Wolfrom planetary gear trains for lightweight, human-centered robotics

Human-Robot Interaction (HRI) devices are becoming increasingly customary to assist humans, both in industrial and clinical environments. Traditional robotic gearbox technologies, like cycloid reducers or Harmonic Drives ©, perform well to solve the need for extreme precision and high speed of industrial robots, but when used in HRI devices they are usually forced above their limits, ultimately restraining the performance and the widespread use of such devices. A closer analysis of the specific needs behind the actuation for human limb assistance and replication highlights the differences with traditional robotic applications. Matching those needs with the main characteristics of different robotic gearboxes displays the limitations of traditional robotic transmissions, but it also unveils the potential of a virtually unexploited kind of planetary gear trains. This paper presents the prototype and associated first test results of the Wolfrom alpha-I concept. This novel concept demonstrates the application potential of Wolfrom-based planetary gear trains in HRI actuation.