Propulsion Unit Control Method for Visualization of Grasping State of Earthworm-type Lunar Excavation Robot

Abstract

Investigation of the lunar subsurface environment is expected to lead to the elucidation of the origin of stars and the discovery of new resources. However, there are still many unknowns in this regard. In a previous study, we developed a drilling robot for lunar exploration and succeeded in drilling vertically up to 938 mm. However, control methods for the robot have not been studied in detail so far, and the grasping state of the propulsion unit during drilling has not been observed. In the study described in this paper, threshold coordination method for the current of the propulsion unit’s motors is introduced to achieve effective hole grasping and propulsion. Subsequently, gripping force and penetrating force characteristics of the propulsion unit are tested to understand the grasping state of the propulsion unit during drilling based on the current value and the angle information of the motor. Finally, in-pipe propulsion and excavation experiments were conducted. From the experimental results, we concluded that the proposed control method can be used to grasp the hole with changing hole diameter and monitor the grasping state of the propulsion unit in the hole.