The problem of collision avoidance among mobile robots moving along crossing and joining paths is formulated as a motion planning problem in terms of the velocity vector modification. In this paper, a local approach based on a nonlinear programming is applied to solve this problem. Here, the velocity vector constraint for robots are set up using the relative position and velocity information of neighboring robots. The desired velocity vector, which enables robots to navigate without collision, is given as the optimal solution of objective function under this velocity vector constraint. This method is implemented using both experimental robots system and computer simulated one. From the results, it is shown that the experimental robots achieves acceptable performance both in case of crossing and joinig. The feasibility and effectiveness of our method are also discussed through the simulation results.
Concurrency is a very important problem in real-time discrete-event systems, and has a crucial effect on control. In this paper, we consider concurrent discrete-event systems modeled by Petri nets with external input places, with a control specification given in terms of a predicate on the set of all reachable markings. First, we derive a simpler condition for the unique existence of the maximally permissive feedback which can be checked without constructing the set of permissive feedbacks. Next, we obtain a necessary and sufficient condition for concurrency to have no effect on the set of permissive feedbacks. And we study the relationship between these two properties. Moreover, we demonstrate synthesis of the unique maximally permissive feedback for a simple manufacturing system.
One of the most them interesting them in modern crytology is the generating of the highly unpredictable pseudo-random sequences. It is difficult that we give the practical definition of the highly unpredictable pseudo-random sequences. However some measures for the unpredictability, or equivalently the randomness, of finite sequences have been proposed. The linear complexity is one of such measures. In this paper we shall give the notes on the growth properties of linear complexity. Especially we shall present and discuss new classes of sequences with the interesting growth property of linear complexity.
Some results are presented concerning use of time-delays as controller for sensitivity shaping in a control system with stable plant represented by a strictly proper rational transfer function. Suppose that the desired shaping can be performed by some fictitious stable controller represented by a, proper rational transfer function. Then, a set of time-delays connected in parallel can replace the fictitious controller without making the change of the shape of sensitivity function exceed a prescribed allowance. In the case where the plant possibly contains small perturbation that allows the plant to remain stable and strictly proper, a set of time-delays can shape the sensitivity function so that the control system possesses stability robustness against such perturbation. Furthermore, small perturbation in the controller parameters like delay-times causes no closed-loop instability nor remarkable change in the shape of the sensitivity function.
In this paper, we propose an estimation method of system parameters for a two-dimensional noisy image and apply the estimation results to restoration of the noisy image data. The unknown parameters required for orthogonal transform are first roughly estimated by the Yule-Walker equation. Using these estimated parameters, the noisy image data are transformed into frequency domain by FFT. The system parameters of the two-dimensional image are estimated by using adaptive digital filter (ADF) in frequency domain. The noisy image in frequency domain is restored by a filtering algorithm based on the system parameters and innovation process obtained by the ADF. The restored image in frequency domain is transformed into spatial domain by inverse FFT. Simulation results show the effectiveness of the present algorithm in comparison with conventional methods.