HIS article presents an overview and assessment of the technology leading to the development of intelligent structures. Intelligent structures are those which incorporate actuators and sensors that are highly integrated into the structure and have structural functionality, as well as highly integrated control logic, signal conditioning, and power amplification electronics. Such actuating, sensing, and signal processing elements are incorporated into a structure for the purpose of influencing its states or characteristics, be they mechanical, thermal, optical, chemical, electrical, or magnetic. For example, a mechanically intelligent structure is capable of altering both its mechanical states (its position or velocity) or its mechanical characteristics (its stiffness or damping). An optically intelligent structure could, for example, change color to match its background.17 Definition of Intelligent Structures Intelligent structures are a subset of a much larger field of research, as shown in Fig. I.123 Those structures which have actuators distributed throughout are defined as adaptive or, alternatively, actuated. Classical examples of such mechanically adaptive structures are conventional aircraft wings with articulated leading- and trailing-edge control surfaces and robotic systems with articulated manipulators and end effectors. More advanced examples currently in research include highly articulated adaptive space cranes. Structures which have sensors distributed throughout are a subset referred to as sensory. These structures have sensors which might detect displacements, strains or other mechanical states or properties, electromagnetic states or properties, temperature or heat flow, or the presence or accumulation of damage. Applications of this technology might include damage detection in long life structures, or embedded or conformal RF antennas within a structure. The overlap structures which contain both actuators and sensors (implicitly linked by closed-loop control) are referred to as controlled structures. Any structure whose properties or states can be influenced by the presence of a closed-loop control system is included in this category. A subset of controlled structures are active structures, distinguished from controlled structures by highly distributed actuators which have structural functionality and are part of the load bearing system.

Intelligent structures for aerospace - A technology overview and assessment

A new methodology named Evolutionary Artificial Potential Field (EAPF) is proposed for real-time robot path planning. The artificial potential field method is combined with genetic algorithms, to derive optimal potential field functions. The proposed EAPF approach is capable of navigating robot(s) situated among moving obstacles. Potential field functions for obstacles and goal points are also defined. The potential field functions for obstacles contain tunable parameters. The multi-objective evolutionary algorithm (MOEA) is utilized to identify the optimal potential field functions. Fitness functions such as goal-factor, obstacle-factor, smoothness-factor and minimum-pathlength-factor are developed for the MOEA selection criteria. An algorithm named escape-force is introduced to avoid the local minima associated with EAPF. Moving obstacles and moving goal positions were considered to test the robust performance of the proposed methodology. Simulation results show that the proposed methodology is efficient and robust for robot path planning with non-stationary goals and obstacles.

Evolutionary artificial potential fields and their application in real time robot path planning

Owls are commonly known for their quiet flight, enabled by three adaptions of their wings and plumage: leading edge serrations, trailing edge fringes and a soft and elastic downy upper surface of the feathers. In order to gain a better understanding of the aeroacoustic effects of the third property that is equivalent to an increased permeability of the plumage to air, an experimental survey on a set of airfoils made of different porous materials was carried out. Several airfoils with the same shape and size but made of different porous materials characterized by their flow resistivities and one non-porous reference airfoil were subject to the flow in an aeroacoustic open jet wind tunnel. The flow speed has been varied between approximately 25 and 50 m/s. The geometric angle of attack ranged from −16° to 20° in 4°-steps. The results of the aeroacoustic measurements, made with a 56-microphone array positioned out of flow, and of the measurements of lift and drag are given and discussed.

Measurement of the noise generation at the trailing edge of porous airfoils

Borrowing a concept from hydrodynamic analysis, this paper presents stream functions which satisfy Laplace's equation as a local-minima free method for producing potential-field based navigation functions in two dimensions. These functions generate smoother paths (i.e. more suited to aircraft-like vehicles) than previous methods. A method is developed for constructing analytic stream functions to produce arbitrary vehicle behaviors while avoiding obstacles, and an exact solution for the case of a single uniformly moving obstacle is presented. The effects of introducing multiple obstacles are discussed and current work in this direction is detailed. Experimental results generated on the Cornell RoboFlag testbed are presented and discussed.

