Hiroshi Okubo

Low-authority control of large space structures by using a tendon control system

This paper deals with the problem of controlling the vibrations of large space structures by the use of a newly conceived torque actuation device, i.e., a tendon control system. It consists of a pair of tension cables transmitting a control torque to the structure at the moment arm position. The purpose of the study is twofold: first, to establish the analytical framework for low-authority control synthesis; second, to validate the proposed concept through a hardware experiment. A nonlinear optimization approach is proposed for the design of the control gains and the moment arm placement. This approach is useful when the total number of control devices is smaller than the number of critical vibrational modes, and exact pole placement is not possible. A hardware experiment has been done successfully, which shows the fundamental feasibility of the active tendon control for a highly flexible beam. However, for its practical application, further studies are needed, especially on the interactions between the dynamics of the tension cables and the flexible structure.

A 3-D position and attitude measurement system using laser scanners and corner cubes

This work proposes a new method for measuring the position and attitude of an autonomous land vehicle navigating in a rough terrain. The measurement system proposed here provides precise information on position and heading quickly and continuously. It consists of two laser scanners mounted on the vehicle and corner cubes placed in the environment as landmarks. Each laser scanner rotates a fan-shaped laser beam for detecting the retro-reflections by the corner cubes and measures their azimuth angles. This work presents the principle of measurement and method of positional and attitude estimation. Simulation results are given to show the accuracy of the proposed method.

Path planning for space manipulators using enhanced disturbance map

The motions of the space manipulators cause dynamic disturbances to the spacecraft attitude. This paper proposes a method for planning the manipulator path that reduces such dynamic disturbances using the Enhanced Disturbance Map approach. The Disturbance Map shows the direction of joint movements in the joint space that causes zero disturbance to the spacecraft attitude as well as the magnitude of the maximum disturbance. The proposed method designs small steps of joint movements in the joint space considering hvo directions. One is the direction to realize the desired terminal joint angles and the other is to reduce the disturbances to the spacecraft attitude. The total direction of the joint movement is determined at each step depending both on the magnitude of the disturbances caused by the joint movements and on the distance from the goal. Results of numerical simulations are given for a free-flying robot having a two-link manipulator.

Identification of a Tendon Control System for Flexible Space Structures

An experimental tendon control system is identified to make an accurate mathematical model for designing a controller. The experimental tendon control system has been constructed for the vibration control of a flexible beam simulating large space structures (LSS). The system has many low-frequency modes of vibration, and a modal survey requires lengthy testing. A proposed scheme needs time histories of responses for a very short period. First, a mathematical model of the system is developed through a finite element method (FEM). Second, unknown characteristic parameters are estimated by using an output error method. The validity of the proposed scheme is demonstrated by good agreement between the transfer functions of the experimental system and an identified model. Finally, the accuracy of the identified model is also verified by the agreement between the computed and the experimental closed-loop responses.

Optical two-way communication system for vehicles using lasers and corner cubes

This paper presents a new two-way data communication system for road vehicle control using laser beams and corner cubes. This system shows good performance for data communication between vehicles on the road or between vehicles and terminals over the road. This system uses laser transceivers and respondent devices to realize two-way communication. The respondent device consists of laser receivers and optical modulators using corner cube prisms and piezoelectric cells. The operation principle of this system is confirmed by experiments.

A method of position and attitude measurement of vehicle using fan shaped laser beam and corner cube

A method is proposed to measure the position and attitude of a vehicle on the road by use of laser transceivers on the vehicle and retro-reflecting targets on a side of the course. The laser transceivers emit fan shaped laser beams and detect the returned laser beams reflected by the retro-reflecting targets. The time data when the laser beams return to the transmitter vary, depending on the movement of the vehicle. An onboard computer calculates the position and attitude from the time data. The measurement principle and the simulation results are reported.

Two-Dimensional Position and Heading Measurement for Vehicle Using Corner Cubes

This paper proposes a method for measuring the position and heading of the vehicle by use of laser and corner cubes. The vehicle has dead reckoning system. The method uses the laser transmitter and receiver on the vehicle and retroreflecting targets on a side of the course. The on-board computer calculates the position and heading from the dead reckoning data when the laser beams hit the corner cube. Each laser beam is set with a certain angle and an offset distance. And the dead reckoning data are stored in memories when the laser beams return to the transmitter. After corner cubes are detected by retroreflected laser beam, position and heading are calculated. The measured data are used for compensating the autonomous position determination.

Measurement of the Position and Heading of a Vehicle Using Corner Cubes on a Road Side

This paper proposes a method for measuring the position and heading of a vehicle moving on a curved course. The method uses laser fan beam transmitters and photo detectors mounted on the vehicle and an array of corner cubes on the course side as retro-reflecting targets. The laser beams have different direction angles and offset distances with each other and, therefore, return to the vehicle at different time according to the position and heading of the vehicle. The on-board computer calculates the position and heading from the time data that indicate the instants of detecting the reflections from the target corner cubes. The measured data are used for correcting the dead reckoning system.