Tomonari Furukawa

Recursive Bayesian search-and-tracking using coordinated uavs for lost targets

This paper presents a coordinated control technique that allows heterogeneous vehicles to autonomously search for and track multiple targets using recursive Bayesian filtering. A unified sensor model and a unified objective function are proposed to enable search-and-tracking (SAT) within the recursive Bayesian filter framework. The strength of the proposed technique is that a vehicle can switch its task mode between search and tracking while maintaining and using information collected during the operation. Numerical results first show the effectiveness of the proposed technique when a found target becomes lost and must be searched for again. The proposed technique was then applied to a practical marine search-and-rescue (SAR) scenario where heterogeneous vehicles coordinated to search for and track multiple targets. The result demonstrates the applicability of the technique to real search world scenarios

Coordinated decentralized search for a lost target in a Bayesian world

This paper describes a decentralized Bayesian approach to coordinating multiple autonomous sensor platforms searching for a single non-evading target. In this architecture, each decision maker builds an equivalent representation of the target state PDF through a Bayesian DDF network enabling him or her to coordinate their actions without exchanging any information about their plans. The advantage of the approach is that a high degree of scalability and real time adaptability can be achieved. The effectiveness of the approach is demonstrated in different scenarios by implementing the framework for a team of airborne search vehicles looking for a stationary, and a drifting target lost at sea.

Recent developments of free mesh method

This paper presents the recent advances on Free Mesh Method by the authors. In this method, elements are locally created at each node in an autonomous manner, so that only nodal information is necessary without global meshing. The method has been tested with various applications such as heat conduction, fluid and fracture analyses, and reliable solutions were obtained with good parallel efficiency. Modifications of Free Mesh Method have been further proposed, and the accuracy of solution has been improved.The overall review of the recent advances has demonstrated the effectiveness of Free Mesh Method. Copyright

Implicit constitutive modelling for viscoplasticity using neural networks

Up to now, a number of models have been proposed and discussed to describe a wide range of inelastic behaviours of materials. The fatal problem of using such models is however the existence of model errors, and the problem remains inevitably as far as a material model is written explicitly. In this paper, the authors define the implicit constitutive model and propose an implicit viscoplastic constitutive model using neural networks. In their modelling, inelastic material behaviours are generalized in a state-space representation and the state-space form is constructed by a neural network using input–output data sets. A technique to extract the input–output data from experimental data is also described. The proposed model was first generated from pseudo-experimental data created by one of the widely used constitutive models and was found to replace the model well. Then, having been tested with the actual experimental data, the proposed model resulted in a negligible amount of model errors indicating its superiority to all the existing explicit models in accuracy.

Decentralized Bayesian negotiation for cooperative search

This paper addresses the problem of coordinating a team of multiple heterogeneous sensing platforms searching for a single lost target. In this approach, the utility of a control sequence is a function of the probability density function (PDF) of the target state. Each decision maker builds an equivalent estimate of this PDF by communicating and fusing the information from the other sensor nodes. Coupled utilities incite the agents to collaborate and to agree on the next best set of actions. Decentralized cooperative planning is achieved via anonymous negotiation based on communication of expected observed information. Simulation results demonstrate the efficiency of the cooperative trajectories for a team of autonomous airborne search vehicles.

An automated system for simulation and parameter identification of inelastic constitutive models

This paper presents an automated system for parameter identification of inelastic constitutive models. The system can find good approximate parameters for various identification problems under a user-friendly environment. In order to identify parameters efficiently and in a robust manner, an optimisation method is first proposed. The paper then describes the generalisations applied of modelling, simulation and identification for its various identification uses. Finally, a system, which is developed in conjunction with the generalisations, is described. The performances of the proposed optimisation method and the developed system were investigated with actual material data, and their effectiveness was consequently confirmed.

Dynamic space reconfiguration for Bayesian search and tracking with moving targets

Abstract This paper presents a technique for dynamically reconfiguring search spaces in order to enable Bayesian autonomous search and tracking missions with moving targets. In particular, marine search and rescue scenarios are considered, highlighting the need for space reconfiguration in situations where moving targets are involved. The proposed technique improves the search space configuration by maintaining the validity of the recursive Bayesian estimation. The advantage of the technique is that autonomous search and tracking can be performed indefinitely, without loss of information. Numerical results first show the effectiveness of the technique with a single search vehicle and a single moving target. The efficacy of the approach for coordinated autonomous search and tracking is shown through simulation, incorporating multiple search vehicles and multiple targets. The examples also highlight the added benefit to human mission planners resulting from the technique’s simplification of the search space allocation task.

Process model, constraints, and the coordinated search strategy

This paper deals with the problem of coordinating a team of mobile sensor platforms searching for a single mobile non-evading target. It follows the general Bayesian active sensor network approach introduced in [2] where each decision maker plans locally based on an equivalent representation of the target state probability density function (PDF). This paper focuses on the prediction stage of the decentralized Bayesian filter. It looks at how different types of realistic external constraints may affect the target motion and how they may be taken into account in the process model. Two general classes of constraints are identified soft and hard. A few constraint examples from each class are given to illustrate their impact on the evolution of the target state PDF. Multiple constraints of various types can be combined to increase the accuracy of the predicted PDF estimate, thus affecting the individual trajectories of the search platforms. The effectiveness of the framework is demonstrated for a team of airborne search vehicles looking for a drifting target lost in a storm at sea.

Time-Subminimal Trajectory Planning for Discrete Non-linear Systems

While several time-optimal trajectory planning techniques have been developed for continuous non-linear systems, there has been little discussion on the subject for discrete non-linear systems. This paper, therefore, presents a technique to search for the time sub-optimal trajectory for general discrete non-linear systems. In this technique, the control inputs with respect to time are partitioned into piecewise constant functions. The piecewise constant functions and the time step interval, which are used in the discretisation of the system, are then searched by a general-purpose non-linear programming optimization method. The example of a time sub-optimal trajectory planning of a SCARA-type manipulator presented in this paper indicates that the proposed technique has the same ability as the existing time sub-optimal trajectory planning techniques for continuous systems. The second numerical example of a non-differentiable car backing-up system shows that the proposed technique also works well for general discrete systems.

Automated polishing of an unknown three-dimensional surface

An automatic system for polishing an unknown three-dimensional surface using a passively compliant end-effector mounted on the wrist of an industrial robot is described. As polishing proceeds, the end-effector uses position sensors to measure the misalignment of the robots wrist from the local surface normal. A personal computer is used to acquire sensory data, to compute the desired configuration of the robot wrist, and to control the robot in a point-to-point mode. Low bandwidth point-to-point control is possible because of the passive compliant movement of the end-effector. Contact with the work surface can be maintained within an angular range of ±8° and a ±10 mm range of normal translational movement. Experimental performance tests show that the polishing system can function well under a variety of working conditions.