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Vehicle motion planning using stream functions

Discusses the generation of a control signal that would instruct the actuators of a robotics manipulator to drive motion along a safe and well-behaved path to a desired target. The proposed concept of navigation control along with the tools necessary for its construction achieve this goal. The most significant tool is the artificial vector potential field which shows a better ability to steer motion than does a scalar potential field. The synthesis procedure emphasizes flexibility so that the effort needed to modify the control is commensurate with the change in the geometry of the workspace. Theoretical development along with simulation results are provided.

Constrained motion control using vector potential fields

Describes the theory and an experiment for a fast path planning method that is available for moving obstacle avoidance for an autonomous mobile robot by the use of the Laplace potential. This new navigation function for path planning is feasible to guide, in real time, a mobile robot avoiding arbitrarily moving obstacles and reaching the goal. The experiment is conducted to verify the effectiveness of the navigation function in obstacle avoidance in the real world. The experimental systems are composed of a position sensing camera, a mobile robot and a computer for processing the position signal and for controlling the velocity vector of the robot. Three examples are presented; firstly the avoidance of a standing obstacle, secondly the avoidance of a moving obstacle in parallel lines-bounded space, and thirdly the avoidance of one moving obstacle and another standing obstacle. The robot can reach the goal after successfully avoiding the obstacles in all cases.

Fast path planning available for moving obstacle avoidance by use of Laplace potential

This paper describes the theory and an experiment of a velocity potential approach to path planning and avoiding moving obstacles for an autonomous mobile robot by use of the Laplace potential. This new navigation function for path planning is feasible for guiding a mobile robot avoiding arbitrarily moving obstacles and reaching the goal in real time. The essential feature of the navigation function comes from the introduction of fluid flow dynamics into the path planning. The experiment is conducted to verify the effectiveness of the navigation function for obstacle avoidance in a real world. Two examples of the experiment are presented; first, the avoidance of a moving obstacle in parallel line-bounded space, and second, the avoidance of one moving obstacle and another standing obstacle. The robot can reach the goal after successfully avoiding the obstacles in these cases.

Velocity potential approach to path planning for avoiding moving obstacles

This paper describes the active control of sound transmission through a clamped rectangular plate by using piezoelectric ceramics as actuators and sensors. Optimal use of the piezo electric ceramic actuator is investigated theoretically by using the transfer function from incident sound pressure to radiated sound pressure and the first order approximated damping ratio. By apply ing direct velocity feedback control by five pieces of the actuators, substantial reduction of peak level at eigen mode frequency is obtained below the frequency range of about 1500 Hz. The use of piezo electric ceramics as actuators and as sensors fails in the direct velocity feedback control experiment, but has potential for the direct position feedback control experiment.

Sound transmission control through rectangular plate by using piezoelectric ceramics as actuators and sensors

We propose a tunable acoustic absorbing device using a Helmholtz resonator. Timing the resolution frequency of the device to a desired frequency makes it possible to absorb variable sounds. The designed device forms an array of the Helmholtz resonator with a tunable compliance. The experimental results on controlling the resonant frequency of the device will be described. A deep hole array formed by X-ray lithography is fabricated into the front plate of the device in order to absorb low-frequency noise. © 1999 Scripta Technica, Electron Comm Jpn Pt 2, 83(1): 1–6, 2000

Tunable acoustic absorber using a micro acoustic hole array

This paper describes a wind tunnel experiment on aero-acoustical effect of finite surface impedance on low Mach number (Ma) flow around a circular cylinder. Modification of surface acoustical properties of source area is said to result in reduction of radiated sound pressure level. In this paper the effect of the finite impedance not only to the acoustical effect but also to the hydrodynamic effects were examined. Three boundary conditions (BC) of surface impedance were supposed: 1) rigid surface, 2) uniform and 3) optimized impedance distribution by introducing an array of micro-scale perforation with a back space. A wind tunnel experiment was conducted according to the three types of BC with three different experimental models under the Reynolds number (Re) condition from 6 000 to 12 000. The third condition caused reduction of the far field pressure level by 6 dB at largest case compared to the first condition.

Sadao Akishita

Papers

Fast path planning available for moving obstacle avoidance by use of Laplace potential

Velocity potential approach to path planning for avoiding moving obstacles

Sound transmission control through rectangular plate by using piezoelectric ceramics as actuators and sensors

Tunable acoustic absorber using a micro acoustic hole array

Experimental Investigation on Surface Impedance Effect of Sound Radiation from Low Mach Number Flow around a Circular Cylinder