Takahiro Yakoh

Bilateral robot system on the real-time network structure

This paper presents a bilateral robot system, which is driven by the static friction-free drive system and implemented on the real-time network structure. The goal is to realize a force reflecting bilateral teleoperation with haptic impression transmission over computer networks. The paper considers two subjects relating to the bilateral robot. The first is static friction, which degrades the performance of manipulation and results in a poor haptic impression. A new transmission mechanism named twin drive system developed by the authors resolves this problem. The transmission mechanism, which resembles the differential gear of automobiles, is essentially free of static friction. This static-friction-free motion greatly contributes to the broad range of motion control applications. The second subject is the time delay of the network, which may cause serious problems such as instability of the feedback system. To avoid such delay, the authors developed a new real-time network protocol stack (RTNP). The detailed mechanism of the twin drive system and architecture of the RTNP are presented, and the control scheme and experimental results are also shown.

An approach to biped robot with parallel mechanism

Describes a 3D biped robot where each leg is composed of a 6 DOF parallel mechanism. The proposed mechanism is suited to walking, and the total weight of each leg is expected to be lighter than a serial linked biped robot. This is one of the remarkable features of the proposed mechanism. One side leg consists of three linked arms. Each arm has two active and four passive joints, and is placed in the same direction. There are two kinds of arms where positions of the active joints are different. Thus, the robot can move without interference of each arm. In the paper, theoretical analysis of the biped robot motion with parallel mechanism is shown. Furthermore a 3D dynamic simulator is developed to implement several simulations. To confirm the feasibility of the proposed mechanism, the walking motion is tested by the developed simulator.

Low delay live video streaming system for interactive use

With the rapid growth of the Internet, users are increasingly seeking real-time multimedia application services. To meet this requirement, many streaming methods are developed. However, most of streaming systems are used for ornamental use such as video on demand (VOD). Users for such application do not require interaction, so reducing jitter is the most important issues. Therefore, users donpsilat demand low delay systems. On the other hand, the systems for the interactive use such as remote control, tele-surgery and so on, demand the extremely low delay and low jitter. This article propose the new live video streaming system featured by the low delay and low jitter. This paper expresses the methods of encoding and transmitting videos and describes the results of the simulations that indicate the availability of the system.

Dynamic model of decentralized systems with informational connection

This paper presents a design method of decentralized systems with informational connection. The informational connection in this paper denotes an event link which establishes a signal links among physical controlled plants via a communication network. A dynamic transition of an informational connection among decentralized systems is considered and the mathematical structures are discussed using a concept of eigenvalues and eigen-connections over the Galois field GF(2). The global system has variable-structure characteristics due to the transition of informational connection. Examples of decentralized variable-structure systems are shown. In industry, there are many engineering systems that have a dynamic transition of an informational connection. The mathematical model would be useful for analysis and synthesis of various informationally connected systems.

A friction compensation in twin drive system

A method of friction compensation based on a twin drive system is discussed in the paper. The twin drive system in composed of two motors connected by a differential mechanism. Then the generated torque of the system is the torque difference between two motors. Also these motors are continuously driven to reduce the influence of static friction in each motor even if the system has a stationary motion. This is one of the remarkable points in the proposed approach of twin drive system. Furthermore the paper introduces virtual coordinates to construct the controller. The validity of the proposed system is confirmed by several experimental results.

Fairness and Utilization in Multipath Network Flow Optimization

Multipath routing is expected to improve the degree of control in network flow managements. Therefore, multi-criteria designs will become indispensable for the next generation of multipath routing algorithms and protocols. This paper shows a theoretical approach to multipath routing problems as a multi- objective optimization of network flows. Two objectives, total link utilization and bandwidth fairness for connections, are introduced into an objective formulation which is solved with a nonlinear programming solver. The numerical analysis shows that drastic fairness improvement can be achieved with small decline of utilization. Compared to standard multipath routing, this approach of bandwidth fair multipath routing can achieve a variance of bit-rate for all connections of 0.0123% with a decline of utilization of 11.4%. In case of single path, a variance of 0.0168% with decline of utilization of 39.7% can be achieved. Finally, the controllability of multipath routing is discussed.

Development of time division switching hub for synchronous TDMA

In this article, the prototyping of a synchronous hybrid switching hub is discussed. It uses the network processor IXP 1200 in multi-hop networks. In general, transmission times caused by a switching hub/router vary according to its load and the traffic of networks. It is because delay distributes whenever packets pass through a router even if real-time communication networks are used for all subnets. To stabilize the transmission time, this article proposes a real-time switching hub for the protocols so as to synchronize all of communication and forwarding processes for a periodical communication for global networks.

A comparison study between parallel and serial linked structures in biped robot system

This article describes the features of two contrastive mechanisms in biped robot systems. One of the compared models is the serial mechanism in which each link is connected in series, and each joint is driven by its own actuator independently. Another model is the parallel mechanism and there is a single close linked chain. One of the important merits of using the parallel mechanism to the biped robot is that all the actuators can be placed on the upper leg, thus the inertia of the leg can be smaller, even if its kinematics and dynamics becomes more complicated. In the biped robot with parallel mechanisms, all the joint angles are set as a variable as well as a serial mechanism, and the geometric constraint function can be defined by the kinematic relation of each closed linked chain. From the second order differential of this function, the angular acceleration of the passive joint is represented by the angular acceleration of the active joint. Thus, the dynamic equation is derived. In this paper, the theoretical analysis of the biped robot motion with parallel and serial mechanisms is shown. The numerical results obtained are useful to the mechanical design.

PULSER: a sensitive operating system for open and distributed human-robot-computer interactive systems

Autonomous mobile robots are required to be sensitive to changes of their surrounding environment for handling physical resources and supporting open and distributed human-robot-computer systems. But it is difficult to incorporate sensitivity into real-time systems, and to identify the owner of a physical resource in an open and distributed human-robot-computer system. In this paper, the authors present an operating system PULSER that supports sensitivity with real-time facility, and provides a physical resource manager that is based on the ownership model, the solution to the physical ownership problem. Also, they describe a new facility for wireless communications in open and distributed systems.<<ETX>>

A controller design method on decentralized systems

In this paper, we propose a new controller design method for decentralized system. The method includes an arrangement scheme of multi-controllers and a controller design procedure via the LMI method. The arrangement scheme is based on analysis of a transitional probability matrix, which is induced from a connection matrix. In the scheme, we characterize the stable equilibrium value of probability matrix as the dense of the connection and determines the order of the subsystem. Multi-controllers are arranged according to the priory order and constitute a decentralized control system. The controller design utilizes the function of LMI based methods, which enables one to put constraints on the form of the feedback controller. By applying a change of variables method and setting up the structure of variable to be the same as the controller structure, the desired controller is obtained. We show a design procedure of a stabilizing controller. The validity of proposed methods is examined on a numerical model.