Masahiro Oya

Robust adaptive motion/force tracking control of uncertain nonholonomic mechanical systems

The position/force tracking control of Lagrangian mechanical systems with classical nonholonomic constraints is addressed in this paper. The main feature of this paper is that 1) control strategy is developed at the dynamic level and can deal with model uncertainties in the mechanical systems; 2) the proposed control law ensures the desired trajectory tracking of the configuration state of the closed-loop system; 3) the tracking error of constraint force is bounded with a controllable bound; and 4) a global asymptotic stability result is obtained in the Lyapunov sense. A detailed numerical example is presented to illustrate the developed method.

Stable adaptive fuzzy control of nonlinear systems preceded by unknown backlash-like hysteresis

This paper deals with adaptive control of nonlinear dynamic systems preceded by unknown backlash-like hysteresis nonlinearities, where the hysteresis is described by a dynamic equation. By utilizing this dynamic model and by combining a fuzzy universal function approximator with adaptive control techniques, a stable adaptive fuzzy control algorithm is developed without constructing a hysteresis inverse. The stability of the closed-loop system is shown using Lyapunov arguments. The effectiveness of the proposed method is demonstrated through simulations.

State observer-based robust control scheme for electrically driven robot manipulators

By using a state observer, a new robust trajectory tracking control scheme is developed in this paper for electrically driven robot manipulators. The role of the observer is to estimate joint angular velocities. The proposed controller does not employ adaptation, but assures robust stability of tracking error between joint angles and desired trajectories. At sacrificing asymptotical stability of the tracking errors, the configuration of the proposed controller becomes very simple, compared with regressor-based adaptive controllers. It is shown in the closed-loop system using the proposed controller that the Euclidian norm of tracking errors arrives at any small closed region with any convergent rate by setting only one design parameter. Especially for the desired trajectories converging to constant ultimate values, it is assured that tracking errors converge to zero.

Robust motion tracking control of partially nonholonomic mechanical systems

This paper proposes a stable motion tracking control law for mechanical systems subject to both nonholonomic and holonomic constraints. The control law is developed at the dynamic level and can deal with model uncertainties. The proposed control law ensures the desired trajectory tracking of the configuration state of the closed-loop system. A global asymptotic stability result is obtained in the Lyapunov sense. A detailed example is presented to illustrate the proposed method.

A safety spacing policy and its impact on highway traffic flow

This paper proposes a Safety Spacing Policy (SSP) that can ensure safe operation while at the same time improving traffic flow for Adaptive Cruise Control (ACC) system. The proposed SSP, a nonlinear function of vehicle velocity, uses both the information of vehicles state and braking capacity to adjust the position and velocity of the controlled vehicle. String stability, traffic flow stability and traffic capacity of the proposed policy are analyzed. The SSP can ensure vehicle string stability and it can also yield stable traffic flow and higher traffic capacity that are superior to the traditional Constant Time Gap (CTG) system. Especially in the high-density traffic conditions, the proposed new policy can provide higher traffic capacity to relief traffic congestion while the CTG policy fails to do so. In addition, traffic simulations show that SSP can ensure vehicle safety in hard brake and acceleration scenarios. The proposed new spacing policy is a promising alternative to the traditional CTG policy.

Adaptive Steering Controller to Improve Handling Stability of Combined Vehicles

If the dynamics of combined vehicle varies large, it may be very difficult for inexperienced drivers to achieve good handling stability. Once combined vehicles become unstable, it is very difficult for all of drivers to stabilize vehicles. However, if the behavior of actual combined vehicle tracks a designed combined vehicle, the good handling property can be maintained even when the dynamics of actual combined vehicle varies large. In the paper, to achieve good handling property even for large variation of vehicle dynamics, a design method of a desired combined vehicle is proposed. Then, an adaptive steering controller is developed so that the actual vehicle tracks the desired vehicle.

Adaptive rollover prevention controller for driver---vehicle systems

In the paper, we propose an adaptive rollover prevention controller for heavy vehicles. At first, a design method for an ideal vehicle model is proposed. The designed ideal vehicle model has the property that good rollover prevention performance can be assured even if the driver steering characteristics vary. If the behavior of the actual heavy vehicle tracks that of the designed ideal vehicle model, rollover prevention can be achieved. Therefore, next, to realize good rollover prevention, we propose an adaptive steering controller. In the heavy vehicle system using the controller, the actual heavy vehicle can track the ideal vehicle model. Then, rollover prevention can be achieved. Finally, to demonstrate the usefulness of the proposed controller, numerical simulations are carried out.

Adaptive control of underwater vehicle-manipulator systems using radial basis function networks

This paper deals with a control scheme for underwater vehicle-manipulator systems with the dynamics of thrusters in the presence of uncertainties in system parameters. We have developed two controllers that overcome thruster nonlinearities, which cause an uncontrollable system: one is a regressor-based adaptive controller and the other is a robust controller. However, the structure of the adaptive controller is very complex due to the feedforward terms including the regressors of dynamic system models, and the error feedback gains of the robust controller with a good control performance are excessively high due to the lack of feedforward terms. In this paper we develop an adaptive controller that uses radial basis function networks instead of the feedforward terms. The replacement leads to a moderately high gain controller whose structure is simpler than that of the regressor-based adaptive controller.

Adaptive steering controller to improve handling stability for driver-combined-vehicles system

If the dynamics of combined vehicles such as tractor-semitrailer varies greatly, it may be very difficult for inexperienced drivers to achieve good handling stability. Moreover, once combined vehicles become unstable, it is very difficult for all drivers to stabilize vehicles. However, if the behavior of actual combined vehicles tracks a designed desired combined vehicle, the good handling property can be maintained even when the dynamics of actual combined vehicles varies large. In this paper, to achieve good handling property even for large variation of vehicle dynamics, a design method for a desired combined vehicle is shown, and then, an adaptive steering controller is developed so that the actual vehicle tracks the desired vehicle. The developed adaptive steering controller has strong robustness for the uncertainties of vehicle parameters. Moreover, a driver model is introduced to show the characteristics of driver. Carrying out numerical simulations, it is shown that the developed adaptive steering controller is very useful for the driver-combined-vehicles system.

Adaptive active suspension controller achieving the best ride comfort at any specified location on vehicles with parameter uncertainties

In this paper, an adaptive active suspension control scheme is developed so that ride comfort becomes best at any specified location on vehicle body even if vehicle parameters are unknown. To meet this end, an ideal vehicle is designed in which the location where the ride comfort becomes best can be easily specified by setting only one design parameter. To achieve the good property also in actual vehicles with parameter uncertainties, an adaptive active suspension controller is proposed so that the actual vehicle tracks the ideal vehicle. It is shown by carrying out numerical simulations that ride comfort at any specified location can be easily improved in vehicles using the proposed adaptive active suspension controller.