大槻 真嗣

JAXA is developing a mobile rover to lunar surface exploration or base construction as a follow-on KAGUYA. Because the lunar surface is covered by regolith, implying an irregular and rough terrain, the rover has difficulty in mobility. Therefore a new low-pressure wheel is recommended for high mobility performance and low power consumption with a less complex mechanism. A low-pressure wheel can change its contact shape and pressure distribution to account for terrain. In this paper, the procedure for the measurement of mobility parameters like contact pressure on the deformable terrain, and a contact mobility model for low-pressure wheels are presented. This measurement is valuable for analyzing the interaction between a low-pressure wheel and the deformable terrain.

Supposing a space mission of setting monitoring devices at suitable positions on the moon, we discuss how to apply a casting manipulation to the mission. This paper addresses a mechanism of a casting manipulator system and control method to launch a penetrator to the desired position. First, we classify launching methods, and focus on a method by using rotation of a boom. We then propose the mechanism that keeps a posture of the penetrator equipped at the tip of the boom constant for the absolute coordinate system during its rotation. This mechanism prevents the wire which connects the penetrator and the robot's base from winding the boom. Analyzing a position error of landing point caused by delay of releasing the penetrator, we propose the motion control of the boom to reduce the error. Finally, we develop the system and verify the effectiveness of the proposed method.

On the landing of a spacecraft, a large shock load leads to undesirable responses, such as rebound and trip. The authors have discussed the control problem of these shock responses by momentum exchange impact dampers (MEIDs). The optimal design parameters of MEIDs for the landing of a spacecraft are investigated. The parameters are crucial for applications of MEIDs. This paper discusses the parameters of MEIDs with single-axis falling type problem, which is the most fundamental problem. It is found that the rebound height is proportional to the mechanical energy of the spacecraft. Thus, the optimal design parameters of the MEIDs correspond to the parameters that minimize the mechanical energy. Then, in order to improve the performance of the MEIDs, a novel MEID - HMEID (Active/Passive-Hybrid-MEID) has been proposed. The HMEID combines actuators with passive elements such as contact springs. Based on the optimal design result of the MEIDs, a stiffness control is applied to the HMEID in order to suppress the mechanical energy further. Simulation studies reveal that the HMEID can effectively reduce the influence of shock responses. The robustness of the HMEID against the stiffness of the landing ground is shown. The feasibility of the HMEID is also discussed. The effectiveness of the HMEID is superior to that of PMEID, even if the actuator has a dynamics with a large electric time constant or force constraint.

JAXA is developing a mobile rover to lunar surface exploration or base construction as a follow-on KAGUYA. Because the lunar surface is covered by regolith, implying an irregular and rough terrain, the rover has difficulty in mobility. Therefore a new low-pressure wheel is recommended for high mobility performance and low power consumption. A low-pressure wheel can change its contact shape and pressure distribution to account for terrain. In this paper, the procedure for the evaluation of drawbar pull calculated by shear stress on the deformable terrain is presented. This procedure is valuable for analyzing the interaction between a low-pressure wheel and the deformable terrain.

In this paper, a comprehensive wheel model for both flexible/rigid wheels driving on deformable terrain is developed. The wheel model exploits a terramechanics-based approach with taking account of pressures generated by wheel elasticity as well as terrain stiffness. Deflection of a (semi-) flexible wheel depends on a relative pressure between the wheel and terrain: the wheel will be significantly deformed on rigid terrain whereas it will be hardly/slightly deformed on soft terrain. The wheel-terrain interaction in the proposed model is divided into three contact sections: wheel front section, wheel deflected (flat) section, and wheel rear section. The stress distribution at each contact section is formulated, and then, the traction force of the wheel is obtained as an integral of normal and shear stresses generated at each section. Simulation studies with varied wheel pressures, such as flexible, semi-flexible, and rigid wheels, are conducted to validate the proposed model. Also, traction performances of flexible/rigid wheels are compared based on a metric called tractive efficiency. The simulation results provide an important finding in terms of an optimal wheel pressure of flexible wheel for better traction.

This paper presents the synthesis procedure of an input profile for a motion control system to simultaneously reduce sinkage and vibration in a planetary rover. The sinkage of the rover changes depending on the degree of a contact force against loose soils in surface of a planet. Through the experiments using the lunar regolith simulant, it is confirmed that the sinkage is largely concerned with acceleration and deceleration in a driving mechanism. Hence, we proposes the method to suppress the sinkage by appropriately designing the acceleration profile with an asymmetric shape. Moreover, the vibration due to flexibility of the wheel is induced by self-motion and we verify the vibration reduction using the command shaping method through the experiment. Consequently, this paper presents the easy design procedure of the acceleration profile and the valuable experimental results.

