For the on-orbit servicing missions of spacecraft, space robot is considered as one of the most promising approaches. Many on-orbit servicing missions are successfully accomplished and most of these missions are designed to service cooperative targets only. Some of the target is non-cooperative spacecraft with unknown motion and kinematics properties. On-orbit servicing is still a challenging research area. The challenge is to ensure the servicing spacecraft safely and stabilize it for subsequent servicing. In order to expand space robot workspace and its task function, this paper presents a new type of space climbing robot which can be carried on mechanical arm. It can climb onto the target spacecraft for repairing, rescuing and removing orbital debris when the connection is established between the space manipulator and the target spacecraft. This robot mobile system is composed of piezoelectric actuation leg, micro adhesive feet, ejector and manipulator. The robot’s crotch joint and ankle joint both have two degrees of freedom with Roll-Pitch organization. In the environment of zero-gravity the obstacles on the target can be crossed by space climbing robot through wriggle movement and turnover movement. The gripping force of the robot is supplied by the adhesive capacity of the robot feet while robot climb along the surface of target spacecraft with weightlessness. The research of its adhesion mechanism is the basis of robot feet design and motion control. The design of robot feet micro array structure imitates the adhesion mechanism of gecko seta. A contact model between the robot feet and spacecraft surface is proposed. A single seta’s DEM (Discrete Element Method) model is set up by stacking micro particles, on the software platform of EDEM. EDEM is a software for discrete element analysis. The attachment and the detachment process of a single seta in different slope angle and its adhesion properties are simulated by using JKR model which is a classical contact mechanics model. The simulation demonstrate that the single seta’s gripping force with 90 degree slope angle is about 20% of the gripping force with 30 degree slope angle. The fiber structure was destroyed by large pressure making failure to its adhesion properties when the slope angle is zero. So the different ways of movement can achieve different adhesion properties of single seta. When the movement of micro array structure is determined, in order to improve the robust adhesion properties, well stability and excellent adaptability of the micro array structure, the structure parameters of seta is optimized. The structure parameters include the cylinder radius, length-diameter ratio and arrangement density of the micro array structure. A group of micro array structure optimized parameters is given according to the DEM comparing simulations with different structure parameters. This work propose a novel adhesion concept for climbing robot in space environment, and the stable attaching and easy detaching mechanism of the robot is also given.
Permanent Magnetic System Design for the Wall-Climbing Robot
