Yamaguchi-Nishi Laboratory is engaged in research to improve the health and function of mechanical systems and to enhance human mobility based on contact and friction control of soft materials such as rubber and living organisms and human motion analysis. Aiming for innovation in the field of life support through the soft mechanics research, we are also focusing on cross-disciplinary and interdisciplinary research with domestic and international research institutions, and industry-academia co-creation for social implementation of research results.

山口・西研究室ではゴムや生体などのやわらかい材料（ソフトマテリアル）の摩擦制御や人間の運動解析を基盤として，機械システムの健全性・機能向上や人間の運動機能向上に向けた研究に取り組んでいます．ライフサポート分野におけるイノベーションの創出を目指して，国内外の研究機関との分野横断型・異分野融合研究や，研究成果の社会実装のための産学共創にも力を入れています．

Tribology of soft materials / ソフトマテリアルのトライボロジー

Soft materials such as rubber exhibit high friction under dry conditions, but under liquid lubrication conditions such as water or oil, a fluid lubrication film forms at the contact interface, resulting in low friction. Therefore, it has been a long-standing issue to improve the friction of rubber materials in liquids for shoe soles and automobile tires. In our laboratory, we develop contact surface observation techniques, ultra-high-friction designs, and ultra-high-friction soft materials to achieve ultra-high friction of soft materials in water and oil. We are also working on friction control of skin contact with fibrous structures such as cloth or non-woven fabrics.

ゴムなどのソフトマテリアルは乾燥状態では高い摩擦を示しますが，水や油などの液体による潤滑条件下では接触界面に流体潤滑膜が形成されやすく低摩擦となります．そのため靴底や自動車タイヤにおいて，ゴム材料の液体中での高摩擦化は長年の課題となっています．当研究室では水中や油中におけるソフトマテリアルの超高摩擦化を目指して，接触面観察技術や超高摩擦意匠，超高摩擦材料の開発に取り組んでいます．また布あるいは不織布などの繊維状構造体と肌の接触における摩擦制御にも取り組んでいます．

Example of research themes / 研究テーマの例

• Elucidation of the mechanism of ultra-high friction of soft materials in oil / 油中におけるソフトマテリアルの超高摩擦発現メカニズムの解明
• Development and application of measurement method for strain distribution in soft materials on contact surface of soft material / ソフトマテリアルの接触面内ひずみ分布計測手法の開発と応用
• Development of high-friction technology for soft materials by non-uniform wetting / 不均一な濡れによるソフトマテリアルの高摩擦化技術の開発
• Development and application of technology to improve high friction of soft materials by non-uniform wetting / スポーツテキスタイルと肌の付着力制御によるべたつき抑制

References/参考文献

1. Takeshi Yamaguchi, Takehiko Sugawara, Motoi Takahashi, Kei Shibata, Kenta Moriyasu, Tsuyoshi Nishiwaki, Kazuo Hokkirigawa, Dry sliding friction of ethylene vinyl acetate blocks: effect of the porosity, Tribology International,116 (2017) 264-271. https://doi.org/10.1016/j.triboint.2017.07.022
2. Toshiaki Nishi, Takeshi Yamaguchi, Kei Shibata, Kazuo Hokkirigawa, Influence of unforced dewetting and enforced wetting on real contact formation and friction behavior between rubber hemisphere and glass plate during contacting and sliding processes, Tribology International, 141 (2020) 105921. https://doi.org/10.1016/j.triboint.2019.105921
3. Toshiaki Nishi, Takeshi Yamaguchi, Kei Shibata, Kazuo Hokkirigawa, Friction behavior   between an artificial skin block and a glass plate in unlubricated and partly/completely water-lubricated conditions, Tribology International，163 (2021) 107179. https://doi.org/10.1016/j.triboint.2021.107179
4. Arata Ishizako, Hide Matsumoto, Takeshi Yamaguchi, Relationship between end-face corner radius of rubber block and friction coefficient and fluid-free gap under lubrication, Tribology International, 184 (2023) 108473. https://doi.org/10.1016/j.triboint.2022.107705

Prevention of slips, trips and falls / すべり・つまずき転倒の防止に関する研究

In recent years, it has been reported that the number of deaths due to falls both indoors and outdoors exceeds the number of deaths due to traffic accidents. Falls among the elderly are a particularly serious problem in Japan’s aging society. Falls are also a major cause of workplace accidents. Many of these accidents are caused by slipping or tripping. Our laboratory focuses on the friction between the sole and the floor surface to experimentally and theoretically elucidate the friction conditions between the sole and the floor surface necessary for stable walking, and to develop technologies to prevent falls caused by slips and trips.

