A directional control valve without a conventional valving element was developed by exploiting the viscosity-temperature dependency of hydraulic oil. The proposed valve consisted of two valving element-free sub-valves, previously developed, which were interconnected to form a branched flow path. The temperature of each sub-valve was independently controlled using Peltier modules, thereby modulating the oil viscosity and regulating flow distribution. The performance of three types of valves was experimentally evaluated under both single and multiple consecutive directional control operations. When one valve body was cooled, the flow rate in the corresponding flow path decreased and, in some cases, ceased entirely, while flow was sustained in the alternate path. Subsequent heating of the cooled valve body restored the flow rate to its initial level. This alternating behavior enabled directional control of the flow without the use of mechanical valving elements. The results further indicate that the heating temperature exerted no significant influence on the valve performance within the tested range. These findings demonstrate that cyclic thermal modulation can effectively realize a novel, non-mechanical directional control mechanism.

The objective of this study is to develop a variable-load bench press machine using pneumatic artificial muscles (PAMs). Unlike conventional plate-loaded training machines, we propose a training system that dynamically adjusts the load based on the motion phase while ensuring safety. In this paper, we describe the configuration of the developed training system and quantitatively evaluate the influence of the proposed variable-load condition on muscle activity using electromyographic (EMG) measurements.

This paper proposes a pneumatic assist suit that achieves posture estimation and gait assistance in a single system through gait-phase classification based on the estimated hip angular velocity. The proposed method switches the gait phase and control law based on the zero-crossing timing of the estimated hip angular velocity. Because the zero-crossings of hip angular velocity correspond to extrema of the hip angle, the proposed method eliminates the need for participant-specific tuning of angle thresholds for gait-phase classification. During phases in which a pneumatic artificial muscle (PAM) is not used for assistance, it is depressurized and closed at low pressure, and the pressure time series generated by PAM length changes during walking is used to estimate the hip angle and angular velocity through random feature mapping and ridge regression. Treadmill walking experiments with two healthy male participants confirmed that posture estimation based on system pressure time series, gait-phase classification based on the estimated posture, and PAM-based gait assistance can be executed in real time within the same pneumatic system. The results also showed that posture estimation performance and the stability of zero-crossing timing detection were mostly maintained even under conditions involving role switching of the PAMs.

Pneumatic artificial rubber muscles (PARMs) are lightweight and high-output soft actuators that generally require compressors and other peripheral devices, increasing system size and noise. To address these issues, gas-liquid phase-change actuators that do not require such devices have been studied. However, because their actuation depends on heat, response delay becomes a significant problem. In this study, the continuous-operation performance was investigated using an antagonistic actuation system composed of two PARMs. The results showed that increasing the driving frequency and force amplitude degraded the force-tracking performance and shortened the time required to reach the safety pressure limit. In addition, insufficient cooling during continuous operation caused increases in internal temperature and average pressure, thereby limiting the range of safe operation. These findings clarify the influence of heat on sustained antagonistic actuation and provide guidelines for improving the long-term stability of phase-change-based artificial muscles.

To extend AUV exploration ranges in the Arctic, this study presents a pneumatically driven peristaltic sea ice drilling robot that deploys communication relays through boreholes. The robot utilizes an earthworm-inspired mechanism to propel itself while excavating, which is essential for navigating variable borehole diameters caused by fluctuating ice hardness. Experiments in tapered acrylic pipes confirmed successful propulsion over 530 ㎜ under changing diameters. Additionally, a pneumatic flow-based estimation method achieved borehole diameter accuracy within 5%. These results validate the robot's adaptability and demonstrate the feasibility of integrating real-time diameter estimation for stable, autonomous under-ice operations.

In a precise positioning control of a pneumatic cylinder, a position sensor is essential to implement a feedback system; however, it also leads to an increase in the total cost since the high-resolution positioning sensor is generally expensive. Cost reduction is therefore an important factor for the further market expansion of pneumatic actuators against other types of actuators. In this research, we propose a position control system that does not use position sensors, based on the state equation of air, and verify its practicality by demonstrating the basic control performance.