Proceedings of the
9th International Conference of Asian Society for Precision Engineering and Nanotechnology (ASPEN2022)
15 – 18 November 2022, Singapore
doi:10.3850/978-981-18-6021-8_OR-02-0208
Investigation to Enhance the Actuation Force Transmission of Cable-Driven Continuum Manipulators with Tethering Lines
Engineering Cluster, Singapore Institute of Technology, 10 Dover Drive, 138683, Singapore
ABSTRACT
Inspecting confined spaces at elevated locations such as pot bearing housings in railway viaducts are challenging. Elevated work platforms are typically used to hoist people and equipment to conduct the inspection manually, which are often time-consuming, laborious and at times, physically inaccessible. A unique combination of an aerial drone, integrated with a lightweight cable-driven manipulator and a ground unit containing the cable winching actuators and the motion control system, is proposed to overcome this challenge. The winching cables in the manipulator are routed from the ground unit using tethering lines based on the Bowden cable concept. However, this results in high loss in force transmission due to the excessive amount of both static and dynamic friction between the cables and the sheath over long lengths, typically 10 to 15 metres, as required by the application scenario. This paper focuses on the investigation of designing tethering lines with high force transmission, through the use of Design-of experiments to identify relevant and dominant design variables for design optimization. The identified design variables consisted of the materials for both sheath and actuation cables, to the type of lubricant used to coat the sheath, the cable pretension and the cable speed. Based on an experimental test-bed that compared the cable tension readings, before and after, passing through the tethering line, the conclusion indicated that an enhanced design results with the use of SP41 Bowden sheath, an uncoated steel cable and applying silicone lubricant on PTFE tube, which improved the force transmission efficiency by 23%, 18% and 2%, respectively. Also, reducing the cable pretension from 25N to 9N and reducing the cable speed from 30mm/s to 5mm/s improved the force transmission efficiency by 1% and 5%, respectively. These results facilitated in selection appropriate materials for the tethering line and cable winching settings, which culminated in enhancing the force transmission through the winching cables.
Keywords: Cable-driven robots, Continuum robots, Force transmission efficiency, Design of Experiments.
Engineering Cluster, Singapore Institute of Technology, 10 Dover Drive, 138683, Singapore
ABSTRACT
Inspecting confined spaces at elevated locations such as pot bearing housings in railway viaducts are challenging. Elevated work platforms are typically used to hoist people and equipment to conduct the inspection manually, which are often time-consuming, laborious and at times, physically inaccessible. A unique combination of an aerial drone, integrated with a lightweight cable-driven manipulator and a ground unit containing the cable winching actuators and the motion control system, is proposed to overcome this challenge. The winching cables in the manipulator are routed from the ground unit using tethering lines based on the Bowden cable concept. However, this results in high loss in force transmission due to the excessive amount of both static and dynamic friction between the cables and the sheath over long lengths, typically 10 to 15 metres, as required by the application scenario. This paper focuses on the investigation of designing tethering lines with high force transmission, through the use of Design-of experiments to identify relevant and dominant design variables for design optimization. The identified design variables consisted of the materials for both sheath and actuation cables, to the type of lubricant used to coat the sheath, the cable pretension and the cable speed. Based on an experimental test-bed that compared the cable tension readings, before and after, passing through the tethering line, the conclusion indicated that an enhanced design results with the use of SP41 Bowden sheath, an uncoated steel cable and applying silicone lubricant on PTFE tube, which improved the force transmission efficiency by 23%, 18% and 2%, respectively. Also, reducing the cable pretension from 25N to 9N and reducing the cable speed from 30mm/s to 5mm/s improved the force transmission efficiency by 1% and 5%, respectively. These results facilitated in selection appropriate materials for the tethering line and cable winching settings, which culminated in enhancing the force transmission through the winching cables.
Keywords: Cable-driven robots, Continuum robots, Force transmission efficiency, Design of Experiments.