In the lunar-planetary exploration, most of landers made a landing on flat areas of surface, because there are a lot of rocks craters and hills on lunar-planetary surface. For the next generation lunar-planetary exploration, the development of a highly accurate landing technology is demanded to land on the complex terrain. The navigation-guidance technology and hazard avoidance have been studied for the safe landing. Moreover the development of landing leg is required for the safe landing in the final phase of landing sequence. This paper presents the development of experimental system of active landing leg, and examine the landing shock response. In addition, we consider the effectiveness of active landing leg and the application to the control method of lander's overturn prevention.

Copyright © 2010 by the Japan Society of Mechanical Engineers. This paper proposes the synthesis procedure for the motion control system to simultaneously reduce slippage and vibration in a planetary rover. It is confirmed that the slippage generating in early phase of the rover motion is involved with acceleration and deceleration of the driving mechanism. The vibration due to flexibility of the rover is also induced by self-motion, that is acceleration and deceleration. Therefore, in this paper, we focus on the design of the acceleration target for the control system. The acceleration profile is then derived only by solving a regulator problem with an initial velocity and taking account of the maximum value in acceleration.

This paper presents the manipulator with the new joint which can passively switch free state to drive state and vice versa. The manipulator with the free-state joint is categorized as a system subjected to a nonholonomic constraint; hence, its smooth feedback control cannot be implemented. In this paper, the issues on its control are clarified through the test with the experimental setup of the manipulator with a free joint. The manipulator with the switching joint is also developed and its effectiveness is verified through the experiment. Consequently, the trivial actuation using the proposed joint accomplishes more precise positioning in the experiment.

In lunar and planetary exploration, a spacecraft is required to select and land in a safe area autonomously. For this purpose, hazard recognition, and obstacles detection methods using a three dimension elevation map constructed from laser range data has been proposed. However, the hardware of laser sensor is generally heavy, consumes a lot of power, and requires a long time to scan a large area. On the other hand, a camera is relatively small and has lower power consumption. Therefore, we propose a method of hazard recognition by using shadows, terrain features, and a priori information such as sun angle or geological knowledge of an image, without the need to construct a three dimensional elevation map. The method detects obstacles like craters and rocks the same way that human intuitively finds obstacles. Concretely, the method detects the edge of the obstacles (such as craters and ridge) by spatial difference of brightness obtained from an image. From shadow and sun light direction, some obstacles like large rocks and craters can be detected. The paper shows the effectiveness of the proposed method by simulation. Copyright ©2010 by the International Astronautical Federation. All rights reserved.

On the landing of a spacecraft, a large shock load leads to undesirable responses, such as rebound and trip of the spacecraft. In this paper, the authors discuss the control problem of these shock responses by means of momentum exchange impact dampers (MEIDs); particularly AMEID (Active-MEID). The MEID is classified into two types. One is a PMEID (Passive-MEID) that is composed of passive elements. The other one is the AMEID that includes active actuators. The AMEID can greatly reduce the influences of shock vibration. First of all, the authors design landing systems with MEIDs for simulations and conduct their modeling as two-legged system. The PMEID mechanism is a one-degree-of-freedom vibratory system. The AMEID mechanism utilizes voice coil motors as actuators in addition to the PMEID components. In order to compare the effectiveness of control systems, we simulate the following three cases of the systems: without MEID, with PMEID, and with AMEID. By the result of simulations, it was verified that the AMEID was superior in the control of spacecraft landing responses such as rebound and trip. Copyright ©2010 by the International Astronautical Federation. All rights reserved.

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.

JAXA is planning moon exploration missions following Kaguya (SELENE), whose missions include technology demonstrations, scientific observations, investigations for future moon utilization, and social or political purposes. As the next step of moon mission, SELENE-2 is planed and phase-A study of it has been conducted since the summer of 2007. SELENE-2 will demonstrate precision landing including hazard avoidance, surface mobility, and night survival technologies. For science, in-situ geological and geophysical observations are essential to improve the knowledge on the origin and the evolution of the moon. Investigations of surface environment and possible in-situ resource will contribute future human exploration. International coordination and contribution arc also important aspect of SELENE-2. In this paper, recent study status of SELENE-2 is presented.

