Itsuro Kajiwara

Microairplane propelled by laser driven exotic target

We propose a propulsion concept to drive a microairplane by laser that can be used for observation of climate and volcanic eruption. Since it does not have to develop thrust for vertical takeoff, and it has no engine in the normal sense, the microairplane can be very light, with its payload consisting only of observation and communication equipment. In order to demonstrate the concept, we succeeded in flying a paper microairplane driven by a 590 mJ, 5 ns pulse yttrium–aluminum–garnet laser that impinges on a double-layer “exotic target.” The coupling efficiency agrees well with simulations and with experiments.

Mechano-actuated ultrafast full-colour switching in layered photonic hydrogels

Photonic crystals with tunability in the visible region are of great interest for controlling light diffraction. Mechanochromic photonic materials are periodically structured soft materials designed with a photonic stop-band that can be tuned by mechanical forces to reflect specific colours. Soft photonic materials with broad colour tunability and fast colour switching are invaluable for application. Here we report a novel mechano-actuated, soft photonic hydrogel that has an ultrafast-response time, full-colour tunable range, high spatial resolution and can be actuated by a very small compressive stress. In addition, the material has excellent mechanical stability and the colour can be reversibly switched at high frequency more than 10,000 times without degradation. This material can be used in optical devices, such as full-colour display and sensors to visualize the time evolution of complicated stress/strain fields, for example, generated during the motion of biological cells.

Approach for Simultaneous Optimization of a Structure and Control System

The design variables of both the structural and the control parameters are optimized simultaneously by the sensitivity analyse to minimize the response due to disturbances of both white noise and colored noise subjected to a constraint so that the system is stable corresponding to high-order natural modes. Three kinds of models are adopted in the approach, namely, the original spatial model by finite element method, the reduced modal model for designing the control system, and the original modal model for assuring stability of the system. The validity and the usefulness of the present approach are verified by a vibration control experiment of a steel plate

Integrated optimum design of structure and H∞ control system

An approach for an integrated optimum design of a structure and an H∞ control system is presented. The complex method and the genetic algorithm are adopted in the optimization process in the integrated design. The structural shape and the control system, including the locations of both sensors and actuators, are optimized simultaneously by the proposed approach. The improvement of frequency response shaping under the constraint of the structural mass can be realized by the integrated optimum design presented in this paper. The desired properties with respect to the control performance and the robustness are realized by the frequency shaping ability of H∞ control. Effectiveness of the presented approach is verified by both simulation and experiment by the integrated design of a panel structure and H∞ control system.

SIMULTANEOUS OPTIMUM DESIGN OF SHAPE AND CONTROL SYSTEM FOR MICRO AIR VEHICLES

Technology for micro air vehicles (MAV) has been attracting the attention of researchers. Multidisciplinary optimization is expected to help achieve the stability and higher performance required for successful MAVs. This paper demonstrates the use of simultaneous aerodynamic shape optimization and control system design for improved stability and performance. The objective of the optimization is to reduce the control energy and improve stability for controlling the roll motion, which becomes increasingly difficult to control as vehicle size gets smaller.

DESIGN OF SHAPE AND CONTROL SYSTEM FOR SMART STRUCTURES WITH PIEZOELECTRIC FILMS

A smart structure is composed of piezoelectric film sensor and actuator in order to reduce the structural vibration. H2 controller is designed with the reduced order model of the smart structure which is obtained by finite element and modal analyses. The control force is applied by the piezoelectric film actuator and the feedback signals are detected by the piezoelectric film sensor and the accelerometer in the system. The modal control and the displacement control with the appropriate actuator placement are conducted by selecting the modal coordinates and the spatial displacement as the controlled response, resulting in the effective vibration reduction. Efficient optimization algorithm based on the two-step procedure is employed in the simultaneous optimization of structural/pi ezoelectric shape and H2 control system. It is verified by some applications that the enhanced performance for the vibration suppression can be achieved by the simultaneous optimization. NOMENCLATURE b; Width of the beam structure bi; Width of z-th piezoelectric actuator element Cs; Damping matrix of the structure F; State feedback gain Hu; Performance index with respect to « Hzim, Performance index with respect to z\ K; Dynamic compensator as controller Ks; Stiffness matrix of the structure L ; Length of the piezoelectric sensor Ms; Mass matrix of the structure Mst; Mass of the structure q ; State vector of the system tB ; Thickness of the structure tc \ Thickness of the piezoelectric film ii; Control input Va ; Input voltage to the piezoelectric film actuator

