別紙42 (課程博士(和文))2022年
機械工学専攻氏名

学籍番号第 153111 号

指導教員

真下智昭

佐藤海二

1月

6日

出原俊介

論文内容の要旨(博士)
博士学位論文名

リニア超音波モータの小型化と高性能化に関する研究(要旨 1,200字程度)
近年,内視鏡のような医療機器やスマートフォンなどのカメラモジュールの小型化が期待されている.そのような装置において,りニアモータの小型化は,ズームやオートフォーカスを行う機構を小型化するために重要な課題である.しかし,モータは小さくなるにつれて,発生力および応答性が低下し,必要な性能が得られなくなるという問題がある.圧電効果を駆動原理とする超音波モータは,シンプルな構造で,体積あたりの推力が大きいことから,小型りニアアクチュエータとしての期待が高い.実際,さまざまな振動モードを使用したりニア超音波モータが提案されており,比較的高い推力を示している.しかし,これらの原理は,ステータが長いもしくは複雑な形状であることや,予圧機構やガイド機構といった追加機構による大型化が問題となっている
本研究は,小型ロボットやカメラデバイスへの応用に向けて小型りニア超音波モータの研究開発を行なった.ーつ目は,ステータが立方体形状のマイクロリニア超音波モータで,ステータの大きさは高さ2.6 mm,幅2.6 mm,奥行き22 mmである.ステータには直径1.4mmの穴があり,スライダが挿入されて直動動作を行う.スライダはスリット加工が施された薄肉円筒であり,弾性変形によって予圧を与えている.ステータの設計するため,振動のモデル化しを行い,最適な形状の検討を行った.さらに,スライダの設計方法にっいては,薄肉円筒の1単陛力学に基づいて明らかにした.試作したモータは実験的に評価され,予圧を最適化することで,10 mN以上の実用的な推力を発揮した.また,入力電圧の印加時間を調整することにより,約l mの微小変位が得られた.二つ目は,駆動方向に短い薄型形状のスライダを用いたりニア超音波モータである.このモータは穴の開いた薄い板状のステータと,スリット加工を施した薄肉円筒のスライダで構成されており,駆動原理の検証とモータの基本nり陛能の評価を行った.小型ステータの高さと幅は約4.5 mm,厚さは約l mmで,スライダを挿入するための中央の穴は2.7 mmである.推力は,電圧50 V̲で約8 m,,N,10O VP̲Pで約B mNと,オートフォーカス機構として実用的な推力を発揮する.さらに,モータとカメラデバイスを組み合わせたオートフォーカス機構を試作し,実際にレンズの位置調節を行う.最後に,この薄型りニア超音波モータの駆動原理を基に大きさ約l mmの超小型りニア超音波モータを開発し,駆動実験によって性能評価を行った
この論文で提案する小型りニア超音波モータは従来の小型りニアモータでは達成できない小さなサイズで実用的な性能を発揮することができ,スマートフォンや内視鏡などの幅広いアプリケーションの小型化を可能にする男1絲氏4

1 (課程博士(英文))Date of submission (month day, year)
Department ofStudentlD Number

Pplicant's name2022

TomoakiMashimo

D153111

Inechanicalengineering

Jan. 6tl】

Supervisors

Kaiji sato

Shunsukelzuhara

Abstract (Doctor)
Title ofThesis

Miniaturization and perforlnance lmprovement ofLinear ultrasonic Motors

Approx.80o words

Miniature linear actuators are required for a variety of future devices ranoing 介om mobile devices
to minimaⅡy invasive medicines. For example, the miniaturization ofcamera modules is required tomeetthe rising demand forthinner and more compact structures in various fields, such as ceⅡPhones,drones, and endoscopes. A camera module for smartphones must be designed to be thin because thethickness of smartphones is strictly limited by uleir specifications.1n these, miniature linear
actuators play an importantrole in controHing optical systems, such as zoom and autofocus features,

to aⅡ0、u camera modules to obtain clearer images. For thinner and smaⅡer appHcations, a further
miniaturization of auto・focus mechanisms is expected. Therefore, miniature of Hnear actuators is aPerman引lt target for such applications, as existing Hnear actuators cannot satisfy the specifications
required for the miniature devices such as dimensions and thrusting force.
Piezoelectric ultrasoniC 1110tors have the potential to become the most appropriate Hnear motors forminiature applications as they feature simple S廿Ucture and high force density.1n fact, several
miniature linear ultrasonic motors have been already implemented to cameras. Their theory ofOperation depends mainly on the simultaneous excitation oft、No vibration modes and resonantimpact
drive mechanisms. This drive mechanisms employs vibration modes that are dependent on the statorIength. Although these miniature linear ultrasonic motors provide a relatively hi今h force density, therequirelnent of a long stator adds to the complexity of further miniaturization.

Further miniaturization of Hnear ultrasonic motors has been studied using several principles in thePast, but stiH none has satisfied the requirement of many applications. This thesis introduces t、NO
miniature linear ultrasonic motors. several vibration modes have been implemented as the driving
Principles ofthe prototypes. The result prototypes, to our knowledge, are the sma11est and the thinner
Iinear motors ever made.

The first prototype is a micro linear ultrasonic motor 圦ノith a cuboid stator. The stator comprises of a
metaⅡic cuboid and piezoelectric elements bonded to its four sides. The size of the prototype stator
With piezoelectric elements measureS 2.6 mm in height,2.6 mm in 、刃idth, and 22 mm in depth (1ength
in slider travel direction). There is a hole of l.4 mm at the stator center, and the slider inserted into
the hole moves linearly. This h0Ⅱ0、入' design is similar to the voice coil motor and is suited as Hnear

actuators for miniature auto・focus mechanisms. As dle driving principle, it uses the simultaneous
excitation of t、vo vibration modes generated by the cuboid stator. Experiments clarify the output
Characteristics in response to the input voltages. By optimizing the preload bet、Neen the stator andSlider experimenta11y, the motor thrust force has been improved to over lo mN,、Nhich is a practicalforce for moving sma110bjects.1n addition, a minute displacement ofabout 1 μm can be obtained byadjusting dle input time ofthe applied voltage.
The second one is a miniature linear piezoelectric ultrasonic motor 、Nith a thin and h0110、入, desion.1t

Consists of a thin square stator 、vith a hole and an elastic cylindrical slider 、Nith a slit. The miniature
Stator has a height and width of 4.5 mm and a thickness of less than l mm 、Nith a center hole of 2.フ

mm forinsertinσ the slider. The slider is designed to have a sHghtly larger diameterthan the diameterOf the stator hole, and the cylinder expands radia11y and contacts the inner surface ofthe rigid stator
representing a preload force. This design provides both a h0Ⅱ0、N structure for centering a lens andan optimal preload for enhancing the motor thrust force. Aftel' optimizing the preload empirica11y,
the fundamental characteristics are evaluated experimentaⅡy.1he output force is improved toapproximately 8 mN at a voltage 50 VP̲P. A higher thrust force of 12.9 mN that leads to a quick
response,、Nhich is a requirement of autofocusing is obtained at a voltage ampHtude of loo vp‑P. A
Practical experiment to prove the feasibility of the prototype for auto・focus mechanisms has been
Carried out. The experiment is conducted by fitting an actua11ens to the prototype, then place theIens at a distance of an image sensor. A feedback control system is then implemented to change thedistance bet、Neen the sensor and the lens to get a clearer image. Furthermore, this motor isminiaturized to a length of lmm and a thickness of 03 mm, and its performances are evaluated.
The findings in this thesis demonstrate thatthe proposed motors provide size and performances that
Cannot be achieved by conventional miniature linear motors.