Abstract
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.
Highlights
Human-Robot Interaction (HRI) devices, like exoskeletons or actuated prostheses, are increasingly common in manufacturing environments and clinical applications [1, 2]
We analyse the needs of HRI actuation in the example of the ankle-prostheses actuation. We demonstrate how these needs force current robotic technologies beyond their possibilities, and how the extreme versatility of planetary gear trains can be used to design transmissions better aimed at the needs of HRI actuation
The possibility to manufacture gears with increasingly high precision has paved the way for the use of low-loss gears: balancing approach and recess paths, while simultaneously optimizing other parameters like contact ratio, pressure angle or teeth module, allows to improve the meshing efficiencies of involute gears by up to 70% [20]. Applying these advances to Wolfrom planetary gear trains (PGTs) could make high gear ratios compatible with maintaining good efficiencies over a very broad range of operating conditions, resulting in a transmission extremely well suited for HRI actuation
Summary
Human-Robot Interaction (HRI) devices, like exoskeletons or actuated prostheses, are increasingly common in manufacturing environments and clinical applications [1, 2]. The performance of such devices is currently strongly limited by the confined possibilities of their actuators in terms of mass, compactness or efficiency [3]. Harmonic Drives©, cycloidal reducers and, to a lesser degree, planetary gear trains (PGTs), have established themselves as the dominant transmission technologies [6]. The structure of the paper is as follows. We demonstrate how these needs force current robotic technologies beyond their possibilities, and how the extreme versatility of planetary gear trains can be used to design transmissions better aimed at the needs of HRI actuation. The conclusions and the list of references close the contents of this paper
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