In recent years, rover missions for exploring lunar or planetary surface has been attracting much attention over the world, culminating the success of the Sojourner rover which explored the Martian surface in 1997.
This paper proposes a new path planning method for navigation of planetary rovers, the surface environment of which is a natural terrain and described by a digital elevation map (DEM) . Given a DEM, a path from a start point to a goal is calculated based on the simple rover model which consists of three parameters. An obstacle map and a new concept of an extended elevation map defined in three dimensional space are introduced which provides the capability to use the DEM height information in three dimensional configuration space. With this extended elevation map, path planning is conducted by solving an optimization problem. Numerical simulations show the effectiveness of the proposed method.

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This paper presents a method to measure the plastic strain of steel specimens with no contact using the laser speckle method. This method is based on a phenomenon that the intensity distribution of the laser speckle changes depending on surface profile change occurred by plastic deformation. The intensity distribution of the laser speckle was analyzed quantitatively using an image processing system. The laser speckle pattern and surface profile were observed for specimens of three kinds of steels plastically deformed by static tension. The distribution of the speckle intensity was evaluated after smoothing by calculating correlation function. A new parameter to express the width of the distribution was derived. It was clarified that there is a fixed relation between speckle distribution and the magnitude of plastic strain and it is possible to estimate plastic strain using the speckle distribution. It was also found that the relation between speckle distribution and plastic strain is almost identical for three kinds of steels treated in this experiment.

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This paper describes a practical control scheme for autonomous retrieval of tumbling satellite with an onboard manipulator using a CCD camera. In the retrieval of a satellite, a reference trajectory for positioning the end-effector of manipulator is generated with time delay because of processing time for target motion estimator and manipulator controller. Consequently, the end-effector fails to capture the target, and the control system shows poor performance. To solve this problem, a control system is proposed, which utilizes predictive trajectory based on target satellite dynamics. The validity and the usefulness of the proposed control scheme are verified by computer simulations and experiments using 3-D hardware simulator with 9 degrees of freedom.

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This paper proposes a new mobility system for planetary exploration robot using springs and linear actuators. In microgravity environment, it is difficult to obtain the horizontal velocity, because the friction force between a robot and the ground is very small. By pushing the ground, however, the robot can not only hop, but also obtain the horizontal velocity. The proposed hopping robot consists of two masses, and can push the ground by using springs. The robot can hop from the stationary state by transforming the elastic energy to the kinetic energy using the sprigs and linear actuators. Furthermore the robot can land without bounding by transforming the kinetic energy to the elastic energy. The simulation studies and the ground experiments show the effectiveness of the proposed mobility system.

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顔料塗工紙の表面強度についてその発現機構や, ピッキングの発生場所の詳細な解析についてはこれまで充分な検討がなされていなかった。本報では, ピッキングの発生場所が塗工紙を作製する際の乾燥条件やラテックスのガラス転移温度によって, どう変化するか電子顕微鏡で観察を行った。
RI印刷機を用いてタック値の高い印刷インキを用いて1回の印刷でピッキングを発生させる方法 (1回印刷) と, タック値の低い印刷インキを用いて4回の重ね刷り印刷でピッキングを発生させる方法 (重ね印刷) でそれぞれピッキングの状態を観察した。
1回印刷の場合, ピッキングの発生場所は塗工層と原紙繊維の界面に限りなく近い塗工層の内部で発生していることが確認され, ピッキングの発生場所も発生形態も, 使用するラテックスのTgや塗工時の乾燥条件に偏らず同一であった。塗工紙の乾燥条件やラテックスのTgによって強度レベルは変化するものの, ピッキングの発生場所や発生形態はそれらに影響されないことが分かった。
重ね印刷の場合, ラテックスのTgによりピッキング発生場所の違いが観察でき, Tgが低いラテックスほどピッキングの発生場所が塗工層表面に近くなった。重ね印刷では, 塗工層中のポリマーがインキ溶剤を吸収し, 塗工層表面から徐々にポリマー自身の凝集力が低下してこのような現象が引き起こされたものと推定される。

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An in-situ observation of small planetary bodies (asteroids or comets) has been of great interest for planetary science. The authors have proposed a small rover for MUSES-C asteroid exploration mission of the Institute of Space and Astronautical Science. The proposed rover adopts a novel and innovative mobility that drives a rover by hopping, which has a lot of advantages under the micro-gravity environment on the surface of small planetary bodies. A test model of the proposed rover was developed and the micro-gravity experiments were conducted. This paper describes the experimental results, which are compared with the simulation analysis.