近年，屋内外における転倒事故による死亡者数は交通事故死亡者数を上回ることが報告されています．特に高齢者の転倒事故は高齢社会に突入した日本では大きな問題です．また転倒事故は労働災害の主要な発生原因ともなっています．転倒事故の多くは「すべり」や「つまずき」によって発生しています．当研究室では足底と床面間の摩擦に着目し，安定に歩行するために必要な足底と床面間の摩擦条件を実験的・理論的に解明するとともに，すべりやつまずきによる転倒を防止するための技術開発に取り組んでいます．

Example of research themes / 研究テーマの例

• Elucidation of the effect of floor friction on slip- and trip-induced falls using a neuromusculoskeletal model / 神経筋骨格モデルを用いたすべり・つまずき転倒に及ぼす床面摩擦の影響の解明
• Development of super high-slip resistant shoe sole / 超耐滑靴底の開発
• Development of a system for measuring the coefficient of friction between shoe soles and floor surface/靴底-床面間の摩擦係数測定システムの開発
• Development of sensor shoes equipped with a compact 3-axis force sensor and an inertial sensor /小型3軸力覚センサと慣性センサを搭載したセンサシューズの開発
• Motion analysis and fall risk assessment of elderly people in real-life environment using sensor shoe / センサシューズを用いた実生活環境における高齢者の運動解析と転倒危険性評価

References / 参考文献

1. Takeshi Yamaguchi, Tomoki Umetsu, Yusuke Ishizuka, Kenichi Kasuga, Takayuki Ito, Satoru Ishizawa and Kazuo Hokkirigawa, Development of new footwear sole surface pattern for prevention of slip-related falls, Safety Science, 50, 4 (2012) 986-994. https://doi.org/10.1016/j.ssci.2011.12.017
2. Kenta Moriyasu, Tsuyoshi Nishiwaki, Takeshi Yamaguchi, and Kazuo Hokkirigawa, Experimental Analysis of the Distribution of Traction Coefficient in the Shoe-Ground Contact Area during Running, Tribology Online, 7, 4 (2012) 267-273. https://doi.org/10.2474/trol.7.267
3. Takeshi Yamaguchi, Kei Shibata, Hiromi Wada, Hiroshi Kakehi, Kazuo Hokkirigawa, Effect of foot-floor friction on the external moment about the body center of mass during shuffling gait: a pilot study, Scientific Reports, 11 (2021) 12133. https://doi.org/10.1038/s41598-021-91683-5
4. Takeshi Yamaguchi, Kei Masani, Effects of age on dynamic balance measures and their correlation during walking across the adult lifespan, Scientific Reports, 12 (2022) 14301. https://doi.org/10.1038/s41598-022-18382-7

Human dynamics and tribology / ヒューマンダイナミクスとトライボロジー

In human walking and grasping movements, force and motion are transmitted through contact and friction between the sole and the floor, and between the fingers and an object, respectively, to achieve the desired motion. For example, in baseball pitching, the number of rotations, velocity, and arrival position of the ball are controlled through friction between the fingertips and the ball. However, the interaction between human motion (human dynamics), contact and friction with the external world (tribology), and the perception of these interactions is still limited to an empirical and sensory understanding. In our laboratory, we study how the perception of friction between the ball and fingertips during baseball pitching modifies kinematics and how it affects performance and injury.

人間の歩行動作や把持動作ではそれぞれ足底と床面間，手指と物体間の接触・摩擦を介して力や運動の伝達が行われ，所望の動作が実現されます．例えば野球の投球では，ボールの回転数や球速，到達位置の制御は指先とボール間の摩擦を介して行われます．しかしながら，人間の運動（ヒューマンダイナミクス）と外界との接触・摩擦（トライボロジー），その知覚との相互作用については，経験的かつ感覚的な理解にとどまっているのが現状です．当研究室では，野球の投球について，ボールと指先間の摩擦の大小とその知覚が動作をどのように変容させ，パフォーマンスや障害にどのような影響を及ぼすのかについて研究を行っています．

Example of research themes / 研究テーマの例

• The effect of fingertip-to-ball friction on pitching performance and elbow strain / 指先-ボール間の摩擦が投球パフォーマンスと肘の負担に及ぼす影響の解明
• The effects of subjective and objective tactile sensitivity of pitchers on their adaptation to balls with different friction / 投手の触覚の主観的感度と客観的感度が摩擦の異なるボールへの適応に及ぼす影響

References / 参考文献

1. Takeshi Yamaguchi, Naoto Yamakura, Shinnosuke Murata, Takehiro Fukuda, Daiki Nasu, Effects of rosin powder application on frictional behavior between a finger pad and baseball, Frontiers in Sports and Active Living, 2 (2020) 30. https://doi.org/10.3389/fspor.2020.00030
2. Takeshi Yamaguchi, Daiki Nasu, Kei Masani, Effect of grip-enhancing agents on sliding friction between a fingertip and a baseball. Communications Materials, 3 (2022) 92. https://doi.org/10.1038/s43246-022-00317-4