IOP Publishing Acta Medica Okayama 0021-4922 65 7 2026 Study of preload mechanism for small piezoelectric transducers with hollow structure for cryogenic environments 07SP13 EN Souta Mimura Graduate School of Environment, Life, Natural Science and Technology, Okayama University Takefumi Kanda Graduate School of Environment, Life, Natural Science and Technology, Okayama University Daisuke Yamaguchi Graduate School of Environment, Life, Natural Science and Technology, Okayama University Kazuki Kubo Graduate School of Environment, Life, Natural Science and Technology, Okayama University Shuichi Wakimoto Graduate School of Environment, Life, Natural Science and Technology, Okayama University In various industrial fields, cryogenic fluids such as liquid hydrogen and liquid nitrogen are increasingly used as fuels and refrigerants. To control the flow rate of those fluids, valves that can be operated in cryogenic environments are needed. In general, the miniaturization of the valve can be achieved by using a piezoelectric ceramic as an actuator to drive the mechanism. Additionally, the properties degradation can be suppressed by applying a preload to the piezoelectric ceramic. To miniaturize the piezoelectric actuator applying preload at low temperature conditions, we use differences in thermal expansion coefficients to apply preload to the piezoelectric ceramics. In this study, we have designed and fabricated a small piezoelectric transducer with a hollow structure for cryogenic environments by using this proposed structure. To evaluate the fabricated transducer, we have measured vibration velocity and estimated the acceleration in cryogenic environments. No potential conflict of interest relevant to this article was reported.

Elsevier BV Acta Medica Okayama 0924-4247 408 2026 A flexible PVDF-based galloping flow sensor 117978 EN Mitsuki Kurose Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Takefumi Kanda Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Yuya Sato Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Shuichi Wakimoto Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Daisuke Yamaguchi Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Shinji Hiejima Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Takeji Ueda Hydro-VENUS Co., Ltd., Okayama University Effective monitoring of low flow velocities in small rivers and irrigation channels is hindered by the power requirements and maintenance costs of existing technologies. This study proposes a novel flexible piezoelectric polymer flow sensor utilizing galloping vibration to detect flow velocity in the low range (≤ 0.1 m/s). The sensor features a flexible cantilever structure composed of a silicone rubber beam embedded with a polyvinylidene fluoride (PVDF) film and a tip pillar. Unlike conventional devices based on flow-induced vibration, the use of low-stiffness materials enables the induction of self-excited vibration even under weak fluid forces. Computational fluid dynamics (CFD) analysis has been conducted to optimize the tip shape; a D-shaped semicylinder is selected over a cylinder and a square prism because the geometry maximizes the lift force per unit mass, ensuring efficient energy conversion. To predict sensor behavior, a coupled mechanical-fluid-electrical model was developed. Specifically, the model accounts for the static deflection angle caused by fluid drag. Water channel experiments demonstrated that sensors with beam thicknesses under 4 mm successfully generated stable periodic outputs at 0.1 m/s, a regime previously difficult for galloping-based devices. Conversely, thicker beam which has a thickness of 8 mm achieved higher outputs at higher velocities but failed to actuate at low speeds. Furthermore, the study showed a vibration suppression phenomenon in flexible beams at high flow velocities due to excessive static deflection, which was accurately reproduced by the analytical model. These findings establish structural stiffness as the critical design parameter for optimizing the operable velocity range of flow sensors. No potential conflict of interest relevant to this article was reported.

Elsevier BV Acta Medica Okayama 0924-4247 408 2026 Tip position estimation of a 3-DOF soft mechanism using artificial muscles with optical fibers 117938 EN Rikimaru Okada Graduate School of Environment, Life, Natural Science and Technology, Okayama University Shuichi Wakimoto Graduate School of Environment, Life, Natural Science and Technology, Okayama University Yuichiro Toda Graduate School of Environment, Life, Natural Science and Technology, Okayama University Shun Miura Graduate School of Environment, Life, Natural Science and Technology, Okayama University Daisuke Yamaguchi Graduate School of Environment, Life, Natural Science and Technology, Okayama University Takefumi Kanda Graduate School of Environment, Life, Natural Science and Technology, Okayama University McKibben-type pneumatic artificial muscles (PAMs) are lightweight and flexible soft actuators with a high power-to-weight ratio, and have been widely applied to rehabilitation devices, power-assist systems, and soft robotic mechanisms. By integrating sensing functions into PAMs, their usability and controllability can be enhanced, enabling the development of more practical and advanced soft mechanisms. We previously proposed a smart artificial muscle (SAM) by integrating an optical fiber into the braided sleeve of a McKibben-type PAM, which enables displacement estimation by measuring optical bending loss. The SAM is compatible with conventional PAM fabrication processes; however, the sensor output exhibits strong nonlinearity and time dependency. In this study, an LSTM-based state estimation framework is extended from a single SAM to a three-degree-of-freedom soft mechanism composed of multiple SAMs, where strong nonlinear coupling and mutual interference arise among actuators. In the proposed framework, the LSTM model jointly processes time-series data of multi-channel optical sensor outputs and applied pressures of the three SAMs, along with past estimated states as inputs. This structure enables the model to capture nonlinear coupling, hysteresis, and time-dependent behavior, allowing estimation of the tip position of the soft mechanism. Experimental results demonstrate that the proposed method accurately captures complex nonlinear dynamics and mutual mechanical interference among multiple SAMs, achieving accurate tip position estimation. These results indicate that SAMs with integrated sensing and actuation capabilities, combined with machine-learning-based estimation, provide an effective approach for state estimation of multi-DOF soft robotic mechanisms. No potential conflict of interest relevant to this article was reported.

