| The Space Robotics Lab,
at the Department of Aeronautics and Space Engineering, Tohoku University
plays an active role in Japan's space programs. Past and currently active
programs include, ETS-VII, JEMRMS, MUSES-C, and a future lunar
mission.
http://www.astro.mech.tohoku.ac.jp/home-e.html
(1) Engineering Test Satellite VII (ETS-VII) ETS-VII was a world-first unmanned space free-flying robot developed and flown by National Space Development of Japan (NASDA) (the name was changed into Japan Aerospace Exploration Agency, JAXA), we carried out a number of exciting experiments using the on-board 6 DOF manipulator arm. The experiments confirmed our ideas for advanced robot control in space, particularly the control with the provision of minimum reaction on the base. The experiments opened a way for simple yet effective operation of a space robot for future satellite servicing. http://www.astro.mech.tohoku.ac.jp/~yoshida/ETS-VII/ (2) The Remote Manipulator System on the Japanese Experimental Module (JEMRMS) We study smart control methods for JEMRMS of the International Space Station (ISS) program. We extensively , to the future application of JEMRMS for high precision and dexterous tasks. JEMRMS are designed by the concept of the macro-micro manipulator system, where the macro arm provides a long-reach capability and the micro arm performs the dexterous manipulation. One drawback however is that the macro part is subject to vibrations due to flexibility. Since the macro and micro parts are dynamically coupled, the motion of the small arm induces vibrations into the macro part hence, resulting in degradation of its positioning accuracy. To cope with this drawback, We study the control strategies for minimization of vibration excitation and for maximization of vibration dumping developped from the minimum reaction concept which was successfully confirmed by ETS-VII.
(3) Contact Dynamics for Satellite Capture Rendezvous-docking demonstration on orbit was carred out successfully by ETS-VII. In this demonstration, a subsatellte (target) was approached and docked with by a main satellite (chaser). At that time, the target was cooperative in the sense that it was equipped with transponders, reflectors and dedicated grappling fixtures that allwed easy but secure capture by the end-effector on the chaser. However, the satellites already existing in orbit and requiring service are non-cooperative targets with no such features. We study about the method for capturing such non-cooperative targets. Using the PAF (Payload Attach Fitting) and the nozzle cone on an apogee kick motor as grapple fixtures are good candidates. However, in such case, there is an important issue that the manipurator of the chaser pushed the target away at their first contact for the capture. We try to prevent a chaser robot from pushing a target away with impedance control for the caser's manipulator.
The program of MUSES-C is a very challenging mission for asteroid sample-return developed by the Institute of Space and Astronautical Science, Japan (ISAS). The spacecraft was successfully launched on May 9th, 2003 from Kagoshima Space Center (KSC). We made some deep contribution in the design of the contact probe to acquire samples and the contact dynamic behavior of the spacecraft. For the analysis of the dynamic behavior, we worked on experiments using a drop-shaft (free fall) microgravity facility and using a hardware-in-the-loop simulator as well as computer simulations. Extensive studies are going for lunar and planetary exploration programs. Regarding the surface locomotion, we study the physical behavior of a rover by the analysis of tire traction mechanics on natural terrain, with field tests using hardware test beds. A motion dynamics simulator with sophisticated graphics is developed based on the model obtained from the field tests and applied for simulated lunar/planetary environments with different gravities. Regarding the subsurface exploration, we study several different ideas, develop test beds, and evaluate their performance as a collaboration research with NASDA. |
| 3. Rover Research |
|
To build up a technical basis for future exploration of the surface of the
Moon or a remote planet, we have been working on the mechanical design and
control issues of wheeled mobile robots, rovers, which can travel
over natural rough terrain. In particular, we pay our most attention to the
understanding of the mechanism of soil/wheel traction, and intensive study
has been conducted both theoretically and experimentally
[1].
We have developed various types of laboratory test beds including Nexus 6
and Lunar Dune Traverser-I. Nexus 6 has six wheels, which are connected by a
passive suspension mechanism called "Rocker-Bogie" system. The rocker-bogie
system was proven effective to traverse over rocky obstacles in the NASA's
PathFinder mission on Mars, 1997. In parallel to the Nexus 6 hardware experiments, we have developed software for the dynamics simulation of the rover, which well represents the motions observed in the experiments. Soil and tire parameters were identified as a key to determine the net traction force, then a silp-based control has been developed to maximize the traction during the traversal over loose soil, such as dry sand (used in the experiments) or lunar regolith (future target) [2]. The Dune Explorer was designed dedicated to the locomotion on the lunar surface with an aboundance of loose soil. Practical mission aspects will be also demonstrated using this test bed. For more information, visit http://www.astro.mech.tohoku.ac.jp/~yoshida/Rover/.
|
|
3. ARLISS 2004 Open class Challenge to Come-Back Competition |
|
Since 2002, we have been challenging the Come-Back Competition, held in Black Rock, Nevada. Unlike aerodynamic "Fly-Back" approach that was taken by most of other participants, we took "Run-Back" approach reflecting our background technology of robotics for the lunar/planetary exploration. Our challenge is to develop a payload that makes successful soft landing, then autonomously travels over the surface of the desert to the goal. In this year, we entried to the Come-Back Competition with 2 different payloads. The one is a 2-wheeled rover, the other is a 4regged rover. Fig.1 and Fig.2 show the overview of the payloads. (1) 2-Wheeled Rover Fig.1 shows the overview of the 2-wheeled rover type payload. The payload is made up of 2 wheels and 1 body. These wheels are driven by two motors independently. The motors and any other components (control circuit, GPS, battery, etc.) are inside of the body. After soft landing by parachute, the rover run to the goal with navigation based on the GPS. The GPS receiver was used to obtain the position and orientation of the payload. Based on the GPS data, the wheels are controlled to reach a given goal. The size of batteries are scaled to achieve the surface travel more than one kilometer. The wheels are made of polyurethane and the body is made of CFRP. These materials are very light weight and have good compliance. Total weight is 40% lighter than old model we launched in 2002 & 2003. The compliance of wheel and body reduce the landing impact for the components. The running expriment before launch was very successful. The rover ran long distance with the navigation. (Movie, 5MB) The launch and payload ejection was successful. But unfortunately, the parachute did not open, then the payload performed the ballistic free-fall for 3000 meters and hard landing. However, it was found on the ground in a good shape mechanically. While, electric components were seriously damaged. (2) 4-Legged Rover Fig.2 shows the overview of the 4-legged rover type payload. Using our background and knowledge on robotics for small-bodies, we challenged the payload launch with a never before tried design for the event, a Small Legged Rover. The rover is an autonomous mobile robot which uses four legs for locomotion. Each of these legs has two servos controlling its lift, and extension, giving each leg two degrees of freedom (DOF). With two DOF, the legs have a narrow range of motion, and can move directly between any two points in that range. The servos are controlled by a microcontroller unit running on-board. This board generates the PWM signals required for the servos; also the “intelligence” of the robot also comes from the same microcontroller. The robot currently walks in a statically-stable mode after standing up from the landing configuration. These systems were not completed at this ARLISS. Therefore, the operater had to input a command to start changing configuration from landing configuration to walking configuration after landing. However,the rover succeed in standing up and walking after input the start command. (Movie, 4MB) |
 |
 |
|
Figure 1: 2 Wheeled Rover
|
Figure 2: 4 Legged Rover
|
2002
2003
(c) The Space Robotics Lab, Tohoku University, JAPAN
All right reserved.
 |
 |
|---|
More research projects
Goto TOP of the Lab.
For any question, please contact to here.