This paper proposes the synthesis procedure for the motion control system to reduce slippage in a planetary rover. The slippage in the rover is mainly due to degree of contact force against the loose soil on the planetary surface. In this paper, particularly, it is confirmed that the slippage generating in early phase of the rover motion is involved with acceleration and deceleration in the driving mechanism through the experiment. Hence, we propose the command shaping method of the target acceleration to prevent the increase of the slippage and the acceleration profile is then derived only by solving a regulator problem with an initial velocity and taking account of the maximum value in acceleration.

This paper describes an application of conventional terramechanic contribution to mobile robots or vehicles in rough terrain. Terramechanics, addressing the interactive mechanics between a vehicle and a terrain, has mainly affected machines for agriculture, construction or planetary exploration. However, it is not clear that wheeled locomotion is able to cope with a critical situation getting stuck into soil. So, the authors elaborate the application of established wheel models in terramechanics to discuss an avoidance capability of such situation. Further to this, different characteristics of a single wheel and a multi-wheeled robot are presented. In this paper the interpretation of the conventional studies and experimental remarks is noted based on simulation analyses.

本論文では月や火星といった惑星を探査するローバの砂上における走行効率を上げるための方法論を提案している．加減速履歴に応じて沈下量が増加することを実験で確認し，数値計算にて加減速履歴修正方法の有効性を確認する．

遠隔地で機能する自律システムに共通で必要となりうる、ミッション実行のためのコマンド計画、実行、およびシステムの状態監視の仕組みについて提案する。宇宙機の自律コマンド実装モデルとして一般的なDeliberation, Execution, Driverという３層構造を基礎として、機能が一意に定義されている通常のコマンド発行だけでなく、「状態によって判断や分岐を伴う論理処理」をもコマンドとして認めるスプリプトエンジンを準備し、それを用いて状態監視をも行う方法である。さらに、この提案を具体的に検証すために試作したAUV（Autonomous Underwater Vehicle）の実験結果を示し、自律システムのための計画表現方法について議論する。

JAXA is examining research and development of a mobile rover required for searching or constructing basement on the lunar surface in succession of KAGUYA. Because the lunar surface is covered by regolith which is an irregular terrain and muddy soil, the rover has a difficulty in running. Therefore newly low contact force mechanism to achieve running with high reliability by changing the contact shape itself. In this research, the stiffness properties on experimental flexible wheel were determined to use flat elongated rectangle sensor made in scattered material pressed against the wheel longitudinal direction. This paper described the longitudinal contact pressure and distribution of flexible wheel by dynamic measurement.

JAXA is planning moon exploration missions following Kaguya (SELENE), whose missions include technology demonstrations, scientific observations, investigations for moon utilization, and social or political purposes. For the first step of moon landing missions, SELENE-2 is planed and phase-A study of it has been conducted since the summer of 2007. SELENE-2 will demonstrate precision landing including hazard avoidance, surface mobility, and night survival technologies. For science, in-situ geological and geophysical observations is essential to improve the knowledge on the origin and the evolution of the moon. Investigations of surface environment and possible in-situ resource will contribute future human exploration. International coordination and contribution are also important aspect of SELENE-2. In this paper, present study status of SELENE-2 is presented.

As space exploration progresses, renewed attention has been given to advanced Lunar exploration technologies. The main objective is to address many open questions about the Moon, such as its origin or chemical components, as most of the current hypotheses are just inferences based on limited evidences. Unmanned subsurface investigation technologies for the Moon are of special significance for future exploration as it may enhance our knowledge of space science. This paper aims to develop a subsurface robotic explorer for the Moon in order to bury an instrument, such as a long period seismometer, for acquiring subsurface information. In previous work, the authors have showed the effectiveness of a novel screw drilling mechanism for burrowing an exploration robot with no-reaction to the body. This paper addresses anew a fundamental dynamics model for a robotic screw explorer. The model includes the geometric model of a conical screw drill and the soil mechanics, allowing us to mathematically estimate a frictional moment around the perimeter of the screw. This theoretical analysis is governed by complex soil behaviors and has not been thoroughly discussed previously. Hence, this challenging study can provide key insight into this matter. The validity of the model developed here is also presented in this paper.

Mobile rovers for lunar or planetary exploration are expected to break a new ground in the field of space science. The realization of adequate locomotion mechanisms for traveling on the surfaces of extraterrestrial bodies is principally a technical challenge. In particular, a reliable mobility on loose soil such as the lunar soil is required for successful rover missions on the Moon. So, the authors propose the novel concept of a micro-rover with an old and new locomotive component, screw unit, and such innovative rover is called Screw Rover. The screw units basically enable the rover to move in various directions by the simple combination of driving modes. Furthermore, Screw Rover can possess a robust and insensitive structure to the serious situation which is a stuck phenomenon caused by slippage and sinkage. In this paper, the fundamental considerations which include the design overview of Screw Rover and the theoretical discussion are presented as the primary study on Screw Rover.

