-moment point, and ground reaction force. From an in-depth analysis of relevant information, sensor requirements are discussed with the robot performance. In addition, the structural design of the sensors is classified into four types and described in detail. This comprehensive review will facilitate the development of force-torque sensors in humanoid robots and will be helpful in extending their application in the various fields of service robots.