MDPI Acta Medica Okayama 1424-8220 25 7 2025 Length Estimation of Pneumatic Artificial Muscle with Optical Fiber Sensor Using Machine Learning 2221 EN Yilei Ni Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Shuichi Wakimoto Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Weihang Tian Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Yuichiro Toda Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Takefumi Kanda Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Daisuke Yamaguchi Graduate School of Environmental, Life, Natural Science and Technology, Okayama University A McKibben artificial muscle is a soft actuator driven by air pressure, characterized by its flexibility, lightweight design, and high power-to-weight ratio. We have developed a smart artificial muscle that is capable of sensing its motion. To enable this sensing function, an optical fiber was integrated into the sleeve consisting of multiple fibers and serving as a component of the McKibben artificial muscle. By measuring the macrobending loss of the optical fiber, the length of the smart artificial muscle is expected to be estimated. However, experimental results indicated that the sensor's characteristics depend not only on the length but also on the load and the applied air pressure. This dependency arises because the stress applied to the optical fiber increases, causing microbending loss. In this study, we employed a machine learning model, primarily composed of Long Short-Term Memory (LSTM) neural networks, to estimate the length of the smart artificial muscle. The experimental results demonstrate that the length estimation obtained through machine learning exhibits a smaller error. This suggests that machine learning is a feasible approach to enhancing the length measurement accuracy of the smart artificial muscle. No potential conflict of interest relevant to this article was reported.

MDPI Acta Medica Okayama 2076-0825 13 3 2024 A Microchannel Device for Droplet Classification by Manipulation Using Piezoelectric Vibrator 95 EN Ao Fujioka Graduate School of Natural Science and Technology, Okayama University Shoko Seo Graduate School of Natural Science and Technology, Okayama University Takefumi Kanda Graduate School of Natural Science and Technology, Okayama University Shuichi Wakimoto Graduate School of Natural Science and Technology, Okayama University Daisuke Yamaguchi Graduate School of Natural Science and Technology, Okayama University Emulsion formulations should be monodispersed in terms of their stability. Therefore, there is a need for a device that can classify droplets of the desired size from polydispersed emulsions in a fluidized bed manufacturing system. In the previous study, we evaluated the fabrication of a droplet manipulation device using acoustic radiation forces through simulation using the finite element method. In this study, particle manipulation experiments using 1, 6, and 10 mu m polystyrene particles were first estimated and evaluated in comparison with their theoretical particle behavior. Based on the results we obtained, the driving conditions and droplet behavior were derived, and the droplet manipulation device using ultrasonic waves to shrink monodisperse emulsions was evaluated. As a result, the droplet classification effect in the microchannel was confirmed to be consistent with the droplet behavior prediction, and the microchannel structure with a constriction component improved its classification effect. No potential conflict of interest relevant to this article was reported.

