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.

Acta Medica Okayama 0924-4247 184 2012 An ultrasonic motor for cryogenic temperature using bolt-clamped Langevin-type transducer 134 140 EN Daisuke Yamaguchi Takefumi Kanda Koichi Suzumori In this study, a small ultrasonic motor driven under cryogenic temperature conditions has been fabricated and evaluated. Since transducer performance generally decreases at cryogenic temperatures, we designed and fabricated a bolt-clamped Langevin-type transducer for operation at cryogenic temperature. We simulated the influence of thermal stress on the transducer. The results from simulation were used to design the transducer, and it was then used to fabricate an ultrasonic motor for cryogenic temperature. The maximum diameter and the height of the motor are 30 mm and 38.7 mm. To enable the motor to be driven at cryogenic temperature, we evaluated the relationship between the contact pre-load and the lowest rotatable temperature. The motor's driving performance was evaluated at both room temperature and cryogenic temperatures. In a 4.5 K helium gas ambient, the rotation speed and starting torque were 133 rpm and 0.03 mu N m when the applied voltage was 50 Vp-p. 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.

Acta Medica Okayama 127 1 2006 A micro ultrasonic motor using a micro-machined cylindrical bulk PZT transducer 131 138 EN Takefumi Kanda Akira Makino Tomohisa Ono Koichi Suzumori Takeshi Morita Minoru Kuribayashi Kurosawa In this paper, a micro ultrasonic motor using a micro-machined bulk piezoelectric transducer is introduced. The cylindrical shaped bulk piezoelectric transducer, a diameter of 0.8 mm and a height of 2.2 mm, was developed as stator transducer for traveling wave type ultrasonic motor. The transducer was made of lead zirconate titanate (PZT) bulk ceramics, and formed by micro machining, Ni plating and laser beam cutting process. Using this stator transducer, we have fabricated a cylindrical micro ultrasonic motor, a diameter of 2.0 mm and a height of 5.9 mm. We have also evaluated some characteristics and succeeded in driving the micro ultrasonic motor. No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 2004 Nutation motor : a new direct-drive stepping motor for robots 21 22 EN Koichi Suzumori Takefumi Kanda Kazuo Uzuka Isao Enomoto A new type of stepping motor, named nutation motor was developed. This motor has a reduction mechanism consisting of a pair of bevel gears, realizing high torque and high resolution stepping motion. Three prototypes, two pneumatic nutation motors and an electric nutation motor, were designed, developed, and tested. We show the basic driving principle and the experimental results in this paper. No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 4 2004 Active link mechanisms for physical man-machine interaction 3895 3900 EN Jumpei Ochi Tatsuya Hashimoto Koichi Suzumori Takefumi Kanda In this paper, we propose a new type of haptic interface, named active link mechanism. This device realizes physical man-machine interaction (PMI) between machines and persons. Two prototypes were developed to demonstrate the potential of the active link mechanisms. Developed interface devices are an active tetrahedron and an active icosahedron. Nine-DOF micro spherical joints and pressure control pneumatic cylinders were developed to realize the active tetrahedron, while fifteen-DOF micro spherical joints and intelligent pneumatic cylinders were developed for the active icosahedron. The tetrahedron successfully realizes "virtual touch"; the operators feel actions, forces, and shapes of the virtual objects in PC and also move and deform them. Real time PMI is realized by building the developed devices into MSC.Visual-Nastran4D. MSC.VisuaI-Nastran4D is a mechanism analysis software, which can make motion analysis in real time. The active icosahedron also realized dynamic interaction with virtual objects in PC, showing the potential of the devices as a haptic interface. No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 2004 Development of active icosahedron and its application to virtual clay modeling 175 180 EN Jumpei Ochi Tatsuya Hashimoto Junichi Tanaka Koichi Suzumori Takefumi Kanda We have developed an active link mechanism for physical man-machine interaction. We report an active icosahedron consisting of intelligent cylinders and its application to virtual clay modeling. Intelligent pneumatic cylinders are newly developed to realize active link mechanisms. This cylinder aims at a novel cylinder in which various sensors and control devices are built. Active link mechanisms are highly integrated and enhanced by intelligent cylinders. A control system is built for the active icosahedron. In the control system, a key element is a control program implementing drawing of a virtual model on display and controlling of active links. Virtual clays are deformed by the program based on the apex positions converted from cylinder lengths. The active icosahedron realized dynamic interaction with virtual objects in PC, showing the potential of the devices as a haptic interface. No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 