Active vibration suppression of membrane structures and evaluation with a non-contact laser excitation vibration test

To realize a vibration suppression of flexible structures like a membrane, our research focuses on introducing smart structures technology into the membrane structure. In this study, the membrane structure is composed of a vibration control system using a flexible Polyvinylidene fluoride (PVDF) film as an actuator. A non-contact vibration test system, which uses a high power Nd: YAG pulse laser for producing an ideal impulse excitation and laser Doppler vibrometers for measuring the response on the membrane, is employed to evaluate the vibration characteristics of the smart membrane structure. To confirm the effectiveness of the proposed method, using a flexible PVDF actuator installed on the membrane structure, control experiments with H ∞ control for reducing single mode and multiple modes vibration are conducted. In the results of the control experiments for single mode vibration suppression, a corresponding resonance peak is reduced by around 20 dB. In case of multiple modes vibration suppression, the first and second resonance peaks are reduced by 14 dB and 24 dB, respectively. This study demonstrates that the present control method using a flexible piezoelectric element and a non-contact vibration test system effectively suppress and evaluate the vibration responses of smart membrane structures.

Dynamic characterizations of underwater structures using non-contact vibration test based on nanosecond laser ablation in water: Investigation of cavitation bubbles by visualizing shockwaves using the Schlieren method

A pulsed-laser ablation method for non-contact experimental vibration analysis of completely submerged underwater structures is proposed. Although impact testing with an impulse hammer is commonly used for vibration analysis due to its simplicity, impact testing has limited use in underwater conditions. An input-detection-free frequency response function measurement in water will greatly contribute to the development of high-precision and high-speed positioning autonomous underwater vehicles, underwater vehicle-manipulators, underwater robots, submarines, etc., which are used in dangerous conditions (e.g., deep oceans, under ice, and nuclear reactor plants). To achieve these high-performance underwater systems, vibrations due to hydrodynamic parameters (such as added mass, buoyant force, drag force, and damping coefficient) should be suppressed, and vibration tests should be conducted on the actual equipment submerged in water. The proposed method yields the frequency response function by applying a pulsed-laser-ablation excitation force to an underwater structure and measuring the output using a laser Doppler vibrometer. Because the direction, strength, and effective duration of the pulsed-laser-ablation force are essentially constant, this force can be estimated by measuring these properties in advance. Hence, the proposed method realizes input-detection-free frequency response function measurements in underwater conditions.

Multidisciplinary Design Optimization for Vibration Control of Smart Laminated Composite Structures

The structure and vibration control system of smart laminated composites consisting of graphite–epoxy composites and piezoelectric actuators are designed for optimum vibration suppression. The placement of piezoelectric actuators, the lay-up configurations of laminated composite plates, and the H2 control system are employed as design variables and they are optimized simultaneously by a simple genetic algorithm. To reduce complexity, only pre-selected families of lay-up configurations are considered. An objective function is the H2 performance with respect to the controlled response for vibration suppression. A multidisciplinary design optimization is performed with the above three design variables and then the output feedback system is reconstructed with a dynamic compensator based on a linear matrix inequality approach. The validity of the modeling and calculation technique is confirmed experimentally. Optimization results show that optimized smart composites with the present approach successfully realize vibration suppression and it is confirmed that the proposed multidisciplinary design optimization technique enhances the vibration suppression of smart composites.

Integrated design of structure and control system considering performance and stability

Integrated optimum design of structure and control system is expected to achieve the higher performance of various mechanical systems. Recently, much efforts have been given to develop the integrated optimization methods in order to improve the dynamic characteristics of the combined structure/control systems. The objective of this paper is to present some concepts of the integrated optimum design in vibration control problems. Some integrated optimization problems are introduced with applications.