IOP Publishing Acta Medica Okayama 0021-4922 63 3 2024 Evaluation of transducer for cryogenic actuators by equivalent circuit model 03SP03 EN Kazuki Kubo Graduate School of Environment, Life, Natural, Science and Technology, Okayama University Kairi Yagi Graduate School of Environment, Life, Natural, Science and Technology, Okayama University Takefumi Kanda Graduate School of Environment, Life, Natural, Science and Technology, Okayama University Koa Yasuda Graduate School of Environment, Life, Natural, Science and Technology, Okayama University Daisuke Yamaguchi Graduate School of Environment, Life, Natural, Science and Technology, Okayama University Shuichi Wakimoto Graduate School of Environment, Life, Natural, Science and Technology, Okayama University Cryogenic environments are increasingly used in scientific and industrial fields. Recently, cryogenic environments are also used for storage and supply of liquid hydrogen, which is considered essential for the realization of a decarbonized society. Actuators to drive a valve that controls such a low-temperature fluid are required. In this study, a piezoelectric transducer that can be driven in the cryogenic environment has been fabricated and evaluated. Although the performance of piezoelectric elements degrades at cryogenic temperatures in general, the application of a preload can suppress the degradation of performance. Equivalent circuits were used for evaluation, and force factors and figures of merit were compared. As a result, the force factor was as high as that at RT even at cryogenic temperatures, and a high figure of merit was obtained. The result indicates that the transducer can be used for the driving of micro actuator at cryogenic temperature. No potential conflict of interest relevant to this article was reported.

MDPI Acta Medica Okayama 1424-8220 22 9 2022 Displacement Sensing of an Active String Actuator Using a Step-Index Multimode Optical Fiber Sensor 3232 EN Weihang Tian Graduate School of Natural Science and Technology, Okayama University Shuichi Wakimoto Graduate School of Natural Science and Technology, Okayama University Takefumi Kanda Graduate School of Natural Science and Technology, Okayama University Daisuke Yamaguchi Graduate School of Natural Science and Technology, Okayama University A thin McKibben artificial muscle is a pneumatic actuator with an outer diameter of only 1.8 mm. We fabricated a string-shaped actuator called an "active string actuator," which achieves a high contractile displacement by accumulating thin McKibben artificial muscles. To control the displacement, the length of the active string actuator should be estimated. However, this is difficult because bulky and rigid sensors are unsuitable for the sensor element of the active string actuator. Therefore, in this study, we propose a new sensing method for estimating the length of an active string actuator. The proposed sensing system is simple and comprises only three components: a step-index multimode optical fiber, a light emitter, and a light receiver. A step-index multimode optical fiber was combined with the active string actuator, and the length was estimated from the change in the amount of light propagating in the optical fiber when the active string actuator was driven. Fundamental experiments were conducted in this study, and the results demonstrated that the optical fiber sensor value changed with the actuator length. This suggests that it is possible to estimate the displacement of an active string actuator using an optical fiber sensor. No potential conflict of interest relevant to this article was reported.

MDPI Acta Medica Okayama 2076-0825 10 3 2021 Core-Shell Droplet Generation Device Using a Flexural Bolt-Clamped Langevin-Type Ultrasonic Transducer 55 EN Kentaro Omori Graduate School of Natural Science and Technology, Okayama University Nozomu Fujimoto Graduate School of Natural Science and Technology, Okayama University Takefumi Kanda Graduate School of Natural Science and Technology, Okayama University Shuichi Wakimoto Graduate School of Natural Science and Technology, Okayama University Norihisa Seno Graduate School of Natural Science and Technology, Okayama University Droplets with a core-shell structure formed from two immiscible liquids are used in various industrial field owing to their useful physical and chemical characteristics. Efficient generation of uniform core-shell droplets plays an important role in terms of productivity. In this study, monodisperse core-shell droplets were efficiently generated using a flexural bolt-clamped Langevin-type transducer and two micropore plates. Water and silicone oil were used as core and shell phases, respectively, to form core-shell droplets in air. When the applied pressure of the core phase, the applied pressure of the shell phase, and the vibration velocity in the micropore were 200 kPa, 150 kPa, and 8.2 mm/s, respectively, the average diameter and coefficient of variation of the droplets were 207.7 mu m and 1.6%, respectively. A production rate of 29,000 core-shell droplets per second was achieved. This result shows that the developed device is effective for generating monodisperse core-shell droplets. No potential conflict of interest relevant to this article was reported.

Elsevier Acta Medica Okayama 0924-4247 164 1-2 2010 Multiplex pneumatic control method for multi-drive system 88 94 EN Yasutaka Nishioka Koichi Suzumori Takefumi Kanda Shuichi Wakimoto Pneumatic actuators have several advantages such as light weight safety low cost and high compliance However many pneumatic actuators have complicated systems that include a compressor air tubes and pneumatic valves with electrical wires This research proposes a new control method for a multiplex pneumatic transmission constructed with special resonant valves and air tubes with a control system driven by air vibration in air tubes without electrical wires The control is simplified and effective for pneumatic systems having many degrees of freedom In this paper the development of a primitive model of the resonant valve and a prototype valve is described In addition two control methods which are a superimposing method and a time-sharing method are shown and the independent driving of four actuators is realized by using one of the control methods with air tubes only. No potential conflict of interest relevant to this article was reported.