1 2005 A cylindrical micro ultrasonic motor using micro-machined piezoelectric vibrator 721 724 EN Takefumi Kanda Akira Makino Yoshitaka Oomori Koichi Suzumori A micro ultrasonic motor using a micro-machined cylindrical bulk piezoelectric vibrator is introduced. This motor consists of the vibrator, a glass case and a rotor. The diameter of the piezoelectric vibrator is 0.8 mm and that of the motor case is 1.8 mm. Since the stator transducer is fixed at the end of the cylinder, it is easy to support the vibrator and the structure of the motor is not complicated. In addition, the vibrator and rotor are supported by the glass case. This is important for the micro ultrasonic motor because it is difficult to support the vibrator when the vibrator is miniaturized. We have fabricated and evaluated the cylindrical shaped traveling type micro ultrasonic motor using this vibrator. No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 1 2005 Development of intelligent McKibben actuator with built-in soft conductive rubber sensor 745 748 EN Shuichi Wakimoto Koichi Suzumori Takefumi Kanda This study aims at the development of an intelligent McKibben actuator, in which a soft rubber displacement sensor is integrated. Recently, the McKibben actuator has attracted engineers because of light weight, high output power and high compliance. But in the case of using it for servo control at present, the systems need encoders or potentiometers, therefore the systems tend to grow in size and take away from compliance which is an important advantage for a safe and secure mechanism. We have developed a soft displacement sensor and incorporated it in a McKibben actuator, named it the intelligent McKibben actuator, and proved its potential. No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 4 2004 Active link mechanisms for physical man-machine interaction 3895 3900 EN J. Ochi Tatsuya Hashimoto Koichi Suzumori J. Tanaka Takefumi Kanda In this paper, we propose a new type of haptic interface, named active link mechanism. This device realizes physical man-machine interaction (PMI) between machines and persons. Two prototypes were developed to demonstrate the potential of the active link mechanisms. Developed interface devices are an active tetrahedron and an active icosahedron. Nine-DOF micro spherical joints and pressure control pneumatic cylinders were developed to realize the active tetrahedron, while fifteen-DOF micro spherical joints and intelligent pneumatic cylinders were developed for the active icosahedron. The tetrahedron successfully realizes "virtual touch"; the operators feel actions, forces, and shapes of the virtual objects in PC and also move and deform them. Real time PMI is realized by building the developed devices into MSC.Visual-Nastran4D. MSC.VisuaI-Nastran4D is a mechanism analysis software, which can make motion analysis in real time. The active icosahedron also realized dynamic interaction with virtual objects in PC, showing the potential of the devices as a haptic interface. No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 2005 Development of intelligent McKibben actuator 487 492 EN Shuichi Wakimoto Koichi Suzumori Takefumi Kanda The aim of this study is to develop an intelligent McKibben actuator with an integrated soft displacement sensor inside, so that displacement of this actuator can be controlled without having any extra devices attached. In addition, the high compliance which is a positive feature of the McKibben actuator is still conserved. This paper consists of four main parts. First of all, different types of soft displacement sensors made out of rubber were composed, and tested for their functional characteristics. Secondly, the intelligent McKibben actuator was developed with the soft displacement sensor incorporated within. Then, experiments of the position servo control with a single intelligent McKibben actuator were carried out. At last a robot arm mechanism was designed with two intelligent McKibben actuators, and those experimental results showed a great potential for its future applications. No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 2003 A micro snake-like robot for small pipe inspection 303 308 EN Shuichi Wakimoto Jun Nakajima Masanori Tanaka Takefumi Kanda Koichi Suzumori The goal of this research is development of a micro robot which can negotiate pipes whose diameter varies widely. The robot mechanism is based on "snaking drive". First, in section 1 to 4, basic characteristics of the snaking drive are discussed: the principle of the snaking drive is shown, theoretical fundamental formulas are derived, and the motions of the robot are simulated. Second, in section 5, a micro robot was designed, fabricated and tested. And fundamental experiments of the robot are shown. Third, in section 6, two application experiments are shown: one is a stabilization of camera image, and the other is a robot steering at branches. The robot moved in pipes whose diameter varies between 18 mm to 100 mm with the maximum speed of 36 mm/s. And the robot could negotiate T-branches and L-bends of pipes. No potential conflict of interest relevant to this article was reported.