Tribology in Space Robotic Actuators: Experimental Method for Evaluation and Analysis of Gearboxes

Abstract

Liquid lubricants are critical to enable long-life operation of high-performance machinery, such as geared actuators employed in robotics. In space applications, actuator gearboxes must operate in low temperatures, where liquid lubricants face inherent problems related to low temperature rheology. Heaters are relied upon to provide acceptable gearbox temperatures. Unfortunately, heating is energy-intense and does not scale well with increasing mechanism mass and performance. Effective boundary lubrication (BL), on the other hand, can minimize problems of low temperature rheology. BL relies on tribofilm formation over conventional fluid film separation. Effective space grade boundary lubricants can potentially allow for drastically reduced amounts of oil and the accompanying rheological problems. In this work, we describe the design of a methodology to evaluate and analyze tribology of actuator gearboxes operated under cryogenic oil-starved conditions in N2 atmosphere. The devised methodology enables research pertinent to space actuator tribology by accelerated testing and advanced analysis, as demonstrated by a lubricant candidate case study. Complementary microscopy techniques are discussed, and a novel methodology devised for gear internal microstructure analysis by X-ray microtomography (XMT) is presented.

The state of art on lubrication methods in space environment

“…Krick and Sawyer (2011) [186] have reported to deliver the pin-on disc tribometers to space stations in low earth orbit environment and it is going to experience UV, ionized radiation, AO, thermal cycling, microgravity, contamination from the meteoroid debris, etc The testing in real life conditions might produce useful data for future missions. Nyberg et al (2021) described the design of a geared actuator test rig (GATR) for the evaluation of actor gear box performance operating under oil starved condition, which is rig is equipped with 3D-profilometre, SEM, x-ray microtomography for the analyses [187].…”

Optimizing Light Intensity with PID Control

“…When discrepancies arise between the Present Value (PV) and the Set Point (SP), the system performs iterative error recalculation until stability is reached. This iterative process facilitates continuous error correction, ensuring alignment with the desired outcomes [18].…”