IOP Publishing Acta Medica Okayama 0964-1726 20 10 2011 Design of a variable-stiffness robotic hand using pneumatic soft rubber actuators EN Jun-ya Nagase Shuichi Wakimoto Toshiyuki Satoh Norihiko Saga Koichi Suzumori In recent years, Japanese society has been ageing, engendering a labor shortage of young workers. Robots are therefore expected to be useful in performing tasks such as day-to-day support for elderly people. In particular, robots that are intended for use in the field of medical care and welfare are expected to be safe when operating in a human environment because they often come into contact with people. Furthermore, robots must perform various tasks such as regrasping, grasping of soft objects, and tasks using frictional force. Given these demands and circumstances, a tendon-driven robot hand with a stiffness changing finger has been developed. The finger surface stiffness can be altered by adjusting the input pressure depending on the task. Additionally, the coefficient of static friction can be altered by changing the surface stiffness merely by adjusting the input air pressure. This report describes the basic structure, driving mechanism, and basic properties of the proposed robot hand. No potential conflict of interest relevant to this article was reported.

日本設計工学会 Acta Medica Okayama 0919-2948 46 9 2011 空気圧剛性可変フィンガを有するバルーン型腱駆動ロボットハンドの開発 517 523 EN Jun-ya Nagase Shuichi Wakimoto Norihiko Saga Koichi Suzumori No potential conflict of interest relevant to this article was reported.

日本ロボット学会 Acta Medica Okayama 0289-1824 29 7 2011 大腸内視鏡挿入支援を目指したラバーチューブアクチュエータの設計と基礎駆動特性 619 625 EN Shuichi Wakimoto Ken Ozaki Koichi Suzumori Colonoscopy is an important medical action to detect disorders like colon cancer. However generally it is difficult to insert a scope into the colon, because the colon is flexible and complex shape. This study aims at development of an actuator which can add propelling ability to a colonoscope. We focus on rubber pneumatic actuators, because advantages of them, for example, high compliance, low cost, water proof, and so on, agree with the required properties of medical devices. In this paper, we design a novel rubber actuator consisting of three air chambers by nonlinear FEM (finite element method) and fabricate the actuator employing the design by extrusion molding method. Basic characteristics of the actuator are clarified by a motion capture system, and functional motion leading assisting colonoscope insertion is observed. Actually using dummy endoscope, transportation ability by the actuators is confirmed experimentally and insertion experiments into a large intestine phantom are conducted. No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 0169-1864 25 9-10 2011 Miniature Pneumatic Curling Rubber Actuator Generating Bidirectional Motion with One Air-Supply Tube 1311 1330 EN Shuichi Wakimoto Koichi Suzumori Keiko Ogura Soft actuators driven by pneumatic pressure are promising actuators for mechanical systems in medical, biological, agriculture, welfare fields and so on, because they can ensure high safety for fragile objects from their low mechanical impedance. In this study, a new rubber pneumatic actuator made from silicone rubber was developed. Composed of one chamber and one air-supply tube, it can generate curling motion in two directions by using positive and negative pneumatic pressure. The rubber actuator, for generating bidirectional motion, was designed to achieve an efficient shape by nonlinear finite element method analysis, and was fabricated by a molding and rubber bonding process using excimer light. The fabricated actuator was able to generate curling motion in two directions successfully. The displacement and force characteristics of the actuator were measured by using a motion capture system and a load cell. As an example application of the actuator, a robotic soft hand with three actuators was constructed and its effectiveness was confirmed by experiments. No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 0169-1864 24 10 2010 Development of an Intelligent Chair Tool System Applying New Intelligent Pneumatic Actuators 1503 1528 EN Ahmad 'Athif Mohd Faudzi Koichi Suzumori Shuichi Wakimoto This paper develops an Intelligent Chair Tool (ICT) - a new chair-type human and machine interaction seating system powered by 36 intelligent pneumatic actuators. This tool can be used to facilitate investigation of chair shapes from spring and damping effects of seating and backrest surfaces. Each actuator used consists of five extensive elements of encoder, laser strip rod, pressure sensor, valves and PSoC microcontroller incorporated in a single device. By using the ICT, different shapes, spring and damping characteristics can be obtained to aid the design of chairs from the control inputs, i.e., position x, stiffness k(s) and viscous coefficient c. Several control algorithms are presented to realize the communication and control system, and to obtain all data in real-time. The control methodology presented contains an inner force loop and an outer position loop implemented using a unified control system. The specification, development design and experimental evaluation of the ICT control system and actuator used are presented and discussed. No potential conflict of interest relevant to this article was reported.