The two-degree-of-freedom cable pulley (2DCP) transmission system: An under-actuated and motion decoupled transmission for robotic applications. (June 2020)

• Record Type: Journal Article
• Authors: Rodriguez-Cianca, D.; Verstraten, T.; Rodriguez-Guerrero, C.; Jimenez-Fabian, R.; Näf, M.B.; Vanderborght, B.; Lefeber, D.
• Is Part Of: Mechanism and machine theory. Volume 148(2020)
• Publication Date: 2020-06
• Subjects: Cable-pulley transmission -- Remote actuation -- Motion decoupling -- Parametric model; Machine theory -- Periodicals; Machinery -- Periodicals; Machines -- Périodiques; Génie mécanique -- Périodiques; Machine theory; Machinery; Periodicals; 621.81
• DOI: 10.1016/j.mechmachtheory.2019.103765
• Languages: English
• ISSNs: 0094-114X

Abstract

Highlights: A method to guide a cable to decouple the motion of several joints is proposed. The 2DCP system can change its transmission angle. The transmission angle is decoupled from the input-output power transmission. A parametric model predicts the output torque regardless of the transmission angle. The 2DCP is useful in applications that involve close human-robot interaction. Abstract: Transmission systems with the ability to decouple the motion of several degrees of freedom (DoFs) can provide a solution for the coupling problem that arises between the joints of a kinematic chain when following a remote actuation approach. Additionally, they can be especially interesting in wearable robotic applications, such as exoskeletons, which benefit from the implementation of kinematic redundancy to compensate for joint misalignment and guarantee full human-robot kinematic compatibility. This paper presents the conceptual development and experimental validation of a novel cable-pulley system, the two-degree-of-freedom Cable-Pulley (2DCP) transmission, that, in contrast to common systems, allows to change the transmission angle between its input and output ports. The 2DCP includes one coupled DoF: the input and output port rotations, kinematically linked by the implemented transmission ratio, and a passive, decoupled, DoF that allows to change their relative orientations, i.e. the transmission angle. The concept, working principle, design equations, main mechanisms and prototype construction of the 2DCP are first presented in this paper. Experiments are finally conducted to characterize and model the mechanical properties of the transmission, confirming both experimentally and statistically its ability to transmit and re-direct the input power to the output port in a direction that can change over time without power loss, effectively decoupling both parameters.