Masaki Hamamoto

New developments in laser-assisted magnetic recording

Recent progress in laser-assisted magnetic recording, which combines optical and magnetic recording technologies, is described in this paper. This study confirms that laser-assisted magnetic recording is a good candidate for high areal density magnetic recording. Improved disk performance was demonstrated in the area of frequency response, media noise, and thermal decay. The improvements in media design include the change in temperature dependence of the recording layer, an increased perpendicular anisotropy, and a thermally efficient layer structure. These improved media properties result in a high linear density and good thermal stability.

Design of Flexible Wing for Flapping Flight by Fluid-Structure Interaction Analysis

We investigated some configurations of middle-size and high-aspect ratio wings for flapping flight by fluid-structure interaction simulation. Mimicking the flapping flight of insects is a useful method of microrobot motion. Its comprehensive unsteady aerodynamics has gradually been unraveled and several types of flapping-flight robots have been proposed. We examined the motion of a dragonfly, and try to apply it to microrobots. In designing such nimble flapping flight, adequate evaluation of the deformation of the wing is unavoidable. Wings of such species have high aspect ratio because a small momentum of inertia around the longitudinal axis is a great advantage in controlling. Such a slender wing is easy to twist around the longitudinal direction. Thus, in order to design such a wing, the wing behavior caused by interaction with the airflow must be analyzed, and the adequate stiffness must be determined. We designed two types of wings based on the architecture of the dragonfly’s wing, and examined the performance of the wings by fluid-structure interaction analysis. Here we show some examples of the designs and the performance of the wings for hovering, as the results of the first trial.

Crosstalk canceling for laser-assisted magnetic recording

A promising method of crosstalk canceling is proposed for laser-assisted magnetic recording, which makes it possible to record and read with a narrow track pitch limited to nearly the size of a focused laser spot. In this method, a track pitch narrower than the laser spot size is obtained by utilizing the canceling of the leakage flux from an adjacent track. We achieved a crosstalk of −24 dB or less with a 0.7 μm track pitch in laser-assisted magnetic recording by using a laser spot size of 1.07 μm in diameter and a magnetoresistive head with a track width of 1.4 μm.

Investigation on force transmission of direct-drive thorax unit with four ultrasonic motors for a flapping microaerial vehicle

We fabricated a trial version of a thorax unit with four ultrasonic motors (USMs) to simulate a dragonfly-scale flapping micro aerial vehicle (MAV). Each wing was directly driven by a two-degree-of-freedom (2-DOF) transmission. An in-house tiny standing-wave USM capable of bidirectional rotation, which weighs just 0.13 g, was employed on trial. The transmission of the thorax unit converts the two USM rotations into strokes and flip motions of the wing. By implementing two 70-mm-long wings, we fabricated a prototype of a 4-DOF MAV and tested its performance. In a lift-compensated situation, upward, forward, and backward movements of the MAV were obtained. The flapping angular velocity was discussed based on quasi-static wing aerodynamics and was accountable for the motor power. Although the power of the USM should be improved, the quick wing drivability, adequate power transmission on the thorax unit, and potential of a 0.2 W motor power in a unidirectional-type USM promise the viability of a direct-drive multi-DOF dragonfly-scale MAV. Graphical Abstract

Basic Design Strategy for Stiffness Distribution on a Dragonfly-Mimicking Wing for a Flapping Micro Aerial Vehicle

A basic configuration of a flexible wing is derived from that of a real dragonfly. To realize the development of a flapping micro aerial vehicle, it is essential to study real insects flight. In particular, the sophisticated structure of the wing contains many helpful hints for the solution of the efficiency. However, to solve the fluid–structure interaction problem between wing deformation and the surrounding airflow has been quite difficult, and the study of the ultimately light wing has been inhibited. We analyzed this problem using a novel numerical simulation — finite element analysis based on the arbitrary Lagrangian–Eulerian method, which can treat the interactive behavior accurately. A comparison of wing deformations and surrounding airflows for 13 wing models, actuated in the same way as is hovering by a real dragonfly and having one-third to 23 times the Youngs modulus of a real dragonfly wing, indicated that the real wing positioned on the lower border of the zone where the flight efficiency was sustained. It was also observed that the wingtip area, the attitude of which plays a dominant role in determining the efficiency, was mainly supported by the structural stiffness of a shallow groove that crosses the wing diagonally.

Free-flight analysis of dragonfly hovering by fluid–structure interaction analysis based on an arbitrary Lagrangian–Eulerian method

A ‘free-flight’ simulation of flapping flight based on fluid–structure interaction analysis, which can treat the large deformation of wings quantitatively, is applied to the hovering of the dragonfly. Recently, experimental methods and numerical simulation have made significant progress in solving the unsteady aerodynamics of flapping flight, and succeeded in quantifying it under a tethered situation. However, to analyze the stability of hovering or acrobatic flight modes, free-flight simulation is essential. Especially, the structural dynamics of a light and resultantly deformable wing may seriously affect the controllability of flight. We implement the interaction between a body and wing in the fluid–structure interaction analysis, and solve the free-flight situation, where the wing lifts the body and the body actuates the wing. Although the modeled dragonfly is artificially designed to have only two wings to avoid needing to consider the problem of contact between wings and it might, therefore, have less controllability than the real dragonfly, the free-flight simulation closely matches the real stable flight of the dragonfly, thus demonstrating of the adequacy of the simulation. In addition, the altitude and pitch angle of the body are confirmed to be recovered by slight artificial tilt of the stroke plane.

Feasibility study of an actuator for flapping flight using fluid-structure interaction analysis

An actuator for a middle-sized flapping flight robot is quantitatively investigated. Flapping flight like that of insects is a potentially useful method of travel for micro robots. Some insect-mimicking robots have been developed, which have actuators with two or more degrees of freedom per wing. For the detailed design of such an actuator, it is necessary to deal with the interaction between the behavior of the actuator and the aerodynamic forces generated by the actuation. In particular, the torque and power requirements of each degree of freedom are essential in the choice of a suitable motor, but it is impossible to determine these without considering the interaction between the driving force of the actuator and the reaction force of the wing from the surrounding airflow. Here, we achieved an analysis of the mechanical aspects of flapping flight, actuator and wing, using finite element analysis based on the arbitrary Lagrangian-Eulerian method, which can treat the fluid-structure interaction problem properly. We worked out the spec of motors for the 2DOF actuator, and investigated the structural tolerance. We developed a useful tool for the design of flapping flight robots

Thorax unit driven by unidirectional USM for under 10-gram flapping MAV platform

A unidirectional ultrasonic motor (USM) is applied to the thorax unit of a flapping micro aerial vehicle (MAV) with the aim to develop an MAV in the 10-gram-range, for which appropriate DC motors with high power-weight ratios are unavailable. As a trial, a unidirectional USM having an ultrasonic transducer with mass of 336 mg and rotor of 3 mm diameter is implemented to a belt drive mechanism in place of a DC motor and spar gear unit. At no load and without wings, the USM works well and achieves a flapping frequency exceeding 32 Hz, while the output power is around 36 mW owing to the mismatch of the two vibration modes that dominate the efficiency of the USM. Although the observed lift force remains low because of the lack of USM power and heaviness of the wings, the appropriateness of the mechanical design is confirmed and improvements toward the 10-gram-range flapping MAV with USM are discussed on the basis of these results. Another actuation mechanism of the flapping MAV is proposed.