This paper presents the modeling and analysis of a novel moving mechanism "tumbling" for asteroid exploration. The system actuation is provided by an internal motor and torque wheel; elastic spring-mounted spikes are attached to the perimeter of a circular-shaped robot, protruding normal to the surface and distributed uniformly. Compared with the conventional motion mechanisms, this simple layout enhances the capability of the robot to traverse a diverse microgravity environment. Technical challenges involved in conventional moving mechanisms, such as uncertainty of moving direction and inability to traverse uneven asteroid surfaces, can now be solved. A tumbling locomotion approach demonstrates two beneficial characteristics in this environment. First, tumbling locomotion maintains contact between the rover spikes and the ground. This enables the robot to continually apply control adjustments to realize precise and controlled motion. Second, owing to the nature of the mechanical interaction of the spikes and potential uneven surface protrusions, the robot can traverse uneven surfaces. In this paper, we present the dynamics modeling of the robot and analyze the motion of the robot experimentally and via numerical simulations. The results of this study help establish a moving strategy to approach the desired locations on asteroid surfaces.

A wheeled mobile robot traveling on loose soil has wheels with grousers (i.e., lugs) on their surface to improve its mobility performance. Although previous studies have analysis and modeling of the mobility performance of a wheel with grousers, most of them did not cover the stress distribution of the wheels. In this study, we measured the three-dimensional forces acting on the grouser and three locations of the wheel surface, respectively. The stress distributions generated beneath the wheel with grousers at every angle of the wheel rotation were represented based on the three-dimensional force data. The stress distributions showed that the shear stress hardly affects the wheel surface between each grouser.

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 null-space. 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.

Owing to the irregular terrain and microgravity environment of an asteroid, an appropriate locomotion mechanism is required for exploring the asteroid by a robot. In this paper, a ground grip locomotive robot is proposed. One of the most important requirements of the robot is the development of the finger gripping mechanism that can be attached on an uneven surface. To meet this requirement, grip condition and friction characteristics between the finger and the surface need to be understood. Therefore, we conducted an experimental evaluation of gripping characteristics by measuring the coefficients of friction between several types of fingers and simulated grounds. Moreover, the range of possible gripping angles for simulated ground was determined by conditional equations and confirmed by an experiment of gripping the ground using an air-floating system. In this paper, conical shape is shown to be effective for ground grip locomotive robot.

This paper addresses a dynamic model and a control method of a space robot with a rigid manipulator and a flexible appendage. The control method has been developed for performing multiple tasks: end-point motion control and vibration suppression control of a flexible appendage. A simple dynamic model that considers coupling between the manipulator and the flexible appendage is proposed for the control method. The tasks are performed simultaneously on the basis of their order of priorities using a redundant manipulator. Additionally, because vibration suppression requires feedback of the state of the flexible appendage, a state estimator of the appendage using a force/torque sensor is developed. Finally, the proposed model, control method, and state estimator were verified experimentally using an air-floating system.

This paper discusses a vibration suppression control method for a space robot with a rigid manipulator and flexible appendage. A suitable dynamic model that considers the coupling between the manipulator and flexible appendage was developed for the controller to accomplish the vibration suppression control of the flexible appendage. The flexible appendage was modeled using a virtual joint model, and the control method was developed on the basis of this model. Although this type of control requires feedback of the flexible appendage state, its direct measurement is generally difficult. Thus, an estimator of the flexible appendage state was constructed using a force/torque sensor attached between the base and flexible appendage. The control method was experimentally verified using an air-floating system.

This paper presents the modeling and analysis of ciliary micro-hopping locomotion actuated by an eccentric motor, for enabling mobile robots to explore asteroids. Under the proposed system, elastic cilia are attached to the surface of the robot; this arrangement should enable the robot to have better mobility in a microgravity environment. However, in the development of the ciliary micro-hopping mechanism theoretical modeling and analysis of the interactive mechanics between the cilia and the environment pose technical challenges that need to be addressed. In this paper, we present the dynamics modeling of the ciliary micro-hopping locomotion actuated by an eccentric motor, along with its experimental validations and numerical simulations. The results of this study contribute to the design optimization of both the cilia mechanism and the motor control scheme.

