# Stochastic Models and Control of Anchoring Mechanisms for Grasping in Microgravity
## 1 Introduction
Even if one of the microspines captures the asperity, other microspines still have the opportunity to grasp asperities when continuously pulling the microspine array. Therefore, determining the stiffness of the microspine and the microspine array is the basis of establishing the grasping model. [PERSON] first defined nine elements in the microspine stiffness matrix [32; 33]. The microspine stiffness matrix for a crawling robot was directly given. However, there is no specific stiffness model in the paper. [PERSON] put forward a grasping model based on the microspine, and measured the stiffness of the microspine by experimental method [34]. The elastic microspine can still be stretched after adhesion, so its stiffness model is an important factor to determine adhesion. Therefore, [PERSON] developed an accurate stiffness model of the microspine and combined it with the grasping model of the microspine array. [PERSON] and [PERSON] made detailed observations on the surface of Ryugu and comet [35; 36]. The surfaces of asteroids may be covered with boulders, craters, and other landforms, while comets may be covered with rough and porous materials. These pores are usually fragile. Therefore, the adhesion of the anchoring mechanism should be controllable in order to grasp the pores without damaging them. [PERSON] tested the adhesion of the anchor mechanism for asteroid exploration, and proposed a method for the desorption of the anchor mechanism [37]. [PERSON] proposed a motion control method based on a hexapod robot [20; 38]. Limbs reacted to the friction under various conditions, and force closure conditions of robot motion were established. The mission of asteroid-exploration robots is not only to land on asteroids, but also to move and sample on asteroids. The role of the anchoring mechanism in the movement of the asteroid-exploration robot should be focused. The anchoring mechanism mainly undertakes two tasks. When the asteroid-exploration robot moves, the anchoring mechanism grasping the ground should provide stable and sufficient adhesion to prevent the robot from flying into space. At the same time, the anchoring mechanism mounted on the swing phase leg should quickly establish adhesion to ensure the stability of the asteroid-exploration robot. Obviously, the motion of the asteroid-exploration robot needs to be further studied. Considering the application of the microspine in the anchoring mechanism, this paper proposes grasping models for the microspine array and a control method for the anchoring mechanism. The article is arranged as follows: Section 2 describes the structure and working principle of the anchoring mechanism. Section 3 establishes stochastic models for grasping. Then the stiffness model of the microspine is established. The grasping cloud diagram of the anchoring mechanism is drawn. Section 4 analyzes potential problems in the movement of the asteroid-exploration robot, and the collision avoidance control method of anchoring mechanism in the movement is proposed. In Section 5, a walking experiment of the prototype is carried out, and the experimental results are analyzed. Section 6 is the conclusion.