The surface of a minor body in space features a harsh terrain and microgravity. To explore such surfaces in detail, a robot with an appropriate moving mechanism is required. To this end, we proposed a robot that moves by gripping the surface like a rock climber. We focus on the robot's gait, where the motion of the idling arm generates the reaction force that acts on the gripper of the supporting arm. The reaction force needs to be controlled to maintain a grip without slipping. Therefore, we formulate a simultaneous control law that combines the tip position control of the idling arm with reactionless control by utilizing the reaction nullspace. Moreover, the validity of the control law was confirmed by an experiment involving an air floating system under microgravity. Furthermore, a planar simulation clarified that the robot can move continuously on an irregular terrain.

The surface of an asteroid features an irregular terrain and microgravity. Therefore, robotic exploration in an asteroid requires the adoption of an appropriate locomotion strategy. Moreover, an exploration robot is expected to be capable of moving to an area of scientific interest. In response to this, we have proposed a ground grip robot that moves by gripping the surface like a rock climber. By gripping the surface, the robot can prevent unintended flotation and rotation while propelling itself across the surface. When the idling arm is moved while the supporting arm's gripper is attached to the surface, all of the reaction forces act on the gripper. If the gripping force is to be exceeded, however, the robot could come adrift from the surface. In this paper, therefore, we propose a motion control method that does not act the reaction force on the gripper by utilizing the reaction null-space. Additionally, the tip position trajectory is generated as an ellipse to enable smooth movement and eliminate any frictional force. This control law was validated by a planar dynamic simulation. The simulation model assumes a dual-armed robot with three degrees of freedom (DOF) in each arm, while the uneven surface is simulated under certain conditions. As a result, the robot was able to move continuously with reactionless motion and the propriety of the control law was confirmed.

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Due to irregular terrain and micro-gravity in an asteroid, particular locomotion mechanism is required for exploring an asteroid by a robot. As one of the asteroid robots, a ground grip locomotion robot is proposed. One of the most important things for realizing the robot is development of the finger mechanism which can certainly grip an uneven surface. In order to do this, it is needed to understand frictional characteristics between the finger and the surface, and to formulate grip condition. Therefore, we conducted the experimental evaluation of gripping characteristics by measuring the coefficient of friction between several finger shapes and simulated ground. Moreover, the possibility of gripping was analyzed by conditional equation. In this paper, the experimental results confirmed that conic shape is effective for ground grip locomotion robot.

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