Rovers that are used to explore craters on the Moon or Mars require the mobility to negotiate sandy slopes, on which slippage can easily occur. Such slippage can be reduced by actively readjusting the attitude of the rovers. By changing attitude, rovers can modify the position of their center of gravity and the wheel-soil contact angle. In this study, we discuss the effects of attitude changes on downhill sideslip based on the slope failure mechanism and experiments on reconfiguring the rover attitude and wheel angles. We conducted slope-traversing experiments using a wheeled rover under various roll angles and wheel angles. The experimental results show that the contact angle between wheels and slopes has a dominant influence on sideslip when compared with that of readjusting the rover's center of gravity.

The surfaces of both the Moon and Mars are covered with loose soil, with numerous steep slopes along their crater rims. Therefore, one of the most important requirements imposed on planetary rovers is their ability to minimize slippage while climbing steep slopes, i.e., the ability to generate a drawbar pull with only a small amount of slippage. To this end, the wheels/tracks of planetary rovers typically have parallel fins called lugs (i.e., grousers) on their surface. Recent studies have reported that these lugs can substantially improve the traveling performances of planetary rovers. Therefore, in this study, we conducted experiments using lightweight two-wheeled and mono-tracked rovers to provide a quantitative confirmation regarding the influence of lugs on the traveling performances of planetary rovers. Based on our experimental results, we confirmed that, although an increase in the number of lugs contributes to the high traveling performance of wheeled rovers, it does not contribute much to that of tracked rovers. Furthermore, an increase in lug height improves the traveling performances of both types of rovers.

Future planetary rovers are expected to probe over steep sandy slopes, such as crater rims, where wheel slippage can be a critical issue. One solution to this issue is to mount redundant actuators on the locomotion mechanisms of the rovers such that they can actively reconfigurate themselves to adapt to the driven terrain. In this study, we propose a mechanical model of a rover based on a wheel-soil contact model combined with the classical terramechanic theory. The effects of the rover reconfiguration on its slippage tendencies are analyzed based on slope traversing experiments and numerical simulations. The validation of the proposed contact model is also discussed based on experimental and numerical simulation results. According to the experimental results, both longitudinal and lateral slippages are greatly reduced by tilting the rover in an uphill direction. The results of the numerical simulation match the experimental results quantitatively, and indicate the possible need to include a slope failure model.

This paper presents the impedance-based contact control of a free-flying space robot utilizing a compliant wrist for non-cooperative satellite capture operation. An open loop impedance control law based on contact dynamics model is introduced to realize a desired coefficient of restitution defined between a manipulator hand of a space robot and a contact point on a free-flying target. The coefficient of restitution and the damping ratio are expressed as a function of contact and impedance parameters; and hence, the impedance parameters are tuned by setting a desired coefficient of restitution and a desired damping ratio. The collision experiment using twodimensional microgravity emulator, called air-floating test bed, verifies that the proposed open loop control law is capable of realizing a desired coefficient of restitution with fairly small errors.

This paper describes the mathematical modeling and the propulsive characteristics of a novel robot driven by Archimedean screw mechanisms, named Screw Drive Rover. For secure locomotion on soft soil, the proposed rover would become one of the good solutions because of its robustness to slipping and getting stuck in the soil. Furthermore, the rover is expected to move in various directions by using the dual screw units. However, the interaction between such screw unit and the surrounding soil is quite complicated and remains undefined. So, this paper attempts to model the tractive effort of the rover on the soil. The mathematical modeling is newly developed based upon terramechanics, addressing soil-vehicle interactive mechanics. Finally, the validity of the proposed model is demonstrated by simulation analyses.

Subsurface exploration on the Moon is a significant mission for future space developments. The authors have studied an autonomous robotic explorer which can burrow into the soils. This paper focuses especially on the excavation mechanism of a burrowing robot for near-future lunar subsurface exploration. The main objective of the proposed robot is to bury a scientific observation instrument, such as a long-term seismometer under the lunar surface, which is covered with very compacted lunar regolith. Therefore, an efficient drilling mechanism is required. In this paper, the authors propose a non-reaction screw drilling mechanism with double rotation, which is called the contra-rotor screw. This paper also evaluates the feasibility and effectiveness of the proposal of a burrowing robotic system through some experimental analyses.