title: Compliant mechanisms in lunar surface exploration: design and technology considerations for dust mitigation
Creators: name: Budzyń, Dorota
Publisher: name: University of Glasgow
Year: 2024

description: The experience gained from Apollo lunar exploration and multiple robotic lunar missions has underscored the considerable challenges posed by the lunar environment for hardware operations. These challenges encompass a wide range of issues, including thermal extremes during the lunar day and night cycle, vacuum conditions limiting the choice of suitable materials (including lubricants), harsh radiation exposure, micro-meteorite impacts, and the prevalent issue of lunar dust and regolith. Lunar regolith, the surface material covering the Moon, consists of particles of varying dimensions, ranging from fine lunar dust with grain sizes measured in micrometres to larger pebbles and rock fragments. Lunar dust, in particular, has proven to be an exceptionally formidable obstacle for lunar exploration. The array of challenges it presents includes obstructed vision for both astronauts and cameras, potential inhalation and irritation of the respiratory system, loss of traction, false instrument readings, thermal control complexities, dust coating and contamination, abrasion, seal failures, and the vexing problem of clogged mechanisms. The primary focus of the work presented here lies in the realm of mechanism design, specifically targeting the pressing issue of mechanism clogging induced by the lunar dust. The solution proposed in this work can be characterised as implicit dust mitigation. It focuses on a deliberate design choice that employs compliant mechanisms to eliminate the most dust-sensitive components within mechanisms, namely, inter-element gaps. Unlike traditional mechanisms that rely on rigid-body joints, such as hinges and sliders, compliant mechanisms leverage elastic deformation to achieve motion. Consequently, they are free of the inter-element gaps susceptible to dust accumulation, which can lead to increased friction and eventual jamming. By replacing traditional tribological contacts with compliant hinges and flexures that facilitate motion through flexible deformation, this approach yields mechanisms that are inherently resistant to dust-induced jamming. However, the design of compliant mechanisms presents its own set of challenges. In this work, a range of design methodologies were explored, encompassing analytical and topology optimisation-based approaches. Additionally, various polymers suitable for additive manufacturing were examined in the context of their compatibility with the compliant mechanism design. The intricate relationship between material properties and design methodologies is discussed within this work, providing useful insight into the potential problems of various methodology and material choices. The culmination of these efforts resulted in the design, manufacturing, and testing of multiple compliant grippers. Early prototypes were tested to refine the methodology, test procedures, and ultimately design more sophisticated compliant grippers that aimed to emulate the functionality of the Apollo geological tool known as Tongs. The final design approach proposed here comprises a two-step process involving topology optimisation followed by an analytical re-design step. The latter is tailored towards reducing stress levels in the flexures and enhancing large-scale deformations. These advances were followed by a series of tests enhanced with the use of Digital Image Correlation tools, enabling the visualisation of deformation fields within the grippers. Finally, an additional set of tests was conducted using the lunar regolith simulant EAC-1A to validate the dust-resilient behaviour of the mechanisms and demonstrate their effectiveness in the lunar environment. This research not only contributes to addressing the specific challenges of lunar dust but also advances the broader understanding of compliant mechanisms, their design methodologies, and their applicability in lunar exploration.