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Tumbling motion makes it difficult to retrieve a satellite with an on-board manipulator. This paper proposes a new control scheme of a space manipulator based on an approximate model for the dynamics of a tumbling satellite. The proposed model is described as a superposition of three rotational motions of constant angular velocities. Kalman filtering technique is adopted to estimate the target motion based on visual information. The parameters of the approximate model are calculated from kinematical constraints using estimated results. Thus, the capture planning becomes simple with the approximate model parameters. The motion of a grapple fixture along a particular principal axis of a target satellite nearly stops relative to the end-effector of a manipulator. In the control scheme, the rendezvous satellite and the manipulator make rotational motions of certain constant angular velocities based on the approximate model. The validity and the usefulness of the proposed scheme are verified by computer simulations and experiments using a 3-D hardware simulator with 9 degrees of freedom.

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This paper describes a retraction control scheme for a space manipulator after grasping a floating object in space. Many control methods for a pre-retracting phase have been proposed by other authors. However those for a retracting phase have been very few, and the essential problem which an object is moving had not been treated so far. Firstly we divide a retracting process into four phases, and clearly show the problems to be resolved. Secondly we derive a new kinematic equation which relates angular velocities of joints with the integral of force and moment at an end-effector in space. Thirdly a force control method is proposed by using that important equation, and the possibility to grasp within the admissible error is proved effective: This control method corresponds to a velocity control for an end-effector feedbacking the integral of force and moment considering the derived kinematic equation. Fourthly we apply that control method to a retraction control, and demonstrate the stability of the proposed control scheme. Finally the effectiveness of the proposed retraction control method is shown by computer simulations.

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An acquisition technique of autonomous distributed rule for posture control of Variable Geometry Truss (VGT) is suggested by applying the Genetic Programming (GP) method. Each control rule produced by GP consists of hierarchical tree structures. The main tree structure contains condition trees and rule selection trees as function nodes, and control trees as terminal nodes. The acquisition system trains individual rule by the posture control simulation for the randomly given initial postures, and evaluates the rule by the simulation of given test postures. The validity of the acquisition system is confirmed numerically by applying to the stiffness maximization of ten-module VGT.

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An autonomous distributed criterion to determine optimum postures of adaptive truss-type manipulators is suggested. A minimum compliance posture of variable geometry trusses for a given working load vector is realized by adjusting variable elements, where the adjusting values are determined independently according to the strain energy sensitivity of each truss part. The validity of the autonomous criterion is confirmed numerically by applying it to the configuration control of variable geometry truss containing ten adjustable elements.

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Hayabusa2 is a Japanese asteroid explorer which aims to get some fragments from the C-type asteroid ``Ryugu'' and bring them back to the Earth. It was launched in December 2014 and arrived at the target asteroid at the end of June 2018 after 3.5 years' interplanetary cruise using an Ion engine propulsion system. The authors developed two tiny twin rovers for Hayabusa2 spacecraft. The objectives of the rovers were performing two technical experiments on the asteroid surface. They had hopping capability fitted for the microgravity environment of small planetary bodies, which was to be evaluated on the asteroid surface. The rovers had full autonomy to move to as many different places as possible and make some observations such as taking images and directly measuring the surface properties. The fully autonomous capability was to be demonstrated on the asteroid surface. The rovers were deployed onto the Northern hemisphere of the target asteroid on 04:06, 21 September 2018 (UTC) at the altitude of approximately 50 meters above the surface. Both rovers made autonomous surface explorations by hopping as planned, which were evidenced by the status and image data transmitted from the rovers. This was the World first surface mobile exploration on small planetary body in our Solar System attained by unmanned robot, as well as the first surface mobile exploration on extraterrestrial body in our country. This paper describes the technical aspects of MINERVA-II rovers, followed by some actual behaviors of the rovers on the asteroid surface which illustlated the great achievments of the two technical challenges by the rovers.

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A method to localize a rover on a small planetary body has been proposed based on measurements of the round-trip propagation delay between the rover and the mother spacecraft. It provides the accurate position of the rover by estimating the rotational parameters of the planetary body. It assumes that the rotational parameters of the planetary body are time invariant. Some planetary bodies may not satisfy this assumption. In this paper, the method has been expanded so that it can be applied to the rovers on planetary body with precessional motion. In order to express the precessional motion of the planetary body, the state vector and the equation for the time update are modified. Numerical simulations assuming the rover on Itokawa-size asteroid have been conducted. These results suggested that the expanded method can provide accurate position of the rover in case that the precessional period is longer than 25% of the rotational period.

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