Akira Mitsuya

Hardware Experiments of a Truss Assembly by an Autonomous Space Learning Robot

An experimental system simulating a free-flying space robot, which has been constructed to study autonomous space robots, is addressed. The experimental system consists of a space robot model, a frictionless table system,a computer system, and a vision sensor system. The robot model is composed of two manipulators and a satellite vehicle and can move freely on a two-dimensional planar table, without friction, using air bearings. The robot model has successfully performed the automatic truss structure assembly, including many tasks, for example, manipulator berthing, component manipulation, arm trajectory control collision avoidance, assembly using force control, etc. Moreover, even if the robot fails in a task planned in advance, the robot replans the task by using reinforcement learning and obtains the task goal. The experiment demonstrates the possibility of the autonomous construction and the usefulness of space robots.

Experimental studies for control of manipulators mounted on a free-flying space robot

An experimental system simulating a free-flying space robot has been constructed to evaluate the performance and/or feasibility of control schemes. The experimental robot model, composed of a satellite base and a manipulator can move on a two-dimensional planar table without friction by using air-bearings. The effectiveness and control performance of various path control methods, i.e. local PD-control, resolved motion rate control and resolved acceleration control, are evaluated and compared with each other through numerical simulations and hardware experiments. The feasibility of the control schemes is examined. Autonomous capture using a moving and floating target is also demonstrated.

Theoretical and experimental studies for continuous path control of flexible manipulator mounted on a free-flying space robot

Some continuous path tracking control schemes for flexible manipulators are proposed by using a concept of virtual rigid manipulator. An extended local PD-control (extended LPDC), pseudo resolved motion rate control (pseudo RMRC), and pseudo resolved acceleration control (pseudo RAC) for flexible manipulators are presented. To suppress vibrating motion, a composite control with a reduced-order modal control is developed. To verify the stability, a sufficient condition for asymptotic stability of PD-control is derived. It is also clarified that the PD-control damps all the vibration modes irrespective of their natural damping. The validity of the proposed control schemes is explained through the singular perturbation method. The robust stability of the proposed control schemes is discussed. The effectiveness of the proposed control schemes is demonstrated through hardware experiments using a flexible manipulator mounted on a freeflying satellite.

HARDWARE EXPERIMENTS OF SPACE TRUSS ASSEMBLY BY AUTONOMOUS SPACE ROBOT

This paper addresses an experimental system simulating a free-flying space robot, which has been constructed to study autonomous space robots. The experimental system consists of a space robot model, a frictionless table system, a computer system, and a vision sensor system. The robot model composed of two manipulators and a satellite vehicle can move freely on a two-dimensional planar table without friction by using air-bearings. The robot model has successfully performed the automatic truss structure construction including many jobs, e.g., manipulator berthing, component manipulation, arm trajectory control avoiding collision, assembly considering contact with the environment, etc. Moreover, even if the robot fails in a task planned in advance, the robot accomplishes it by re-planning task-sequence using reinforcement learning. The experiment demonstrates the possibility of the automatic construction and the usefulness of space robots.

System identification and resolved acceleration control of space robots by using experimental system

An experimental system is constructed to evaluate performance and feasibility of modeling, identification and control methods for space robots. The experimental system achieves a two-dimensional weightless condition by means of a horizontal table and air-pads. As a preliminary experimental study, two identification methods for space robots are discussed. The first identification method is a conventional method for manipulators on an inertially fixed base. The second identification method can determine dynamic parameters of space robots under the condition that the satellite base is free to both translate and rotate. This method is based upon the conservation laws of linear and angular momentum of a space robot. Finally implementation schemes of resolved acceleration control are considered for the experimental system.<<ETX>>

Control Experiments of a Docking Mechanism Composed of a Planar Variable Geometry Truss

This paper addresses an experimental docking system using a variable geometry truss (VGT), which is a kind of intelligent adaptive structures. The experimental system is composed of a docking mechanism, a frictionless table system, a computer system, and a vision sensor system. By using the developed experimental system, a PD-control and a computed torque method (CTM) are examined. The dynamics-based control, CTM, shows the superiority over the kinematics-based PD control. This paper proposes a resolved acceleration control (RAG), i.e., a position control, with redundancy considering. The proposed control scheme can avoid a bad condition caused by the redundancy. The CTM and the RAC use the efficient formulation of inverse dynamics that was proposed for real time controls by the present authors. Feasibility and effectiveness of those methods are examined by numerical simulations and experiments.

A study on control of planar variable geometry truss used for autonomous docking system

This paper is concerned with a control of a redundant variable geometry truss (VGT). A dynamics-based control cannot guarantee the asymptotic stability of closedloop system if the controller directly uses a pseudo inverse of Jacobian matrix. To avoid this problem, a resolved acceleration control is proposed with the redundancy considering. The control scheme can achieve the asymptotic stability in spite of the redundant system. To make the control be a real-time one, an efficient formulation of inverse dynamics for the VGT is used. Then an experimental docking system of VGT is constructed, which is a redundant system with many sensors and actuators. The experimental system is composed of a docking mechanism, a frictionless table system, a computer system, and a vision sensor system. Feasibility and effectiveness of the control method are examined by numerical simulations and experiments using the developed system.