JAXA is examining research and development of an autonomous system, such as mobile rover required for searching ground and constructing basement on the lunar surface in succession of KAGUYA (SELENE) project. Because the lunar surface covered by irregular terrain and muddy soil called regolith, rover has a difficulty in running on such harsh environment. Therefore rover is required of taking a sustainable running mechanism that does not become cautions of fatal functional and mission stop. Then some functions are needed for rover running system on lunar surface, for example certain acting on brake and drive, removing adhered soil and tightens muddy soil. Newly flexible wheel is required to achieve running with high reliability by changing the wheel contact shape itself and being lower contact force on the ground. This paper describes the static measuring test results of flexible wheel contact and distributed pressure, and analysis results of flexible wheel dynamics model.

In the future lunar exploration missions, global information respect to the origin, the internal structure, and the chemical components is important from the viewpoint of solar exploration. Any system burying the seismometer in the lunar soil is required in order to retain the temperature and improve the coupling with the soil. The authors propose a small burrowing robot for burying it in the lunar soil. In this paper, firstly the authors explain some requirements for the lunar robotic system and discuss the comparison with the other planetary excavation systems. Then the authors present the strategy for subsurface propulsion. Based on the analysis, the authors propose a new type screw drilling mechanism for a burrowing subsurface robot. Through some experiments and theory analysis, the authors evaluate the performances of the proposed system.

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.

Hayabusa spacecraft performed the final descents and touchdowns twice in November 2005. In final descent phase, terrain alignment maneuvers were accomplished to control both altitude and attitude with respect to the surface by using four beams Laser Range Finder onboard. Then Hayabusa spacecraft made dynamic touchdowns the surface of the asteroid by the sampler system to collect samples automatically. This paper presents the terrain alignment maneuver and touchdown scheme. This paper also describes the novel sample horn system and touchdown dynamics. Touchdown tests on the ground are presented. Then the flight results on descent and touchdown dynamics are shown and discussed.

To clarify the internal and global information of the Moon is very important in future lunar exploration. This paper describes a lunar subsurface exploration system to bury a seismometer in the lunar regolith by a burrowing robot. The authors have proposed a new screw drilling mechanism for a burrowing robot to achieve that purpose, in particular this paper describes the concept of expansion to the complete burrowing system applying the screw mechanism. The authors call the novel robot BSR (Burrowing Screw Robot). Also in this paper, the authors consider the requirements of the design concepts for developing the BSR and the experimental environments.

This paper presents a synthesis method of a robust input that simultaneously controls position and vibration of a time-varying flexible structure. The robust input is synthesized as a type of feedforward control input taking into consideration of its practical uses and it is calculated through the numerical calculation that simulates a feedback control by using the nonstationary robust controller designed on the basis of a time-varying generalized plant with a structured uncertainty. Further, this input becomes independent of positioning distance and time schedule by the proposed design procedure. The performance of vibration suppression and robustness against parameter variation in the proposed methodology are examined in the numerical calculation compared with those of a previous method. Finally, the usefulness of the proposed input is obtained, and the specific procedure for synthesizing and implementing the input is also presented. © 2007 IEEE.

This paper presents a synthesis method of a robust input that simultaneously controls position and vibration of a time-varying flexible structure. The robust input is synthesized as a type of feedforward control input taking into consideration of its practical uses and it is calculated through the numerical calculation that simulates a feedback control by using the nonstationary robust controller designed on the basis of a time-varying generalized plant with a structured uncertainty. Further, this input becomes independent of positioning distance and time schedule by the proposed design procedure. The performance of vibration suppression and robustness against parameter variation in the proposed methodology are examined in the numerical calculation compared with those of a previous method. Finally, the usefulness of the proposed input is obtained, and the specific procedure for synthesizing and implementing the input is also presented.

An approach to the lunar and planetary subsurface exploration by an excavation robot is a novel and challenging project. There are few proposals including an excavation system for planetary exploration by an autonomic and small robot. So, this paper describes a basic concept about subsurface exploration by viewpoint of soil dynamics and robotics. This paper considers the fundamental strategies to advance under the surface and the contents serve as a guideline to establish the total system of the lunar excavation robot.