Shigeyuki Hosoe

Bifurcation in vehicle dynamics and robust front wheel steering control

A control strategy is proposed for designing a steering control for automotive vehicles to protect the vehicle from spin and to realize the improved cornering performance. The saturation characteristics of rear tires are modeled by a linear function with uncertainty terms of a special structure. The nonlinearity of the saturation is included in the part of uncertainty. The linear H/sup /spl infin// control theory is applied to the design of a front wheel steering controller which compensates the instability against the nonlinear uncertainty. The designed controller is shown to work quite well for nonlinear systems in achieving robust stability and protecting the vehicle from spin. Furthermore, the computer simulations show that the control improves cornering performance in critical motions. The motion realized by the controller resembles the one known as a counter steering which skilful drivers often use.

Development of a nursing-care assistant robot RIBA that can lift a human in its arms

In aging societies, there is a strong demand for robotics to tackle problems caused by the aging population. Patient transfer, such as lifting and moving a bedridden patient from a bed to a wheelchair and back, is one of the most physically challenging tasks in nursing care, the burden of which should be reduced by the introduction of robot technologies. We have developed a new prototype robot named RIBA with human-type arms that is designed to perform heavy physical tasks requiring human contact, and we succeeded in transferring a human from a bed to a wheelchair and back. To use RIBA in changeable and realistic environments, cooperation between the caregiver and the robot is required. The caregiver takes responsibility for monitoring the environment and determining suitable actions, while the robot undertakes hard physical tasks. The instructions can be intuitively given by the caregiver to RIBA through tactile sensors using a newly proposed method named tactile guidance. In the present paper, we describe RIBAs design concept, its basic specifications, and the tactile guidance method. Experiments including the transfer of humans are also reported.

D.C. optimization approach to robust control: Feasibility problems

The feasibility problem for constant scaling in output feedback control is considered. This is an inherently difficult problem since the set of feasible solutions is non-convex and may be disconnected. Nevertheless, we show that this problem can be reduced to the global minimization of a concave function over a convex set, or alternatively, to the global minimization of a convex program with an additional reverse convex constraint. Thus this feasibility problem belongs to the realm of d.c. optimization, a new field which has recently emerged as an active promising research direction in nonconvex global optimization. By exploiting the specific d.c. structure of the problem, several algorithms are proposed which at every iteration require solving only either convex or linear subproblems. Analogous algorithms with new characterizations are proposed for the bilinear matrix inequality (BMI) feasibility problem.

Optimal trajectory formation of constrained human arm reaching movements

Abstract.Opening a door, turning a steering wheel, and rotating a coffee mill are typical examples of human movements that are constrained by the physical environment. The constraints decrease the mobility of the human arm and lead to redundancy in the distribution of actuator forces (either joint torques or muscle forces). Due to this actuator redundancy, there is an infinite number of ways to form a specific arm trajectory. However, humans form trajectories in a unique way. How do humans resolve the redundancy of the constrained motions and specify the hand trajectory? To investigate this problem, we examine human arm movements in a crank-rotation task. To explain the trajectory formation in constrained point-to-point motions, we propose a combined criterion minimizing the hand contact force change and the actuating force change over the course of movement. Our experiments show a close matching between predicted and experimental data.

Determination of generic dimensions of controllable subspaces and its application

The controllable subspace and its dimension of a structured linear system vary as a function of the free parameters. However, the dimension is stable in the sense that it takes, for almost any system parameters, some maximal constant which is the generic rank of the controllability matrix. In this paper, this maximal constant is called the generic dimension of the controllable subspace. Two simple methods for determining generic dimensions of controllable subspaces are derived. As an application, the results are applied to the determination of system types of linear multivariable unity feedback systems.

Nonlinear H/sub /spl infin// control for an integrated suspension system via parameterized linear matrix inequality characterizations

The automotive hydro-pneumatic integrated suspen- sion model is nonlinear with large dimension. As a consequence, the nonlinear control methodology based on the traditional Hamilton-Jacoby-Isaacs equation is impractical in this appli- cation. An alternative so-called parameterized linear matrix inequality (PLMI) approach is proposed for solving this hard nonlinear control problem. The validity of the proposed approach is confirmed not only by detailed and realistic simula- tions but also by extensive experiments. Specifically, the proposed nonlinear control method outperforms the more classical feedback linearization control technique.

Gain-scheduled filtering for time-varying discrete systems

This paper deals with the design of gain-scheduled filters, whose state-space realization depends on real-time parameters of plants. Similar to well-recognized advantages of gain-scheduled controllers in control theory, gain-scheduled filters are expected to provide enhanced performance in comparison with customary nonadjustable filters. Our construction technique is based on nonlinear fractional transformation (NFT) representations of systems that are a generalization of widely used linear fractional transformation (LFT) representations. Both generalized H/sub 2/ and H/sub /spl infin// discrete-time filter design problems are investigated together with their extension to mixed designs. This study leads to new linear matrix inequality (LMI) formulations, which in turn provide an effective and reliable design tool. The proposed design technique is finally evaluated in the light of simulation examples.

On the irreducibility condition in the structural controllability theorem

It is known that the structural system (A,B) is structurally controllable if and only if the corresponding matrix [A B] is generically full rank and irreducible. In this paper it is shown that the irreducibility condition alone implies that every nonzero mode of (A,B) is generically controllable. This result provides an easy proof to the structural controllability theorem stated above. In addition, it is shown that the basic structure of the Jordan canonical form of (A,B) remains unaffected, in the generic sense, under the variation of the free parameters of (A,B).

On the stiffness and stability of Gough-Stewart platforms

This paper deals with a class of parallel mechanisms, called Gough-Stewart platforms. For these mechanisms, pre-loaded by driving forces, the stiffness matrix is derived and its basic properties are established. It is shown when the stiffness matrix becomes asymmetric, how the parametric imbalance may influence the system stability, and how the center of stiffness depends on the force pre-loading. Next, some necessary and some sufficient conditions for the stability are established in an analytical form by transforming the stiffness matrix to the center of stiffness.

A Soft Human-Interactive Robot RI-MAN

Our goal is to create advanced engineering systems such as a soft human interactive robot. The robot developed here is named RI-MAN. RI-MAN exhibits the skill and ability to realize human care and welfare tasks. RI-MAN can search out a specific person in real time by fuing audio and visual information, and understand human speech based on a sound recognition function. In addition, RI-MANs body is coverd with soft touch sensors, and RI-MAN can react to the amplitude and location of external forces. Using all these sensor functions, RI-MAN can successfully follow human commands and hold up a dummy of the same size as an adult human. RI-MAN will become an invaluable partner robot.